阅读说明：本技术 方向性电磁钢板 (Grain-oriented electromagnetic steel sheet ) 是由 中村修一 川村悠祐 冈田慎吾 伊藤知昭 矢野慎也 于 2019-07-31 设计创作，主要内容包括：一种方向性电磁钢板,其具有朝着高斯取向进行取向的织构,在将在板面上相邻并且间隔为1mm的2个测定点测定的晶体取向的偏离角表示为(α_1β_1γ_1)和(α_2β_2γ_2),将边界条件BA定义为|β_2-β_1|≥0.5°,将边界条件BB定义为[(α_2-α_1)~2+(β_2-β_1)~2+(γ_2-γ_1)~2]~(1/2)≥2.0°时,存在满足边界条件BA并且不满足边界条件BB的晶界。(A grain-oriented electrical steel sheet having a texture oriented in a Gaussian orientation, wherein the off-angle of the crystal orientation measured at 2 measurement points adjacent to each other on the sheet surface at 1mm intervals is represented by (alpha) 1 β 1 γ 1 ) And (alpha) 2 β 2 γ 2 ) The boundary condition BA is defined as | beta 2 ‑β 1 | ≧ 0.5 °, the boundary condition BB is defined as [ (α) 2 ‑α 1 ) 2 +(β 2 ‑β 1 ) 2 +(γ 2 ‑γ 1 ) 2 ] 1/2 When the temperature is not less than 2.0 ℃, a grain boundary satisfying the boundary condition BA and not satisfying the boundary condition BB exists.)

1. A grain-oriented electrical steel sheet characterized by having the following chemical composition: contains by mass%:

Si：2.0～7.0％、

Nb：0～0.030％、

V：0～0.030％、

Mo：0～0.030％、

Ta：0～0.030％、

W：0～0.030％、

C：0～0.0050％、

Mn：0～1.0％、

S：0～0.0150％、

Se：0～0.0150％、

Al：0～0.0650％、

N：0～0.0050％、

Cu：0～0.40％、

Bi：0～0.010％、

B：0～0.080％、

P：0～0.50％、

Ti：0～0.0150％、

Sn：0～0.10％、

Sb：0～0.10％、

Cr：0～0.30％、

ni: 0 to 1.0%, the remainder comprising Fe and impurities,

and the grain-oriented electrical steel sheet has a texture oriented toward a gaussian orientation, wherein,

the off-angle from the ideal gaussian orientation with the rolling surface normal direction Z as the axis of rotation is defined as α, the off-angle from the ideal gaussian orientation with the rolling vertical direction C as the axis of rotation is defined as β, the off-angle from the ideal gaussian orientation with the rolling direction L as the axis of rotation is defined as γ, and the off-angle of the crystal orientation measured at 2 measurement points adjacent to each other on the plate surface and spaced at 1mm intervals is expressed as (α)₁β₁γ₁) And (alpha)₂β₂γ₂) The boundary condition BA is defined as | beta₂-β₁| ≧ 0.5 °, the boundary condition BB is defined as [ (α)₂-α₁)²+(β₂-β₁)²+(γ₂-γ₁)²]^1/2And at 2.0 DEG or more, a grain boundary satisfying the boundary condition BA and not satisfying the boundary condition BB exists.

2. The grain-oriented electrical steel sheet according to claim 1, wherein an average crystal grain size in the rolling direction L determined based on the boundary condition BA is defined as a grain size RA_LAverage crystal in the rolling direction L obtained based on the boundary condition BBParticle size is defined as the particle size RB_LWhen the particle diameter RA is larger_LAnd the particle diameter RB_LRB of 1.10 or less is satisfied_L÷RA_L。

3. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein an average crystal grain diameter in the rolling perpendicular direction C determined based on the boundary condition BA is defined as a grain diameter RA_CAnd the average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BB is defined as a grain diameter RB_CWhen the particle diameter RA is larger_CAnd the particle diameter RB_CRB of 1.10 or less is satisfied_C÷RA_C。

4. The grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein an average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as a grain diameter RA_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as a grain diameter RA_CWhen the particle diameter RA is larger_LAnd the particle diameter RA_CRA is satisfied at 1.15. ltoreq._C÷RA_L。

5. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein an average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as a grain diameter RB_LAnd the average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BB is defined as a grain diameter RB_CWhen the particle diameter RB is larger_LAnd the particle diameter RB_CRB of 1.50 or less is satisfied_C÷RB_L。

6. The grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein an average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as a grain diameter RA_LThe average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as a grain diameter RB_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as a grain diameter RA_CAnd the average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BB is defined as a grain diameter RB_CWhen the particle diameter RA is larger_LThe particle diameter RA_CThe particle diameter RB_LAnd the particle diameter RB_CSatisfy (RB)_C×RA_L)÷(RB_L×RA_C)<1.0。

7. The grain-oriented electrical steel sheet according to any one of claims 1 to 6, wherein an average crystal grain diameter in the rolling direction L determined based on the boundary condition BB is defined as a grain diameter RB_LAnd the average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BB is defined as a grain diameter RB_CWhen the particle diameter RB is larger_LAnd the particle diameter RB_CIs 22mm or more.

8. The grain-oriented electrical steel sheet according to any one of claims 1 to 7, wherein an average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as a grain diameter RA_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as a grain diameter RA_CWhen the particle diameter RA is larger_L30mm or less, the particle diameter RA_CIs 400mm or less.

9. The grain-oriented electrical steel sheet according to any one of claims 1 to 8, wherein a standard deviation σ (| β |) of an absolute value of the deviation angle β is 0 ° to 1.70 °.

10. The grain-oriented electrical steel sheet according to any one of claims 1 to 9, wherein the chemical composition contains at least 1 selected from Nb, V, Mo, Ta and W in a total amount of 0.0030 to 0.030 mass%.

11. The grain-oriented electrical steel sheet according to any one of claims 1 to 10, wherein magnetic domains are subdivided by at least one of imparting local micro-deformation and forming local grooves.

12. The grain-oriented electrical steel sheet according to any one of claims 1 to 11, comprising an intermediate layer disposed in contact with the grain-oriented electrical steel sheet, and an insulating coating disposed in contact with the intermediate layer.

13. The grain-oriented electrical steel sheet according to claim 12, wherein the intermediate layer is a forsterite coating film having an average thickness of 1 to 3 μm.

14. The grain-oriented electrical steel sheet according to claim 12, wherein the intermediate layer is an oxide film having an average thickness of 2 to 500 nm.

Technical Field

The present invention relates to a grain-oriented electrical steel sheet.

The present application claims priority based on the Japanese application laid-open in Japanese application No. 2018-143541 at 31.7.7.2018, Japanese application laid-open in Japanese application No. 2018-143897 at 31.7.7.2018, and Japanese application laid-open in Japanese application No. 2018-143903 at 31.7.7.2018, and the contents thereof are applied thereto.

Background

The grain-oriented electrical steel sheet contains 7 mass% or less of Si and has a secondary recrystallized texture concentrated in a {110} <001> orientation (Gaussian orientation). The {110} <001> orientation means that the {110} plane of the crystal is arranged parallel to the rolling plane, and the <001> axis of the crystal is arranged parallel to the rolling direction.

The magnetic properties of grain-oriented magnetic steel sheets are greatly affected by the concentration of {110} <001> orientation. In particular, it is considered that the relationship between the rolling direction of the steel sheet, which is the main magnetization direction when the steel sheet is used, and the <001> direction of the crystal, which is the easy magnetization direction, is important. Therefore, in a grain-oriented electrical steel sheet which has been practically used in recent years, the angle formed between the <001> direction of the crystal and the rolling direction is controlled to be within a range of about 5 °.

The deviation of the actual crystal orientation of the grain-oriented electrical steel sheet from the ideal {110} <001> orientation can be expressed by 3 components, i.e., a deviation angle α around the normal direction Z of the rolling surface, a deviation angle β around the rolling vertical direction C, and a deviation angle γ around the rolling direction L.

Fig. 1 is a schematic diagram illustrating a deviation angle α, a deviation angle β, and a deviation angle γ. As shown in FIG. 1, the off-angle α is an angle formed between the <001> direction of the crystal projected onto the rolled surface and the rolling direction L when viewed from the rolling surface normal direction Z. The off-angle β is an angle formed between the rolling direction L and the <001> direction of the crystal projected onto the L cross section (cross section with the rolling vertical direction as a normal line) when viewed from the rolling vertical direction C (sheet width direction). The off-angle γ is an angle formed by the <110> direction of the crystal projected onto the C-section (the section having the rolling direction as a normal line) when viewed from the rolling direction L and the rolling surface normal line direction Z.

It is known that the deviation angle β of the deviation angles α, β, γ has an influence on magnetostriction (also referred to as magnetostriction). Magnetostriction is a phenomenon in which a magnetic material changes its shape by application of a magnetic field. Since magnetostriction causes vibration and noise, grain-oriented electrical steel sheets used in transformers and the like of transformers are required to have reduced magnetostriction.

For example, patent documents 1 to 3 disclose control of the slip angle β. Further, the control of the slip angle α in addition to the slip angle β is disclosed in patent documents 4 and 5. Further, patent document 6 discloses a technique for improving the iron loss characteristics by classifying the concentration of crystal orientation in further detail using the off-angle α, off-angle β, and off-angle γ as indices.

Further, techniques for controlling not only the magnitude and average of the absolute values of the slip angles α, β, and γ, but also fluctuations (deviations) are disclosed in, for example, patent documents 7 to 9. Further, patent documents 10 to 12 disclose that Nb, V, and the like are added to grain-oriented electrical steel sheets.

Further, grain-oriented electrical steel sheets are required to have excellent magnetostriction and excellent magnetic flux density. Hitherto, there have been proposed methods for obtaining a steel sheet having a high magnetic flux density by controlling the growth of crystal grains in secondary recrystallization. For example, in patent documents 13 and 14, the following methods are disclosed: in the final annealing step, secondary recrystallization is performed while applying a temperature gradient to the steel sheet in the tip region of the secondary recrystallized grains of the primary recrystallized grains being eaten by silkworm.

When the secondary recrystallized grains are grown using a temperature gradient, although the grain growth is stable, the grains may become excessively large. If the crystal grains become too large, the effect of increasing the magnetic flux density may be inhibited by the influence of the curvature of the coil. For example, patent document 15 discloses the following processing: when performing secondary recrystallization while applying a temperature gradient, the free growth of secondary recrystallization (for example, a treatment of applying mechanical stress to the end portions in the width direction of the steel sheet) occurring at the initial stage of secondary recrystallization is suppressed.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2001-294996

Patent document 2: japanese patent laid-open No. 2005-240102

Patent document 3: japanese patent laid-open publication No. 2015-206114

Patent document 4: japanese laid-open patent publication No. 2004-060026

Patent document 5: international publication No. 2016/056501

Patent document 6: japanese laid-open patent publication No. 2007-314826

Patent document 7: japanese patent laid-open publication No. 2001-192785

Patent document 8: japanese patent laid-open publication No. 2005-240079

Patent document 9: japanese patent laid-open publication No. 2012-052229

Patent document 10: japanese laid-open patent publication No. 52-024116

Patent document 11: japanese patent laid-open publication No. H02-200732

Patent document 12: japanese patent No. 4962516

Patent document 13: japanese laid-open patent publication No. 57-002839

Patent document 14: japanese laid-open patent publication No. 61-190017

Patent document 15: japanese laid-open patent publication No. H02-258923

Disclosure of Invention

Problems to be solved by the invention

As a result of research, the inventors of the present invention have found that the conventional techniques disclosed in patent documents 1 to 9, although controlling the crystal orientation, cannot be said to sufficiently reduce the magnetostriction in particular.

Further, the conventional techniques disclosed in patent documents 10 to 12 contain only Nb and V, and therefore the reduction of magnetostriction is not sufficient. Further, the conventional techniques disclosed in patent documents 13 to 15 have problems in terms of productivity, and the reduction in magnetostriction is not sufficient.

The present invention addresses the problem of providing a grain-oriented electrical steel sheet with improved magnetostriction in view of the current situation in which reduction of magnetostriction is required in grain-oriented electrical steel sheets. In particular, it is an object to provide a grain-oriented electrical steel sheet improved in magnetostriction in a low magnetic field region (magnetic field of about 1.5T).

Means for solving the problems

The gist of the present invention is as follows.

(1) A grain-oriented electrical steel sheet according to one embodiment of the present invention has the following chemical composition: contains by mass%: si: 2.0 to 7.0%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0-0.030%, W: 0-0.030%, C: 0-0.0050%, Mn: 0-1.0%, S: 0-0.0150%, Se: 0-0.0150%, Al: 0-0.0650%, N: 0-0.0050%, Cu: 0 to 0.40%, Bi: 0-0.010%, B: 0-0.080%, P: 0-0.50%, Ti: 0-0.0150%, Sn: 0-0.10%, Sb: 0-0.10%, Cr: 0-0.30%, Ni: 0 to 1.0%, and the balance of Fe and impurities, and the grain-oriented electrical steel sheet has a texture oriented toward a Gaussian orientation in which the deviation in the direction Z from the normal to the rolling plane isThe off-angle from the ideal gaussian orientation of the axis of rotation is defined as α, the off-angle from the ideal gaussian orientation with the rolling perpendicular direction C as the axis of rotation is defined as β, the off-angle from the ideal gaussian orientation with the rolling direction L as the axis of rotation is defined as γ, and the off-angle from the crystal orientation measured at 2 measurement points adjacent to each other on the plate surface and spaced at 1mm intervals is represented as (α)₁β₁γ₁) And (alpha)₂β₂γ₂) The boundary condition BA is defined as | beta₂-β₁| ≧ 0.5 °, the boundary condition BB is defined as [ (α)₂-α₁)²+(β₂-β₁)²+(γ₂-γ₁)²]^1/2When the temperature is not less than 2.0 ℃, a grain boundary satisfying the boundary condition BA and not satisfying the boundary condition BB exists.

(2) The grain-oriented electrical steel sheet according to the above (1), wherein the average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as a grain diameter RA_LThe average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as the grain diameter RB_LWhen the particle diameter RA is small_LAnd particle diameter RB_LOr may satisfy RB of 1.10. ltoreq_L÷RA_L。

(3) The grain-oriented electrical steel sheet according to the above (1) or (2), wherein the average crystal grain diameter in the rolling perpendicular direction C determined based on the boundary condition BA is defined as a grain diameter RA_CThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RA is small_CAnd particle diameter RB_COr may satisfy RB of 1.10. ltoreq_C÷RA_C。

(4) The grain-oriented electrical steel sheet according to any one of the above (1) to (3), wherein the average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as a grain diameter RA_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as the grain diameter RA_CWhen the particle diameter RA is small_LAnd particle size RA_CRA may be 1.15. ltoreq_C÷RA_L。

(5) The method according to any one of the above (1) to (4)The grain-oriented electrical steel sheet, wherein the average crystal grain diameter in the rolling direction L determined based on the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RB_LAnd particle diameter RB_CAlso can satisfy RB of 1.50. ltoreq._C÷RB_L。

(6) The grain-oriented electrical steel sheet according to any one of the above (1) to (5), wherein the average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as the grain diameter RA_LThe average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as the grain diameter RA_CThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RA is small_LParticle diameter RA_CParticle diameter RB_LAnd particle diameter RB_CCan also satisfy (RB)_C×RA_L)÷(RB_L×RA_C)<1.0。

(7) The grain-oriented electrical steel sheet according to any one of the above (1) to (6), wherein the average crystal grain diameter in the rolling direction L determined based on the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RB_LAnd particle diameter RB_CThe thickness may be 22mm or more.

(8) The grain-oriented electrical steel sheet according to any one of the above (1) to (7), wherein the average crystal grain diameter in the rolling direction L determined based on the boundary condition BA is defined as the grain diameter RA_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as the grain diameter RA_CWhen the particle diameter RA is small_LCan be less than 30mm, and has particle diameter RA_CMay be 400mm or less.

(9) The grain-oriented electrical steel sheet according to any one of the above (1) to (8), wherein a standard deviation σ (| β |) of an absolute value of the off-angle β may be 0 ° to 1.70 °.

(10) The grain-oriented electrical steel sheet according to any one of the above (1) to (9), wherein the chemical composition may contain at least 1 selected from Nb, V, Mo, Ta and W in a total amount of 0.0030 to 0.030 mass%.

(11) The grain-oriented electrical steel sheet according to any one of the above (1) to (10), wherein the magnetic domains can be subdivided by at least one of imparting local micro-deformation and forming local grooves.

(12) The grain-oriented electrical steel sheet according to any one of the above (1) to (11), which may have an intermediate layer disposed in contact with the grain-oriented electrical steel sheet and an insulating film disposed in contact with the intermediate layer.

(13) The grain-oriented electrical steel sheet according to any one of the above (1) to (12), wherein the intermediate layer may be a forsterite coating film having an average thickness of 1 to 3 μm.

(14) The grain-oriented electrical steel sheet according to any one of the above (1) to (13), wherein the intermediate layer may be an oxide film having an average thickness of 2 to 500 nm.

Effects of the invention

According to the aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet in which magnetostriction in a low magnetic field region (particularly, a magnetic field of about 1.5T) is improved.

Drawings

Fig. 1 is a schematic diagram illustrating a deviation angle α, a deviation angle β, and a deviation angle γ.

Fig. 2 is a schematic view illustrating grain boundaries of grain-oriented electrical steel sheets.

Fig. 3 is a schematic cross-sectional view of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Fig. 4 is a flowchart of a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Detailed Description

A preferred embodiment of the present invention will be described in detail. However, the present invention is not limited to the configurations disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention. In the following numerical limitation ranges, the lower limit value and the upper limit value are included in the range. With respect to values expressed as "beyond" or "below," the value is not included in the range of values. The "%" of the chemical composition means "% by mass" unless otherwise specified.

In general, in order to reduce magnetostriction, the crystal orientation is controlled so that the off-angle β is reduced (specifically, so that the maximum value and the average value of the absolute value | β | of the off-angle β are reduced). In fact, it was confirmed that: conventionally, the magnetic field strength during magnetization is a magnetic field region around 1.7T (hereinafter, sometimes simply referred to as "middle magnetic field region") which is a magnetic field strength generally used in measuring magnetic characteristics, and the dependence of the off angle β on magnetostriction is relatively high.

On the other hand, secondary recrystallization in a practical grain-oriented electrical steel sheet is performed in a state of being wound into a coil. That is, the secondary recrystallized grains are grown in a state where the steel sheet has curvature. Therefore, even if the off-angle β is small in the initial stage of the secondary recrystallization, the off-angle β inevitably becomes large as the crystal grains grow.

Of course, if only a large number of crystal grains having a small off-angle β can be generated in advance at the generation stage of the secondary recrystallized grains, even if these crystal grains do not grow so large, the entire area of the steel sheet can be filled with the secondary recrystallized grains having the substantially ideal {110} <001> orientation. However, in practice, a large number of crystal grains having uniform orientation cannot be produced as described above.

The inventors of the present invention have studied the relationship between the crystal orientation of the steel sheet used as a material for a practical iron core and the noise, and have found that the correlation between the slip angle β and the noise may be weak for some materials. Namely, the following conditions were confirmed: even when a grain-oriented electrical steel sheet having a small magnetostriction and having a deviation angle β controlled as in the conventional art is used, noise in an actual use environment cannot be sufficiently reduced.

The inventors of the present invention presume the reason as follows. First, in an actual usage environment, the magnetic flux does not flow uniformly in the steel sheet, and a portion where the magnetic flux is locally concentrated is generated. There is also a region of reduced magnetic flux density, which is larger in area than the region of reduced magnetic flux. Therefore, it is considered that the noise in the actual use environment is strongly influenced not only by the magnetostriction under the excitation condition of about 1.7T in general but also by the magnetostriction in the lower excitation region.

Based on this estimation, the fact that the correlation between the slip angle β and the noise is low was examined, and as a result, it was found that the behavior thereof can be evaluated by the "difference between the minimum value and the maximum value of magnetostriction" (hereinafter referred to as "λ p-p @ 1.5T"), which is the amount of magnetic deformation at 1.5T. It is also considered that if the above behavior can be optimally controlled, the noise of the transformer can be further reduced.

Therefore, the inventors of the present invention have studied to grow a crystal while changing the orientation without maintaining the crystal orientation at the growth stage of the secondary recrystallized grains. As a result, it was found that, in the growth process of the secondary recrystallized grains, a large amount of local and small-tilt-angle orientation change of such a degree that has not been conventionally recognized as grain boundaries occurs, and a state in which one secondary recrystallized grain is divided into small regions having slightly different off-angles β is advantageous for the reduction of magnetostriction in the low magnetic field region.

It has been found that, in the control of the above-described orientation change, it is important to consider factors that facilitate the occurrence of the orientation change itself and factors that cause the orientation change to continue in one crystal grain. Further, in order to facilitate the occurrence of the orientation change itself, it is effective to start the secondary recrystallization from a lower temperature, and it has been confirmed that, for example, the primary recrystallization particle diameter can be controlled and an element such as Nb is used. Further, it was confirmed that by using AlN or the like, which has been conventionally used, as an inhibitor at an appropriate temperature and in an atmosphere, it is possible to continue the occurrence of the orientation change in one crystal grain in the secondary recrystallization until reaching a high-temperature region.

[ embodiment 1 ]

In the grain-oriented electrical steel sheet according to embodiment 1 of the present invention, the secondary recrystallized grains are divided into a plurality of regions having slightly different off-angles β. That is, the grain-oriented electrical steel sheet of the present embodiment has a grain boundary having a relatively large angle difference with respect to the grain boundary of the secondary recrystallized grains, and also has a local small-angle grain boundary dividing the inside of the secondary recrystallized grains.

Specifically, the grain-oriented electrical steel sheet of the present embodiment has the following chemical composition: contains by mass%: si: 2.0 to 7.0%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0-0.030%, W: 0-0.030%, C: 0-0.0050%, Mn: 0-1.0%, S: 0-0.0150%, Se: 0-0.0150%, Al: 0-0.0650%, N: 0-0.0050%, Cu: 0 to 0.40%, Bi: 0-0.010%, B: 0-0.080%, P: 0-0.50%, Ti: 0-0.0150%, Sn: 0-0.10%, Sb: 0-0.10%, Cr: 0-0.30%, Ni: 0 to 1.0%, the balance comprising Fe and impurities, and the grain-oriented electrical steel sheet having a texture oriented to a Gaussian orientation, wherein a deviation angle from an ideal Gaussian orientation with a rolling surface normal direction Z as a rotation axis is defined as α, a deviation angle from an ideal Gaussian orientation with a rolling vertical direction (sheet width direction) C as a rotation axis is defined as β, a deviation angle from an ideal Gaussian orientation with a rolling direction L as a rotation axis is defined as γ, and deviation angles of crystal orientations measured at 2 measurement points adjacent to each other on the sheet surface and spaced at 1mm intervals are respectively represented as (α)₁β₁γ₁) And (alpha)₂β₂γ₂) The boundary condition BA is defined as | beta₂-β₁| ≧ 0.5 °, the boundary condition BB is defined as [ (α)₂-α₁)²+(β₂-β₁)²+(γ₂-γ₁)²]^1/2At not less than 2.0 °, the grain-oriented electrical steel sheet of the present embodiment has a grain boundary (grain boundary corresponding to secondary recrystallized grain boundary) satisfying the boundary condition BB, and also has a grain boundary (grain boundary dividing secondary recrystallized grain) satisfying the boundary condition BA and not satisfying the boundary condition BB.

The grain boundaries satisfying the boundary condition BB substantially correspond to secondary recrystallized grain boundaries observed when a conventional grain-oriented electrical steel sheet is subjected to macro corrosion. The grain-oriented electrical steel sheet of the present embodiment has a grain boundary satisfying the boundary condition BB, and also has a grain boundary satisfying the boundary condition BA and not satisfying the boundary condition BB at a relatively high frequency. The grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB correspond to local small-inclination grain boundaries that divide the secondary recrystallized grains. That is, in the present embodiment, the secondary recrystallized grains are further finely divided into small regions having slightly different off-angles β.

Conventional grain-oriented electrical steel sheets may have secondary recrystallized grain boundaries satisfying boundary condition BB. In addition, conventional grain-oriented electrical steel sheets may have a shift in the off angle β within the grains of the secondary recrystallized grains. However, since the conventional grain-oriented electrical steel sheet has a strong tendency to continuously shift the off-angle β within the secondary recrystallized grains, it is difficult for the shift of the off-angle β in the conventional grain-oriented electrical steel sheet to satisfy the boundary condition BA.

For example, in a conventional grain-oriented electrical steel sheet, although it is possible to recognize the displacement of the off angle β in the long range region in the secondary recrystallized grains, it is difficult to recognize (hardly satisfies the boundary condition BA) because the displacement of the off angle β is minute in the short range region in the secondary recrystallized grains. On the other hand, in the grain-oriented electrical steel sheet of the present embodiment, the off angle β is locally displaced in the short range region and can be recognized as a grain boundary. Specifically, | β is measured between 2 measurement points adjacent to each other at an interval of 1mm in the secondary recrystallized grains₂-β₁A displacement with a value of | of 0.5 ° or more exists at a relatively high frequency.

In the grain-oriented electrical steel sheet of the present embodiment, grain boundaries (grain boundaries dividing secondary recrystallized grains) satisfying boundary condition BA and not satisfying boundary condition BB are intentionally produced by precisely controlling the production conditions as described later. In the grain-oriented electrical steel sheet of the present embodiment, the secondary recrystallized grains are divided into small regions having slightly different off-angles β, and the magnetostriction in the low magnetic field region is reduced.

The grain-oriented electrical steel sheet according to the present embodiment will be described in detail below.

1. Crystal orientation

First, description of crystal orientation in the present embodiment will be described.

In the present embodiment, 2 {110} <001> orientations, which are "actual {110} <001> orientation" and "ideal {110} <001> orientation", are distinguished. The reason is that: in the present embodiment, it is necessary to distinguish the {110} <001> orientation representing the crystal orientation of a practical steel sheet from the {110} <001> orientation which is an academic crystal orientation.

In general, in the measurement of the crystal orientation of a practical recrystallization steel sheet, the crystal orientation is specified so that the difference in angle of about ± 2.5 ° is not strictly differentiated. In a conventional grain-oriented electrical steel sheet, an angular range region of about ± 2.5 ° centered on a geometrically strict {110} <001> orientation is set as a "{ 110} <001> orientation". However, in the present embodiment, it is necessary to clearly distinguish the angular difference of ± 2.5 ° or less.

Therefore, in the present embodiment, when the orientation of the grain-oriented electrical steel sheet is expressed in a practical sense, it is described as "{ 110} <001> orientation (gaussian orientation)" as in the related art. On the other hand, when the {110} <001> orientation is expressed as a geometrically strict crystal orientation, in order to avoid the mixture with the {110} <001> orientation used in conventional publicly known documents and the like, the orientation is described as "ideal {110} <001> orientation (ideal gaussian orientation)".

Therefore, in the present embodiment, for example, "the {110} <001> orientation of the grain-oriented electrical steel sheet of the present embodiment is deviated from the ideal {110} <001> orientation by 2 °" in some cases.

In the present embodiment, the following 4 angles α, β, γ, and Φ associated with the crystal orientation observed in the grain-oriented electrical steel sheet are used.

Deviation angle α: the deviation angle of crystal orientation observed in a grain-oriented electrical steel sheet from an ideal {110} <001> orientation in the normal direction Z of a rolling plane.

Deviation angle β: the deviation of crystal orientation observed in a grain-oriented electrical steel sheet from an ideal {110} <001> orientation around the rolling vertical direction C is an off-angle.

Deviation angle γ: the deviation of the crystal orientation observed in the grain-oriented electrical steel sheet from the ideal {110} <001> orientation around the rolling direction L is an off-angle.

A schematic diagram of the above-described slip angle α, slip angle β, and slip angle γ is shown in fig. 1.

Angle phi: the above-mentioned off-angles of crystal orientation measured at 2 measurement points adjacent to each other at 1mm intervals on the rolling plane of a grain-oriented electrical steel sheet are represented by (α)₁、β₁、γ₁) And (alpha)₂、β₂、γ₂) When, by phi ═ alpha [ (. alpha. ])₂-α₁)²+(β₂-β₁)²+(γ₂-γ₁)²]^1/2The resulting angle.

This angle Φ may be described as "a spatial three-dimensional orientation difference".

2. Grain boundaries of grain-oriented electromagnetic steel sheet

The grain-oriented electrical steel sheet of the present embodiment utilizes, in order to control the off angle β, a change in local crystal orientation that occurs particularly in secondary recrystallized grain growth to such an extent that it has not been conventionally considered as a grain boundary. In the following description, the above-described orientation change that occurs in order to divide one secondary recrystallized grain into small regions having slightly different off-angles β is sometimes referred to as "commutation".

Further, a grain boundary (a grain boundary satisfying the boundary condition BA) in which the angle difference of the deviation angle β is taken into consideration may be described as "β grain boundary", and a grain divided by β grain boundary may be described as "β grain".

Note that, regarding the characteristics relating to the present embodiment, that is, the magnetostriction (λ p-p @1.5T) at the time of 1.5T excitation, the following description may be simply referred to as "low-field (medium) magnetostriction".

The above-mentioned reversal is considered that the change in crystal orientation is around 1 ° (less than 2 °), and occurs during the growth of the secondary recrystallized grains continues. The details will be described later in connection with the manufacturing method, but it is important to grow secondary recrystallized grains in a state where commutation is likely to occur. For example, it is important to start the secondary recrystallization at a relatively low temperature by controlling the primary recrystallization particle size, and to continue the secondary recrystallization up to a high temperature by controlling the kind and amount of the inhibitor.

The reason why the control of the slip angle β affects the low-field magnetostriction is not necessarily clear, but is estimated as follows.

Generally, the magnetization behavior in low magnetic fields is caused by the movement of the 180 ° magnetic domain. It is considered that this domain movement is particularly affected by the continuity of the magnetic domain of the crystal grains adjacent to the grain boundary, and the difference in orientation with the adjacent crystal grains may cause the magnitude of disturbance in magnetization behavior. As described above, secondary recrystallization in a practical grain-oriented electrical steel sheet is performed in a state of being wound into a coil, and therefore, it is considered that a difference in the off angle β between adjacent grains in the grain boundary becomes large. It is believed that the commutation controlled in this embodiment functions in the following manner: by causing a change in orientation (local orientation change) at a high frequency in one secondary recrystallized grain, a relative orientation difference with respect to adjacent grains is reduced, and continuity of the crystal orientation of the grain-oriented electrical steel sheet as a whole is improved.

In the present embodiment, 2 kinds of boundary conditions are defined for the change of crystal orientation including the inversion. In the present embodiment, the definition of "grain boundary" based on the above boundary conditions is important.

Conventionally, the crystal orientation of a grain-oriented electrical steel sheet produced in practice is controlled so that the off-angle between the rolling direction and the <001> direction is substantially 5 ° or less. This control is also the same for the grain-oriented electrical steel sheet of the present embodiment. Therefore, when defining "grain boundaries" of a grain-oriented electrical steel sheet, the definition of normal grain boundaries (large tilt angle grain boundaries), that is, "boundaries in which the difference in orientation between adjacent regions is 15 ° or more" cannot be applied. For example, in a conventional grain-oriented electrical steel sheet, grain boundaries are developed by macro corrosion of the steel sheet surface, but the difference in crystal orientation between both side regions of the grain boundaries is usually about 2 to 3 °.

In the present embodiment, as described later, it is necessary to strictly define the boundaries between crystals. Therefore, as a method for determining the grain boundary, a method based on visual observation such as macro corrosion is not used.

In the present embodiment, in order to identify the grain boundaries, measurement lines including at least 500 measurement points at 1mm intervals are set on the rolled surface to measure the crystal orientation. For example, the crystal orientation can be measured by an X-ray diffraction method (laue method). The laue method is a method of irradiating a steel sheet with an X-ray beam and analyzing a transmitted or reflected diffraction spot. By analyzing the diffraction spots, the crystal orientation of the portion irradiated with the X-ray beam can be identified. When the irradiation position is changed and diffraction spots are analyzed at a plurality of positions, the crystal orientation distribution at each irradiation position can be measured. The laue method is a method suitable for measuring the crystal orientation of a metal structure having coarse grains.

The measurement point of the crystal orientation may be at least 500 points, but it is preferable to increase the measurement point as appropriate depending on the size of the secondary recrystallized grains. For example, when the number of secondary recrystallized grains contained in the measurement line is less than 10 when the measurement point for measuring the crystal orientation is set to 500 points, it is preferable to increase the number of measurement points at intervals of 1mm and extend the measurement line so that 10 or more secondary recrystallized grains are contained in the measurement line.

The crystal orientation was measured at 1mm intervals on the rolled surface, and the above-mentioned off-angle α, off-angle β and off-angle γ were determined for each measurement point. Whether grain boundaries exist between the adjacent 2 measurement points is judged according to the deviation angle of each determined measurement point. Specifically, it is determined whether or not the adjacent 2 measurement points satisfy the boundary condition BA and/or the boundary condition BB.

Specifically, the off-angles of the crystal orientation measured at 2 adjacent measurement points are represented by (α)₁、β₁、γ₁) And (alpha)₂、β₂、γ₂) Then, the boundary condition BA is defined as | β₂-β₁| ≧ 0.5 °, the boundary condition BB is defined as [ (α)₂-α₁)²+(β₂-β₁)²+(γ₂-γ₁)²]^1/2Not less than 2.0 degree. Judging whether the measured values are between 2 adjacent measurement pointsWhether or not a grain boundary satisfying the boundary condition BA and/or the boundary condition BB exists.

The grain boundary satisfying the boundary condition BB is a grain boundary in which the difference in spatial three-dimensional orientation (angle Φ) between 2 points sandwiching the grain boundary is 2.0 ° or more, and is substantially the same as the grain boundary of conventional secondary recrystallized grains recognized by macro corrosion.

Unlike the grain boundaries satisfying the boundary condition BB described above, in the grain-oriented electrical steel sheet of the present embodiment, the grain boundaries strongly associated with "commutation", specifically, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, exist at a relatively high frequency. The grain boundaries defined in this way correspond to the grain boundaries that divide one secondary recrystallized grain into small regions having slightly different off angles β.

The 2 grain boundaries can be obtained by using other measurement data. However, if consideration is given to the measurement trouble and the deviation from the actual state due to the difference in data, it is preferable to obtain the 2 grain boundaries by using the deviation angle of crystal orientation obtained from the same measurement line (measurement points at least 500 points at 1mm intervals on the rolled surface).

In the grain-oriented electrical steel sheet of the present embodiment, in addition to the grain boundaries satisfying the boundary condition BB, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are included at a relatively high frequency, and therefore the grain boundaries are divided into small regions having slightly different off angles β for secondary recrystallization, and as a result, the magnetostriction in the low magnetic field region is reduced.

In the present embodiment, the steel sheet may have "grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB". However, in order to substantially reduce magnetostriction in the low magnetic field region, it is preferable that grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB exist at a relatively high frequency.

For example, in the present embodiment, the secondary recrystallized grain is divided into small regions having slightly different off-angles β, and therefore β grain boundaries are preferably present at a relatively high frequency compared to conventional secondary recrystallized grain boundaries.

Specifically, the crystal orientation may be measured at least 500 measurement points at 1mm intervals on the rolled surface, the off-angle may be determined at each measurement point, and when the boundary condition is determined at 2 adjacent measurement points, "the grain boundary satisfying the boundary condition BA" may be present at a ratio of 1.10 times or more as compared with "the grain boundary satisfying the boundary condition BB". That is, when the boundary condition is determined as described above, the value obtained by dividing "the number of boundaries satisfying the boundary condition BA" by "the number of boundaries satisfying the boundary condition BB" may be 1.10 or more. In the present embodiment, when the above value is 1.10 or more, it is determined that "grain boundaries satisfying boundary condition BA and not satisfying boundary condition BB" exist in the grain-oriented electrical steel sheet.

The upper limit of the value obtained by dividing "the number of boundaries satisfying boundary condition BA" by "the number of boundaries satisfying boundary condition BB" is not particularly limited. For example, the value may be 80 or less, may be 40 or less, and may be 30 or less.

[ 2 nd embodiment ]

Next, a grain-oriented electrical steel sheet according to embodiment 2 of the present invention will be described below. In the embodiments described below, differences from embodiment 1 are mainly described, and other features are the same as those of embodiment 1, and redundant description is omitted.

In the grain-oriented electrical steel sheet according to embodiment 2 of the present invention, the grain size of the β crystal grains in the rolling direction is smaller than the grain size of the secondary recrystallized grains in the rolling direction. That is, the grain-oriented electrical steel sheet of the present embodiment has β crystal grains and secondary recrystallized grains, the grain size of which is controlled with respect to the rolling direction.

Specifically, in the grain-oriented electrical steel sheet of the present embodiment, the average crystal grain size in the rolling direction L determined based on the boundary condition BA is defined as the grain size RA_LThe average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as the grain diameter RB_LWhen the particle diameter RA is small_LAnd particle diameter RB_LRB of 1.10 or less is satisfied_LRA. In addition, RB is preferable_L÷RA_L≤80。

This specification indicates the above-described "reversal" with respect to the rolling direction.That is, it means that at least one | β is contained in secondary recrystallized grains having a grain boundary at a boundary with an angle of 2 ° or more₂-β₁The crystal grains having | of 0.5 ° or more and the boundary of an angle Φ of less than 2 ° exist at corresponding frequencies with respect to the rolling direction. In the present embodiment, the grain size RA in the rolling direction is used for the change of the direction_LAnd particle diameter RB_LTo evaluate and specify.

Fig. 2 is a schematic view showing the state of grain boundaries of secondary recrystallized grains and the occurrence of grain inversion in the secondary recrystallized grains of a grain-oriented electrical steel sheet. Fig. 2 shows a state in which the steel sheet immediately after the finish annealing (immediately after the secondary recrystallization) is wound into a coil and has a curvature, and a state in which the steel sheet after the flattening (in use) is unwound from the coil.

As shown in fig. 2, when the steel sheet is wound into a coil, the rolling direction of the steel sheet (the longitudinal direction of the steel sheet) is curved in space according to the curvature of the steel sheet. On the other hand, in general, crystals grown at the time of secondary recrystallization do not change orientation in space. Therefore, in one grain, the rolling direction and the crystal direction have an angle that varies depending on the position in space. The variation becomes larger as the grains grow. That is, in the vicinity of the grain boundaries of secondary recrystallized grains, which are coarsened to such an extent that other secondary recrystallized grains are grown in the final stage of grain growth, the orientation change due to the curvature of the steel sheet becomes particularly large.

Further, if the secondary recrystallized grains are adjacent to each other, the difference in orientation between adjacent grains (difference in orientation of grain boundaries) becomes larger than the difference in orientation that each grain has when it is produced. That is, even if each crystal grain itself (recrystallization nucleus) is generated as a crystal grain having a nearly gaussian orientation and a small orientation difference, the orientation difference at the grain boundary when the crystal grains grow and are adjacent becomes larger.

For example, consider a case where the steel sheet is secondarily recrystallized in a state of being wound into a coil having a diameter of about 1000 mm. When this steel sheet is uncoiled from a coil and flattened after the finish annealing, the orientation of the steel sheet changes by about 0.1 ° per 1mm in the rolling direction due to the curvature of the steel sheet. The secondary recrystallized grains of the grain-oriented electrical steel sheet are coarse, and for example, if the grain size in the rolling direction is 50mm, the difference in orientation at the grain boundaries of the adjacent grains in the rolling direction also reaches 5 °.

In general, secondary recrystallization, that is, secondary recrystallization in a conventional grain-oriented electrical steel sheet, is not reversed (local change in crystal orientation) in the grain growth of secondary recrystallized grains. Therefore, if the grain size in the rolling direction is about 50mm, the difference in orientation at the grain boundaries of crystal grains adjacent to each other in the rolling direction, which is caused by the curvature of the steel sheet at the time of secondary recrystallization, becomes about 5 °.

On the other hand, in the grain-oriented electrical steel sheet of the present embodiment, local orientation change (commutation) occurs during the secondary recrystallization. This orientation change acts to suppress an increase in grain boundary energy and surface energy of the crystal as described later, and occurs so as to approach an orientation with high symmetry of the crystal. In the grain-oriented electrical steel sheet of the present embodiment, the crystal orientation is controlled to be in the vicinity of the gaussian orientation, and the above-described commutation basically occurs so as to approach the gaussian orientation, which is an orientation with high symmetry of the crystal. That is, the reversal acts to cancel the orientation change due to the curvature of the steel sheet and to return to the gaussian orientation for each secondary recrystallized grain. As a result, the difference in orientation at the grain boundaries of crystal grains adjacent in the rolling direction is reduced as compared with the case where no commutation occurs.

As described later, the above-described reversal is considered to occur due to rearrangement of dislocations remaining in the secondary recrystallized grains in the secondary recrystallization. In this rearrangement, the dislocations are locally arranged, and the orientation change corresponding to the inversion can be recognized as a local boundary, that is, the grain boundary. In the grain-oriented electrical steel sheet of the present embodiment, | β can be recognized between 2 measurement points adjacent to each other at an interval of 1mm in the secondary recrystallized grains₂-β₁A change in orientation of | ≧ 0.5 °.

In the grain-oriented electrical steel sheet of the present embodiment, the grain size in the rolling direction of the β crystal grains is made smaller than the grain size in the rolling direction of the secondary recrystallized grains by controlling the above-described "reversal". Specifically, the particle diameter RA of the β crystal grains_LAnd the grain size RB of the secondary recrystallized grains_LRB of 1.10 or less is satisfied_L÷RA_L. By particle size RA_LAnd particle diameter RB_LSatisfying the above conditions, the magnetostriction of the low magnetic field region is preferably reduced.

Due to the particle diameter RB_LSmall or due to even the particle size RB_LLarge but less direction change, particle size RA_LLarge, therefore, RB_L/RA_LIf the value is less than 1.10, the commutation frequency becomes insufficient, and the low-field magnetostriction may not be sufficiently improved. RB (radio B)_L/RA_LThe value is preferably 1.30 or more, more preferably 1.50 or more, further preferably 2.0 or more, further preferably 3.0 or more, and still further preferably 5.0 or more.

About RB_L/RA_LThe upper limit of the value is not particularly limited. If the frequency of occurrence of commutation is high, RB_L/RA_LWhen the value is increased, the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet is increased, and therefore, it is preferable for improvement of magnetostriction. On the other hand, since the commutation is also a residual of lattice defects in the crystal grains, if the frequency of occurrence is too high, the effect of improving the iron loss in particular may be reduced. Thus as RB_L/RA_LThe maximum value of the practical value is 80. Especially if iron losses need to be taken into account, RB_L/RA_LThe maximum value of the value is preferably 40, more preferably 30.

In addition, RB_L/RA_LThe value sometimes becomes lower than 1.0. RB (radio B)_LThe average grain size in the rolling direction is determined by the grain boundaries having an angle phi of 2 DEG or more. On the other hand, RA_LIs according to | beta₂-β₁I is a grain boundary of 0.5 ° or more and defines an average grain diameter in the rolling direction. In a simple manner, it is considered that the frequency of detecting a grain boundary having a small lower limit of the angle difference is high. That is, it is considered as RB_LGeneral ratio of RA_LBecome large, RB_L/RA_LValues above 1.0 are generally reached.

However, RB_LIs the grain diameter, RA, determined from the grain boundary of the angle phi_LBy basing on the angle of departure betaGrain size determined from grain boundary for RB_LAnd RA_LIn other words, the definition of the grain boundary for determining the grain size is different. Thus, RB_L/RA_LThe value sometimes becomes lower than 1.0.

For example, | β₂-β₁Even if | is less than 0.5 ° (e.g., 0 °), if the off-angle α and/or the off-angle γ are large, the angle Φ becomes sufficiently large. That is, there are grain boundaries that do not satisfy the boundary condition BA but satisfy the boundary condition BB. If the grain boundary increases, the grain size RB_LBecomes smaller, as a result, RB_L/RA_LThe value may become lower than 1.0. In the present embodiment, each condition is controlled so that the frequency of occurrence of commutation by the slip angle β becomes high. When the control of the commutation is insufficient and the deviation from the present embodiment is large, the deviation angle β does not change, RB_L/RA_LThe value becomes lower than 1.0. As described above, in the present embodiment, the generation frequency of β -grain boundaries and RB are sufficiently increased_L/RA_LA value of 1.10 or more is a requirement.

In addition, in the grain-oriented electrical steel sheet according to the present embodiment, boundaries between 2 measurement points adjacent to each other on the rolled surface and spaced apart by 1mm are classified into cases 1 to 4 in table 1. Particle diameter RB described above_LThe grain size RA is determined from the grain boundaries satisfying case 1 and/or case 2 in Table 1_LThe grain boundaries are determined from the grain boundaries satisfying case 1 and/or case 3 in table 1. For example, the off-angle of crystal orientation is measured on a measurement line including at least 500 measurement points along the rolling direction, and the average value of the length of the line segment sandwiched by the grain boundaries of case 1 and/or case 2 on the measurement line is set as the grain diameter RB_L. Similarly, the average value of the length of the line segment sandwiched by the grain boundaries in case 1 and/or case 3 on the above-mentioned measurement line was set as the particle diameter RA_L。

TABLE 1

RB_L/RA_LControl of value to low field magnetThe reason why the expansion and contraction have an influence is not necessarily clear, but it is considered that, as schematically illustrated in fig. 2, by causing a change in orientation (local change in orientation) in one secondary recrystallized grain, a relative orientation difference with respect to adjacent crystal grains can be reduced (a change in crystal orientation in the vicinity of a grain boundary becomes gentle), and the continuity of crystal orientation of the entire grain-oriented electrical steel sheet can be improved.

[ embodiment 3 ]

Next, a grain-oriented electrical steel sheet according to embodiment 3 of the present invention will be described below. Hereinafter, differences from the above-described embodiment will be mainly described, and redundant description will be omitted.

In the grain-oriented electrical steel sheet according to embodiment 3 of the present invention, the grain size of the β crystal grains in the direction perpendicular to the rolling direction is smaller than the grain size of the secondary recrystallized grains in the direction perpendicular to the rolling direction. That is, the grain-oriented electrical steel sheet of the present embodiment has β crystal grains and secondary recrystallized grains, the grain size of which is controlled in the direction perpendicular to the rolling direction.

Specifically, in the grain-oriented electrical steel sheet of the present embodiment, the average crystal grain size in the rolling perpendicular direction C determined based on the boundary condition BA is defined as the grain size RA_CThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RA is small_CAnd particle diameter RB_CRB of 1.10 or less is satisfied_C÷RA_C. In addition, RB is preferable_C÷RA_C≤80。

This specification indicates the above-described "reversal" situation with respect to the direction perpendicular to the rolling. That is, it means that at least one | β is contained in secondary recrystallized grains having a grain boundary at a boundary with an angle of 2 ° or more₂-β₁The crystal grains having | of 0.5 ° or more and the boundary of an angle Φ of less than 2 ° exist at corresponding frequencies with respect to the rolling vertical direction. In the present embodiment, the grain size RA in the vertical direction of rolling is used for the state of the change_CAnd particle diameter RB_CTo evaluate and specify.

Due to the particle diameter RB_CSmall or due to even the particle size RB_CLarge but less direction change, particle size RA_CLarge, thus RB_C/RA_CIf the value is less than 1.10, the commutation frequency becomes insufficient, and the low-field magnetostriction may not be sufficiently improved. RB (radio B)_C/RA_CThe value is preferably 1.30 or more, more preferably 1.50 or more, further preferably 2.0 or more, further preferably 3.0 or more, and still further preferably 5.0 or more.

About RB_C/RA_CThe upper limit of the value is not particularly limited. If the frequency of occurrence of commutation is high, RB_C/RA_CWhen the value is increased, the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet is increased, and therefore, it is preferable for improvement of magnetostriction. On the other hand, since the commutation is also a residual of lattice defects in the crystal grains, if the frequency of occurrence is too high, the effect of improving the iron loss in particular may be reduced. Thus as RB_C/RA_CThe maximum value of the practical value is 80. Especially if iron losses need to be taken into account, RB_C/RA_CThe maximum value of the value is preferably 40, more preferably 30.

In addition, RB_CIs the grain diameter, RA, determined from the grain boundary of the angle phi_CThe grain size is determined by the grain boundary based on the off angle β. For RB_CAnd RA_CIn other words, RB is different in the definition of grain boundaries for determining the particle size_C/RA_CThe value sometimes becomes lower than 1.0.

Particle diameter RB described above_CThe grain size RA is determined from the grain boundaries satisfying case 1 and/or case 2 in Table 1_CThe grain boundaries are determined from the grain boundaries satisfying case 1 and/or case 3 in table 1. For example, the off-angle of crystal orientation is measured on a measurement line including at least 500 measurement points in the direction perpendicular to rolling, and the average value of the lengths of the line segments sandwiched by the grain boundaries in case 1 and/or case 2 on the measurement line is set as the grain diameter RB_C. Similarly, the average value of the length of the line segment sandwiched by the grain boundaries in case 1 and/or case 3 on the above-mentioned measurement line was set as the particle diameter RA_C。

RB_C/RA_CThe reason why the control of the value has an influence on the low-field magnetostriction is not necessarily clear, but it is considered that the value is controlled by a secondary recombinationThe occurrence of a change in orientation (local change in orientation) in the crystal grains reduces a relative orientation difference with respect to adjacent crystal grains, and serves to improve the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet.

[ 4 th embodiment ]

Next, a grain-oriented electrical steel sheet according to embodiment 4 of the present invention will be described below. Hereinafter, differences from the above-described embodiment will be mainly described, and redundant description will be omitted.

In the grain-oriented electrical steel sheet according to embodiment 4 of the present invention, the grain size of the β crystal grains in the rolling direction is smaller than the grain size of the β crystal grains in the direction perpendicular to the rolling direction. That is, the grain-oriented electrical steel sheet of the present embodiment has β crystal grains whose grain sizes are controlled in the rolling direction and the direction perpendicular to the rolling direction.

Specifically, in the grain-oriented electrical steel sheet of the present embodiment, the average crystal grain size in the rolling direction L determined based on the boundary condition BA is defined as the grain size RA_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as the grain diameter RA_CWhen the particle diameter RA is small_LAnd particle size RA_CRA is satisfied at 1.15. ltoreq._C÷RA_L. In addition, RA is preferred_C÷RA_L≤10。

In the following description, the shape of the crystal grain may be referred to as "in-plane anisotropy" or "flat (shape)". The shapes of these crystal grains are described as viewed from the surface (rolling surface) of the steel sheet. That is, the size of the crystal grains in the thickness direction (the shape observed in the thickness cross section) is not considered. Incidentally, in a grain-oriented electrical steel sheet, substantially all crystal grains have the same size as the thickness of the steel sheet in the sheet thickness direction. That is, in grain-oriented electrical steel sheets, the thickness of the steel sheet is often occupied by one crystal grain except for a specific region such as the vicinity of a grain boundary.

RA as described above_C/RA_LThe value specification indicates the above-described "reversal" with respect to the rolling direction and the direction perpendicular to the rolling direction. That is, the frequency at which local changes in crystal orientation, which means the degree of commutation, occur depends on the in-plane direction of the steel sheetThe direction is different. In the present embodiment, the state of the change is defined by the grain sizes RA in 2 directions orthogonal to each other in the plane of the steel sheet_CAnd particle size RA_LTo evaluate and specify.

RA_C/RA_LA value exceeding 1 indicates that the β crystal grains defined by the direction change extend in the direction perpendicular to the rolling direction on average, and have a flattened form flattened in the rolling direction. That is, it indicates that the form of crystal grains defined by β crystal grain boundaries has anisotropy.

The reason why the low-field magnetostriction is improved by the shape of the β crystal grains having in-plane anisotropy is not clear, but the following is conceivable. As described above, in a low magnetic field, when the 180 ° magnetic domain moves, "continuity" with the adjacent crystal grains is important. For example, when one secondary recrystallized grain is divided into small regions by inversion, if the number of the small regions is the same (the areas of the small regions are the same), the existence ratio of the boundaries (β grain boundaries) caused by the inversion of the anisotropic shape becomes larger for the shape of the small regions than for the isotropic shape. I.e. by RA_C/RA_LThe control of the value increases the frequency of occurrence of the commutation as a local orientation change, and is considered to improve the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet.

The anisotropy caused by such a commutation is considered to be caused by some of the following anisotropy existing in the steel sheet before the secondary recrystallization: for example, anisotropy of shape of primary recrystallized grains; anisotropy (population distribution) of crystal orientation distribution of primary recrystallized grains caused by anisotropy of shape of hot-rolled sheet grains; the arrangement of precipitates stretched during hot rolling and precipitates broken into rows in the rolling direction; distribution of precipitates caused by variation in thermal history in the width direction or the longitudinal direction of the coil; anisotropy of crystal grain size distribution; and so on. However, the details of the mechanism of occurrence are not clear. However, if the steel sheet in the secondary recrystallization has a temperature gradient, direct anisotropy is imparted to the growth of crystal grains (disappearance of dislocations and formation of grain boundaries). That is, the temperature gradient in the secondary recrystallization becomes a very effective control condition for controlling the anisotropy defined in the present embodiment. The details will be described in connection with the manufacturing method.

In addition, although the process of imparting anisotropy by utilizing the temperature gradient at the time of the secondary recrystallization is also involved, it is also preferable in view of the general production method in the related art that the direction in which the β crystal grains extend be the rolling perpendicular direction in the present embodiment. In this case, the grain diameter RA in the rolling direction_LGrain diameter RA in the direction perpendicular to rolling_CAnd smaller values. The relationship between the rolling direction and the rolling direction perpendicular to the rolling direction will be described in association with the manufacturing method. The direction in which the β crystal grains extend is not determined by the temperature gradient, but is determined by the frequency of occurrence of the β crystal grain boundaries.

Due to the particle size RA_CSmall or due to even particle size RA_CLarge particle size RA_LIs also large, and therefore RA_C/RA_LIf the value is less than 1.15, the commutation frequency becomes insufficient, and the low-field magnetostriction may not be sufficiently improved. RA_C/RA_LThe value is preferably 1.50 or more, more preferably 1.80 or more, and further preferably 2.10.

In connection with RA_C/RA_LThe upper limit of the value is not particularly limited. If the frequency of occurrence and the direction of extension of the commutation are limited to a particular direction, RA_C/RA_LWhen the value is increased, the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet is increased, and therefore, it is preferable for improvement of magnetostriction. On the other hand, since the commutation is also a residual of lattice defects in the crystal grains, if the frequency of occurrence is too high, the effect of improving the iron loss in particular may be reduced. Thus, as RA_C/RA_LThe maximum practical value of the value is 10. Especially if iron losses need to be taken into account, RA_C/RA_LThe maximum value of the value is preferably 6, more preferably 4.

In addition, the grain-oriented electrical steel sheet of the present embodiment includes RA described above_C/RA_LOther than the control of the value, the particle diameter RA is the same as that of embodiment 2_LAnd particle diameter RB_LPreferably 1.10. ltoreq. RB_L÷RA_L。

This provision specifies that "commutation" has taken place. For example, the particle diameter RA_CAnd RA_LBased on | β between 2 adjacent measurement points₂-β₁The grain size, | is 0.5 ° or more of grain boundary, but even if "commutation" does not occur at all, all the grain boundaries have an angle Φ of 2.0 ° or more, and the above-mentioned RA may be satisfied_C/RA_LThe value is obtained. Even if RA is satisfied_C/RA_LIf the angles Φ of all grain boundaries are 2.0 ° or more, the secondary recrystallized grains recognized in general become only flat shapes, and thus the above-described effects of the present embodiment cannot be preferably obtained. In the present embodiment, since it is assumed that there are grain boundaries (grain boundaries dividing secondary recrystallized grains) satisfying the boundary condition BA and not satisfying the boundary condition BB, it is difficult for all the grain boundaries to have an angle Φ of 2.0 ° or more, but it is preferable that the angle Φ be not less than the angle Φ satisfying RA described above_C/RA_LIn addition to the value, RB is satisfied_L/RA_LThe value is obtained.

In addition, in the present embodiment, except for the control of RB for the rolling direction_L/RA_LIn addition to the above values, the grain size RA in the direction perpendicular to the rolling direction is the same as in embodiment 3_CAnd particle diameter RB_CRB of 1.10 or less is satisfied_C/RA_CThis is not problematic, but rather preferable from the viewpoint of improving the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet.

Further, in the grain-oriented electrical steel sheet of the present embodiment, it is preferable that the grain diameters of the secondary recrystallized grains in the rolling direction and the direction perpendicular to the rolling direction be controlled.

Specifically, in the grain-oriented electrical steel sheet of the present embodiment, the average crystal grain diameter in the rolling direction L determined based on the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RB_LAnd particle diameter RB_CPreferably 1.50. ltoreq. RB_C÷RB_L. In addition, RB is preferable_C÷RB_L≤20。

This provisionRegardless of the "reversal" described above, the secondary recrystallized grains are elongated in the direction perpendicular to the rolling. Thus, this feature is not distinctive per se. However, in the present embodiment, it is preferable that RA be controlled_C/RA_LOn the basis of the value, RB_C/RB_LThe values satisfy the above numerical ranges.

In the present embodiment, the above-described commutation is performed in RA of β crystal grains_C/RA_LWhen the value is controlled, the form of the secondary recrystallized grains tends to have a large in-plane anisotropy. Conversely, when the off angle β is reversed as in the present embodiment, the shape of the secondary recrystallized grains tends to have in-plane anisotropy and the shape of the β crystal grains tends to have in-plane anisotropy.

RB_C/RB_LThe value is preferably 1.80 or more, more preferably 2.00 or more, and further preferably 2.50 or more. RB (radio B)_C/RB_LThe upper limit of the value is not particularly limited.

As control RB_C/RB_LPractical methods of values include, for example, the following processes: in the final annealing, heating is performed preferentially from the end of the coil width, and a temperature gradient is applied in the coil width direction (coil axis direction) to grow secondary recrystallized grains. In this case, the grain size in the coil width direction (for example, the direction perpendicular to rolling) of the secondary recrystallized grains may be controlled to be the same as the coil width while maintaining the grain size in the coil circumferential direction (for example, the rolling direction) of the secondary recrystallized grains at about 50 mm. For example, the full width of a coil having a width of 1000mm may be occupied by one grain. In this case, as RB_C/RB_LThe upper limit of the value is 20.

Further, when the secondary recrystallization is performed by the continuous annealing process so that the rolling direction, not the rolling perpendicular direction, has a temperature gradient, the maximum value of the grain size of the secondary recrystallized grains is not limited to the coil width, and can be set to a larger value. Even in this case, according to the present embodiment, the crystal grains are appropriately divided by the β -grain boundaries generated by the commutation, and the above-described effects of the present embodiment can be obtained.

In the grain-oriented electrical steel sheet of the present embodiment, the frequency of occurrence of the commutation with respect to the off angle β is preferably controlled with respect to the rolling direction and the direction perpendicular to the rolling direction.

Specifically, in the grain-oriented electrical steel sheet of the present embodiment, the average crystal grain size in the rolling direction L determined based on the boundary condition BA is defined as the grain size RA_LThe average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the rolling vertical direction C determined based on the boundary condition BA is defined as the grain diameter RA_CThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RA is small_LParticle diameter RA_CParticle diameter RB_LAnd particle diameter RB_CPreferably satisfies (RB)_C×RA_L)÷(RB_L×RA_C)<1.0. The lower limit is not particularly limited, but is 0.2 if the conventional technique is assumed<(RB_C×RA_L)÷(RB_L×RA_C) And (4) finishing.

This specification represents the in-plane anisotropy of the frequency of occurrence of the above-described "commutation". I.e., (RB) described above_C·RA_L)/(RB_L·RA_C) "the degree of occurrence of reversal in which the secondary recrystallized grains are divided in the rolling vertical direction: RB (radio B)_C/RA_C"and" degree of occurrence of reversal of division of secondary recrystallized grains in the rolling direction: RB (radio B)_L/RA_L"ratio of the two components. When the value is less than 1, it means that one secondary recrystallized grain is largely divided in the rolling direction by the commutation (β grain boundary).

In addition, from another point of view, the above (RB)_C·RA_L)/(RB_L·RA_C) To the extent of "secondary recrystallized grains are flattened: RB (radio B)_C/RB_LDegree of flatness of "and" β grains: RA_C/RA_L"ratio of the two components. When the value is less than 1, it means that the β crystal grains dividing one secondary recrystallized grain become a shape flatter than the secondary recrystallized grains.

That is, the β -grain boundary is more apt to divide the secondary recrystallized grains in the rolling direction than to divide the secondary recrystallized grains in the rolling perpendicular direction. That is, the β -grain boundary tends to extend in the direction in which the secondary recrystallized grains extend. It is considered that this tendency of the β -grain boundary is that when the secondary recrystallized grains are extended, the inversion acts to increase the occupied area of the crystals of a specific orientation.

(RB_C·RA_L)/(RB_L·RA_C) The value of (b) is preferably 0.9 or less, more preferably 0.8 or less, and still more preferably 0.5 or less. As described above, (RB)_C·RA_L)/(RB_L·RA_C) The lower limit of (b) is not particularly limited, but may be more than 0.2 in consideration of industrial realizability.

Particle diameter RB described above_LAnd particle diameter RB_CThe grain boundaries are determined from the case 1 and/or case 2 satisfying table 1. The above particle diameter RA_LAnd particle size RA_CThe grain boundaries were determined from the case 1 and/or case 3 satisfying table 1. For example, the off-angle of crystal orientation is measured on a measurement line including at least 500 measurement points in the direction perpendicular to rolling, and the average value of the lengths of the line segments sandwiched by the grain boundaries of cases 1 and/or 3 on the measurement line is set as the grain diameter RA_C. Particle size RA_LParticle diameter RB_LParticle diameter RB_CCan be obtained in the same manner.

[ features common to the embodiments ]

Next, the grain-oriented electrical steel sheets according to the above embodiments will be described with respect to common technical features.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the average crystal grain diameter in the rolling direction L determined based on the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the vertical rolling direction C determined based on the boundary condition BB is defined as the grain diameter RB_CWhen the particle diameter RB_LAnd particle diameter RB_CPreferably 22mm or more.

The commutation is considered to be caused by dislocations accumulated during the growth of secondary recrystallized grains. I.e. after a commutation has taken place, toUntil the next commutation occurs, the secondary recrystallized grains need to grow to a considerable extent. Thus, particle diameter RB_LAnd particle diameter RB_CIf the thickness is less than 15mm, commutation hardly occurs, and sufficient improvement of low-field magnetostriction by commutation may become difficult. Particle size RB_LAnd particle diameter RB_CPreferably 15mm or more. Particle size RB_LAnd particle diameter RB_CPreferably 22mm or more, more preferably 30mm or more, and further preferably 40mm or more.

Particle size RB_LAnd particle diameter RB_CThe upper limit of (b) is not particularly limited. In the production of a normal grain-oriented electrical steel sheet, a steel coil material after primary recrystallization is taken as a coil, and {110} is caused by secondary recrystallization in a state where the coil material has a curvature in the rolling direction<001>Oriented grains are generated and grown, so that the off-angle β continuously changes depending on the position in the rolling direction within one grain. Therefore, if the particle diameter RB_LIf the deviation angle β is increased, the magnetostriction may be increased. Therefore, it is preferable to avoid increasing the particle diameter RB without limitation_L. If industrial realizability is also taken into consideration, RB is the particle diameter_LThe upper limit is preferably 400mm, more preferably 200mm, and still more preferably 100 mm.

In the production of a normal grain-oriented electrical steel sheet, a steel coil material after primary recrystallization is coiled and heated, and {110} is caused to be recrystallized secondarily<001>The oriented crystal grains are generated and grown, so that the secondary recrystallized grains grow from the end portion side of the coil where the temperature rises first toward the center side of the coil where the temperature rises later. In the above-mentioned production method, for example, if the coil width is set to 1000mm, 500mm which is about half the coil width is given as the particle diameter RB_CThe upper limit of (3). Of course, in various embodiments, it is not excluded that the full width of the coil is the particle size RB_CThe case (1).

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the average crystal grain size in the rolling direction L determined based on the boundary condition BA is defined as the grain size RA_LIn the rolling vertical direction C obtained based on the boundary condition BAThe average crystal particle diameter is defined as the particle diameter RA_CWhen it is used, the particle diameter RA is preferred_LHas a particle diameter RA of 30mm or less_CIs 400mm or less.

Particle size RA_LA smaller value of (b) means a higher frequency of occurrence of the reversal in the rolling direction. Particle size RA_LIt may be 40mm or less, but is preferably 30mm or less, and more preferably 20mm or less.

In addition, the particle diameter RA is not changed sufficiently_CIf the angle is increased, the slip angle β may be increased, and the magnetostriction may be increased. Therefore, it is preferable to avoid increasing the particle diameter RA without limitation_C. If industrial realizability is also taken into consideration, the particle size RA is used_CThe upper limit is preferably 400mm, more preferably 200mm, still more preferably 100mm, yet more preferably 40mm, and yet more preferably 30 mm.

Particle size RA_LAnd particle size RA_CThe lower limit of (b) is not particularly limited. In each embodiment, the measurement interval of the crystal orientation is set to 1mm, and therefore the particle diameter RA is set to be the particle diameter RA_LAnd particle size RA_CThe lowest value of (2) is 1 mm. However, in each embodiment, it is not excluded that the particle size RA is made smaller than 1mm, for example, by setting the measurement interval to be smaller than 1mm_LAnd particle size RA_CA steel plate which becomes lower than 1 mm. However, since commutation is accompanied by the presence (although very few) of lattice defects in the crystal, there is also a concern about adverse effects on the magnetic properties when the frequency of commutation is too high. In addition, if industrial realizability is also considered, the particle size RA is considered_LAnd particle size RA_CA preferable lower limit is 5 mm.

Further, in the measurement of the crystal grain size in the grain-oriented electrical steel sheet of each embodiment, uncertainty of the grain size of at most 2mm is included for one crystal grain. Therefore, the grain size measurement (the measurement of the orientation of at least 500 points at 1mm intervals on the rolled surface) is a measurement of 5 or more points in total on positions sufficiently spaced apart in the direction orthogonal to the direction of the predetermined grain size in the steel sheet surface, that is, positions for measurement of different crystal grains. All the particle diameters obtained by the measurement of 5 or more positions in total are measuredLine averaging, the above uncertainty can be eliminated. For example, for the particle size RA_CAnd particle diameter RB_CThe grain diameter RA is measured at 5 or more positions sufficiently spaced in the rolling direction_LAnd particle diameter RB_LThe average grain size may be determined by performing the measurement at 5 or more positions sufficiently spaced apart in the vertical direction of rolling and performing the orientation measurement at measurement points of 2500 or more in total.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the standard deviation σ (| β |) of the absolute value of the off-angle β is preferably 0 ° to 1.70 °.

In the case where commutation does not occur so much, the low-field magnetostriction cannot be sufficiently reduced. This is believed to be: a decrease in low field magnetostriction indicates that the off-angle is uniform in a particular direction. That is, it is considered that the decrease in low-field magnetostriction does not result from orientation selection by predation at the initial generation stage or growth stage including nucleus generation of secondary recrystallization. That is, in order to obtain the effects of the above-described embodiments, it is not particularly necessary to make the crystal orientation approach a specific direction, for example, to reduce the absolute value and standard deviation of the off angle, as in the conventional orientation control. However, even in a steel sheet in which the above-described commutation has sufficiently occurred, the "slip angle" can be easily controlled within a characteristic range. For example, when the crystal orientation changes little by little due to the commutation with respect to the off-angle β, the absolute value of the off-angle approaching zero does not become an obstacle in the above-described embodiment. Further, for example, when the crystal orientation changes little by little due to the change of direction with respect to the off-angle β, the crystal orientation itself converges to a specific orientation, and as a result, the standard deviation of the off-angle approaches zero, which does not become an obstacle in the above-described embodiment.

Therefore, in each embodiment, the standard deviation σ (| β |) of the absolute value of the deviation angle β may be 0 ° to 1.70 °.

The standard deviation σ (| β |) of the absolute value of the deviation angle β can be obtained as follows.

The grain-oriented electrical steel sheet has a concentration ratio toward the {110} <001> orientation increased by forming secondary recrystallization of crystal grains grown to a size of about several cm. In each embodiment, it is necessary to recognize the above-described variation in crystal orientation in the grain-oriented electrical steel sheet. Therefore, the crystal orientation at 500 points or more was measured for a region containing at least 20 secondary recrystallized grains.

In addition, in each embodiment, it should not be considered that "one secondary recrystallized grains are regarded as a single crystal, and the secondary recrystallized grains have exactly the same crystal orientation". That is, in each embodiment, local orientation change in the single coarse secondary recrystallized grain to the extent that it has not been conventionally considered as a grain boundary exists, and it is necessary to detect such orientation change.

Therefore, for example, it is preferable that the measurement points of the crystal orientation are distributed at equal intervals in a certain area set so as not to be related to the boundaries (grain boundaries) of the crystal grains. Specifically, it is preferable that: on the steel sheet surface, measurement points were distributed at equal intervals of 5mm in length and width in an area of Lmm × Mmm (L, M >100 among them) so as to include at least 20 crystal grains or more, and the crystal orientation of each measurement point was measured to obtain data of 500 points or more in total. When the measured points are grain boundaries and some specific points, the data thereof is not used. In addition, it is necessary to expand the measurement range described above from the region necessary for specifying the magnetic properties of the target steel sheet (for example, if the coil is an actual coil, the range in which the magnetic properties described in the manufacturing process specifications are measured).

Then, the deviation angle β is determined for each measurement point, and the standard deviation σ (| β |) of the absolute value of the deviation angle β is calculated. In the grain-oriented electrical steel sheet according to each embodiment, σ (| β |) is preferably within the above numerical range.

Further, σ (| β |) is generally considered as a factor that should be reduced in order to improve magnetic characteristics or magnetostriction in a middle magnetic field of about 1.7T. However, the characteristics achieved only by the control of σ (| β |) are limited. In each of the above embodiments, in addition to the above technical features, σ (| β |) is controlled together, thereby preferably affecting the continuity of the crystal orientation of the entire grain-oriented electrical steel sheet.

The standard deviation σ (| β |) of the absolute value of the deviation angle β is more preferably 1.50 or less, still more preferably 1.30 or less, and still more preferably 1.10 or less. σ (| β |) may of course also be 0.

The grain-oriented electrical steel sheet of the present embodiment may have an interlayer, an insulating coating, or the like on the steel sheet, and the above-described crystal orientation, grain boundary, average crystal grain size, or the like may be determined depending on the steel sheet having no coating or the like. That is, when the grain-oriented electrical steel sheet as a measurement sample has an insulating film or the like on the surface, the film or the like may be removed and then the crystal orientation or the like may be measured.

For example, as a method for removing the insulating film, a grain-oriented electrical steel sheet having a coating film may be immersed in a high-temperature alkaline solution. Specifically, in the presence of NaOH: 30 to 50 mass% + H₂O: the insulating film can be removed from the grain-oriented electrical steel sheet by immersing the sheet in a 50 to 70 mass% aqueous solution of sodium hydroxide at 80 to 90 ℃ for 5 to 10 minutes, and then washing with water and drying. The time for immersing in the aqueous sodium hydroxide solution can be varied depending on the thickness of the insulating film.

For example, as a method for removing the intermediate layer, the electrical steel sheet from which the insulating film has been removed may be immersed in high-temperature hydrochloric acid. Specifically, the concentration of hydrochloric acid preferable for removing the intermediate layer to be dissolved is examined in advance, and the intermediate layer can be removed by immersing the substrate in hydrochloric acid having such a concentration, for example, 30 to 40 mass% hydrochloric acid, at 80 to 90 ℃ for 1 to 5 minutes, and then washing with water and drying. In general, the respective coatings are removed by using a treating liquid separately so that an alkali solution is used for removing the insulating coating and hydrochloric acid is used for removing the intermediate layer.

Next, the chemical composition of the grain-oriented electrical steel sheet according to each embodiment will be described. The grain-oriented electrical steel sheet according to each embodiment contains a basic element, a selective element if necessary, and Fe and impurities in the remaining part as chemical components.

The grain-oriented electrical steel sheet according to each embodiment contains, as basic elements (main alloying elements), Si (silicon): 2.0 to 7.0 percent.

In order to concentrate the crystal orientation to the {110} <001> orientation, the content of Si is preferably 2.0 to 7.0%.

In each embodiment, impurities may be contained as a chemical composition. The term "impurities" refers to elements mixed from ores and scraps as raw materials or from a production environment or the like in the industrial production of steel. The upper limit of the total content of impurities may be, for example, 5%.

In addition, in each embodiment, a selective element may be contained in addition to the above-described basic elements and impurities. For example, as an optional element, Nb, V, Mo, Ta, W, C, Mn, S, Se, Al, N, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni, or the like may be contained instead of a part of Fe as the above-described remainder. The above-mentioned optional elements may be contained according to the purpose. Therefore, the lower limit of the above-mentioned optional element is not necessarily limited, and the lower limit may be 0%. Further, even if these optional elements are contained as impurities, the above effects are not impaired.

Nb (niobium): 0 to 0.030%

V (vanadium): 0 to 0.030%

Mo (molybdenum): 0 to 0.030%

Ta (tantalum): 0 to 0.030%

W (tungsten): 0 to 0.030%

Nb, V, Mo, Ta, and W can be used as elements having characteristic effects in each embodiment. In the following description, one or two or more elements among Nb, V, Mo, Ta, and W may be collectively referred to as "Nb group element".

The Nb group element may preferably function to form a commutation which is a feature of the grain-oriented electrical steel sheet of each embodiment. However, since the Nb group element contributes to the occurrence of the commutation during the manufacturing process, the Nb group element does not necessarily have to be finally contained in the grain-oriented electrical steel sheet of each embodiment. For example, the Nb group element is likely to be discharged outside the system by purification in the final annealing described later. Therefore, even when the slab contains the Nb group element and the Nb group element is used in the manufacturing process to increase the frequency of commutation, the Nb group element may be discharged out of the system by the subsequent purification annealing. Therefore, the Nb group element may not be detected as the chemical composition of the final product.

Therefore, in each embodiment, only the upper limit of the content of the Nb group element is defined as the chemical composition of the grain-oriented electrical steel sheet as the final product. The upper limit of each Nb group element is preferably 0.030%. On the other hand, as described above, even if the Nb group element is used in the manufacturing process, the content of the Nb group element in the final product may be 0. Therefore, the lower limit of the content of the Nb group element is not particularly limited, and each lower limit may be 0%.

The grain-oriented electrical steel sheet according to each embodiment of the present invention preferably contains at least 1 selected from Nb, V, Mo, Ta, and W in a total amount of 0.0030 to 0.030 mass% as a chemical composition.

Since it is difficult to consider that the content of the Nb group element increases during the manufacturing process, if the Nb group element is detected as the chemical composition of the final product, it indicates that the commutation control is performed using the Nb group element during the manufacturing process. In order to preferably control the commutation during the manufacturing process, the total content of the Nb group element of the final product is preferably 0.0030% or more, more preferably 0.0050% or more. On the other hand, if the total content of the Nb group elements in the final product exceeds 0.030%, although the occurrence frequency of the commutation can be maintained, the magnetic characteristics may be degraded. Therefore, the total content of Nb group elements in the final product is preferably 0.030% or less. The function of the Nb group element will be described later in connection with the production method.

C (carbon): 0 to 0.0050%

Mn (manganese): 0 to 1.0%

S (sulfur): 0 to 0.0150 percent

Se (selenium): 0 to 0.0150 percent

Al (acid-soluble aluminum): 0 to 0.0650%

N (nitrogen): 0 to 0.0050%

Cu (copper): 0 to 0.40 percent

Bi (bismuth): 0 to 0.010%

B (boron): 0 to 0.080%

P (phosphorus): 0 to 0.50 percent

Ti (titanium): 0 to 0.0150 percent

Sn (tin): 0 to 0.10 percent

Sb (antimony): 0 to 0.10 percent

Cr (chromium): 0 to 0.30 percent

Ni (nickel): 0 to 1.0%

These optional elements may be contained according to a known purpose. The lower limit of the content of these optional elements is not necessarily required, and the lower limit may be 0%. The total content of S and Se is preferably 0 to 0.0150%. The total of S and Se means that at least one of S and Se is contained, and is the total content thereof.

Further, in the grain-oriented electrical steel sheet, since the decarburization annealing and the purification annealing at the time of the secondary recrystallization are performed, a relatively large change in chemical composition (decrease in content) occurs. Depending on the element, the content may be reduced to such a level (1ppm or less) that cannot be detected by a usual analytical method by purification annealing. The above chemical composition of the grain-oriented electrical steel sheet of each embodiment is a chemical composition in a final product. Generally, the chemical composition of the final product is different from the chemical composition of the slab as the starting raw material.

The chemical composition of the grain-oriented electrical steel sheet according to each embodiment may be measured by a usual analysis method. For example, the chemical composition of a grain-oriented electrical steel sheet can be measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). Specifically, a 35mm square test piece collected from a grain-oriented electrical steel sheet was measured under conditions based on a previously prepared calibration curve using an ICPS-8100 (measuring apparatus) manufactured by Shimadzu corporation, to determine the chemical composition. C and S can be measured by a combustion-infrared coefficient method, and N can be measured by an inert gas melting-thermal conductivity method.

The chemical composition is a component of a grain-oriented electrical steel sheet. When the surface of the grain-oriented electrical steel sheet as a measurement sample has an insulating coating or the like, the chemical composition is measured after removing the coating or the like by the above-described method.

The grain-oriented electrical steel sheet according to each embodiment of the present invention is characterized in that the secondary recrystallized grains are divided into small regions having slightly different off-angles β, and therefore, the magnetostriction in the low magnetic field region is reduced. Therefore, the grain-oriented electrical steel sheet according to each embodiment is not particularly limited in the film structure on the steel sheet, the presence or absence of the domain-refining treatment, and the like. In each embodiment, an arbitrary coating film may be formed on the steel sheet according to the purpose, and the magnetic domain segmentation process may be performed as necessary.

The grain-oriented electrical steel sheet according to each embodiment of the present invention may have an intermediate layer disposed in contact with the grain-oriented electrical steel sheet (silicon steel sheet), and an insulating film disposed in contact with the intermediate layer.

Fig. 3 is a schematic cross-sectional view of a grain-oriented electrical steel sheet according to a preferred embodiment of the present invention. As shown in fig. 3, the grain-oriented electrical steel sheet 10 (silicon steel sheet) according to the present embodiment may have an intermediate layer 20 disposed in contact with the grain-oriented electrical steel sheet 10 (silicon steel sheet) and an insulating film 30 disposed in contact with the intermediate layer 20, when viewed from a cut plane parallel to the sheet thickness direction in the cutting direction.

For example, the intermediate layer may be a layer mainly composed of an oxide, a layer mainly composed of a carbide, a layer mainly composed of a nitride, a layer mainly composed of a boride, a layer mainly composed of a silicide, a layer mainly composed of a phosphide, a layer mainly composed of a sulfide, a layer mainly composed of an intermetallic compound, or the like. These intermediate layers can be formed by heat treatment in an atmosphere in which oxidation-reduction is controlled, Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), or the like.

In the grain oriented electrical steel sheet according to each embodiment of the present invention, the intermediate layer may be a forsterite coating film having an average thickness of 1 to 3 μm. The forsterite coating is formed of Mg₂SiO₄Is a coating film of the main body. When viewed in cross section, the interface between the forsterite coating and the grain-oriented electrical steel sheet is an interface where the forsterite coating is embedded in the steel sheet.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the intermediate layer may beAn oxide film having an average thickness of 2 to 500 nm. The oxide film is formed of SiO₂Is a coating film of the main body. The interface between the oxide film and the grain-oriented electrical steel sheet becomes a smooth interface when viewed on the cross section.

The insulating film may be mainly composed of phosphate and colloidal silica and has an average thickness of 0.1 to 10 μm, or may be mainly composed of alumina sol and boric acid and has an average thickness of 0.5 to 8 μm.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the magnetic domains may be subdivided by at least one of imparting local micro-deformation and forming local grooves. In addition, local micro-deformations or local grooves may be imparted or formed by laser, plasma, mechanical methods, etching, or other methods. For example, local micro-deformations or local grooves may be imparted or formed in the following manner: the rolling direction of the steel sheet is formed in a linear or dot shape so as to extend in a direction intersecting the rolling direction, and the rolling direction interval is 4mm to 10 mm.

[ method for producing grain-oriented Electrical Steel sheet ]

Next, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described.

Fig. 4 is a flowchart illustrating a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention. As shown in fig. 4, the method for manufacturing a grain-oriented electrical steel sheet (silicon steel sheet) according to the present embodiment includes: the method comprises the following steps of casting, hot rolling, hot rolled plate annealing, cold rolling, decarburization annealing, annealing separating agent coating and finished product annealing.

Specifically, the method for manufacturing a grain-oriented electrical steel sheet (silicon steel sheet) according to the present embodiment is as follows:

the following slabs were cast in the casting process: as a chemical composition, Si: 2.0 to 7.0%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0-0.030%, W: 0-0.030%, C: 0-0.0850%, Mn: 0-1.0%, S: 0-0.0350%, Se: 0-0.0350%, Al: 0-0.0650%, N: 0-0.0120%, Cu: 0 to 0.40%, Bi: 0-0.010%, B: 0-0.080%, P: 0-0.50%, Ti: 0-0.0150%, Sn: 0-0.10%, Sb: 0-0.10%, Cr: 0-0.30%, Ni: 0-1.0%, the remainder comprising Fe and impurities;

in the decarburization annealing step, the primary recrystallization grain size is controlled to 24 μm or less;

in the annealing step, when the total content of Nb, V, Mo, Ta and W in the chemical composition of the slab is 0.0030 to 0.030%, the temperature is adjusted to a pH of 700 to 800 ℃ in the heating process₂O/PH₂Set to 0.10 to 1.0 or set to a pH of 950 to 1000 DEG C₂O/PH₂Setting at least one of the temperature ranges of 0.010 to 0.070, and setting the holding time at 850 to 950 ℃ to 120 to 600 minutes; when the total content of Nb, V, Mo, Ta and W in the chemical composition of the plate blank is not 0.0030-0.030%, the pH value is adjusted to 700-800 ℃ in the heating process₂O/PH₂Set to 0.10 to 1.0, and the pH is adjusted to 950 to 1000 DEG₂O/PH₂0.010 to 0.070, and the holding time at 850 to 950 ℃ is set to 120 to 600 minutes.

The above pH value₂O/PH₂Referred to as the oxygen potential, is the partial pressure PH of water vapor of the atmosphere gas₂O and hydrogen partial pressure PH₂The ratio of.

The "reversal" in the present embodiment is mainly controlled by two factors, i.e., a factor that easily causes the change in orientation (reversal) itself and a factor that causes the change in orientation (reversal) to continue in one secondary recrystallized grain.

In order to make the reversal itself easy, it is effective to start the secondary recrystallization from a lower temperature. For example, by controlling the primary recrystallization grain size, the start of secondary recrystallization can be controlled to a lower temperature by the Nb group element.

In order for the commutation to continuously occur in one secondary recrystallized grain, it is effective to continuously grow the secondary recrystallized grain from a low temperature to a high temperature. For example, by using AlN, which is a conventionally used inhibitor, at an appropriate temperature and in an appropriate atmosphere, secondary recrystallized grains can be generated at a low temperature, the inhibitor effect can be continuously exerted on a high temperature, and the transition can be continuously generated in one secondary recrystallized grain until the temperature reaches the high temperature.

That is, in order to make the commutation preferably occur, in the case of controlling the occurrence of secondary recrystallized grains at high temperature, it is effective to preferentially grow secondary recrystallized grains generated at low temperature up to high temperature.

In addition, in the present embodiment, in addition to the above two factors, in order to impart in-plane anisotropy to the shape of the β crystal grains, a method of imparting anisotropy to the growth of the secondary recrystallized grains in the final secondary recrystallization process may be employed.

The above-described factors are important in controlling the commutation, which is a feature of the present embodiment. Other manufacturing conditions may be applied to a conventionally known method for manufacturing a grain-oriented electrical steel sheet. Examples include: a manufacturing method using MnS or AlN formed by heating a high-temperature slab as an inhibitor; or a method of producing AlN as an inhibitor by heating a low-temperature slab and then nitriding the same. The characteristic of the present embodiment can be changed by any manufacturing method, and is not limited to a specific manufacturing method. Hereinafter, a method of controlling the commutation by a manufacturing method using the nitriding process will be described as an example.

(casting step)

In the casting process, a slab is prepared. An example of a method of manufacturing a slab is as follows. Molten steel is produced (smelted). A slab is manufactured using molten steel. The slab may also be manufactured by continuous casting. A steel ingot may be produced from molten steel, and a slab may be produced by cogging rolling the steel ingot. The thickness of the slab is not particularly limited. The thickness of the slab is, for example, 150 to 350 mm. The thickness of the slab is preferably 220-280 mm. As the slab, a so-called thin slab having a thickness of 10 to 70mm may be used. When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling step.

The chemical composition of the slab may be the chemical composition of a slab used for manufacturing a normal grain-oriented electrical steel sheet. The chemical composition of the slab contains, for example, the following elements.

C：0～0.0850％

Carbon (C) is an element effective for controlling the primary recrystallized structure during the production process, but if the C content of the final product is excessive, it adversely affects the magnetic properties. Therefore, the C content of the plate blank is only 0-0.0850%. The preferable upper limit of the C content is 0.0750%. C is purified in the decarburization annealing step and the finish annealing step described later, and becomes 0.0050% or less after the finish annealing step. In the case of containing C, the lower limit of the C content may be more than 0% or may be 0.0010% in consideration of productivity in industrial production.

Si：2.0～7.0％

Silicon (Si) can increase the electrical resistance of grain-oriented electrical steel sheets and reduce the iron loss. If the Si content is less than 2.0%, austenite transformation occurs during annealing of the finished product, and the crystal orientation of the grain-oriented electrical steel sheet is impaired. On the other hand, if the Si content exceeds 7.0%, cold workability is lowered, and cracks are likely to occur during cold rolling. The preferable lower limit of the Si content is 2.50%, more preferably 3.0%. The preferable upper limit of the Si content is 4.50%, more preferably 4.0%.

Mn：0～1.0％

Manganese (Mn) can combine with S or Se to form MnS or MnSe, acting as an inhibitor. The Mn content is 0-1.0%. When Mn is contained, the secondary recrystallization is stable when the Mn content is in the range of 0.05 to 1.0%, and thus it is preferable. In the present embodiment, there is a possibility that a part of the function of the inhibitor is carried by the nitride of the Nb group element. In this case, the strength of MnS or MnSe, which is a general inhibitor, is controlled to be weak. Therefore, the preferable upper limit of the Mn content is 0.50%, more preferably 0.20%.

S：0～0.0350％

Se：0～0.0350％

Sulfur (S) and selenium (Se) can combine with Mn to form MnS or MnSe, acting as inhibitors. The S content is 0-0.0350%, and the Se content is 0-0.0350%. When at least one of S and Se is contained, the total content of S and Se is preferably 0.0030 to 0.0350%, since secondary recrystallization is stable. In the present embodiment, there is a possibility that a part of the function of the inhibitor is carried by the nitride of the Nb group element. In this case, the strength of MnS or MnSe, which is a general inhibitor, is controlled to be weak. Therefore, the preferable upper limit of the total of the S and Se contents is 0.0250%, more preferably 0.010%. If S and Se remain after annealing of the finished product, compounds are formed, deteriorating the iron loss. Therefore, it is preferable to minimize S and Se by purification in the final annealing.

Here, "the total content of S and Se is 0.0030 to 0.0350%", the chemical composition of the slab may contain either S or Se, and the content of either S or Se is 0.0030 to 0.0350%, or the slab may contain both S and Se, and the total content of S and Se is 0.0030 to 0.0350%.

Al：0～0.0650％

Aluminum (Al) can be bonded to N to precipitate as (Al, Si) N, and functions as an inhibitor. The Al content is 0-0.0650%. When Al is contained, if the content of Al is in the range of 0.010 to 0.065%, AlN, which is an inhibitor formed by nitriding described later, is preferable because the secondary recrystallization temperature range can be widened, and in particular, the secondary recrystallization in the high temperature range is stable. The lower limit of the Al content is preferably 0.020%, more preferably 0.0250%. From the viewpoint of stability of secondary recrystallization, the upper limit of the Al content is preferably 0.040%, and more preferably 0.030%.

N：0～0.0120％

Nitrogen (N) may combine with Al to act as an inhibitor. The content of N is 0-0.0120%. Since N can be contained by nitriding during the production process, the lower limit may be 0%. On the other hand, if the content of N exceeds 0.0120%, blisters, which are one type of defects, tend to occur in the steel sheet. The preferable upper limit of the N content is 0.010%, more preferably 0.0090%. N is purified in the finish annealing step, and becomes 0.0050% or less after the finish annealing step.

Nb：0～0.030％

V：0～0.030％

Mo：0～0.030％

Ta：0～0.030％

W：0～0.030％

Nb, V, Mo, Ta and W are Nb group elements. The content of Nb is 0-0.030%, the content of V is 0-0.030%, the content of Mo is 0-0.030%, the content of Ta is 0-0.030%, and the content of W is 0-0.030%.

Further, the Nb group element preferably contains at least 1 selected from Nb, V, Mo, Ta and W in a total amount of 0.0030 to 0.030 mass%.

When the commutation is controlled by the Nb group element, if the total content of the Nb group element in the slab is 0.030% or less (preferably 0.0030% to 0.030%), the secondary recrystallization can be started at an appropriate timing. Further, the orientation of the generated secondary recrystallized grains becomes very desirable, and in the subsequent growth process, the commutation which is a feature of the present embodiment becomes easy to occur, and finally, the structure which is preferable for the magnetic properties can be controlled.

By containing the Nb group element, the primary recrystallized grain size after decarburization annealing can be made smaller than that in the case where the Nb group element is not contained. It is considered that the primary recrystallized grains are refined by the pinning effect of precipitates such as carbides, carbonitrides, and nitrides, the dragging effect as a solid solution element, and the like. In particular, Nb and Ta can preferably obtain the above effects.

The smaller the primary recrystallization grain size by the Nb group element increases the driving force for secondary recrystallization, and secondary recrystallization starts at a lower temperature than before. In addition, since the precipitates of the Nb group element are decomposed at a lower temperature than the conventional inhibitor such as AlN, secondary recrystallization starts at a lower temperature than the conventional one in the temperature increase process of the final annealing. As will be described later, the secondary recrystallization starts at a low temperature, and therefore, the reversal, which is a characteristic of the present embodiment, easily occurs.

Further, when the precipitates of the Nb group element are used as the secondary recrystallization inhibitor, since the carbides and carbonitrides of the Nb group element become unstable in a temperature range lower than the temperature range in which secondary recrystallization can occur, the effect of shifting the secondary recrystallization start temperature to a low temperature is considered to be small. Therefore, in order to shift the secondary recrystallization start temperature to a low temperature, it is preferable to use a nitride of the Nb group element that is stable to a temperature range in which secondary recrystallization can occur.

By using a combination of a precipitate (preferably nitride) of an Nb group element which can shift the secondary recrystallization start temperature to a lower temperature more favorably and a conventional inhibitor such as AlN (Al, Si) N which is stable to a high temperature even after the start of secondary recrystallization, the preferential growth temperature range of {110} <001> oriented crystal grains, which are secondary recrystallization crystal grains, can be expanded more than in the conventional case. Therefore, the commutation occurs over a wide temperature range from low temperature to high temperature, and the orientation selection continues over a wide temperature range. As a result, the frequency of existence of the final β -grain boundaries is increased, and the concentration of the {110} <001> orientation of the secondary recrystallized grains constituting the grain-oriented electrical steel sheet can be effectively increased.

When the primary recrystallized grains are to be refined by the pinning effect of the carbide, carbonitride, or the like of the Nb group element, the C content of the slab is preferably 50ppm or more at the time of casting. However, since the secondary recrystallization inhibitor is preferably a nitride rather than a carbide or carbonitride, it is preferable that the C content is set to 30ppm or less, preferably 20ppm or less, and more preferably 10ppm or less by decarburization annealing after the completion of the primary recrystallization, so that the carbide or carbonitride of the Nb group element in the steel is sufficiently decomposed. Most of the Nb group elements are brought into a solid solution state by the decarburization annealing, and therefore, in the subsequent nitriding treatment, the nitride (inhibitor) of the Nb group elements can be adjusted to a form (a form in which secondary recrystallization is easy to proceed) preferable for the present embodiment.

The total content of the Nb group element is preferably 0.0040% or more, and more preferably 0.0050% or more. The total content of the Nb group elements is preferably 0.020% or less, and more preferably 0.010%.

The remainder of the chemical composition of the slab comprises Fe and impurities. The "impurities" referred to herein are elements that are inevitably mixed from components contained in raw materials or components mixed during production in the industrial production of a slab and do not substantially affect the effects of the present embodiment.

In addition to solving the problems in production, the slab may contain a known optional element in place of part of Fe in consideration of the strengthening of the inhibitor function and the influence on the magnetic properties due to the formation of the compound. Examples of the optional elements include the following elements.

Cu：0～0.40％

Bi：0～0.010％

B：0～0.080％

P：0～0.50％

Ti：0～0.0150％

Sn：0～0.10％

Sb：0～0.10％

Cr：0～0.30％

Ni：0～1.0％

These optional elements may be contained according to a known purpose. The lower limit of the content of these optional elements is not necessarily set, and the lower limit may be 0%.

(Hot Rolling Process)

The hot rolling step is a step of hot rolling a slab heated to a predetermined temperature (for example, 1100 to 1400 ℃) to obtain a hot-rolled steel sheet. In the hot rolling step, for example, after the casting step, the heated silicon steel material (slab) is roughly rolled, and then finish rolling is performed to produce a hot-rolled steel sheet having a predetermined thickness, for example, 1.8 to 3.5 mm. After finishing the finish rolling, the hot-rolled steel sheet is wound at a predetermined temperature.

Since the MnS strength as an inhibitor is not so necessary, the slab heating temperature is preferably set to 1100 to 1280 ℃ if productivity is considered.

In the hot rolling step, the crystal structure, crystal orientation, and precipitates may be made non-uniform in the in-plane position of the steel sheet by setting the temperature gradient in the width or length direction of the steel strip within the above range. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and the shape of the β crystal grains necessary for the present embodiment is preferably imparted with in-plane anisotropy. For example, in slab heating, a temperature gradient is provided in the plate width direction to refine precipitates in the high-temperature portion, thereby improving the inhibitor function of the high-temperature portion, and thus, it is possible to induce preferential grain growth from the low-temperature portion toward the high-temperature portion at the time of secondary recrystallization.

(Hot rolled sheet annealing step)

The hot-rolled sheet annealing step is a step of annealing the hot-rolled sheet obtained in the hot-rolling step under a predetermined temperature condition (for example, 750 to 1200 ℃ for 30 seconds to 10 minutes) to obtain a hot-rolled annealed sheet.

In the hot-rolled sheet annealing step, the crystal structure, crystal orientation, and precipitates may be made non-uniform in the in-plane position of the steel sheet by providing a temperature gradient in the width or length direction of the steel strip within the above range. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and the shape of the β crystal grains necessary for the present embodiment is preferably imparted with in-plane anisotropy. For example, in hot-rolled sheet annealing, a temperature gradient is provided in the sheet width direction to refine precipitates in the high-temperature portion, thereby improving the suppressor function of the high-temperature portion, and thus, it is possible to induce preferential grain growth from the low-temperature portion toward the high-temperature portion at the time of secondary recrystallization.

(Cold Rolling Process)

The cold rolling process is as follows: the hot-rolled annealed sheet obtained in the hot-rolled sheet annealing step is subjected to cold rolling for 1 time or to cold rolling for a plurality of times (2 times or more) through annealing (intermediate annealing) (for example, the total cold rolling reduction is 80 to 95%), thereby obtaining a cold-rolled steel sheet having a thickness of, for example, 0.10 to 0.50 mm.

(decarburization annealing step)

The decarburization annealing step is a step of: the cold-rolled steel sheet obtained in the cold rolling step is subjected to decarburization annealing (for example, at 700 to 900 ℃ for 1 to 3 minutes) to obtain a decarburization annealed steel sheet in which primary recrystallization occurs. The cold-rolled steel sheet is decarburized to remove C contained therein. In order to remove "C" contained in the cold-rolled steel sheet, decarburization annealing is preferably performed in a wet atmosphere.

In the method of manufacturing a grain-oriented electrical steel sheet according to the present embodiment, the primary recrystallized grain size of the decarburization annealed steel sheet is preferably controlled to 24 μm or less. By making the primary recrystallization particle size fine, the secondary recrystallization starting temperature can be preferably shifted to a low temperature.

For example, the primary recrystallized grain size can be reduced by controlling the conditions of the hot rolling and hot strip annealing described above or by lowering the decarburization annealing temperature as necessary. Alternatively, by containing the Nb group element in the slab, primary recrystallized grains can be reduced by the pinning effect of carbide, carbonitride or the like of the Nb group element.

In addition, since the amount of decarbonation by decarburization annealing and the state of the surface oxide layer affect the formation of the intermediate layer (glass coating film), the amount can be appropriately adjusted by a conventional method to exhibit the effects of the present embodiment.

The Nb group element which can be contained as an element which easily causes a change in direction exists as a carbide, a carbonitride, a solid solution element, or the like at this time, and influences the primary recrystallized grain size to be fine. The primary recrystallized grain size is preferably 23 μm or less, more preferably 20 μm or less, and still more preferably 18 μm or less. The primary recrystallized grain size may be 8 μm or more, or may be 12 μm or more.

In the decarburization annealing step, the crystal structure, crystal orientation, and precipitates may be made non-uniform in the in-plane position of the steel sheet by providing a temperature gradient or a difference in decarburization behavior in the above-described range in the width or length direction of the steel strip. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and the shape of the β crystal grains necessary for the present embodiment is preferably imparted with in-plane anisotropy. For example, in slab heating, a temperature gradient is provided in the width direction of the slab to refine the primary recrystallization grain size in the low-temperature portion, thereby increasing the driving force for the start of secondary recrystallization, and the secondary recrystallization in the low-temperature portion is started early, so that it is possible to induce preferential grain growth from the low-temperature portion toward the high-temperature portion at the time of growth of secondary recrystallized grains.

(nitriding treatment)

The nitriding treatment is performed to adjust the strength of the inhibitor in the secondary recrystallization. In the nitriding treatment, the nitrogen content of the steel sheet may be increased to about 40 to 300ppm at any time from the start of the decarburization annealing to the start of secondary recrystallization in the finish annealing described later. Examples of the nitriding treatment include: a treatment of annealing a steel sheet in an atmosphere containing a nitriding gas such as ammonia, a treatment of annealing a decarburized annealed steel sheet coated with an annealing separator containing a nitriding powder such as MnN, and the like.

When the slab contains the Nb group element in the above numerical range, secondary recrystallization starts from a lower temperature than before because the nitride of the Nb group element formed by the nitriding treatment functions as an inhibitor that the grain growth inhibiting function disappears at a relatively low temperature. This nitride also contributes favorably to selectivity of nucleus generation of secondary recrystallized grains, and it is considered that it is possible to achieve high magnetic flux density. In addition, AlN is also formed in the nitriding treatment, and this AlN functions as an inhibitor that can maintain the grain growth inhibition function up to a relatively high temperature. In order to obtain these effects, the nitriding amount after the nitriding treatment is preferably set to 130 to 250ppm, more preferably 150 to 200 ppm.

In the nitriding treatment, the difference in the nitriding amount may be set within the above range in the width or length direction of the steel strip, so that the inhibitor strength may be made non-uniform at the in-plane position of the steel sheet. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and the shape of the β crystal grains necessary for the present embodiment is preferably imparted with in-plane anisotropy. For example, by providing a difference in the amount of nitriding in the plate width direction to improve the inhibitor function of the high-nitride portion, preferential grain setting from the low-nitride portion toward the high-nitride portion can be induced at the time of secondary recrystallization.

(annealing separator application step)

The annealing separator application step is a step of applying the annealing separator to the decarburization annealed steel sheet. As the annealing separator, for example, an annealing separator containing MgO as a main component or an annealing separator containing alumina as a main component can be used.

Further, when an annealing separator containing MgO as a main component is used, a forsterite coating (containing Mg) as an intermediate layer can be easily formed by the finish annealing₂SiO₄A coating film mainly) and when an annealing separator mainly composed of alumina is used, an oxide film (composed of SiO) as an intermediate layer can be easily formed by finish annealing₂A coating film as a main body). These intermediate layers may also be removed as desired.

The decarburization annealed steel sheet coated with the annealing separator is subjected to finish annealing in a finish annealing process described below in a state of being wound into a coil shape.

(annealing Process for finished product)

The finish annealing step is a step of performing finish annealing on the decarburized annealed steel sheet coated with the annealing separator to generate secondary recrystallization. In this step, the secondary recrystallization is performed in a state where the growth of the primary recrystallized grains is suppressed by the inhibitor, so that {100} <001> oriented grains preferentially grow, thereby dramatically increasing the magnetic flux density.

The finish annealing is an important step for controlling the reversal which is a feature of the present embodiment. In the present embodiment, the off angle β is controlled based on the following 3 conditions (a), (B), and (D) in the finish annealing.

The "total content of Nb group elements" in the description of the finish annealing step means the total content of Nb group elements in the steel sheet (decarburization annealed steel sheet) immediately before finish annealing. That is, the chemical composition of the steel sheet immediately before finish annealing is influenced by the finish annealing conditions, regardless of the chemical composition after finish annealing and purification (for example, the chemical composition of grain-oriented electrical steel sheet (finish annealed steel sheet)).

(A) Heating during annealing of the finished productIn the process, the PH in the atmosphere with the temperature range of 700-800 DEG C₂O/PH₂When PA is set, PA: 0.10 to 1.0.

(B) In the heating process of annealing the finished product, the PH in the atmosphere with the temperature range of 950-1000 DEG C₂O/PH₂When PB is set, PB: 0.010-0.070.

(D) In the heating process of annealing of the finished product, when the holding time in the temperature range of 850-950 ℃ is set as TD, TD: 120-600 minutes.

In addition, when the total content of the Nb group elements is 0.0030 to 0.030%, at least one of the conditions (a) and (B) and the condition (D) may be satisfied.

When the total content of the Nb group elements is not 0.0030 to 0.030%, 3 of the conditions (A), (B), and (D) may be satisfied.

In the case where the conditions (a) and (B) contain the Nb group element in the above range, two factors, i.e., "the start of secondary recrystallization in the low temperature range" and "the continuation of secondary recrystallization until the high temperature range", are strongly exerted due to the effect of suppressing recovery recrystallization possessed by the Nb group element. As a result, the control conditions for obtaining the effects of the present embodiment are alleviated.

PA is preferably 0.30 or more, and preferably 0.60 or less.

PB is preferably 0.020 or more and preferably 0.050 or less.

The TD is preferably 180 minutes or more, more preferably 240 minutes or more, and preferably 480 minutes or less, more preferably 360 minutes or less.

The details of the mechanism by which commutation occurs are not known at present. However, in view of the observation result of the secondary recrystallization process and the manufacturing conditions under which the reversal can be preferably controlled, it is presumed that two factors of "the start of secondary recrystallization in the low temperature range" and "the continuation of secondary recrystallization until the high temperature range" are important.

The reasons for limitations of the above (A), (B) and (D) will be explained in view of these two factors. In the following description, the description of the mechanism includes an assumption.

The condition (a) is a condition in a temperature range sufficiently lower than the temperature at which the secondary recrystallization occurs, and has no direct influence on the phenomenon recognized as the secondary recrystallization. However, this temperature range is a temperature range in which the surface layer of the steel sheet is oxidized by moisture or the like due to the annealing separator applied to the surface of the steel sheet, that is, a temperature range in which the formation of the primary coating (intermediate layer) is affected. The condition (a) is important because the formation of the primary coating is controlled to enable the subsequent "continuation of secondary recrystallization until the high temperature range". By setting this temperature range to the above atmosphere, the primary coating has a dense structure, and at the stage of the occurrence of secondary recrystallization, it functions as a barrier to discharge the constituent elements (for example, Al, N, and the like) of the inhibitor to the outside of the system. Thus, the secondary recrystallization can be continued to a high temperature, and the reversal can be sufficiently caused.

The condition (B) is a condition corresponding to a temperature range in the middle stage of grain growth of the secondary recrystallization, and affects adjustment of the strength of the inhibitor during the grain growth of the secondary recrystallization. By setting this temperature range to the above atmosphere, the growth of the secondary recrystallized grains proceeds at a rate controlled by the decomposition of the inhibitor at the middle stage of the grain growth. As will be described in detail later, according to the condition (b), dislocations are effectively accumulated in the grain boundaries ahead of the growth direction of the secondary recrystallized grains, and therefore the frequency of occurrence of the commutation is increased and the commutation continues to occur.

The condition (D) is a condition corresponding to a temperature range from the formation of nuclei of the secondary recrystallization to the initial stage of grain growth. Maintenance in this temperature range is important to initiate good secondary recrystallization. However, if the holding time is long, primary recrystallized grain growth also tends to occur. For example, if the particle diameter of the primary recrystallized grains is increased, accumulation of dislocations (accumulation of dislocations in the grain boundaries ahead of the growth direction of the secondary recrystallized grains) which is a driving force for the generation of the commutation hardly occurs. If the holding time in this temperature range is set to 600 minutes or less, the initial growth of the secondary recrystallized grains can be advanced in a state in which the coarsening of the primary recrystallized grains is suppressed, and therefore the selectivity of the specific off angle can be improved. In the present embodiment, the shift of the off angle β is largely generated and continued on the background that the secondary recrystallization start temperature is shifted to a low temperature by the refinement of the primary recrystallization crystal grains, the use of the Nb group element, and the like.

In the manufacturing method of the present embodiment, when the Nb group element is used, even if both of the conditions (a) and (B) are not satisfied, if one of the conditions is selectively satisfied, the grain-oriented electrical steel sheet satisfying the commutation condition of the present embodiment can be obtained. That is, if the commutation frequency at a specific off-angle (off-angle β in the present embodiment) in the initial stage of secondary recrystallization is controlled to be increased, secondary recrystallized grains grow while maintaining the orientation difference due to commutation, the influence thereof continues to the later stage, and the final commutation frequency also increases. Further, even if a new commutation occurs after the influence of this, commutation occurs in which the change in the slip angle β is large, and the commutation frequency of the final slip angle β also increases. Of course, even if Nb group elements are used, it is preferable to satisfy both conditions (a) and (B).

In the method for producing a grain-oriented electrical steel sheet according to the present embodiment, the secondary recrystallized grains may be controlled to be divided into small regions having slightly different off-angles β. Specifically, in the above-described method, grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB may be formed in the grain-oriented electrical steel sheet as described in embodiment 1 in addition to the grain boundaries satisfying the boundary condition BB.

Next, preferred production conditions in the production method of the present embodiment will be described.

In the production method of the present embodiment, in the finish annealing step, when the total content of Nb, V, Mo, Ta, and W in the chemical composition of the slab is not 0.0030 to 0.030%, the retention time at 1000 to 1050 ℃ in the heating history is preferably set to 300 to 1500 minutes.

Similarly, in the production method of the present embodiment, in the finish annealing step, when the total content of Nb, V, Mo, Ta, and W in the chemical composition of the slab is 0.0030 to 0.030%, the retention time at 1000 to 1050 ℃ in the heating history is preferably set to 150 to 900 minutes.

Hereinafter, the above-mentioned production conditions are set as the conditions (E-1).

(E-1) in the heating process of annealing the final product, when the holding time (total retention time) in the temperature range of 1000 to 1050 ℃ is set to TE1, and the total content of Nb group elements is 0.0030 to 0.030%, TE 1: more than 150 minutes; when the total content of the Nb group elements is outside the above range, TE 1: over 300 minutes.

When the total content of the Nb group elements is 0.0030 to 0.030%, TE1 is preferably 200 minutes or more, more preferably 300 minutes or more, preferably 900 minutes or less, more preferably 600 minutes or less.

When the total content of the Nb group elements is out of the above range, TE1 is preferably 360 minutes or more, more preferably 600 minutes or more, preferably 1500 minutes or less, more preferably 900 minutes or less.

The condition (E-1) is a factor for controlling the direction of extension of the grain boundaries in the steel sheet surface, in which the direction change occurs. By sufficiently maintaining the temperature at 1000 to 1050 ℃, the reversing frequency in the rolling direction can be increased. In the holding process in the above temperature range, it is considered that the change in the frequency of the change in the rolling direction is increased because the morphology (for example, the arrangement and the shape) of the precipitates in the inhibitor-containing steel is changed.

Since the steel sheet subjected to finish annealing is subjected to hot rolling and cold rolling, it is considered that the arrangement and shape of precipitates (in particular, MnS) in the steel have anisotropy in the plane of the steel sheet and tend to be deviated in the rolling direction. It is not clear in detail, but it is considered that the retention in the above temperature range changes the degree of the deviation of the form of the above precipitates in the rolling direction, and affects in which direction the β -grain boundaries easily extend in the steel sheet surface at the time of the growth of the secondary recrystallized grains. Specifically, if a steel sheet is held at a relatively high temperature of 1000 to 1050 ℃, the form of precipitates in the steel is not biased in the rolling direction, and therefore the proportion of β -grain boundaries extending in the rolling direction decreases, and the tendency of β -grain boundaries extending in the direction perpendicular to the rolling direction increases. As a result, it is considered that the frequency of β grain boundaries measured in the rolling direction becomes high.

In addition, when the total content of the Nb group elements is 0.0030 to 0.030%, the frequency of existence of the β -grain boundaries itself is high, and therefore, the effect of the present embodiment can be obtained even if the retention time of the condition (E-1) is short.

By the production method including the above condition (E-1), the grain diameter of the β crystal grains in the rolling direction can be controlled to be smaller than the grain diameter of the secondary recrystallized grains in the rolling direction. Specifically, by controlling the grain size RA in combination with the above condition (E-1), as described in embodiment 2, the grain size RA can be controlled in the grain-oriented electrical steel sheet_LAnd particle diameter RB_LRB of 1.10 or less is satisfied_L÷RA_L。

In the production method of the present embodiment, in the final annealing step, when the total content of Nb, V, Mo, Ta, and W in the chemical composition of the slab is not 0.0030 to 0.030%, the retention time at 950 to 1000 ℃ in the heating history is preferably set to 300 to 1500 minutes.

Similarly, in the production method of the present embodiment, in the finish annealing step, when the total content of Nb, V, Mo, Ta, and W in the chemical composition of the slab is 0.0030 to 0.030%, the retention time at 950 to 1000 ℃ in the heating history is preferably set to 150 to 900 minutes.

Hereinafter, the above-mentioned production conditions are set as the conditions (E-2).

(E-2) in the heating process of the annealing of the final product, when the retention time (total retention time) in the temperature range of 950 to 1000 ℃ is set to TE2 and the total content of Nb group elements is 0.0030 to 0.030%, TE 2: more than 150 minutes; when the total content of the Nb group elements is outside the above range, TE 2: over 300 minutes.

When the total content of the Nb group elements is 0.0030 to 0.030%, TE2 is preferably 200 minutes or more, more preferably 300 minutes or more, preferably 900 minutes or less, more preferably 600 minutes or less.

When the total content of the Nb group elements is out of the above range, TE2 is preferably 360 minutes or more, more preferably 600 minutes or more, preferably 1500 minutes or less, more preferably 900 minutes or less.

The condition (E-2) is a factor for controlling the direction of extension of the grain boundaries in the steel sheet surface, in which the direction change occurs. By sufficiently maintaining the temperature of 950 to 1000 ℃, the reversing frequency in the vertical direction of rolling can be increased. In the holding process in the above temperature range, it is considered that the change in the frequency of the commutation in the direction perpendicular to the rolling is increased because the morphology (for example, the arrangement and the shape) of precipitates in the inhibitor-containing steel is changed.

Since the steel sheet subjected to finish annealing is subjected to hot rolling and cold rolling, it is considered that the arrangement and shape of precipitates (in particular, MnS) in the steel have anisotropy in the plane of the steel sheet and tend to be deviated in the rolling direction. It is not clear in detail, but it is considered that the retention in the above temperature range changes the degree of the deviation of the form of the above precipitates in the rolling direction, and affects in which direction the β -grain boundaries easily extend in the steel sheet surface at the time of the growth of the secondary recrystallized grains. Specifically, if a steel sheet is held at a relatively low temperature of 950 to 1000 ℃, the form of precipitates in the steel increases in the rolling direction, and therefore the proportion of β -grain boundaries extending in the direction perpendicular to the rolling direction decreases, and the tendency of β -grain boundaries extending in the rolling direction increases. As a result, it is considered that the frequency of β grain boundaries measured in the direction perpendicular to rolling becomes high.

In addition, when the total content of the Nb group elements is 0.0030 to 0.030%, the existence frequency itself of the β -grain boundary is high, and therefore, the effect of the present embodiment can be obtained even if the retention time of the condition (E-2) is short.

By the production method including the above condition (E-1), the grain diameter of the β crystal grains in the direction perpendicular to rolling can be controlled to be smaller than the grain diameter of the secondary recrystallized grains in the direction perpendicular to rolling. Specifically, by controlling the grain size RA in combination with the above condition (E-2), as described in embodiment 3, the grain size RA can be controlled in the grain-oriented electrical steel sheet_CAnd particle diameter RB_CRB of 1.10 or less is satisfied_C÷RA_C。

In the manufacturing method according to the present embodiment, it is preferable that secondary recrystallization is generated while a temperature gradient exceeding 0.5 ℃/cm is applied to a boundary portion between the primary recrystallization region and the secondary recrystallization region in the steel sheet in the heating history of the finish annealing. For example, it is preferable to impart the above-described temperature gradient to the steel sheet during the secondary recrystallization grain growth in the temperature range of 800 ℃ to 1150 ℃ of the heating history of the finish annealing.

The direction in which the temperature gradient is applied is preferably the rolling vertical direction C.

The finish annealing step can be effectively used as a step of imparting in-plane anisotropy to the shape of β crystal grains. For example, when a box-type annealing furnace is used and a coil-shaped steel sheet is placed in the furnace and heated, the position and arrangement of the heating device and the temperature distribution in the annealing furnace may be controlled so that a sufficient temperature difference is generated between the outside and the inside of the coil. Alternatively, an induction heating device, a high-frequency heating device, an electric heating device, or the like may be disposed to actively heat only a part of the coil, thereby forming a temperature distribution in the annealed coil.

The method for applying the temperature gradient is not particularly limited, and a known method can be applied. When a temperature gradient is applied to a steel sheet, secondary recrystallized grains having a sharp orientation are formed from a portion in a coil which reaches a secondary recrystallization start state at an early stage, and the secondary recrystallized grains grow anisotropically due to the temperature gradient. For example, the secondary recrystallized grains may also be grown throughout the coil. Therefore, the in-plane anisotropy of the shape of the β crystal grains can be preferably controlled.

When a coil-shaped steel sheet is heated, since the coil edge portion is easily heated, it is preferable to grow secondary recrystallized grains by applying a temperature gradient from one end side to the other end side in the width direction (the sheet width direction of the steel sheet).

Further, in consideration of the control to the gaussian orientation to obtain the target magnetic properties and further in consideration of the industrial productivity, the secondary recrystallized grains may be grown by performing the finish annealing while providing a temperature gradient exceeding 0.5 ℃/cm (preferably 0.7 ℃/cm or more). The direction in which the temperature gradient is applied is preferably the rolling vertical direction C. The upper limit of the temperature gradient is not particularly limited, but it is preferable to continue the growth of the secondary recrystallized grains while maintaining the temperature gradient. In consideration of the thermal conductivity of the steel sheet and the growth rate of the secondary recrystallized grains, the upper limit of the temperature gradient may be 10 ℃/cm in a usual manufacturing process.

By the production method including the above conditions, the grain diameter of the β crystal grains in the rolling direction can be controlled to be smaller than the grain diameter of the β crystal grains in the direction perpendicular to the rolling direction. Specifically, by controlling the temperature gradient in combination with the above conditions, as described in embodiment 4, the grain size RA can be controlled in the grain-oriented electrical steel sheet_LAnd particle size RA_CRA is satisfied at 1.15. ltoreq._C÷RA_L。

In the manufacturing method of the present embodiment, the holding time of 1050 to 1100 ℃ may be set to 300 to 1200 minutes in the heating process of the final annealing.

Hereinafter, the above-described production conditions are set as the condition (F).

(F) In the heating process of annealing of the finished product, when the holding time in the temperature range of 1050-1100 ℃ is set as TF, TF: 300-1200 minutes.

In the heating process of the final annealing, when the secondary recrystallization is not completed up to 1050 ℃, the secondary recrystallization can be continued to a high temperature by lowering the heating rate (slow heating) at 1050 to 1100 ℃, specifically, by setting TF to 300 to 1200 minutes, and the magnetic flux density can be preferably increased. For example, TF is preferably 400 minutes or more, and preferably 700 minutes or less. In addition, in the case where the secondary recrystallization is completed to 1050 ℃ in the heating history of the finish annealing, the condition (F) may not be controlled. For example, when the secondary recrystallization is completed to 1050 ℃, if the temperature rise rate is increased in a temperature range of 1050 ℃ or higher than that in the conventional case and the product annealing time is shortened, the cost can be reduced.

In the production method of the present embodiment, in the finish annealing step, the control is performed based on the 3 conditions of the above-described condition (A), condition (B) and condition (D), and the condition (E-1), condition (E-2) and the temperature gradient condition may be combined as necessary. For example, a plurality of conditions among the condition (E-1), the condition (E-2) and/or the temperature gradient may be combined. Further, the condition (F) may be combined as necessary.

The method for producing a grain-oriented electrical steel sheet according to the present embodiment includes the above-described steps. However, the manufacturing method of the present embodiment may further include an insulating film forming step after the finish annealing step as necessary.

(insulating coating Forming Process)

The insulating film forming step is a step of forming an insulating film on the grain-oriented electrical steel sheet (finished annealed steel sheet) after the finished annealing step. An insulating film mainly composed of phosphate and colloidal silica, or an insulating film mainly composed of alumina sol and boric acid may be formed on the finished annealed steel sheet.

For example, the finished annealed steel sheet may be coated with a coating solution containing phosphoric acid or phosphate, chromic anhydride or chromate, and colloidal silica and sintered (for example, at 350 to 1150 ℃ for 5 to 300 seconds) to form an insulating film. When the coating is formed, the degree of oxidation of the atmosphere, the dew point, and the like may be controlled as necessary.

Alternatively, the finished annealed steel sheet may be coated with a coating solution containing alumina sol and boric acid and sintered (for example, at 750 to 1350 ℃ for 10 to 100 seconds) to form an insulating coating. When the coating is formed, the degree of oxidation of the atmosphere, the dew point, and the like may be controlled as necessary.

The manufacturing method according to the present embodiment may further include a magnetic domain control step as necessary.

(magnetic domain control step)

The magnetic domain control step is a step of performing a process of subdividing the magnetic domains of the grain-oriented electrical steel sheet. For example, a grain-oriented electrical steel sheet may be formed with local minute deformations or local grooves by a known method such as laser, plasma, mechanical method, or etching. The magnetic domain segmentation process described above does not impair the effects of the present embodiment.

The local micro-strain and the local grooves described above are abnormal points in the measurement of the crystal orientation and the particle size defined in the present embodiment. Therefore, in the measurement of the crystal orientation, the measurement point does not overlap with the local minute distortion and the local groove. In the measurement of the particle size, local fine deformation and local grooves are not considered as grain boundaries.

(mechanism for occurrence of commutation)

The reversal defined in the present embodiment occurs during the growth of the secondary recrystallized grains. This phenomenon is influenced by various control conditions such as the chemical composition of the raw material (slab), the introduction of an inhibitor until the growth of the secondary recrystallized grains, and the control of the grain size of the primary recrystallized grains. Therefore, the commutation is not only possible with one control condition, but a plurality of control conditions needs to be controlled compositely and inseparably.

It is believed that the commutation occurs due to the grain boundary energy and surface energy between adjacent grains.

Regarding the grain boundary energy, if 2 crystal grains having an angle difference are adjacent, the grain boundary energy becomes large, so it is considered that in the process of secondary recrystallization grain growth, the commutation occurs so as to reduce the grain boundary energy, that is, so as to approach a specific uniform orientation.

Further, regarding the surface energy, even if the orientation deviates from the {110} plane having a relatively high point symmetry, the surface energy increases, and therefore, it is considered that in the process of secondary recrystallization grain growth, the inversion occurs so that the surface energy is reduced, that is, the deviation angle becomes smaller by approaching the {110} plane orientation.

However, the energy difference is not an energy difference that causes orientation change before the reversal occurs during the secondary recrystallization grain growth under normal conditions. Therefore, in a normal condition, the secondary recrystallized grains are grown in a state having an angle difference or off-angle. For example, the off angle β corresponds to an angle caused by a deviation in orientation at the time when the secondary recrystallized grains are generated at the initial stage of the secondary recrystallization. If the secondary recrystallized grains having the off angle β grow, particularly, in a state where the secondary recrystallized grains have a curvature in the rolling direction, the angle of the off angle β with respect to the steel sheet surface changes. That is, the secondary recrystallized grains are controlled such that the off-angle β becomes smaller at the occurrence time, but the off-angle β inevitably becomes larger at the tip of the secondary recrystallized grains grown to a certain size.

On the other hand, when the secondary recrystallization is started from a lower temperature and the growth of the secondary recrystallized grains is continued for a long time until the temperature is high as in the grain-oriented electrical steel sheet of the present embodiment, the commutation can be remarkably generated. The reason for this is not clear, but it is considered that, in the process of growing the secondary recrystallized grains, dislocations for eliminating the variation in the geometric orientation at a relatively high density remain at the front portion in the growth direction, that is, in the region adjacent to the primary recrystallized grains. The remaining dislocations correspond to the commutation and β -grain boundaries of the present embodiment.

In the present embodiment, since the secondary recrystallization starts at a lower temperature than in the conventional case, the disappearance of dislocations is delayed, and dislocations are accumulated in a swept-away manner at the grain boundary ahead of the growing direction of the growing secondary recrystallized grains, thereby increasing the dislocation density. Therefore, the rearrangement of atoms becomes easy to occur in front of the grown secondary recrystallized grains, and as a result, it is considered that the commutation occurs so as to reduce the difference in angle with the adjacent secondary recrystallized grains, that is, to reduce the grain boundary energy or to reduce the surface energy.

The reversal leaves grain boundaries (β -grain boundaries) having a particular orientation relationship within the secondary recrystallized grains. Further, if other secondary recrystallized grains are generated before the occurrence of the commutation, the growing secondary recrystallized grains reach the generated secondary recrystallized grains, the grain growth stops, and thus the commutation itself becomes not to occur. Therefore, in the present embodiment, it is advantageous to reduce the frequency of occurrence of new secondary recrystallized grains and to control the rate controlled by the inhibitor so that only the existing secondary recrystallized grains continue to grow at the growth stage of the secondary recrystallized grains. Therefore, in the present embodiment, it is preferable to use both an inhibitor capable of shifting the secondary recrystallization start temperature to a low temperature and an inhibitor stable up to a relatively high temperature.

In the present embodiment, the reason why the change of orientation mainly occurs at the off angle β is not clear, but the following is considered. What kind of orientation change occurs in the commutation affects the kind of dislocation that is a basic unit of the commutation (i.e., the balger vector in the dislocation that is swept away during growth and accumulated in front of the secondary recrystallized grains, etc.). In the present embodiment, the influence of the inhibitor control (the above condition (B)) from the initial stage to the middle stage of the secondary recrystallization process is large with respect to the control of the off angle β. For example, if the inhibitor strength varies depending on the atmosphere in the temperature range of 950 ℃ or less or 1000 ℃ or more, the contribution of the slip angle β in the commutation becomes small. That is, the weakening timing of the inhibitor affects the change of the primary recrystallized structure (orientation and particle diameter change), the disappearance of the dislocations that are cleaned and accumulated, and the growth rate of the secondary recrystallized grains, and as a result, it is considered that the reversed orientation (i.e., the type and amount of the dislocations that enter the secondary recrystallized grains) formed in the growing secondary recrystallized grains changes.

Examples

The effects of one aspect of the present invention will be described in more detail below with reference to examples, in which the conditions are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is not limited to the one example of conditions. The present invention can employ various conditions as long as the object of the present invention can be achieved without departing from the gist of the present invention.

(example 1)

Grain-oriented electrical steel sheets (silicon steel sheets) having the chemical compositions shown in table a2 were produced using slabs having the chemical compositions shown in table a1 as raw materials. Further, these chemical compositions were determined based on the above-described methods. In tables a1 and a2, "-" indicates that the content was not controlled and manufactured in consideration of the content and that the content was not measured. In tables a1 and a2, the numerical values with a "<" indicate that the content was measured while the content was controlled and manufactured in consideration of the content, but a measurement value with sufficient reliability was not obtained as the content (the measurement result was not more than the detection limit).

TABLE A1

TABLE A2

Grain-oriented electrical steel sheets were produced under the production conditions shown in tables A3 to a 7. Specifically, a slab is cast, hot rolling, hot-rolled sheet annealing, cold rolling, and decarburization annealing are performed, and in part, the steel sheet after decarburization annealing is subjected to nitriding treatment (nitriding annealing) in a mixed atmosphere of hydrogen, nitrogen, and ammonia.

Further, an annealing separator containing MgO as a main component was applied to the steel sheet, and finish annealing was performed. In the final process of the finish annealing, the steel sheet was kept at 1200 ℃ for 20 hours in a hydrogen atmosphere (purification annealing), and was naturally cooled.

TABLE A3

TABLE A4

TABLE A5

TABLE A6

TABLE A7

A coating solution for forming an insulating film mainly composed of phosphate and colloidal silica and containing chromium is applied to a primary coating film (intermediate layer) formed on the surface of a produced grain-oriented electrical steel sheet (finished annealed steel sheet), and the resultant coating solution is subjected to a treatment in which the ratio of hydrogen: nitrogen 75% by volume: the insulating film was formed by heating and holding in an atmosphere of 25 vol% and cooling.

The produced grain-oriented electrical steel sheet has an intermediate layer disposed in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and an insulating film disposed in contact with the intermediate layer, when viewed in a cut plane parallel to the sheet thickness direction in the cutting direction. The intermediate layer is a forsterite coating having an average thickness of 2 μm, and the insulating coating is mainly composed of phosphate and colloidal silica having an average thickness of 1 μm.

The obtained grain-oriented electrical steel sheet was evaluated for various properties. The evaluation results are shown in tables A8 to A12.

(1) Crystal orientation of grain-oriented electrical steel sheet

The crystal orientation of a grain-oriented electrical steel sheet is measured by the above-described method. The off-angle was determined from the measured crystal orientation at each measurement point, and the grain boundaries present between the adjacent 2 measurement points were determined from the off-angle. When the boundary condition is determined at 2 measurement points at intervals of 1mm, if the value obtained by dividing "the number of boundaries satisfying boundary condition BA" by "the number of boundaries satisfying boundary condition BB" is 1.10 or more, it is determined that "grain boundaries satisfying boundary condition BA and not satisfying boundary condition BB" are present, and it is indicated in the table that "commutation grain boundaries" are present. Further, "the number of boundaries satisfying the boundary condition BA" means the grain boundaries corresponding to the cases 1 and/or 3 in table 1, and "the number of boundaries satisfying the boundary condition BB" means the grain boundaries corresponding to the cases 1 and/or 2. Further, the average crystal grain size was calculated from the specified grain boundaries. Further, the standard deviation σ (| β |) of the absolute value of the deviation angle β is determined by the above-described method.

(2) Magnetic properties of grain-oriented electrical steel sheet

The magnetic properties of the grain-oriented electrical steel sheet are measured according to JIS C2556: the magnetic properties of the Single plate (SST) specified in 2015 were measured by the Single Sheet Tester.

As magnetic properties, at an ac frequency: 50Hz, excitation flux density: iron loss W defined as power loss per unit weight (1kg) of the steel sheet was measured under the condition of 1.7T_17/50(W/kg). Further, the magnetic flux density B in the rolling direction of the steel sheet was measured when the sheet was excited at 800A/m₈(T)。

Further, as magnetic properties, the following were measured at an ac frequency: 50Hz, excitation flux density: the magnetostriction λ p-p @1.5T of the steel plate under the condition of 1.5T. Specifically, the maximum length L of the test piece (steel plate) under the excitation condition described above is used_maxAnd a minimum length L_minAnd the length L of the test piece at a magnetic flux density of 0T₀By λ p-p @1.5T ═ L (L)_max-L_min)÷L₀To calculate.

TABLE A8

TABLE A9

TABLE A10

TABLE A11

TABLE A12

The properties of grain-oriented electrical steel sheets vary greatly depending on the chemical composition and the manufacturing method. Therefore, it is necessary to compare and examine the evaluation results of the respective properties within the range of the steel sheet in which the chemical composition and the production method are limited to appropriate levels. Therefore, the evaluation results of the properties of each grain-oriented electrical steel sheet obtained from a chemical composition and a manufacturing method having several characteristics will be described below.

(examples manufactured by Low temperature slab heating Process)

Nos. 1001 to 1064 are examples produced by the following processes: the slab heating temperature was lowered, and the primary inhibitor of secondary recrystallization was formed by nitriding after primary recrystallization.

(embodiments of Nos. 1001 to 1023)

Nos. 1001 to 1023 are examples obtained by using Nb-free steel grades and mainly changing the conditions of PA, PB, TD and TE1 at the time of finish annealing.

In Nos. 1001 to 1023, when λ p-p @1.5T was 0.320 or less, the magnetostrictive property was judged to be good.

In Nos. 1001 to 1023, the present invention examples all showed excellent low-field magnetostriction with the presence of grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

No.1003 is a comparative example in which the strength of the inhibitor is improved by setting the N content after nitriding to 300 ppm. In general, if the amount of nitrogen is increased, the elongation is decreased, but the strength of the inhibitor is increased by increasing the amount of nitrogen, and B₈And (4) rising. In No.1003, B₈Also becomes a higher value. However, in the case of No.1003, since the finish annealing condition is not preferable, the value of λ p-p @1.5T becomes insufficient. That is, in No.1003, no reversal occurred during the secondary recrystallization, and as a result, reversal did not occurThat is, low field magnetostriction was not improved. On the other hand, No.1006 is an example of the present invention in which the N content after nitriding is set to 220 ppm. As for No.1006, though B₈Not particularly high, but since the final annealing conditions are preferred, λ p-p @1.5T becomes a preferred lower value. That is, in No.1006, commutation occurs at the time of secondary recrystallization, and as a result, low-field magnetostriction is improved.

In addition, Nos. 1017 to 1023 are examples in which TF is raised so that secondary recrystallization is continued to a high temperature. In Nos. 1017 to 1023, B₈Becomes high. However, of these, nos. 1021 and 1022 are not preferable because of the annealing conditions of the finished product, and therefore, the low-field magnetostriction cannot be improved as in No. 1003. On the other hand, Nos. 1017 to 1020 and 1023 of the above are other than B₈In addition to a higher value, the final annealing conditions are also preferred, so λ p-p @1.5T is a preferred lower value.

(examples of No.1024 to 1034)

Nos. 1024 to 1034 are examples in which steel grades containing 0.002% of Nb at the time of slab are used, and conditions of PA, PB, and TE1 are mainly changed at the time of finish annealing.

In Nos. 1024 to 1034, when λ p-p @1.5T was 0.390 or less, it was judged that the magnetostrictive property was good.

In Nos. 1024 to 1034, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB exist in the examples of the present invention, and all of them show excellent low-magnetic-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

(examples of Nos. 1035 to 1046)

Nos. 1035 to 1046 are examples in which steel grades containing 0.007% Nb at the time of slab are used, and conditions of PA, PB, TD, and TE1 are mainly changed at the time of finish annealing.

No.1035 to No. 1046 were judged to have good magnetostrictive properties when λ p-p @1.5T was 0.310 or less.

In Nos. 1035 to 1046, all of the present invention examples had grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

In nos. 1035 to 1046, Nb was contained at 0.007% at the time of slab, Nb was purified in the finish annealing, and the Nb content was 0.006% or less at the time of grain-oriented electrical steel sheet (finish annealed steel sheet). In Nos. 1035 to 1046, Nb is contained better than in Nos. 1001 to 1034 at the time of slab, and therefore, λ p-p @1.5T is a low value. In addition, B₈High, W_17/50And also becomes a small value. That is, if the Nb-containing slab is used to control the finish annealing conditions, the annealing conditions for B₈、W_17/50And λ p-p @1.5T produce a beneficial effect. In particular, No.1042 is an example of the present invention in which purification is enhanced in finish annealing and the Nb content becomes the detection limit or less at the time of grain-oriented electrical steel sheet (finish annealed steel sheet). In No.1042, the use of Nb group elements could not be verified by grain-oriented electrical steel sheets as final products, but the above-described effects were remarkably obtained.

(examples of No.1047 to 1054)

Nos. 1047 to 1054 are examples in which TE1 was set to a short time of less than 300 minutes, and particularly, the influence of the Nb content was confirmed.

In Nos. 1047 to 1054, when λ p-p @1.5T was 0.295 or less, it was judged that the magnetostrictive property was good.

In Nos. 1047 to 1054, the crystal boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB exist in the examples of the present invention, and all of them showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

Further, as shown in Nos. 1047 to 1054, if Nb is contained in an amount of 0.0030 to 0.030 mass% at the time of slab, even if TE1 is short, commutation occurs at the time of secondary recrystallization, and low-field magnetostriction is improved.

(examples of No.1055 to 1064)

Nos. 1055 to 1064 are examples in which TE1 was set to a short time of less than 300 minutes and the influence of the content of Nb group element was confirmed.

In Nos. 1055 to 1064, when λ p-p @1.5T was 0.340 or less, it was judged that the magnetostrictive property was good.

In Nos. 1055 to 1064, the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB existed in the examples of the present invention, and all showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

Further, as shown in Nos. 1055 to 1064, if a predetermined amount of Nb group elements other than Nb is contained in the slab, even if TE1 is short, commutation occurs at the time of secondary recrystallization, and low-field magnetostriction is improved.

(examples manufactured by high temperature slab heating Process)

No.1065 to 1101 are examples produced by the following processes: the slab heating temperature is increased to sufficiently dissolve MnS in the slab heating, and the dissolved MnS is re-precipitated in the subsequent step and utilized as a main inhibitor.

In Nos. 1065 to 1101, when λ p-p @1.5T was 0.260 or less, it was judged that the magnetostrictive property was good.

In Nos. 1065 to 1101, all of the examples of the present invention had grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

In addition, Nos. 1083 to 1101 of Nos. 1065 to 1101 were each increased in B by including Bi at the slab timing₈Examples of (1).

As shown in Nos. 1065-1101, even in the high-temperature slab heating process, by properly controlling the annealing conditions of the finished product, commutation can be performed during secondary recrystallization, and low-magnetic-field magnetostriction can be improved. In addition, similarly to the low-temperature slab heating process, even in the high-temperature slab heating process, if the finished product annealing conditions are controlled using Nb-containing slabs, then B is subjected to₈、W_17/50And λ p-p @1.5T play a favorable role.

(example 2)

Grain-oriented electrical steel sheets having chemical compositions shown in table B2 were produced using slabs having chemical compositions shown in table B1 as raw materials. The method of measuring the chemical composition and the method described in the table are the same as those in example 1 described above.

TABLE B1

TABLE B2

Grain-oriented electrical steel sheets were produced under the production conditions shown in tables B3 to B7. The production conditions other than those shown in the table were the same as those in example 1 described above.

TABLE B3

TABLE B4

TABLE B5

TABLE B6

TABLE B7

An insulating coating film similar to that of example 1 was formed on the surface of the produced grain-oriented electrical steel sheet (finished annealed steel sheet).

The produced grain-oriented electrical steel sheet has an intermediate layer disposed in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and an insulating film disposed in contact with the intermediate layer, when viewed in a cut plane parallel to the sheet thickness direction in the cutting direction. The intermediate layer is a forsterite coating having an average thickness of 1.5 μm, and the insulating coating is mainly composed of phosphate and colloidal silica having an average thickness of 2 μm.

The obtained grain-oriented electrical steel sheet was evaluated for various properties. The evaluation method was the same as in example 1 described above. The evaluation results are shown in tables B8 to B12.

TABLE B8

TABLE B9

TABLE B10

TABLE B11

TABLE B12

The evaluation results of the properties of each grain-oriented electrical steel sheet obtained from a chemical composition and a manufacturing method having several characteristics will be described below in the same manner as in example 1.

(examples manufactured by Low temperature slab heating Process)

No.2001 to 2063 are examples produced by the following processes: the slab heating temperature was lowered, and the primary inhibitor of secondary recrystallization was formed by nitriding after primary recrystallization.

(examples of No.2001 to 2023)

Nos. 2001 to 2023 are examples obtained by using Nb-free steel grades and mainly changing the conditions of PA, PB, TD and TE2 in the finish annealing.

In Nos. 2001 to 2023, when λ p-p @1.5T was 0.300 or less, it was judged that the magnetostrictive property was good.

In Nos. 2001 to 2023, the present invention examples all showed excellent low-field magnetostriction with the presence of grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

Further, No.2003 is a comparative example in which the strength of the inhibitor is improved by setting the N content after nitriding to 300 ppm. For No.1003, B₈The value was high, but since the finish annealing conditions were not preferable, the value of λ p-p @1.5T became insufficient. I.e. No.1003, no commutation occurred at the time of secondary recrystallization, and as a result, low-field magnetostriction was not improved. On the other hand, No.2006 is an inventive example in which the amount of N after nitriding is set to 220 ppm. As for No.2006, though B₈Not particularly high, but since the final annealing conditions are preferred, λ p-p @1.5T becomes a preferred lower value. That is, in No.2006, commutation occurs at the time of secondary recrystallization, and as a result, low-field magnetostriction is improved.

Nos. 2017 to 2023 are examples in which TF is increased so that secondary recrystallization is continued to a high temperature. In Nos. 2017 to 2023, B₈Becomes high. However, among them, Nos. 2021 to 2023 do not improve low-field magnetostriction as in No.2003 since the annealing conditions for the finished product are not preferable.

(examples of Nos. 2024 to 2034)

Nos. 2024 to 2034 are examples in which steel grades containing 0.001% of Nb at the time of slab are used, and the conditions of PA, PB, and TE2 are mainly changed at the time of finish annealing.

No.2024 to 2034, when λ p-p @1.5T was 0.370 or less, the magnetostrictive property was judged to be good.

In Nos. 2024 to 2034, all of the present invention examples had crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

(examples of Nos. 2035 to 2045)

Nos. 2035 to 2045 are examples in which steel grades containing 0.009% of Nb at the time of slab are used, and the conditions of PA, PB, TD, and TE2 are mainly changed at the time of finish annealing.

In Nos. 2035 to 2045, when λ p-p @1.5T is 0.310 or less, it is judged that the magnetostrictive property is good.

In Nos. 2035 to 2045, the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB exist in the examples of the present invention, and all of them showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

In nos. 2035 to 2045, Nb was contained at 0.009% at the time of slab annealing, Nb was purified in the finish annealing, and the Nb content was 0.007% or less at the time of grain-oriented electrical steel sheet (finish annealed steel sheet). Since nos. 2035 to 2045 can preferably contain Nb at the slab time than nos. 2001 to 2034, λ p-p @1.5T is a low value. In addition, B₈High, W_17/50And also becomes a small value. That is, if the Nb-containing slab is used to control the finish annealing conditions, the annealing conditions for B₈、W_17/50And λ p-p @1.5T produce a beneficial effect. In particular, No.2042 is an invention example in which purification is enhanced in the finish annealing, and the Nb content becomes the detection limit or less at the time of grain-oriented electrical steel sheet (finish annealed steel sheet). In No.1042, although the use of Nb group elements cannot be verified from grain-oriented electrical steel sheets as final products, the above-described effects are remarkably obtained.

(examples of Nos. 2046 to 2053)

Nos. 2046 to 2053 are examples in which TE2 was set to a short time of less than 300 minutes, and particularly, the influence of the Nb content was confirmed.

In Nos. 2046 to 2053, when λ p-p @1.5T was 0.295 or less, it was judged that the magnetostrictive property was good.

In Nos. 2046 to 2053, the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB existed in the examples of the present invention, and all showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

Further, as shown in Nos. 2046 to 2053, if Nb is contained in an amount of 0.0030 to 0.030 mass% at the time of slab, even if TE2 is short, commutation occurs at the time of secondary recrystallization, and low-field magnetostriction is improved.

(examples of Nos. 2054 to 2063)

Nos. 2054 to 2063 are examples in which TE2 was set to a short time of less than 300 minutes and the influence of the content of Nb group element was confirmed.

In Nos. 2054 to 2063, when λ p-p @1.5T was 0.340 or less, it was judged that the magnetostrictive property was good.

In Nos. 2054 to 2063, the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB existed in the examples of the present invention, and all showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

Further, as shown in Nos. 2054 to 2063, if a predetermined amount of Nb group elements other than Nb is contained in the slab, even if TE2 is short, commutation occurs at the time of secondary recrystallization, and low-field magnetostriction is improved.

(examples manufactured by high temperature slab heating Process)

No.2064 to 2101 is an example produced by the following process: the slab heating temperature is increased to sufficiently dissolve MnS in the slab heating, and the dissolved MnS is re-precipitated in the subsequent step and utilized as a main inhibitor.

In Nos. 2064 to 2101, when λ p-p @1.5T was 0.260 or less, it was judged that the magnetostrictive property was good.

In Nos. 2064 to 2101, the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB exist in the examples of the present invention, and all of them showed excellent low-magnetic-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

In addition, in Nos. 2064 to 2101, Nos. 2082 to 2101 contain Bi at the time of slab, and B is improved₈Examples of (1).

As shown in No. 2064-2101, even in a high-temperature slab heating process, by properly controlling the annealing conditions of a finished product, commutation can be performed during secondary recrystallization, and low-magnetic-field magnetostriction is improved. In addition, similarly to the low-temperature slab heating process, even in the high-temperature slab heating process, if the finished product annealing conditions are controlled using Nb-containing slabs, then B is subjected to₈、W_17/50And λ p-p @1.5T play a favorable role.

(example 3)

Grain-oriented electrical steel sheets having chemical compositions shown in table C2 were produced using slabs having chemical compositions shown in table C1 as raw materials. The method of measuring the chemical composition and the method described in the table are the same as those in example 1 described above.

TABLE C1

TABLE C2

The grain-oriented electrical steel sheets were manufactured under the manufacturing conditions shown in tables C3 to C6. In the finish annealing, in order to control anisotropy in the occurrence direction of the reversion, a heat treatment is performed by applying a temperature gradient in the direction perpendicular to the rolling direction of the steel sheet. The temperature gradient and the production conditions other than those shown in the table were the same as those in example 1.

TABLE C3

TABLE C4

TABLE C5

TABLE C6

An insulating coating film similar to that of example 1 was formed on the surface of the produced grain-oriented electrical steel sheet (finished annealed steel sheet).

The produced grain-oriented electrical steel sheet has an intermediate layer disposed in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and an insulating film disposed in contact with the intermediate layer, when viewed in a cut plane parallel to the sheet thickness direction in the cutting direction. The intermediate layer is a forsterite coating having an average thickness of 3 μm, and the insulating coating is mainly composed of phosphate and colloidal silica having an average thickness of 3 μm.

The obtained grain-oriented electrical steel sheet was evaluated for various properties. The evaluation method was the same as in example 1 described above. The evaluation results are shown in tables C7 to C10.

In almost all grain-oriented electrical steel sheets, crystal grains extend in the direction of the temperature gradient, and the crystal grain size of β crystal grains also becomes large in this direction. That is, the crystal grains extend in the rolling vertical direction. However, in some grain-oriented electrical steel sheets having a small temperature gradient, the grain size in the direction perpendicular to rolling becomes smaller than the grain size in the rolling direction with respect to the β crystal grains. When the grain size in the direction perpendicular to the rolling direction is smaller than the grain size in the rolling direction, the column of "the direction of temperature gradient is not uniform" in the table is indicated by "+".

TABLE C7

TABLE C8

TABLE C9

TABLE C10

The evaluation results of the properties of each grain-oriented electrical steel sheet obtained from a chemical composition and a manufacturing method having several characteristics will be described below in the same manner as in example 1.

(examples manufactured by Low temperature slab heating Process)

No.3001 to 3070 are examples produced by the following processes: the slab heating temperature was lowered, and the primary inhibitor of secondary recrystallization was formed by nitriding after primary recrystallization.

(examples of No.3001 to 3035)

Nos. 3001 to 3035 are examples obtained by using steel grades containing no Nb, and mainly changing the conditions of PA, PB, TD and temperature gradient during the annealing of the final product.

In Nos. 3001 to 3035, when λ p-p @1.5T was 0.300 or less, it was judged that the magnetostrictive property was good.

In Nos. 3001 to 3035, all of the samples of the present invention had grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

(example No.3036 to 3070)

Nos. 3036 to 3070 are examples in which steel grades containing Nb group elements at the time of slab are used, and conditions of PA, PB, TD and temperature gradient are mainly changed at the time of finish annealing.

No.3036 to 3070, when λ p-p @1.5T was 0.300 or less, the magnetostrictive property was judged to be good.

In Nos. 3036 to 3070, the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB existed in the examples of the present invention, and all showed excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

(example No. 3071)

No.3071 is an example made by the process of: the slab heating temperature is increased to sufficiently dissolve MnS in the slab heating, and the dissolved MnS is re-precipitated in the subsequent step and utilized as a main inhibitor.

In No.3071, when λ p-p @1.5T was 0.300 or less, it was judged that the magnetostrictive property was good.

As shown in No.3071, even in the high temperature slab heating process, the low magnetic field magnetostriction can be improved by appropriately controlling the product annealing conditions.

(example 4)

Grain-oriented electrical steel sheets having chemical compositions shown in table D2 were produced using slabs having chemical compositions shown in table D1 as raw materials. The method of measuring the chemical composition and the method described in the table are the same as those in example 1 described above.

TABLE D1

TABLE D2

The grain-oriented electrical steel sheet was produced under the production conditions shown in table D3. The production conditions other than those shown in the table were the same as those in example 1.

In addition to No.4009, as an annealing separator, an annealing separator containing MgO as a main component was applied to a steel sheet, and finish annealing was performed. On the other hand, No.4009 had an annealing separator containing alumina as a main component applied to a steel sheet as an annealing separator, and finished product annealing was performed.

TABLE D3

In the above tables, the symbol "1" indicates that "the PH is adjusted to 700 to 750 ℃₂O/PH₂Set to 0.2 and the pH is adjusted to 750 to 800 DEG₂O/PH₂Set to 0.03 ".

An insulating coating film similar to that of example 1 was formed on the surface of the produced grain-oriented electrical steel sheet (annealed steel sheet).

The produced grain-oriented electrical steel sheet has an intermediate layer disposed in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and an insulating film disposed in contact with the intermediate layer, when viewed in a cut plane parallel to the sheet thickness direction in the cutting direction.

In the grain-oriented electrical steel sheet other than No.4009, the intermediate layer was a forsterite coating having an average thickness of 1.5 μm, and the insulating coating was an insulating coating mainly composed of phosphate and colloidal silica having an average thickness of 2 μm. On the other hand, in the grain-oriented electrical steel sheet of No.4009, the intermediate layer was an oxide film (SiO) having an average thickness of 20nm₂Mainly a coating), the insulating coating is mainly a phosphate and colloidal silica having an average thickness of 2 μm.

Further, after the insulating film is formed, the grain-oriented electrical steel sheets of nos. 4012 and 4013 are subjected to laser irradiation to impart linear micro-strain on the rolling surface of the steel sheet so as to extend in a direction intersecting the rolling direction and so as to have a rolling direction interval of 4 mm. It is known that by applying laser light, an effect of reducing the iron loss is obtained.

The obtained grain-oriented electrical steel sheet was evaluated for various properties. The evaluation method was the same as in example 1 described above. The evaluation results are shown in table D4.

TABLE D4

In Nos. 4001 to 4013, when λ p-p @1.5T is 0.430 or less, it is judged that the magnetostrictive property is good.

In Nos. 4001 to 4013, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB exist in the examples of the present invention, and all of them show excellent low-field magnetostriction. On the other hand, in the comparative example, although the off-angle β is slightly and continuously shifted in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB are not sufficiently present, and the preferable low-field magnetostriction cannot be obtained.

Industrial applicability

According to the aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet in which magnetostriction in a low magnetic field region (particularly, a magnetic field of about 1.5T) is improved, and therefore, the present invention has high industrial applicability.

Description of the symbols

10 grain-oriented electromagnetic steel sheet (silicon steel sheet)

20 middle layer

30 insulating coating