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 于 2019-07-31 设计创作，主要内容包括：一种方向性电磁钢板,其具有在高斯取向上进行取向的织构,在将以在板面上相邻且间隔为1mm的两个测定点进行测定的晶体取向的偏离角表示为(α_1β_1γ_1)及(α_2β_2γ_2),将边界条件BA定义为|γ_2-γ_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 two measurement points adjacent to each other on the sheet surface and spaced at a distance of 1mm is represented by (alpha) 1 β 1 γ 1 ) And (alpha) 2 β 2 γ 2 ) The boundary condition BA is defined as | γ 2 ‑γ 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 which meets the boundary condition BA and does not meet 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：0～1.0％、

the remainder comprising Fe and impurities,

and has a texture oriented in a gaussian orientation, wherein,

the off-angle from the ideal gaussian orientation with the rolling surface normal direction Z as the rotation axis is defined as α, the off-angle from the ideal gaussian orientation with the rolling orthogonal direction C as the rotation axis is defined as β, the off-angle from the ideal gaussian orientation with the rolling direction L as the rotation axis is defined as γ, and the off-angle of the crystal orientation measured at two measurement points adjacent to each other on the plate surface and spaced by 1mm is represented as (α)₁β₁γ₁) And (alpha)₂β₂γ₂) The boundary condition BA is defined as | γ₂-γ₁| ≧ 0.5 °, the boundary condition BB is defined as [ (α)₂-α₁)²+(β₂-β₁)²+(γ₂-γ₁)²]^1/2And when the temperature is more than or equal to 2.0 degrees, a grain boundary which meets the boundary condition BA and does not meet 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_LThe average crystal grain diameter in the rolling direction L obtained based on the boundary condition BB is defined as a grain diameter 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 orthogonal direction C determined based on the boundary condition BA is defined as a grain diameter RA_CThe average crystal grain diameter in the rolling 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 direction C determined based on the boundary condition BA is defined as a grain diameter RA_CWhen the particle diameter RA is larger_LWith said particle size 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_LThe above-mentioned obtained based on the above-mentioned boundary condition BBThe average crystal grain diameter in the rolling direction C is defined as the 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 direction C determined based on the boundary condition BA is defined as a grain diameter RA_CThe average crystal grain diameter in the rolling 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_LThe average crystal grain diameter in the rolling 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 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 (| γ |) of an absolute value of the deviation angle γ is 0 ° to 3.50 °.

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 applying at least 1 of local micro strain or local groove formation.

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 Japanese application laid-open in Japanese application No. 2018-143542 at 7/31.2018, Japanese application laid-open in Japanese application No. 2018-143896 at 7/31.2018, and Japanese application laid-open in Japanese application No. 2018-143899 at 7/31.2018, and the contents thereof are incorporated herein by reference.

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 (Goss) 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 electrical steel sheets are greatly affected by the concentration of {110} <001> orientation. In particular, it is believed 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 easy magnetization direction, that is, the <001> direction of the crystal is important. Therefore, in the 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 so as to fall 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 three components, namely, a deviation angle α around the normal direction Z of the rolling surface, a deviation angle β around the rolling orthogonal 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 on the rolling surface and the rolling direction L when viewed from the rolling surface normal direction Z. The off-angle β is an angle formed by the rolling direction L and the <001> direction of the crystal projected on the L section (the section in which the rolling orthogonal direction is set as a normal line) when viewed from the rolling orthogonal direction C (the sheet width direction). The off-angle γ is an angle formed by the <110> direction of the crystal projected on the C section (the section in which the rolling direction is set as the normal) and the rolling surface normal direction Z when viewed from the rolling direction L.

It is known that the deviation angle β among the deviation angles α, β, γ affects magnetostriction (also referred to as magnetostriction). The magnetostriction is a phenomenon in which a magnetic material changes its shape by application of a magnetic field. Since magnetostriction of grain-oriented electrical steel sheets used in converters of transformers and the like causes vibration and noise, it is required to reduce the magnetostriction.

For example, patent documents 1 to 3 disclose controlling the slip angle β. Patent documents 4 and 5 disclose that the slip angle α is controlled in addition to the slip angle β. 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, the off-angle β, and the off-angle γ as indices.

Further, for example, patent documents 7 to 9 disclose that not only the magnitude and average value of the absolute values of the slip angles α, β, and γ are simply controlled, but also control is performed including fluctuation (variation). Further, patent documents 10 to 12 disclose that Nb, V, or the like is added to a grain-oriented electrical steel sheet.

Further, grain-oriented electrical steel sheets are required to have not only excellent magnetostriction but also excellent magnetic flux density. Heretofore, a method of controlling the growth of crystal grains in secondary recrystallization to obtain a steel sheet having a high magnetic flux density has been proposed. For example, patent documents 13 and 14 disclose a method of performing secondary recrystallization while applying a temperature gradient to a steel sheet in a tip region of secondary recrystallized grains of primary recrystallized grains being eaten by silkworm in a finish annealing step.

In the case where 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 are 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 a process of suppressing free growth of secondary recrystallization (for example, a process of applying mechanical strain to an end portion in the width direction of a steel sheet) generated at the initial stage of secondary recrystallization when the secondary recrystallization is performed while applying a temperature gradient.

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

Grain-oriented electrical steel sheets are used as core materials for various transformers. For example, in a relatively small transformer such as a pole-mounted transformer, further miniaturization of the transformer is required. Accordingly, it is strongly desired to deal with a high magnetic field region in grain-oriented electrical steel sheets, and further improvement of magnetic properties in a high magnetic field is required.

As a result of studies by the present inventors, the conventional techniques disclosed in patent documents 1 to 9 cannot sufficiently reduce magnetostriction particularly in a high magnetic field, although crystal orientation is controlled.

In addition, the conventional techniques disclosed in patent documents 10 to 12 contain only Nb and V, and therefore the reduction of magnetostriction in a high magnetic field is not sufficient. Further, the conventional techniques disclosed in patent documents 13 to 15 have problems from the viewpoint of productivity, and the reduction of magnetostriction in a high magnetic field is not sufficient.

The present invention addresses the problem of providing a grain-oriented electrical steel sheet in which magnetostriction is improved in view of the current situation in which a reduction in magnetostriction is required in the grain-oriented electrical steel sheet. In particular, it is an object to provide a grain-oriented electrical steel sheet in which magnetostriction in a high magnetic field region (magnetic field of about 1.9T) is improved.

Means for solving the problems

The gist of the present invention is as follows.

(1) A grain-oriented electrical steel sheet according to one aspect of the present invention has the following chemical composition: contains 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 of Fe and impurities, and a texture oriented in a Gaussian orientation,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 orthogonal 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 two measurement points adjacent to each other on the plate surface and spaced 1mm apart is expressed as (α)₁β₁γ₁) And (alpha)₂β₂γ₂) The boundary condition BA is defined as | γ₂-γ₁| ≧ 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 which meets the boundary condition BA and does not meet 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 right angle direction C determined based on the boundary condition BA is defined as a grain diameter RA_CThe average crystal grain diameter in the 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 direction C determined based on the boundary condition BA is defined as the grain diameter RA_CWhen the particle diameter RA is small_LWith particle size RA_CRA may be 1.15. ltoreq_C÷RA_L。

(5) The grain-oriented electrical steel sheet according to any one of the above (1) to (4), 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 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 direction C determined based on the boundary condition BA is defined as the grain diameter RA_CThe average crystal grain diameter in the 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 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 direction C determined based on the boundary condition BA is defined as the grain diameter RA_CWhen this is the case, the particle diameter RA may be_LHas a particle diameter RA of 30mm or less_CIs 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 (| γ |) of an absolute value of the off-angle γ may be 0 ° to 3.50 °.

(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 may be subdivided by at least 1 of applying local micro strain and forming local grooves.

(12) The grain-oriented electrical steel sheet according to any one of the above (1) to (11), wherein the grain-oriented electrical steel sheet 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, a grain-oriented electrical steel sheet having improved magnetostriction in a high magnetic field region (particularly, a magnetic field of about 1.9T) can be obtained.

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

Fig. 3 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 embodiments, and various modifications can be made without departing from the scope 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 "above" or "below," the value is not included in the range of values. In addition, "%" with respect to 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 becomes small (specifically, so that the maximum value and the average value of the absolute value | β | of the off angle β become small). In fact, it was confirmed that: heretofore, when the intensity of the magnetic field at the time of magnetization is a magnetic field region in the vicinity of 1.7T (hereinafter, may be simply referred to as "middle magnetic field region") which is the intensity of the magnetic field at the time of measuring the magnetic properties in general, the correlation between the off angle β and the magnetostriction is relatively high.

Further, the inventors of the present invention examined the relationship between the crystal orientation and the magnetostriction in detail for a material having relatively good magnetostriction. As a result, they found that: in addition to the slip angle β, the slip angle γ also has an effect on magnetostriction. In particular, the state of improvement in magnetostriction at the off angle γ was examined, and as a result, it was found that: this behavior can be evaluated by the amount of magnetostriction at 1.9T, i.e., "difference between minimum and maximum values of magnetostriction" (hereinafter, referred to as "λ p-p @ 1.9T"). Thus, it is believed that: the noise of the transformer can be further reduced if this behavior can be optimally controlled.

It should be noted that: in a grain-oriented electrical steel sheet, the <001> orientation, which is an easy magnetization axis, is preferentially aligned with the rolling direction, and the magnetic properties are less affected by the off-angle γ generated by crystal rotation about the rolling direction L. Therefore, a general grain-oriented electrical steel sheet is manufactured in the following manner: nuclei of secondary recrystallized grains are generated which are subjected to fine orientation control mainly with respect to the off-angle α and the off-angle β, and the grains are grown while maintaining the crystal orientation. It is generally believed that: in addition to controlling the slip angle α and the slip angle β as described above, it is difficult to further precisely control the slip angle γ.

Therefore, the inventors of the present invention have studied on the fact that the crystal is grown while changing the orientation, but the crystal is not grown in a state of maintaining the crystal orientation at the stage of the growth of the secondary recrystallized grains. As a result, it was found that: the following states become advantageous for the magnetostriction reduction in the high magnetic field region: in the process of growing the secondary recrystallized grains, a large amount of local and small-tilt-angle orientation changes of a degree that has not been conventionally recognized as grain boundaries are generated, and one secondary recrystallized grain is divided into small regions having slightly different off-angles γ.

In addition, it is recognized that: for the control of the orientation change described above, the following factors are considered important: factors that make the orientation change itself easy to occur; and a factor causing orientation change to be continuously generated in one crystal grain. Thus, it was confirmed that: in order to facilitate the occurrence of the orientation change itself, it is effective to start the secondary recrystallization from a lower temperature, and for example, the primary recrystallization grain size can be controlled to effectively use an element such as Nb. Further, it was confirmed that: by using AlN or the like, which has been a conventionally used inhibitor, at an appropriate temperature and in an atmosphere, it is possible to cause a change in orientation to continue in one crystal grain in secondary recrystallization to 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 γ. That is, the grain-oriented electrical steel sheet of the present embodiment has not only grain boundaries having a large angle difference between grain boundaries corresponding to the secondary recrystallized grains, but also local and small-angle grain boundaries dividing the secondary recrystallized grains.

Specifically, the grain-oriented electrical steel sheet of the present embodiment has the following chemical composition: contains 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 impuritiesAnd a texture oriented in 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 alpha, a deviation angle from an ideal Gaussian orientation with a rolling orthogonal direction (plate width direction) C as a rotation axis is defined as beta, a deviation angle from an ideal Gaussian orientation with a rolling direction L as a rotation axis is defined as gamma, and deviation angles of crystal orientation measured at two measurement points adjacent to each other on a plate surface and spaced by 1mm are respectively represented as (alpha)₁β₁γ₁) And (alpha)₂β₂γ₂) The boundary condition BA is defined as | γ₂-γ₁| ≧ 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 not only grain boundaries satisfying the boundary condition BB (grain boundaries corresponding to secondary recrystallized grain boundaries) but also grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB (grain boundaries dividing secondary recrystallized grains).

The grain boundaries satisfying the boundary condition BB substantially correspond to secondary recrystallized grain boundaries observed when conventional grain-oriented electrical steel sheets are subjected to macroscopic etching. The grain-oriented electrical steel sheet of the present embodiment has not only the grain boundaries satisfying the boundary condition BB described above but also grain boundaries 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 and small-inclination grain boundaries that divide the secondary recrystallized grains. That is, in the present embodiment, the secondary recrystallized grains are more finely divided into small regions having slightly different off-angles γ.

Conventional grain-oriented electrical steel sheets may have secondary recrystallized grain boundaries satisfying boundary condition BB. In addition, the conventional grain-oriented electrical steel sheet may have a shift in the off angle γ in 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 γ in the secondary recrystallized grains, it is difficult for the shift of the off angle γ 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 there is a possibility that the displacement of the off angle γ can be recognized in the long range region within the secondary recrystallized grains, the displacement of the off angle γ is very small in the short range region within the secondary recrystallized grains, and therefore recognition is difficult (it is difficult to satisfy the boundary condition BA). On the other hand, in the grain-oriented electrical steel sheet of the present embodiment, the off angle γ is locally displaced in the short range region and can be recognized as a grain boundary. Specifically, between two measurement points adjacent to each other at an interval of 1mm in the secondary recrystallized grains, | γ exists at a relatively high frequency₂-γ₁The value of |, is a displacement of 0.5 ° or more.

In the grain-oriented electrical steel sheet of the present embodiment, grain boundaries (grain boundaries into which secondary recrystallized grains are divided) satisfying boundary condition BA and not satisfying boundary condition BB are intentionally produced by strictly 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 γ, and the magnetostriction in the high 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, two {110} <001> orientations, that is, "the actual {110} <001> orientation of a crystal" and "the 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 steel sheet after recrystallization, the crystal orientation is defined without strictly distinguishing the difference in angle of about ± 2.5 °. In the case of a conventional grain-oriented electrical steel sheet, an angular range region of about ± 2.5 ° centered around a geometrically strict {110} <001> orientation is set as the "{ 110} <001> orientation". However, in the present embodiment, the angular difference of ± 2.5 ° or less also needs to be clearly distinguished.

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

Therefore, in the present embodiment, for example, the following description may be given: "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 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 off-angle of the crystal orientation observed in a grain-oriented electrical steel sheet from the ideal {110} <001> orientation in the normal direction Z around the rolling plane.

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

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

Fig. 1 shows a schematic diagram of the slip angle α, the slip angle β, and the slip angle γ.

Angle phi: the above-mentioned off-angles of crystal orientation measured at two measurement points adjacent to each other at a distance of 1mm on the rolling surface 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 "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 local crystal orientation changes, which have not been recognized as grain boundaries in the past, particularly in the growth of secondary recrystallized grains, in order to control the off angle γ. In the following description, the above-described orientation change that occurs by dividing one secondary recrystallized grain into small regions having slightly different off-angles γ is sometimes referred to as "inversion".

Further, crystal grain boundaries (grain boundaries satisfying the boundary condition BA) in which the angle difference of the off-angle γ is taken into consideration may be described as "γ grain boundaries", and crystal grains distinguished by the γ grain boundaries may be described as "γ grains".

Note that the characteristic relating to the present embodiment, that is, the magnetostriction (λ p-p @1.9T) when excited at 1.9T, may be simply referred to as "magnetostriction (in) at a high magnetic field" in the following description.

It is believed that: in the above-described reversal, the change in crystal orientation is around 1 ° (less than 2 °), which occurs during the growth of the secondary recrystallized grains. Details are based on the association with the manufacturing method as will be described later, but it is important to grow secondary recrystallized grains under conditions where commutation is likely to occur. For example, the following matters are important: the secondary recrystallization is started at a relatively low temperature by controlling the primary recrystallization particle size, and is continued to a high temperature by controlling the kind and amount of the inhibitor.

The reason why the control of the slip angle γ affects the high magnetic field magnetostriction is not necessarily clear, but is estimated as follows.

In a grain-oriented electrical steel sheet in which secondary recrystallization is completed, the crystal orientation is controlled to be gaussian, but actually, the crystal orientation is slightly different in crystal grains on both sides across the crystal grain boundary. Therefore, when the grain-oriented electrical steel sheet is excited, a special magnetic domain (closed magnetic domain) for adjusting the magnetic domain structure is induced in the vicinity of the crystal grain boundary. In the closed magnetic domain, it is difficult for the magnetic moment in the magnetic domain to coincide with the direction of the external magnetic field, and therefore, the closed magnetic domain remains in the high magnetic field region during magnetization to suppress the movement of the magnetic domain wall. On the other hand, it is believed that: if the occurrence of closed magnetic domains in the vicinity of crystal grain boundaries can be reduced, magnetization of the entire steel sheet is facilitated in a high magnetic field region, resulting in a reduction in magnetostriction. It is believed that: however, in the present embodiment, the change in the crystal orientation near the grain boundary is slowed by a relatively slow orientation change accompanying the commutation, and as a result, the generation of closed magnetic domains is suppressed.

In the present embodiment, two boundary conditions are defined for the change in crystal orientation including the inversion. In the present embodiment, the definition of "grain boundary" based on these 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 approximately 5 ° or less. This control is also applied to 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 a general grain boundary (large tilt angle grain boundary), that is, "a boundary in which a 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 macroscopic etching of the steel sheet surface, but the difference in crystal orientation between the regions on both sides of the grain boundaries is usually about 2 to 3 °.

In the present embodiment, as will be 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 etching is not used.

In the present embodiment, in order to identify the grain boundaries, a measurement line including at least 500 measurement points at 1mm intervals is set on the rolled surface to measure the crystal orientation. For example, the crystal orientation may 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 transmitted or reflected diffraction spots. 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 number of measurement points of the crystal orientation may be at least 500, but it is preferable to increase the number of measurement points as appropriate depending on the size of the secondary recrystallized grains. For example, when the number of secondary recrystallized grains included in the measurement line is less than 10 when the number of measurement points for measuring the crystal orientation is set to 500 points, it is preferable to lengthen the measurement line by increasing the number of measurement points at intervals of 1mm so that 10 or more secondary recrystallized grains are included 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. Based on the deviation angles at the respective measurement points thus determined, it is determined whether or not a grain boundary exists between two adjacent measurement points. Specifically, it is determined whether or not the adjacent two measurement points satisfy the boundary condition BA and/or the boundary condition BB.

Specifically, the off-angles of the crystal orientations measured at two adjacent measurement points are represented by (α)₁、β₁、γ₁) And (alpha)₂、β₂、γ₂) When, the boundary condition BA is defined as | γ₂-γ₁| ≧ 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. It is determined whether or not a grain boundary satisfying boundary condition BA and/or boundary condition BB exists between two adjacent measurement points.

The grain boundary satisfying the boundary condition BB is considered to be substantially the same as the grain boundary of the conventional secondary recrystallized grain recognized in the macro etching, since the difference in the spatial three-dimensional orientation (angle Φ) between 2 points across the grain boundary is 2.0 ° or more.

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

The two grain boundaries can be determined using other measurement data. However, if the deviation from the actual state due to the difference in measurement time and data is considered, it is preferable to determine the two 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).

Since the grain-oriented electrical steel sheet of the present embodiment has not only grain boundaries satisfying the boundary condition BB but also grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB at a relatively high frequency, the secondary recrystallized grains are divided into small regions having slightly different drift angles γ, and as a result, magnetostriction in a high magnetic field region is reduced.

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

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

Specifically, when the crystal orientation is measured at least at 500 measurement points at 1mm intervals on the rolled surface, the off-angle is determined at each measurement point, and the boundary condition is determined at two 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 the boundary condition BA" by "the number of boundaries satisfying the boundary condition BB" is not particularly limited. For example, the value may be 80 or less, 40 or less, or 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 set to be 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 γ 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 the γ crystal grains and the secondary recrystallized grains whose grain sizes are 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_L÷RA_L. In addition, RB is preferable_L÷RA_L≤80。

This specification means that the above-mentioned "reversing" is relative to the rollingThe situation of the direction. That is, it means that at least one | γ is included in secondary recrystallized grains having a crystal grain boundary at a boundary where the angle φ is 2 ° or more₂-γ₁The crystal grains having | of 0.5 ° or more and the boundary of which the angle Φ becomes 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_LEvaluation was performed and specified.

Due to the particle diameter RB_LSmall or even particle diameter RB_LLarge but less direction change and particle size RA_LLarge, therefore if RB_L/RA_LIf the value is less than 1.10, the commutation frequency may become insufficient, and the high magnetic 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, further preferably 5.0 or more.

For RB_L/RA_LThe upper limit of the value is not particularly limited. If the frequency of occurrence of commutation is high and RB_L/RA_LA larger value is preferable for improvement of magnetostriction because continuity of crystal orientation in the entire grain-oriented electrical steel sheet becomes higher. On the other hand, since the commutation is also a residue of lattice defects in the crystal grains, if the frequency of occurrence is too high, the effect of improving particularly the iron loss may be reduced. Thus as RB_L/RA_LThe practical maximum value of the value is 80. As RB if iron loss is particularly required to be considered_L/RA_LThe maximum value of the value is preferably 40, more preferably 30.

Note that RB is_L/RA_LThe value may become lower than 1.0. RB (radio B)_LThe average grain size in the rolling direction is determined based on the grain boundaries having an angle phi of 2 DEG or more. On the other hand, RA_LIs based on | γ₂-γ₁I is a grain boundary of 0.5 ° or more and defines an average grain diameter in the rolling direction. If considered simply, the frequency detected by the grain boundary having a small lower limit of the angle difference is considered to be high. That is, it is considered that: RB (radio B)_LAlways becomes greater than RA_LBig, RB_L/RA_LThe value is always 1.0 or more.

However, RB_LIs the grain size, RA, determined from the grain boundaries at the angle phi_LIs the grain size determined from the grain boundary at the off-angle γ, in the case of RB_LAnd RA_LThe grain boundaries used to determine the grain size are defined differently. Thus, RB_L/RA_LThe value may become lower than 1.0.

For example, even if | γ₂-γ₁I is lower than 0.5 deg. (e.g., 0 deg.), but if the deviation angle a and/or the deviation angle beta are large, the angle phi becomes sufficiently large. That is, there are grain boundaries that do not satisfy the boundary condition BA but satisfy the boundary condition BB. If such grain boundaries are increased, the grain diameter 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 commutation is increased by the slip angle γ. When the control of the commutation is insufficient and the deviation from the present embodiment is large, RB does not cause a change in the slip angle γ_L/RA_LThe value becomes lower than 1.0. In the present embodiment, the generation frequency of γ grain boundaries and RB are sufficiently increased_L/RA_LThe fact that the value is 1.10 or more is a necessary condition has already been explained in the foregoing.

In the grain-oriented electrical steel sheet according to the present embodiment, the boundaries between two measurement points adjacent to each other on the rolling 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 based on the grain boundaries satisfying case 1 and/or case 2 in Table 1_LThe grain boundaries were determined based on 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 between the grain boundaries of cases 1 and/or 3 on the measurement line is set as the particle diameter RA_L。

[ Table 1]

RB_L/RA_LThe reason why the control of the value affects the high magnetic field magnetostriction is not necessarily clear, but it is considered that: by causing a change in orientation (local change in orientation) in one secondary recrystallized grain, a difference in orientation with respect to the adjacent grains is reduced (the change in crystal orientation in the vicinity of the crystal grain boundary becomes gradual), and as a result, the generation of closed magnetic domains is suppressed.

[ 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 γ 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 the γ crystal grains and the secondary recrystallized grains, the grain diameters of which are 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 orthogonal direction C determined based on the boundary condition BA is defined as the grain size RA_CThe average crystal grain diameter in the 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" in the direction perpendicular to the rolling direction. That is, it means that at least one | γ is included in secondary recrystallized grains having a crystal grain boundary at a boundary where the angle φ is 2 ° or more₂-γ₁The crystal grains having | of 0.5 ° or more and the boundary of which the angle Φ becomes less than 2 ° exist at corresponding frequencies with respect to the rolling orthogonal direction. In the present embodiment, the condition of the direction change is performed by rollingParticle diameter RA in the right angle direction_CAnd particle diameter RB_CEvaluation was performed and specified.

Due to the particle diameter RB_CSmall or even particle diameter RB_CLarge but less direction change and particle size RA_CLarge, therefore if RB_C/RA_CIf the value is less than 1.10, the commutation frequency may become insufficient, and the high magnetic 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, further preferably 5.0 or more.

For RB_C/RA_CThe upper limit of the value is not particularly limited. If the frequency of occurrence of commutation is high and RB_C/RA_CA larger value is preferable for improvement of magnetostriction because continuity of crystal orientation in the entire grain-oriented electrical steel sheet becomes higher. On the other hand, since the commutation is also a residue of lattice defects in the crystal grains, if the frequency of occurrence is too high, the effect of improving particularly the iron loss may be reduced. Thus as RB_C/RA_CThe practical maximum value of the value is 80. As RB if iron loss is particularly required to be considered_C/RA_CThe maximum value of the value is preferably 40, more preferably 30.

Note that RB is_CIs the grain size, RA, determined from the grain boundaries at the angle phi_CThe grain size is determined from the grain boundary at the off angle γ. Then RB_CAnd RA_CIn addition, RB is different in the definition of grain boundaries for determining the particle size_C/RA_CThe value may become lower than 1.0.

Particle diameter RB described above_CThe grain size RA is determined based on the grain boundaries satisfying case 1 and/or case 2 in Table 1_CThe grain boundaries were determined based on 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 between the grain boundaries of cases 1 and/or 2 on the measurement line is set as the grain diameter RB_C. Likewise, will be on the measurement line described aboveThe average value of the lengths of the grain boundaries sandwiched between the grain boundaries of cases 1 and/or 3 was set as the grain size RA_C。

RB_C/RA_CThe reason why the control of the value affects the high magnetic field magnetostriction is not necessarily clear, but it is considered that: by causing a change in orientation (local change in orientation) in one secondary recrystallized grain, a difference in orientation with respect to the adjacent grains is reduced (the change in crystal orientation in the vicinity of the crystal grain boundary becomes gradual), and as a result, the generation of closed magnetic domains is suppressed.

[ 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 γ crystal grains in the rolling direction is smaller than the grain size of the γ crystal grains in the direction perpendicular to the rolling direction. That is, the grain-oriented electrical steel sheet of the present embodiment has γ grains whose grain size is 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 direction C determined based on the boundary condition BA is defined as the grain diameter RA_CWhen the particle diameter RA is small_LWith particle size RA_CRA is satisfied at 1.15. ltoreq._C÷RA_L. In addition, RA is preferable_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 shape of the crystal grain is not considered with respect to the size in the thickness direction (the observed shape in the thickness cross section). In addition, in a grain-oriented electrical steel sheet, almost all crystal grains have the same size as the thickness of the steel sheet in the sheet thickness direction. That is, in many cases, the grain-oriented electrical steel sheet has a thickness occupied by one crystal grain except for a specific region such as a vicinity of a crystal grain boundary.

RA as described above_C/RA_LThe specification of the value indicates the state of the above-described "reversal" with respect to the rolling direction and the direction perpendicular to the rolling direction. That is, the frequency of local crystal orientation change, which means a degree of commutation, varies depending on the in-plane direction of the steel sheet. In the present embodiment, the state of the direction change is determined by the grain diameters RA in two directions orthogonal to each other in the steel sheet surface_CAnd particle diameter RA_LEvaluation was performed and specified.

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

The reason why the magnetostriction of a high magnetic field is improved by the shape of the γ crystal grains having in-plane anisotropy is not clear, but is considered as follows. In high magnetic fields, "continuity" with adjacent grains is important when the 180 ° domain moves, as previously described. For example, in the case where one secondary recrystallized grain is divided into small regions by the commutation, if the number of the small regions is the same (the area of the small regions is the same), the existence ratio of the boundary (γ grain boundary) resulting from the commutation becomes larger when the shape of the small region is anisotropic than when the shape of the small region is isotropic. Namely, it is considered that: by controlling RA_C/RA_LThe orientation change, that is, the frequency of existence of the commutation increases, and the continuity of the crystal orientation in the entire grain-oriented electrical steel sheet is improved.

It is believed that: the anisotropy of such commutation occurs through some of the anisotropy present in the steel sheet before the second recrystallization: for example, anisotropy of shape of primary recrystallized grains; anisotropy of crystal orientation distribution of primary recrystallized grains (distribution of population) caused by anisotropy of shape of crystal grains of the hot-rolled sheet; an arrangement of precipitates stretched by hot rolling and precipitates crushed and aligned in the rolling direction; precipitate distribution caused by the variation of the thermal history in the width direction or the length direction of the coil; anisotropy of crystal particle size distribution, and the like. However, the details of the mechanism of occurrence are not known. 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 means 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 the temperature gradient at the time of the secondary recrystallization is also related, it is preferable in the present embodiment to set the direction in which the γ crystal grains extend to the rolling orthogonal direction if the present general manufacturing method is considered. In this case, the grain diameter RA in the rolling direction_LGrain diameter RA in the direction perpendicular to rolling_CA small value. The relationship between the rolling direction and the rolling orthogonal direction will be described in connection with the manufacturing method. The direction in which the γ grains extend is determined not by the temperature gradient but by the frequency of occurrence of γ grain boundaries.

Due to the particle size RA_CSmall or even particle size RA_CLarge particle size RA_LIs also large, therefore if RA_C/RA_LIf the value is less than 1.15, the commutation frequency may become insufficient, and the high magnetic 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 or more.

For 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_LA larger value is preferable for improvement of magnetostriction because continuity of crystal orientation in the entire grain-oriented electrical steel sheet becomes higher. On the other hand, since the commutation is also a residue of lattice defects in the crystal grains, if the frequency of occurrence is too high, the effect of improving particularly the iron loss may be reduced. Thus, as RA_C/RA_LThe practical maximum value of the value is 10. If particularly necessary, taking into account iron lossAs 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 is preferably controlled not only by the RA described above_C/RA_LThe particle size RA is also set to the same value as in embodiment 2_LAnd particle diameter RB_LRB of 1.10 or less is satisfied_L÷RA_L。

This provision makes clear that the "commutation" has taken place. For example, the particle diameter RA_CAnd RA_LBased on | γ between two adjacent measurement points₂-γ₁If the grain size is 0.5 DEG or more, the angle phi of all grain boundaries is 2.0 DEG or more, and the above-mentioned RA can be satisfied even if the "grain inversion" is not caused at all_C/RA_LThe value is obtained. Even if RA is satisfied_C/RA_LHowever, if the angle Φ of all the grain boundaries is 2.0 ° or more, only the secondary recrystallized grains recognized in general simply become flat, and therefore 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 to satisfy not only the RA described above_C/RA_LValue, also satisfies RB_L/RA_LThe value is obtained.

In addition, in the present embodiment, RB is controlled not only with respect to the rolling direction_L/RA_LIn addition, the grain size RA is also adjusted in the right angle direction of rolling in the same manner 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 crystal orientation in the entire grain-oriented electrical steel sheet.

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

Specifically, in the grain-oriented electrical steel sheet of the present embodiment, the grain-oriented electrical steel sheet is formed by joiningThe average crystal grain diameter in the rolling direction L obtained under the boundary condition BB is defined as the grain diameter RB_LThe average crystal grain diameter in the 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 definition is not related to the "reversal" described above, and indicates that the secondary recrystallized grains extend in the direction perpendicular to the rolling direction. Therefore, this feature is not particular in itself. However, in the present embodiment, it is preferable to control RA_C/RA_LOn the basis of the value, RB_C/RB_LThe values satisfy the above numerical ranges.

In the present embodiment, RA of γ crystal grains is controlled in association with the above-described commutation_C/RA_LIn the case of the value, the form of the secondary recrystallized grains tends to have a large in-plane anisotropy. Conversely, when the direction change of the off-angle γ occurs as in the present embodiment, the shape of the γ crystal grains tends to have in-plane anisotropy by controlling the shape of the secondary recrystallized grains 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. For RB_C/RB_LThe upper limit of the value is not particularly limited.

As control RB_C/RB_LExamples of the method of practical value include the following processes: in the final annealing, preferential heating is performed from the end of the coil width, and a temperature gradient in the coil width direction (coil axial direction) is applied to grow secondary recrystallized grains. In this case, the grain size of the secondary recrystallized grains in the coil width direction (for example, the direction perpendicular to rolling) may be controlled to be the same as the coil width while the grain size of the secondary recrystallized grains in the coil circumferential direction (for example, the rolling direction) is maintained 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_LOf valueThe upper limit value is 20.

Further, if the secondary recrystallization is performed by the continuous annealing process in such a manner that it has a temperature gradient not in the rolling orthogonal direction but in the rolling direction, the maximum value of the grain size of the secondary recrystallized grains is not limited to the coil width, but may be set to a larger value. Even in this case, according to the present embodiment, the above-described effects of the present embodiment can be obtained by appropriately dividing the crystal grains by the γ -grain boundaries due to the commutation.

Further, in the grain-oriented electrical steel sheet of the present embodiment, it is preferable that the frequency of occurrence of the reversal with respect to the off-angle γ be 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 direction C determined based on the boundary condition BA is defined as the grain diameter RA_CThe average crystal grain diameter in the 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, and is 0.2 if the current state of the art 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 "the reversal of the division of the secondary recrystallized grains in the direction perpendicular to the rolling direction: RB (radio B)_C/RA_CAnd the occurrence degree of the reversal of the division of the secondary recrystallized grains in the rolling direction: RB (radio B)_L/RA_L"ratio of the two components. The value less than 1 means that a secondary recrystallized grain is largely divided in the rolling direction by the direction change (γ grain boundary)And (6) cutting.

In addition, if the above is replaced, the above (RB)_C·RA_L)/(RB_L·RA_C) Degree of flattening into "secondary recrystallized grains: RB (radio B)_C/RB_LDegree of flatness of "and" γ grains: RA_C/RA_L"ratio of the two components. A value less than 1 indicates that the γ crystal grains obtained by dividing one secondary recrystallized grain have a flat shape as compared with the secondary recrystallized grains.

That is, the secondary recrystallized grains tend to be cut in the rolling direction rather than in the direction perpendicular to the rolling direction by the γ grain boundaries. That is, the γ grain boundary tends to extend in the direction in which the secondary recrystallized grains extend. It is believed that: this tendency of the γ grain boundary acts to reverse the direction during the secondary recrystallization grain extension and increase the occupied area of the crystal 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 if industrial applicability is considered.

Particle diameter RB described above_LAnd particle diameter RB_CThe grain boundaries were determined based on the grain boundaries satisfying case 1 and/or case 2 in table 1. The above particle diameter RA_LAnd particle diameter RA_CThe grain boundaries were determined based on 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 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_CThe same applies to the calculation.

[ features common to the respective embodiments ]

Next, the following description will be given of the common technical features of the grain-oriented electrical steel sheets according to the above embodiments.

In the direction of the various embodiments of the inventionIn a linear electromagnetic steel sheet, the average crystal grain size in the rolling direction L determined based on the boundary condition BB is defined as the grain size RB_LThe average crystal grain diameter in the 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.

It is believed that: the commutation is generated by dislocations accumulated during the growth of the secondary recrystallized grains. That is, after the commutation is once caused, in order to cause the next commutation, it is necessary to grow the secondary recrystallized grains to a considerable extent. Therefore, if the particle diameter RB_LAnd particle diameter RB_CIf the diameter is less than 15mm, commutation may be difficult to occur, and sufficient improvement of high magnetic field magnetostriction due to the commutation may be 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 still more preferably 40mm or more.

Particle size RB_LAnd particle diameter RB_CThe upper limit of (b) is not particularly limited. For example, in the production of a general grain-oriented electrical steel sheet, a steel sheet having undergone primary recrystallization is wound into a coil, and {110} is caused to undergo secondary recrystallization in a state having curvature in the rolling direction<001>Oriented grains are generated and grown. Therefore, if the grain diameter RB in the rolling direction_LIf the deviation angle γ increases, the magnetostriction may increase. Therefore, it is preferable to avoid increasing the particle diameter RB without limitation_L. With respect to the particle diameter RB, if industrial realizability is also considered_LA preferable upper limit is 400mm, a more preferable upper limit is 200mm, and a further preferable upper limit is 100 mm.

In general, in the production of grain-oriented electrical steel sheets, a steel sheet having undergone primary recrystallization is heated in a state of being wound into a coil, and {110} is recrystallized by secondary recrystallization<001>Since oriented crystal grains are generated and grown, secondary recrystallized grains grow from the coil end side where the temperature rise is advanced toward the coil center side where the temperature rise is delayed. In such a manufacturing method, for example if the coil is to be woundWhen the width is set to 1000mm, 500mm which is about half the width of the coil is used 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_C。

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 BA is defined as the grain diameter RA_LThe average crystal grain diameter in the rolling direction C determined based on the boundary condition BA is defined as the grain 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_LThe smaller the value of (b) is, the higher the occurrence frequency of the direction change in the rolling direction is. Particle size RA_LIt is preferably 40mm or less, more preferably 30mm or less, and still more preferably 20mm or less.

In addition, if the particle diameter RA is not sufficient to cause sufficient reversal_CIf the deviation angle γ increases, the magnetostriction may increase. Therefore, it is preferable to avoid increasing the particle diameter RA without limitation_C. Regarding the particle size RA, if industrial realizability is also considered_CThe preferable upper limit is 400mm, the more preferable upper limit is 200mm, the more preferable upper limit is 100mm, the more preferable upper limit is 40mm, and the more preferable upper limit is 30 mm.

Particle size RA_LAnd particle diameter RA_CThe lower limit of (b) is not particularly limited. In each embodiment, the grain size RA is set to 1mm because the measurement interval of the crystal orientation is set to 1mm_LAnd particle diameter RA_CThe minimum value of (2) is 1 mm. However, in each embodiment, for example, by setting the measurement interval to be less than 1mm, the particle diameter RA is not excluded_LAnd particle diameter RA_CA steel sheet having a thickness of less than 1 mm. However, since the commutation is slightly accompanied by the presence of lattice defects in the crystal, if the frequency of the commutation is too high, there is a concern about adverse effects on the magnetic characteristics. In addition, if industrial realizability is considered, the particle size RA is considered_LAnd particle diameter RA_CA preferable lower limit is 5 mm.

In the measurement of the crystal grain size in the grain-oriented electrical steel sheet according to each embodiment, the grain size of one crystal grain includes no ambiguity of 2mm at most. Therefore, the grain size measurement (the orientation measurement of at least 500 points at 1mm intervals on the rolled surface) is preferably performed at 5 or more sites in total at positions sufficiently separated from the direction of the predetermined grain size in the direction perpendicular to the steel sheet surface, that is, at positions for measuring different crystal grains. In addition, the above ambiguity can be resolved by averaging all the particle diameters obtained by the measurement of 5 or more sites in total. For example, for the particle size RA_CAnd particle diameter RB_CThe particle diameter RA is determined by measuring at least 5 sites sufficiently separated in the rolling direction_LAnd particle diameter RB_LThe average grain size may be determined by performing measurement on 5 or more portions sufficiently separated in the direction perpendicular to rolling and performing orientation measurement on a total of 2500 or more measurement points.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the standard deviation σ (| γ |) of the absolute value of the off-angle γ is preferably 0 ° to 3.50 °.

The high magnetic field magnetostriction is not sufficiently reduced without causing a large amount of commutation. It is believed that: this indicates that the off angle coincides with a specific direction when the high magnetic field magnetostriction is reduced. Namely, it is considered that: the reduction in high-field magnetostriction is not caused by orientation selection by predation in the initial generation stage or growth stage of nucleus generation including 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, in a steel sheet in which the above-described commutation is sufficiently caused, the "slip angle" is also easily controlled to a characteristic range. For example, when the crystal orientation changes little by reversing the off-angle γ, the absolute value of the off-angle approaches zero, which does not become an obstacle in the above-described embodiment. Further, for example, when the crystal orientation changes little by reversing the off-angle γ, the crystal orientation itself converges along 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 (| γ |) of the absolute value of the deviation angle γ may be 0 ° to 3.50 °.

The standard deviation σ (| γ |) of the absolute value of the deviation angle γ is obtained as follows.

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

In each embodiment, it should not be considered that: "one secondary recrystallized grain is understood to mean a single crystal, having exactly the same crystal orientation within the secondary recrystallized grain". That is, in each embodiment, local orientation change of a degree that has not been conventionally recognized as a grain boundary exists in one coarse secondary recrystallized grain, and it is necessary to detect the 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 independently of the crystal grain boundary (crystal grain boundary). Specifically, it is preferable that the measurement points are distributed at equal intervals of 5mm in length and breadth within an area of Lmm × Mmm (of L, M >100) so as to include at least 20 crystal grains on the steel sheet surface, and the crystal orientation at each measurement point is measured to obtain data of 500 points or more in total. In the case where the measurement point is a crystal grain boundary and a specific point, the data is not used. In addition, it is necessary to expand the measurement range described above in accordance with a region necessary for determining the magnetic properties of the target steel sheet (for example, in the case of a coil of an actual machine, a range for measuring the magnetic properties described in a manufacturing process schedule (mill sheet)).

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

The off angle β is generally considered to be a factor to be reduced in order to improve the magnetic characteristics or magnetostriction in a middle magnetic field of about 1.7T. However, there is a limit to the characteristics achieved by controlling only the deviation angle β. In the above embodiment, attention is paid to the off angle γ to improve magnetostriction in a high magnetic field of about 1.9T. In the above-described embodiments, it is preferable that the continuity of the crystal orientation in the entire grain-oriented electrical steel sheet is influenced by controlling not only the above-described technical features but also σ (| γ |).

The standard deviation σ (| γ |) of the absolute value of the deviation angle γ is more preferably 3.00 or less, still more preferably 2.50 or less, and still more preferably 2.00 or less. σ (| γ |) 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, but the above-described crystal orientation, grain boundaries, average crystal grain size, and the like may be determined based on the steel sheet without the coating or the like. That is, when the grain-oriented electrical steel sheet to be a measurement sample has an insulating coating or the like on the surface, the crystal orientation or the like may be measured after removing the coating or the like.

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, the reaction is carried out by reacting 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, washing with water, and drying. The time for immersing in the aqueous sodium hydroxide solution may 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 intermediate layer in hydrochloric acid having such a concentration, for example, 30 to 40 mass% hydrochloric acid at 80 to 90 ℃ for 1 to 5 minutes, washing with water, and drying. In general, each coating is removed by using a treatment 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 basic elements as a chemical composition, optional elements as needed, and Fe and impurities in the remaining part.

The grain-oriented electrical steel sheet according to each embodiment contains, as basic elements (main alloying elements), Si (silicon): 2.00 to 7.00 percent.

Si is preferably contained in an amount of 2.0 to 7.0% in order to concentrate the crystal orientation in the {110} <001> orientation.

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, an optional element may be contained in addition to the above-described basic elements and impurities. For example, Nb, V, Mo, Ta, W, C, Mn, S, Se, Al, N, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni and the like may be contained as optional elements in place of a part of Fe which is the remainder of the above. These optional elements may be contained depending on the purpose. Therefore, the lower limit of these optional elements is not necessarily limited, and the lower limit may be 0%. In addition, these optional elements do not impair the above-described effects even if they are contained as impurities.

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 the respective embodiments. In the following description, one or two or more elements of Nb, V, Mo, Ta, and W may be collectively referred to as "Nb group element".

The Nb group element preferably acts on the characteristics of the grain-oriented electrical steel sheet of each embodiment, i.e., the formation of the commutations. However, since the Nb group element acts on the grain-oriented electrical steel sheet in the commutation process, it is not necessary that the Nb group element is finally included in the grain-oriented electrical steel sheet according to each embodiment. For example, the following tendency is present for Nb group elements: the resultant was discharged to the outside of the system by purification in finish 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 the 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, it is possible that the content of the Nb group element in the final product becomes zero. Therefore, the lower limit of the content of the Nb group element is not particularly limited, and the lower limit may be 0% each.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, it is preferable that at least 1 selected from Nb, V, Mo, Ta, and W is contained 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 is suggested that the commutation is controlled by using the Nb group element during the manufacturing process. In order to preferably control the reversal in the manufacturing process, the total content of the Nb group elements in the final product is preferably 0.0030% or more, and more preferably 0.0050% or more. On the other hand, if the total content of Nb group elements in the final product exceeds 0.030%, although the frequency of occurrence of commutation can be maintained, there is a possibility that the magnetic properties are degraded. Therefore, the total content of Nb group elements in the final product is preferably 0.030% or less. Further, the function of the Nb group element will be described below in connection with the manufacturing 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 set, 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 is a total content of S and Se including at least one of S and Se.

In addition, in grain-oriented electrical steel sheets, a relatively large change in chemical composition (decrease in content) is caused by decarburization annealing and purification annealing at the time of secondary recrystallization. Depending on the element, the content may be reduced to a level (1ppm or less) that cannot be detected by a general analytical method by purification annealing. The above chemical composition of the grain-oriented electrical steel sheet of each embodiment is the chemical composition in the final product. In general, 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 general analysis method of steel. For example, the chemical composition of the grain-oriented electrical steel sheet may be measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry). Specifically, a 35mm square test piece obtained from a grain-oriented electrical steel sheet is measured under conditions based on a previously prepared calibration curve by ICPS-8100 manufactured by shimadzu corporation (measuring apparatus), to determine the chemical composition. C and S may be measured by a combustion-infrared absorption method, and N may be measured by an inert gas melting-thermal conductivity method.

The chemical composition described above is a component of a grain-oriented electrical steel sheet. When a grain-oriented electrical steel sheet to be a measurement sample has an insulating coating or the like on its surface, the coating or the like is removed by the above-described method, and then the chemical composition is measured.

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 γ, and the magnetostriction in the high magnetic field region is reduced by this feature. Therefore, in the grain-oriented electrical steel sheet according to each embodiment, the film structure on the steel sheet, the presence or absence of the domain-refining treatment, and the like are not particularly limited. 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. 2 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. 2, 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 in which the cutting direction is parallel to the sheet thickness direction.

For example, the intermediate layer may be any of the following layers: 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, and 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 Mg₂SiO₄A coating film as a main body. 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 when viewed in the cross section.

In the grain-oriented electrical steel sheet according to each embodiment of the present invention, the intermediate layer may be an oxide film having an average thickness of 2 to 500 nm. The oxide film is formed of SiO₂A coating film as a main body. The interface between the oxide film and the grain-oriented electrical steel sheet becomes a smooth interface when viewed in the cross section.

The insulating film may be an insulating film mainly composed of phosphate and colloidal silica and having an average thickness of 0.1 to 10 μm, or an insulating film mainly composed of alumina sol and boric acid and having 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 applying at least 1 of local minute strain or local groove formation. The local micro strain or the local groove may be provided or formed by laser, plasma, mechanical method, etching, or other methods. For example, the local minute strain or the local groove may be provided or formed on the rolled surface of the steel sheet in a linear or dot shape so as to extend in a direction intersecting the rolling direction, and so as to have a rolling direction interval of 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. 3 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. 3, the method for producing a grain-oriented electrical steel sheet (silicon steel sheet) according to the present embodiment includes a casting step, a hot rolling step, a hot-rolled sheet annealing step, a cold rolling step, a decarburization annealing step, an annealing separator application step, and a finish annealing step. Further, the nitriding treatment may be performed at any timing from the decarburization annealing step to the finish annealing step, if necessary, or the finish annealing step may be followed by an insulating film forming step.

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

in the casting process, a slab is cast, which contains, as a chemical composition, in 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: 0-0.0850%, 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 to 1.0% and the balance of Fe and impurities;

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

in the final 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 pH is adjusted to 700 to 800 ℃ during the heating process₂O/PH₂Set to 0.10 to 1.0 or set to a pH of 1000 to 1050 DEG C₂O/PH₂Setting at least one of the temperature ranges of 0.0020 to 0.030, and setting the holding time at 850 to 950 ℃ to 120-600 minutes; when the total content of Nb, V, Mo, Ta and W in the chemical composition of the plate blank is not 0.0030 to 0.030%, the pH is adjusted to 700 to 800 ℃ during the heating process₂O/PH₂Setting the pH value to 0.10-1.0 at 1000-1050 deg.C₂O/PH₂The temperature is set to 0.0020 to 0.030, 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 in the atmosphere₂O and hydrogen partial pressure PH₂The ratio of.

The "commutation" of this embodiment is controlled primarily by two factors: factors that predispose the orientation change (commutation) itself to occur; and a factor causing orientation change (reversal) to occur continuously among one secondary recrystallized grains.

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

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

That is, in order for the commutation to preferably occur, the following is effective: in a state in which the generation of secondary recrystallized grains at high temperature is suppressed, secondary recrystallized grains generated at low temperature are preferentially grown 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 γ 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 factors are important in order to control the characteristic of the present embodiment, i.e., commutation. As for other manufacturing conditions, a conventionally known method for manufacturing a grain-oriented electrical steel sheet can be applied. Examples of the method include a method for producing an inhibitor of MnS or AlN formed by high-temperature slab heating, a method for producing an inhibitor of AlN formed by low-temperature slab heating and subsequent nitriding, and the like. The feature of the present embodiment, that is, the commutation, can be applied regardless of any manufacturing method, and is not limited to a specific manufacturing method. Hereinafter, a method of controlling the commutation by a manufacturing method using a nitriding process will be described as an example.

(casting step)

A slab is prepared in the casting process. An example of a method of manufacturing a slab is as follows. Molten steel is produced (smelted). Molten steel is used to produce slabs. The slab may also be manufactured by a continuous casting method. A steel ingot may be produced from molten steel, and a slab may be produced by cogging 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. In the case of using a thin slab, 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 general 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 preferred 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, if productivity in industrial production is taken into consideration, the lower limit of the C content may be more than 0%, and may be 0.0010%.

Si：2.0～7.0％

Silicon (Si) increases the electrical resistance of grain-oriented electrical steel sheets and reduces the iron loss. If the Si content is less than 2.0%, austenite transformation occurs at the time of 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 cracking is likely to occur during cold rolling. The lower limit of the Si content is preferably 2.50%, and more preferably 3.0%. The upper limit of the Si content is preferably 4.50%, and more preferably 4.0%.

Mn：0.～1.0％

Manganese (Mn) bonds with S or Se to form MnS or MnSe, and functions 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%, which is preferable. In the present embodiment, a part of the function of the inhibitor can be assumed by the nitride of the Nb group element. In this case, the intensity of MnS or MnSe as a general inhibitor is controlled to be weak. Therefore, the upper limit of the Mn content is preferably 0.50%, and more preferably 0.20%.

S：0～0.0350％

Se：0～0.0350％

Sulfur (S) and selenium (Se) combine with Mn to form MnS or MnSe, and function 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, it is preferable that the secondary recrystallization is stable if the total content of S and Se is 0.0030 to 0.0350%. In the present embodiment, a part of the function of the inhibitor can be assumed by the nitride of the Nb group element. In this case, the intensity of MnS or MnSe as a general inhibitor is controlled to be weak. Therefore, the upper limit of the total of the S and Se contents is preferably 0.0250%, and more preferably 0.010%. If S and Se remain after annealing of the final product, compounds are formed, and the iron loss is deteriorated. Therefore, it is preferable to reduce S and Se as much as possible by purification in the finish annealing.

Wherein "the total content of S and Se is 0.0030 to 0.0350%": the chemical composition of the slab can contain only one of S and Se, and the content of the one of S and Se is 0.0030-0.0350%; 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) is 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, it is preferable that the content of Al is in the range of 0.010 to 0.065%, because AlN as an inhibitor formed by nitriding described later expands the secondary recrystallization temperature region, and in particular, stabilizes the secondary recrystallization in the high temperature region. The lower limit of the Al content is preferably 0.020%, and 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) bonds to Al to function as an inhibitor. The content of N is 0-0.0120%. Since N may be contained by nitriding during the manufacturing process, the lower limit may be 0%. On the other hand, in the case of containing N, if the N content exceeds 0.0120%, blisters, which are one type of defects, are likely to be generated in the steel sheet. The upper limit of the N content is preferably 0.010%, and 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%.

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 Nb group elements are used for the commutation control, if the total content of the Nb group elements in the slab is 0.030% or less (preferably 0.0030% to 0.030%), the secondary recrystallization is started at an appropriate timing. Further, the orientation of the generated secondary recrystallized grains becomes very preferable, and the characteristic reversal of the present embodiment is likely to occur in the subsequent growth process, and finally, the structure preferable for the magnetic properties can be controlled.

By containing the Nb group element, the primary recrystallized grain size after decarburization annealing is preferably made smaller than that in the case of not containing the Nb group element. It is believed that: the primary recrystallized grains are refined by a pinning effect due to precipitates such as carbides, carbonitrides, and nitrides, a dragging effect as a solid solution element, and the like. In particular, Nb and Ta are preferable to obtain the effect strongly.

The smaller diameter of 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 in the past. In addition, since the precipitates of the Nb group element are decomposed at a relatively lower temperature than conventional inhibitors such as AlN, secondary recrystallization starts at a lower temperature than conventional in the temperature increase process of the final annealing. These mechanisms will be described later, but starting the secondary recrystallization at a low temperature easily causes the reversal of the characteristic of the present embodiment.

Further, it is considered that: when precipitates of the Nb group element are used as the secondary recrystallization inhibitor, 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 be performed, and therefore the effect of shifting the secondary recrystallization start temperature to a low temperature is 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 up to a temperature region in which secondary recrystallization can be performed.

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

When the primary recrystallized grains are oriented to be finer by the pinning effect of the carbide, carbonitride, or the like of the Nb group element, the C content of the slab is preferably set to 50ppm or more at the time of casting. However, since nitrides are preferable as compared with carbides or carbonitrides as inhibitors in the secondary recrystallization, it is preferable that the carbides or carbonitrides of the Nb group element in the steel be sufficiently decomposed by setting the C content to 30ppm or less, preferably 20ppm or less, and more preferably 10ppm or less by decarburization annealing after the primary recrystallization is completed. By making most of the Nb group element in a solid solution state in the decarburization annealing, the nitride (inhibitor) of the Nb group element can be adjusted to a form (a form in which secondary recrystallization is easily performed) preferable for the present embodiment in the subsequent nitriding treatment.

The total content of the Nb group elements 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. Here, "impurities" mean elements that are inevitably mixed from components contained in raw materials or components mixed in during production in the industrial production of a slab, and that do not substantially affect the effects of the present embodiment.

In addition to solving the manufacturing problems, the slab may contain known optional elements in place of part of Fe in consideration of the strengthening of the inhibitor function by the formation of a compound and the influence on the magnetic properties. 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 obtaining a hot-rolled steel sheet by hot rolling a slab heated to a predetermined temperature (for example, 1100 to 1400 ℃). In the hot rolling step, for example, after the casting step, rough rolling of a heated silicon steel material (slab) is performed, and then finish rolling is performed to produce a hot-rolled steel sheet having a predetermined thickness of, for example, 1.8 to 3.5 mm. After the finish rolling is completed, the hot-rolled steel sheet is wound at a predetermined temperature.

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

In the hot rolling step, the temperature gradient may be set in the above range in the width or length direction of the steel strip, thereby causing positional nonuniformity in the steel sheet surface with respect to the crystal structure, crystal orientation, and precipitates. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and preferably to impart in-plane anisotropy to the shape of γ grains necessary for the present embodiment. For example, in slab heating, by providing a temperature gradient in the plate width direction to refine precipitates in the high-temperature portion and improve the inhibitor function of the high-temperature portion, 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: the hot-rolled steel sheet obtained in the hot-rolling step is annealed under a predetermined temperature condition (for example, at 750 to 1200 ℃ C. for 30 seconds to 10 minutes) to obtain a hot-rolled annealed sheet.

In the hot-rolled sheet annealing step, the temperature gradient may be set in the above range in the width or length direction of the steel strip, whereby the in-plane positional unevenness of the steel sheet with respect to the crystal structure, crystal orientation, and precipitates may be generated. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and preferably to impart in-plane anisotropy to the shape of γ grains necessary for the present embodiment. 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 and improve the suppressor function of the high-temperature portion, thereby inducing 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 comprises the following steps: the hot-rolled annealed sheet obtained in the hot-rolled sheet annealing step is subjected to 1-time cold rolling or multiple (2 or more) cold rolling (for example, 80 to 95% in total cold rolling reduction) through annealing (intermediate annealing) to obtain 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, the 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 finer, the secondary recrystallization starting temperature can be shifted preferably 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, the slab may contain the Nb group element, and the primary recrystallized grains may be reduced by the pinning effect of the carbide, carbonitride, or the like of the Nb group element.

The amount of decarburization oxidation and the state of the surface oxide layer caused by the decarburization annealing affect the formation of the intermediate layer (glass coating), and therefore, can be appropriately adjusted by a conventional method in order to exhibit the effects of the present embodiment.

The Nb group element contained as an element which easily causes the transformation may exist as carbide, carbonitride, solid solution element, or the like at this time, and may exert an influence to refine the primary recrystallized grain size. 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, and may be 12 μm or more.

In the decarburization annealing step, 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, nonuniformity in the in-plane position of the steel sheet with respect to the crystal structure, crystal orientation, and precipitates can be generated. This makes it possible to impart anisotropy to the growth of secondary recrystallized grains in the final secondary recrystallization process, and preferably to impart in-plane anisotropy to the shape of γ grains necessary for the present embodiment. For example, in slab heating, by providing a temperature gradient in the width direction of the slab to refine the primary recrystallization grain size in the low-temperature portion to increase the driving force for the start of secondary recrystallization, the secondary recrystallization in the low-temperature portion is started early, and thus, when the secondary recrystallization grains grow, preferential grain growth from the low-temperature portion toward the high-temperature portion can be induced.

(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 timing 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: annealing the steel sheet in an atmosphere containing a gas having nitriding ability such as ammonia; and (3) subjecting the decarburized and annealed steel sheet coated with an annealing separator containing MnN or other nitriding powder to finish annealing.

When the slab contains the Nb group element in the above numerical range, 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, and therefore the secondary recrystallization starts at a lower temperature than in the past. It is also believed possible to: the selectivity of the nitride with respect to the generation of nuclei of secondary recrystallized grains also favorably works, achieving high magnetic flux density. In addition, AlN is also formed in the nitriding treatment, and this AlN functions as an inhibitor that continues the grain growth inhibition function 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, and 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, whereby the inhibitor strength may be unevenly distributed in 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 preferably to impart in-plane anisotropy to the shape of γ grains necessary for the present embodiment. For example, by providing a difference in the amount of nitriding in the plate width direction to improve the function of the inhibitor for the high-nitrided portion, it is possible to induce preferential grain growth from the low-nitrided portion toward the high-nitrided portion 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 and an annealing separator containing alumina as a main component can be used.

In addition, in useIn the case of an annealing separator containing MgO as a main component, a forsterite coating (containing Mg) is easily formed by the finish annealing₂SiO₄A coating film as a main body) as an intermediate layer; in the case of using an annealing separator containing alumina as a main component, an oxide film (SiO) is easily formed by the finish annealing₂A coating film as a main body) as an intermediate layer. These intermediate layers may be removed as necessary.

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

(annealing Process for finished product)

The finish annealing process is a process of performing finish annealing on the decarburized annealed steel sheet coated with the annealing separator to produce 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 and the magnetic flux density is dramatically improved.

The finish annealing is an important step for controlling the commutation which is a feature of the present embodiment. In the present embodiment, the off angle γ is controlled by using the following three conditions (a), (B), and (D) as a basis in the finish annealing.

In the description of the finish annealing step, the "total content of Nb group elements" means the total content of Nb group elements in the steel sheet immediately before finish annealing (decarburized annealed steel sheet). That is, what affects the finish annealing conditions is the chemical composition of the steel sheet immediately before finish annealing, regardless of the chemical composition (for example, the chemical composition of grain-oriented electrical steel sheet (finish annealed steel sheet)) after finish annealing and purification has occurred.

(A) In the heating process of annealing the finished product, the PH of the atmosphere in the temperature region 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 of the atmosphere in the temperature region of 1000-1050 DEG C₂O/PH₂When PB is set, PB: 0.0020 to 0.030;

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

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

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

In the case where the Nb group element is contained in the above range, the two factors of "the start of the secondary recrystallization in the low temperature region" and "the continuation of the secondary recrystallization to the high temperature region" strongly act due to the effect of suppressing the recovery recrystallization of the Nb group element. As a result, the control conditions for obtaining the effects of the present embodiment are relaxed.

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

PB is preferably 0.0050 or more, and preferably 0.020 or less.

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

The details of the mechanism by which the commutation occurs are not presently clear. However, considering 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 region" and "the continuation of secondary recrystallization up to the high temperature region" are important.

The reasons for the limitations of the above-mentioned items (A), (B) and (D) will be explained in consideration 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 region sufficiently lower than the temperature at which the secondary recrystallization is caused, and this condition 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 introduced by the annealing separator applied to the surface of the steel sheet, that is, a temperature range that affects the formation of the primary coating (intermediate layer). The condition (a) is important for realizing "continuation of secondary recrystallization to a high temperature region" after that by controlling the formation of the primary coating. 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 for the constituent elements (e.g., Al, N, etc.) of the inhibitor to be discharged outside the system. Thereby, the secondary recrystallization can be continued to a high temperature, and commutation can be sufficiently caused.

The condition (B) is a condition in a temperature region corresponding to the middle stage of grain growth of the secondary recrystallization, which affects the adjustment of the strength of the inhibitor during the growth of the secondary recrystallization grains. By setting this temperature region to the above atmosphere, the growth rate of the secondary recrystallized grains is limited to the decomposition of the inhibitor in the later stage of the grain growth. Although details will be described later, since the dislocation is efficiently accumulated in the grain boundary ahead of the growth direction of the secondary recrystallized grains by the condition (B), the occurrence frequency of the commutation is increased and the commutation continues to occur.

The condition (D) is a condition in a temperature region corresponding to the initial stage of grain growth from the start of the formation of nuclei in the secondary recrystallization.

With regard to the holding in this temperature region, it is important to cause good secondary recrystallization, but if the holding time is extended, it becomes easy to cause growth of primary recrystallized grains as well. For example, if the grain size of the primary recrystallized grains is large, accumulation of dislocations (accumulation of dislocations to the grain boundaries ahead of the growth direction of the secondary recrystallized grains) which are driving forces for the occurrence of commutation is less likely to occur. If the holding time in this temperature region is set to 600 minutes or less, the initial growth of the secondary recrystallized grains can be performed in a state in which the coarsening of the primary recrystallized grains is suppressed, and therefore the selectivity of the specific off angle is improved.

In the present embodiment, a large amount of commutation by the off angle γ is generated and continued against the background of shifting the secondary recrystallization start temperature 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 Nb group elements are used, if one of the conditions (a) and (B) is selectively satisfied even if both of the conditions are not satisfied, a grain-oriented electrical steel sheet satisfying the commutation conditions of the present embodiment can be obtained. That is, if the control is performed so as to increase the commutation frequency based on a specific off-angle (off-angle γ in the case of the present embodiment) in the initial stage of the secondary recrystallization, secondary recrystallization grains grow while maintaining the orientation difference due to the commutation, and this influence continues to the later stage, and the final commutation frequency also increases. Further, even if a new commutation occurs after the influence continues to the later stage, commutation occurs in which the change in the slip angle γ is large, and the commutation frequency of the final slip angle γ also increases. Of course, even if the Nb group element is used, it is preferable to satisfy both of the conditions (a) and (B).

Basically, the method for producing a grain-oriented electrical steel sheet according to the present embodiment described above may be used to control the secondary recrystallized grains to be divided into small regions having slightly different off-angles γ. Specifically, basically, as described above, it is sufficient to produce grain boundaries that satisfy not only the boundary condition BB but also the boundary condition BA and do not satisfy the boundary condition BB in the grain-oriented electrical steel sheet as described as embodiment 1.

Next, preferred production conditions for 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 holding time at 1000 to 1050 ℃ is preferably set to 300 to 1500 minutes during the heating process.

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 holding time at 1000 to 1050 ℃ is preferably set to 150 to 900 minutes in the heating process.

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

(E-1) in the heating process of the final annealing, 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 out of 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, and more preferably 900 minutes or less.

The condition (E-1) is a factor for controlling the direction of elongation in the steel sheet plane of the γ grain boundary causing the commutation. By sufficiently maintaining the temperature at 1000 to 1050 ℃, the reversing frequency in the rolling direction can be increased. It is believed that: in the holding in the temperature range, the change in the form (for example, arrangement and shape) of the precipitates in the steel containing the inhibitor is changed, and the frequency of the change in the rolling direction is increased.

It is believed that: since the steel sheet subjected to the finish annealing is subjected to hot rolling and cold rolling, 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 biased in the rolling direction. Although the details are not clear, it is believed that: the retention in the above-described temperature range changes the degree of the deviation of the form of such precipitates in the rolling direction, and affects in which direction the γ -grain boundaries easily extend in the steel sheet surface during the growth of secondary recrystallized grains. Specifically, if the 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 the γ -grain boundaries extending in the rolling direction is reduced, and the tendency of the γ -grain boundaries extending in the direction perpendicular to the rolling direction is increased. It is believed that the result is: the frequency of γ 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 γ 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 γ 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 above conditions (E-1) together, it is possible to control the grain size RA of the grain-oriented electrical steel sheet as described in embodiment 2_LAnd particle diameter RB_LRB of 1.10 or less is satisfied_L÷RA_LThe manner of (c) is controlled.

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 holding time at 950 to 1000 ℃ is preferably set to 300 to 1500 minutes in the heating process.

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 holding time at 950 to 1000 ℃ is preferably set to 150 to 900 minutes in the heating process.

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

(E-2) in the heating process of the final annealing, when the holding 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 out of 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, and more preferably 900 minutes or less.

The condition (E-2) is a factor for controlling the direction of elongation in the steel sheet plane of the γ grain boundary causing the commutation. By sufficiently maintaining the temperature at 950 to 1000 ℃, the reversing frequency in the direction of rolling right angles can be increased. It is believed that: in the holding in the temperature range, the change in the form (for example, the arrangement and the shape) of the precipitates in the steel containing the inhibitor is changed, and the frequency of the change in the rolling direction is increased.

It is believed that: since the steel sheet subjected to the finish annealing is subjected to hot rolling and cold rolling, 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 biased in the rolling direction. Although the details are not clear, it is believed that: the retention in the above-described temperature range changes the degree of the deviation of the form of such precipitates in the rolling direction, and affects in which direction the γ -grain boundaries easily extend in the steel sheet surface during the growth of secondary recrystallized grains. Specifically, if the steel sheet is held at a relatively low temperature of 950 to 1000 ℃, the form of precipitates in the steel tends to increase in the rolling direction, and therefore the proportion of the γ grain boundaries extending in the rolling direction at right angles decreases, and the tendency to extend in the rolling direction increases. It is believed that the result is: the frequency of γ 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 effect of the present embodiment can be obtained even if the retention time of the condition (E-2) is short, because the existence frequency itself of the γ grain boundary is high.

By the production method including the above condition (E-2), the grain diameter of the γ crystal grains in the direction perpendicular to the rolling direction can be controlled to be smaller than the grain diameter of the secondary recrystallized grains in the direction perpendicular to the rolling direction. Specifically, by controlling the above conditions (E-2) together, it is possible to control the grain size RA of the grain-oriented electrical steel sheet as described in embodiment 3_CAnd particle diameter RB_CRB of 1.10 or less is satisfied_C÷RA_CThe manner of (c) is controlled.

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

The direction in which the temperature gradient is applied is preferably the rolling right-angle direction C.

The finish annealing step can be effectively used as a step of imparting in-plane anisotropy to the shape of the γ crystal grains. For example, when a coil-shaped steel sheet is placed in a box-type annealing furnace and heated, the position or 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, only a part of the coil may be actively heated by induction heating, high-frequency heating, arrangement of an electric heating device, or the like, thereby forming a temperature distribution in the annealed coil.

The method for applying the temperature gradient is not particularly limited, and a known method may be applied. When a temperature gradient is applied to a steel sheet, secondary recrystallized grains having a sharp orientation are generated from a portion in a coil which has reached a secondary recrystallization start state in advance, and the secondary recrystallized grains grow anisotropically due to the temperature gradient. For example, the secondary recrystallized grains may be grown throughout the coil. Therefore, it becomes possible to preferably control the in-plane anisotropy of the shape of the γ crystal grains.

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, if the control to the gaussian orientation is considered to obtain the target magnetic properties and further, if the industrial productivity is considered, 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 orthogonal direction C. The upper limit of the temperature gradient is not particularly limited, but it is preferable to continuously grow 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, for example, 10 ℃/cm in the case of a general production process.

By the manufacturing method of the temperature gradient including the above-described conditions, the grain diameter of the γ crystal grains in the rolling direction can be controlled to be smaller than the grain diameter of the γ crystal grains in the direction perpendicular to the rolling direction. Specifically, by controlling the temperature gradient under the above-described conditions, as described as embodiment 4, the grain diameter RA of the grain-oriented electrical steel sheet can be adjusted_LWith particle size RA_CRA is satisfied at 1.15. ltoreq._C÷RA_LThe manner of (c) is controlled.

In the manufacturing method of the present embodiment, the holding time at 1050 to 1100 ℃ may be set to 300 to 1200 minutes in the heating process of the finish 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 retention time in a temperature region of 1050-1100 ℃ is set as TF, TF: 300-1200 minutes.

In the case where the secondary recrystallization is not completed until 1050 ℃ in the heating process of the finish annealing, the secondary recrystallization is continued to a high temperature by lowering the heating rate of 1050 to 1100 ℃ (slow heating), specifically, by setting TF to 300 to 1200 minutes so that the magnetic flux density is 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 up to 1050 ℃ in the heating process 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 region of 1050 ℃ or higher than that in the conventional case to shorten the finish annealing time, the cost can be reduced.

In the production method of the present embodiment, in the finish annealing step, the conditions (A), (B) and (D) may be controlled based on the three conditions as described above, and the conditions (E-1), (E-2) and/or the temperature gradient may be combined as necessary. For example, a plurality of conditions among the condition (E-1), the condition (E-2) and 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, if 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. The finished annealed steel sheet may be provided with an insulating film mainly composed of phosphate and colloidal silica, and an insulating film mainly composed of alumina sol and boric acid.

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, dew point, and the like of the atmosphere 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 film. When the coating is formed, the degree of oxidation, dew point, and the like of the atmosphere may be controlled as necessary.

The manufacturing method of 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 local minute strain or a local groove may be formed in the grain-oriented electrical steel sheet by a known method such as laser, plasma, mechanical method, or etching. Such a domain subdivision process does not impair the effects of the present embodiment.

The local minute strain and the local groove described above become abnormal points in the measurement of the crystal orientation and the grain size defined in the present embodiment. Therefore, in the measurement of the crystal orientation, the measurement point is not overlapped with the local minute strain and the local groove. In the measurement of the particle size, local minute strain and local groove are not recognized as grain boundaries.

(mechanism for occurrence of commutation)

The commutation specified in the present embodiment occurs during the secondary recrystallization grain growth. 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 is reached, and the control of the grain size of the primary recrystallized grains. Therefore, the commutation is not simply controlled for one condition, and a plurality of control conditions need to be controlled comprehensively and inseparably.

It is believed that: the commutation is caused by the grain boundary energy and the surface energy between adjacent crystal grains.

Regarding the above-mentioned grain boundary energy, it is considered that: if two crystal grains having an angle difference are adjacent, the grain boundary energy becomes large, and therefore, commutation is caused in a manner of reducing the grain boundary energy, that is, in a manner of approaching a specific same orientation, in the process of secondary recrystallized grain growth.

Further, regarding the surface energy described above, it is considered that: if the orientation deviates even slightly from the {110} plane as high as the symmetry, the surface energy increases, and therefore, in the process of secondary recrystallization grain growth, commutation is caused in such a manner that the surface energy is reduced, that is, the orientation approaches the {110} plane and the deviation angle becomes smaller.

However, these energy differences are not energy differences that cause orientation changes in the process of secondary recrystallization grain growth until the occurrence of a reversal in a general situation. Therefore, in a general situation, the secondary recrystallized grains grow in a state having an angle difference or an off angle. For example, in the case where secondary recrystallized grains are grown in a general situation, the off-angle γ corresponding to an angle generated by orientation unevenness at the time of generation of the secondary recrystallized grains is not reversed. The standard deviation σ (| γ |) of the absolute value of the final off-angle γ also corresponds to a value obtained due to the orientation unevenness at the time of generation of secondary recrystallized grains. That is, the off-angle γ hardly changes during the growth of the secondary recrystallized grains.

On the other hand, when the secondary recrystallization is started from a lower temperature and the growth of the secondary recrystallized grains is continued to a high temperature for a long time as in the grain-oriented electrical steel sheet of the present embodiment, the commutation remarkably occurs. Although the reason is not clear, it is considered that: during the growth of the secondary recrystallized grains, dislocations for eliminating the deviation in the geometric orientation remain at a relatively high density in the front portion in the growth direction, i.e., in the region adjacent to the primary recrystallized grains. It is believed that: the remaining dislocations correspond to the commutation and γ grain boundaries in the present embodiment.

In the present embodiment, the secondary recrystallization starts at a lower temperature than in the prior art, so that disappearance of dislocations is delayed, dislocations accumulate in such a manner as to pile up at the grain boundaries ahead of the growing direction of the grown secondary recrystallized grains, and the dislocation density increases. It is therefore believed that: it becomes easy to cause rearrangement of atoms in front of the grown secondary recrystallized grains, and as a result, commutation is caused so as to reduce the difference in angle with the adjacent secondary recrystallized grains, that is, so as to reduce the grain boundary energy or so as to reduce the surface energy.

The reversal leaves grain boundaries (γ grain boundaries) having a particular orientation relationship within the secondary recrystallized grains. Further, if another secondary recrystallized grains are generated before the commutation is caused, and the growing secondary recrystallized grains reach the generated secondary recrystallized grains, the grain growth stops, and the commutation itself does not occur. Therefore, in the present embodiment, the following is advantageous: in the growth stage of the secondary recrystallized grains, the frequency of generation of new secondary recrystallized grains is reduced, and the rate is controlled by an inhibitor so that only the existing secondary recrystallization continues to grow. Therefore, in the present embodiment, it is preferable to use the following inhibitors in combination: an inhibitor that shifts the secondary recrystallization start temperature preferably toward a low temperature; and inhibitors that are stable up to relatively high temperatures.

In the present embodiment, the reason why the direction change is caused mainly by the off angle γ is not clear, but is considered as follows. It is believed that: what kind of orientation change the commutation generates (i.e., the barger vector, etc. in the dislocations accumulated in front of the secondary recrystallized grains during growth) affects the dislocation of the basic unit also called commutation. In the present embodiment, the influence of the control of the inhibitor at a relatively high temperature in the secondary recrystallization process (the above condition (B)) is large with respect to the control of the off angle γ. For example, if the inhibitor strength changes due to the atmosphere in the temperature region of 1000 ℃ or less, the contribution of the slip angle γ in commutation becomes small. Namely, it is considered that: the weakening timing of the inhibitor affects the change of the primary recrystallized structure (orientation and particle diameter change), the disappearance of the accumulated dislocations, and the growth rate of the secondary recrystallized grains, and as a result, the reversed orientation formed in the growing secondary recrystallized grains (i.e., the type and amount of the dislocations introduced into the secondary recrystallized grains) is changed.

Examples

Next, the effects of one embodiment of the present invention will be described in more detail by way of examples, but the conditions in the examples are one example of conditions adopted for confirming the feasibility and the effects of the present invention, and the present invention is not limited to this example of conditions. Various conditions may be adopted in the present invention 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 methods described above. In tables a1 and a2, "-" indicates that the control and production of the content were not taken into consideration and that the content was not measured. In table a1 and table a2, the numerical values denoted by "<" represent: although the content was measured in consideration of the control and production of the content, a measurement value having sufficient reliability as the content was not obtained (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 held at 1200 ℃ for 20 hours in a hydrogen atmosphere (purification annealing), and 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 film (intermediate layer) formed on the surface of a grain-oriented electrical steel sheet (finished annealed steel sheet) to be produced, and the coating solution is formed by mixing 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 from 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 grain-oriented electrical steel sheet obtained was evaluated for various properties. The evaluation results are shown in tables A8 to a 12.

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

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

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

The magnetic properties of grain-oriented electrical steel sheets are based on 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: under the condition of 1.7T, the iron loss W defined as the power loss per unit weight (1kg) of the steel sheet was measured_17/50(W/kg). Further, the magnetic flux density B in the rolling direction of the steel sheet was measured when the steel sheet was excited at 800A/m₈(T)。

Further, as magnetic properties, at an ac frequency: 50Hz, excitation flux density: the magnetostriction λ p-p @1.9T generated in the steel sheet was measured under the condition of 1.9T. 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 when the magnetic flux density is 0T₀By λ p-p @1.9T ═ L (L)_max-L_min)÷L₀And (6) calculating.

[ 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 production method. Therefore, the evaluation results of the respective properties need to be compared and studied within a 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 grain-oriented electrical steel sheets obtained by using chemical compositions and manufacturing methods having several characteristics will be described below.

(examples manufactured by Low temperature slab heating Process)

Nos. 1001 to 1066 are examples produced by the following processes: the primary inhibitor of secondary recrystallization is formed by lowering the slab heating temperature and using nitridation after primary recrystallization.

(embodiments of Nos. 1001 to 1023)

Nos. 1001 to 1023 are examples in which steel grades not containing Nb are used, and conditions of PA, PB, TD, and TE1 are mainly changed during finish annealing.

In Nos. 1001 to 1023, when λ p-p @1.9T was 0.510 or less, the magnetostrictive property was judged to be good.

In Nos. 1001 to 1023, the present invention examples all have grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and exhibit excellent high magnetic field magnetostriction. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

In addition, No.1003 is a comparative example in which the strength of the inhibitor was improved by setting the N content after nitriding to 300 ppm. In general, if the amount of nitrification is increased, the productivity is lowered, but the inhibitor strength is increased by increasing the amount of nitrification, and B is thereby increased₈And (4) rising. For No.1003, B₈Also becomes a higher value. However, in the case of No.1003, since the finish annealing condition was not preferable, the value of λ p-p @1.9T became insufficient. That is, in sample 1003, no commutation was caused at the time of secondary recrystallization, and as a result, high magnetic 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. For No.1006, though B₈Not particularly high, but since the final annealing conditions are preferred, λ p-p @1.9T is preferably made lower. That is, in sample 1006, commutation occurs at the time of secondary recrystallization, and as a result, high magnetic field magnetostriction is improved.

In addition, Nos. 1017 to 1023 are examples in which TF is increased and secondary recrystallization is continued to a high temperature. No.1017 to 1023, B₈Becomes high. However, among them, as for nos. 1021 and 1022, since the finish annealing conditions are not preferable, the high-field magnetostriction is not improved as in No. 1003. On the other hand, among the above, with respect to No.1023, not only B₈To a higher value and since the final annealing conditions are preferred, λ p-p @1.9T is also preferably to a lower value.

(examples of No.1024 to 1034)

Nos. 1024 to 1034 are examples in which a steel type containing 0.001% of Nb is used for a slab, and conditions of PA, PB, and TE1 are changed mainly during finish annealing.

No.1024 to 1034 were judged to have good magnetostrictive properties when λ p-p @1.9T was 0.580 or less.

In Nos. 1024 to 1034, the present invention shows excellent high magnetic field magnetostriction in all of the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

(examples of Nos. 1035 to 1048)

Nos. 1035 to 1048 are examples in which steel grades containing 0.009% of Nb were used for slabs, and conditions of PA, PB, TD, and TE1 were changed mainly during product annealing.

No.1035 to No. 1048 were judged to have good magnetostrictive properties when λ p-p @1.9T was 0.490 or less.

In Nos. 1035 to 1048, in the examples of the present invention, there were crystal boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and excellent high magnetic field magnetostriction was exhibited. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

In nos. 1035 to 1048, Nb was contained in an amount of 0.009% in slab, and Nb was purified in the finish annealing, and the Nb content in grain-oriented electrical steel sheets (finished annealed steel sheets) was 0.007% or less. In Nos. 1035 to 1048, Nb is preferably contained in the slab as compared with Nos. 1001 to 1034, and therefore, λ p-p @1.9T is a low value. In addition, B₈Becomes high. That is, if the Nb-containing slab is used to control the finish annealing conditions, the annealing conditions for B₈And λ p-p @1.9T will work advantageously. In particular, No.1044 is an example of the present invention in which purification is strengthened in the finish annealing and the Nb content in the grain-oriented electrical steel sheet (finish annealed steel sheet) is below the detection limit. In No.1044, it could not be verified that Nb group elements were used in grain-oriented electrical steel sheets as final products, but the above-described effects were remarkably obtained.

(examples of Nos. 1049 to 1056)

Nos. 1049 to 1056 are examples in which TE1 was set to a short time of less than 300 minutes, and the influence of the Nb content was particularly confirmed.

No.1049 to 1056, when λ p-p @1.9T was 0.490 or less, the magnetostrictive property was judged to be good.

In Nos. 1049 to 1056, the present examples have grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and all show excellent high magnetic field magnetostriction. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

Further, as shown in Nos. 1049 to 1056, if Nb is contained in an amount of 0.0030 to 0.030 mass% in the slab, even if TE1 is short, commutation occurs at the time of secondary recrystallization, and the high magnetic field magnetostriction is improved.

(examples of No.1057 to 1066)

Nos. 1057 to 1066 are examples in which the influence of the content of Nb group element was confirmed by setting TE1 to a short time of less than 300 minutes.

In Nos. 1057 to 1066, when λ p-p @1.9T was 0.530 or less, it was judged that the magnetostrictive property was good.

In Nos. 1057 to 1066, the present examples exhibited excellent high magnetic field magnetostriction in all of the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

Further, as shown in nos. 1057 to 1066, 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 high magnetic field magnetostriction improves.

(examples manufactured by high temperature slab heating Process)

Nos. 1067 to 1103 are examples produced by the following processes: MnS, which is sufficiently dissolved in slab heating by raising the slab heating temperature, is re-precipitated in the subsequent step and utilized as a main inhibitor.

In Nos. 1067 to 1103, when λ p-p @1.9T was 0.430 or less, it was judged that the magnetostrictive property was good.

In Nos. 1067 to 1103, the present examples all had crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and exhibited excellent high magnetic field magnetostriction. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

In addition, in Nos. 1067 to 1103, Nos. 1085 to 1103 contain Bi in the slab to increase B content₈Examples of (1).

As shown in nos. 1067 to 1103, even in the high-temperature slab heating process, by appropriately controlling the product annealing conditions, commutation is generated at the time of secondary recrystallization and high magnetic field magnetostriction is improved. In addition, even in the high-temperature slab heating process, similarly to the low-temperature slab heating process, if the finished product annealing conditions are controlled using the Nb-containing slab, the B is also subjected to₈And λ p-p @1.9T work advantageously.

(example 2)

Grain-oriented electrical steel sheets having the chemical compositions shown in table B2 were produced using slabs having the 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 in example 1 described above.

[ Table B3]

[ Table B4]

[ Table B5]

[ Table B6]

[ Table B7]

An insulating coating 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 from a cut plane parallel to the sheet thickness direction in the cutting direction. 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.

The grain-oriented electrical steel sheet obtained 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]

Similarly to example 1 described above, the evaluation results of the properties of grain-oriented electrical steel sheets obtained by using chemical compositions and manufacturing methods having several characteristics will be described below.

(examples manufactured by Low temperature slab heating Process)

No.2001 to 2066 are examples produced by the following processes: the primary inhibitor of secondary recrystallization is formed by lowering the slab heating temperature and using nitridation after primary recrystallization.

(examples of No.2001 to 2023)

Nos. 2001 to 2023 are examples in which steel grades containing no Nb are used, and conditions of PA, PB, TD, and TE2 are mainly changed during finish annealing.

In Nos. 2001 to 2023, when λ p-p @1.9T was 0.510 or less, it was judged that the magnetostrictive property was good.

In Nos. 2001 to 2023, the present examples all have grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and exhibit excellent high magnetic field magnetostriction. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

Further, No.2003 is a comparative example in which the strength of the inhibitor was improved by setting the N amount after nitriding to 300 ppm. In No.2003, though B₈To a higher value, but since the finish annealing conditions are not preferred, the value of λ p-p @1.9T becomes insufficient. That is, in No.2003, no commutation is caused at the time of secondary recrystallization, and as a result, high magnetic field magnetostriction is 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. For No.2006, though B₈Not particularly high, but since the final annealing conditions are preferred, λ p-p @1.9T is preferably made lower. That is, in No.2006, commutation occurs at the time of secondary recrystallization, and as a result, high magnetic field magnetostriction improves.

Nos. 2017 to 2023 are examples in which TF is increased and secondary recrystallization is continued to a high temperature. Nos. 2017 to 2023, B₈Becomes high. However, among them, No.2020 to 2022 do not improve the high magnetic field magnetostriction as in No.2003 since the finish annealing condition is not preferable.

(examples of Nos. 2024 to 2034)

Nos. 2024 to 2034 are examples in which a steel grade containing 0.001% of Nb is used for slab, and the conditions of PA, PB, and TE2 are mainly changed during finish annealing.

No.2024 to 2034, when λ p-p @1.9T was 0.580 or less, the magnetostrictive property was judged to be good.

No.2024 to 2034 show excellent high magnetic field magnetostriction in all cases of the present invention where the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

(examples of Nos. 2035 to 2048)

Nos. 2035 to 2048 are examples in which steel grades containing 0.009% Nb were used for slabs, and the conditions of PA, PB, TD, and TE2 were changed mainly during finish annealing.

In Nos. 2035 to 2048, when λ p-p @1.9T is 0.500 or less, it is judged that the magnetostrictive property is good.

In Nos. 2035 to 2048, the present invention shows excellent high magnetic field magnetostriction in all of the grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

In addition, nos. 2035 to 2048 contain 0.009% of Nb in slab, and Nb is purified in finish annealing, and the Nb content in grain-oriented electrical steel sheet (finish annealed steel sheet) is 0.007% or less. In the case of the slabs, Nos. 2035 to 2048 preferably contain Nb in comparison with the above Nos. 1001 to 1034, and therefore λ p-p @1.9T is a low value. In addition, B₈Becomes high. That is, if the Nb-containing slab is used to control the finish annealing conditions, the annealing conditions for B₈And λ p-p @1.9T will work advantageously. In particular, No.2044 is an example of the present invention in which purification is strengthened in the finish annealing, and the Nb content in grain-oriented electrical steel sheets (finished annealed steel sheets) is below the detection limit. No.2044, which cannot be verified from grain-oriented electrical steel sheets as final products, uses Nb group elements, remarkably achieves the above-described effects.

(examples of Nos. 2049 to 2056)

Nos. 2049 to 2056 are examples in which TE2 was set to a short time of less than 300 minutes, and the influence of the Nb content was particularly confirmed.

No.2049 to 2056 were judged to have good magnetostrictive properties when λ p-p @1.9T was 0.480 or less.

In nos. 2049 to 2056, the present examples exhibited excellent high magnetic field magnetostriction in all of the crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

Further, as shown in Nos. 2049 to 2056, if Nb is contained in an amount of 0.0030 to 0.030 mass% in the slab, even if TE2 is short, commutation occurs at the time of secondary recrystallization, and the high magnetic field magnetostriction is improved.

(examples of Nos. 2057 to 2066)

Nos. 2057 to 2066 are examples in which the TE2 was set to a short time of less than 300 minutes, and the influence of the content of the Nb group element was confirmed.

In Nos. 2057 to 2066, when λ p-p @1.9T was 0.530 or less, it was judged that the magnetostrictive property was good.

In Nos. 2057 to 2066, in the examples of the present invention, there were crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and excellent high magnetic field magnetostriction was exhibited. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

Further, as shown in nos. 2057 to 2066, 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 high magnetic field magnetostriction improves.

(examples manufactured by high temperature slab heating Process)

Nos. 2067 to 2104 are examples produced by the following processes: MnS, which is sufficiently dissolved in slab heating by raising the slab heating temperature, is re-precipitated in the subsequent step and utilized as a main inhibitor.

In Nos. 2067 to 2104, when λ p-p @1.9T was 0.430 or less, it was judged that the magnetostrictive property was good.

In Nos. 2067 to 2104, the present invention examples had grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and all showed excellent high magnetic field magnetostriction. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

In addition, in Nos. 2067 to 2104, Nos. 2085 to 2104 contain Bi in the case of slab to increase B₈Examples of (1).

Even in the high-temperature slab heating process, as shown in nos. 2067 to 2104, commutation was generated at the time of secondary recrystallization by appropriately controlling the product annealing conditions, and the high-field magnetostriction was improved. In addition, even in the high-temperature slab heating process, similarly to the low-temperature slab heating process, if the finished product annealing conditions are controlled using the Nb-containing slab, the B is also subjected to₈And λ p-p @1.9T work advantageously.

(example 3)

Grain-oriented electrical steel sheets having the chemical compositions shown in table C2 were produced using slabs having the 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 sheet was produced under the production conditions shown in tables C3 to C6. In the finish annealing, in order to control anisotropy in the direction in which the direction changes, a heat treatment is performed by applying a temperature gradient in the direction perpendicular to the rolling direction of the steel sheet. The production conditions other than the temperature gradient and those shown in the table were the same as those in example 1.

[ Table C3]

[ Table C4]

[ Table C5]

[ Table C6]

An insulating coating 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 from a cut plane parallel to the sheet thickness direction in the cutting direction. The intermediate layer was a forsterite coating having an average thickness of 3 μm, and the insulating coating was mainly composed of phosphate and colloidal silica having an average thickness of 3 μm.

The grain-oriented electrical steel sheet obtained 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 most of the grain-oriented electrical steel sheets, the crystal grains extend in the direction of the temperature gradient, and the crystal grain size of the γ crystal grains also increases in this direction. That is, the grains extend in the rolling orthogonal direction. However, in some grain-oriented electrical steel sheets having a small temperature gradient, the grain size in the direction perpendicular to the rolling direction is smaller than the grain size in the rolling direction with respect to the γ -grains. When the grain size in the right angle direction of rolling is smaller than the grain size in the rolling direction, the column of "the temperature gradient direction is not uniform" in the table is indicated by "+".

[ Table C7]

[ Table C8]

[ Table C9]

[ Table C10]

Similarly to example 1 described above, the evaluation results of the properties of grain-oriented electrical steel sheets obtained by using chemical compositions and manufacturing methods having several characteristics will be described below.

(examples manufactured by Low temperature slab heating Process)

The examples 3001 to 3070 are produced by the following processes: the primary inhibitor of secondary recrystallization is formed by lowering the slab heating temperature and using nitridation after primary recrystallization.

(examples of No.3001 to 3035)

Nos. 3001 to 3035 are examples in which steel grades not containing Nb were used, and conditions of PA, PB, TD and temperature gradient were mainly changed during annealing of the final product.

In Nos. 3001 to 3035, when λ p-p @1.9T was 0.470 or less, it was judged that the magnetostrictive property was good.

In nos. 3001 to 3035, the present examples exhibited excellent high magnetic field magnetostriction in both of the grain boundaries satisfying boundary condition BA and not satisfying boundary condition BB. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

(example No.3036 to 3070)

Nos. 3036 to 3070 are examples in which steel grades containing Nb group elements were used for slabs, and the conditions of PA, PB, TD and temperature gradient were mainly changed during product annealing.

No.3036 to 3070, when λ p-p @1.9T was 0.470 or less, the magnetostrictive property was judged to be good.

No.3036 to 3070, in the examples of the present invention, there were crystal grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and excellent high magnetic field magnetostriction was exhibited. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not obtained.

(example No. 3071)

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

In No.3071, when λ p-p @1.9T was 0.470 or less, it was judged that the magnetostrictive property was good.

As shown in No.3071, even in the high temperature slab heating process, high magnetic field magnetostriction is improved by appropriately controlling the finish annealing conditions.

(example 4)

Grain-oriented electrical steel sheets having the chemical compositions shown in table D2 were produced using slabs having the 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 manufactured based on the manufacturing conditions shown in table D3. The production conditions other than those shown in the table were the same as in example 1 described above.

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

[ Table D3]

In the above table, the term "about 1" means 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 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 from a cut plane parallel to the sheet thickness direction in the cutting direction.

Further, 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 had an average thickness of 20nmOxide film (with SiO)₂A coating film as a main body), and the insulating coating film is an insulating coating film mainly composed of phosphate and colloidal silica having an average thickness of 2 μm.

Further, in the grain-oriented electrical steel sheets of nos. 4012 and 4013, after the insulating film is formed, a linear micro strain is applied to the rolled surface of the steel sheet by laser irradiation so as to extend in a direction intersecting the rolling direction and so as to have a rolling direction interval of 4 mm. Knowing: by applying the laser beam, an effect of reducing the iron loss is obtained.

The grain-oriented electrical steel sheet obtained 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 @1.9T was 0.620 or less, it was judged that the magnetostrictive property was good.

In Nos. 4001 to 4013, the present invention examples all have grain boundaries satisfying the boundary condition BA and not satisfying the boundary condition BB, and exhibit excellent high magnetic field magnetostriction. On the other hand, in the comparative example, although the deviation angle γ slightly and continuously shifts in the secondary recrystallized grains, the grain boundaries satisfying the boundary condition BA and the boundary condition BB are not sufficiently present, and the preferable high magnetic field magnetostriction is not 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 high magnetic field region (particularly, a magnetic field of about 1.9T) 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