阅读说明：本技术 方向性电磁钢板及其制造方法 (Grain-oriented electromagnetic steel sheet and method for producing same ) 是由 片冈隆史 牛神义行 中村修一 藤井浩康 奥村俊介 于 2018-07-13 设计创作，主要内容包括：一种方向性电磁钢板,该方向性电磁钢板以质量％计含有C：0.010％以下、Si：2.50～4.00％、酸可溶性Al：0.010％以下、N：0.012％以下、Mn：1.00％以下、S：0.020％以下,剩余部分包含Fe及不可避免的杂质,在钢板表面具有张力绝缘皮膜,并且在张力绝缘皮膜与钢板表面的界面具有平均膜厚为1.0nm～1.0μm的SiO_2中间氧化膜层,其中,在SiO_2中间氧化膜层的表面的反射型红外分光分析中,1250(cm~(-1))的峰强度I_A与1200(cm~(-1))的峰强度I_B满足I_B/I_A≥0.010。(A grain-oriented electrical steel sheet comprising, in mass%, C: 0.010% or less, Si: 2.50-4.00%, acid-soluble Al: 0.010% or less, N: 0.012% or less, Mn: 1.00% or less, S: less than 0.020%, the balance of Fe and FeHas a tensile insulating film on the surface of the steel sheet, and has SiO with an average film thickness of 1.0nm to 1.0 μm at the interface between the tensile insulating film and the surface of the steel sheet 2 An intermediate oxide film layer of SiO 2 1250 (cm) in reflection type infrared spectroscopic analysis of the surface of the intermediate oxide film layer ‑1 ) Peak intensity of (1) A And 1200 (cm) ‑1 ) Peak intensity of (1) B Satisfy I B /I A ≥0.010。)

1. A grain-oriented electrical steel sheet, comprising:

a base steel plate;

an intermediate oxide film layer formed on the base steel sheet and containing SiO₂The average film thickness is 1.0 nm-1.0 μm; and

a tensile insulating film formed on the intermediate oxide film layer,

the base steel sheet contains, as chemical components, in mass%, C: 0.010% or less, Si: 2.50-4.00%, acid-soluble Al: 0.010% or less, N: 0.012% or less, Mn: 1.00% or less, S: the content of the active carbon is less than 0.020%,

the remainder comprising Fe and impurities,

1250cm in reflection type infrared spectroscopic analysis of the surface of the intermediate oxide film layer^-1Peak intensity of (1)_AAnd 1200cm^-1Peak intensity of (1)_BSatisfies the following formula (1):

I_B/I_A≥0.010 (1)。

2. the grain-oriented electrical steel sheet according to claim 1, further comprising, as the chemical components, in mass%: 0.001 to 0.010%.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, further comprising, as the chemical components, in mass%: 0.01-0.20%, Cr: 0.01 to 0.50%, Cu: 0.01-0.50% of 1 or more than 2.

4. A grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein a time differential curve f of a glow discharge emission analysis spectrum of element M on the surface of said intermediate oxide film layer_M(t) satisfies the following formula (2):

M：Mn、Al、B；

tp: time t (sec) corresponding to the minimum value of the second-order time differential curve of the glow discharge luminescence analysis spectrum of Si;

ts: time t (sec) corresponding to the start point of glow discharge luminescence analysis of Si.

5. A method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4,

which comprises an oxide film forming step of forming an intermediate oxide film layer on the surface of a steel sheet,

in the oxide film forming step, the annealing temperature T1: and (2) annealing at 600-1200 ℃ for: 5-200 seconds, partial pressure of oxygen P_H2O/P_H2: average heating rate HR1 in the temperature region of 100 ℃ to 600 ℃ of 0.15 or less: annealing is performed under the condition of 10-200 ℃, after the annealing, the average cooling speed CR1 of a temperature region of T2-T1 ℃ is set to be below 50 ℃/s, and the average cooling speed CR2 of a temperature region of more than 100 ℃ and less than T2 ℃ is set to be less than CR1, wherein T2 ℃ represents the temperature represented by T1-100.

Technical Field

The present invention relates to a grain-oriented electrical steel sheet used as an iron core material of a transformer and a method for producing the same, and particularly to a grain-oriented electrical steel sheet excellent in adhesion of a tensile insulating film and a method for producing the same.

Background

Grain-oriented electrical steel sheets are silicon steel sheets containing 7 mass% or less of Si, which are composed of crystal grains having high orientation concentrated in {110} <001> orientation (hereinafter, gaussian (Goss) orientation), and are mainly used as iron core materials of transformers. The high orientation concentration of the gaussian orientation in the grain-oriented electrical steel sheet is achieved by utilizing a grain growth phenomenon called secondary recrystallization.

Grain-oriented electrical steel sheets are required to have high magnetic flux density (represented by B8 value) and low iron loss (represented by W17/50 value) as magnetic properties, but recently, from the viewpoint of energy saving, the demand for reduction in power loss, that is, reduction in iron loss has been further increased.

In a grain-oriented electrical steel sheet, a magnetic domain changes with the movement of a magnetic domain wall under an alternating-current magnetic field. Although the smooth movement of the magnetic domain walls is effective for the reduction of the core loss, if the movement of the magnetic domains is observed, there are also inactive magnetic domains.

To further reduce the iron loss of grain-oriented electrical steel sheet and eliminate the resistanceForsterite (Mg) on surface of steel sheet to inhibit movement of magnetic domains₂SiO₄) The pinning effect due to the unevenness of the interface of the coating (hereinafter, sometimes referred to as "glass coating") is important. In order to eliminate this pinning effect, it is effective to prevent the formation of a glass coating film on the surface of the steel sheet, which inhibits the movement of magnetic domains.

As means for eliminating the pinning effect, for example, patent documents 1 to 21 disclose the following: controlling the dew point of the decarburization annealing so that Fe-based oxide (Fe) is not formed in the oxide layer formed during the decarburization annealing₂SiO₄FeO, etc.); and, as an annealing separating agent, a substance such as alumina that does not react with silica is used, and the surface is smoothed after the product is annealed.

When grain-oriented electrical steel sheets are used as core materials of transformers, insulation properties of the steel sheets must be ensured, and therefore, an insulating film having tension is formed on the surfaces of the steel sheets. For example, the method disclosed in patent document 6, in which a coating liquid mainly composed of colloidal silica and a phosphate is applied to the surface of a steel sheet and sintered to form an insulating film, is effective not only in ensuring insulation but also in reducing iron loss because of a large effect of imparting tension to the steel sheet.

Forming an insulating film mainly composed of phosphate on a glass film generated in the final annealing step in this manner is a general method for producing unidirectional silicon steel sheets.

When the insulating film is formed on the glass film, a considerable film adhesion can be obtained, but when the glass film is removed or when the glass film is not intentionally formed in the finish annealing step, the film adhesion is insufficient.

When the glass coating is removed, a required coating tension needs to be ensured only by a tension insulating coating formed by applying a coating liquid, and therefore, the thickness inevitably has to be increased, and further coating adhesion is required.

Therefore, it is difficult to achieve a film tension of such a degree that the effect of making the mirror surface sufficiently appears and also to ensure film adhesion in the conventional film forming method, and iron loss cannot be sufficiently reduced. As a technique for ensuring the film adhesion of the tensile insulating film, for example, patent documents 22 to 25 propose a method of forming an oxide film on the surface of a unidirectional silicon steel sheet subjected to final annealing before forming the tensile insulating film.

For example, the technique disclosed in patent document 23 is a method of: the unidirectional silicon steel sheet, which is prepared in a mirror-finished state or a state close to a mirror-finished state and has been finished with finish annealing, is annealed at each temperature in a specific atmosphere to form an external oxidation-type oxide film on the surface of the steel sheet, and the adhesion between the tensile insulating film and the steel sheet is ensured by the oxide film.

The technique disclosed in patent document 24 is as follows: when the tension insulating film is crystalline, an amorphous oxide base film is formed on the surface of a finished product annealed unidirectional silicon steel sheet having no inorganic mineral film, thereby preventing the oxidation of the steel sheet, i.e., the reduction of the mirror surface degree, caused when the crystalline tension insulating film is formed.

The technique disclosed in patent document 25 is a method of: the technique disclosed in patent document 8 is further developed to control the film structure of a metal oxide film containing Al, Mn, Ti, Cr, and Si at the interface between the tensile insulating film and the steel sheet, so as to improve the adhesion of the insulating film. However, the adhesion at the interface between the metal oxide layer and the steel sheet, which is the most problematic in stress sensitivity, is not controlled, and the technique disclosed in patent document 25 is not sufficient as a technique for improving the film adhesion.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 64-062417

Patent document 2: japanese laid-open patent publication No. H07-118750

Patent document 3: japanese laid-open patent publication No. H07-278668

Patent document 4: japanese laid-open patent publication No. H07-278669

Patent document 5: japanese laid-open patent publication No. H07-278670

Patent document 6: japanese laid-open patent publication No. 10-046252

Patent document 7: japanese laid-open patent publication No. 11-106827

Patent document 8: japanese laid-open patent publication No. 11-152517

Patent document 9: japanese laid-open patent publication No. 2002-

Patent document 10: japanese laid-open patent publication No. 2002-173715

Patent document 11: japanese patent laid-open publication No. 2002-348613

Patent document 12: japanese laid-open patent application No. 2002-363646

Patent document 13: japanese patent laid-open publication No. 2003-055717

Patent document 14: japanese patent laid-open publication No. 2003-268541

Patent document 15: japanese patent laid-open publication No. 2003-003213

Patent document 16: japanese patent laid-open publication No. 2003-041320

Patent document 17: japanese patent laid-open publication No. 2003-247021

Patent document 18: japanese patent laid-open publication No. 2003-247024

Patent document 19: japanese laid-open patent publication No. 2008-001980

Patent document 20: japanese patent publication No. 2011-518253

Patent document 21: japanese laid-open patent publication No. Sho 48-039338

Patent document 22: japanese laid-open patent publication No. 60-131976

Patent document 23: japanese laid-open patent publication No. H06-184762

Patent document 24: japanese laid-open patent publication No. H07-278833

Patent document 25: japanese patent laid-open publication No. 2002-348643

Non-patent document

Non-patent document 1: iron and steel, vol99(2013)40.

Disclosure of Invention

Problems to be solved by the invention

In a grain-oriented electrical steel sheet having a tensile insulating film formed on the surface of the steel sheet, when the insulating film is formed on a glass film (forsterite-based film), the film adhesion of the insulating film is good, but when the generation of the glass film is intentionally suppressed, or the glass film is removed by means such as search or pickling, and the surface of the steel sheet is further flattened to show a mirror gloss to form the tensile insulating film, the film adhesion of the insulating film is insufficient, and it is difficult to achieve both the film adhesion and the magnetic stability.

Accordingly, an object of the present invention is to form a tensile insulating film having excellent film adhesion without impairing magnetic properties and stability thereof on the surface of a grain-oriented electrical steel sheet subjected to finish annealing until the surface of the steel sheet is flattened to exhibit mirror gloss by intentionally suppressing the formation of a glass film or removing the glass film by means of grinding or pickling, and to provide a grain-oriented electrical steel sheet and a method for producing the same, which solve the above problems.

Means for solving the problems

The present inventors have conducted extensive studies with attention paid to the influence of additive elements on a method for improving the film adhesion of a tensile insulating film in order to solve the above problems. As a result, they found that: before the tensile insulating film is formed, an oxide film (hereinafter sometimes referred to as "intermediate oxide film layer" or "SiO" film) is formed on the surface of a grain-oriented electrical steel sheet subjected to final annealing₂Intermediate oxide film layer "), if the thermal history and oxygen partial pressure are controlled, the film adhesion of the tensile insulating film is dramatically improved.

Further, the inventors of the present invention conducted an intensive investigation on the composition of the intermediate oxide film layer which is considered to have the greatest influence on the film adhesion. As a result, they found that: the oxide of the intermediate oxide film layer is Si oxide (SiO)₂) If Mn and the like is in SiO₂When the intermediate oxide film layer is dissolved in a solid, the film adhesion is improved.

It is believed that: solid solution in SiO₂Atoms in the intermediate oxide film layer improve SiO₂Lattice matching of the intermediate oxide film layer with the steel sheet, as a result, SiO₂The adhesion of the intermediate oxide film layer is improved.

The present invention has been made based on the above-described knowledge, and the gist thereof is as follows.

[1]A grain-oriented electrical steel sheet according to one aspect of the present invention includes: a base steel plate; an intermediate oxide film layer formed on the base steel sheet and containing SiO₂The average film thickness is 1.0 nm-1.0 μm; and a tensile insulating film formed on the intermediate oxide film layer.

The base steel sheet contains, as chemical components, in mass%, C: 0.010% or less, Si: 2.50-4.00%, acid-soluble Al: 0.010% or less, N: 0.012% or less, Mn: 1.00% or less, S: 0.020% or less, and the balance of Fe and impurities.

In SiO₂1250cm in reflection-type infrared spectroscopic analysis of the surface of the intermediate oxide film layer^-1Peak intensity of (1)_AAnd 1200cm^-1Peak intensity of (1)_BSatisfies the following formula (1).

I_B/I_A≥0.010 (1)

[2] The grain-oriented electrical steel sheet according to [1] above may further comprise, in mass%, B: 0.001 to 0.010%.

[3] The grain-oriented electrical steel sheet according to [1] or [2] above may further contain, in mass%, Sn: 0.01-0.20%, Cr: 0.01 to 0.50%, Cu: 0.01-0.50% of 1 or more than 2.

[4]Above-mentioned [1]～[3]The grain-oriented electrical steel sheet according to any one of the above aspects may be the SiO₂Time differential curve f of glow discharge luminescence analysis spectrum of element M (M: Mn, Al, B) on surface of intermediate oxide film layer_M(t) satisfies the following formula (2).

[ mathematical formula 1]

Tp: time t (second) corresponding to minimum value of second-order time differential curve of glow discharge luminescence analysis spectrum of Si

Ts: time t (second) corresponding to the start point of glow discharge luminescence analysis of Si

[5] A method for producing a grain-oriented electrical steel sheet according to another aspect of the present invention is the method for producing a grain-oriented electrical steel sheet according to any one of the aspects [1] to [4], including an oxide film forming step of forming an intermediate oxide film layer on a surface of the steel sheet.

In the oxide film forming step, the annealing temperature T1: and (2) annealing at 600-1200 ℃ for: 5-200 seconds, partial pressure of oxygen P_H2O/P_H2: average heating rate HR1 in the temperature region of 100 ℃ to 600 ℃ of 0.15 or less: annealing is performed under the condition of 10-200 ℃, and after the annealing, the average cooling speed CR1 of a temperature region of T2-T1 ℃ is set to be below 50 ℃/s, and the average cooling speed CR2 of a temperature region of more than 100 ℃ and less than T2 ℃ is set to be less than CR 1. Wherein T2 ℃ represents a temperature represented by T1 ℃ -100.

Effects of the invention

According to the present invention, it is possible to form a tension-imparting insulating coating film having excellent coating film adhesion without impairing magnetic properties and stability thereof on the surface of a unidirectional silicon steel sheet subjected to finish annealing, in which generation of a glass coating film is intentionally suppressed, the glass coating film is removed by means of grinding, pickling or the like, and the surface of the steel sheet is further flattened to exhibit a mirror surface gloss.

Drawings

FIG. 1 shows SiO₂A diagram of an example of a reflection-type infrared spectroscopic analysis spectrum of the surface of the intermediate oxide film layer.

Detailed Description

The grain-oriented electrical steel sheet of the present invention (hereinafter, sometimes referred to as "electrical steel sheet of the present invention") includes: a base steel plate; an intermediate oxide film layer formed on the base steel sheet and containing SiO₂The average film thickness is 1.0 nm-1.0 μm; and a tensile insulating film formed on the intermediate oxide film layer.

The base steel sheet contains, as chemical components, in mass%, C: 0.010% or less, Si: 2.50-4.00%, acid-soluble Al: 0.01% or less, N: 0.012% or less, Mn: 1.00% or less, S: less than 0.02%, and the balance of Fe and impurities.

The electromagnetic steel sheet of the present invention is characterized in that it is formed of SiO₂1250cm in reflection-type infrared spectroscopic analysis of the surface of the intermediate oxide film layer^-1Peak intensity of (1)_AAnd 1200cm^-1Peak intensity of (1)_BSatisfies the following formula (1).

I_B/I_A≥0.010 (1)

The base steel sheet may further contain, in mass%: 0.001 to 0.010% and/or (b) Sn: 0.01-0.20%, Cr: 0.01 to 0.50%, Cu: 0.01-0.50% of 1 or more than 2.

SiO may be used as the SiO component in the electrical steel sheet of the present invention₂Time differential curve f of glow discharge luminescence analysis spectrum of element M (M: Mn, Al, B) on surface of intermediate oxide film layer_M(t) satisfies the following formula (2).

[ mathematical formula 2]

Tp: time t (second) corresponding to minimum value of second-order time differential curve of glow discharge luminescence analysis spectrum of Si

Ts: time t (second) corresponding to the start point of glow discharge luminescence analysis of Si

The method for producing a grain-oriented electrical steel sheet according to the present invention (hereinafter, sometimes referred to as "the method for producing the present invention") includes an oxide film forming step of forming an intermediate oxide film layer on the surface of the steel sheet, wherein in the oxide film forming step, the annealing temperature T1: and (2) annealing at 600-1200 ℃ for: 5-200 seconds, partial pressure of oxygen P_H2O/P_H2: average heating rate HR1 in the temperature region of 100 ℃ to 600 ℃ of 0.15 or less: annealing at 10-200 deg.C, setting average cooling rate CR1 in T2-T1 deg.C region to be below 50 deg.C/sec, and setting average cooling rate CR2 in temperature region of above 100 deg.C and below T2 deg.C to be below CAnd R1. Wherein T2 ℃ represents a temperature represented by T1 ℃ -100.

The electrical steel sheet of the present invention and the production method of the present invention will be described below.

[ base Steel sheet ]

< composition of ingredients >

First, the reasons for limiting the composition of the base steel sheet will be described. Hereinafter, "%" relating to the component composition means "% by mass".

C: 0.010% or less

If C exceeds 0.010%, C inhibits SiO₂And Al or other element concentration layer at the interface between the intermediate oxide film layer and the steel plate. Therefore, C is set to 0.010% or less. From the viewpoint of improvement of the iron loss characteristics, it is preferably 0.008% or less.

The lower limit of C includes 0%, but since the detection limit of C is about 0.0001%, 0.0001% is a substantial lower limit in the case of practical steel sheets.

Si：2.50～4.00％

If Si is less than 2.50%, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained, so Si is set to 2.50% or more. Preferably 2.75% or more, more preferably 3.00% or more.

On the other hand, if Si exceeds 4.00%, the steel sheet becomes brittle and the sheet passing property in the production process deteriorates significantly, so Si is set to 4.00% or less. Preferably 3.75% or less, more preferably 3.50% or less.

Acid-soluble Al: 0.010% or less

The acid-soluble Al is contained in the slab composition at an upper limit of 0.07% from the viewpoint of the general plate property in cold rolling. In this sense, the upper limit of the acid-soluble Al is 0.07%, but actually, Al is discharged to the outside of the steel sheet by the secondary recrystallization annealing. As a result, the acid-soluble Al contained in the base steel sheet may be 0.010% or less. Although there is no problem in the pass-through properties if the acid-soluble Al content is 0.07% or less, the less the acid-soluble Al content in the base steel sheet, the better the iron loss characteristics, preferably 0.006% or less.

The lower limit of the acid-soluble Al is 0%, but since the detection limit is about 0.0001% as in C, 0.0001% is a substantial lower limit in practical steel sheets.

N: 0.012% or less

If N exceeds 0.012%, then blisters (voids) will form in the steel sheet during cold rolling, the strength of the steel sheet will increase, and the sheet passing properties during manufacture will deteriorate, so N is set to 0.012% or less. Preferably 0.010% or less, and more preferably 0.009% or less.

The lower limit of N includes 0%, but since the detection limit of N is about 0.0001%, 0.0001% is a substantial lower limit in practical steel sheets.

Mn: 1.00% or less

If Mn exceeds 1.00%, the steel undergoes phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained, so Mn is set to 1.00% or less. Preferably 0.50% or less, more preferably 0.20% or less.

Although MnS may be used as an inhibitor in the secondary recrystallization, MnS is not essential in the case of AlN as an inhibitor, and therefore the lower limit of Mn includes 0%. When MnS is used as the inhibitor, Mn is set to 0.02% or more. Preferably 0.05% or more, more preferably 0.07% or more.

S: 0.020% or less

If S exceeds 0.020%, SiO is suppressed in the same manner as C₂And Al or other element concentration layer at the interface between the intermediate oxide film layer and the steel plate. Therefore, S is set to 0.020% or less. Preferably 0.010% or less.

The lower limit of S includes 0%, but since the detection limit of S is about 0.0001%, 0.0001% is a substantial lower limit for practical steel sheets.

In addition, a part of S may be replaced with Se or Sb, and in this case, S may be used_eqS +0.406Se or S_eqThe value obtained by conversion of S +0.406 Sb.

The electrical steel sheet of the present invention may contain, in addition to the above elements, in order to improve the properties of the electrical steel sheet of the present invention, (a) B: 0.001 to 0.010% and/or (b) Sn: 0.01-0.20%, Cr: 0.01 to 0.50%, Cu: 0.01-0.50% of 1 or more than 2.

B：0.001～0.010％

B is in SiO as in Cr and Cu₂The interface between the intermediate oxide film layer and the steel sheet is concentrated (confirmed by the inventors of the present invention using GDS), and an element contributing to improvement of the film adhesion is added. When B is less than 0.001%, the effect of improving the film adhesion cannot be sufficiently obtained, so B is set to 0.001% or more. Preferably 0.002% or more, more preferably 0.003% or more.

On the other hand, if B exceeds 0.010%, the steel sheet strength increases and the pass-through property during cold rolling deteriorates, so B is set to 0.010% or less. Preferably 0.008% or less, more preferably 0.006% or less.

Sn：0.01～0.20％

Although Sn is not in SiO₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet, but contributes to the improvement of the film adhesion. Although the mechanism of improvement in the coating adhesion of Sn is not clear, the smoothness of the steel sheet surface after secondary recrystallization is examined and improvement in smoothness is confirmed, and therefore it is considered that: sn reduces and smoothes irregularities on the surface of the steel sheet, and contributes to the formation of SiO having few irregularities₂The interface between the intermediate oxide film layer and the steel plate.

If Sn is less than 0.01%, the effect of smoothing the steel sheet surface cannot be sufficiently obtained, so Sn is set to 0.01% or more. Preferably 0.02% or more, more preferably 0.03% or more.

On the other hand, if it exceeds 0.20%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate, so Sn is set to 0.20% or less. Preferably 0.15% or less, more preferably 0.10% or less.

Cr：0.01～0.50％

Cr is in SiO as in B, Cu₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet and contributes to the improvement of the film adhesion. Cr less than 0.01% andsince the effect of improving the film adhesion is sufficiently obtained, Cr is set to 0.01% or more. Preferably 0.03% or more, more preferably 0.05% or more.

On the other hand, if Cr exceeds 0.50%, Cr and Si compete for O, possibly inhibiting SiO₂Since the intermediate oxide film layer is formed, Cr is set to 0.50% or less. Preferably 0.30% or less, more preferably 0.20% or less.

Cu：0.01～0.50％

Cu and B, Cr are in SiO₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet and contributes to the improvement of the film adhesion. When Cu is less than 0.01%, the effect of improving the film adhesion cannot be sufficiently obtained, and therefore Cu is set to 0.01% or more. Preferably 0.03% or more, more preferably 0.05% or more.

On the other hand, if Cu exceeds 0.50%, the steel sheet becomes brittle during hot rolling, so Cu is set to 0.50% or less. Preferably 0.20% or less, more preferably 0.10% or less.

The remainder of the composition of the base steel sheet is Fe and impurities (inevitable impurities), but may contain 1 or 2 or more of Mo, W, In, Bi, Sb, Ag, Te, Ce, V, Co, Ni, Se, Ca, Re, Os, Nb, Zr, Hf, Ta, Y, La, and the like In total In an amount of 5.00% or less, preferably 3.00% or less, more preferably 1.00% or less, for the purpose of improving magnetic properties, improving properties required for structural members such as strength, corrosion resistance, fatigue properties, and the like, improving castability and general plate properties, and improving productivity due to the use of scrap and the like.

[ intermediate oxide film layer ]

Next, an intermediate oxide film layer (hereinafter, sometimes referred to as SiO) which plays an important role in improving the adhesion of the film₂Intermediate oxide film layer). The electrical steel sheet of the present invention is manufactured by removing a glass coating by grinding, pickling, or the like, or intentionally preventing the formation of a glass coating. In order to sufficiently ensure the film adhesion of the tension insulating film, SiO having a desired film thickness at the interface between the tension insulating film and the steel sheet₂An intermediate oxide film layer.

SiO₂Average film thickness of intermediate oxide film layer: 1.0 nm-1.0 mu m

If SiO₂If the average thickness of the intermediate oxide film layer is less than 1.0nm, the film adhesion of the tensile insulating film cannot be sufficiently ensured, and therefore SiO is not sufficient₂The average thickness of the intermediate oxide film layer is set to 1.0nm or more. Preferably 5.0nm or more, more preferably 9.0nm or more.

On the other hand, if SiO₂If the average thickness of the intermediate oxide film layer exceeds 1.0 μm, the thickness of the intermediate oxide film layer is larger than that of the SiO₂Cracks that become starting points of fracture occur in the intermediate oxide film layer, and the film adhesion is deteriorated, so SiO₂The average thickness of the intermediate oxide film layer is set to 1.0 μm or less. Preferably 0.7 μm (═ 700nm) or less, and more preferably 0.4 μm (═ 400nm) or less.

SiO₂The thickness of the intermediate oxide film layer was measured by observing the cross section of the sample with a Transmission Electron Microscope (TEM) or a Scanning Electron Microscope (SEM).

Form SiO₂The oxide of the intermediate oxide film layer is' SiO₂"this fact can be confirmed by elemental analysis using Energy Dispersive Spectroscopy (EDS) attached to a TEM or SEM.

In particular, in SiO₂In the EDS spectrum of the intermediate oxide film layer, "SiO" was confirmed by detecting Si-Ka rays at a position of energy of 1.8. + -. 0.3kev and O-Ka rays at a position of 0.5. + -. 0.3kev on the horizontal axis₂"is present. Identification of elements can be performed by using L α rays and K γ rays in addition to K α rays.

However, since the EDS spectrum of Si may include a spectrum derived from Si in the steel sheet, it is precisely determined whether Si is a steel sheet source or SiO by analyzing the surface of the steel sheet with an Electron Probe Microanalyzer (EPMA)₂The intermediate oxide film layer is from.

In addition, for SiO₂The surface of the intermediate oxide film layer was analyzed by reflection-type infrared spectroscopic analysis at a wave number of 1250cm^-1±20cm^-1In the presence of SiO₂Of originPeaks, the constituent SiO was confirmed₂The compound of the intermediate oxide film layer is' SiO₂”。

However, since the reflection-type infrared spectroscopic analysis is a method of selectively detecting a compound on the outermost surface of a sample, the analysis is performed after (a) a sample in a state where a tensile insulating film is not present and (b) a material having a tensile insulating film on the surface of a steel sheet is completely removed by alkali washing or the like.

As for infrared spectroscopy (IR), there are reflection method and absorption method. In the absorption method, information on the outermost surface of the sample is superimposed on information on the inside of the steel sheet, and thus, the SiO constituting the sample is subjected to₂The identification of the compound of the intermediate oxide film layer is preferably a reflection method. In addition, the absorption method is derived from SiO₂The wave number of the intermediate oxide film layer does not become 1250 (cm)^-1) According to SiO₂The formation state of (3) is subjected to peak shift.

I_B/I_A: 0.010 or more

1200cm^-1Peak intensity of (1)_BRelative to 1250cm^-1Peak intensity of (1)_AThe ratio of: will I_B/I_AIs set to 0.010 or more.

By mixing SiO₂The intermediate oxide film layer is controlled to be 1.0nm to 1.0 μm, so that the film adhesion of the tensile insulating film can be secured, but if it is SiO₂If lattice defects exist at the interface between the intermediate oxide film layer and the steel sheet, the film adhesion may be reduced.

The lattice defect at the interface is caused by SiO₂The difference between the lattice constant of the intermediate oxide film layer and the lattice constant of the steel sheet is caused by the solid solution of Mn in SiO₂In the intermediate oxide film layer, the film adhesion of the tensile insulating film can be further improved. The mechanism of improving the adhesion of the coating is considered as follows.

In SiO₂The surface of the intermediate oxide film layer is extended from dangling bonds (fluctuation function) of Si, so that SiO₂The surface of the intermediate oxide film layer becomes to have an electric attraction force, i.e., an adsorption force. Thus, SiO₂Intermediate oxygenThe chemical film layer is in close contact with the steel sheet, but on the other hand, it is in SiO₂The interface between the intermediate oxide film layer and the steel plate has poor lattice matching property, and is in SiO₂The interface between the intermediate oxide film layer and the steel plate inevitably introduces lattice defects.

However, if Mn is dissolved in SiO₂In the intermediate oxide film layer, SiO₂SiO at the interface of the intermediate oxide film layer and the steel plate₂Periodically changing the lattice of SiO₂The lattice matching of the interface between the intermediate oxide film layer and the steel plate is improved. As a result, lattice defects derived from lattice mismatch are reduced, and film adhesion of the tensile insulating film is finally improved.

The mechanism described above contributes to improvement in film adhesion of the tensile insulating film to the Mn — SiO₂The state of solid solution or the state of concentration in the intermediate oxide film layer can be analyzed by reflection-type infrared spectroscopic analysis.

In the electromagnetic steel sheet of the present invention, the wave number is 1250cm^-1In the presence of the usual SiO₂Peaks of origin, furthermore, at 1200cm^-1And 1150cm^-1In the presence of SiO resulting from a change in lattice constant₂(hereinafter sometimes referred to as "Si (Mn) O_x". ) Peak of (2). And Si (Mn) O after the lattice constant is changed_xIs present in an amount of 1200cm from a wave number^-1Or 1150cm^-1Is reflected by the peak intensity of (c). The wave number, which is the horizontal axis of the reflection-type infrared spectroscopic analysis, may be within. + -. 20cm depending on the measurement conditions, the fitting method, and the like^-1May be varied within the range of (1).

SiO is shown in FIG. 1₂An example of a reflection type infrared spectroscopic analysis spectrum of the surface of the intermediate oxide film layer. The spectrum shown in FIG. 1 is SiO assuming a Gaussian (Gauss) distribution₂An example of a peak overlap method. In addition, when the superposition is legal, the distribution function is set to any one of the froude (Voigt), Gaussian (Gaussian), and Lorentz (Lorentz).

The peak intensity may be defined by the height of the peak after subtraction of the background by the analysis software, or may be defined by the integrated intensity of the peak.

In the presence of Si (Mn) O_xIn the case where the source peak does not appear clearly, the peak intensity can be extracted by a superposition method of peaks by fitting.

The present inventors have found that: at a wavenumber of 1250cm^-1SiO of (2)₂Peak intensity of origin I_AWave number of 1200cm^-1Si (Mn) O of_xPeak intensity of origin I_BWhen the following formula (1) is satisfied, good film adhesion can be obtained.

I_B/I_A≥0.010 (1)

I_B/I_AThe upper limit of (B) is not defined, but there is a limit to the amount of Mn dissolved or concentrated, and if this limit is taken into consideration, I_B/I_AThe upper limit of (B) is about 10. From the viewpoint of reliably ensuring excellent film adhesion, I_B/I_APreferably 0.010 to 5. More preferably 0.010 to 1.

When the element M (M: Mn, Al, B) is dissolved in SiO₂In the case of the intermediate oxide film layer, the solid solution form of the element M can be analyzed by glow discharge luminescence analysis (GDS). In this case, SiO₂The relationship between the depth position of the intermediate oxide film layer and the depth position of the element M is important.

SiO₂The depth position of the intermediate oxide film layer can be determined by the GDS spectrum (hereinafter, F) of Si source_Si(t)) was analyzed. The following description is made.

The GDS spectrum may be smoothed by using peak analysis software. In addition, the interval Δ t of the measurement time is preferably small, and preferably 0.05 seconds or less, from the viewpoint of improving the accuracy of peak analysis. Hereinafter, t represents a time (second) corresponding to the depth position of the sample.

t is a parameter when the GDS spectrum is set as a function of time. If SiO is present on the surface of a sample taken from a steel sheet₂The intermediate oxide film layer is observed in the GDS spectrum derived from Si in a region corresponding to the surface of the sample, wherein (a) the position of the peak rising from the background, (B) the position of the peak apex, and (C) the position of the peak ending to the background are observed.

Here, the time t corresponding to the peak-up position is set to Ts, the time t corresponding to the peak top is set to Tp, and the time t corresponding to the peak end position is set to Tf. SiO 2₂The intermediate oxide film layer corresponds to the outermost surface of the measurement sample. That is, t at the measurement start point of the GDS spectrum is preferably associated with the peak rising position, and the measurement start point of the GDS is preferably defined as Ts. The peak is bilaterally symmetric with respect to the normal distribution, and may be defined as Tf 2 Tp-Ts.

Since the measurement time interval Δ t of the GDS spectrum is as small as 0.05 seconds or less, Ts ≈ 0 and Tf may be set to 2 × Tp. Hereinafter, a method for determining Tp will be described.

Tp corresponds to the peak-top position of the GDS spectrum from Si. To determine the peak position, F is simply added_Si(t) second order differentiation with time, finding a curve corresponding to the second order differentiation (in FIG. 1, refer to "d²F(t)/dt²") may be used. However, the minimum value is limited to a value found in a range of t 0 seconds to Δ t × 100 seconds. The reason for this is that: SiO 2₂The intermediate oxide film layer is present only on the surface of the sample and not inside the steel sheet, and therefore t has a relatively small value.

Then, F is added_Si(t) curve f obtained by first differentiating with time_Si(t)(＝dF_Si(t)/dt) (in FIG. 1, refer to "dF (t)/dt"), if t is within the range of Ts to Tp, f is always present_Si(t) ≧ 0, then Tp is more deterministic in correspondence with the peak vertex position.

In addition, the derivative function may be obtained for the differential curve, or may be approximated as f (t) by the difference method_n)＝[F(t_n)-F(t_n-1)]/[t_n-t_n-1]To obtain the final product. Wherein the nth measurement point (time) is set to t_nThe spectral intensity at this time was set to F (t)_n)。

When the Si-derived peak is unclear, the GDS spectrum [ F below ] derived from Fe may be used_Fe(t)]And (6) carrying out analysis. In this case, at F_FeFirst order differential curve of (t) (hereinafter, f is set to_Fe(t)) setting t corresponding to the maximum value to tIf Tf is defined, Tp is 0.5 × (Tf + Ts), but Ts may be approximated by Ts ≈ 0 and Tp may be 0.5 × Tf. This is due to: f. of_FeMaximum value of (t) corresponds to SiO₂Interface with the base metal.

The maximum value is limited to a value found in a range of t 0 seconds to Δ t × 100 seconds. The reason for this is that: SiO 2₂The intermediate oxide film layer is present only on the surface of the sample and not inside the steel sheet, and therefore t has a relatively small value.

In the electrical steel sheet of the present invention, in order to improve the film adhesion, it is necessary to add an element M such as Mn, Al, or B to SiO₂And concentrating at the position corresponding to t-Tp in the central part of the intermediate oxide film layer. However, it is impossible to make the element M such as Mn, Al, and B stay at the position t equal to Tp, and actually, it is distributed over the entire range t equal to Ts to Tp.

I.e. dissolved in SiO₂The solid solution state of the element M in the intermediate oxide film layer can be determined by GDS spectrum (hereinafter, F) derived from the element M_M(t)) was confirmed. Specifically, if f is to be_M(t) in the integration range: the value of t when integrated within Ts to Tp may satisfy the following formula (2).

[ mathematical formula 3]

Since the element M contains a plurality of kinds of Mn, Al, B, and the like, at least one or two or more of the following formulas (3) to (5) may be satisfied.

[ mathematical formula 4]

Note that t in GDS analysis is not continuous, and f is not continuous even when t is t to Tp_M(t) is also a set of discontinuous points. Thus, to f_MThe points (t) are connected in a straight line and integrated by approximation so as to form a continuous function. In addition, an integration value obtained using Σ may be set.

The element M such as Mn, Al, B and the like can also be detected by chemical analysis. The steel sheet portion of the sample before the formation of the tensile insulating film or the sample from which the tensile insulating film has been removed is dissolved by the iodomethanol method, and SiO is extracted₂An intermediate oxide film layer. Then, the extracted SiO₂The intermediate oxide film layer is chemically analyzed using ICP or the like. Thereby, the intrusion SiO can be captured₂And the metal element M in the intermediate oxide film layer.

SiO₂The amount of the metal element M dissolved (or concentrated) in the intermediate oxide film layer may be 0.01% or more of Mn and Al and 0.001% or more of B in mass%. The upper limit is not particularly limited, but it is difficult to achieve solid solution (concentration) of more than 0.5% in Mn and Al, and difficult to achieve solid solution (concentration) of more than 0.2% in B.

Verification of the effect of improving the film adhesion by reflection-type infrared spectroscopy, GDS, chemical analysis, and the like, SiO was formed on the surface of the steel sheet₂The steel sheet sample in a state after the intermediate oxide film layer and before the tensile insulating film is formed is most suitable, but the steel sheet sample having the tensile insulating film formed on the surface thereof may be subjected to analysis by completely removing only the tensile insulating film after alkali washing by acid washing or ultrasonic washing with alcohol, water, or the like.

After pickling or ultrasonic washing with alcohol, water, or the like, annealing may be performed in an atmosphere of 100% hydrogen at 800 to 1100 ℃ for 1 to 5 hours for the purpose of further cleaning the surface of the steel sheet sample. SiO 2₂SiO is a stable compound in the above annealing₂Can not be reducedTo make SiO₂The intermediate oxide film layer disappears.

< production method >

The electrical steel sheet of the present invention is produced by subjecting a steel slab, which is melted in a converter and continuously cast, to hot rolling, hot plate annealing, cold rolling, primary recrystallization annealing, secondary recrystallization annealing to form SiO, in the same manner as a normal electrical steel sheet₂Annealing the intermediate oxide film layer and annealing the insulating film layer.

The hot rolling may be direct hot rolling or continuous hot rolling, and the slab heating temperature is not limited. The cold rolling may be performed by two or more cold rolling and warm rolling, and the reduction ratio is not limited. The secondary recrystallization annealing may be either batch annealing or continuous line annealing using a box furnace, and is not dependent on the annealing method.

The annealing separator may contain an oxide such as alumina, magnesia or silica, and is not limited to the kind thereof.

In the case of producing a grain-oriented electrical steel sheet having excellent coating adhesion, SiO is used₂When the intermediate oxide film layer is formed, SiO is generated₂The metal elements M such as Mn and the like are converted into SiO at the middle oxide film layer₂The heat treatment conditions for solid solution or concentration in the intermediate oxide film layer are important. That is, the metal element M is selected to be SiO₂The temperature and time of solid solution or concentration in the intermediate oxide film layer is important.

In the electromagnetic steel sheet of the present invention, SiO₂The intermediate oxide film layer is formed by annealing the steel sheet after the secondary recrystallization at a temperature T1 (DEG C) of 600 to 1200 ℃.

If the annealing temperature is lower than 600 ℃, SiO is not generated₂Without formation of SiO₂The annealing temperature is set to 600 ℃ or higher because of the intermediate oxide film layer. On the other hand, if the annealing temperature exceeds 1200 ℃, SiO₂Non-uniform reaction of formation of intermediate oxide film layer, SiO₂The intermediate oxide film layer and the base steel sheet have severe unevenness, and the film adhesion is deteriorated. Therefore, the annealing temperature is set to 1200 ℃ or lower. SiO is preferred₂The precipitation temperature is 700-1100 ℃.

To make SiO₂The intermediate oxide film layer is grown to ensure a layer thickness necessary for ensuring excellent film adhesion, and the annealing time is set to 5 seconds or more. Preferably 20 seconds or more. From the viewpoint of ensuring excellent film adhesion, the annealing time is preferably long, but from the viewpoint of productivity, 200 seconds is set as the upper limit. Preferably 100 seconds or less.

The annealing atmosphere is set to form external oxidation type silicon dioxide (SiO)₂Intermediate oxide film layer) and avoids the generation of lower oxides such as fayalite, wustite, magnetite, and the like. Therefore, the oxygen partial pressure P, which is the ratio of the water vapor pressure to the hydrogen pressure in the annealing atmosphere_H2O/P_H2The oxygen partial pressure is set to satisfy the following formula (6). Preferably 0.05 or less.

P_H2O/P_H2≤0.15 (6)

Partial pressure of oxygen P_H2O/P_H2The lower the content, the external oxidation type of Silica (SiO)₂Intermediate oxide film layer) is more easily formed and the effect of the present invention is more easily exhibited, but it is difficult to control the oxygen partial pressure P_H2O/P_H2Controlled to be lower than 5.0 x 10^-4Thus, industrially, 5.0X 10^-4The lower limit is substantial.

In order to convert the metal element M such as Mn, Al, B to SiO₂The intermediate oxide film layer is effectively solid-dissolved (or concentrated), and a temperature at which the metal element M can diffuse needs to be ensured. Thus, SiO is formed₂Cooling the intermediate oxide film layer after annealing to SiO₂The temperature region in which the intermediate oxide film layer diffuses, that is, the temperature region from T2 (DEG C) to T1 (DEG C) defined by the following formula (7), is cooled at an average cooling rate CR1 (DEG C/sec) of 50 ℃/sec or less.

The electrical steel sheet of the present invention is not deteriorated in properties by cooling at an average cooling rate CR1 of 50 ℃/sec or less, but CR1 is preferably 0.1 ℃/sec or more from the viewpoint of productivity. After cooling to T2 (deg.c), since thermal strain is introduced and the film adhesiveness and magnetic properties are degraded if the cooling rate is increased, the average cooling rate CR2 in the temperature range of 100 to T2 (deg.c) is set to an average cooling rate satisfying the following expression (8).

T2(℃)＝T1(℃)-100 (7)

CR1>CR2 (8)

SiO with excellent adhesion to coating₂In the formation of the intermediate oxide film, the heating rate at which the steel sheet is heated is also important. Due to SiO₂The other oxides not only reduce the adhesion of the tensile insulating film but also inhibit the surface smoothness of the steel sheet to reduce the iron loss characteristics, and therefore it is necessary to use an oxide which does not generate SiO as much as possible₂Other than the heating rate of the oxide.

SiO, as described in non-patent document 1₂Since Fe-based oxides are unstable compared to other Fe-based oxides, it is preferable to use a thermal history in which Fe-based oxides are not generated during heating. Specifically, by setting the average heating rate HR1 in the temperature range from 100 ℃ to 600 ℃ to 10 ℃/sec or more, Fe can be avoided_XAnd (4) generating O. The heating rate in this temperature range is preferably higher, but for industrial reasons, the upper limit of the average heating rate HR1 is preferably 200 ℃/sec. Preferably, HR1 is 20 to 150 ℃/sec, more preferably 50 to 100 ℃/sec.

Examples

Hereinafter, the technical contents of the present invention will be further described by referring to examples of the present invention. The conditions in the examples shown below are one example of conditions adopted for confirming the feasibility and the effect of the present invention, and the present invention is not limited to this example of conditions. In addition, as long as the object of the present invention is achieved without departing from the gist of the present invention, various conditions can be adopted in the present invention.

< example 1>

Silicon steel having a composition shown in Table 1-1 was soaked at 1100 ℃ for 60 minutes, then subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.6mm, annealed at 1100 ℃, pickled, and subjected to one cold rolling or multiple cold rolling with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.

[ tables 1-1]

A cold rolled steel sheet having a final thickness of 0.23mm was subjected to decarburization annealing and nitriding annealing. Thereafter, the coating of an aqueous slurry of an annealing separator mainly composed of alumina was performed, and the final annealing was performed at 1200 ℃ for 20 hours. Then, the finished annealed plate is placed at an oxygen partial pressure P_H2O/P_H2: 0.12, annealing temperature T1: annealing time at 1000 ℃: average heating rate HR1 in the temperature region of 100 to 600 ℃ for 30 seconds: annealing is carried out under the condition of 30 ℃/second to form SiO on the surface of the steel plate₂An intermediate oxide film layer.

The average cooling rate CR1 in the temperature range of T2 ℃ (800 ℃) to T1 ℃ (900 ℃) was set to 50 ℃/sec, and the average cooling rate CR2 at 100 ℃ or higher and lower than T2 ℃ (800 ℃) was set to 30 ℃/sec.

Then, the coating liquid for forming an insulating film is applied to the surface of the steel sheet and sintered to form a tensile insulating film. Chemical compositions of base steel sheets of the produced grain-oriented electrical steel sheets are shown in tables 1 to 2. The coating adhesion of the insulating coating was evaluated, and the magnetic properties (magnetic flux density) were also evaluated.

[ tables 1-2]

The film adhesion of the tensile insulating film was evaluated by winding the test specimen for evaluation around a cylinder having a diameter of 20mm and bending the test specimen at 180 ° to obtain a film remaining area ratio. For the evaluation, VG (very excellent) was set for the case where the film remaining area ratio was 95% or more without peeling from the steel sheet, G (excellent) was set for the case where the film remaining area ratio was 90% or more and less than 95%, F was set for the case where the film remaining area ratio was 80% or more and less than 90% (effective), and B was set for the case where the film remaining area ratio was less than 80% (ineffective).

The magnetic properties were evaluated in accordance with JIS C2550. The magnetic flux density was evaluated by using B8. B8 is the magnetic flux density at a magnetic field strength of 800A/m, and is the criterion for determining the quality of the secondary recrystallization. A sample in which secondary recrystallization was performed was judged as B8 equal to or greater than 1.89T.

In addition, SiO was formed on a part of the samples₂After the intermediate oxidation film layer, no tensile insulating film is formed for SiO₂Film thickness investigation of intermediate oxide film layer and SiO₂And (5) investigating the lattice matching degree of the intermediate oxide film layer. SiO 2₂The thickness of the intermediate oxide film layer was determined by TEM observation according to the method described in patent document 25. SiO 2₂The lattice matching degree of the intermediate oxide film layer was investigated by reflection-type infrared spectroscopic analysis. A series of evaluation results are shown in table 2.

[ Table 2]

The symbols B1 to B13 are examples of the invention, and the invention effects are obtained. The inventive steels B1-B6 did not contain any optional elements. The inventive steel B1 was evaluated to stay at "F" because S was out of the preferred range, B2 and B4 were out of the preferred range for Si, B3 was out of the preferred range for acid-soluble Al, and B5 was out of the preferred range for N. However, the inventive steel B6 was evaluated as "G" even though it did not contain any optional elements, and was relatively good. This is because, in the case of inventive steel B6, Si, Mn, acid-soluble Al, and N were controlled to be in the preferable or more preferable ranges. The inventive steels B7 to B13 contained any one of Cr, Cu, Sn and B as an optional element. Since B7 to B12 contain 1 or 2 of Cr, Cu, Sn, and B as optional elements, a relatively good result, "G" was obtained. The invention steel B13 contained 3 kinds of Cr, Cu, and Sn, and therefore "VG" was obtained as a particularly favorable result.

On the other hand, reference symbols b1 to b7 represent comparative examples. Since the comparative examples denoted by b3 to b5 each contain a large amount of Si, Al, and N, the brittleness at room temperature is poor, and cold rolling itself is impossible. Therefore, in the comparative examples with the reference numerals b3 to b5, the evaluation of adhesion was not achieved.

SymbolIn the comparative examples of b1, b2, and b6, since the content of the additive element deviates from the scope of the present invention, the secondary recrystallization was not performed. In addition, the samples not subjected to the secondary recrystallization had poor film adhesion. This is believed to be due to: when the secondary recrystallization is not performed, the crystal grain size of the steel sheet is fine, the surface unevenness is severe, and the formation of the oxide layer does not proceed properly. Comparative steel b7 since S departed from the upper limit of the present invention, SiO₂The intermediate oxide film layer is not formed properly, and therefore the film adhesion is poor.

< example 2>

Silicon steel having a composition shown in Table 1-1 was soaked at 1100 ℃ for 60 minutes, then subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.6mm, annealed at 1100 ℃, pickled, and subjected to one cold rolling or multiple cold rolling with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.

A cold-rolled steel sheet having a final thickness of 0.23mm was subjected to decarburization annealing and nitriding annealing, and then subjected to water slurry coating of an annealing separator mainly composed of alumina, followed by finish annealing at 1200 ℃ for 20 hours. Then, the finished annealed plate is placed at an oxygen partial pressure P_H2O/P_H2: 0.01, annealing temperature T1: annealing time at 800 ℃: average heating rate HR1 in the temperature region of 100 to 600 ℃ for 60 seconds: annealing at 90 deg.C/sec to form SiO on the surface of the steel plate₂An intermediate oxide film layer.

In addition, the average cooling rate CR1 in the temperature region of T2 ℃ (700 ℃) to T1 ℃ (800 ℃) is set to 50 ℃/sec, and the average cooling rate CR2 of more than 100 ℃ and less than T2 ℃ (700 ℃) is set to 30 ℃/sec.

After that, the coating liquid for forming an insulating film was applied to the surface of the steel sheet and sintered to form a tensile insulating film, and the film adhesion of the insulating film and the magnetic properties (magnetic flux density) were evaluated.

For a portion of the sample, SiO was formed₂After the intermediate oxide film layer, no tension-imparting insulating film is formed for SiO₂Investigation of film thickness of intermediate oxide film layer and SiO₂Investigation of lattice matching degree of intermediate oxide film layer and SiO₂Solid solubility of Mn in the intermediate oxide film layer was investigated. The solid solubility of Mn was determined by GDS analysis.

SiO is shown in Table 3₂Film thickness of intermediate oxide film layer, SiO obtained by reflection-type infrared spectroscopic analysis₂The lattice matching degree of the intermediate oxide film layer, the solid solubility of Mn, Al, and B obtained by GDS, and the evaluation result of the film adhesion were obtained. The measurement time of GDS was set to 100 seconds, and the time interval was set to 0.05 seconds. Any of the measurement methods and evaluation methods were carried out in accordance with example 1.

The chemical compositions of the base steel sheets of the produced grain-oriented electrical steel sheets are shown in tables 1 to 2. When equations (3) to (5) are satisfied, "OK" is set, and when the equations are not satisfied, "NG" is set.

[ Table 3]

The symbols C1 to C7 are inventive examples, and it was confirmed by reflection-type infrared spectroscopic analysis that SiO having excellent lattice matching was formed in all of them₂An intermediate oxide film layer.

Since the invention steel C7 contains 4 kinds of optional elements, Cr, Cu, Sn, and B, "VG" which is particularly excellent film adhesion was obtained, compared with the evaluation "G" of the invention steels C1 to C6 which do not contain any optional elements or stay only in 1 kind even if any optional elements are contained.

< example 3>

Silicon steel having a composition shown in Table 1-1 was soaked at 1100 ℃ for 60 minutes, then subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.6mm, annealed at 1100 ℃, pickled, and subjected to one cold rolling or multiple cold rolling with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.

A cold rolled steel sheet having a final thickness of 0.23mm was subjected to decarburization annealing and nitriding annealing. Then, an aqueous slurry coating of an annealing separator mainly composed of alumina was performed to obtain a coating filmAnd annealing the finished product at 1200 ℃ for 20 hours. Next, the finished annealed sheets were annealed under the conditions shown in tables 4-1 and 4-2 to form SiO on the surfaces of the steel sheets₂An intermediate oxide film layer. After that, the coating liquid for forming an insulating film was applied to the surface of the steel sheet and sintered to form a tensile insulating film, and the adhesiveness of the insulating film and the magnetic properties (magnetic flux density) were evaluated.

The chemical compositions of the base steel sheets of the produced grain-oriented electrical steel sheets are shown in tables 1 to 2.

SiO is shown in Table 4-1 and Table 4-2₂Film thickness of intermediate oxide film layer, SiO obtained by reflection-type infrared spectroscopic analysis₂The crystal lattice matching degree and the film adhesion of the intermediate oxide film layer were evaluated. Any of the measurement methods and evaluation methods were carried out in accordance with example 1.

[ Table 4-1]

[ tables 4-2]

The symbols D1 to D27 are examples of the invention, and all of them enjoy the effects of the invention.

In the invention steels D1 to D9, the invention steels D1 to D3 were evaluated to stay at "F" because the annealing temperature, annealing time, temperature rising rate HR1, and oxygen partial pressure were controlled to be out of the preferable ranges, but the invention steels D4 to D6 were good results of "G" because the annealing temperature, annealing time, temperature rising rate HR1, and oxygen partial pressure were all controlled to be within the preferable ranges.

The annealing temperature, annealing time and oxygen partial pressure of the inventive steels G7 to G9 were controlled to be within the preferable ranges, and the temperature increase rate HR1 was controlled to be within the more preferable range. Thus, good film adhesion, i.e., "G", was obtained.

Although the annealing temperature, annealing time, temperature increase rate HR1, and oxygen partial pressure were out of the preferable ranges in the invention steels D10 to D13, "G" was obtained as a relatively good film adhesion because Cr and Sn were contained as optional elements.

The invention steels D14 to D15 had the annealing temperature, annealing time, heating rate HR1, and oxygen partial pressure controlled to be within the preferred ranges, and contained Cr and Sn as optional elements, and therefore had relatively good film adhesion, "G".

The invention steels D16 to D18 contained Cr and Sn as optional elements while controlling the annealing temperature, annealing time, and oxygen partial pressure within preferred ranges, and further controlled the temperature increase rate HR1 within more preferred ranges, and therefore obtained "VG" which is particularly excellent film adhesion.

In the invention steels D19 to D21, although the annealing temperature, annealing time, temperature increase rate HR1, and oxygen partial pressure were outside the preferable ranges, relatively good film adhesion, "G", was obtained because Cr, Cu, and Sn were contained as optional elements. The annealing temperature, annealing time, and oxygen partial pressure of the inventive steels D22 to D27 were controlled to be within the preferable ranges, and therefore "VG" which is particularly excellent film adhesion was obtained.

On the other hand, reference symbols d1 to d9 represent comparative examples. In the comparative examples marked with d1 to d3 and d5, SiO was formed₂Any one of the annealing temperature, the annealing time and the oxygen partial pressure at the time of the intermediate oxide film layer is out of the range of the present invention, and therefore SiO is not formed₂The intermediate oxide film layer cannot be evaluated by reflection-type infrared spectroscopy.

The comparative examples with the symbols d4, d8 and d9 are SiO₂The cooling rate of the intermediate oxide film layer is outside the range of the present invention, and therefore SiO₂The intermediate oxide film layer had a poor lattice matching degree, and the film adhesion was evaluated as "B".

In d6, HR1 exceeds the upper limit, and in d7, HR1 is less than the lower limit, and therefore Fe-based oxides are formed in a large amount. Therefore, the evaluation of the film adhesion was B.

Industrial applicability

As described above, according to the present invention, it is possible to form a tension-imparting insulating film having excellent film adhesion without impairing magnetic properties and stability thereof on the surface of a unidirectional silicon steel sheet subjected to finish annealing, in which generation of a glass film is intentionally suppressed, the glass film is removed by means of grinding, pickling, or the like, and the surface of the steel sheet is further flattened to exhibit a mirror gloss. Therefore, the present invention is highly applicable to the electrical steel sheet manufacturing industry and the electrical steel sheet utilization industry.