阅读说明：本技术 方向性电磁钢板 (Grain-oriented electromagnetic steel sheet ) 是由 高谷真介 牛神义行 藤井浩康 中村修一 今井武 于 2018-07-13 设计创作，主要内容包括：一种方向性电磁钢板，其具有：钢板；和形成于上述钢板上的非晶质氧化物覆膜，上述方向性电磁钢板的表面的光泽度为150％以上。(A grain-oriented electrical steel sheet comprising: a steel plate; and an amorphous oxide coating film formed on the steel sheet, wherein the surface of the grain-oriented electrical steel sheet has a glossiness of 150% or more.)

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

a steel plate; and

an amorphous oxide coating film formed on the steel sheet,

the surface of the grain-oriented electrical steel sheet has a glossiness of 150% or more.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet comprises, as a chemical composition, in mass%:

c: less than 0.085 percent of,

Si：0.80～7.00％、

Mn: less than 1.00 percent,

Al: less than 0.065%,

S: less than 0.013%,

Cu：0～0.80％、

N：0～0.012％、

P：0～0.5％、

Ni：0～1.0％、

Sn：0～0.3％、

Sb：0～0.3％、

The remainder comprising Fe and impurities.

3. The grain-oriented electrical steel sheet according to claim 2, wherein the steel sheet contains, as the chemical composition, in mass%, Cu: 0.01 to 0.80 percent.

4. The grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the glossiness is measured by the method described in JIS Z-8741.

Technical Field

The present invention relates to a grain-oriented electrical steel sheet used as an iron core material of a transformer, and more particularly to a grain-oriented electrical steel sheet with an amorphous oxide coating having excellent adhesion of a tensile insulating coating.

The present application claims priority based on Japanese application laid-open at 2017, No. 2017-137408, on 13.07.7, the contents of which are incorporated herein by reference.

Background

Grain-oriented electrical steel sheets are mainly used for transformers. The transformer is continuously excited for a long time from the time of installation to the time of disposal, and energy loss continues to occur. Therefore, the iron loss, which is the energy loss when the transformer is magnetized by alternating current, is a main index for determining the performance of the transformer.

In order to reduce the iron loss of grain-oriented electrical steel sheets, a large number of techniques have been developed from the following viewpoints: (a) increasing the clustering into the {110} <001> orientation (gaussian orientation); (b) increasing the content of solid solution elements such as Si to increase the electric resistance of the steel sheet; or (c) reducing the thickness of the electromagnetic steel sheet.

In addition, imparting tension to the steel sheet is effective for reducing the iron loss. Forming a coating film made of a material having a thermal expansion coefficient lower than that of the steel sheet on the surface of the steel sheet at a high temperature is an effective means for reducing the iron loss. In the final annealing step of the electrical steel sheet, the forsterite-based coating film having excellent coating film adhesion, which is formed by the reaction of the oxide on the surface of the steel sheet with the annealing separator, is a coating film capable of imparting tension to the steel sheet.

For example, the method disclosed in patent document 1, in which a coating liquid mainly composed of colloidal silica and phosphate is sintered on the surface of a steel sheet to form an insulating coating, is effective for reducing the iron loss because of a large effect of imparting tension to the steel sheet. Therefore, a general method for producing a grain-oriented electrical steel sheet is carried out by leaving the forsterite-based coating film formed in the final annealing step and then applying an insulating coating mainly containing phosphate.

However, in recent years, it has been clarified that: the forsterite-based coating film interferes with the movement of the magnetic domain wall, and adversely affects the iron loss. In a grain-oriented electrical steel sheet, a magnetic domain wall moves and changes under an alternating-current magnetic field. It is believed that: while it is effective to smoothly and rapidly reduce the iron loss by the movement of the magnetic domain wall, the forsterite-based coating has an uneven structure at the steel sheet/coating interface, and the uneven structure interferes with the movement of the magnetic domain wall, thereby adversely affecting the iron loss.

Therefore, a technique for suppressing the formation of a forsterite-based coating film and smoothing the surface of a steel sheet has been studied. For example, patent documents 2 to 5 disclose a technique of smoothing the surface of a steel sheet without forming a forsterite-based film in the finish annealing by controlling the atmosphere dew point of the decarburization annealing and using alumina as an annealing separating agent.

However, when the surface of the steel sheet is smoothed by such an operation, it is necessary to form a tensile insulating film having sufficient adhesion on the surface of the steel sheet in order to impart tension to the steel sheet.

In order to solve such a problem, patent document 6 discloses a method of forming an amorphous oxide film on the surface of a steel sheet and then forming a tensile insulating film. Patent documents 7 to 11 disclose techniques for controlling the structure of an amorphous oxide film for the purpose of forming a tensile insulating film having a further high adhesion.

Patent document 7 discloses a method for ensuring the coating adhesion between a tensile insulating coating and a steel sheet. In this method, the film adhesion is ensured by: after a pretreatment for introducing fine irregularities is performed on the surface of a unidirectional electromagnetic steel sheet having a steel sheet surface smoothed, an external oxide type oxide is formed, and further a granular external oxide mainly composed of silica is formed so as to penetrate the thickness of the external oxide film.

Patent document 8 discloses a method for ensuring the coating adhesion between a tensile insulating coating and a steel sheet. In this method, the film adhesion between the tensile insulating film and the steel sheet is ensured by: in a heat treatment step for forming an external oxide film on a unidirectional electromagnetic steel sheet having a steel sheet surface smoothed, the rate of temperature rise in a temperature range of 200 to 1150 ℃ is controlled to 10 to 500 ℃/sec, and the percentage of the cross-sectional area of a metal oxide such as iron, aluminum, titanium, manganese, or chromium in the external oxide film is set to 50% or less.

Patent document 9 discloses a method for ensuring the coating adhesion between a tensile insulating coating and a steel sheet. In this method, the film adhesion between the tensile insulating film and the steel sheet is ensured by: an external oxide film is formed on a unidirectional electromagnetic steel sheet having a smoothed steel sheet surface, and in the subsequent tensile insulating film forming step, the contact time between the steel sheet having the external oxide film formed thereon and the coating liquid for forming a tensile insulating film is set to 20 seconds or less, thereby setting the ratio of the density-decreasing layer in the external oxide film to 30% or less.

Patent document 10 discloses a method for ensuring the coating adhesion between a tensile insulating coating and a steel sheet. In this method, the film adhesion between the tensile insulating film and the steel sheet is ensured by: in order to form an external oxide film on a unidirectional electromagnetic steel sheet having a steel sheet surface smoothed, heat treatment is performed at a temperature of 1000 ℃ or higher, the cooling rate in a temperature range from the formation temperature of the external oxide film to 200 ℃ is controlled to 100 ℃/sec or less, and voids in the external oxide film are set to 30% or less in terms of the cross-sectional area ratio.

Patent document 11 discloses a method for ensuring the coating adhesion between a tensile insulating coating and a steel sheet. In this method, the film adhesion between the tensile insulating film and the steel sheet is ensured by: in a heat treatment step for forming an external oxidation-type oxide film on a unidirectional electromagnetic steel sheet having a steel sheet surface smoothed, annealing is performed under conditions in which a heat treatment temperature is set to 600 to 1150 ℃ and an atmosphere dew point is set to-20 to 0 ℃, and a cooling atmosphere dew point at this time is set to 5 to 60 ℃, and the external oxidation-type oxide film contains 5 to 30% of metallic iron in terms of a cross-sectional area percentage.

However, in any of the methods disclosed in patent documents 7 to 11, sufficient adhesion between the tensile insulating coating and the steel sheet may not be obtained, and the expected iron loss reduction effect may not be sufficiently exhibited.

Disclosure of Invention

Problems to be solved by the invention

In view of the current state of the art, the present invention addresses the problem of improving the adhesion between a tensile insulating film and a steel sheet when the surface of a grain oriented electrical steel sheet having no forsterite-based film on the surface thereof is coated with the tensile insulating film in order to significantly reduce the iron loss. That is, an object of the present invention is to provide a grain-oriented electrical steel sheet having excellent adhesion to a tensile insulating film.

Means for solving the problems

The present inventors have conducted intensive studies on a method for solving the above problems. As a result, they found that: when an amorphous oxide coating is formed on the surface of a steel sheet having no forsterite coating on the surface thereof obtained by removing the forsterite coating or intentionally preventing the generation of forsterite, the glossiness of the steel sheet after the coating is 150% or more, the adhesion between the tensile insulating coating and the steel sheet is remarkably improved.

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

(1) A grain-oriented electrical steel sheet according to one aspect of the present invention includes: a steel plate; and an amorphous oxide coating film formed on the steel sheet, wherein the surface of the grain-oriented electrical steel sheet has a glossiness of 150% or more.

(2) The grain-oriented electrical steel sheet according to the item (1), wherein the steel sheet may contain, as a chemical composition, in mass%, C: 0.085% or less, Si: 0.80 to 7.00%, Mn: 1.00% or less, Al: 0.065% or less, S: 0.013% or less, Cu: 0-0.80%, N: 0-0.012%, P: 0-0.5%, Ni: 0-1.0%, Sn: 0-0.3%, Sb: 0 to 0.3%, and the balance of Fe and impurities.

(3) The grain-oriented electrical steel sheet according to the above (2), wherein the steel sheet may contain, as the chemical composition, Cu: 0.01 to 0.80 percent.

(4) The grain-oriented electrical steel sheet according to any one of the above (1) to (3), wherein the glossiness may be measured by the method described in JISZ-8741.

Effects of the invention

According to the aspect of the present invention, a grain-oriented electrical steel sheet having excellent adhesion between the tensile insulating coating and the steel sheet can be provided.

Drawings

Fig. 1 is a graph showing a relationship between the glossiness and the residual area ratio of the coating film.

Fig. 2 is a graph showing the relationship between the oxygen partial pressure and the glossiness in the annealing atmosphere in which the amorphous oxide film is formed.

Detailed Description

A grain-oriented electrical steel sheet according to an embodiment of the present invention (hereinafter, sometimes referred to as "electrical steel sheet according to the present embodiment") is a grain-oriented electrical steel sheet having an amorphous oxide coating on a surface of a steel sheet, and has a surface glossiness of 150% or more. In other words, the grain-oriented electrical steel sheet of the present embodiment is characterized by having a steel sheet and an amorphous oxide coating formed on the steel sheet, and the surface gloss of the grain-oriented electrical steel sheet is 150% or more.

The electrical steel sheet of the present embodiment will be described below.

The inventors of the present invention have studied a method for securing film adhesion of a tensile insulating film for reducing iron loss when the surface of a steel sheet without a forsterite-based film is covered with the tensile insulating film. As a result, it is thought that the following matters are important: an amorphous oxide coating film is formed on the surface of a steel sheet without a forsterite-based coating film (particularly, an amorphous oxide coating film is formed so as to be in direct contact with the surface of the steel sheet), and the morphology of the amorphous oxide coating film is made uniform, thereby suppressing stress concentration at the interface between the tensile insulating film and the steel sheet as much as possible. The steel sheet without the forsterite-based coating film may be formed by: removing the forsterite-based coating after the final annealing; or intentionally prevent the production of forsterite. For example, the formation of forsterite can be intentionally prevented by adjusting the composition of the annealing separator.

As described above, it is considered that: by forming an amorphous oxide coating on the surface of a steel sheet (base steel sheet) having no forsterite-based coating and then making the morphology of the amorphous oxide coating uniform, the adhesion between the tensile insulating coating formed thereon and the steel sheet can be improved. However, the thickness of the amorphous oxide is about several nm and is very thin, and it is extremely difficult to determine whether the morphology is uniform. Therefore, the inventors of the present invention have studied a method for evaluating the morphological uniformity of the amorphous oxide film. As a result, they found that: the uniformity of the morphology of the amorphous oxide film can be evaluated if the gloss of the surface of the steel sheet having the amorphous oxide film is used. Namely, it can be seen that: the higher the glossiness of the steel sheet surface, the more uniform the morphology of the amorphous oxide coating film covering the steel sheet surface.

Based on the above-described idea, the inventors of the present invention conducted the following experiment to investigate the relationship between the adhesion of the tensile insulating film (film adhesion) and the gloss of the surface of the steel sheet of the grain-oriented electrical steel sheet having the amorphous oxide film.

As a material for experiments, a grain-oriented electrical steel sheet having no forsterite-based coating was prepared by applying an annealing separator mainly composed of alumina to a decarburized annealed sheet having a thickness of 0.23mm and containing 3.4% of Si, and performing final annealing and secondary recrystallization. The grain-oriented electrical steel sheet is subjected to a heat treatment in an atmosphere of 25% nitrogen, 75% hydrogen and a dew point of-30 to 5 ℃ for a soaking time of 10 seconds to form silicon dioxide (SiO) on the surface of the steel sheet₂) An amorphous oxide film as a main body.

The glossiness of the surface of the grain-oriented electrical steel sheet having an amorphous oxide coating was measured by the method defined in JISZ-8741 (the method of defining the glossiness by setting the value obtained by measuring a black glass standard plate (refractive index of 1.567) at an incident angle of 60 ° as 100).

Next, a coating solution mainly containing phosphate, chromic acid, and colloidal silica was applied to the surface of the grain-oriented electrical steel sheet having the amorphous oxide coating film, and the sheet was sintered at 835 ℃ for 30 seconds in a nitrogen atmosphere to form a tensile insulating film.

The coating adhesion of the tensile insulating coating in the grain-oriented electrical steel sheet with the tensile insulating coating thus produced was examined.

The film adhesion of the tensile insulating film was evaluated at the following area ratio (hereinafter referred to as "film remaining area ratio"): the area ratio of the portion remaining in a state where the tensile insulating coating was not peeled off from the steel sheet and was in close contact with the steel sheet in a state where the tensile insulating coating was recovered after the sample collected from the steel sheet was wound (bent at 180 °) on a cylinder having a diameter of 20 mm. The residual area ratio of the coating film may be measured by visual observation.

Fig. 1 shows the relationship between the glossiness and the residual area ratio of the coating film. The conditions for ensuring the film adhesion of the tensile insulating film are as follows if the conditions are determined from fig. 1.

(i) When the glossiness is 150% or more, the residual area ratio of the film becomes 80% or more, and the film adhesion of the tensile insulating film is good.

(ii) When the glossiness is 230% or more, the residual area ratio of the coating film becomes 90% or more, and the coating film adhesion of the tensile insulating coating film is further improved.

Based on the above results specify: the electrical steel sheet of the present embodiment has a steel sheet and an amorphous oxide coating formed on the surface of the steel sheet, and the surface of the grain-oriented electrical steel sheet having the amorphous oxide coating has a glossiness of 150% or more. The gloss is preferably 230% or more.

Here, amorphous is a solid in which atoms and molecules do not form a regular space lattice and are arranged in a disordered manner. Specifically, when X-ray diffraction is performed, the following states are exhibited: only a halo is detected and no specific peak is detected.

In the electrical steel sheet of the present embodiment, the amorphous oxide coating is a coating formed substantially only of an amorphous oxide. Whether or not the coating film has an oxide can be confirmed by using TEM or FT-IR.

The gloss can be measured by the following method.

The gloss was measured by a commercially available gloss meter, for example, a Micro-TRI-gloss meter (4446) manufactured by BYK-Gardner corporation, by a method specified in JISZ-8741 (a method in which the gloss is specified by setting a value obtained by measuring a black glass standard plate (refractive index of 1.567) at an incident angle of 60 ° as 100).

When a tensile insulating film is formed on an amorphous oxide film, the tensile insulating film of a product steel sheet on which the tensile insulating film is formed may be selectively removed by wet etching in an etching solution of 20% sodium hydroxide at 80 ℃ for 20 minutes, and then the glossiness may be measured.

The amorphous oxide film is preferably an external oxidation type amorphous oxide film in terms of ensuring the morphological uniformity of the amorphous oxide film.

When an amorphous oxide film of an external oxidation type is not formed on the surface of the steel sheet, but an amorphous oxide film of an internal oxidation type is formed on the surface of the steel sheet, there is a possibility that the tensile insulating film peels off from the amorphous oxide as a starting point. Here, the internal oxidation type amorphous oxide film is an amorphous oxide film in a state where an amorphous oxide is trapped inside a steel sheet at an interface between the steel sheet and the amorphous oxide, and an amorphous oxide in which a ratio of a length of a depth direction of a trapping portion to a length of a bottom side of the trapping portion, that is, an aspect ratio is 1.2 or more is defined as an internal oxidation type amorphous oxide.

The composition (chemical composition) of the steel sheet for forming the amorphous oxide coating of the electrical steel sheet of the present embodiment is not particularly limited, since the composition of the steel sheet (base steel sheet) does not directly affect the glossiness of the steel sheet surface. However, when the amorphous oxide film and/or the tensile insulating film are formed on the surface to obtain preferable properties as a grain-oriented electrical steel sheet, the following range is preferable. Hereinafter, "%" relating to the component composition means "% by mass".

C: less than 0.085%

C is an element that significantly deteriorates the iron loss characteristics by magnetic aging. If the C content exceeds 0.085%, C remains even after decarburization annealing, and the iron loss characteristics deteriorate. Therefore, the C content is set to 0.085% or less. The smaller the amount of C, the more preferable the iron loss characteristics, but the detection limit is about 0.0001%, so 0.0001% is a substantial lower limit of the C content. From the viewpoint of improving the iron loss characteristics, the C content is preferably 0.010% or less, and more preferably 0.005% or less.

Si：0.80～7.00％

Si is an element contributing to improvement of magnetic characteristics. When the Si content is less than 0.80%, the steel undergoes phase transition during secondary recrystallization annealing, secondary recrystallization cannot be controlled, and good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, the Si content is set to 0.80% or more. Preferably 2.50% or more, more preferably 3.00% or more.

On the other hand, if the Si content exceeds 7.00%, the steel sheet becomes brittle, and the pass-through property in the production process is significantly deteriorated. Therefore, the Si content is set to 7.00% or less. Preferably 4.00% or less, more preferably 3.75% or less.

Mn: 1.00% or less

If the Mn content exceeds 1.00%, the steel undergoes phase transformation during secondary recrystallization annealing, and good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, the Mn content is set to 1.00% or less. Preferably 0.70% or less, more preferably 0.50% or less. The Al content may be 0%.

On the other hand, Mn is an austenite formation promoting element. If the Mn content is less than 0.01%, the effect cannot be sufficiently obtained, and the steel sheet becomes brittle during hot rolling. Therefore, the Mn content may be set to 0.01% or more. Preferably 0.05% or more, more preferably 0.10% or more.

Al: less than 0.065%

If the Al content exceeds 0.065%, the steel sheet becomes brittle and AlN is unevenly precipitated. As a result, a desired secondary recrystallized structure cannot be obtained, and the magnetic flux density is reduced. Therefore, the Al content is set to 0.065% or less. Preferably 0.060% or less, more preferably 0.055% or less. The Al content may be 0%.

On the other hand, Al is an element that contributes to the improvement of magnetic properties by forming AlN that functions as an inhibitor. Therefore, when the Al content in the slab used for production is less than 0.010%, the amount of AlN produced is small, and secondary recrystallization does not sufficiently proceed. Therefore, the content of Al in the slab used for manufacturing is preferably set to 0.010% or more, and this Al may remain in the steel sheet.

S: less than 0.013%

S is an element that forms fine sulfides and deteriorates the iron loss characteristics. The smaller the amount of S, the more preferable, but the detection limit is about 0.0001%, and therefore the S content may be set to 0.0001% or more. More preferably 0.003% or more, and still more preferably 0.005% or more.

On the other hand, if the S content exceeds 0.013%, the iron loss characteristics are significantly reduced. Therefore, the S content is set to 0.013% or less. Preferably 0.010% or less, more preferably 0.005% or less.

The electromagnetic steel sheet of the present embodiment basically contains Fe and impurities as the remainder other than the above elements, but may contain Cu in the following range in order to improve magnetic properties in addition to the above elements. Since Cu is not always contained, the lower limit is 0%.

Cu：0～0.80％

Cu is an element that bonds with S to form precipitates that function as inhibitors. When the Cu content is less than 0.01%, the effect of containing Cu cannot be sufficiently obtained, and therefore, when the effect is obtained, the Cu content is preferably set to 0.01% or more. More preferably 0.04% or more, and still more preferably 0.08% or more.

On the other hand, if the Cu content exceeds 0.80%, the precipitates are unevenly dispersed, and the iron loss reduction effect is saturated. Therefore, even when Cu is contained, the Cu content is set to 0.80% or less. Preferably 0.60% or less, more preferably 0.50% or less.

The above-described composition may contain 1 or 2 or more of N, P, Ni, Sn, and Sb in the following ranges within ranges not impairing the properties of the electrical steel sheet of the present embodiment. Since these elements are not always contained, the lower limit thereof is 0%.

N：0～0.012％

N is an element that forms AlN functioning as an inhibitor. When the N content is less than 0.004%, AlN formation becomes insufficient, and therefore, in order to obtain the above-described effects, the N content is preferably set to 0.004% or more. More preferably 0.006% or more, and still more preferably 0.007% or more.

On the other hand, N is also an element that forms blisters (voids) in the steel sheet at the time of cold rolling. If the N content exceeds 0.012%, blisters (voids) may be formed in the steel sheet during cold rolling, and therefore even if N is contained, the N content is set to 0.012% or less. The N content is preferably 0.010% or less, and more preferably 0.009% or less.

P：0～0.50％

P is an element that increases the specific resistance of the steel sheet and contributes to the reduction of the iron loss. In the case where the effect of containing P is surely obtained, the content of P is preferably set to 0.02% or more.

On the other hand, if the P content exceeds 0.50%, the rolling property is lowered. Therefore, even when P is contained, the content of P is set to 0.50% or less. Preferably 0.35% or less.

Ni：0～1.00％

Ni is an element that increases the specific resistance of the steel sheet, contributes to a reduction in iron loss, controls the metal structure of the hot-rolled steel sheet, and contributes to an improvement in magnetic properties. In the case where the effect of Ni content is surely obtained, the Ni content is preferably set to 0.02% or more.

On the other hand, if the Ni content exceeds 1.00%, secondary recrystallization does not proceed stably. Therefore, even when Ni is contained, Ni is set to 1.00% or less. The Ni content is preferably 0.25% or less.

Sn：0～0.30％

Sb：0～0.30％

Sn and Sb are elements that segregate in crystal grain boundaries and have the effect of preventing Al from being oxidized by moisture released from the annealing separator during the final annealing (due to this oxidation, the strength of the inhibitor varies at the coil position, and the magnetic properties vary). In the case where the effects of containing them are surely obtained, it is preferable that the content of any element is 0.02% or more.

On the other hand, if the content of any element exceeds 0.30%, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, the content of both Sn and Sb is set to 0.30% or less. Preferably, any element is 0.25% or less.

That is, the electrical steel sheet of the present embodiment contains the above elements, and the remainder contains Fe and impurities.

A steel sheet having such a composition can be obtained by manufacturing using a slab containing C: 0.085% or less, Si: 0.80 to 7.00%, Mn: 0.01 to 1.00%, Al: 0.010-0.065%, S: 0.001 to 0.013%, Cu: 0-0.01-0.80%, N: 0-0.012%, P: 0-0.50%, Ni: 0-1.00%, Sn: 0-0.30%, Sb: 0-0.30%, and the balance of Fe and impurities.

Next, a preferred method for manufacturing an electrical steel sheet according to the present embodiment will be described.

A molten steel adjusted to a desired composition is cast by a usual method (for example, continuous casting) to produce a slab for producing a grain-oriented electrical steel sheet. Next, the slab is subjected to normal hot rolling to produce a hot-rolled steel sheet, and the hot-rolled steel sheet is wound to produce a hot-rolled coil. Next, the hot-rolled coil was uncoiled, hot-rolled sheet annealing was performed, and then, 1-time cold rolling or multiple cold rolling with intermediate annealing interposed was performed to produce a steel sheet having the same thickness as that of the final product. The cold-rolled steel sheet is subjected to decarburization annealing.

The decarburization annealing is preferably performed by heating in a wet hydrogen atmosphere. By performing decarburization annealing in the above atmosphere, the C content in the steel sheet can be reduced to a region where deterioration of magnetic properties due to magnetic aging does not occur in the product steel sheet, and primary recrystallization can be performed. This primary recrystallization becomes a preparation for secondary recrystallization.

After the decarburization annealing, the steel sheet is annealed in an ammonia atmosphere to form an AlN inhibitor in the steel sheet.

Next, the steel sheet is subjected to finish annealing at a temperature of 1100 ℃ or higher. The final annealing may be performed in the form of a coil after coiling the steel sheet, but for the purpose of preventing the steel sheet from being sintered, Al is applied to the surface of the steel sheet₂O₃The annealing separating agent as the main component is then subjected to final annealing.

After the end of the final annealing, the excess annealing separator was removed from the steel sheet using a washer, and the surface state of the steel sheet was controlled. When the removal of the excess annealing separator is performed, it is preferable to perform a treatment using a scrubber and perform water washing.

The washer preferably has a brush with a yarn diameter of 0.2mm to 0.6 mm. When the brush has a yarn diameter of more than 0.6mm, the surface of the steel sheet becomes rough (roughness becomes large), and the glossiness after the amorphous oxide film is formed is lowered, which is not preferable. On the other hand, if the brush has a yarn diameter of less than 0.2mm, the removal of the excess annealing separator becomes insufficient, and the glossiness after the amorphous oxide film is formed is undesirably reduced.

The surface roughness (arithmetic mean Ra of JISB 0601) of the steel sheet after the annealing separator is removed by the washer is preferably set to about 0.2 to 0.6 μm.

Then, the oxygen partial pressure (P) was adjusted for the steel sheet_H2O/P_H2) And annealing is performed in a mixed atmosphere of hydrogen and nitrogen to form an amorphous oxide film on the surface of the steel sheet.

As described above, the glossiness of the surface (uniformity due to the morphology of the amorphous oxide film) affects the residual area ratio of the film (an index indicating the quality of the film adhesion of the tensile insulating film). The inventors of the present invention set the oxygen partial pressure (P) of the annealing atmosphere in forming the amorphous oxide film in the final annealed steel sheet_H2O/P_H2) Changes the oxygen partial pressure (P) to the annealing atmosphere_H2O/P_H2) The relationship with the gloss was investigated.

Fig. 2 shows the relationship between the oxygen partial pressure and the glossiness in the annealing atmosphere in which the obtained amorphous oxide film was formed, and in fig. 2, the case where the residual area ratio of the film was 90% or more is represented by "○", the case where the residual area ratio of the film was 80% or more and less than 90% is represented by "△", and the case where the residual area ratio of the film was less than 80% is represented by "x" in the evaluation of the film adhesion.

As can be seen from fig. 2: oxygen partial pressure (P) of annealing atmosphere in which amorphous oxide film having a glossiness of 150% or more is formed_H2O/P_H2) 0.010 or less; oxygen partial pressure (P) of annealing atmosphere capable of forming amorphous oxide film having glossiness of 230% or more_H2O/P_H2) 0.005 or less; and then toAn oxygen partial pressure (P) of an annealing atmosphere in which an amorphous oxide film having a surface gloss of 250% or more can be formed_H2O/P_H2) Is 0.001 or less.

Therefore, when the electrical steel sheet of the present embodiment is obtained, the oxygen partial pressure (P) of the annealing atmosphere in which the amorphous oxide film is formed_H2O/P_H2) Preferably 0.010 or less, more preferably 0.005 or less, and still more preferably 0.001 or less.

In the annealing for forming the amorphous oxide film, the annealing temperature is preferably 600 to 1150 ℃, and more preferably 700 to 900 ℃.

When the annealing temperature is lower than 600 ℃, an amorphous oxide film is not sufficiently formed. Further, when the annealing temperature exceeds 1150 ℃, the equipment load becomes high, which is not preferable.

In the annealing for forming the amorphous oxide film, the cooling rate after the annealing may be not limited, but in order to control the morphology of the external oxidation type amorphous oxide film so that the aspect ratio of the amorphous oxide is less than 1.2, the oxygen partial pressure (P) at the time of annealing cooling is preferably controlled so as to be uniform_H2O/P_H2) The content is set to 0.005 or less.

As described above, a grain-oriented electrical steel sheet with an amorphous oxide coating having excellent coating adhesion of a tensile insulating coating can be obtained.