JP2002348643A - Unidirectional silicon steel sheet excellent in film adhesion of tension imparting insulating film and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide a unidirectional silicon steel sheet having good adhesion of a tension imparting insulating film to a finish-annealed unidirectional silicon steel sheet having no inorganic mineral film on the surface of the steel sheet. SOLUTION: An external oxidation type mainly composed of silica having a film thickness of 2 nm or more and 500 nm or less and a cross-sectional area ratio of a metal oxide of 50% or less between a tension imparting insulating film and a finish-annealed unidirectional silicon steel sheet. A unidirectional silicon steel sheet excellent in film adhesion of a tension imparting insulating film for forming an oxide film and a method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing an inorganic mineral substance film composed of forsterite (Mg ₂ SiO ₄ ) or the like by intentionally preventing the formation of the film or by means of grinding or pickling. Removed, or even finish-annealed unidirectional silicon steel sheet prepared by flattening the surface until it has a specular gloss, and a unidirectional silicon steel sheet with a tension imparting insulating film formed The present invention relates to a method for forming the insulating film.

[0002]

2. Description of the Related Art A grain-oriented silicon steel sheet is frequently used as a magnetic iron core material. In particular, a material having a small iron loss is required to reduce energy loss. It is effective to apply tension to the steel sheet to reduce iron loss, so by forming a film made of a material having a smaller coefficient of thermal expansion at a high temperature compared to the steel sheet, the tension is applied to the steel sheet to reduce iron loss. It has been planned. The forsterite-based coating formed by the reaction between the oxide on the steel sheet surface and the annealing separator in the finish annealing step can give tension to the steel sheet and has excellent coating adhesion.

For example, a method of forming an insulating film by applying a coating liquid mainly composed of colloidal silica and phosphate to a steel sheet surface and baking the coating liquid disclosed in Japanese Patent Application Laid-Open No. 48-39338 is disclosed in The effect of applying tension to the steel sheet is great, and is effective in reducing iron loss. Therefore, it is a general method for producing a unidirectional silicon steel sheet to form an insulating film mainly composed of phosphate while leaving the forsterite-based film generated in the finish annealing step.

In recent years, it has become clear that the disordered interface structure between the forsterite-based film and the ground iron has reduced the effect of improving iron loss due to the film tension to some extent. Therefore,
For example, as disclosed in Japanese Patent Application Laid-Open No. 49-96920, the forsterite-based film generated in the final annealing step is removed, or after a mirror finish is performed, a tension film is formed again to further improve the strength. Technology to reduce iron loss has been developed.

[0005] However, when the above-mentioned insulating film is formed on a film mainly composed of forsterite, considerable adhesion can be obtained, but the forsterite-based film is removed, or the insulating film is intentionally formed in the final annealing step. The film adhesion is not sufficient for the one without stellite formation. When the forsterite-based film is removed, it is necessary to secure a required film tension only with a tension-applying insulating film formed by applying a coating liquid, and the film must be thickened inevitably. Further adhesion is required. Therefore, the conventional film forming method achieves a film tension enough to bring out the effect of mirror finishing,
In addition, it is difficult to secure film adhesion, and a sufficient reduction in iron loss has not been achieved. Therefore, as a technique for securing the adhesion of the tension-imparting insulating film, prior to the formation of the tension-imparting insulating film, a method of forming an oxide film on the surface of a finish-annealed unidirectional silicon steel sheet, for example,
JP-A-60-131976, JP-A-6-1847
No. 62, JP-A-7-278833, JP-A-8
Japanese Patent Application Laid-Open No. 191010 and Japanese Patent Application Laid-Open No. 9-078252.

[0006] The technique disclosed in Japanese Patent Application Laid-Open No. 60-131976 is a method in which a finish-annealed unidirectional silicon steel sheet is mirror-finished and then internally oxidized in the vicinity of the steel sheet surface. This is a method in which internal adhesion, that is, iron loss deterioration caused by a decrease in specularity, is supplemented by an increase in applied tension caused by improved film adhesion.

Further, the technique disclosed in Japanese Patent Application Laid-Open No. 6-184762 discloses that a finish-annealed unidirectional silicon steel sheet which has been mirror-finished or adjusted to a state close to mirror finish is annealed in a specific atmosphere for each temperature. In this method, an external oxidation type oxide film is formed on the surface of the steel sheet, and the oxide film is used to secure adhesion between the film of the tension imparting insulating film and the steel sheet.

[0008] Further, the technique disclosed in Japanese Patent Application Laid-Open No. 7-278833 discloses a method in which a surface of a finish-annealed unidirectional silicon steel sheet without an inorganic mineral substance film is used when the tension-imparting insulating film is crystalline. This is a technique for preventing oxidation of a steel sheet, that is, a decrease in specularity, which occurs when a crystalline tension-imparting insulating film is formed by forming an amorphous oxide base film on the substrate.

The technique disclosed in Japanese Patent Application Laid-Open No. Hei 8-191010 discloses a method of forming a crystal of firelite by forming a crystallite firelite on the surface of a finish-annealed unidirectional silicon steel sheet from which nonmetallic substances have been removed. This is a method for reducing iron loss by the effect of applying tension and the effect of improving the adhesion to an insulating film having a tension-imparting property. Further, JP-A-9-07825
The technique disclosed in Japanese Patent Publication No. 2 (2003) discloses a method of securing the adhesion of a tension coating by setting the amount of a base silica layer formed on the surface of a finish-annealed unidirectional silicon steel sheet having no inorganic mineral substance coating to 100 mg / m2 or less. Not only that, but also a method of realizing a good iron loss value.

[0010]

SUMMARY OF THE INVENTION By applying the above technique,
By forming an oxide film on the surface of a grain-oriented silicon steel sheet free of inorganic minerals, the effect of improving the film adhesion and reducing the iron loss value is recognized as such, but the film adhesion of the tension imparting insulating film is not necessarily perfect. However, it was difficult to stably obtain a unidirectional silicon steel sheet with low iron loss.

[0011]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and provides a tensile strength so that a sufficient coating adhesion can be obtained with a finish-annealed unidirectional silicon steel sheet having no inorganic mineral substance coating. This is a unidirectional silicon steel sheet on which an application-type insulating film is formed. The gist of the present invention is as follows.

(1) A unidirectional silicon steel sheet having a tension imparting insulating film formed on the surface of a steel sheet substantially free of a finish annealing film, wherein a film is formed at an interface between the tension imparting insulating film and the steel sheet. A silica-based material having a thickness of 2 nm or more and 500 nm or less, and in which an oxide composed of one or more elements selected from iron, aluminum, titanium, manganese, and chromium accounts for 50% or less in cross-sectional area ratio. A unidirectional silicon steel sheet having an excellent adhesion to a tension imparting insulating film characterized by having an external oxidation type oxide film.

(2) A tension imparting insulating material is applied to the surface of a finish-annealed unidirectional silicon steel sheet manufactured by removing an inorganic mineral film such as forsterite by means of pickling or intentionally preventing the formation thereof. Prior to the formation of the film, the steel sheet was heated at a temperature rising rate of 200 ° C. or more and 1150 ° C. or less at a heating rate of 10 ° C.
An oxide which is heated at a temperature of not less than 500 ° C./sec and not more than 500 ° C./sec, has a film thickness of not less than 2 nm and not more than 500 nm, and is composed of one or more elements selected from iron, aluminum, titanium, manganese and chromium Forming an external oxidized oxide film mainly composed of silica occupying 50% or less in terms of a sectional area ratio at an interface between the tension-imparting insulating film and the steel sheet. Method for forming an insulating film on a unidirectional silicon steel sheet that is excellent in quality.

(3) The above-mentioned (1) or (1), wherein the tension-imparting insulating film is a tension-imparting insulating film formed by baking a coating solution mainly composed of phosphate and colloidal silica. 2) A unidirectional silicon steel sheet having excellent film adhesion of the tension-imparting insulating film described in the above. (4) The tension-imparting insulating film according to the above (1) or (2), wherein the tension-imparting insulating film is a tension-imparting insulating film formed by baking an application solution mainly composed of alumina sol and boric acid. Unidirectional silicon steel sheet with excellent film adhesion of insulating film.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. The inventors have found that the cause of the film adhesion is not always perfect is the condition for forming the external oxidized oxide film, particularly, the temperature rising rate in the temperature rising region. It is presumed that the adhesion of the insulating film having a tension may fluctuate due to the difference.
Therefore, the following experiment was conducted to examine the relationship between the temperature increase rate with respect to the film adhesion and the external oxidation type oxide film structure.

As an experimental material, a decarburized annealed plate having a thickness of 0.225 mm is coated with an annealing separator mainly composed of alumina, subjected to finish annealing, secondary recrystallized, and has a unidirectional mirror gloss. A silicon steel sheet was prepared. The steel sheet is subjected to a heat treatment in an atmosphere of 25% nitrogen, 75% hydrogen and a dew point of -2 ° C for a soaking time of 15 seconds and at various temperatures and heating rates, and an external oxidation mainly comprising silica is carried out. A type oxide film was formed. Next, in order to form a tension-imparting insulating film, a coating solution mainly composed of aluminum phosphate, chromic acid, and colloidal silica was applied, and baked at 835 ° C. for 30 seconds in a nitrogen atmosphere. The steel sheet thus produced was examined for film adhesion.

The film adhesion is defined as an area ratio of a portion where the film did not peel off when the sample was wound around a cylinder having a diameter of 20 mm and the steel film and the film remained in close contact (hereinafter referred to as a film remaining area ratio). evaluated. When the adhesion was poor and the film was completely peeled, it was judged as 0%, and when the film adhesion was good and the film was not peeled at all, it was judged as 100%. The evaluation was x when the film remaining area ratio was 90% or less, ○ when 91 to 95%, and ◎ when 96 to 100%.

Further, in order to examine the interface structure between the steel plate and the tension-imparting insulating film including the external oxidation type oxide film, a thin section sample was prepared by a focused ion beam method (FIB method).
The cross-sectional structure was observed with a transmission electron microscope (TEM). As a result of the cross-sectional observation, an oxide composed of one or more of iron, aluminum, titanium, manganese, and chromium (for example, Si—Mn—Cr oxide) Material, Si-Mn-Cr-Al
—Ti oxide, Fe oxide, etc., which are hereinafter collectively referred to as metal oxides. ) Was partially observed. The cross-sectional area ratio of this metal-based oxide in the silica-based external oxidation-type oxide film was calculated from a TEM photograph.

Table 1 shows the results of the investigation. 1 and 2 show cross-sectional observation images of the sample of sample number 23 and the sample of sample number 30 as an example of the cross-sectional observation result.

[0020]

[Table 1]

From Table 1, conditions for securing the adhesion of the tension-imparting insulating film are obtained as follows. First, regardless of the cross-sectional area ratio of the metal-based oxide, the film adhesion cannot be ensured under the conditions of the heat treatment temperature of 500 ° C. in Sample Nos. 1 to 4 in which the thickness of the external oxidation type oxide film is less than 2 nm.
On the other hand, the heat treatment temperature of Sample No. 5 to Sample No. 40 in which the film thickness of the external oxidation type oxide film is 2 nm or more is 600 ° C. to 115 °
Under the condition of 0 ° C., film adhesion can be generally secured. In particular, the heat treatment temperature at which the film thickness of the external oxidized oxide film of Sample Nos. 26 to 40 is 40 nm or more is 1
Under conditions of 000 ° C. or higher, the film adhesion is remarkably good. However, the heating rate in the heating zone is 10 ° C./sec or more and 500 ° C.
When the cross-sectional area ratio of the metal-based oxide in the external oxidation type oxide film is 50% or less at a rate of 5% / second or less, the film adhesion is good. Under the condition that the sectional area ratio of the oxide is larger than 50%, even if the thickness of the external oxidation type oxide film is large, the film adhesion is not always perfect, and the film remaining area ratio is 90% or less. Further, when the heating rate is 50 ° C./sec or more and 500 ° C./sec or less, the cross-sectional area ratio of the metal oxide in the external oxidation type oxide film is 30% or less, and the film remaining area ratio is 96% or less. % Or more,
Film adhesion is even better.

As can be seen from Table 1, in the present invention, in order to secure the film adhesion of the tension-imparting insulating film, the thickness of the external oxidized oxide film is 2 nm or more and the metal occupying the external oxidized oxide film is It is essential that the cross-sectional area ratio of the system oxide is not more than 50%.
The heating rate in the heating zone of 150 ° C or less is 10 ° C / sec or more and 50
It is understood that the temperature needs to be set to 0 ° C./second or less. When further film adhesion is required, the cross-sectional area ratio of the metal oxide in the external oxidation type oxide film is desirably 30% or less. In order to form such an external oxidation type oxide film, In the heat treatment step, it is desirable that the heat treatment is performed at a temperature of 600 ° C. or more, particularly preferably 1000 ° C. or more, and that the rate of temperature rise in the temperature rise region is 20 ° C./sec or more and 500 ° C./sec or less. The upper limit of the heating rate is not clear at present.

The inventors of the present invention consider the mechanism as follows regarding the fact that the film thickness of the external oxidation type oxide film and the cross-sectional area ratio occupied by the metal oxide greatly affect the film adhesion. I have. First, the thickness dependency of the external oxidation type oxide film will be described. The adhesion between the steel sheet and the tension-imparting insulating film is determined by the external oxidation type oxide film formed at the interface between the two. It is generally said that an external oxidation type oxide film grows when metal atoms diffuse from the steel to the surface and react with the oxidizing gas on the surface. Therefore, the growth rate of the oxide film is determined by the diffusion rate of atoms. Atomic diffusion is enhanced by thermal energy. Therefore, the higher the temperature is, the more the diffusion of atoms is promoted, and the external oxidation type oxide film grows more. Due to such a mechanism, when the heat treatment temperature is as low as 500 ° C., the growth of the external oxidation type oxide film is not sufficient.
Film adhesion is not enough, while heat treatment temperature is 600
It is considered that when the temperature is not lower than ° C, the external oxidation type oxide film grows sufficiently and the film adhesion is good, and when the temperature is higher than 1000 ° C, the oxide film grows more easily and the film adhesion is considered to be extremely good.

It can be seen from the results of the measurement of the thickness of the external oxidation type oxide film using a transmission electron microscope that the above assumption is appropriate. That is, when the film thickness is 1 nm, the growth of the external oxidized oxide film is not sufficient, and when the heat treatment temperature is 500 ° C., the adhesion of the tension imparting type insulating film is poor.
When the heat treatment temperature is 600 ° C. or more, the film adhesion is good when the external oxidation type oxide film has grown to a thickness of at least nm.

Next, the relationship between the adhesion of the tension-imparting insulating film and the metal oxide present in the external oxidation type oxide film will be described. The details of the mechanism of the formation of the metal-based oxide in the external oxidation type oxide film are not yet clear, but at present, the present inventors consider as follows. First, when the heating rate in the heating zone is slow, the staying time in the low temperature zone becomes longer as viewed from the steel sheet subjected to the heat treatment. Therefore, not only Si but also Fe, Mn, Cr, Al,
Elements other than Si, such as Ti, are also oxidized. afterwards,
After reaching the soaking temperature, an oxide film mainly composed of silica is formed. At this time, the metal oxide generated during the temperature rise is left in the silica film.

On the other hand, when the heating rate in the heating zone is high, the staying time in the low temperature zone becomes short, so that Fe, Mn, C
Elements such as r, Al, and Ti are not oxidized. as a result,
Even if an oxide film mainly composed of silica is formed after the temperature reaches the soaking temperature, the metal oxide is not included in the oxide film. Next, the relationship between the adhesion of the tension imparting insulating film to the steel sheet and the external oxidation type oxide film structure will be described.

The application of tension to the steel sheet by the tension-imparting insulating film is caused by a difference in thermal expansion coefficient between the tension-imparting insulating film and the steel sheet. At this time, a great deal of stress is generated at the interface between the tension imparting insulating film and the steel sheet. Withstand this stress,
The external oxidation type oxide film ensures the adhesion between the steel sheet and the tension-imparting insulating film. The present inventors speculate that the ratio of the metal-based oxide, which is a kind of defective portion, in the external oxidation-type oxide film may affect the stress resistance. In other words, when the amount of the metal oxide is small and the cross-sectional area ratio is 50% or less, it can withstand the stress, but when the amount of the metal oxide is large and the cross-sectional area ratio is more than 50%, the external oxidation type oxide film is formed. However, it is considered that the stress applied by the tension-imparting insulating film cannot withstand and the external oxidation type oxide film may be destroyed.

[0028]

<Example 1> Sheet thickness 0.225 mm, Si:
A cold rolled sheet for producing a unidirectional silicon steel sheet of 3.35% by mass was decarburized and annealed, and a water slurry of an annealing separator mainly composed of magnesia and bismuth chloride was applied to the surface and dried. Then, in a dry hydrogen atmosphere, finish annealing was performed at 1200 ° C. for 20 hours to obtain a unidirectional silicon steel sheet which had been subjected to secondary recrystallization and had almost no inorganic minerals on its surface. For this steel plate,
By performing heat treatment at a temperature of 1150 ° C. in an atmosphere of nitrogen 25%, hydrogen 75% and a dew point of −20 ° C., an external oxidation type oxide film mainly composed of silica was formed. At this time, the heating was performed under two conditions of a heating rate of 65 ° C./sec (Example) and 8 ° C./sec (Comparative Example). 50 ml of a 50% magnesium phosphate aqueous solution, 20% concentration
Of a colloidal silica aqueous dispersion (100 ml) and 5 g of chromic anhydride were applied and baked at 850 ° C. for 30 seconds to form a tension-imparting insulating film.

The adhesion of the insulating film to the thus-prepared unidirectional silicon steel sheet with the insulating film was evaluated based on the film remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm.
Table 2 shows the results.

[0030]

[Table 2]

From Table 2, the heating rate was 65 ° C./sec. In the examples in which the cross-sectional area ratio is 10% and the film remaining area ratio is 100%, the film adhesion is excellent and excellent. Example 2 A cold rolled sheet for producing a unidirectional silicon steel sheet having a thickness of 0.225 mm and Si of 3.25 mass% is subjected to decarburizing annealing, and a water slurry of an annealing separator mainly composed of alumina is provided on the surface. -Was applied and dried. Then, in a dry hydrogen atmosphere, 12
Finish annealing was performed at 00 ° C. for 20 hours to obtain a unidirectional silicon steel sheet which had almost no inorganic minerals on the surface and had a secondary recrystallization having a mirror gloss. Nitrogen 25
%, Hydrogen 75%, dew point -15 ° C, temperature 800
An external oxidation type oxide film was formed by performing a heat treatment at ℃. At this time, the heating rate in the heating area was 35 ° C./sec (Example)
And 4 ° C./sec (comparative example). A mixture of 50 ml of a 50% aluminum phosphate aqueous solution, 100 ml of a 20% concentration aqueous dispersion of colloidal silica, and 5 g of chromic anhydride was applied to the steel sheet thus prepared, and baked at 850 ° C. for 30 seconds to give tension. Was formed.

With respect to the thus-prepared unidirectional silicon steel sheet with an insulating film, the film adhesion was evaluated based on the film remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm. Table 3 shows the results.

[0033]

[Table 3]

Table 3 shows that the rate of temperature rise was 35 ° C./sec compared to the comparative example in which the rate of temperature rise was 4 ° C./sec, the sectional area ratio of the metal oxide was 55%, and the area ratio of the remaining film was 90%. In Examples where the cross-sectional area ratio is 15% and the film remaining area ratio is 100%, the film adhesion is excellent and excellent. Example 3 A cold rolled sheet for producing a unidirectional silicon steel sheet having a thickness of 0.225 mm and Si of 3.30% by mass was subjected to decarburizing annealing, and then the surface oxide layer was mixed with ammonium fluoride and sulfuric acid. It was pickled in the solution and dissolved and removed. Then, alumina powder was applied by an electrostatic coating method, and finish annealing was performed at 1200 ° C. for 20 hours in a dry hydrogen atmosphere. The surface of the thus-prepared unidirectional silicon steel sheet after the completion of the secondary recrystallization is free of inorganic minerals and has a mirror gloss. Nitrogen 25
%, Hydrogen 75%, dew point -5 ° C, temperature 900 ° C
An external oxidation type oxide film was formed by performing a heat treatment in the above. At this time, the heating rate in the heating area was 90 ° C./sec (Example)
And 7 ° C./sec (comparative example). A mixture of 50 ml of a 50% magnesium phosphate aqueous solution / aluminum solution, 66 ml of an aqueous dispersion of colloidal silica having a concentration of 30%, and 5 g of chromic anhydride was applied to the steel sheet thus prepared, and baked at 850 ° C. for 30 seconds. An imparting insulating film was formed.

With respect to the thus-prepared unidirectional silicon steel sheet with an insulating film, the film adhesion was evaluated based on the film remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm. Table 4 shows the results.

[0036]

[Table 4]

As shown in Table 4, the heating rate was 7 ° C./sec, the heating rate was 90 ° C./sec, and the metal oxide was 90 ° C./sec. In the examples in which the cross-sectional area ratio is 5% and the film remaining area ratio is 100%, the film adhesion is excellent and excellent. <Example 4> Plate thickness 0.23 mm, Si: 3.30 mass%
Decarburizing annealing of cold rolled sheet for producing unidirectional silicon steel sheet,
Water slurry of magnesia-based annealing separator on the surface
And dried, and then dried in a dry hydrogen atmosphere at 1200
Finish annealing was performed at 20 ° C. for 20 hours. A film mainly composed of forsterite is formed on the surface of the thus-prepared unidirectional silicon steel sheet after the secondary recrystallization. Then, after pickling in a mixed solution of ammonium fluoride and sulfuric acid, dissolving and removing the surface film, and chemically polishing in a mixed solution of hydrofluoric acid and hydrogen peroxide, the steel sheet surface has no inorganic minerals, and A steel plate having a specular gloss was obtained. Nitrogen 2
5%, 75% hydrogen, dew point 0 ° C, temperature 1050
An external oxidation type oxide film was formed by performing a heat treatment at ℃. At this time, the heating was performed under two conditions of a heating rate of 250 ° C./sec (Example) and 6 ° C./sec (Comparative Example). A mixture of 100 ml of a 10% concentration aqueous colloidal alumina dispersion, 10 g of amorphous alumina powder, 5 g of boric acid, and 200 ml of water was applied to the steel sheet thus prepared,
Baking was performed at 0 ° C. for 30 seconds to form a tension-imparting insulating film.

With respect to the thus-prepared unidirectional silicon steel sheet provided with an insulating film, the film adhesion was evaluated by the film remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm. Table 5 shows the results.

[0039]

[Table 5]

As shown in Table 5, the temperature rise rate was 6 ° C./sec and the metal oxide was 6 ° C./sec compared with the comparative example in which the rate of temperature rise was 250 ° C./sec, the cross-sectional area ratio of the metal oxide was 55%, and the area ratio of the remaining film was 90%. Examples having a cross-sectional area ratio of 10% and a film remaining area ratio of 100% have better and better film adhesion.

[0041]

According to the present invention, a unidirectional silicon steel sheet having good film adhesion can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional TEM observation image of a sample of Sample No. 23 (Table 1) according to the present invention.

FIG. 2 is a view showing a cross-sectional TEM observation image of a sample of Sample No. 30 (Table 1) according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kenichi Murakami 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Yoshiyuki Ushigami 20 Shintomi, Futtsu-shi, Chiba -1 Nippon Steel Corporation Technology Development Division (72) Inventor Shuichi Nakamura 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (72) Inventor Masaaki Sugiyama 20 Shintomi, Futtsu City, Chiba Prefecture -1 F-term in Nippon Steel Corporation Technology Development Division (Reference) 4K026 AA03 BA01 BA03 BA07 BB10 CA16 CA18 CA21 CA23 CA41 DA02 EA07 EA17 EB11 4K033 AA02 GA00 LA01 MA01 MA02 TA01 TA04

Claims (4)

[Claims] 1. A unidirectional silicon steel sheet having a tension imparting insulating film formed on a steel sheet surface substantially free of a finish annealing film, wherein a film thickness is formed at an interface between the tension imparting insulating film and the steel sheet. Is not less than 2 nm and not more than 500 nm, and is selected from iron, aluminum, titanium, manganese, and chromium.
The tension-imparting insulating film is excellent in film adhesion, characterized in that it has an external oxidized oxide film mainly composed of silica in which an oxide composed of one or more kinds of elements occupies 50% or less in cross-sectional area ratio. Unidirectional silicon steel sheet. 2. A tension-imparting insulating film on a surface of a finish-annealed unidirectional silicon steel sheet manufactured by removing an inorganic mineral material film such as forsterite by means of pickling or intentionally preventing the formation thereof. Prior to the formation of
The heating rate is 10 ° C /
Heating at a temperature of at least 500 ° C./sec.
External oxidation mainly composed of silica whose oxide is composed of one or more elements selected from iron, aluminum, titanium, manganese, and chromium in an area of not more than 50% in terms of a sectional area ratio of not more than 00 nm. A method for forming an insulating film on a unidirectional silicon steel sheet having excellent adhesion to a steel sheet of a tension applying insulating film, wherein a mold oxide film is formed at an interface between the tension applying insulating film and the steel sheet. 3. The tension imparting insulating film according to claim 1, wherein the tension imparting insulating film is a tension imparting insulating film formed by baking a coating solution mainly composed of phosphate and colloidal silica. Unidirectional silicon steel sheet with excellent film adhesion of tension imparting insulating film. 4. The tension-imparting insulating film according to claim 1, wherein the tension-imparting insulating film is a tension-imparting insulating film formed by baking a coating solution mainly composed of alumina sol and boric acid. Unidirectional silicon steel sheet with excellent film adhesion.