JP2003293149A - Grain-oriented silicon steel sheet with excellent adhesion to tension-imparting insulation film, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a finish-annealed grain-oriented silicon steel sheet free from an inorganic mineral film on the surface of the steel sheet and having excellent adhesion to a tension-imparting insulation film. <P>SOLUTION: An external oxidation type oxide film having 2 to 500 nm film thickness and ≤30% proportion of a low density layer and composed essentially of silica is formed between the tension-imparting insulation film and the finish- annealed grain-oriented silicon steel sheet. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended for production by intentionally preventing the formation of an inorganic mineral film composed of forsterite (Mg ₂ SiO ₄ ) or the like, or means for grinding or pickling. Of the unidirectional silicon steel sheet which has been subjected to finish annealing and which has been prepared by removing it by the above method or further flattening the surface until it exhibits a mirror gloss, The present invention relates to a steel plate and a manufacturing method thereof.

[0002]

2. Description of the Related Art Unidirectional silicon steel sheets are widely used as magnetic iron core materials, and in particular, materials having a low iron loss are required to reduce energy loss. Since it is effective to apply tension to the steel sheet to reduce iron loss, tension is applied to the steel sheet by forming a film made of a material having a smaller coefficient of thermal expansion than the steel sheet at high temperature, which reduces iron loss. It has been planned.

The forsterite type coating formed by the reaction between the oxide on the surface of the steel sheet and the annealing separator in the finish annealing step can give tension to the steel sheet and has excellent coating adhesion. The method of forming an insulating film by applying the coating liquid containing colloidal silica and phosphate as a main component, which is disclosed in JP-A-48-39338, on the surface of the steel sheet and baking the coating solution has the effect of applying tension to the steel sheet. Large and effective in reducing iron loss.

Therefore, a general method for producing a unidirectional silicon steel sheet is to leave the forsterite film formed in the finish annealing step and then to form an insulating film mainly containing phosphate. .

In recent years, it has become clear that the disordered interface structure between the forsterite coating and the base iron reduces the iron loss improving effect due to the coating tension to some extent. Therefore,
For example, as disclosed in JP-A-49-96920, by removing the forsterite-based film generated in the finish annealing step, further performing mirror finishing, and then forming a tension film again, Has been developed.

[0006] However, although the above-mentioned insulating film exhibits a considerable adhesiveness when formed on a film mainly composed of forsterite, it is intended to remove the forsterite-based film or to be used in the finish annealing process. The film adhesion is not sufficient for those for which forsterite formation was not performed.

When the forsterite-based film is removed, it is necessary to secure the required film tension only with the tension-imparting insulating film formed by applying the coating liquid. It is necessary to further improve the adhesion. Therefore, the conventional film forming method achieves a film tension sufficient to bring out the effect of mirror-finishing,
At the same time, it is difficult to secure the film adhesion, and the iron loss has not been sufficiently reduced.

Therefore, as a technique for ensuring the adhesion of the tension-imparting insulating film, there is a method of forming an oxide film on the surface of the finish-annealed unidirectional silicon steel sheet prior to the formation of the tension-imparting insulating film. , For example, JP-A-60-131
976, JP-A-6-184762, JP-A-7-278833, JP-A-8-191010, and JP-A-9-078252.

Japanese Patent Laid-Open No. 60-131976 discloses a method in which a mirror-finished finish-annealed unidirectional silicon steel sheet is mirror-finished and then the surface of the steel sheet is internally oxidized. Improve the internal properties, internal oxidation,
That is, this is a method of compensating for the iron loss deterioration caused by the decrease in specularity by increasing the applied tension brought about by the improvement of the film adhesion.

Japanese Unexamined Patent Publication (Kokai) No. 6-184762 discloses that a finish-annealed unidirectional silicon steel sheet prepared to have a mirror-like finish or a state close to that is annealed in a specific atmosphere at each temperature to externally oxidize the steel sheet surface. This is a method of forming an oxide film of a mold and ensuring the film adhesion between the film of the tension-imparting insulating film and the steel sheet with this oxide film.

Japanese Unexamined Patent Publication (Kokai) No. 7-278833 discloses that when the tension-imparting insulating film is crystalline, an amorphous oxide is formed on the surface of the finish-annealed unidirectional silicon steel plate without the inorganic mineral film. This is a technique for preventing the steel sheet oxidation that occurs when the crystalline tension-imparting insulating film is formed, that is, the decrease in specularity, by forming the undercoating film.

Japanese Unexamined Patent Publication (Kokai) No. Hei 8-191010 discloses a method of forming a crystalline firelite on the surface of a finish-annealed unidirectional silicon steel sheet from which non-metallic substances have been removed, thereby providing a tensioning effect and a tensioning force by the firelite crystal. This is a method for reducing iron loss by the effect of improving the adhesiveness with a conductive insulating film.

Japanese Unexamined Patent Publication (Kokai) No. 9-078252 discloses that the amount of an underlying silica layer formed on the surface of a finish-annealed unidirectional silicon steel sheet having no inorganic mineral film is 100 mg / m ² or less, thereby forming a tension film. This is a method that not only ensures adhesion but also achieves a good iron loss value.

[0014]

Applying the above-mentioned technique,
It is recognized that forming an oxide film on the surface of a unidirectional silicon steel sheet free of inorganic minerals has the effect of improving the film adhesion and the effect of reducing the iron loss value. However, the film adhesion of the tension-imparting insulating film was not always perfect.

[0015]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a tension so that sufficient film adhesion can be obtained for a finish-annealed unidirectional silicon steel sheet without an inorganic mineral film. A unidirectional silicon steel sheet excellent in adhesion to a tension-imparting insulating film formed with an imparting type insulating film, and a method for producing the same.

The gist of the present invention is as follows.

(1) Unidirectional silicon having a tension imparting insulating film formed after the inorganic mineral film such as forsterite is removed by means such as pickling or intentionally prevented from producing. A steel sheet having an external oxidation type oxide film mainly composed of silica having a thickness of 2 nm or more and 500 nm or less at the interface between the tension-imparting insulating film and the steel sheet, and A unidirectional silicon steel sheet having excellent adhesion to a tension-imparting insulating film, characterized in that the average thickness of the density-reduced layer at the interface is 30% or less of the total thickness of the oxide film.

(2) The above-mentioned (1), wherein the tension-imparting insulating film is a tension-imparting insulating film formed by baking a coating liquid mainly containing phosphate and colloidal silica. A unidirectional silicon steel sheet with excellent tensile strength and insulating film adhesion.

(3) The tension imparting insulating film according to the above (1), wherein the tension imparting insulating film is a tension imparting insulating film formed by baking a coating liquid mainly containing alumina sol and boric acid. A unidirectional silicon steel plate with excellent insulation film adhesion.

(4) Tension imparting property to the finish-annealed unidirectional silicon steel sheet produced by removing the inorganic mineral film such as forsterite by means such as pickling or intentionally preventing its formation. In order to secure the adhesion between the insulating film and the steel sheet, prior to forming the tension-imparting insulating film, an external oxidation type oxide film mainly composed of silica is formed, and then a coating liquid for forming the tension-imparting insulating film is applied. A method for producing a unidirectional silicon steel sheet by forming a tension-imparting insulating film by coating and baking, and a steel sheet having a coating liquid for forming a tension-imparting insulating film and an external oxidation type oxide film mainly composed of silica. A unidirectional silicon steel sheet having excellent adhesion to a tension-imparting insulating film, characterized in that the tension-imparting insulating film is manufactured by keeping the time of contact with 100 ° C. or less for 20 seconds or less. Law.

[0021]

DETAILED DESCRIPTION OF THE INVENTION The details of the invention will be described below.

The inventors have suspected that there is a problem in the step of forming the tension-imparting insulating film after forming the external oxidation type oxide film as a cause that the film adhesion is not always perfect. In particular, it was estimated that the time during which the coating liquid and the steel sheet are in contact with each other in the low temperature temperature range may be affected when the coating liquid for forming the tension imparting insulating film is applied to the steel plate and baked.

That is, the interface structure between the external oxidation type oxide film and the tension-imparting insulating film, especially on the side of the external oxidation type oxide film, is different depending on the contact time between the steel sheet and the coating liquid, and therefore the tension-imparting insulating film. I thought that the adhesiveness of would fluctuate.

Therefore, the following experiment was conducted to examine the relationship between the coating time and the contact time between the coating solution and the steel sheet with the external oxidation type oxide film and the structure of the external oxidation type oxide film. In addition, the external oxidation type oxide film here is an oxide formed on a steel plate, and when the oxide covers 70% or more of the steel plate surface, it means the oxide. .

As a material for experimentation, a decarburized annealed plate having a plate thickness of 0.225 mm was coated with an annealing separator containing alumina as a main component, subjected to finish annealing, secondary recrystallized, and one direction having a mirror gloss. Silicon steel sheet was prepared. This steel sheet was heat-treated in an atmosphere of nitrogen 20%, hydrogen 80%, dew point + 2 ° C. for a soaking time of 8 seconds and at various temperatures to form an external oxidation type oxide film mainly composed of silica. .

Then, in order to form an insulating film having a tension imparting property, a coating liquid mainly containing aluminum phosphate, chromic acid and colloidal silica is applied, and 835 is applied in a nitrogen atmosphere.
Baked at 30 ° C for 30 seconds. At this time, the tension-imparting insulating film was formed by changing the time during which the coating solution was in contact with the steel plate at a temperature of 100 ° C. or lower. The film adhesion of the steel sheet thus produced was examined.

The coating adhesion is evaluated by the area ratio (hereinafter referred to as the coating residual area ratio) of the portion where the coating was not peeled from the steel sheet and the coating remained in contact when the sample was wound around a cylinder having a diameter of 20 mm. did. The case where the adhesion was poor and the film was completely peeled off was judged as 0%, and the case where the film adhesion was good and the film was not peeled at all was judged as 100%. In the evaluation, when the film residual area ratio was 90% or less, x was given, when more than 90% and 95% or less was given, and when more than 95% and 100% or less, was given.

Further, in order to investigate the interface structure between the steel sheet and the tension-imparting insulating film including the external oxidation type oxide film, a sample was prepared by the focused ion beam method (hereinafter referred to as FIB method), and the transmission electron microscope was used. The cross-sectional structure was observed with (hereinafter referred to as TEM). Further, the density distribution in the film thickness direction of the external oxidation type oxide film mainly composed of silica was examined by electron energy-loss spectroscopy (hereinafter referred to as EELS method).

The FIB method is the thickness of several μ formed on a steel plate.
A thin sample with a thickness of several μm was prepared from the desired position of the coated steel plate sample so that the film of m could be observed from the cross-sectional direction.
This is a method of collecting.

The EELS method is a method of measuring the intensity of scattered electron beam against the loss energy when a thin sample prepared by the FIB method or the like is irradiated with an electron beam in the thickness direction. This method utilizes the fact that the ratio of the elastic scattering intensity and the inelastic scattering intensity is proportional to the density of the substance constituting the film, and calculates the density by the intensity ratio of both.

A thin film sample was prepared by the FIB method, and TEM-E
When the density in the external oxidation type oxide film mainly composed of silica was examined by the ELS method, a density distribution was observed. In particular, the density of the external oxidation type oxide film in the vicinity of the interface between the silica-based external oxidation type oxide film and the tension-imparting insulating film is lower than that of the oxide film center part or the steel plate side interface part. Was observed.

When the density of the portion of the external oxidation type oxide film near the interface with the steel sheet is Di, the portion where the measured external oxidation type oxide film density Ds is 0.8 Di or less is defined as the density reduced portion, and this density The average film thickness occupied by the reduced portion in the external oxidation type oxide film was determined and defined as the ratio to the total thickness of the external oxidation type oxide film, which was defined as the density reduced layer ratio.

The total thickness means the total thickness of the external oxidation type oxide film, and from the interface between the external oxidation type oxide film and the steel sheet in the cross-sectional observation image by TEM, the external oxidation type oxide film and the tension imparting property are obtained. Indicates the distance to the interface with the insulating film.

The results of the examinations thus made are summarized in Table 1 and Table 2 (continued from Table 1).

[0035]

[Table 1]

[0036]

[Table 2]

From Tables 1 and 2, the conditions for ensuring the adhesion of the tension-imparting insulating film are as follows.

First, heat treatment of Sample Nos. 1 to 5 in which the film thickness of the external oxidation type oxide film is less than 2 nm is irrespective of the length of the contact time between the coating liquid and the steel plate mainly composed of silica and having the external oxidation type oxide film. Under the condition of a temperature of 500 ° C, the film adhesion cannot be secured. On the other hand, the heat treatment temperature of Sample No. 6 to Sample No. 40 having the thickness of the external oxidation type oxide film of 2 nm or more is 600
Under the conditions of ℃ to 1150 ℃, the film adhesion can be generally secured.

In particular, the heat treatment temperature of the sample No. 26 to sample No. 40 at which the thickness of the external oxidation type oxide film is 40 nm or more is 1
Under conditions of 000 ° C or higher, the film adhesion is remarkably good.

However, under the conditions that the contact time between the steel sheet having a silica-based external oxidation type oxide film and the coating solution is 20 seconds or less and the ratio of the density-reduced layer in the external oxidation type oxide film is 30% or less, the coating film Adhesiveness is good, but under the condition that the contact time is 30 seconds and the density-reduced layer ratio is larger than 30%, even if the film thickness of the external oxidation type oxide film is thick, the film adhesion cannot be said to be perfect and the film remains. The area ratio was 90%.

From Tables 1 and 2, in order to secure the film adhesion of the tension imparting insulating film, the thickness of the external oxidation type oxide film is 2 nm or more, and the density reduction layer ratio in the external oxidation type oxide film is It is indispensable to be 30% or less. In order to form such an external oxidation type oxide film, in the heat treatment step for forming the external oxidation type oxide film, the heat treatment temperature is 600 ° C. or higher, particularly preferably 1000 ° C. It can be seen that in the step of forming the tension-imparting insulating film as described above, the contact time between the steel sheet with the external oxidation type oxide film and the coating solution for forming the tension-imparting insulating film needs to be 20 seconds or less. .

Although not described in Tables 1 and 2, when the film thickness of the external oxidation type oxide film is 500 nm or more, the tension due to the tension imparting insulating film is remarkably relaxed by the external oxidation type oxide film. Since sufficient tension is not applied to the steel sheet, even if the adhesion property of the tension-imparting insulating film is excellent, it is not preferable as a product property. Therefore, the upper limit of the thickness of the external oxidation type oxide film is set to 500 nm.

The lower limit of the contact time between the steel sheet with an external oxidation type oxide film and the coating liquid for forming the tension-imparting insulating film is not clear at present, but if it is shorter than 0.1 seconds, both the steel plate and the coating liquid will be used. Since it is considered that there is no time for the sheet to fit in, and so-called coating unevenness is likely to occur, the contact time between the steel sheet and the coating liquid at 100 ° C. or lower is preferably 0.1 seconds or longer.

As described above, the inventors consider the mechanism that the film thickness and the density-reduced layer ratio of the external oxidation type oxide film have a great influence on the film adhesion.

First, the film thickness dependence of the external oxidation type oxide film will be described.

The adhesion between the steel sheet and the tension-imparting insulating film is
It depends on the external oxidation type oxide film formed at the interface between the two. It is generally said that the 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, the more the diffusion of atoms is promoted, and the external oxidation type oxide film grows more.

Due to such a mechanism, the heat treatment temperature is 500 ° C.
Under low conditions, the growth of the external oxidation type oxide film is not sufficient, so the film adhesion is insufficient. On the other hand, when the heat treatment temperature is 600 ° C or higher, the external oxidation type oxide film grows sufficiently, so the film adhesion It is considered that the adhesiveness is excellent, and further that the oxide film is more likely to grow at 1000 ° C. or higher, so that the film adhesion is extremely good.

It can be seen from the result of the film thickness measurement of the external oxidation type oxide film using the TEM that this estimation is valid.
That is, the adhesion of the tension-imparting insulating film is poor under the condition of the heat treatment temperature of 500 ° C. where the thickness of the film is 1 nm and the growth of the external oxidation type oxide film is not sufficient, while the film thickness of 2 nm or more is sufficient for the external oxidation. The film adhesion is good under the condition that the heat treatment temperature at which the mold oxide film is grown is 600 ° C. or higher.

Next, the relationship between the adhesion of the tension-imparting insulating film and the density-reduced layer ratio existing in the external oxidation type oxide film will be described.

Although the details of the mechanism of forming the density-reduced layer in the external oxidation type oxide film are unknown,
At present, the inventors think as follows.

The inventors of the present invention, when a coating liquid for forming a tension-imparting insulating film is applied to a steel sheet with an external oxidation type oxide film, a kind of swelling reaction occurs in the external oxidation type oxide film, and the external oxidation type oxide film I think that structural relaxation of will occur. It is speculated that such structural relaxation is caused by water contained in the coating liquid.

Therefore, it is presumed that, even in the external oxidation type oxide film, when viewed from the cross-sectional direction, it occurs on the interface side in contact with the coating liquid. Actually, a sample was prepared by the FIB method, and TEM
When the density distribution of the cross section was measured by the -EELS method, a decrease in density was observed in the portion where the external oxidation type oxide film was in contact with the tension imparting insulating film.

Next, the relationship between the ratio of the density reducing layer to the total thickness of the oxide film and the contact time with the coating solution will be described.

First, when the contact time between the steel sheet and the coating liquid at 100 ° C. or lower is short, the swelling-like reaction of the external oxidation type oxide film due to the moisture contained in the coating liquid is unlikely to occur, so that the density decreasing layer ratio is Low. On the other hand, 100 ° C between the steel plate and the coating liquid
If the contact time below is long, a swelling-like reaction of the external oxidation type oxide film due to water contained in the coating solution or the like is likely to occur, and the density-reduced layer ratio increases.

Next, the relationship between the adhesion of the tension imparting insulating film to the steel sheet and the density-reduced layer ratio in the external oxidation type oxide film will be described.

The application of tension to the steel sheet by the tension-providing insulating film is brought about by the difference in the coefficient of thermal expansion between the tension-providing insulating film and the steel sheet. At this time, a large amount 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 secures the adhesion between the steel sheet and the tension-imparting insulating film.

The inventors have speculated that the stress-resistance may be affected by the density-reduced layer, which is a kind of defective portion. That is, when the density reduction layer in the external oxidation type oxide film is small and the ratio to the total thickness of the oxide film is 30% or less, it can withstand stress, but the density reduction layer ratio is high and the ratio is higher than 30%. In this case, the external oxidation type oxide film cannot withstand the stress applied by the tension imparting insulating film, and the external oxidation type oxide film may be destroyed.

[0058]

EXAMPLES Example 1 A cold rolled sheet for producing a unidirectional silicon steel sheet having a sheet thickness of 0.225 mm and a Si concentration of 3.30% was subjected to decarburization annealing, and then the surface oxide layer was formed with ammonium fluoride. The solution was removed by dissolution by pickling in a mixed solution of sulfuric acid.

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 secondary recrystallized unidirectional silicon steel sheet is free of inorganic minerals and has a specular gloss.

With respect to this steel sheet, nitrogen 25%, hydrogen 75
%, The external oxidation type oxide film was formed by performing heat treatment at a temperature of 900 ° C. in an atmosphere having a dew point of −3 ° C. Then, with respect to the prepared steel sheet, magnesium phosphate having a concentration of 50% /
A mixed solution of 50 ml of an aluminum aqueous solution, 66 ml of an aqueous dispersion of colloidal silica having a concentration of 30%, and 5 g of chromic anhydride was applied and baked at 850 ° C. for 30 seconds to form a tension-imparting insulating film.

At this time, the contact time between the steel sheet and the coating liquid at 100 ° C. or lower was 3 seconds (Example 1) and 35 seconds (Comparative Example 1).

With respect to the unidirectional silicon steel sheet with an insulating film thus prepared, the film adhesion was evaluated by the tension-providing insulating film remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm. The results are shown in Table 3.

[0063]

[Table 3]

From Table 3, as compared with Comparative Example 1 in which the contact time is 35 seconds, the density-reduced layer ratio is 40%, and the tension-providing insulating film residual area ratio is 90%, the contact time is 3 seconds and the density-reduced layer ratio is 5%. Example 1 in which the residual area ratio of the impartable insulating film is 100%
It can be seen that the film has better film adhesion and is superior.

Example 2 A cold rolled sheet for producing a unidirectional silicon steel sheet having a sheet thickness of 0.225 mm and a Si concentration of 3.35% was subjected to decarburization annealing, and the surface was annealed mainly with magnesia and bismuth chloride. A water slurry as a separating agent was applied and dried. Then, finish annealing was performed at 1200 ° C. for 20 hours in a dry hydrogen atmosphere to obtain a unidirectional silicon steel sheet in which secondary recrystallization with almost no inorganic mineral substance on the surface was completed.

With respect to this steel sheet, nitrogen 25%, hydrogen 75
%, A heat treatment was performed at a temperature of 1150 ° C. in an atmosphere having a dew point of −15 ° C. to form an external oxidation type oxide film mainly composed of silica. Then, the concentration of the prepared steel sheet is 50%
50 ml of an aqueous magnesium phosphate solution, 100 ml of a 20% aqueous colloidal silica dispersion, and 5 g of chromic anhydride were applied, and baked at 850 ° C. for 30 seconds.
An insulating film having a tension imparting property was formed. At this time, the contact time between the steel sheet and the coating liquid at 100 ° C. or lower was 10 seconds (Example 2) and 25 seconds (Comparative Example 2).

With respect to the unidirectional silicon steel sheet with an insulating coating thus prepared, the adhesion of the insulating coating was evaluated by the tension-providing insulating coating remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm. The results are shown in Table 4.

[0068]

[Table 4]

From Table 4, as compared with Comparative Example 2 in which the contact time is 25 seconds, the density-reduced layer ratio is 35%, and the tension-applying insulating film remaining area ratio is 90%, the contact time is 10 seconds and the density-reduced layer ratio is 10.
It can be seen that in Example 2 in which the residual area ratio of the tension-imparting insulating film is 100% in%, the film adhesion is better and superior.

Example 3 A cold-rolled sheet for producing a unidirectional silicon steel sheet having a plate thickness of 0.225 mm and a Si concentration of 3.25% was subjected to decarburization annealing, and the surface of an annealing separator containing alumina as a main component was used. A water slurry was applied and dried. Then, finish annealing was carried out at 1200 ° C. for 20 hours in a dry hydrogen atmosphere to obtain a unidirectional silicon steel sheet having almost no inorganic mineral substance on the surface and having secondary gloss re-crystallization having a mirror gloss.

With respect to this steel sheet, nitrogen 30%, hydrogen 70%
%, The external oxidation type oxide film was formed by performing heat treatment at a temperature of 800 ° C. in an atmosphere having a dew point of −10 ° C. Then, to the prepared steel sheet, a mixed solution consisting of 50 ml of an aqueous solution of aluminum phosphate having a concentration of 50%, 100 ml of an aqueous dispersion of colloidal silica having a concentration of 20%, and 5 g of chromic anhydride was applied, and baked at 850 ° C. for 30 seconds to apply tension. Formed an insulating film.

At this time, the contact time between the steel sheet and the coating liquid at 100 ° C. or lower was 1 second (Example 3) and 40 seconds (Comparative Example 3).

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

[0074]

[Table 5]

From Table 5, as compared with Comparative Example 3 in which the contact time is 40 seconds, the density-reduced layer ratio is 35%, and the tension-providing insulating film residual area ratio is 90%, the contact time is 1 second and the density-reduced layer ratio is 5%. Example 3 in which the remaining area ratio of the impartable insulating film is 100%
It can be seen that the film has better film adhesion and is superior.

Example 4 A cold-rolled sheet for producing a unidirectional silicon steel sheet having a sheet thickness of 0.23 mm and a Si concentration of 3.30% was subjected to decarburization annealing, and the surface of the annealing separator mainly composed of magnesia was used. After applying a water slurry and drying, in a dry hydrogen atmosphere,
Finish annealing was performed at 1200 ° C. for 20 hours. On the surface of the thus-prepared secondary recrystallized unidirectional silicon steel sheet, a film mainly composed of forsterite is formed.

Then, after pickling in a mixed solution of ammonium fluoride and sulfuric acid to dissolve and remove the surface film, chemical polishing was carried out in a mixed solution of hydrofluoric acid and hydrogen peroxide solution, and the surface of the steel sheet was covered with inorganic mineral substances. A steel plate having no specular gloss was obtained. This steel sheet was heat-treated at a temperature of 1050 ° C. in an atmosphere of nitrogen 50%, hydrogen 50% and a dew point of −10 ° C. to form an external oxidation type oxide film.

Next, to the prepared steel sheet, a mixed solution of 100 ml of 10% aqueous colloidal alumina dispersion, 10 g of amorphous alumina powder, 5 g of boric acid, and 200 ml of water was applied, and baked at 900 ° C. for 30 seconds to give a tension. An imparting insulating film was formed. At this time, the contact time with the coating liquid was 0.5 seconds (Example 4) and 50 seconds (Comparative Example 4).

With respect to the thus prepared unidirectional silicon steel sheet with an insulating film, the film adhesion was evaluated by the tension-providing insulating film remaining area ratio when the sample was wound around a cylinder having a diameter of 20 mm. The results are shown in Table 6.

[0080]

[Table 6]

From Table 6, as compared with Comparative Example 4 in which the contact time is 50 seconds, the density-reduced layer ratio is 35%, and the residual area ratio of the tension-giving insulating film is 90%, the contact time is 0.5 seconds and the density-reduced layer ratio is 1.
It can be seen that the adhesiveness of the film of Example 4 in which the residual area ratio of the tension-imparting insulating film is 100% is better and the film adhesion is better.

[0082]

According to the present invention, it is possible to produce a unidirectional silicon steel sheet having excellent adhesion to a tension-imparting insulating film and provide a magnetic iron core material with less energy loss.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Murakami             1-1 Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka             Inside the Yawata Works of Hontan Works (72) Inventor Yoshiyuki Ushigami             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Shuichi Nakamura             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Masaaki Sugiyama             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division F term (reference) 4K026 AA03 AA22 BA03 BA12 BB05                       CA16 CA23 CA41 DA02 EA04                       EA07 EB11                 5E041 AA02 BC01 BC08 CA01 HB11

Claims (4)

[Claims] 1. A unidirectional silicon steel sheet on which a tension imparting insulating film is formed after the inorganic mineral film such as forsterite is removed by means such as pickling or intentionally prevented from producing the film. And an interface between the tension-imparting insulating film and the steel sheet has an external oxidation type oxide film mainly composed of silica and having a thickness of 2 nm or more and 500 nm or less, and the interface of the oxide film with the tension-imparting insulating film. A unidirectional silicon steel sheet having excellent adhesion to a tension-imparting insulating film, characterized in that the average thickness of the density-reduced layer in a portion is 30% or less of the total thickness of the oxide film. 2. The tension-imparting insulating film according to claim 1, wherein the tension-imparting insulating film is formed by baking a coating liquid mainly containing phosphate and colloidal silica. A unidirectional silicon steel sheet with excellent adhesion to the insulating coating. 3. The tension-imparting insulation film according to claim 1, wherein the tension-imparting insulation film is formed by baking a coating solution mainly containing alumina sol and boric acid. Unidirectional silicon steel sheet with excellent adhesion. 4. A tension-imparting insulation for a finish-annealed unidirectional silicon steel sheet produced by removing an inorganic mineral film such as forsterite by means such as pickling or intentionally preventing its formation. In order to secure the adhesion between the film and the steel sheet, an external oxidation type oxide film mainly composed of silica is formed before the formation of the tension-imparting insulating film, and then a coating liquid for forming the tension-imparting insulating film is applied. Then, in the method for producing a unidirectional silicon steel sheet by forming a tension-imparting insulating coating by baking, a coating solution for forming a tension-imparting insulating coating and a steel sheet on which a silica-based external oxidation type oxide film is formed are used. A method for producing a unidirectional silicon steel sheet having excellent adhesion to a tension-imparting insulating film, which comprises forming the tension-imparting insulating film for 20 seconds or less in a temperature range of 100 ° C. or less.