JP3280279B2 - Ultra-low iron loss grain-oriented electrical steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a grain-oriented electrical steel sheet, and more particularly to a grain-oriented electrical steel sheet having an extremely low iron loss value and excellent film adhesion.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as iron core materials for electrical equipment such as transformers, but are basically required to have excellent magnetic properties such as magnetic flux density and iron loss value. I have. In particular, in order to reduce energy loss, a grain-oriented electrical steel sheet with low iron loss is required. To reduce iron loss, reduce sheet thickness, increase Si content,
In addition to methods such as increasing the orientation of the crystal orientation,
It is known that applying tension to a steel sheet is effective.

At present, tension is applied to a steel sheet by forming a film made of a material having a smaller thermal expansion coefficient than the steel sheet on the surface of the steel sheet. As a film for imparting tension, the oxide on the steel sheet surface and the annealing separator applied to the steel sheet surface react during the secondary recrystallization that finally aligns the crystal orientation and the finish annealing step that combines the purification of the steel sheet. A coating mainly composed of forsterite to be formed is generally used. This film has a large tension that can be applied to the steel sheet and has a great effect on reducing iron loss.However, in order to further increase the tension effect, a low thermal expansion tension-added insulating coating (top coat) is applied on the forsterite film. It is generally used as a product.

[0004] As described in JP-B-53-28375 and JP-B-56-52117, for example, as disclosed in JP-B-53-28375 and JP-B-56-52117, phosphors of Al and alkaline earth metals are used. In many cases, a treatment liquid mainly containing an acid salt and colloidal silica, chromic anhydride or chromate is applied to the surface of a steel sheet and baked. An inorganic coating typified by colloidal silica having a smaller thermal expansion coefficient than that of a steel sheet is formed at a high temperature, and a tension is applied to the steel sheet at room temperature by utilizing a difference in thermal expansion between the ground iron and the insulating coating. The insulating coating formed by this method has a large effect of imparting tension to the steel sheet, and is effective in reducing iron loss.

On the other hand, in recent years, a method of magnetically smoothing the surface of a steel sheet has been proposed, and it has become clear that a remarkable decrease in iron loss value is recognized. For example, Japanese Patent Publication No. 52-24499 discloses a method of removing the surface oxide by pickling after finish annealing, and then finishing the surface to a mirror surface by chemical polishing or electrolytic polishing. Further, Japanese Patent Publication No. 6-37694 proposes a method of obtaining a magnetically smooth surface by graining the surface of a steel sheet using a chloride aqueous solution electrolysis method. The iron loss value is reduced by such a surface treatment because pinning sites that hinder domain wall movement near the steel sheet surface during the magnetization process are reduced.

[0006] The above-mentioned tension-added insulating coating is
If the forelite coating is present on the surface of the steel sheet, there is no problem if the coating with greater tension has less adhesion to the substrate if the adhesion to the substrate is not strong. When the forsterite film was not present on the steel sheet surface, the film could not be adhered.

[0007] To address this problem, several methods have been proposed for applying a tensioned insulating coating to a surface without a forsterite coating or a conditioned smooth surface. For example, Japanese Patent Publication No. 52-24499 discloses a method of applying a coating solution after applying a metal plating to the surface of a ground iron, followed by baking. In addition,
Japanese Patent Application Laid-Open No. 6-184762 discloses a method in which a SiO ₂ thin film is formed on the surface of a ground iron, and then a coating solution is applied and baked. Japanese Patent Publication No. 56-4150 discloses a method of forming a ceramic thin film by vapor deposition, sputtering, thermal spraying, and the like, and Japanese Patent Publication No. 63-54767 discloses a ceramic material comprising nitride, carbide, or a combination thereof. A method of forming a film by ion plating or ion implantation is disclosed in Japanese Patent Publication No. Hei 6-99822. In CVD, ion plating or ion implantation, two different layers of nitride and / or carbide and oxide are disclosed. A method for forming a ceramic film as described above and Japanese Patent Publication No. 2-243770 disclose a method for forming a ceramic film by a sol-gel method.

[0008]

[Problems to be solved by the invention]
In the technology described in 52-24499, the adhesion of the coating is not sufficient, and in the technology described in JP-A-6-84762, the effect of imparting tension is insufficient and the effect of reducing the iron loss value is small. The problem remained. Also, JP-B 63-54767
In the ceramic coating formed by the technique described in Japanese Patent Application Publication No. 6-99822, the thermal expansion coefficient of the coating is about 2 to 7 × 10 ⁻⁶ K ⁻¹ , 13 × 10
⁻⁶ K ⁻¹ ), the effect of imparting tension due to the difference in thermal expansion is large, but there was a problem in the adhesion to the base steel.

Further, a method of forming a ceramic thin film by vapor deposition, sputtering, thermal spraying or the like described in JP-B-56-4150, or a sol-gel method described in JP-B-2-243770. The method of forming the coating is expensive and has a problem in the uniformity of the coating when a large area is processed in a large amount. It had been.

[0010] The present invention advantageously solves the above problems,
An object of the present invention is to propose an ultra-low iron loss grain-oriented electrical steel sheet that can achieve both an iron loss reduction technique using magnetic smoothing and an iron loss reduction technique using a tension-applied coating to further improve magnetic properties.

[0011]

Means for Solving the Problems In order to achieve the above object, the present inventors, when applying a tension-added insulating coating to a grain-oriented electrical steel sheet having a smooth surface or a magnetically smoothed surface, As a result of intensive studies on the conditions for forming a film with good adhesion, it is possible to achieve both iron loss reduction technology by magnetic smoothing and iron loss reduction technology by applying tension-type coating by laminating films with different coefficients of thermal expansion. It was found that a grain-oriented electrical steel sheet having excellent coating adhesion and extremely low iron loss value can be obtained.

First, the experimental results on which the present invention is based will be described. Decarburized and primary recrystallization annealing is applied to a silicon steel cold-rolled sheet containing 3% Si that has been rolled to a final sheet thickness of 0.23 mm, and then an annealing separator containing MgO as a main component is applied. A final finish annealing including a recrystallization process and a purification process was performed. The final finish annealed plate was subjected to sulfuric acid washing to remove forsterite on the surface, and then subjected to electrolytic polishing in a phosphoric acid-chromic acid bath to magnetically smooth the surface.

The obtained steel sheet was coated with an inorganic coating mainly composed of chromic acid or the like as a coating on the ground iron side. The thickness of the inorganic coating was about 0.5 μm, and the coefficient of thermal expansion of the coating was changed by changing the content of the contained colloidal silica from 0 to 35%. On the inorganic coating, as a surface-side coating, a tension-imparting insulating coating liquid having a thermal expansion coefficient of 4.6 × 10 ⁻⁶ K ⁻¹ containing magnesium phosphate-50% colloidal silica as a main component is applied and baked at 800 ° C. Was.

With respect to such a steel sheet, the iron loss value (W _17/50 ) and the coating adhesion before and after coating were evaluated. Table 1 shows the results. The coating adhesion was evaluated by winding a round bar of various diameters around a coated steel sheet and bending the same to obtain the minimum diameter (minimum bending diameter) at which the coating did not peel off, and evaluated the minimum bending diameter (mm). The smaller the minimum bending diameter, the better the film adhesion.

[0015]

[Table 1]

If a coating having a coefficient of thermal expansion of 8.0 × 10 ⁻⁶ K ⁻¹ or more is formed as a ground iron side coating, the minimum bending diameter is 35
mm or less, the film adhesion was improved, and the iron loss value was found to be significantly reduced by the effect of applying tension. In this way, after forming a coating having a relatively large coefficient of thermal expansion close to the coefficient of thermal expansion on the surface of the base iron,
It has been found that when a film having a small coefficient of thermal expansion is formed on the film, a tension-applied insulating coating having excellent adhesion is obtained.

The present invention has been made based on the above findings. The present invention is a grain-oriented electrical steel sheet which has been subjected to a final finish annealing in which an adhesion type coating is formed on a surface of the iron base, wherein the surface of the iron base is a smooth surface or a magnetically smooth surface, and the adhesion type coating is , made to be the multi-layer coating baking, a coating having a thermal expansion coefficient thermal expansion coefficient toward the coating outermost surface is inclined in the thickness direction to decrease average thermal expansion coefficient of said adhesion-type coating 7 × 10 ^-6 A water treatment in which the portion of the adhesion type coating which is less than K ^-1 and which is in contact with the ground iron is mainly composed of phosphoric acid-chromic acid.
It is formed by applying and baking the liquid and has a coefficient of thermal expansion of 8 × 10
^-6 K ^-1 or more is an ultra-low iron loss grain-oriented electrical steel sheet. The smooth surface is Ra: 0.3 and [mu] m or less smooth surface, the magnetic smooth surface Rmax: the preferred arbitrarily to the graining like surface having a 0.1 [mu] m or more grain boundary step.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The grain-oriented electrical steel sheet of the present invention is a steel sheet subjected to final finish annealing, and the surface of the steel sheet is a smooth surface or a magnetically smooth surface. The finish-annealed steel sheet is subjected to pickling (for example, pickling with sulfuric acid) or mechanical removal such as cutting or grinding or a combination thereof to remove the forsterite film formed on the surface, and then subjected to electrolytic polishing or chemical polishing. Is a smooth surface or a magnetically smooth surface. The electrolytic polishing is preferably performed in a phosphoric acid-chromic acid bath or a halide bath, and the chemical polishing is preferably performed in a hydrofluoric acid-hydrogen peroxide aqueous solution.

By such treatment, the steel sheet has Ra: 0.3 μm.
It is preferable that the surface be a smooth surface of m or less. Surface roughness is Ra
If it exceeds 0.3 μm, the surface roughness is rough, and no effect of reducing iron loss by surface smoothing is observed. However, even if the surface roughness of the ground iron exceeds Ra: 0.3 μm, the grain boundary has an Rmax of 0.1 μm.
It is preferable to use a so-called graining-like surface having a grain boundary step of not less than m and a smooth inside of the grain. The graining-like surface is a magnetically smooth surface that has achieved magnetic smoothing, has a low iron loss value, has good magnetic properties, and has good film adhesion.

In the present invention, an adhesion type coating is formed on the ground iron surface of a steel plate having such a smooth surface or a magnetically smooth surface. The term "adhesive coating" as used in the present invention means a substance other than a reactive coating
By weight of the film, a film made under more only coated fabric baking. The reactive coating is a coating formed by reacting with the base iron at the time of forming the coating, and for example, forsterite is an example. In the reaction type coating, the reaction at the time of formation of the coating impairs the smoothness of the interface between the ground iron and the coating, so that a significant decrease in iron loss cannot be expected.

FIG. 1 shows the adhesion type coating formed on the surface of the base iron.
As shown in (1), the film has a thermal expansion coefficient inclined in the thickness direction in which the coefficient of thermal expansion decreases toward the outermost surface of the film. In order to obtain a film having a coefficient of thermal expansion inclined in the thickness direction, it is preferable to form a multilayer film in which the component composition of the film changes stepwise, preferably continuously, in the film thickness direction. Preparation of attachment type coating is preferably more multilayer film only coated fabric baking.

In the film formation by multilayer plating and multilayer deposition, a slight decrease in magnetic properties due to slight surface modification is recognized. Also, plating, evaporation, ion plating,
When a multilayer film is formed by ion implantation, CVD, or the like, the layer interface becomes very clear, the coefficient of thermal expansion changes clearly stepwise, and it becomes difficult to smoothly reduce the difference in thermal expansion.

On the other hand, when a multilayer film is formed by a method in which a coating solution is applied in multiple layers and baked, interdiffusion of components progresses between layers during baking, the layer interface becomes unclear, and stress concentrates on the layer interface during a bending test. Even at this time, peeling does not occur at the interface of the multilayer film, which is advantageous for improving adhesion. Further, the coefficient of thermal expansion also changes more continuously. Multi-layer coating of a coating solution by a roll coater method or a dip method is particularly advantageous since a coating film can be uniformly formed over a large area.

The coating formed on the surface of the ground iron is 8.0 ×
A film having a thermal expansion coefficient of 10 ^-6 K ^-1 or more. The thermal expansion coefficient of the coating formed in contact with the surface of the ground iron is 8.0 × 10 ^-6 K
^{At a value of -1} or more, as shown in FIG. 2, the minimum bending diameter is 40 mm or less, indicating good film adhesion. The minimum bending diameter is a value for evaluating the adhesion of the coating, and is a minimum diameter at which a round bar of various diameters is wound around a coated steel sheet, bent, and the coating does not peel.

On the other hand, when the coefficient of thermal expansion is less than 8.0 × 10 ⁻⁶ K ⁻¹ , the minimum bending diameter is large and the adhesion of the coating film is deteriorated. For this reason, the coating directly formed on the surface of the ground iron is limited to a coating having a thermal expansion coefficient of 8.0 × 10 ⁻⁶ K ⁻¹ or more. For example, when a coating having a coefficient of thermal expansion of 4.6 × 10 ⁻⁶ K ⁻¹ is directly applied to the base steel, the coating is peeled off during the formation due to a large difference in thermal expansion from the base steel.

The coating formed directly on the surface of the base iron is preferably an inorganic coating mainly composed of chromic acid or the like. Specifically, a water treatment liquid mainly containing phosphoric acid-chromic acid such as magnesium phosphate-potassium dichromate or aluminum phosphate-sodium dichromate is applied.
0-650 that form the coatings baked at ° C.. These water treatment liquids may be the same as those applied for forming a film on the surface of a non-oriented silicon steel sheet having no oxide film.

After forming a coating having a thermal expansion coefficient of 8.0 × 10 ^-6 K ^-1 or more on the surface of the base iron, the coating having a smaller thermal expansion coefficient than the thermal expansion coefficient of the coating is superimposed on the coating. At least one layer. At this time, the coating to be formed on top of the coating in contact with the surface of the base iron has a coefficient of thermal expansion that is sequentially smaller than the thermal expansion coefficient of the coating in contact with the surface of the base iron, and finally the thermal expansion toward the outermost surface of the coating It is important that the coating has a coefficient of thermal expansion inclined in the thickness direction in which the coefficient decreases. That is, the coating formed on the grain-oriented electrical steel sheet of the present invention is a plurality of layers having a thermal expansion coefficient inclined in the thickness direction. The average thermal expansion coefficient of the coating formed of a plurality of layers is less than 7.0 × 10 ⁻⁶ K ⁻¹ . When the average thermal expansion coefficient of the coating is 7.0 × 10 ⁻⁶ K ⁻¹ or more, the effect of imparting tension is small, and as shown in FIG. 3, the reduction of the iron loss value is small.

The coefficient of thermal expansion of the film to be formed is preferably adjusted by changing the amount of colloidal silica added to the water treatment solution containing phosphoric acid-chromic acid as a main component. The method for producing a grain-oriented electrical steel sheet according to the present invention will be described. The grain-oriented electrical steel sheet to which the present invention is directed is a product in which the crystal orientation is aligned in a certain direction by secondary recrystallization, and can be applied to various component systems, but generally has the following components.

That is, Si is an effective component for increasing the electrical resistance of the product and reducing iron loss, and is often contained, but if it exceeds 7.0%, the hardness becomes high and the production and processing become difficult. Contains up to 7.0%. However, when the saturation magnetic flux density is emphasized, Si is not contained. Mn also has the effect of increasing the electrical resistance and has the effect of facilitating hot working during manufacturing. For this purpose, it is necessary to contain 0.03% or more. However, if it exceeds 2.5%, γ transformation is induced at the time of heat treatment to deteriorate magnetic properties.
Contains 5%.

Further, C is 0.003% or less as an impurity.
More preferably, 0.001% or less, S and N are 0.002% or less,
More preferably, it is reduced to 0.001% or less. If these impurities exceed this value, they have a detrimental effect on magnetic properties, and particularly deteriorate iron loss. In addition to these components, the following components can be contained as needed. That is, B, Sb, Ge, P, Sn, Cu, Cr, Pb, Zn, In, and the like added to steel as an inhibitor element, and components such as Mo, Ni, and Co added to steel to improve the structure. Is added to make secondary recrystallization favorable.

The steel adjusted to the specified composition is usually subjected to slab heating and then hot-rolled to form a hot-rolled coil. When the slab heating temperature is set to a high temperature of 1300 ° C. or higher, or 1250 ° C. In any case, such as when the temperature is low. In recent years, a method of performing direct hot rolling after continuous casting without performing slab heating has been developed. However, the present invention can be applied to a case where hot rolling is performed by this method.

The hot-rolled steel sheet is subjected to hot-rolling annealing if necessary, and is finally rolled into a final cold-rolled sheet by rolling once or rolling a plurality of times with intermediate annealing. These rollings may be those subjected to so-called hot rolling for dynamic aging or inter-pass aging for static aging. The steel sheet after the final rolling is subjected to primary recrystallization annealing, which also serves as decarburization annealing, if necessary, and is subjected to secondary recrystallization treatment by final finish annealing to obtain directionality.

At this time, continuous short-time annealing serving both primary recrystallization annealing and secondary recrystallization annealing may be performed, or secondary recrystallization annealing may be performed by continuous short-time annealing. Further, the secondary recrystallization treatment may be performed by long-time annealing (final finish annealing). In the present invention, since it is more effective not to generate forsterite particularly to simplify the subsequent smoothing treatment of the steel sheet surface, Al ₂ O ₃ , ZrO ₂ , and TiO _{2 are} used as annealing separators.
To use by mixing the MgO etc., preferably mainly composed of Al ₂ O _3, SiO ₂ or the like.

[0034] The final finish-annealed steel sheet is subjected to removal of oxides and the like on the surface to obtain a smooth surface, and then the above-mentioned adhesive coating is formed on the surface. The steel sheet thus obtained may be irradiated with a laser, an electron beam or a plasma flame to further subdivide the magnetic domains for the purpose of further reducing the iron loss value. Irradiation with a laser, electron beam or plasma flame does not cause any problem in the adhesion of the coating. For the purpose of further reducing iron loss, magnetic domains may be refined by etching or forming grooves at regular intervals on the surface of the steel plate at an arbitrary stage of the manufacturing process using a toothed roll.

[0035]

【Example】

(Example 1) C: 0.08%, Si: 3.4%, Mn: 0.07%, A
l: 0.02%, Se: 0.02%, Cu: 0.04%, Sb: 0.04%, and two cold rolling including intermediate annealing, using a hot-rolled directional magnetic steel sheet consisting essentially of Fe Thus, a final cold-rolled sheet having a sheet thickness of 0.23 mm was obtained. After that, decarburize in wet hydrogen at 800 ° C.
After the first recrystallization annealing, an annealing separator containing MgO as a main component is applied, and a second recrystallization process at 900 ° C. for 10 hours is performed.
A final finish annealing including a purification process in dry hydrogen at 00 ° C. was performed. The final finish-annealed steel sheet is pickled with H ₂ SO ₄ to remove forsterite on the surface, and then H ₃ PO ₄ -CrO ₃
Electropolishing was performed in a bath to magnetically smooth the surface. The surface roughness of the steel sheet after polishing was 0.17 μm in Ra.

An aqueous treatment solution containing magnesium phosphate-potassium dichromate as a main component was applied to the surface of the ground iron of the grain-oriented electrical steel sheet having a smooth surface obtained in this manner.
A film having a thickness of about 0.5 μm was baked at 0 ° C. to form an underlayer film. Then, an aqueous treatment liquid containing magnesium phosphate-colloidal silica-chromic anhydride as a main component was applied as a tension-adding type coating on the coating, and baked at 800 ° C. to form a coating of about 2.0 μm. An upper layer coating was formed. The coefficient of thermal expansion of the lower layer coating and the upper layer coating was adjusted by changing the composition of the coating solution (mainly the amount of colloidal silica).

With respect to the grain-oriented electrical steel sheet coated in this manner, the iron loss value (W _17/50 ) and the coating adhesion before and after coating were evaluated. The coating adhesion was evaluated by winding a test steel sheet around a round bar of various diameters and bending it to determine the minimum diameter (minimum bending diameter: mm) at which the coating did not peel. The smaller the minimum bending diameter, the better the film adhesion. Table 2 shows the evaluation results of the _iron loss value (W _17/50 ) and the adhesion of the coating.

[0038]

[Table 2]

The grain-oriented electrical steel sheets (No. 1 to N
o.3) is that the iron loss value is greatly reduced by coating
The minimum bending diameter is as small as 40 mm or less, and the coating adhesion is excellent.
You. On the other hand, comparative examples (No. 4 to No.
7) is little or no reduction in iron loss value due to coating
Or the adhesion of the coating film has deteriorated. Comparative Example No. 4 is heat of the coating
Since the coefficient of expansion is smaller than that of base steel,
Sometimes the coating peeled off. Comparative Example No. 5 shows the lower layer
The thermal expansion coefficient of the membrane is 8.0 × 10^-6K^-1Smaller, coating
Poor adhesion. Comparative Example No. 6 shows the thermal expansion of the coating in contact with the ground iron.
Tensile coefficient is 8.0 × 10^-6K^-1Less than the film adhesion is poor
Furthermore, the coefficient of thermal expansion of the coating of each layer increases toward the outer surface of the coating.
The coating structure becomes larger, and the average thermal expansion coefficient of the coating increases.
7.0 × 10 ^-6K^-1As described above, the effect of reducing the iron loss value is small.
Comparative Example No. 7 had a coefficient of thermal expansion of 8.0 ×
Ten^-6K^-1As described above, the film adhesion is good, but the film
Average thermal expansion coefficient is 7.0 × 10^-6K^-1Above all, low iron loss value
Small reduction effect. (Embodiment 2) Same steps as in Embodiment 1 until the final finish annealing
Manufactured final finish-annealed grain-oriented electrical steel sheet (sheet thickness 0.23
mm), H_TwoSO_FourPickling, forsterite on the surface
After removal, the steel sheet_FourSteel sheet in Cl aqueous solution
50A / dm as anode^Two, 2000C / dm^TwoElectrolytic treatment under the conditions of
And apply a beautiful graining-like surface (Ra =
0.25 μm, Rmax = 0.30 μm with a grain boundary step).
Next, a grain-oriented electrical steel having such a magnetically smooth surface
Aluminum phosphate-dichromate on the surface of the steel plate
Apply an aqueous treatment solution containing mainly lithium and bake at 400 ° C.
Then, a coating having a thickness of about 0.5 μm was formed to form a lowermost coating.
Then, the aluminum phosphate-roller
Idal silica-Chromic anhydride as the main component and thermal expansion coefficient
By changing the amount of colloidal silica added for various changes
Apply the added aqueous treatment liquid to form a coating of about 1.0 μm.
Then, an intermediate layer film was formed. Furthermore, this intermediate layer coating
Hey, aluminum phosphate-colloidal silica-anhydrous
Water whose main component is humic acid and whose thermal expansion coefficient has been similarly varied
Coating with a water-soluble treatment liquid and baking at 800 ° C.
A layer coating was formed. The thickness of the applied coating was 1.5 μm.
Was.

With respect to the _grain- oriented electrical steel sheet coated in this manner, the iron loss value (W _17/50 ) and the coating adhesion were evaluated in the same manner as in Example 1. Table 3 shows the evaluation results of the _iron loss value (W _17/50 ) and the adhesion of the coating.

[0041]

[Table 3]

The grain-oriented electrical steel sheets (No. 8 to N
o.10) indicates that the reduction in iron loss value due to coating
The minimum bending diameter is as small as 40 mm or less and excellent in film adhesion
You. On the other hand, the comparative examples (No. 11 to N
o.15) indicates that the reduction in iron loss value due to coating
Alternatively, the adhesion of the coating film has deteriorated. Comparative Example No. 13
Because the thermal expansion coefficient of the membrane is smaller than that of
The film peeled off during film formation. Comparative Examples No. 11 and No. 14
Thermal expansion coefficient of the bottom layer coating in contact with iron is 8.0 × 10 ^-6K^-1Yo
, The film adhesion is inferior. Comparative Example No. 12
 No. 15, the thermal expansion coefficient of the coating in contact with the ground iron was 8.0 × 1
0^-6K^-1Although the average thermal expansion coefficient of the coating is 7.0 × 1
0^-6K^-1As described above, reduction of iron loss value by coating
Few. Also, in this example, the film structure has three layers,
That the coefficient change shows a continuous change
Coating adhesion due to iron surface with graining surface
Is better than the example of Example 1 (No. 1 to No. 3).
You.

[0043]

According to the present invention, it is possible to uniformly form a tension-imparting coating having excellent coating adhesion over a large area, and to manufacture a grain-oriented electrical steel sheet having extremely low iron loss on an industrial scale. It is expected that the applications of grain-oriented electrical steel sheets will be expanded, and it will have a remarkable industrial effect.

[Brief description of the drawings]

FIG. 1 is a graph schematically showing a change in a coefficient of thermal expansion of an adhesive film formed on the surface of a grain-oriented electrical steel sheet of the present invention.

FIG. 2 is a graph showing a relationship between a minimum bending diameter and a coefficient of thermal expansion of a portion of a coating in contact with a ground iron.

FIG. 3 is a graph showing a relationship between a minimum bending diameter and an average thermal expansion coefficient of a coating film.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-279747 (JP, A) JP-A-2-213483 (JP, A) JP-A-1-306570 (JP, A) JP-A-63- 227719 (JP, A) JP-A-63-186826 (JP, A) JP-A-62-103374 (JP, A) JP-A-3-75354 (JP, A) JP-A-62-182222 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 C23C 28/04 H01F 1/16 C21D 9/46 501

Claims (2)

(57) [Claims] 1. A grain-oriented electrical steel sheet which has been subjected to a final finish annealing in which an adhesive coating is formed on a surface of a ground iron, wherein the surface of the iron is a smooth surface or a magnetically smooth surface. Is a film having a coefficient of thermal expansion inclined in the thickness direction in which the coefficient of thermal expansion is reduced toward the outermost surface of the film , the film having an average coefficient of thermal expansion of 7 × 10 ^{− The} portion of the adhesion type coating which is less than ⁶ K ^-1 and which is in contact with the ground iron is a water treatment liquid containing phosphoric acid-chromic acid as a main component.
Coated and baked, has a coefficient of thermal expansion of 8 × 10 ^-6 K
An ultra-low iron loss grain-oriented electrical steel sheet characterized by being ^-1 or more. 2. The ultra-low surface according to claim 1, wherein the smooth surface is a smooth surface with Ra: 0.3 μm or less, and the magnetic smooth surface is a graining-like surface having a grain boundary step with Rmax: 0.1 μm or more. Iron loss oriented magnetic steel sheet.