JP2001164344A - Double oriented silicon steel sheet excellent in magnetic property, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a double oriented silicon steel sheet excellent in magnetic properties, in which deterioration in magnetic properties due to working strain is inhibited. SOLUTION: The structure of ferrite of the silicon steel sheet is composed of secondary recrystallized grains integrated at Miller indices 100} <100>. Further, the amount of oxides at the ferrite surface excluding a coating is controlled to <=1.0 g/m2 per side expressed in terms of the amount of oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention mainly relates to a transformer,
The present invention relates to a bi-directional electrical steel sheet having excellent magnetic properties suitable for use in iron core materials such as motors and generators, and a method for producing the same.

[0002]

2. Description of the Related Art Magnetic properties such as iron loss and magnetic permeability of an electromagnetic steel sheet depend on the crystal orientation. That is, the crystal grains of iron are easily magnetized in the direction of the Miller index <100> axis, and exhibit extremely good magnetic properties in this direction. Conventionally, widely used grain-oriented electrical steel sheets have a Miller index {110} <
001>, and exhibit good magnetic properties in the rolling direction (hereinafter, referred to as L direction).

On the other hand, Miller index {100} <00
The bidirectional electrical steel sheet obtained by secondary recrystallization of the normal cube orientation represented by 1> has excellent magnetic properties in two directions, a rolling direction and a direction perpendicular to the rolling direction (hereinafter, referred to as C direction). This is a magnetic steel sheet having the following characteristics. As a method of manufacturing a bidirectional magnetic steel sheet, a method of cross-rolling steel containing AlN as an inhibitor component, a method of secondary recrystallization using surface energy, and the like have been proposed. However, in these production methods, a wide and homogeneous steel strip cannot be produced at a low cost, so that mass production has not been achieved. Therefore, it cannot be said that the characteristics when such an electromagnetic steel sheet is actually processed into a core material such as a transformer or a generator have been sufficiently studied.

[0004]

SUMMARY OF THE INVENTION A bidirectional electrical steel sheet is
Compared with conventional one-way electrical steel sheets and non-oriented electrical steel sheets used in transformers, motors, generators, and the like, there is a problem that the characteristic deterioration due to processing is large. The reason for this is that bi-directional electrical steel sheets made by the conventionally known secondary recrystallization have a much larger crystal grain size than non-oriented electrical steel sheets. This is because deformation tends to occur and large distortion easily occurs.

[0005] A hard oxide film mainly composed of forsterite formed by high-temperature finish annealing also increases the end distortion. As a countermeasure against this, Japanese Patent Application Laid-Open No. 5-275222
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes reducing the non-magnetic oxide on the surface by pickling, polishing, or the like. However, simply reducing the nonmetallic material on the surface in this way reduces the insulating properties between the steel plates, and increases the iron loss even if the magnetic flux density increases, which is not preferable as an iron core material. In addition, pickling, polishing, and the like have an adverse effect on iron loss, such as uneven removal of oxides and introduction of distortion.

On the other hand, in the case of a grain-oriented electrical steel sheet similarly made by secondary recrystallization, the influence of strain is exerted by applying tension to the steel sheet by a forsterite film formed on the surface and a silica-phosphate coating. Technology to mitigate this is used. However, when such a tension coating is applied to a bidirectional magnetic steel sheet, there is a problem that the magnetic properties in either the L direction or the C direction are improved, but the other magnetic properties are deteriorated. The reason for this is that the industrially produced polycrystalline bidirectional electrical steel sheet has a variation in crystal grain orientation, so that only the characteristic of the one with the larger <001> axis accumulation in either the L direction or the C direction. This is because the tension is preferentially improved and the other property is rather deteriorated. This finding cannot be predicted from the results of experiments using a conventional unidirectional magnetic steel sheet, a single crystal having a normal cube orientation with small variation in crystal grain orientation, or a cut sample having a small size.

An object of the present invention is to propose a bi-directional electrical steel sheet having excellent magnetic properties, in which the deterioration of magnetic properties due to such processing strain is suppressed.

[0008]

Means for Solving the Problems The inventors of the present invention have comprehensively studied the magnetic properties of various bidirectional electrical steel sheets, including the effects of work strain, and as a result, have obtained good magnetic properties. A product form of grain-oriented electrical steel sheet was found.

[0009] That is, the oxide on the steel sheet surface that increases the processing strain is mainly formed by finish annealing. This finish annealing is intended for secondary recrystallization and purification of AlN and the like contained as an inhibitor, and is usually performed at a high temperature of 1200 ° C., so that oxidation of the base iron component cannot be avoided. In addition, the higher the temperature, the greater the deformation of the steel sheet, and the more likely it is for the steel sheets to adhere to each other. However, the oxide formed on the steel sheet surface increases as the annealing temperature increases, and the oxide formed on the steel sheet surface also increases due to the moisture and oxygen contained in the annealing separating agent as the annealing separating agent increases.

[0010] In this respect, if an inhibitor component that requires purification is previously removed from components in steel, purification during finish annealing becomes unnecessary, and the generation of oxides is suppressed by lowering the annealing temperature. It becomes possible. Therefore, the present inventors have searched for a method of obtaining a secondary recrystallized structure in a normal cube orientation from a Si-containing steel containing no inhibitor component,
Experiments on hot rolling, hot-rolled sheet annealing, cold rolling, recrystallization annealing, and finish annealing using a steel slab having a reduced inhibitor content of inhibitors such as Al, O, N, S, and Se were repeated.
As a result, a method for manufacturing a bidirectional electrical steel sheet consisting of a secondary recrystallized structure integrated in the normal cube orientation was developed.
-289523.

[0011] Next, the inventors have improved the above technique to further reduce the amount of surface oxides and eliminate the adverse effects of such oxides and the applied tension from the coating applied to the surface. In order to further improve the magnetic properties, the finish annealing atmosphere was changed in various ways, the type and thickness of the coating to be formed were changed, and a small EI core was manufactured by punching, and the magnetic properties were evaluated. While searching for conditions under which good core characteristics could be obtained. As a result, as a result of trial and error, they have come to develop a bidirectional electrical steel sheet that can obtain good iron core characteristics as described below.

That is, the gist configuration of the present invention is as follows. 1. An electromagnetic steel sheet with a coating on the surface,
The base iron consists of secondary recrystallized grains with a Miller index of {100} <001>, and the amount of oxides on the base iron surface excluding the coating is reduced to 1.0 g / m ² or less per surface in terms of oxygen content. A bi-oriented electrical steel sheet with excellent magnetic properties, characterized by being suppressed.

2. 2. The bidirectional electrical steel sheet according to 1 above, wherein a tension exerted on the steel sheet by the oxide and the coating on the surface of the ground iron is 5 MPa or less.

3. C: 0.003 to 0.08 wt%, Si: 2.0 to 8.
0 wt% and Mn: 0.005 to 3.0 wt%,
A steel slab having a composition of 02 wt% or less and S, Se, O and N reduced to 30 ppm or less is hot-rolled and, if necessary, subjected to hot-rolled sheet annealing. Cold rolling is performed two or more times between the layers to finish to the final sheet thickness, then, after recrystallization annealing, an annealing separator is applied as necessary, and then final finish annealing is performed, and further, flattening annealing is performed as necessary. After the application, in a method for producing a bidirectional electrical steel sheet comprising a series of steps of performing a coating pretreatment, (1) the average crystal grain size before final cold rolling is 200μm or more,
And the final rolling reduction is 60% or more and 90% or less. (2)
A method for producing a bi-directional electrical steel sheet having excellent magnetic properties, wherein the final finish annealing is performed at a temperature of 1100 ° C or less in an atmosphere having a dew point of ≦ 10 ° C. and O ₂ ≦ 0.1 vol%.

4. In the above 3, in the coating forming treatment, an organic resin coating or a semi-organic coating comprising an organic resin and an inorganic component is formed with a thickness of 5 μm or less, or an inorganic glassy coating is formed with a film thickness of 2 μm or less. A method for producing a bi-directional electrical steel sheet.

5. In the above item 3 or 4, the Al content is
A method for producing a bidirectional electrical steel sheet, comprising using a steel slab of less than 0.01 wt%.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the bidirectional electrical steel sheet of the present invention is composed of secondary recrystallized grains accumulated in a positive cube orientation. This is to improve the magnetic properties in both the L and C directions. As the components,
When Si is contained in an amount of 2 to 8% by weight, iron loss under AC excitation is effectively reduced, but even when Si is not contained, there is an effect. A thickness of 0.6 mm or less is advantageous for reducing iron loss under AC excitation, but is not limited to this thickness.

Next, the oxide formed mainly on the surface of the steel sheet at the time of finish annealing is 1.0 g / oxygen equivalent per one surface in terms of oxygen content.
it is important to suppress the m ² or less. Since the deformation of the cut or cutting surface during punching and these oxide content exceeds 1.0 g / m ² oxygen amount conversion is increased, a large strain is introduced into the peripheral cutting portion, significant degradation of the core loss This is because

This oxide is a single oxide or a composite oxide of a steel component and an annealing separator component, and is mainly forsterite, silica, alumina, magnesia or a spinel compound thereof. In addition, such an oxide may be formed by heat treatment such as decarburization annealing or flattening annealing in addition to the finish annealing. In this case as well, the final amount is 1.0 g / m ^{2 in} terms of oxygen content. It is necessary to suppress the following.

Further, it is necessary to apply a coating on the surface of the ground iron in order to enhance the insulating property. Further, the total tension exerted on the ground iron by the surface oxide and this coating is preferably 5 MPa or less. I mean,
If the tension is greater than 5 MPa, the magnetic characteristics of the <100> axis in the L direction and the C direction with the lower degree of integration are deteriorated. In order to reduce the tension exerted on this steel sheet, reduce the thickness of the oxide and coating, apply a material with a low baking temperature as a coating material, and use a coating with a small coefficient of thermal expansion or a small Young's modulus. It is effective to apply.

Next, the manufacturing method of the present invention will be described. The component composition of the material is as follows. C: 0.003 to 0.08 wt% By containing C in the range of 0.003 to 0.08 wt%, the normal cube orientation can be suitably obtained by secondary recrystallization. Although the reason is not clear, it is presumed that the formation of a deformation zone during rolling is promoted by the effect of solid solution C, and the number of recrystallization nuclei in the normal cube orientation increases.

Si: 2.0-8.0 wt% Si is a useful element for increasing electric resistance and improving iron loss, but its effect is poor if the content is less than 2.0 wt%.
In addition, γ transformation occurs and the hot-rolled structure changes significantly, and it transforms in the final finish annealing, so that good magnetic properties cannot be obtained. On the other hand, if the Si content exceeds 8.0 wt%, the secondary workability of the product deteriorates and the saturation magnetic flux density also decreases, so the Si content was limited to the range of 2.0 to 8.0 wt%.

Mn: 0.005 to 3.0 wt% Mn is an element necessary for improving hot workability, but if it is less than 0.005 wt%, the effect of its addition is poor.
If the content exceeds 3.0 wt%, secondary recrystallization becomes difficult, so the Mn content is limited to the range of 0.005 to 3.0 wt%.

Al: 0.02 wt% or less When Al is made 0.02 wt% or less, preferably less than 0.01 wt%,
Since secondary recrystallization occurs at a lower temperature, the finish annealing temperature can be lowered, not only to prevent coil adhesion,
An effect of suppressing oxide formation can be obtained.

S, Se, O and N: 30 ppm or less All of these elements inhibit the development of secondary recrystallization,
Moreover, it is a harmful element that remains in the base iron and deteriorates iron loss. Therefore, Se, S, O and N are all reduced to 30 ppm or less (preferably 20 ppm or less).

The molten steel adjusted to the above preferable composition is usually made into a slab by an ingot-making method or a continuous casting method. Further, a thin slab having a thickness of 100 mm or less may be directly manufactured using a direct casting method. The slab is heated by a usual method and hot rolled, but may be subjected to hot rolling immediately after casting without heating. In the case of thin cast slabs, hot rolling may be performed, or hot rolling may be omitted and the process may proceed to the subsequent steps. Since the slab heating temperature does not include the inhibitor component in the raw material component, a minimum temperature of about 1100 ° C. at which hot rolling is possible is sufficient.

Then, after hot-rolled sheet annealing is performed, if necessary, cold rolling is performed once or twice or more with intermediate annealing. Hot rolled sheet annealing is useful for improving magnetic properties. Similarly, sandwiching intermediate annealing between cold rollings is useful for stabilizing magnetic properties. However, since all of these will increase production costs, the selection of hot-rolled sheet annealing and intermediate annealing, and the annealing temperature and time are determined from the economic point of view and the need to keep the grain size before final cold rolling in an appropriate range. Is done.

In the present invention, after finish annealing,
In order to grow the 0｝ <001> structure, it is important that the average crystal grain size before final cold rolling is increased to 200 µm or more and the rolling reduction is in the range of 60 to 90%. Further, it is effective to perform such cold rolling at a temperature of 150 ° C. or more in order to cause secondary recrystallization in the normal cube orientation. Furthermore, cross rolling or cold rolling under rolling conditions in which the width of a steel strip is increased by low tension can also be applied.

Next, recrystallization annealing is performed. The annealing conditions are preferably 800 to 950 ° C. for 5 to 200 seconds in a wet hydrogen atmosphere, and it is preferable to reduce C in the steel to 0.003 wt% or less at which magnetic aging does not occur by this annealing.

Thereafter, an annealing separator is applied as required. As the annealing separator, a slurry or a colloid solution of a refractory powder such as silica, alumina, and magnesia is preferable. A method of attaching these refractory powders to a steel sheet by dry coating such as electrostatic coating is more preferable because moisture is not contained in the finish annealing atmosphere. Furthermore, a method of sandwiching a steel sheet whose surface is coated with these refractories by thermal spraying or the like can also be applied.

Next, finish annealing is performed. Here, in the finish annealing, in order to recrystallize the positive cube orientation again and grow sufficiently, it is desirable to maintain the temperature in a temperature range of 800 ° C. or more for 10 hours or more. On the other hand, the amount of oxides formed on the surface of the base iron must be 1 g / m ² or less per one surface in terms of oxygen content.
° C, O ₂ ≤ 0.1 vol%. Also,
To suppress oxide formation, the final annealing temperature should be 11
The temperature must be lower than 00 ° C, more preferably lower than 900 ° C. In order to limit the finish annealing temperature to 900 ° C. or lower as described above, it is preferable to limit Al to less than 0.01 wt% in order to lower the temperature at which secondary recrystallization occurs as described above.

Next, a coating forming treatment is performed. In such a coating forming treatment, in order to reduce the tension applied to the steel sheet, the thickness of the oxide and the coating is reduced, a material having a low baking temperature is applied as a coating material, the coefficient of thermal expansion is small or It is effective to apply a coating having a small Young's modulus.

The type of coating is not particularly limited as long as the applied tension is 5 MPa or less. For example, an organic resin coating or a semi-organic coating comprising an organic resin and an inorganic component is preferable. this house,
Examples of the inorganic component include one or more selected from phosphoric acid, phosphate, chromate, chromate, dichromate, boric acid, silicate, silica, and alumina. Coatings containing these organic resins are suitable because they also have the effect of suppressing distortion of the cut portion during cutting and punching, and preventing iron loss deterioration. The thickness of the organic resin coating or semi-organic coating is preferably 0.5 μm or more from the viewpoint of ensuring interlayer insulation, and is preferably approximately 5 μm or less from the viewpoint of reducing the tension and preventing the space factor from lowering.

Also, phosphate and chromate, chromate,
An inorganic vitreous coating comprising one or more components selected from dichromate and boric acid can also be applied. In the case of this inorganic glassy coating, the tension is 5MP
In order to keep the temperature below a, the baking temperature is preferably 400 ° C. or less, and the thickness of the coating is preferably 2 μm or less per side. In order to improve heat resistance, a small amount of silica or alumina fine powder or colloid may be contained.

[0035]

EXAMPLES Example 1 Si: 3.1 wt%, C: 0.012 wt%, Mn: 0.1 wt%, Al: 0.
009 wt%, N: 10 ppm, O: 13 ppm, S: 5 ppm and S
e: A steel slab containing 4 ppm and the balance being substantially Fe was produced by continuous casting. Then, a hot-rolled sheet having a thickness of 2.7 mm is formed by hot rolling, and then hot-rolled sheet annealing is performed at 1140 ° C and a soaking temperature of 60 seconds, and cold rolling is performed at 270 ° C.
Finished to a final thickness of 0.35mm. Here, the average crystal grain size before final cold rolling was 280 μm. Then 40% H ₂ -60%
Recrystallization annealing was performed at 920 ° C. and 30% soaking in an atmosphere of N ₂ and a dew point of 50 ° C. to reduce C in steel to 0.002 wt%. Then, an annealing separator in which silica powder and alumina powder were mixed at a ratio of 3: 1 was electrostatically applied to the surface of the steel sheet, wound around a coil, and then subjected to finish annealing. Finish annealing was performed by raising the temperature from room temperature to 800 ° C. in 5 hours, from 800 ° C. to 950 ° C. in 25 hours, maintaining the temperature at 950 ° C. for 36 hours, and then cooling the furnace. Here, the amount of oxide formed on the surface of the steel sheet was controlled by changing the amount of water vapor introduced into the furnace atmosphere.

Thereafter, after removing the annealing separator from the coil by washing, the steel strip is annealed at 840 ° C. for 60 seconds in a 5% H ₂ -95% N ₂ atmosphere while applying tension to flatten the organic strip. A 1.0 μm thick semi-organic coating dispersed in an inorganic component consisting of magnesium dichromate and boric acid was formed. Through the above steps, a bidirectional electrical steel sheet comprising secondary recrystallized grains accumulated in a positive cube orientation with a grain size of about 20 mm was obtained. Next, an EI-48 type EI core sample was manufactured from this steel plate by punching, and the iron loss characteristics at 1.5 T and 50 Hz were measured. Table 1 shows the obtained results in relation to the oxygen basis weight of the steel sheet surface.

[0037]

[Table 1]

As shown in Table 1, when the amount of oxide on the surface of the steel sheet was suppressed to 1.0 g / m ² or less in terms of the amount of oxygen, excellent iron loss characteristics could be obtained.

Example 2 A steel plate produced in the same manner as in Example 1 and comprising secondary recrystallized grains in a positive cube orientation having a surface oxide amount of 0.4 g / m ^{2 in} terms of oxygen amount, with a different thickness. An inorganic coating was applied. This coating is obtained by baking at 800 ° C. a solution obtained by mixing colloidal silica with a solution comprising aluminum phosphate, potassium chromate and boric acid to form a film having a thickness of 1 μm. Here, increasing the content of colloidal silica reduces the thermal expansion coefficient of the coating,
The tension applied to the steel sheet increases. 0-6MPa
And the magnetostriction was measured, and the compressive stress when the magnetostriction rapidly increased was defined as the tension applied to the steel sheet. Table 2 shows the results obtained by measuring the iron loss of this steel sheet when excited in the L and C directions at 1.5 T and 50 Hz by the Epstein test.

[0040]

[Table 2]

As apparent from Table 2, when the applied tension to the steel sheet exceeds 5 MPa, the iron loss in the C direction is greatly deteriorated, which is not preferable. On the other hand, when the magnitude of the applied tension is 5
When the pressure is less than MPa, especially less than 3 MPa, deterioration of iron loss in the C direction becomes extremely small, and suitable iron loss characteristics are obtained.
The coating baked at 350 ° C. without adding colloidal silica and the semi-organic coating used in Example 1 hardly give tension to the steel sheet, and therefore, the iron loss after the coating was formed also averaged in the L direction: 1.22 W / kg, C direction average: 1.
A good result of 45 W / kg was obtained.

Example 3 A steel slab having the composition shown in Table 3 was prepared by changing the conditions of hot rolling, hot-rolled sheet annealing, cold rolling, recrystallization annealing and finish annealing to various 0.35 mm-thick electromagnetic steel sheets. After that, flattening annealing and coating forming treatment were performed. These samples were evaluated for iron loss at 1.5 T and 50 Hz by an Epstein test. Note that the Epstein test sample is in the L direction and C direction.
Samples cut in the direction were used in half. Table 3 shows the measurement results of samples having the lowest iron loss among samples obtained from steel having the same composition under various manufacturing conditions.

[0043]

[Table 3]

As shown in Table 3, all of those satisfying the component composition range of the present invention had good iron loss, whereas C, Mn, Al, S, Se, O, Any one of N out of the proper range has increased iron loss, and is not suitable as a core material.

Example 4 The secondary recrystallization onset temperature of a steel in which only the Al content was changed was investigated based on the components of conforming example 10 in Table 3. A sample cut to a length of 400 mm and a width of 50 mm from a steel plate that has been subjected to recrystallization annealing is placed in an electric furnace having a temperature difference of 800 to 1200 ° C., held for 50 hours, and then subjected to macro etching. The secondary recrystallization initiation temperature was evaluated by comparing the presence or absence of secondary recrystallization with the corresponding temperature. Table 4 shows the obtained results.

[0046]

[Table 4]

As shown in Table 4, secondary recrystallization occurs when the content of Al is 0.02 wt% or less. In particular, when the Al content is less than 0.01 wt%, the secondary recrystallization onset temperature becomes lower, and the finish annealing at a lower temperature becomes possible, which is extremely advantageous in reducing the amount of oxides generated on the steel sheet surface. .

[0048]

Thus, according to the present invention, by suppressing the amount of oxide on the surface of the base iron to 1.0 g / m ² or less in terms of oxygen, a bidirectional electrical steel sheet with small characteristic deterioration due to working can be effectively obtained. be able to. Further, by setting the total tension exerted on the steel sheet by the oxide and the coating to 5 MPa or less, it is possible to obtain a bidirectional electromagnetic steel sheet having good magnetic properties in both the L direction and the C direction. And the iron loss of iron cores, such as a transformer, a motor, and a generator, can be reduced remarkably by the above-mentioned bidirectional electrical steel sheet showing good magnetic characteristics of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 22/28 C23C 22/28 H01F 1/16 H01F 1/16 A 1/18 1/18 (72) Invention Person Takeshi Imamura 1-chome, Kawasaki-dori Mizushima, Kurashiki-shi, Okayama Pref. (72) Inside Mizushima Steel Works, Kawasaki Steel Corporation (72) Inventor Mitsumasa Kurosawa 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Mizushima, Kawasaki Steel F-term in the steelworks (reference) 4K026 AA03 AA22 BA01 BA02 BA03 BA08 BB05 BB10 CA16 CA20 CA22 CA24 CA39 CA41 DA16 EA07 EB08 EB11 4K033 RA04 SA03 TA02 5E041 AA02 AA19 BC01 BC05 BC08 CA02 CA04 HB05 NN07NN05N

Claims (5)

[Claims] 1. An electromagnetic steel sheet having a coating on its surface, wherein the ground iron is composed of secondary recrystallized grains accumulated at a Miller index of {100} <001>, and the oxide of the ground iron surface excluding the coating is removed. The amount is 1.
A bi-directional electrical steel sheet having excellent magnetic properties, characterized by being suppressed to 0 g / m ² or less. 2. The bidirectional electrical steel sheet according to claim 1, wherein the tension exerted on the steel sheet by the oxide and the coating on the surface of the ground iron is 5 MPa or less. 3. C: 0.003 to 0.08 wt%, Si: 2.0 to 8.0
wt% and Mn: 0.005 to 3.0 wt%, and Al
A steel slab having a component composition in which S, Se, O, and N are reduced to 30 ppm or less, respectively, is hot-rolled, and if necessary, subjected to hot-rolled sheet annealing, and then subjected to one or intermediate annealing. Finished to the final thickness by performing cold rolling two or more times between
Next, after recrystallization annealing, an annealing separating agent is applied as necessary, a final finish annealing is applied, and further, a flattening annealing is applied as necessary, followed by a series of steps for performing coating treatment. In the method for producing grain-oriented electrical steel sheets, (1) the average crystal grain size before final cold rolling is 200 μm or more, and the final cold rolling reduction is 60% or more and 90% or less; A method for producing a bidirectional electrical steel sheet having excellent magnetic properties, wherein the method is performed at a temperature of 1100 ° C. or less in an atmosphere with a dew point ≦ 10 ° C. and O ₂ ≦ 0.1 vol%. 4. The coating forming treatment according to claim 3, wherein an organic resin coating or a semi-organic coating comprising an organic resin and an inorganic component is formed with a thickness of 5 μm or less, or an inorganic vitreous coating is formed. Thickness: a method for producing a bidirectional electrical steel sheet, wherein the thickness is 2 μm or less. 5. The method according to claim 3, wherein the Al content is
A method for producing a bidirectional electrical steel sheet, comprising using a steel slab of less than 0.01 wt%.