KR20140085747A - Tension coating composite for oriented electrical steel steet, forming method of tension coating using the same and oriented electrical steel steet using the method - Google Patents

Abstract

The present invention relates to a tension coating composite for a grain-oriented electrical steel sheet, a method of forming a tension coating of the grain-oriented electrical steel sheet using the same, and a grain-oriented electrical steel sheet manufactured by the method. The tension coating composite contains colloidal silica, metal phosphate, organic modified colloidal silica, and an oxidation promoter, in which the organic modified colloidal silica is obtained by substituting a part of oxygen of the colloidal silica with an organic matter.

Description

TECHNICAL FIELD [0001] The present invention relates to a tensile coating composition for a directional electric steel sheet, a method for forming a tensile film of a directional electric steel sheet using the same, and a directional electric steel sheet produced by the method. BACKGROUND ART METHOD}

TECHNICAL FIELD The present invention relates to a tension coating composition for a directional electric steel sheet, a method for forming a tensile film of a directional electric steel sheet using the same, and a directional electric steel sheet produced by the method, and more particularly to a method for preventing formation of a base coat layer To a tensile coating composition for a directional electric steel sheet and a method for forming an insulating film using the same.

Generally, a grain oriented electrical steel sheet has 3.1% Si component, and the grain orientation is oriented in the (110) [001] direction, and has excellent magnetic properties in the rolling direction, It is used as an iron core material for electric motors, generators, and other electronic devices.

Recently, oriented electrical steel sheets with high magnetic flux density have been commercialized, and materials with low core loss are required. For electrical steel, iron loss improvement can be approached in four technical ways.

First, a method of accurately orienting the {110} < 001 > crystal grain orientations including the easy magnetization axis of the grain-oriented electrical steel sheet in the rolling direction, second, the materialization of the material, and third, the magnetic domain miniaturization through chemical and physical methods A method of micronization, and fourth, improvement of surface physical properties by chemical methods such as surface treatment or surface tensioning.

As a representative example, it is possible to improve the magnetic properties of the material by positively improving the properties of the surface of the oriented electrical steel sheet. It is produced through the chemical reaction of the MgO slurry used as an adhesion preventive agent for the oxide layer and the coil necessarily generated in the decarburization annealing process The purpose can be achieved by removing the base coat layer.

Techniques for removing the base coating include a method for forcibly removing a base coated product such as a conventional material with sulfuric acid or hydrochloric acid and a technique for removing or suppressing the base coating in the process of producing the base coating (US Pat. No. 4,543,134) discloses a method in which chlorides are added to MgO, which is an annealing separator, and then Al ₂ O ₃ powder is applied as an annealing separator by using a surface etching effect in a high temperature annealing process, And the technique of not forming the base coating itself in the process.

The ultimate direction of the above-mentioned technology is to prevent the base coating layer generated through the chemical reaction of the MgO slurry used as the anti-fusion agent between the oxide layer and the coil, which are generated in the decarburization annealing process, The present invention relates to a manufacturing method of remarkably improving the magnetic properties of a grain-oriented electrical steel sheet by removing surface pinning sites which cause deterioration.

However, the most serious problem when the base-coated free electric steel sheet is manufactured is that it is most difficult to form an insulating coating on the material because the surface of the manufactured material is too smooth and the roughness is low. As a base insulating coating material, There is a problem that the insulation of the level required by the conventional directional electrical steel sheet can not be matched.

On the other hand, in the case of a glass-less type oriented electrical steel sheet in which the base coating is excluded, the adhesion of the coating agent is remarkably poor compared with that of the conventional resin, and various methods for overcoming this problem have been proposed. Japanese Patent Publication No. 1993-279746 discloses that the adhesion of the insulating coating is improved by pretreatment through formation of a thin oxide layer on a directional electric steel sheet free from a forsterite coating. Japanese Patent Publication No. 1993-311453 discloses a method of immersing a specimen in a sulfuric acid solution, Through the formation of fine pits, good adhesion between the film and the material was induced.

However, all of the methods used in the above-described techniques are required to be pre-treated before coating, and in this case, commercialization of glass-free or base-coated free-form steel sheet can be inhibited due to cost increase due to pretreatment and process complexity.

Therefore, it is urgent to develop an effective coating agent for a steel sheet without austenite coating, such as glass-free or base coating free.

In order to solve the above problems, the present invention provides a tension coating composition using organic substituted silica, colloidal silica, metal phosphate or the like, in which a part of the molecular structure is substituted with an organic material, A method for forming a film, and a directional electrical steel sheet produced thereby.

In one or more embodiments of the present invention, the organic substituted colloidal silica comprises a colloidal silica, a metal phosphate, an organic substituted colloidal silica, and an oxidation promoter, wherein the organic substituted colloidal silica is an aromatic A tension coating composition for an electric steel sheet may be provided.

Wherein the metal phosphate is a mixed solution of magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ), and the colloidal silica May be 15 to 50 parts by weight, and the oxidation promoting agent may be 2 to 15 parts by weight.

The metal phosphate may be mixed with the first magnesium phosphate and the first aluminum phosphate in a volume ratio of 0.5 / 9.5 to 3/7.

The organic substituted colloidal silica may be mixed in an amount of 70 to 150 parts by weight based on 100 parts by weight of the metal phosphate solution, and the organic substance contained in the organic substituted colloidal silica is at least one selected from the group consisting of an alkyl group, a methyl group, .

The colloidal silica has a solid fraction of 25 to 35% by weight.

The oxidation promoter is selected from the group consisting of NaNO ₃ , Zn (NO ₃ ), Ni (NO ₃ ), sodium perborate, pyridine, hydroxylamine sulfate, sodium bromate, Hydroxyethyl ammonium chloride, N-cyclohexylsulfamic acid, and the like.

In one or more embodiments of the present invention, the tensile coating composition is coated on a directional electric steel sheet having a primary coating film which is annealed and heated to 550 to 900 DEG C to form a tensile film. A method of forming a tension film for an electric steel sheet can be provided.

The tension coating composition is controlled at a temperature ranging from 15 to 25 ° C, and the coating amount is applied in a range of 0.5 to 6.0 g / m ² , and the heating time is 10 to 50 seconds .

In one or more embodiments of the present invention, a directional electrical steel sheet formed by any one of the above methods can be provided.

According to the embodiment of the present invention, it is possible to improve the adhesion of the coating agent of the base-coated pre-oriented electrical steel sheet having a very low surface roughness and excellent gloss.

In addition, when the tensile coating agent is applied and dried, the organic component in the coating agent is thermally dissipated to induce a regular fine pore shape to improve the insulating property, and by appropriately controlling the solid fraction of the metal phosphate, excellent adhesion can be secured, It is possible to improve the tensile force.

FIG. 1 shows the molecular structure of a conventional inorganic component-based coating agent when dried.
2 shows the molecular structure upon drying of the tension coating composition according to an embodiment of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

In the embodiment according to the present invention, when applying a tension coating agent for a grain-oriented electrical steel sheet to a conventional glass-type oriented electrical steel sheet or a base-coated free material, the insulating defect due to the absence of the base coat layer is introduced into the coating agent, , Selective thermal degradation of organic materials in silica during high temperature drying and resulting nanoporous porosity.

Further, in the embodiment according to the present invention, the poor adhesion between the directional electrical steel sheet (material) and the coating agent is controlled by suitably adjusting the solid fraction of the metal phosphate, thereby exhibiting excellent adhesion and interface characteristics with the material and correspondingly improving the film tension Respectively.

First, the main components of a conventional Cr-type tensile coating agent will be discussed below.

In order to impart the film tension to the electrical steel sheet, it is made up of colloidal silica, a coating agent, metal phosphate which imparts adhesion to the steel sheet interface, CrO ₃ and a small amount of additives for reinforcing other functions. Therefore, if Cr is excluded from such a constitution, the adhesion and the ability of ultimately imparting tensile force due to the coating due to the coating are lowered, and a glassless type directional electric steel sheet or a base coating free material It is difficult to ensure insulation and adhesiveness after forming a film because the absence of the base coating layer and the surface roughness of the base coating layer are more favorable than those of ordinary materials.

Typically, a major component of the Cr-based tensile coating agent is a colloidal silica that imparts a film tension, a coating agent, and a metal phosphate (such as magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) Aluminum (Al (H ₂ PO ₄ ) ₃ ) mixed solution, CrO _3, and a small amount of additives for reinforcing other functions.

At this time, the colloidal silica serves to impart a film tension to the tension coating agent, and the metal phosphate is used as a binder of the tension coating agent to provide adhesion between the coating agent and the base material.

Metal phosphates that provide such adhesion proceed with the dehydration condensation reaction depending on the drying temperature, and the reaction of forming the metal phosphates proceeds as follows.

- Low temperature (coating temperature ≤ 550 ℃)

Phosphate: 2Al (H ₂ PO ₄ ) ₃ -> Al ₂ (H ₂ P ₂ O ₇ ) ₃ + 3H ₂ O ↑ --------------- (1)

- High temperature (coating temperature ≥ 650 ℃)

Phosphate: nAl ₂ (H ₂ P ₂ O ₇ ) ₃ -> [Al (PO ₃ ) ₃ ] _2n + 3nH ₂ O ↑ --------------- (2)

At this time, when Cr is present in the coating agent, the free phosphate existing in a low temperature state as shown in the formula (1) can be made into a state capable of forming a film at a low temperature through the following reaction.

CrO ₃ + 2H ₃ PO ₄ -> Cr (PO ₄ ) ₂ + 6 H ₂ O (3)

In the case of the tension coating agent containing Cr as described above, chromium oxide improves the reactivity of phosphate even at a low temperature as well as suppressing the generation of free phosphoric acid which causes sticky failure after drying the film, as in the formula (3).

During drying of the film, hexavalent chromium (Cr ⁶⁺ ) reacts with water present in the coating to change into a H ₂ CrO ₄ compound. H ₂ CrO ₄ reacts with Fe present in the steel sheet to form FeO, Make a condition that can react with phosphate. This action is very helpful in improving the adhesion between the steel sheet and the coating agent, and consequently helps to improve the film tension.

As well as, Cr ⁶⁺ can be reacted vorticity generated FeO increase the film denseness by condensation polymerization of the Cr ³⁺ reduction and also reduced to Cr ^3+, which has a profound effect on improving the film tension. However, since chromium is excluded, it is not possible to have such an effect. Therefore, in the examples according to the present invention, attention is paid to the relationship between the drying mechanism of each of the tension coating agent components, the electrical insulation and the film tension.

In the examples according to the present invention, it was found that the drying mechanism between the components is different, and when the drying is not completed, the insulating property and the coating adhesion property are lowered. In particular, the water constituting the tension coating agent is composed of water added to give a total weight to the water contained in each component itself, and the interpretation of their drying mechanism is not yet known.

However, in the embodiment according to the present invention, the drying rate of the metal phosphate, especially the magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) phosphate, in the tension coating agent component is inferior to the other components and the constitution of the metal phosphate The composition ratio of the aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) was designed to improve the drying ability of the coating agent.

Therefore, in the case of the metal phosphate, the ratio of the first magnesium phosphate to the first aluminum phosphate is preferably 0.5 / 9.5 to 3/7 when the mixed solution of the first magnesium phosphate and the first aluminum phosphate is constituted, The best adhesion between the material and the film is maintained by maintaining the range.

In addition, the adhesion between the coating and the steel sheet is improved to improve the tensile stress as a main purpose of the coating agent, and the tensile stress due to the coating can be confirmed by the following equation (4) because of the improved adhesion.

As shown in Equation (4), in addition to the chain reaction of silica generated at a high temperature of 800 ° C or higher in drying the coating, a process of forming a solid film by a complex chemical reaction between components that can be generated at a low temperature, And the metal phosphate serving as a binder of the coating agent.

Therefore, the adhesion can be indirectly confirmed by measuring the tensile force due to the film, and in the embodiment according to the present invention, the film tension is the best at a ratio of the first magnesium phosphate / aluminum phosphate to the aluminum phosphate / 0.5 to 9/3 to 7/7 Respectively.

However, as can be seen from Table 1 of Example 1 to be described later, adhesion can be ensured by adjusting the composition of the metal phosphate in the coating agent, but insulation is extremely low as compared with conventional materials, There was no. The reason for this is that when applied to a conventional glass-less type oriented electrical steel sheet or base coated free material, the insulation of the product can be expected only by the effect of the insulation coating due to the absence of the base coating layer. This is because the double insulation effect by the tension coating could not be seen.

In order to solve the above problems, in the embodiment of the present invention, the limit of the insulation contribution by the conventional insulating coating, that is, the tension coating, is grasped, and the insulating coating by the tension coating alone Respectively.

For this purpose, in the embodiment according to the present invention, a material having a low dielectric constant is introduced into the coating material so that an air layer having the lowest dielectric constant can be formed in the coating material.

As described above, since the main components of the conventional tension coating agent are inorganic materials, they are thermally stable and form a very dense film at around 850 ° C, which is a drying condition. However, when porous irregular voids are formed on a dense film for the purpose of improving insulation, the corrosion resistance of the coating surface is drastically lowered due to penetration of a material such as moisture.

In order to prevent the degradation of corrosion resistance while improving the insulation of the densely formed film, it is important to uniformly form nano-level pores in the film. In the embodiment of the present invention, the organic substituted colloidal silica is coated with a coating , And when the coating agent is dried, only the organic substituted chemical chain selectively induces thermal degradation, thereby forming very fine pores in the coating film.

FIG. 2 illustrates the molecular structure upon drying of the tensile coating agent according to an embodiment of the present invention. Referring to FIG. 2, by selectively deteriorating only colloidal silica that is organically substituted in an organic substituted chemical chain, micropores .

On the other hand, FIG. 1 shows a molecular structure of a conventional tension coating agent upon drying. Referring to FIG. 1, it can be seen that voids are not formed during drying.

In the same manner as described above, the insulating property of the coating is improved, and a nanoporous tension coating agent which does not deteriorate the corrosion resistance can be obtained.

Hereinafter, the tension film composition according to the present invention will be described. The tensile coating compositions in the examples according to the present invention include organic substituted colloidal silica, metal phosphates, colloidal silica and an oxidation promoter. The organic substituted colloidal silica makes a decisive contribution to the improvement of the insulation of the coating. The organic substituted colloidal silica in the examples according to the present invention means that the oxygen component in the colloidal silica component is partially replaced with an organic substance.

The tensile strength film composition according to the present invention includes 15 to 50 parts by weight of colloidal silica, 70 to 150 parts by weight of organic substituted colloidal silica, and 2 to 15 parts by weight of an oxidation promoter per 100 parts by weight of the metal phosphate solution do.

If the amount of the organic substituted colloidal silica added is less than 70 parts by weight, adequate pores can not be formed in the film, resulting in poor film insulation. If the added amount exceeds 150 parts by weight, coarse pores are formed in the film, The content of the organic substituted colloidal silica in the examples according to the invention is limited to the above range. At this time, the organic substance contained in the organic substituted silica may be any one or more selected from an alkyl group, a methyl group, an ethyl group and a propyl group.

 The colloidal silica serves to impart a tensile stress to the material by forming a ceramic layer having a low thermal expansion coefficient when the coating material is baked, and includes 15 to 50 parts by weight of colloidal silica relative to 100 parts by weight of the metal phosphate solution. In the embodiment of the present invention, the solid fraction of the colloidal silica is 25 to 35% by weight, and in particular, the pH-acidic substance is used.

If the addition amount of the colloidal silica is less than 15 parts by weight, a proper ceramic layer can not be formed and it is difficult to impart tensile stress to the material. When the amount exceeds 50 parts by weight, the solid content ratio of the coating material increases, The content of the colloidal silica in the examples according to the present invention is limited to the above range.

In addition, in the embodiment of the present invention, the adhesion of the coating agent can be improved by adding a film-forming accelerator for facilitating the drying of the film. As the film-forming accelerator, an oxidizer form can be used. In the embodiment of the present invention, NaNO ₃ , Zn (NO ₃ ), Ni (NO ₃ ), Sodium perborate, Pyridine, Hydroxyl amine sulfate, Sodium Bromate, Hydroxyl ammonium chloride ), N-cyclohexylsulfamic acid, and the like.

If the amount of the oxidation promoter is less than 2 parts by weight, the corrosion resistance of the coating is lowered. When the amount of the oxidation promoter is more than 15 parts by weight, The viscosity may be increased to cause problems in applicability. Therefore, the oxidation promoter in the examples according to the present invention is limited to the above range.

In the examples according to the present invention, the tensile coating composition having the above composition was applied on the surface of the grain-oriented electrical steel sheet so that the dry coating amount was 0.5 to 6.0 g / m ² , particularly 4.0 to 5.0 g / m ² , And an insulating film is formed by heating for 10 to 50 seconds in a temperature range of 900 占 폚. At this time, the solution temperature of the tension coating composition is controlled at 15 to 25 ° C. so that the coating amount can be realized to be 4.0 to 5.0 g / m ² .

If the temperature of the tension coating composition is lower than 15 ° C, the viscosity increases and it is difficult to control a uniform amount of coating. When the temperature is higher than 25 ° C, gelation of colloidal silica as a main component of the coating accelerates, The temperature of the composition of the tension coating agent in the examples according to the present invention is limited to the above range.

Hereinafter, embodiments of the present invention will be described in more detail.

[Example 1]

Si: 3.26%, C: 0.055%, Mn: 0.12%, Sol. (Comparative Example) in which a base coating is present, and a forsterite layer is formed for reducing iron loss, in addition to the above-mentioned directional electric steel sheet containing 0.026% of Al, 0.042% of N, 0.0042% of S, 0.0045% of S and Sn, Free coating of the base coating (intrinsic) was intentionally prevented.

When the steel sheet was dried at 850 ° C for 30 seconds by using a directional electric steel sheet (300 * 60 mm) having a primary coating film of 0.23 mm thickness and finishing annealed, the coated surface had a tensile stress due to the coating agent , And the degree of such warpage (H) was measured to evaluate the tensile strength of the film.

The evaluation method is as follows.

SRA (stress relief annealing) was heat treated in a dry 100% N2 gas atmosphere at 750 ° C for 2 hours. The insulation was expressed as the stored current value when a current of 0.5 V, 1.0 A was applied under 300 PSI pressure , And the adhesion is a minimum arc diameter without peeling off when the SRA before and after SRA are bent at 180 ° in contact with a circular arc of 10, 20, 30 to 100 mmf.

In order to improve the insulation and adhesion of the tensile coating agent, first the magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) phosphate component, which is a main component that lowers the drying speed and causes incomplete drying, Phosphate.

The coating thus prepared was applied to the specimen at a rate of 4 g / m &lt; ² &gt; and the insulation and coating tension were measured. At this time, as shown in Table 1, when the Mg ratio in the metal phosphate composition ratio was increased, the insulating property and the coating tension were lowered. This is because, as described above, the magnesium phosphate monobasic phosphate has a slow drying rate compared to the aluminum phosphate monobasic, and the other components of the coating agent are prevented from being completely dried in the drying furnace. As a result, And it is expected that the adhesion and the coating tension will be lowered.

Particularly, these results show that the base coating does not exist on the surface of the base material, but the base coating free material exhibits a remarkable contrast. In the case of the base coating free material having a smooth surface, the wettability of the coating material In the case of a component system where the ratio between the components falls and the general tension coating agent, that is, the metal phosphate component, is not appropriately adjusted, it shows a coating adhesion that is not commercially available.

In the embodiment according to the present invention, in the case of a component system in which the composition ratio of aluminum phosphate is too high (when the magnesium phosphate ratio in Table 1 is less than 0.5), sticky defects may occur due to sensitivity to humidity present in the air after coating The case was excluded as a component system.

Therefore, in the embodiment of the present invention, the magnesium / aluminum phosphate ratio in Table 1 was set to a condition of 2.5 / 7.5, and a method of improving the insulation based on the composition ratio of this standard was sought.

Psalter
Kinds Metal phosphate
(50 g) Silica
(g) Solid silica
(g) Insulation
(mA) Coating tension
(kgf / mm ² ) Sticky Castle Mg Al Normal material
(Base
coating)
0 100 48 2.5 95 0.45 sticky 5 95 48 2.5 110 0.42 Good 15 85 48 2.5 143 0.41 Good 25 75 48 2.5 150 0.41 Good 40 60 48 2.5 250 0.39 Good 50 50 48 2.5 263 0.39 Good 75 25 48 2.5 270 0.38 Good 90 10 48 2.5 298 0.36 Good 100 0 48 2.5 310 0.36 Good Base
coating
free
product


0 100 48 2.5 350 0.39 sticky 5 95 48 2.5 362 0.36 Good 15 85 48 2.5 388 0.37 Good 25 75 48 2.5 392 0.40 Good 40 60 48 2.5 400 0.34 Good 50 50 48 2.5 436 0.33 Good 75 25 48 2.5 449 0.31 Good 90 10 48 2.5 498 0.30 Good 100 0 48 2.5 520 0.28 Good Typically, Cr-type coating 630 0.15 Bad

Psalter
Kinds Metal phosphate
(100 g) Colloidal silica
(g) Organic substitution
Colloidal
Silica
(g) Insulation
(mA) Coating tension
(kgf / mm ² ) Remarks Mg Al Base
coating
free 25 75 35 0 332 0.40 25 150 0.46 50 98 0.49 70 46 0.50 90 32 0.51 120 55 0.49 150 84 0.42 170 106 0.43 200 120 0.42 50 50 100 - 392 0.40 Cr-type
Coating agent
apply Normal material
(Base
coating) 50 50 100 - 150 0.41

Table 2 shows the surface properties of a coating material prepared by applying organic substituted colloidal silica to the specimen.

As can be seen from Table 2, the insulating properties vary depending on the weight of the organic substituted colloidal silica. In particular, when 50 g or more is added, the insulating layer exhibits an excellent insulating property over 50 to 100 mA compared to a conventional oriented electrical steel sheet insulating coating having both a base coating layer and a tension coating layer, and the coating tension is improved by more than 20% Able to know.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (11)

Colloidal silica, metal phosphates, organic substituted colloidal silica, and an oxidation promoter,
Wherein the organically substituted colloidal silica is obtained by replacing a part of oxygen of the colloidal silica with an organic material. The method according to claim 1,
The metal phosphate is a mixture of magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and aluminum phosphate (Al (H ₂ PO ₄ ) ₃ )
Wherein the colloidal silica is contained in an amount of 15 to 50 parts by weight based on 100 parts by weight of the metal phosphate solution and 2 to 15 parts by weight of the oxidation accelerator is added. 3. The method according to claim 1 or 2,
Wherein the metal phosphate is a mixture of the first magnesium phosphate and the first aluminum phosphate in a volume ratio of 0.5 / 9.5 to 3/7. The method of claim 3,
Wherein the organically substituted colloidal silica is mixed in an amount of 70 to 150 parts by weight per 100 parts by weight of the metal phosphate solution. The method of claim 3,
Wherein the organic substance contained in the organic substituted colloidal silica is at least one selected from the group consisting of an alkyl group, a methyl group, an ethyl group and a propyl group. The method according to claim 1,
Wherein the colloidal silica has a solid fraction of 25 to 35% by weight. 6. The method of claim 5,
The oxidation promoter is selected from the group consisting of NaNO ₃ , Zn (NO ₃ ), Ni (NO ₃ ), sodium perborate, pyridine, hydroxylamine sulfate, sodium bromate, Wherein the coating composition is at least one selected from the group consisting of hydroxylamine hydrochloride, N-cyclohexylsulfamic acid, and the like. A method for producing a tensile strength film, which comprises applying a tensile coating composition according to any one of claims 1 to 8 on a directional electric steel sheet having a primary coated film and finishing and annealing at 550 to 900 ° C to form a tensile film A method of forming a tensile strength film for a steel sheet. 9. The method of claim 8,
Wherein the tension coating composition is controlled at a temperature ranging from 15 to 25 占 폚. 10. The method according to claim 8 or 9,
Wherein the coating amount is in the range of 0.5 to 6.0 g / m ² , and the heating time is 10 to 50 seconds. A directional electrical steel sheet formed by any one of claims 8 to 10.

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