JP5236077B2 - Non-chromium coating agent for grain-oriented electrical steel sheet, electrical steel sheet using the same, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a coating agent that does not contain chromium, exhibits corrosion resistance after formation of an insulating film, excellent adhesion to the material and interface characteristics, and improves film tension, a method for producing the same, and directional electricity using the same. It is related with a steel plate and its manufacturing method.

  The coating agent of the present invention is a coating agent that does not contain chromium, and can be used as a coating agent for grain-oriented electrical steel sheets.

  The grain-oriented electrical steel sheet contains 3.1% Si component and has excellent magnetic properties in the rolling direction. Therefore, iron cores such as transformers, electric motors, generators and other electronic devices are used. Used as a material.

  A good insulating coating must basically have a uniform hue with no defects in appearance, but recently, high-flux-density grain-oriented electrical steel sheets have been commercialized to pursue higher tension in the final insulating film. In fact, it was confirmed that the high-strength insulating film greatly contributes to the improvement of the magnetic properties of the final product.

  Various methods have been proposed to form a high-strength film, but the directional electrical steel sheet currently commercialized has a coefficient of thermal expansion between the steel sheet and the insulating film formed on the forsterite base film. By using the difference to give a tensile stress to the steel sheet, the iron loss reduction effect is achieved. As a conventional representative method for forming an insulating film, Japanese Patent Application Laid-Open No. 11-71683 proposes a method in which film tension is improved using colloidal silica having a high glass transition temperature, and Japanese Patent No. 3098691 and Japan Japanese Patent No. 2688147 proposes a technique for forming a high-tensile oxide film on an electrical steel sheet using a mixed liquid of alumina sol (alumina sol) mainly composed of alumina and boric acid. Also, in Korean Patent No. 10-0377566, a forsterite base is formed by forming a first layer composed of hydrogen phosphate containing a specific metal atom and silica on a forsterite base film. A technique has been proposed in which an improvement in adhesion between the film and the insulating film is induced, and a second layer mainly composed of aluminum borate is formed thereon, thereby providing a stronger film tension effect.

  However, the composition of the coating liquid according to the above-described conventional technology necessarily contains chromium oxide, and its use is limited in view of the fact that environmental regulations are strengthened.

  For this reason, in recent years, non-chromatization has been actively performed on electrical steel sheets in response to stricter environmental regulations. However, in the case of non-oriented electrical steel sheet coating agents, corrosion resistance and adhesion are weakened by non-chromatization. In order to reinforce, a method of introducing a phosphate and a method of inducing a barrier effect by introducing colloidal silica have been actively proposed. However, all of the non-chromium coating agents that have phosphate or colloidal silica as the main axis have the limitations on the wettability (sticky) of phosphate and the corrosion resistance of colloidal silica. ing.

  As a conventional non-chromium tension coating agent for grain-oriented electrical steel sheet, as disclosed in Japanese Patent No. 2007-23329, a method of introducing colloidal silica modified with Fe, Al, Ga, Ti, etc., and As disclosed in Korean Published Patent No. 10-2008-0025733, a method for improving corrosion resistance and film tension by introducing an oxide such as Fe, Co, or Cu has been proposed. In the former case, the process of modifying colloidal silica by reacting with Fe, Al, etc. is considerably complicated and disadvantageous in terms of manufacturing cost, but the effect is not sufficient, so that it can be implemented in the industry. difficult. In the latter case, it can be used more easily than in the former case, but the introduced oxide simply increases the film density or film tension by preventing the free phosphoric acid generated when the coating agent is dried. Improve. Both the former and the latter have limitations in satisfying the level of recent high-grade grain-oriented electrical steel sheets that require high corrosion resistance and film tension.

  Therefore, the actual situation is that no commercialized technology of a directional non-chromium coating agent that satisfies all the required physical properties has been proposed yet.

  The present invention overcomes the above-described problems of the prior art, and overcomes the deterioration of compatibility, corrosion resistance and adhesion of non-chromium coating agents, and has non-chromium characteristics having an insulating film excellent in film tension. TECHNICAL FIELD The present invention relates to a system coating agent and a manufacturing method thereof, and a grain-oriented electrical steel sheet using the same and a manufacturing method thereof. Accordingly, an object of the present invention is to provide a coating agent which is environmentally advantageous since it does not contain chromium oxide, and has improved corrosion resistance and film tension.

  In order to achieve the above object, the present invention is environmentally advantageous and corrosion resistant by adding metal phosphate, colloidal silica and hematite sol instead of containing chromium oxide. And a coating agent having improved film tension.

  The coating agent of the present invention is excellent in compatibility, and when an insulating film of a grain-oriented electrical steel sheet is formed using the coating agent, it causes a reaction of hematite-silica and hematite-phosphate at a low temperature, and between silica at a high temperature. By this reaction, a strong and dense film can be formed, and the adhesion between the material and the film can be improved. In addition, the insulating film produced in this way is significantly improved in the tension imparted by the insulating film as compared with the conventional insulating film, and is very excellent in corrosion resistance.

The change in film tension due to the component ratio of metal phosphate, colloidal silica, and hematite sol is expressed by two-dimensional contour lines. This is a three-dimensional representation of the change in film tension due to the component ratio of metal phosphate, colloidal silica and hematite sol. This is a comparison of the corrosion resistance of the conventional chromium type and the examples of the present invention.

  The coating agent of the present invention is characterized by containing phosphate, colloidal silica, and hematite sol.

  The phosphate of the coating agent of the present invention is a mixture of a first aluminum phosphate and a first magnesium phosphate.

  In addition, the colloidal silica of the coating agent of the present invention is contained in an amount of 25 to 300 g by weight per 100 g of phosphate.

  The colloidal silica of the coating agent of the present invention is an acidic type.

  The hematite sol of the coating agent of the present invention is characterized by having a hydroxyl group on the surface.

  In addition, the hematite sol of the coating agent of the present invention is contained in an amount of 0.5 to 40 g by weight per 100 g of phosphate.

  Further, the coating agent of the present invention is a group consisting of 0.5 to 5.0 g of cobalt hydroxide in a solid part weight per 100 g of the phosphate and 1 to 7 g of boric acid in a weight per 100 g of the phosphate salt. It further includes one or more selected.

  The method for producing a coating agent according to the present invention includes a step of producing a silica-hematite mixed solution 1 by introducing a hematite sol into colloidal silica and stirring, and gradually adding phosphate to the produced silica-hematite mixed solution 1. And a mixed solution 2 is produced.

  Moreover, in the manufacturing method of the coating agent of this invention, the said phosphate is a mixture containing 1st aluminum phosphate and 1st zinc phosphate, It is characterized by the above-mentioned.

  Further, in a further aspect of the method for producing a coating agent of the present invention, instead of adding a phosphate to the mixed solution 1, boric acid is first added and dissolved in the phosphate, and then cobalt hydroxide is further added. A mixed solution 4 prepared by adding and stirring is used.

  The coated steel sheet of the present invention is characterized in that the surface of the steel sheet is coated with a coating agent containing phosphate, colloidal silica, and hematite sol.

  Moreover, the phosphate of the said coating agent used for manufacture of the coated steel plate of this invention is a mixture of the 1st aluminum phosphate and the 2nd zinc phosphate, It is characterized by the above-mentioned.

  In addition, the coating agent used for the production of the coated steel sheet of the present invention is characterized in that one or more components selected from the group consisting of cobalt hydroxide and boric acid are further added.

  In the method for producing the coated steel sheet of the present invention, the surface of the steel sheet is coated with a coating agent containing phosphate, colloidal silica, and hematite sol, and after heat treatment at a low temperature of 800 ° C. or lower for 10 seconds to 10 minutes, 800 ° C. It includes a two-stage heat treatment in which heat treatment is performed at the above high temperature.

  The coating agent used in the method for producing a coated steel sheet according to the present invention further includes at least one of cobalt hydroxide and boric acid.

  The present invention will be described in detail below.

In the case of a chromium-based tension coating agent, hexavalent chromium ions (Cr ⁶⁺ ) react with water in the coating agent when the film is dried to change to a chromic acid (H ₂ CrO ₄ ) compound, and further chromic acid (H ₂ CrO). ₄ ) reacts with iron (Fe) present in the steel sheet to produce iron oxide (FeO), thereby creating a state capable of reacting with iron oxide (FeO) and metal phosphate. Such an action greatly helps to improve the adhesion between the steel sheet and the coating agent, and as a result, improves the film tension. In addition, hexavalent chromium ions (Cr ⁶⁺ ) may react with the produced iron oxide (FeO) to be reduced to trivalent chromium ions (Cr ³⁺ ), and the reduced trivalent chromium (Cr ³⁺ ) Condensation polymerization can increase the denseness of the film, which greatly affects the improvement of corrosion resistance. Further, chromium oxide improves surface physical properties by suppressing the generation of free phosphoric acid that causes poor wettability after film drying.

  Colloidal silica uses basic colloidal silica having excellent film tension and relatively low production costs. At this time, the colloidal silica is not compatible with the acidic metal phosphate used as the binder of the tension coating agent, and thus causes gelation. In such a case, when chromium oxide is added, gelation is prevented when the two components are mixed, and the coating agent can have a stable liquid phase. Therefore, when the coating agent does not contain chromium oxide, a decrease in compatibility due to the pH difference between the colloidal silica and the metal phosphate becomes a serious problem in the production of the coating agent.

  Therefore, the present invention proposes the following technique in order to solve the problems of film tension, corrosion resistance and compatibility that are generated when a coating agent not containing chromium oxide is used.

First, an iron oxide (FeO) -based oxide sol that can induce a condensation reaction with the hydroxy group of silica and improve the strength and density of the coating compared to the silica coating alone is introduced. did. As a result, it not only improves the denseness and corrosion resistance of the film, but also greatly improves the adhesion of the metal phosphate, and ultimately an excellent film tension can be obtained. At this time, the used iron oxide (FeO) is in a colloidal state, the inside of the particle exists as a ferric trioxide (Fe ₂ O ₃ ) state, and the surface of the particle is colloidal with silica or metal phosphate. It is more preferable to adopt an iron hydroxide (FeO—OH) form for a smooth reaction.

Second, the problem of reduced surface moisture absorption and corrosion resistance that can occur in non-chromium phosphate-containing coating agents has been solved by introducing cobalt hydroxide. Over time, after surface coating is performed using a coating agent containing a large amount of phosphate, the hygroscopicity, powdering and corrosion resistance decrease due to free phosphoric acid. Therefore, in order to reduce surface defects due to free phosphoric acid, pure phosphate and metal oxide must be configured with an appropriate composition ratio, and the proportion of phosphate occupied in the coating agent is appropriate. There must be. In the present invention, as described above, 100 g of a mixed solution of first aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) and first magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) (solid content ratio 60 wt. Cobalt hydroxide serves as a substitute for the function of suppressing free phosphoric acid by the reaction of chromium oxide and phosphoric acid by adding 0.5% or more of cobalt hydroxide to (weight%) by weight of solid part.

Third, the order of blending between components was differentiated to ensure excellent solution stability after the coating was manufactured. An acidic colloidal silica is introduced into a mixture of acidic primary aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) and primary magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) to form a coating agent. The mutual mixing property, that is, the compatibility between these components was ensured. As described above, in the case of general colloidal silica, basic type colloidal silica, which is relatively low in production cost, is used and is not compatible with acidic metal phosphate due to the difference in pH. Bring. Therefore, in the present invention, the compounding order of the metal phosphate, colloidal silica, boric acid, cobalt hydroxide, and hematite sol is specially improved to improve the storage stability. I tried not to be a problem.

  Hereinafter, the present invention will be described in more detail while examining these proposed techniques.

  Recently, with the trend of upgrading graded electrical steel sheets, magnetic improvement by increasing the tension of the insulation film has become an important factor. However, oriented electrical steel sheets are the final process of insulating coating and flattening annealing. The material that has been thermally expanded while undergoing annealing after the insulation coating is further shrunk upon cooling, while the already ceramicized insulation coating layer prevents the material from shrinking. By increasing the difference in coefficient of thermal expansion between the base material and the coating agent, the film tension can be improved.

  However, since there is a limit to the formation of a high-tensile film due to the difference in coefficient of thermal expansion between a simple base material and a coating agent, the present invention forms a strong film layer by the chain reaction of silica, and has a strong film tension. Tried to give. In order to form such a dense film layer, a substance capable of improving the adhesive force by reacting with silica and metal phosphate is required. In addition, the present invention has overcome the drawbacks of forming a ceramic layer single film using an iron oxide (FeO) sol that is excellent in compatibility with other components.

  The hematite contained in the coating agent of the present invention has an effect of preventing corrosion of the magnetic material, but when introduced as a simple hematite form, it is difficult to react with silica and metal phosphate at a low temperature during drying. It is preferable to adopt a form in which the surface is substituted with a hydroxyl group.

  The hematite sol increases the strength of the film by causing a condensation reaction with the hydroxyl group of silica to form an iron-silica composite, thereby forming a stronger film than the ceramic layer formed of silica alone, and metal phosphate It also reacts to improve the adhesion of the coating agent.

  In order to achieve high tension, from the microscopic viewpoint of the silica ceramic layer, a film more dense than a film in which many porous layers are formed must be formed. In order to solve this problem, a coating reaction with silica and metal phosphate is induced to improve the adhesion of the coating. In order to increase the strength of the film by forming an iron-silica composite by a condensation reaction of silica and hematite sol, thereby forming a very strong film as compared with a ceramic layer formed of silica alone, Heat treatment is performed at a low temperature of ℃ or less. Therefore, in the present invention, two-stage heat treatment is performed, that is, a low temperature heat treatment at 800 ° C. or lower for 10 seconds to 1 minute and a high temperature heat treatment at 800 ° C. or higher for 10 seconds to 1 minute so that a dense film is formed.

  On the other hand, a metal phosphate is introduced as a main component in the coating agent for bonding the coating agent and the base material. In such a case, surface wettability due to free phosphoric acid is inevitably generated. . At this time, the limit of the technology in solving such problems, that is, the effect of preventing the free phosphoric acid generated when the coating agent is dried, is incidentally improved in the film denseness or film tension, but the effect is There is a problem that it is not big. Therefore, as described above, the improvement in film tension and adhesive force was solved by using a hematite sol, and the wettability phenomenon due to free phosphoric acid was solved by introducing cobalt hydroxide which is another metal oxide.

  If the tension coating agent does not contain chromium oxide, a severe gelation phenomenon occurs between the colloidal silica and the metal phosphate, which causes a problem from the time of manufacturing the coating agent. Therefore, in order to avoid the gelation phenomenon, an acidic coating agent is required, but in this case as well, much attention is required for the mixing method. In other words, even if the two components are in the same acidic state, colloidal silica is a product made by modifying the basic state in order to make it acidic, so this also induces a gelling phenomenon when mixed rapidly. . For this reason, it is important to give time so that the two components can be sufficiently mixed while introducing the metal phosphate very slowly while stirring the mixed solution 1 of colloidal silica and hematite sol. is there. Examples thus produced are detailed in Table 1.

  As shown in Table 1, the production order of the respective components constituting the coating agent has a very important influence on the compatibility and stability of the coating agent. In the present invention, the coating agent is used using colloidal silica in an acidic state. It is possible to produce a solution having excellent compatibility and stability.

The phosphate used in the coating agent should be a mixture of primary magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and primary aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) Is preferred. The amount of phosphate added to the coating agent is preferably about 30 to 60 g when the total weight of the coating agent is 100 g, and if it is less than 30 g, the adhesive strength of the coating agent is reduced and the film tension is reduced. If it is 60 g or more, wettability (sticky) by free phosphoric acid can be induced.

  Colloidal silica forms a ceramic layer having a low coefficient of thermal expansion during the heat treatment of the coating agent and exerts an action of applying a tensile stress to the material. When the amount of colloidal silica input is 25 g or less, an appropriate ceramic layer is not formed, so the tensile stress applied to the material is insufficient, and when the amount of colloidal silica input is 300 g or more, the solid content ratio to the coating agent Increases, and the surface quality of the steel sheet decreases. Therefore, in this invention, content of the said colloidal silica is restrict | limited to the range of 25-300g with respect to 100g of said phosphate solutions.

  Boric acid added in the production of the metal phosphate is dissolved by adding 1 to 7 g per 100 g of the phosphate solution. When added to 7 g or less, magnesium present in the phosphate is added. Alternatively, it is difficult to perform an appropriate condensation reaction with alumina, and when it is added to 7 g or more, a precipitation phenomenon due to excessive addition occurs, so 1 to 7 g is preferably added to 100 g of the phosphate solution. .

  It is preferable to add 0.5 to 40 g of hematite sol with respect to 100 g of the phosphate solution. When the amount of hematite sol input is 0.5 g or less, the film tension is not sufficient because the amount of appropriate ceramic-iron oxide (FeO) or phosphate-iron oxide (FeO) is not large in the drying process due to the lack of hematite particles. When the amount of hematite sol is not less than 40 g, the hematite fraction with respect to the coating agent becomes high, which rather hinders the formation of the ceramic layer. Therefore, in the present invention, it is preferable to add 0.5 to 40 g of the hematite sol with respect to 100 g of the phosphate solution.

  In the case of cobalt hydroxide, physical properties can be improved by adding 0.5 to 5.0 g of solid weight to 100 g of the phosphate solution.

  A grain-oriented electrical steel sheet (300 × 60 mm) containing a primary film having a final annealing thickness of Si containing 3.1% by weight and having a thickness of 0.23 mm is used as a test material and dried at 850 ° C. for 30 seconds. Then, the coated surface was deflected in one direction by applying a tensile stress by the coating agent, and the degree of such bending was measured to evaluate the tension by the film.

SRA was heat-treated at 750 ° C. for 2 hours in a dry 100% N ₂ gas atmosphere. Insulation is shown as stored current value when current of 0.5V and 1.0A is passed under pressure of 300PSI. Adhesion is in contact with arcs of 10, 20, 30-100mmΦ before and after SRA. When bending by 180 °, it was shown as the minimum arc diameter with no peeling of the film, and the appearance of the film was evaluated by observing the striped pattern, glossiness, etc. with the naked eye. Corrosion resistance is 5%, 35 ° C., and the presence or absence of rust on the specimen is evaluated for 8 hours in NaCl solution. In this test, when the rust generation area was 5% or less, it was indicated as excellent, 20% or less as good, 20 to 50% as slightly defective, and 50% or more as defective.

  When the coating agent was non-chromated, the inferior physical properties were examined one by one. When the coating agent did not contain chromium oxide, the mixed state of colloidal silica and metal phosphate was confirmed, and the results are shown in Table 1.

  As shown in Table 1, gelation occurred when normal basic colloidal silica and acidic metal phosphate were used, but the product used acidic colloidal silica having a pH similar to that of metal phosphate. In this case, the gelation phenomenon could be prevented. In addition, although there is a very close relationship with the blending order and compatibility, when acidic colloidal silica is applied, cobalt hydroxide is first dissolved in phosphate as described in Examples 1 to 3. After that, when the colloidal silica and hematite sol were introduced, excellent compatibility was shown. In particular, in Example 3, there was no increase in viscosity over time. On the other hand, when two components were simultaneously introduced into the phosphate, the compatibility was not good, and the viscosity with time showed a large increase.

From the results shown in Table 1, the present inventors employed phosphate, boric acid, cobalt hydroxide, acidic colloidal silica, and hematite sol as basic components of the non-chromic tension coating agent. In addition, in the case of cobalt hydroxide introduced for suppressing free phosphoric acid and enhancing corrosion resistance, the amount that can be dissolved in phosphate is 2.5 g or less. Based on metal phosphates with 2.0 g of cobalt and boric acid introduced. Therefore, the degree of influence on the film tension was measured for the three components of metal phosphate, hematite sol, and colloidal silica in which cobalt hydroxide and boric acid were dissolved. The coating amount was adjusted to 4.0 g / m ² . The coating agent applied in this way undergoes a two-stage drying process. As the first stage, after drying in a drying furnace at a temperature of 750 ° C. for 10 seconds to 1 minute, the second stage is performed at a drying furnace at a temperature of 900 ° C. For 30 seconds to 9 minutes.

  Table 2 shows the effects of film tension and corrosion resistance due to metal phosphate, acidic colloidal silica, and hematite sol components. First, from the viewpoint of film tension, most of the examples containing hematite sol do not contain hematite sol, and show a film tension superior to that of the conventional example to which chromium is added.

  From these results, when the hematite sol introduced in the present invention is introduced into the coating agent, it complements the drawbacks of the existing chromium-based coating agent, that is, the formation of a porous ceramic film. It is judged that the phosphate composite has a greater adhesion effect than the adhesion provided by the metal phosphate, and ultimately contributes to the improvement of the film tension. The relationship between each component and the film tension is shown in FIGS.

  Moreover, as shown in FIG. 3, the corrosion resistance was compared with the conventional chromium coating agent and the component systems of the examples in Table 2. As can be confirmed from the figure, the corrosion resistance of the examples was higher than that of the conventional examples. And excellent. Such a result well shows the effect of chemical reaction and film denseness due to the introduction of hematite sol as described above.

  Table 3 shows the degree of influence due to drying conditions after the coating liquid was produced based on the component systems of Examples 1 to 3 in Table 2. As shown in Table 3, it can be seen that the use of a system that performs one-stage drying at a low temperature and two-stage drying at a high temperature greatly contributes to an improvement in film tension. This suggests that the chemical reaction between the phosphate and the FeO system is greatly affected depending on the drying conditions, and an excellent film tension is obtained when the two-stage heat treatment is performed as in the present invention. It proves to be effective.

Claims (12)

And phosphate, by weight per the phosphate 100 g, 0.5 to 5.0 g saw including 25~300g the acid form of colloidal silica, 0.5 to 40 g hematite sol, and cobalt hydroxide, the A hematite sol is a non-chromium coating agent for grain-oriented electrical steel sheets, characterized in that the surface contains a hydroxyl group .   The non-chromium coating agent for grain-oriented electrical steel sheets according to claim 1, wherein the phosphate is a mixture of a first aluminum phosphate and a first magnesium phosphate. The non-chromium coating agent for grain-oriented electrical steel sheets according to claim 1 or 2 , wherein the hematite sol is in the form of iron hydroxide (FeO-OH) . The grain-oriented electrical steel sheet non-chromium coating agent according to any one of claims 1 to 3 , further comprising 1 to 7 g of boric acid by weight per 100 g of the phosphate. A step of producing a silica-hematite mixed solution 1 by introducing a hematite sol containing a hydroxyl group on the surface of acidic colloidal silica and stirring the mixture;
The manufacturing silica - phosphate into hematite mixed solution 1 was gradually poured, silica - hematite - a stage of producing a phosphate mixed solution 2 seen including,
Before adding the phosphate to the silica-hematite mixed solution, boric acid is added to the phosphate and dissolved therein to produce a mixed solution 3 having a solid content ratio of 50 to 65% by weight and a viscosity of 200 to 300 cp. Stages,
The method further includes adding cobalt hydroxide to the mixed solution 3 and stirring to produce the mixed solution 4 . The phosphate used in the manufacturing stage of the silica-hematite-phosphate mixed solution 2 is a mixture of a first aluminum phosphate and a first magnesium phosphate, according to claim 5 . A method for producing a non-chromium coating agent for grain-oriented electrical steel sheets. The method for producing a non-chromium coating agent for grain-oriented electrical steel sheets according to claim 5 or 6 , wherein the hematite sol is in the form of iron hydroxide (FeO-OH) . Phosphate, acid form colloidal silica, coating tension of hematite sol and coating steel sheet coating agent containing cobalt hydroxide is formed is coated on the surface of the steel sheet 0.30~1.02kg / mm ² der Ri The grain- oriented electrical steel sheet , wherein the hematite sol contains a hydroxyl group on the surface . The grain-oriented electrical steel sheet according to claim 8 , wherein the phosphate of the coating agent is a mixture of a first aluminum phosphate and a first magnesium phosphate. The coating agent is characterized in that the boric acid was further added, oriented electrical steel sheet according to claim 8 or 9. Steel sheet with phosphate, acidic colloidal silica , hematite sol containing hydroxyl group on the surface, coating agent containing cobalt hydroxide and boric acid so that the dry film coating amount is 0.5-6.0 g / m ² And apply two-stage heat treatment ,
The high-strength grain-oriented electrical steel sheet , wherein the two-stage heat treatment is a heat treatment for 10 seconds to 1 minute at a low temperature of 800 ° C. or lower and then a heat treatment for 30 seconds to 9 minutes at a high temperature of 800 ° C. or higher. Manufacturing method. The method of manufacturing a high-tensile-oriented electrical steel sheet according to claim 11 , wherein the hematite sol is in the form of iron hydroxide (FeO-OH) .