PRE-COATING AGENT COMPOSITION FOR GRAIN-ORIENTED ELECTRICAL STEEL SHEET, GRAIN-ORIENTED ELECTRICAL STEEL SHEET COMPRISING SAME, AND MANUFACTURING METHOD THEREFOR

Abstract

A pre-coating agent composition for a grain-oriednted electrical steel sheet, a grain-oriednted electrical steel sheet including the same, and a manufacturing method thereof are provided. Particularly, a pre-coating agent composition for a grain-oriednted electrical steel sheet including an acid containing boron (B); and a solvent, a grain-oriednted electrical steel sheet including the same, and a manufacturing method thereof are provided.

Claims

1-38. (canceled)

39. A pre-coating agent composition for a grain-oriednted electrical steel sheet comprising: acid containing boron (B); and solvent, wherein the acid containing boron (B) is at least one selected from the group consisting of borinic acid, boronic acid, boric acid and a combination thereof, and the pre-coating agent composition comprises 20 to 40 parts by weight of the silicate compound, 5 to 15 parts by weight of the acid containing boron (B), and 300 to 500 parts by weight of the solvent, based on 100 parts by weight of the metal dihydrogen phosphates.

40. The pre-coating agent composition of claim 39, further comprising: metal dihydrogen phosphates; and a silicate compound.

41. The pre-coating agent composition of claim 39, wherein: the metal dihydrogen phosphates are one or more selected from the group consisting of aluminum dihydrogen phosphate (Al(H.sub.2PO.sub.4).sub.3), magnesium dihydrogen phosphate (Mg((H.sub.2PO.sub.4).sub.2) and a combination thereof.

42. The pre-coating agent composition of claim 41, wherein: the metal dihydrogen phosphates include aluminum dihydrogen phosphate (Al(H.sub.2PO.sub.4).sub.3) and magnesium dihydrogen phosphate (Mg((H.sub.2PO.sub.4).sub.2), and aluminum dihydrogen phosphate (Al(H.sub.2PO.sub.4).sub.3) is included at 20 to 80 wt %, based on total 100 wt % of the metal dihydrogen phosphates.

43. The pre-coating agent composition of claim 41, wherein: the silicate compound is one or more selected from the group consisting of silica dispersed in a dispersion medium in a colloid form, solid silica in a powder form and a combination thereof.

44. A grain-oriednted electrical steel sheet comprising: a pre-coating layer formed on a surface of the grain-oriednted electrical steel sheet; and a tension coating layer formed on a surface of the pre-coating layer, wherein the grain-oriednted electrical steel sheet is a grain-oriednted electrical steel sheet from which a forsterite (Mg.sub.2SiO.sub.4) film is removed, the pre-coating layer includes an acid containing boron (B) and a solvent, and adhesion between the grain-oriednted electrical steel sheet and the tension coating layer is controlled by the pre-coating layer, wherein the acid containing boron (B) is at least one selected from the group consisting of borinic acid, boronic acid, boric acid and a combination thereof, and the pre-coating layer comprises 20 to 40 parts by weight of the silicate compound, 5 to 15 parts by weight of the acid containing boron (B), and 300 to 500 parts by weight of the solvent, based on 100 parts by weight of the metal dihydrogen phosphates.

45. The grain-oriednted electrical steel sheet of claim 44, wherein: the pre-coating layer further includes: metal dihydrogen phosphates; and a silicate compound.

46. The grain-oriednted electrical steel sheet of claim 44, wherein: the metal dihydrogen phosphates in the pre-coating layer are one or more selected from the group consisting of aluminum dihydrogen phosphate (Al(H.sub.2PO.sub.4).sub.3), magnesium dihydrogen phosphate (Mg((H.sub.2PO.sub.4).sub.2) and a combination thereof.

47. The grain-oriednted electrical steel sheet of claim 46, wherein: the silicate compound in the pre-coating layer is one or more selected from the group consisting of silica dispersed in a dispersion medium in a colloid form, solid silica in a powder form and a combination thereof.

48. The grain-oriednted electrical steel sheet of claim 46, wherein: a composition of the grain-oriednted electrical steel sheet includes Sn: 0.03 to 0.07 wt %, Sb: 0.01 to 0.05 wt %, P: 0.01 to 0.05 wt %, Fe and other inevitably added impurities.

49. A method of manufacturing a grain-oriednted electrical steel sheet, comprising: preparing a grain-oriednted electrical steel sheet from which a forsterite (Mg.sub.2SiO.sub.4) film is removed; forming a pre-coating layer on a surface of the grain-oriednted electrical steel sheet from which the forsterite (Mg.sub.2SiO.sub.4) coat is removed; and forming a tension coating layer on a surface of the pre-coated grain-oriednted electrical steel sheet, wherein the pre-coating layer includes an acid containing boron (B) and a solvent, and adhesion between the grain-oriednted electrical steel sheet from which the forsterite (Mg.sub.2SiO.sub.4) film is removed and the tension coating layer is controlled by the pre-coating layer.

50. The method of claim 49, wherein: the preparing of a grain-oriednted electrical steel sheet from which a forsterite (Mg.sub.2SiO.sub.4) film is removed includes: preparing a steel slab including Sn: 0.03 to 0.07 wt %, Sb: 0.01 to 0.05 wt %, P: 0.01 to 0.05 wt %, Fe and other inevitably added impurities; hot-rolling the steel slab to prepare a hot-rolled sheet; subjecting the hot-rolled sheet to annealing and acid-washing; Cold-rolling the annealed and acid-washed steel sheet to prepare a cold-rolled sheet; decarbonizing and nitriding-annealing the cold-rolled sheet; and high temperature annealing the decarbonized and nitrided-annealed steel sheet, wherein the decarbonizing and nitriding-annealing is carried out at dew point in a range of 35 to 55° C., and the high temperature annealing is carried out by applying an additive containing MgO.

51. The method of claim 49, wherein: the additive includes: MgO; an annealing separating agent including antimony oxychloride (SbOCl) and antimony sulfate (Sb.sub.2(SO.sub.4).sub.3); and water.

52. The method of claim 49, wherein: the high temperature annealing is carried out at a heating rate of 18 to 75° C./hr in a temperature range of 700 to 950° C., and at a heating rate of 10 to 15° C./hr in a temperature range of 950 to 1200° C.

53. The method of claim 49, wherein: the forming of a pre-coating layer on a surface of the grain-oriednted electrical steel sheet from which the forsterite (Mg.sub.2SiO.sub.4) film is removed includes: preparing a mixed solution of an acid containing boron (B) and water; applying the mixed solution on the grain-oriednted electrical steel sheet; and drying the grain-oriednted electrical steel sheet on which the mixed solution is applied.

54. The method of claim 49, wherein: the acid containing boron (B) is at least one selected from the group consisting of borinic acid, boronic acid, boric acid and a combination thereof.

55. The method of claim 54, wherein: the mixed solution further includes: metal dihydrogen phosphates; and a silicate compound.

56. The method of claim 55, wherein: the preparing of a mixed solution including an acid containing boron (B) and water is carried out by adding and mixing 20 to 40 parts by weight of the silicate compound, 5 to 15 parts by weight of the acid containing boron (B), and 300 to 500 parts by weight of the water, based on 100 parts by weight of the metal dihydrogen phosphates.

57. The method of claim 53, wherein: the applying of the mixed solution on the grain-oriednted electrical steel sheet is carried out by evenly distributing 0.5 to 3.0 g/m.sup.2 of the mixed solution on a surface of the grain-oriednted electrical steel sheet.

58. The method of claim 53, wherein: the drying of the grain-oriednted electrical steel sheet on which the mixed solution is applied is carried out at a temperature range of 250 to 550° C. for 15 to 30 seconds.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0165] Hereinafter, the preferred Preparation Example and Examples of the present invention will be described. However, these are only one preferred Preparation Example and one preferred Example of the present invention, and the present invention is not limited thereto.

(Preparation Example) Formation of Pre-Coating Layer on Grain-Oriednted Electrical Steel Sheet from which Base Coating Layer is Removed

[0166] A pre-coating layer was formed on a grain-oriednted electrical steel sheet from which the base coating layer is removed, according to an embodiment of the present invention.

Preparation of Grain-Oriednted Electrical Steel Sheet from which Base Coating Layer is Removed

[0167] Specifically, the preparation course of the grain-oriednted electrical steel sheet from which the base coating layer is removed is as follows:

[0168] First, a steel slab including Si: 3.26 wt %, C: 0.055 wt %, Mn: 0.12 wt %, Sol. Al: 0.026 wt %, N: 0.0042%, S: 0.0045 wt %, Sn: 0.05 wt %, Sb: 0.03 wt %, and P: 0.03 wt % was prepared.

[0169] The prepared steel slab was hot-rolled using a rolling mill, and subjected to annealing and acid-washing, and thereafter, cold-rolled into a thickness of 0.23 mm.

[0170] On the cold-rolled steel sheet, an additive was applied at a dew point range of 50 to 70° C. using a decarbonizing annealing furnace, and then the steel sheet was decarbonizing-annealed. Here, the additive was a mixed solution of MgO, an annealing separating agent including antimony oxychloride (SbOCl) and antimony sulfate (Sb.sub.2(SO.sub.4).sub.3), and water at a weight ratio of 1:0.25:10.

[0171] The decarbonized and nitrided-annealed steel sheet was heated at a heating rate of 50° C./hr from room temperature to 700° C., at a heating rate of 25° C./hr from 700 to 950° C., and at a heating rate of 12.5° C./hr from 950 to 1200° C., and finally was high temperature annealed.

[0172] The grain-oriednted electrical steel sheet from which the base coating layer is removed was obtained through the high temperature annealing step, and then treated with 5% dilute sulfuric acid for 10 seconds in order to remove unreacted MgO, and washed with water and dried at 60° C. for 15 seconds, thereby being subjected to acid-washing and correction.

Formation of Pre-Coating Layer

[0173] The course for forming the pre-coating layer on the grain-oriednted electrical steel sheet from which the base coating layer is removed is as follows:

[0174] As the composition shown in the following Table 1, a mixed solution (i.e., pre-coating agent) of metal dihydrogen phosphates, a silicate compound, borinic acid and water was prepared.

[0175] Specifically, the pre-coating agent was prepared by adding 10 g of borinic acid, 400 g of water, and no colloidal silica, or varied amount in a range of 5 to 60 g of colloidal silica, based on 100 g of mixed aluminum and magnesium phosphates.

[0176] After the prepared pre-coating agent was evenly applied on the grain-oriednted electrical steel sheet from which the base coating layer is removed, drying at 850° C. for 30 seconds was carried out.

[0177] As a result, the base coating layer was removed, and the grain-oriednted electrical steel sheet on which the pre-coating layer was formed was obtained.

(Preparation Comparative Example) Formation of Pre-Coating Layer on General Grain-Oriednted Electrical Steel Sheet

[0178] In the Preparation Example, the pre-coating layer was formed in the same manner, except for not removing the base coating layer.

[0179] As a result, a general grain-oriednted electrical steel sheet on which the pre-coating layer was formed was obtained.

(Preparation Experimental Example) Evaluation of Adhesion of Pre-Coating Layer

[0180] In the case that the pre-coating layer is formed by the Preparation Example and the Preparation Comparative Example, the pre-coated surface bends in one direction by tensile stress addition. The tension by a coat may be evaluated by measuring this bending degree.

[0181] Further, through the evaluation results of the tension by a coat, the adhesion may be indirectly confirmed. Specifically, the effect of improved tensile stress by the coating may be confirmed by the following Equation:

σ.sub.RD=2E.sub.cδ(α.sub.Si-Fe-α.sub.chemical reaction)ΔT(1−v.sub.RD)+Adhesion effect

[0182] More specifically, SRA was subjected to heat treatment at 750° C. for 2 hours under the 100% dry N.sub.2 gas atmosphere, an insulation property is represented as a receiving current value when flowing current of 0.5 V, 1.0 A under pressure of 300 PSI, and adhesion is represented as a minimum circular arc diameter without coat release when bending specimens at 180° in contact with 10, 20, 30, 40 and 100 mmφ circular arcs, respectively, before and after SRA.

[0183] Here, Table 1 is results of each adhesion, for Preparation Example and Preparation Comparative Example according to various contents of the silicate compound in the pre-coating agent.

[0184] As shown in Table 1, it may be confirmed that the adhesion of the Preparation Example is better than that of Preparation Comparative Example, and among the Preparation Example, the adhesion is particularly excellent when the silicate compound is at 20 g to 40 g (Preparation Examples 5 to 7).

[0185] That is, it may be evaluated that the pre-coating layer in this case has strong adhesion with the grain-oriednted electrical steel sheet from which the base coating is removed, and has a thermal expansion coefficient to overcome coat release. Furthermore, it is inferred that the pre-coating layer is adhered to the surface of the grain-oriednted electrical steel sheet from which the base coating layer is removed well, and serves to improve the adhesion with the tension coating layer to be treated later.

[0186] As a result, the content of the silicate compound in the pre-coating agent according to an embodiment of the present invention is defined as being 20 to 40 parts by weight, based on 100 parts by weight of the metal dihydrogen phosphates.

TABLE-US-00001 TABLE 1 <Evaluation of adhesion by pre-coating layer> Metal dihydrogen Silicate Borinic phosphates compound acid Adhesion Specimen type Classification (g) (g) (g) (mmφ)) Remarks Base coating- Preparation 100 0 10 50 free product Example 1 Preparation 100 5 10 45 Example 2 Preparation 100 10 10 30 Example 3 Preparation 100 15 10 25 Example 4 Preparation 100 20 10 20 Example 5 Preparation 100 30 10 20 Example 6 Preparation 100 40 10 20 Example 7 Preparation 100 50 10 60 Example 8 Preparation 100 60 10 80 Example 9 Preparation — — — 100 General Comparative tension Example coating

(Example) Manufacture of Grain-Oriednted Electrical Steel Sheet from which Base Coating Layer is Removed and on which Pre-Coating Layer and Tension Coating Layer on Surface of the Pre-Coating Layer are Formed

[0187] According to Preparation Example 6, the base coating layer was removed, and a tension coating layer was formed on the surface of the grain-oriednted electrical steel sheet on which the pre-coating layer was formed.

[0188] For this purpose, tension coating agent was applied at 4.0 g/m.sup.2 and dried, and then slowly cooled. The tension coating agent was obtained by mixing 100 g of metal dihydrogen phosphates having a weight ratio of aluminum dihydrogen phosphate:magnesium dihydrogen phosphate of 6:4, 130 g of colloidal silica, 12 g of chromium oxide, 6 g of solid silica powder, and 50 g of a solvent.

[0189] However, the drying and slow cooling pattern was variously added according to the following Table 2.

[0190] Specifically, the temperature when drying was varied in a temperature range of 800 to 900° C., and the slow cooling time was the same at 25 seconds, but the temperature of 250 or 300° C. was applied. According to each condition, they were referred to as Examples 1 to 6.

(Comparative Example) Modification of Drying and Slow Cooling Conditions of Example

[0191] In the Example, the tension coating layer was formed by the same process, except that the drying and slow cooling pattern was differentiated.

[0192] Specifically, the temperature when drying was varied at a temperature range of 800 to 900° C., and the slow cooling process was not applied, or the slow cooling time was the same at 10 seconds, but the temperature of 100 or 200° C. was applied. According to each condition, they were referred to as Examples 1 to 9.

(Experimental Example) Evaluation of Adhesion and Coating Tension for Example and Comparative Example

[0193] For the Example and Comparative Example, the adhesion and coating tension were evaluated, and the evaluation method thereof is as described above.

[0194] According to the evaluation results shown in Table 2, it was confirmed that in the case of immediately cooling at room temperature regardless of the drying temperature (Comparative Examples 1, 4 and 7), coat release by thermal impact was not overcome, thereby deteriorating adhesion.

[0195] In contrast, when slowly cooling at a certain temperature for a certain period of time, coat release may be overcome, and it was confirmed that in the case of being at 250° C. or more for 25 seconds, such effect is particularly excellent (Examples 1 to 6).

[0196] Accordingly, the slow cooling step according to an embodiment of the present invention is defined as carrying out at a temperature range of 250 to 550° C. for 15 to 30 seconds.

TABLE-US-00002 TABLE 2 <Evaluation of adhesion and coating tension by tension coating layer> Drying step Slow cooling step Coating Specimen temperature temperature time Adhesion tension type Classification (° C.) (° C.) (sec) (mmφ) (kgf/mm.sup.2) Pretreatment Example 1 800 250 25 15 0.45 coating (base coating-free specimen) Example 2 800 300 25 15 0.48 Example 3 850 250 25 15 0.45 Example 4 850 300 25 15 0.60 Example 5 900 250 25 25 0.45 Example 6 900 300 25 25 0.45 Comparative 800 — — 60 0.05 Example 1 Comparative 800 100 10 35 0.35 Example 2 Comparative 800 200 10 30 0.40 Example 3 Comparative 850 — — 80 0.05 Example 4 Comparative 850 100 10 80 0.25 Example 5 Comparative 850 200 10 45 0.30 Example 6 Comparative 900 — — 70 0.06 Example 7 Comparative 900 100 10 55 0.04 Example 8 Comparative 900 200 10 45 0.30 Example 9

[0197] The present invention is not limited to the Preparation Example and Examples, but may be manufactured in various forms which are different from each other, and a person skilled in the art to which the present invention pertains may understand that other specific forms may be carried out without modifying the technical concept or essential features of the present invention. Therefore, it should be understood that the Preparation Example and Example as described above are illustrative, and not restrictive in all aspects.