Grain-oriented electrical steel sheet

Abstract

A grain-oriented electrical steel sheet has a steel sheet and an insulating coating which is formed on a surface of the steel sheet. In the insulating coating, a metal phosphate and a colloidal silica are contained, the colloidal silica is contained in an amount of 20 to 150 parts by mass with respect to 100 parts by mass of the metal phosphate, one or more kinds of fine particles selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, sialon, and cordierite are further contained in an amount of 0.5 to 7 parts by mass with respect to 100 parts by mass of the metal phosphate, an average particle size of the fine particles is 0.3 to 7.0 μm, crystallized ratio of the metal phosphate is 2% to 40%, and chromium is not contained.

Claims

1. A grain-oriented electrical steel sheet comprising: a steel sheet; and an insulating coating which is formed on a surface of the steel sheet, wherein in the insulating coating, a metal phosphate and a colloidal silica are contained, the colloidal silica is contained in an amount of 40 to 55 parts by mass with respect to 100 parts by mass of the metal phosphate, one or more kinds of fine particles selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, sialon, and cordierite are further contained in an amount of 0.5 to 7 parts by mass with respect to 100 parts by mass of the metal phosphate, an average particle size of the fine particles is 3.6 to 7.0 μm, crystallized ratio of the metal phosphate is 2% to 40%, and chromium is not contained.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the metal phosphate is one or more of metal salts selected from the group consisting of Al, Ba, Co, Fe, Mg, Mn, Ni, and Zn.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein an arithmetic average roughness Ra of the insulating coating is within a range of 0.1 to 0.4 μm in a rolling direction, and is within a range of 0.3 to 0.6 μm in a direction perpendicular to the rolling direction.

4. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the steel sheet contains 0.005% or less of C and 2.5% to 7.0% of Si in terms of mass %, and in a structure of the steel sheet, an average grain size is 1 to 10 mm, and crystal orientation has a deviation of orientation of 8° or less on average in a rolling direction with respect to (110)[001] orientation.

5. The grain-oriented electrical steel sheet according to claim 1 or 2, further comprising: a forsterite layer which is provided between the steel sheet and the insulating coating.

6. The grain-oriented electrical steel sheet according to claim 3, wherein the steel sheet contains 0.005% or less of C and 2.5% to 7.0% of Si in terms of mass %, and in a structure of the steel sheet, an average grain size is 1 to 10 mm, and crystal orientation has a deviation of orientation of 8° or less on average in a rolling direction with respect to (110)[001] orientation.

7. The grain-oriented electrical steel sheet according to claim 3, further comprising: a forsterite layer which is provided between the steel sheet and the insulating coating.

8. The grain-oriented electrical steel sheet according to claim 4, further comprising: a forsterite layer which is provided between the steel sheet and the insulating coating.

9. The grain-oriented electrical steel sheet according to claim 6, further comprising: a forsterite layer which is provided between the steel sheet and the insulating coating.

10. The grain-oriented electrical steel sheet according to claim 1, wherein a crystal system of the fine particles is hexagonal or cubic.

Description

EXAMPLES

(1) Next, examples of the invention will be described. In the examples, conditions are just an example employed to confirm the feasibility and effects of the invention, and the invention is not limited to this example. The invention can employ various conditions as long as the object of the invention is achieved without deviating from the gist of the invention.

(2) A slab was manufactured by casting molten steel containing 3.2 mass % of Si, 0.027 mass % of Al, 0.008 mass % of N, and 0.08 mass % of C. The slab was heated to be hot rolled to obtain a hot rolled steel sheet. The hot rolled steel sheet was annealed at 1,100° C. for 5 minutes, and then cooled. The hot rolled steel sheet after the annealing was cold rolled to obtain a cold rolled steel sheet having a thickness of 0.23 mm. After that, the cold rolled steel sheet was subjected to decarburization annealing at 850° C. for 3 minutes, and an annealing separating agent containing MgO as a main component was applied. Then, the cold rolled steel sheet was subjected to final annealing for 20 hours at 1,200° C. A sample with a width of 7 cm and a length of 32 cm was cut out from the cold rolled steel sheet after the final annealing, and while the forsterite layer was allowed to remain, the annealing separating agent remaining on the surface was removed by water washing. Then, stress relief annealing was performed to obtain a steel sheet.

(3) The obtained steel sheet contained 0.001 mass % of C and 3.2 mass % of Si. In the structure, the average grain size was 1 to 10 mm, and the crystal orientation had a deviation of orientation of 8° or less on average in a rolling direction with respect to the (110)[001] orientation.

(4) Next, using fine particles shown in Table 1, a metal phosphate solution was prepared with a mixing ratio shown in Table 2, and then applied to the steel sheet with a roll coater such that the coating amount was 4.5 g/m.sup.2. The solution was baked under conditions described in Table 2, and cooled to a temperature of 200° C. or lower in a non-oxidizing atmosphere to obtain grain-oriented electrical steel sheets of Examples 1 to 12 and Comparative Examples 1 to 13. The surface roughness, the coating characteristics, and the magnetic characteristics of the obtained grain-oriented electrical steel sheets were evaluated. The results are shown in Tables 2 and 3.

(5) For boron nitride, aluminum nitride, silicon nitride, silicon carbide, alumina, sialon, and boehmite, commercially available products with respective particle sizes were used. Regarding cordierite, powders of magnesium carbonate, kaolinite, and quartz were combined to obtain a cordierite composition, and after the powders were mixed, baking was performed, and then pulverization was performed to obtain a predetermined particle size. Regarding mullite, alumina and quartz powders were combined to obtain a mullite composition, mixed, stirred, and then baked. Then, pulverization was performed to obtain a predetermined particle size. The used colloidal silica had an average particle size of 15 nm.

(6) As the surface roughness, an arithmetic average roughness Ra was measured in the rolling direction and in the direction perpendicular to the rolling direction based on JISB0601 (2013).

(7) The coating characteristic evaluation methods are as follows.

(8) Regarding adhesion, Sellotape (registered trademark) was adhered to a steel sheet sample of 30 mm×200 mm, and then wound and bent around a round bar having a diameter of 10 mm4), a round bar having a diameter of 20 mmϕ, and a round bar having a diameter of 30 mmϕ. Then, the Sellotape (registered trademark) was peeled off to observe the peeling state. The peeling state was evaluated on a scale of 0 to 30 as follows, and judged to be acceptable in a case where the point is 10 or lower.

(9) 0: No peeling even on round bar of 10 mmϕ

(10) 10: peeling on round bar of 10 mmϕ

(11) 20: peeling on round bar of 20 mmϕ

(12) 30: peeling on round bar of 30 mmϕ

(13) The corrosion resistance was evaluated by a 5% salt spray test. The exposure time was 10 hours, and the rusting state was evaluated on a scale of 1 to 10. 10 points were given in a case where no rusting occurred, and 1 point was given in a case where the area ratio of rust was 50%. Rusting states with 7 points or higher were accepted.

(14) The coating tension was calculated by calculating backward from the bending state when one side of the insulating coating was peeled off.

(15) The crystallized ratio of the metal phosphate was measured by a profile fitting method described in Japanese Patent No. 5063902. First, X-ray diffraction measurement (measurement using Cu as an X-ray target) of the insulating coating was performed to obtain a diffraction diagram. In the diffraction diagram, the amorphous halo as an amorphous component appears near 2θ=20°, and the metal phosphate as a crystalline component appears as a main peak. For example, in the case of Ni phosphate, a main peak appears near 30°. From the peaks of the amorphous component and the crystalline component, the background was separated to obtain the respective scattering intensities, and crystallized ratio X (%) was calculated using the following expression. Since the colloidal silica also contained the amorphous component, amorphous scattering intensity A was corrected by calculating the contribution of the amorphous halo from the colloidal silica content.
X=C/(C+A)×100

(16) C: crystalline scattering intensity A: amorphous scattering intensity

(17) As the magnetic characteristics, B8 and W17/50 were obtained by a method based on JIS C 2550.

(18) TABLE-US-00001 TABLE 1 Average Fine Particle Par- Chemical Crystal Size ticles Name Formula System (μm) A Boron Nitride BN Hexagonal 0.5 B Boron Nitride BN Hexagonal 11.0  C Boron Nitride BN Hexagonal 0.2 D Aluminum AIN Hexagonal 1.1 Nitride E Aluminum AIN Hexagonal 9.0 Nitride F Silicon Nitride Si.sub.3N.sub.4 Hexagonal 4.2 G Alumina Al.sub.2O.sub.3 Hexagonal 4.6 H Cordierite 2Al.sub.2O.sub.3•2MgO•5SiO.sub.2 Hexagonal 3.6 I Sialon Si.sub.3O.sub.4•Al.sub.2O.sub.3 Cubic 5.0 J Mullite 3Al.sub.2O.sub.3•2SiO.sub.2 Orthorhombic 5.0 K Boehmite AlO(OH) Trigonal 6.1 L Silicon Carbide SiC Hexagonal 0.7 The underline indicates that the underlined substance or numerical value is out of the scope of the invention.

(19) TABLE-US-00002 TABLE 2 Silica 100 Parts by Content in Mass of Colloidal Added Metal Silica** Fine Baking Conditions Phosphate* Parts Particles Temperature Soaking Soaking Cooling Kind: Ratio by Parts Rising Rate Temperature Time Rate (mass %) Mass Kind by Mass ° C./sec ° C. sec ° C./sec Example 1 Al: 75, Mg: 25 50 A 2 40 860 15 80 Example 2 Al: 95, Mg: 5 45 A 3 60 900 15 60 Example 3 Al: 100 40 F 4 60 900 15 80 Example 4 Al: 45, Zn: 55 35 F 5 70 900 30 50 Example 5 Al: 70, Ni: 30 50 H 6 90 900 30 100 Example 6 Al: 55, Mn: 45 40 I   0.8 40 850 30 80 Example 7 Al: 75, Zn: 25 55 D 3 40 920 55 80 Example 8 Al: 85, Co15 50 L 3 60 880 55 60 Example 9 Al: 100 50 L 3 60 880 30 60 Example 10 Al: 90, Fe: 10 50 H 1 60 850 30 60 Example 11 Al: 97, Ba: 3 40 I   1.5 40 850 30 50 Example 12 Mg: 75, Ni: 25 50 A 2 40 860 30 50 Comparative Al: 50, Mg: 50 40 A   0.3 40 840 30 50 Example 1 Comparative Al: 100 40 A 10  40 800 120 100 Example 2 Comparative Al: 75, Mg: 25 40 C 2 40 880 15 100 Example 3 Comparative Al: 100 45 B 3 60 800 15 60 Example 4 Comparative Al: 75, Mg: 25 40 E 4 60 900 15 60 Example 5 Comparative Al: 75, Mg: 25 40 F   0.2 60 880 30 60 Example 6 Comparative Al: 100 40 I 11  40 880 30 100 Example 7 Comparative Al: 75, Mg: 25 170  D 3 40 880 10 50 Example 8 Comparative Al: 100 15 D 3 40 880 30 60 Example 9 Comparative Al: 100 40 G 5 40 800 30 60 Example 10 Comparative A1: 100 40 J 3 40 840 30 60 Example 11 Comparative Al: 100 40 K 4 40 840 30 60 Example 12 Comparative Al: 100 40 — 0 40 840 10 50 Example 13 Surface Roughness Direction C Rolling Perpendicular to Rolling Additive Direction L Direction Parts Ra (μm) Ra (μm) Kind by Mass Example 1 0.20 0.35 — Example 2 0.15 0.33 Phosphonic Acid 10 Example 3 0.21 0.34 Phosphonic Acid 10 Example 4 0.13 0.31 Boric Acid 5 Example 5 0.26 0.41 — Example 6 0.25 0.34 — Example 7 0.23 0.47 — Example 8 0.17 0.33 Phosphonic Acid 10 Example 9 0.15 0.36 Boric Acid 5 Example 10 0.14 0.36 — Example 11 0.16 0.33 — Example 12 0.13 0.29 — Comparative 0.13 0.28 — Example 1 Comparative 0.34 0.67 — Example 2 Comparative 0.36 0.71 — Example 3 Comparative 0.18 0.36 — Example 4 Comparative 0.17 0.41 — Example 5 Comparative 0.14 0.29 — Example 6 Comparative 0.36 0.51 — Example 7 Comparative 0.12 0.28 — Example 8 Comparative 0.18 0.31 — Example 9 Comparative 0.16 0.31 — Example 10 Comparative 0.17 0.28 — Example 11 Comparative 0.19 0.33 — Example 12 Comparative 0.14 0.27 — Example 13 The underline indicates that the underlined substance or numerical value is out of the scope or the preferable scope of the invention. *The phosphate in Table 2 was adjusted such that the solid content thereof was 40 wt %, and mixed such that the ratio of each metal element in the phosphate was as in the table. **As the colloidal silica in Table 2, a commercially available colloidal silica solution having a concentration of 30 wt % was used.

(20) In each case, the treatment liquid was prepared such that the silica content was as shown in the table (parts by mass) with respect to 100 parts by mass of the phosphate in terms of solid content in the coating.

(21) TABLE-US-00003 TABLE 3 Components of Insulating Coating Amount of Adhered Amount Crystallized ratio of Fine Particles of Insulating Insulating Coating Characteristics Phosphate Added Coating Corrosion (%) (parts by mass) (g/m.sup.2) Adhesion Resistance Example 1 30 2 4.3 0 10 Example 2 25 3 4.6 0 10 Example 3 15 4 4.4 0 9 Example 4 20 5 4.3 0 9 Example 5 15 6 4.5 0 9 Example 6 35 0.8 4.6 0 9 Example 7 15 3 4.4 0 9 Example 8 10 3 4.3 0 10 Example 9 5 3 4.4 0 9 Example 10 10 1 4.4 10 9 Example 11 10 1.5 4.4 0 9 Example 12 35 2.0 4.5 0 10 Comparative Example 1 30 0.3 4.5 0 10 Comparative Example 2 45 10 4.6 30 8 Comparative Example 3 50 2 4.7 10 8 Comparative Example 4 10 3 4.3 30 8 Comparative Example 5 10 4 4.5 20 8 Comparative Example 6 10 0.2 4.7 10 10 Comparative Example 7 50 11 4.6 30 6 Comparative Example 8 0 3 4.5 20 7 Comparative Example 9 10 3 4.6 0 9 Comparative Example 10 10 5 4.5 10 7 Comparative Example 11 5 3 4.6 10 8 Comparative Example 12 10 4 4.3 10 6 Comparative Example 13 0 0 4.5 0 10 Insulating Coating Magnetic Remarks Characteristics Characteristics Stability of Treatment Coating Tension B8 W 17/50 Liquid, Surface (kgf/mm.sup.2) (T) (W/kg) Appearance, etc. Example 1 0.92 1.92 0.76 Uniform and Beautiful Example 2 0.97 1.93 0.73 Uniform and Beautiful Example 3 0.93 1.91 0.75 Significantly High Uniformity Example 4 0.89 1.92 0.75 Glossy and Uniform Example 5 0.87 1.92 0.78 Uniform Color Tone Example 6 0.93 1.92 0.76 Significantly High Uniformity Example 7 0.94 1.93 0.78 Uniform Color Tone Example 8 0.89 1.92 0.75 Glossy and Uniform Example 9 0.86 1.93 0.78 Glossy and Uniform Example 10 0.88 1.92 0.79 Uniform Color Tone Example 11 0.86 1.93 0.78 Uniform Color Tone Example 12 0.89 1.92 0.77 Significantly High Uniformity Comparative Example 1 0.74 1.93 0.84 Glossy and Uniform Comparative Example 2 0.65 1.89 0.81 Light Gray and Non- Uniform Comparative Example 3 0.79 1.93 0.81 Not Glossy, but Uniform Comparative Example 4 0.63 1.92 0.86 Whitish and Non- Uniform Comparative Example 5 0.81 1.92 0.81 Whitish and Non- Uniform Comparative Example 6 0.76 1.92 0.82 Glossy and Uniform Comparative Example 7 0.73 1.93 0.81 White and Non-Uniform Comparative Example 8 0.51 1.93 0.89 Not Glossy, but Uniform Comparative Example 9 0.41 1.93 0.94 Glossy and Non-Uniform Comparative Example 10 0.65 1.91 0.91 White and Non-Uniform Comparative Example 11 0.81 1.93 0.82 Not Glossy, but Uniform Comparative Example 12 0.63 1.91 0.92 Not Glossy, but Uniform Comparative Example 13 0.79 1.93 0.84 Glossy and Uniform

(22) As a result of the tests, as shown in Table 3, the electrical steel sheets (Examples 1 to 12) having a chromium-free insulating coating in a surface, which contained a metal phosphate and a colloidal silica as main components, and in which the colloidal silica was contained in an amount of 20 to 150 parts by mass with respect to 100 parts by mass of the metal phosphate, and one or more kinds of fine particles selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, sialon, and cordierite are contained in an amount of 0.5 to 7 parts by mass with respect to 100 parts by mass of the metal phosphate had a higher coating tension, were more excellent in adhesion and corrosion resistance of the insulating coating, and had a more remarkable magnetic characteristic improvement effect than in Comparative Examples 1 to 13.

INDUSTRIAL APPLICABILITY

(23) According to the invention, it is possible to provide a grain-oriented electrical steel sheet which has a coating having various good coating characteristics such as adhesion and corrosion resistance and capable of applying a significantly higher tension to the steel sheet than in conventional cases despite not containing chromium, and has good magnetic characteristics.