GRAIN-ORIENTED ELECTRICAL STEEL SHEET, AND STEEL SHEET SERVING AS BASE SHEET FOR GRAIN-ORIENTED ELECTRICAL STEEL SHEET

Abstract

A grain-oriented electrical steel sheet according to an aspect of the present invention includes an underlying steel sheet and a tension-insulation coating arranged on the surface of the underlying steel sheet, and a ten-point average roughness RzL in an L direction obtained when the tension-insulation coating is removed from the grain-oriented electrical steel sheet with an alkaline solution, and then the surface of the underlying steel sheet is measured in a rolling direction is 6.0 μm or less.

Claims

1. A grain-oriented electrical steel sheet comprising an underlying steel sheet and a tension-insulation coating arranged on a surface of the underlying steel sheet, wherein the underlying steel sheet obtained by removing the tension-insulation coating from the grain-oriented electrical steel sheet with an alkaline solution has a ten-point average roughness RzL in a rolling direction of 6.0 μm or less.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the underlying steel sheet obtained by removing the tension-insulation coating from the grain-oriented electrical steel sheet with an alkaline solution has a ten-point average roughness RzC in a direction perpendicular to the rolling direction of 8.0 μm or less.

3. The grain-oriented electrical steel sheet according to claim 1, wherein the ten-point average roughness RzL in the rolling direction and the ten-point average roughness RzC in the direction perpendicular to the rolling direction satisfy RzL/RzC<1.0.

4. The grain-oriented electrical steel sheet according to claim 1, wherein an arithmetic average roughness RaL in the rolling direction is less than 0.4 μm.

5. The grain-oriented electrical steel sheet according to claim 1, wherein an arithmetic average roughness RaC in the direction perpendicular to the rolling direction is less than 0.6 μm.

6. A steel sheet serving as a base sheet of the grain-oriented electrical steel sheet according to claim 1, wherein a ten-point average roughness RzL in the rolling direction is 6.0 μm or less.

7. The steel sheet according to claim 6, wherein a ten-point average roughness RzC in the direction perpendicular to the rolling direction is 8.0 μm or less.

8. The steel sheet according to claim 6, wherein the ten-point average roughness RzL in the rolling direction and the ten-point average roughness RzC in the direction perpendicular to the rolling direction satisfy RzL/RzC<1.0.

9. The steel sheet according to claim 6, wherein an arithmetic average roughness RaL in the rolling direction is less than 0.4 μm.

10. The steel sheet according to claim 6, wherein an arithmetic average roughness RaC in the direction perpendicular to the rolling direction is less than 0.6 μm.

11. The grain-oriented electrical steel sheet according to claim 2, wherein the ten-point average roughness RzL in the rolling direction and the ten-point average roughness RzC in the direction perpendicular to the rolling direction satisfy RzL/RzC<1.0.

12. The grain-oriented electrical steel sheet according to claim 2, wherein an arithmetic average roughness RaL in the rolling direction is less than 0.4 μm.

13. The grain-oriented electrical steel sheet according to claim 2, wherein an arithmetic average roughness RaC in the direction perpendicular to the rolling direction is less than 0.6 μm.

14. The steel sheet according to claim 7, wherein the ten-point average roughness RzL in the rolling direction and the ten-point average roughness RzC in the direction perpendicular to the rolling direction satisfy RzL/RzC<1.0.

15. The steel sheet according to claim 7, wherein an arithmetic average roughness RaL in the rolling direction is less than 0.4 μm.

16. The steel sheet according to claim 7, wherein an arithmetic average roughness RaC in the direction perpendicular to the rolling direction is less than 0.6 μm.

Description

EXAMPLES

[0069] Next, a grain-oriented electrical steel sheet and a method of forming a tension-insulation coating on a grain-oriented electrical steel sheet according to the present invention will be described in detail with reference to examples and comparative examples. Here, the following examples are only examples of the grain-oriented electrical steel sheet and the method of forming a tension-insulation coating on a grain-oriented electrical steel sheet according to the present invention, and the grain-oriented electrical steel sheet and the method of forming a tension-insulation coating on a grain-oriented electrical steel sheet according to the present invention are not limited to the following examples.

Example 1

[0070] Decarburization annealing was performed on a cold-rolled steel sheet for producing a grain-oriented electrical steel sheet having a sheet thickness of 0.23 mm and containing 3.2 mass % of Si, and an aqueous slurry of an annealing separator containing components shown in Table 1 was applied to the surface of the decarburized and annealed steel sheet, and dried, and the sheet was then coiled into a coil. Next, the decarburized and annealed steel sheet was subjected to secondary recrystallization in a dry nitrogen atmosphere, purification annealing (final annealing) was performed at 1,200° C. in the BAF atmosphere shown in Table 1, and thereby a finally annealed grain-oriented silicon steel sheet was obtained.

[0071] These finally annealed steel sheets were subjected to the powder removal pickling treatment under various conditions shown in Table 1. Then, the steel sheet after pickling was annealed by baking. The conditions for annealing by baking were as follows. A tension-insulation coating composed of aluminum phosphate and colloidal silica was applied at 5 g/m.sup.2 per one side. Then, the sheet was held in an annealing atmosphere containing 75% of hydrogen and 25% of nitrogen and having a dew point of 30° C. at a temperature of 850° C. for 30 seconds, and baked.

[0072] According to the above procedure, various grain-oriented electrical steel sheets including an underlying steel sheet and a tension-insulation coating arranged on the surface of the underlying steel sheet were obtained. For these, the magnetic domain was controlled by laser emission, and the following evaluations were performed.

(1) Evaluation of Magnetic Characteristics

[0073] The magnetic characteristics were evaluated according to B8 defined in JIS C 2553: 2012 (a material-specific magnetic flux density at a magnetic field strength of 800 A/m) and W17/50 (watt value per kilogram (W/kg) with a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T).

[0074] In this example, it was determined that the grain-oriented electrical steel sheet having B8 of 1.93 T or more and W17/50 of 0.70 W/kg or less had excellent magnetic characteristics.

[0075] However, since this pass/fail criterion varied depending on components such as the sheet thickness and the amount of Si, it was not an absolute reference for the grain-oriented electrical steel sheet according to the present invention. For example, in materials having the same B8, when the sheet thickness was reduced by about 0.025 mm, the iron loss value tended to be improved by about 0.05 W/kg, and when the amount of Si was increased by 0.1%, the iron loss value was further improved by about 0.02 W/kg. That is, the above pass/fail criterion was a threshold value for evaluating the grain-oriented electrical steel sheet according to the present invention, which was a grain-oriented electrical steel sheet having a sheet thickness of 0.23 mm and containing 3.2 mass % of Si.

(2) Measurement of Surface Roughness of Underlying Steel Sheet

[0076] The tension-insulation coating on the grain-oriented electrical steel sheet was removed by the following procedure. First, 48% caustic soda (sodium hydroxide aqueous solution, specific gravity of 1.5) and water were mixed at a volume ratio of 6:4 to prepare a 33% caustic soda aqueous solution (sodium hydroxide aqueous solution). The temperature of the 33% caustic soda aqueous solution was raised to 85° C. or higher. Then, the grain-oriented electrical steel sheet with a tension-insulation coating was immersed in the caustic soda aqueous solution for 20 minutes. Then, the grain-oriented electrical steel sheet was washed with water and dried to remove the tension-insulation coating on the grain-oriented electrical steel sheet.

[0077] Next, according to JIS B 0660: 1998, the ten-point average roughness RzL and the arithmetic average roughness RaL in the L direction (rolling direction in the underlying steel sheet) and the ten-point average roughness RzC and the arithmetic average roughness RaC in the C direction (direction perpendicular to the rolling direction of the underlying steel sheet) were measured.

[0078] Here, the surface roughness of the underlying steel sheet (base sheet) immediately before the tension-insulation coating was formed was measured. As a result, it was confirmed that the surface roughness of the underlying steel sheet after the tension-insulation coating was removed from the grain-oriented electrical steel sheet and the surface roughness of the base sheet before the tension-insulation coating was formed were substantially the same.

[0079] These evaluation results are shown in Table 1.

TABLE-US-00001 TABLE 1 Annealing BAF separator atmosphere Amount Partial of MgO pressure of added per N.sub.2 in 100 g of mixed gas Pickling Pickling Base Al.sub.2O.sub.3 containing Acid temperature time Rz(L) Rz(C) Ra(L) Ra(C) Rz(L)/ W17/50 sheet (g) N.sub.2-H.sub.2 (%) (concentration) (° C.) (sec) (μm) (μm) (μm) (μm) Rz(C) B8(T) (W/kg) Invention A0 0 25 1% H.sub.2SO.sub.4 20 10 7 2.9 0.3 0.30 2.41 1.953 0.730 Comparative example A1 20 25 1% H.sub.2SO.sub.4 20 10 3.9 3.5 0.21 0.31 1.11 1.947 0.670 Present invention example A2 40 25 1% H.sub.2SO.sub.4 20 10 4.2 6.1 0.21 0.36 0.69 1.946 0.648 Present invention example A3 40 50 1% H.sub.2SO.sub.4 20 10 2.5 3.3 0.21 0.32 0.76 1.945 0.658 Present invention example A4 40 100 1% H.sub.2SO.sub.4 20 10 1.9 3.0 0.17 0.31 0.63 1.943 0.643 Present invention example A5 60 100 1% H.sub.2SO.sub.4 20 10 5.2 7.2 0.19 0.33 0.72 1.932 0.688 Present invention example A6 60 25 1% H.sub.2SO.sub.4 20 10 6.3 8.5 0.22 0.38 0.74 1.925 0.714 Comparative example

[0080] All of the grain-oriented electrical steel sheets including the underlying steel sheet having RzL within the range of the present invention exhibited favorable magnetic characteristics.

[0081] On the other hand, in the grain-oriented electrical steel sheet in which the RzL was beyond the range of the present invention because the production method did not satisfy production conditions of the present invention, the magnetic characteristics were impaired. Specifically, the grain-oriented electrical steel sheets produced from base sheets A0 and A6 did not satisfy RzL≤6.0, and the magnetic characteristics were impaired.

[0082] It was considered that the reason why the surface roughness of the underlying steel sheet of the grain-oriented electrical steel sheet produced from the base sheet A0 was not preferably controlled was that the amount of magnesia in the annealing separator was too small. It was considered that the reason why the surface roughness of the underlying steel sheet of the grain-oriented electrical steel sheet produced from the base sheet A6 was not preferably controlled was that the amount of magnesia in the annealing separator was too large. However, in A5 in which the amount of magnesia in the annealing separator was the same as that of A6, when the partial pressure of nitrogen in the BAF atmosphere was lowered, it was possible to control the surface roughness of the underlying steel sheet.

Example 2

[0083] A grain-oriented electrical steel sheet was prepared according to the same procedure as in Example 1 under production conditions in which the pickling time was changed as shown in Table 2. Here, production conditions not shown in Table 2 were the same as those of the base sheet A4 in Table 1. These evaluation results are shown in Table 2.

TABLE-US-00002 TABLE 2 Pickling Pickling Base Acid temperature time Rz(L) Rz(C) Ra(L) Ra(C) W17/50 sheet (concentration) (° C.) (sec) (μm) (μm) (μm) (μm) Rz(L)/Rz(C) B8(T) (W/kg) Invention A4   1% H.sub.2SO.sub.4 20 10 1.9 3 0.17 0.31 0.63 1.943 0.643 Present invention example A4 0.3% H.sub.2SO.sub.4 80 15 1.6 3 0.14 0.32 0.53 1.945 0.631 Present invention example A4 0.3% H.sub.2SO.sub.4 80 30 1.8 2.9 0.15 0.28 0.62 1.943 0.638 Present invention example A4 0.3% H.sub.2SO.sub.4 80 45 2.5 2.8 0.14 0.27 0.89 1.94 0.652 Present invention example A4 0.3% H.sub.2SO.sub.4 80 60 3.2 3.4 0.26 0.27 0.94 1.938 0.668 Present invention example A4 0.3% H.sub.2SO.sub.4 80 90 5.5 5.6 0.33 0.35 0.98 1.930 0.691 Present invention example A4 0.3% H.sub.2SO.sub.4 80 120 7 6.5 0.33 0.35 1.08 1.920 0.721 Comparative example

[0084] All of the grain-oriented electrical steel sheets including the underlying steel sheet having RzL within the range of the present invention exhibited favorable magnetic characteristics.

[0085] On the other hand, in the grain-oriented electrical steel sheet in which the surface roughness in the L direction was beyond the range of the present invention because the production conditions of the present invention were not satisfied, the magnetic characteristics were impaired. Specifically, in the grain-oriented electrical steel sheet in which the pickling time was 120 seconds, since RzL≤6.0 did not satisfy, the magnetic characteristics were impaired. This is estimated to be due to the pickling time being too long.

Example 3

[0086] A grain-oriented electrical steel sheet was prepared according to the same procedure as in Example 1 under production conditions in which the pickling temperature and the acid concentration were variously changed as shown in Table 3. Here, the production conditions not shown in Table 3 were the same as those of the base sheet A3 in Table 1. These evaluation results are shown in Table 3.

TABLE-US-00003 TABLE 3 Pickling Pickling Base Acid temperature time Rz(L) Rz(C) Ra(L) Ra(C) W17/50 sheet (concentration) (° C.) (sec) (μm) (μm) (μm) (μm) Rz(L)/Rz(C) B8(T) (W/kg) Invention A3   1% H.sub.2SO.sub.4 20 10 2.5 3.3 0.21 0.32 0.76 1.945 0.658 Present invention example A3   1% H.sub.2SO.sub.4 50 10 2.3 3.2 0.2 0.31 0.72 1.946 0.648 Present invention example A3   1% H.sub.2SO.sub.4 80 10 2 2.9 0.18 0.33 0.69 1.945 0.642 Present invention example A3   1% H.sub.2SO.sub.4 90 10 1.8 3.1 0.19 0.32 0.58 1.94 0.637 Present invention example A3 0.3% H.sub.2SO.sub.4 80 30 1.7 3.1 0.16 0.27 0.55 1.944 0.632 Present invention example A3 0.6% H.sub.2SO.sub.4 80 30 1.8 3.2 0.17 0.26 0.56 1.940 0.633 Present invention example A3   1% H.sub.2SO.sub.4 80 30 1.9 3.2 0.17 0.27 0.59 1.938 0.635 Present invention example A3 1.5% H.sub.2SO.sub.4 80 30 2.0 3.3 0.16 0.26 0.61 1.935 0.644 Present invention example A3 3.0% H.sub.2SO.sub.4 80 30 2.5 3.5 0.19 0.28 0.71 1.935 0.672 Present invention example A3 0.3% H.sub.2SO.sub.4 90 30 1.9 3.3 0.15 0.29 0.58 1.942 0.642 Present invention example A3 0.6% H.sub.2SO.sub.4 90 30 2.1 3.5 0.15 0.30 0.60 1.938 0.653 Present invention example A3 1.0% H.sub.2SO.sub.4 90 30 2.5 4.1 0.18 0.31 0.61 1.935 0.681 Present invention example A3 1.5% H.sub.2SO.sub.4 90 30 3.1 4.9 0.21 0.35 0.63 1.930 0.691 Present invention example A3 3.0% H.sub.2SO.sub.4 90 30 6.5 6.0 0.25 0.41 1.08 1.925 0.721 Comparative example

[0087] All of the grain-oriented electrical steel sheets including the underlying steel sheet having RzL within the range of the present invention exhibited favorable magnetic characteristics.

[0088] On the other hand, in the grain-oriented electrical steel sheet in which the RzL was beyond the range of the present invention because the production conditions of the present invention were not satisfied, the magnetic characteristics were impaired. Specifically, when the temperature of the pickling solution was as high as 90° C., since the influence of the acid concentration became significant, if pickling was performed using 3% H.sub.2SO.sub.4, the RzL exceeded 6.0 μm.

INDUSTRIAL APPLICABILITY

[0089] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having excellent magnetic characteristics and a base sheet as a material thereof. Therefore, the present invention has tremendous industrial applicability.