METHOD FOR MANUFACTURING NON-ORIENTED ELECTRICAL STEEL SHEET

Abstract

A method for manufacturing a non-oriented electrical steel sheet includes a step of performing hot rolling on a steel material having a predetermined chemical composition, a step of performing first cold rolling, a step of performing process annealing, a step of performing second cold rolling, and a step of performing any one or both of final annealing and stress relief annealing. A final pass of finish rolling is performed in a temperature range equal to or higher than an Ar1 temperature, the steel sheet is held for 2 hours or less in a temperature range lower than an Ac1 temperature in the final annealing, and the steel sheet is held for 1200 sec or more in a temperature range equal to or higher than 600° C. and lower than the Ac1 temperature in the stress relief annealing.

Claims

1. A method for manufacturing a non-oriented electrical steel sheet, the method comprising: a step of obtaining a hot-rolled steel sheet by performing hot rolling on a steel material and winding the steel material in a temperature range higher than 250° C. and equal to or lower than 550° C., the steel material having a chemical composition that contains, by mass %, 0.0100% or less of C, 1.50 to 4.00% of Si, 0.0001 to 1.000% of sol.Al, 0.0100% or less of S, 0.0100% or less of N, 2.50 to 5.00% of Mn, Ni, Co, Pt, Pb, Cu, and Au in total, 0.000 to 0.400% of Sn, 0.000 to 0.400% of Sb, 0.000 to 0.400% of P, and 0.0000 to 0.0100% of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd in total with a remainder of Fe and impurities, and satisfies the following Expression (1) in a case where, by mass %, a Mn content is denoted by (Mn), a Ni content is denoted by (Ni), a Co content is denoted by (Co), a Pt content is denoted by (Pt), a Pb content is denoted by (Pb), a Cu content is denoted by (Cu), an Au content is denoted by (Au), a Si content is denoted by (Si), and a sol.Al content is denoted by (sol.Al); a step of performing first cold rolling on the hot-rolled steel sheet; a step of performing process annealing after the first cold rolling; a step of performing second cold rolling after the process annealing; and a step of performing any one or both of final annealing and stress relief annealing after the second cold rolling, wherein a final pass of finish rolling during the hot rolling is performed in a temperature range equal to or higher than an Ar1 temperature, the steel sheet is held for 2 hours or less in a temperature range lower than an Ac1 temperature in the final annealing, and the steel sheet is held for 1200 sec or more in a temperature range equal to or higher than 600° C. and lower than the Ac1 temperature in the stress relief annealing
((Mn)+(Ni)+(Co)+(Pt)+(Pb)+(Cu)+(Au))—((Si)+(sol.Al))>0.00%  (1).

2. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the steel material contains one or more selected from the group consisting of, by mass %, 0.020 to 0.400% of Sn, 0.020 to 0.400% of Sb, 0.020 to 0.400% of P, and 0.0005 to 0.0100% of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd in total.

3. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the steel sheet is held for 10 to 1200 sec in a temperature range equal to or higher than 600° C. and lower than the Ac1 temperature in the final annealing.

4. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the steel sheet is held for 1 hour or more in a temperature range equal to or higher than 750° C. and lower than the Ac temperature in the stress relief annealing.

5. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein cold rolling is performed at a cumulative rolling reduction of 80 to 92% in the step of performing the first cold rolling, and cold rolling is performed at a cumulative rolling reduction of 5 to 25% in the step of performing the second cold rolling.

6. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the process annealing is performed in a temperature range lower than the Ac1 temperature.

7. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein both the final annealing and the stress relief annealing are performed.

8. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein the steel sheet is held for 10 to 1200 sec in a temperature range equal to or higher than 600° C. and lower than the Ac1 temperature in the final annealing.

9. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein the steel sheet is held for 1 hour or more in a temperature range equal to or higher than 750° C. and lower than the Ac temperature in the stress relief annealing.

10. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein cold rolling is performed at a cumulative rolling reduction of 80 to 92% in the step of performing the first cold rolling, and cold rolling is performed at a cumulative rolling reduction of 5 to 25% in the step of performing the second cold rolling.

11. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein the process annealing is performed in a temperature range lower than the Ac1 temperature.

12. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein both the final annealing and the stress relief annealing are performed.

Description

EXAMPLES

[0108] Next, the method for manufacturing a non-oriented electrical steel sheet according to the embodiment of the invention will be specifically described with reference to examples. Examples to be described below are merely examples of the method for manufacturing a non-oriented electrical steel sheet according to the embodiment of the invention, and the method for manufacturing a non-oriented electrical steel sheet according to the embodiment of the invention is not limited to the following examples.

First Example

[0109] Molten steel was casted to produce slabs having chemical compositions shown in Table 1 to be described below. The left side of Expression shown in Table 1 represents the value of the left side of Expression (1) having been described above. After that, the produced slabs were heated up to 1150° C. and were subjected to hot rolling under conditions shown in Table 2, so that hot-rolled steel sheets having a sheet thickness of 2.5 mm were obtained.

[0110] The finishing temperature of finish rolling was 800° C., and was a temperature higher than the Ar1 temperatures of all the steel sheets.

[0111] Then, pickling was performed on the obtained hot-rolled steel sheets to remove scale. After that, first cold rolling was performed at a cumulative rolling reduction of 85% until a sheet thickness reached 0.385 mm, so that steel sheets (cold-rolled steel sheets) were obtained. Process annealing for heating the obtained steel sheets and holding the steel sheets for 5 to 60 sec at 700° C., which is a temperature lower than the Ac1 temperatures of all the steel sheets, in a non-oxidizing atmosphere was performed. Then, second cold rolling (skin pass rolling) was performed at a cumulative rolling reduction of 9% until a sheet thickness reached 0.35 mm.

[0112] Ac1 temperatures of all the examples shown in Table 1 were about 850° C. The Ar1 temperature was obtained from a change in the thermal expansion of the steel sheet that was being cooled at an average cooling rate of 1° C./sec, and the Ac1 temperature was obtained from a change in the thermal expansion of the steel sheet that was being heated at an average heating rate of 1° C./sec.

[0113] After the second cold rolling (skin pass rolling) was performed, final annealing was performed. Achieving temperatures (holding temperatures) and holding times in this case are shown in Table 2.

[0114] In order to evaluate the workability of a non-oriented electrical steel sheet, a test for evaluating punching accuracy was performed after the final annealing. A punching die of 3 mm×50 mm was used in the test to measure the shape of a punched material. Punching was performed so that a long side direction was parallel to the rolling direction of the steel sheet. The long side and the short side of the punched material were measured in the measurement of a shape, and one end of the punched material in the long side direction was pressed with a finger and the lift distance of the other end thereof was measured.

[0115] After the final annealing was performed, stress relief annealing for holding the steel sheets for 2 hours at 800° C. was performed. After the stress relief annealing was performed, magnetic flux densities B50 were measured using a single-sheet magnetic measurement device. Samples of 55 mm square were taken in two directions that were inclined with respect to the rolling directions of the steel sheets by 0° and 45°, and magnetic flux densities B50 were measured. The magnetic flux density in the direction inclined with respect to the rolling direction by 45° was referred to as the magnetic flux density B50 in a 45° direction. The whole circumferential average of the magnetic flux densities B50 was obtained from the calculation of an average value of the magnetic flux densities in directions inclined with respect to the rolling direction by 0°, 45°, 90°, and 135°.

[0116] Further, energy losses (W/kg) of the samples, which were obtained from the non-oriented electrical steel sheets, on the whole circumferential average, which were generated in a case where an AC magnetic field having a frequency of 400 Hz was applied so that the maximum magnetic flux density was 1.0 T, were measured, so that iron losses W10/400 were obtained.

TABLE-US-00001 TABLE 1 Chemical composition (mass %) Remainder iron and impurities Left side of No. C Si sol-Al S N Mn Ni Co Pt Pb Cu Au Expression 101 0.0013 2.50 0.013 0.0020 0.0022 3.12 — — — — — — 0.61 102 0.0010 2.51 0.012 0.0017 0.0019 — 3.11 — — — — — 0.58 103 0.0008 2.51 0.009 0.0023 0.0018 — — 3.08 — — — — 0.56 104 0.0011 2.54 0.012 0.0021 0.0018 — — — 3.08 — — — 0.53 105 0.0011 2.48 0.010 0.0024 0.0019 — — — — 3.08 — — 0.59 106 0.0008 2.53 0.011 0.0017 0.0023 — — — — — 3.10 — 0.55 107 0.0010 2.52 0.013 0.0019 0.0018 — — — — — — 3.08 0.54 108 0.0011 2.49 0.010 0.0022 0.0024 3.12 — — — — — — 0.63 109 0.0014 2.48 0.011 0.0020 0.0021 3.07 — — — — — — 0.59 110 0.0012 2.48 0.007 0.0019 0.0022 3.11 — — — — — — 0.62 111 0.0007 2.51 0.010 0.0019 0.0021 3.14 — — — — — — 0.62 112 0.0007 2.49 0.009 0.0018 0.0023 3.10 — — — — — — 0.61 113 0.0011 2.51 0.014 0.0023 0.0019 3.14 — — — — — — 0.61 114 0.0014 2.53 0.010 0.0017 0.0017 3.09 — — — — — — 0.56 115 0.0013 2.46 0.010 0.0020 0.0023 3.09 — — — — — — 0.62 116 0.0012 2.49 0.013 0.0021 0.0023 3.09 — — — — — 0.58 117 0.0012 2.47 0.007 0.0020 0.0017 3.08 — — — — — — 0.60 118 0.0011 2.47 0.009 0.0018 0.0018 3.09 — — — — — — 0.61 119 0.0008 2.50 0.010 0.0021 0.0021 3.12 — — — — — — 0.61 120 0.0010 2.48 0.298 0.0021 0.0022 3.40 — — — — — — 0.63 121 0.0011 2.49 0.299 0.0019 0.0020 — 3.42 — — — — — 0.62 122 0.0010 2.49 0.301 0.0022 0.0022 — — 3.41 — — — — 0.62 123 0.0009 2.52 0.302 0.0021 0.0020 — — — 3.39 — — — 0.56 124 0.0011 2.51 0.298 0.0022 0.0021 — — — — 3.41 — — 0.60 125 0.0011 2.49 0.297 0.0019 0.0022 — — — — — 3.41 — 0.62 126 0.0009 2.50 0.299 0.0019 0.0018 — — — — — — 3.41 0.61 127 0.0011 2.50 0.298 0.0018 0.0020 3.38 — — — — — — 0.59 128 0.0009 2.50 0.297 0.0021 0.0018 3.40 — — — — — — 0.60 129 0.0008 2.51 0.297 0.0020 0.0019 3.40 — — — — — — 0.59 130 0.0008 2.49 0.299 0.0019 0.0019 3.42 — — — — — — 0.63 131 0.0010 2.50 0.303 0.0021 0.0020 3.42 — — — — — — 0.61 132 0.0011 2.54 0.600 0.0020 0.0022 3.71 — — — — — — 0.57

TABLE-US-00002 TABLE 2 Final annealing conditions Time in Magnetic characteristics after annealing Hot rolling temperature range Punching test performed for 2 hours at 800° C. Winding Achieving equal to or higher Length of Length of Lift B50 in 45° B50 on whole temperature temperature than 600° C. and long side short side distance direction circumferential W10/400 No. (° C.) (° C.) lower than Ac1 (sec) (mm) (mm) (μm) (T) average (T) (W/kg) Note 101 500 700 30 49.997 2.999 0 1.812 1.678 15.15 Example of invention 102 500 700 30 49.997 2.999 0 1.811 1.681 15.03 Example of invention 103 500 700 30 49.997 2.999 0 1.811 1.677 15.05 Example of invention 104 500 700 30 49.997 2.999 0 1.812 1.681 15.01 Example of invention 105 500 700 30 49.997 2.999 0 1.810 1.677 15.11 Example of invention 106 500 700 30 49.997 2.999 0 1.812 1.677 15.06 Example of invention 107 500 700 30 49.997 2.999 0 1.813 1.676 15.14 Example of invention 108 500 650 30 49.997 2.999 0 1.810 1.676 15.17 Example of invention 109 500 750 30 49.997 2.999 0 1.809 1.679 15.10 Example of invention 110 500 800 30 49.997 2.999 0 1.811 1.681 15.02 Example of invention 111 500 900 30 49.990 2.995 0 1.528 1.613 19.13 Comparative Example 112 500 700 15 49.997 2.999 10 1.809 1.683 15.19 Example of invention 113 500 700 120 49.996 2.998 0 1.810 1.682 15.05 Example of invention 114 500 700 1100 49.995 2.998 0 1.811 1.683 15.18 Example of invention 115 500 700 1500 49.992 2.996 0 1.814 1.678 15.17 Example of invention 116 500 700 7200 49.991 2.995 0 1.814 1.680 15.15 Example of invention 117 500 700 5 49.998 3.000 156 1.814 1.677 15.17 Example of invention 118 600 700 30 49.997 2.999 0 1.788 1.648 16.53 Comparative Example 119 200 700 30 49.997 2.999 0 1.791 1.651 16.42 Comparative Example 120 500 700 30 49.997 2.999 0 1.805 1.669 14.73 Example of invention 121 500 700 30 49.997 2.999 0 1.804 1.669 14.70 Example of invention 122 500 700 30 49.997 2.999 0 1.806 1.667 14.77 Example of invention 123 500 700 30 49.997 2.999 0 1.804 1.669 14.73 Example of invention 124 500 700 30 49.997 2.999 0 1.803 1.669 14.76 Example of invention 125 500 700 30 49.997 2.999 0 1.806 1.671 14.80 Example of invention 126 500 700 30 49.997 2.999 0 1.804 1.669 14.67 Example of invention 127 600 700 30 49.997 2.999 0 1.784 1.643 15.25 Comparative Example 128 400 700 30 49.997 2.999 0 1.803 1.670 14.76 Example of invention 129 300 700 30 49.997 2.999 0 1.801 1.665 14.82 Example of invention 130 200 700 30 49.997 2.999 0 1.784 1.643 15.27 Comparative Example 131 500 900 30 49.990 2.995 0 1.518 1.608 19.17 Comparative Example 132 500 700 30 49.997 2.999 0 1.801 1.661 14.21 Example of invention

[0117] Underlines shown in Table 2 represent conditions out of the scope of the invention. Nos. 101 to 110, Nos. 112 to 114, Nos. 120 to 126, No. 128, and Nos. 129 and 132, which were the examples of the invention, were excellent in workability (also had high dimensional accuracy after punching and had almost no lift distance), and had excellent magnetic characteristics both in the 450 direction and on the whole circumferential average (high magnetic flux densities B50 and low iron losses W10/400). Further, Nos. 115 to 117, which were the examples of the invention, had excellent magnetic characteristics but were slightly inferior to the other examples of the invention in terms of workability.

[0118] On the other hand, since the holding temperature of No. 111, which was a comparative example, during the final annealing was higher than the Ac1 temperature, the dimensional accuracy of No. 111 deteriorated and the magnetic flux density thereof also deteriorated. Further, since the winding temperatures of Nos. 118, 119, 127, and 130, which were comparative examples, were not appropriate, the magnetic flux densities thereof deteriorated and/or the iron losses thereof were increased.

Second Example

[0119] Molten steel was casted to produce slabs having chemical compositions shown in Table 3 to be described below. The left side of Expression shown in Table 3 represents the value of the left side of Expression (1) having been described above. After that, the produced slabs were heated up to 1150° C. and were subjected to hot rolling under conditions shown in Table 4, so that hot-rolled steel sheets having a sheet thickness of 2.5 mm were obtained.

[0120] The hot-rolled steel sheets were cooled up to 500° C. by water after finish rolling, and were then wound.

[0121] The finishing temperature of finish rolling was 800° C., and was a temperature higher than the Ar1 temperatures of all the steel sheets.

[0122] Then, pickling was performed on the obtained hot-rolled steel sheets to remove scale. After that, first cold rolling was performed at a cumulative rolling reduction of 85% until a sheet thickness reached 0.385 mm, so that steel sheets (cold-rolled steel sheets) were obtained. Process annealing for heating the obtained steel sheets and holding the steel sheets for 5 to 60 sec at 700° C., which is a temperature lower than the Ac1 temperatures of all the steel sheets, in a non-oxidizing atmosphere was performed. Then, second cold rolling (skin pass rolling) was performed at a cumulative rolling reduction of 9% until a sheet thickness reached 0.35 mm.

[0123] After the second cold rolling (skin pass rolling) was performed, final annealing for holding the steel sheets for 30 sec at 700° C., which was lower than the Ac temperatures of all the steel sheets, was performed. Then, the evaluation of workability and the measurement of magnetic flux densities B50 and iron losses W10/400 were performed by the same methods as in the first example. The Ar1 temperatures and the Ac1 temperatures were measured by the same methods as in the first example.

TABLE-US-00003 TABLE 3 Chemical composition (mass %) Remainder iron and impurities No. C Si sol-Al S N Mn Sn Sb P Mg Ca 201 0.0010 2.46 0.013 0.0023 0.0024 3.08 — — — — — 202 0.0007 2.50 0.013 0.0019 0.0020 3.11 0.050 — — — — 203 0.0011 2.54 0.007 0.0018 0.0022 3.10 — 0.054 — — — 204 0.0012 2.49 0.011 0.0021 0.0020 3.12 — — 0.047 — — 205 0.0006 2.47 0.011 0.0018 0.0019 3.09 — — — 0.0047 — 206 0.0014 2.49 0.010 0.0018 0.0022 3.08 — — — — 0.0048 207 0.0007 2.51 0.008 0.0018 0.0023 3.08 — — — — — 208 0.0012 2.51 0.013 0.0017 0.0023 3.10 — — — — — 209 0.0010 2.46 0.008 0.0020 0.0019 3.09 — — — — — 210 0.0010 2.49 0.009 0.0021 0.0020 3.09 — — — — — 211 0.0012 2.51 0.010 0.0021 0.0018 3.09 — — — — — 212 0.0008 2.49 0.006 0.0016 0.0024 3.13 — — — — — 213 0.0006 2.48 0.007 0.0017 0.0018 3.14 — — — — — 214 0.0007 2.53 0.008 0.0021 0.0024 3.10 — — — — — 215 0.0008 2.50 0.306 0.0023 0.0022 3.42 0.051 — — — — 216 0.0012 2.53 0.601 0.0019 0.0020 3.73 0.050 — — — — Chemical composition (mass %) Remainder iron and impurities Left side of No. Sr Ba Ce La Nd Pr Zn Cd Expression 201 — — — — — — — — 0.60 202 — — — — — — — — 0.59 203 — — — — — — — — 0.56 204 — — — — — — — — 0.62 205 — — — — — — — — 0.61 206 — — — — — — — — 0.58 207 0.0048 — — — — — — — 0.56 208 — 0.0052 — — — — — — 0.57 209 — — 0.0053 — — — — — 0.62 210 — — — 0.0052 — — — — 0.59 211 — — — — 0.0050 — — — 0.58 212 — — — — — 0.0052 — — 0.63 213 — — — — — — 0.0054 — 0.65 214 — — — — — — — 0.0050 0.57 215 — — — — — — — — 0.61 216 — — — — — — — — 0.60

TABLE-US-00004 TABLE 4 Final annealing conditions Time in Magnetic characteristics after annealing temperature range Punching test performed for 2 hours at 800° C. Achieving equal to or higher Length of Length of Lift B50 in 45° B50 on whole temperature than 600° C. and long side short side distance direction circumferential W10/400 No. (° C.) lower than Ac1 (sec) (mm) (mm) (μm) (T) average (T) (W/kg) Note 201 700 30 49.997 2.999 0 1.807 1.678 15.13 Example of invention 202 700 30 49.997 2.999 0 1.821 1.688 15.07 Example of invention 203 700 30 49.997 2.999 0 1.821 1.689 15.07 Example of invention 204 700 30 49.997 2.999 0 1.822 1.693 15.12 Example of invention 205 700 30 49.997 2.999 0 1.811 1.681 14.72 Example of invention 206 700 30 49.997 2.999 0 1.811 1.682 14.67 Example of invention 207 700 30 49.997 2.999 0 1.807 1.677 14.68 Example of invention 208 700 30 49.997 2.999 0 1.813 1.682 14.67 Example of invention 209 700 30 49.997 2.999 0 1.811 1.679 14.71 Example of invention 210 700 30 49.997 2.999 0 1.812 1.682 14.74 Example of invention 211 700 30 49.997 2.999 0 1.808 1.682 14.70 Example of invention 212 700 30 49.997 2.999 0 1.814 1.678 14.74 Example of invention 213 700 30 49.997 2.999 0 1.807 1.679 14.67 Example of invention 214 700 30 49.997 2.999 0 1.813 1.677 14.71 Example of invention 215 700 30 49.997 2.999 0 1.815 1.683 14.66 Example of invention 216 700 30 49.997 2.999 0 1.809 1.677 14.25 Example of invention

[0124] All of Nos. 201 to 216 were examples of the invention, were excellent in workability (had good dimensional accuracy after punching and had short lift distances), and had excellent magnetic characteristics (high magnetic flux densities B50 and low iron losses W10/400). In particular, the magnetic flux densities B50 of Nos. 202 to 204 were higher than those of No. 201 and Nos. 205 to 214. The iron losses W10/400 of Nos. 205 to 214 were lower than those of Nos. 201 to 204. The iron losses W10/400 of Nos. 215 and 216 were lower than the iron loss W10/400 of No. 202, but the magnetic flux densities B50 of Nos. 215 and 216 were lower than the magnetic flux density B50 of No. 202.

Third Example

[0125] Molten steel was casted to produce slabs having chemical compositions shown in Table 5 to be described below. The left side of Expression shown in Table 5 represents the value of the left side of Expression (1) having been described above. After that, the produced slabs were heated up to 1150° C. and were subjected to hot rolling under conditions shown in Table 6, so that hot-rolled steel sheets having a sheet thickness of 2.5 mm were obtained.

[0126] The finishing temperature of finish rolling was 800° C., and was a temperature higher than the Ar1 temperatures of all the steel sheets.

[0127] Then, pickling was performed on the obtained hot-rolled steel sheets to remove scale. After that, first cold rolling was performed at a cumulative rolling reduction of 85% until a sheet thickness reached 0.385 mm, so that steel sheets (cold-rolled steel sheets) were obtained. Process annealing for heating the obtained steel sheets and holding the steel sheets for 5 to 60 sec at 700° C., which is a temperature lower than the Ac1 temperatures of all the steel sheets, in a non-oxidizing atmosphere was performed. Then, second cold rolling (skin pass rolling) was performed at a cumulative rolling reduction of 9% until a sheet thickness reached 0.35 mm.

[0128] The Ac1 temperatures of all examples shown in Table 5 were about 850° C.

[0129] After the second cold rolling (skin pass rolling) was performed, final annealing was performed. Achieving temperatures (holding temperatures) and holding times in this case are shown in Table 6. Then, the evaluation of workability and the measurement of magnetic flux densities B50 and iron losses W10/400 were performed by the same methods as in the first example. The Ar1 temperatures and the Ac1 temperatures were measured by the same methods as in the first example.

[0130] Stress relief annealing was not performed in this example.

TABLE-US-00005 TABLE 5 Chemical composition (mass %) Remainder iron and impurities Left side of No. C Si sol-Al S N Mn Ni Co Pt Pb Cu Au Expression 301 0.0010 2.48 0.011 0.0018 0.0018 3.08 — — — — — — 0.59 302 0.0012 2.54 0.011 0.0019 0.0019 — 3.09 — — — — — 0.54 303 0.0012 2.51 0.011 0.0018 0.0020 — — 3.10 — — — — 0.57 304 0.0008 2.48 0.011 0.0019 0.0019 — — — 3.12 — — — 0.63 305 0.0009 2.53 0.011 0.0018 0.0021 — — — — 3.07 — — 0.53 306 0.0009 2.53 0.011 0.0020 0.0021 — — — — — 3.11 — 0.57 307 0.0008 2.48 0.011 0.0021 0.0020 — — — — — — 3.08 0.59 308 0.0011 2.51 0.011 0.0019 0.0020 3.09 — — — — — — 0.57 309 0.0008 2.51 0.011 0.0020 0.0022 3.14 — — — — — — 0.61 310 0.0011 2.52 0.011 0.0020 0.0019 3.10 — — — — — — 0.56 311 0.0010 2.47 0.011 0.0018 0.0018 3.06 — — — — — — 0.58 312 0.0010 2.53 0.011 0.0019 0.0019 3.08 — — — — — — 0.53 313 0.0010 2.48 0.011 0.0018 0.0020 3.11 — — — — — — 0.62 314 0.0009 2.47 0.011 0.0020 0.0021 3.07 — — — — — — 0.58 315 0.0010 2.49 0.011 0.0021 0.0019 3.08 — — — — — — 0.58 316 0.0012 2.53 0.011 0.0020 0.0022 3.08 — — — — — — 0.54 317 0.0008 2.49 0.011 0.0019 0.0018 3.06 — — — — — — 0.56 318 0.0008 2.51 0.011 0.0020 0.0021 3.08 — — — — — — 0.56 319 0.0011 2.49 0.011 0.0020 0.0022 3.11 — — — — — — 0.61 320 0.0012 2.48 0.300 0.0020 0.0021 3.37 — — — — — — 0.59 321 0.0011 2.52 0.600 0.0019 0.0021 3.73 — — — — — — 0.61

TABLE-US-00006 TABLE 6 Final annealing conditions Time in Magnetic characteristics after annealing Hot rolling temperature range Punching test performed for 2 hours at 800° C. Winding Achieving equal to or higher Length of Length of Lift B50 in 45° B50 on whole temperature temperature than 600° C. and long side short side distance direction circumferential W10/400 No. (° C.) (° C.) lower than Ac1 (sec) (mm) (mm) (μm) (T) average (T) (W/kg) Note 301 500 700 30 49.997 2.999 0 1.819 1.690 19.56 Example of invention 302 500 700 30 49.997 2.999 0 1.819 1.694 19.62 Example of invention 303 500 700 30 49.997 2.999 0 1.818 1.686 19.58 Example of invention 304 500 700 30 49.997 2.999 0 1.818 1.691 19.57 Example of invention 305 500 700 30 49.997 2.999 0 1.818 1.690 19.63 Example of invention 306 500 700 30 49.997 2.999 0 1.821 1.688 19.60 Example of invention 307 500 700 30 49.997 2.999 0 1.823 1.687 19.61 Example of invention 308 500 650 30 49.997 2.999 0 1.821 1.689 19.59 Example of invention 309 500 750 30 49.997 2.999 0 1.820 1.694 19.59 Example of invention 310 500 800 30 49.997 2.999 0 1.822 1.690 19.60 Example of invention 311 500 900 30 49.990 2.995 0 1.529 1.614 21.14 Comparativ Example 312 500 700 15 49.997 2.999 8 1.820 1.692 19.63 Example of invention 313 500 700 120 49.996 2.998 0 1.817 1.687 19.59 Example of invention 314 500 700 1100 49.995 2.998 0 1.824 1.689 19.62 Example of invention 315 500 700 1500 49.992 2.996 0 1.817 1.691 19.59 Example of invention 316 500 700 7200 49.991 2.995 0 1.822 1.691 19.60 Example of invention 317 500 700 5 49.998 3.000 161 1.817 1.688 19.58 Example of invention 318 600 700 30 49.997 2.999 0 1.800 1.672 20.56 Comparative Example 319 200 700 30 49.997 2.999 0 1.802 1.670 20.58 Comparative Example 320 500 700 30 49.997 2.999 0 1.812 1.682 18.50 Example of invention 321 500 700 30 49.997 2.999 0 1.805 1.677 17.51 Example of invention

[0131] Underlines shown in Table 6 represent conditions out of the scope of the invention. Nos. 301 to 310, Nos. 312 to 314, and Nos. 320 and 321, which were the examples of the invention, were excellent in workability (also had high dimensional accuracy after punching and had almost no lift distance), and had excellent magnetic characteristics both in the 45° direction and on the whole circumferential average (high magnetic flux densities B50 and low iron losses W10/400). Further, Nos. 315 to 317, which were the examples of the invention, had good magnetic characteristics but were slightly inferior to the other examples of the invention in terms of workability.

[0132] On the other hand, since the holding temperature of No. 311, which was a comparative example, during the final annealing was higher than the Ac1 temperature, the dimensional accuracy of No. 311 deteriorated and the magnetic flux density thereof also deteriorated. Further, since the winding temperatures of Nos. 318 and 319, which were comparative examples, were not appropriate, the magnetic flux densities thereof deteriorated and the iron losses thereof were increased.

Fourth Example

[0133] Molten steel was casted to produce slabs having chemical compositions shown in Table 7 to be described below. The left side of Expression shown in Table 7 represents the value of the left side of Expression (1) having been described above. After that, the produced slabs were heated up to 1150° C. and were subjected to hot rolling under conditions shown in Table 8, so that hot-rolled steel sheets having a sheet thickness of 2.5 mm were obtained.

[0134] The finishing temperature of finish rolling was 800° C., and was a temperature higher than the Ar1 temperatures of all the steel sheets.

[0135] Then, pickling was performed on the obtained hot-rolled steel sheets to remove scale. After that, first cold rolling was performed at a cumulative rolling reduction of 85% until a sheet thickness reached 0.385 mm, so that steel sheets (cold-rolled steel sheets) were obtained. Process annealing for heating the obtained steel sheets and holding the steel sheets for 5 to 60 sec at 700° C., which is a temperature lower than the Ac1 temperatures of all the steel sheets, in a non-oxidizing atmosphere was performed. Then, second cold rolling (skin pass rolling) was performed at a cumulative rolling reduction of 9% until a sheet thickness reached 0.35 mm.

[0136] The Ac1 temperatures of all examples shown in Table 7 were about 850° C.

[0137] After the second cold rolling (skin pass rolling) was performed, workability was evaluated by the same method as in the first example.

[0138] Final annealing was not performed in this example.

[0139] Stress relief annealing for holding the steel sheets for 2 hours at 800° C. was performed after a test for evaluating workability. After the stress relief annealing was performed, magnetic flux densities B50 and iron losses W10/400 were measured by the same methods as in the first example. The Ar1 temperatures and the Ac1 temperatures were measured by the same methods as in the first example.

TABLE-US-00007 TABLE 7 Chemical composition (mass %) Remainder iron and impurities Left side of No. C Si sol-Al S N Mn Ni Co Pt Pb Cu Au Expression 401 0.0008 2.49 0.010 0.0021 0.0019 3.14 — — — — — — 0.64 402 0.0011 2.50 0.009 0.0022 0.0020 — 3.13 — — — — — 0.62 403 0.0011 2.51 0.009 0.0019 0.0019 — — 3.14 — — — — 0.62 404 0.0009 2.51 0.011 0.0021 0.0021 — — — 3.12 — — — 0.60 405 0.0012 2.52 0.010 0.0021 0.0022 — — — — 3.13 — — 0.61 406 0.0011 2.49 0.012 0.0020 0.0021 — — — — — 3.11 — 0.61 407 0.0011 2.51 0.009 0.0022 0.0018 — — — — — — 3.11 0.59 408 0.0011 2.51 0.010 0.0020 0.0019 3.11 — — — — — — 0.58 409 0.0011 2.48 0.010 0.0019 0.0020 3.11 — — — — — — 0.61 410 0.0008 2.51 0.013 0.0019 0.0019 3.12 — — — — — — 0.59 411 0.0009 2.52 0.011 0.0018 0.0020 3.39 — — — — — — 0.86 412 0.0009 2.48 0.012 0.0020 0.0019 3.69 — — — — — — 1.19

TABLE-US-00008 TABLE 8 Magnetic characteristics after annealing Hot rolling Punching test performed for 2 hours at 800° C. Winding Length of Length of Lift B50 in 45° B50 on whole temperature long side short side distance direction circumferential W10/400 No. (° C.) (mm) (mm) (μm) (T) average (T) (W/kg) Note 401 500 49.997 2.999 185 1.812 1.677 15.17 Example of invention 402 500 49.997 2.999 188 1.811 1.676 15.10 Example of invention 403 500 49.997 2.999 186 1.810 1.679 15.11 Example of invention 404 500 49.997 2.999 197 1.810 1.679 15.11 Example of invention 405 500 49.997 2.999 179 1.808 1.679 15.11 Example of invention 406 500 49.997 2.999 190 1.810 1.677 15.13 Example of invention 407 500 49.997 2.999 194 1.809 1.676 15.12 Example of invention 408 500 49.997 2.999 176 1.812 1.678 15.15 Example of invention 409 600 49.997 2.999 199 1.788 1.647 16.53 Comparative Example 410 200 49.997 2.999 168 1.792 1.650 16.38 Comparative Example 411 500 49.997 2.999 170 1.805 1.674 14.66 Example of invention 412 500 49.997 2.999 198 1.798 1.669 14.13 Example of invention

[0140] Underlines shown in Table 8 represent conditions out of the scope of the invention. Nos. 401 to 408 and Nos. 411 and 412, which were the examples of the invention, had good dimensional accuracy after punching but had slight lift distances. Further, Nos. 401 to 408 and Nos. 411 and 412 had excellent magnetic characteristics both in the 450 direction and on the whole circumferential average (high magnetic flux densities B50 and low iron losses W10/400).

[0141] On the other hand, since the winding temperatures of Nos. 409 and 410, which were comparative examples, were not appropriate, the magnetic flux densities thereof deteriorated and the iron losses thereof were increased.