Method for producing grain-oriented electrical steel sheet

1. A method for producing a grain-oriented electrical steel sheet by comprising a series of steps of hot rolling a raw steel material comprising C: 0.002-0.10 mass %, Si: 2.0-8.0 mass %, Mn: 0.005-1.0 mass % and the remainder being Fe and inevitable impurities to obtain a hot rolled sheet, subjecting the hot rolled steel sheet to a hot band annealing as required and further to one cold rolling or two or more cold rollings including an intermediate annealing therebetween to obtain a cold rolled sheet having a final sheet thickness, subjecting the cold rolled sheet to primary recrystallization annealing combined with decarburization annealing, applying an annealing separator to the steel sheet surface and then subjecting to final annealing, characterized in that rapid heating is performed at a rate of not less than 50° C./s in a region of 200-700° C. in the heating process of the primary recrystallization annealing, and the steel sheet is held at any temperature of 250-600° C. in the region of 200-700° C. for 1-5 seconds, while a soaking process of the primary recrystallization annealing is controlled to a temperature range of 750-900° C., a time of 90-180 seconds and P H2O /P H2 in an atmosphere of 0.25-0.40, where P H2O means a partial water vapor pressure of the atmosphere and P H2 means a partial hydrogen pressure of the atmosphere.

2. The method for producing a grain-oriented electrical steel sheet according to claim 1 , wherein the raw steel material further contains Al: 0.010-0.050 mass % and N: 0.003-0.020 mass %, or Al: 0.010-0.050 mass %, N: 0.003-0.020 mass %, Se: 0.003-0.030 mass % and/or S: 0.002-0.03 mass %.

3. The method for producing a grain-oriented electrical steel sheet according to claim 2 , wherein the steel sheet is subjected to nitriding treatment on the way of or after the primary recrystallization annealing to increase nitrogen content in the steel sheet to 50-1000 massppm.

4. The method for producing a grain-oriented electrical steel sheet according to claim 3 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-0.50 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Si; 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0.001-0.010 mass % and Ta: 0.001-0.010 mass %.

5. The method for producing a grain-oriented electrical steel sheet according to claim 2 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-030 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Si: 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0,001-0,010 mass % and Ta: 0,001-0,010 mass %.

6. The method for producing a grain-oriented electrical steel sheet according to claim 1 , wherein the steel sheet is subjected to nitriding treatment on the way of or after the primary recrystallization annealing to increase nitrogen content in the steel sheet to 50-1000 massppm.

7. The method for producing a grain-oriented electrical steel sheet according to claim 6 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-0.50 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Bi: 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0.001-0.010 mass % and Ta: 0.001-0.010 mass %.

8. The method for producing a grain-oriented electrical steel sheet according to claim 1 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-0.50 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Bi: 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0.001-0.010 mass % and Ta: 0.001-0.010 mass %.

9. A method for producing a grain-oriented electrical steel sheet by comprising a series of steps of hot rolling a raw steel material comprising C: 0.002-0.10 mass %, Si: 2.0-8.0 mass %, Mn: 0.005-1.0 mass % and the remainder being Fe and inevitable impurities to obtain a hot rolled sheet, subjecting the hot rolled steel sheet to a hot band annealing as required and further to one cold rolling or two or more cold rollings including an intermediate annealing therebetween to obtain a cold rolled sheet having a final sheet thickness, subjecting the cold rolled sheet to primary recrystallization annealing combined with decarburization annealing, applying an annealing separator to the steel sheet surface and then subjecting to final annealing, characterized in that rapid heating is performed at a rate of not less than 50° C./s in a region of 200-700° C. in the heating process of the primary recrystallization annealing, and the steel sheet is held at any temperature of 250-600° C. in the region of 200-700° C. for 1-5 seconds, wherein a soaking process of the primary recrystallization annealing is divided into N stages (N: an integer of not less than 2), and the process from the first stage to (N−1) stage is controlled to a temperature of 750-900° C., a time of 80-170 seconds and P H2O /P H2 in an atmosphere of 0.25-0.40, and the process of the final N stage is further controlled to a temperature of 750-900° C., a time of 10-60 seconds and P H2O /P H2 in an atmosphere of not more than 0.20, where P H2O means a partial water vapor pressure of the atmosphere and P H2 means a partial hydrogen pressure of the atmosphere.

10. The method for producing a grain-oriented electrical steel sheet according to claim 9 , wherein the raw steel material further contains Al; 0.010-0.050 mass % and N: 0.003-0.020 mass %, or Al: 0.010-0.050 mass %, N: 0.003-0.020 mass %, Se: 0.003-0.030 mass % and/or S: 0.002-0.03 mass %.

11. The method for producing a grain-oriented electrical steel sheet according to claim 9 , wherein the steel sheet is subjected to nitriding treatment on the way of or after the primary recrystallization annealing to increase nitrogen content in the steel sheet to 50-1000 massppm.

12. The method for producing a grain-oriented electrical steel sheet according to claim 9 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-0.50 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Bi: 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0.001-0.010 mass % and Ta: 0.001-0.010 mass %.

13. A method for producing a grain-oriented electrical steel sheet by comprising a series of steps of hot rolling a raw steel material comprising C: 0.002-0.10 mass %, Si: 2.0-8.0 mass %, Mn: 0.005-1.0 mass % and the remainder being Fe and inevitable impurities to obtain a hot rolled sheet, subjecting the hot rolled steel sheet to a hot band annealing as required and further to one cold rolling or two or more cold rollings including an intermediate annealing therebetween to obtain a cold rolled sheet having a final sheet thickness, subjecting the cold rolled sheet to primary recrystallization annealing combined with decarbunzation annealing, applying an annealing separator to the steel sheet surface and then subjecting to final annealing, characterized in that rapid heating is performed at a rate of not less than 50° C./s in a region of 200-700° C. in the heating process of the primary recrystallization annealing, and the steel sheet is held at any temperature of 250-600° C. in the region of 200-700° C. for 1-5 seconds, wherein a soaking process of the primary recrystallization annealing is divided into N stages (N: an integer of not less than 2), the first stage is controlled to a temperature of 820-900° C., a time of 10-60 seconds and P H2O /P H2 in an atmosphere of 0.25-0.40, and the second and later stages are controlled to a temperature of 750-900° C., a time of 80-170 seconds and P H2O /P H2 in an atmosphere of 0.25-0.40, provided that the temperature of the first stage is higher than those of the second and later stages, where P H2O means a partial water vapor pressure of the atmosphere and P H2 means a partial hydrogen pressure of the atmosphere.

14. The method for producing a grain-oriented electrical steel sheet according to claim 13 , wherein the raw steel material further contains Al: 0.010-0.050 mass % and N: 0.003-0.020 mass %, or Al: 0,010-0,050 mass %, N: 0.003-0.020 mass %, 0.003-0.030 mass % and/or S: 0.002-0.03 mass %.

15. The method for producing a grain-oriented electrical steel sheet according to claim 13 , wherein the steel sheet is subjected to nitriding treatment on the way of or after the primary recrystallization annealing to increase nitrogen content in the steel sheet to 50-1000 massppm.

16. The method for producing a grain-oriented electrical steel sheet according to claim 13 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-0.50 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Bi: 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0.001-0.010 mass % and Ta: 0.001-0.010 mass %.

17. A method for producing a grain-oriented electrical steel sheet by comprising a series of steps of hot rolling a raw steel material comprising C: 0.002-0.10 mass %, Si: 2.0-8.0 mass %, Mn: 0.005-1.0 mass % and the remainder being Fe and inevitable impurities to obtain a hot rolled sheet, subjecting the hot rolled steel sheet to a hot band annealing as required and further to one cold rolling or two or more cold rollings including an intermediate annealing therebetween to obtain a cold rolled sheet having a final sheet thickness, subjecting the cold rolled sheet to primary recrystallization annealing combined with decarburization annealing, applying an annealing separator to the steel sheet surface and then subjecting to final annealing, characterized in that rapid heating is performed at a rate of not less than 50° C./s in a region of 200-700° C. in the heating process of the primary recrystallization annealing, and the steel sheet is held at any temperature of 250-600° C. in the region of 200-700° C. for 1-5 seconds, wherein a soaking process of the primary recrystallization annealing is divided into N stages (N: an integer of not less than 3), and the first stage is controlled to a temperature of 820-900° C., a time of 10-60 seconds and P H2O /P H2 in an atmosphere of 0.25-0.40, and the second to (N−1) stages are controlled to a temperature of 750-900° C., a time of 70-160 seconds and P H2O /P H2 in an atmosphere of 0.25-0.40, and the last stage is controlled to a temperature of 750-900° C., a time of 10-60 seconds and P H2O /P H2 in an atmosphere of not more than 0.20, provided that the temperature of the first stage is higher than those of the second stage to the N−1 stage, where P H2O means a partial water vapor pressure of the atmosphere and P H2 means a partial hydrogen pressure of the atmosphere.

18. The method far producing a grain-oriented electrical steel sheet according to claim 17 , wherein the raw steel material further contains Al: 0.010-0.050 mass % and N: 0.003-0.020 mass %, or Al: 0.010-0.050 mass %, N: 0.003-0.020 mass %, Se: 0.003-0.030 mass % and/or S: 0.002-0.03 mass %.

19. The method for producing a grain-oriented electrical steel sheet according to claim 17 , wherein the steel sheet is subjected to nitriding treatment on the way of or after the primary recrystallization annealing to increase nitrogen content in the steel sheet to 50-1000 massppm.

20. The method for producing a grain-oriented electrical steel sheet according to claim 17 , wherein the raw steel material further contains one or more selected from the group consisting of Ni: 0.010-1.50 mass %, Cr: 0.01-0.50 mass %, Cu: 0.01-0.50 mass %, P: 0.005-0.50 mass %, Sb: 0.005-0.50 mass %, Sn: 0.005-0.50 mass %, Bi: 0.005-0.50 mass %, Mo: 0.005-0.10 mass %, B: 0.0002-0.0025 mass %, Te: 0.0005-0.010 mass %, Nb: 0.0010-0.010 mass %, V: 0.001-0.010 mass % and Ta: 0,001-0,010 mass %.