Method of producing grain-oriented electrical steel sheet having excellent iron loss properties

Abstract

In the production of a grain-oriented electrical steel sheet by hot rolling a steel slab comprising C: 0.001˜0.10 mass %, Si: 1.0˜5.0 mass %, Mn: 0.01˜0.5 mass %, sol. Al: 0.003˜0.050 mass %, N: 0.0010˜0.020 mass %, one or two selected from S and Se: 0.005˜0.040 mass % in total, cold rolling, primary recrystallization annealing, and final annealing, a heating rate S1 between a temperature T1 (° C.): 500+2×(NB−NA) and a temperature T2 (° C.): 600+2×(NB−NA) in a heating process of the primary recrystallization annealing is set to not less than 80° C./sec, and an average heating rate S2 from the temperature T2 to 750° C. is set to 0.1˜0.7 times of S1, whereby a grain-oriented electrical steel sheet having a low iron loss over a full length of a product coil is obtained.

1 . A method of producing a grain-oriented electrical steel sheet which comprises:
 hot rolling a steel slab having a chemical composition of C: 0.001˜0.10 mass %, Si:1.0˜5.0 mass %, Mn:0.01˜0.5 mass %, sol. Al: 0.003˜0.050 mass %, N: 0.0010˜0.020 mass %, one or two selected from S and Se: 0.005˜0.040 mass % in total, and the remainder being Fe and inevitable impurities,   subjecting the resulting sheet to a hot band annealing if necessary,   conducting a single cold rolling or two or more cold rollings with an intermediate annealing therebetween to form a cold rolled sheet having a final thickness,   conducting a primary recrystallization annealing,   applying an annealing separator, and   conducting a final annealing,   wherein in a heating process of the primary recrystallization annealing, a heating rate S1 from a temperature T1 to a temperature T2, which are determined by the following equations (1) and (2):
   T1 (° C.): 500+2×(NB−NA)   (1)
 
   T2 (° C.): 600+2×(NB−NA)   (2)
 
   
       is set to not less than 80° C./sec, and an average heating rate S2 from the temperature T2 to 750° C. is set to 0.1˜0.7 times of S1, wherein NA represents N amount (massppm) precipitated after the final cold rolling and NB represents N amount (massppm) precipitated after the primary recrystallization annealing in the equations (1) and (2). 
     
     
         2 . The method of producing a grain-oriented electrical steel sheet according to  claim 1 , wherein a total N content in the steel slab NB′(massppm) is used instead of the N amount precipitated after the primary recrystallization annealing NB (massppm). 
     
     
         3 . The method of producing a grain-oriented electrical steel sheet according to  claim 1 , wherein the steel slab contains one or more selected from Cu: 0.01˜0.2 mass %, Ni: 0.01˜0.5 mass %, Cr: 0.01˜0.5 mass %, Mo: 0.01˜0.5 mass %, Sb: 0.01˜0.1 mass %, Sn: 0.01˜0.5 mass %, Bi: 0.001˜0.1 mass %, P: 0.001˜0.05 mass %, Ti: 0.005˜0.02 mass % and Nb: 0.0005˜0.0100 mass % in addition to the above chemical composition. 
     
     
         4 . The method of producing a grain-oriented electrical steel sheet according to  claim 2 , wherein the steel slab contains one or more selected from Cu: 0.01˜0.2 mass %, Ni: 0.01˜0.5 mass %, Cr: 0.01˜0.5 mass %, Mo: 0.01˜0.5 mass %, Sb: 0.01˜0.1 mass %, Sn: 0.01˜0.5 mass %, Bi: 0.001˜0.1 mass %, P: 0.001˜0.05 mass %, Ti: 0.005˜0.02 mass % and Nb: 0.0005˜0.100 mass % in addition to the above chemical composition.