Patent ID: 6444051
Filing Date: 2002-09-03
Classification: C21D,C22C

Abstract:
In a method of making a grain oriented electromagnetic steel sheet having a high magnetic flux density and a very low iron loss, from a steel slab comprising about 0.030 to 0.095 wt % carbon, about 1.5 to 7.0 wt % silicon, about 0.03 to 2.50 wt % manganese, about 0.003 to 0.040 wt % sulfur and/or selenium, and about 0.0010 to 0.0070 wt % boron,said steel slab containing nitrogen in an amount of about 30 to 120 wtppm, a limited aluminum impurity of about 0.015 wt % or less, and a limited vanadium impurity of about 0.010 wt % or less, and said slab containing an element effective to accelerate fine precipitation of BN, comprising the steps of: reheating said steel slab at a temperature of over about 1,350Â° C., hot-rolling the reheated steel slab to make a sheet, said hot rolling being performed for a period of about 50 to 220 seconds and at a hot rolling finishing temperature of at least about 850Â° C.; rapidly cooling said steel sheet after completion of said hot rolling at a cooling rate of at least about 30Â° C./sec, coil said sheet at a temperature of about 700Â° C. or less, subjecting said hot-rolling steel sheet to one or more stages of cold rolling under conditions including a final cold rolling reduction of from about 80 to 95% into a final thickness, conducting primary recrystallization annealing of said sheet, coating said sheet with an annealing separator, applying final annealing including applying secondary recrystallization annealing to said sheet, and accelerating said precipitation of BN to improve the texture of primary recrystallized gains of the steel immediately before subjecting the same to said secondary recrystallization annealing with said element present in said steel sheet.