Patent ID: 7749343
Filing Date: 2010-07-06
Classification: C21D,C22C,C23C,C25D

Abstract:
1. A method for producing a steel sheet excellent in formability, comprising the steps of: hot rolling a steel consisting essentially of, by mass, 0.08 to 0.25% C, 0.001 to 1.5% Si, 0.01 to 2.0% Mn, 0.001 to 0.007% P, at most 0.05% S, 0.001 to 0.007% N, 0.008 to 0.2% Al, and a balance of Fe and unavoidable impurities, at a finishing temperature of the Ar coiling the hot rolled steel sheet at 500° C. or lower; cold rolling the hot rolled steel sheet at a reduction ratio of more than 25% to less than 60%, wherein the hot rolled steel sheet has a structure composed of more than 97% bainite single phase; heating the cold rolled steel sheet at an average heating rate of 4 to 200° C./h.; annealing the heated steel sheet at a maximum arrival temperature of 600° C. to 800° C.; and cooling the annealed steel sheet at a cooling rate of more than 5° C./h. to not exceeding 17° C./h.