Patent ID: 7485195
Filing Date: 2009-02-03
Classification: B21B,C21D,C22C

Abstract:
1. A method of producing a high-strength hot-rolled steel sheet excellent in shape fixability comprising the following steps, hot-rolling a cast slab as cast or cooled once, said cast slab containing, in terms of weight %, C: 0.02 to 0.3%, at least one or more element selected from the group consisting of, total 0.1 to 3.5%, in terms of weight %, at least one or both of, total 0.02 to 3% in terms of weight %, Si: 3% or less and Al: 3% or less and remainder Fe and unavoidable impurities, then reheated to a range of 1000 to 1300° C., with a total reduction ratios of 25% or more at Ar cooling hot-rolled steel sheet, then coiling at below critical temperature T where, B is found from the composition of the steel expressed by weight %, Δε is found from the equivalent strain εi (i is 1 to n) given at each stand of the n stages of finishing rolling for the rolling, time ti (sec) (i=1 to n−1) between stands, time tn (sec) from the final stand to the start of cooling, rolling temperature Ti(K) (i=1 to n) at each stand, and a constant R=1.987,