Patent ID: 7396423
Filing Date: 2008-07-08
Classification: C21D,C22C

Abstract:
1. A method for manufacturing a welding structural steel product, comprising the steps of: preparing a steel slab containing, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, at most 0.03% P, at most 0.03% S, at most 0.005% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, and 6.5≦(Ti+2Al+4B)/N≦14; heating the steel slab at a temperature ranging from 1,100° C. to 1,250° C. for 60 to 180 minutes; hot rolling the heated steel slab in an austenite recrystallization range at a rolling reduction rate of 40% or more; and cooling the hot-rolled steel slab at a rate of 1° C./min or more to a temperature corresponding to ±10° C. from a ferrite transformation finish temperature.