Patent ID: 7749338
Filing Date: 2010-07-06
Classification: C21D,C22C

Abstract:
1. High burring, high strength, hot-rolled steel sheet excellent in softening resistance of the weld heat affected zone characterized by consisting essentially of, by wt %, C: 0.01 to 0.1%, Si: 0.01 to 2%, Mn: 0.05 to 3%, P≦0.1%, S≦0.03%, Al: 0.005 to 1%, N: 0.0005 to 0.005%, Ti: 0.05 to 0.5%, and Nb: 0.01 to 0.5% and further containing C, S, N, Ti, Nb, Cr, and Mo in ranges satisfying 0%<C−(12/48Ti+12/93Nb−12/14N−12/32S)≦0.05%, and Mo+Cr≧0.2%, Cr≦0.5%, and Mo≦0.5%, the balance comprising Fe and unavoidable impurities, wherein the microstructure is composed of only bainitic ferrite and bainite, wherein an effective amount of solid solution C is present in said hot-rolled steel sheet to form carbon clusters or precipitates with Mo and Cr to achieve excellent softening resistance at the weld heat affected zone when welded.