Patent ID: 8062438
Filing Date: 2011-11-22
Classification: B21B,C21D,C22C

Abstract:
1. A hot-rolled thin steel sheet having a thickness of less than 6 mm and having high strength and excellent formability and having excellent strength and toughness after heat treatment, wherein the hot-rolled thin steel sheet has a composition containing, as mass %, C: 0.10 to 0.20%, Si: 0.01 to 1.0%, Mn: 0.5 to 2.0%, P: 0.03% or less, S: 0.01% or less, Al: 0.01 to 0.10%, N: 0.005% or less, Ti: 0.01 to 0.15%, B: 0.0005 to 0.0050%, the balance of Fe, and unavoidable impurities; and a structure of a bainitic ferrite single phase having an area fraction of 95% or more, and the hot-rolled thin steel sheet satisfies a tensile strength of 440 to 640 MPa.