High-strength steel sheet and manufacturing method thereof excellent in deep drawability and stretch flange formability

摘要

PROBLEM TO BE SOLVED: To provide a high strength steel sheet having excellent stretch flange formability and deep drawability, and to provide its production method.;SOLUTION: The high strength steel sheet has a componential composition comprising, by mass, 0.010 to 0.050% C, ≤1.0% Si, 1.0 to 3.0% Mn, 0.005 to 0.1% P, ≤0.01% S, 0.005 to 0.5% Al, ≤0.01% N and 0.01 to 0.3% Nb, also satisfying prescribed expressions, and the balance substantially Fe with inevitable impurities, and has a steel structure composed of a ferritic phase as the main phase and a second phase in which the ratio H(S) of the hardness H(S) of the second phase to the hardness H(F) of the ferritic phase, H(S)/H(F) lies in the range of 1.5 to 3.0, the area ratio of the ferritic phase to the whole of the structure is ≥50%, and the second phase includes a martensitic phase of 1 to 15% by area ratio to the whole of the structure.;COPYRIGHT: (C)2005,JPO&NCIPI