| 摘要 |
The following steel sheets and methods for manufacturing the same are provided: a high-strength cold-rolled steel sheet and high-strength galvanized steel sheet having a TS of 1180 MPa or more and excellent formability including stretch flangeability and bendability. A high-strength cold-rolled steel sheet having excellent formability contains 0.05% to 0.3% C, 0.5% to 2.5% Si, 1.5% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 1.5% or less Cr (including 0%) on a mass basis, the remainder being Fe and unavoidable impurities; satisfies Inequalities (1) and (2) below; and contains a ferritic phase and a martensitic phase, the area fraction of the martensitic phase in a microstructure being 30% or more, the quotient (the area occupied by the martensitic phase) / (the area occupied by the ferritic phase) being greater than 0.45 to less than 1.5, the average grain size of the martensitic phase being 2 µm or more: C 1 / 2 × Mn + 0.6 × Cr ‰¥ 1 - 0.12 × Si
and 550 - 350 × C * - 40 × Mn - 20 × Cr + 30 × Al ‰¥ 340
where C* = [C] / (1.3 × [C] + 0.4 × [Mn] + 0.45 × [Cr] - 0.75). |
