| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet having a TS of 500 MPa or more and superior ductility and formability for an extension flange, and to provide a manufacturing method therefor. SOLUTION: This steel sheet has a component composition including, by mass%, 0.04-0.12% C, 0.8-2.5% Si, 0.5-2.0% Mn, 0.003-0.100% P, 0.0200% or less S, 0.01-0.10% Al while Si and Mn satisfy the expression of [%Si]+4[%Mn]≤8, and the balance iron with unavoidable impurities; and has a structure in which an area rate of a ferrite phase is 70-94%, a volume fraction V<SB>γR</SB>of a residual austenite phase is 2-10%, an area rate S<SB>B</SB>of a bainite phase is 4-20%, and a ratio S<SB>B</SB>/V<SB>γR</SB>of the area rate S<SB>B</SB>of the bainite phase to the volume fraction V<SB>γR</SB>of the residual austenite phase is 2 or more. COPYRIGHT: (C)2011,JPO&INPIT
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