HIGH-STRENGTH COLD-ROLLED STEEL SHEET EXCELLENT IN WORKABILITY AND METHOD FOR PRODUCTION THEREOF

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PROBLEM TO BE SOLVED : To provide a high-strength cold-rolled steel sheet with a tensile strength TS of 1, 180 MPa or more, which is improved in workability such as elongation, stretch flanging property, and bendability by adjusting a metal structure without containing expensive rare metals from a viewpoint of weldability and formability. SOLUTION : The high-strength cold-rolled steel sheet has a component composition including, by mass%, 0.16-0.26% C, 1.2-2.2% Si, 2.6-3.6% Mn, 0.020% or less P, 0.0040% or less S, 0.005-0.08% Al, 0.008% or less N, 0.001-0.040% Ti, and 0.0001-0.0020% B, with the balance comprising Fe and unavoidable impurities and has a structure including, by volume fraction, 40-70% ferrite phase, 15-35% bainite phase, 5-25% tempered martensite phase, and 2-20% retained austenite phase, wherein the volume fraction of a martensite phase with a long axis length of ≥10 μm accounts for 30% or less of the total volume fraction of the tempered martensite phase. COPYRIGHT : (C)2013, JPO&INPIT