HIGH-STRENGTH COLD-ROLLED STEEL SHEET HAVING EXCELLENT WORKABILITY, MOLTEN GALVANIZED HIGH-STRENGTH STEEL SHEET, AND METHOD FOR PRODUCING THE SAME

摘要

Provided is a high-strength cold-rolled steel sheet having a TS of 1,180 MPa or greater and excellent workability, such as stretch flange workability and bendability.  Also provided are a molten galvanized high-strength steel sheet, and a method for producing the same. The high-strength cold-rolled steel sheet having excellent workability has a composition that comprises, by mass%, C: 0.05 to 0.3, Si: 0.5 to 2.5, Mn: 1.5 to 3.5, P: 0.001 to 0.05, S: 0.0001 to 0.01, Al: 0.001 to 0.1, N: 0.0005 to 0.01, and Cr: 1.5 or less (including 0) and satisfies formulas (1) and (2), with the balance being Fe and inevitable impurities. The steel sheet has a microtexture wherein there is a ferrite phase and a martensite phase, the percentage of the texture total surface area occupied by martensite phase is 30% or greater, (the surface area occupied by martensite phase)/(surface area occupied by ferrite phase) exceeds 0.45 but is less than 1.5, and the average particle diameter of the martensite phase is 2 µm or larger. [C]1/2×([Mn]+0.6×[Cr])?1-0.12×[Si]···(1), 550-350×C*-40×[Mn]-20×[Cr]+30×[Al]?340···(2) where C*=[C]/(1.3×[C]+0.4×[Mn]+0.45×[Cr]-0.75).