Cold Rolled Steel Sheet And Method For Producing Cold Rolled Steel Sheet

Abstract: The present invention provides a cold-rolled steel sheet which has high strength and excellent bore expanding properties. A cold-rolled steel sheet according to the present invention has a chemical composition that contains, in mass%, 0.10-0.30% of C, 2.50% or less of Si, 0.50-3.50% of Mn, 0.100% or less of P, 0.020% or less of S, 0.010-0.100% of Al, 0.0100% or less of N, 0-0.100% of Ti, 0-0.100% of Nb, 0-0.50% of V, 0-0.50% of Mo, 0-0.50% of W, 0-0.0050% of B, 0-0.0100% of Ca, 0-0.0100% of Mg and 0-0.0100% of REM, with the balance being made up of Fe and impurities, while having a metal structure that contains a total of 85% by volume or more of tempered martensite and bainite and 5% by volume or less of structures other than tempered martensite, bainite and ferrite, with 0.05-1.5% by area of regions that have an Mn concentration of 8.0% by mass or more in the metal structure.

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