Cold Rolled Steel Sheet And Method For Producing Same

Abstract: This cold-rolled steel sheet has a specific chemical composition, and a surface layer part thereof ranging from the surface to a depth of 10 µm to 20 µm in the sheet thickness direction has a metal structure which contains, in volume percentage, 10% to 95% of ferrite, with the balance being made up of one or more selected from among martensite, bainite, pearlite, cementite and residual austenite. At a position of 1/4 the thickness ranging from 1/8 to 3/8 of the sheet thickness from the surface in the sheet thickness direction, the metal structure contains, in volume percentage, 0% to 60% of ferrite and 0% to 3% of residual austenite, with the balance being made up of one or more selected from among martensite and bainite. The volume percentage of tempered martensite in the martensite is 50% or more. The ratio of the dislocation density of the surface layer part to the dislocation density at the position of 1/4 the thickness is not less than 0.20 but less than 0.90. The tensile strength of this cold-rolled steel sheet is 1,180 MPa or more.

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