Cold Rolled Steel Sheet And Manufacturing Method Thereof

Abstract: This cold-rolled steel sheet has a prescribed chemical composition, and when a range from 1/8 to 3/8 of the sheet thickness in a sheet thickness direction from a surface is defined as a t/4 section, and a range of 20 µm from the surface in the sheet thickness direction is defined as a surface layer section, a microstructure in the t/4 section comprises, in terms of volume fractions, 0-10.0% of residual austenite and 90.0-100% of martensite and/or tempered martensite, the ratio of the dislocation density of the surface layer section to the dislocation density of the t/4 section is 0.80 or greater, the ratio of the hardness of the surface layer section to the hardness of the t/4 section is 0.90 or greater, and the tensile strength is 1310 MPa or greater.

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