LOW YIELD RATIO HIGH-STRENGTH COLD-ROLLED STEEL SHEET WITH EXCELLENT ELONGATION AND STRETCH FLANGE FORMABILITY, AND MANUFACTURING METHOD THEREOF

摘要

A high-strength cold-rolled steel sheet having a low yield ratio and excellent elongation and stretch flange formability, and a manufacturing method thereof are provided. This high-strength cold-rolled steel sheet having a low yield ratio and excellent elongation and stretch flange formability is characterized in that the chemical components of the steel sheet include, in mass%, C: 0.05-0.13%, Si: 0.6-1.2%, Mn: 1.6-2.4%, P: 0.10% or less, S: 0.0050% or less, Al: 0.01-0.10%, and N: less than 0.0050%, and the remainder consists of Fe and unavoidable impurities, and in that the steel sheet has a composite microstructure containing, by volume percentage, 80% or more ferrite, 3-15% martensite, and 0.5-10% pearlite, the yield ratio is 70% or less, and the tensile strength is 590 MPa or greater.