Patent ID: 7591977

Claim:
A high strength and low yield ratio cold rolled steel sheet having a high elongation property and a high flange drawing property, the steel sheet comprising: 0.10 to 0.25% by mass of C; 1.0 to 2.0% by mass of Si; and 1.5 to 3.0% by mass of Mn, wherein the steel sheet has a structure comprising at least 5% by volume of residual austenite; at least 60% by volume of banitic ferrite; and 20% by volume or less (including 0%) of polygonal ferrite, and wherein the steel sheet has a tensile strength of 980 MPa or higher; and a total elongation measured using a JIS No. 5 test piece (El in %), a flange drawing property (λ in %), a tensile strength (TS in MPa) and a yield strength (YP in MPa) satisfy the inequality [(El×λ×TS)/YP]≧645.