Patent ID: 7371294

Claim:
A high-strength cold-rolled steel sheet, excellent in elongation and stretch flange formability, which comprises a steel including C: 0.05 to 0.13 mass %, Si: 0.5 to 2.5 mass %, Mn: 0.5 to 3.5 mass %, and at least one of Mo: 0.05 to 0.6 mass % and Cr: 0.05 to 1.0 mass %, wherein the steel is of composite structure of a ferrite + a second phase, the second phase having an area ratio of 30 to 70% and being combined approximately in a shape of a network, a circle-equivalent average ferrite grain size being not more than 10 μm, and a circle-equivalent diameter of ferrite grain aggregate that exists continuously in an area surrounded by the second phase being not more than 3 times of the average ferrite grain size.