Patent ID: 8197617

Claim:
A high-strength steel sheet having excellent elongation, stretch flangeability and weldability, comprising a steel containing the following elements in % by mass: C: 0.10 to 0.25%, Si: 1.0 to 3.0%, Mn: 1.5 to 3.0%, P: 0.15% or less, S: 0.02% or less, Al: 0.4% or less, and comprising the remnant made from iron and unavoidable impurities, wherein a ratio of the contents of Si and C (Si/C) is within the range from 7 to 14 in terms of a mass ratio, an Ac 3 point is from 822° C. to 900° C., and a microstructure in a longitudinal section comprises, by an occupancy ratio based on the entire structure, 1) bainitic ferrite: 50% or more, 2) lath-type residual austenite: 3% or more, and 3) block-type residual austenite: 1% or more to ½×occupancy ratio of lath-type residual austenite, and 4) average size of block-type residual austenite is 10 μm or less.