| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet which is improved in elongation and stretch-flangeability and exhibits more excellent formability. SOLUTION: The cold-rolled steel sheet has a composition consisting of, by mass, 0.03 to 0.30% C, 0.1 to 3.0% Si, 0.1 to 5.0% Mn,≤0.1% P,≤0.005% S,≤0.01% N, 0.01 to 1.00% Al and the balance iron with inevitable impurities and also has a structure which consists of≥40% (up to 100% inclusive) in terms of area fraction of tempered martensite having 300 to 380 Hv hardness and the balance ferrite. Cementite particles in the tempered martensite are dispersed in such a way that≥10 cementite particles of 0.02 to <0.1μm circle-equivalent diameter are present per 1μm<SP>2</SP>of the tempered martensite and≤3 cementite particles of≥0.1μm circle-equivalent diameter are present per 1μm<SP>2</SP>of the tempered martensite. COPYRIGHT: (C)2009,JPO&INPIT
|
