| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet having superior press processability at the forming (mainly by bulging) of such as hood, door, fender, side panel, surface roughing resistance after pressing, excellent in surface characteristic and secondary processability. SOLUTION: The high strength steel sheet has a chemical composition consisting of, by mass, 0.0040-0.01% C, <=1.0% Si, 0.1-1.0% Mn, 0.01-0.07% P, <=0.02% S, 0.01-0.1% sol.Al, <=0.004% N, 0.01-0.14% Nb and the balance essentially iron with inevitable impurities and also has >=0.21 n-value at <=10% deformation by the uniaxial tensile test and satisfies the following inequality: YP<=-60×d+770 (wherein, YP represents yield strength [MPa]; and d represents average ferrite grain diameter [μm]).
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