| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot-rolled steel plate having excellent stretch-flange formability and fatigue property. SOLUTION: The steel plate has a composition containing, by mass, 0.02 to 0.10% C, 0.5 to 1.2% Si, 0.5 to 2.5% Mn,≤0.1% P,≤0.01% S,≤0.01% N,≤0.002% Al,≤0.002% Ti, 0.1 to 0.6% Nb and the balance Fe with inevitable impurities and containing, if necessary, 0.8 to 2.0% Cu and 0.4 to 1.0% Ni. Further, the steel plate has a structure in which the phase largest in the area ratio is composed of one or more among polygonal ferrite, bainitic ferrite and bainite. COPYRIGHT: (C)2006,JPO&NCIPI
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