| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet excellent in formability as well as in fatigue characteristic of spot welded joint, and capable of remarkably improving the fatigue resistance of automobile parts, etc. SOLUTION: This steel sheet has a composition consisting of, by mass, <=0.005% C, <=0.1% Si, <=0.5% Mn, <=0.05% P, <=0.02% S, <=0.004% Al, 0.0001-0.01% Mg, 0.001-0.01% 0, 0.001-0.01% N, either or both of Ti and Nb so that Ti/48>N/14 and [(Ti/48+Nb/93)> (C/12+N/14+S/32)] are satisfied, and the balance Fe with inevitable impurities. Moreover, the steel sheet contains oxides and/or compound oxides of Mg and Ti, having 0.005-0.1μm average grain size, by >=40 pieces/mm<2> by surface density.
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