| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel member for automobile structure, constituting an automobile body and excellent in silence characteristic. SOLUTION: The member is formed by applying tube hydroforming to a steel tube having a composition consisting of, by mass, 0.05 to 0.30% C, 0.5 to 3.0% Si, 0.5 to 2.5% Mn, and the balance Fe with inevitable impurities and has a structure containing, by volume, >=0.25% retained austenitic phase and >=2.25% martensitic phase stress-induced from the retained austenitic phase. Further, <=3 mass %, in total, of one or >=2 elements among Cr, Ni, Mo, Cu, Ti, and Nb are incorporated into the above composition.
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