| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tension steel which is suitable for automobile structural member and has high strength, excellent formability and excellent torsional fatigue resistance after cross-sectional forming in combination, and a manufacturing method therefor. SOLUTION: A steel stock having the composition containing, by mass, 0.03-0.24% C, 0.021-0.044% V and further, Nb and/or Ti, is subjected to hot-rolling at higher temperature than a balanced solid-solution temperature T<SB>v</SB>calculated from log[V][C]=-9500/T<SB>v</SB>+6.72 (wherein, V, C are contents (mass%) of each element) to form the high tension hot-rolled steel sheet for automobile undercarriage component excellent in the formability and the torsional fatigue resistance, and further, this steel sheet is used as the stock for steel pipe, and a welded steel pipe is made through a pipe-making and welding processes. COPYRIGHT: (C)2011,JPO&INPIT
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