| 摘要 |
PROBLEM TO BE SOLVED: To provide a tailored steel tube having high strength and excellent hydroforming workability in which deterioration in hydroforming workability in its weld zone is suppressed in spite of its having a structure such that a plurality of steel tubes are welded. SOLUTION: The steel tube has a composition containing, by weight ratio, 0.01 to 0.2% C, 0.005 to 2.0% Si, 0.1 to 3.0% Mn, 0.001 to 0.06% P, 0.001 to 0.01% S, 0.001 to 0.1% Al and Fe as principal components and satisfying relationship (C+(Si/30)+(Mn/20)+P+(2S)+(TS(MPa)/5000))≤(0.33×Ln(TS(MPa))-1.78). By this method, allowance for reduction in a tube expanding rate in the weld zone can be controlled to≤20% of the tube expanding rate of the material tube before welding. COPYRIGHT: (C)2004,JPO
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