| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-tensile welded steel pipe for automobile member which has high strength, high toughness and excellent strength/ductility balance, wherein there is small difference of hardness between a base material part and a welded part and homogeneous material in the circumferential direction without performing heat treatment after steel pipe making. SOLUTION: A high tensile welded steel pipe contains, by mass, 0.02-0.20% C, 0.001-1.0% Si, 0.01-1.5% Mn,≤0.1% P,≤0.01% S, 0.01-0.1% Al, 0.01-0.5% Ti and further≤0.5% Mo, and/or≤0.5% V and uses a ferrite phase having≤10μm average particle diameter as a main phase and has a structure which has Ti having≤10 nm average particle diameter and in which composite carbide containing Mo and/or V is dispersed. As a result, the homogeneous steel pipe having≥780 MPa tensile strength Ts,≤-40°C fracture transition temperature Trs<SB>50</SB>,≥11,000 MPa TS×E1, and small hardness difference is obtained without performing heat treatment after steel pipe making. COPYRIGHT: (C)2011,JPO&INPIT |
