Workability and high strength welded steel pipe and a method of manufacturing the same excellent fatigue properties, as well as welded steel pipe material for steel strip

摘要

PROBLEM TO BE SOLVED: To provide a high tensile strength welded steel tube which has a strength satisfying a tensile strength of ≥590 MPa and combines excellent workability and excellent fatigue properties, and to provide a production method thereof.;SOLUTION: The high tensile strength welded steel tube has a composition containing, by weight, 0.035 to 0.185% C, 0.75 to 1.95% Mn, 0.01 to 0.49% Mo, 0.010 to 0.145% Ti, 0.011 to 0.10% Al, ≤0.03% P, ≤0.004% S, ≤0.006% N and ≤0.004% O, and the balance substantially Fe. The fraction of a ferritic structure in which (Ti, Mo) multiple carbides with a particle diameter of ≤10 nm satisfying, by an atomic ratio, Mo/(Ti+Mo)=0.33 to 0.77 are precipitated in the structural face is 60 to 100%.;COPYRIGHT: (C)2004,JPO