| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel pipe which satisfies X80 to X100 of API (American Petroleum Institute) standards, and has excellent weld zone toughness and deformability. SOLUTION: As a base material in the steel pipe, there is provided the base material part which has a composition fundamentally consisting of a low C-Nb-Ti based componential system, in which the contents of Mg, N and O are strictly limited, and which comprises fine carbides including oxides consisting of Mg and Al and a composite consisting of oxides and sulfides. Further, in the steel pipe consisting of a low C-Mn-Ti-B based weld metal zone, the X80 to X100-class high strength steel pipe which has satisfactory HAZ (Heat Affected Zone) toughness and high uniform elongation in the base material part, in which the uniform elongation in a tensile test in the pipe-axis direction of the weld metal zone is≥3% and which has excellent deformability is provided. COPYRIGHT: (C)2004,JPO
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