| 摘要 |
Provided is a steel pipe for a linepipe having high compressive strength, a heavy wall thickness and excellent sour gas resistance by optimizing the metal microstructure of a steel plate without requiring particular forming conditions in forming the steel pipe and without requiring heat treatment after pipe making. Specifically, in a welded steel pipe for a linepipe having high compressive strength, and excellent sour gas resistance, the steel pipe has the composition which contains by mass% 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0015% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance, C(%) - 0.065Nb (%) is 0. 025 or more, a CP value is 0.95 or less, a Ceq value is 0.28 or more, and the steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of M-A constituent is 2% or less and an average grain size of bainite is 5 µm or less. |
