| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel pipe for a pipe line having excellent strength, and further having sufficient deformability even after being subjected to aging by heating in coating treatment or the like, and to provide its production method. SOLUTION: The high strength steel pipe for a pipe line having excellent deformation properties after aging satisfying an X70 to X100 class in the API standards is obtained by subjecting a steel sheet containing, by mass, 0.02 to 0.09% C, 0.001 to 0.8% Si, 0.5 to 2.5% Mn,≤0.02% P,≤0.005% S, 0.005 to 0.03% Ti, 0.005 to 0.3% Nb, 0.001 to 0.1% Al and 0.001 to 0.008% N, and further two or more kinds selected from 0.1 to 1.0% Ni, 0.1 to 1.0% Cu and 0.05 to 0.6% Mo, wherein (Ni+Cu)-Mo>0.5 is satisfied, and the balance iron with inevitable impurities to cold forming into a cylindrical shape, and subjecting the edge faces to seam welding each other. In the steel pipe, after heating at 200 to 300°C, the difference between the flow stress of 2% and the flow stress of 0.5% in the pipe axis direction is≥30 MPa. COPYRIGHT: (C)2006,JPO&NCIPI |
