| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel pipe of API X100 grade, superior in buckling resistance and toughness at low temperatures after coating treatment, a method for producing the high strength steel pipe, and a method for producing a steel sheet serving as a base material.SOLUTION: In a steel pipe, a base material includes, by mass%, more than 0.03% and 0.08% or less of C, 0.01-0.5% of Si, 1.5-3.0% of Mn, 0.01-0.08% of P, S and Al, 0.005-0.025% of Nb, 0.005-0.025% of Ti, 0.001-0.010% of N, 0.005% or less of O, and one or two or more of Cu, Ni, Cr, Mo, V and B, with 0.19≤P≤0.25 and the remainder being Fe and inevitable impurities, has a TS of 760-930 MPa, a uniform elongation of 5% or more and a YR of 85% or less; the micro structure of the base material mainly comprises bainite including island martensite, and includes 1-10% of a lower part bainite and 3% or less of residual austenite; seam welding by submerged arc welding is performed at a heat-input of 80 kJ/cm or less; and seam welding metal has a specified component composition. |
