Patent ID: 7959745

Claim:
A high-strength steel pipe having sour resistance and a strength of API X65 grade or higher consisting essentially of, by mass %, 0.032 to 0.08% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, 0.05 to 0.50% Mo, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, optionally at least one element selected from the group consisting of Ca, Cu, Ni, W and Cr, and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase, said carbides having a fine size of 10 nm or smaller, and wherein Ceq is not higher than 0.34 where Ceq is defined as follows: Ceq=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5, wherein a ratio R of the content in mass % of C to the total content in mass % of Mo, Ti, Nb, V and W, expressed as R=(C/12)/[(Mo/96)+(Ti/48)+(Nb/93)+(V/51)+(W/184)], is 0.7 to 2.0.