Patent ID: 8685182

Claim:
A high-strength steel pipe comprising, by mass %: C: 0.02% to 0.09%, Mn: 0.4% to 2.5%, Cr: 0.1% to 1.0%, Ti: 0.005% to 0.03%, Nb: 0.005% to 0.3%, and a balance consisting of Fe and inevitable impurities, wherein Si is limited to 0.6% or less, Al is limited to 0.1% or less, P is limited to 0.02% or less, S is limited to 0.005% or less, N is limited to 0.008% or less, a bainite transformation index BT obtained by the following equation (3) is 650Â° C. or lower, and a microstructure thereof is a single bainite microstructure including a first bainite and a second bainite, the first bainite being a gathered microstructure of a bainitic ferrite including no carbide, the second bainite being a mixed microstructure of a bainitic ferrite and cementite, in which the bainitic ferrite of the second bainite includes no carbide and in which the cementite of the second bainite exists between the bainitic ferrites of the second bainite, and a ferrite being limited to 5% or less, wherein BT=830âˆ’270[C]âˆ’90[Mn]âˆ’37[Mo]âˆ’70[Ni]âˆ’83[Cr]â€ƒâ€ƒ(3) where the [C], [Mn], [Mo], [Ni], and [Cr] are the amounts of C, Mn, Mo, Ni, and Cr, respectively.