| 摘要 |
Provided is a high strength steel pipe that has excellent ductility and low temperature toughness and that is obtained by welding a base material steel sheet formed in a tubular shape. The base material steel sheet contains, in terms of mass %, 0.010 to 0.080% of C, 0.01 to 0.50% of Si, 1.2 to 2.8% of Mn, 0.0001 to 0.0050% of S, 0.003 to 0.030% of Ti, 0.0003 to 0.005% of B, 0.0010 to 0.008% of N and 0.0001 to 0.0080% of O, contains at least one of Cr, Cu and Ni, has a P content restricted to 0.050% or lower, has an Al content restricted to 0.020% or lower, has a Mo content restricted to 0.03% or lower, has a carbon equivalent (Ceq) of 0.30 to 0.53, and has a weld cracking parameter Pcm of 0.10 to 0.20. The remainder of the base material steel sheet comprises iron and unavoidable impurities, and the areal ratio of polygonal ferrite in the metal structure of the base material steel sheet is 27 to 90%, with the remainder being a hard phase comprising bainite and/or martensite. |
