HIGH STRENGTH STEEL PIPE HAVING STRENGTH HIGHER THAN THAT OF API X65 GRADE

摘要

A high strength steel pipe having a strength higher than that of API X65 grade, which has a chemical composition, in mass %: C: 0.02 to 0.08 %, Si: 0.01 to 0.5 %, Mn: 0.5 to 1.8 %, P: 0.01 % or less, S: 0.002 % or less, Al: 0.01 to 0.07 %, Ti: 0.005 to 0.04 %, Mo: 0.05 to 0.50 %, at least on element selected from between Nb: 0.005 to 0.05 and V: 0.005 to 0.10 %, and balance: Fe, and a structure wherein a ferrite phase accounts for 90 vol % or more, and a composite carbide containing at least one element selected from among Ti, Mo, and Nb, V is deposited in the ferrite phase. The high strength steel pipe is excellent in the resistance to HIC and the toughness after welding, and also can be produced with stability at a low cost.