Seamless steel pipe for line pipe used in sour environments

Abstract

A seamless steel pipe has a yield strength of 400 MPa or less and excellent HIC resistance. The seamless steel pipe includes: a chemical composition consisting, in mass %, of, C: 0.01 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.3 to 2.0%, P: 0.02% or less, S: 0.01% or less, Cr: 0.02 to 0.2%, sol.Al: 0.001 to 0.100%, O: 0.0050% or less, N: 0.0100% or less, Ca: 0 to 0.0050%, Ti: 0 to 0.012%, and Nb: 0 to 0.012%, the balance being Fe and impurities; and a structure consisting, in area ratio, of 10 to 50% of ferrite and 0 to less than 5% of pearlite, the balance being tempered bainite and/or tempered martensite, and the number of inclusions each having a grain diameter of 50 mm or more is not more than 15 per 100 mm2, and the seamless steel pipe has a yield strength of 400 MPa or less.

Dependencies are inferred from the claim text.