US Patent 7416617 High strength seamless steel pipe excellent in hydrogen-induced cracking resistance

A high strength seamless steel pipe having mgh yield stress and excellent hydrogen-induced cracking resistance, comprises by mass %, C: 0.03-0.11%, Si: 0.05-0.5%, Mn: 0.8-1.6%, p: 0.025% or less, S: 0.003% or less, Ti: 0.002-0.017%, Al: 0.001-0.10%, Cr: 0.05-0.5%, Mo: 0.02-0.3%, V: 0.02-0.20%, Ca 0.0005-0.005%, N: 0.008% or less and O (Oxygen): 0.004% or less, the balance Fe and impurities. The steel microstructure is bainite and/or martensite and ferrite is precipitated at grain boundaries. The seamless steel pipe can contain at least one of Cu: 0.05-0.5% and Ni: 0.05-0.5%. To produce the pipe, it is desirable to limit a starting temperature of quenching after rolling, a cooling rate and a tempering temperature.