Patent ID: 7416617

Claim:
A high strength seamless steel pipe excellent in hydrogen-induced cracking resistance, characterized by consisting essentially of, 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: 0.02-0.3V: 0.02-0.20%, Ca: 0.0005-0.005%, N: 0.008% or less and O (Oxygen): 0.004% or less, and the balance Fe and impurities, and also characterized in that the microstructure of the steel is bainite and martensite, ferrite is precipitated at grain boundaries and yield stress is 483 MPa or more.