| abstract |
[Subject] To provide a low alloy steel for oil well pipes excellent in sulfide stress cracking resistance, which are suitable for a casing or tubing for oil wells or gas wells. [Means for Solution] A low alloy steel for oil well pipes excellent in sulfide stress cracking resistance containing, by mass %, C: 0.2 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.05 to 1.0%, P: 0.025% or less, S: 0.01% or less, Al: 0.005 to 0.10%, Cr: 0.1 to 1.0%, Mo: 0.5 to 1.0%, Ti: 0.002 to 0.05%, V: 0.05 to 0.3%, B: 0.0001 to 0.005%, N: 0.01% or less, O (oxygen): 0.01% or less, Nb: 0 to 0.1%, Ca: 0 to 0.01%, Mg: 0 to 0.01% and Zr: 0 to 0.1%, in which a half-value width H and a hydrogen diffusion coefficient D (10 -6 cm 2 /s) satisfy the following equation (1): 30 ¢ H + D 19.5 |