| abstract |
A weakly alloyed steel, with an elastic limit of 758 to 965 MPa, for oil well pipes, consisting of (% 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 sol .: 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 0.20%, B: 0.0001 to 0.005%, N: 0.01% or less, O (oxygen): 0.01% or less, Ca: 0 to 0.01%, Mg: 0 to 0.01% and Zr: 0 to 0.1%, the rest being Fe and impurities, in which the relation between the average depth (H) corresponding to the peak of the face [211] of the crystals and the hydrogen diffusion coefficient (D) (10-6 cm2 / s) satisfies the following equation (1): 30H + D < = 19.5 |