LOW ALLOY STEEL FOR OIL COUNTRY TUBULAR GOODS HAVING EXCELLENT SULFIDE STRESS CRACKING RESISTANCE AND MANUFACTURING METHOD THEREFOR

摘要

Provided is a low-alloy steel for oil well pipes, which has an yield stress of 862 MPa (125 ksi) or more and excellent sulfide stress cracking resistance (SSC resistance). The low-alloy steel for oil well pipes according to the present invention has a chemical composition comprising, in mass%, 0.56 to 1.00% of C, 0.05 to 0.50% of Si, 0.05 to 1.00% of Mn, 0.025% or less of P, 0.010% or less of S, 0.005 to 0.100% of Al, 0.40 to 1.00% of Mo, 0.07 to 0.30% of V, 0.010% or less of O, 0.0300% or less of N and a remainder made up by Fe and impurities, has an yield stress of 862 MPa or more, and a half width of a crystal face [211] of 0.50° or less as determined by X-ray diffraction.