LOW -ALLOY STEEL FOR OIL WELL PIPES WHICH HAS EXCELLENT SULFIDE STRESS CRACKING RESISTANCE, AND METHOD FOR MANUFACTURING LOW -ALLOY STEEL FOR OIL WELL PIPES

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.