LOW ALLOY STEEL FOR THE PIPE FOR OIL WELL USE AND SEAMLESS STEEL PIPE

摘要

A low alloy steel is provided for oil country tubular goods with a yield strength between 654 MPa and 757 MPa, and possessing excellent resistance to HIC and SSC in high-pressure hydrogen sulfides environment, and comprising, by mass %: 0.10 to 0.60% C; 0.05 to 0.5% Si; 0.05 to 3.0% Mn; 0.025% or less P; 0.010% or less S; 0.005 to 0.10% Al; 0.01% or less O (oxygen); 3.0% or less Cr; and 3.0% or less Mo, wherein the amount of Cr and Mo content is 1.2% or more, with the balance being Fe and impurities, and the number of nonmetallic inclusions whose major axis is 10 µm or more is 10 per square millimeter in the inspected cross section. The present invention provides a low alloy steel for oil country tubular goods possessing excellent resistance to sulfide stress cracking, and a seamless steel pipe.