MARTENSITIC STAINLESS-STEEL SEAMLESS PIPE FOR OIL WELL PIPE AND PROCESS FOR PRODUCING THE SAME

摘要

A seamless steel pipe for oil country tubular goods which simultaneously has a high strength of a 110 ksi grade of yield strength and a superior low temperature toughness and a method for manufacturing the same are provided. A quenching treatment is performed on a stainless steel seamless pipe having a composition which contains on a mass percent basis, less than 0.010% of C, 1.0% or less of Si, 0.1% to 2.0% of Mn, 0.020% or less of P, 0.010% or less of S, 0.10% or less of Al, 10% to 14% of Cr, 0.1% to 4.0% of Ni, 0.05% or less of N, and the balance being Fe and inevitable impurities in which after heating is performed to a heating temperature for quenching equivalent to or more than the Ac 3 transformation point, cooling is performed to a temperature range of 100°C or less at a cooling rate equivalent to or more than that of air cooling; and following the quenching treatment, a tempering treatment is performed in which heating is performed to a tempering temperature in the range of more than 450°C to 550°C, and cooling is then performed. As a result, a martensitic stainless steel seamless pipe for oil country tubular goods is obtained which simultaneously has a high strength of a 110 ksi grade of yield strength and a superior low temperature toughness having a vTrs of -60°C or less. In addition to the above composition, at least one selected from the group consisting of Cu, Mo, V, Nb, and Ti may also be contained.