LOW-ALLOYED STEEL, SEAMLESS STEEL PIPES OF OIL-FIELD GAGE AND METHOD FOR PRODUCTON OF SEAMLESS STEEL PIPE

摘要

A low-alloy steel characterized by containing, in terms of mass%, 0.10-0.20% C, 0.05-1.0% Si, 0.05-1.5% Mn, 1.0-2.0% Cr, 0.05-2.0% Mo, up to 0.10% Al, and 0.002-0.05% Ti and having a value of Ceq calculated with the following equation (1) of 0.65 or higher, the remainder being iron and impurities. It is further characterized in that the impurities include up to 0.025% P, up to 0.010% S, up to 0.007% N, and less than 0.0003% B and that the number of MCprecipitate (M is a metal element) particles having a particle diameter of 1 m or larger is 0.1 or smaller per mm. The low-alloy steel retains suitability for quenching and toughness and improves resistance to sulfide stress corrosion cracking. Ceq = C + (Mn/6) + (Cr+Mo+V)/5 (1) In the equation (1), C, Mn, Cr, Mo, and V indicate the proportions in mass% of the respective elements.