MX2007011570A - Steel for oil well pipe having excellent sulfide stress cracking resistance and method for manufacturing seamless steel pipe for oil well. - Google Patents

Abstract

Disclosed is a steel for oil well pipe having high strength and excellent sulfide stress cracking resistance. Also disclosed is a method for manufacturing a seamless steel pipe for oil well having such characteristics. Specifically disclosed is a steel for oil well pipe containing, in mass%, C: 0.30-0.60%, Si: 0.05-0.5%, Mn: 0.05-1.0%, Al: 0.005-0.10%, Cr+Mo: 1.5-3.0% (wherein Mo is not less than 0.5%), V: 0.05-0.3%, Nb: 0-0.1%, Ti: 0-0.1%, Zr: 0-0.1%, N:0-0.03%, Ca: 0-0.01% and the balance of Fe and impurities. The impurities include not more than 0.025% of P, not more than 0.01% of S, not more than 0.0010% of B and not more than 0.01% of O (oxygen). Also specifically disclosed is a method for manufacturing a seamless steel pipe for oil well wherein a steel ingot having the above-described chemical composition is heated to a temperature not less than 1150 degree C and formed into a seamless steel pipe by hot working, and the seamless steel pipe is immediately water-cooled after the working to a temperature within the range of 400-600 degree C and then directly subjected to a bainite isothermal transformation treatment within the temperature range of 400-600 degree C. A complementary heat treatment may be performed before the water cooling at 900-950 degree C.