Patent ID: 8617462
Filing Date: 2013-12-31
Classification: C21D,C22C

Abstract:
1. A steel for an oil well pipe that has a yield strength of 758 MPa or more and less than 862 MPa, excellent in sulfide stress cracking resistance estimated as not fractured for 720 hours by the constant load test, loaded by 90% of the true yield strength, according to the NACE TM 0177 A method, which adopts a test solution of 5% sodium chloride and 0.5% of acetic acid at normal temperature, saturated with 1 atm of hydrogen sulfide gas, wherein the steel has a bainite single phase structure and a chemical composition consisting, by mass %, of C: 0.35 to 0.60%, Si: 0.05 to 0.5%, Mn: 0.05 to 0.76%, Al: 0.005 to 0.10%, Cr+Mo: 1.5 to 3.0%, Mo is 0.5% or more, V: 0.05 to 0.3%, Nb: 0 to 0.1%, Ti: 0 to 0.1%, Zr: 0 to 0.1%, N: 0 to 0.03%, Ca: 0 to 0.01%, and the balance Fe and impurities, and P as an impurity is 0.025% or less, S as an impurity is 0.01% or less, B as an impurity is 0.0010% or less and O (oxygen) as an impurity is 0.01% or less.