| 摘要 |
PURPOSE:To produce steel for oil wells having excellent sulfide stress corrosion cracking resistance and high strength by hot rolling steel contg. C, Si, Mn, Cr, Co, Al, and limited values or below of unavoidable impurities then subjecting the same to hardening and tempering treatments under specific conditions. CONSTITUTION:The steel contg., by weight %, 0.10-0.45% C, 0.1-2.0% Si, 0.3- 1.5% Mn, 0.1-2.0% Cr, 0.3-5.0% Co, 0.001-0.15% Al, and consisting of the balance Fe and unavoidable impurities is used. In this case, the contents of P, S, Mo and W as unavoidable impurities are limited respectively at <=0.025% P, <=0.010% S, <=0.05% Mo, and <=0.05% W. Such steel is hot rolled at >=2 rolling reduction ratio and is subjected to hardening under the conditions of 5-80 deg.C/sec heating rate, heating to >=AC3 transformation point temp., and <=10sec holding time, whereby the steel is transformed to fine grain austenite of >=No. 10 old austenite grain size number. The steel is subjected to a tempering treatment at temp. lower than the AC1 transformation point to transform the principal material to tempered martensite structure, whereby >=70kg/mm.<2> yield strength is obtained. |
