PURPOSE: To develop a stainless steel for oil well excellent in corrosion resistance in a severe corrosive environment by quenching and tempering a Cr-Ni-Mo base stainless steel whose essential structure is martensite under a specified temp. condition.
CONSTITUTION: The stainless steel which contains, by wt.%, <1.0% Si, <1.0% Mn, 10.0-l4.0% Cr, 0.5-7.0% Mo, 4.0-8.0% Ni, 0.001-0.1% Al and Ti which satisfies the formula I, has a composition which satisfies the formulas II, III, contains <0.05% C, <0.04% P, <0.005% S, <0.05% N and <0.2% V as impurities, or further contains one or two kinds of 0.001-0.05% Mg and 0.0001-0.05% Ce and also Zr which satisfies the formula IV is tempered at a temp. between the point Ac1 and 700°C after quenching it at 850-1000°C. The stainless steel for oil well which contains, by volume ratio, the retained austenite of 2-20% in the martainsite and is suitable to use in a corrosive atmosphere in which CO2, H2S, Cl ions are contained.
UEDA MASAKATSU
IGARASHI MASAAKI
KONDO KUNIO
