Abstract: A stainless steel for oil wells which has excellent high-temperature corrosion resistance and can stably obtain a strength of not less than 758 MPa is provided. The stainless steel for oil wells contains, by masse, C: not more than 0.05%, Si: not more than 1.0%, Mn: 0.01 to 1.0%, P: not more than 0.05%, S: less than 0.002%, Cr: 16 to 18%, Mo: 1.8 to 3%, Cu: 1.0 to 3.5%, Ni: 3.0 to 5.5%, Co: 0.01 to 1.0%, Al: 0.001 to 0.1%, O: not more than 0.05%, and N: not more than 0.05%, the balance being Fe and impurities, and satisfies Formulas (1) and (2): Cr+4Ni+3Mo+2Cu?44??(1) Cr+3Ni+4Mo+2Cu/3?46??(2) where each symbol of element in Formulas (1) and (2) is substituted by the content (mass %) of a corresponding element.

Abstract: A process for producing a welded joint, which includes a weld metal having high strength and high toughness, and containing fewer blowholes, includes the steps of: preparing a base material containing, by mass %, not less than 10.5% of Cr; and subjecting the base material to GMA welding using a shielding gas containing 1 to 2 volume % or 35 to 50 volume % of CO2 gas, and the balance being inert gas, thereby forming a weld metal includes, by mass %, C: not more than 0.080%, Si: 0.20 to 1.00%, Mn: not more than 8.00%, P: not more than 0.040%, S: not more than 0.0100%, Cu: not more than 2.0%, Cr: 20.0 to 30.0%, Ni: 7.00 to 12.00%, N: 0.100 to 0.350%, O: 0.02 to 0.11%, sol. Al: not more than 0.040%, at least one of Mo: 1.00 to 4.00% and W: 1.00 to 4.00%, and the balance being Fe and impurities.

Abstract: Provided is a process for producing a welded joint which includes a weld metal having high strength and high toughness, and containing fewer blowholes. The process for producing a welded joint according to the present embodiment includes the steps of: preparing a base material containing, by mass %, not less than 10.5% of Cr; and subjecting the base material to GMA welding using a shielding gas containing 1 to 2 volume % or 35 to 50 volume % of CO2 gas, and the balance being inert gas, thereby forming a weld metal includes, by mass %, C: not more than 0.080%, Si: 0.20 to 1.00%, Mn: not more than 8.00%, P: not more than 0.040%, S: not more than 0.0100%, Cu: not more than 2.0%, Cr: 20.0 to 30.0%, Ni: 7.00 to 12.00%, N: 0.100 to 0.350%, O: 0.02 to 0.11%, sol. Al: not more, than 0.040%, at least one of Mo: 1.00 to 4.00% and W: 1.00 to 4.00%, and the balance being Fe and impurities.

Abstract: A stainless steel for oil wells which has excellent high-temperature corrosion resistance and can stably obtain a strength of not less than 758 MPa is provided. The stainless steel for oil wells contains, by masse, C: not more than 0.05%, Si: not more than 1.0%, Mn: 0.01 to 1.0%, P: not more than 0.05%, S: less than 0.002%, Cr: 16 to 18%, Mo: 1.8 to 3%, Cu: 1.0 to 3.5%, Ni: 3.0 to 5.5%, Co: 0.01 to 1.0%, Al: 0.001 to 0.1%, O: not more than 0.05%, and N: not more than 0.05%, the balance being Fe and impurities, and satisfies Formulas (1) and (2): Cr+4Ni+3Mo+2Cu?44??(1) Cr+3Ni+4Mo+2Cu/3?46??(2) where each symbol of element in Formulas (1) and (2) is substituted by the content (mass %) of a corresponding element.