Abstract: A martensitic stainless steel material that achieves both a high yield strength and excellent SSC resistance is provided. The martensitic stainless steel material according to the present disclosure consists of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Cu: 0.01 to 3.50%, Cr: 10.00 to 14.00%, Ni: 4.50 to 7.50%, Mo: 1.00 to 4.00%, Ti: 0.050 to 0.300%, V: 0.01 to 1.00%, Al: 0.001 to 0.100%, Co: 0.010 to 0.500%, Ca: 0.0005 to 0.0050%, Sn: 0.0005 to 0.0500%, N: 0.0010 to 0.0500%, O: 0.050% or less, and the balance: Fe and impurities, and has a yield strength of 758 MPa or more. Within this range, the contents of elements and the yield strength satisfy Formula (1) described in the description.

Abstract: A Fe—Cr—Ni alloy material that has high strength and reduced strength anisotropy is provided. A Fe—Cr—Ni alloy material according to the present disclosure consists of, by mass %, C: 0.030% or less, Si: 0.01 to 1.00%, Mn: 0.01 to 2.00%, P: 0.030% or less, S: 0.0050% or less, Ni: 29.0 to 36.5%, Cr: 23.0 to 27.5%, Mo: 2.00 to 6.00%, Al: 0.01 to 0.30%, rare earth metal: 0.016 to 0.100%, N: 0.220 to 0.500%, and O: 0.010% or less, with the balance being Fe and impurities, and satisfies Formula (1). In a microstructure, a standard deviation of the grain size numbers of austenite grains is 0.80 or less. The tensile yield strength is 758 MPa or more: 3 × Ni - 2 × Cr - 150 × N < 15. ( 1 ) where, a content of a corresponding element in percent by mass is substituted for each symbol of an element in Formula (1).

Abstract: An alloy material is provided that has a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, P: 0.030% or less, S: 0.0050% or less, Cr: 28.0 to 40.0%, Ni: 32.0 to 55.0%, sol. Al: 0.010 to 0.30%, N: more than 0.30% and not more than 0.000214×Ni2?0.03012×Ni+0.00215×Cr2?0.08567×Cr+1.927, O: 0.010% or less, Mo: 0 to 6.0%, W: 0 to 12.0%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, V: 0 to 0.50%, Ti: 0 to 0.50%, Nb: 0 to 0.50%, Co: 0 to 2.0%, Cu: 0 to 2.0%, REM: 0 to 0.10%, and the balance: Fe and impurities, and in which Fn1=Mo+(½)W is 1.0 to 6.0, and a yield strength at a 0.2% proof stress is 1103 MPa or more.

Abstract: A martensitic stainless steel seamless pipe according to the present disclosure has a chemical composition and the microstructure described in the description, and a yield strength of 862 MPa or more. An observation field of view region which is 1.0 ?m long in each of L direction and T direction and which includes an inner surface is composed of an inner surface vicinity region, an interior region that is below contact with the inner surface vicinity region, and a hollow region. An inner surface Cu occupancy OScu which is defined as the numerical proportion of sections in which a Cu concentration is more than 2.0% in the inner surface vicinity region, and an interior Cu occupancy OIcu which is defined as the numerical proportion of sections in which the Cu concentration is more than 2.0% in the interior region satisfy Formula (2). OS Cu / OI Cu ? 1.

Abstract: A martensitic stainless steel round bar of the present disclosure contains, in mass %, C: 0.030% or less, Cr: 10.00 to 14.00%, Ni: 5.00 to 7.50%, Mo: 1.50 to 4.00%, Cu: 1.00 to 3.50%, W: 0.01 to 2.00%, and Co: 0.010 to 0.500%, and has a yield strength of 862 MPa or more. When, at the center position of a cross section perpendicular to the axial direction of the martensitic stainless steel round bar, a dissolved Mo concentration is defined as [Mo]C, a dissolved W concentration is defined as [W]C, an Mo concentration in a residue obtained by constant-current electrolysis is defined as [Mo]R, and a W concentration in the residue is defined as [W]R, Formula (1) and Formula (2) are satisfied. F ? 1 = [ Mo ] C + 0.5 [ W ] C ? 2.45 ( 1 ) F ? 2 = F ? 1 / ( [ Mo ] R + [ W ] R ) ? 13.

Abstract: A steel material according to the present disclosure has a chemical composition consisting of, in mass %: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr 0.55 to 1.10%, Mo: 0.70 to 1.00%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: less than 0.0020%, and the balance being Fe and impurities, and satisfying Formula (1) described in the specification. A grain diameter of a prior-austenite grain is 15.0 ?m or less, and an average area of precipitate which is precipitated in a prior-austenite grain boundary is 12.5×10?3 ?m2 or less. A yield strength is 758 to 862 MPa.

Abstract: An alloy material is provided that has a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, P: 0.030% or less, S: 0.0050% or less, Cr: 28.0 to 40.0%, Ni: 32.0 to 55.0%, sol. Al: 0.010 to 0.30%, N: more than 0.30% and not more than 0.000214×Ni2?0.03012×Ni+0.00215×Cr2?0.08567×Cr+1.927, O: 0.010% or less, Mo: 0 to 6.0%, W: 0 to 12.0%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, V: 0 to 0.50%, Ti: 0 to 0.50%, Nb: 0 to 0.50%, Co: 0 to 2.0%, Cu: 0 to 2.0%, REM: 0 to 0.10%, and the balance: Fe and impurities, and in which Fn1=Mo+(½)W is 1.0 to 6.0, and a yield strength at a 0.2% proof stress is 1103 MPa or more.

Abstract: A steel material according to the present disclosure has a chemical composition consisting of, in mass %: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr 0.55 to 1.10%, Mo: 0.70 to 1.00%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: less than 0.0020%, and the balance being Fe and impurities, and satisfying Formula (1) described in the specification. A grain diameter of a prior-austenite grain is 15.0 ?m or less, and an average area of precipitate which is precipitated in a prior-austenite grain boundary is 12.5×10?3 ?m2 or less. A yield strength is 758 to 862 MPa.

Abstract: A steel bar for a downhole member is provided that is excellent in SCC resistance and SSC resistance. A martensitic stainless steel bar material for a downhole member of the present embodiment has a chemical composition that contains, by mass %, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.01% or less, Cu: 0.10 to 2.50%, Cr: 10 to 14%, Ni: 1.5 to 7.0%, Mo: 0.2 to 3.0%, Ti: 0.05 to 0.3%, V: 0.01 to 0.10%, Nb: 0.1% or less, Al: 0.001 to 0.1% and N: 0.05% or less, with the balance being Fe and impurities, and satisfies Formula (1) and Formula (2). [Mo]?4×[total Mo amount in precipitate at R/2 position]?1.30??(1) [Total Mo amount in precipitate at center position]?[total Mo amount in precipitate at R/2 position]?0.

Abstract: A steel bar for a downhole member is provided that is excellent in SCC resistance and SSC resistance. A martensitic stainless steel bar material for a downhole member of the present embodiment has a chemical composition that contains, by mass %, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.01% or less, Cu: 0.10 to 2.50%, Cr: 10 to 14%, Ni: 1.5 to 7.0%, Mo: 0.2 to 3.0%, Ti: 0.05 to 0.3%, V: 0.01 to 0.10%, Nb: 0.1% or less, Al: 0.001 to 0.1% and N: 0.05% or less, with the balance being Fe and impurities, and satisfies Formula (1) and Formula (2). [Mo]?4×[total Mo amount in precipitate at R/2 position]?1.30??(1) [Total Mo amount in precipitate at center position]?[total Mo amount in precipitate at R/2 position]?0.

Abstract: A martensitic Cr-containing steel having excellent corrosion resistance, SSC resistance, and IGHIC resistance is provided. A martensitic Cr-containing steel according to the present invention includes: a chemical composition consisting of, by mass %, Si: 0.05 to 1.0%, Mn: 0.1 to 1.0%, Cr: 8 to 12%, V: 0.01 to 1.0%, sol. Al: 0.005 to 0.10%, with the balance being Fe and impurities, wherein an effective Cr amount defined by “Cr?16.6×C” is not less than 8%, and an Mo equivalent defined by “Mo+0.5×W” is 0.03 to 2%; a micro-structure wherein a grain size number of prior-austenite crystal grain is not less than 8.0; and a yield strength of less than 379 to 551 MPa, wherein a grain-boundary segregation ratio of Mo and W is not less than 1.5.

Abstract: Provided is duplex stainless steel having high strength, SCC resistance and SSC resistance excellent in a high-temperature chloride environment, and capable of suppressing precipitation of a ? phase. The duplex stainless steel of the present embodiment includes, in mass %, of: C: at most 0.03%; Si: 0.2 to 1%; Mn: more than 5.0% to at most 10%; P: at most 0.040%; S: at most 0.010%; Ni: 4.5 to 8%; sol. Al: at most 0.040%; N: more than 0.2% to at most 0.4%; Cr: 24 to 29%; Mo: 0.5 to less than 1.5%; Cu: 1.5 to 3.5%; W: 0.05 to 0.2%; the balance being Fe and impurities, wherein the duplex stainless steel satisfies Formula (1): Cr+8Ni+Cu+Mo+W/2?65 . . . (1), where a symbol of each element in Formula (1) represents a content of the element (in mass %).

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: A martensitic Cr-containing steel having excellent corrosion resistance, SSC resistance, and IGHIC resistance is provided. A martensitic Cr-containing steel according to the present invention includes: a chemical composition consisting of, by mass %, Si: 0.05 to 1.0%, Mn: 0.1 to 1.0%, Cr: 8 to 12%, V: 0.01 to 1.0%, sol. Al: 0.005 to 0.10%, with the balance being Fe and impurities, wherein an effective Cr amount defined by “Cr?16.6×C” is not less than 8%, and an Mo equivalent defined by “Mo+0.5×W” is 0.03 to 2%; a micro-structure wherein a grain size number of prior-austenite crystal grain is not less than 8.0; and a yield strength of less than 379 to 551 MPa, wherein a grain-boundary segregation ratio of Mo and W is not less than 1.5.

Abstract: The chemical composition of a stainless steel in accordance with the present invention consists of C: not more than 0.05%, Si: not more than 0.5%, Mn: 0.01 to 0.5%, P: not more than 0.04%, S: not more than 0.01%, Cr: more than 16.0 and not more than 18.0%, Ni: more than 4.0 and not more than 5.6%, Mo: 1.6 to 4.0%, Cu: 1.5 to 3.0%, Al: 0.001 to 0.10%, and N: not more than 0.050%, the balance being Fe and impurities, and satisfies Formulas (1) and (2). Also, the micro-structure thereof contains a martensitic phase and a ferritic phase having a volume ratio of 10 to 40%, and the ferritic phase distribution ratio is higher than 85%. Cr+Cu+Ni+Mo ?25.5??(1) ?8 ?30(C+N)+0.5Mn+Ni+Cu/2+8.2?1.

Abstract: A high-strength stainless steel for oil well having corrosion resistance excellent in a high-temperature environment, having excellent SSC resistance at normal temperature, and having better workability than 13% Cr steels has a chemical composition containing, by mass percent, C: at most 0.05%, Si: at most 1.0%, Mn: at most 0.3%, P: at most 0.05%, S: less than 0.002%, Cr: over 16% and at most 18%, Mo: 1.5 to 3.0%, Cu: 1.0 to 3.5%, Ni: 3.5 to 6.5%, Al: 0.001 to 0.1%, N: at most 0.025%, and O: at most 0.01%, the balance being Fe and impurities, a microstructure containing a martensite phase, 10 to 48.5%, by volume ratio, of a ferrite phase and at most 10%, by volume ratio, of a retained austenite phase, yield strength of at least 758 MPa and uniform elongation of at least 10%.

Abstract: The chemical composition of a stainless steel in accordance with the present invention consists of C: not more than 0.05%, Si: not more than 0.5%, Mn: 0.01 to 0.5%, P: not more than 0.04%, S: not more than 0.01%, Cr: more than 16.0 and not more than 18.0%, Ni: more than 4.0 and not more than 5.6%, Mo: 1.6 to 4.0%, Cu: 1.5 to 3.0%, Al: 0.001 to 0.10%, and N: not more than 0.050%, the balance being Fe and impurities, and satisfies Formulas (1) and (2). Also, the micro-structure thereof contains a martensitic phase and a ferritic phase having a volume ratio of 10 to 40%, and the ferritic phase distribution ratio is higher than 85%. Cr+Cu+Ni+Mo 25.5??(1) ?8 ?30(C+N)+0.5Mn+Ni+Cu/2+8.2?1.

Abstract: The chemical composition of a stainless steel in accordance with the present invention consists of C: not more than 0.05%, Si: not more than 0.5%, Mn: 0.01 to 0.5%, P: not more than 0.04%, S: not more than 0.01%, Cr: more than 16.0 and not more than 18.0%, Ni: more than 4.0 and not more than 5.6%, Mo: 1.6 to 4.0%, Cu: 1.5 to 3.0%, Al: 0.001 to 0.10%, and N: not more than 0.050%, the balance being Fe and impurities, and satisfies Formulas (1) and (2). Also, the micro-structure thereof contains a martensitic phase and a ferritic phase having a volume ratio of 10 to 40%, and the ferritic phase distribution ratio is higher than 85%. Cr+Cu+Ni+Mo?25.5??(1) ?8?30(C+N)+0.5Mn+Ni+Cu/2+8.2?1.

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.