Abstract: A duplex stainless steel with good low-temperature toughness is provided. The duplex stainless steel has a chemical composition of, in mass %: up to 0.03% C; 0.1 to 0.8% Si; up to 2.3% Mn; up to 0.040% P; up to 0.010% S; up to 0.040% sol. Al; 3 to 7% Ni; 20 to 28% Cr; 0.5 to 2.0% Mo; more than 2.0% and not more than 4.0% Cu; 0.02 to 0.5% Co; 0.1 to 0.35% N; up to 0.010% O; and other elements, the steel having a microstructure including an austenite phase and a ferrite phase, the ferrite phase having an area percentage of 30 to 60%, the steel satisfying the following Formula, (1); 0.70×NiL?NiH??(1), where NiH and NiL are obtained by using an electron-beam microanalyzer to measure Ni content and, in a distribution of Ni content, determining two maximum frequencies, and treating the one with a higher Ni content as NiH and treating the one with a lower Ni content as NiL.

Abstract: A duplex stainless steel with good low-temperature toughness is provided. The duplex stainless steel has a chemical composition of, in mass %; up to 0.03% C; 0.1 to 0.8% Si; up to 2.3% Mn; up to 0.040% P; up to 0.010% S; up to 0.040% sol. Al; 3 to 7% Ni; 20 to 28% Cr; 0.5 to 2.0% Mo; more than 2.0% and not more than 4.0% Cu; 0.02 to 0.5% Co; 0.1 to 0.35% N; up to 0.010% O; and other elements, the steel having a microstructure including an austenite phase and a ferrite phase, the ferrite phase having an area percentage of 30 to 60%, the steel satisfying the following Formula, (1); 0.70×NiL?NiH??(1), where NiH and NiL are obtained by using an electron-beam microanalyzer to measure Ni content and, in a distribution of Ni content, determining two maximum frequencies, and treating the one with a higher Ni content as NiH and treating the one with a lower Ni content as NiL.

Abstract: A stainless steel pipe has a composition of, in mass %: C: up to 0.02%; Si: 0.05 to 1.00%; Mn: 0.1 to 1.0%; P: up to 0.030%; S: up to 0.002%; Ni: 5.5 to 8%; Cr: 10 to 14%; Mo: 2 to 4%; V: 0.01 to 0.10%; Ti: 0.05 to 0.3%; Nb: up to 0.1%; Al: 0.001 to 0.1%; N: up to 0.05%; Cu: up to 0.5%; Ca: 0 to 0.008%; Mg: 0 to 0.05%; B: 0 to 0.005%; and balance Fe and impurities. The pipe having a microstructure including martensite and, by volume fraction, 12 to 18% retained austenite. The martensite has prior austenite grains of a crystal grain size number lower than 8.0 in accordance with ASTM E112. The stainless steel pipe has a yield strength of 550 to 700 MPa.

Abstract: Provided is a duplex stainless steel having a high strength and a high toughness. A stainless steel according to the present invention includes: a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 30.0%, Mo: at least 0.50% and less than 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities; and a structure, wherein a rate of ferrite in the structure is 30 to 70%, and a hardness of the ferrite in the structure is at least 300 Hv10gf.

Abstract: A welded joint of duplex stainless steel, which can suppress precipitation ? phase under high heat input welding, is excellent in SCC resistance under high-temperature chloride environments. A weld metal of the welded joint contains, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: at most 2.00%, Ni: 7.00 to 12.00%, Cr: 20.0 to 30.0%, Mo: 1 to 4%, N: 0.100 to 0.350%, sol. Al: at most 0.040%, and O: at most 0.035%, the balance being Fe and impurities. The weld metal satisfies Expressions (1) and (3): 2.2Cr+7Mo+3Cu>66??(1) Cr+11Mo+10Ni?12(Cu+30N)<100??(3) where a content (mass percent) of each element in one of the base metal and weld metal is used for each element in Expressions (1) and (3).

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 welded joint of duplex stainless steel, which can suppress precipitation of ? phase under high heat input welding, is excellent in SCC resistance under high-temperature chloride environments. A weld metal of the welded joint contains, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: at most 2.00%, Ni: 7.00 to 12.00%, Cr: 20.0 to 30.0%, Mo: 1 to 4%, N: 0.100 to 0.350%, sol. Al: at most 0.040%, and O: at most 0.035%, the balance being Fe and impurities. The weld metal satisfies Expressions (1) and (3): 2.2Cr+7Mo+3Cu>66??(1) Cr+11Mo+10Ni?12(Cu+30N)<100??(3) where a content (mass percent) of each element in one of the base metal and weld metal is used for each element in Expressions (1) and (3).

Abstract: A duplex stainless steel, which can suppress precipitation of a ? phase under high heat input welding, is excellent in SCC resistance under high-temperature chloride environments and has a high strength. The duplex stainless steel includes a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 28.0%, Mo: 0.50 to 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities, and satisfying Expression (1) and Expression (2); a structure having a ferrite rate of at least 50%; and a yield strength of at least 550 MPa or more: 2.

Abstract: Provided is a duplex stainless steel having a high strength and a high toughness. A stainless steel according to the present invention includes: a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 30.0%, Mo: at least 0.50% and less than 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities; and a structure, wherein a rate of ferrite in the structure is 30 to 70%, and a hardness of the ferrite in the structure is at least 300 Hv10gf.