Abstract: The seamless steel pipe according to the present disclosure includes a chemical composition consisting 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, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 5.00 to 6.50%, Cr: more than 10.00 to 13.40%, Cu: more than 1.50 to 3.50%, Mo: 1.00 to 4.00%, V: 0.01 to 1.00%, Ti: 0.050 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), wherein a depassivation pH of an inner surface is 3.00 or less. Cr+2.0 Mo+0.5 Ni+2.0 Cu+0.5 Co?20.

Abstract: The seamless steel pipe according to the present disclosure includes a chemical composition consisting 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, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 3.00 to 6.50%, Cr: more than 10.00 to 13.40%, Mo: 0.50 to 4.00%, V: 0.01 to 1.00%, Ti: 0.010 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), and a microstructure containing, in volume ratio, 80.0% or more of martensite, wherein a depassivation pH of an inner surface is 3.50 or less. Cr+2.0Mo+0.5Ni+0.5Co?16.

Abstract: The duplex stainless steel seamless pipe according to the present disclosure has the chemical composition described in the description and a microstructure consisting of 30 to 55% of ferrite, and austenite. In a square observation field of view region with sides of 250 ?m including a center portion of the wall thickness and including a T direction and a C direction, a number of intersections NT which is a number of intersections between the line segment T1 to T4 described in the description and ferrite interfaces is 65 or more. A number of intersections NC which is a number of intersections between the line segments C1 to C4 described in the description and ferrite interfaces is 50 or more.

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: The seamless steel pipe according to the present disclosure includes a chemical composition consisting 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, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 3.00 to 6.50%, Cr: more than 10.00 to 13.40%, Mo: 0.50 to 4.00%, V: 0.01 to 1.00%, Ti: 0.010 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), and a microstructure containing, in volume ratio, 80.0% or more of martensite, wherein a depassivation pH of an inner surface is 3.50 or less. Cr+2.0Mo+0.5Ni+0.5Co?16.

Abstract: The seamless steel pipe according to the present disclosure includes a chemical composition consisting 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, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 5.00 to 6.50%, Cr: more than 10.00 to 13.40%, Cu: more than 1.50 to 3.50%, Mo: 1.00 to 4.00%, V: 0.01 to 1.00%, Ti: 0.050 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), wherein a depassivation pH of an inner surface is 3.00 or less. Cr+2.0Mo+0.5Ni+2.0Cu+0.5Co?20.

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: An austenitic stainless steel is provided which has a chemical composition that consists, by mass %, of: C: 0.015% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.05% or less, S: 0.030% or less, Cr: 16.0% or more and less than 22.0%, Ni: 11.0 to 16.0%, Mo: 2.5 to 5.0%, N: 0.07% or more and less than 0.15%, Nb: 0.20 to 0.50%, Al: 0.005 to 0.040%, Sn: 0 to 0.080%, Zn: 0 to 0.0060%, Pb: 0 to 0.030%, and the balance: Fe and impurities, and that satisfies the formula [MoSS/Mo?0.98] (MoSS: Mo amount dissolved in the steel).

Abstract: A duplex stainless steel with occurrence of pitting suppressed is provided. A duplex stainless steel according to the present disclosure has a chemical composition consisting of, in mass %, Cr: more than 27.00% to 29.00%, Mo: 2.50 to 3.50%, Ni: 5.00 to 8.00%, W: 4.00 to 6.00%, Cu: 0.01 to less than 0.10%, N: more than 0.400% to 0.600%, C: 0.030% or less, Si: 1.00% or less, Mn 1.00% or less, sol.Al: 0.040% or less, V: 0.50% or less, O: 0.010% or less, P: 0.030% or less, and S: 0.020% or less with the balance being Fe and impurities and satisfying Formula (1), a microstructure consisting of 35 to 65 volume % of ferrite phase with the balance being the austenite phase, and the area fraction of Cu precipitated in the ferrite phase is 0.5% or less. Cr+4.0×Mo+2.0×W+20×N?5×ln(Cu)?65.

Abstract: A Ni—Cr alloy material has a chemical composition that consists of; Si: 0.01 to 0.5%, Mn: 0.01 to less than 1.0%, Cu: 0.01 to less than 1.0%, Ni: 48 to less than 55%, Cr: 22 to 28%, Mo: 5.6 to less than 7.0%, N: 0.04 to 0.16%, sol.Al: 0.03 to 0.20%, REM: 0.01 to 0.074%, W: 0% or more and less than 8.0%, Co: 0 to 2.0%; one or more of Ca and Mg: 0.0003 to 0.01% in total, and one or more of Ti, Nb, Zr, and V: 0 to 0.5% in total, the balance thereof being Fe and impurities. The impurities include C £ 0.03%, P £ 0.03%, S £ 0.001%, and O £ 0.01%. The dislocation density r of the Ni—Cr alloy material expressed in m?2 satisfies a formula [7.0?1015£r£2.7?1016?2.67?1017?REM].

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: An austenitic stainless steel includes base metal and a coating film formed on at least part of a surface of the base metal, a chemical composition of the base metal containing, in mass percent: C: 0.05% or less; Si: 1.0% or less; Mn: 2.0% or less; P: 0.040% or less; S: 0.010% or less; O: 0.020% or less; N: less than 0.050%; Ni: 12.0 to 27.0%; Cr: 15.0% or more to less than 20.0%; Cu: more than 3.5% to 8.0% or less; Mo: more than 2.0% to 5.0% or less; Co: 0.05% or less; Sn: 0.05% or less, V: 0 to 0.5%, Nb: 0 to 1.0%, Ti: 0 to 0.5%, W: 0 to 5.0%, Zr: 0 to 1.0%, Al: 0 to 0.5%, Ca: 0 to 0.01%, B: 0 to 0.01%, REM: 0 to 0.01%, and the balance: Fe and impurities, wherein a chemical composition at a maximum-Cr depth where a concentration of Cr in the coating film reaches a maximum satisfies, in at %, [(Cr+Ni+Cu+Mo)/Fe?1.0].

Abstract: An austenitic stainless steel is provided which has a chemical composition that consists, by mass %, of: C: 0.015% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.05% or less, S: 0.030% or less, Cr: 16.0% or more and less than 22.0%, Ni: 11.0 to 16.0%, Mo: 2.5 to 5.0%, N: 0.07% or more and less than 0.15%, Nb: 0.20 to 0.50%, Al: 0.005 to 0.040%, Sn: 0 to 0.080%, Zn: 0 to 0.0060%, Pb: 0 to 0.030%, and the balance: Fe and impurities, and that satisfies the formula [MoSS/Mo?0.98] (MoSS: Mo amount dissolved in the steel).

Abstract: The high alloy for oil well according to the present embodiment consists of, in mass %, C: 0.03% or less, Si: 1.0% or less, Mn: 0.05 to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 26.0 to 40.0%, Cr: 22.0 to 30.0%, Mo: 0.01% or more to less than 5.0%, Cu: 0.1 to 3.0%, Al: 0.001 to 0.30%, N: more than 0.05% to 0.30% or less, O: 0.010% or less, and Ag: 0.005 to 1.0%, wherein the alloy satisfies the following Formula (1) and (2), wherein the high alloy for oil well has yield strength of 758 MPa or more: 5×Cu+(1000×Ag)2?40??(1) Cu+6×Ag?500×(Ca+Mg+REM)?3.5??(2) where, each element symbol in each Formula is substituted by the content (in mass %) of each element.

Abstract: There is provided a welding structure member excellent in corrosion resistance in an environment where high-concentration sulfuric acid condenses, the welding structure member including base material having a chemical composition containing, in mass percent, C?0.05%, Si?1.0%, Mn?2.0%, P?0.04%, S?0.01%, Ni: 12.0 to 27.0%, Cr: 15.0% or more to less than 20.0%, Cu: more than 3 0% to 8.0% or less, Mo: more than 2.0% to 5.0% or less, Nb?1.0%, Ti?0.5%, Co?0.5%, Sn?0.1%, W?5.0%, Zr?1.0%, Al?0.5%, N<0.05%, Ca?0.01%, B?0.01%, and REM?0.01%, with the balance: Fe and unavoidable impurities, and the welding structure member including including weld metal having a chemical composition containing, in mass percent, C?0.10%, Si?0.50%, Mn?3.5%, P?0.03%, S?0.03%, Cu?0.50%, Ni: 51.0 to 69.0%, Cr: 14.5 to 23.0%, Mo: 6.0 to 17.0%, Al?0.40%, Ti+Nb+Ta?4.90%, Co?2.5%, V?0.35%, and W?4.5%, with the balance: Fe and unavoidable impurities.

Abstract: There is provided a welding structure member excellent in corrosion resistance in an environment where high-concentration sulfuric acid condenses, the welding structure member including base material having a chemical composition containing, in mass percent, C?0.05%, Si?1.0%, Mn?2.0%, P?0.04%, S?0.01%, Ni: 12.0 to 27.0%, Cr: 15.0% or more to less than 20.0%, Cu: more than 3.0% to 8.0% or less, Mo: more than 2.0% to 5.0% or less, Nb?1.0%, Ti?0.5%, Co?0.5%, Sn?0.1%, W?5.0%, Zr?1.0%, Al?0.5%, N<0.05%, Ca?0.01%, B?0.01%, and REM?0.01%, with the balance: Fe and unavoidable impurities, and the welding structure member including weld metal having a chemical composition containing, in mass percent, C?0.10%, Si?0.50%, Mn?3.5%, P?0.03%, S?0.03%, Cu?0.50%, Ni: 51.0 to 80.0%, Cr: 14.5 to 23.0%, Mo?0.10%, Al?0.40%, Ti+Nb+Ta?4.90%, Co?2.5%, V?0.35%, and W?4.5%, with the balance: Fe and unavoidable impurities.

Abstract: A stainless steel contains, by mass %, C: 0.005% to 0.03%, Si: 0.05% to 1.0%, Mn: 0.1% to 4.0%, Ni: 3% to 8%, Cr: 20% to 35%, Mo: 0.01% to 4.0%, Al: 0.001% to 0.30%, N: 0.05% to 0.60%, one or more selected from Re: 2.0% or less, Ga: 2.0% or less, and Ge: 2.0% or less, and a balance consisting of Fe and impurities.

Abstract: The high alloy for oil well according to the present embodiment consists of, in mass %, C: 0.03% or less, Si: 1.0% or less, Mn: 0.05 to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 26.0 to 40.0%, Cr: 22.0 to 30.0%, Mo: 0.01% or more to less than 5.0%, Cu: 0.1 to 3.0%, Al: 0.001 to 0.30%, N: more than 0.05% to 0.30% or less, O: 0.010% or less, and Ag: 0.005 to 1.0%, wherein the alloy satisfies the following Formulae (1) and (2), wherein the high alloy for oil well has yield strength of 758 MPa or more: 5×Cu+(1000×Ag)2?40 ??(1) Cu+6×Ag?500×(Ca+Mg+REM)?3.5 ??(2) where, each element symbol in each Formula is substituted by the content (in mass %) of each element.

Abstract: A Ni—Cr alloy material has a chemical composition that consists of; Si: 0.01 to 0.5%, Mn: 0.01 to less than 1.0%, Cu: 0.01 to less than 1.0%, Ni: 48 to less than 55%, Cr: 22 to 28%, Mo: 5.6 to less than 7.0%, N: 0.04 to 0.16%, sol.Al: 0.03 to 0.20%, REM: 0.01 to 0.074%, W: 0% or more and less than 8.0%, Co: 0 to 2.0%; one or more of Ca and Mg: 0.0003 to 0.01% in total, and one or more of Ti, Nb, Zr, and V: 0 to 0.5% in total, the balance thereof being Fe and impurities. The impurities include C £ 0.03%, P £ 0.03%, S £ 0.001%, and O £ 0.01%. The dislocation density r of the Ni—Cr alloy material expressed in m?2 satisfies a formula [7.0?1015£r£2.7?1016?2.67?1017?REM].

Abstract: A stainless steel contains, by mass % C: 0.005% to 0.03%, Si: 0.05% to 1.0%, Mn: 0.1% to 4.0%, Ni: 3% to 8%, Cr: 20% to 35%, Mo: 0.01% to 4.0%, Al: 0.001% to 0.30%, 0.05% to 0.60%, one or more selected from Re: 2.0% or less, Ga: 2.0% or less, and Ge: 2.0% or less, and a balance consisting of Fe and impurities.