Abstract: A purpose of the present invention is to provide a martensitic stainless steel tube exhibiting excellent performance even in severe corrosive environments in which a partial pressure of hydrogen sulfide exceeds 0.03 bar. Provided is a low C-high Cr alloy steel tube for OCTG (Oil Country Tubular Goods) having minimum yield strength of 862 MPa and excellent corrosion resistance, wherein the steel tube contains, in percent by mass, 0.005 to 0.05% C, 12 to 16% Cr, 1.0% or less Si, 2.0% or less Mn, 3.5 to 7.5% Ni, 1.5 to 3.5% Mo, 0.01 to 0.05% V, 0.02% or less N, and 0.01 to 0.06% Ta and satisfies the relationship in the following formula (1), and the rest comprises Fe and unavoidable impurities. 25-25 (% Ni)+5 (% Cr)+25 (% Mo)?0??(1).

Abstract: A purpose of the present invention is to provide a martensitic stainless steel applicable in environments involving both wet carbon dioxide gas and wet hydrogen sulfide and excellent in weldability, manufacturability, and resistance to strain age hardening. Provided is a martensitic stainless steel having excellent corrosion resistance and resistance to strain age hardening comprising, in percent by mass, 0.02% or less of C, 0.02% or less of N, 0.1 to 0.5% of Si, 0.1 to 0.5% of Mn, 10 to 13% Cr, Ni exceeding 5.0% but 8% or less, 1.5 to 3% of Mo, 0.01 to 0.05% of V, 0.16 to 0.30% of Zr, 0.01 to 0.05% of Ta, and the balance of Fe and unavoidable impurities, wherein the martensitic stainless steel satisfies the condition that the sum of the carbon and the nitrogen exceeds 0.02% but 0.04% or less.

Abstract: A purpose of the present invention is to provide a martensitic stainless steel tube exhibiting excellent performance even in severe corrosive environments in which a partial pressure of hydrogen sulfide exceeds 0.03 bar. Provided is a low C-high Cr alloy steel tube for OCTG (Oil Country Tubular Goods) having minimum yield strength of 862 MPa and excellent corrosion resistance, wherein the steel tube contains, in percent by mass, 0.005 to 0.05% C, 12 to 16% Cr, 1.0% or less Si, 2.0% or less Mn, 3.5 to 7.5% Ni, 1.5 to 3.5% Mo, 0.01 to 0.05% V, 0.02% or less N, and 0.01 to 0.06% Ta and satisfies the relationship in the following formula (1), and the rest comprises Fe and unavoidable impurities.

Abstract: A purpose of the present invention is to provide a martensitic stainless steel applicable in environments involving both wet carbon dioxide gas and wet hydrogen sulfide and excellent in weldability, manufacturability, and resistance to strain age hardening. Provided is a martensitic stainless steel having excellent corrosion resistance and resistance to strain age hardening comprising, in percent by mass, 0.02% or less of C, 0.02% or less of N, 0.1 to 0.5% of Si, 0.1 to 0.5% of Mn, 10 to 13% Cr, Ni exceeding 5.0% but 8% or less, 1.5 to 3% of Mo, 0.01 to 0.05% of V, 0.16 to 0.30% of Zr, 0.01 to 0.05% of Ta, and the balance of Fe and unavoidable impurities, wherein the martensitic stainless steel satisfies the condition that the sum of the carbon and the nitrogen exceeds 0.02% but 0.04% or less.

Abstract: The present invention relates to an austenitic stainless steel tube for boiler, used for superheater or reheater in thermal power plant, giving excellent resistance to high temperature steam oxidation, in particular to an austenitic stainless steel tube containing 16 to 20% Cr by weight, and being cold-worked at the inner surface of the tube. The Cr concentration in the vicinity of the inner surface of the steel tube is 14% by weight or larger, and the hardness at 100 ?m depth from the inner surface of the steel tube is 1.5 times or larger the average hardness of the mother material or is HV 300 or larger.

Abstract: The present invention relates to an austenitic stainless steel tube for boiler, used for superheater or reheater in thermal power plant, giving excellent resistance to high temperature steam oxidation, in particular to an austenitic stainless steel tube containing 16 to 20% Cr by weight, and being cold-worked at the inner surface of the tube. The Cr concentration in the vicinity of the inner surface of the steel tube is 14% by weight or larger, and the hardness at 100 ?m depth from the inner surface of the steel tube is 1.5 times or larger the average hardness of the mother material or is HV 300 or larger.