Abstract: The steel for steel pipes of the present invention is the one for steel pipes excellent in sour-resistance performance including C, Mn, Si, P, S, Ti, Al, Ca, N and O, and optionally including a predetermined amount of one or more of Cr, Ni, Cu, Mo, V, B and Nb, in which inclusions in the steel have Ca, Al, O and S as main components, the CaO content in the inclusions is 30 to 80%, the ratio of the N content in the steel (ppm) to the CaO content in the inclusions (%) is from 0.28 to 2.0, and the CaS content in the inclusions is 25% or less. In addition, the method of producing steel for steel pipes of the present invention is to produce steel for steel pipes in which Ca is added so that the ratio of the N content in the steel to the amount of Ca addition (kg/t) into the molten steel is from 200 to 857.

Abstract: A method of producing steel pipe excellent in sour-resistance performance, uses comprises controlling the amount of Ca addition charged into molten steel in a ladle according to a N content in the molten steel prior to Ca addition. As a result of the controlling step, a CaO content in the inclusions is in the range of 30 to 80%, the ratio of the N content in the steel to the CaO content in the inclusions satisfies the relation expressed by equation (1), and a CaS content in the inclusions satisfies the relation expressed by equation (2). 0.28?[N]/(% CaO)?2.0??(1) (% CaS)?25%??(2) where [N] represents the mass content (ppm) of N in the steel, (% CaO) represents the mass content (%) of CaO in the inclusions, and (% CaS) represents the mass content (%) of CaS in the inclusions.

Abstract: An austenitic stainless steel for use in a hydrogen gas atmosphere comprises, in mass %, C: 0.10% or less, Si: 1.0% or less, Mn: 0.01 to 30%, P: 0.040% or less, S: 0.01% or less, Cr: 15 to 30%, Ni: 5.0 to 30%, Al: 0.10% or less, N: 0.001 to 0.30% with the balance Fe and inevitable impurities. An X-ray (111) integration intensity of a cross section along the direction rectangular to the working direction is five times that in a random direction or less, and the X-ray integration intensity ratio of a cross section along the working direction satisfies I(220)/I(111)?10. The high strength steel can also contain one or more of the groups of Mo and W; V, Nb, Ta, Ti, Zr and Hf; B; Cu and Co; Mg, Ca, La, Ce, Y, Sm, Pr and Nd.

Abstract: A seamless steel pipe for line pipe having high strength and stable toughness and having resistance to sulfide corrosion cracking at low temperatures to room temperature is provided. A seamless steel pipe according to the present invention has a chemical composition comprising, in mass percent, C: 0.03-0.08%, Si: 0.05-0.5%, Mn: 1.0-3.0%, Mo: greater than 0.4% to 1.2%, Al: 0.005-0.100%, Ca: 0.001-0.005%, a remainder of Fe and impurities including N, P, S, O, and Cu, with the impurities containing at most 0.01% of N, at most 0.05% of P, at most 0.01% of S, at most 0.01% of O, and at most 0.1% of Cu, and having a microstructure comprising a bainitic-martensitic dual phase structure.

Abstract: A high-strength stainless steel, having good mechanical properties and corrosion resistance in a high-pressure hydrogen gas environment, is used as a container or other device for high-pressure hydrogen gas, and consists of, by mass %, C: not more than 0.04%, Si: not more than 1.0%, Mn: 7 to 30%, Cr: 15 to 22%, Ni: 5 to 20%, V: 0.001 to 1.0%, N: 0.20 to 0.50% and Al: not more than 0.10%, and the balance Fe and impurities. Among the impurities, P is not more than 0.030%, S is not more than 0.005%, and Ti, Zr and Hf are not more than 0.01% respectively, and the contents of Cr, Mn and N satisfy the relationship, 2.5Cr+3.4Mn?300N. The weld metal of the welded joint of the container or other device made of the said stainless steel satisfies the relationship, ?11?Nieq?1.1×Creq??8.

Abstract: The steel for steel pipes of the present invention is the one for steel pipes excellent in sour-resistance performance including C, Mn, Si, P, S, Ti, Al, Ca, N and O, and optionally including a predetermined amount of one or more of Cr, Ni, Cu, Mo, V, B and Nb, in which inclusions in the steel have Ca, Al, O and S as main components, the CaO content in the inclusions is 30 to 80%, the ratio of the N content in the steel (ppm) to the CaO content in the inclusions (%) is from 0.28 to 2.0, and the CaS content in the inclusions is 25% or less. In addition, the method of producing steel for steel pipes of the present invention is to produce steel for steel pipes in which Ca is added so that the ratio of the N content in the steel to the amount of Ca addition (kg/t) into the molten steel is from 200 to 857.

Abstract: Low alloy steel for oil country tubular goods contains, in percentage by mass, 0.20% to 0.35% C, 0.05% to 0.5% Si, 0.05% to 0.6% Mn, at most 0.025% P, at most 0.01% S, 0.005% to 0.100% Al, 0.8% to 3.0% Mo, 0.05% to 0.25% V, 0.0001% to 0.005% B, at most 0.01% N, and at most 0.01% O, the balance comprising Fe and impurities, the steel satisfying Expression (1): 12V+1?Mo?0 (1) where the symbols of elements represent the contents of the elements in percentage by mass. In this way, the steel according to the present invention has high SSC resistance.

Abstract: A steel product for a line pipe according to the invention has a composition containing, in mass %, C : 0.03% to 0.15%, Si: 0.05% to 1.0%, Mn: 0.5% to 1.8%, P: 0.015% or less, S: 0.004% or less, O: 0.01% or less, N: 0.007% or less, sol. Al: 0.01% to 0.1%, Ti: 0.024% or less, Ca: 0.0003% to 0.02%, and the balance consisting of Fe and impurities. The size of TiN in the steel product for a line pipe is at most 30 ?m. The steel product has high HIC resistance and its crack area ratio can be reduced to 3% or less.

Abstract: A low alloy steel, which has a chemical composition by mass %, of C: 0.1 to 0.55%, Si: 0.05 to 0.5%, Mn: 0.1 to 1%, S: 0.0001 to 0.005%, Al: 0.005 to 0.08%, Ti: 0.005 to 0.05%, Cr: 0.1 to 1.5%, Mo: 0.1 to 1%, O: 0.0004 to 0.005%, Ca: 0.0005 to 0.0045%, Nb: 0 to 0.1%, V: 0 to 0.5%, B: 0 to 0.005%, Zr: 0 to 0.10%, P?0.03%, and N?0.006%, with the balance being Fe and impurities, is manufactured by adjusting the value of ([Ti]/47.9)([N]/14)/([Ca])/40.1) satisfies not less than 0.0008 and not more than 0.0066, at the time of melting the said low alloy steel, wherein [Ti], [N] and [Ca] are the contents in the molten steel by mass % of Ti, N and Ca respectively. The thus-manufactured low steel alloy has a high SSC resistance with a yield stress of not less than 758 MPa.

Abstract: Provided is a low alloy steel for high-pressure hydrogen gas environments, which contains, by mass percent, C: 0.15 to 0.60%, Si: 0.05 to 0.5%, Mn: 0.05 to 3.0%, P: not more than 0.025%, S: not more than 0.010%, Al: 0.005 to 0.10%, Mo: 0.5 to 3.0%, V: 0.05 to 0.30%, O (oxygen): not more than 0.01%, N: not more than 0.03%, and the balance Fe and impurities, and has tensile strength of not less than 900 MPa. This low alloy steel desirably contains B of 0.0003 to 0.003%, but in this case, N is limited to not more than 0.010%. It is desirable to contain at least one among Cr, Nb, Ti, Zr, and Ca. The contents of Mo and V desirably satisfy the following formula (1): [Mo(%)]·[V(%)]0.2?0.32??(1).

Abstract: A high-strength stainless steel, having good mechanical properties and corrosion resistance in a high-pressure hydrogen gas environment, and excellent in stress corrosion cracking resistance, and a container or other device for high-pressure hydrogen gas, which is made of the said stainless steel, are provided. The stainless steel is characterized in that it consists of, by mass %, C: not more than 0.02%, Si: not more than 1.0%, Mn: 3 to 30%, Cr: more than 22% but not more than 30%, Ni: 17 to 30%, V: 0.001 to 1.0%, N: 0.10 to 0.50% and Al: not more than 0.10%, and the balance Fe and impurities. Among the impurities, P is not more than 0.030%, S is not more than 0.005%, and Ti, Zr and Hf are not more than 0.01% respectively, and the contents of Cr, Mn and N satisfy the following relationship [1]: 5Cr+3.4 Mn?500 N??[1].

Abstract: A low alloy steel is provided for oil country tubular goods with a yield strength between 654 MPa and 757 MPa, and possessing excellent resistance to HIC and SSC in high-pressure hydrogen sulfides environment, and comprising, by mass %: 0.10 to 0.60% C; 0.05 to 0.5% Si; 0.05 to 3.0% Mn; 0.025% or less P; 0.010% or less S; 0.005 to 0.10% Al; 0.01% or less O (oxygen); 3.0% or less Cr; and 3.0% or less Mo, wherein the amount of Cr and Mo content is 1.2% or more, with the balance being Fe and impurities, and the number of nonmetallic inclusions whose major axis is 10 ?m or more is 10 per square millimeter in the inspected cross section. The present invention provides a low alloy steel for oil country tubular goods possessing excellent resistance to sulfide stress cracking, and a seamless steel pipe.

Abstract: A low alloy steel comprising, by mass %, C: 0.10 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.05 to 1.5%, Cr: 1.0 to 2.0%, Mo: 0.05 to 2.0%, Al: 0.10 % or less and Ti: 0.002 to 0.05%, and with a Ceq value obtained by the following formula (1) of 0.65 or more, with the balance being Fe and impurities, wherein in the impurities, P is 0.025% or less, S is 0.010% or less, N is 0.007% or less, and B is less than 0.0003%, and the number per unit area of M23C6 type precipitates (M: a metal element) whose grain diameter is 1 ?m or more is 0.1/mm2 or less. This invention provides a low alloy steel possessing both hardenability and toughness and improves the resistance to sulfide stress corrosion cracking. Ceq=C+(Mn/6)+(Cr+Mo+V)/5 ??formula (1) where C, Mn, Cr, Mo and V in the formula (1) denote the mass % of respective elements.

Abstract: A seamless steel pipe for line pipe having high strength and stable toughness and having resistance to sulfide corrosion cracking at low temperatures to room temperature is provided. A seamless steel pipe according to the present invention has a chemical composition comprising, in mass percent, C: 0.03-0.08%, Si: 0.05-0.5%, Mn: 1.0-3.0%, Mo: greater than 0.4% to 1.2%, Al: 0.005-0.100%, Ca: 0.001-0.005%, a remainder of Fe and impurities including N, P, S, O, and Cu, with the impurities containing at most 0.01% of N, at most 0.05% of P, at most 0.01% of S, at most 0.01% of O, and at most 0.1% of Cu, and having a microstructure comprising a bainitic-martensitic dual phase structure.

Abstract: A duplex stainless steel containing C, Si, Mn, P, S, Al, Ni, Cr, Mo, N (nitrogen, O (oxygen), Ca, Mg, Cu, B, and W, and the balance Fe and impurities, where a number of oxide-based inclusions, which have a total content of Ca and Mg of 20 to 40% by mass and also have a long diameter of not less than 7 ?m, is not more than a 10 per 1 mm2 of the cross section perpendicular to the working direction, or further, the number of oxide-based inclusions, which have a content of S of not less than 15% by mass and also have a long diameter of not less than 1 ?m, is not more than 10 per 0.1 mm2 of the cross section perpendicular to the working direction. Particularly, the contents of Cu, B and W are desirably 0.2 to 2%, 0.001 to 0.01%, and 0.1 to 4% by mass, respectively.

Abstract: A weld joint having a base material and a weld metal both of an austenitic steel, wherein the weld metal has a chemical composition, in mass %, that C: 0.04% or less, Si: 1.0% or less, Mn: 3% or less, P: 0.02% or less, S: 0.005% or less, Cr: 15 to 25%, Ni: 30% or more, Mo: 10% or less, Nb: 2.5 to 5%, Al: 3.0% or less, Ti: 0.5% or less, and the balance: Fe and inevitable impurities, the contents of Al and Ti satisfying the following: (Ti+Al)>Nb/8. The weld joint is a high strength austenitic steel weld joint which exhibits excellent toughness at a low temperature and excellent resistance to hydrogen embrittlement, which are required for a piping and a vessel for high pressure hydrogen, particularly also in a welded zone.

Abstract: Low alloy steel for oil country tubular goods contains, in percentage by mass, 0.20% to 0.35% C, 0.05% to 0.5% Si, 0.05% to 0.6% Mn, at most 0.025% P, at most 0.01% S, 0.005% to 0.100% Al, 0.8% to 3.0% Mo, 0.05% to 0.25% V, 0.0001% to 0.005% B, at most 0.01% N, and at most 0.01% O, the balance comprising Fe and impurities, the steel satisfying Expression (1): 12V+1?Mo?0 (1) where the symbols of elements represent the contents of the elements in percentage by mass. In this way, the steel according to the present invention has high SSC resistance.

Abstract: A steel for an oil well pipe, having high strength and excellent SSC resistance, consists of, by mass %, C: 0.30 to 0.60%, Si: 0.05 to 0.5%, Mn: 0.05 to 1.0%, Al: 0.005 to 0.10%, Cr+Mo: 1.5 to 3.0%, wherein Mo is 0.5% or more, V: 0.05 to 0.3%, Nb: 0 to 0.1%, Ti: 0 to 0.1%, Zr: 0 to 0.1%, N (nitrogen): 0 to 0.03%, Ca: 0 to 0.01%, and the balance Fe and impurities; P 0.025% or less, S 0.01% or less, B 0.0010% or less and O (oxygen) 0.01% or less. The method involves heating the steel at 1150° C. or more; producing a seamless steel pipe by hot working; water-cooling the pipe to a temperature in a range of 400 to 600° C. immediately after finishing the working; and subjecting the pipe to a heat treatment for bainite isothermal transformation in a range of 400 to 600° C.

Abstract: A steel product for a line pipe according to the invention has a composition containing, in mass %, C : 0.03% to 0.15%, Si: 0.05% to 1.0%, Mn: 0.5% to 1.8%, P: 0.015% or less, S: 0.004% or less, O: 0.01% or less, N: 0.007% or less, sol. Al: 0.01% to 0.1%, Ti: 0.024% or less, Ca: 0.0003% to 0.02%, and the balance consisting of Fe and impurities. The size of TiN in the steel product for a line pipe is at most 30 ?m. The steel product has high HIC resistance and its crack area ratio can be reduced to 3% or less.

Abstract: A steel for steel pipes which comprises, on the percent by mass basis, C: 0.2 to 0.7%, Si: 0.01 to 0.8%, Mn: 0.1 to 1.5%, S: 0.005% or less, P: 0.03% or less, Al: 0.0005 to 0.1%, Ti: 0.005 to 0.05%, Ca: 0.0004 to 0.005%, N: 0.007% or less, Cr: 0.1 to 1.5%, Mo: 0.2 to 1.0%, Nb: 0 to 0.1%, Zr: 0 to 0.1%, V: 0 to 0.5% and B: 0 to 0.005%, with the balance being Fe and impurities, in which non-metallic inclusions containing Ca, Al, Ti, N, O, and S are present, and in the said inclusions (Ca %)/(Al %) is 0.55 to 1.72, and (Ca %)/(Ti %) is 0.7 to 19 can be used as a raw material for oil country tubular goods, being used at a greater depth and in severer corrosive circumstances, such as casings and tubings for oil and/or natural gas wells, drilling pipes and drilling collars for excavation, and the like.