Abstract: A martensitic stainless steel oil country tubular good contains, by mass, 0.005% to 0.1% C, 0.05% to 1% Si, 1.5% to 5% Mn, at most 0.05% P, at most 0.01% S, 9% to 13% Cr, at most 0.5% Ni, at most 2% Mo, at most 2% Cu, 0.001% to 0.1% Al, and 0.001% to 0.1% N, with the balance being Fe and impurities, and the pipe has a Cr-depleted region under the surface. The martensitic stainless steel oil country tubular good according to the present invention does not have a passive film on the surface and corrodes wholly at low speed. In addition, the Ni content is reduced, which allows uneven corrosion to be prevented. Therefore, SCC can be prevented from being generated in spite of the presence of a Cr-depleted region.

Abstract: A martensitic stainless steel for welded structures including by mass %, C: 0.001 to 0.05%, Si: 0.05 to 1%, Mn: 0.05 to 2%, P: 0.03% or less, REM: 0.0005 to 0.1%, Cr: 8 to 16%, Ni: 0.1 to 9% and sol. Al: 0.001 to 0.1%; and further including one or more elements selected from among Ti: 0.005 to 0.5%, Zr: 0.005 to 0.5%, Hf: 0.005 to 0.5%, V: 0.005 to 0.5% and Nb: 0.005 to 0.5%; and O: 0.005% or less, N: 0.1% or less, with the balance being Fe and impurities; and the P and REM content satisfies: P?0.6×REM. This steel possesses excellent SCC (stress corrosion cracking) resistance in welded sections in Sweet environments.

Abstract: A martensitic stainless steel comprising C: 0.01-0.10%, Si: 0.05-1.0%, Mn: 0.05-1.5%, P: not more than 0.03%, S: not more than 0.01%, Cr: 9-15%, Ni: 0.1-4.5%, Al: not more than 0.05% and N: not more than 0.1% in mass %, and further comprising at least one of Cu: 0.05-5% and Mo: 0.05-5%, the residual being Fe and impurities, is provided, wherein the contents of Cu and Mo satisfy the following formula (a) or (b), 0.2%?Mo+Cu/4?5%??(a) 0.55%?Mo+Cu/4?5%??(b) and wherein the hardness is 30-45 in HRC and the carbide amount in grain boundaries of the prior austenite is not more than 0.5 volume %. The marensitic stainless steel has excellent properties regarding the sulfide stress cracking resistance, the resistance to corrosive wear and the localized corrosion.

Abstract: An oil country tubular good for expansion according to the invention is expanded in a well. The oil country tubular good for expansion has a composition containing, in percentage by mass, 0.05% to 0.08% C, at most 0.50% Si, 0.80% to 1.30% Mn, at most 0.030% P, at most 0.020% S, 0.08% to 0.50% Cr, at most 0.01% N, 0.005% to 0.06% Al, at most 0.05% Ti, at most 0.50% Cu, and at most 0.50% Ni, and the balance consisting of Fe and impurities, and a structure having a ferrite ratio of at least 80%. The oil country tubular good for expansion has a yield strength in the range from 276 MPa to 379 MPa and a uniform elongation of at least 16%. Therefore, the oil country tubular good according to the invention has a high pipe expansion characteristic.

Abstract: A martensitic stainless steel for welded structures including by mass %, C: 0.001 to 0.05%, Si: 0.05 to 1%, Mn: 0.05 to 2%, P: 0.03% or less, REM: 0.0005 to 0.1%, Cr: 8 to 16%, Ni: 0.1 to 9% and sol. Al: 0.001 to 0.1%; and further including one or more elements selected from among Ti: 0.005 to 0.5%, Zr: 0.005 to 0.5%, Hf: 0.005 to 0.5%, V: 0.005 to 0.5% and Nb: 0.005 to 0.5%; and O: 0.005% or less, N: 0.1% or less, with the balance being Fe and impurities; and the P and REM content satisfies: P?0.6×REM. This steel possesses excellent SCC (stress corrosion cracking) resistance in welded sections in Sweet environments.

Abstract: The martensitic stainless steel according to the invention includes, in percent by mass, 0.010% to 0.030% C, 0.30% to 0.60% Mn, at most 0.040% P, at most 0.0100% S, 10.00% to 15.00% Cr, 2.50% to 8.00% Ni, 1.00% to 5.00% Mo, 0.050% to 0.250% Ti, at most 0.25% V, at most 0.07% N, and at least one of at most 0.50% Si and at most 0.10% Al, the balance consists of Fe and impurities, and the martensitic stainless steel satisfies Expression (1) and has a yield stress in the range from 758 MPa to 862 MPa. In this way, the martensitic stainless steel has a yield stress of 110 ksi grade (a yield stress in the range from 758 MPa to 862 MPa) and the value produced by subtracting the yield stress from the tensile stress is not less than 20.7 MPa. 6.0?Ti/C?10.

Abstract: A metal pipe according to the invention has a plurality of ridges that have different heights, extend in the axial direction, and are arranged in the circumferential direction at its inner circumferential surface. If the Reynolds number changes and the streak structure and the scale of a hairpin vortex change, the streak and the hairpin vortex each match any one of the ridges. Therefore, the fluid friction can be reduced in a wide Reynolds number range.

Abstract: A martensitic stainless steel oil country tubular good contains, by mass, 0.005% to 0.1% C, 0.05% to 1% Si, 1.5% to 5% Mn, at most 0.05% P, at most 0.01% S, 9% to 13% Cr, at most 0.5% Ni, at most 2% Mo, at most 2% Cu, 0.001% to 0.1% Al, and 0.001% to 0.1% N, with the balance being Fe and impurities, and the pipe has a Cr-depleted region under the surface. The martensitic stainless steel oil country tubular good according to the present invention does not have a passive film on the surface and corrodes wholly at low speed. In addition, the Ni content is reduced, which allows uneven corrosion to be prevented. Therefore, SCC can be prevented from being generated in spite of the presence of a Cr-depleted region.

Abstract: An oil country tubular good for expansion according to the invention is expanded in a well. The oil country tubular good for expansion according to the invention is formed of duplex stainless steel having a composition containing, in percentage by mass, 0.005% to 0.03% C, 0.1% to 1.0% Si, 0.2% to 2.0% Mn, at most 0.04% P, at most 0.015% S, 18.0% to 27.0% Cr, 4.0% to 9.0% Ni, at most 0.040% Al, and 0.05% to 0.40% N, and the balance consisting of Fe and impurities, a structure including an austenite ratio in the range from 40% to 90%. The oil country tubular good for expansion according to the invention has a yield strength from 256 MPa to 655 MPa, and a uniform elongation more than 20%. Therefore, the oil country tubular good for expansion according to the invention has a high pipe expansion characteristic.

Abstract: An oil country tubular good for expansion according to the invention is expanded in a well. The oil country tubular good for expansion has a composition containing, in percentage by mass, 0.05% to 0.08% C, at most 0.50% Si, 0.80% to 1.30% Mn, at most 0.030% P, at most 0.020% S, 0.08% to 0.50% Cr, at most 0.01% N, 0.005% to 0.06% Al, at most 0.05% Ti, at most 0.50% Cu, and at most 0.50% Ni, and the balance consisting of Fe and impurities, and a structure having a ferrite ratio of at least 80%. The oil country tubular good for expansion has a yield strength in the range from 276 MPa to 379 MPa and a uniform elongation of at least 16%. Therefore, the oil country tubular good according to the invention has a high pipe expansion characteristic.

Abstract: The present invention provides a martensitic stainless steel in which specified elements in a steel composition are limited. The martensitic stainless steel can have high strength of 0.2% proof stress of 860 MPa or more and excellent carbon dioxide gas corrosion resistance and sulfide stress-corrosion cracking resistance by limiting the steel composition of specified elements and defining Mo content in the steel by relationships with IM values as well as by forming microstructure of the steel with main tempered martensite, carbide precipitated during tempering, and intermetallic compounds such as a Laves phase, a ? phase and the like. As a result the martensitic stainless steels of the present invention can be applied to practical steels, which can be widely used in oil well tubes and the like under environment including carbon dioxide gas, hydrogen sulfide, chlorine ions or two or more of them, in wide fields.

Abstract: A martensitic stainless steel comprising C: 0.01-0.10%, Si: 0.05-1.0%, Mn: 0.05-1.5%, P: not more than 0.03%, S: not more than 0.01%, Cr: 9-15%, Ni: 0.1-4.5%, Al: not more than 0.05% and N: not more than 0.1% in mass %, and further comprising at least one of Cu: 0.05-5% and Mo: 0.05-5%, the residual being Fe and impurities, is provided, wherein the contents of Cu and Mo satisfy the following formula (a) or (b), 0.2%?Mo+Cu/4?5%??(a) 0.55%?Mo+Cu/4?5%??(b) and wherein the hardness is 30-45 in HRC and the carbide amount in grain boundaries of the prior austenite is not more than 0.5 volume %. The marensitic stainless steel has excellent properties regarding the sulfide stress cracking resistance, the resistance to corrosive wear and the localized corrosion.

Abstract: A steel for oil well pipe, which has excellent resistance to localized corrosion in CO2 environments and corrosion in seawater, and a seamless pipe made of the steel. The steel includes, in weight %, more than 0.10 to 0.30% C, 0.10 to 1.0% Si, 0.1 to 3.0% Mn, 2.0 to 9.0% Cr, 0.01 to 0.10% Al and optionally 0.05 to 0.5% Cu, and the balance including Fe and incidental impurities including not more than 0.03% P and not more than 0.01% S. The steel has a substantially single phase martensitic structure in the as-quenched or as-normalized condition, and yield strength of not lower than 552 MPa in the as-quenched-tempered or as-normalized-tempered condition.

Abstract: A martensitic stainless steel pipe comprises, on the weight basis, C: 0.005 to 0.2%, Si: 1% or below, Mn: 0.1 to 5%, Cr: 7 to 15%, and Ni: 0 to 8%, wherein a wall thickness t (mm) and contents of C and Cr satisfy the relationship represented by the following equation (1).t(mm).ltoreq.exp{5.21-18.1C(%)-0.0407Cr(%)} (1)The steel pipe can be made by employing water quenching as a quenching method.

Abstract: Welded high-strength steel structure with excellent SSC and corrosion resistance in a wet carbon dioxide environment having a low H.sub.2 S concentration. A structure having a Vickers hardness of at most 350 and a joint tensile strength of at least 620 MPa and composed of a base metal comprising a martensitic stainless steel with a martensitic or tempered martensitic structure containing 0.001 to 0.05% C and 9 to 14% Cr and a weld metal comprising an austenitic-ferritic stainless steel having a duplex structure composed of austenite and 35 to 75% by volume of ferrite and containing 22 to 27% Cr,7 to 11% Ni and 1.5 to 5% Mo, and at most 0.03% C as an impurity.

Abstract: The present invention provides (1) diffusion bonding methods for joining metallic materials like carbon steels or stainless steels,interposing a bonding material, such as 10 to 80 .mu.m thick Ni-based alloy with the melting point of 1150.degree. C. or lower,between base materials, heating so that the length heated at 800.degree. C. or above measures from 3 to 20 mm, in case of joining stainless steels a bonded layer, further, being heated between the both melting points, and applying the compressive stress, for example 0.5 to 2 kgf/mm.sup.2, so that a lateral expansion ratio is made within 1.0 to 1.1, and (2) a joined structure having the bonded joint formed thereby.

Abstract: The method provides a diffusion-bonding of dual-phase stainless steel material having excellent strength and corrosion. The method includes: cold-working a material to be bonded so as to enhance the proof stress; inserting into the bonding portion an insert material; applying pressure thereto while performing shielding by mixed nitrogen/argon gas; heating the restricted bonding portion; cooling at a restricted rate; so as to form a bonded portion having the ferritic phase percentage of 30-70% by volume.

Abstract: A high-Cr and high-Ni alloy of the invention comprises the following chemical composition and has excellent corrosion resistance to hydrogen sulfide in an environment where a partial pressure of hydrogen sulfide is about 1 atm., or below and the temperature is about 150.degree. C. The alloy is free of any expensive Mo and W and is thus inexpensive, with the attendant feature that mass production is possible: Si: 0.05-1.0%, Mn: 0.1-1.5%, Cr: 20-30%, Ni: 20-40%, sol. Al: 0.01-0.3%, Cu: 0.5-5.0%, REM: 0-0.10%, Y: 0-0.20%, Mg: 0-0.10%, Ca: 0-0.10%, and balance: Fe and incidental impurities, provided that C, P and S in the incidental impurity are, respectively, 0.05% or below, 0.03% or below and 0.01% or below. As set out above, each of REM, Y, Mg and Ca do not have to be added at all. If these elements are used, one or more of REM, Y, Mg and Ca are added. Preferable ranges of the contents of these elements when added are such that REM: 0.001-0.10%, Y: 0.001-0.20%, Mg: 0.001-0.10%, and Ca: 0.001-0.10%.

Abstract: A super duplex stainless steel with low susceptibility to weld cracks and high weldability, as well as the resistance to stress corrosion cracking and toughness of the weld zones. The steel is therefore suitable for a wide range of applications including heat exchangers exposed to sea water, brine-resistant equipment and structures, pipings in chemical plants, line pipes, and oil well pipes. The steel includes, in weight %, 2.0% or less Si, 2.0% or less Mn, 22.0-24.0% Cr, 4.5-6.5% Ni, 4.0-4.8% Mo, 0.001-0.15% Al, and 0.25-0.35% N, the remains of Fe and inevitable impurities including 0.03% or less C, 0.05% or less P and 0.005% or less S, and a RVS, the index of susceptibility to cracking on welding, 7 or less, and a PREW, the index of pitting resistance, greater than 40.

Abstract: A low corrosion resistant pipe 1 is jointed with a high corrosion resistant pipe 2 directly or via a coupling 3. An insulating ceramic film having a thickness of 0.4 .mu.m and a resistivity of 10.sup.8 .OMEGA. cm or more is formed on the outer and inner surfaces of the pipes 1 and 2 at a length L of 60 mm or more from the end of the pipe and on the surface which forms a space when the pipes 1 and 2 are jointed at a coverage ratio of 90% or more to less than 100%.