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 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 martensitic stainless steel having a C content of 0.01 to 0.1 mass %, a Cr content of 9 to 15 mass % and a N content of not more than 0.1 mass %, wherein the maximum length of the carbides in the steel is 10 to 200 nm in the direction of the minor axis, or wherein the ratio of the average Cr concentration [Cr] to the average Fe concentration [Fe] in carbides in the steel ([Cr]/[Fe]) is not more than 0.4, or wherein the content of M23C6 type carbides is not more than 1 volume %, the content of M3C type carbides is 0.01 to 1.5 volume % and the content of MN type or M2N type nitrides is not more than 0.3 volume % is provided. This stainless steel has a high toughness in spite of both a relatively more C content and a high strength, thereby providing a, wide applicability to pipe material for oil wells containing carbon dioxide and a small amount of hydrogen sulfide, in particular for oil wells having a much greater depth.

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 martensitic stainless steel having a C content of 0.01 to 0.1 mass %, a Cr content of 9 to 15 mass % and a N content of not more than 0.1 mass %, wherein the maximum length of the carbides in the steel is 10 to 200 nm in the direction of the minor axis, or wherein the ratio of the average Cr concentration [Cr] to the average Fe concentration [Fe] in carbides in the steel ([Cr]/[Fe]) is not more than 0.4, or wherein the content of M23C6 type carbides is not more than 1 volume %, the content of M3C type carbides is 0.01 to 1.5 volume % and the content of MN type or M2N type nitrides is not more than 0.3 volume % is provided. This stainless steel has a high toughness in spite of both a relatively more C content and a high strength, thereby providing a, wide applicability to pipe material for oil wells containing carbon dioxide and a small amount of hydrogen sulfide, in particular for oil wells having a much greater depth.

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 pipe is provided which is excellent in resistance to outer surface stress corrosion cracking (SCC) when used for a pipeline without impairing the fundamental requirement for the steel as a pipeline. The steel pipe has a surface adjusted to have a mean line roughness Ra of up to 7 &mgr;m and a maximum height Rmax of up to 50 &mgr;m. The surface is adjusted by sand blasting to have this roughness.

Abstract: This invention relates to a large-diameter, thick-wall martensitic stainless steel welded pipe. For this welded pipe, the size of the raised weld bead portion on the inside surface is restricted to be small based on a conditional formula derived by considering the bead width and height and the yield strength of the base metal and of the weld metal. As a result, the base metal portion and pipe inside surface seam portion of this welded pipe are superior in corrosion resistance, in particular stress corrosion cracking resistance (SCC resistance). The sulfide stress corrosion resistance (sour gas resistance) and carbon dioxide corrosion resistance can be further improved by selecting the chemical compositions. This welded pipe is very well suited for use as a pipe for a pipeline for conveying a crude oil and a natural gas with no dehydration treatment, which is highly corrosive to metals.

Abstract: This invention relates to a large-diameter, thick-wall martensitic stainless steel welded pipe. For this welded pipe, the size of the raised weld bead portion on the inside surface is restricted to be small based on a conditional formula derived by considering the bead width and height and the yield strength of the base metal and of the weld metal. As a result, the base metal portion and pipe inside surface seam portion of this welded pipe are superior in corrosion resistance, in particular stress corrosion cracking resistance (SCC resistance). The sulfide stress corrosion resistance (sour gas resistance) and carbon dioxide corrosion resistance can be further improved by selecting the chemical compositions. This welded pipe is very well suited for use as a pipe for a pipeline for conveying a crude oil and a natural gas with no dehydration treatment, which is highly corrosive to metals.

Abstract: A low alloy steel for oil country tubular well which has a yield stress of 110 ksi or above, and excellent sulfide stress cracking resistance. The low alloy steel comprises, by weight, 0.2 to 0.35% carbon, 0.2 to 0.7% chromium, 0.1 to 0.5% molybdenum, 0.1 to 0.3% vanadium, 0 to 0.5% silicon, 0 to 1% manganese, 0 to 0.1% aluminum, 0 to 0.1% niobium, 0 to 0.05% titanium, 0 to 0.005% boron, 0 to 0.1% zirconium, 0 to 1% tungsten, 0 to 0.01% calcium, 0.025% or less phosphorus, 0.01% or less sulfur, 0.01% or less nitrogen, and 0.01% or less oxygen. The low alloy steel further comprises a total amount of precipitated carbides between about 2 to 5% by weight, and a ratio of the MC type carbide to the total amount of the precipitated carbides is between about 8 to 40% by weight.

Abstract: A hot rolled martensite stainless steel plate which is excellent in formability and corrosion resistance has a chemical composition comprising, by mass %, 0.05% or less carbon, 10 to 15% chromium, 0 to 3% molybdenum, 0 to 0.75% titanium, and 1 to 8% nickel, with the balance being iron and impurities, and has a yield stress of 110 ksi (758 MPa) or less and a specific amount of austenitic phase according to the plate thickness.

Abstract: A process for producing a seamless steel pipe wherein pipe manufacturing steps and the heat treatment steps are carried out in one production line. The properties of the pipe are comparative or superior to those of the pipe manufactured in the conventional reheating, quenching and tempering process. The process is characterized by using the billet of a low alloy steel containing C: 0.15-0.50%, Cr: 0.1-1.5%, Mo: 0.1-1.5%, Al: 0.005-0.50%, Ti: 0.005-0.50% and Nb: 0.003-0.50%, and comprising the following steps (1) to (5).(1) hot rolling with 40% or more of cross sectional reduction ratio,(2) finishing the hot rolling in a temperature range of 800-1100.degree. C.,(3) putting the manufactured steel pipe promptly in a complementary heating apparatus after the finish rolling, and complementarily heating at the temperature and time satisfying the following formula (a).

Abstract: A steel product, such as a steel pipe for line-pipe, excellent in sulfide cracking resistance sufficient to accept a CAPCIS test. The steel product is manufactured by rolling or forging to have a matrix not including B type inclusions having lengths of 200 .mu.m or more in the longitudinal direction.Furthermore, the steel pipe is manufactured by rolling or forging to have a matrix not including B type inclusions having dimensions of 200 .mu.m or more in the longitudinal direction within 4 mm of the inner surface.

Abstract: A martensitic stainless steel for use in oil wells has improved stability in strength and good resistance to sulfide stress corrosion cracking The steel has a chemical composition consisting essentially, on a weight basis, of: Si: not greater than 1.0%, Mn: not greater than 1.0%, Cr: 10.0-14.0%, Mo: 0.5-7.0%, Ni: 4.0-8.0%, Al: 0.001-0.1%, either Ti in an amount satisfying the following inequality (1) or Zr in an amount satisfying the following inequality (2), optionally one or both of Mg: 0.001-0.05% and Ce: 0.001-0.05%, and a balance of Fe and incidental impurities in which the contents of C, P, S, N, and V as impurities are limited to 0.05% or less, 0.04% or less, 0.005% or less, 0.05% or less, and 0.2% or less, respectively, the composition further satisfying the following inequalities (3) and (4):4(%C).ltoreq.%Ti.ltoreq.{-0.01/(%C+0.015))}+0.75 (1)10(%C).ltoreq.%Zr.ltoreq.2 0% (2)30(%Cr)+36(%Mo)+14(%Si)-28(%Ni).ltoreq.455 (3)21(%Cr)+25(%Mo)+17(%Si)+35(%Ni).ltoreq.731 (4).