Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
  • C21D9/085—Cooling or quenching
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the present invention relates to high-strength stainless steel seamless pipes for oil wells, which are suitable for use in crude oil or natural gas oil wells and gas wells (hereinafter simply referred to as "oil wells").
• 13Cr martensitic stainless steel pipes have been widely used as oil country tubular goods for mining in oil and gas fields in environments containing carbon dioxide gas (CO 2 ), chlorine ions (Cl - ), etc. Furthermore, in recent years, the use of improved 13Cr martensitic stainless steel with a composition system in which the C content of 13Cr martensitic stainless steel is reduced and the Ni, Mo, etc. are increased has also become widespread.
• Patent Documents 1 to 5 In response to such demands, there are technologies listed in Patent Documents 1 to 5, for example.
• Patent Document 1 discloses a stainless steel pipe for oil wells that has improved corrosion resistance by having a steel composition that contains, by mass%, C: 0.05% or less, Si: 0.50% or less, Mn: 0.20-1.80%, P: 0.03% or less, S: 0.005% or less, Cr: 14.0-18.0%, Ni: 5.0-8.0%, Mo: 1.5-3.5%, Cu: 0.5-3.5%, Al: 0.05% or less, V: 0.20% or less, N: 0.01-0.15%, O: 0.006% or less, and satisfies a specified formula, with the remainder being Fe and unavoidable impurities.
• Patent Document 2 also discloses a high-strength stainless steel seamless pipe for oil wells that contains, by mass%, C: 0.005-0.05%, Si: 0.05-0.50%, Mn: 0.20-1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 12.0-17.0%, Ni: 4.0-7.0%, Mo: 0.5-3.0%, Al: 0.005-0.10%, V: 0.005-0.20%, Co: 0.01-1.0%, N: 0.005-0.15%, and O: 0.010% or less, and that satisfies a specific formula, with the remainder being Fe and unavoidable impurities, and thus has a yield strength of 655 MPa or more.
• Patent Document 3 also describes the following composition by mass: C: 0.05% or less, Si: 0.50% or less, Mn: 0.10-1.80%, P: 0.03% or less, S: 0.005% or less, Cr: 14.0-17.0%, Ni: 5.0-8.0%, Mo: 1.0-3.5%, Cu: 0.5-3.5%, Al: 0.05% or less, V: 0.20% or less, N: 0.03-0.15%, O: 0
• a high-strength stainless steel pipe for oil wells is disclosed that has high strength and high corrosion resistance due to its composition containing 0.006% or less of C, one or two selected from 0.2% or less of Nb and 0.3% or less of Ti, the balance being Fe and unavoidable impurities, and having a structure in which MC-type carbonitrides in the precipitates account for 3.0% or more of the total precipitate amount by mass%.
• Patent Document 4 also discloses a high-strength stainless steel pipe for oil wells that has a composition containing Cr and Ni and a structure with tempered martensite as the main phase, the composition of which satisfies Cr/Ni ⁇ 5.3, and has a surface structure in which a phase that turns white when etched with a Virela etching solution has a thickness of 10 ⁇ m to 100 ⁇ m from the outer surface of the pipe in the wall thickness direction and is dispersed in an area ratio of 50% or more of the outer surface of the pipe.
• Patent Document 5 discloses a high-strength martensitic stainless steel seamless pipe for oil wells that contains, by mass%, C: 0.01% or less, Si: 0.5% or less, Mn: 0.1-2.0%, P: 0.03% or less, S: 0.005% or less, Cr: 14.0-15.5%, Ni: 5.5-7.0%, Mo: 2.0-3.5%, Cu: 0.3-3.5%, V: 0.20% or less, Al: 0.05% or less, N: 0.06% or less, with the balance being Fe and unavoidable impurities, and has a yield strength of 655-862 MPa and a yield ratio of 0.90 or more, and has improved resistance to carbon dioxide corrosion and sulfide stress corrosion cracking.
• seawater is often used for water injection because it is abundant. Chloride ions, dissolved oxygen, microorganisms, etc. present in seawater increase corrosiveness, so they are sometimes removed, but due to the cost, untreated seawater is sometimes used for water injection. High corrosion resistance is required for seamless steel pipes used in such environments, and the technologies described in Patent Documents 1 to 5, although having good resistance to carbon dioxide corrosion, did not have sufficient crevice corrosion resistance in untreated seawater environments. Furthermore, low-temperature toughness is also required due to the active development in cold regions and deep seas.
• the present invention aims to solve the problems of the conventional technology and provide a high-strength stainless steel seamless pipe for oil wells that has high strength, excellent low-temperature toughness, and excellent resistance to crevice corrosion in untreated seawater environments.
• high strength refers to a yield strength YS of 110 ksi (758 MPa) or more.
• excellent low-temperature toughness refers to a case where a Charpy impact test is performed on a V-notch test piece (10 mm thick) in accordance with the provisions of JIS Z 2242, with the test piece longitudinal direction perpendicular to the molding direction and the notch parallel to the molding direction, and the absorbed energy vE -10 at a test temperature of -10°C in the Charpy impact test is 40 J or more.
• excellent crevice corrosion resistance in untreated seawater refers to a case where a test piece with crevice is immersed in artificial seawater (liquid temperature: 25°C, atmospheric saturation at 1 atmospheric pressure) for 30 days, and the test piece after the corrosion test is observed for the presence or absence of crevice on the surface of the test piece using a 10x magnifying glass, and no crevice corrosion has occurred to a depth of 0.1 mm or more.
• the present inventors have conducted extensive research into the effects of various compositions of stainless steel pipes on crevice corrosion resistance in untreated seawater environments, and have found that the contents of Cr, Mo, Cu, Ni, W and Co in the composition of stainless steel materials must be adjusted to satisfy formula (1).
• Cr, Ni, Mo, W, Cu, and Co in formula (1) are the contents (mass %) of each element, and the content of elements that are not contained is zero.
• Cr, Ni, Mo, W, Cu, and Co in formula (1) are the contents (mass %) of each element, and the content of elements that are not contained is zero.
• Co and Nb in formula (2) are the contents (mass %) of each element.
• V 0.50% or less
• Ti 0.20% or less
• Zr 0.20% or less
• B 0.01% or less
• REM 0.01% or less
• Ca 0.0100% or less
• Sn 0.20% or less
• Sb 0.50% or less
• Ta 0.1% or less
• Mg 0.0100% or less.
• the present invention provides a high-strength stainless steel seamless pipe for oil wells that has high strength, excellent low-temperature toughness, and excellent resistance to crevice corrosion in untreated seawater.
• C is an important element for increasing the strength of martensitic stainless steel.
• the C content is set to 0.002% or more.
• the C content is preferably set to 0.010% or more, more preferably set to 0.015% or more, and further preferably set to 0.020% or more.
• the most preferable C content is 0.022% or more.
• the C content is set to 0.050% or less, preferably 0.040% or less, more preferably 0.035% or less, and further preferably 0.030% or less.
• the C content is most preferably 0.028% or less.
• Si 0.05-0.50% Silicon is an element that acts as a deoxidizer. This effect can be obtained with a silicon content of 0.05% or more. Therefore, the silicon content is set to 0.05% or more.
• the silicon content is preferably The Si content is set to 0.10% or more, more preferably 0.15% or more.
• the Si content is further preferably set to 0.20% or more, and most preferably set to 0.22% or more. %, the crevice corrosion resistance in the untreated seawater environment is deteriorated. Therefore, the Si content is set to 0.50% or less.
• the Si content is preferably set to 0.45% or less.
• the Si content is preferably 0.40% or less, more preferably 0.30% or less, and most preferably 0.25% or less.
• Mn 0.04-1.80% Mn is an element that suppresses the formation of ⁇ -ferrite during hot working and improves hot workability.
• the Mn content must be 0.04% or more.
• the Mn content is preferably 0.10% or more, more preferably 0.20% or more, and further preferably 0.25% or more.
• the Mn content is most preferably The Mn content is set to 0.35% or more.
• the Mn content is set to 1.80% or less. is preferably 1.60% or less, more preferably 0.80% or less, further preferably 0.60% or less, and most preferably 0.40% or less.
• P 0.030% or less
• P is an element that reduces crevice corrosion resistance in an untreated seawater environment. In the present invention, it is preferable to reduce it as much as possible, but an extreme reduction leads to an increase in manufacturing costs. For this reason, the P content is set to 0.030% or less as a range that can be implemented industrially at a relatively low cost without causing an extreme decrease in characteristics.
• the P content is 0.025% or less, more preferably 0.020% or less.
• the P content is further preferably 0.018% or less, and most preferably 0.015% or less.
• the lower limit of the P content is not particularly limited. However, as described above, an excessive reduction leads to an increase in manufacturing costs, so it is preferably 0.005% or more.
• S 0.0020% or less S significantly reduces hot workability and deteriorates low-temperature toughness by segregation to prior austenite grain boundaries, so it is preferable to reduce it as much as possible. If the S content is 0.0020% or less, the segregation of S to prior austenite grain boundaries can be suppressed, and the low-temperature toughness targeted in the present invention can be obtained. For this reason, the S content is set to 0.0020% or less. Preferably, the S content is set to 0.0015% or less. More preferably, the S content is set to 0.0010% or less, and further preferably, the S content is set to 0.0007% or less. The lower limit of the S content is not particularly limited. However, since excessive reduction leads to an increase in manufacturing costs, it is preferably set to 0.0005% or more.
• Cr:16.0 ⁇ 20.0% Cr is an element that forms a protective film and contributes to crevice corrosion resistance in an untreated seawater environment.
• the Cr content is required to be 16.0% or more.
• the Cr content is The Cr content is preferably 16.5% or more, more preferably 16.8% or more, and further preferably 17.0% or more.
• the Cr content is most preferably
• the Cr content exceeds 20.0%, the martensite transformation is not caused and the residual austenite is easily generated, which reduces the stability of the martensite phase.
• the ⁇ ferrite phase precipitates, significantly reducing hot workability.
• the Cr content is set to 20.0% or less.
• Cr Content The Cr content is preferably 19.5% or less, more preferably 19.0% or less, and further preferably 18.5% or less.
• the Cr content is most preferably 18.0% or less.
• Ni 4.0-7.5%
• Ni is an element that strengthens the protective film and improves crevice corrosion resistance in an untreated seawater environment. Ni also inhibits the precipitation of the ⁇ -ferrite phase and improves hot workability. In addition, Ni increases the strength of steel by dissolving in solid solution. This effect can be obtained with a Ni content of 4.0% or more. For this reason, the Ni content is set to 4.0% or more. The Ni content is preferably 5.0% or more, more preferably 6.0% or more, and further preferably 6.1% or more. The Ni content is most preferably 6.3% or more.
• Ni content exceeds 7.5%, the martensite transformation is not carried out and the residual austenite is easily generated, which reduces the stability of the martensite phase and decreases the strength.
• the Ni content is preferably 7.0% or less, and more preferably 6.5% or less.
• Mo 1.5-3.7%
• Mo is an element that increases resistance to pitting corrosion caused by Cl- or low pH.
• the Mo content must be 1.5% or more. If the Mo content is less than 1.5%, severe corrosion will occur. However, Mo content is not sufficient to prevent deterioration of carbon dioxide corrosion resistance and crevice corrosion resistance in a severe corrosive environment. Therefore, the Mo content is set to 1.5% or more.
• the Mo content is preferably set to 2.0% or more, and more preferably 2.0% or more.
• the Mo content is preferably 2.2% or more, and more preferably 2.5% or more.
• the Mo content is most preferably 2.7% or more.
• the Mo content of more than 3.7% increases ⁇ It generates ferrite, which leads to deterioration of hot workability, carbon dioxide corrosion resistance, and SSC resistance in a low temperature environment. For this reason, the Mo content is set to 3.7% or less.
• the Mo content is preferably The Mo content is set to 3.5% or less, more preferably 3.3% or less, and further preferably 3.0% or less.
• the Mo content is most preferably set to 2.8% or less.
• Al 0.005-0.10%
• Al is an element that acts as a deoxidizer. This effect can be obtained by including 0.005% or more of Al. Therefore, the Al content is set to 0.005% or more.
• the Al content is The Al content is preferably 0.01% or more, more preferably 0.015% or more.
• the Al content is further preferably 0.017% or more, and most preferably 0.02% or more. If the Al content exceeds 10%, the amount of oxides becomes too large, adversely affecting the crevice corrosion resistance. Therefore, the Al content is set to 0.10% or less.
• the Al content is preferably The Al content is set to 0.05% or less, more preferably 0.04% or less, and further preferably 0.03% or less.
• the Al content is most preferably set to 0.025% or less.
• N 0.002-0.15%
• the N content is 0.002% or more.
• the N content is preferably 0.01% or more, more preferably 0.02% or more.
• the N content is further preferably 0.03% or more, and most preferably
• the N content is set to 0.15%.
• the N content is preferably 0.12% or less, more preferably 0.10% or less, and further preferably 0.08% or less.
• the N content is most preferably 0.06% or less. % or less.
• Co is an element that improves crevice corrosion resistance. Such an effect can be obtained by including 0.2% or more of Co. Therefore, the Co content is set to 0.2% or more.
• the Co content is preferably 0.25% or more, more preferably 0.3% or more, further preferably 0.35% or more, and most preferably 0.4% or more.
• the Co content is set to 1.0% or less.
• the Co content is preferably The Co content is preferably 0.8% or less, more preferably 0.7% or less.
• the Co content is further preferably 0.65% or less, most preferably 0.6% or less.
• Nb 0.005-0.20%
• Nb is an element that increases the Ms point and is necessary to achieve both crevice corrosion resistance and high strength. Such an effect can be obtained by including 0.005% or more of Nb.
• the Nb content is set to 0.005% or more, preferably 0.01% or more, more preferably 0.05% or more, and further preferably 0.07% or more.
• the Nb content is most preferably 0.09% or more.
• the Nb content is set to 0.20% or less.
• the Nb content is preferably 0.17% or less, more preferably 0.15% or less, and further preferably 0.13% or less.
• the Nb content is most preferably 0.11% or less. do.
• O (oxygen) 0.010% or less
• O (oxygen) exists as an oxide in steel and has a detrimental effect on various properties. For this reason, it is desirable to reduce O as much as possible.
• the O content exceeds 0.010%, the crevice corrosion resistance is significantly reduced.
• the O content is set to 0.010% or less.
• the O content is set to 0.007% or less, more preferably 0.004% or less.
• the O content is further preferably 0.003% or less, and most preferably 0.002% or less. Since excessive reduction leads to an increase in manufacturing costs, it is preferably set to 0.0005% or more.
• Cu 3.5% or less
• W 3.5% or less
• Cu 3.5% or less
• Cu is an element that strengthens the protective film and enhances crevice corrosion resistance, and can be contained as necessary. Since such an effect can be obtained by containing 0.5% or more of Cu, the Cu content is preferably 0.5% or more, more preferably 0.7% or more. The Cu content is further preferably 1.0% or more, and most preferably 1.2% or more. On the other hand, the Cu content exceeding 3.5% leads to grain boundary precipitation of CuS, and the hot workability is reduced. For this reason, the Cu content is 3.5% or less.
• the Cu content is preferably 3.0% or less, more preferably 2.5% or less, and even more preferably 2.0% or less.
• the Cu content is most preferably 1.5% or less.
• W 3.5% or less W is an element that contributes to increasing strength and enhances crevice corrosion resistance, and can be contained as necessary. Since such effects can be obtained by containing 0.05% or more of W, the W content is preferably 0.05% or more, more preferably 0.2% or more, even more preferably 0.3% or more, and most preferably 0.5% or more. On the other hand, even if W is contained in an amount exceeding 3.5%, the effect is saturated. For this reason, the W content is 3.5% or less.
• the W content is preferably 3.0% or less, more preferably 2.0% or less, and even more preferably 1.5% or less.
• the W content is most preferably 1.0% or less.
• one or two selected from Cu: 3.5% or less and W: 3.5% or less means, when Cu and W are contained, Cu: 3.5% or less and W: 3.5% or less, and when one of Cu and W exceeds 3.5%, it is a comparative example.
• Cr, Ni, Mo, W, Cu and Co are contained within the above-mentioned ranges and so as to satisfy the following formula (1).
• Cr, Ni, Mo, W, Cu and Co in formula (1) are the contents (mass %) of each element, and the content of elements that are not contained is zero.
• the left side value of the formula (1) ("Cr + 0.22 ⁇ Ni + 0.38 ⁇ (Mo + 0.5 ⁇ W) + If the value of "0.89 x Cu + 0.09 x Co" is less than 21.4, the crevice corrosion resistance in an untreated seawater environment is reduced.
• the left side value of formula (1) is 21.4 or more.
• the left side value of formula (1) is preferably 21.6 or more, more preferably 21.8 or more, and even more preferably 22.0 or more.
• the left side value of formula (1) is preferably 26.0 or less. More preferably, it is 24.0 or less, and even more preferably, it is 23.8 or less.
• Co and Nb are contained within the above-mentioned ranges and so as to satisfy the following formula (2).
• Co and Nb in formula (2) are the contents (mass %) of each element.
• the desired crevice corrosion resistance in an untreated seawater environment can be obtained by setting the value of the left side of formula (1) to 21.4 or more.
• adding Nb is effective for raising the Ms point, but if Nb is contained in excess, low-temperature toughness deteriorates.
• Co an element that improves crevice corrosion resistance without lowering the Ms point, in an amount of 0.13% or more more than Nb, it is possible to achieve both excellent crevice corrosion resistance, high strength, and low-temperature toughness.
• the value of the left side of formula (2) (the value of "Co-Nb") is less than 0.13, the low-temperature toughness value decreases.
• Co and Nb are contained so as to satisfy formula (2).
• the value on the left side of formula (2) is preferably 0.13 or more.
• the value on the left side of formula (2) is preferably 0.17 or more, more preferably 0.20 or more, and even more preferably 0.30 or more. There is no particular upper limit on the value on the left side of formula (2).
• the value on the left side of formula (2) is 1.00 or less. It is more preferable that the value on the left side of formula (2) is 0.80 or less.
• the remainder other than the above components consists of iron (Fe) and unavoidable impurities.
• the above-mentioned components are the basic components, and the high-strength stainless steel seamless pipe for oil wells of the present invention can obtain the desired properties with these basic components.
• the present invention can contain the following optional elements as necessary.
• Each of the following components V, Ti, Zr, B, REM, Ca, Sn, Sb, Ta, and Mg can be contained as necessary, so these components may be 0%.
• V 0.50% or less
• Ti 0.20% or less
• Zr 0.20% or less
• B 0.01% or less
• REM 0.01% or less
• Ca 0.0100% or less
• Sn 0.20% or less
• Sb 0.50% or less
• Ta 0.1% or less
• Mg 0.0100% or less.
• V 0.50% or less
• V is an element that improves the strength of steel by precipitation strengthening, and can be contained as necessary. This effect can be obtained by containing V at 0.005% or more, so the V content is preferably 0.005% or more.
• the V content is more preferably 0.03% or more, and even more preferably 0.04% or more.
• the V content is most preferably 0.05% or more.
• V content is 0.50% or less.
• the V content is preferably 0.40% or less, and more preferably 0.30% or less.
• the V content is more preferably 0.25% or less, and most preferably 0.20% or less.
• Ti 0.20% or less
• Ti is an element that exists in oxide-based or sulfide-based inclusions and improves the chemical stability of the inclusions to improve crevice corrosion resistance in an untreated seawater environment, and can be contained as necessary. Since such an effect can be obtained by containing 0.002% or more of Ti, the Ti content is preferably 0.002% or more. The Ti content is more preferably 0.003% or more. On the other hand, if Ti is contained in an amount exceeding 0.20%, TiN precipitates as an inclusion, and the crevice corrosion resistance is deteriorated conversely. Therefore, when Ti is contained, the Ti content is 0.20% or less.
• the Ti content is preferably 0.15% or less, more preferably 0.10% or less.
• the Ti content is further preferably 0.07% or less, and most preferably 0.05% or less.
• Zr 0.20% or less
• Zr is an element that contributes to increasing strength, and can be contained as necessary. Such an effect can be obtained by containing 0.01% or more of Zr. Therefore, the Zr content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, even if Zr is contained in an amount exceeding 0.20%, the effect is saturated. Therefore, when Zr is contained, the Zr content is 0.20% or less.
• the Zr content is preferably 0.17% or less, more preferably 0.13% or less, and even more preferably 0.10% or less.
• the Zr content is most preferably 0.07% or less.
• B 0.01% or less
• B is an element that contributes to increasing strength, and can be contained as necessary. Since such an effect can be obtained by containing 0.0005% or more of B, the B content is preferably 0.0005% or more. More preferably, it is 0.001% or more. Even more preferably, it is 0.002% or more. On the other hand, if B is contained in excess of 0.01%, the hot workability decreases. Therefore, when B is contained, the B content is 0.01% or less.
• the B content is preferably 0.007% or less, more preferably 0.005% or less.
• the B content is even more preferably 0.003% or less.
• REM 0.01% or less REM (rare earth metal) is an element that contributes to improving crevice corrosion resistance, and can be contained as necessary. Since such an effect can be obtained by containing 0.0005% or more of REM, the content is preferably 0.0005% or more. More preferably, the content is 0.001% or more. The REM content is further preferably 0.0015% or more. On the other hand, even if the REM content exceeds 0.01%, the effect is saturated and the effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when REM is contained, the REM content is 0.01% or less. The REM content is more preferably 0.007% or less. The REM content is further preferably 0.005% or less, and most preferably 0.003% or less.
• Ca 0.0100% or less
• Ca is an element that contributes to improving crevice corrosion resistance, and can be contained as necessary. Such an effect can be obtained by containing 0.0005% or more of Ca.
• the Ca content is preferably 0.0005% or more.
• the Ca content is more preferably 0.0010% or more.
• the Ca content is even more preferably 0.0015% or more.
• the Ca content is more preferably 0.0070% or less.
• the Ca content is even more preferably 0.0050% or less, and most preferably 0.0030% or less.
• Sn 0.20% or less
• Sn is an element that contributes to improving crevice corrosion resistance, and can be contained as necessary. Since such an effect can be obtained by containing 0.02% or more of Sn, the Sn content is preferably 0.02% or more, more preferably 0.05% or more. The Sn content is further preferably 0.07% or more. On the other hand, even if the Sn content exceeds 0.20%, the effect is saturated, and the effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when Sn is contained, the Sn content is 0.20% or less. The Sn content is more preferably 0.15% or less. The Sn content is further preferably 0.13% or less, and most preferably 0.10% or less.
• Sb 0.50% or less
• Sb is an element that contributes to improving crevice corrosion resistance, and can be contained as necessary. Since such an effect can be obtained by containing 0.02% or more of Sb, the Sb content is preferably 0.02% or more. More preferably, it is 0.05% or more. On the other hand, even if Sb is contained in an amount exceeding 0.50%, the effect is saturated, and the effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when Sb is contained, the Sb content is 0.50% or less.
• the Sb content is preferably 0.40% or less, more preferably 0.30% or less, and even more preferably 0.15% or less.
• the Sb content is most preferably 0.10% or less.
• Ta 0.1% or less
• Ta is an element that increases strength and has the effect of improving crevice corrosion resistance.
• Ta is an element that brings about the same effect as Nb, and part of Nb can be replaced with Ta. Since such an effect can be obtained by containing 0.01% or more of Ta, the Ta content is preferably 0.01% or more.
• the Ta content is more preferably 0.03% or more.
• the Ta content is further preferably 0.04% or more.
• the Ta content is if Ta is contained in an amount exceeding 0.1%, the low temperature toughness decreases. Therefore, when Ta is contained, the Ta content is 0.1% or less.
• the Ta content is preferably 0.09% or less, more preferably 0.07% or less.
• the Ta content is further preferably 0.06% or less, and most preferably 0.05% or less.
• Mg 0.0100% or less
• Mg is an element that improves crevice corrosion resistance and can be contained as necessary. Since such an effect can be obtained by containing 0.0002% or more of Mg, the Mg content is preferably 0.0002% or more, more preferably 0.0004% or more. On the other hand, even if the Mg content exceeds 0.0100%, the effect is saturated and an effect commensurate with the content cannot be expected. Therefore, when Mg is contained, the Mg content is preferably 0.0100% or less.
• the Mg content is preferably 0.0080% or less, more preferably 0.0050% or less, and even more preferably 0.0020% or less.
• the Mg content is most preferably 0.0010% or less.
• the steel pipe structure of the high-strength stainless steel seamless pipe for oil wells of the present invention is not particularly limited, and it is preferable that the structure be, for example, as follows.
• the high-strength stainless steel seamless pipe for oil wells of the present invention preferably has a steel pipe structure consisting of a martensite phase (tempered martensite phase), a retained austenite phase, and a ferrite phase.
• the area fraction of the retained austenite phase is preferably 32% or less.
• the area fraction of the retained austenite phase is more preferably 30% or less, and even more preferably 28% or less.
• the lower limit is preferably 1% or more. If only a small amount of ferrite phase is present, strain is concentrated in the ferrite phase during hot working, reducing hot workability, so the area fraction is preferably 14% or more.
• the area fraction of the ferrite phase is more preferably 16% or more, and even more preferably 18% or more.
• the upper limit is preferably 50% or less.
• Each of the above-mentioned tissues can be measured by the following method.
• a test piece for microstructural observation was taken from the center of the wall thickness of a cross section perpendicular to the tube axis direction, and corroded with Villela's reagent (a mixture of picric acid, hydrochloric acid, and ethanol in proportions of 2 g, 10 ml, and 100 ml, respectively).
• the structure was then imaged using a scanning electron microscope (magnification: 1000 times), and the structure fraction (area %) of the ferrite phase was calculated using an image analyzer.
• the test piece for X-ray diffraction is then ground and polished so that the cross section (C cross section) perpendicular to the tube axis direction becomes the measurement surface, and the amount of retained austenite ( ⁇ ) is measured using X-ray diffraction.
• the amount of retained austenite is determined by measuring the integrated intensity of diffracted X-rays from the (220) plane of ⁇ and the (211) plane of ⁇ (ferrite), and converting it using the following formula. Note that the volume fraction of retained austenite is regarded as the area fraction here.
• ⁇ (volume ratio) 100/(1+(I ⁇ R ⁇ /I ⁇ R ⁇ ))
• I ⁇ is the integrated intensity of ⁇
• R ⁇ is the theoretically calculated value of ⁇
• I ⁇ is the integrated intensity of ⁇
• R ⁇ is the theoretically calculated value of ⁇
• the fraction (area %) of the martensite phase is the remainder other than the ferrite phase and the residual gamma phase.
• the fraction of the martensite phase is preferably 18% or more in area percentage. It is more preferably 30% or more. It is also preferably 85% or less. It is more preferably 75% or less.
• the temperature refers to the surface temperature of the steel pipe material and the steel pipe (seamless steel pipe after pipe making) unless otherwise specified. These surface temperatures can be measured with a radiation thermometer or the like.
• the starting material is a steel pipe material having the above-mentioned composition.
• the manufacturing method of the starting steel pipe material there are no particular limitations on the manufacturing method of the starting steel pipe material.
• the heating temperature is preferably in the range of 1100 to 1350°C. If the heating temperature is less than 1100°C, the hot workability decreases and many defects occur during pipe making. Therefore, the heating temperature is preferably 1100°C or higher, more preferably 1150°C or higher. The heating temperature is even more preferably 1170°C or higher, and most preferably 1200°C or higher. On the other hand, if the heating temperature exceeds 1350°C and becomes too high, the crystal grains become coarse and the low-temperature toughness decreases. Therefore, the heating temperature in the heating process is preferably 1350°C or lower. The heating temperature is more preferably 1300°C or lower. The heating temperature is even more preferably 1280°C or lower, and most preferably 1250°C or lower.
• the seamless steel pipe is cooled to room temperature at a cooling rate faster than air cooling. This ensures that the steel pipe structure has martensite as the main phase.
• the steel pipe (seamless steel pipe after pipe making) is preferably subjected to heat treatment (quenching treatment, tempering treatment). Specifically, it is preferable to perform a quenching treatment on the steel pipe (seamless steel pipe after pipe making) by reheating to a temperature (heating temperature) in the range of 850°C to 1120°C, holding the temperature for a predetermined time, and then cooling at a cooling rate faster than air cooling until the surface temperature of the steel pipe reaches a temperature of 100°C or less (cooling stop temperature).
• the "cooling rate faster than air cooling” is 0.01°C/s or more.
• the reheating temperature is preferably set to 850° C. or higher.
• the reheating temperature (heating temperature of the quenching treatment) is more preferably 870°C or higher in order to prevent coarsening of the structure and dissolve the intermetallic compounds. It is even more preferably 900°C or higher.
• the reheating temperature is most preferably 950°C or higher. It is preferable that the temperature be in the range of 1120°C or lower.
• the reheating temperature is more preferably 1100°C or lower, even more preferably 1050°C or lower, and most preferably 1000°C or lower.
• the steel pipe it is preferable to hold the steel pipe at the reheating temperature mentioned above for 5 minutes or more. It is more preferable to set the holding time to 10 minutes or more, and even more preferable to set the holding time to 15 minutes or more. Furthermore, the holding time is preferably 30 minutes or less. It is more preferable to set the holding time to 25 minutes or less, and even more preferable to set the holding time to 20 minutes or less.
• the cooling stop temperature after quenching is 100°C or less.
• the cooling stop temperature is more preferably 75°C or less, and even more preferably 50°C or less.
• the cooling stop temperature is preferably 30°C or more, and more preferably 40°C or more.
• the steel pipe that has been subjected to the above-mentioned quenching treatment is then subjected to a tempering treatment.
• the tempering treatment is preferably a process in which the pipe is heated to a temperature (tempering temperature) of 500°C or higher and 650°C or lower, held for a predetermined period of time, and then air-cooled.
• a temperature tempering temperature
• other cooling methods such as water cooling, oil cooling, mist cooling, etc. may also be used.
• the tempering temperature is preferably 500°C or higher.
• the tempering temperature is more preferably 530°C or higher.
• the tempering temperature is even more preferably 550°C or higher, and most preferably 570°C or higher. This makes it easier for the steel pipe structure to have tempered martensite phase as the main phase, resulting in a seamless steel pipe with the strength and crevice corrosion resistance desired in the present invention.
• the tempering temperature is preferably 650°C or lower.
• the tempering temperature is more preferably 640°C or lower. Even more preferably, it is 620°C or lower.
• the tempering temperature is most preferably 600°C or lower.
• the steel pipe at the above-mentioned tempering temperature for 10 minutes or more.
• the holding time is preferably 90 minutes or less.
• the above quenching and tempering treatments may be repeated two or more times. This improves the low-temperature toughness value.
• a high-strength stainless steel seamless pipe for oil wells can be obtained, which has an absorbed energy vE -10 of 40 J or more at a test temperature of -10°C in a Charpy impact test, excellent crevice corrosion resistance in untreated seawater, and high strength of a yield strength YS of 758 MPa or more.
• the absorbed energy vE -10 at a test temperature of -10°C in the Charpy impact test is 40 J or more.
• the absorbed energy vE- 10 at a test temperature of -10°C in the Charpy impact test is preferably 50 J or more, more preferably 60 J or more, and even more preferably 70 J or more.
• the upper limit is not particularly limited, but may be 200 J or less.
• the yield strength YS is 758 MPa or more.
• the yield strength YS is preferably 800 MPa or more, and more preferably 850 MPa or more.
• the upper limit is not particularly limited, but may be 1000 MPa or less.
• the intermediate products (billets, etc.) produced during the manufacturing process of the product have excellent hot workability.
• the hot workability can be evaluated by the following method. A round bar test piece having a parallel section diameter of 10 mm taken from a steel pipe material (cast piece) was heated to 1250°C in a Gleeble tester, held for 100 seconds, cooled to 1000°C at 1°C/sec, held for 10 seconds, and then pulled until fractured to measure the reduction in area (%). The smaller the reduction in area, the worse the hot workability.
• the reduction in area is preferably 60% or more. More preferably, it is 70% or more.
• the reduction in area is preferably 90% or less. More preferably, it is 85% or less.
• test specimen materials were cut out from the steel obtained by hot working.
• the dimensions of the steel were length: 1100 mm, width: 160 mm, and thickness: 15 mm.
• Each test specimen material was heated at the heating temperature (reheating temperature) and soaking time shown in Table 2, and then quenched by air cooling to the cooling stop temperature shown in Table 2.
• tempering was performed by heating at the tempering temperature and soaking time shown in Table 2, and then air cooling.
• Some test specimens (steel pipes No. 2 and 4) were quenched and tempered twice under the conditions shown in Table 2. Note that the cut test specimens were quenched and tempered, but this can be considered to be the same as when a seamless steel pipe is quenched and tempered.
• test piece with an absorbed energy vE -10 of 40J or more at -10°C was evaluated as having high toughness and was deemed to have passed.
• test piece with a vE -10 of less than 40J was deemed to have failed.
• a test piece for microstructure observation was prepared from the test piece material that had been subjected to quenching and tempering, and each structure was measured.
• the observation surface of the structure was a cross section (C cross section) perpendicular to the rolling direction.
• the test piece for microstructure observation was corroded with Villela's reagent (a reagent made by mixing picric acid, hydrochloric acid, and ethanol in the ratio of 2 g, 10 ml, and 100 ml, respectively), and the structure was imaged with a scanning electron microscope (accelerating voltage: 15 kV, magnification: 1000 times), and the structure fraction (area %) of the ferrite phase was calculated using an image analyzer (Image-J).
• the test piece for X-ray diffraction was ground and polished so that the cross section (C cross section) perpendicular to the rolling direction was the measurement surface, and the amount of retained austenite ( ⁇ ) was measured using an X-ray diffraction method.
• the amount of retained austenite was determined by measuring the integrated intensity of the diffracted X-rays of the (220) plane of ⁇ and the (211) plane of ⁇ (ferrite) and converting it using the following formula.
• the volume fraction of the retained austenite was regarded as the area fraction.
• ⁇ (volume ratio) 100/(1+(I ⁇ R ⁇ /I ⁇ R ⁇ ))
• I ⁇ is the integrated intensity of ⁇
• R ⁇ is the theoretically calculated value of ⁇
• I ⁇ is the integrated intensity of ⁇
• R ⁇ is the theoretically calculated value of ⁇ .
• the fraction (area %) of the martensite phase (tempered martensite phase) was defined as the remainder other than the ferrite phase and the residual ⁇ phase.

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