EP4578564A1 - Stahlrohr für ein leitungsrohr mit hervorragenden wasserstoffversprödungsbeständigkeitseigenschaften, verfahren zur herstellung davon, stahlmaterial für ein leitungsrohr und verfahren zur herstellung davon - Google Patents

Stahlrohr für ein leitungsrohr mit hervorragenden wasserstoffversprödungsbeständigkeitseigenschaften, verfahren zur herstellung davon, stahlmaterial für ein leitungsrohr und verfahren zur herstellung davon Download PDF

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Publication number
EP4578564A1
EP4578564A1 EP23872572.5A EP23872572A EP4578564A1 EP 4578564 A1 EP4578564 A1 EP 4578564A1 EP 23872572 A EP23872572 A EP 23872572A EP 4578564 A1 EP4578564 A1 EP 4578564A1
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EP
European Patent Office
Prior art keywords
less
steel
temperature
steel pipe
steel material
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Application number
EP23872572.5A
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English (en)
French (fr)
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EP4578564A4 (de
Inventor
Hiroshi Okano
Yoshihiro Nishihara
Naho INOUE
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JFE Steel Corp
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JFE Steel Corp
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Publication of EP4578564A1 publication Critical patent/EP4578564A1/de
Publication of EP4578564A4 publication Critical patent/EP4578564A4/de
Pending legal-status Critical Current

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    • 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
    • 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
    • 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
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • 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")
    • 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
    • C21D1/26—Methods of annealing
    • 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
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C21D9/085—Cooling or quenching
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/005—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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/42—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
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/48—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
    • C22C38/54—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
    • C22C38/18—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
    • 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
    • C21D2211/002—Bainite
    • 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 a steel pipe for a line pipe with high hydrogen embrittlement resistance, a method for producing the steel pipe, a steel material for a line pipe, and a method for producing the steel material, suitable for applications, such as a line pipe for transporting hydrogen gas.
  • a steel material used in such an environment has a concern about the occurrence of "hydrogen embrittlement” in which hydrogen enters the steel and degrades its characteristics.
  • hydrogen embrittlement in which hydrogen enters the steel and degrades its characteristics.
  • An austenite stainless steel such as SUS 316L, which is more resistant to hydrogen embrittlement than low-alloy steels, has been used for a steel structure used in a high-pressure hydrogen gas environment.
  • an austenite stainless steel such as SUS 316L
  • SUS 316L is high in steel material cost and has low strength, and when designed to withstand a high hydrogen pressure, has a large wall thickness and results in an increased price of a structure for hydrogen itself.
  • a steel for a high-pressure hydrogen environment described in Patent Literature 1 is a steel used in a high-pressure hydrogen environment, in which Ca/S is less than 1.5 or 11 or more to reduce a relative concentration of diffusible hydrogen and suppress embrittlement due to diffusible hydrogen.
  • Patent Literature 2 discloses a technique of finding that a low-alloy high-strength steel adjusted to have a specific chemical composition has, within the tensile strength range of 900 to 950 MPa in the atmosphere, increased drawing and elongation as compared with JIS G 3128 SHY685NS in a 45-MPa hydrogen atmosphere and improve high-pressure hydrogen environment embrittlement resistance.
  • a Cr-Mo high-strength low-alloy steel described in Patent Literature 3 is a low-alloy high-strength steel with good elongation and drawing characteristics even in a 45-MPa hydrogen atmosphere and with high high-pressure hydrogen environment embrittlement resistance provided by tempering at a relatively high temperature of 560°C to 580°C to adjust the grain size number after tempering to 8.4 or more and the tensile strength in a very narrow range of 900 to 950 MPa.
  • Patent Literature 5 proposes a steel for a high-pressure hydrogen gas storage container with high hydrogen resistance. According to the technique described in Patent Literature 5, stress relief annealing for an extended period after normalizing treatment in the production of a steel sheet finely and densely disperses and precipitates an MC carbide (Mo, V)C and improves the hydrogen resistance, such as hydrogen embrittlement resistance, of the steel.
  • MC carbide Mo, V
  • Patent Literature 6 proposes a steel material with a metallic microstructure composed of 90% or more by area of a bainite-based microstructure in which cementite with an average grain size of 50 nm or less and an average aspect ratio of 3 or less is dispersedly precipitated in the bainite.
  • Non Patent Literature 1 it is known that the fatigue life of a material decreases in a high-pressure hydrogen environment. This means that the service life of a line pipe material decreases when the line pipe material is designed on the basis of a conventional natural gas line pipe.
  • the related art described above can suppress the occurrence of hydrogen-induced cracking in a sour environment but cannot sufficiently increase the fatigue strength in hydrogen gas. Therefore, there is a problem in that it is difficult to achieve both the suppression of the occurrence of hydrogen-induced cracking in a sour environment and high fatigue strength in hydrogen gas.
  • a steel pipe for a line pipe with high strength and high hydrogen embrittlement resistance in a high-pressure hydrogen gas environment a method for producing the steel pipe, a steel material for a line pipe, and a method for producing the steel material, suitable for a steel structure used in a high-pressure hydrogen gas environment, such as a line pipe for 100% hydrogen gas or a natural gas containing hydrogen at a hydrogen partial pressure of 1 MPa or more (natural gas is a gas containing hydrocarbons, such as methane and ethane, as main components).
  • the natural gas containing hydrogen at a hydrogen partial pressure of 1 MPa or more for example, has a hydrogen concentration of 30% or less by volume and
  • the fatigue limit stress in hydrogen in the above environment is 200 MPa or more and the fatigue limit stress in hydrogen of a steel material in the above environment/fatigue limit stress in an inert gas environment is 0.90 or more, it is possible to design a steel structure for hydrogen, such as a long-life line pipe, within a thickness range that is available by a process of producing a steel pipe, such as a seamless steel pipe or UOE.
  • steel material includes a steel sheet, a steel plate, a seamless steel pipe, an electric-resistance-welded steel pipe, a shaped steel, a steel bar, and the like.
  • the present inventors have extensively studied conditions to be satisfied by a steel material for producing a steel pipe for a line pipe and a steel material for a line pipe with high hydrogen embrittlement resistance and have invented a new steel pipe for a line pipe and a new steel material for a line pipe.
  • a steel pipe and a steel material according to the present invention have high strength.
  • the term "high strength”, as used herein, refers to a tensile strength of 520 MPa or more.
  • the gist of the present invention is as follows:
  • the present invention can easily and simply produce a steel pipe and a steel material with considerably improved hydrogen embrittlement resistance in a high-pressure hydrogen gas environment and exhibits industrially significant effects.
  • the present invention can considerably improve the hydrogen embrittlement resistance of a steel structure, such as a high-pressure hydrogen gas line pipe, improve the fatigue resistance, and greatly contributes to the extension of the life of the steel structure.
  • An implementation method for a steel pipe is more specifically described as a first embodiment, and then an implementation method for a steel material is more specifically described as a second embodiment.
  • the C content is an element necessary to increase strength.
  • the C content is 0.10% or more.
  • the C content is preferably 0.13% or more.
  • a C content of more than 0.45% may result in quenching crack during quenching, and the C content is therefore 0.45% or less.
  • the C content is preferably 0.25% or less, more preferably 0.20% or less, still more preferably 0.17% or less.
  • the Si is added for deoxidization, but the deoxidization effect is not sufficient at a Si content of less than 0.01%.
  • the Si content is 0.01% or more.
  • the Si content is preferably 0.08% or more, more preferably 0.1% or more.
  • the effect becomes saturated at a Si content of more than 2.0%, and the Si content is therefore 2.0% or less.
  • the Si content is preferably 1.8% or less, more preferably 1.0% or less.
  • more than 0.5% results in lower toughness or weldability, and the Si content is still more preferably 0.5% or less.
  • the Mn content effectively contributes to the improvement of strength and toughness, but the effect of addition is insufficient at a content of less than 0.5%.
  • the Mn content is 0.5% or more.
  • the Mn content is preferably 0.6% or more, more preferably 0.7% or more, still more preferably 0.8% or more.
  • more than 1.5% results in a decrease in SSCC resistance (resistance to sulfide stress corrosion cracking) and HIC (hydrogen-induced cracking) resistance due to an increase in the hardness of a surface layer portion or a center segregation zone during controlled cooling. Furthermore, weldability also deteriorates.
  • the Mn content is limited to 1.5% or less.
  • the Mn content is preferably 1.4% or less, more preferably 1.3% or less.
  • P is an incidental impurity element, reduces weldability, and reduces the HIC resistance due to an increase in the hardness of a center segregation zone. This tendency becomes remarkable at more than 0.015%, so that the upper limit of the P content is 0.015%.
  • the P content is preferably 0.010% or less, more preferably 0.008% or less. Although a lower P content is better, from the perspective of refining costs, the P content is 0.0001% or more.
  • S is an incidental impurity element, forms a MnS inclusion in steel, and reduces the HIC resistance, so that a lower S content is preferred, but 0.0015% or less is allowable.
  • the S content is 0.0015% or less.
  • the S content is preferably 0.0010% or less, more preferably 0.0008% or less. Although a lower S content is better, from the perspective of refining costs, the S content is 0.0002% or more.
  • Al is added as a deoxidizing agent, but there is no effect of addition at less than 0.005%.
  • the Al content is 0.005% or more.
  • the Al content is preferably 0.01% or more, more preferably 0.03% or more.
  • more than 0.15% results in steel with lower cleanliness and toughness, so that the Al content is limited to 0.15% or less.
  • the Al content is preferably 0.10% or less, more preferably 0.08% or less, still more preferably 0.05% or less.
  • O can form an oxide inclusion, and a lower O content is more preferred, but an O content of 0.01% or less causes no problem.
  • the O content is 0.01% or less.
  • the O content is preferably 0.005% or less.
  • the O content is more preferably less than 0.003%.
  • the lower limit is not particularly limited, the O content is preferably 0.001% or more because reducing the oxygen content to 0% increases the cost.
  • N has a small influence on the fatigue property of a steel pipe, and the advantages of the present invention are not impaired at a N content of 0.010% or less from the perspective of toughness.
  • the N content is 0.010% or less.
  • the N content is preferably 0.008% or less, more preferably 0.006% or less.
  • the N content is still more preferably 0.004% or less.
  • a lower N content is desirable, but excessive reduction increases the steelmaking cost, so that the N content is preferably 0.00001% or more.
  • the N content is preferably 0.001% or more.
  • H may be introduced into a steel material in various steps during production, and a large amount of H introduced increases the risk of cracking after solidification and accelerates fatigue crack growth. A large amount of H introduced also reduces the fatigue limit stress, and it is therefore important to decrease the amount of hydrogen in the steel pipe. Since these effects are not problematic at a H content of 0.0010% or less, the H content is 0.0010% or less.
  • the H content is preferably 0.0005% or less, more preferably 0.0003% or less, still more preferably 0.0001% or less.
  • a H content of less than 0.00001% causes an increase in cost, and the H content is therefore preferably 0.00001% or more.
  • the amount of hydrogen is the amount of residual hydrogen after forming of a steel material, a steel pipe, UOE, or the like.
  • the chemical composition in the present disclosure may optionally contain at least one selected from Nb, Ti, Ca, Ni, Cu, Cr, Mo, W, V, Zr, REM, Mg, B, Hf, Ta, Re, Sn, and Sb in the following ranges.
  • Nb 0% to 0.10% and Ti: 0% to 0.1%
  • Ca is an element effective in improving the HIC resistance by the shape control of a sulfide inclusion, not only the effect is saturated but also the HIC resistance decreases due to a decrease in the cleanliness of steel, so that when Ca is contained the Ca content is limited to 0.005% or less.
  • the Ca content is preferably 0.003% or less.
  • the Ca content is more preferably 0.002% or less.
  • the Ca content may be 0% or more, the effect of addition is difficult to obtain at less than 0.0001%, so that when Ca is contained the Ca content is preferably 0.0001% or more.
  • the Ca content is more preferably 0.001% or more.
  • Cu is an element effective in improving the toughness and increasing the strength, but an excessively high Cu content results in a decrease in weldability, so that when Cu is contained the Cu content is 1.0% or less.
  • the Cu content is preferably 0.5% or less.
  • the Cu content is more preferably 0.3% or less, still more preferably 0.2% or less.
  • the Cu content may be 0% or more and is preferably 0.01% or more to achieve the above effects.
  • Cr is an element effective in obtaining sufficient strength even at a low C content, but an excessively high Cr content results in excessive hardenability and a decrease in the SSCC resistance. Furthermore, weldability also deteriorates.
  • the Cr content is 1.0% or less.
  • the Cr content is preferably 0.8% or less.
  • the Cr content is more preferably 0.5% or less, still more preferably 0.1% or less.
  • the Cr content may be 0% or more and is preferably 0.01% or more to achieve the effect.
  • the Cr content is more preferably 0.02% or more.
  • Mo is an element effective in improving the toughness and increasing the strength and effective in improving the SSCC resistance regardless of the hydrogen sulfide partial pressure, but an excessively high Mo content results in excessive hardenability and a decrease in the SSCC resistance. Furthermore, weldability also deteriorates.
  • the Mo content when Mo is contained, the Mo content is 0.60% or less, more preferably 0.50% or less, still more preferably 0.40% or less. Most preferably, the Mo content is 0.03% or less.
  • the Mo content may be 0% or more and is preferably 0.005% or more to achieve the above effects.
  • the Mo content is more preferably 0.01% or more.
  • W contributes to an increase in the strength of a steel pipe, but a W content of more than 1.0% results in saturation of the effect and causes an increase in cost, so that when W is contained the W content is 1.0% or less.
  • the W content is preferably 0.8% or less. To further reduce the cost, the W content is more preferably 0.5% or less.
  • the W content is still more preferably 0.03% or less.
  • the W content may be 0% or more and is preferably 0.01% or more to achieve the effect.
  • V 0% to 0.10%
  • V is an element that can be optionally contained to increase the strength and toughness of a steel pipe, but a V content of more than 0.10% results in a weld with lower toughness, so that when V is contained the V content is 0.10% or less.
  • the V content is preferably 0.08% or less.
  • the V content is more preferably 0.06% or less, still more preferably 0.03% or less.
  • the V content may be 0% or more, but the effects of containing V are difficult to obtain at a content of less than 0.01%, so that the V content is preferably 0.01% or more.
  • Zr, REM, and Mg are elements that can be optionally contained to increase the toughness through grain refinement or to increase cracking resistance through the control of inclusion properties.
  • the effects are saturated at more than 0.050%, so that when they are contained each content is 0.050% or less. More specifically, when Zr is contained, the Zr content is 0.050% or less.
  • the Zr content is preferably 0.040% or less.
  • the Zr content is more preferably 0.030% or less.
  • the Zr content is still more preferably 0.010% or less, most preferably 0.005% or less.
  • REM is contained, the REM content is 0.050% or less.
  • the REM content is preferably 0.040% or less.
  • the REM content is more preferably 0.030% or less.
  • the Mg content is 0.050% or less.
  • the Mg content is preferably 0.040% or less.
  • the Mg content is more preferably 0.030% or less.
  • Each element content may be 0% or more, but the effects of containing these elements are difficult to obtain at a content of less than 0.0001%, so that each content is preferably 0.0001% or more.
  • the Zr content is preferably 0.0001% or more.
  • the Zr content is more preferably 0.0005% or more.
  • the REM content is preferably 0.0001% or more.
  • the REM content is more preferably 0.0005% or more.
  • the Mg content is preferably 0.0001% or more.
  • the Mg content is more preferably 0.0005% or more.
  • Hf hydrogen fluoride
  • the Hf content is preferably 0.1% or less.
  • the Hf content is more preferably 0.05% or less.
  • Ta is contained, the Ta content is 0.2% or less.
  • the Ta content is preferably 0.1% or less.
  • the Ta content is more preferably 0.05% or less.
  • the Hf or Ta content may be 0% or more and is preferably 0.0001% or more to achieve the effect.
  • the Hf content is preferably 0.0001% or more. More preferably, the Hf content is 0.0010% or more.
  • the Ta content is preferably 0.0001% or more. More preferably, the Ta content is 0.0010% or more.
  • Re contributes to an increase in the strength of a steel pipe, but a content of more than 0.005% results in saturation of the effect and causes an increase in cost, so that when Re is contained the Re content is 0.005% or less.
  • the Re content is preferably 0.003% or less.
  • the Re content is more preferably 0.002% or less.
  • the Re content may be 0% or more and is preferably 0.0001% or more to achieve the effect. 0.001% or more is more preferred.
  • the Sn content is 0.3% or less.
  • the Sn content is preferably 0.2% or less.
  • the Sn content is more preferably 0.1% or less.
  • the Sb content is 0.3% or less.
  • the Sb content is preferably 0.2% or less.
  • the Sb content is more preferably 0.1% or less.
  • the Sb content is still more preferably 0.01% or less.
  • the Sn or Sb content may be 0% or more and is preferably 0.0001% or more to achieve the effects.
  • the Sn content is preferably 0.0001% or more. More preferably, the Sn content is 0.0010% or more.
  • the Sb content is preferably 0.0001% or more. More preferably, the Sb content is 0.0010% or more.
  • the remainder other than these components is composed of Fe and an incidental impurity element.
  • Austenite remaining in a steel pipe may increase the amount of hydrogen in the steel and increase hydrogen embrittlement sensitivity. Furthermore, when austenite is transformed into martensite by stress loading during use, hydrogen cracking is likely to occur because martensite is very hard, and cracking may occur from the martensite portion.
  • area fraction of retained austenite is 3% or less to reduce the fatigue crack growth rate. Retained austenite is preferably 2% or less, more preferably 1% or less. The retained austenite may be 0%.
  • Bainite or martensite presents at a quarter thickness position from the inner surface of a steel pipe (for a steel material, a quarter thickness position from a surface of the steel material), and area fraction of bainite is 90% or more or area fraction of martensite is 90% or more
  • the steel microstructure needs to be a bainite or martensite microstructure.
  • fatigue damage preferentially accumulates in the soft phase and is likely to cause cracking, thus reducing the fatigue limit stress.
  • a hydrogen environment promotes local deformation, further accelerates fatigue damage to the soft phase, and reduces the fatigue limit stress in hydrogen. Consequently, the fatigue limit stress in hydrogen/fatigue limit stress in an inert gas environment becomes less than 0.90. To address this, it is necessary to reduce the relative proportion of the soft phase.
  • the metallic microstructure needs to be a single microstructure of bainite or martensite and, therefore, defined to be containing either one of bainite or martensite with an area fraction of the microstructure of 90% or more.
  • the area fraction of the bainite or martensite microstructure is 92% or more, more preferably 95% or more, still more preferably 98% or more.
  • the upper limit may be, but is not limited to, 100%.
  • the uniformity of the microstructure of the inner surface of the steel pipe is important.
  • the metallic microstructure at the quarter thickness position from the inner surface of a steel pipe is defined, and for a steel material, the metallic microstructures at the quarter thickness positions are defined to achieve the above effects regardless of which surface is the inner surface side of a steel pipe.
  • the bainite microstructure includes bainitic ferrite or granular bainite that transforms during or after cooling (accelerated cooling or quenching) contributing to transformation strengthening, and also includes tempered bainite.
  • a different microstructure, such as ferrite, martensite, pearlite, a martensite-austenite constituent (MA), or retained austenite, in the bainite microstructure reduces the strength or toughness, and the volume fraction of a microstructure other than the bainite phase is therefore preferably as small as possible.
  • the martensite microstructure includes tempered martensite.
  • the bainite and martensite microstructures can be tempered to precipitate a carbide, such as cementite.
  • a fine carbide can be precipitated to inhibit the straightness of a fatigue crack propagation path in hydrogen and further reduce the fatigue crack growth rate.
  • a tempered bainite or tempered martensite microstructure is preferred.
  • carbides preferably have an average size of 200 nm or less, more preferably 50 nm or less.
  • the fatigue limit stress in hydrogen at 1 MPa or more is 200 MPa or more, and the fatigue limit stress in hydrogen at 1 MPa or more/fatigue limit stress in an inert gas environment is 0.90 or more
  • a steel pipe needs to have a fatigue limit stress of 200 MPa or more in hydrogen at 1 MPa or more.
  • the fatigue limit stress in hydrogen at 1 MPa or more is preferably 220 MPa or more.
  • the fatigue limit stress in hydrogen at 1 MPa or more is more preferably 250 MPa or more, still more preferably 270 MPa or more.
  • the upper limit is not particularly limited, the fatigue limit stress in hydrogen at 1 MPa or more is preferably 500 MPa or less.
  • the fatigue limit stress in hydrogen at 1 MPa or more/fatigue limit stress in an inert gas environment in a steel pipe needs to be 0.90 or more.
  • the fatigue limit stress in hydrogen at 1 MPa or more/fatigue limit stress in an inert gas environment is preferably 0.92 or more.
  • the fatigue limit stress in hydrogen at 1 MPa or more/fatigue limit stress in an inert gas environment is more preferably 0.94 or more, still more preferably 0.96 or more.
  • the upper limit is not particularly limited, the fatigue limit stress in hydrogen at 1 MPa or more/fatigue limit stress in an inert gas environment may be 1.10 or less.
  • the term "inert gas”, as used herein, includes six elements of Group 0 of the periodic table, helium, neon, argon, krypton, xenon, and radon, as well as air, and the term “inert gas environment" refers to an environment containing any one of these.
  • the chemical composition and metallic microstructure described above can suppress the toughness degradation in a high-pressure hydrogen atmosphere and can achieve a tensile strength of 520 MPa or more.
  • the present invention can be applied to a hydrogen line pipe.
  • the upper limit of the tensile strength is preferably, but not limited to, 950 MPa or less.
  • the sheet thickness is preferably 5 mm or more, preferably 30 mm or less.
  • a steel pipe according to the present invention can be produced by sequentially performing the following steps (1) to (3).
  • the temperature in the following description is the temperature at the middle of the sheet thickness of a steel raw material or a steel pipe.
  • the average cooling rate means the temperature at a quarter thickness position from the inner surface of a steel pipe.
  • the temperature at the middle of the sheet thickness and the temperature at the quarter thickness position from the inner surface of a steel pipe are estimated from the surface temperature of the steel pipe measured with a radiation thermometer using heat-transfer calculation or the like in consideration of the heat transfer coefficient of the steel material.
  • the casting speed is 1.8 m/min or less, preferably 1.5 m/min or less, more preferably 1.0/min or less, still more preferably 0.5 m/min or less, most preferably 0.1 m/min or less.
  • the casting speed may be more than 0 m/min.
  • the steel raw material can be, for example, but is not limited to, a billet or the like produced by an ordinary continuous casting method.
  • a heating temperature of more than 1350°C in the heating step results in prior austenite grains with an excessively large average grain size and a degradation of various characteristics.
  • the heating temperature is 1350°C or less.
  • the heating temperature is preferably 1300°C or less, more preferably 1250°C or less, most preferably 1200°C or less.
  • the heating temperature is preferably lowered to reduce the amount of hydrogen in the steel, but an excessively low heating temperature results in a decrease in the finish rolling temperature and makes rolling difficult.
  • the heating temperature is preferably 950°C or more.
  • the heating temperature is more preferably 1000°C or more.
  • the heating time is not particularly specified, an excessively long heating time increases the risk of increasing the amount of hydrogen introduced into a steel pipe, so that 180 minutes or less is preferred.
  • the heating time is more preferably 150 minutes or less, still more preferably 120 minutes or less.
  • the lower limit is not particularly limited, the heating time is preferably 30 minutes or more, more preferably 60 minutes or more.
  • [M] denotes the element M content (% by mass).
  • the average cooling rate is preferably 50°C/s or less, more preferably 45°C/s or less, still more preferably 40°C/s or less. Furthermore, cooling to 50°C or less at an average cooling rate of 15°C/s or less from 550°C to 50°C can decrease retained austenite and reduce the amount of hydrogen in the steel. Thus, the average cooling rate from 550°C to 50°C is 15°C/s or less. The average cooling rate from 550°C to 50°C is preferably 12°C/s or less, more preferably 10°C/s or less. Although the lower limit is not particularly limited, the average cooling rate from 550°C to 50°C is preferably 1°C/s or more.
  • the cooling method is not particularly limited, and an arbitrary method, such as water cooling, oil cooling, or natural cooling, can be used alone or in combination, but water cooling or oil cooling is preferred from 800°C to 550°C, and natural cooling is preferred from 550°C to 50°C.
  • the average cooling rate from 800°C to 300°C at the quarter thickness position from the inner surface of a steel pipe is less than 10°C/s, 90% or more of a martensite microstructure cannot be formed, mixing with a bainite microstructure occurs, and the fatigue limit stress in hydrogen decreases.
  • the average cooling rate at the quarter thickness position from the inner surface of a steel pipe is 10°C/s or more.
  • the average cooling rate from 800°C to 300°C is preferably 12°C/s or more, more preferably 15°C/s or more, still more preferably 17°C/s or more.
  • the upper limit is not particularly limited, the average cooling rate is preferably 60°C/s or less.
  • Reheating temperature before tempering Ac 3 point or higher and 1000°C or less
  • Average cooling rate during quenching the following Group A or Group B
  • Group A cooling to 50°C or less at an average cooling rate of 15°C/s or more from 800°C to 550°C and at an average cooling rate of 15°C/s or less from 550°C to 50°C at the quarter thickness position from the inner surface of a steel pipe
  • the average cooling rate at the quarter thickness position from the inner surface of a steel pipe is 15°C/s or more.
  • the average cooling rate is preferably 17°C/s or more, more preferably 20°C/s or more, still more preferably 22°C/s or more.
  • the average cooling rate is preferably 50°C/s or less, more preferably 47°C/s or less, still more preferably 45°C/s or less.
  • cooling to 50°C or less at an average cooling rate of 15°C/s or less from 550°C to 50°C can decrease retained austenite and reduce the amount of hydrogen in the steel.
  • the average cooling rate from 550°C to 50°C is 15°C/s or less.
  • the average cooling rate from 550°C to 50°C is preferably 12°C/s or less, more preferably 10°C/s or less.
  • the lower limit is not particularly limited, the average cooling rate from 550°C to 50°C is preferably 1°C/s or more.
  • the cooling method is not particularly limited, and an arbitrary method, such as water cooling, oil cooling, or natural cooling, can be used alone or in combination, but water cooling or oil cooling is preferred from 800°C to 550°C, and natural cooling is preferred from 550°C to 50°C.
  • Group B cooling to 50°C or less at an average cooling rate of 10°C/s or more from 800°C to 300°C and at an average cooling rate of 5°C/s or less from 300°C to 50°C at the quarter thickness position from the inner surface of a steel pipe
  • the average cooling rate at the quarter thickness position from the inner surface of a steel pipe is 10°C/s or more.
  • the average cooling rate is preferably 17°C/s or more, more preferably 20°C/s or more, still more preferably 25°C/s or more.
  • the lower limit is preferably, but not limited to, 0.1°C/s or more.
  • the cooling method is not particularly limited, and an arbitrary method, such as water cooling, oil cooling, or natural cooling, can be used alone or in combination, but water cooling or oil cooling is preferred from 800°C to 300°C, and natural cooling is preferred from 300°C to 50°C.
  • Cooling stop temperature during quenching 50°C or less
  • the cooling stop temperature is more than 50°C, the transformation is not completed, and a desired steel microstructure cannot be formed after tempering. Thus, quenching is performed to a temperature of 50°C or less.
  • the cooling stop temperature is preferably 45°C or less, more preferably 40°C or less. Although the lower limit is not particularly limited, the cooling stop temperature is preferably 25°C or more.
  • a tempering temperature of 400°C or more can result in a decrease in retained austenite and a decrease in hydrogen in the steel.
  • the tempering temperature is preferably 450°C or more, more preferably 500°C or more.
  • heating to a temperature higher than the Ac 1 point may result in an increase in retained austenite and an increase in hydrogen in the steel.
  • the tempering temperature is the Ac 1 point or lower, preferably, (Ac 1 - 30)°C or less.
  • the upper limit of the average heating rate during tempering is preferably, but not limited to, 1°C/s or less.
  • the tempering time is preferably, but not limited to, 60 minutes or more because retained austenite and hydrogen in a steel pipe decreases as the tempering time increases.
  • the tempering time is more preferably 80 minutes or more, still more preferably 100 minutes or more.
  • An excessively long tempering time results in an excessive decrease in the material strength and saturation of the effects.
  • the tempering time is preferably 180 minutes or less.
  • Each element symbol in the formula represents the element content (% by mass) of the steel and is 0 for an element not contained.
  • the holding time R (h) is preferably determined from the sheet thickness or the wall thickness t (mm) of a steel pipe and the hydrogen diffusion coefficient D (mm ⁇ s -2 ) in the steel at room temperature using the following formula (A). R ⁇ t 2 / D
  • the hydrogen diffusion coefficient varies depending on a component contained and the metallic microstructure and may range from, for example, 1 x 10 -11 to 5 x 10 -9 m 2 /s, more preferably 5 x 10 -10 m 2 /s or less.
  • the dehydrogenation treatment temperature T is preferably room temperature or higher for the reason that the dehydrogenation treatment at a temperature lower than room temperature increases the treatment time and cost.
  • the dehydrogenation treatment temperature T is more preferably 50°C or more.
  • the dehydrogenation treatment temperature T is still more preferably 100°C or more, most preferably 150°C or more.
  • the dehydrogenation treatment temperature T herein is the temperature of the ambient in the dehydrogenation treatment step.
  • the room temperature refers to 20°C ⁇ 10°C.
  • At least the former can appropriately control the amount of hydrogen in the steel material in the surface layer portion of the steel material or the steel pipe, and when the latter is also performed, the amount of hydrogen in the steel material from the surface layer portion to the middle of the sheet thickness of the steel material or the steel pipe can be appropriately controlled.
  • the temperature Tc at the middle of the sheet thickness may be actually measured with a thermocouple or the like or may be predicted using a finite element method or the like.
  • the scale on the steel surface inhibits dehydrogenation and is therefore preferably removed before the dehydrogenation treatment.
  • the scale removal method may be, for example, but is not limited to, physical cleaning by high-pressure cleaning or a chemical method using a scale remover.
  • the thickness of scale to be removed is not particularly limited, the scale removal effect can be obtained when the scale is removed by approximately 100 ⁇ m.
  • Heating temperature after hot rolling Ac 3 point or higher and 1000°C or less
  • a steel sheet is preferably coiled, although it is not necessary for a thick sheet.
  • the product was expanded by a Mannesmann-plug mill process or a Mannesmann-mandrel mill process to produce a seamless steel pipe with a finish rolling temperature of 850°C or more.
  • the seamless steel pipe was then slowly cooled by natural cooling.
  • the steel pipes produced by the above method were heated and held at 950°C for steel pipes with an Ac 3 point of 950°C or less or at 1000°C for steel pipes with an Ac 3 point of more than 950°C and were then cooled to 50°C or less at an average cooling rate shown in Tables 3-1, 3-2, 3-3, 4-1, and 4-2. Tempering was then performed, the steel pipes Nos. 16, 29, 35, 37, and 39 were subjected to dehydrogenation treatment, and the metallic microstructure and mechanical properties were evaluated.
  • the tempering temperature was adjusted in the range of 400°C to 680°C so that the tensile strength of the material ranged from 520 MPa to 700 MPa.
  • Tc temperature at the middle of the sheet thickness reached room temperature as the target temperature, held for R (s) to satisfy the formula (A).
  • Tables 3-1, 3-2, 3-3, 4-1, and 4-2 show evaluation results. The evaluation method is described below. A steel material taken from a central portion in the longitudinal direction of a steel pipe was treated as a steel material of the present invention.
  • a sample for metallic microstructure observation was taken from a central portion of the sheet width in a central portion in the longitudinal direction of each of the steel materials and the steel pipes thus produced.
  • a cross section parallel to the longitudinal direction was buffed as an observation surface.
  • the surface layer was then removed by chemical polishing using picric acid etching, and X-ray diffractometry was performed. More specifically, a Co-K ⁇ radiation source was used for an incident X-ray, and the area fraction of retained austenite was calculated from the intensity ratios of the (200), (211), and (220) planes of ferrite to the (200), (220), and (311) planes of austenite.
  • microstructure fractions were determined as area fractions of respection phases from an image obtained by dividing the SEM photograph into regions based on the above identification by image analysis (for example, to calculate the fraction of bainite, the bainite and the other region were binarized to determine the fraction of bainite).
  • JIS No. 14 proportional test pieces (parallel portion diameter: 7 mm, gauge length: 35 mm) were taken in accordance with JIS Z 2201 from the steel pipes and the steel materials thus produced, and the tensile strength was measured.
  • the amount of hydrogen remaining in the steel was measured by thermal desorption spectrometry using a low-temperature programmed hydrogen analyzer ⁇ gas chromatograph type> (JTF-20AL).
  • the thermal desorption spectrometry was performed in the temperature range of room temperature to 400°C at a heating rate of 200°C/h, and the sum total thereof was taken as the amount of hydrogen.
  • the specimen has a cylindrical shape with 30 mm in length and 7 ⁇ in diameter in the longitudinal direction of the steel pipe at the quarter thickness position of the steel sheet and at the quarter thickness position from the inner surface of the steel pipe.
  • the amount of hydrogen is the amount of H shown in Tables 1-1, 1-2, 1-3, 2-1, and 2-2 before being subjected to a high-pressure hydrogen fatigue test as explained in the item described later.
  • the stress at which no fracture occurred at a number of repetitions of 10,000,000 was defined as the fatigue limit strength in the atmosphere.
  • the stress at which no fracture occurred at a number of repetitions of 2,000,000 was defined as the fatigue limit stress in hydrogen.
  • the fatigue limit stress in hydrogen was 200 MPa or more
  • its ratio to the fatigue limit strength in the inert gas atmosphere that is, the fatigue limit stress in hydrogen/fatigue limit stress in the inert gas environment
  • the tensile strength was 520 MPa or more
  • high hydrogen embrittlement resistance was satisfied.

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JP6859835B2 (ja) 2017-05-01 2021-04-14 日本製鉄株式会社 鋼材及び油井用継目無鋼管
WO2019069771A1 (ja) * 2017-10-03 2019-04-11 新日鐵住金株式会社 鋼板および鋼板の製造方法
JP6989004B2 (ja) 2018-12-26 2022-01-05 Ｊｆｅスチール株式会社 高圧水素ガス環境用鋼材および高圧水素ガス環境用鋼構造物ならびに高圧水素ガス環境用鋼材の製造方法
WO2020166638A1 (ja) * 2019-02-13 2020-08-20 日本製鉄株式会社 燃料噴射管用鋼管およびそれを用いた燃料噴射管
EP3925715A4 (de) * 2019-02-13 2023-06-14 Nippon Steel Corporation Stahlrohr für ein kraftstoffeinspritzrohr und kraftstoffeinspritzrohr damit
KR20230145592A (ko) * 2021-03-30 2023-10-17 제이에프이 스틸 가부시키가이샤 고압 수소용 강관, 고압 수소용 용기 및 상기 강관의 제조 방법

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EP4578564A4 (de) 2026-02-25
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