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WO2024185593A1 - Tuyau en acier sans soudure et à haute résistance pour récipient d'hydrogène haute pression et son procédé de fabrication - Google Patents

Tuyau en acier sans soudure et à haute résistance pour récipient d'hydrogène haute pression et son procédé de fabrication Download PDF

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Publication number
WO2024185593A1
WO2024185593A1 PCT/JP2024/007115 JP2024007115W WO2024185593A1 WO 2024185593 A1 WO2024185593 A1 WO 2024185593A1 JP 2024007115 W JP2024007115 W JP 2024007115W WO 2024185593 A1 WO2024185593 A1 WO 2024185593A1
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less
steel pipe
precipitates
content
seamless steel
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PCT/JP2024/007115
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English (en)
Japanese (ja)
Inventor
奈穂 井上
ヴァナディア イリスカ ユッサラ
拓史 岡野
健一郎 江口
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JFE Steel Corp
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JFE Steel Corp
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Priority to EP24766964.1A priority Critical patent/EP4636111A1/fr
Priority to JP2024540982A priority patent/JP7697601B2/ja
Priority to CN202480015585.6A priority patent/CN120787267A/zh
Priority to KR1020257028497A priority patent/KR20250141195A/ko
Priority to AU2024231754A priority patent/AU2024231754A1/en
Publication of WO2024185593A1 publication Critical patent/WO2024185593A1/fr
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
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    • 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 by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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    • 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
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    • 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
    • C21D9/14—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes wear-resistant or pressure-resistant pipes
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    • 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
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—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
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    • 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
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    • 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
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    • 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
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    • 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
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
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    • 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 high-strength seamless steel pipe for high-pressure hydrogen containers and a manufacturing method thereof.
  • Fuel cell vehicles that use hydrogen as fuel do not emit carbon dioxide ( CO2 ) and have excellent energy efficiency, and are therefore expected to be vehicles that can solve the CO2 emission and energy problems.
  • containers with excellent strength and durability that can safely store high-pressure hydrogen of 35 MPa or more, particularly 70 MPa or more, are needed for hydrogen stations that supply hydrogen to fuel cell vehicles and for on-board use to load hydrogen onto fuel cell vehicles, and development of such containers is underway.
  • Patent Document 1 describes a liner made of an Al-Mg-Si alloy with excellent fatigue properties.
  • low alloy steels such as Cr-Mo steel are known to be embrittled by hydrogen.
  • materials for high-pressure hydrogen storage tanks of 35 MPa or more are limited to aluminum alloys and SUS316, which are less susceptible to material degradation by hydrogen.
  • Patent Document 4 proposes a steel for high-pressure hydrogen environments that uses fine V-Mo precipitates as trap sites for hydrogen in the steel to make the hydrogen non-diffusible, thereby suppressing embrittlement caused by diffusible hydrogen.
  • Patent Document 5 proposes a low-alloy, high-strength steel with excellent resistance to embrittlement in a high-pressure hydrogen environment, in which the tensile strength is controlled within an extremely narrow range of 900 to 950 MPa by performing a tempering process at a relatively high temperature during the thermal refining process of Cr-Mo steel.
  • a high-pressure hydrogen gas environment here refers to an environment with a total pressure of 1 MPa or more and a hydrogen partial pressure of 1 MPa or more.
  • the present invention was made in consideration of the above circumstances, and aims to provide a high-strength seamless steel pipe for high-pressure hydrogen containers that has excellent resistance to hydrogen embrittlement, and a manufacturing method thereof.
  • the inventors of the present invention have conducted extensive research into various factors that affect strength and hydrogen embrittlement resistance, since it is necessary to achieve both the desired high strength and hydrogen embrittlement resistance in order to produce a high-strength seamless steel pipe for high-pressure hydrogen containers (hereinafter simply referred to as high-strength seamless steel pipe) that achieves the above-mentioned objectives.
  • high-strength seamless steel pipe for high-pressure hydrogen containers (hereinafter simply referred to as high-strength seamless steel pipe) that achieves the above-mentioned objectives.
  • high-strength seamless steel pipe for high-pressure hydrogen containers
  • the inventors have come to the realization that in order to further improve the hydrogen embrittlement resistance of high-strength seamless steel pipes, it is necessary to increase the amount of Mo contained in the precipitates, and in particular to adjust the amount of Mo contained in precipitates of 50 nm or less to an appropriate amount or more.
  • the steel is subjected to a quenching treatment at least once, in which the steel is rapidly cooled to a surface temperature of 200°C or less.
  • a tempering treatment is performed by heating to a tempering temperature of 600 to 740 ° C.
  • a method for producing a high-strength seamless steel pipe for high-pressure hydrogen containers wherein the average heating rate until the tempering temperature is reached is 0.5°C/min or more, and the holding time at the tempering temperature is 10 minutes or more and less than 60 minutes.
  • the present invention it is possible to easily and inexpensively manufacture high-strength seamless steel pipes for high-pressure hydrogen containers that have a high strength of tensile strength TS of 850 MPa or more and excellent resistance to hydrogen embrittlement, which is of great industrial benefit.
  • a manufacturing method that contains appropriate amounts of alloying elements and promotes the formation of Mo precipitates it is possible to stably manufacture high-strength seamless steel pipes that have the desired high strength for pressure containers as well as excellent resistance to hydrogen embrittlement.
  • C 0.20-0.50% C contributes to increasing the strength of steel by dissolving in solid solution, improves the hardenability of steel, and contributes to the formation of a structure in which the martensite phase is the main phase during quenching.
  • the C content must be 0.20% or more.
  • the C content is preferably 0.22% or more, more preferably 0.25% or more, and further preferably 0.28% or more.
  • the C content is set to 0.50% or less.
  • the C content is preferably 0.45% or less, more preferably 0.40% or less, and further preferably 0.35% or less.
  • Si 0.05-2.00% Silicon is added for deoxidation, but if the content is less than 0.05%, the deoxidation effect is insufficient. Therefore, the silicon content is set to 0.05% or more.
  • the silicon content is 0.10%. It is preferable that the Si content is 0.20% or more, more preferable that the Si content is 0.30% or more. On the other hand, when the Si content exceeds 2.00%, the effect is saturated. Therefore, the Si content is set to 2.00% or less.
  • the Si content is preferably set to 1.00% or less, and more preferably set to 0.80% or less. Furthermore, if the Si content exceeds 0.50%, Since Si deteriorates toughness and weldability, the Si content is more preferably 0.50% or less.
  • Mn 0.30-1.50%
  • Mn is an element that improves the hardenability of steel and contributes to increasing the strength of steel, similar to C. In order to obtain such effects, the Mn content is set to 0.30% or more.
  • the Mn content is preferably 0.40% or more, more preferably 0.45% or more, and even more preferably 0.50% or more.
  • Mn is an element that segregates in steel and locally hardens the steel. When a large amount of Mn is contained, localized hardened regions are formed, which adversely affects the hydrogen embrittlement resistance. Therefore, in the present invention, the Mn content is set to 1.50% or less.
  • the Mn content is preferably 1.20% or less, more preferably 1.00% or less, and further preferably 0.80% or less.
  • P 0.015% or less
  • P is an element that not only segregates to grain boundaries in the steel structure to cause grain boundary embrittlement, but also segregates to locally harden the steel.
  • P is an unavoidable impurity and is preferably reduced as much as possible, but up to 0.015% is acceptable.
  • the P content is set to 0.015% or less.
  • the P content is preferably 0.008% or less.
  • the P content is more preferably 0.005% or less, and even more preferably 0.003% or less.
  • the P content is preferably 0.0001% or more, and more preferably 0.001% or more.
  • S 0.005% or less
  • S is an inevitable impurity, and most of it exists as sulfide-based inclusions in steel, which reduces ductility, toughness, and even SSC resistance. Therefore, it is preferable to reduce the content as much as possible, but up to 0.005% is acceptable. For this reason, the S content is set to 0.005% or less.
  • the S content is preferably 0.003% or less. More preferably, it is 0.002% or less. The lower the content, the better, but from the viewpoint of refining costs, the S content is preferably 0.0002% or more.
  • the S content is more preferably 0.001% or more.
  • Al 0.005-0.150%
  • Al is added as a deoxidizer, but if the content is less than 0.005%, the addition effect is ineffective. Therefore, the Al content is set to 0.005% or more.
  • the Al content is set to 0.010% or more.
  • the content of Al exceeds 0.150%, the cleanliness of the steel decreases and the toughness deteriorates.
  • the Al content is preferably 0.130% or less, more preferably 0.100% or less, and most preferably 0.080% or less.
  • N 0.006% or less N exists in steel as an inevitable impurity, but it combines with Al to form AlN, and when Ti is contained, it forms TiN, which has the effect of refining crystal grains and improving toughness.
  • the N content is preferably 0.0005% or more. More preferably, it is 0.001% or more.
  • the N content is set to 0.006% or less.
  • the N content is preferably set to 0.005% or less, more preferably set to 0.004% or less, and even more preferably set to 0.003% or less.
  • Cr more than 0.2% and not more than 1.7% Cr is an element that increases the strength of steel through improving hardenability and improves corrosion resistance.
  • Cr is an element that combines with C during tempering to form precipitates such as M3C , M7C3 , and M23C6 (M is a metal element) and improves temper softening resistance, and is a necessary element especially for increasing the strength of steel pipes.
  • M3C type precipitates have a strong effect of improving temper softening resistance.
  • the Cr content is made to be more than 0.2%.
  • the Cr content is preferably 0.3% or more, and more preferably 0.5% or more.
  • the Cr content is made to be more than 1.7%, a large amount of M7C3 and M23C6 are formed, which act as hydrogen trap sites and reduce hydrogen erosion resistance.
  • the Mo precipitates become coarse. Since fine Mo precipitates become coarse due to aggregation and coalescence, the number density of the fine Mo precipitates decreases, and the hydrogen embrittlement resistance decreases.
  • the Cr content is set to 1.7% or less.
  • the Cr content is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0.8% or less.
  • Mo more than 1.0% and not more than 3.0%
  • Mo is an element that forms precipitates and contributes to strengthening steel by precipitation strengthening, and effectively contributes to ensuring the desired high strength after reducing dislocation density by tempering.
  • Mo dissolves in steel and segregates at the prior austenite grain boundaries, contributing to improving hydrogen embrittlement resistance.
  • Mo has the effect of densifying corrosion products and suppressing the generation and growth of pits that are the starting points of cracks.
  • the Mo content is made to be more than 1.0%.
  • the Mo content is preferably more than 1.1%, more preferably more than 1.2%, even more preferably 1.3% or more, and most preferably 1.4% or more.
  • the Mo content exceeds 3.0%, it promotes the formation of needle-shaped M 2 C precipitates and, in some cases, Laves phase (Fe 2 Mo), thereby reducing hydrogen embrittlement resistance.
  • the Mo content is made to be 3.0% or less.
  • the Mo content is preferably 2.8% or less, more preferably 2.5% or less, further preferably 1.8% or less, and most preferably 1.5% or less.
  • Nb 0.001-0.020%
  • Nb forms precipitates or carbonitrides, and contributes to increasing the strength of steel through precipitation strengthening, and also contributes to refining austenite grains.
  • the Nb content is 0.001% or more.
  • the Nb content is preferably 0.005% or more, more preferably 0.006% or more, and further preferably 0.007% or more.
  • coarse Nb precipitates Since Nb precipitates are likely to become crack initiation points for hydrogen-induced cracking, the presence of a large amount of Nb precipitates due to a large Nb content exceeding 0.020% leads to a significant decrease in hydrogen embrittlement resistance in high-strength steel materials. Therefore, from the viewpoint of achieving both the desired high strength and excellent hydrogen embrittlement resistance, the Nb content is set to 0.020% or less in the present invention. It is preferably less than 0.015%, and more preferably less than 0.010%.
  • B 0.0003-0.0030% B segregates at the austenite grain boundaries and inhibits ferrite transformation from the grain boundaries, thereby enhancing the hardenability of steel even when contained in small amounts.
  • the B content is preferably 0.0007% or more, and more preferably 0.0010% or more.
  • the B content is set to 0.0030% or less.
  • the B content is preferably set to 0.0025% or less.
  • the B content is more preferably 0.0020% or less, and further preferably 0.0015% or less.
  • O (oxygen) 0.0030% or less
  • O (oxygen) is an inevitable impurity and exists as oxide-based inclusions in steel. These inclusions become the starting point of generation in a hydrogen gas environment and reduce hydrogen embrittlement resistance, so in the present invention, it is preferable to reduce O (oxygen) as much as possible. However, excessive reduction leads to high refining costs, so the O (oxygen) content is permissible up to 0.0030%. For this reason, the O (oxygen) content is limited to 0.0030% or less.
  • the O content is preferably 0.0025% or less, and more preferably, the O content is 0.0020% or less.
  • the O content is further preferably 0.0015% or less.
  • the lower limit is not particularly limited, the O content is preferably 0.0010% or more.
  • Ti 0.003-0.025%
  • Ti combines with N when molten steel solidifies and precipitates as fine TiN, and its pinning effect contributes to the refinement of austenite grains. To obtain this effect, Ti should be 0.003% or more. It is necessary to include Ti. If the Ti content is less than 0.003%, the effect is small. Therefore, the Ti content is set to 0.003% or more. The Ti content is set to 0.005% or more. On the other hand, if the Ti content exceeds 0.025%, TiN becomes coarse, the pinning effect described above cannot be exerted, and the toughness is deteriorated. Furthermore, the hydrogen embrittlement resistance is deteriorated due to the coarse TiN. For these reasons, the Ti content is set to 0.025% or less. The Ti content is set to 0.020% or less. It is preferable to set the content at 0.015% or less, and more preferable to set the content at 0.015% or less.
  • Mo/C over 2.0 to 12.0
  • Mo/C is set to more than 2.0.
  • Mo/C is preferably set to 2.5 or more, more preferably set to 3.0 or more, and more preferably set to 3.5 or more.
  • Mo/C is greater than 12.0, the Mo precipitates tend to become coarse, and the toughness and hydrogen embrittlement resistance are deteriorated.
  • the Mo/C ratio is preferably 10.0 or less, more preferably 8.0 or less, further preferably 6.0 or less, and most preferably 5.0 or less.
  • the above components are the basic components, but in addition to the basic composition, optional elements may be included, such as one or more selected from V: 0.30% or less, Cu: 1.00% or less, Ni: 2.0% or less, W: 3.0% or less, H: 0.0010% or less, or Ca: 0.0005-0.005%, or any combination of these.
  • V 0.30% or less
  • Cu 1.00% or less
  • Ni 2.0% or less
  • W 3.0% or less.
  • V, Cu, Ni and W are all elements that contribute to increasing the strength of steel, and one or more can be selected and contained as necessary.
  • V 0.30% or less
  • V is an element that forms precipitates and carbonitrides and contributes to strengthening of steel.
  • the V content may be 0% or more, but in order to obtain the above-mentioned effects, the V content is preferably 0.02% or more, and more preferably 0.03% or more.
  • the V content is set to 0.30% or less.
  • the V content is preferably 0.20% or less, and more preferably 0.15% or less.
  • Cu 1.00% or less
  • Cu is an element effective in improving toughness and increasing strength, but if the content is too high, weldability deteriorates. Therefore, when Cu is contained, the Cu content is limited to 1.00% or less.
  • the Cu content is preferably 0.75% or less, more preferably 0.50% or less, and even more preferably 0.25% or less.
  • the Cu content may be 0% or more, but it is preferable to contain 0.01% or more to obtain the above effect.
  • Ni 2.0% or less
  • Ni is an element that contributes to increasing the strength of steel and improves toughness and corrosion resistance.
  • the Ni content is desirably 0.03% or more.
  • the Ni content is more preferably 0.1% or more.
  • Ni content is limited to 2.0% or less.
  • the Ni content is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.
  • W 3.0% or less W is an element that forms precipitates, contributes to increasing the strength of steel by precipitation strengthening, and also dissolves and segregates at prior austenite grain boundaries to contribute to improving hydrogen embrittlement resistance. In order to obtain such effects, it is desirable to set the W content to 0.03% or more.
  • the W content is preferably 0.1% or more.
  • the W content is preferably 2.5% or less.
  • the W content is more preferably 2.0% or less, even more preferably 1.5% or less, and most preferably 1.0% or less.
  • H 0.0010% or less H may be introduced into the steel material in various processes during manufacturing. If the amount of H introduced is large, the risk of cracking after solidification increases and the hydrogen embrittlement resistance deteriorates, so it is important to reduce the amount of hydrogen in the steel material. These effects do not cause problems if the H content is 0.0010% or less, so if H is contained, the H content is set to 0.0010% or less.
  • the H content is preferably 0.0008% or less, more preferably 0.0005% or less, and even more preferably 0.0001% or less. Since a H content of less than 0.00001% causes an increase in cost, the H content is preferably 0.00001% or more. The H content is more preferably 0.00005% or more.
  • the amount of hydrogen is the amount of hydrogen remaining after forming of a plate, steel pipe, etc.
  • Ca 0.0005-0.005%
  • Ca is an element that combines with S to form CaS and effectively controls the morphology of sulfide-based inclusions. Through the control of the morphology of sulfide-based inclusions, it is possible to improve toughness and hydrogen embrittlement resistance.
  • the Ca content when Ca is contained, the Ca content must be 0.0005% or more.
  • the Ca content is 0.001% or less.
  • the Ca content exceeds 0.005%, the effect is saturated and the effect commensurate with the content cannot be expected, which is economically disadvantageous.
  • the Ca content is limited to 0.005% or less.
  • the Ca content is preferably 0.004% or less, more preferably 0.003% or less, and further preferably 0.002% or less. % or less.
  • the balance other than the above components consists of Fe and unavoidable impurities.
  • unavoidable impurities for example, Mg: 0.0008% or less, Co: 0.0008% or less are acceptable.
  • the high-strength seamless steel pipe of the present invention has the above-mentioned composition, and further has a structure in which tempered martensite is the main phase, in which precipitates are present, and further contains precipitates having a diameter of 50 nm or less.
  • Main phase tempered martensite phase
  • the structure in order to ensure a high strength of tensile strength TS of 850 MPa or more, the structure is made mainly of martensite phase, but in order to maintain the ductility and toughness required for a structure, the tempered martensite phase obtained by tempering the martensite phase is made the main phase.
  • the "main phase” here refers to a single phase in which the tempered martensite phase is 100% in area ratio, or a tempered martensite phase of 95% or more containing a second phase of 5% or less in area ratio that does not affect the characteristics.
  • the tempered martensite phase is preferably 97% or more, and more preferably 98% or more. As described above, the tempered martensite phase may be 100%.
  • the second phase in the present invention can be exemplified by a bainite phase, a retained austenite phase, pearlite, or a mixture thereof.
  • the above-mentioned structure of the high-strength seamless steel pipe for high-pressure hydrogen containers of the present invention can be adjusted by appropriately selecting the heating temperature during quenching and the cooling rate during cooling according to the steel composition.
  • the grain size number of the prior austenite grains is 8.5 or more.
  • the grain size number of the prior austenite grains is preferably 9.0 or more, more preferably 9.6 or more, and even more preferably 10.0 or more. It is most preferable that the grain size number of the prior austenite grains is 12.0 or more. There is no particular upper limit, and the smaller the better, but for reasons such as the difficulty of observation and appropriate evaluation, 18.0 or less is preferable.
  • the grain size number is a value measured in accordance with the provisions of JIS G 0551.
  • the grain size number of the prior austenite grains can be adjusted by changing the heating rate, heating temperature, and holding temperature during the quenching process, as well as the number of times the quenching process is performed.
  • the concentration of Mo precipitates is adjusted within an appropriate range depending on the size in order to improve hydrogen embrittlement resistance.
  • the Mo precipitates were identified by the extraction method described in Patent Document 6 and Reference Document 1 using filter filtration.
  • a 10 mm square sample taken at a cross section perpendicular to the rolling direction of the steel pipe (cross section perpendicular to the tube axis direction: C cross section) was electrolyzed with an electrolytic solution, and the precipitates attached to the steel billet surface were placed in a dispersive liquid and irradiated with ultrasonic waves to extract the precipitates in the aqueous solution.
  • the aqueous solution from which the precipitates were extracted was filtered, the precipitates were separated by size, and the precipitates classified by size were dissolved in a dissolving solution, and the Mo concentration was analyzed by ICP to calculate the Mo content of the precipitates at each size.
  • the solution is introduced into plasma to emit an element-specific spectrum, and the concentration of the element in the solution can be obtained from the emission intensity of the light, so that the concentration (mass%) of Mo in the precipitate can be calculated.
  • This method allows the content of Mo in the entire precipitate to be calculated, and the ratio (mass%) of Mo contained in the precipitate to the Mo contained in the steel can be obtained from this value and the content of Mo in the steel.
  • the solid solution concentration of Mo in the steel was obtained by analyzing the concentration of the above-mentioned electrolytic solution by ICP in accordance with Patent Document 7. Furthermore, the content of Mo contained in the precipitates remaining on the filter is analyzed by ICP, and the content of Mo contained in the precipitates exceeding 50 nm is analyzed. The ratio (mass%) of Mo contained in the precipitates having a diameter of 50 nm or less to the Mo contained in the precipitates can be obtained by subtracting the content of Mo contained in the precipitates exceeding 50 nm from the content of Mo contained in the entire precipitates.
  • Patent Document 6 JP 2010-127791 A
  • Patent Document 7 JP 2009-031269 A
  • Reference 1 Ishida et al., Analysis of the Formation State of Fine Precipitates in Steel, Tetsu to Hagane Vol. 107 No. 08
  • the Mo contained in the steel 50% or more by mass is contained in the precipitates.
  • the presence of Mo in the composition of the steel as precipitates improves the hydrogen environment characteristics. Even if the amount of Mo contained in the steel is increased, the effect cannot be expected if it is in solid solution.
  • the greater the amount of Mo precipitates the better the hydrogen trapping ability, and the greater the improvement is achieved by having 50% or more of the Mo contained in the steel in the precipitates. For this reason, it is necessary that 50% or more by mass of the Mo contained in the steel is contained in the precipitates.
  • the upper limit is not particularly limited, but it is preferable that 95% or less by mass of the Mo contained in the steel is present in the precipitates. More preferably, it is 90% or less by mass.
  • Mo precipitates trap hydrogen in steel, inhibiting hydrogen accumulation at grain boundaries and improving grain boundary strength in a hydrogen environment.
  • the size is larger than 50 nm, the hydrogen trapping ability decreases, and the effect on improving grain boundary strength decreases. Therefore, it is necessary that a large amount of Mo is contained in precipitates with a diameter of 50 nm or less.
  • the hydrogen trapping ability improves as the amount of Mo in the precipitate increases, and the Mo contained in fine precipitates with a diameter of 50 nm or less occupies 50% or more by mass of the Mo in the precipitate, which improves the hydrogen trapping ability.
  • the Mo contained in fine precipitates with a diameter of 50 nm or less is limited to the case where the Mo contained in the precipitate is 50% or more by mass. It is preferable that the Mo contained in fine precipitates with a diameter of 50 nm or less is 60% or more by mass of the Mo contained in the precipitate. It is more preferable that the content is 65% or more by mass, and even more preferable that the content is 70% or more by mass. Although the upper limit is not particularly limited, the Mo contained in the fine precipitates having a diameter of 50 nm or less is preferably 95% or less by mass, and more preferably 90% or less by mass, of the Mo contained in the precipitates.
  • the precipitates have a diameter of 20 nm or less.
  • the coarsening of Mo precipitates occurs due to the aggregation and coalescence of fine Mo precipitates, so that the coarsening leads to a decrease in the number of fine Mo precipitates.
  • the lower limit of the diameter of the target precipitates is not particularly limited, it is preferable that the target precipitates are 1 nm or more.
  • nitride-based inclusions and oxide-based inclusions that can be the starting point of fracture in order to improve hydrogen embrittlement resistance.
  • management of the molten steel refining process is important. Desulfurization and dephosphorization are performed in the hot metal pretreatment, and decarburization and dephosphorization are performed in the converter, followed by heating and stirring refining process (LF) and RH vacuum degassing process in the ladle. Sufficient processing time is then ensured for the heating and stirring refining process (LF), as well as the RH vacuum degassing process, and the RH return flow rate is controlled.
  • LF heating and stirring refining process
  • the steel pipe material having the above composition is heated and hot rolled to produce a seamless steel pipe of a specified shape.
  • seamless steel pipes for high-pressure hydrogen containers are used in hydrogen containers with a hydrogen pressure of 1 MPa or more, and more preferably 20 MPa or more. There is no particular upper limit to the hydrogen pressure, but it is intended for pressures up to 120 MPa.
  • the steel pipe material (hereinafter also simply referred to as steel material) used in the present invention is preferably produced by melting molten steel having the above-mentioned composition using a conventional melting method such as a converter, and forming a slab (round slab) using a conventional casting method such as a continuous casting method.
  • the slab may be further hot-rolled to produce a round slab of a specified shape, or may be produced by undergoing ingot making and blooming rolling.
  • the manufacturing method will be described by taking the case where the steel pipe is a seamless steel pipe as an example, but it goes without saying that electric resistance welded pipes and UOE steel pipes can be manufactured by performing processing so as to have a similar thermal history.
  • a steel plate is hot rolled under a temperature condition in the range of from the Ac 3 transformation point to 1000°C, followed by one or more quenching treatments in which the steel plate is rapidly cooled to a surface temperature of 200°C or less, and then, after the quenching treatment, a tempering treatment is performed in which the steel plate is heated to a temperature in the range of 600 to 740°C, and the average heating rate until the tempering treatment temperature is reached is 0.5°C/min or more and the holding time at the tempering temperature is 10 minutes or more and less than 60 minutes, and then welding is performed to manufacture an electric resistance welded pipe, which can obtain similar characteristics.
  • the steel pipe of the present invention can be produced by sequentially carrying out the following steps (1) to (3).
  • (2) A process for casting a steel pipe material after adjusting its composition (2) A rolling process for heating and rolling a slab (cast material) to obtain a steel pipe, and (3) A process for cooling and tempering the steel pipe obtained in the rolling process.
  • Each process will be described below. Note that, unless otherwise specified, the temperature in the following description refers to the temperature at the surface of the slab or steel pipe.
  • Casting speed 1.8 m/min or less If the casting speed is too fast, the number of inclusions increases and hydrogen embrittlement resistance deteriorates, so the casting speed is preferably 1.8 m/min or less. The slower the casting speed, the more hydrogen concentration and inclusions in the steel can be reduced, and the effect is more pronounced at 1.0 m/min or less, so the casting speed is more preferably 1.0 m/min or less. More preferably, it is 0.5 m/min or less, and most preferably, it is 0.1 m/min or less. The lower limit is not particularly limited, but it is preferably 0.01 m/min or more because it is difficult to control the device.
  • a slab having the above-mentioned composition is heated.
  • the slab is not particularly limited, but for example, a billet obtained by a normal continuous casting method can be used.
  • Heating temperature 1050-1350°C If the heating temperature is less than 1050°C, the precipitates in the steel pipe material will not dissolve sufficiently. Therefore, the heating temperature is set to 1050°C or higher.
  • the heating temperature is preferably 1100°C or higher, and more preferably 1150°C or higher.
  • the crystal grains become coarse, and the precipitates such as TiN that precipitated during solidification also become coarse, and the cementite also becomes coarse, so that the toughness of the steel pipe decreases.
  • the heating temperature is limited to a temperature of 1350° C. or less.
  • the heating temperature is preferably 1300° C. or less.
  • the heating temperature is more preferably 1250° C. or less.
  • the predetermined shape refers to, for example, a cylindrical shape such as a steel pipe, and examples thereof include a steel pipe whose end diameter is smaller than the center diameter and a cylinder shape represented by a pressure vessel.
  • the steel pipe having the cylindrical shape preferably has an outer diameter of 200 to 600 mm and a steel pipe length in the pipe axis direction of 500 to 12000 mm.
  • the steel pipe whose end diameter is smaller than the center diameter preferably has an outer diameter of the center part of 200 to 600 mm, an end diameter of 50 to 550 mm, and a steel pipe length in the pipe axis direction of 500 to 12000 mm. It is also preferable that the cylinder has an outer diameter of 200 to 600 mm and a length of the cylinder in the axial direction of 500 to 12,000 mm.
  • the hot rolling also includes a method in which a step of rolling a billet into a steel pipe shape (hot working step) and a pipe expansion step are carried out simultaneously.
  • a sizing process for adjusting the plate thickness may be carried out after the reheating process described below.
  • the resulting seamless steel pipe is subjected to a cooling process in which it is cooled at a rate faster than air cooling until the surface temperature reaches 200°C or below.
  • Cooling treatment after hot rolling average cooling rate: air cooling or more, cooling stop temperature: 200 ° C or less
  • average cooling rate air cooling or more
  • cooling stop temperature 200 ° C or less
  • the average cooling rate is less than 0.1 ° C / s, the metal structure after cooling becomes non-uniform, and the metal structure after the subsequent heat treatment becomes non-uniform.
  • the average cooling rate is preferably 1.0 ° C / s or more, more preferably 10.0 ° C / s or more. Although the upper limit is not particularly limited, the average cooling rate is preferably 1000.0 ° C / s or less.
  • the above-mentioned average cooling rate is the average value of the cooling rate from the Ac3 transformation point to 200°C.
  • [Heat treatment process] Reheating temperature for quenching: Ac 3 transformation point or higher and 1000°C or lower
  • the reheating temperature is set to Ac 3 transformation point or higher.
  • the reheating temperature is preferably Ac 3 +30°C or higher, and more preferably Ac 3 +50°C or higher.
  • Ac 3 point +30°C and Ac 3 point +50°C exceed 1000°C, the above Ac 3 point +30°C or higher and Ac 3 point +50°C or higher are not applied.
  • the reheating temperature for the quenching treatment is limited to 1000° C. or less, preferably 980° C. or less, and more preferably 950° C. or less.
  • the plate After reheating, the plate is quenched, and the plate is quenched until the surface temperature is 200°C or less.
  • the quenching is performed by cooling the plate from the Ac 3 transformation point to 200°C at an average cooling rate of 2.0°C/s or more.
  • the average cooling rate is preferably 5.0°C/s or more, and more preferably 10.0°C/s or more.
  • the upper limit is not particularly limited, but the average cooling rate is preferably 1000.0°C/s or less.
  • the plate After satisfying the above, the plate is preferably water-cooled at an average cooling rate of 2.0°C/s or more from the temperature at the center of the plate thickness to a temperature between the Ac 3 transformation point and 400°C or less.
  • the upper limit is not particularly limited, but the average cooling rate is preferably 1000.0°C/s or less.
  • the surface temperature is preferably cooled to a temperature of 100°C or less.
  • the surface temperature after cooling is preferably low, and the plate is preferably cooled to room temperature.
  • the quenching treatment may be repeated two or more times.
  • the Ac3 transformation point is calculated using the following formula.
  • Ac 3 transformation point (°C) 937-476.5C + 56Si-19.7Mn-16.3Cu-4.9Cr-26.6Ni + 38.1Mo + 124.8V + 136.3Ti + 198Al + 3315B (Here, C, Si, Mn, Cu, Cr, Ni, Mo, V, Ti, Al, B: Content of each element (mass%)) In calculating the Ac3 transformation point, when an element described in the above formula is not contained, the content of the element is set to zero percent.
  • the material After cooling at a rate faster than air cooling, the material is tempered.
  • the tempering process involves heating the material to a temperature in the range of 600-740°C.
  • Tempering temperature 600-740°C
  • the tempering treatment is carried out for the purpose of reducing the dislocation density and precipitating Mo precipitates, thereby improving the toughness and hydrogen embrittlement resistance. Since the precipitation is insufficient, it is not possible to ensure excellent hydrogen embrittlement resistance. Therefore, the tempering temperature is set to 600° C. or higher.
  • the tempering temperature is preferably set to 620° C. or higher, and more preferably set to 640° C. or higher. It is more preferable that the tempering temperature is 660°C or higher, and even more preferable that the tempering temperature is 660°C or higher.
  • the tempering temperature is set to 740°C or lower.
  • the tempering temperature is preferably 710° C. or less, more preferably 700° C. or less, and further preferably 680° C. or less.
  • the average heating rate until the tempering temperature is reached is 0.5°C/min or more Mo precipitates are precipitated during the temperature rise process of tempering, and their size increases. Therefore, if the heating rate until the specified temperature in the tempering process is reached is slow, the size of the precipitates becomes too large, and the desired hydrogen embrittlement resistance properties cannot be obtained. Therefore, the average heating rate until the tempering temperature is reached is set to 0.5°C/min or more, preferably 1.0°C/min or more, and more preferably 2.0°C/min or more. Most preferably, it is set to 5.0°C/min or more. There is no particular upper limit, but if it is too fast, unevenness in the temperature distribution occurs, resulting in inhomogeneity in the material structure, so 50.0°C/min or less is preferable.
  • Holding time at tempering temperature is 10 minutes or more and less than 60 minutes Mo precipitates are most precipitated during tempering. If this time is short, they do not precipitate sufficiently and the desired hydrogen embrittlement resistance cannot be obtained. Holding time at tempering temperature is 10 minutes or more. Holding time at tempering temperature is preferably 15 minutes or more, more preferably 20 minutes or more. In addition, if the holding time at tempering temperature is too long, the size of the precipitates becomes too large, so it is less than 60 minutes. In addition, since the holding time is a factor of increased costs in terms of energy, the tempering time is preferably less than 50 minutes, more preferably less than 40 minutes. It is further preferably less than 30 minutes.
  • the material is cooled at a rate faster than air cooling, and then reheated and quenched at least once by water cooling or the like, after which the above-mentioned tempering process is carried out.
  • the number of quenching processes it is preferable to carry out the process five times or less.
  • a straightening process may be performed in a warm or cold state to correct any defects in the shape of the steel pipe.
  • Table 1 shows the composition of steel No. 1 to 24.
  • Table 2 shows the tempering conditions for each of No. 1 to 24, the area ratio of tempered martensite, the prior austenite grain size number, the percentage by mass of Mo contained in precipitates out of Mo contained in the steel, the percentage of Mo contained in precipitates with a diameter of 50 nm or less out of Mo contained in the precipitates, TS, and relative reduction of area (RRA).
  • Billets having the composition shown in No. 1 to No. 24 in Table 1 were produced at a casting speed of 0.6 m/min, and the billets were heated to 1250 ° C., hot worked and expanded to obtain seamless steel pipes.
  • the seamless steel pipes were produced under conditions in which the expansion was completed at 820 ° C. or higher, and after the hot working, the pipes were cooled to a temperature at which the surface temperature was 200 ° C. or lower at a cooling rate of air cooling or higher.
  • the obtained steel pipes were heated and held at 950 ° C. for steel pipes having an Ac 3 transformation point of 950 ° C. or lower, and heated and held at 1000 ° C.
  • any one of billets No. 5, 8, and 12 having the composition shown in Table 1 was produced at various casting speeds, and the billet was heated to 1250°C and expanded to obtain seamless steel pipes.
  • the steel pipes were produced under conditions in which expansion was completed at 820°C or higher, and after hot working, cooling was performed at a cooling rate of air cooling or higher to a temperature at which the surface temperature was 200°C or lower.
  • the obtained steel pipes having an Ac3 transformation point of 950°C or lower were heated and held at 950°C, and the steel pipes having an Ac3 transformation point of more than 950°C were heated and held at 1000°C, and then water-cooled to 200°C or lower at a condition of 5.0°C/s, and then tempered under the conditions shown in Table 3.
  • the metal structure and mechanical properties of the obtained steel pipes were evaluated.
  • the evaluation method is as follows:
  • the metal structure at the 1/4 position of the wall thickness on the inner side of the obtained steel pipe was evaluated as follows. In a cross section parallel to the longitudinal direction and the thickness direction of the steel pipe, samples were taken so that the 1/4 position of the wall thickness on the inner side and the center position of the wall thickness were the observation surfaces, and the cross section of the taken sample was etched using a 3 vol% nital solution. Scanning electron microscope photographs were taken at an appropriate magnification between 1000 and 5000 times, and tempered martensite, ferrite, bainite, and pearlite were observed.
  • the tempered martensite was judged visually by comparing with the structure photograph in Reference 2, and the structure fraction was determined by binarizing martensite and other regions by image analysis using an image obtained by dividing the SEM photograph into regions based on the above judgment, and the tempered martensite fraction was determined, which was taken as the area fraction of the tempered martensite.
  • Prior austenite ( ⁇ ) was measured by polishing a cross section (C cross section) of a test piece for microstructural observation perpendicular to the longitudinal direction of the pipe, etching it (picral (picric acid-ethanol mixed liquid)) to reveal the prior ⁇ grain boundaries, and observing it using an optical microscope (magnification: 1000 times) and taking images in a field of view of three or more points.
  • the grain size number of the prior ⁇ grains was determined using a cut-off method in accordance with the provisions of JIS G 0551. The average value determined above was taken as the grain size number of the prior ⁇ grains of each steel pipe.
  • the method for measuring Mo precipitates in steel material collected from steel pipes is as follows. Identification of Mo precipitates was performed by an extraction method in which the steel material was electrolyzed and the obtained precipitates were filtered. A 10 mm square sample collected at a cross section perpendicular to the rolling direction of the steel pipe (cross section perpendicular to the tube axis direction: C cross section) was dissolved in a steel piece by constant current electrolysis using a 10% AA-based electrolyte, placed in a 0.05 wt% sodium hexametaphosphate aqueous solution, and irradiated with ultrasonic waves to extract the precipitates.
  • the solution was filtered through a filter with a filter diameter of 50 nm to obtain precipitates of 50 nm or less.
  • the precipitates of 50 nm or less that passed through the filter and those of more than 50 nm on the filter were subjected to heating white smoke treatment with sulfuric acid, perchloric acid, and nitric acid, and then dissolved in hydrochloric acid.
  • the precipitate solution and the electrolyte solution containing the dissolved Mo were then subjected to concentration analysis by ICP to calculate the Mo concentration (mass%) and the dissolved Mo concentration (mass%) in the precipitates of each size.
  • the Mo amount and the dissolved Mo amount in all the precipitates obtained as above were added together to obtain the total Mo amount in the steel, and the Mo amount in all precipitates/total Mo amount and the Mo amount in precipitates of 50 nm or less/the Mo amount in all precipitates were obtained.
  • Test pieces were taken from a cross section perpendicular to the steel pipe axis (C direction) at a position 1/4 of the wall thickness from the inner surface of the steel pipe, with the longitudinal direction of the test piece being in the C direction.
  • a bar-shaped test piece as specified in JIS Z 2201 "Tensile test piece for metal materials" was used. The test was performed using the method specified in JIS Z2241, and the maximum load was taken as the TS of the steel pipe. It is preferable to center the sampling at the 1/4 position of the wall thickness, but for steel pipes with a small wall thickness (for example, a wall thickness of 45 mm or less), a method of sampling without centering the sampling at the 1/4 position of the wall thickness can also be used.
  • Hydrogen embrittlement resistance was evaluated from the relative reduction of area (RRA) of the test piece after a slow strain rate tensile test in hydrogen gas in accordance with ASTM G 142.
  • RRA relative reduction of area
  • ASTM G 142 ASTM G 142.
  • the steel undergoes plastic deformation, and the area of the fracture surface becomes smaller, so the reduction of area ⁇ air becomes larger.
  • the elongation of the steel decreases, so the material breaks before it can be reduced, and the area of the fracture surface remains large. Therefore, the reduction of area ⁇ H of the fracture surface after the test in hydrogen becomes smaller, unlike in air. Hydrogen embrittlement resistance was evaluated from this decrease in reduction of area.
  • RRA ⁇ H / ⁇ air ⁇ 100
  • the relative reduction in area obtained from a slow strain rate tensile test (tensile speed 0.002 mm/s) at room temperature under 105 MPa hydrogen gas is shown in Table 2.
  • ⁇ air is the test piece cross-sectional area after the test in air/the cross-sectional area before the test
  • ⁇ H is the test piece cross-sectional area after the test in hydrogen/the cross-sectional area before the test.
  • All of the inventive examples satisfied the conditions of a TS of 850 MPa or more in tensile tests in air, and an RRA of 60% or more in slow strain rate tensile tests in hydrogen gas.

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Abstract

Le but de la présente invention est de fournir : un tuyau en acier sans soudure à haute résistance qui est destiné à un récipient d'hydrogène à haute pression et a une excellente résistance à la fragilisation par l'hydrogène; et un procédé de fabrication y relatif.　Ce tuyau en acier sans soudure et à haute résistance pour un récipient d'hydrogène haute pression a une composition spécifique et a une structure dont le rapport surfacique de revenu martensitique est d'au moins 95%, sachant qu'au moins 50% en masse du Mo contenu dans l'acier sont contenus dans des précipités, qu'au moins 50% en masse du Mo contenu dans les précipités sont contenus dans des précipités d'un diamètre de maximum 50 nm, et dont la résistance à la traction TS est de minimum 850 MPa.
PCT/JP2024/007115 2023-03-07 2024-02-27 Tuyau en acier sans soudure et à haute résistance pour récipient d'hydrogène haute pression et son procédé de fabrication Pending WO2024185593A1 (fr)

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