US20250327154A1 - Fe-Cr-Ni ALLOY MATERIAL - Google Patents

Fe-Cr-Ni ALLOY MATERIAL

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US20250327154A1
US20250327154A1 US18/718,534 US202318718534A US2025327154A1 US 20250327154 A1 US20250327154 A1 US 20250327154A1 US 202318718534 A US202318718534 A US 202318718534A US 2025327154 A1 US2025327154 A1 US 2025327154A1
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alloy material
content
alloy
present
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Hideki Takabe
Kazuya NAKANE
Kohei Matsuda
Seiya Okada
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Nippon Steel Corp
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Nippon Steel Corp
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    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
    • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
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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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    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
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    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite

Definitions

  • the present disclosure relates to an alloy material, and more particularly relates to a Fe—Cr—Ni alloy material.
  • oil wells and gas wells In oil wells and gas wells (hereinafter, oil wells and gas wells are collectively referred to simply as “oil wells”), alloy materials for oil wells which are typified by oil country tubular goods are used.
  • Many oil wells are sour environments that contain hydrogen sulfide, which is corrosive.
  • the term “sour environment” means an acidified environment containing hydrogen sulfide. In some cases, sour environments also contain carbon dioxide, and not just hydrogen sulfide. Materials used in such sour environments are required to have excellent corrosion resistance.
  • Examples of materials which are required to have excellent corrosion resistance include 18-8 stainless steel materials such as SUS304H, SUS316H, SUS321H, and SUS347H, and Fe—Cr—Ni alloy materials represented by Alloy 800H, which is defined as NCF800H by the JIS Standard.
  • Fe—Cr—Ni alloy materials have excellent corrosion resistance in comparison to 18-8 stainless steel.
  • Fe—Cr—Ni alloy materials are also more excellent in economic efficiency in comparison to a Ni-base alloy material represented by Alloy 617. Therefore, Fe—Cr—Ni alloy materials may in some cases be used as alloy materials for oil wells for use in a sour environment.
  • Patent Literature 1 Japanese Patent Application Publication No. 2-217445 (Patent Literature 1) and International Application Publication No. WO2015/072458 (Patent Literature 2) each proposes an alloy material for oil wells that has excellent corrosion resistance.
  • Patent Literature 1 discloses an alloy material which is a Fe—Cr—Ni alloy that consists essentially of Ni: 27 to 32%, Cr: 24 to 28%, Cu: 1.25 to 3.0%, Mo: 1.0 to 3.0%, Si: 1.5 to 2.75%, and Mn: 1.0 to 2.0%, and the following elements whose amounts are controlled as follows: N: 0.015% or less, B: 0.10% or less, C: 0.10% or less, Al: 0.30% or less, P: 0.03% or less, and S: 0.02% or less, with the balance being Fe and impurities. It is disclosed in Patent Literature 1 that this alloy material has high strength, galling resistance, and corrosion resistance under stress.
  • Patent Literature 2 discloses an alloy material that is an Ni—Cr alloy material having a chemical composition consisting of, by mass %, Si: 0.01 to 0.5%, Mn: 0.01 to less than 1.0%, Cu: 0.01 to less than 1.0%, Ni: 48 to less than 55%, Cr: 22 to 28%, Mo: 5.6 to less than 7.0%, N: 0.04 to 0.16%, sol.
  • Patent Literature 2 It is disclosed in Patent Literature 2 that this alloy material is excellent in hot workability and toughness, and is also excellent in corrosion resistance (stress corrosion cracking resistance in environments in which the temperature is a high temperature of more than 200° C. and which contain hydrogen sulfide), and has a yield strength (0.2% proof stress) of 965 MPa or more.
  • Patent Literature 1 Japanese Patent Application Publication No. 2-217445
  • Patent Literature 2 International Application Publication No. WO2015/072458
  • an inclined well in addition to vertical wells that are drilled straight down vertically.
  • An inclined well is formed by drilling in such a way that the extending direction of the well is bent from vertically downward to the horizontal direction.
  • an inclined well can cover a wide range of strata in which a production fluid such as crude oil or gas is buried, and can thus increase the efficiency of producing a production fluid.
  • the alloy material when used for such kinds of inclined wells, the alloy material may be loaded with a compressive force.
  • a Fe—Cr—Ni alloy material which is expected to be used in an inclined well not only has high strength, but also has a reduced strength anisotropy of the alloy material.
  • the strength of the relevant Fe—Cr—Ni alloy material only the tensile yield strength is investigated. That is, in the aforementioned Patent Literatures 1 and 2, the strength anisotropy of the alloy material has not been investigated.
  • An objective of the present disclosure is to provide a Fe—Cr—Ni alloy material that has high strength and in which strength anisotropy has been reduced.
  • a Fe—Cr—Ni alloy material according to the present disclosure consists of, by mass %,
  • the Fe—Cr—Ni alloy material according to the present disclosure has high strength, and strength anisotropy of the Fe—Cr—Ni alloy material is reduced.
  • the present inventors focused their attention on a Fe—Cr—Ni alloy material having a tensile yield strength of 110 ksi (758 MPa) or more.
  • the present inventors conducted studies from the viewpoint of the chemical composition with regard to the strength anisotropy of a Fe—Cr—Ni alloy material having a tensile yield strength of 758 MPa or more.
  • the present inventors considered that if a Fe—Cr—Ni alloy material consists of, by mass %, C: 0.030% or less, Si: 0.01 to 1.00%, Mn: 0.01 to 2.00%, P: 0.030% or less, S: 0.0050% or less, Ni: 29.0 to 36.5%, Cr: 23.0 to 27.5%, Mo: 2.00 to 6.00%, Al: 0.01 to 0.30%, rare earth metal: 0.016 to 0.100%, N: 0.220 to 0.500%, O: 0.010% or less, W: 0 to 6.0%, Cu: 0 to 2.00%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, V: 0 to 0.50%, Ti: 0 to 0.50%, Nb: 0 to 0.50%, and Co: 0 to 2.00%, with the balance being Fe and impurities, there is a possibility that the Fe—Cr—Ni alloy material will have a tensile yield strength of
  • the stacking fault energy is liable to become large.
  • the degree of work hardening in response to applied strain decreases. That is, if the stacking fault energy can be made small, it will be easier for work hardening to occur in response to strain.
  • the alloy material will be less susceptible to the influence of anisotropy of strain applied in the production process, and thus the strength anisotropy of the alloy material can be reduced.
  • the present inventors focused their attention on the stacking fault energy of a Fe—Cr—Ni alloy material having the chemical composition described above and a tensile yield strength of 758 MPa or more, and conducted detailed studies regarding a technique for reducing the strength anisotropy of the alloy material.
  • a technique for reducing the strength anisotropy of the alloy material As a result of the detailed studies of the present inventors, it was revealed that in a Fe—Cr—Ni alloy material having the chemical composition described above, when the chemical composition also satisfies the following Formula (1), on the condition that the other requirements of the present embodiment are satisfied, the Fe—Cr—Ni alloy material has a tensile yield strength of 758 MPa or more and, in addition, strength anisotropy can be reduced.
  • I is an index of the stacking fault energy of an alloy material having the above chemical composition.
  • a ratio (compressive YS/tensile YS) of the compressive yield strength (compressive YS) to the tensile yield strength (tensile YS) is also referred to as an “anisotropy index AI”.
  • I that is an index of the stacking fault energy of an alloy material and the anisotropy index AI of the alloy material is described specifically using the drawings.
  • FIG. 1 is a view illustrating the relation between a value of I and the anisotropy index AI in the present examples.
  • FIG. 1 was created using the value of I and the anisotropy index AI in, among examples to be described later, those examples in which the composition and the like other than I satisfied the conditions of the present embodiment.
  • the anisotropy index AI is increased to 0.800 or more.
  • the anisotropy index AI decreases to less than 0.800. Therefore, in the Fe—Cr—Ni alloy material according to the present embodiment, the chemical composition described above is satisfied, and in addition, I is made less than 15.0. As a result, in the Fe—Cr—Ni alloy material according to the present embodiment, on the condition that the other requirements of the present embodiment are satisfied, the strength anisotropy can be reduced.
  • a Fe—Cr—Ni alloy material having the chemical composition described above has the microstructure consisting of austenite.
  • the phrase “the microstructure consisting of austenite” means that the amount of any phase other than austenite is negligibly small. Therefore, the present inventors focused their attention on the austenite grains of a Fe—Cr—Ni alloy material having the above chemical composition including Formula (1) and having a tensile yield strength of 758 MPa or more, and conducted detailed studies regarding a technique for reducing the strength anisotropy of the alloy material.
  • FIG. 2 is a view illustrating the relation between a value of the standard deviation ⁇ of the grain size numbers and the anisotropy index AI in the present examples.
  • the anisotropy index AI is increased to 0.800 or more.
  • the standard deviation ⁇ of the grain size numbers is more than 0.80, the anisotropy index AI decreases to less than 0.800. Therefore, in the Fe—Cr—Ni alloy material according to the present embodiment, the chemical composition described above is satisfied, I is less than 15.0, the tensile yield strength is 758 MPa or more, and in addition, the standard deviation ⁇ of the grain size numbers is made 0.80 or less. As a result, in the Fe—Cr—Ni alloy material according to the present embodiment, the strength anisotropy can be reduced.
  • the gist of the Fe—Cr—Ni alloy material according to the present embodiment which has been completed based on the findings described above, is as follows.
  • the shape of the Fe—Cr—Ni alloy material according to the present embodiment is not particularly limited.
  • the shape of the Fe—Cr—Ni alloy material according to the present embodiment may be a plate shape, may be a bar shape having a circular cross section, or may be a pipe shape.
  • the Fe—Cr—Ni alloy material according to the present embodiment may be an alloy plate, may be an alloy bar having a circular cross section, or may be an alloy pipe.
  • the term “alloy pipe” may refer to a seamless alloy pipe or may refer to a welded alloy pipe. In a case where the alloy material is an alloy pipe for oil wells, the alloy material is preferably a seamless alloy pipe.
  • the chemical composition of the Fe—Cr—Ni alloy material according to the present embodiment contains the following elements.
  • Carbon (C) is an impurity which is unavoidably contained. That is, a lower limit of the content of C is more than 0%. If the content of C is too high, even if the contents of other elements are within the range of the present embodiment, Cr carbides will form at grain boundaries. The Cr carbides will increase cracking susceptibility at grain boundaries. As a result, corrosion resistance of the alloy material will decrease. Therefore, the content of C is to be 0.030% or less.
  • a preferable upper limit of the content of C is 0.028%, more preferably is 0.025%, further preferably is 0.020%, and further preferably is 0.015%.
  • the content of C is preferably as low as possible. However, extremely reducing the content of C will significantly increase the production cost. Therefore, when industrial manufacturing is taken into consideration, a preferable lower limit of the content of C is 0.001%, and more preferably is 0.003%.
  • Silicon (Si) deoxidizes the alloy. If the content of Si is too low, the aforementioned advantageous effect will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of Si is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. Therefore, the content of Si is to be 0.01 to 1.00%. A preferable lower limit of the content of Si is 0.05%, more preferably is 0.10%, and further preferably is 0.20%. A preferable upper limit of the content of Si is 0.80%, more preferably is 0.60%, and further preferably is 0.50%.
  • Manganese (Mn) deoxidizes and desulfurizes the alloy. If the content of Mn is too low, the aforementioned advantageous effect will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of Mn is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. Therefore, the content of Mn is to be 0.01 to 2.00%.
  • a preferable lower limit of the content of Mn is 0.10%, more preferably is 0.20%, and further preferably is 0.30%.
  • a preferable upper limit of the content of Mn is 1.80%, more preferably is 1.50%, further preferably is 1.20%, further preferably is 1.00%, and further preferably is 0.80%.
  • Phosphorus (P) is an impurity which is unavoidably contained. That is, a lower limit of the content of P is more than 0%. P segregates to grain boundaries. Therefore, if the content of P is too high, hot workability and corrosion resistance of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. Accordingly, the content of P is to be 0.030% or less. A preferable upper limit of the content of P is 0.025%, and more preferably is 0.020%. The content of P is preferably as low as possible. However, extremely reducing the content of P will significantly increase the production cost. Therefore, when industrial manufacturing is taken into consideration, a preferable lower limit of the content of P is 0.001%, more preferably is 0.002%, and further preferably is 0.003%.
  • Sulfur(S) is an impurity which is unavoidably contained. That is, a lower limit of the content of S is more than 0%. S segregates to grain boundaries. Therefore, if the content of S is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. Therefore, the content of S is to be 0.0050% or less.
  • a preferable upper limit of the content of S is 0.0040%, more preferably is 0.0030%, and further preferably is 0.0020%.
  • the content of S is preferably as low as possible. However, extremely reducing the content of S will significantly increase the production cost. Therefore, when industrial manufacturing is taken into consideration, a preferable lower limit of the content of S is 0.0001%, more preferably is 0.0003%, and further preferably is 0.0005%.
  • Nickel (Ni) is an austenite forming element, and stabilizes the austenite in the alloy material. If the content of Ni is too low, the aforementioned advantageous effect will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of Ni is too high, even if the contents of other elements are within the range of the present embodiment, the amount of dissolved N will decrease, and in some cases strength of the alloy material will decrease. In such a case, in addition, the production cost will significantly increase. Therefore, the content of Ni is to be 29.0 to 36.5%. A preferable lower limit of the content of Ni is 29.5%, and more preferably is 30.0%. A preferable upper limit of the content of Ni is 36.0%, more preferably is 35.5%, and further preferably is 35.0%.
  • Chromium (Cr) increases corrosion resistance of the alloy material. Cr also increases the amount of dissolved N, thereby increasing strength of the alloy material. If the content of Cr is too low, the aforementioned advantageous effects will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of Cr is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. In such a case, in addition, intermetallic compounds typified by the ⁇ phase will be easily formed, and corrosion resistance of the alloy material will decrease. Therefore, the content of Cr is to be 23.0 to 27.5%. A preferable lower limit of the content of Cr is 23.5%, more preferably is 24.0%, and further preferably is 24.5%. A preferable upper limit of the content of Cr is 27.0%, and more preferably is 26.5%.
  • Molybdenum (Mo) contributes to stabilization of a corrosion protection film, thereby increasing corrosion resistance of the alloy material. Mo also increases strength of the alloy material by solid-solution strengthening. If the content of Mo is too low, the aforementioned advantageous effects will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of Mo is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. In such a case, in addition, the production cost will significantly increase. Therefore, the content of Mo is to be 2.00 to 6.00%. A preferable lower limit of the content of Mo is 2.20%, more preferably is 2.40%, and further preferably is 2.50%. A preferable upper limit of the content of Mo is 5.50%, more preferably is 5.00%, further preferably is 4.50%, and further preferably is 4.00%.
  • Al also forms oxides to immobilize oxygen, and thereby increases hot workability of the alloy material.
  • Al enhances an impact resistance property and corrosion resistance of the alloy material. If the content of Al is too low, the aforementioned advantageous effects will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of Al is too high, even if the contents of other elements are within the range of the present embodiment, Al oxides will excessively form and hot workability of the alloy material will, on the contrary, decrease. Therefore, the content of Al is to be 0.01 to 0.30%.
  • a preferable lower limit of the content of Al is 0.02%, more preferably is 0.03%, and further preferably is 0.05%.
  • a preferable upper limit of the content of Al is 0.25%, and more preferably is 0.20%. Note that, in the present description, the term “content of Al” means the content of “acid-soluble Al”, that is, the content of sol. Al.
  • Rare earth metal (REM) fixes S in the alloy as a sulfide to make it harmless, thereby increasing hot workability of the alloy material.
  • REM also increases the corrosion resistance of the alloy material. If the content of REM is too low, aforementioned advantageous effects will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of REM is too high, even if the contents of other elements are within the range of the present embodiment, coarse oxides will be formed in the alloy material, and hot workability of the alloy material will, on the contrary, decrease. Therefore, the content of REM is to be 0.016 to 0.100%. A preferable lower limit of the content of REM is 0.018%, and more preferably is 0.020%. A preferable upper limit of the content of REM is 0.080%, more preferably is 0.060%, and further preferably is 0.050%.
  • REM means one or more elements selected from the group consisting of scandium (Sc) which is the element with atomic number 21, yttrium (Y) which is the element with atomic number 39, and the elements from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71 that are lanthanoids.
  • content of REM means the total content of these elements.
  • Nitrogen (N) increases strength of the alloy material by solid-solution strengthening. If the content of N is too low, the aforementioned advantageous effect will not be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the content of N is too high, even if the contents of other elements are within the range of the present embodiment, a large amount of Cr nitrides will be formed, and corrosion resistance of the alloy material will decrease. Therefore, the content of N is to be 0.220 to 0.500%.
  • a preferable lower limit of the content of N is 0.225%, more preferably is 0.230%, further preferably is 0.235%, and further preferably is 0.240%.
  • a preferable upper limit of the content of N is 0.480%, more preferably is 0.450%, and further preferably is 0.400%.
  • Oxygen (O) is an impurity which is unavoidably contained. That is, a lower limit of the content of O is more than 0%. O combines with REM to form oxides. Therefore, if the content of O is too high, even if the contents of other elements are within the range of the present embodiment, coarse oxides will be formed in the alloy material, and hot workability of the alloy material will decrease. In such a case, in addition, corrosion resistance of the alloy material will decrease. Therefore, the content of O is to be 0.010% or less. A preferable upper limit of the content of O is 0.008%, and more preferably is 0.005%. The content of O is preferably as low as possible. However, extremely reducing the content of O will significantly increase the production cost. Therefore, when industrial manufacturing is taken into consideration, a preferable lower limit of the content of O is 0.0001%, more preferably is 0.001%, and further preferably is 0.002%.
  • the balance of the chemical composition of the Fe—Cr—Ni alloy material according to the present embodiment is Fe and impurities.
  • impurities means substances which are mixed in from ore and scrap as the raw material or from the production environment or the like when industrially producing the Fe—Cr—Ni alloy material, and which are permitted within a range that does not have a noticeable adverse effect on the operational advantages of the Fe—Cr—Ni alloy material according to the present embodiment.
  • the chemical composition of the Fe—Cr—Ni alloy material according to the present embodiment may further contain one or more elements selected from the group consisting of W and Cu. Each of these elements increases corrosion resistance of the alloy material.
  • Tungsten (W) is an optional element, and does not have to be contained. That is, the content of W may be 0%. When contained, W contributes to stabilization of a corrosion protection film, thereby increasing corrosion resistance of the alloy material. W also increases strength of the alloy material by solid-solution strengthening. If even a small amount of W is contained, the aforementioned advantageous effects will be obtained to a certain extent. However, if the content of W is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. Therefore, the content of W is to be 0 to 6.0%. A preferable lower limit of the content of W is more than 0%, more preferably is 0.1%, further preferably is 0.5%, and further preferably is 1.0%. A preferable upper limit of the content of W is 5.5%, more preferably is 5.0%, further preferably is 4.5%, and further preferably is 4.0%.
  • Copper (Cu) is an optional element, and does not have to be contained. That is, the content of Cu may be 0%. When contained, Cu contributes to stabilization of a corrosion protection film, thereby increasing corrosion resistance of the alloy material. If even a small amount of Cu is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of Cu is too high, hot workability of the alloy material will decrease even if the contents of other elements are within the range of the present embodiment. Therefore, the content of Cu is to be 0 to 2.00%. A preferable lower limit of the content of Cu is more than 0%, more preferably is 0.01%, further preferably is 0.02%, and further preferably is 0.04%. A preferable upper limit of the content of Cu is 1.80%, more preferably is 1.50%, and further preferably is 1.00%.
  • the chemical composition of the Fe—Cr—Ni alloy material according to the present embodiment may further contain one or more elements selected from the group consisting of Ca and Mg. Each of these elements increases hot workability of the alloy material.
  • Ca is an optional element, and does not have to be contained. That is, the content of Ca may be 0%. When contained, Ca fixes S in the alloy as a sulfide to make it harmless, thereby increasing hot workability of the alloy material. If even a small amount of Ca is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of Ca is too high, even if the contents of other elements are within the range of the present embodiment, coarse oxides will be formed in the alloy material, and hot workability of the alloy material will, on the contrary, decrease. Therefore, the content of Ca is to be 0 to 0.0100%.
  • a preferable lower limit of the content of Ca is more than 0%, more preferably is 0.0001%, further preferably is 0.0003%, and further preferably is 0.0005%.
  • a preferable upper limit of the content of Ca is 0.0080%, more preferably is 0.0060%, and further preferably is 0.0050%.
  • Magnesium (Mg) is an optional element, and does not have to be contained. That is, the content of Mg may be 0%. When contained, Mg fixes S in the alloy as a sulfide to make it harmless, thereby increasing hot workability of the alloy material. If even a small amount of Mg is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of Mg is too high, even if the contents of other elements are within the range of the present embodiment, coarse oxides will be formed in the alloy material, and hot workability of the alloy material will, on the contrary, decrease. Therefore, the content of Mg is to be 0 to 0.0100%.
  • a preferable lower limit of the content of Mg is more than 0%, more preferably is 0.0001%, further preferably is 0.0003%, and further preferably is 0.0005%.
  • a preferable upper limit of the content of Mg is 0.0080%, more preferably is 0.0060%, and further preferably is 0.0040%.
  • the chemical composition of the Fe—Cr—Ni alloy material according to the present embodiment may further contain one or more elements selected from the group consisting of V, Ti, and Nb. Each of these elements increases strength of the alloy material.
  • Vanadium (V) is an optional element, and does not have to be contained. That is, the content of V may be 0%. When contained, V forms carbo-nitrides and the like with C and N, thereby increasing strength of the alloy material. If even a small amount of V is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of V is too high, even if the contents of other elements are within the range of the present embodiment, carbo-nitrides and the like will be excessively formed and ductility of the alloy material will decrease. Therefore, the content of V is to be 0 to 0.50%.
  • a preferable lower limit of the content of V is more than 0%, more preferably is 0.01%, further preferably is 0.03%, and further preferably is 0.05%.
  • a preferable upper limit of the content of V is 0.40%, more preferably is 0.30%, and further preferably is 0.20%.
  • Titanium (Ti) is an optional element, and does not have to be contained. That is, the content of Ti may be 0%. When contained, Ti forms carbo-nitrides and the like with C and N, thereby increasing strength of the alloy material. If even a small amount of Ti is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of Ti is too high, even if the contents of other elements are within the range of the present embodiment, carbo-nitrides and the like will be excessively formed and ductility of the alloy material will decrease. Therefore, the content of Ti is to be 0 to 0.50%.
  • a preferable lower limit of the content of Ti is more than 0%, more preferably is 0.01%, further preferably is 0.03%, and further preferably is 0.05%.
  • a preferable upper limit of the content of Ti is 0.40%, more preferably is 0.30%, further preferably is 0.20%, and further preferably is 0.10%.
  • Niobium (Nb) is an optional element, and does not have to be contained. That is, the content of Nb may be 0%. When contained, Nb forms carbo-nitrides and the like with C and N, thereby increasing strength of the alloy material. If even a small amount of Nb is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of Nb is too high, even if the contents of other elements are within the range of the present embodiment, carbo-nitrides and the like will be excessively formed and ductility of the alloy material will decrease. Therefore, the content of Nb is to be 0 to 0.50%.
  • a preferable lower limit of the content of Nb is more than 0%, more preferably is 0.01%, further preferably is 0.03%, and further preferably is 0.05%.
  • a preferable upper limit of the content of Nb is 0.40%, more preferably is 0.30%, further preferably is 0.20%, and further preferably is 0.10%.
  • the chemical composition of the Fe—Cr—Ni alloy material according to the present embodiment may further contain Co.
  • Co Co
  • the content of Co may be 0%.
  • Co stabilizes the austenite in the alloy material. If even a small amount of Co is contained, the aforementioned advantageous effect will be obtained to a certain extent. However, if the content of Co is too high, the production cost will significantly increase even if the contents of other elements are within the range of the present embodiment. Therefore, the content of Co is to be 0 to 2.00%.
  • a preferable lower limit of the content of Co is more than 0%, more preferably is 0.01%, further preferably is 0.05%, and further preferably is 0.10%.
  • a preferable upper limit of the content of Co is 1.50%, more preferably is 1.20%, further preferably is 1.00%, and further preferably is 0.50%.
  • the Fe—Cr—Ni alloy material according to the present embodiment has the chemical composition described above, and also satisfies the following Formula (1):
  • the alloy material has the chemical composition described above, if I is less than 15.0, the stacking fault energy will be small.
  • the anisotropy index AI can be increased to 0.800 or more. Therefore, in the Fe—Cr—Ni alloy material according to the present embodiment, on the premise that the Fe—Cr—Ni alloy material has the chemical composition described above, I is made less than 15.0.
  • the strength anisotropy can be reduced even when the Fe—Cr—Ni alloy material has a tensile yield strength of 758 MPa or more.
  • a preferable upper limit of I is 14.5, more preferably is 14.0, further preferably is 13.5, and further preferably is 13.0.
  • a lower limit of I is not particularly limited, and for example is ⁇ 70.0.
  • a preferable lower limit of I is ⁇ 60.0.
  • the Fe—Cr—Ni alloy material according to the present embodiment has the chemical composition described above, satisfies Formula (1), and, in addition, the standard deviation ⁇ of the grain size numbers of austenite grains is made 0.80 or less. As a result, in the Fe—Cr—Ni alloy material according to the present embodiment, strength anisotropy can be reduced even when the Fe—Cr—Ni alloy material has a tensile yield strength of 758 MPa or more.
  • the present inventors surmise that, because of the mechanism described above, in a Fe—Cr—Ni alloy material that has the above chemical composition and satisfies Formula (1), if the standard deviation ⁇ of the grain size numbers of austenite grains is made 0.80 or less, even when the Fe—Cr—Ni alloy material has a tensile yield strength of 758 MPa or more, strength anisotropy can be decreased.
  • a preferable upper limit of the standard deviation ⁇ of the grain size numbers of austenite grains is 0.78, more preferably is 0.75, and further preferably is 0.73.
  • the standard deviation ⁇ of the grain size numbers of austenite grains can be determined by the following method. Specifically, a test specimen for microstructure observation is prepared from the Fe—Cr—Ni alloy material according to the present embodiment. If the alloy material is plate-shaped, the test specimen is to be prepared from a central portion of the thickness. If the alloy material is pipe-shaped, the test specimen is to be prepared from a central portion of the wall thickness. If the alloy material is bar-shaped having a circular cross section, the test specimen is to be prepared from an R/2 position. In the present description, the term “R/2 position” means the center position of a radius R in a cross section perpendicular to the axial direction. Note that, the size of the test specimen is not particularly limited as long as an observation surface to be described later can be obtained.
  • etching is performed using aqua regia (solution in which hydrochloric acid and nitric acid are mixed at a ratio of 3:1) to reveal austenite grain boundaries.
  • aqua regia solution in which hydrochloric acid and nitric acid are mixed at a ratio of 3:1
  • An arbitrary 10 visual fields are specified from the observation surface, and observation is performed with an optical microscope and photographic images are generated.
  • the magnification in the microscopic observation can be set as appropriate according to the grain size. Specifically, in the microscopic observation, for example, the magnification is set so that 50 or more grains are included in each visual field.
  • the Fe—Cr—Ni alloy material according to the present embodiment has the chemical composition described above, satisfies Formula (1), and, in addition, in the Fe—Cr—Ni alloy material, the standard deviation ⁇ of the grain size numbers of austenite grains is 0.80 or less. As a result, in the Fe—Cr—Ni alloy material according to the present embodiment, strength anisotropy is reduced even when the Fe—Cr—Ni alloy material has a tensile yield strength of 758 MPa or more.
  • a preferable lower limit of the tensile yield strength is 800 MPa, more preferably is 830 MPa, and further preferably is 860 MPa.
  • an upper limit of the tensile yield strength is not particularly limited, and for example may be 1240 MPa, may be 1200 MPa, or may be 1150 MPa.
  • the compressive yield strength is not particularly limited.
  • a lower limit of the compressive yield strength in the present embodiment may be 606 MPa, may be 630 MPa, or may be 660 MPa.
  • An upper limit of the compressive yield strength in the present embodiment for example, may be less than 1240 MPa, may be less than 1200 MPa, or may be less than 1150 MPa. Methods for measuring the tensile yield strength and the compressive yield strength in the present embodiment will be described later.
  • the Fe—Cr—Ni alloy material according to the present embodiment has the chemical composition described above, satisfies Formula (1), and in addition, the standard deviation ⁇ of the grain size numbers of austenite grains in the Fe—Cr—Ni alloy material is 0.80 or less. As a result, even when the Fe—Cr—Ni alloy material according to the present embodiment has a tensile yield strength of 758 MPa or more, strength anisotropy is reduced.
  • the phrase “strength anisotropy is reduced” means that an anisotropy index AI is 0.800 or more.
  • anisotropy index AI means the ratio (compressive YS/tensile YS) of the compressive yield strength (compressive YS) to the tensile yield strength (tensile YS).
  • a preferable lower limit of the anisotropy index AI is 0.820, more preferably is 0.830, and further preferably is 0.850. Note that, an upper limit of the anisotropy index AI is practically less than 1.000, more preferably is 0.999, further preferably is 0.990, and further preferably is 0.980.
  • the anisotropy index AI, the tensile yield strength, and the compressive yield strength of the Fe—Cr—Ni alloy material according to the present embodiment can be determined by the following methods. First, the tensile yield strength and the compressive yield strength of the Fe—Cr—Ni alloy material according to the present embodiment are determined.
  • the tensile yield strength of the Fe—Cr—Ni alloy material according to the present embodiment can be determined by the following method.
  • a tensile test is carried out by a method in accordance with ASTM E8/E8M (2021).
  • a round bar specimen is prepared from the alloy material according to the present embodiment. If the alloy material is plate-shaped, the round bar specimen is prepared from a central portion of the thickness. If the alloy material is pipe-shaped, the round bar specimen is prepared from a central portion of the wall thickness. If the alloy material is bar-shaped having a circular cross section, the round bar specimen is prepared from an R/2 position. Regarding the size of the round bar specimen, for example, the round bar specimen has a parallel portion diameter of 4 mm and a gage length of 20 mm.
  • the axial direction of the round bar specimen is to be parallel to the rolling elongation direction of the alloy material.
  • a tensile test is carried out in air at normal temperature (25° C.) using the round bar specimen, and the obtained 0.2% offset proof stress is defined as the tensile yield strength (MPa).
  • MPa tensile yield strength
  • MPa tensile yield strength
  • the compressive yield strength of the Fe—Cr—Ni alloy material according to the present embodiment can be determined by the following method.
  • a compression test is carried out by a method in accordance with ASTM E9 (2019).
  • a cylindrical test specimen is prepared from the alloy material according to the present embodiment. If the alloy material is plate-shaped, the cylindrical test specimen is prepared from a central portion of the thickness. If the alloy material is pipe-shaped, the cylindrical test specimen is prepared from a central portion of the wall thickness. If the alloy material is a bar-shaped having a circular cross section, the cylindrical test specimen is prepared from an R/2 position. Regarding the size of the cylindrical test specimen, for example, the cylindrical test specimen has a parallel portion diameter of 4 mm and a length of 8 mm.
  • the axial direction of the cylindrical test specimen is to be parallel to the rolling elongation direction of the alloy material.
  • a compression test is carried out in air at normal temperature (25° C.) using the cylindrical test specimen, and the obtained 0.2% offset proof stress is defined as the compressive yield strength (MPa).
  • MPa compressive yield strength
  • MPa a value obtained by rounding off decimals of the obtained numerical value is adopted as the compressive yield strength (MPa).
  • the method for producing a seamless alloy pipe includes a process of preparing a starting material (starting material preparation process), a process of producing a hollow shell from the starting material (hot working process), a process of subjecting the produced hollow shell to cold working (first cold working process), a process of performing a solution treatment (solution treatment process), and a process of performing cold working on the hollow shell that underwent the solution treatment (second cold working process).
  • starting material preparation process a process of producing a hollow shell from the starting material
  • hot working process a process of subjecting the produced hollow shell to cold working
  • solution treatment process solution treatment
  • a process of performing cold working on the hollow shell that underwent the solution treatment second cold working process.
  • a method for producing the Fe—Cr—Ni alloy material according to the present embodiment is not limited to the production method described hereunder.
  • a Fe—Cr—Ni alloy having the chemical composition described above is melted.
  • the Fe—Cr—Ni alloy may be melted by an electric furnace, or may be melted by an Ar—O 2 mixed gas bottom-blowing decarburization furnace (AOD furnace). Further, the Fe—Cr—Ni alloy may be melted by a vacuum decarburization furnace (VOD furnace).
  • the melted Fe—Cr—Ni alloy may be made into an ingot by an ingot-making process, or may be made into a slab, a bloom, or a billet by a continuous casting process. As necessary, the slab, the bloom, or the ingot may be subjected to blooming to produce a billet.
  • the starting material (a slab, a bloom, or a billet) is produced by the above process.
  • the prepared starting material is subjected to hot working to produce an intermediate alloy material (hollow shell).
  • the method of hot working is not particularly limited, and it suffices to use a well-known method. That is, in the present embodiment, the hot working may be hot rolling, may be hot extrusion, or may be hot forging. In the hot working, the heating temperature of the starting material is, for example, 1100 to 1300° C.
  • a round billet is subjected to piercing-rolling using a piercing machine.
  • the piercing ratio is, for example, 1.0 to 4.0.
  • the hollow shell that was subjected to piercing-rolling may be further subjected to hot rolling with a mandrel mill, a reducer, a sizing mill or the like to produce a hollow shell.
  • the term “intermediate alloy material” refers to a plate-shaped alloy material in a case where the end product is an alloy plate, refers to a hollow shell in a case where the end product is an alloy pipe, and refers to an alloy material in which a cross section perpendicular to the axial direction is a circular shape in a case where the end product is a solid material with a circular cross section.
  • the alloy material is a solid material with a circular cross section
  • the starting material is heated in a reheating furnace.
  • the heating temperature is, for example, 1100 to 1300° C.
  • the starting material extracted from the reheating furnace is subjected to hot working to produce an intermediate alloy material in which a cross section perpendicular to the axial direction is a circular shape.
  • the hot working is, for example, blooming performed using a blooming mill or hot rolling performed using a continuous mill.
  • a continuous mill a horizontal stand having a pair of grooved rolls arranged one on the other in the vertical direction, and a vertical stand having a pair of grooved rolls arranged side by side in the horizontal direction are alternately arranged.
  • the alloy material is an alloy plate
  • the starting material is heated in a reheating furnace.
  • the heating temperature is, for example, 1100 to 1300° C.
  • the starting material extracted from the reheating furnace is subjected to hot rolling using a blooming mill and a continuous mill to produce an intermediate alloy material having an alloy plate shape.
  • the produced intermediate alloy material (hollow shell) is subjected to cold working.
  • the cold working may be cold drawing or may be cold rolling.
  • a continuous mill equipped with a plurality of cold rolling stands may be used. That is, in the first cold working process according to the present embodiment, it suffices to perform well-known cold working under well-known conditions.
  • the temperature of the intermediate alloy material (hollow shell) during cold working may be, for example, room temperature to 300° C.
  • a preferable cold working rate R1(%) is 5% or more.
  • the term “cold working rate R1” means the rate of reduction in the cross-sectional area of the intermediate alloy material (hollow shell) between before the start of the first cold working process and after the end of the first cold working process.
  • the cold working rate R1(%) in the first cold working process is defined by the following Formula (A).
  • the cold working rate R1 in the first cold working process is preferably made 5% or more. Note that, in the present embodiment, although an upper limit of the cold working rate R1 in the first cold working process is not particularly limited, for example, the upper limit is 30%.
  • the intermediate alloy material (hollow shell) on which the cold working was performed is subjected to a solution treatment.
  • the method for performing the solution treatment is not particularly limited, and it suffices to perform a well-known method.
  • the hollow shell is loaded into a heat treatment furnace, and after being held at a desired temperature, is rapidly cooled.
  • the temperature at which the solution treatment is performed means the temperature (° C.) of the heat treatment furnace for performing the solution treatment.
  • the time for which the solution treatment is performed means the time for which the hollow shell is held at the solution treatment temperature.
  • the residence time in the temperature range from 900 to 1050° C. is set to nine minutes or more.
  • the residence time in the temperature range from 900 to 1050° C. is too short, temperature variations tend to occur in the intermediate alloy material, and recrystallization and grain growth will be liable to become non-uniform.
  • the residence time in the temperature range from 900 to 1050° C. is nine minutes or more, recrystallization and grain growth will tend to be uniform.
  • the residence time in the temperature range from 900 to 1050° C. during heating in the solution treatment process is preferably set to nine minutes or more.
  • a more preferable lower limit of the residence time in the temperature range from 900 to 1050° C. during heating in the solution treatment process is 10 minutes. Note that, even if the residence time in the temperature range from 900 to 1050° C. is a very long time period, the aforementioned advantageous effect will be saturated. Therefore, in the present embodiment, an upper limit of the residence time in the temperature range from 900 to 1050° C. during heating in the solution treatment process is, for example, 30 minutes.
  • the solution treatment temperature in the solution treatment process according to the present embodiment is set to 1060 to 1300° C. If the solution treatment temperature is too low, precipitates (for example, the ⁇ phase that is intermetallic compounds or the like) may sometimes remain in the hollow shell after the solution treatment. In such a case, the corrosion resistance of the produced Fe—Cr—Ni alloy material may decrease. On the other hand, if the solution treatment temperature is too high, the advantageous effect of the solution treatment will be saturated. Therefore, in the present embodiment, preferably the solution treatment temperature in the solution treatment process is set in the range of 1060 to 1300° C.
  • the holding time is not particularly limited, and it suffices that the holding time is in accordance with a well-known condition.
  • the holding time is, for example, 5 to 180 minutes.
  • the rapid cooling method is, for example, water-cooling.
  • the cold working is performed on the intermediate alloy material (hollow shell) that was subjected to the solution treatment, to thereby produce a Fe—Cr—Ni alloy material.
  • the cold working may be cold drawing or may be cold rolling. That is, in the second cold working process according to the present embodiment also, similarly to the first cold working process, it suffices to perform well-known cold working under well-known conditions.
  • the temperature of the intermediate alloy material (hollow shell) when performing the cold working may be, for example, room temperature to 300° C.
  • a preferable cold working rate R2(%) is 5 to 50%.
  • the term “cold working rate R2” means the rate of reduction in the cross-sectional area of the intermediate alloy material (hollow shell) between before the start of the second cold working process and after the end of the second cold working process.
  • the cold working rate R2(%) is defined by the following Formula (B).
  • R ⁇ 2 ⁇ ( % ) 100 ⁇ ( 1 - S ⁇ 1 ⁇ ( 2 ) / S ⁇ 0 ⁇ ( 2 ) ) ( B )
  • the cold working rate R2 is 5 to 50%, the tensile yield strength can be stably made 758 MPa or more in the Fe—Cr—Ni alloy material after the second cold working process. Therefore, preferably the cold working rate R2 is made to fall within the range of 5 to 50%.
  • the aforementioned cold working rate R1(%) in the first cold working process and cold working rate R2(%) in the second cold working process satisfy the respective ranges described above, and the total cold working rate in the production process is not particularly limited.
  • the Fe—Cr—Ni alloy material according to the present embodiment can be produced by the above production method.
  • a method for producing a seamless alloy pipe has been described as an example.
  • the Fe—Cr—Ni alloy material according to the present embodiment may be another shape, such as a plate shape.
  • a method for producing a Fe—Cr—Ni alloy material that is another shape, such as a plate shape also includes, for example, the starting material preparation process, the hot working process, the solution treatment process, and the cold working process, similarly to the production method described above.
  • the production method described above is an example, and the Fe—Cr—Ni alloy material according to the present embodiment may also be produced by another production method.
  • the present invention is described more specifically by way of examples.
  • the ingot of each test number was heated for three hours at 1200° C., and thereafter was subjected to hot forging to produce a rectangular bar having a cross section of 50 mm ⁇ 50 mm.
  • Each obtained rectangular bar was heated for one hour at 1200° C., and thereafter was subjected to hot rolling to produce a plate (alloy plate) having a thickness of 30 mm.
  • the obtained alloy plate of each test number was subjected to the first cold working.
  • the cold working rate R1(%) in the first cold working performed on the alloy plate of each test number at such time is shown in Table 2.
  • the alloy plate of each test number on which the first cold working had been performed was subjected to the solution treatment.
  • the alloy plate on which the first cold working had been performed was heated, and after being held at the solution treatment temperature (° C.) shown in Table 2 for the holding time (min) shown in Table 2, was water-cooled.
  • the residence time in the temperature range from 900 to 1050° C. when being heated to the solution treatment temperature is shown in the column “Residence Time (min)” in Table 2.
  • the alloy plate of each test number on which the solution treatment had been performed was subjected to the second cold working.
  • the cold working rate R2(%) in the second cold working that was performed on the alloy plate of each test number at such time is shown in Table 2. Note that, in Test Nos. 2 and 5, cold drawing was performed as the cold working. In each test number other than Test Nos. 2 and 5, cold rolling was performed as the cold working.
  • the total cold working rate R (%) of the cold working performed on the alloy plate of each test number is shown in Table 2. Note that, in the present examples, the total cold working rate R (%) is defined by the following Formula (C):
  • R ⁇ ( % ) R ⁇ 1 ⁇ ( % ) + R ⁇ 2 ⁇ ( % ) ( C )
  • the alloy plate of each test number produced by the above method was subjected to a grain size number measurement test and a strength anisotropy measurement test which are described hereunder.
  • the alloy plate of each test number was subjected to the grain size number measurement test, and the standard deviation ⁇ of the grain size numbers was determined.
  • test specimens prepared by the method described above were subjected to microscopic observation by the method described above. Photographic images obtained by the microscopic observation were subjected to image analysis, and the grain size number was measured in accordance with ASTM E112 (2021).
  • ASTM E112 2021
  • the grain size numbers obtained in 10 visual fields are shown in Table 3.
  • the mean value of the grain size numbers determined based on the obtained 10 grain size numbers, and the standard deviation ⁇ are shown in Table 3.
  • the alloy plate of each test number was subjected to the strength anisotropy measurement test, and the anisotropy index AI was determined. Specifically, first, the tensile yield strength (MPa) and the compressive yield strength (MPa) were determined by the methods described above. Specifically, a round bar specimen for a tensile test and a cylindrical test specimen for a compression test were prepared from a central portion of the thickness of the alloy plate of each test number. The round bar specimen had a parallel portion diameter of 4 mm, and a gage length of 20 mm. The cylindrical test specimen had a parallel portion diameter of 4 mm, and a length of 8 mm. The axial direction of each of the round bar specimen and the cylindrical test specimen was parallel to the rolling elongation direction of the alloy plate.
  • the round bar specimen for a tensile test was subjected to a tensile test at normal temperature (25° C.) in air by a method in accordance with ASTM E8/E8M (2021).
  • the 0.2% offset proof stress obtained by the tensile test was defined as the tensile yield strength (MPa).
  • the cylindrical test specimen for a compression test was subjected to a compression test at normal temperature (25° C.) in air by a method in accordance with ASTM E9 (2019).
  • the 0.2% offset proof stress obtained by the compression test was defined as the compressive yield strength (MPa).
  • the ratio (compressive YS/tensile YS) of the obtained compressive yield strength (compressive YS) to the obtained tensile yield strength (tensile YS) was determined, and the determined value was defined as the anisotropy index AI.
  • the obtained tensile yield strength is shown in the column “Tensile YS (MPa)”
  • the obtained compressive yield strength is shown in the column “Compressive YS (MPa)”
  • the obtained anisotropy index AI is shown in the column “Anisotropy index AI”.
  • the cold working rate R1 in the first cold working process was too low. Consequently, in these alloy plates, the standard deviation ⁇ of the grain size numbers was more than 0.80. As a result, in these alloy plates, although the tensile yield strength satisfied the condition of being 758 MPa or more, the anisotropy index AI was less than 0.800, and strength anisotropy had not been reduced.

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