Austenitic alloy material

Abstract

An austenitic alloy material according to the present disclosure has a chemical composition that contains, in mass%, more than 0% but not more than 0.020% of C, 0.02-0.80% of Si, 0.10-1.00% of Mn, more than 0% but not more than 0.030% of P, more than 0% but not more than 0.0015% of S, 16.00-28.00% of Ni, 0.01-1.00% of Co, not less than 19.00% but less than 21.00% of Cr, 3.00-9.00% of Mo, 0.150-0.250% of N, 0.005-0.200% of sol. Al, more than 0% but not more than 0.0150% of O, 0.0005-0.0100% of Ca, 0-0.50% of Cu, and 0-3.00% of W, with the balance being made up of Fe and impurities. The austenitic alloy material satisfies formula (1), and has a dislocation density of 1.0 × 1014 m-2 or more.　(1): Mo / Ni ≥ 0.20 In formula (1), the content in mass% of the corresponding element is substituted for each element symbol.

Description

Austenitic alloy

[0001] This disclosure relates to alloy materials, and more specifically to austenitic alloy materials whose microstructure consists of austenite.

[0002] Geothermal power generation is attracting attention as one of the clean energy sources. Geothermal power generation uses CO2 ２ With virtually zero emissions and unaffected by weather and other natural conditions, it is possible to generate electricity stably. Conventional geothermal power generation involves drilling production wells into geothermal reservoirs, which are underground reservoirs of hot water and steam, and generating electricity using the steam that naturally erupts. However, depending on the geothermal reservoir, the amount of hot water and steam in the reservoir may become insufficient over time. In this case, the amount of electricity generated decreases.

[0003] To address these problems, the following next-generation geothermal power generation methods have recently been proposed. These next-generation geothermal power generation methods utilize geothermal reservoirs located at even greater depths than those used in conventional geothermal power generation, thereby utilizing hot water and steam at temperatures exceeding 300°C. As a result, power generation efficiency can be increased compared to conventional geothermal power generation. In particular, next-generation geothermal power generation aims to realize supercritical geothermal power generation using hot water, steam, or supercritical fluids exceeding 374°C.

[0004] The next-generation geothermal power generation described above utilizes geothermal reservoirs located even deeper underground than those used in conventional geothermal power generation. Therefore, the geothermal reservoirs in next-generation geothermal power generation are at high temperatures of approximately 300-500°C, and H ２ This is a corrosive environment containing corrosive substances, such as sulfur, and having a low pH. In this specification, such a high-temperature, acidic environment of about 300-500°C is referred to as a "next-generation geothermal environment." Alloy materials used in production wells in such next-generation geothermal environments require excellent corrosion resistance.

[0005] Alloy materials for geothermal power generation applications are proposed in International Publication No. 2021 / 256128 (Patent Document 1) and International Publication No. 2001 / 090432 (Patent Document 2).

[0006] The alloy material disclosed in Patent Document 1 has a chemical composition containing, by mass%, Cr: 11.5 to 35.0%, Ni: 23.0 to 60.0%, and Mo: 0.5 to 17.0%, and has an austenite phase as its microstructure, with the Mo concentration (by mass%) at the grain boundaries of the austenite phase being 4.0 times or less than the Mo concentration (by mass%) within the austenite grains. In this alloy material, the difference in Mo concentration between the grain boundaries and within the austenite crystal grains is reduced. As a result, corrosion resistance can be maintained, as stated in Patent Document 1.

[0007] The austenitic alloy material disclosed in Patent Document 2 consists of, by mass%, Cr: 23-30%, Ni: 25-35%, Mo: 3-6%, Mn: 1-6%, N: 0-0.40%, C: 0.05% or less, Si: 1.0% or less, S: 0.02% or less, Cu: 3.0% or less, and the remainder being iron and impurities. Patent Document 2 states that this austenitic alloy material, having the above chemical composition, provides excellent corrosion resistance.

[0008] International Publication No. 2021 / 256128, International Publication No. 2001 / 090432

[0009] H. M. Rietveld, “A Profile Refinement Method for Nuclear and Magnetic Structures”, Journal of Applied Crystallography, 1969, Volume 2, p. 65-71

[0010] However, Patent Documents 1 and 2 do not consider corrosion resistance in the context of next-generation geothermal environments.

[0011] The purpose of this disclosure is to provide an austenitic alloy material that exhibits excellent corrosion resistance even in next-generation geothermal environments.

[0012] The austenitic alloy material disclosed herein has a chemical composition in mass percent of: C: greater than 0% and 0.020% or less, Si: 0.02 to 0.80%, Mn: 0.10 to 1.00%, P: greater than 0% and 0.030% or less, S: greater than 0% and 0.0015% or less, Ni: 16.00 to 28.00%, Co: 0.01 to 1.00%, Cr: less than 19.00 to 21.00%, Mo: 3.00 to 9.00%, N: 0.150 to 0.250%, sol. Al: 0.005-0.200%, O: greater than 0% and less than or equal to 0.0150%, Ca: 0.0005-0.0100%, Cu: 0-0.50%, W: 0-3.00%, and the remainder: Fe and impurities, satisfying formula (1), and having a rearrangement density of 1.0 × 10⁻⁶ １４ I understand －２ That is all. Mo / Ni≧0.20 (1) Here, the elemental symbols in equation (1) are substituted with the mass percentage content of the corresponding element.

[0013] The austenitic alloy material disclosed herein exhibits excellent corrosion resistance even in next-generation geothermal environments.

[0014] Figure 1 shows a chemical composition that satisfies the chemical composition of this embodiment and has a rearrangement density of 1.0 × 10⁻⁶ １４ I understand －２ The above describes the Mo / Ni ratio and the corrosion rate (g·m), which is an indicator of corrosion resistance, for austenitic alloy materials. －２ ・h －１ This graph shows the relationship between ( ) and ( ).

[0015] The inventors investigated alloy materials that can obtain excellent corrosion resistance even in next-generation geothermal environments, which are corrosive environments of about 300 to 500°C, from the perspective of chemical composition. In high-temperature corrosive environments such as next-generation geothermal environments, it is thought that not only Cr but also Mo contributes to improving corrosion resistance. In next-generation geothermal environments, Mo forms a sulfide film on the surface of the alloy material. This sulfide film enhances the corrosion resistance of the alloy material. Therefore, it is thought that by increasing the Mo content in addition to the Cr content, corrosion resistance in next-generation geothermal environments can be improved. Furthermore, Co reduces the corrosion rate of alloy materials in next-generation geothermal environments.

[0016] Based on the above considerations, the inventors of the present invention examined alloy materials suitable for use in the next-generation geothermal environment from the perspective of chemical composition. As a result, in terms of mass%, C: more than 0% and 0.020% or less, Si: 0.02 to 0.80%, Mn: 0.10 to 1.00%, P: more than 0% and 0.030% or less, S: more than 0% and 0.0015% or less, Ni: 16.00 to 28.00%, Co: 0.01 to 1.00%, Cr: less than 19.00 to 21.00%, Mo: 3.00 to 9.00%, N: 0.150 to 0.250%, sol.Al: 0.005 to 0.200%, O: more than 0% and 0.0150% or less, Ca: 0.0005 to 0.0100%, Cu: 0 to 0.50%, W: 0 to 3.00%, and the balance: Fe and impurities. The inventors considered that if it is an austenitic alloy material having such a chemical composition, excellent corrosion resistance may be obtained even in the next-generation geothermal environment.

[0017] Furthermore, the inventors of the present invention examined means for enhancing the corrosion resistance in the next-generation geothermal environment from the perspective of the microstructure in the austenitic alloy material having the above chemical composition.

[0018] As described above, in order to increase the Mo content to 3.00 to 9.00% and enhance the corrosion resistance by the action of Mo, it is effective to make Mo easily diffusible to the surface layer of the austenitic alloy material in the next-generation geothermal environment. Here, the inventors considered that the dislocations in the austenitic alloy material function as diffusion paths for Mo. Specifically, if the dislocation density in the austenitic alloy material is increased, Mo will be more likely to diffuse to the surface layer through dislocations in the next-generation geothermal environment. As a result, a sulfide film formed by Mo is stably formed on the surface of the austenitic alloy material, and the corrosion resistance is enhanced in the next-generation geothermal environment.

[0019] Based on the above considerations, the inventors of the present invention investigated and examined the relationship between the dislocation density of the austenitic alloy material having the above chemical composition and the corrosion resistance in the next-generation geothermal environment. As a result, in the austenitic alloy material having the above chemical composition, when the dislocation density is 1.0×10 １４ m －２ or more, it was found that the corrosion resistance is enhanced even in the next-generation geothermal environment.

[0020] However, having the above chemical composition and a rearrangement density of 1.0 × 10⁻⁶ １４ I understand －２ Even with the austenitic alloy materials described above, excellent corrosion resistance in next-generation geothermal environments was still sometimes not achieved. Therefore, the inventors conducted further investigations and studies. As a result, the inventors obtained the following new findings.

[0021] In high-temperature corrosive environments such as next-generation geothermal environments, if the Ni and Mo content in austenitic alloy materials is high, Ni inhibits the diffusion of Mo. On the other hand, Ni is an element necessary to enhance stress corrosion cracking resistance, and if the Ni content is reduced to less than 16.00%, sufficient stress corrosion cracking resistance in next-generation geothermal environments cannot be obtained. Therefore, the inventors considered that if the Ni content is maintained in the above chemical composition, and the ratio of Mo content to Ni content (= Mo / Ni) is further increased, Mo will diffuse more easily in next-generation geothermal environments.

[0022] Based on the above findings, the present inventors have found a chemical composition that satisfies the above-mentioned chemical composition and has a rearrangement density of 1.0 × 10 １４ I understand －２ In the austenitic alloy materials described above, we further investigated the relationship between the ratio of Mo content to Ni content and corrosion resistance in next-generation geothermal environments.

[0023] Figure 1 shows a chemical composition that satisfies the above-mentioned chemical composition and has a rearrangement density of 1.0 × 10⁻⁶. １４ I understand －２ The above describes the Mo / Ni ratio and the corrosion rate (g·m), which is an indicator of corrosion resistance, for austenitic alloy materials. －２ ・h －１ This graph shows the relationship between the two factors. Figure 1 was created based on the results of the example described later.

[0024] Referring to Figure 1, when Mo / Ni is less than 0.20, the corrosion rate does not change significantly even if Mo / Ni increases. On the other hand, when Mo / Ni is 0.20 or higher, the corrosion rate decreases significantly as Mo / Ni increases to 0.100 g·m －２ ・h －１The following is true. In other words, in curve C1 in Figure 1, an inflection point exists near Mo / Ni = 0.20. Therefore, having the above chemical composition and a dislocation density of 1.0 × 10⁻⁶ １４ I understand －２ Furthermore, if the Mo / Ni ratio is set to 0.20 or higher, excellent corrosion resistance can be obtained even in next-generation geothermal environments.

[0025] Based on the above findings, the austenitic alloy material of this embodiment has the following form.

[0026] The first form of austenitic alloy material has a chemical composition in mass percent of: C: greater than 0% and less than or equal to 0.020%, Si: 0.02 to 0.80%, Mn: 0.10 to 1.00%, P: greater than 0% and less than or equal to 0.030%, S: greater than 0% and less than or equal to 0.0015%, Ni: 16.00 to 28.00%, Co: 0.01 to 1.00%, Cr: less than 19.00 to 21.00%, Mo: 3.00 to 9.00%, N: 0.150 to 0.250%, sol. Al: 0.005-0.200%, O: greater than 0% and less than or equal to 0.0150%, Ca: 0.0005-0.0100%, Cu: 0-0.50%, W: 0-3.00%, and the remainder: Fe and impurities, satisfying formula (1), and having a rearrangement density of 1.0 × 10⁻⁶ １４ I understand －２ That is all. Mo / Ni≧0.20 (1) Here, the elemental symbols in equation (1) are substituted with the mass percentage content of the corresponding element.

[0027] The second form of the austenitic alloy material is the austenitic alloy material of the first form, and its chemical composition contains one or more elements selected from the group consisting of Cu: 0.01 to 0.50% and W: 0.01 to 3.00% by mass.

[0028] The third form of the austenitic alloy material is the first or second form of the austenitic alloy material, and its chemical composition contains, by mass%, W: 0.10 to 3.00%.

[0029] The fourth form of austenitic alloy material is an austenitic alloy material of any one of the first to third forms, and is an alloy tube.

[0030] The austenitic alloy material of this embodiment will be described in detail below. Unless otherwise specified, the "%" for elements refers to mass percentage. In the following description, the austenitic alloy material will also be simply referred to as the "alloy material".

[0031] [Characteristics of the Austenitic Alloy Material of This Embodiment] The austenitic alloy material of this embodiment satisfies the following characteristics 1 to 3. (Characteristic 1) The chemical composition, in mass%, is as follows: C: greater than 0% and 0.020% or less, Si: 0.02 to 0.80%, Mn: 0.10 to 1.00%, P: greater than 0% and 0.030% or less, S: greater than 0% and 0.0015% or less, Ni: 16.00 to 28.00%, Co: 0.01 to 1.00%, Cr: less than 19.00 to 21.00%, Mo: 3.00 to 9.00%, N: 0.150 to 0.250%, sol. The composition consists of Al: 0.005 to 0.200%, O: greater than 0% and less than or equal to 0.0150%, Ca: 0.0005 to 0.0100%, Cu: 0 to 0.50%, W: 0 to 3.00%, and the remainder being Fe and impurities. (Feature 2) The chemical composition satisfies formula (1). Mo / Ni ≥ 0.20 (1) Here, the elemental symbols in formula (1) are substituted with the mass percentage content of the corresponding elements. (Feature 3) The dislocation density is 1.0 × 10 １４ I understand －２ That concludes the explanation. Features 1 through 3 will now be described.

[0032] [(Feature 1) Chemical Composition] The chemical composition of the austenitic alloy material of this embodiment contains the following elements.

[0033] C: Greater than 0% and less than or equal to 0.020%. Carbon (C) stabilizes austenite. Even if only a small amount of C is present, the above effect can be obtained to some extent. However, if the C content exceeds 0.020%, Cr carbides are formed at the grain boundaries. The formation of Cr carbides creates Cr-deficient regions with low Cr content within the alloy material. Therefore, even if the content of other elements is within the range of this embodiment, the corrosion resistance of the alloy material in next-generation geothermal environments will decrease. Accordingly, the C content is greater than 0% and less than or equal to 0.020%. The preferred lower limit of the C content is 0.001%, more preferably 0.003%, more preferably 0.004%, more preferably 0.006%, and more preferably 0.008%. The preferred upper limit of the C content is 0.018%, more preferably 0.016%, and more preferably 0.014%.

[0034] Si: 0.02 to 0.80% Silicon (Si) deoxidizes the alloy during the steelmaking process. If the Si content is less than 0.02%, the above effects cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Si content exceeds 0.80%, the hot workability of the alloy material decreases, even if the content of other elements is within the range of this embodiment. Therefore, the Si content is 0.02 to 0.80%. The preferred lower limit of the Si content is 0.05%, more preferably 0.08%, and even more preferably 0.10%. The preferred upper limit of the Si content is 0.70%, more preferably 0.60%, even more preferably 0.55%, and even more preferably 0.50%.

[0035] Mn: 0.10-1.00% Manganese (Mn) deoxidizes and desulfurizes the alloy in the steelmaking process. Mn further stabilizes the austenite. If the Mn content is less than 0.10%, the above effects cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Mn content exceeds 1.00%, the hot workability of the alloy material decreases, even if the content of other elements is within the range of this embodiment. Therefore, the Mn content is 0.10-1.00%. The preferred lower limit of the Mn content is 0.15%, more preferably 0.20%, more preferably 0.30%, and still more preferably 0.40%. The preferred upper limit of the Mn content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, and still more preferably 0.60%.

[0036] P: Greater than 0% and less than or equal to 0.030%. Phosphorus (P) is an unavoidable impurity. That is, the P content is greater than 0%. If the P content exceeds 0.030%, P will excessively segregate at the grain boundaries. In this case, even if the content of other elements is within the range of this embodiment, the corrosion resistance of the alloy material in next-generation geothermal environments will decrease. Therefore, the P content is greater than 0% and less than or equal to 0.030%. It is preferable to have as low a P content as possible. However, excessive reduction of the P content increases manufacturing costs. Therefore, considering normal industrial production, the preferred lower limit of the P content is 0.001%, more preferably 0.002%, and still more preferably 0.003%. The preferred upper limit of the P content is 0.028%, more preferably 0.026%, still more preferably 0.020%, and still more preferably 0.015%.

[0037] S: Greater than 0% and less than or equal to 0.0015%. Sulfur (S) is an unavoidable impurity. That is, the S content is greater than 0%. If the S content exceeds 0.0015%, S will combine with Mn to produce excess MnS. In this case, even if the content of other elements is within the range of this embodiment, the pitting corrosion resistance of the alloy material will decrease. Therefore, the S content is greater than 0% and less than or equal to 0.0015%. It is preferable to have as low an S content as possible. However, excessive reduction of the S content increases manufacturing costs. Therefore, considering normal industrial production, the preferred lower limit of the S content is 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The preferred upper limit of the S content is 0.0012%, more preferably 0.0010%, and even more preferably 0.0008%.

[0038] Ni: 16.00–28.00% Nickel (Ni) stabilizes austenite and increases high-temperature strength in next-generation geothermal environments. Ni further enhances stress corrosion cracking resistance in next-generation geothermal environments. If the Ni content is less than 16.00%, the above effects cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Ni content exceeds 28.00%, the above effects become saturated. Furthermore, the manufacturing cost increases. Therefore, the Ni content is 16.00–28.00%. The preferred lower limit of the Ni content is 16.50%, more preferably 17.00%, more preferably 17.30%, more preferably 17.50%, more preferably 18.00%, and more preferably 18.50%. The preferred upper limit for the Ni content is 27.50%, more preferably 27.00%, even more preferably 26.00%, and even more preferably 25.00%.

[0039] Co: 0.01-1.00% Cobalt (Co) stabilizes austenite and increases high-temperature strength in next-generation geothermal environments. Furthermore, Co reduces the corrosion rate of the alloy material in next-generation geothermal environments. If the Co content is less than 0.01%, the above effects cannot be fully obtained even if the content of other elements is within the range of this embodiment. On the other hand, if the Co content exceeds 1.00%, the manufacturing cost increases significantly. Therefore, the Co content is 0.01-1.00%. The preferred lower limit of the Co content is 0.02%, more preferably 0.03%, more preferably 0.05%, more preferably 0.08%, and more preferably 0.10%. The preferred upper limit of the Co content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.50%, and more preferably 0.20%.

[0040] Cr: 19.00 to less than 21.00% Chromium (Cr) forms a passivation film, improving the corrosion resistance of the alloy material in next-generation geothermal environments. If the Cr content is less than 19.00%, the above effect cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Cr content is 21.00% or more, the hot workability of the alloy material decreases, even if the content of other elements is within the range of this embodiment. Therefore, the Cr content is 19.00 to less than 21.00%. The preferred lower limit of the Cr content is 19.10%, more preferably 19.20%, more preferably 19.25%, more preferably 19.30%, and still more preferably 19.40%. The preferred upper limit of the Cr content is 20.90%, more preferably 20.80%, more preferably 20.70%, and still more preferably 20.60%.

[0041] Mo: 3.00 to 9.00% Molybdenum (Mo) forms a sulfide film on the surface of the alloy material in next-generation geothermal environments. This enhances the corrosion resistance of the alloy material in next-generation geothermal environments. If the Mo content is less than 3.00%, the above effect cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Mo content exceeds 9.00%, the hot workability of the alloy material decreases, even if the content of other elements is within the range of this embodiment. Therefore, the Mo content is 3.00 to 9.00%. The preferred lower limit of the Mo content is 3.10%, more preferably 3.20%, more preferably 3.30%, more preferably 3.50%, more preferably 4.00%, and more preferably 4.50%. The preferred upper limit for the Mo content is 8.90%, more preferably 8.80%, more preferably 8.50%, more preferably 8.00%, more preferably 7.50%, and more preferably 7.10%.

[0042] N: 0.150-0.250% Nitrogen (N) is dissolved in the alloy material to stabilize the austenite. Solid-solution N further increases the high-temperature strength of the alloy material in next-generation geothermal environments. If the N content is less than 0.150%, the above effect cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the N content exceeds 0.250%, the hot workability of the alloy material decreases, even if the content of other elements is within the range of this embodiment. Therefore, the N content is 0.150-0.250%. The preferred lower limit of the N content is 0.160%, more preferably 0.170%, more preferably 0.180%, and still more preferably 0.190%. The preferred upper limit of the N content is 0.240%, more preferably 0.230%, and still more preferably 0.220%.

[0043] sol. Al: 0.005 to 0.200% Aluminum (Al) deoxidizes the alloy in the steelmaking process. Al further enhances the oxidation resistance of the alloy material in next-generation geothermal environments. If the Al content is less than 0.005%, the above effects cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Al content exceeds 0.200%, coarse oxides are formed. In this case, even if the content of other elements is within the range of this embodiment, the cleanliness of the alloy material decreases. Therefore, the hot workability of the alloy material decreases. Accordingly, the sol. Al content is 0.005 to 0.200%. The preferred lower limit of the sol. Al content is 0.010%, more preferably 0.015%, and even more preferably 0.020%. sol. The preferred upper limit for the Al content is 0.150%, more preferably 0.120%, more preferably 0.100%, more preferably 0.080%, more preferably 0.050%, more preferably 0.030%, and more preferably 0.025%. Note that the sol. Al content refers to the content (mass%) of acid-soluble Al (sol. Al).

[0044] O: Greater than 0% and less than or equal to 0.0150% Oxygen (O) is an unavoidable impurity. In other words, the O content is greater than 0%. If the O content exceeds 0.0150%, oxides will be excessively generated. In this case, even if the content of other elements is within the range of this embodiment, the cleanliness of the alloy material will decrease. As a result, the hot workability of the alloy material will decrease. Therefore, the O content is greater than 0% and less than or equal to 0.0150%. It is preferable to have as low an O content as possible. However, excessive reduction of the O content increases manufacturing costs. Therefore, considering normal industrial production, the preferred lower limit of the O content is 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit of the O content is 0.0085%, more preferably 0.0065%, and even more preferably 0.0045%.

[0045] Ca: 0.0005 to 0.0100% Calcium (Ca) fixes O (oxygen) and S (sulfur) as inclusions, improving the hot workability of the alloy material. If the Ca content is less than 0.0005%, the above effect cannot be fully obtained, even if the content of other elements is within the range of this embodiment. On the other hand, if the Ca content exceeds 0.0100%, the cleanliness of the alloy material decreases. Therefore, even if the content of other elements is within the range of this embodiment, the hot workability of the alloy material decreases. Accordingly, the Ca content is 0.0005 to 0.0100%. The preferred lower limit of the Ca content is 0.0010%, more preferably 0.0015%, and even more preferably 0.0020%. The preferred upper limit for the Ca content is 0.0090%, more preferably 0.0080%, more preferably 0.0075%, more preferably 0.0065%, more preferably 0.0055%, and more preferably 0.0045%.

[0046] The remainder of the chemical composition of the austenitic alloy material in this embodiment consists of Fe and impurities. Here, impurities refer to substances that are introduced during the industrial production of the austenitic alloy material from the raw materials such as ore, scrap, or the manufacturing environment, and are acceptable within a range that does not adversely affect the austenitic alloy material in this embodiment.

[0047] [Regarding Optional Elements] The chemical composition of the austenitic alloy material of this embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Cu: 0 to 0.50% and W: 0 to 3.00%. All of these elements are optional elements and enhance the corrosion resistance of the alloy material in next-generation geothermal environments. These optional elements will be described below.

[0048] Cu: 0-0.50% Copper (Cu) is an optional element and may not be included. In other words, the Cu content may be 0%. When Cu is included, that is, when the Cu content is greater than 0%, Cu enhances the corrosion resistance of the alloy material in next-generation geothermal environments. Even if only a small amount of Cu is included, the above effect can be obtained to some extent. However, if the Cu content exceeds 0.50%, even if the content of other elements is within the range of this embodiment, the corrosion resistance of the alloy material in next-generation geothermal environments will actually decrease. Therefore, the Cu content is 0-0.50%. The preferred lower limit of the Cu content is 0.01%, more preferably 0.10%, and even more preferably 0.15%. The preferred upper limit of the Cu content is 0.47%, more preferably 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

[0049] W: 0-3.00% Tungsten (W) is an optional element and may not be present. In other words, the W content may be 0%. When W is present, that is, when the W content is greater than 0%, W enhances the corrosion resistance of the alloy material in next-generation geothermal environments. Even if only a small amount of W is present, the above effect can be obtained to some extent. However, if the W content exceeds 3.00%, the hot workability of the alloy material decreases, even if the content of other elements is within the range of this embodiment. Therefore, the W content is 0-3.00%. The preferred lower limit of the W content is 0.01%, more preferably 0.05%, more preferably 0.10%, and still more preferably 0.12%. As will be described later, in the austenitic alloy material of this embodiment, if features 1 to 3 are satisfied and the W content is 0.10% or more, the corrosion resistance is significantly enhanced. The preferred upper limit for the W content is 2.50%, more preferably 2.00%, even more preferably 1.50%, and even more preferably 1.00%.

[0050] [Regarding (Feature 2) Equation (1)] The chemical composition of the austenitic alloy material of this embodiment satisfies Feature 1, and further satisfies the following equation (1): Mo / Ni ≥ 0.20 (1) Here, the elemental symbols in equation (1) are substituted with the mass percentage content of the corresponding element.

[0051] F1 is defined as follows: F1 = Mo / Ni. F1 is an index indicating the ease of Mo diffusion in a next-generation geothermal environment. In high-temperature corrosive environments such as next-generation geothermal environments, if an austenitic alloy material has a chemical composition that satisfies characteristic 1, the diffusion of Mo is easily inhibited by Ni. If F1 is 0.20 or higher, the inhibition of Mo diffusion by Ni in a next-generation geothermal environment can be suppressed. As a result, Mo can easily diffuse onto the surface of the alloy material. Consequently, as shown in Figure 1, the corrosion rate in a next-generation geothermal environment can be sufficiently suppressed, and excellent corrosion resistance can be obtained.

[0052] Specifically, referring to Figure 1, when Mo / Ni is less than 0.20, the corrosion rate does not change significantly even if Mo / Ni increases. On the other hand, when Mo / Ni is 0.20 or higher, as Mo / Ni increases, the corrosion rate decreases significantly, and the corrosion resistance increases significantly. In other words, in curve C1 in Figure 1, there is an inflection point near Mo / Ni = 0.20. If F1 is 0.20 or higher, assuming that features 1 and 3 are satisfied, the corrosion rate obtained by the method described in [Method for Evaluating Corrosion Resistance] below is 0.100 g·m －２ ・h －１ The following can be done:

[0053] The preferred lower limit for F1 is 0.25. In this case, as shown in Figure 1, which was created based on the examples described later, the corrosion rate is 0.080 g·m －２ ・h －１ The following is possible. A more preferable lower limit for F1 is 0.30. In this case, the corrosion rate is 0.040 g·m －２ ・h －１ The following is possible. A more preferable lower limit for F1 is 0.35.

[0054] In Figure 1, plots labeled 9, 10, and 22 correspond to test numbers 9, 10, and 22 in the examples described later, respectively. The austenitic alloy materials of these test numbers contain 0.10% or more W by mass. Curve C2 in Figure 1 is composed of plots 9, 10, and 22, which contain 0.10% or more W. On the other hand, curve C1 in Figure 1 is composed of plots with a W content of less than 0.10%. Referring to curves C1 and C2, the corrosion rate in curve C2, where the W content is 0.10% or more, is significantly lower compared to curve C1, where the W content is less than 0.10%. Therefore, in the austenitic alloy material of this embodiment, if features 1 and 3 are satisfied, F1 is 0.20 or more (feature 2), and furthermore, the W content is 0.10% or more, corrosion resistance can be significantly improved. The upper limit of F1 is not particularly limited, but when the alloy material satisfies feature 1, the upper limit of F1 is 0.56. Note that F1 is the value obtained by rounding the third decimal place of the obtained value to the second decimal place.

[0055] [(Feature 3) Regarding dislocation density] In the austenitic alloy material of this embodiment, the dislocation density is 1.0 × 10⁻⁶ １４ I understand －２ That concludes the explanation. Dislocations function as diffusion paths for Mo to diffuse from the interior to the surface of the alloy material in next-generation geothermal environments. Dislocation density is 1.0 × 10⁻⁶ １４ I understand －２ If the value is less than [value], the amount of diffusion paths in the alloy material is insufficient. Therefore, in this case, even if the austenitic alloy material satisfies features 1 and 2, a sufficient amount of Mo will not diffuse to the surface of the alloy material in the next-generation geothermal environment. As a result, excellent corrosion resistance in the next-generation geothermal environment cannot be obtained.

[0056] Dislocation density is 1.0 × 10 １４ I understand －２ If the above conditions are met, a sufficient amount of Mo diffusion paths are present in the alloy material. Therefore, assuming that features 1 and 2 are satisfied, excellent corrosion resistance can be obtained in next-generation geothermal environments.

[0057] The preferred lower limit of dislocation density is 1.1 × 10⁻⁶. １４ I understand －２ And more preferably 1.2 × 10１４ I understand －２ And more preferably 1.3 × 10 １４ I understand －２ And more preferably 1.5 × 10 １４ I understand －２ And more preferably 2.0 × 10 １４ I understand －２ Therefore, there is no particular upper limit to the dislocation density. For example, the upper limit of the dislocation density is 100.0 × 10⁻⁶. １４ I understand －２ For example, 10.0 × 10 １４ I understand －２ For example, 5.0 × 10 １４ I understand －２ That is the case.

[0058] [Method for Measuring Dislocation Density] Dislocation density is measured by the following methods: A test specimen is taken from the austenitic alloy material. If the alloy material is an alloy tube, the test specimen is taken from the center of the wall thickness. The size of the test specimen is, for example, 20 mm wide, 20 mm long, and 2 mm thick. The thickness direction of the test specimen is in the direction of the tube diameter. The length direction of the test specimen is in the direction of the tube axis. The surface with a width of 20 mm and a length of 20 mm is used as the measurement surface. If the alloy material is an alloy plate, a test specimen is taken from the center of the plate thickness. The size of the test specimen is, for example, 20 mm wide, 20 mm long, and 2 mm thick. The thickness direction of the test specimen is in the direction of the plate thickness. The length direction of the test specimen is in the rolling direction. The surface with a width of 20 mm and a length of 20 mm is used as the measurement surface. If the alloy material is a round bar, a test specimen is taken from the R / 2 position. Here, the R / 2 position refers to the center position of radius R in a cross section perpendicular to the longitudinal direction of the round bar. The size of the test specimen is, for example, 20 mm in width, 20 mm in length, and 2 mm in thickness. The thickness direction of the test specimen is the radial direction of the round bar. The length direction of the test specimen is the axial direction. The surface with a width of 20 mm and a length of 20 mm is used as the measurement surface.

[0059] The measurement surface of the collected test specimen is polished to a mirror finish. After mirror polishing, the measurement surface is electropolished using an electrolytic solution containing 10% by volume of perchloric acid with acetic acid as the solvent to remove strain from the surface of the test specimen.

[0060] X-ray diffraction (XRD) is used to measure the X-ray diffraction profile of the measurement surface after electropolishing. In X-ray diffraction, a Co tube is used as the cathode tube and CoKα rays are used as the X-ray source. The acceleration voltage is set to 40 kV and the acceleration current to 40 mA. The θ-2θ method is used for profiling. The scan range is 40 to 130° in 2θ. The X-ray diffractometer used is, for example, a Rigaku Corporation product named Rint-2500.

[0061] The obtained X-ray diffraction profiles are analyzed, and the diffraction of the {111}, {220}, and {311} planes of the FCC crystal structure is fitted using the Rietveld method described in Non-Patent Literature 1 to obtain the full width at half maximum (FWHM) ΔK. For the measurement of the X-ray profile originating from the X-ray diffractometer, an austenitic alloy material that satisfies Feature 1 and is considered to have an extremely low dislocation density, which has been solution-treated at 1180°C (an austenitic alloy material that satisfies Feature 1), is used.

[0062] Based on the full width at half maximum ΔK obtained by the method described above and the Williamson-Hall equation (A), the heterogeneous strain ε of the specimen is determined. ΔK × cosθ / λ = 0.9 / D + 2ε × sinθ / λ (A) Here, in equation (A), θ: diffraction angle, λ: wavelength of X-ray (m), and D: grain size (m). Specifically, the data plotted with ΔK × cosθ / λ on the vertical axis and 2 × sinθ / λ on the horizontal axis is approximated by a linear equation, and the resulting slope ε is taken as the heterogeneous strain ε.

[0063] Furthermore, using the obtained heterogeneous strain ε and equation (B), the dislocation density ρ (m －２ ) is calculated as follows: ρ = 14.4 × ε ２ / b ２ (B) Here, in equation (B), b is the Burgers vector of the FCC crystal structure (b = 0.2545 × 10⁻¹⁰ －９ Substitute (m). Note that the dislocation density ρ is expressed as a floating-point number consisting of a mantissa, base, and exponent, based on the value obtained from equation (B). In this case, the base is 10 and the exponent is 14. Furthermore, the value of the mantissa is rounded to the first decimal place.

[0064] [Effects of the austenitic alloy material of this embodiment] The austenitic alloy material of this embodiment satisfies features 1 to 3. Therefore, excellent corrosion resistance can be obtained in next-generation geothermal environments.

[0065] [Method for evaluating corrosion resistance] The corrosion resistance of the austenitic alloy material of this embodiment is evaluated by the following method.

[0066] A test specimen is taken from the austenitic alloy material. If the alloy material is an alloy tube, the test specimen is taken from the center of the wall thickness. The size of the test specimen is, for example, 20 mm in length, 10 mm in width, and 3 mm in thickness. A through hole with a diameter of 5 mm extending in the thickness direction is made at the longitudinal end of the test specimen. The through hole is formed to set the test specimen in a suspended state inside the autoclave, as described later. The thickness direction of the test specimen is the diameter direction of the tube (wall thickness direction). The length direction of the test specimen is the axis direction of the tube. If the alloy material is an alloy plate, a test specimen is taken from the center of the plate thickness. The size of the test specimen is, for example, 20 mm in length, 10 mm in width, and 3 mm in thickness. A through hole with a diameter of 5 mm extending in the thickness direction is made at the longitudinal end of the test specimen. The thickness direction of the test specimen is the plate thickness direction. The length direction of the test specimen is the rolling direction. If the alloy material is a round bar, a test specimen is taken from the R / 2 position. The size of the test specimen is, for example, 20 mm in length, 10 mm in width, and 3 mm in thickness. A through hole with a diameter of 5 mm and extending in the thickness direction is made at the longitudinal end of the test specimen. The thickness direction of the test specimen is the radial direction of the round bar. The length direction of the test specimen is the axial direction.

[0067] The surface of the collected test specimen is wet-polished with emery paper up to 600 grit, and then degreased with acetone. The mass of the degreased test specimen is measured and taken as the mass of the test specimen before the start of the test.

[0068] As a test solution, H₂O₃ is added to a 1.7% by mass aqueous solution of NaCl. ２ SO ４ Prepare a solution adjusted to pH 2.0 using [a specific method / tool]. Place the test specimen in the autoclave while suspended from a fixture. The contact points between the fixture and the test specimen are electrically insulated with a ceramic component.

[0069] N inside the autoclave ２Allow gas to pass through to thoroughly replace the gas with the atmosphere. Prepare the test solution in a separate container beforehand using N2. ２ The test solution is thoroughly degassed by passing gas through it. The thoroughly degassed test solution is injected into the autoclave using a vacuum pump. The entire test specimen is immersed in the test solution. The ratio of the test specimen to the test solution is 30 ± 10 mL / cm³. ２ Set it so that it becomes like this. Then, further N into the liquid phase and gas phase in the autoclave. ２ The gas is then passed through to ensure sufficient degassing. After that, 1 atmH is used as the test gas. ２ S and 5 atmCO ２ The gas is sealed inside.

[0070] The autoclave is heated to 350°C using a heater and maintained at 350°C for 336 hours. After 336 hours, the heater is turned off and the autoclave is cooled to room temperature (20±15°C). After cooling to room temperature, the test gas inside the autoclave is changed to N2. ２ Replace with gas. Use N as the test gas. ２ After replacing the gas, remove the test specimen.

[0071] The corrosion products are removed from the extracted test specimens. The removal of corrosion products from the test specimens is carried out, for example, according to the method specified in ASTM G31-21.

[0072] Measure the mass of the test specimen from which the corrosion products have been removed. Corrosion rate (g·m) －２ ・h －１ ) (1 m per hour) ２ The mass loss per unit area is calculated by dividing the difference between the mass of the test specimen before the start of the test and the mass of the test specimen after the test time has elapsed and the corrosion products have been removed by the surface area of ​​the test specimen and the test time. (Corrosion rate: 0.100 g·m) －２ ・h －１ The following conditions will be met to determine that excellent corrosion resistance has been achieved in the next-generation geothermal environment:

[0073] [Regarding the microstructure of the austenitic alloy material] The microstructure of the austenitic alloy material of this embodiment consists of austenite. Here, in this specification, "the microstructure consists of austenite" means that the amount of other structures is negligibly small.

[0074] [Shape of the Austenitic Alloy Material] The shape of the austenitic alloy material in this embodiment is not particularly limited. The austenitic alloy material may be an alloy tube, an alloy plate, or a round bar. Preferably, the austenitic alloy material in this embodiment is an alloy tube, and more preferably a seamless alloy tube.

[0075] [Manufacturing Method] An example of a manufacturing method for the austenitic alloy material of this embodiment having the above-described configuration will be explained. Note that the manufacturing method for the austenitic alloy material according to this embodiment is not limited to the manufacturing method described below. An example of a manufacturing method for the austenitic alloy material of this embodiment includes the following steps: (Step 1) Material preparation step (Step 2) Hot working step (Step 3) Cold working step (Step 4) Solution treatment step Each manufacturing step will be described in detail below.

[0076] [Material Preparation Process] In the material preparation process, a molten alloy is produced by a well-known method. The method for producing the molten alloy is not particularly limited. For example, the molten alloy may be subjected to a well-known primary refining, followed by a well-known secondary refining. During refining, alloying elements for component adjustment are added to the molten alloy to produce a molten alloy that satisfies the chemical composition of Feature 1 and Feature 2.

[0077] The material is manufactured using the molten alloy. Specifically, cast slabs (slabs, blooms, or billets) are produced by continuous casting using the molten alloy. Alternatively, ingots are produced by the ingot-making method using the molten alloy.

[0078] [Hot Working Process] In the hot working process, the material (cast slab or ingot) manufactured in the material preparation process is hot-worked to produce an intermediate alloy material. In this specification, the intermediate alloy material is a raw tube if the final product is an alloy tube, a plate-shaped alloy material if the final product is an alloy plate, and a rod-shaped alloy material extending in the axial direction if the final product is a round bar. The hot working may be hot forging, hot extrusion, or hot rolling. The method of hot working is not particularly limited and any well-known method may be used.

[0079] If the intermediate alloy material is a raw pipe (seamless steel pipe), hot extrusion such as the Eugene Séjournet method or the Erhardt push bench method may be performed. Alternatively, hot rolling such as perforation rolling by the Mannesmann method may be performed. When hot extrusion is used, a round billet is manufactured by hot forging or bloc rolling of the bloom or ingot. The heating temperature for hot forging or bloc rolling is, for example, 1000 to 1300°C. A through hole is formed in the manufactured round billet by machining. The through hole is formed coaxially with the central axis of the round billet. A raw pipe, which is the intermediate alloy material, is manufactured by hot extrusion using the round billet with the through hole formed therein. The heating temperature during hot extrusion is, for example, 1000 to 1300°C. When the Mannesmann method is used, a round billet is manufactured by bloc rolling of the bloom or ingot. The heating temperature for bloc rolling is, for example, 1000 to 1300°C. The round billets produced by bract rolling are cooled to room temperature. The round billets are then reheated. The heating temperature is, for example, 1000 to 1300°C. After the round billets are extracted from the heating furnace, they are subjected to perforation rolling and then stretch rolling to produce the raw tubes, which are intermediate alloy materials.

[0080] If the intermediate alloy material is an alloy sheet, first, the slab or ingot is heated in a heating furnace. The heating temperature is, for example, 1000 to 1300°C. The slab or ingot extracted from the heating furnace is then hot-rolled using a roughing mill and a finishing mill to produce the alloy sheet, which is the intermediate alloy material.

[0081] If the intermediate alloy material is a round bar, a billet is produced by bloc rolling of the bloom or ingot. The heating temperature for bloc rolling is, for example, 1000 to 1300°C. The billet produced by bloc rolling may be further hot-rolled in a continuous rolling mill to produce smaller billets. The produced billet is cooled to room temperature. The billet is reheated. The heating temperature is, for example, 1000 to 1300°C. After heating, the billet is hot-rolled in a finish rolling mill to produce a round bar, which is the intermediate alloy material.

[0082] [Cold Working Process] In the cold working process, cold working is performed on the intermediate alloy material after hot working. If the intermediate alloy material is an alloy tube or round bar, the cold working is, for example, cold drawing. If the intermediate alloy material is an alloy sheet, the cold working is, for example, cold rolling. The dislocation density of the manufactured austenitic alloy material is adjusted by performing the cold working process. This will be discussed later.

[0083] [Solution Treatment Process] In the solution treatment process, the intermediate alloy material is subjected to solution treatment as a heat treatment. Specifically, the intermediate alloy material is placed in a heat treatment furnace and heated to the solution temperature. After holding the intermediate alloy material at the solution temperature for a predetermined time, the intermediate alloy material is removed from the heat treatment furnace and cooled with water. In the heat treatment process, the solution temperature is set to 1050 to 1230°C. The holding time at the solution temperature is set to 1 to 60 minutes.

[0084] [Conditions in the Manufacturing Process] In the manufacturing process described above, the following conditions 1 and 2 must be met. (Condition 1) The reduction ratio RR in the cold working process shall be 1.0 to 60.0%. Here, the reduction ratio RR (%) is given by the following formula: Reduction ratio RR = {1 - Cross-sectional area perpendicular to the longitudinal direction of the intermediate alloy material after cold working / Cross-sectional area perpendicular to the longitudinal direction of the intermediate alloy material before cold working} × 100 In the formula, "longitudinal direction" refers to the axial direction of the tube if the intermediate alloy material is an alloy tube, the rolling direction if it is an alloy plate, and the axial direction if it is a round bar. (Condition 2) In the solution treatment process, during the process of heating the intermediate alloy material to the solution temperature, the average heating rate HR from 700°C to 900°C of the intermediate alloy material shall be 0.03 to 0.10°C / second. Conditions 1 and 2 will be explained below.

[0085] [Regarding Condition 1 (Area Reduction Ratio RR in Cold Working Process)] The area reduction ratio RR in the cold working process affects the dislocation density of the austenitic alloy material after manufacturing. If the area reduction ratio RR is less than 1.0%, even if Condition 2 is met, the dislocation density of the austenitic alloy material after manufacturing will not be sufficient. If the area reduction ratio RR is 1.0% or more, assuming that Condition 2 is met, the dislocation density of the austenitic alloy material after manufacturing will be 1.0 × 10⁻⁶. １４ I understand－２ This concludes the explanation. Note that there is no particular upper limit to the area reduction ratio RR. For example, the upper limit of the area reduction ratio RR is 60.0%.

[0086] [Regarding Condition 2 (Heating Rate HR in Solution Treatment Process)] Dislocations introduced into the intermediate alloy material by the cold working process are more likely to annihilate each other due to the heat applied in the solution treatment process. Therefore, it is necessary to suppress the decrease in dislocation density introduced into the intermediate alloy material during the solution treatment process.

[0087] As shown in Feature 1, the austenitic alloy material of this embodiment has a high nitrogen content. Therefore, in the temperature range where the surface temperature of the intermediate alloy material is between 700°C and 900°C, fine precipitates, which are fine nitrides and / or carbonitrides, tend to form. The fine precipitates formed in this temperature range hinder the movement of dislocations in the intermediate alloy material. The easier it is for dislocations to move, the more likely dislocation annihilation is to occur. Therefore, the fine precipitates suppress dislocation annihilation during solution treatment and suppress the decrease in dislocation density.

[0088] If the average heating rate HR of the intermediate alloy material exceeds 0.10°C / second in the temperature range from 700°C to 900°C, the average heating rate HR is too fast. In this case, the amount of fine precipitates generated is insufficient. Therefore, even if condition 1 is met, the introduced dislocations are excessively annihilated during the solution treatment. As a result, a sufficient dislocation density cannot be obtained in the austenitic alloy material after manufacturing.

[0089] On the other hand, if the average heating rate HR is less than 0.03°C / second, the precipitates that are formed grow coarse. These coarse precipitates do not act as a barrier to dislocation movement, and the dislocations move around them. Therefore, even in this case, the introduced dislocations are excessively annihilated during the solution treatment. As a result, the dislocation density in the austenitic alloy material after manufacturing is not sufficient.

[0090] If the average heating rate HR is 0.03 to 0.10°C / second, assuming that condition 1 is met, it is possible to suppress the excessive reduction of dislocation density introduced in the cold working process during the solution treatment. As a result, in the austenitic alloy material after manufacturing, the dislocation density is 1.0 × 10⁻⁶. １４ I understand －２That's all.

[0091] The average heating rate HR (°C / sec) can be measured using well-known methods. For example, the average heating rate HR (°C / sec) can be determined from the surface temperature of the intermediate steel material measured with a non-contact thermometer and the heating time.

[0092] The austenitic alloy material of this embodiment can be manufactured through the above process. Note that the above-described method for manufacturing the austenitic alloy material is merely an example, and austenitic alloy materials satisfying features 1 to 3 may be manufactured by other methods. The austenitic alloy material of this disclosure will be described in more detail below with reference to examples.

[0093] Austenitic alloy materials having the chemical compositions shown in Tables 1A and 1B were manufactured. Here, the F1 value is shown in the "F1" column of Table 1B. In Tables 1A and 1B, "-" means that when the significant figures of the corresponding element content are rounded to the Nth decimal place (where N is a natural number), the digit at the N+1th decimal place is rounded to 0 (zero). For example, "-" in the "Co" column means that the digit at the third decimal place is rounded to 0 (zero).

[0094]

[0095]

[0096] Specifically, the molten alloy for each test number was manufactured in a vacuum melting furnace. Ingots were manufactured using the ingot-forming method with the molten alloy. After heating the ingot to 1250°C, hot forging was performed to produce round billets. The round billets were cooled to room temperature. Subsequently, the round billets were reheated to 1250°C, and raw tubes were manufactured by hot extrusion based on the Eugène Séjournay method. Furthermore, cold drawing was performed on the raw tubes. The reduction ratio RR (%) in cold drawing is shown in the "Reduction Ratio RR (%)" column of Table 2.

[0097]

[0098] Solution treatment was performed on the raw tubes after cold drawing. The solution treatment temperature was set to 1180°C, and the holding time at the solution treatment temperature was set to 15 minutes. After the holding time, the raw tubes were water-cooled. The average heating rate HR (°C / sec) in the temperature range from 700°C to 900°C of the raw tube surface temperature is shown in the "Average heating rate HR (°C / sec)" column of Table 2. For test number 36, solution treatment was performed without cold drawing after hot forging and perforated rolling. For test number 36, the "Area reduction ratio RR (%)" column in Table 2 is shown as "-". Austenitic alloy materials (seamless alloy tubes) for each test number were manufactured using the above manufacturing process.

[0099] [Evaluation Tests] The following evaluation tests were conducted on each austenitic alloy material with the specified test number: (Test 1) Dislocation density measurement test (Test 2) Corrosion resistance test. Each test is described below.

[0100] [(Test 1) Dislocation Density Measurement Test] Based on the method described in [Method for Measuring Dislocation Density] above, the dislocation density (m) of the austenitic alloy material for each test number was measured. －２ The dislocation density was determined. The size of the test specimen was 20 mm wide, 20 mm long, and 2 mm thick. The thickness direction of the test specimen was in the direction of the diameter of the pipe, and the length direction of the test specimen was in the direction of the axis of the pipe. The surface with a width of 20 mm and a length of 20 mm was used as the measurement surface. The X-ray diffractometer used was a Rigaku Corporation product name: Rint-2500. The obtained dislocation density was shown in Table 2 as "Dislocation Density (×10)". １４ I understand －２ This is shown in the ) column.

[0101] [(Test 2) Corrosion Resistance Test] Based on the method described in "Method for Evaluating Corrosion Resistance" above, the corrosion resistance of each test number in a next-generation geothermal environment was evaluated. The size of the test specimen was 20 mm in length, 10 mm in width, and 3 mm in thickness, with the thickness direction of the test specimen being in the direction of the pipe diameter and the length direction of the test specimen being in the direction of the pipe axis. The obtained corrosion rate (g·m) －２ ・h －１ ) is shown in Table 2 as "Corrosion rate (g・m) －２ ・h －１ This is shown in the ) column.

[0102] [Evaluation Results] Referring to Table 1A, Table 1B, and Table 2, the austenitic alloy materials of Test Nos. 1 to 25 satisfied Features 1 to 3. Therefore, the corrosion rate was 0.100 g·m －２ ·h －１ or less, and excellent corrosion resistance was obtained in the next-generation geothermal environment.

[0103] On the other hand, in Test Nos. 26 to 30, F1 (= Mo / Ni) did not satisfy Equation (1). Therefore, the corrosion rate exceeded 0.100 g·m －２ ·h －１ and excellent corrosion resistance was not obtained in the next-generation geothermal environment.

[0104] In Test No. 31, the Mo content was too low and F1 did not satisfy Equation (1). Therefore, the corrosion rate exceeded 0.100 g·m －２ ·h －１ and excellent corrosion resistance was not obtained in the next-generation geothermal environment.

[0105] In Test Nos. 32 and 33, the Co content was too low. Therefore, the corrosion rate exceeded 0.100 g·m －２ ·h －１ and excellent corrosion resistance was not obtained in the next-generation geothermal environment.

[0106] In Test No. 34, the Cr content was too low. Therefore, the corrosion rate exceeded 0.100 g·m －２ ·h －１ and excellent corrosion resistance was not obtained in the next-generation geothermal environment.

[0107] In Test No. 35, the Cu content was too high. Therefore, the corrosion rate exceeded 0.100 g·m －２ ·h －１ and excellent corrosion resistance was not obtained in the next-generation geothermal environment.

[0108] In Test No. 36, cold drawing was not performed. Therefore, the dislocation density was less than 1.0 × 10 １４ m －２ As a result, the corrosion rate exceeded 0.100 g·m －２ ·h －１ and excellent corrosion resistance was not obtained in the next-generation geothermal environment.

[0109] In test number 37, the average heating rate HR during the heat treatment process exceeded 0.10°C / second. As a result, the dislocation density was 1.0 × 10⁻⁶ １４ I understand －２ It was less than 0.100 g·m. As a result, the corrosion rate was 0.100 g·m －２ ・h －１ It exceeded the limit, and excellent corrosion resistance could not be obtained in next-generation geothermal environments.

[0110] In test number 38, the average heating rate HR during the heat treatment process was less than 0.03°C / second. Therefore, the dislocation density was 1.0 × 10⁻⁶. １４ I understand －２ It was less than 0.100 g·m. As a result, the corrosion rate was 0.100 g·m －２ ・h －１ It exceeded the limit, and excellent corrosion resistance could not be obtained in next-generation geothermal environments.

[0111] The embodiments of this disclosure have been described above. However, the embodiments described above are merely examples for implementing this disclosure. Therefore, this disclosure is not limited to the embodiments described above, and the embodiments described above can be modified as appropriate without departing from the spirit of this disclosure.

Claims

1. The chemical composition, in mass percent, is as follows: C: greater than 0% and less than or equal to 0.020%, Si: 0.02 to 0.80%, Mn: 0.10 to 1.00%, P: greater than 0% and less than or equal to 0.030%, S: greater than 0% and less than or equal to 0.0015%, Ni: 16.00 to 28.00%, Co: 0.01 to 1.00%, Cr: less than 19.00 to 21.00%, Mo: 3.00 to 9.00%, N: 0.150 to 0.250%, sol. Al: 0.005-0.200%, O: greater than 0% and less than or equal to 0.0150%, Ca: 0.0005-0.0100%, Cu: 0-0.50%, W: 0-3.00%, and the remainder being Fe and impurities, satisfying formula (1), and having a rearrangement density of 1.0 × 10⁻⁶ １４ I understand －２ The above is for austenitic alloy materials. Mo / Ni ≥ 0.20 (1) Here, the elemental symbols in equation (1) are substituted with the mass percentage content of the corresponding element.

2. An austenitic alloy material according to claim 1, wherein the chemical composition contains one or more elements selected from the group consisting of Cu: 0.01 to 0.50% and W: 0.01 to 3.00% by mass.

3. An austenitic alloy material according to claim 1, wherein the chemical composition contains, by mass%, W: 0.10 to 3.00%.

4. An austenitic alloy material according to any one of claims 1 to 3, wherein the austenitic alloy material is an alloy tube.

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