alloy material

Abstract

Provided is an alloy material that has sufficient creep strength in a high temperature environment and is capable of attaining both excellent resistance to stress relaxation cracking and excellent resistance to welding hot cracking. The alloy material according to the present disclosure contains, in mass%, 0.050-0.100 % of C, 1.00 % or less of Si, 1.50 % or less of Mn, 0.035 % or less of P, 0.0015 % or less of S, 19.00-23.00 % of Cr, 30.00-35.00 % of Ni, 0.100 % or less of N, 0.15-0.70 % of Al, 0.15-0.70 % of Ti, and 0.0010-0.0050 % of B, with the remainder consisting of Fe and impurities. The alloy material satisfies formulae (1) and (2).　(1): 0.60<AL+Ti<1.20 (2): 1.12≤Ti / Al

Description

[Technical Field]

[0001] This disclosure relates to alloy materials, and more specifically, to alloy materials that can be used in high-temperature environments. [Background technology]

[0002] Alloy materials used in steam reformers, ethylene cracking furnaces, heating furnace tubes for petroleum refining and petrochemical plants, and polycrystalline silicon manufacturing equipment are used in high-temperature environments of 500 to 1000°C. Therefore, alloy materials used in such high-temperature environments require high creep strength and excellent corrosion resistance at high temperatures. Alloy 800, Alloy 800H, and Alloy 800HT are known as alloy materials used in such high-temperature environments.

[0003] Alloy 800, Alloy 800H, and Alloy 800HT contain large amounts of Cr and Ni. Therefore, these alloys are known to have excellent corrosion resistance at high temperatures. These alloys also contain Al and Ti. Consequently, a gamma prime (γ') phase (Ni3(Al,Ti)) is formed within the alloy during use in high-temperature environments. Due to precipitation strengthening by the γ' phase, these alloys possess excellent creep strength.

[0004] However, Alloy 800, Alloy 800H, and Alloy 800HT are prone to high-temperature cracking in the heat-affected zone (HAZ) during welding. Furthermore, as described in Non-Patent Documents 1 and 2, stress relaxation cracking may occur in these alloy materials when used in high-temperature environments. Therefore, alloy materials with a chemical composition equivalent to Alloy 800, Alloy 800H, and Alloy 800HT require excellent resistance to high-temperature cracking and excellent resistance to stress relaxation cracking.

[0005] To improve the stress relaxation cracking resistance of the aforementioned alloy materials, conventional methods have been proposed, such as limiting the total content of Al and Ti, or performing heat treatment after welding. However, limiting the total content of Al and Ti results in insufficient creep strength. Furthermore, performing heat treatment after welding increases construction costs, and in some cases, equipment design prevents post-welding heat treatment.

[0006] A technique for improving the stress relaxation cracking resistance of alloy materials containing Al and Ti is disclosed in International Publication No. 2018 / 066579. This document focuses on the γ' phase that is formed in the alloy material during use in high-temperature environments in order to achieve excellent stress relaxation cracking resistance in high-temperature environments. This document describes how the chemical composition of the alloy material is adjusted to generate an appropriate amount of γ' phase during use in high-temperature environments. Patent Document 1 states that this results in excellent stress relaxation cracking resistance during use in high-temperature environments. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2018 / 066579 [Non-patent literature]

[0008] [Non-Patent Document 1] Hans van Wortel: “Control of Relaxation Cracking in Austenitic High Temperature Components”, CORROSION 2007(2007), NACE, Paper No.07423 [Non-Patent Document 2] Richard Colwell and Cathleen Shargay: “Alloy 800H: Material and fabrication challenges associated with the mitigation of stress relaxation cracking”, ASME Pressure Vessels & Piping Conference 2020, Paper No.2020-21842

Summary of the Invention

Problems to be Solved by the Invention

[0009] Even with the alloy material described in Patent Document 1, excellent stress relaxation cracking resistance can be obtained in a high-temperature environment. However, excellent stress relaxation cracking resistance may also be obtained by other means. Furthermore, Patent Document 1 does not discuss at all the compatibility of excellent stress relaxation cracking resistance and excellent welding hot cracking resistance.

[0010] An object of the present disclosure is to provide an alloy material that has sufficient creep strength in a high-temperature environment and enables compatibility of excellent stress relaxation cracking resistance and excellent welding hot cracking resistance.

Means for Solving the Problems

[0011] The alloy material according to the present disclosure is The chemical composition is in mass%, C: 0.050 to 0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00 to 23.00%, Ni: 30.00 to 35.00%, N: 0.100% or less, Al: 0.15 to 0.70%, Ti: 0.15 to 0.70%, B: 0.0010 to 0.0050%, Nb: 0 to 0.30%, Ta: 0 to 0.50%, V: 0 to 1.00%, Zr: 0 to 0.10% Hf: 0 to 0.10%, Cu: 0 to 1.00%, Mo: 0 to 1.00%, W: 0 to 1.00%, Co: 0 to 1.00%, Ca: 0 to 0.0200%, Mg: 0 to 0.0200%, Rare earth elements: 0 to 0.1000%, and, The balance consists of Fe and impurities, satisfying Formula (1) and Formula (2). 0.60 < Al + Ti < 1.20 (1) 1.12 ≤ Ti / Al (2) Here, for each element symbol in Formula (1) and Formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass%.

Advantages of the Invention

[0012] The alloy material according to the present disclosure has sufficient creep strength in a high-temperature environment, and it is possible to achieve both excellent stress relaxation cracking resistance and excellent weld heat-affected zone cracking resistance.

Brief Description of the Drawings

[0013] [Figure 1] Figure 1 is a diagram for explaining the mechanism of stress relaxation cracking during use in a high-temperature environment in an alloy material in which the content of each element in the chemical composition is within the range of the present embodiment.

Modes for Carrying Out the Invention

[0014] The inventors first investigated, from the perspective of chemical composition, an alloy material that possesses sufficient creep strength in a high-temperature environment and can simultaneously achieve excellent stress relaxation crack resistance and excellent high-temperature crack resistance for welding. As a result, the inventors found that, in mass%, C: 0.050~0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00~23.00%, Ni: 30.00~35.00%, N: 0.100% or less, Al: 0.15~0.70%, Ti: 0.15~0.70%, B: 0.0010~0.0050%, Nb: 0~0.30%, Ta: 0~0.50%, V: 0~1.00%, Zr We considered that an alloy material having a chemical composition consisting of 0-0.10% of iron, 0-0.10% of Hf, 0-1.00% of Cu, 0-1.00% of Mo, 0-1.00% of W, 0-1.00% of Co, 0-1.00% of Ca, 0-0.0200% of Mg, 0-0.0200% of rare earth elements, and the remainder being Fe and impurities, could potentially possess sufficient creep strength in high-temperature environments and simultaneously achieve excellent resistance to stress relaxation cracking and excellent resistance to high-temperature welding cracking.

[0015] The inventors further investigated means of increasing the creep strength in high-temperature environments for alloy materials having the above-mentioned chemical composition. As a result, they found that in alloy materials where the content of each element in the chemical composition is within the above-mentioned range, the creep strength in high-temperature environments is sufficiently increased if the following formula (1) is satisfied. 0.60 <Al+Ti<1.20 (1) Here, each element symbol in equation (1) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

[0016] The inventors further investigated how to achieve both excellent resistance to stress relaxation cracking and excellent resistance to high-temperature welding cracking. Specifically, the inventors first investigated the mechanism by which stress relaxation cracking occurs when an alloy material having the above-mentioned chemical composition is used in a high-temperature environment. As a result, the inventors obtained the following findings.

[0017] Figure 1 is a diagram illustrating the mechanism by which stress relaxation cracking occurs in an alloy material whose chemical composition contains elements within the range of this embodiment during use in a high-temperature environment. The horizontal axis of Figure 1 represents time. The vertical axis of Figure 1 represents elongation or strain. Curve CRD0 in Figure 1 represents creep fracture elongation. Curve IS0 represents the amount of strain accumulated in the Cr-deficient region within the crystal grains due to creep deformation.

[0018] Generally, alloy materials used in high-temperature environments undergo solution treatment during the manufacturing process, which causes precipitates in the alloy to be dissolved. Because the precipitates are sufficiently dissolved in the alloy during the manufacturing process, a γ' phase is formed when used in high-temperature environments. High creep strength is obtained through precipitation strengthening by the γ' phase.

[0019] When such alloy materials are used in a high-temperature environment, as shown in Figure 1, the creep fracture elongation CRD0 gradually decreases over time from the initial stage of use in the high-temperature environment. On the other hand, the aforementioned γ' phase is formed inside the alloy material from the initial stage of use in the high-temperature environment (i.e., the initial stage of the stress relaxation process).

[0020] During use of alloy materials in high-temperature environments, not only the γ' phase mentioned above but also TiC is generated. The generation of TiC creates Cr-deficient regions near grain boundaries. In Cr-deficient regions, the strength is lower compared to other regions within the grain. Therefore, creep strain tends to concentrate in Cr-deficient regions during the stress relaxation process. Dislocations that constitute the strain are trapped in TiC within the Cr-deficient regions. Over time, the amount of TiC generated in the Cr-deficient regions increases. Therefore, the amount of dislocations trapped in TiC also increases. Consequently, the amount of creep strain IS0 in the Cr-deficient regions also increases. At time t0, when the increased creep strain IS0 exceeds the creep fracture elongation CRD0, stress relaxation cracking occurs in the alloy material.

[0021] As described above, the increase in creep strain, which is a factor in the occurrence of stress relaxation cracking, occurs in the Cr-deficient region, and the Cr-deficient region is caused by the formation of TiC. Therefore, the inventors considered that TiC has a greater influence on stress relaxation cracking than the γ' phase. Accordingly, the inventors focused on TiC in the alloy material during the stress relaxation process.

[0022] The inventors initially considered that suppressing the formation of TiC during the stress relaxation process would suffice. To suppress TiC, the Ti content in the alloy material should be reduced. However, if the Ti content does not satisfy equation (1), sufficient γ' phase will not be formed during use in high-temperature environments. In this case, sufficient creep strength cannot be obtained in high-temperature environments.

[0023] Therefore, the inventors reversed their thinking and came up with the idea of ​​generating a certain amount of TiC in the alloy material beforehand, rather than suppressing TiC formation, before use in a high-temperature environment. Then, they investigated the stress relaxation cracking resistance using such an alloy material. As a result, they found that the stress relaxation cracking resistance was improved.

[0024] If an alloy material already contains a certain amount of TiC before use in a high-temperature environment, a certain amount of TiC will be generated during the manufacturing process of the alloy material. Due to the pinning effect of this TiC, the crystal grains in the alloy material become finer. If the crystal grains in the alloy material are finer, the creep fracture elongation increases from CRD0 to CRD1.

[0025] Furthermore, in the initial stages of the stress relaxation process, TiC is generated in the Cr-deficient region, as in the previous case. However, in alloy materials before use in high-temperature environments, a certain amount of TiC is already present. Therefore, TiC generation saturates in the initial stages of the stress relaxation process. After TiC generation saturates, the already generated TiC becomes coarser. As TiC coarses, dislocations that were trapped in the TiC are released from the TiC. As a result, the amount of creep strain accumulated in the Cr-deficient region decreases. Therefore, the amount of creep strain accumulated in the Cr-deficient region takes the form of a curve like IS1 in Figure 1.

[0026] The peak of creep strain IS1 is formed in the early stages of the stress relaxation process. The peak of creep strain IS1 corresponds to the point when TiC formation is saturated. In the early stages of the stress relaxation process, the creep fracture elongation CRD1 is higher than the peak of creep strain IS1. After exceeding the peak, creep strain IS1 gradually decreases over time. Therefore, the time at which creep fracture elongation CRD1 and creep strain IS1 intersect becomes later than time t0. As a result, resistance to stress relaxation cracking is increased.

[0027] Furthermore, as mentioned above, the inclusion of a certain amount of TiC in the alloy material results in finer crystal grains within the alloy. This also improves resistance to high-temperature cracking during welding. Consequently, it becomes possible to achieve both excellent resistance to stress relaxation cracking and excellent resistance to high-temperature cracking during welding.

[0028] Furthermore, if the crystal grains become finer, the creep strength may decrease. However, as mentioned above, the alloy material already contains a certain amount of TiC, and during use in a high-temperature environment, not only the γ' phase but also additional TiC is generated. The TiC that was already present, as well as the TiC newly generated during use in a high-temperature environment, precipitates and strengthens the alloy material. Therefore, sufficient creep strength can be maintained in a high-temperature environment.

[0029] Based on the above findings, the inventors investigated the appropriate amount of TiC in the alloy material to achieve sufficient creep strength in a high-temperature environment, while simultaneously providing excellent stress relaxation crack resistance and excellent high-temperature crack resistance for welding. As a result, the following findings were obtained.

[0030] In an alloy material where the content of each element in the chemical composition is within the above-mentioned range, in order to generate a certain amount of TiC, the Ti content must be higher than the Al content. Specifically, the Ti content and Al content should satisfy equation (2). 1.12 ≤ Ti / Al (2) Here, each element symbol in equation (2) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

[0031] If the content of each element in the chemical composition is within the above range and equations (1) and (2) are satisfied, then an appropriate amount of TiC is present in the alloy material. In this case, stress relaxation cracking resistance can be improved, and high-temperature cracking resistance during welding is also improved. Furthermore, sufficient creep strength can be obtained during use in high-temperature environments due to the formation of the γ' phase and TiC.

[0032] Based on the above findings, the alloy material according to this embodiment has the following configuration.

[0033] [1] The chemical composition is expressed in mass percent. C: 0.050~0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00~23.00%, Ni: 30.00~35.00%, N: 0.100% or less, Al: 0.15~0.70%, Ti: 0.15~0.70%, B: 0.0010~0.0050%, Nb: 0~0.30%, Ta: 0~0.50%, V: 0~1.00%, Zr: 0~0.10%, Hf: 0~0.10%, Cu: 0~1.00%, Mo: 0~1.00%, W: 0~1.00%, Co: 0~1.00%, Ca: 0~0.0200%, Mg: 0~0.0200%, Rare earth elements: 0-0.1000%, and, The remainder consists of Fe and impurities. The following conditions satisfy equations (1) and (2): Alloy material. 0.60 <Al+Ti<1.20 (1) 1.12 ≤ Ti / Al (2) Here, the elemental symbols in equations (1) and (2) are substituted with the content of the corresponding element in the chemical composition of the alloy material, expressed in mass percent.

[0034] [2] [1] The alloy material described above, The Ti content in the residue obtained by electrolytic extraction is defined as [Ti] (by mass percentage). R When defined as such, the equation (3) satisfies, Alloy material. 0.050<[Ti] R <0.72Ti-0.01(Ti / Al)-0.11 (3) Here, each element symbol in equation (3) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

[0035] [3] The alloy material described in [1] or [2], Nb: 0.01~0.30%, Ta: 0.01~0.50%, V: 0.01~1.00%, Zr: 0.01~0.10% Hf: 0.01~0.10% Cu: 0.01~1.00%, Mo: 0.01~1.00%, W: 0.01~1.00%, Co: 0.01~1.00%, Ca: 0.0001~0.0200%, Mg: 0.0001~0.0200%, and, Rare earth elements: 0.001~0.1000%, It contains one or more elements selected from the group consisting of, Alloy material.

[0036] The alloy material of this embodiment will be described in detail below. Unless otherwise specified, the "%" in relation to elements refers to mass percent.

[0037] [Characteristics of the alloy material of this embodiment] The alloy material of this embodiment has the following characteristics. (Feature 1) The chemical composition, in mass percent, is as follows: C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.100% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0010-0.0050%. The composition consists of Nb: 0-0.30%, Ta: 0-0.50%, V: 0-1.00%, Zr: 0-0.10%, Hf: 0-0.10%, Cu: 0-1.00%, Mo: 0-1.00%, W: 0-1.00%, Co: 0-1.00%, Ca: 0-0.0200%, Mg: 0-0.0200%, rare earth elements: 0-0.1000%, and the remainder being Fe and impurities. (Feature 2) The chemical composition of feature 1 further satisfies formula (1). 0.60 <Al+Ti<1.20 (1) Here, each element symbol in equation (1) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material. (Feature 3) The chemical composition of characteristic 1 further satisfies equation (2). 1.12 ≤ Ti / Al (2) Here, each element symbol in equation (2) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

[0038] The alloy material of this embodiment satisfies the above-described features 1 to 3. Therefore, the alloy material of this embodiment has sufficient creep strength in high-temperature environments and enables both excellent stress relaxation crack resistance and excellent high-temperature crack resistance during welding. Features 1 to 3 will be described below.

[0039] [(Feature 1) Regarding chemical composition] The chemical composition of the alloy in this embodiment contains the following elements:

[0040] C: 0.050~0.100% Carbon (C) increases the creep strength of alloy materials in high-temperature environments. If the C content is less than 0.050%, 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 C content exceeds 0.100%, even if the content of other elements is within the range of this embodiment, M will be present at the grain boundaries. 23 This process generates C6-type Cr carbides. In this case, Cr-deficient regions are formed at the grain boundaries. As a result, the stress-relaxation cracking resistance of the alloy material decreases. Therefore, the C content is 0.050-0.100%. The preferred lower limit of the C content is 0.053%, more preferably 0.055%, even more preferably 0.057%, and even more preferably 0.060%. The preferred upper limit for the C content is 0.095%, more preferably 0.090%, even more preferably 0.085%, and even more preferably 0.080%.

[0041] Si: 1.00% or less Silicon (Si) is inevitably present; that is, the Si content is greater than 0%. Si deoxidizes the alloy during the steelmaking process. Furthermore, Si enhances the oxidation resistance of the alloy material in high-temperature environments. Even if only a small amount of Si is present, the above effects can be obtained to some extent, even if the content of other elements is within the range of this embodiment. However, if the Si content exceeds 1.00%, the resistance to hot cracking during welding decreases, even if the content of other elements is within the range of this embodiment. Therefore, the Si content is 1.00% or less. The preferred lower limit of the Si content is 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.12%, and more preferably 0.15%. The preferred upper limit for the Si content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, more preferably 0.60%, more preferably 0.55%, and more preferably 0.50%.

[0042] Mn: 1.50% or less Manganese (Mn) is inevitably present; that is, the Mn content is greater than 0%. Mn deoxidizes the weld area of ​​the alloy material during welding. Furthermore, Mn stabilizes the austenite. Even a small amount of Mn present will provide some of the above effects. However, if the Mn content exceeds 1.50%, even if the content of other elements is within the range of this embodiment, the sigma phase (σ phase) is more likely to form when used in a high-temperature environment. The σ phase reduces the toughness and creep ductility of the alloy material in a high-temperature environment. Therefore, the Mn content is 1.50% or less. The preferred lower limit of the Mn content is 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.40%, more preferably 0.50%, and more preferably 0.60%. The preferred upper limit for the Mn content is 1.45%, more preferably 1.40%, more preferably 1.35%, more preferably 1.30%, more preferably 1.25%, and more preferably 1.20%.

[0043] P:0.035% or less Phosphorus (P) is inevitably present. In other words, the P content is greater than 0%. During high-heat input welding, P segregates at the grain boundaries of the alloy material. If the P content exceeds 0.035%, even if the content of other elements is within the range of this embodiment, the above-mentioned segregation occurs, and the stress relaxation crack resistance decreases. Therefore, the P content is 0.035% or less. A low P content is preferable. However, excessive reduction of the P content increases the manufacturing cost of the alloy material. Therefore, considering normal industrial production, the preferred lower limit of the P content is 0.001%, more preferably 0.002%, and even more preferably 0.005%. The preferred upper limit for the P content is 0.030%, more preferably 0.025%, even more preferably 0.020%, and even more preferably 0.015%.

[0044] S: 0.0015% or less Sulfur (S) is inevitably present. In other words, the S content is greater than 0%. During high-heat input welding, S segregates at the grain boundaries of the alloy material. If the S content exceeds 0.0015%, even if the content of other elements is within the range of this embodiment, the above-mentioned segregation occurs, and the stress relaxation crack resistance decreases. Therefore, the S content is 0.0015% or less. A low sulfur (S) content is preferable. However, excessive reduction of the S content increases the manufacturing cost of the alloy material. Therefore, considering normal industrial production, the preferred lower limit of the S content is 0.0001%, and more preferably 0.0002%. The preferred upper limit for the S content is 0.0012%, more preferably 0.0010%, even more preferably 0.0008%, and even more preferably 0.0006%.

[0045] Cr: 19.00~23.00% Chromium (Cr) enhances the corrosion resistance of alloy materials in high-temperature 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 exceeds 23.00%, the stability of austenite in high-temperature environments decreases, even if the content of other elements is within the range of this embodiment. In this case, the creep strength of the alloy material decreases. Therefore, the Cr content is 19.00 to 23.00%. The preferred lower limit for the Cr content is 19.20%, more preferably 19.40%, and even more preferably 19.60%. The preferred upper limit for the Cr content is 22.50%, more preferably 22.00%, more preferably 21.50%, more preferably 21.00%, more preferably 20.50%, and more preferably 20.00%.

[0046] Ni: 30.00~35.00% Nickel (Ni) stabilizes austenite, increasing the creep strength of the alloy material in high-temperature environments. If the Ni content is less than 30.00%, 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 Ni content exceeds 35.00%, the above effect saturates. Furthermore, the raw material cost increases. Therefore, the Ni content is 30.00 to 35.00%. The preferred lower limit of the Ni content is 30.20%, more preferably 30.40%, more preferably 30.60%, more preferably 30.80%, more preferably 31.20%, more preferably 31.40%, and more preferably 31.60%. The preferred upper limit for the Ni content is 34.50%, more preferably 34.00%, even more preferably 33.50%, and even more preferably 33.00%.

[0047] N: 0.100% or less Nitrogen (N) is inevitably present; that is, the N content is greater than 0%. N dissolves in the matrix (parent phase) to stabilize the austenite. The dissolved N further forms fine nitrides in the alloy material when used in high-temperature environments. These fine nitrides strengthen the Cr-deficient regions, thereby increasing the stress-relaxation cracking resistance of the alloy material. The fine nitrides formed during use in high-temperature environments further increase the creep strength through precipitation strengthening. Even a small amount of N content will provide some of the above effects. However, if the N content exceeds 0.100%, coarse TiN will be formed, even if the content of other elements is within the range of this embodiment. Coarse TiN reduces the toughness of the alloy material. Therefore, the N content is 0.100% or less. The preferred lower limit for the N content is 0.001%. The preferred upper limit for the N content is 0.090%, more preferably 0.080%, more preferably 0.070%, more preferably 0.060%, more preferably 0.050%, more preferably 0.040%, more preferably 0.030%, more preferably 0.020%, and more preferably 0.010%.

[0048] Al: 0.15~0.70% Aluminum (Al) deoxidizes alloy materials in the steelmaking process. Al further enhances the oxidation resistance of alloy materials in high-temperature environments. Al also generates a γ' phase in high-temperature environments, increasing the creep strength of alloy materials in high-temperature environments. If the Al content is less than 0.15%, 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 0.70%, even if the content of other elements is within the range of this embodiment, a large amount of the γ' phase will be generated during the manufacturing process of the alloy material. In this case, the hot workability during the manufacturing process of the alloy material will decrease. Furthermore, if the Al content exceeds 0.70%, TiC will not be sufficiently generated. In this case, the crystal grains in the alloy material will not be sufficiently fine due to the TiC. Therefore, during welding of the alloy material, the resistance to high-temperature cracking in the heat-affected zone of the weld will decrease. In addition, since the amount of Ti that satisfies equation (1) decreases, the amount of TiC that precipitates and strengthens at 700°C decreases, and the creep strength of the alloy material will not increase sufficiently. Furthermore, TiC will not be sufficiently generated in the initial stages of the stress relaxation process. Therefore, the resistance to stress relaxation cracking in high-temperature environments will decrease. Therefore, the Al content is 0.15-0.70%. The preferred lower limit for the Al content is 0.17%, more preferably 0.19%, even more preferably 0.21%, and even more preferably 0.23%. The preferred upper limit for the Al content is 0.65%, more preferably 0.60%, more preferably 0.57%, more preferably 0.55%, more preferably 0.53%, more preferably 0.51%, more preferably 0.45%, and more preferably 0.40%. Note that the Al content refers to the total Al content (mass %).

[0049] Ti: 0.15~0.70% Titanium (Ti) combines with Ni and Al in high-temperature environments to form the γ' phase, increasing the creep strength of the alloy material in high-temperature environments. If the Ti content is less than 0.15%, 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 Ti content exceeds 0.70%, coarse TiC is formed, even if the content of other elements is within the range of this embodiment. In this case, the resistance to hot cracking during welding of the alloy material decreases in the heat-affected zone of the weld. Furthermore, if the Ti content exceeds 0.70%, a large amount of the γ' phase is formed during the manufacturing process of the alloy material. In this case, the hot workability during the manufacturing process of the alloy material decreases. Therefore, the Ti content is between 0.15% and 0.70%. The preferred lower limit of the Ti content is 0.17%, more preferably 0.19%, even more preferably 0.21%, and even more preferably 0.25%. The preferred upper limit for the Ti content is 0.65%, more preferably 0.60%, more preferably 0.59%, more preferably 0.57%, more preferably 0.55%, more preferably 0.50%, and more preferably 0.45%.

[0050] B: 0.0010~0.0050% Boron (B) segregates at grain boundaries in high-temperature environments, increasing grain boundary strength. This enhances the stress relaxation cracking resistance of the alloy material. If the B content is less than 0.0010%, 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 B content exceeds 0.0050%, even if the content of other elements is within the range of this embodiment, B promotes the formation of Cr carbides at grain boundaries. In this case, the stress relaxation cracking resistance of the alloy material decreases. Therefore, the B content is between 0.0010% and 0.0050%. The preferred lower limit for the B content is 0.0012%, more preferably 0.0014%, and even more preferably 0.0015%. The preferred upper limit for the B content is 0.0045%, more preferably 0.0040%, even more preferably 0.0035%, and even more preferably 0.0030%.

[0051] The remainder of the chemical composition of the alloy material according to this embodiment consists of Fe and impurities. Here, impurities refer to substances that are introduced during the industrial production of the alloy material from the raw materials such as ore, scrap, or the manufacturing environment, and are not intentionally included, but are acceptable within a range that does not adversely affect the alloy material of this embodiment. Typical examples of impurities are Sn, As, Zn, Pb, and Sb. The total content of these impurities is 0.1% or less.

[0052] [Optional Elements] The chemical composition of the alloy material in this embodiment is further as follows: Replacing some of the Fe, Nb: 0~0.30%, Ta: 0~0.50%, V: 0~1.00%, Zr: 0~0.10% Hf: 0~0.10%, Cu: 0~1.00%, Mo: 0~1.00%, W: 0~1.00%, Co: 0~1.00%, Ca: 0~0.0200%, Mg: 0~0.0200%, Rare earth elements: 0~0.1000%, It may contain one or more elements selected from the group consisting of the following. The following describes these arbitrary elements.

[0053] [Group 1: Regarding Nb, Ta, V, Zr, and Hf] The chemical composition of the alloy material according to this embodiment may further contain one or more elements selected from the group consisting of Nb, Ta, V, Zr, and Hf in place of a portion of Fe. All of these elements combine with C to form carbides, reducing the amount of solid-solution C. This suppresses the formation of Cr carbides at grain boundaries in high-temperature environments. As a result, the formation of Cr-depleted layers is suppressed. Consequently, the stress-relaxation cracking resistance of the alloy material in high-temperature environments is further enhanced.

[0054] Nb: 0~0.30% Niobium (Nb) is an optional element and may not be present. In other words, the Nb content may be 0%. If Nb is present, that is, if the Nb content is greater than 0%, Nb combines with C to form carbides. By forming carbides and fixing C, the amount of dissolved C in the alloy material is reduced. This suppresses the formation of Cr carbides at grain boundaries in high-temperature environments. Therefore, the formation of Cr-deficient regions is suppressed. As a result, the stress relaxation crack resistance of the alloy material is increased. Furthermore, during use in high-temperature environments, Nb, together with N, forms fine nitrides in the alloy material. These fine nitrides strengthen the Cr-deficient regions, thus increasing the stress relaxation crack resistance of the alloy material. The fine nitrides formed during use in high-temperature environments further increase the creep strength through precipitation strengthening. Even if only a small amount of Nb is present, the above effects can be obtained to some extent. However, if the Nb content exceeds 0.30%, even if the content of other elements is within the range of this embodiment, the heat-affected zone of the alloy material will have reduced resistance to high-temperature cracking during welding. Therefore, the Nb content is 0 to 0.30%. The preferred lower limit of the Nb content is 0.01%, more preferably 0.02%, more preferably 0.05%, and still more preferably 0.08%. The preferred upper limit for the Nb content is 0.25%, more preferably 0.20%, and even more preferably 0.15%.

[0055] Ta: 0~0.50% Tantalum (Ta) is an optional element and may not be present. In other words, the Ta content may be 0%. If Ta is present, that is, if the Ta content is greater than 0%, Ta combines with C to form carbides. By forming carbides and fixing C, the amount of dissolved C in the alloy material is reduced. This suppresses the formation of Cr carbides at grain boundaries in high-temperature environments. Therefore, the formation of Cr-deficient regions is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. Even if only a small amount of Ta is present, the above effect can be obtained to some extent. However, if the Ta content exceeds 0.50%, even if the content of other elements is within the range of this embodiment, the heat-affected zone of the alloy material will experience reduced resistance to high-temperature cracking during welding. Therefore, the Ta content is 0-0.50%. The preferred lower limit for the Ta content is 0.01%, more preferably 0.02%, more preferably 0.05%, and still more preferably 0.08%. The preferred upper limit for the Ta content is 0.45%, more preferably 0.40%, even more preferably 0.35%, and even more preferably 0.30%.

[0056] V: 0~1.00% Vanadium (V) is an optional element and may not be present. In other words, the V content may be 0%. If V is present, that is, if the V content is greater than 0%, V combines with C to form carbides. By forming carbides and fixing C, the amount of dissolved C in the alloy material is reduced. This suppresses the formation of Cr carbides at grain boundaries in high-temperature environments. Therefore, the formation of Cr-deficient regions is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. Even if only a small amount of V is present, the above effect can be obtained to some extent. However, if the V content exceeds 1.00%, even if the content of other elements is within the range of this embodiment, the heat-affected zone of the alloy material will experience reduced resistance to high-temperature cracking during welding. Therefore, the V content is 0-1.00%. The preferred lower limit of the V content is 0.01%, more preferably 0.02%, even more preferably 0.04%, and even more preferably 0.06%. The preferred upper limit for the V content is 0.80%, more preferably 0.50%, more preferably 0.40%, more preferably 0.35%, and still more preferably 0.30%.

[0057] Zr: 0~0.10% Zirconium (Zr) is an optional element and may not be present. In other words, the Zr content may be 0%. If Zr is present, that is, if the Zr content is greater than 0%, Zr combines with C to form carbides. By forming carbides and fixing C, the amount of dissolved C in the alloy material is reduced. This suppresses the formation of Cr carbides at grain boundaries in high-temperature environments. Therefore, the formation of Cr-deficient regions is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. Even if only a small amount of Zr is present, the above effect can be obtained to some extent. However, if the Zr content exceeds 0.10%, even if the content of other elements is within the range of this embodiment, the heat-affected zone of the alloy material will experience reduced resistance to high-temperature cracking during welding. Therefore, the Zr content is 0 to 0.10%. The preferred lower limit for the Zr content is 0.01%, and more preferably 0.02%. The preferred upper limit for the Zr content is 0.09%, more preferably 0.08%, even more preferably 0.07%, and even more preferably 0.06%.

[0058] Hf: 0~0.10% Hafnium (Hf) is an optional element and may not be present. In other words, the Hf content may be 0%. When Hf is present, that is, when the Hf content is greater than 0%, Hf combines with C to form carbides. By forming carbides and fixing C, the amount of dissolved C in the alloy material is reduced. This suppresses the formation of Cr carbides at grain boundaries in high-temperature environments. Therefore, the formation of Cr-deficient regions is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. Even if only a small amount of Hf is present, the above effect can be obtained to some extent. However, if the Hf content exceeds 0.10%, even if the content of other elements is within the range of this embodiment, the heat-affected zone of the alloy material will experience reduced resistance to high-temperature cracking during welding. Therefore, the Hf content is 0 to 0.10%. The preferred lower limit for the Hf content is 0.01%, and more preferably 0.02%. The preferred upper limit for the Hf content is 0.09%, more preferably 0.08%, even more preferably 0.07%, and even more preferably 0.06%.

[0059] [Group 2: Regarding Cu, Mo, W, and Co] The chemical composition of the alloy material according to this embodiment may further contain one or more elements selected from the group consisting of Cu, Mo, W, and Co in place of a portion of Fe. All of these elements enhance the creep strength of the alloy material in high-temperature environments.

[0060] Cu: 0~1.00% Copper (Cu) is an optional element and may not be present at all. In other words, the Cu content may be 0%. If Cu is present, that is, if the Cu content is greater than 0%, the Cu will precipitate as a Cu phase within the grains during use of the alloy material in a high-temperature environment. This precipitation strengthening increases the creep strength of the alloy material. Even if only a small amount of Cu is present, the above effect can be obtained to some extent. However, if the Cu content exceeds 1.00%, even if the content of other elements is within the range of this embodiment, the Cu phase will precipitate excessively within the crystal grains. In this case, the strength difference between the crystal grain and the grain boundary will increase. As a result, the stress relaxation crack resistance will decrease. Therefore, the Cu content should be between 0 and 1.00%. The preferred lower limit of the Cu content is 0.01%, more preferably 0.02%, more preferably 0.05%, more preferably 0.10%, more preferably 0.15%, and more preferably 0.20%. The preferred upper limit for the Cu content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.60%, more preferably 0.55%, and more preferably 0.50%.

[0061] Mo: 0~1.00% Molybdenum (Mo) is an optional element and does not need to be present. In other words, the Mo content may be 0%. When Mo is present, that is, when the Mo content is greater than 0%, Mo increases the creep strength of the alloy material through solid solution strengthening during use in high-temperature environments. Even if only a small amount of Mo is present, the above effect can be obtained to some extent. However, if the Mo content exceeds 1.00%, intermetallic compounds such as the LAVES phase will form within the crystal grains, even if the content of other elements is within the range of this embodiment. In this case, secondary induced precipitation hardening increases, and the strength difference between the crystal grain and the grain boundary becomes larger. As a result, the stress relaxation crack resistance decreases. Therefore, the Mo content is 0 to 1.00%. The preferred lower limit of the Mo content is 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.04%, more preferably 0.05%, more preferably 0.10%, more preferably 0.20%, and more preferably 0.30%. The preferred upper limit for the Mo content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, and more preferably 0.60%.

[0062] W: 0~1.00% Tungsten (W) is an optional element and does not need to be included. In other words, the W content may be 0%. If W is included, that is, if the W content is greater than 0%, W increases the creep strength of the alloy material through solid solution strengthening when the alloy material is used in a high-temperature environment. Even if only a small amount of W is included, the above effect can be obtained to some extent. However, if the W content exceeds 1.00%, intermetallic compounds such as the LAVES phase will form within the crystal grains, even if the content of other elements is within the range of this embodiment. In this case, secondary induced precipitation hardening increases, and the strength difference between the crystal grain and the grain boundary becomes larger. As a result, the stress relaxation crack resistance decreases. Therefore, the W content is 0 to 1.00%. The preferred lower limit of the W content is 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.04%, more preferably 0.05%, and more preferably 0.10%. The preferred upper limit for the W content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, more preferably 0.60%, and more preferably 0.50%.

[0063] Co: 0~1.00% Cobalt (Co) is an optional element and may not be present at all. In other words, the Co content may be 0%. If Co is present, i.e., if the Co content is greater than 0%, Co stabilizes the austenite and increases the creep strength of the alloy material in high-temperature environments. Even a small amount of Co will provide some degree of this effect. However, if the CO content exceeds 1.00%, the raw material cost increases. Therefore, the CO content is between 0% and 1.00%. The preferred lower limit of the Co content is 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.05%, and more preferably 0.10%. The preferred upper limit for the Co content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.60%, and more preferably 0.50%.

[0064] [Group 3: Ca, Mg, and Rare Earth Elements (REM)] The chemical composition of the alloy material according to this embodiment may further contain, in place of some of the Fe, one or more elements selected from the group consisting of Ca, Mg, and rare earth elements (REM). All of these elements enhance the hot workability of the alloy material.

[0065] Ca: 0~0.0200% Calcium (Ca) is an optional element and may not be present. In other words, the Ca content may be 0%. When Ca is present, that is, when the Ca content is greater than 0%, Ca fixes O (oxygen) and S (sulfur) as inclusions, improving the hot workability of the alloy material. Furthermore, Ca fixes S, suppressing grain boundary segregation of S. Therefore, during welding of the alloy material, the resistance to hot cracking during welding is improved in the heat-affected zone (HAZ) of the alloy material. Even if only a small amount of Ca is present, the above effects can be obtained to some extent. However, if the Ca content exceeds 0.0200%, even if the content of other elements is within the range of this embodiment, the cleanliness of the alloy material will decrease, and the hot workability of the alloy material will actually decrease. Therefore, the Ca content is 0 to 0.0200%. The preferred lower limit of the Ca content is 0.0001%, more preferably 0.0002%, even more preferably 0.0005%, and even more preferably 0.0010%. The preferred upper limit for the Ca content is 0.0150%, more preferably 0.0100%, even more preferably 0.0080%, even more preferably 0.0050%, and even more preferably 0.0040%.

[0066] Mg: 0~0.0200% Magnesium (Mg) is an optional element and does not need to be included. In other words, the Mg content may be 0%. When Mg is present, that is, when the Mg content is greater than 0%, Mg fixes O (oxygen) and S (sulfur) as inclusions, improving the hot workability of the alloy material. Furthermore, Mg fixes S, suppressing grain boundary segregation of S. Therefore, during welding of the alloy material, it improves the resistance to high-temperature cracking in the HAZ (heat-affected zone) of the alloy material. Even if only a small amount of Mg is present, the above effects can be obtained to some extent. However, if the Mg content exceeds 0.0200%, even if the content of other elements is within the range of this embodiment, the cleanliness of the alloy material will decrease, and the hot workability of the alloy material will actually decrease. Therefore, the Mg content is 0 to 0.0200%. The preferred lower limit of the Mg content is 0.0001%, more preferably 0.0002%, more preferably 0.0005%, and still more preferably 0.0010%. The preferred upper limit for the Mg content is 0.0150%, more preferably 0.0100%, even more preferably 0.0080%, even more preferably 0.0050%, and even more preferably 0.0040%.

[0067] Rare earth elements: 0~0.1000% Rare earth elements (REMs) are optional and do not need to be present. In other words, the REM content may be 0%. When REMs are present, that is, when the REM content is greater than 0%, the REMs fix oxygen (O) and sulfur (S) as inclusions, improving the hot workability of the alloy material. Furthermore, REMs fix sulfur, suppressing grain boundary segregation of sulfur. Therefore, during welding of the alloy material, the heat-affected zone (HAZ) of the alloy material improves its resistance to high-temperature cracking during welding. Even if only a small amount of REMs are present, the above effects can be obtained to some extent. However, if the REM content exceeds 0.1000%, even if the content of other elements is within the range of this embodiment, the cleanliness of the alloy material will decrease, and the hot workability of the alloy material will actually decrease. Therefore, the REM content is 0 to 0.1000%. The preferred lower limit of the REM content is 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, and even more preferably 0.0020%. The preferred upper limit for the REM content is 0.0800%, more preferably 0.0600%, and even more preferably 0.0400%.

[0068] In this specification, REM refers to a material containing at least one element from Sc, Y, and lanthanides (La with atomic number 57 to Lu with atomic number 71), and the REM content refers to the total content of these elements.

[0069] [Regarding (Feature 2) Equation (1)] The chemical composition of the alloy material in this embodiment further satisfies formula (1). 0.60 <Al+Ti<1.20 (1) Here, each element symbol in equation (1) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

[0070] F1 is defined as Al + Ti. F1 is an indicator of the amount of γ' phase formation. In the alloy material of this embodiment, the γ' phase is formed during use in a high-temperature environment. This γ' phase increases the creep strength of the alloy material in a high-temperature environment.

[0071] Even if the content of each element in the chemical composition is within the range of this embodiment, if F1 is 0.60 or less, a sufficient amount of γ' phase will not be formed in the alloy material in a high-temperature environment. In this case, the creep strength of the alloy material in a high-temperature environment will decrease. On the other hand, even if the content of each element in the chemical composition is within the range of this embodiment, if F1 is 1.20 or higher, an excessive amount of the γ' phase will be formed in the alloy material. In this case, the weld resistance to high-temperature cracking of the alloy material will decrease. Therefore, F1 is greater than 0.60 and less than 1.20.

[0072] A preferred lower limit for F1 is 0.62, more preferably 0.64, even more preferably 0.66, even more preferably 0.68, and even more preferably 0.70. A preferred upper limit for F1 is 1.15, more preferably 1.10, more preferably 1.05, more preferably 1.00, and still more preferably 0.95.

[0073] [Regarding (Feature 3) Equation (2)] The chemical composition of the alloy material in this embodiment further satisfies formula (2). 1.12 ≤ Ti / Al (2) Here, each element symbol in equation (2) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

[0074] F2 is defined as Ti / Al. F2 is an index of the stress relaxation cracking resistance of alloy materials in high-temperature environments. In order to achieve both creep strength and resistance to stress relaxation cracking in high-temperature environments, the alloy material of this embodiment has a high Ti content relative to the Al content. In this case, the alloy material contains a certain amount of TiC. Therefore, the crystal grains in the alloy material become finer due to the TiC. As a result, the creep fracture elongation of the alloy material in high-temperature environments increases. Furthermore, in the alloy material of this embodiment, by increasing the Ti content relative to the Al content, TiC formation saturates in the early stages of the stress relaxation process. After TiC formation saturates, the TiC becomes coarser over time. As a result, the amount of creep strain accumulated in the Cr-deficient region forms a peak in the early stages of the stress relaxation process. Thereafter, the amount of creep strain decreases over time. As a result, the resistance to stress relaxation cracking in high-temperature environments increases. If F2 is less than 1.12, the above effect cannot be sufficiently obtained. Therefore, F2 is 1.12 or higher.

[0075] The preferred lower limit of F2 is 1.13, more preferably 1.15, even more preferably 1.30, even more preferably 1.40, and even more preferably 1.50. The upper limit of F2 is not particularly limited. From the viewpoint of improving the oxidation resistance of the alloy material, a preferred upper limit of F2 is 4.00, more preferably 3.90, even more preferably 3.70, even more preferably 3.50, and even more preferably 3.30.

[0076] [Preferred form of alloy material in this embodiment] Preferably, the alloy material of this embodiment satisfies features 1 to 3, and further satisfies the following feature 4. (Feature 4) The Ti content in the residue obtained by electrolytic extraction is defined as [Ti] (by mass percentage). R When defined as such, equation (3) is satisfied. 0.050<[Ti] R <0.72Ti-0.01(Ti / Al)-0.11 (3) Here, each element symbol in equation (3) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material. The following explains Feature 4.

[0077] [(Feature 4) Regarding Equation (3)] [Ti], which is the Ti content in the residue R is an indicator of the amount of TiC in the alloy material. In order to achieve both excellent stress relaxation cracking resistance and excellent welding hot cracking resistance, it is preferable that the amount of TiC and the amount of dissolved Ti in the alloy material are appropriate.

[0078] [Ti] R If [Ti] is higher than 0.050, before using the alloy material in a high-temperature environment, a certain amount of TiC exists in the alloy material. In this case, the pinning effect by TiC can be obtained. Therefore, the crystal grains in the alloy material are refined. As a result, the creep rupture elongation of the alloy material in a high-temperature environment increases. Furthermore, before using the alloy material in a high-temperature environment, a certain amount of TiC already exists in the alloy material. Therefore, as described above using FIG. 1, during high-temperature use, the generation of TiC saturates at the initial stage of the stress relaxation process. As a result, the creep strain amount in the Cr-deficient region also forms a peak at the initial stage of the stress relaxation process. After that, as time passes, the creep strain amount decreases. As a result, the stress relaxation cracking of the alloy material in a high-temperature environment is further suppressed.

[0079] On the other hand, [Ti] R If it is lower than F3 (= 0.72Ti - 0.01(Ti / Al) - 0.11), the amount of TiC in the alloy material is appropriate and not excessive. If there is an excessive amount of TiC in the alloy material, welding hot cracking caused by TiC will occur during the welding construction of the alloy material. That is, if [Ti] R is less than F3, the welding hot cracking resistance of the alloy material is further enhanced. Also, if there is an excessive amount of TiC in the alloy material, furthermore, during use in a high-temperature environment, sufficient γ' phase cannot be generated. In this case, the creep strength does not increase in a high-temperature environment. That is, if [Ti] R is less than F3, the creep strength of the alloy material is further enhanced. Therefore, preferably, [Ti] R is higher than 0.050 and less than F3 (= 0.72Ti - 0.01(Ti / Al) - 0.11).

[0080] [Ti] R A further preferred lower limit is 0.055, more preferably 0.060, more preferably 0.065, more preferably 0.070, and still more preferably 0.075. [Ti] R A more preferred upper limit (F3) is 0.72Ti-0.01(Ti / Al)-0.15, more preferably 0.72Ti-0.01(Ti / Al)-0.18, and even more preferably 0.72Ti-0.01(Ti / Al)-0.20.

[0081] [[Ti] R [Measurement Method] [Ti] R It can be measured by the following electrolytic extraction method. A test specimen is taken from a depth of 1 mm or more from the surface of the alloy material. The size of the test specimen is not particularly limited. For example, the test specimen may be 10 mm in diameter and 70 mm in length.

[0082] The surface of the collected test specimen is polished to a depth of approximately 50 μm using preliminary electrolytic polishing to obtain a new surface. The electrolytically polished test specimen is subjected to main electrolysis using an electrolyte (10% acetylacetone + 1% tetraammonium + methanol) at a current of 270 mA. At this time, the electrolysis depth is set to approximately 31 μm. The electrolyte after main electrolysis is filtered through a 0.2 μm filter to capture the residue. The obtained residue is acid-decomposed, and the mass of Ti (g) in the residue is determined by ICP (inductively coupled plasma) emission spectrometry. Furthermore, the mass (g) of the test specimen before main electrolysis and the mass (g) of the test specimen after main electrolysis are measured. The value obtained by subtracting the mass of the test specimen after main electrolysis from the mass of the test specimen before main electrolysis is defined as the amount of matrix material that was electrolyzed (g). The Ti content (mass%) in the residue is determined by dividing the mass of Ti in the residue by the amount of matrix material that was electrolyzed. In other words, the Ti content in the residue is calculated based on the following formula: [Ti] R Calculate the (mass %). [Ti] R = Mass of Ti in the residue / Amount of base material × 100

[0083] [Effects of alloy materials] The alloy material of this embodiment satisfies the above-described features 1 to 3. As a result, the alloy material of this embodiment has sufficient creep strength in high-temperature environments and can achieve both excellent stress relaxation cracking resistance and excellent weld cracking resistance. If the alloy material of this embodiment further satisfies feature 4, the creep strength and high-temperature weld cracking resistance will be further enhanced.

[0084] [Microstructure of alloy materials] The microstructure of the alloy material in this embodiment consists of austenite.

[0085] [Shape of alloy material] The shape of the alloy material in this embodiment is not particularly limited. The alloy material may be an alloy tube, an alloy plate, or an alloy rod. Preferably, the alloy material in this embodiment is an alloy tube.

[0086] [Method for manufacturing alloy materials] A method for manufacturing the alloy material of this embodiment that satisfies features 1 to 4 will be described. The manufacturing method described below is an example of a method for manufacturing the alloy material of this embodiment. Therefore, an alloy material that satisfies features 1 to 4 may be manufactured by a manufacturing method other than the one described below. However, the manufacturing method described below is a preferred example of a method for manufacturing the alloy material of this embodiment.

[0087] The method for manufacturing the alloy material of this embodiment includes the following steps. (Process 1) Preparation process (Process 2) Hot working process (Process 3) Cold working process (Step 4) Heat treatment process

[0088] In the hot working process of step 2, the following condition 1 is met. (Condition 1) The heating temperature T1 (°C) and the holding time t1 (minutes) at the heating temperature T1 during the heating process before hot working are within the following ranges. T1: 1100~1280℃ t1:3~120 minutes

[0089] Furthermore, the heat treatment process in step 4 satisfies the following condition 2. (Condition 2) The heat treatment temperature T2 (°C) and the holding time t2 (minutes) at the heat treatment temperature T2 are within the following ranges. T2: 1050~1300℃ t2:1~60 minutes The following describes each step.

[0090] [(Process 1) Preparation process] In the preparation process, a material having the chemical composition described in Feature 1 above is prepared. The material may be supplied by a third party or manufactured. The material may be in the form of an ingot, slab, bloom, or billet.

[0091] When manufacturing the material, the material is manufactured by the following method: Molten steel having the chemical composition described above is manufactured. An ingot is manufactured using the manufactured molten steel by the ingot-making method. A slab, bloom, or billet may be manufactured using the manufactured molten steel by the continuous casting method. A billet may be manufactured by hot working on the manufactured ingot, slab, or bloom. For example, a cylindrical billet may be manufactured by hot forging on an ingot, and this billet may be used as the material. In this case, the temperature of the material immediately before the start of hot forging is not particularly limited, but for example, it is 1000 to 1300°C. The method of cooling the material after hot forging is not particularly limited.

[0092] [(Process 2) Hot working process] In the hot working process, the material prepared in the preparation process is subjected to hot working to produce an intermediate alloy material. The intermediate alloy material may be, for example, an alloy tube, an alloy plate, or an alloy rod.

[0093] When the intermediate alloy material is an alloy tube, the following processes are carried out in the hot working process: First, a cylindrical material is prepared. A through hole is formed along the central axis of the cylindrical material by machining. The cylindrical material with the through hole is heated. Hot extrusion, such as the Eugène Séjournet method, is performed on the heated cylindrical material to produce the intermediate alloy material (alloy tube). Instead of the hot extrusion method, the hot stamping method may be used.

[0094] Alternatively, alloy tubes may be manufactured by perforation rolling using the Mannesmann method instead of hot extrusion. In this case, the cylindrical material is heated. Perforation rolling is performed on the heated cylindrical material using a perforation machine. When perforation rolling, the perforation ratio is not particularly limited, but for example, it is 1.0 to 4.0. The perforated and rolled cylindrical material is further hot-rolled using a mandrel mill, reducer, sizing mill, etc., to make a hollow tube (alloy tube). The cumulative reduction ratio in the hot working process is not particularly limited, but for example, it is 20 to 80%. When manufacturing alloy tubes by hot working, it is preferable that the temperature of the hollow tube immediately after the completion of hot working (finishing temperature) is 800°C or higher.

[0095] When the intermediate alloy material is an alloy sheet, the hot working process involves, for example, using one or more rolling mills equipped with a pair of work rolls. The material, such as a slab, is heated. Hot rolling is performed on the heated material using the rolling mill to produce an alloy sheet.

[0096] In the hot working process, condition 1 described above is satisfied. That is, the heating temperature T1 (°C) during heating before hot working and the holding time t1 (minutes) at heating temperature T1 are within the following ranges. T1: 1100~1280℃ t1:3~120 minutes

[0097] Preferably, the hot working process satisfies the following condition 3. (Condition 3) The heating temperature T1 (°C) and the holding time t1 (minutes) at the heating temperature T1 should satisfy the following equation (A). 800 ≤ T1 × LOG(t1) ≤ 2100 (A)

[0098] FA is defined as FA = T1 × LOG(t1). FA is influenced by the amount of TiC in the alloy material after manufacturing. If FA is 800 or higher, a sufficient amount of TiC is generated during heating before hot working. Therefore, in the alloy material after manufacturing, [Ti] R The value will be higher than 0.050. On the other hand, if FA is 2100 or less, an appropriate amount of TiC is generated during heating before hot working. Therefore, in the alloy material after manufacturing, [Ti] R This results in F3 (=0.72Ti - 0.01(Ti / Al) - 0.11). Therefore, preferably, FA is between 800 and 2100.

[0099] A further preferred lower limit for FA is 820, more preferably 840, more preferably 860, more preferably 1000, and more preferably 1200. A more preferred upper limit for FA is 2050, even more preferably 2000, even more preferably 1950, and even more preferably 1850.

[0100] [(Process 3) Cold working process] Cold working is performed as needed. In other words, cold working is not required. If cold working is performed, the intermediate alloy material is pickled before cold working. If the intermediate alloy material is an alloy tube or alloy rod, 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. Cold working can induce recrystallization and grain uniformity. The reduction in surface area during cold working is not particularly limited, but is, for example, 10-90%.

[0101] [(Step 4) Heat Treatment Process] In the heat treatment process, the intermediate alloy material after the hot working process or cold working process is subjected to heat treatment to adjust the amount of TiC in the alloy material and the size of the crystal grains.

[0102] The heat treatment process satisfies condition 2 described above. That is, the heat treatment temperature T2 (°C) and the holding time t2 (minutes) at the heat treatment temperature T2 are within the following ranges. T2: 1050~1300℃ t2:1~60 minutes

[0103] Preferably, the heat treatment process satisfies the following condition 4. (Condition 4) The heat treatment temperature T2 (°C) and the holding time t2 (minutes) at the heat treatment temperature T2 should satisfy the following equation (B). 2600≦T2×(LOG(t2)+2)≦4400 (B)

[0104] FB is defined as FB = T2 × (LOG(t2) + 2). Similar to FA, FB is influenced by the amount of TiC in the alloy material after manufacturing. If FB is 2600 or higher, a sufficient amount of TiC will be generated in the alloy material after manufacturing. Therefore, [Ti] R The value will be higher than 0.050. On the other hand, if FB is 4400 or less, TiC will be generated in an appropriate amount in the alloy material after manufacturing. Therefore, [Ti] R The ratio becomes less than 0.72Ti-0.01(Ti / Al)-0.11. Therefore, preferably, FB is between 2600 and 4400.

[0105] A more preferred lower limit for FB is 2650, even more preferably 2700, and even more preferably 2750. A more preferred upper limit for FB is 4350, even more preferably 4300, even more preferably 4250, even more preferably 4000, and even more preferably 3800.

[0106] After holding the intermediate alloy material at a heat treatment temperature T2 (°C) for a holding time t2 (minutes), it is cooled. Rapid cooling (water cooling) is preferred.

[0107] Preferably, the hot working process and the heat treatment process further satisfy the following condition 5. (Condition 5) 0.30 ≤ FA / FB (C)

[0108] FC is defined as FA / FB. Like FA and FB, FC affects the amount of TiC in the alloy material after manufacturing. If FC is 0.30 or higher, a sufficient amount of TiC is likely to be obtained in the alloy material after manufacturing. Therefore, [Ti] R The value will be higher than 0.050. Therefore, preferably, FC is 0.30 or higher.

[0109] A more preferred lower limit for FC is 0.33, even more preferably 0.35, and even more preferably 0.38. There is no particular upper limit to FC. For example, the upper limit of FC is 0.60.

[0110] The alloy material of this embodiment can be manufactured through the above process. The above-described manufacturing method is just one example of a method for manufacturing the alloy material of this embodiment. Therefore, the method for manufacturing the alloy material of this embodiment is not limited to the method described above. The method for manufacturing the alloy material is not limited to the method described above as long as features 1 to 3 or features 1 to 4 are satisfied.

[0111] [Method for manufacturing welded joints of alloy materials] The alloy welded joint of this embodiment can be manufactured by the following method.

[0112] Prepare the alloy material of this embodiment as the base material. Form a groove in the prepared base material. Specifically, form a groove at the end of the base material by a well-known processing method. The groove shape may be V-shaped, U-shaped, X-shaped, or any other shape other than V-shaped, U-shaped, and X-shaped.

[0113] A welded joint is manufactured by welding to prepared base materials. Specifically, two base materials with grooves formed are prepared. The grooves of the prepared base materials are butted together. Then, welding is performed on the butted pair of grooves using a well-known welding material to form a weld metal having the chemical composition described above. The welding material is, for example, AWS standard name: ER NiCr-3. However, the welding material is not limited to this.

[0114] The welding method may involve forming a single layer of weld metal or performing multi-layer welding. Examples of welding methods include TIG welding (GTAW), shielded metal arc welding (SMAW), flux-cored wire arc welding (FCAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). The welded joint of the alloy material according to this embodiment can be manufactured through the above manufacturing process. [Examples]

[0115] The effects of the alloy material of this embodiment will be further explained in detail by the following examples. The conditions in the following examples are just one example of conditions adopted to confirm the feasibility and effects of the alloy material of this embodiment. Therefore, the alloy material of this embodiment is not limited to this one example of conditions.

[0116] [Manufacturing of alloy materials] Ingots having the chemical compositions shown in Tables 1-1 and 1-2 were manufactured. The ingots were cylindrical with an outer diameter of 120 mm and a mass of 30 kg.

[0117] [Table 1-1]

[0118] [Table 1-2]

[0119] In Table 1-2, a "-" indicates that the content of the corresponding element was below the impurity level.

[0120] Hot forging was performed on the manufactured ingots to produce a 30mm thick material (alloy plate). The heating temperature of the ingots during hot forging was 1000-1300°C. A hot working process was performed on the manufactured material. Specifically, the material was heated in a heating furnace. The heating temperature T1 in the hot working process was 1100 to 1280°C, and the holding time t1 at heating temperature T1 was 3 to 120 minutes. The FA values ​​are shown in Table 2. After heating, the material was hot-rolled to produce an intermediate alloy material (alloy sheet) with a thickness of 15 mm.

[0121] [Table 2]

[0122] A heat treatment process was performed on the intermediate alloy material. The heat treatment temperature T2 was 1050 to 1300°C, and the holding time t2 at heat treatment temperature T2 was 1 to 60 minutes. The FB and FC values ​​are shown in Table 2. After the holding time t2, the intermediate alloy material was water-cooled to room temperature. Through the above process, alloy materials (alloy plates) for each test number were manufactured.

[0123] [Evaluation Test] The following evaluation tests were conducted using the manufactured alloy material. (Test 1) [Ti] R Measurement test (Test 2) Creep Strength Evaluation Test (Test 3) Stress relaxation cracking resistance evaluation test (Test 4) Evaluation test for resistance to high-temperature cracking during welding The following describes each evaluation test.

[0124] [(Test 1)[Ti] R [Measurement Test] Test specimens were taken from a depth of 1 mm or more from the surface of the alloy material for each test number. The size of the test specimens was 10 mm in diameter and 70 mm in length. [[Ti] R Based on the measurement method, the Ti content in the residue [Ti] R The (mass %) was calculated. The obtained [Ti]R See "[Ti]" in Table 2. R This is shown in the "(mass %)" column.

[0125] [(Test 2) Creep Strength Evaluation Test] The following creep strength evaluation tests were performed on the alloy material (alloy plate) for each test number. Creep rupture test specimens were taken from the center of the width and thickness of each alloy material (alloy sheet) according to JIS Z2271:2010. The cross-section perpendicular to the axial direction of the parallel section of the creep rupture test specimen was circular. The outer diameter of the parallel section was 6 mm and the length was 30 mm. The longitudinal direction of the creep rupture test specimen was parallel to the rolling direction of the alloy sheet.

[0126] A creep rupture test was conducted using the collected creep rupture specimens in accordance with JIS Z2271:2010. Specifically, the creep rupture specimens were heated to 700°C. The creep rupture test was then performed. The test stress was set to 80 MPa. The creep rupture time (hours) was determined during the test.

[0127] The creep strength was evaluated as follows, based on the obtained creep rupture time. Rating E (Excellent): Creep rupture time is longer than 4000 hours. Rating G (Good): Creep rupture time is 2000-4000 hours Rating B (Bad): Creep rupture time is shorter than 2000 hours. A rating of G or E indicates that excellent creep strength was achieved. The evaluation results are shown in the "Creep Strength" column of Table 2.

[0128] [(Test 3) Stress Relaxation Cracking Resistance Evaluation Test] The following stress relaxation crack resistance evaluation tests were performed on the alloy material (alloy plate) for each test number. A rectangular specimen was taken from the center of the width and thickness of each alloy sheet (alloy plate) for each test number. The cross-section of the rectangular specimen perpendicular to the longitudinal direction was a rectangle of 10 mm x 10 mm. The length of the rectangular specimen was 100 mm. The longitudinal direction of the rectangular specimen was parallel to the rolling direction of the alloy sheet (alloy plate).

[0129] Using a high-frequency thermal cycling apparatus, the following thermal history was applied to the collected horn-shaped test specimens. Specifically, the horn-shaped test specimens were heated in air from room temperature to 1300°C at a rate of 70°C / second. They were then held at 1300°C for 180 seconds. Afterward, the horn-shaped test specimens were cooled to room temperature at a rate of 50°C / second. By applying this thermal history to the horn-shaped test specimens, weld simulation test specimens were prepared.

[0130] A stress relaxation test was conducted in accordance with ASTM E328-02 using a welded simulated specimen. Specifically, a specimen for the stress relaxation test was prepared from the welded simulated specimen. The specimen was a flanged creep specimen with a length of 80 mm and a gauge length of GL = 30 mm. An initial cold strain of 20% was applied to the specimen using a deflection displacement loading test jig. The test jig with the cold-strained specimen attached was placed in a heating furnace and held at 650°C for 300 hours.

[0131] The results of the stress relaxation test in accordance with ASTM E328-02 were evaluated as follows. Evaluation E (Excellent): The test specimen remains intact after 300 hours. Rating G (Good): The test specimen fractured after 200-300 hours. Rating B (Bad): The test specimen fractured in less than 200 hours. A rating of G or E indicates that excellent stress relaxation cracking resistance was achieved. The evaluation results are shown in the "Stress Relaxation Cracking Resistance" column of Table 2.

[0132] [(Test 4) Welding High-Temperature Cracking Resistance Evaluation Test] A test specimen measuring 12 mm in thickness, 40 mm in width, and 300 mm in length was taken from the center of the width and thickness of the alloy material (alloy plate) for each test number. The following longitudinal strain test was performed on the collected test specimens.

[0133] Specifically, TIG tack welding was performed along the longitudinal direction at the center of the plate width of the test specimen under welding conditions of a welding current of 200A, a voltage of 12V, and a welding speed of 15cm / min. During the TIG tack welding, a bending stress was instantaneously applied parallel to the welding direction so that a 2% strain was applied to the surface layer.

[0134] The portion containing the weld crack that occurred due to the application of bending stress was cut out to a size that could be observed with an optical microscope. The size of the cut-out sample was 40 mm x 40 mm x 12 mm.

[0135] The scale on the weld surface of the cut-out sample was removed by buffing. Then, using a 100x optical microscope, the presence or absence of cracks in the heat-affected zone (HAZ), and if cracks were present, their length, was measured. Specifically, the length of cracks propagating perpendicular to the welding direction (length perpendicular to the welding direction) was measured, starting from the boundary between the weld metal and the HAZ. The length perpendicular to the welding direction of all cracks that occurred in the test specimen was determined. The sum of these crack lengths was defined as the total crack length (mm). The total crack length was determined for each of the two test specimens. The arithmetic mean of the determined total crack lengths was defined as the average total crack length.

[0136] Based on the average total crack length obtained, the resistance to hot cracking during welding was evaluated as follows. Rating E (Excellent): Average total crack length is 2.0 mm or less. Rating G (Good): Average total crack length is greater than 2.0 mm but less than 3.0 mm. Rating B (Bad): The average total crack length is 3.0 mm or more. A rating of G or E indicates that excellent resistance to high-temperature cracking during welding was achieved. The evaluation results are shown in the "High-Temperature Cracking Resistance During Welding" column of Table 2.

[0137] [Test Results] Table 2 shows the test results.

[0138] Referring to Tables 1-1, 1-2, and 2, the alloy material met characteristics 1 to 3 in test numbers 1 to 35. Therefore, sufficient creep strength was obtained in high-temperature environments. Furthermore, excellent stress relaxation cracking resistance and excellent high-temperature weld cracking resistance were achieved.

[0139] Furthermore, in tests 1 to 28, the manufacturing conditions FA satisfied equation (A), FB satisfied equation (B), and FC satisfied equation (C). As a result, in tests 1 to 28, the alloy material satisfied not only features 1 to 3 but also feature 4. Therefore, in tests 1 to 28, a rating of E was obtained in the creep strength evaluation test, stress relaxation cracking resistance evaluation test, and weld high-temperature cracking resistance evaluation test, demonstrating even better creep strength, stress relaxation cracking resistance, and weld high-temperature cracking resistance.

[0140] On the other hand, in test number 36, the Al content was too high. As a result, sufficient stress relaxation cracking resistance and high-temperature welding cracking resistance could not be obtained. Furthermore, sufficient creep strength could not be obtained.

[0141] In test number 37, although the content of each element in the chemical composition was appropriate, F1 was below the lower limit of equation (1). Therefore, sufficient creep strength was not obtained.

[0142] In test number 38, although the content of each element in the chemical composition was appropriate, F1 exceeded the upper limit of formula (1). Therefore, sufficient resistance to high-temperature cracking during welding could not be obtained.

[0143] In test number 39, although the content of each element in the chemical composition was appropriate, F2 was below the lower limit of equation (2). As a result, sufficient stress relaxation crack resistance was not obtained.

[0144] Embodiments of the present invention have been described above. However, the embodiments described above are merely illustrative examples for carrying out the present invention. Therefore, the present invention is not limited to the embodiments described above, and the embodiments described above can be appropriately modified and implemented without departing from the spirit of the invention.

Claims

1. The chemical composition is expressed in mass percent. C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.100% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0010-0.0050%, Nb: 0 to 0.30%, Ta: 0 to 0.50%, V: 0-1.00%, Zr: 0 to 0.10%, Hf: 0-0.10%, Cu: 0 to 1.00%, Mo: 0-1.00%, W: 0-1.00%, Co: 0-1.00%, Ca: 0-0.0200%, Mg: 0 to 0.0200%, Rare earth elements: 0-0.1000%, and The remainder consists of Fe and impurities. The following conditions satisfy equations (1) and (2): Alloy material. 0.60<Al+Ti<1.20 (1) 1.12≦Ti / Al (2) Here, the elemental symbols in formulas (1) and (2) are substituted with the content of the corresponding element in the chemical composition of the alloy material, expressed in mass percent.

2. The alloy material according to claim 1, further, The Ti content in mass percent of the residue obtained by electrolytic extraction is [Ti] Ｒ When defined as such, equation (3) satisfies, Alloy material. 0.050 <[Thu] Ｒ <0. Here, each element symbol in equation (3) is substituted with the mass percentage of the content of the corresponding element in the chemical composition of the alloy material.

3. The alloy material according to claim 1 or claim 2, Nb: 0.01-0.30%, Ta: 0.01-0.50%, V: 0.01-1.00%, Zr: 0.01~0.10% Hf: 0.01-0.10%, Cu: 0.01 to 1.00%, Mo: 0.01-1.00%, W: 0.01-1.00%, Co: 0.01 to 1.00%, Ca: 0.0001-0.0200%, Mg: 0.0001 to 0.0200%, and, Rare earth elements: 0.001 to 0.1000%, It contains one or more elements selected from the group consisting of, Alloy material.

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