Alloy material

Abstract

Provided is an alloy material with which it is possible to obtain high creep strength and excellent welding hot cracking resistance and hot workability. This alloy material contains, in mass%, 0.050 to 0.100% of C, 1.00% or less of Si, 1.50% or less of Mn, 19.00 to 23.00% of Cr, 30.00 to 35.00% of Ni, 0.010% or less of N, 0.15 to 0.70% of Al, 0.15 to 0.70% of Ti, 0.0001 to 0.0030% of B, 0.0010 to 0.5000% of Nb, 0.01 to 1.00% of Mo, and 0.0001 to 0.0200% of Ca, with the remainder being Fe and impurities, and satisfies formula (1) and formula (2), and also satisfies formula (3) when B is less than or equal to 0.0010%. 0.60 lt, 0.60 lt; al + Tilt; 1.20 (1), 3.3-41 C-Si + 2Mo + 3Ti + 245B-12Nb < = 2.00 (2), and 0.4 + 67 C + 1.3 Si + 5.5 Mo + 5.2 Ti + 13.4 Nb < = 8.25 (3).

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 modification units, ethylene decomposition furnaces, heating furnace tubes for petroleum refining and petrochemical equipment, and polysilicon manufacturing equipment operate at high temperatures of 500–1000°C. Therefore, alloy materials used in such high-temperature environments require excellent corrosion resistance and high creep strength. Alloys 800, 800H, and 800HT are known as alloys for use in such high-temperature environments.

[0003] Alloys 800, 800H, and 800HT contain significant amounts of Cr and Ni. Therefore, these alloys exhibit excellent corrosion resistance at high temperatures. These alloys also contain Al and Ti. Consequently, during high-temperature use, a γ' (gamma prime) phase (Ni3(Al,Ti)) is formed in these alloys. Through precipitation strengthening based on the γ' phase, these alloys achieve high creep strength.

[0004] However, in Al and Ti-containing alloys 800, 800H, and 800HT, welding hot cracking is prone to occur in the heat-affected zone (HAZ) during welding. Furthermore, these alloys are manufactured by hot working in a temperature range of approximately 900°C, but are susceptible to cracking due to embrittlement during hot working. Therefore, these alloys require excellent resistance to welding hot cracking and excellent hot workability.

[0005] Japanese Patent Application Publication No. 2022-163425 (Patent Document 1), Japanese Patent Application Publication No. 2022-163585 (Patent Document 2), and Japanese Patent Application Publication No. 2022-163586 (Patent Document 3) disclose techniques for improving the resistance to welding hot cracking of alloy materials containing Al and Ti.

[0006] The alloy material disclosed in Patent Document 1 has a chemical composition containing, by mass percent, less than 0.15% C, less than 0.05% to 2.0% Si, less than 0.05% to 2.0% Mn, less than 0.05% to 2.0% P, less than 0.035% S, less than 0.0015% Cr, less than 16% to 30% Ni, less than 18% to 50% Al, less than 0.01% to 1.0% Ti, less than 0.01% to 1.5% N, less than 0.35% O, less than 0.003% Mo, less than 8% Cu, less than 4% Co, less than 3% Ca, less than 0.0003% to 0.0050% Mg and less than 0.0045%, with the balance being Fe and impurities. Furthermore, the mass ratio of CaO, MgO, and Al2O3 in the inclusions, calculated based on the average Ca, Mg, and Al concentrations of the detected O or S inclusions, satisfies [CaO - 0.6 × MgO] / [CaO + MgO + Al2O3] ≥ 0.20. In Patent Document 1, the mass ratio of oxide inclusions (CaO, MgO, and Al2O3) in the alloy is appropriately controlled. This suppresses the formation of coarse TiC, thereby improving the alloy's resistance to weld hot cracking.

[0007] The alloy material disclosed in Patent Document 2 has a chemical composition containing, by mass percent: C: 0.15% or less, Si: 0.05-2.0%, Mn: 0.05-2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 16-30%, Ni: 18-50%, Al: 0.01-1.0%, Ti: 0.01-1.5%, N: 0.35% or less, O: 0.003% or less, Mo: 8% or less, Cu: 4% or less, Co: 3% or less, Ca: 0.0003-0.0050%, and Mg: 0.0060% or less, with the balance being Fe and impurities. Furthermore, the number density of TiC precipitates with an equivalent circle diameter of 1.0 μm or more and the Mg content in the steel satisfy the TiC number density (cells / mm²). 2 The Mg concentration in the steel is ≤463-9.5 × ppm (mass). In Patent Document 2, the amount of coarse TiC precipitation is appropriately controlled according to the Mg concentration in the alloy material. As a result, the resistance of the alloy material to weld hot cracking is improved.

[0008] The alloy material disclosed in Patent Document 3 has the following chemical composition by mass percent: C: 0.15% or less, Si: 0.05-2.0%, Mn: 0.05-2.0%, P: 0.035% or less, S: 0.0015% or less, O: 0.0020% or less, and the sum of O and S is 0.0020% or less, Cr: 16-30%, Ni: 18-50%, Al: 0.01-1.0%, Ti: 0.01-1.5%, N: 0.02% or less, Mo: 8% or less, Cu: 4% or less, Co: 3% or less, Ca: 0.0010-0.0050%, and Mg: 0.0010-0.0050%, with the balance being Fe and impurities. Furthermore, the average concentration of S in oxide-based inclusions and sulfide-based inclusions is 0.70% or more by mass percent. In Patent Document 3, S, which lowers the grain boundary strength and melting point, is fixed within the inclusions. This improves the alloy's resistance to weld hot cracking.

[0009] Furthermore, Japanese Patent Application Publication No. 2021-070838 (Patent Document 4) discloses a technique for improving the hot workability of alloy materials containing Al and Ti.

[0010] The alloy material disclosed in Patent Document 4 has a chemical composition, by mass percent, of C: 0.10% or less, Si: 0.05-1.0%, Mn: 0.05-2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 18-25%, Ni: 18-50%, Al: 0.05-1.0%, Ti: 0.15-1.5%, N: 0.02% or less, O: 0.003% or less, Mo: 5% or less, W: 2% or less, Cu: 3% or less, Co: 2.0% or less, Ca: 0.0003-0.005%, and Mg: 0.006% or less, with the balance being Fe and unavoidable impurities. Furthermore, the Ca / Al mass ratio in the oxide inclusions is 1.0-15. Furthermore, the excess Ca (ΔCa) calculated using ΔCa = Ca - 1.25 × SK(Ca / O) × O is 0.0003 to 0.0030%. In Patent Document 4, ΔCa in the alloy material is appropriately controlled. As a result, the hot workability of the alloy material is improved.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2022-163425

[0014] Patent Document 2: Japanese Patent Application Publication No. 2022-163585

[0015] Patent Document 3: Japanese Patent Application Publication No. 2022-163586

[0016] Patent Document 4: Japanese Patent Application Publication No. 2021-070838 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] While the alloy materials described in Patent Documents 1-3 exhibit excellent resistance to weld hot cracking, their hot workability was not investigated in these documents. Similarly, while the alloy material described in Patent Document 4 exhibits excellent hot workability, its resistance to weld hot cracking was not investigated.

[0019] The purpose of this disclosure is to provide an alloy material that can achieve high creep strength, excellent resistance to weld hot cracking, and excellent hot workability.

[0020] Solution for solving the problem

[0021] The chemical composition of the alloy material disclosed herein, in mass percent, is as follows:

[0022] C: 0.050~0.100%

[0023] Si: below 1.00%

[0024] Mn: below 1.50%

[0025] P: below 0.035%

[0026] S: less than 0.0015%

[0027] Cr: 19.00~23.00%

[0028] Ni: 30.00~35.00%

[0029] N: less than 0.010%

[0030] Al: 0.15–0.70%

[0031] Ti: 0.15–0.70%

[0032] B: 0.0001~0.0030%

[0033] Nb: 0.0010~0.5000%

[0034] Mo: 0.01~1.00%

[0035] Ca: 0.0001~0.0200%

[0036] Ta: 0-0.50%

[0037] V: 0~1.00%

[0038] Zr: 0~0.100%

[0039] Hf: 0~0.10%

[0040] Cu: 0–1.00%

[0041] W: 0~1.00%

[0042] Co: 0-1.00%

[0043] Rare earth elements: 0~0.1000%

[0044] Mg: 0–0.0200%, and

[0045] The balance consists of Fe and impurities.

[0046] The alloy material satisfies equations (1) and (2).

[0047] When the B content in the chemical composition is less than 0.0010%, equation (3) is also satisfied.

[0048] 0.60 <Al+Ti<1.20(1)

[0049] 3.3-41C-Si+2Mo+3Ti+245B-12Nb≤2.00(2)

[0050] 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb≤8.25(3)

[0051] In formulas (1) to (3), the content of the corresponding element in the chemical composition is substituted into the element symbol in formula (1) to (3) by mass%.

[0052] Invention Effects

[0053] The alloy material disclosed herein exhibits high creep strength, excellent resistance to weld hot cracking, and excellent hot workability. Detailed Implementation

[0054] The inventors first investigated alloys that exhibit high creep strength, excellent resistance to weld hot cracking, and excellent hot workability from a chemical composition perspective. As a result, the inventors concluded that an alloy with the following composition (by mass%) is suitable for achieving high creep strength, excellent resistance to weld hot cracking, and excellent hot workability. Alloys with the chemical composition of Fe and impurities, containing 0.01-1.00% Ca, 0.0001-0.0200% Ta, 0-0.50% V, 0-1.00% Zr, 0-0.100% Hf, 0-0.10% Cu, 0-1.00% W, 0-1.00% Co, 0-1.00% rare earth elements, 0-0.1000% Mg, and the balance being Fe and impurities, can be used in high-temperature environments and may exhibit excellent resistance to weld hot cracking and excellent hot workability.

[0055] Therefore, the inventors further investigated the creep strength, resistance to weld hot cracking, and hot workability of alloy materials satisfying the above-mentioned chemical composition. As a result, the inventors obtained the following insights.

[0056] [Regarding creep strength]

[0057] The inventors have investigated a method for improving the creep strength of alloys with the above-described chemical composition at high temperatures. As described above, Al and Ti form a γ' (gamma prime) phase (Ni3(Al,Ti)) in the alloy during use at high temperatures. The γ' phase improves the creep strength. Therefore, the total content of Al and Ti affects the creep strength. Specifically, in an alloy having the above-described chemical composition, sufficient creep strength can be obtained if the following formula (1) is satisfied.

[0058] 0.60 <Al+Ti<1.20(1)

[0059] In formula (1), the content of the corresponding element in the chemical composition of the alloy material is substituted into the element symbol in the formula (in terms of mass%).

[0060] [Regarding resistance to weld hot cracking and hot workability]

[0061] Among the elements in the aforementioned chemical composition, P, S, and Mg tend to segregate at grain boundaries. If these elements segregate, the grain boundaries become embrittled, and the hot workability at around 900°C decreases. Borosilicate (B) suppresses the decrease in hot workability caused by the segregation of these elements to grain boundaries. Specifically, B segregates at grain boundaries, suppressing the segregation of other elements at the grain boundaries. Therefore, grain boundaries are strengthened through B segregation. As a result, the hot workability of the alloy is improved.

[0062] However, if boron (B) is present, the solidification temperature of the grain boundaries of the HAZ (Half-Altitude Zone) of the alloy melts during the heating process in welding decreases. Therefore, while boron improves hot workability, it reduces resistance to weld hot cracking.

[0063] Therefore, the inventors investigated a method that can improve both hot workability and resistance to weld hot cracking by including B. As a result, the inventors concluded that, in order to further improve resistance to weld hot cracking while including B, it is effective to (A) increase the melting and solidification temperatures of Ti-based precipitates formed at grain boundaries, and (B) increase the solidification temperature of grain boundaries that melt due to compositional liquefaction during the heating process in welding.

[0064] [Regarding (A) increasing the melting and solidification temperatures of Ti-based precipitates formed at grain boundaries]

[0065] In this specification, Ti-based precipitates refer to precipitates containing Ti. Ti-based precipitates are mainly Ti-containing carbides. Ti-based precipitates may also contain other elements besides Ti (such as Si, Nb, etc.).

[0066] C, Si, and Nb increase the melting and solidification temperatures of Ti-based precipitates. Specifically, C and Si improve the stability of Ti-based precipitates at high temperatures. Therefore, the melting and solidification temperatures of Ti-based precipitates are increased. Additionally, the presence of Nb in Ti-based precipitates increases both their melting and solidification temperatures. Therefore, C, Si, and Nb are elements that increase the melting and solidification temperatures of Ti-based precipitates formed at grain boundaries.

[0067] [Regarding (B) increasing the solidification temperature of grain boundaries that melt due to liquefaction of the composition during the heating process in welding]

[0068] Even when the melting and solidification temperatures of Ti-based precipitates are high, resistance to weld hot cracking decreases if compositional liquefaction occurs. Specifically, during welding heating, the alloy is locally and rapidly heated. In this case, in the heated portion (HAZ) of the alloy, a eutectic melting reaction occurs in the Ti precipitates at the grain boundaries and the grain boundary regions, causing the Ti-based precipitates and grain boundaries to liquefy at temperatures lower than their melting points. This phenomenon is called compositional liquefaction.

[0069] Grain boundaries where compositional liquefaction occurs become the initiation point for cracks. Therefore, to improve resistance to weld hot cracking, it is effective to increase not only the melting and solidification temperatures of Ti-based precipitates but also the solidification temperature of grain boundaries where compositional liquefaction occurs. Consequently, the inventors investigated methods for increasing the solidification temperature of grain boundaries where compositional liquefaction occurs. The results showed that Mo, Ti, and B promote compositional liquefaction at grain boundaries. When Mo, Ti, or B is present at grain boundaries where compositional liquefaction occurs, the solidification temperature of these grain boundaries decreases. If the solidification temperature of grain boundaries where compositional liquefaction occurs is low, weld hot cracking is more likely to occur.

[0070] Based on the above insights, the inventors believe that by increasing the C, Si, and Nb content, the melting and solidification temperatures of Ti-based precipitates in the alloy can be increased, and by suppressing the Mo, Ti, and B content, the solidification temperature of grain boundaries where compositional liquefaction occurs can be increased, thereby improving resistance to weld hot cracking. Therefore, the relationship between these elements and resistance to weld hot cracking was further investigated. The results showed that in the alloy with the above chemical composition, if the following equation (2) is further satisfied, excellent resistance to weld hot cracking and excellent hot workability can be obtained.

[0071] 3.3-41C-Si+2Mo+3Ti+245B-12Nb≤2.00(2)

[0072] In formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted into the element symbol in the formula (in terms of mass%).

[0073] [For cases where the B content is below 0.0010%]

[0074] However, even for alloys that satisfy the above chemical composition and formulas (1) and (2), if the B content is below 0.0010%, excellent resistance to weld hot cracking may be obtained, but sufficient hot workability may not be achieved. Therefore, the inventors further investigated a method that can achieve both excellent hot workability and excellent resistance to weld hot cracking at a low B content. As a result, the inventors obtained the following insights.

[0075] In alloys with the above chemical composition, Ti-based precipitates sometimes occur within the grains during hot working at approximately 900°C. The alloy hardens due to these Ti-based precipitates. As a result, the hot workability of the alloy decreases. Therefore, it is effective to suppress the hardening of the alloy caused by Ti-based precipitates in order to improve its hot workability at approximately 900°C.

[0076] Therefore, the inventors investigated a method for sufficiently suppressing the hardening of alloy materials caused by Ti-based precipitates during hot working when the B content is below 0.0010%. As a result, the inventors obtained the following insights.

[0077] In the aforementioned hot working temperature range, C, Ti, Si, and Nb promote the formation of Ti-based precipitates. C and Ti directly contribute to the formation of Ti-based precipitates. Si increases the diffusion rate of C and Ti, thus contributing to the formation of Ti-based precipitates. Nb substitutes for Ti sites in Ti-based precipitates (that is, the lattice points occupied by Ti atoms in Ti-based precipitates), promoting the formation of Nb-containing Ti-based precipitates (composite precipitates). Furthermore, in the aforementioned chemical composition, Mo provides solid solution strengthening within the grains, and also hardens the alloy in the hot working temperature range.

[0078] Based on the above insights, the inventors believe that, when the B content is below 0.0010%, the hot workability at approximately 900°C can be improved by appropriately controlling the C, Ti, Si, Nb, and Mo contents.

[0079] Therefore, based on the above insights, the relationship between the content of the aforementioned elements (C, Si, Mo, Ti, and Nb) and hot workability when the B content is below 0.0010% was further investigated. The results showed that in alloys satisfying the above chemical composition and formulas (1) and (2), when the B content is below 0.0010%, by further satisfying formula (3), both excellent resistance to weld hot cracking and excellent hot workability can be achieved.

[0080] 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb≤8.25(3)

[0081] In formula (3), the content of the corresponding element in the chemical composition is substituted into the element symbol in terms of mass%.

[0082] The alloy material of this embodiment is based on the above insights and has the following composition.

[0083] The chemical composition of the alloy material of component 1, expressed in mass percent, is as follows:

[0084] C: 0.050~0.100%

[0085] Si: below 1.00%

[0086] Mn: below 1.50%

[0087] P: below 0.035%

[0088] S: less than 0.0015%

[0089] Cr: 19.00~23.00%

[0090] Ni: 30.00~35.00%

[0091] N: less than 0.010%

[0092] Al: 0.15–0.70%

[0093] Ti: 0.15–0.70%

[0094] B: 0.0001~0.0030%

[0095] Nb: 0.0010~0.5000%

[0096] Mo: 0.01~1.00%

[0097] Ca: 0.0001~0.0200%

[0098] Ta: 0-0.50%

[0099] V: 0~1.00%

[0100] Zr: 0~0.100%

[0101] Hf: 0~0.10%

[0102] Cu: 0–1.00%

[0103] W: 0~1.00%

[0104] Co: 0-1.00%

[0105] Rare earth elements: 0~0.1000%

[0106] Mg: 0–0.0200%, and

[0107] The balance consists of Fe and impurities.

[0108] The alloy material satisfies equations (1) and (2).

[0109] The chemical composition also satisfies equation (3) when the B content is less than 0.0010%.

[0110] 0.60 <Al+Ti<1.20(1)

[0111] 3.3-41C-Si+2Mo+3Ti+245B-12Nb≤2.00(2)

[0112] 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb≤8.25(3)

[0113] In formulas (1) to (3), the content of the corresponding element in the chemical composition is substituted into the element symbol in formula (1) to (3) by mass%.

[0114] According to the first alloy material, the chemical composition of the second alloy material contains, in mass percent, a selection of [missing information].

[0115] Ta: 0.01~0.50%

[0116] V: 0.01~1.00%

[0117] Zr: 0.001~0.100%

[0118] Hf: 0.01~0.10%

[0119] Cu: 0.01~1.00%

[0120] W: 0.01~1.00%

[0121] Co: 0.01~1.00%

[0122] Rare earth elements: 0.0001~0.1000%, and

[0123] Mg: 0.0001 to 0.0200% of one or more of the group.

[0124] According to the alloy material of the first or second composition, the alloy material of the third composition contains, in mass percent, B: greater than 0.0010% and less than 0.0030%.

[0125] The Ti content [Ti] in the residue obtained by the extraction method, expressed as a percentage by mass, is less than 0.020%, or...

[0126] The [Ti] content is 0.020% or more, and the Nb content [Nb] in the residue is 0.015% or more by mass, wherein the [Ti] and the [Nb] satisfy equation (4).

[0127] [Ti]+[Nb]≥0.050(4)

[0128] According to the alloy material of composition 1 or composition 2, the alloy material of composition 4 contains B in the following chemical composition (by mass%): 0.0001 to 0.0010%.

[0129] The Ti content [Ti] in the residue obtained by the residue extraction method, expressed as a percentage by mass, is less than 0.031%, or...

[0130] The [Ti] content is greater than 0.031%, and the Nb content [Nb] in the residue, expressed as a percentage by mass, is 0.3 × [Ti]% or more.

[0131] The alloy material of this embodiment will now be described in detail. Furthermore, unless otherwise stated, "%" related to elements refers to mass percentage.

[0132] [Characteristics of the alloy material in this embodiment]

[0133] The alloy material of this embodiment satisfies the following characteristics 1 to 4.

[0134] (Feature 1)

[0135] The chemical composition, in mass percent, is as follows: C: 0.050–0.100%, Si: less than 1.00%, Mn: less than 1.50%, P: less than 0.035%, S: less than 0.0015%, Cr: 19.00–23.00%, Ni: 30.00–35.00%, N: less than 0.010%, Al: 0.15–0.70%, Ti: 0.15–0.70%, B: 0.0001–0.0030%, Nb: 0.0010~0.5000%, Mo: 0.01~1.00%, Ca: 0.0001~0.0200%, Ta: 0~0.50%, V: 0~1.00%, Zr: 0~0.100%, Hf: 0~0.10%, Cu: 0~1.00%, W: 0~1.00%, Co: 0~1.00%, rare earth elements: 0~0.1000%, Mg: 0~0.0200%, with the balance being Fe and impurities.

[0136] (Feature 2)

[0137] The chemical composition of feature 1 also satisfies equation (1).

[0138] 0.60 <Al+Ti<1.20(1)

[0139] In formula (1), the content of the corresponding element in the chemical composition of the alloy material is substituted into the element symbol in the formula (in terms of mass%).

[0140] (Feature 3)

[0141] The chemical composition of feature 1 also satisfies equation (2).

[0142] 3.3-41C-Si+2Mo+3Ti+245B-12Nb≤2.00(2)

[0143] In formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted into the element symbol in the formula (in terms of mass%).

[0144] (Feature 4)

[0145] The chemical composition of feature 1 also satisfies equation (3) when the B content is less than 0.0010%.

[0146] 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb≤8.25(3)

[0147] In formula (3), the content of the corresponding element in the chemical composition of the alloy material is substituted into the element symbol in the formula (in terms of mass%).

[0148] The alloy material of this embodiment satisfies features 1 to 4 described above. Therefore, the alloy material of this embodiment exhibits high creep strength, excellent resistance to weld hot cracking, and excellent hot workability. Features 1 to 4 will be described below.

[0149] [Regarding (Characteristic 1) Chemical Composition]

[0150] The alloy material of this embodiment has the following chemical composition.

[0151] C: 0.050~0.100%

[0152] Carbon (C) improves the creep strength of alloys at high temperatures. If the C content is less than 0.050%, the above-mentioned effect cannot be fully obtained even if the contents of other elements are within the range of this embodiment.

[0153] On the other hand, if the C content is greater than 0.100%, M will be generated at the grain boundaries. 23 C6 type Cr carbides. In this case, Cr-depleted regions are formed at the grain boundaries. Therefore, even if the contents of other elements are within the range of this embodiment, the stress relaxation crack resistance of the alloy decreases.

[0154] Therefore, the C content is 0.050–0.100%.

[0155] The preferred lower limit for the C content is 0.055%, more preferably 0.060%, more preferably 0.065%, and more preferably 0.070%.

[0156] The preferred upper limit for the C content is 0.097%, more preferably 0.095%, more preferably 0.093%, more preferably 0.090%, more preferably 0.085%, and more preferably 0.080%.

[0157] Si: below 1.00%

[0158] Silicon (Si) deoxidizes alloys during the steelmaking process. Si also improves the oxidation resistance of alloys at high temperatures. Even with only a small amount of Si, the aforementioned effects can be achieved to some extent, even within the range of other element concentrations described in this embodiment.

[0159] However, if the Si content is greater than 1.00%, the resistance to hot cracking and hot workability will decrease even if the contents of other elements are within the range of this embodiment.

[0160] Therefore, the Si content is below 1.00%.

[0161] The preferred lower limit of Si content is greater than 0%, more preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.15%, and more preferably 0.20%.

[0162] 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%.

[0163] Mn: below 1.50%

[0164] Manganese (Mn) deoxidizes the weld area of ​​alloys during welding. Mn also stabilizes austenite. These effects can be achieved to some extent with only a small amount of Mn. However, if the Mn content exceeds 1.50%, the σ phase (sigma phase) is easily formed when used at high temperatures. The σ phase reduces the toughness and creep ductility of the alloy at high temperatures. Therefore, the Mn content should be below 1.50%.

[0165] The preferred lower limit of Mn content is greater than 0%, more preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.40%, more preferably 0.50%, and more preferably 0.60%.

[0166] The preferred upper limit for 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%.

[0167] P: below 0.035%

[0168] Phosphorus (P) is an unavoidable impurity. That is, the P content is greater than 0%. During welding, P segregates at the grain boundaries of the alloy, reducing its resistance to stress relaxation cracking. P segregation at grain boundaries also reduces hot workability.

[0169] Therefore, the P content is below 0.035%.

[0170] The phosphorus (P) content is preferably as low as possible. However, excessively reducing the P content would significantly increase manufacturing costs. Therefore, considering industrial production, the preferred lower limit for the P content is 0.001%, more preferably 0.002%, and even more preferably 0.005%.

[0171] The preferred upper limit for the P content is 0.030%, more preferably 0.025%, more preferably 0.020%, and more preferably 0.015%.

[0172] S: below 0.0015%

[0173] Sulfur (S) is an unavoidable impurity. That is, the S content is greater than 0%. During welding and hot working, S segregates at the grain boundaries of the alloy, which reduces the resistance to weld hot cracking and the hot workability.

[0174] Therefore, the sulfur content is below 0.0015%.

[0175] The sulfur (S) content is preferably as low as possible. However, excessive reduction in S content would significantly increase manufacturing costs. Therefore, considering industrial production, the preferred lower limit for S content is greater than 0%, more preferably 0.0001%, and even more preferably 0.0002%.

[0176] The preferred upper limit for the sulfur content is 0.0012%, more preferably 0.0010%, more preferably 0.0008%, and more preferably 0.0006%.

[0177] Cr: 19.00~23.00%

[0178] Chromium (Cr) improves the corrosion resistance of alloys in high-temperature environments. If the Cr content is less than 19.00%, the above-mentioned effects cannot be fully achieved even if the contents of other elements are within the range of this embodiment.

[0179] On the other hand, if the Cr content is greater than 23.00%, the stability of austenite decreases at high temperatures. In this case, even if the contents of other elements are within the range of this embodiment, the creep strength of the alloy will decrease.

[0180] Therefore, the Cr content is 19.00%–23.00%.

[0181] The preferred lower limit for Cr content is 19.20%, more preferably 19.40%, and even more preferably 19.60%.

[0182] 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%.

[0183] Ni: 30.00~35.00%

[0184] Nickel (Ni) stabilizes austenite and improves the creep strength of alloys at high temperatures. If the Ni content is less than 30.00%, the above-mentioned effects cannot be fully achieved even if the contents of other elements are within the range of this embodiment.

[0185] On the other hand, if the Ni content is greater than 35.00%, the above effects become saturated. Furthermore, the cost of raw materials increases.

[0186] Therefore, the Ni content is 30.00–35.00%.

[0187] The preferred lower limit for Ni content is 30.20%, more preferably 30.40%, more preferably 30.60%, and more preferably 30.80%.

[0188] The preferred upper limit for Ni content is 34.70%, more preferably 34.50%, more preferably 34.00%, more preferably 33.50%, more preferably 33.00%, more preferably 32.50%, more preferably 32.00%, more preferably 31.50%, and more preferably 31.00%.

[0189] N: below 0.010%

[0190] Nitrogen (N) is an impurity. N dissolves in the matrix (parent phase), stabilizing austenite. Solid-dissolved N also forms fine nitrides in the alloy during high-temperature use. These fine nitrides strengthen chromium-depleted regions, thus improving the alloy's resistance to stress relaxation cracking. The fine nitrides formed during high-temperature use also improve creep strength through precipitation strengthening. These effects can be achieved to some extent with only a small amount of N. However, if the N content is greater than 0.010%, excessive and coarse Ti nitrides are formed. In this case, the alloy's resistance to weld hot cracking decreases, and its toughness and hot workability also decrease. Therefore, the N content should be below 0.010%.

[0191] The preferred lower limit for nitrogen content is 0.001%.

[0192] The preferred upper limit for the nitrogen content is 0.007%, more preferably 0.006%, and even more preferably 0.005%.

[0193] Al: 0.15–0.70%

[0194] Aluminum (Al) deoxidizes alloys during the steelmaking process. Al also improves the oxidation resistance of alloys at high temperatures. Al also forms a γ' phase at high temperatures, increasing the creep strength of alloys at high temperatures. If the Al content is less than 0.15%, the above effects cannot be fully achieved even with the contents of other elements within the range specified in this embodiment.

[0195] On the other hand, if the Al content is greater than 0.70%, a large amount of γ' phase will be generated during the manufacturing process of the alloy material. In this case, even if the contents of other elements are within the range of this embodiment, the hot workability of the alloy material will decrease during the manufacturing process.

[0196] Therefore, the Al content is 0.15–0.70%.

[0197] The preferred lower limit for the Al content is 0.17%, more preferably 0.19%, more preferably 0.21%, more preferably 0.23%, and more preferably 0.30%.

[0198] 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%.

[0199] In addition, Al content refers to the content of so-called total Al (mass%).

[0200] Ti: 0.15–0.70%

[0201] Titanium (Ti) combines with Ni and Al at high temperatures to form a γ' phase, which improves the creep strength of the alloy at high temperatures. If the Ti content is less than 0.15%, the above-mentioned effect cannot be fully obtained even if the contents of other elements are within the range of this embodiment.

[0202] On the other hand, if the Ti content is greater than 0.70%, the Ti-based precipitates become coarser or a large amount of γ' phase is generated during the alloy manufacturing process. In this case, even if the contents of other elements are within the range of this embodiment, the resistance to weld hot cracking or the hot workability will decrease.

[0203] Therefore, the Ti content is 0.15–0.70%.

[0204] The preferred lower limit for the Ti content is 0.16%, more preferably 0.17%, more preferably 0.18%, and more preferably 0.20%.

[0205] The preferred upper limit for the Ti content is 0.65%, more preferably 0.60%, more preferably 0.57%, more preferably 0.55%, more preferably 0.50%, and more preferably 0.45%.

[0206] B: 0.0001~0.0030%

[0207] Boron (B) segregates at grain boundaries at a high temperature of approximately 900°C, increasing grain boundary strength. Therefore, the hot workability of the alloy is improved. If the B content is less than 0.0001%, the above-mentioned effects cannot be fully achieved even with the contents of other elements within the range of this embodiment.

[0208] On the other hand, if the boron content is greater than 0.0030%, boron lowers the solidification temperature of the molten grain boundaries during welding heating. In this case, even if the contents of other elements are within the range of this embodiment, the resistance to weld hot cracking will decrease.

[0209] Therefore, the content of B is 0.0001 to 0.0030%.

[0210] The preferred lower limit for the content of B is 0.0003%, more preferably 0.0005%, and even more preferably 0.0010%.

[0211] The preferred upper limit for the B content is 0.0028%, more preferably 0.0025%, more preferably 0.0023%, and more preferably 0.0020%.

[0212] Nb: 0.0010~0.5000%

[0213] When niobium (Nb) is present in Ti-based precipitates, the melting and solidification temperatures of the precipitates are increased. As a result, the resistance of the alloy to weld hot cracking is improved. Nb also forms fine precipitates in the alloy at high temperatures, improving the creep strength of the alloy. If the Nb content is less than 0.0010%, the above-mentioned effects cannot be fully obtained even if the contents of other elements are within the range of this embodiment.

[0214] On the other hand, if the Nb content is greater than 0.5000%, the hot workability of the alloy will decrease even if the contents of other elements are within the range of this embodiment.

[0215] Therefore, the Nb content is 0.0010–0.5000%.

[0216] The preferred lower limit for Nb content is 0.0020%, more preferably 0.0050%, more preferably 0.0080%, and more preferably 0.0100%.

[0217] The preferred upper limit for Nb content is 0.4500%, more preferably 0.4000%, more preferably 0.3000%, more preferably 0.2500%, and more preferably 0.2400%.

[0218] Mo: 0.01~1.00%

[0219] Because it contains molybdenum (Mo) along with boron, it strengthens grain boundaries through co-segregation, thus improving the hot workability of the alloy. Even if the boron content is greater than 0.0010%, the above effect cannot be fully obtained if the molybdenum content is less than 0.01%.

[0220] On the other hand, if the Mo content is greater than 1.00%, intermetallic compounds such as Laves phase are formed within the grains. In this case, the strength difference between the grains and grain boundaries increases. Therefore, hot workability decreases. Furthermore, when the B content is below 0.0010%, not only does the aforementioned effect of Mo decrease, but the hardness within the grains also increases due to the solid solution strengthening of Mo. Therefore, hot workability around 900°C decreases.

[0221] Therefore, the Mo content is 0.01–1.00%.

[0222] The preferred lower limit for the Mo content is 0.02%, more preferably 0.03%, more preferably 0.04%, and more preferably 0.05%.

[0223] The preferred upper limit for the Mo content is 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.60%, and more preferably 0.50%.

[0224] Ca: 0.0001~0.0200%

[0225] Calcium (Ca) fixes sulfur (S) as inclusions, improving the hot workability of the alloy. Ca also fixes sulfur, suppressing its grain boundary segregation. In this case, resistance to weld hot cracking is improved. If the Ca content is less than 0.0001%, the above-mentioned effects cannot be fully obtained even if the contents of other elements are within the range of this embodiment.

[0226] On the other hand, if the Ca content is greater than 0.0200%, the cleanliness of the alloy material decreases. In this case, even if the contents of other elements are within the range of this embodiment, the hot workability of the alloy material also decreases.

[0227] Therefore, the Ca content is 0.0001–0.0200%.

[0228] The preferred lower limit for Ca content is 0.0002%, more preferably 0.0005%, and even more preferably 0.0010%.

[0229] The preferred upper limit for Ca content is 0.0150%, more preferably 0.0100%, more preferably 0.0080%, more preferably 0.0050%, more preferably 0.0040%, and more preferably 0.0030%.

[0230] The balance of the chemical composition of the alloy material in this embodiment is Fe and impurities. Here, impurities in the chemical composition refer to substances that are introduced into the alloy material during industrial manufacturing from raw materials such as ore, waste, or the manufacturing environment, and are permissible within a range that does not adversely affect the alloy material of this embodiment. Representative examples of impurities are Sn, As, Zn, Pb, Sb, Bi, and O (oxygen). The total content of these impurities is 0.10% or less.

[0231] [Optional Elements]

[0232] The chemical composition of the alloy material in this embodiment may also contain selected...

[0233] Ta: 0-0.50%

[0234] V: 0~1.00%

[0235] Zr: 0~0.100%

[0236] Hf: 0~0.10%

[0237] Cu: 0–1.00%

[0238] W: 0~1.00%

[0239] Co: 0-1.00%

[0240] Rare earth elements: 0–0.1000%, and

[0241] Mg: One or more elements from the group consisting of 0 to 0.0200% replace a portion of Fe. These arbitrary elements will be described below.

[0242] [Regarding Group 1: Ta, V, Zr, and Hf]

[0243] The chemical composition of the alloy material in this embodiment may also contain one or more elements selected from the group consisting of Ta, V, Zr, and Hf to replace a portion of the Fe. These elements are arbitrary. These elements all increase the melting temperature of Ti carbides, thereby stabilizing the Ti carbides and improving their resistance to welding hot cracking.

[0244] Ta: 0~0.50%

[0245] Tantalum (Ta) can be any element, or it can be absent. That is to say, the Ta content can also be 0%.

[0246] In the presence of Ta, i.e., when the Ta content is greater than 0%, Ta combines with Ti and C and is contained within Ti-based precipitates. The melting and solidification temperatures of Ta-containing Ti-based precipitates are higher. Therefore, the solidification temperature of the molten grain boundaries during welding is higher. As a result, resistance to weld hot cracking is improved. Even a small amount of Ta can achieve these effects to some extent.

[0247] However, if the Ta content is greater than 0.50%, the resistance to hot cracking in the heat-affected zone of the alloy material decreases during welding. If the Ta content is greater than 0.50%, the hot workability further decreases.

[0248] Therefore, the Ta content is 0–0.50%.

[0249] The preferred lower limit for Ta content is 0.01%, more preferably 0.02%, more preferably 0.05%, and more preferably 0.08%.

[0250] The preferred upper limit for the Ta content is 0.45%, more preferably 0.40%, more preferably 0.35%, and even more preferably 0.30%.

[0251] V: 0~1.00%

[0252] Vanadium (V) can be any element, or it can be absent. That is to say, the V content can also be 0%.

[0253] In the presence of V, i.e., when the V content is greater than 0%, V combines with Ti and C and is contained within the Ti carbides. The melting and solidification temperatures of V-containing Ti-based precipitates are higher. Therefore, the solidification temperature of the molten grain boundaries during welding is higher. As a result, resistance to weld hot cracking is improved. Even a small amount of V can achieve these effects to some extent.

[0254] However, if the V content is greater than 1.00%, the resistance to hot cracking in the heat-affected zone of the alloy material decreases during welding.

[0255] Therefore, the V content is 0–1.00%.

[0256] The preferred lower limit for the V content is 0.01%, more preferably 0.02%, more preferably 0.04%, and more preferably 0.06%.

[0257] The preferred upper limit for the V content is 0.80%, more preferably 0.50%, more preferably 0.40%, more preferably 0.35%, and more preferably 0.30%.

[0258] Zr: 0~0.100%

[0259] Zirconium (Zr) can be any element, or it can be absent. That is to say, the Zr content can also be 0%.

[0260] In the presence of Zr, i.e., when the Zr content is greater than 0%, Zr combines with Ti and C and is contained within the Ti carbides. The melting and solidification temperatures of the Zr-containing Ti-based precipitates are higher. Therefore, the solidification temperature of the molten grain boundaries during welding is higher. As a result, resistance to weld hot cracking is improved. Even a small amount of Zr can achieve these effects to some extent.

[0261] However, if the Zr content is greater than 0.100%, the resistance to hot cracking in the heat-affected zone of the alloy material will actually decrease during welding.

[0262] Therefore, the Zr content is 0–0.100%.

[0263] The preferred lower limit for Zr content is 0.001%, and more preferably 0.002%.

[0264] The preferred upper limit for Zr content is 0.090%, more preferably 0.080%, more preferably 0.050%, more preferably 0.030%, and more preferably 0.010%.

[0265] Hf: 0~0.10%

[0266] Hafnium (Hf) can be any element, or it can be absent. That is, the Hf content can be 0%. When Hf is present, i.e., when the Hf content is greater than 0%, Hf combines with Ti and C and is contained within Ti-based precipitates. The melting and solidification temperatures of Ti-based precipitates containing Hf are higher. Therefore, the solidification temperature of the molten grain boundaries during welding is higher. As a result, resistance to weld hot cracking is improved. Even a small amount of Hf can achieve these effects to some extent.

[0267] However, if the Hf content is greater than 0.10%, the resistance to hot cracking in the heat-affected zone of the alloy material will actually decrease during welding.

[0268] Therefore, the Hf content is 0–0.10%.

[0269] The preferred lower limit for Hf content is 0.01%, and more preferably 0.02%.

[0270] The preferred upper limit for Hf content is 0.09%, more preferably 0.08%, more preferably 0.07%, and more preferably 0.06%.

[0271] [Regarding Group 2: Cu, W, and Co]

[0272] The chemical composition of the alloy material in this embodiment may also contain one or more elements selected from the group consisting of Cu, W, and Co to replace a portion of the Fe. These elements are arbitrary and all improve the creep strength of the alloy material.

[0273] Cu: 0~1.00%

[0274] Copper (Cu) can be any element, or it can be absent. That is to say, the Cu content can also be 0%.

[0275] In alloys containing Cu (i.e., with a Cu content greater than 0%), Cu precipitates as a Cu phase within the grains during use at high temperatures. This precipitation strengthens the alloy, improving its creep strength. Even a small amount of Cu can achieve this effect to some extent.

[0276] However, if the Cu content is greater than 1.00%, an excessive amount of Cu phase precipitates within the grains. In this case, the strength difference between the grains and grain boundaries increases. Therefore, resistance to stress relaxation cracking decreases.

[0277] Therefore, the Cu content is 0–1.00%.

[0278] The preferred lower limit for 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%.

[0279] 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%.

[0280] W: 0~1.00%

[0281] Tungsten (W) can be any element, or it can be absent. That is to say, the W content can also be 0%.

[0282] In alloys containing W (i.e., with a W content greater than 0%), W enhances the creep strength of the alloy through solid solution strengthening in high-temperature environments. Even a small amount of W can achieve this effect to some extent.

[0283] However, if the W content is greater than 1.00%, intermetallic compounds such as Laves phase are formed within the grains. In this case, secondary induced precipitation hardening increases, and the strength difference between the grains and grain boundaries becomes larger. Therefore, resistance to stress relaxation cracking decreases.

[0284] Therefore, the W content is 0–1.00%.

[0285] The preferred lower limit for 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%.

[0286] 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%.

[0287] Co: 0~1.00%

[0288] Cobalt (Co) can be any element, or it can be absent. That is to say, the Co content can also be 0%.

[0289] In the presence of Co, i.e., when the Co content is greater than 0%, Co stabilizes austenite and improves the creep strength of alloys at high temperatures. Even a small amount of Co can achieve this effect to some extent.

[0290] However, if the Co content is greater than 1.00%, the cost of raw materials will increase.

[0291] Therefore, the Co content is 0–1.00%.

[0292] The preferred lower limit for the Co content is 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.05%, and more preferably 0.10%.

[0293] 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%.

[0294] [Regarding Group 3: Rare Earth Elements (REM)]

[0295] The chemical composition of the alloy material in this embodiment may also contain rare earth elements (REM) to replace a portion of the Fe.

[0296] Rare earth elements: 0~0.1000%

[0297] Rare earth elements (REM) can be any element, or they can be absent. In other words, the REM content can also be 0%.

[0298] In the presence of REM (i.e., when the REM content is greater than 0%), REM fixes sulfur (S) as inclusions, improving the hot workability of the alloy. REM also fixes sulfur, suppressing its segregation at grain boundaries. In this case, resistance to weld hot cracking is improved. Even a small amount of REM can achieve these effects to some extent.

[0299] However, if the REM content is greater than 0.1000%, the cleanliness of the alloy decreases. In this case, the hot workability of the alloy also decreases.

[0300] Therefore, the REM content is 0–0.1000%.

[0301] The preferred lower limit for REM content is 0.0001%, more preferably 0.0005%, more preferably 0.0010%, and more preferably 0.0020%.

[0302] The preferred upper limit for REM content is 0.0800%, more preferably 0.0600%, and even more preferably 0.0400%.

[0303] The REM content in this specification contains at least one of the following elements: Sc, Y, and lanthanides (La, atom number 57, to Lu, atom number 71). The REM content refers to the total content of these elements.

[0304] [Regarding Group 4: Mg]

[0305] The chemical composition of the alloy material in this embodiment may also contain Mg to replace a portion of Fe.

[0306] Mg: 0% or more and less than 0.0200%

[0307] Magnesium (Mg) is an impurity and may be absent. In other words, the Mg content can be 0%.

[0308] If the Mg content is greater than 0.0200%, Mg will segregate at the grain boundaries at a high temperature of approximately 900°C, causing grain boundary embrittlement. In this case, the hot workability of the alloy decreases.

[0309] Therefore, the Mg content is 0–0.0200%.

[0310] The Mg content is preferably as low as possible. However, excessive reduction in Mg content would significantly increase manufacturing costs. Therefore, considering typical industrial production conditions, the preferred lower limit for Mg content is greater than 0%, more preferably 0.0001%, and even more preferably 0.0002%.

[0311] The preferred lower limit for Mg content is 0.0150%, more preferably 0.0100%, more preferably 0.0080%, more preferably 0.0050%, and more preferably 0.0040%.

[0312] [Regarding (Feature 2) Equation (1)]

[0313] The chemical composition of the alloy material in this embodiment also satisfies formula (1).

[0314] 0.60 <Al+Ti<1.20(1)

[0315] In Equation (1), the content of the corresponding element in the chemical composition of the alloy material is substituted into the element symbol in terms of mass%.

[0316] F1 is defined as Al + Ti. F1 is an indicator of the amount of γ' phase generated during use of the alloy material of this embodiment at high temperatures. In the alloy material of this embodiment, the γ' phase is generated during use at high temperatures. Based on this γ' phase, the creep strength of the alloy material at high temperatures is improved.

[0317] Even if the alloy material satisfies characteristics 1, 3, and 4, if F1 is below 0.60, a sufficient amount of γ' phase will not be generated in the alloy material under high-temperature conditions. In this case, the creep strength of the alloy material decreases under high-temperature conditions.

[0318] On the other hand, even if the alloy material meets characteristics 1, 3, and 4, if F1 is 1.20 or higher, excessive γ' phase will be generated in the alloy material. In this case, the resistance to weld hot cracking decreases.

[0319] Therefore, F1 is greater than 0.60 and less than 1.20.

[0320] The preferred lower limit for F1 is 0.61, more preferably 0.62, more preferably 0.64, more preferably 0.66, more preferably 0.68, and more preferably 0.70.

[0321] The preferred upper limit for F1 is 1.15, more preferably 1.10, more preferably 1.05, more preferably 1.00, and more preferably 0.95.

[0322] The value of F1 is set to the value obtained by rounding the third decimal place to the second decimal place.

[0323] [Regarding (Feature 3) Equation (2)]

[0324] The chemical composition of the alloy material in this embodiment also satisfies formula (2).

[0325] 3.3-41C-Si+2Mo+3Ti+245B-12Nb≤2.00(2)

[0326] In formula (2), the content of the corresponding element in the chemical composition of the alloy is substituted into the element symbol in terms of mass%.

[0327] F2 is defined as 3.3-41C-Si+2Mo+3Ti+245B-12Nb. F2 is an indicator of resistance to weld hot cracking. To improve the hot workability during hot working at approximately 900°C, the alloy material of this embodiment contains B. However, in an alloy material having a chemical composition that satisfies characteristic 1, the solidification temperature of the grain boundaries decreases due to the segregation of B towards the grain boundaries. Therefore, the resistance to weld hot cracking tends to decrease. Therefore, in the alloy material of this embodiment, as described above, (A) the melting temperature and solidification temperature of the Ti-based precipitates that precipitate at the grain boundaries are increased, and (B) the solidification temperature of the grain boundaries that melt due to the liquefaction of the composition during the heating process during welding is increased. As a result, the resistance to weld hot cracking is improved.

[0328] Specifically, in the chemical composition satisfying characteristic 1, C, Si, and Nb increase the solidification temperature of the Ti-based precipitates after molten formation. On the other hand, Mo, Ti, and B promote the liquefaction of the composition, lowering the solidification temperature of the grain boundaries after molten formation. Therefore, by appropriately controlling the C, Si, Nb, Mo, Ti, and B contents, both (A) and (B) above can be achieved simultaneously, increasing the solidification temperature of the grain boundaries after molten formation during welding, thereby improving resistance to weld hot cracking. Even when the alloy material satisfies characteristics 1, 2, and 4, if F2 is greater than 2.00, the above effect cannot be sufficiently obtained. Therefore, F2 is 2.00 or less.

[0329] The preferred upper limit for F2 is 1.97, further preferably 1.95, further preferably 1.93, and further preferably 1.90.

[0330] The lower limit of F2 is not particularly limited, but is preferably -7.00, more preferably -6.00, more preferably -5.00, and even more preferably -4.00.

[0331] The value of F2 is set to the value obtained by rounding the third decimal place to the second decimal place.

[0332] [Regarding (Feature 4) Equation (3)]

[0333] When the B content in the chemical composition that satisfies feature 1 is 0.0010% or less, the chemical composition of the alloy material of this embodiment also satisfies formula (3).

[0334] 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb≤8.25(3)

[0335] In formula (3), the content of the corresponding element in the chemical composition of the alloy is substituted into the element symbol in terms of mass%.

[0336] F3 is defined as 0.4 + 67C + 1.3Si + 5.5Mo + 5.2Ti + 13.4Nb. F3 is an indicator of hot workability under hot working conditions at approximately 900°C.

[0337] As described above, B segregates at the grain boundaries of the alloy, causing a decrease in the solidification temperature of the grain boundaries. Therefore, in alloys that satisfy feature 1 and contain B, the resistance to weld hot cracking tends to decrease. Therefore, in this embodiment, by having the chemical composition of the alloy satisfy formula (2), the solidification temperature of the grain boundaries after melting during welding is increased, thereby improving the resistance to weld hot cracking.

[0338] However, in cases involving welding extremely thick-walled materials or high-heat welding, alloys with high resistance to weld hot cracking are used. In such cases, the boron content in the alloy is sometimes adjusted to below 0.0010%.

[0339] When the boron content is set to 0.0010% or less, the resistance to weld hot cracking is improved by reducing the boron content. However, the hot workability tends to decrease due to the reduction in boron content. Therefore, when the boron content in the chemical composition is set to 0.0010% or less, the hot workability of the alloy material in this embodiment is improved by suppressing the hardening of the alloy material caused by Ti-based precipitates.

[0340] C, Si, Mo, Ti, and Nb promote the formation of Ti-based precipitates. Therefore, by appropriately adjusting the value of F3, which consists of the contents of C, Si, Mo, Ti, and Nb, while keeping the B content in the chemical composition below 0.0010%, the formation of Ti-based precipitates can be suppressed. As a result, the hot workability at around 900°C is improved.

[0341] Even if the alloy material satisfies characteristics 1 to 3, if F3 is greater than 8.25, the above-mentioned effect cannot be fully obtained. Therefore, F3 should be 8.25 or less.

[0342] The preferred upper limit for F3 is 8.20, further preferably 8.15, further preferably 8.13, and further preferably 8.10.

[0343] The lower limit of F3 is not particularly limited, but is preferably 4.60, more preferably 4.80, more preferably 5.00, and more preferably 5.50.

[0344] The value of F3 is set to the value obtained by rounding the third decimal place to the second decimal place.

[0345] [Effects of Alloy Materials]

[0346] The alloy material of this embodiment satisfies features 1 to 4 above. As a result, the alloy material of this embodiment has sufficient creep strength in high-temperature environments, and can achieve both excellent resistance to weld hot cracking and excellent hot workability.

[0347] [Microstructure and morphology of alloy materials]

[0348] The microstructure of the alloy material in this embodiment is composed of austenite. Furthermore, the shape of the alloy material in this embodiment is not particularly limited. The alloy material can be an alloy tube or an alloy plate. The alloy material can also be rod-shaped. Preferably, the alloy material in this embodiment is an alloy tube or an alloy plate.

[0349] [Preferred embodiment of the alloy material when the B content is greater than 0.0010%]

[0350] In the chemical composition that satisfies features 1 to 3, if the B content is greater than 0.0010% and less than 0.0030%, it is preferable that the alloy material of this embodiment also satisfies the following feature 5.

[0351] (Feature 5)

[0352] The Ti content [Ti] in the residue obtained by the extraction residue method is less than 0.020% by mass, or [Ti] is more than 0.020%, and the Nb content [Nb] in the residue is more than 0.015% by mass, and [Ti] and [Nb] satisfy equation (4).

[0353] [Ti]+[Nb]≥0.050(4)

[0354] Feature 5 will be explained below.

[0355] [(Feature 5) Relationship between Ti content [Ti] and Nb content [Nb] in the residue (Part 1)]

[0356] In the alloy material of this embodiment, when the B content in the chemical composition is greater than 0.0010% and less than 0.0030%, by satisfying characteristics 1 to 3, it has sufficient creep strength in high-temperature environments, and can take into account both excellent resistance to welding hot cracking and excellent hot workability.

[0357] However, in the alloy material of this embodiment, there is a certain amount of Ti-based precipitates before welding. Therefore, during the heating process when welding the alloy material, the Ti-based precipitates trapped at the grain boundaries eutectic melt. Since the alloy material of this embodiment contains boron, boron segregates at the grain boundaries. Therefore, the solidification temperature of the molten grain boundaries decreases due to boron. As a result, the resistance to welding hot cracking decreases.

[0358] Therefore, in the alloy material of this embodiment, when the B content is greater than 0.0010% and less than 0.0030%, it is preferable to adopt either of the following two countermeasures I and countermeasure II.

[0359] (Countermeasure I)

[0360] Minimize the amount of Ti-based precipitates pre-existing in the alloy. This suppresses low-temperature eutectic melting at grain boundaries and increases the solidification temperature of the grain boundaries.

[0361] (Countermeasure II)

[0362] The Ti-based precipitates are made to contain Nb, stabilizing them up to high temperatures. Under these conditions, the eutectic melting temperature of the grain boundaries containing the Ti-based precipitates is increased, as is the solidification temperature of the grain boundaries.

[0363] Therefore, in the case where the B content is greater than 0.0010% and less than 0.0030%, the alloy material of this embodiment preferably satisfies either condition I or condition II below.

[0364] (Condition I)

[0365] The Ti content [Ti] in the residue is less than 0.020%.

[0366] (Condition II)

[0367] The residue obtained by the residue extraction method contains more than 0.020% [Ti] and more than 0.015% [Nb] in the residue, and [Ti] and [Nb] satisfy equation (4).

[0368] [Ti]+[Nb]≥0.050(4)

[0369] [Regarding Condition I]

[0370] When the B content is greater than 0.0010% and less than 0.0030%, if the amount of Ti-based precipitates generated is small, it is difficult to generate welding hot cracks caused by the eutectic melting of Ti-based precipitates and grain boundaries.

[0371] In condition I, the Ti content [Ti] in the residue is less than 0.020%. At this point, the formation of Ti-based precipitates in the alloy is sufficiently suppressed. Therefore, superior resistance to weld hot cracking can be obtained.

[0372] Under condition I, the preferred upper limit for the Ti content [Ti] in the residue is 0.019%, and more preferably 0.017%.

[0373] [Regarding Condition II]

[0374] When the boron content is greater than 0.0010% and less than 0.0030%, if Ti-based precipitates are formed in a certain amount, it is preferable to increase the solidification temperature of the eutectic melt of the Ti-based precipitates and grain boundaries. If the Ti-based precipitates in the alloy contain Nb, the Ti-based precipitates are stabilized at high temperatures. Therefore, it is possible to increase the solidification temperature of the grain boundaries after the eutectic melt of the Ti-based precipitates and grain boundaries.

[0375] In condition II, the [Ti] content in the residue is 0.020% or more, and the Nb content [Nb] in the residue is 0.015% or more, and [Ti] and [Nb] satisfy equation (4).

[0376] [Ti]+[Nb]≥0.050(4)

[0377] In this case, the proportion of Nb-containing Ti-based precipitates in the alloy is relatively high. Therefore, the solidification temperature of the grain boundaries after the eutectic melting of the Ti-based precipitates and grain boundaries is sufficiently high. As a result, superior resistance to weld hot cracking can be obtained.

[0378] The preferred lower limit for [Ti]+[Nb] in the residue under condition II is 0.052%, more preferably 0.060%, more preferably 0.070%, more preferably 0.080%, and more preferably 0.090%.

[0379] [Preferred embodiment of the alloy material when the B content is 0.0010% or less]

[0380] In the chemical composition that satisfies features 1 to 4, and with a B content of 0.0001 to 0.0010%, the alloy material of this embodiment also satisfies the following feature 6.

[0381] (Feature 6)

[0382] The residue obtained by the extraction method has a Ti content [Ti] of less than 0.031% by mass, or a [Ti] greater than 0.031%, and the Nb content [Nb] of the residue is more than 0.3 × [Ti]% by mass.

[0383] Feature 6 will be explained below.

[0384] [(Feature 6) The Relationship Between [Ti] and [Nb] in the Residue (Part Two)]

[0385] When the B content is 0.0001 to 0.0010%, it is preferable to satisfy either condition III or condition IV below.

[0386] (Condition III)

[0387] The Ti content [Ti] in the residue is less than 0.031%.

[0388] (Condition IV)

[0389] The [Ti] content in the residue is greater than 0.031%, and the Nb content [Nb] in the residue is greater than 0.3 × [Ti]%.

[0390] [Regarding Condition III]

[0391] When the B content is below 0.0010%, the decrease in weld hot crack resistance caused by B content can be suppressed compared with condition (I). Therefore, if the [Ti] content in the residue is below 0.031%, the formation of Ti precipitates in the alloy is sufficiently suppressed, and better weld hot crack resistance can be obtained.

[0392] [Regarding condition (IV)]

[0393] Even when the boron content is below 0.0010%, the formation of Ti-based precipitates in a certain amount improves the high-temperature stability of the Ti-based precipitates and increases the solidification temperature of the grain boundaries after the eutectic melting of the Ti-based precipitates and grain boundaries. Specifically, in alloy materials, the proportion of Ti-based precipitates containing Nb is increased.

[0394] If the [Ti] content in the residue is greater than 0.031%, and the Nb content [Nb] in the residue is 0.3 × [Ti]%, then the proportion of Ti-based precipitates containing Nb is sufficiently high. As a result, superior resistance to weld hot cracking can be obtained.

[0395] [Methods for determining Ti and Nb content in residues]

[0396] The [Ti] and [Nb] in the residue of the alloy material are determined by the following residue extraction method.

[0397] Test specimens are collected from the alloy material. The cross-section of the test specimen perpendicular to its length can be either circular or rectangular.

[0398] When the alloy material is an alloy tube, the test piece is collected by taking the center of the cross section perpendicular to the length direction of the test piece as the center position of the wall thickness of the alloy tube, and taking the length direction of the test piece as the tube axis direction of the alloy tube.

[0399] When the alloy material is an alloy plate, the test piece is collected in such a way that the center of the cross section of the test piece perpendicular to the length direction is the center position of the width and the center position of the thickness of the alloy plate, and the length direction of the test piece is the length direction of the alloy plate.

[0400] When the alloy material is a round bar, the test piece is collected with the center of the cross section perpendicular to the length direction of the test piece as the R / 2 position of the round bar (the center of the radius in the cross section perpendicular to the length direction of the round bar) and the length direction of the test piece as the length direction of the round bar.

[0401] The surface of the collected test pieces was ground to approximately 50 μm using pre-electrolytic grinding to obtain a new surface. The pre-ground test pieces were then electrolyzed using an electrolyte solution (10% acetylacetone + 1% tetraammonium + methanol) (formal electrolysis). The electrolyte solution after formal electrolysis was then passed through a 0.2 μm filter to capture residues. The obtained residues were then acid-decomposed, and the mass of Ti and Nb in the residues was determined using ICP (inductively coupled plasma) luminescence analysis.

[0402] Furthermore, the mass of the alloy material after formal electrolysis is determined. Specifically, the mass of the test piece before formal electrolysis and the mass of the test piece after formal electrolysis are measured. Then, the value obtained by subtracting the mass of the test piece after formal electrolysis from the mass of the test piece before formal electrolysis is defined as the mass of the alloy material after formal electrolysis.

[0403] The Ti content [Ti] (mass%) in the residue is calculated by dividing the mass of Ti in the residue by the mass of the alloy material after formal electrolysis. Similarly, the Nb content [Nb] (mass%) in the residue is calculated by dividing the mass of Nb in the residue by the mass of the alloy material after formal electrolysis.

[0404] [Manufacturing methods for alloy materials]

[0405] This section describes a method for manufacturing the alloy material according to this embodiment. The manufacturing method described below is one example of the method for manufacturing the alloy material according to this embodiment. Therefore, the alloy material of this embodiment can also be manufactured by other manufacturing methods besides the method described below. However, the manufacturing method described below is a preferred example of the method for manufacturing the alloy material according to this embodiment.

[0406] The method for manufacturing the alloy material according to this embodiment includes the following steps.

[0407] (Process 1) Preparation Process

[0408] (Process 2) Hot working process

[0409] (Process 3) Cold working process

[0410] (Process 4) Heat treatment process

[0411] Step 3 (cold processing step) mentioned above is an optional step and may be omitted. The following is a description of each step.

[0412] [(Process 1) Preparation Process]

[0413] In the preparation process, a billet having a chemical composition satisfying characteristics 1 to 4 above is prepared. The billet may be supplied by a third party or manufactured. The billet may be a steel ingot, a slab, a large steel billet, or a steel billet.

[0414] In the case of manufacturing billets, the billets are manufactured by the following methods: A molten alloy having the aforementioned chemical composition is manufactured. The manufactured molten alloy is used to manufacture steel ingots by casting. Alternatively, the manufactured molten alloy can be used to manufacture slabs, large steel billets, or steel billets by continuous casting. Steel billets can also be manufactured by hot working the manufactured steel ingots, slabs, or large steel billets. For example, steel ingots can be hot-forged to manufacture cylindrical steel billets, which are then used as billets. In this case, the temperature of the billet before hot forging is not particularly limited, for example, 1100–1300°C. The cooling method for the hot-forged billet is not particularly limited.

[0415] [(Process 2) Hot working process]

[0416] In the hot working process, the blank prepared in the preparation process is hot-worked to produce an intermediate alloy material. The intermediate alloy material can be, for example, an alloy tube, an alloy plate, or an alloy round bar.

[0417] When the intermediate alloy material is an alloy tube, the following processing is performed in the hot working process. First, a cylindrical blank is prepared. A through hole is formed along the central axis of the cylindrical blank by machining. The cylindrical blank with the through hole is heated. The heated cylindrical blank is then subjected to hot extrusion, such as high-speed extrusion with glass lubricant, to manufacture the intermediate alloy material (alloy tube).

[0418] Alternatively, alloy tubes can be manufactured by piercing rolling using the Mannesmann process, instead of hot extrusion. In this case, the cylindrical billet is heated. The heating temperature is not particularly limited, for example, 1100–1300°C. The heated cylindrical billet is then subjected to piercing rolling using a piercing mill. In the case of piercing rolling, the piercing ratio is not particularly limited, for example, 1.0–4.0. The pierced cylindrical billet is further hot-rolled using a continuous rolling mill, reducing mill, sizing mill, etc., to produce a hollow tube blank (alloy tube). The cumulative reduction of area during the hot working process is not particularly limited, for example, 20–80%. When manufacturing alloy tubes by hot working, the temperature of the hollow tube blank immediately after hot working (finishing temperature) is preferably 800°C or higher. Furthermore, the hot working process includes hot working at around 900°C.

[0419] When the intermediate alloy material is an alloy sheet, the hot working process uses one or more rolling mills equipped with a pair of work rolls. The billet, such as a slab, is heated. The heated billet is then hot-rolled using the rolling mill to produce the alloy sheet. The heating temperature of the billet before hot rolling is not particularly limited, but is, for example, 1100–1300°C. Furthermore, the hot working process includes hot working at approximately 900°C.

[0420] When the intermediate alloy material is a round bar, the hot working process uses one or more rolling mills equipped with a pair of work rolls. A pass is formed on the pair of work rolls. A billet such as a large steel billet is heated. The heated billet is then hot-rolled using a rolling mill to produce a round bar. The heating temperature of the billet before hot rolling is not particularly limited, but is, for example, 1100–1300°C. Furthermore, the hot working process includes hot working at approximately 900°C.

[0421] [(Process 3) Cold working process]

[0422] Cold working is performed as needed. That is, it may be optional to omit cold working. When it is performed, cold working is carried out after pickling the intermediate alloy material. If the intermediate alloy material is an alloy tube or rod, cold working is, for example, cold drawing. If the intermediate alloy material is an alloy sheet, cold working is, for example, cold rolling. By performing the cold working process, recrystallization and granulation can be achieved. The reduction of area for the cold working process is not particularly limited, but is, for example, 10% to 90%.

[0423] [(Process 4) Heat treatment process]

[0424] In the heat treatment process, intermediate alloy materials are subjected to heat treatment after hot working or cold working to adjust the amount of dissolved Ti and the grain size in the alloy. The heat treatment temperature T1 is 1170–1300℃. There is no particular limitation on the holding time at the heat treatment temperature T1, for example, 5–30 minutes. After the holding time, the intermediate alloy material is rapidly cooled.

[0425] Through the above processes, the alloy material of this embodiment can be manufactured. The above-described manufacturing method is an example of the manufacturing method of the alloy material of this embodiment. Therefore, the manufacturing method of the alloy material of this embodiment is not limited to the above-described manufacturing method. If features 1 to 4 are satisfied, the manufacturing method of the alloy material is not limited to the above-described manufacturing method.

[0426] [Preferred conditions in the heat treatment process]

[0427] Preferably, the heat treatment temperature T1 in the heat treatment process satisfies the following formula (X).

[0428] T1≤1600+33011×(Nb) 2 -6995×(Nb)(X)

[0429] In formula (X), the Nb content in the chemical composition of the alloy is substituted into (Nb) by mass%.

[0430] FA is defined as follows.

[0431] FA = 1600 + 33011 × (Nb) 2 -6995×(Nb)

[0432] FA is an indicator that affects the composition of precipitates in alloy materials; more specifically, it is an indicator that affects the Ti content [Ti] and Nb content [Nb] in the residue.

[0433] If the heat treatment temperature T1 is below FA, then when the B content in the alloy is greater than 0.0010 and less than 0.0030%, characteristic 5 (condition (I) or condition (II)) is easily satisfied. In addition, when the B content in the alloy is between 0.0001 and 0.0010%, characteristic 6 (condition (III) or condition (IV)) is easily satisfied.

[0434] [Manufacturing method for welded joints of alloy materials]

[0435] The welded joint of the alloy material in this embodiment can be manufactured by the following method.

[0436] As the base material, an alloy material for this embodiment is prepared. A bevel is formed on the prepared base material. Specifically, a bevel is formed at the end of the base material using a well-known processing method. The bevel shape can be a letter V, a letter U, a letter X, or any other shape besides a letter V, a letter U, or a letter X.

[0437] A welded joint is created by welding prepared base materials. Specifically, two base materials with bevels are prepared. The bevels of the prepared base materials are then joined together. The joined bevels are then welded using a well-known welding material to form a weld metal with the aforementioned chemical composition. For example, the welding material is the AWS standard name: ER NiCr-3. However, the welding material is not limited to this.

[0438] The welding method can form a single layer of weld metal or multiple layers of weld overlay. Examples of welding methods include TIG welding (GTAW), SMAW (Smooth Surface Arc Welding), FCAW (Fluid Cored Wire Arc Welding), GMAW (Gas Shielded Metal Arc Welding), and SAW (Submerged Arc Welding). Through the above manufacturing processes, a welded joint of the alloy material of this embodiment can be manufactured.

[0439] [Example]

[0440] The effects of the alloy material of this embodiment will be explained in more detail with reference to the embodiments. The conditions in the following embodiments are examples 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 these examples of conditions.

[0441] [Manufacturing of Alloy Materials]

[0442] Manufacture steel ingots having the chemical compositions shown in Tables 1A and 1B. The steel ingots are cylindrical in shape with an outer diameter of 120 mm and have a mass of 30 kg.

[0443] [Table 1A]

[0444] Table 1A

[0445]

[0446] [Table 1B]

[0447] Table 1B

[0448]

[0449] In Table 1B, "-" indicates that the content of the corresponding element is below the impurity level.

[0450] Gleeble test pieces (described later) are collected from the manufactured steel ingots. The steel ingots with collected Gleeble test pieces are then hot-forged to produce billets (alloy plates) with a thickness of 30 mm. The heating temperature of the steel ingots during hot forging is 1100–1300 °C. The produced billets undergo a hot working process. Specifically, the billets are heated in a furnace. The heating temperature during the hot working process is 1200 °C. The heated billets are then hot-rolled to produce intermediate alloy materials (alloy plates) with a thickness of 15 mm.

[0451] The intermediate alloy material undergoes a heat treatment process. The heat treatment temperature T1 (°C) is shown in the "T1 (°C)" column of Table 2. The holding time at the heat treatment temperature is 30 minutes. After the holding time, the intermediate alloy material is water-cooled to room temperature. Through the above processes, alloy materials (alloy plates) for each test number are manufactured.

[0452] [Table 2]

[0453] Table 2

[0454]

[0455] Furthermore, in the "B Content Type" column of Table 2, "H" indicates that the B content of the alloy is greater than 0.0010% and less than 0.0030%. "L" indicates that the B content of the alloy is between 0.0001% and 0.0010%. The F1, F2, and F3 values ​​for each test number are shown in the "F1," "F2," and "F3" columns. The FA value for each test number is shown in the "FA" column. In the "T1≤FA" column, "T (Yes)" is shown if T1 satisfies formula (X), and "F (No)" is shown if T1 does not satisfy formula (X).

[0456] [Evaluation Test]

[0457] The following evaluation tests were conducted using the manufactured alloy material.

[0458] (Experiment 1) Determination of Ti content [Ti] and Nb content [Nb] in the residue of alloy materials

[0459] (Experiment 2) Gleeble Test (Evaluation of Hot Workability)

[0460] (Experiment 3) Evaluation Test of Resistance to Welding Hot Crack

[0461] (Experiment 4) Creep Strength Evaluation Test

[0462] The following is a description of each experiment.

[0463] [(Experiment 1) Determination of Ti and Nb content in alloy residue]

[0464] Based on the method described above for determining the Ti content [Ti] and Nb content [Nb] in the residue, the Ti content [Ti] (mass%) and Nb content [Nb] (mass%) in the residue were determined. Furthermore, test pieces were collected with the center of the cross-section perpendicular to the length direction of the test piece coinciding with the center of the width and thickness of the alloy material (alloy plate), and the length direction of the test piece coinciding with the length direction of the alloy material (alloy plate). The dimensions of the test piece were set to 10 mm × 30 mm × plate thickness (15 mm). The obtained Ti content [Ti] (mass%) and Nb content [Nb] (mass%) are shown in the "[Ti] (mass%)" and "[Nb] (mass%)" columns in Table 3. Additionally, the 0.3 × [Ti] value and the [Ti] + [Nb] value are shown in the "0.3 × [Ti]" and "[Ti] + [Nb]" columns in Table 3.

[0465] [Table 3]

[0466] Table 3

[0467]

[0468] Furthermore, in the "B Content Type" column of Table 3, "H" indicates that the B content of the alloy material is greater than 0.0010% and less than 0.0030%. "L" indicates that the B content of the alloy material is between 0.0001% and 0.0010%. In the "Condition I" column, "T (Yes)" is displayed when the B content of the alloy material is greater than 0.0010% and less than 0.0030% and Condition I is met. In the "Condition II" column, "T (Yes)" is displayed when the B content of the alloy material is greater than 0.0010% and less than 0.0030% and Condition II is met. In the "Condition III" column, "T (Yes)" is displayed when the B content of the alloy material is between 0.0001% and 0.0010% and Condition III is met. In the "Condition IV" column, "T (Yes)" is displayed when the B content of the alloy material is between 0.0001% and 0.0010% and Condition IV is met.

[0469] [(Experiment 2) Gleeble Test (Evaluation of Hot Workability)]

[0470] To evaluate the hot workability of the alloys for each test number, the necking rate at 900°C was determined using a Gleeble tester.

[0471] Gleeble test pieces were collected from the R / 2 position of each test ingot (a cylinder with an outer diameter of 120 mm). Here, R / 2 position refers to the center of the radius in the cross-section perpendicular to the axial direction of the ingot. The Gleeble test piece was a cylindrical piece with a radius of 10 mm and a length of 120 mm. The central axis of the Gleeble test piece was parallel to the axial direction of the ingot. Using the Gleeble testing apparatus, the Gleeble test piece was heated from room temperature to 1200 °C over 60 seconds and held at 1200 °C for 300 seconds. Afterward, it was cooled to 900 °C using He gas at a cooling rate of 100 °C / min and held at 900 °C for 10 seconds. After the holding time, a tensile test was performed on the Gleeble test piece at a displacement rate of 10 mm / s until the Gleeble test piece fractured. The dimensions of the cross-section of the fractured Gleeble test piece were measured, and the necking value (%) was determined.

[0472] When the necking value is 60% or more, the hot workability is rated as excellent (indicated by "E (Excellent)" in the "Gleeble Test" column of Table 3). On the other hand, when the necking value is less than 60%, the hot workability is rated as poor (indicated by "B (Poor)" in the "Gleeble Test" column of Table 3).

[0473] [(Experiment 3) Evaluation Test for Resistance to Welding Hot Crack]

[0474] Two test pieces were collected, each with a thickness of 12 mm, a width of 40 mm, and a length of 300 mm, centered at the center of the width and thickness of the alloy material (alloy plate) for each test number. The longitudinal strain tests shown below were then performed on the two collected test pieces.

[0475] Specifically, TIG co-welding (surfacing welding) was carried out along the longitudinal direction of the central portion of the width of each test piece under welding conditions of 200A welding current, 12V voltage, and 15cm / min speed. Midway through the TIG welding, bending stress was instantaneously applied parallel to the welding direction to apply a 2% strain to the surface layer.

[0476] The portion containing the weld cracks caused by the applied bending stress was cut to a size that could be observed under an optical microscope. The cut sample dimensions were 12 mm thick, 30 mm wide, and 30 mm long.

[0477] The oxide scale on the weld surface of the cut samples was removed by polishing and grinding. Then, the presence and length of cracks at the HAZ (weld area zone) were determined using a 100x optical microscope. Specifically, the length of cracks propagating in the direction perpendicular to the welding direction was measured, starting from the boundary between the weld metal and the HAZ. The lengths of all cracks produced on the test piece in the direction perpendicular to the welding direction were calculated. The sum of these crack lengths was defined as the total crack length (mm). The total crack length was calculated for both test pieces. The arithmetic mean of the calculated total crack lengths was defined as the average total crack length.

[0478] The average total crack length is evaluated as follows.

[0479] Evaluation E: The average total crack length is less than 1.5 mm.

[0480] Evaluation G (Good): The average total crack length is greater than 1.5 mm and less than 2.0 mm.

[0481] Evaluation B: The average total crack length is greater than 2.0 mm.

[0482] When evaluated as G or E, the weld hot cracking resistance is rated as excellent (indicated by "G" or "E" in the "Weld Hot Cracking Resistance" column of Table 3). On the other hand, when evaluated as B, the weld hot cracking resistance is rated as insufficient (indicated by "B" in the "Weld Hot Cracking Resistance" column of Table 3).

[0483] [(Experiment 4) Creep Strength Evaluation Test]

[0484] The following creep evaluation tests were conducted on the alloy materials (alloy plates) for each test number.

[0485] Creep fracture test specimens, collected according to JIS Z 2271:2019, were taken from the center of the width and center of the thickness of the alloy material (alloy plate) for each test number. The cross-section of the parallel portion of the creep fracture test specimen, perpendicular to the axial direction, is circular. The outer diameter of the parallel portion is 6 mm, and the length is 30 mm. The length direction of the creep fracture test specimen is parallel to the rolling direction of the alloy plate.

[0486] Creep fracture tests were conducted using collected creep fracture test specimens according to JIS Z2271:2019. Specifically, the creep fracture test specimens were heated to 700°C. Then, the creep fracture test was performed. The test stress was set to 80 MPa. During the test, the creep fracture time (in hours) was determined.

[0487] When the creep rupture time is 2000 hours or more, the creep strength is rated as excellent (indicated by "E" in the "Creep Strength" column of Table 3). On the other hand, when the creep rupture time is less than 2000 hours, the creep strength is rated as low (indicated by "B" in the "Creep Strength" column of Table 3).

[0488] [Experimental Results]

[0489] Referring to Tables 1A, 1B, 2, and 3, in tests 1-30, when the B content is greater than 0.0010% and less than 0.0030%, the alloy material satisfies characteristics 1-3; when the B content is between 0.0001% and 0.0010%, the alloy material satisfies characteristics 1-4. Therefore, sufficient creep strength is obtained under high-temperature conditions. Furthermore, excellent resistance to weld hot cracking and excellent hot workability are also achieved.

[0490] Tests 1-13 with a B content greater than 0.0010% and less than 0.0030%, as well as tests 2 and 3, also satisfy condition I of characteristic 5, while tests 4-13 satisfy condition II of characteristic 5. Therefore, compared with test 1, which does not satisfy characteristic 5, the resistance to weld hot cracking is superior.

[0491] Tests 14-30 with a B content of 0.0001-0.0010% and tests 15-29 satisfy condition III of feature 6, while test 30 satisfies condition IV of feature 6. Therefore, compared with test 14, which does not satisfy feature 6, the resistance to weld hot cracking is superior.

[0492] On the other hand, in tests 31-34, although the content of each element in the chemical composition was appropriate, F1 was too low. Therefore, sufficient creep strength could not be obtained.

[0493] In tests 35-38, the content of each element in the chemical composition was appropriate, but F1 was too high. Therefore, sufficient resistance to weld hot cracking could not be obtained.

[0494] In tests 39–43, although the content of each element in the chemical composition was appropriate, the F2 content was too high. Therefore, sufficient resistance to weld hot cracking could not be obtained.

[0495] In tests 44 and 45, the chemical composition contained appropriate amounts of each element, but the B content was below 0.0010% and the F3 content was too high. Therefore, sufficient hot workability could not be obtained.

[0496] The embodiments of the present invention have been described above. However, the above embodiments are merely illustrative examples for implementing the present invention. Therefore, the present invention is not limited to the above embodiments, and can be implemented by appropriate modifications without departing from its spirit.

Claims

1. An alloy material, the chemical composition of which, by mass%, is C: 0.050–0.100%. Si: below 1.00% Mn: below 1.50% P: below 0.035% S: less than 0.0015% Cr：19.00～23.00％、 Ni: 30.00~35.00% N: less than 0.010% Al：0.15～0.70％、 Ti: 0.15–0.70% B：0.0001～0.0030％、 Nb: 0.0010~0.5000% Mo: 0.01~1.00% Ca: 0.0001~0.0200% Ta: 0-0.50% V：0～1.00％、 Zr：0～0.100％、 Hf: 0~0.10% Cu: 0–1.00% W：0～1.00％、 Co: 0-1.00% Rare earth elements: 0~0.1000% Mg: 0–0.0200%, and The balance consists of Fe and impurities. The alloy material satisfies equations (1) and (2). When the B content in the chemical composition is less than 0.0010%, the alloy material also satisfies formula (3). 0.60 <Al+Ti<1.20(1), 3.3-41C-Si+2Mo+3Ti+245B-12Nb≤2.00 (2), 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb≤8.25 (3), in, Substitute the content of the corresponding element in the chemical composition into the element symbols in equations (1) to (3) in terms of mass % 2. The alloy material according to claim 1, wherein, The chemical composition contains, by mass%, selected from [amount]. Ta: 0.01~0.50% V：0.01～1.00％、 Zr：0.001～0.100％、 Hf: 0.01~0.10% Cu: 0.01~1.00% W：0.01～1.00％、 Co: 0.01~1.00% Rare earth elements: 0.0001~0.1000%, and Mg: 0.0001 to 0.0200% of one or more of the group.

3. The alloy material according to claim 1 or claim 2, wherein, The chemical composition, expressed as a percentage by mass, contains B: greater than 0.0010% and less than 0.0030%. The Ti content [Ti] in the residue obtained by the extraction method, expressed as a percentage by mass, is less than 0.020%, or... The [Ti] content is 0.020% or more, and the Nb content [Nb] in the residue, expressed as a mass percentage, is 0.015% or more, wherein the [Ti] and the [Nb] satisfy equation (4). [Ti]+[Nb]≥0.050 (4).

4. The alloy material according to claim 1 or claim 2, wherein, The chemical composition contains B: 0.0001–0.0010% by mass. The Ti content [Ti] in the residue obtained by the residue extraction method, expressed as a percentage by mass, is less than 0.031%, or... The [Ti] content is greater than 0.031%, and the Nb content [Nb] in the residue, expressed as a percentage by mass, is 0.3 × [Ti]% or more.

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