Fe-ni-cr alloy material, method for producing same, and component and ammonia combustion equipment component having fe-ni-cr alloy material in at least a portion thereof

Abstract

Provided are: an Fe-Ni-Cr alloy material having red scale resistance and intergranular cracking resistance even against gas having a temperature of approximately 500-700°C and containing a large amount of nitrogen and water (water vapor), such as ammonia combustion exhaust gas; a method for producing the same; and a component and an ammonia combustion equipment component having the Fe-Ni-Cr alloy material in at least a portion thereof.　The Fe-Ni-Cr alloy material according to the present invention has a prescribed component composition and satisfies formula (1), and the maximum values of the amounts of Al, Si, and Cr in a surface layer of the alloy material satisfy formula (2).　Formula 1: Ni+Cr+3Si≥30.0. Formula 2: Al+2Si+Cr≥32.0.

Description

Fe-Ni-Cr alloy material and method for manufacturing the same, and parts and ammonia combustion equipment parts having at least a portion of the Fe-Ni-Cr alloy material.

[0001] The present invention relates to an alloy material made of Fe-Ni-Cr alloy (hereinafter referred to as Fe-Ni-Cr alloy material, or simply alloy material; the form of the alloy material is not particularly limited and includes all shapes such as plate-shaped, rod-shaped, wire-shaped, groove-shaped, and angular-shaped), a method for manufacturing the same, and a part using the Fe-Ni-Cr alloy material.

[0002] Global warming has become an international environmental problem, and technological development is actively underway to realize a decarbonized society, such as carbon-zero or carbon-neutral. In this context, ammonia is attracting attention as an alternative fuel to carbon fuels. The combustion reaction equation for ammonia is 4NH₄ ３ +3O ２ →2N ２ +6H ２ Ammonia is an oxygen-based fuel that produces water and nitrogen, resulting in a low environmental impact and making it a promising renewable fuel. The combustion temperature of ammonia is 1750°C at the adiabatic flame temperature, which is lower than that of hydrogen (2120°C), methane (1970°C), and gasoline (approximately 2000°C). As a result, the combustion temperature in actual engines and gas turbines is also lower than that of these existing fuels. Therefore, when ammonia is used as fuel, the exhaust gas temperature is also lower than that of existing fuels, at around 500-700°C. This temperature range of 500-700°C is where steel materials used in exhaust pipes and other components are prone to oxidation, and is the temperature range where so-called red scale is likely to form.

[0003] Patent Document 1 proposes an austenitic stainless steel that exhibits good corrosion resistance even in environments containing high levels of sulfur (S) and chlorine (Cl), such as boiler superheater tubes, waste incinerators, and ammonia synthesis equipment.

[0004] Patent Document 2 proposes an austenitic stainless steel that exhibits good corrosion resistance in an ammonia atmosphere without the addition of chromic acid, for use in ammonia-water absorption heat exchangers and the like.

[0005] JP-A-3-126842 JP-A-10-280100 JP-A-2019-035122

[0006] The use of ammonia as a fuel is being explored not only through single-fuel combustion but also through co-firing with other fuels (heavy oil, light oil, hydrogen, etc.). However, even with co-firing, because ammonia has a lower combustion temperature than existing fuels, the combustion exhaust gas temperature is lower than that of existing fuels, at around 500-700°C. Furthermore, the combustion gas of ammonia contains large amounts of nitrogen and water vapor.

[0007] The presence of water vapor makes red scale (water vapor oxidation) more likely to occur. Furthermore, the combustion gas temperature of around 500-700°C is also a temperature range where red scale is likely to occur. For this reason, steel materials used in ammonia combustion gas systems and similar applications require heat resistance and red scale resistance.

[0008] Furthermore, the large amount of nitrogen contained in ammonia combustion exhaust gas causes nitrogen to penetrate (nitriding) into the surface of the steel, leading to embrittlement caused by intergranular cracking. Therefore, steel materials for ammonia combustion gas systems are also required to have resistance to intergranular cracking (nitriding).

[0009] While Patent Document 1 describes the applicability of stainless steel to ammonia synthesis equipment, it does not address ammonia combustion gas (combustion exhaust gas), and does not consider countermeasures against grain boundary cracking due to nitriding or red scale at 500-700°C.

[0010] The stainless steel described in Patent Document 2 is intended for use in ammonia-water absorption heat exchangers, i.e., it is intended for contact with ammonia gas or ammonia solution, and does not take into account measures against intergranular cracking due to nitriding or red scale at 500-700°C.

[0011] Furthermore, if grain boundary cracking occurs due to nitriding, external factors such as vibration can cause cracks to propagate from the grain boundary cracks, potentially worsening creep properties. Austenitic Fe-Ni-Cr alloys are known as alloys that possess corrosion resistance and high-temperature creep properties. For example, Patent Document 3 proposes an Fe-Ni-Cr-Mo alloy in which resistance to overall corrosion, pitting corrosion, crevice corrosion, and stress corrosion cracking is improved by increasing the concentrations of Ni, Cr, and Mo. However, even with such heat-resistant austenitic Fe-Ni-Cr-Mo alloys, although stress corrosion cracking resistance has been improved, further improvements in red scale resistance and grain boundary cracking resistance are required for application to ammonia combustion exhaust gas.

[0012] The present invention aims to provide an Fe-Ni-Cr alloy material and a method for producing the same, which have resistance to red scale and grain boundary cracking even against gases containing large amounts of nitrogen and water (water vapor) at temperatures of around 500 to 700°C, such as ammonia combustion exhaust gas, as well as parts and ammonia combustion equipment parts that have at least a portion of the Fe-Ni-Cr alloy material.

[0013] To achieve the above objectives, the inventors conducted diligent research and obtained the following findings.

[0014] (a) In the combustion of ammonia, which contains trace amounts of oxygen, not only nitrogen but also water vapor is present. Nitrogen in the combustion gas of ammonia forms a nitride layer on the surface of the alloy material that comes into contact with the combustion gas. However, it has been found that water vapor present in the combustion gas allows oxygen to penetrate into the formed nitride layer, generating oxides, which then become the starting point for cracking within the nitride layer. In other words, alloy materials used with ammonia combustion gas require not only resistance to intergranular cracking but also resistance to red scale.

[0015] (b) Our research has revealed that the diffusion pathway for nitrogen and oxygen near the surface of the alloy material is the grain boundary, and we surmise that oxides formed within the grain boundary induce cracking. Therefore, we conceived that if we could prevent the penetration of oxygen and nitrogen into the grain boundary at a very shallow depth just below the surface of the alloy material, we could not only suppress nitriding but also suppress the formation of oxides and nitrides and prevent cracking, and proceeded with development based on this idea.

[0016] (c) The inventors have found that by forming an internal oxide layer on the surface layer of the alloy material, the diffusion and intrusion of oxygen and nitrogen can be suppressed, and the formation of oxides can be suppressed. As the internal oxide layer, since it can be composed of Al oxide (Al ２ O ３ ), Si oxide (SiO ２ ), and Cr oxide (Cr ２ O ３ ), it has been found that the components of Al, Si, and Cr in the alloy material can be optimized, and an internal oxide layer can be formed on the surface layer of the alloy material by heat treatment. If the following formula is satisfied in the surface layer of the alloy material, it has been led that an appropriate internal oxide layer is formed. Al + 2Si + Cr ≧ 32.0

[0017] (d) Further, alloy design was performed by optimizing elements from the viewpoint of nitride suppression. As a result, it has been found that not only Ni but also Cr and Si are effective for nitride resistance, and it has been considered that the contents of these elements should be optimized. As a result, a nitride resistance index indicating the degree of nitride resistance of the alloy material was derived, and it has been found that this nitride resistance index should be 30 or more. Nitride resistance index: Ni + Cr + 3Si ≧ 30.0

[0018] The present invention is based on these findings, and the gist thereof is as follows.

[0019] [1] In mass%, C: 0.150% or less, Si: 0.05-4.50%, Mn: 0.05-3.00%, P: 0.050% or less, S: 0.0050% or less, Ni: 6.00-46.00%, Cr: 15.00-30.00%, Al: 0.003-0.800%, N: 0.001-0.300%, Cu: 0.01-3.50%, Mo: 0.01-3.00%, Nb: 0.001-1.000%, Ti: 0.001-0.600%, V: 0-1.00%, B: 0-0.0100%, Hf: 0-0.60%. Fe-Ni-Cr alloy material characterized by containing Zr: 0-0.60%, Sb: 0-0.60%, Co: 0-1.50%, W: 0-2.00%, Sn: 0-1.00%, Ta: 0-1.00%, Ca: 0-0.015%, Bi: 0-0.30%, Ga: 0-0.50%, Mg: 0-0.0050%, REM: 0-0.200%, satisfying the following formula 1, with the remainder being Fe and impurities, and having maximum Al, Si, and Cr content determined by GDS analysis in a region perpendicular to the surface, at a distance of 50 nm to 500 nm from the surface in the direction perpendicular to the surface, satisfying the following formula 2. Ni + Cr + 3Si ≥ 30.0 .....(Equation 1) Al + 2Si + Cr ≥ 32.0 .....(Equation 2) However, the element symbols in Equation 1 indicate the content (mass %) of the element in the alloy material, and 0 is substituted if the element is not present. Also, the element symbols in Equation 2 indicate the maximum value of the content (mass %) of the element in the aforementioned region, and 0 is substituted if the element is not present. [2] The alloy material has the following composition in mass%, C: 0.010-0.150%, V: 0.01-1.00%, B: 0.0005-0.0100%, Hf: 0.001-0.60%, Zr: 0.01-0.60%, Sb: 0.005-0.60%, Co: 0.01-1.50%, W: 0.01-2.00%, Sn: 0.002-1.00%, Ta: 0.001-1.00%, Ca: 0.0002-0.015%, Bi: 0.0002-0.30%, Ga: 0.0002-0.50%, Mg: 0.0003-0.0050% The Fe-Ni-Cr alloy material according to [1] above, comprising one or more of the following: REM: 0.001 to 0.200%.[3] The Fe-Ni-Cr alloy material according to [1] or [2], wherein in a cross section perpendicular to the surface of the alloy material, the oxygen content in a region at a distance of 15 μm or more and 45 μm or less from the surface in the direction perpendicular to the surface is 2.00 mass% or less. [4] The Fe-Ni-Cr alloy material according to any one of [1] to [3], wherein in a cross section perpendicular to the surface of the alloy material, one field of view is defined as a 50 μm square area centered on a point at a distance of 40 μm from the surface in the direction perpendicular to the surface, and the sum of the grain boundary crack lengths of any three fields of view is 20 μm or less. [5] The Fe-Ni-Cr alloy material according to any one of [1] to [4], for use in ammonia combustion equipment. [6] A part having at least a portion of the Fe-Ni-Cr alloy material according to any one of [1] to [4]. [7] The part according to [6], for use in ammonia combustion equipment. [8] A method for producing an Fe-Ni-Cr alloy material according to any one of [1] to [4] above, comprising: a final annealing step of heating and holding an Fe-Ni-Cr alloy material having the components described in [1] or [2] above to a temperature range of 1050 to 1200°C; a primary cooling step of cooling from 1050°C to 850°C at a cooling rate of 10°C / second or less after the final annealing step; and a secondary cooling step of cooling from 850°C to 100°C at a cooling rate of 15 to 30°C / second after the primary cooling step.

[0020] The Fe-Ni-Cr alloy material according to the present invention exhibits resistance to red scale and grain boundary cracking even when in contact with gases containing large amounts of nitrogen and water (water vapor) at temperatures of around 500 to 700°C, such as ammonia combustion exhaust gas.

[0021] The following describes one embodiment of the present invention (hereinafter simply referred to as "the present invention"). Unless otherwise specified, "%" for components indicates the mass percentage in the alloy material. In cases where no lower limit is specified or where the lower limit is 0%, it also includes cases where the component is not present (0%).

[0022] <About the alloy material composition> C: 0.150% or less Since C is an element that reduces formability (r value), it is preferable to have less of it. Therefore, the C content should be 0.150% or less. From the viewpoint of formability, the upper limit of the C content is preferably 0.140%, 0.120%, or 0.100%. There is no particular limit to the lower limit of the C content, but excessive reduction will lead to an increase in refining costs, so it is preferable to have a C content of 0.001% or more. Therefore, the preferred range for the C content is 0.001 to 0.150%. On the other hand, C is an element that contributes to maintaining non-magnetic properties and is also effective in solid solution strengthening of the austenite phase. Therefore, it may be included as needed. If the above effects are to be obtained, the lower limit of the C content should preferably be 0.010% or 0.050%.

[0023] Si: 0.05-4.50% Si is not only useful as an element that forms the internal oxide layer of the surface, but it also suppresses nitriding and is effective against grain boundary cracking. Furthermore, it is an element that is effective in suppressing red scale. For this reason, the Si content should be 0.05% or more. The lower limit of the Si content is preferably 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, or 0.50%. On the other hand, increasing the Si content deteriorates workability and weldability. For this reason, the Si content should be 4.50% or less. The upper limit of the Si content is preferably 4.00%, 3.50%, 3.00%, 2.50%, or 2.00%.

[0024] Mn: 0.05-3.00% Mn is an element that is effective in improving oxidation resistance from the viewpoint of improving scale adhesion. For this reason, the Mn content should be 0.05% or more. The lower limit of the Mn content is preferably 0.10%, 0.15%, 0.20%, 0.25%, or 0.30%. On the other hand, a high Mn content deteriorates processability. For this reason, the Mn content should be 3.00% or less. The upper limit of the Mn content is preferably 2.80%, 2.60%, 2.50%, 2.40%, 2.20%, or 2.00%.

[0025] P: 0.050% or less. Since phosphorus (P) reduces toughness, hot workability, and corrosion resistance, the less P it contains, the better. Therefore, the P content should be 0.050% or less. Preferably, the upper limit of the P content is 0.040%. However, excessive reduction increases the load during refining or requires the use of expensive raw materials, so in reality, it is preferable to have a P content of 0.001% or more. Therefore, the preferred range for the P content is 0.001% to 0.050%.

[0026] S: 0.0050% or less. Since sulfur (S) reduces toughness, hot workability, and corrosion resistance, the less S it contains, the better. Therefore, the S content should be 0.0050% or less. Preferably, the upper limit of the S content is 0.0030%. However, excessive reduction increases the load during refining or requires the use of expensive raw materials, so in reality, it is preferable for the S content to be 0.0001% or more. Therefore, the preferred range for the S content is 0.0001% to 0.0050%.

[0027] Ni: 6.00–46.00% Ni not only suppresses nitriding and is effective against grain boundary cracking, but it is also an element that stabilizes the austenite phase and improves corrosion resistance to various acids and low-temperature toughness. For this reason, the Ni content should be 6.00% or more. The lower limit of the Ni content should preferably be 10.00%, 13.00%, 16.00%, 18.00%, 20.00%, 22.00%, 24.00%, or 25.00%. On the other hand, since it is an expensive element, including a large amount does not yield an effect that justifies the increase in alloy cost. For this reason, the Ni content should be 46.00% or less. The upper limit of the Ni content should preferably be 44.00%, 42.00%, 40.00%, 38.00%, or 35.00%.

[0028] Cr: 15.0-30.0% Cr is useful not only as an element that forms the internal oxide layer of the surface, but also as an element that suppresses nitriding and is effective against grain boundary cracking. Furthermore, it is an element that provides corrosion resistance. For this reason, the Cr content should be 15.0% or more. The lower limit of the Cr content should preferably be 16.0%, 17.0%, 18.0%, 19.0%, 20.0%, or 21.0%. On the other hand, a large amount of Cr content leads to a decrease in processability. For this reason, the Cr content should be 30.0% or less. The upper limit of the Cr content should preferably be 28.0%, 27.0%, 26.0%, 25.0%, or 24.0%.

[0029] Al: 0.003-0.800% Al is useful as an element that forms an internal oxide layer on the surface and also has the effect of improving corrosion resistance by desulfurizing. For this reason, the Al content should be 0.003% or more. The lower limit of the Al content should preferably be 0.005%, 0.010%, 0.015%, 0.020%, 0.030%, or 0.040%. On the other hand, Al is an element that combines with N to produce AlN, which promotes grain boundary cracking, and further excessive addition reduces processability. For this reason, the Al content should be 0.800% or less. The upper limit of the Al content should preferably be 0.700%, 0.600%, or 0.500%.

[0030] Ti: 0.001 to 0.600% Ti is an element that promotes nitriding, and if added in excess, TiN is significantly generated, leading to nozzle clogging during manufacturing and surface defects in the product. Therefore, the Ti content should be 0.600% or less. The upper limit of the Ti content is preferably 0.500%, 0.400%, or 0.300%. On the other hand, Ti ensures corrosion resistance through the stabilizing effect of C and N. Therefore, the Ti content should be 0.001% or more. The lower limit of the Ti content is preferably 0.005%, 0.010%, 0.020%, 0.030%, 0.040%, or 0.050%.

[0031] N: 0.001 to 0.300% From the viewpoint of suppressing grain boundary cracking caused by N, a lower N content is preferable. Furthermore, N reduces workability and reduces corrosion resistance by bonding with Cr. For this reason, the N content should be 0.300% or less. The upper limit of the N content should preferably be 0.200%, 0.180%, 0.160%, 0.140%, 0.120%, or 0.100%. On the other hand, excessive reduction places a heavy burden on the refining process, so the N content should be 0.001% or more. The lower limit of the N content should preferably be 0.005% or 0.010%.

[0032] Nb: 0.001 to 1.000% Nb enhances moldability and corrosion resistance. Therefore, the Nb content should be 0.001% or higher. The lower limit of the Nb content is preferably 0.005% or 0.010%. On the other hand, adding too much Nb makes recrystallization difficult and results in a coarser structure. Therefore, the Nb content should be 1.000% or less. The upper limit of the Nb content is preferably 0.800%, 0.600%, or 0.500%.

[0033] Mo: 0.01-3.00% Adding Mo further enhances the already high corrosion resistance. Therefore, the Mo content should be 0.01% or more. The lower limit of the Mo content is preferably 0.05% or 0.10%. On the other hand, excessive Mo content makes it easier to form nitrides containing Mo and Cr (Cr-based nitrides), which reduces the Cr concentration in the matrix phase and makes it easier for red scale to form. It also promotes the precipitation of the sigma phase (σ phase), leading to embrittlement and a decrease in corrosion resistance. Therefore, the Mo content should be 3.00% or less. The upper limit of the Mo content is preferably 2.50% or 2.20%.

[0034] Cu: 0.01-3.50% Adding Cu further enhances the already high corrosion resistance. Therefore, the Cu content should be 0.01% or more. The lower limit of the Cu content is preferably 0.03%, 0.05%, or 0.10%. On the other hand, excessive addition does not result in performance improvements commensurate with the manufacturing costs. Therefore, the Cu content should be 3.50% or less. The upper limit of the Cu content is preferably 3.20%, 3.00%, 2.80%, 2.50%, or 2.00%.

[0035] V: 0 to 1.00% V has the effect of further enhancing high corrosion resistance when added. Therefore, it may be contained as necessary. On the other hand, when contained at a high concentration, it causes a decrease in toughness. Therefore, the V content should be 1.00% or less. The upper limit of the V content is preferably 0.90%, 0.70%, or 0.50%. The lower limit of the V content is not particularly limited, but when it is desired to obtain the above effects, the lower limit of the V content is preferably 0.01%.

[0036] B: 0 to 0.0100% B is an element that enhances the strength of grain boundaries and contributes to the improvement of workability. Therefore, it may be contained as necessary. On the other hand, excessive addition rather causes a decrease in workability due to a decrease in elongation. Therefore, the B content should be 0.0100% or less. The upper limit of the B content is preferably 0.0090%, 0.0070%, or 0.0050%. The lower limit of the B content is not particularly limited, but it may be 0.0001%. When it is desired to obtain the above effects, the lower limit of the B content is preferably 0.0005%, 0.0010%, or 0.0050%.

[0037] Ca: 0 to 0.015% Ca contributes to the improvement of oxidation resistance by immobilizing S as CaS and suppressing the segregation and generation of sulfides such as MnS at the center. Therefore, it may be contained as necessary. On the other hand, excessive content causes coarsening of inclusions and a decrease in toughness, ductility, or low-temperature impact properties. Therefore, the Ca content should be 0.015% or less. The upper limit of the Ca content is preferably 0.014%, 0.012%, 0.009%, 0.007%, or 0.005%. The lower limit of the Ca content is not particularly limited, but it may be 0.0001%. When it is desired to obtain the above effects, the lower limit of the Ca content is preferably 0.0002%, 0.0003%, or 0.0005%.

[0038] Sn: 0-1.00% Adding Sn further enhances the already high corrosion resistance. Therefore, it may be included as needed. On the other hand, excessive addition leads to a decrease in processability. For this reason, the Sn content should be 1.00% or less. The upper limit of the Sn content is preferably 0.90%, 0.70%, 0.50%, or 0.30%. The lower limit of the Sn content is not particularly limited, but it may be 0.001%. If the above effects are to be obtained, the lower limit of the Sn content is preferably 0.002% or 0.003%.

[0039] In addition, the following elements may be included in mass percent. These elements enhance corrosion resistance when added, and may be included as needed. However, since these elements are expensive, excessive amounts will not yield benefits commensurate with the increased cost; therefore, upper limits have been set for the content of each element. There is no particular lower limit for the content of these elements, but a preferred lower limit has been set for achieving the above effects.

[0040] Hf: 0-0.60% The Hf content is preferably set with a lower limit of 0.001% or 0.005% and an upper limit of 0.55%, 0.50%, or 0.40%.

[0041] Zr: 0-0.60% The Zr content is preferably set with a lower limit of 0.01% or 0.05% and an upper limit of 0.50% or 0.40%.

[0042] Sb: 0-0.60% The lower limit of the Sb content may be 0.001%. To obtain the above effect, the lower limit of the Sb content is preferably 0.005% or 0.010%. The upper limit of the Sb content is preferably 0.55%, 0.50%, or 0.40%.

[0043] Co: 0-1.50% The Co content is preferably set to a lower limit of 0.01% or 0.10% and an upper limit of 1.00% or 0.80%.

[0044] W: 0-2.00% The W content is preferably set to a lower limit of 0.01% or 0.05% and an upper limit of 1.90%, 1.50%, or 1.00%.

[0045] Ta: 0-1.00% The Ta content is preferably set to a lower limit of 0.001% or 0.005%, and an upper limit of 0.95%, 0.80%, or 0.50%.

[0046] Ga: 0-0.50% The lower limit of the Ga content may be 0.0001%. To obtain the above effect, the lower limit of the Ga content is preferably 0.0002% or 0.0004%. The upper limit of the Ga content is preferably 0.30%, 0.20%, or 0.15%.

[0047] Bi: 0-0.30% The lower limit of the Bi content may be 0.0001%. To obtain the above effect, the lower limit of the Bi content is preferably 0.0002% or 0.0010%. The upper limit of the Bi content is preferably 0.20% or 0.10%.

[0048] Mg: 0 to 0.0050%. The lower limit of the Mg content may be 0.0001%. To obtain the above effect, the lower limit of the Mg content is preferably 0.0003%. The upper limit of the Mg content is preferably 0.0030% or 0.0010%.

[0049] REM: 0-0.200% The REM content is preferably set to a lower limit of 0.001% or 0.005% and an upper limit of 0.100% or 0.050%. REM (rare earth elements) is a general term for Sc, Y, and lanthanides (15 elements from La to Lu in order of atomic number), and may contain one or more of these elements. The REM content refers to the total content of the elements contained in REM.

[0050] The remainder of the alloy material components is Fe and impurities. Here, impurities refer to components that are mixed in during the industrial production of the alloy material due to various factors in the manufacturing process, including raw materials such as ore and scrap, and are acceptable as long as they do not adversely affect the present invention. For example, the alloy may contain 0.02% or less of oxygen as an impurity.

[0051] <Nitriding Resistance Index> From the perspective of suppressing grain boundary cracking due to nitriding of alloy materials, the alloy composition was optimized, and the relationship between the content of elements that affect nitriding was considered. It is known that Ni has high nitriding resistance. Furthermore, the inventors have found that having a strong Cr-based oxide film and a Si-based oxide film on the surface also has the effect of suppressing nitriding. Therefore, conceiving of a balanced combination of Ni, Cr, and Si that are effective in suppressing nitriding, it was found that the nitriding resistance index of Fe-Ni-Cr alloy material can be evaluated by the nitriding resistance index shown in the following formula 1. From the perspective of ensuring grain boundary cracking resistance, it was found that this nitriding resistance index should be 30.0 or higher.

[0052] In short, the nitriding resistance index is an indicator of the nitriding suppression effect, and a higher value is preferable as it suppresses nitriding more effectively. Therefore, the nitriding resistance index should ideally be 30.0 or higher, preferably 35.0 or higher, 40.0 or higher, 45.0 or higher, 50.0 or higher, 55.0 or higher, or 60.0 or higher.

[0053] Nitriding resistance index: Ni + Cr + 3Si ≥ 30.0 ..... (Equation 1) However, the elemental symbols in Equation 1 indicate the content (mass%) of the element in the alloy material, and 0 is substituted if the element is not contained.

[0054] <Internal Oxidation Index> The alloy material according to the present invention has an internal oxide layer on its surface. When in contact with a gas containing nitrogen and water (water vapor), nitrogen and oxygen penetrate and diffuse from the surface of the alloy material, forming a nitride layer and oxide or nitride inclusions on the surface of the alloy material, which causes surface cracking. The grain boundaries are the pathways through which nitrogen and oxygen in this atmosphere move within the alloy material. The present invention has an internal oxide layer on the surface of the alloy material, and oxides generated at the grain boundaries inside the alloy material block the pathways through which nitrogen and oxygen penetrate and diffuse from the outside.

[0055] The internal oxide layer is an oxide of Al, Si, and Cr, which are components in the alloy material that are easily oxidized (i.e., Al ２ O ３ SiO ２ , Cr ２ O ３) is composed of the above. The internal oxide layer on the surface is formed because Al, Si, and Cr in the alloy matrix diffuse to the vicinity of the surface, so the content of these elements is higher on the surface than in the center of the alloy. The inventors have found that the internal oxidation index of the Fe-Ni-Cr alloy material according to the present invention can be evaluated by the internal oxidation index shown in the following formula 2. From the viewpoint of securing the internal oxide layer on the surface, it has been found that it is desirable for the internal oxidation index on the surface to be 32.0 or higher. It has been confirmed that if the internal oxidation index is 32.0 or higher, the thickness of the nitride layer does not increase even in a nitrogen-rich gas atmosphere, and good resistance to grain boundary cracking can be obtained. From the viewpoint of resistance to grain boundary cracking, a higher internal oxidation index is preferable. Therefore, it is preferable for the internal oxidation index to be 33.0 or higher, 35.0 or higher, 37.0 or higher, 39.0 or higher, or 40.0 or higher. The upper limit of the internal oxidation index is not particularly limited, but is determined by the upper limit of the Al, Cr, and Si content.

[0056] Internal oxidation index: Al + Cr + 2Si ≥ 32.0 ..... (Equation 2) However, the elemental symbols in Equation 2 indicate the maximum mass %) of the element in question in the surface layer, and 0 is substituted if the element is not present.

[0057] Here, the surface layer refers to the region of the alloy material perpendicular to the surface (also called the thickness direction of the alloy material) at a distance from the surface (also called the depth from the surface) of 50 nm to 500 nm (this region from the surface to a depth of 50 nm to 500 nm is called the surface layer). The region from the surface to a depth of 50 nm is excluded because Fe-Ni-Cr alloy materials form a passive film on the surface. Since the passive film of Fe-Ni-Cr alloy materials is usually only a few nm thick, the region up to a depth of 50 nm below the surface is excluded to ensure its exclusion. The reason for limiting the depth to 500 nm from the surface is that by generating an internal oxide layer in this region, the blocking effect of nitrogen and oxygen can be enhanced. Since the thickness of the nitride layer from the surface of the alloy material in an atmosphere containing nitrogen and oxygen is about 30 to 125 μm, generating an internal oxide layer in the surface layer up to 500 nm (0.5 μm) from the surface will block the diffusion of nitrogen and oxygen, thereby greatly enhancing the nitriding suppression effect.

[0058] As mentioned above, an internal oxide layer is formed at the surface, causing Al, Si, and Cr to diffuse towards the surface. Therefore, the content of each of Al, Si, and Cr at the surface is higher than the content in the alloy matrix outside the surface (for example, the region from the surface to a depth of 100 μm or more and to the center of the plate thickness (half the plate thickness from the surface)).

[0059] Surface component analysis (especially analysis of Al, Si, and Cr) can be performed by GDS analysis (Glow Discharge Optical Emission Spectroscopy) with the following measurement specifications: • Gas replacement time: 200 seconds, • Pre-sputtering time: 30 seconds, • Background: 5 seconds, • Depth: 1.01 μm, • Pressure: 600 Pa, • Output: 35 W, • RMS value: 8.75 W, • Module: 8 V, • Phase: 4 V, • Frequency: 100 Hz, • Duty cycle: 0.25

[0060] The internal oxidation index is calculated by substituting the maximum mass percentages of Al, Si, and Cr content in the surface layer, obtained by GDS analysis, into Equation 2. Since oxides are formed near the region where the Al, Si, and Cr content is at its maximum in the surface layer, whether or not an internal oxide layer has been formed can be evaluated by the maximum values ​​of each element. Since GDS analysis provides information on the depth direction (perpendicular to the surface) of the content of each element, the maximum content of each element in the region from the surface to a depth of 50 nm to 500 nm (the surface layer) can be determined.

[0061] Furthermore, if Al is detected in the surface component analysis, the oxide (Al ２ O ３ It is possible that not only nitrogen but also nitrides (AlN) are being detected. However, in the Fe-Ni-Cr alloy material of the present invention, when it has not been exposed to a nitriding environment after manufacturing, the N content is 0.300% or less, so the formation of AlN is extremely small, and oxides (Al) are formed by internal oxidation. ２ O ３ ) is preferentially formed. Therefore, Al in the internal oxide layer is Al oxide (Al ２ O ３ It is reasonable to assume that this is the case.

[0062] <Thickness of the Nitrided Layer> The alloy material according to the present invention has its composition adjusted to suppress nitriding and has an internal oxide layer on its surface, resulting in a thinner nitrided layer on average. In particular, there is a clear tendency for the nitrided layer to be thinner as the nitriding resistance index value increases. The nitrided layer thickness also varies slightly depending on the nitrogen (N) concentration (content) of the gas in contact, but it has been confirmed that surface embrittlement is suppressed if the thickness is 125 μm or less. The nitrided layer thickness is preferably 120 μm or less, 115 μm or less, 110 μm or less, 105 μm or less, 100 μm or less, 95 μm or less, 90 μm or less, 85 μm or less, or 80 μm or less. A thinner nitrided layer is preferable. Therefore, the lower limit of the nitrided layer thickness is not particularly limited, but it may be, for example, 0.1 μm or more.

[0063] The thickness of the nitrided layer can be measured by cutting a test piece after nitriding and oxidation treatment, electrolytic etching with a 10% oxalic acid aqueous solution at a voltage of 6V for 5 seconds, and measuring it using an optical microscope. The nitrided layer thickness is defined as the thickness in the depth direction (depth) of the region with a nitrogen concentration of 3% by mass or more, measured by EPMA in the cross-section after etching.

[0064] <Oxygen Concentration in the Deep Nitrided Layer> When oxides are present in the nitrided layer, oxides tend to form at grain boundaries and easily become the starting point for grain boundary cracking. Therefore, the alloy material according to the present invention has an internal oxide layer on the surface to suppress internal diffusion of oxygen. As a result, the oxygen concentration in the deep nitrided layer is kept to about the same level as that of the alloy base material. Even if oxygen penetrates and diffuses from the outside, grain boundary cracking in the nitrided layer is suppressed if the oxygen concentration (oxygen content) in the deep nitrided layer is 2.00% (mass%) or less. The oxygen concentration (oxygen content) in the deep nitrided layer is preferably 1.50% or less, more preferably 1.00% or less, and even more preferably 0.90% or less, 0.80% or less, or 0.70% or less.

[0065] Here, the term "deep nitride layer" refers to the region of the alloy material perpendicular to the surface (thickness direction) at a distance of 15 μm to 45 μm from the surface (the region from the surface to a depth of 15 μm to 45 μm). This region is within the nitride layer, excluding the internal oxide layer of the surface (the part unaffected by the internal oxide layer). Specifically, in a cross-section perpendicular to the surface, a square measurement area is extracted with a center point 30 μm from the surface, and a dimension of 30 μm perpendicular to the surface (thickness direction) and 30 μm parallel to the surface. This area can then be analyzed using EPMA (Electron Probe Micro Analyzer). Three measurement areas are arbitrarily selected, and the arithmetic mean of the oxygen content (mass%) measured at these three locations is taken as the oxygen concentration (oxygen content) of the deep nitride layer of the alloy material.

[0066] <Grain boundary crack length in the nitrided layer> As a result of suppressing nitriding on the alloy surface, grain boundary cracks caused by the intrusion of nitrogen (N) and oxygen (O) are suppressed. The length of grain boundary cracks can be directly measured by observing the grain boundaries with an optical microscope in a cross section perpendicular to the surface of the alloy. Specifically, three arbitrary fields of view are selected, each consisting of a 50 μm square area (a square measurement area of ​​50 μm in the thickness direction and 50 μm parallel to the surface) centered on an arbitrary point at a distance of 40 μm from the surface (40 μm depth from the surface) in the direction perpendicular to the surface (thickness direction). The grain boundary crack length is then measured in each of these three fields of view, and the measured values ​​from the three fields of view are summed. The measurement can also be performed using image processing. Specifically, the grain boundary crack area is marked on the measurement image, and its length can be measured by image processing.

[0067] If the sum of the grain boundary crack lengths in the three observation areas is 20 μm or less, embrittlement of the alloy surface can be suppressed, and the strength of the alloy material can be ensured in the temperature range of 500 to 700°C. The shorter the sum of the grain boundary crack lengths, the better, and it is more preferable if it is 19 μm or less, 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, 10 μm or less, 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, or 5 μm or less.

[0068] <Manufacturing Method> Next, the manufacturing method will be described. The manufacturing method described below is one embodiment for obtaining the alloy material according to the present invention, and is not limited to this manufacturing method. The manufacturing method is not limited as long as the alloy material according to the present invention can be obtained.

[0069] One embodiment of the method for manufacturing an alloy material according to the present invention involves manufacturing an alloy material by a conventional method, and then performing heat treatment to generate an internal oxide layer on the surface of the alloy material. The following explanation will use the example that the alloy material is in the form of a plate (alloy plate).

[0070] The alloy material before final annealing can be manufactured using conventional methods. For example, it can be manufactured using processes such as melting and hot rolling, melting and hot rolling and annealing, or melting and hot rolling, pickling and cold rolling.

[0071] However, in the melting process, it is preferable to melt an alloy containing components adjusted to the aforementioned composition in a vacuum melting furnace or the like, followed by secondary refining. The alloy thus adjusted to the predetermined composition is then formed into a slab according to a known casting method (for example, continuous casting or ingot casting). The slab is heated to a predetermined temperature and hot-rolled to a predetermined thickness. After hot-rolling, cold-rolling may be performed as needed. Cold-rolling can also be carried out by conventional methods.

[0072] The conditions in the manufacturing process can be selected as appropriate. For example, the slab thickness and hot-rolled sheet thickness can be set as appropriate. The hot-rolled sheet may be immersed in a water-cooling pool after being coiled. There are no particular limitations on the pickling process after hot rolling or hot-rolled annealing, and any mechanical descaling method such as shot blasting, bending, or brushing can be selected as appropriate. There are no particular limitations on the pickling solution after hot rolling, so existing conditions such as sulfuric acid or hydrofluoric acid can be used.

[0073] <Final Annealing Process> The hot-rolled alloy material, hot-rolled annealed alloy material, and cold-rolled alloy material obtained in this way are subjected to final annealing. In the final annealing process, the material is heated and held at a temperature in the range of 1050 to 1200°C. The holding time is preferably 30 seconds to 3 minutes. The annealing atmosphere is, for example, an atmospheric atmosphere.

[0074] <Primary Cooling Process> After the final annealing process, the alloy is cooled from 1050°C to 850°C at a cooling rate of 10°C / second or less (primary cooling). By slowly cooling from 1050°C to 850°C, the outward diffusion of Al, Si, and Cr from within the alloy is promoted, and an internal oxide layer is formed on the surface. Therefore, the slower the cooling rate, the better, preferably 9°C / second or less, 8°C / second or less, 7°C / second or less, 6°C / second or less, or 5°C / second or less. There is no lower limit to the cooling rate, but if it is too slow, productivity will deteriorate, so it is preferable to set it to 1°C / second or more, or 2°C / second or more.

[0075] Furthermore, if the alloy material temperature at the end of the final annealing (final annealing completion temperature) is higher than 1050°C, the cooling rate from the final annealing completion temperature to 1050°C should be between 5°C / second and 10°C / second. This is because slow cooling at 10°C / second or less, even in the high-temperature range above 1050°C, promotes the outward diffusion of Al, Si, and Cr within the alloy material. On the other hand, if the cooling rate in the high-temperature range above 1050°C is too low, productivity will be severely reduced, so a cooling rate of 5°C / second or higher is preferable.

[0076] <Secondary Cooling Process> After the primary cooling process, the material is cooled from 850°C to 100°C at a cooling rate of 15°C / second or more (secondary cooling). It is preferable to cool from 850°C to 100°C at a slightly rapid rate. Below 850°C, oxide formation in the surface layer does not progress much, so the cooling rate below 850°C can be increased. Also, by passing through this temperature range quickly, the residence time in the embrittlement region, which is characteristic of high-Ni alloy materials, can be reduced. The faster the cooling rate, the better, so it is preferable to set it to 20°C / second or more, or 25°C / second or more. There is no particular upper limit to the cooling rate, but from the perspective of the cooling equipment performance, it is generally preferable to set it to 30°C / second or less.

[0077] By the above manufacturing method, an internal oxide layer can be formed on the surface, and this internal oxide layer makes it possible to obtain an Fe-Ni-Cr alloy material with good resistance to intergranular cracking even when exposed to a gas atmosphere containing high concentrations of nitrogen and oxygen.

[0078] <Applications> The alloy material according to the present invention exhibits excellent resistance to intergranular cracking, resulting in less nitrogen penetration into the surface layer of the alloy material and suppression of intergranular cracking, even when used in gas environments with high nitrogen (N) and water (water vapor) (H2O) content. Furthermore, it also possesses resistance to red scale, and is particularly effective against the formation of red scale, which is a problem with conventional Fe-Ni-Cr alloy materials, in the medium-to-high temperature range of approximately 500 to 700°C. For this reason, it can be used, for example, in ammonia combustion equipment where the nitrogen content is high and the gas temperature is in the medium-to-high temperature range of 500 to 700°C. It can be used particularly in exhaust components of ammonia combustion equipment.

[0079] Of course, due to its resistance to intergranular cracking and red scale, even when used in containers or piping components that come into direct contact with substances such as ammonia or urea, the penetration of nitrogen ions from the solution, ammonia, urea, and nitrogen from the evaporated gas into the surface layer of the alloy is suppressed, thereby inhibiting intergranular cracking.

[0080] Furthermore, the Fe-Ni-Cr alloy material according to the present invention can be efficiently utilized when applied to parts requiring resistance to intergranular cracking and red scale.

[0081] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0082] Alloys with the component composition shown in Table 1 were melted in a vacuum melting furnace and cast into 30 kg slabs. After heating the slabs to 1230°C, they were hot-rolled to obtain hot-rolled alloy sheets with a thickness of 4.0 mm. The hot-rolled alloy sheets were then annealed at temperatures of 1050 to 1200°C for 1 minute of soaking, depending on the alloy composition, to obtain hot-rolled annealed alloy sheets. The obtained alloy sheets were pickled with a 60°C nitrate-hydrofluoric acid solution (3% hydrofluoric acid, 10% nitric acid, the remainder water) to remove oxide scale. Subsequently, the alloy sheets were cold-rolled to obtain cold-rolled alloy sheets with a thickness of 2.0 mm. The obtained cold-rolled alloy sheets were annealed by holding them at a temperature of 1100°C for 5 minutes (final annealing). After that, they were cooled outside the furnace to 850°C at a cooling rate of 5°C / sec to 7°C / sec (primary cooling), and then cooled from 850°C to 100°C at a cooling rate of 20°C / sec (secondary cooling).

[0083] Four 20 mm x 25 mm test pieces were cut from the obtained alloy plate. One of these pieces was used to measure the Al, Si, and Cr components of the surface layer in a cross-section perpendicular to the surface of the alloy plate, and an oxygen concentration analysis was performed deep within the nitrided layer. The remaining three pieces were evaluated by nitriding and oxidation treatment simulating ammonia combustion gas.

[0084] The Al, Si, and Cr component analysis in the surface layer was performed according to the following specifications: • Analytical instrument: Rigaku GDA750 glow discharge emission spectrometer • Gas replacement time: 200 seconds • Pre-sputtering time: 30 seconds • Background: 5 seconds • Depth: 1.01 μm • Pressure: 600 Pa • Output: 35 W • RMS: 8.75 W • Module: 8 V • Phase: 4 V • Frequency: 100 Hz • Duty cycle: 0.25 • Analysis area: From the surface to a depth of 600 nm

[0085] The oxygen concentration analysis in the deep nitride layer was performed according to the following specifications: • Analytical instrument: JEOL EPMA (JXA-8530F Field Emission Electron Probe Analyzer) • Acceleration voltage: 15 kV • Irradiation current: 2.0 × 10⁻¹⁰ －７ A. Measurement time: 50 ms. Analysis area: 30 μm x 30 μm. Analysis area depth: Any three locations in the region from 15 μm to 45 μm from the surface.

[0086] For the nitriding and oxidation treatment, a 100 vol% ammonia gas was introduced into the annealing furnace at a rate of 100 ml / min as the atmospheric gas. The test specimen was placed in the furnace, heated to 600°C, held for 50 hours, then cooled and removed. The grain boundary crack length and nitrided layer thickness were measured to evaluate red scale resistance.

[0087] The length of grain boundary cracks was determined by cutting a specimen after nitriding and oxidation treatment so that the cross-section in the thickness direction could be observed, and then observing the cross-section of the specimen using an optical microscope. For observation, a 50 μm × 50 μm area (a square measurement area of ​​50 μm in the thickness direction and 50 μm parallel to the surface) was defined as one field of view, centered on a point 40 μm deep from the surface of the specimen. Three randomly selected fields of view in the sample cross-section were observed, and the length of grain boundary crack occurrence was measured. A sum of grain boundary crack lengths in the three observation areas of the field of view of 20 μm or less was considered good.

[0088] The thickness of the nitrided layer was determined by cutting the test specimen after nitriding and oxidation treatment, electrolytic etching with a 10% oxalic acid aqueous solution at a voltage of 6V for 5 seconds, and observation using an optical microscope. The thickness of the nitrided layer was measured using photographs. The nitrided layer thickness was defined as the thickness in the depth direction (depth) of the region with a nitrogen concentration of 3% by mass or more as measured by EPMA. A nitrided layer thickness of 125 μm or less in the depth direction from the surface is considered good.

[0089] Red scale resistance was checked visually, and samples in which no red scale was found were deemed to pass (○), while samples in which even a small amount of red scale was found were deemed to fail (×). These measurement results are shown in Table 2. As shown in Table 2, in Examples and Tests No. 1 to 11 that satisfy the provisions of the present invention, the grain boundary crack length was reduced, and no red scale was found, resulting in excellent grain boundary crack resistance and red scale resistance.

[0090] In comparative example No. 101, the protective film did not grow sufficiently due to the low Cr content, resulting in poor red scale resistance. Furthermore, the nitridation resistance index decreased, making it more susceptible to nitriding. Additionally, the internal oxidation index decreased, which is thought to have prevented sufficient formation of the internal oxide layer.

[0091] In comparative example No. 102, not only did the nitriding resistance index decrease, making it easier to nitride, but the primary cooling rate was also fast, resulting in a low internal oxidation index and insufficient formation of the internal oxide layer. Furthermore, it is thought that the high carbon content led to the formation of Cr-based carbides, preventing sufficient growth of the protective film and thus deteriorating red scale resistance.

[0092] Comparative Example / Test No. 103 showed a lower nitriding resistance index and was easily nitrided, but the nitrided layer thickness was kept to 122 μm. However, the primary cooling rate was fast, resulting in a low internal oxidation index and insufficient formation of the internal oxide layer. Furthermore, it is thought that the high Ti content led to the generation of a large amount of TiN, which not only promoted grain boundary cracking but also worsened red scale resistance.

[0093] Comparative Example / Test No. 104 had high Ni and Al content. It is thought that the excessive Al content led to the formation of a large amount of AlN at the grain boundaries, thus exacerbating grain boundary cracking. Furthermore, it is thought that the high Mn content worsened red scale resistance.

[0094] In comparative example No. 105, not only did the internal oxidation index decrease, making it easier to nitride, but the primary cooling rate was also fast, resulting in a low internal oxidation index and insufficient formation of the internal oxide layer, which is thought to have led to a deterioration in red scale resistance. Furthermore, because the nitridation resistance index was not satisfied, it is thought that the grain boundary cracking resistance deteriorated.

[0095] In comparative example No. 106, not only did the nitriding resistance index decrease, making it easier to nitride, but the primary cooling rate was also fast, resulting in a low internal oxidation index and insufficient formation of the internal oxide layer. Furthermore, due to the high carbon and molybdenum content, molybdenum carbides were formed, making grain boundary cracking more likely. In addition, due to the high molybdenum content, nitrides containing molybdenum and Cr (Cr-based nitrides) were formed, reducing the matrix Cr concentration and worsening red scale resistance.

[0096] Comparative Example / Test No. 107 is thought to have suffered from poor resistance to intergranular cracking due to its low Ni content, and further deterioration of red scale resistance due to its high Mn content.

[0097] Comparative Example / Test No. 108 not only showed a lower nitriding resistance index and became easier to nitrid, but it is also thought that the faster primary cooling rate resulted in a lower internal oxidation index and insufficient formation of the internal oxide layer. Furthermore, it is thought that the low Si content prevented sufficient growth of the protective film, and the high Mn content worsened the red scale resistance.

[0098]

[0099]

[0100] This invention can be used in a wide range of industries, including the automotive industry and the general machinery industry.

Claims

1. In mass%, C: 0.150% or less, Si: 0.05-4.50%, Mn: 0.05-3.00%, P: 0.050% or less, S: 0.0050% or less, Ni: 6.00-46.00%, Cr: 15.00-30.00%, Al: 0.003-0.800%, N: 0.001-0.300%, Cu: 0.01-3.50%, Mo: 0.01-3.00%, Nb: 0.001-1.000%, Ti: 0.001-0.600%, V: 0-1.00%, B: 0-0.0100%, Hf: 0-0.60%. Fe-Ni-Cr alloy material characterized by containing Zr: 0-0.60%, Sb: 0-0.60%, Co: 0-1.50%, W: 0-2.00%, Sn: 0-1.00%, Ta: 0-1.00%, Ca: 0-0.015%, Bi: 0-0.30%, Ga: 0-0.50%, Mg: 0-0.0050%, REM: 0-0.200%, satisfying the following formula 1, with the remainder being Fe and impurities, and having maximum Al, Si, and Cr content determined by GDS analysis in a region perpendicular to the surface, at a distance of 50 nm to 500 nm from the surface in the direction perpendicular to the surface, satisfying the following formula 2. Ni + Cr + 3Si ≥ 30.0 .....(Equation 1) Al + 2Si + Cr ≥ 32.0 .....(Equation 2) However, the element symbols in Equation 1 indicate the content (mass %) of the element in the alloy material, and 0 is substituted if the element is not present. Also, the element symbols in Equation 2 indicate the maximum value of the content (mass %) of the element in the aforementioned region, and 0 is substituted if the element is not present.

2. The alloy material has the following composition in mass%, C: 0.010-0.150%, V: 0.01-1.00%, B: 0.0005-0.0100%, Hf: 0.001-0.60%, Zr: 0.01-0.60%, Sb: 0.005-0.60%, Co: 0.01-1.50%, W: 0.01-2.00%, Sn: 0.002-1.00%, Ta: 0.001-1.00%, Ca: 0.0002-0.015%, Bi: 0.0002-0.30%, Ga: 0.0002-0.50%, Mg: 0.0003-0.0050% The Fe-Ni-Cr alloy material according to claim 1, comprising one or more of the following: REM: 0.001 to 0.200%.

3. The Fe-Ni-Cr alloy material according to claim 1 or 2, wherein in a cross section perpendicular to the surface of the alloy material, the oxygen content in a region at a distance of 15 μm or more and 45 μm or less from the surface in the direction perpendicular to the surface is 2.00 mass% or less.

4. The Fe-Ni-Cr alloy material according to claim 1 or 2, wherein in a cross section perpendicular to the surface of the alloy material, a 50 μm square region is defined as one field of view, centered on a point 40 μm from the surface in the direction perpendicular to the surface, and the sum of the grain boundary crack lengths of any three fields of view is 20 μm or less.

5. The Fe-Ni-Cr alloy material according to claim 1 or 2, for use in ammonia combustion equipment.

6. A part having at least a portion of the Fe-Ni-Cr alloy material described in claim 1 or 2.

7. The part according to claim 6, which is a component of an ammonia combustion equipment.

8. A method for producing an Fe-Ni-Cr alloy material according to claim 1 or 2, comprising: a final annealing step of heating and holding an Fe-Ni-Cr alloy material having the components described in claim 1 to a temperature range of 1050 to 1200°C; a primary cooling step of cooling from 1050°C to 850°C at a cooling rate of 10°C / second or less after the final annealing step; and a secondary cooling step of cooling from 850°C to 100°C at a cooling rate of 15 to 30°C / second after the primary cooling step.

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