JP2023120710A - Fe-Ni-Cr-BASED ALLOY PRODUCT - Google Patents

Abstract

To provide an Fe-Ni-Cr-based alloy product which shows creep withstand temperature for 100,000 hours or more, equivalent to or higher than that of a cast austenitic steel product and that of sintered austenitic steel material.SOLUTION: The Fe-Ni-Cr-based alloy product according to the present invention has a chemical composition including: 25-50 mass% of Ni; 12-25 mass% of Cr; 3-6 mass% of Nb; 0.2-1.6 mass% of Ti; 0.5 mass% or less of Zr; 0.001-0.05 mass% of B; 0.001-0.2 mass% of N; and the balance composed of Fe and inevitable impurities, and is a polycrystal in which an average grain diameter of parent phase crystal grains is 10--200 μm. In the parent phase crystal grains, there are formed segregated cells having an average size of 1 μm to 5 μm. In the parent phase crystal grains, TiN phase grains are precipitated with an average inter-grain distance of 1-2 μm.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to the technology of Fe-based alloy materials, and more particularly to Fe--Ni--Cr based alloy products made from Fe--Ni--Cr based alloy materials.

From the viewpoint of energy saving (for example, fossil fuel saving) and global environment protection (for example, CO ₂ gas emission reduction), it is strongly desired to improve the efficiency of thermal power plants (for example, to improve efficiency in steam turbines). One of the effective means for improving the efficiency of steam turbines is to increase the main steam temperature.

In order to enable the high temperature of the main steam, high temperature components of the steam turbine (for example, turbine rotor blades, turbine stator vanes, rotor discs, casing members, boiler members) must withstand the high temperature of the main steam and Required mechanical properties (eg, creep properties, tensile properties) must be satisfied. Therefore, the development of heat-resistant alloy materials is also one of the important issues.

A strong candidate for heat-resistant alloy materials is Ni-based alloy materials. However, Ni-based alloy materials have higher material costs and process costs than Fe-based alloy materials that have been used in conventional 600°C class steam turbines. Therefore, research and development of Fe-based alloy materials with high endurance temperatures have been carried out.

For example, Patent Document 1 (JP 2017-088963) discloses an austenitic steel that achieves both excellent strength and castability, and an austenitic steel casting using the same.

In addition, Patent Document 2 (WO 2020/105496 A1) describes an austenitic steel sintered material that has strength equal to or higher than that of a Ni-based alloy and is less susceptible to oxygen, and a turbine using the austenitic steel sintered material A member is disclosed.

JP 2017-088963 A WO2020/105496

In recent years, the additive manufacturing (AM) method has attracted attention as a technology for near-net-shape manufacturing of final products with complex shapes, and research and development has been actively carried out to apply it to heat-resistant alloy members. The manufacturing of heat-resistant alloy members by the AM method can contribute to shortening manufacturing work times and improving manufacturing yields (reducing manufacturing costs) because even members with complex shapes can be directly formed.

The austenitic steel casting described in Patent Document 1 and the austenitic steel sintered material described in Patent Document 2 have mechanical properties equal to or higher than precipitation-strengthened Ni-based alloy materials such as Alloy 625 and Alloy 718 (for example, , high temperature 0.2% proof stress, 100,000 hours creep resistance temperature). However, in Patent Document 1, a mold is used during casting, and in Patent Document 2, a capsule to be filled with powder is required when applying Hot Isostatic Pressing (HIP method), and a complicated shape is required. When manufacturing , it is difficult to prepare a mold and a capsule for HIP.

Accordingly, an object of the present invention is to provide an Fe--Ni--Cr alloy product exhibiting a 100,000-hour creep endurance temperature equal to or greater than that of conventional austenitic steel castings and austenitic steel sintered materials.

(I) One aspect of the present invention is an Fe-Ni-Cr alloy product,
25% by mass or more and 50% by mass or less of Ni (nickel);
12% by mass or more and 25% by mass or less of Cr (chromium),
3% by mass or more and 6% by mass or less of Nb (niobium),
0.2% by mass or more and 1.6% by mass or less of Ti (titanium);
0.5% by mass or less of Zr (zirconium);
0.001% by mass or more and 0.05% by mass or less of B (boron);
0.001% by mass or more and 0.2% by mass or less of N (nitrogen),
having a chemical composition with the balance being Fe and unavoidable impurities,
A polycrystalline body with an average grain size of 10 μm or more and 200 μm or less of the mother phase crystal grains,
Segregation cells having an average size of 1 μm or more and 5 μm or less are formed in the mother phase crystal grains,
TiN phase particles are precipitated at an average interparticle distance of 1 μm or more and 2 μm or less in the mother phase crystal grains,
The present invention provides an Fe-Ni-Cr alloy product characterized by:

According to the present invention, the following improvements and changes can be made in the above Fe-Ni-Cr alloy product (I).
(i) Particles of the Laves phase (Fe ₂ Nb phase) are precipitated on the grain boundaries of the parent phase crystal grains.
(ii) the chemical composition is 25% by mass to 45% by mass of Ni, 12% by mass to 20% by mass of Cr, 3% by mass to 5% by mass of Nb, and 0.3% by mass to 1.3% by mass; % or less Ti, 0.4% by mass or less Zr, 0.001% by mass or more and 0.02% by mass or less of B, 0.001% by mass or more and 0.1% by mass or less of N, and the balance consisting of Fe and unavoidable impurities.
(iii) the chemical composition is 30% by mass to 40% by mass of Ni, 15% by mass to 20% by mass of Cr, 3.5% by mass to 4.5% by mass of Nb, and 0.5% by mass to 1.1% by mass; % or less of Ti, 0.3 mass % or less of Zr, 0.001 mass % or more and 0.02 mass % or less of B, 0.001 mass % or more and 0.1 mass % or less of N, and the balance consists of Fe and unavoidable impurities.

(II) Yet another aspect of the present invention is a steam turbine member comprising:
The present invention provides a steam turbine member comprising the above Fe-Ni-Cr alloy product.

The present invention can add the following improvements and changes to the above steam turbine member (II).
(iv) said steam turbine member is a casing member or a rotor disk;

According to the present invention, it is possible to provide an Fe--Ni--Cr alloy product exhibiting a 100,000-hour creep endurance temperature equal to or higher than that of conventional austenitic steel castings and austenitic steel sintered materials.

1 is a flowchart showing an example of steps of a method for manufacturing an Fe--Ni--Cr based alloy product according to the present invention; FIG. 4 is a scanning electron microscope (SEM) observation image showing an example of the microstructure of the Fe—Ni—Cr alloy product obtained in the aging treatment step S4. 4 is an SEM observation image showing another example of the microstructure of the Fe—Ni—Cr alloy product obtained in the aging treatment step S4. 1 is a schematic perspective view showing an example of a casing member made of the Fe--Ni--Cr alloy product of the present invention; FIG. 1 is a schematic perspective view showing an example of a rotor disk made of the Fe--Ni--Cr alloy product of the present invention; FIG. 4 is an SEM observation image showing an example of the microstructure of the sintered body of Reference Example 1. FIG. 2 is a graph showing the relationship between the 0.2% proof stress ratio at 700° C. (Reference Example 3 standard) and the 100,000-hour creep durability temperature ratio at a load of 400 MPa (Reference Example 2 standard). 2 is a graph showing the relationship between the 0.2% yield strength ratio at 700° C. (Reference Example 3 standard) and the creep durability temperature ratio for 100,000 hours at a load of 200 MPa (Reference Example 2 standard).

[Basic idea of the present invention]
In the present invention, based on the alloy composition of the austenitic steel sintered material described in Patent Document 2, the technology to further improve the creep temperature for 100,000 hours, in particular, the possibility of precipitation strengthening within the matrix grains. did

Specifically, by producing an alloy powder in which the N content is controlled within a predetermined range and performing additive manufacturing (additive manufacturing) using the alloy powder, an additive manufacturing body having a special microstructure can be obtained. It was found that TiN particles can be finely dispersed and precipitated in the mother phase crystal grains by subjecting the addition product to a predetermined heat treatment. The present invention has been completed based on this finding.

Hereinafter, an embodiment according to the present invention will be described along the manufacturing procedure with reference to the drawings.

[Manufacturing method of Fe-Ni-Cr alloy product]
FIG. 1 is a flow diagram showing an example of steps of a method for manufacturing an Fe--Ni--Cr alloy product according to the present invention. As shown in FIG. 1, the method for producing an Fe--Ni--Cr alloy product according to the present invention generally comprises an alloy powder preparation step S1 for preparing an Fe--Ni--Cr alloy powder as a starting material. Then, a selective laser melting step S2 of forming an additional manufactured body (AM body) of a desired shape using the prepared Fe-Ni-Cr alloy powder, and generating and precipitating TiN particles in the formed AM body. It has a solution treatment step S3 for heat treatment and an aging treatment step S4. The AM-solution treated article and the AM-aged article respectively obtained in steps S3 and S4 are one form of the Fe--Ni--Cr based alloy product according to the present invention.

If necessary, the AM-aged article obtained in step S4 is further subjected to a finishing step S5 for forming a surface treatment layer (for example, thermal barrier coating: TBC) or finishing the surface. may Step S5 is not an essential step, but may be performed as appropriate in consideration of the shape of the Fe--Ni--Cr alloy product and the usage environment. The AM-aged article that has undergone step S5 is also one form of the Fe--Ni--Cr alloy product according to the present invention. If the formation of the surface treatment layer involves heat treatment and the heat treatment temperature matches the temperature conditions of step S4, this corresponds to performing step S4 and step S5 at the same time.

Each step will be described in more detail below.

(Alloy powder preparation process)
This step S1 is a step of preparing Fe—Ni—Cr alloy powder having a predetermined alloy composition. The alloy composition comprises 25% by mass to 50% by mass of Ni, 12% by mass to 25% by mass of Cr, 3% by mass to 6% by mass of Nb, and 0.2% by mass to 1.6% by mass of It preferably contains Ti, 0.5% by mass or less of Zr, 0.001% by mass or more and 0.05% by mass or less of B, 0.001% by mass or more and 0.2% by mass or less of N, and the balance being Fe and unavoidable impurities.

By controlling the N content within a preferred range, TiN particles are finely dispersed and precipitated within the matrix grains in the final alloy product. As a result, it can contribute to good mechanical properties (high 100,000-hour creep endurance temperature) of alloy products.

Methods and techniques for preparing the alloy powder include, for example, a master alloy ingot preparation step (S1a) in which raw materials are mixed, melted, and solidified so as to have a desired composition to prepare a master alloy ingot (master ingot); An atomizing step (S1b) of forming alloy powder from the mother alloy ingot is preferably performed. It is preferable to control the N content and O content in the atomizing step S1b. As for the atomizing method, conventional methods and methods can be used basically. For example, a gas atomization method using an inert gas (eg, Ar (argon) gas, N ₂ gas) as an atomization gas medium, or a centrifugal atomization method can be preferably used.

The particle size of the alloy powder is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 70 μm or less, and more preferably 10 μm or more and 50 μm or less, from the viewpoints of handling property and filling property of the alloy powder bed in the next selective laser melting step S2. More preferred. When the particle size of the alloy powder is less than 5 μm, the fluidity of the alloy powder is lowered (the formability of the alloy powder bed is lowered) in the next step S2, which is a factor in lowering the shape accuracy of the AM body. On the other hand, when the grain size of the alloy powder exceeds 100 μm, it becomes difficult to control the local melting and rapid solidification of the alloy powder bed in the next step S2, resulting in insufficient melting of the alloy powder and an increase in the surface roughness of the AM body. It becomes a factor to do.

In view of the above, it is preferable to perform the alloy powder classification step (S1c) for classifying the alloy powder so that the particle size of the alloy powder falls within the range of 5 μm or more and 100 μm or less. In the present invention, when the particle size distribution of the obtained alloy powder is measured and confirmed to be within the desired range, it is considered that the main step S1c has been performed.

Next, the alloy composition will be explained.

N: 0.001% by mass or more and 0.2% by mass or less
The N component is an essential component for producing TiN phase particles. By finely dispersing and precipitating TiN phase particles in the matrix grains, the final alloy product contributes to the improvement of mechanical properties.

The N content is preferably 0.001% by mass (10 ppm) or more and 0.2% by mass (2000 ppm) or less. If the N content is less than 0.001% by mass, the amount of TiN phase particles generated becomes insufficient, and the effect of improving mechanical properties cannot be obtained. However, it is only substantially the same as in Patent Document 2, and no negative problem arises. On the other hand, when the N content exceeds 0.2% by mass, it becomes a factor of deterioration of mechanical properties. The N content is more preferably 0.001% by mass or more and 0.1% by mass or less.

O: 0.003% by mass or more and 0.05% by mass or less
The O component is usually treated as an impurity and should be reduced as much as possible, but in the present invention, it is a component that contributes to suppressing excessive coarsening of the mother phase crystal grains. The O component is thought to form oxide films and oxide particles in the grain boundary regions of the matrix crystal grains.

The O content is preferably 0.003% by mass or more and 0.05% by mass or less. If the O content is less than 0.003% by mass, the amount of oxide films and oxide particles produced becomes insufficient, and the effect of suppressing coarsening of the matrix crystal grains cannot be obtained. However, it is only substantially the same as in Patent Document 2, and no negative problem arises. On the other hand, when the O content exceeds 0.05% by mass, it causes deterioration of mechanical properties.

Ti: 0.2% by mass or more and 1.6% by mass or less
A Ti component is an essential component for producing TiN phase particles. As described above, the finely dispersed precipitation of TiN phase particles in the matrix crystal grains contributes to the improvement of the mechanical properties of the final alloy product. It also has the effect of promoting the formation of an intermetallic compound phase (δ phase: Ni ₃ Nb phase), which will be described later. The δ-phase particles also precipitate in the matrix grains, thereby contributing to intragranular strengthening.

The Ti content is preferably 0.2% by mass or more and 1.6% by mass or less. By setting the Ti content to 0.2% by mass or more, it is possible to secure a TiN precipitation amount that contributes to the improvement of mechanical properties. On the other hand, when the Ti content exceeds 1.6% by mass, a Ti oxide phase is likely to be generated and precipitated, which causes deterioration of mechanical properties. The Ti content is more preferably 0.3% by mass or more and 1.3% by mass or less, and still more preferably 0.5% by mass or more and 1.1% by mass or less.

Ni: 25% by mass or more and 50% by mass or less
The Ni component is a component that stabilizes the austenite phase (γ phase) that serves as the parent phase. It is also a component that constitutes the δ phase. The δ phase is generated and precipitates inside the matrix crystal grains, contributing to intragranular strengthening. From the viewpoint of γ-phase stability, the Ni content is preferably 25% by mass or more and 50% by mass or less, more preferably 25% by mass or more and 45% by mass or less, and even more preferably 30% by mass or more and 40% by mass or less.

Cr: 12% by mass or more and 25% by mass or less
The Cr component is a component that improves oxidation resistance and steam oxidation resistance. The Cr content is preferably 12% by mass or more and 25% by mass or less. By setting the Cr content to 12% by mass or more, sufficient oxidation resistance and steam oxidation resistance can be obtained. On the other hand, when the Cr content exceeds 25% by mass, undesirable intermetallic compound phases (for example, σ phase: intermetallic compound phase based on Fe and Cr) are precipitated, leading to a decrease in ductility and toughness (so-called σ phase embrittlement). The Cr content is more preferably 12% by mass or more and 20% by mass or less, and even more preferably 15% by mass or more and 20% by mass or less.

Nb: 3% by mass or more and 6% by mass or less
The Nb component is an essential component for producing the δ phase and the Laves phase (Fe ₂ Nb phase). As described above, the δ phase mainly precipitates inside the matrix crystal grains and contributes to intragranular strengthening. The Laves phase mainly precipitates on the grain boundaries of the matrix crystal grains and contributes to grain boundary strengthening. The Nb content is preferably 3% by mass or more and 6% by mass or less. The Nb content of 3% by mass or more contributes to the improvement of creep properties. On the other hand, when the Nb content exceeds 6% by mass, the precipitated particles of the δ phase and the Laves phase become excessively coarse, and their effects are lost. The Nb content is more preferably 3% by mass or more and 5% by mass or less, and even more preferably 3.5% by mass or more and 4.5% by mass or less.

Zr: 0.5% by mass or less
The Zr component is a component that promotes the formation of the Laves phase that precipitates on the grain boundaries of the matrix crystal grains. Since the Zr component is not an essential component, it may not be contained, but if it is contained, the Zr content is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and even more preferably 0.3% by mass or less.

B: 0.001% by mass or more and 0.05% by mass or less
The B component is a component that is effective in suppressing intergranular cracking of the mother phase crystal grains, and is also a component that promotes the formation of the Laves phase that precipitates on the grain boundaries of the mother phase crystal grains. The B content is preferably 0.001% by mass or more and 0.05% by mass or less. By setting the B content to 0.001% by mass or more, those effects can be obtained. On the other hand, if the B content exceeds 0.05% by mass, the melting point tends to decrease locally, deteriorating the creep properties. The B content is more preferably 0.001% by mass or more and 0.02% by mass or less.

(Selective laser melting process)
The selective laser melting step S2 is a step of forming an AM body having a desired shape by a selective laser melting (SLM) method using the prepared Fe--Ni--Cr alloy powder. Specifically, an alloy powder bed preparatory step (S2a) in which an alloy powder bed of a predetermined thickness is prepared by spreading Fe-Ni-Cr alloy powder, and a laser beam is irradiated to a predetermined area of the alloy powder bed. and a laser melting and solidification step (S2b) for locally melting and rapidly solidifying the Fe--Ni--Cr alloy powder in the region, and repeating to form an AM body.

In this step S2, local melting and rapid solidification of the alloy powder bed are controlled to control the microstructure of the AM body in order to obtain the desired microstructure in the final Fe--Ni--Cr alloy product.

The laser light output P (unit: W) and the laser light scanning speed S (unit: mm/s) basically depend on the configuration of the laser device. S ≤ 7000”. P/S (unit: W·s/mm=J/mm) corresponds to local heat input, and control of local heat input corresponds to control of cooling rate.

(Solution treatment process)
The solution treatment step S3 is a heat treatment step for finely dispersing and precipitating TiN phase particles in the mother phase crystal grains of the formed Fe—Ni—Cr alloy AM body. The temperature of the solution treatment is preferably 1000°C or higher and 1300°C or lower. The holding time in the solution treatment is not particularly limited, and may be appropriately set in consideration of the volume/heat capacity and temperature of the object to be heat treated. There is no particular limitation on the cooling method after the solution treatment, and any of water cooling, oil cooling, air cooling, and furnace cooling may be used.

By applying the solution heat treatment, the components segregated in the boundary region of the segregation cells begin to diffuse and combine on the boundary (along the boundary) to form TiN phase particles, and the entire matrix grain (crystal finely distributed within grains and on grain boundaries).

Recrystallization of the matrix phase grains occurs simultaneously with the generation and precipitation of the TiN phase particles, but excessive coarsening of the matrix phase grains is suppressed by oxide films and oxide particles resulting from the contained O component. Also, the recrystallization of the matrix grains can relieve the residual internal strain of the AM body that may occur during the rapid solidification of the SLM step S2, preventing unwanted deformation in service of the alloy product. can do. The AM-solution treated article obtained in step S3 is one form of the Fe--Ni--Cr based alloy product according to the present invention.

(Aging treatment process)
The aging treatment step S4 is a step of subjecting the solution-treated article to aging treatment. As the aging treatment conditions, a temperature range of 600°C or higher and 1000°C or lower is preferable. The holding time in the aging treatment is not particularly limited, and may be appropriately set in consideration of the volume/heat capacity and temperature of the object to be heat treated. There is no particular limitation on the cooling method after the aging treatment, and any of water cooling, oil cooling, air cooling, and furnace cooling may be used.

FIG. 2 is a scanning electron microscope (SEM) observation image showing an example of the microstructure of the Fe—Ni—Cr alloy product obtained in the aging treatment step S4. The observation sample was obtained by polishing the cross section of the Fe--Ni--Cr alloy product and then etching it with aqua regia.

In the Fe—Ni—Cr alloy product, segregation cells having an average size of 1 μm or more and 5 μm or less are formed in the mother phase crystal grains. The size of the segregation cell is basically defined as the average of the major axis and the minor axis, but if the aspect ratio between the major axis and the minor axis is 3 or more, the size of the segregation cell is twice the minor axis. .

In addition, particles of the Fe ₂ Nb phase (Laves phase) are precipitated on the grain boundaries of the matrix crystal grains. From the viewpoint of the mechanical properties of the final alloy product, the size of the parent phase crystal grains is preferably controlled to an average grain size of 10 μm or more and 200 μm or less.

In the present invention, a segregation cell refers to a cell in which a part of the alloy constituents is segregated in a boundary region such as a cell wall to form a cell-like fine structure. It is evident that there is some segregation in the alloy constituents, as the etch rate is different between the boundary region and the interior of the segregation cell (not evenly etched).

A scanning transmission electron microscope-energy dispersive X-ray spectrometer (STEM-EDX) was used to investigate the composition distribution of the segregation cells. component) segregated in the boundary region of the segregation cells (peripheral region of microcells, region such as cell wall).

FIG. 3 is an SEM observation image showing another example of the microstructure of the Fe—Ni—Cr alloy product obtained in the aging treatment step S4. The observation sample was obtained by polishing the cross section of the Fe--Ni--Cr alloy product and then subjecting it to oxalic acid etching.

As shown in FIG. 3, in the microstructure, TiN phase particles are precipitated at an average interparticle distance of 1 μm or more and 2 μm or less in mother phase crystal grains of an average grain size of 10 μm or more and 200 μm or less. It is also confirmed that Laves phase grains are precipitated on the grain boundaries. Oxalic acid etching is less corrosive/oxidizing than aqua regia etching, making it difficult to confirm segregation cells within the matrix grains. suitable etching.

(Finishing process)
As described above, the finishing step S5 is a step of forming a surface treatment layer or finishing the surface of the AM-aged article that has undergone the step S4. This step S5 is not an essential step, but may be performed as appropriate according to the application and usage environment of the Fe--Ni--Cr alloy product. Formation of the surface treatment layer and surface finishing are not particularly limited, and conventional methods can be used as appropriate. The AM-aged article that has undergone this step S5 is also one form of the Fe--Ni--Cr alloy product according to the present invention.

[Steam turbine member made of Fe-Ni-Cr alloy product]
FIG. 4 is a schematic perspective view showing an example of a casing member made of the Fe--Ni--Cr alloy product of the present invention, and FIG. 5 is a rotor disk made of the Fe--Ni--Cr alloy product of the present invention. It is a perspective schematic diagram showing an example of. The Fe-Ni-Cr-based alloy product of the present invention exhibits a 100,000-hour creep endurance temperature equal to or higher than that of a conventional austenitic steel sintered material. Suitable for disk 11 (see FIG. 5).

Hereinafter, the present invention will be described more specifically by way of experimental examples. The present invention is not limited to these experimental examples.

[Experiment 1]
(Preparation of Examples 1-2 and Reference Examples 1-3)
Fe—Ni—Cr alloy powders (Examples 1 and 2 and Reference Example 1) having chemical compositions shown in Table 1, which will be described later, were prepared (alloy powder preparation step S1). Specifically, after mixing the raw materials, a master alloy ingot producing step S1a was performed in which the raw materials were melted and cast by a vacuum high-frequency induction melting method to produce a master alloy ingot (mass: about 2 kg). Next, an atomizing step S1b was performed in which the master alloy ingot was melted again to form an alloy powder by a gas atomizing method.

In Example 1, the atomizing step S1b was performed in an N ₂ gas atmosphere. In Example 2 and Reference Example 1, the atomizing step S1b was performed in an Ar (argon) atmosphere. The alloy powder classifying step S1c for controlling the particle size of the alloy powder was performed on each of the obtained alloy powders to classify the powder particle size in the range of 15 to 45 μm.

Using the alloy powders of Examples 1 and 2, AM bodies were formed by the SLM method (selective laser melting step S2). The SLM conditions were a laser light output P of 95 W, an alloy powder bed thickness h of 25 μm, and a laser light scanning speed S of 600 mm/s. The obtained AM body was subjected to solution treatment at 1160° C. (solution treatment step S3). Next, the solution-treated articles were subjected to aging treatment at 900° C. (aging treatment step S4), and samples of Fe—Ni—Cr alloy products of Examples 1 and 2 were produced.

On the other hand, using the alloy powder of Reference Example 1, hot isostatic pressing (temperature: 1160 ° C., pressure: 100 MPa) was performed according to the description of Patent Document 2 to obtain a sintered body sample of Reference Example 1. was made.

As examples of conventional precipitation-strengthened Ni-based alloy materials, commercially available Alloy 718 (forged material) and Alloy 625 (cast material) were prepared and compared with Example 1 and Example 2. The chemical compositions of Alloy 718 and Alloy 625 are listed in Table 1 together.

[Experiment 2]
(Microstructure observation)
From the sample of the Fe--Ni--Cr based alloy product of Example 1 and the sample of the sintered body of Reference Example 1, test pieces for microstructure observation were taken, and cross-sectional structure observation was performed by SEM. 2 and 3 are SEM observation images of the Fe—Ni—Cr alloy product of Example 1, and FIG. 6 is an SEM observation image showing an example of the microstructure of the sintered body of Reference Example 1. . The sample of Reference Example 1 was subjected to oxalic acid etching after the cross section of the sintered body was polished.

Comparing FIGS. 2, 3, and 6, Example 1 (FIGS. 2-3), which is a solidified body, and Reference Example 1 (FIG. 6), which is a solid phase sintered body, are different in the matrix crystal grains. It is confirmed that there is a complete difference in the presence or absence of dispersed precipitation of TiN phase particles. In the solid-phase sintered body of Reference Example 1, the Laves phase particles are precipitated so as to be linked (in a string of beads) along the grain boundaries of the mother phase, but the TiN phase particles are dispersed within the mother phase crystal grains. No precipitation is observed. Although not shown in FIG. 6, it was confirmed that TiN particles were precipitated at grain boundaries of the parent phase.

On the other hand, in the solidified body of Example 1, the number of Laves phase particles precipitated on the grain boundaries of the mother phase crystal grains is relatively low, but TiN phase particles within the mother phase crystal grains finely dispersed precipitation is observed. That is, it was confirmed that Example 1 and Reference Example 1 had a large difference in microstructure due to the difference in the manufacturing method. Also in Example 2, it was confirmed that the same microstructure as in Example 1 was obtained.

[Experiment 3]
(Measurement of mechanical properties)
For the samples of Example 1 and Reference Examples 1 to 3 prepared in Experiment 1, 0.2% proof stress and 100,000 hour creep endurance temperature were measured. The 0.2% yield strength was measured according to JIS G 0567, and the creep test was performed according to JIS Z 22761.

Fig. 7A shows the 0.2% yield strength ratio (MPa/MPa) at 700°C based on Reference Example 3 and the creep resistance temperature ratio (°C/°C) for 100,000 hours at a load of 400 MPa based on Reference Example 2. FIG. 7B shows the 0.2% yield strength ratio (MPa/MPa) at 700°C based on Reference Example 3 and the creep durability for 100,000 hours at a load of 200 MPa based on Reference Example 2. It is a graph which shows the relationship with a temperature ratio (°C/°C).

In general, there is a trade-off relationship between the 0.2% yield strength and the creep temperature. shown). That is, in FIGS. 7A and 7B, both the creep endurance temperature and the 0.2% proof stress are large in the upper right direction of the graphs, and the mechanical properties are more desirable.

As shown in FIGS. 7A and 7B, in Example 1 of the present invention, the 0.2% yield strength at 700° C. is higher than that of Reference Example 3 and is at the same level as Reference Examples 1 and 2, and the 100,000-hour creep endurance temperature is higher than any of Reference Examples 1-3. In other words, it can be said that Example 1 of the present invention is located in the upper right direction (at least in the right direction) of the graph than Reference Examples 1 to 3, and it can be said that the mechanical properties are large.

The above-described embodiments and experimental examples are described to aid understanding of the present invention, and the present invention is not limited only to the specific configurations described. For example, it is possible to replace part of the configuration of the embodiment with a configuration of common technical knowledge of a person skilled in the art, and it is also possible to add a configuration of common general technical knowledge of a person skilled in the art to the configuration of the embodiment. That is, in the present invention, part of the configurations of the embodiments and experimental examples of the present specification can be deleted, replaced with other configurations, or added with other configurations without departing from the technical idea of the invention. It is possible.

10... Casing member, 11... Rotor disk.

Claims (6)

An Fe-Ni-Cr alloy product,
25% by mass or more and 50% by mass or less of Ni;
12% by mass or more and 25% by mass or less of Cr;
3% by mass or more and 6% by mass or less of Nb;
0.2% by mass or more and 1.6% by mass or less of Ti;
0.5% by mass or less of Zr;
0.001% by mass or more and 0.05% by mass or less of B;
0.001% by mass or more and 0.2% by mass or less of N,
having a chemical composition with the balance being Fe and unavoidable impurities,
A polycrystalline body with an average grain size of 10 μm or more and 200 μm or less of the mother phase crystal grains,
Segregation cells having an average size of 1 μm or more and 5 μm or less are formed in the mother phase crystal grains,
TiN phase particles are precipitated at an average interparticle distance of 1 μm or more and 2 μm or less in the mother phase crystal grains,
An Fe-Ni-Cr alloy product characterized by: In the Fe-Ni-Cr alloy product according to claim 1,
An Fe—Ni—Cr alloy product, characterized in that Laves phase grains are precipitated on the grain boundaries of the parent phase grains. In the Fe-Ni-Cr alloy product according to claim 1 or claim 2,
The chemical composition is
25% by mass or more and 45% by mass or less of Ni;
12% by mass or more and 20% by mass or less of Cr;
3% by mass or more and 5% by mass or less of Nb;
0.3% by mass or more and 1.3% by mass or less of Ti;
0.4% by mass or less of Zr;
0.001% by mass or more and 0.02% by mass or less of B;
0.001% by mass or more and 0.1% by mass or less of N
and
An Fe--Ni--Cr alloy product characterized in that the balance consists of Fe and unavoidable impurities. In the Fe-Ni-Cr alloy product according to claim 1 or claim 2,
The chemical composition is
30% by mass or more and 40% by mass or less of Ni;
15% by mass or more and 20% by mass or less of Cr;
3.5% by mass or more and 4.5% by mass or less of Nb;
0.5% by mass or more and 1.1% by mass or less of Ti;
0.3% by mass or less of Zr;
0.001% by mass or more and 0.02% by mass or less of B;
0.001% by mass or more and 0.1% by mass or less of N,
An Fe--Ni--Cr alloy product characterized in that the balance consists of Fe and unavoidable impurities. A steam turbine component,
A steam turbine member comprising the Fe-Ni-Cr alloy product according to any one of claims 1 to 4. A steam turbine component according to claim 5, wherein
A steam turbine member, wherein the steam turbine member is a casing member or a rotor disk.

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