WO2020110326A1 - Ni-based alloy softened powder, and method for producing said softened powder - Google Patents

Abstract

The present invention addresses the problem of providing: a Ni-based alloy softening powder which is a powder having better shaping processability/molding processability than before in spite of the fact that the powder is produced using a strongly precipitation-hardened Ni-based alloy material, and which is suitable for a powder metallurgy technique; and a method for producing the softened powder. The Ni-based alloy softened powder according to the present invention is a powder which has such a chemical composition that the equilibrium precipitation amount of a γ' phase precipitated in a γ phase that serves as a matrix phase becomes 30 to 80% by volume at 700°C, and has an average grain size of 5 to 500 μm, wherein each of grains of the softened powder is formed from a polycrystalline body of microcrystals of the γ phase, the powder being characterized in that the γ' phase is precipitated in an amount of 20% by volume or more on the grain boundaries of the microcrystals of the γ phase which constitute the grains, and the Vickers hardness of the grains at room temperature is 370 Hv or less.

Description

Ni-based alloy softening powder and method for producing the softening powder

TECHNICAL FIELD The present invention relates to a technology of a Ni (nickel) base alloy material, and more particularly to a Ni base alloy softening powder which is made of a strong precipitation strengthening Ni base alloy material and is suitable for powder metallurgy technology and a method for producing the softening powder. ..

In turbines (gas turbines, steam turbines) of aircrafts and thermal power plants, increasing the main fluid temperature to improve thermal efficiency has become one technological trend. This is an important technical issue. High temperature turbine components exposed to the harshest environments (eg, turbine blades, turbine vanes, rotor disks, combustor components, boiler components) are subject to rotational centrifugal forces during operation and thermal stress associated with vibration and start/stop. Therefore, it is very important to improve mechanical properties (for example, creep property, tensile property, fatigue property).

Precipitation-strengthened Ni-based alloy materials are widely used as materials for turbine high-temperature members in order to satisfy various required mechanical properties. When high temperature characteristics are especially important, strong precipitation strengthened Ni with a high ratio of γ'(gamma prime) phase (eg, Ni ₃ (Al,Ti) phase) to be precipitated in the γ(gamma) phase that is the matrix phase. A base alloy material (for example, a Ni base alloy material that precipitates 30% by volume or more of the γ'phase) is used.

As a main manufacturing method, precision casting methods (particularly, unidirectional solidification method and single crystal solidification method) have been conventionally used for members such as turbine blades and turbine stationary blades from the viewpoint of creep characteristics. On the other hand, hot forging methods have often been used for turbine disks and combustor members from the viewpoint of tensile properties and fatigue properties.

However, in precipitation-strengthened Ni-based alloy materials, if the volume ratio of the γ'phase is further increased in order to further improve the high temperature characteristics of the high temperature member, the workability and formability deteriorate and the manufacturing yield of the high temperature member decreases. There is a weak point that it does (that is, manufacturing cost increases). Therefore, in parallel with the research on improving the characteristics of the high temperature member, various researches on techniques for stably manufacturing the high temperature member have been conducted.

For example, Patent Document 1 (Japanese Patent Laid-Open No. 9-302450) discloses a method for producing a Ni-based superalloy article having a controlled grain size from a forging preform, which comprises mixing a γ phase and a γ′ phase. Prepare a Ni-base superalloy preform having a microstructure including, a recrystallization temperature and a γ'solvus temperature (where the γ'phase occupies at least 30% by volume of the Ni-base superalloy) and at about 1600°F or higher. However, at a temperature lower than the γ'solvus temperature, the superalloy preform was hot die forged at a strain rate of about 0.03 to about 10 per second, and the resulting hot die forging superalloy workpiece was isothermally forged. To form a processed article and subject the finished article to a supersolvus heat treatment to produce a substantially uniform grain microstructure of approximately ASTM 6-8, and cooling the article from the supersolvus heat treatment temperature. A method consisting of is disclosed.

Japanese Unexamined Patent Publication No. 9-302450 Japanese Patent No. 5869624 US Pat. No. 5,649,280

According to Patent Document 1, it is said that even a Ni-based alloy material having a high γ'phase volume ratio can be manufactured with a high manufacturing yield without cracking. However, the technique of Patent Document 1 requires a special manufacturing apparatus and a long work time because the hot forging step of superplastic deformation at a low strain rate and the isothermal forging step thereafter are performed (that is, a long work time is required). , Equipment cost and process cost are high).

Naturally, there is a strong demand for cost reduction for industrial products, and establishment of technology for manufacturing products at low cost is one of the most important issues.

For example, Patent Document 2 (Patent No. 5869624) discloses a method for manufacturing a Ni-based alloy softening material composed of a Ni-based alloy having a γ'phase solid solution temperature of 1050°C or higher, in which the softening treatment is performed in the next step. A material preparation step of preparing a Ni-based alloy material to be carried out, and a softening treatment step of improving the workability by softening the Ni-based alloy material, the softening treatment step, the solid of the γ'phase. The first step of hot forging the Ni-based alloy material at a temperature lower than the solid solution temperature of the γ'phase, which is a step performed in a temperature range lower than the melting temperature, and lower than the solid solution temperature of the γ'phase The amount of incoherent γ'phase crystal grains precipitated on the grain boundaries of the γ phase crystal grain, which is the parent phase of the Ni-based alloy, by slow cooling at a cooling rate of 100°C/h or less from And a second step of obtaining a Ni-based alloy softening material whose content is increased to 20% by volume or more, and a manufacturing method of the Ni-based alloy softening material. The technique reported in Patent Document 2 can be said to be an epoch-making technique in that a strong precipitation strengthened Ni-based alloy material can be processed/formed at low cost.

However, in the case of super-strong precipitation strengthened Ni-based alloy materials with a volume ratio of γ'phase of 45% by volume or more (for example, Ni-based alloy material that precipitates γ'phase in 45 to 80% by volume), the solid content of γ'phase is In the process of hot forging at a temperature lower than the melting temperature (temperature region where two phases of γ phase and γ'coexist), a normal forging device (a forging device without a special heating and heat retaining mechanism) was used. In this case, the manufacturing yield is likely to decrease due to the temperature decrease during the forging process (their unwanted precipitation of the γ'phase).

From the viewpoint of energy saving and global environmental protection in recent years, it is expected that the main fluid temperature will be raised to improve the thermal efficiency of the turbine, and the turbine output will be increased by lengthening the turbine blades. That means that the usage environment of the turbine high temperature member will become more severe in the future, and the turbine high temperature member is required to have further improved mechanical properties. On the other hand, as described above, cost reduction of industrial products (in particular, improvement of molding processability/molding processability and improvement of manufacturing yield) is one of the most important issues.

On the other hand, one of the technologies for manufacturing compacts/moldings of difficult-to-process materials at low cost is powder metallurgy technology using metal powder.

For example, in Patent Document 3 (US Pat. No. 5,649,280), a fine-grained Ni-base superalloy preform (for example, a solidified metal powder preform) is completely recrystallized by a heat treatment in a subsequent step to be uniform. Forging so as to give residual strain to form a fine structure with a small grain size, and a long-time subsolvus at a temperature higher than the recrystallization temperature and lower than the γ'phase solvus temperature for the forged material. Performing a heat treatment step, and subsequently performing a step of precipitating a γ′ phase in the alloy material and cooling it at a predetermined cooling rate from the subsolvus temperature in order to control the distribution, and the particles of the Ni-based superalloy material A method of controlling the diameter is disclosed.

However, the method of Patent Document 3 uses powder metallurgy as a means for refining the particle size of the preform to be forged in order to control the particle size of the final Ni-based superalloy material. However, there is no teaching or suggestion of a technique for improving the moldability/moldability of difficult-to-process materials.

Even if it is a powder, the strong precipitation strengthened Ni-based alloy material cannot be said to have extremely good moldability/moldability due to the hardness of each powder particle. Therefore, conventionally, when applying a powder metallurgy technique, high temperature and/or high pressure processing was required, and it was difficult to drastically reduce the manufacturing cost of a strong precipitation strengthening Ni-based alloy member. In other words, if there is a Ni-based alloy powder that has high formability/formability and is suitable for powder metallurgy, it is expected that the production cost of strong precipitation strengthened Ni-based alloy members will be dramatically reduced. To be done.

The present invention has been made in view of the above problems, and an object thereof is a powder having a better formability/formability than the conventional one while using a strong precipitation strengthened Ni-based alloy material. Another object of the present invention is to provide a softened Ni-based alloy softening powder and a method for producing the softened powder.

(I) One aspect of the present invention is a Ni-based alloy softening powder,
The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount at 700° C. of the γ′ phase that precipitates in the γ phase that is the mother phase is 30% by volume or more and 80% by volume or less, and the average of the softening powder is Particle size is 5μm or more 500μm or less, the particles of the softening powder is a powder composed of a polycrystalline body of fine crystals of the γ phase,
20% by volume or more of the γ'phase is deposited on the grain boundaries of the fine crystals of the γ phase that constitute the particles,
A Ni-based alloy softening powder, characterized in that the particles have a Vickers hardness at room temperature of 370 Hv or less.

In the present invention, the following improvements and changes can be added to the above Ni-based alloy softening powder (I).
(I) The chemical composition is 5 mass% or more and 25 mass% or less of Cr (chrome), 0 mass% to 30 mass% or less of Co (cobalt), and 1 mass% or more and 8 mass% or less of Al (aluminum). ), and a total of 1% by mass or more and 10% by mass or less of Ti (titanium), Nb (niobium) and Ta (tantalum), 10% by mass or less of Fe (iron), and 10% by mass or less of Mo (molybdenum). , 8 mass% or less W (tungsten), 0.1 mass% or less Zr (zirconium), 0.1 mass% or less B (boron), 0.2 mass% or less C (carbon), and 2 mass% or less It contains Hf (hafnium), 5 mass% or less of Re (rhenium), and 0.003 mass% or more and 0.05 mass% or less of O (oxygen), and the balance is Ni and inevitable impurities.
(Ii) The chemical composition is such that the solid solution temperature of the γ'phase is 1100°C or higher.
(Iii) The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount of the γ′ phase at 700° C. is 45% by volume or more and 80% by volume or less.
(Iv) The Vickers hardness at room temperature of the particles is 350 Hv or less.

(II) Another aspect of the present invention is a method for producing the above Ni-based alloy softening powder,
The manufacturing method,
A precursor powder preparation step of preparing a precursor powder having powder particles having the above chemical composition and composed of a polycrystal of fine crystals of the γ phase,
The precursor powder is heated to a temperature not lower than the melting point of the γ phase above the solid solution temperature of the γ′ phase (in the present invention, referred to as high temperature), and the γ′ phase is referred to as the γ phase. After the solid solution, the powder particles are subjected to a high temperature-slow cooling heat treatment for gradually cooling from the temperature to a temperature lower than the solid solution temperature of the γ′ phase at a cooling rate of 100° C./h or less. A powder softening high temperature-annealing heat treatment step for producing the Ni-based alloy softening powder in which the γ'phase is deposited in an amount of 20% by volume or more on the grain boundaries of the fine crystals of the γ phase constituting the A method for producing a softening powder of Ni-based alloy is provided.

(III) Yet another aspect of the present invention is a method for producing the above Ni-based alloy softening powder,
The manufacturing method,
A single-phase precursor powder preparation step of preparing a single-phase precursor powder having a chemical composition and powder particles comprising a polycrystal of a single-phase fine crystal of the γ phase,
With respect to the single-phase precursor powder, by heating to a temperature lower than the solid solution temperature of 80° C. lower than the solid solution temperature of the γ′ phase (in the present invention, referred to as sub-high temperature). On the grain boundary of the single-phase fine crystal of the γ-phase constituting the particles of the single-phase precursor powder, a sub-high temperature-slow cooling heat treatment for gradually cooling at a cooling rate of 100° C./h or less from the temperature is performed. And a powder softening sub-high temperature-slow cooling heat treatment step for producing the Ni-based alloy softening powder in which the γ'phase is precipitated in an amount of 20% by volume or more, and a method for producing a Ni-based alloy softening powder, To do.

(IV) Yet another aspect of the present invention is a method for producing the above Ni-based alloy softening powder,
The manufacturing method,
A single-phase precursor powder preparation step of preparing a single-phase precursor powder having a chemical composition and powder particles comprising a polycrystal of a single-phase fine crystal of the γ phase,
With respect to the single-phase precursor powder, after heating to a temperature lower than the melting point of the γ phase at a solid solution temperature of the γ'phase or higher, 100 to a temperature lower than the solid solution temperature of the γ'phase from the temperature. By performing a high temperature-slow cooling heat treatment for slow cooling at a cooling rate of ℃/h or less, the γ'phase is formed on the grain boundaries of the single phase fine crystal of the γ phase constituting the particles of the single phase precursor powder. And a powder softening high temperature-annealing heat treatment step for producing the Ni-based alloy softening powder precipitated in an amount of 20% by volume or more.

INDUSTRIAL APPLICABILITY In the present invention, the following improvements and changes can be added to the above-mentioned production methods (II) to (IV) for softening Ni-based alloy powder.
(V) The precursor powder preparing step or the single-phase precursor powder preparing step includes an atomizing element step.

In the present invention, the equilibrium precipitation amount of γ′ phase at 700° C., the solid solution temperature, and the melting point (solidus temperature) of the γ phase are equilibrium determined by thermodynamic calculation based on the chemical composition of the Ni-based alloy material. The amount of precipitation and the temperature can be used.

According to the present invention, while using a strong precipitation strengthened Ni-based alloy material, a powder having better moldability/moldability than before, which is suitable for powder metallurgy, a Ni-based alloy softening powder and the softening powder A manufacturing method can be provided. Further, by applying powder metallurgy technology using the Ni-based alloy softening powder, it becomes possible to provide a strong precipitation-strengthened Ni-based alloy member with a high production yield (that is, at a lower cost than conventional). ..

It is a schematic diagram which shows the relationship between (gamma) phase and (gamma)' phase in precipitation strengthening Ni base alloy material, (a) When (gamma)' phase precipitates in the crystal grain of (g) phase, (b) The crystal grain of (gamma) phase This is the case where the γ'phase is precipitated on the grain boundaries of. It is a flow figure showing an example of a process of a manufacturing method of a Ni basis alloy member using a Ni basis alloy softening powder concerning the present invention. FIG. 3 is a schematic diagram showing an example of changes in the microstructure of Ni-based alloy powder in the manufacturing method according to the present invention. FIG. 6 is a flow chart showing another example of steps of a method for manufacturing a Ni-based alloy member using the Ni-based alloy softening powder according to the present invention. FIG. 3 is a schematic diagram showing an example of changes in the microstructure of the Ni-based alloy powder in the single-phase precursor powder preparation step-powder softening sub-high temperature-annealing heat treatment step. FIG. 6 is a flow chart showing still another example of the steps of the method for producing a Ni-based alloy member using the Ni-based alloy softening powder according to the present invention.

[Basic idea of the present invention]
The present invention is based on the mechanism of precipitation strengthening/softening in the γ'phase precipitation Ni-based alloy material described in Patent Document 2 (Patent No. 5869624). FIG. 1 is a schematic diagram showing a relationship between a γ phase and a γ′ phase in a precipitation strengthened Ni-based alloy material. (a) When the γ′ phase is precipitated in the crystal grains of the γ phase, (b) γ This is the case where the γ′ phase is precipitated on the grain boundaries of the crystal grains of the phase.

As shown in FIG. 1A, when the γ′ phase is precipitated in the crystal grains of the γ phase, the atom 1 forming the γ phase and the atom 2 forming the γ′ phase form the matching interface 3. (The γ'phase precipitates while lattice matching with the γ phase). Such a γ'phase is referred to as an intragranular γ'phase (sometimes referred to as a matched γ'phase). The intragranular γ'phase is considered to hinder the movement of dislocations within the γ-phase crystal grains because it forms the matching interface 3 with the γ-phase, thereby improving the mechanical strength of the Ni-based alloy material. it is conceivable that. The precipitation-strengthened Ni-based alloy material usually means the state shown in FIG.

On the other hand, as shown in FIG. 1B, when the γ′ phase is precipitated on the grain boundaries of the γ phase crystal grains (in other words, between the γ phase crystal grains), the atoms forming the γ phase are 1 and the atom 2 forming the γ′ phase form a non-coherent interface 4 (the γ′ phase is precipitated in a state not lattice-matched with the γ phase). Such a γ'phase is referred to as a grain boundary γ'phase (may be referred to as an intergranular γ'phase or an incoherent γ'phase). The grain boundary γ′ phase does not hinder the movement of dislocations within the γ phase crystal grain because it forms the non-coherent interface 4 with the γ phase. As a result, it is considered that the grain boundary γ'phase hardly contributes to the strengthening of the Ni-based alloy material. From these facts, in the Ni-based alloy material, if the grain boundary γ′ phase is positively deposited instead of the intragranular γ′ phase, the alloy material becomes in a softened state and the formability is dramatically improved. be able to.

The present invention does not precipitate a grain boundary γ′ phase by performing hot forging in a two-phase coexisting temperature region of γ phase/γ′ phase on an alloy lump (ingot) as in Patent Document 2, Forming a precursor powder/single-phase precursor powder of a Ni-based alloy in which powder particles are composed of a polycrystal of γ-phase fine crystals or single-phase fine crystals, and the precursor powder/single-phase precursor powder A major feature of the softening powder is that the grain boundary γ′ phase is precipitated in an amount of 20% by volume or more on the grain boundaries of the fine crystals of the γ phase constituting the powder particles by subjecting the powder to a predetermined heat treatment. It can be said that the Ni-based alloy precursor powder/single-phase precursor powder is one of the key points.

The precipitation of the γ'phase basically requires the diffusion and rearrangement of the atoms that form the γ'phase. It is considered that the γ′ phase preferentially precipitates in the γ phase crystal grains, which requires a short rearrangement distance. Even if it is a cast material, it cannot be denied that the γ'phase is precipitated on the grain boundaries of the γ-phase crystal.

On the other hand, when the γ-phase crystal grains become finer, the distance to the crystal grain boundary becomes shorter, and the grain boundary energy becomes higher than the volume energy of the crystal grain. Rather than solid-phase diffusion and rearrangement within the crystal grains, it is considered that diffusion on the crystal grain boundaries of the γ phase and rearrangement on the grain boundaries has an energy advantage and is likely to occur preferentially. ..

Here, in order to promote the formation of the γ′ phase on the grain boundary of the γ phase, at least in the temperature region where the γ′ phase forming atoms easily diffuse (for example, near the solid solution temperature of the γ′ phase) It is important to maintain the crystal grains in a fine state (in other words, suppress grain growth of γ-phase crystal grains). Therefore, the present inventors have earnestly studied a technique for suppressing the grain growth of γ phase crystal grains even in the vicinity of the solid solution temperature of the γ′ phase or in the temperature region above the solid solution temperature.

As a result, by forming a Ni-based alloy powder containing a controlled amount of a predetermined amount of oxygen component, the powder particles will be composed of a polycrystalline γ-phase fine crystal (powder particles It was found that the grain boundaries of the γ-phase fine crystals exist inside the powder particles, which are composed of the γ-phase fine crystals. Furthermore, such powder particles can suppress the grain growth of γ phase fine crystals even if the temperature is raised to around the solid solution temperature of the γ′ phase or above the solid solution temperature (the powder particles are single crystal bodies of the γ phase). It was found that the grain boundary γ'phase can be positively precipitated and grown on the grain boundaries of the γ phase fine crystal by maintaining the polycrystal without changing the temperature) and gradually cooling from the temperature. .. The present invention is based on this finding.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments taken up here, and can be appropriately combined with the known technology or improved based on the known technology without departing from the technical idea of the invention. ..

[Production method of Ni-based alloy softening powder]
FIG. 2 is a flow chart showing a process example of a method for manufacturing a Ni-based alloy member using the Ni-based alloy softening powder according to the present invention. As shown in FIG. 2, the manufacturing method of the Ni-based alloy member using the Ni-based alloy softening powder of the present invention is roughly a polycrystalline body having a predetermined chemical composition and powder particles of γ-phase fine crystals. A precursor powder preparation step (S1) for preparing a precursor powder composed of the above, and a predetermined high temperature-slow cooling heat treatment is applied to the precursor powder to precipitate 20% by volume or more of the grain boundary γ'phase. A powder softening high temperature-slow cooling heat treatment step (S2) for producing a Ni-based alloy softened powder, and a molding processing step (S3) for forming a molded body having a desired shape by powder metallurgy technology using the softened powder. A solution-aging heat treatment step of subjecting the formed body to a solution heat treatment for forming a solid solution of a grain boundary γ'phase in the γ phase and an aging heat treatment for precipitating an intragranular γ'phase in the crystal grains of the γ phase (S4), and. The precursor powder preparation step S1 and the powder softening high temperature-slow cooling heat treatment step S2 are the method for producing the Ni-based alloy softening powder according to the present invention.

Incidentally, the precursor powder, the powder particles are composed of a polycrystalline γ-phase fine crystals, γ'phase is not precipitated on the grain boundaries of the γ-phase fine crystals (at least intentionally A powder in a state where the grain boundary γ'phase is not precipitated). The softening powder refers to a powder in which 20% by volume or more of the grain boundary γ'phase is precipitated on the grain boundary of the γ phase fine crystal.

FIG. 3 is a schematic diagram showing an example of changes in the microstructure of the Ni-based alloy powder in the manufacturing method according to the present invention. First, the Ni-based alloy precursor powder prepared in the precursor powder preparing step is a powder having an average particle size of 500 μm or less, and the powder particles are composed of a polycrystal of γ-phase fine crystals. Strictly speaking, it is strongly affected by the temperature history (eg, cooling rate) in the process of forming the precursor powder, but the γ phase (consistent γ′ phase) is not precipitated in the γ phase fine crystal. The fine crystals and the γ phase fine crystals in which the γ′ phase in the grains are partially precipitated may coexist. Intragranular γ'phase is not precipitated γ-phase fine crystals or γ-phase fine crystals in the region where intragranular γ'phase is not precipitated is the composition before the supersaturated state of γ'phase or γ'phase is formed. It is considered to be in a fluctuating state.

In addition, the particles of the precursor powder are basically composed of a polycrystal of γ-phase fine crystals, but it cannot be ruled out that a part of the particles is composed of a γ-phase single crystal. .. In other words, in the precursor powder, most of the particles are composed of a polycrystal of gamma phase fine crystals, but particles composed of a gamma phase single crystal may be mixed.

Next, the precursor powder is heated to a temperature above the solid solution temperature of the γ'phase and below the melting point of the γ phase. When the heating temperature is equal to or higher than the solid solution temperature of the γ'phase, in terms of thermal equilibrium, all the γ'phases are solid-dissolved in the γ phase to form the γ phase single phase. In the present invention, at this stage, it is important to maintain the powder particles in a state of being a polycrystalline body of γ-phase fine crystals (preventing excessive coarsening of the γ-phase fine crystals).

Next, by gradually cooling from the heating temperature at a cooling rate of 100° C./h or less, a softened powder in which 20% by volume or more of the grain boundary γ′ phase is precipitated on the grain boundaries of the γ phase fine crystals of the powder particles is obtained. .. Since the softening powder has a sufficiently small amount of precipitation of the intragranular γ'phase, the mechanism of precipitation strengthening does not act, and the formability/formability is dramatically improved. Since the surface of the powder particle can be regarded as a kind of grain boundary of the γ-phase fine crystal, the γ′ phase precipitated on the surface of the powder particle is also regarded as the grain boundary γ′ phase.

As shown in FIG. 2, next, the softening powder obtained is used to apply a powder metallurgy technique to form a molded body having a desired shape (molding step S3). At this time, since the softening powder of the present invention has dramatically improved molding processability as compared with the conventional strong precipitation strengthening Ni-based alloy powder, the temperature and/or pressure during the molding process can be kept higher than the conventional one. Can also be lowered. This means that the apparatus cost and/or the process cost can be reduced in the molding process.

After that, the formed body having the desired shape is subjected to solution heat treatment in which most of the grain boundary γ'phase is dissolved in the γ phase (for example, the grain boundary γ'phase is set to 10% by volume or less). Then, an aging heat treatment for precipitating an intragranular γ'phase in an amount of 30% by volume or more in the crystal grains of the γ phase is performed (solution treatment-aging heat treatment step S4). As a result, a strong precipitation strengthened Ni-based alloy member having a desired shape and being sufficiently precipitation strengthened can be obtained. The ease of the molding process by using the softening powder of the present invention leads to a reduction in the device cost, a reduction in the process cost, and an improvement in the production yield (that is, a reduction in the production cost of the Ni-based alloy member).

The obtained strong precipitation strengthened Ni-based alloy member can be suitably used as a next-generation turbine high temperature member (for example, turbine rotor blade, turbine stationary blade, rotor disk, combustor member, boiler member, heat resistant coating material).

As described above, the technique of Patent Document 2 intentionally leaves the coherent γ′ phase (intragranular γ′ phase) while precipitating the noncoherent γ′ phase (grain boundary γ′ phase, intergranular γ′ phase). Since a softened body is produced, highly precise control is required. On the other hand, the technique of the present invention produces a softened powder in which the intragranular γ'phase is once eliminated and then the grain boundary γ'phase is precipitated. In the present invention, since the softened powder can be obtained by the combination of the precursor powder forming step S1 with low industrial difficulty and the powder softening high temperature-slow cooling heat treatment step S2 with low industrial difficulty, it is more versatile than the technique of Patent Document 2. The cost is high and the cost of the entire manufacturing process can be reduced. In particular, it is effective for producing a softened powder made of a super strong precipitation strengthened Ni-based alloy material having a volume ratio of γ'phase of 45% by volume or more.

In the following, each step of S1 to S2 above will be described in more detail.

(Precursor powder preparation step S1)
This step S1 is a step of preparing a Ni-based alloy precursor powder having a predetermined chemical composition (in particular, intentionally containing a predetermined amount of oxygen component). As a method/method for preparing the precursor powder, basically the conventional method/method can be used. For example, a master alloy ingot preparation step (S1a) of preparing a master alloy ingot by mixing, melting, and casting raw materials so as to have a predetermined chemical composition, and forming a precursor powder from the master alloy ingot. The atomizing element process (S1b) is performed. If necessary, a classifier step (S1c) for making the particle size of the precursor powder uniform may be performed.

It is preferable to control the oxygen content in the atomizing element process S1b. As the atomizing method, the conventional method/method can be used except that the oxygen content in the Ni-based alloy is controlled. For example, a gas atomizing method or a centrifugal atomizing method while controlling the oxygen amount (oxygen partial pressure) in the atomizing atmosphere can be preferably used.

The content of the oxygen component in the precursor powder (sometimes referred to as the content rate) is preferably 0.003 mass% (30 ppm) or more and 0.05 mass% (500 ppm) or less, more preferably 0.005 mass% or more and 0.04 mass% or less. , More preferably 0.007 mass% or more and 0.02 mass% or less. If it is less than 0.003 mass %, the effect of suppressing the grain growth of γ-phase fine crystals is small, and if it exceeds 0.05 mass %, the mechanical strength and ductility of the final Ni-based alloy member are reduced. It is considered that the oxygen atoms form a solid solution inside the powder particles or generate nuclei of oxide on the surface or inside.

From the viewpoint of strong precipitation strengthening and the efficiency of formation of grain boundary γ'phase grains, it is preferable to adopt, as the chemical composition of the Ni-based alloy, one in which the γ'phase solid solution temperature is 1020°C or higher. It is more preferable to use a material having a temperature of 1050° C. or higher, and it is more preferable to use a material having a temperature of 1100° C. or higher. Details of the chemical composition other than oxygen components will be described later.

The average particle size of the precursor powder is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less, still more preferably 20 μm or more and 200 μm or less. When the average particle size of the precursor powder is less than 5 μm, the handling property in the next step S2 is deteriorated, and the powder particles are easily coalesced with each other during the next step S2, which makes it difficult to control the average particle size of the softened powder. If the average particle size of the precursor powder exceeds 500 μm, it becomes a factor that the shape controllability and the shape accuracy of the molded product are deteriorated in the subsequent molding process. The average particle size of the precursor powder can be measured using, for example, a laser diffraction type particle size distribution measuring device.

As described above, the particles of the precursor powder basically consist of a polycrystalline body of γ-phase fine crystals, and the average grain size of the γ-phase fine crystals in the powder particles is 5 μm or more and 50 μm or less. Is preferred. Further, when the precursor powder is formed by rapid solidification as in the atomization method, normally, the γ'phase (for example, a eutectic γ'phase that directly crystallizes from the liquid phase) precipitates on the grain boundaries of the γ phase fine crystals. do not do.

(Powder softening high temperature-slow cooling heat treatment step S2)
In this step S2, the precursor powder prepared in the previous step S1 is heated to a temperature equal to or higher than the solid solution temperature of the γ′ phase to once dissolve the γ′ phase in the γ phase, and then from the temperature. It is a step of producing a softened powder by generating and increasing the grain boundary γ′ phase by slow cooling. In order to suppress undesired coarsening of the γ-phase fine crystals during this step as much as possible, the slow cooling start temperature is preferably lower than the melting point of the γ-phase (below the solidus temperature) and 35°C higher than the solid-solution temperature of the γ'phase. The temperature is preferably higher than or equal to the high temperature, and more preferably 25° C. or higher than the solid solution temperature of the γ′ phase.

If the melting point of the γ phase is lower than the “solid solution temperature of the γ′ phase +35°C” or the “solid solution temperature of the γ′ phase +25°C”, the “less than the melting point of the γ phase” naturally takes precedence. ..

The heat treatment atmosphere is a non-oxidizing atmosphere (an atmosphere containing no partial pressure of oxygen that causes oxidation) to prevent undesired oxidation of the Ni-based alloy powder (oxidation exceeding the oxygen content controlled in the previous step S1). If there is no particular limitation, a reducing atmosphere (for example, hydrogen gas atmosphere) is more preferable.

Also, in this step S2, it cannot be denied that the intragranular γ'phase does not completely disappear as a result of the high temperature-slow cooling heat treatment, and that it exists only slightly. For example, assuming that the grain boundary γ′ phase is precipitated in an amount of 20% by volume or more, if the amount of the intragranular γ′ phase is 10% by volume or less, the molding processability in the subsequent molding process step is strongly hindered. It is acceptable because it does not. The amount of the intragranular γ'phase present is more preferably 5% by volume or less, further preferably 3% by volume or less.

Here, in the technique of Patent Document 2, when the Ni-based alloy forging material obtained by the melting/casting/forging process is heated to a temperature higher than the solid solution temperature of the γ′ phase, the grain boundary movement of the γ phase crystal is pinned. Since the γ′ phase that has been removed disappears, the γ-phase crystal grains are likely to suddenly become coarse. As a result, precipitation/growth of the grain boundary γ′ phase is scarcely promoted even if the material is heated to or above the solid solution temperature of the γ′ phase and then gradually cooled as in this step S2.

On the other hand, in the present invention, the precursor powder prepared in the precursor powder preparing step S1 contains more oxygen component as the alloy composition than the conventional Ni-based alloy material (see that it contains a large amount of oxygen component. Controlled by). Then, when such a precursor powder is subjected to a heat treatment at a solid solution temperature of the γ'phase or higher, it is considered that the contained oxygen atoms combine with the metal atoms of the alloy to form a local oxide.

It is considered that the oxide formed at this time suppresses the grain boundary migration of γ-phase fine crystals (that is, grain growth of γ-phase fine crystals). That is, it is considered that even if the γ'phase disappears in this step S2, the coarsening of the γ phase fine crystals can be prevented.

As described above, the strengthening mechanism of the precipitation strengthened Ni-based alloy material is that it contributes to strengthening by forming a coherent interface between the γ phase and the γ′ phase, and the non-coherent interface does not contribute to strengthening. By reducing the amount of intragranular γ'phase (coherent γ'phase) and increasing the amount of grain boundary γ'phase (intergranular γ'phase, non-coherent γ'phase), it has excellent moldability. A softened powder can be obtained.

ㆍLower cooling rate in the slow cooling process is more advantageous for precipitation and growth of grain boundary γ'phase. The cooling rate is preferably 100° C./h or less, more preferably 50° C./h or less, even more preferably 10° C./h or less. If the cooling rate is higher than 100° C./h, the intragranular γ′ phase is preferentially precipitated and the effect of the present invention cannot be sufficiently obtained.

Specifically, in order to secure excellent moldability/moldability, it is preferable to gradually cool the grain boundary γ′ phase to a temperature at which the precipitation amount is 20% by volume or more. It is more preferable that the amount of precipitation is 30% by volume or more. At this time, the precipitation amount of the intragranular γ'phase is preferably 10% by volume or less, and more preferably 5% by volume or less. The precipitation amount of the γ′ phase can be measured by microstructural observation and image analysis (for example, ImageJ, public domain software developed by National Institutes of Health in the US).

As an example of the end temperature of the slow cooling process, when the γ'phase solid solution temperature is relatively low 1020 °C or more and less than 1100 °C, a temperature lower than the γ'phase solid solution temperature by 50 °C or more is preferable, and the γ'phase solid solution A temperature lower than the temperature by 100° C. or more is more preferable, and a temperature lower than the γ′ phase solid solution temperature by 150° C. or more is further preferable. Further, when the γ'phase solid solution temperature is 1100°C or higher which is relatively high, the end temperature of the slow cooling process is preferably 100°C or more lower than the γ'phase solid solution temperature, and 150°C from the γ'phase solid solution temperature. The lower temperature is more preferable, and the temperature lower than the γ'phase solid solution temperature by 200°C or more is further preferable. More specifically, it is preferable to gradually cool to a temperature of 1000°C or lower and 800°C or higher.

For cooling from the slow cooling end temperature, a higher cooling rate is preferable in order to suppress precipitation of the intragranular γ'phase during cooling (for example, to set the precipitation amount of the intragranular γ'phase to 10% by volume or less). For example, water cooling or gas cooling is preferable.

The Vickers hardness (Hv) of the softened powder at room temperature can be used as an index of moldability/moldability. The softened powder obtained by performing this step S2 has a room temperature Vickers hardness even if it is a super strong precipitation strengthening Ni-based alloy material such that the equilibrium precipitation amount of the γ'phase at 700°C is 45% by volume or more. You can get less than 370 Hv. The room temperature Vickers hardness is more preferably 350 Hv or less, and further preferably 330 Hv or less.

FIG. 4 is a flow chart showing another example of steps of the method for manufacturing a Ni-based alloy member using the Ni-based alloy softening powder according to the present invention. As shown in FIG. 4, another manufacturing method of the Ni-based alloy softening powder using the Ni-based alloy softening powder of the present invention is a manufacturing method of the Ni-based alloy softening powder (single-phase precursor powder preparation step S1′ and powder In the softening sub-high temperature-slow cooling heat treatment step S2'), unlike the step of FIG. 2, the forming step S3 and the solution-aging heat treatment step S4 are the same as those of FIG. FIG. 5 is a schematic diagram showing an example of changes in the microstructure of the Ni-based alloy powder in steps S1' and S2'.

Hereinafter, the steps S1′ to S2′ (that is, the other method for producing the Ni-based alloy softening powder according to the present invention) will be described focusing on the difference from the steps S1 to S2 described above with reference to FIGS. Explained.

(Single-phase precursor powder preparation step S1')
This step S1′ is a step of preparing a single-phase precursor powder having a predetermined chemical composition and powder particles composed of a single-phase microcrystalline polycrystal of γ phase. In the present invention, the single-phase precursor powder means a γ-phase single-phase (γ′) measured by a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX) and/or an X-ray diffractometer (XRD). It means a powder that can be judged to have no phase detected). It does not require strictness at the level of transmission electron microscope (TEM) or scanning transmission electron microscope (STEM).

This step S1' includes a mother alloy ingot producing element step (S1a) similar to step S1, and an atomizing element step (S1'b) for forming a single-phase precursor powder, and if necessary, the step The classifier step (S1c) similar to S1 may be performed. The atomizing element step S1'b is the same atomizing method as the atomizing element step S1b of step S1 except that the average cooling rate in the temperature range where the γ'phase is easily generated and precipitated (eg, 1100°C to 600°C) is controlled. Is available. The average cooling rate to be controlled is preferably 500° C./min or higher, more preferably 1000° C./min or higher, further preferably 1500° C./min or higher, most preferably 2000° C./min or higher.

As a result of the step S1' (particularly, the atomizing element step S1'b), a single-phase precursor powder composed of a single-phase fine-crystal polycrystal of the γ phase is obtained as shown in FIG. The content of the oxygen component in the single-phase precursor powder, the average grain size, and the average crystal grain size of the single-phase fine crystals are the same as those of the precursor powder obtained in step S1.

(Powder softening sub-high temperature-slow cooling heat treatment step S2')
This step S2' is a Ni-based alloy in which 20 volume% or more of the grain boundary γ'phase is precipitated by subjecting the single-phase precursor powder prepared in the previous step S1' to a predetermined sub-high temperature-annealing heat treatment. This is a step of producing a softened powder. Sub-high temperature-slow cooling heat treatment is heating at a temperature 80°C lower than the solid solution temperature of the γ'phase to a temperature lower than the solid solution temperature, and then gradually cooled from that temperature at a cooling rate of 100°C/h or less. Heat treatment. The heating temperature (that is, the gradual cooling start temperature) is more preferably 50° C. or more lower than the solid solution temperature of the γ′ phase, and further preferably 30° C. or more lower than the solid solution temperature of the γ′ phase. As in step S2, the cooling rate in the slow cooling process is preferably 50° C./h or less, more preferably 10° C./h or less.

Since the single-phase precursor powder is used, the grain boundary γ'phase preferentially nucleates and grows even when the slow cooling start temperature is in the sub-high temperature range (see Fig. 5). Further, regarding the gradual cooling end temperature in step S2′, the cooling from the gradual cooling end temperature, the precipitation amount of the grain boundary γ′ phase and the existing amount of the intragranular γ′ phase as a result of the sub-high temperature-gradual cooling heat treatment, It is similar to those of the softened powder obtained in S2.

Here, a little consideration is given to the reason why the softened powder similar to the softened powder obtained in step S2 can be obtained by the sub-high temperature-slow cooling heat treatment for the single-phase precursor powder. The exact mechanism has not been clarified at this stage, but it is possible that the single-phase precursor powder composed of a single-phase microcrystalline polycrystal of the γ phase is an important point. Can be considered.

For a single-phase crystal of the γ phase (in the situation where the γ′ phase is substantially absent), a temperature of 80° C. or more lower than the solid solution temperature of the γ′ phase and lower than the solid solution temperature (in the present invention, a sub-high temperature) Is considered to be a temperature range in which the degree of supercooling associated with the precipitation of the γ'phase is small. Precipitation of the γ'phase (that is, intragranular γ'phase) in the γ-phase crystal is considered to be a kind of homogeneous nucleation (at least a phenomenon similar to homogeneous nucleation). In other words, the nucleation frequency of the intragranular γ'phase in the sub-high temperature region in the γ-phase single-phase crystal is considered to be very low.

On the other hand, it is considered that oxygen atoms are unevenly distributed or fine oxides are formed in the grain boundaries of the single-phase fine crystal of the γ phase, as described above. In this case, it is considered that the grain boundaries of the fine crystals are likely to act as heterogeneous nucleation sites for the γ'phase. Furthermore, from the viewpoint of thermodynamics, since the activation energy of heterogeneous nucleation is much lower than that of homogeneous nucleation, it is known that the nucleation frequency is sufficiently high even in a state of low supercooling. There is.

Taking these into consideration comprehensively, the sub-high temperature-slow cooling heat treatment for the single-phase precursor powder is performed by competing the homogeneous nucleation and the heterogeneous nucleation in the temperature region where the degree of supercooling of the γ′ phase is small, It is considered that the heat treatment is carried out by preferentially nucleating the grain boundary γ'phase due to the heterogeneous nucleation, and then grain-growing the nuclei generated in the slow cooling process. The consideration (model) is considered to be applicable to "preferential nucleation of grain boundary γ'phase and subsequent grain growth of grain boundary γ'phase" in the powder softening high temperature-slow cooling heat treatment step S2.

Note that the present invention does not deny that the powder softening high temperature-slow cooling heat treatment step S2 is applied to the single-phase precursor powder. FIG. 6 is a flow chart showing still another process example of the method for producing a Ni-based alloy member using the Ni-based alloy softening powder according to the present invention. As shown in FIG. 6, the manufacturing method of the Ni-based alloy member using the Ni-based alloy softening powder of the present invention is, in the production of the Ni-based alloy softening powder, after the single-phase precursor powder preparing step S1′. The powder softening high temperature-slow cooling heat treatment step S2 is performed. The forming step S3 and the solution heat treatment-aging heat treatment step S4 may be the same as those in FIG.

(Chemical composition of Ni-based alloy softening powder)
The chemical composition of the Ni-based alloy material used in the present invention will be described. The Ni-based alloy material has a chemical composition such that the equilibrium precipitation amount of the γ′ phase at 700° C. is 30% by volume or more and 80% by volume or less. Specifically, in mass%, 5% or more and 25% or less of Cr, 0% or more and 30% or less of Co, 1% or more and 8% or less of Al, and the sum of Ti, Nb, and Ta is 1% or more and 10% or less. Fe of 10% or less, Mo of 10% or less, W of 8% or less, Zr of 0.1% or less, B of 0.1% or less, C of 0.2% or less, Hf of 2% or less, and Re of 5% or less, And a chemical composition containing 0.003% or more and 0.05% or less O and the balance being Ni and inevitable impurities. Hereinafter, each component will be described.

The Cr component dissolves in the γ phase and has the effect of improving the corrosion resistance and oxidation resistance by forming an oxide film (Cr ₂ O ₃ ) on the surface under the actual use environment of the Ni-based alloy material. .. In order to apply it to a turbine high temperature member, it is necessary to add 5 mass% or more. On the other hand, since excessive addition promotes the formation of a harmful phase, it is preferably 25% by mass or less.

　The Co component is an element close to Ni and forms a solid solution in the γ phase in the form of substitution with Ni, and has the effect of improving creep strength and corrosion resistance. Further, it also has the effect of lowering the solid solution temperature of the γ'phase, and improves the high temperature ductility. However, excessive addition promotes the formation of a harmful phase, so the content is preferably more than 0% and 30% by mass or less.

The Al component is an essential component for forming the γ'phase which is the precipitation strengthening phase of the Ni-based alloy. Furthermore, by forming an oxide film (Al ₂ O ₃ ) on the surface of the Ni-based alloy material in the actual use environment, it contributes to the improvement of oxidation resistance and corrosion resistance. The amount is preferably 1% by mass or more and 8% by mass or less depending on the desired amount of γ'phase precipitation.

　Ti component, Nb component and Ta component have the effect of forming γ'phase and improving high temperature strength like Al component. Further, the Ti component and the Nb component also have the effect of improving the corrosion resistance. However, since excessive addition promotes the formation of a harmful phase, it is preferable that the total amount of Ti, Nb, and Ta components is 1% by mass or more and 10% by mass or less.

By replacing the Fe component with the Co component and Ni component, it has the effect of reducing the material cost of the alloy. However, excessive addition promotes the formation of a harmful phase, so it is preferably made 10 mass% or less.

The Mo component and W component have the effect of forming a solid solution in the γ phase to improve the high temperature strength (solid solution strengthening), and it is preferable to add at least one of them. The Mo component also has the effect of improving corrosion resistance. However, since excessive addition promotes the formation of a harmful phase or reduces ductility and high temperature strength, it is preferable that the Mo component is 10 mass% or less and the W component is 8 mass% or less.

Zr component, B component, and C component strengthen the γ-phase grain boundaries (strengthen the tensile strength in the direction perpendicular to the γ-phase grain boundaries) and improve the high temperature ductility and creep strength. There is. However, since excessive addition deteriorates moldability, it is preferable that the Zr component is 0.1 mass% or less, B is 0.1 mass% or less, and C is 0.2 mass% or less.

The Hf component has the effect of improving oxidation resistance. However, since excessive addition promotes the formation of a harmful phase, it is preferable to set the content to 2% by mass or less.

　Re component contributes to the solid solution strengthening of γ phase and also has the effect of contributing to the improvement of corrosion resistance. However, excessive addition promotes the formation of harmful phases. In addition, since Re is an expensive element, increasing the amount of addition has the demerit of increasing the material cost of the alloy. Therefore, Re is preferably 5% by mass or less.

The O component is usually treated as an impurity and is a component to be reduced as much as possible, but in the present invention, as described above, the grain growth of the γ phase fine crystal is suppressed and the formation of grain boundary γ′ phase grains is suppressed. It is an essential ingredient for promotion. The O content is preferably 0.003 mass% or more and 0.05 mass% or less.

Residual components of the Ni-based alloy material become unavoidable impurities other than Ni and O components. Examples of unavoidable impurities other than the O component include N (nitrogen), P (phosphorus), and S (sulfur).

The present invention will be described in more detail below by various experiments. However, the present invention is not limited to these experiments.

[Experiment 1]
(Preparation of Ni-based alloy precursor powders PP1 to PP8 and single-phase precursor powders PP9 to PP10)
A master ingot (10 kg) was prepared by mixing, melting, and casting the Ni-based alloy raw materials. The dissolution was performed by the vacuum induction heating dissolution method. Next, the obtained master ingot was redissolved and a Ni-based alloy powder was produced by the gas atomizing method while controlling the oxygen partial pressure in the atomizing atmosphere.

In the Ni-based alloy powder preparation by the gas atomization method, it was confirmed that some alloy powders had an average cooling rate of 1100°C to 600°C of 500°C/min or more. In addition, when observing the fine structure of the powder particles with SEM-EDX at a magnification of 1000 times, it was not possible to detect the γ'phase and the γ phase It was judged to be a single phase. The fine structure of the powder particles was not observed for the powder for which the average cooling rate was not confirmed during the production of the alloy powder by the gas atomization method.

Next, the obtained Ni-based alloy powder is classified to select alloy powders having a particle size in the range of 25 to 150 μm, and Ni-based alloy precursor powders PP1 to PP8 and single-phase precursor powders PP9 to PP10 are prepared. .. Table 1 shows the chemical compositions of the obtained powders PP1 to PP10.

[Experiment 2]
(Production of Ni-based alloy softening powders of Examples 1 to 11 and Comparative Examples 1 to 12 and evaluation of molding processability)
The precursor powders PP1 to PP8 and the single-phase precursor powders PP9 to PP10 obtained in Experiment 1 were softened under the heat treatment conditions (slow cooling start temperature, slow cooling process cooling rate) shown in Table 2 below. By performing the treatment, the Ni-based alloy softening powders of Examples 1 to 11 and Comparative Examples 1 to 12 were produced. The end temperature of the slow cooling process was 950° C. except for Comparative Examples 1 and 12. In Comparative Examples 1 and 12, gas was rapidly cooled from the slow cooling start temperature to room temperature.

For each softening powder of Ni-based alloy obtained, microstructure observation (grain boundary γ'phase precipitation amount) and room temperature Vickers hardness were measured to evaluate the formability.

The precipitation amount of the grain boundary γ'phase was determined by observing the softened powder with an electron microscope and image analysis (ImageJ). The room temperature Vickers hardness of the softened powder was measured by randomly extracting 10 particles and using a micro Vickers hardness meter (Akashi Seisakusho, Model: MVK-E). Of the 10 particles at room temperature Vickers hardness, the average value of the room temperature Vickers hardness of 8 particles excluding the maximum value and the minimum value was defined as the room temperature Vickers hardness of the softened powder. In the moldability evaluation, a room temperature Vickers hardness of 370 Hv or less was judged as "pass", and a room temperature Vickers hardness of more than 370 Hv was judged as "fail".

Table 2 shows specifications and evaluation results of the Ni-based alloy softening powders of Examples 1 to 11 and Comparative Examples 1 to 12. In Table 2, the equilibrium precipitation amount and the solid solution temperature of the γ'phase at 700°C of the γ'phase are obtained from the alloy composition of Table 1 based on thermodynamic calculation.

As shown in Table 2, the softening powders of Comparative Examples 1 to 7 in which the starting temperature and/or the cooling rate of the slow cooling process in the high temperature-slow cooling heat treatment were out of the range of the present invention, were the precipitation amount of the grain boundary γ'phase. Is less than 20% by volume (instead, an increase in the amount of γ'phase precipitation in grains is confirmed), and the room temperature Vickers hardness is more than 370 Hv. As a result, the moldability was judged to be unacceptable. If the slow cooling start temperature (that is, the heating temperature) in the high temperature-slow cooling heat treatment is too low, or if the cooling rate in the slow cooling process is too high, the grain boundary γ'phase hardly precipitates and grows. It was confirmed that the sex could not be secured.

The softened powder of Comparative Example 8 in which the equilibrium precipitation amount of the γ'phase at 700°C deviates from the definition of the present invention, the softening powder of Comparative Example 8 has an equilibrium precipitation amount of the γ'phase of less than 30% by volume. It does not apply to the targeted strong precipitation strengthened Ni-based alloy materials. However, since the amount of γ'phase precipitation is absolutely small, there has been no particular problem in molding processability/molding processability.

In contrast to Comparative Examples 1 to 8, in the softened powders of Examples 1 to 7, the precipitation amount of the grain boundary γ′ phase was 20% by volume or more, and the room temperature Vickers hardness was 370 Hv or less. As a result, the moldability was judged to be acceptable. That is, the effect of the present invention was confirmed.

In addition, the softened powders of Examples 8 to 9 using the single-phase precursor powders PP9 to PP10 have a grain size even if they are subjected to the sub-high temperature-annealing heat treatment in which the annealing start temperature is lower than the solid solution temperature of the γ'phase. The precipitation amount of the boundary γ'phase is 20% by volume or more, and the room temperature Vickers hardness is 370 Hv or less. As a result, the moldability was judged to be acceptable. That is, the effect of the present invention was confirmed.

Further, the softened powders of Examples 10 to 11 in which the high temperature-slow cooling heat treatment was applied to the single-phase precursor powders PP9 to PP10 also had the precipitation amount of the grain boundary γ'phase of 20% by volume or more, and the room temperature Vickers hardness. Is less than 370 Hv. As a result, the moldability was judged to be acceptable. That is, the effect of the present invention was confirmed.

On the other hand, even if the single-phase precursor powders PP9 to PP10 were used, the softening powders of Comparative Examples 9 to 12 in which the starting temperature or the cooling rate of the slow cooling process in the softening process did not satisfy the requirements of the present invention, the precipitation of the grain boundary γ'phase was observed. The amount is less than 20% by volume, and the room temperature Vickers hardness is more than 370 Hv. As a result, the moldability was judged to be unacceptable. If the slow cooling start temperature in the sub-high temperature-slow cooling heat treatment is too low, or if the cooling rate in the slow cooling process in the high temperature-slow cooling heat treatment is too high, the grain boundary γ'phase hardly precipitates and grows, resulting in sufficient molding. It was confirmed that the workability could not be secured.

From the above results, by applying the method for producing a Ni-based alloy softening powder according to the present invention, even if it is a strong precipitation strengthening Ni-based alloy material or a super strong precipitation strengthening Ni-based alloy material, good moldability/ It has been shown that it is possible to provide a softened powder exhibiting moldability. It is expected that a strong precipitation strengthened Ni-based alloy member can be provided at low cost by applying powder metallurgy technology using the Ni-based alloy softening powder.

The above-described embodiments and experimental examples are described to help understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, a part of the configuration of the embodiment can be replaced with the configuration of the technical common sense of those skilled in the art, and the configuration of the technical common sense of those skilled in the art can be added to the configuration of the embodiment. That is, in the present invention, a part of the configuration of the embodiment or the experimental example of the present specification may be deleted, replaced with another configuration, or added with another configuration without departing from the technical idea of the invention. It is possible.

1... Atoms that make up the γ phase, 2... Atoms that make up the γ'phase, 3... Coherent interface between the γ and γ'phases, 4... Non-coherent interface between the γ and γ'phases

Claims (13)

1. Ni-based alloy softening powder,
   The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount at 700° C. of the γ′ phase that precipitates in the γ phase that is the mother phase is 30% by volume or more and 80% by volume or less, and the average of the softening powder is Particle size is 5μm or more 500μm or less, the particles of the softening powder is a powder composed of a polycrystalline body of fine crystals of the γ phase,
   20% by volume or more of the γ'phase is deposited on the grain boundaries of the fine crystals of the γ phase that constitute the particles,
   The Ni-based alloy softening powder, wherein the particles have a Vickers hardness at room temperature of 370 Hv or less.
2. In the Ni-based alloy softening powder according to claim 1,
   The chemical composition is
   5 mass% or more and 25 mass% or less of Cr,
   Co of more than 0 mass% and 30 mass% or less,
   1% by mass or more and 8% by mass or less of Al,
   1% by mass or more and 10% by mass or less of Ti, Nb and Ta in total,
   Fe of 10 mass% or less,
   Mo of 10 mass% or less,
   W of 8 mass% or less,
   Zr of 0.1 mass% or less,
   B of 0.1 mass% or less,
   0.2% by mass or less of C,
   2% by mass or less of Hf,
   Re of 5 mass% or less,
   Contains 0.003% by mass or more and 0.05% by mass or less of O,
   A Ni-based alloy softening powder, the balance of which is Ni and inevitable impurities.
3. In the Ni-based alloy softening powder according to claim 1 or 2,
   The Ni-based alloy softening powder, wherein the chemical composition is such that the solid solution temperature of the γ'phase is 1100°C or higher.
4. In the Ni-based alloy softening powder according to claim 3,
   The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount of the γ′ phase at 700° C. is 45% by volume or more and 80% by volume or less.
5. The Ni-based alloy softening powder according to any one of claims 1 to 4,
   The Ni-based alloy softening powder, wherein the particles have a Vickers hardness at room temperature of 350 Hv or less.
6. A method for producing a Ni-based alloy softening powder,
   The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount at 700° C. of the γ′ phase that precipitates in the γ phase that is the mother phase is 30% by volume or more and 80% by volume or less, and the average of the softening powder is Particle size is 5μm or more 500μm or less, the particles of the softening powder is a powder composed of a polycrystalline body of fine crystals of the γ phase,
   Room temperature Vickers hardness of the particles is 370 Hv or less,
   The manufacturing method,
   A precursor powder preparation step of preparing a precursor powder having powder particles having the above chemical composition and composed of a polycrystal of fine crystals of the γ phase,
   With respect to the precursor powder, after heating to a temperature below the melting point of the γ phase above the solid solution temperature of the γ'phase to form a solid solution of the γ'phase in the γ phase, the temperature from the temperature By performing a high temperature-slow cooling heat treatment for gradually cooling to a temperature lower than the solid solution temperature of the γ′ phase at a cooling rate of 100° C./h or less, the fine crystals of the γ phase constituting the particles of the precursor powder are formed. A powder softening high temperature-slow cooling heat treatment step of producing the Ni-based alloy softening powder in which 20% by volume or more of the γ'phase is precipitated on a grain boundary, the method for producing a Ni-based alloy softening powder.
7. A method for producing a Ni-based alloy softening powder,
   The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount at 700° C. of the γ′ phase that precipitates in the γ phase that is the mother phase is 30% by volume or more and 80% by volume or less, and the average of the softening powder is Particle size is 5μm or more 500μm or less, the particles of the softening powder is a powder composed of a polycrystalline body of fine crystals of the γ phase,
   Room temperature Vickers hardness of the particles is 370 Hv or less,
   The manufacturing method,
   A single-phase precursor powder preparation step of preparing a single-phase precursor powder having a chemical composition and powder particles comprising a polycrystal of a single-phase fine crystal of the γ phase,
   The single-phase precursor powder is heated to a temperature lower than the solid solution temperature at a temperature 80°C lower than the solid solution temperature of the γ'phase, and a cooling rate of 100°C/h or lower from the temperature. By subjecting the single phase precursor powder to the sub-high temperature-slow cooling heat treatment, 20% by volume or more of the γ′ phase is precipitated on the grain boundaries of the single phase fine crystal of the γ phase that constitutes the particles of the single phase precursor powder. A method for producing a Ni-based alloy softening powder, comprising: a powder softening sub-high temperature-annealing heat treatment step for producing a Ni-based alloy softening powder.
8. A method for producing a Ni-based alloy softening powder,
   The Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount at 700° C. of the γ′ phase that precipitates in the γ phase that is the mother phase is 30% by volume or more and 80% by volume or less, and the average of the softening powder is Particle size is 5μm or more 500μm or less, the particles of the softening powder is a powder composed of a polycrystalline body of fine crystals of the γ phase,
   Room temperature Vickers hardness of the particles is 370 Hv or less,
   The manufacturing method,
   A single-phase precursor powder preparation step of preparing a single-phase precursor powder having a chemical composition and powder particles comprising a polycrystal of a single-phase fine crystal of the γ phase,
   With respect to the single-phase precursor powder, after heating to a temperature lower than the melting point of the γ phase at a solid solution temperature of the γ'phase or higher, 100 to a temperature lower than the solid solution temperature of the γ'phase from the temperature. By performing a high temperature-slow cooling heat treatment for slow cooling at a cooling rate of ℃/h or less, the γ'phase is formed on the grain boundaries of the single phase fine crystal of the γ phase constituting the particles of the single phase precursor powder. A method for producing a Ni-based alloy softening powder, comprising: a powder softening high temperature-annealing heat treatment step of producing the Ni-based alloy softening powder precipitated in an amount of 20% by volume or more.
9. The method for producing a Ni-based alloy softening powder according to any one of claims 6 to 8,
   The chemical composition is
   5 mass% or more and 25 mass% or less of Cr,
   Co of more than 0 mass% and 30 mass% or less,
   1% by mass or more and 8% by mass or less of Al,
   1% by mass or more and 10% by mass or less of Ti, Nb and Ta in total,
   Fe of 10 mass% or less,
   Mo of 10 mass% or less,
   W of 8 mass% or less,
   Zr of 0.1 mass% or less,
   B of 0.1 mass% or less,
   0.2% by mass or less of C,
   2% by mass or less of Hf,
   Re of 5 mass% or less,
   Contains 0.003% by mass or more and 0.05% by mass or less of O,
   A method for producing a Ni-based alloy softening powder, characterized in that the balance comprises Ni and inevitable impurities.
10. The method for producing a Ni-based alloy softening powder according to any one of claims 6 to 9,
    The precursor powder preparation step or the single-phase precursor powder preparation step includes an atomizing element step, and a method for manufacturing a Ni-based alloy softening powder.
11. The method for producing a Ni-based alloy softening powder according to any one of claims 6 to 10,
    The method for producing a Ni-based alloy softening powder, wherein the chemical composition is a chemical composition in which the solid solution temperature of the γ′ phase is 1100° C. or higher.
12. The method for producing a Ni-based alloy softening powder according to claim 11,
    The method for producing a Ni-based alloy softening powder, wherein the Ni-based alloy softening powder has a chemical composition such that the equilibrium precipitation amount of the γ′ phase at 700° C. is 45% by volume or more and 80% by volume or less.
13. The method for producing a Ni-based alloy softening powder according to any one of claims 6 to 12,
    The method for producing a Ni-based alloy softening powder, wherein the particles have a Vickers hardness at room temperature of 350 Hv or less.

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