JP6826235B2 - Ni-based alloy softened powder and method for producing the softened powder - Google Patents

Description

The present invention relates to a technique for a Ni (nickel) -based alloy material, and more particularly to a Ni-based alloy softened powder which is composed of a strongly precipitation-reinforced Ni-based alloy material and is suitable for powder metallurgy technology, and a method for producing the softened powder. ..

In turbines (gas turbines, steam turbines) of aircraft and thermal power plants, increasing the temperature of the main fluid with the aim of improving thermal efficiency has become a technological trend, and improving the mechanical properties of high temperatures in turbine high-temperature members is This is an important technical issue. Turbine high temperature components exposed to the harshest environments (eg, turbine vanes, turbine vanes, rotor disks, combustor components, boiler components) are subject to rotational centrifugal force during operation, vibration, and thermal stress associated with start / stop. It is very important to improve the mechanical properties (for example, creep properties, tensile properties, fatigue properties).

Precipitation-hardened 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 particularly important, strong precipitation strengthened Ni with an increased ratio of the γ'(gamma prime) phase (for example, Ni ₃ (Al, Ti) phase) precipitated in the γ (gamma) phase that is the parent 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 the main manufacturing method, precision casting methods (particularly, one-way solidification method and single crystal solidification method) have been conventionally used for members such as turbine blades and turbine blades from the viewpoint of creep characteristics. On the other hand, in turbine discs and combustor members, the hot forging method has often been used from the viewpoint of tensile characteristics and fatigue characteristics.

However, in the precipitation-strengthened Ni-based alloy material, if the volume fraction of the γ'phase is further increased in order to further enhance the high temperature characteristics of the high temperature member, the workability and moldability deteriorate and the production yield of the high temperature member decreases. There was a weakness that it did (that is, the manufacturing cost increased). Therefore, in parallel with the research on improving the characteristics of the high temperature member, various studies on the technique for stably manufacturing the high temperature member have been conducted.

For example, Patent Document 1 (Japanese Patent Laid-Open No. 9-302450) describes a method for producing a Ni-based superalloy article having a controlled crystal grain size from a preform for forging, wherein a mixture of a γ phase and a γ'phase is prepared. Prepare Ni-based superalloy preforms with microstructure, including microstructure, recrystallization temperature and γ'solvus temperature (where the γ'phase accounts for at least 30% by volume of the Ni-based superalloy) at about 1600 ° F and above. However, at a temperature lower than the γ'solvus temperature, the superalloy preform was hot-molded with a strain rate of about 0.03 to about 10 per second, and the obtained hot-mold forged superalloy work was forged at isothermal. The processed article is formed by supersolvent heat treatment of the finished article to produce a substantially uniform particle microstructure of approximately ASTM 6-8, and the article is cooled from the supersolvent heat treatment temperature. A method consisting of is disclosed.

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

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

As a matter of course, 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) describes a method for producing a Ni-based alloy softening material composed of a Ni-based alloy having a γ'phase solidification temperature of 1050 ° C. or higher, wherein the softening treatment is performed in the next step. The softening treatment step includes a material preparation step of preparing a Ni-based alloy material to be carried out and a softening treatment step of softening the Ni-based alloy material to improve workability, and the softening treatment step is a solidification of the γ'phase. This is a step performed in a temperature range lower than the melting temperature, and is a first step of hot forging the Ni-based alloy material at a temperature lower than the solid melting temperature of the γ'phase and a step lower than the solid melting temperature of the γ'phase. The amount of unmatched γ'phase crystal grains precipitated on the grain boundaries of the γ phase crystal grains, which is the parent phase of the Ni-based alloy, by slowly cooling from the above temperature at a cooling rate of 100 ° C./h or less. A second step of obtaining a Ni-based alloy softening material having an amount of 20% by volume or more is disclosed, and a method for producing a Ni-based alloy softening material, which comprises the method. 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 and molded at low cost.

However, in an ultra-strong precipitation-strengthened Ni-based alloy material in which the volume ratio of the γ'phase is 45% by volume or more (for example, a Ni-based alloy material that precipitates 45 to 80% by volume of the γ'phase), the γ'phase is solid. In the process of hot forging at a temperature lower than the melting temperature (temperature range where two phases of γ phase and γ'phase coexist), a normal forging device (forging device not equipped with a special heat insulation mechanism) was used. In some cases, the production yield tends to decrease due to the temperature decrease during the forging process (resulting in unwanted precipitation of the γ'phase).

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

On the other hand, there is a powder metallurgy technique using a metal powder as one of the techniques for producing a molded body / molded body of a difficult-to-process material at low cost.

For example, in Patent Document 3 (US Patent No. 5649280), a fine-grained Ni-based superalloy preform (for example, a hardened metal powder preform) is completely recrystallized by a heat treatment in a subsequent step to be uniform. In the process of forging so as to impart residual strain for forming a fine structure of fine particle size, and for the forged material, a long-time subsolvus at a temperature higher than the recrystallization temperature and lower than the γ'phase sorbus temperature. A step of performing a heat treatment and subsequently, a step of precipitating the γ'phase in the alloy material and cooling it from the subsolvus temperature at a predetermined cooling rate in order to control the distribution are performed to obtain grains of the Ni-based superalloy material. A method of controlling the diameter is disclosed.

However, the method of Patent Document 3 utilizes powder metallurgy technology as a means for reducing the particle size of the preformed body to be forged in order to control the particle size of the final Ni-based superalloy material. However, no technique has been taught or suggested to improve the moldability / moldability of difficult-to-process materials.

Even if the strong precipitation strengthened Ni-based alloy material is powder, it cannot be said that the molding processability / molding processability is extremely good due to the hardness of each powder particle. Therefore, conventionally, when applying powder metallurgy technology, high temperature and / or high pressure processing is required, and it has been difficult to dramatically reduce the manufacturing cost of a strong precipitation strengthened Ni-based alloy member. In other words, if there is a Ni-based alloy powder that has high molding processability / molding processability and is suitable for powder metallurgy technology, it is expected that the manufacturing cost of the strong precipitation strengthened Ni-based alloy member can be dramatically reduced. Will be done.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain a powder having better molding processability / molding processability than conventional ones while using a strong precipitation strengthened Ni-based alloy material. It is an object of the present invention to provide a Ni-based alloy softened powder suitable for the above and a method for producing the softened powder.

(I) One aspect of the present invention is a Ni-based alloy softened powder.
The Ni-based alloy softened powder has a chemical composition in which the equilibrium precipitation amount of the γ'phase precipitated in the γ phase as the parent phase at 700 ° C. is 30% by volume or more and 80% by volume or less, and the average of the softened powders. The powder has a particle size of 5 μm or more and 500 μm or less, and the particles of the softened powder are composed of polycrystals of fine crystals of the γ phase.
20% by volume or more of the γ'phase is precipitated on the grain boundaries of the fine crystals of the γ phase constituting the particles.
Provided is a Ni-based alloy softened powder, characterized in that the Vickers hardness of the particles at room temperature is 370 Hv or less.

The present invention can make the following improvements and modifications to the above-mentioned Ni-based alloy softened powder (I).
(I) The chemical composition consists of Cr (chromium) of 5% by mass or more and 25% by mass or less, Co (cobalt) of more than 0% by mass and 30% by mass or less, and Al (aluminum) of 1% by mass or more and 8% by mass or less. ), Ti (titanium), Nb (niob) and Ta (tantal) of 1% by mass or more and 10% by mass or less, Fe (iron) of 10% by mass or less, and Mo (molybdenum) of 10% by mass or less. , W (tungsten) of 8% by mass or less, Zr (zirconium) of 0.1% by mass or less, B (boron) of 0.1% by mass or less, C (carbon) of 0.2% by mass or less, and 2% by mass or less. It contains Hf (hafnium), Re (renium) of 5% by mass or less, and O (oxygen) of 0.003% by mass or more and 0.05% by mass or less, and the balance consists of Ni and unavoidable 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 softened powder has a chemical composition in which 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 of the particles at room temperature is 350 Hv or less.

(II) Another aspect of the present invention is a method for producing the above-mentioned Ni-based alloy softened powder.
The manufacturing method is
A precursor powder preparation step of preparing a precursor powder having the chemical composition and having powder particles composed of polycrystals of fine crystals of the γ phase.
The precursor powder is heated to a temperature equal to or higher than the solid solution temperature of the γ'phase and lower than the melting point of the γ phase (referred to as a high temperature in the present invention) to heat the γ'phase to the γ phase. The powder particles are subjected to a high-temperature slow-cooling heat treatment in which the powder particles are slowly cooled 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. It is characterized by having a powder softening high temperature-slow cooling heat treatment step for producing the Ni-based alloy softened powder in which 20% by volume or more of the γ'phase is precipitated on the grain boundaries of the fine crystals of the γ phase. It provides a method for producing a Ni-based alloy softened powder.

(III) Yet another aspect of the present invention is a method for producing the above-mentioned Ni-based alloy softened powder.
The manufacturing method is
A single-phase precursor powder preparation step of preparing a single-phase precursor powder having the chemical composition and having powder particles composed of polycrystals of the γ-phase single-phase fine crystals.
The single-phase precursor powder is heated to a temperature 80 ° C. lower than the solid solution temperature of the γ'phase and lower than the solid solution temperature (referred to as subhigh temperature in the present invention). By performing a sub-high temperature-slow cooling heat treatment that slowly cools the temperature at a cooling rate of 100 ° C./h or less, on the grain boundaries of the γ-phase single-phase fine crystals constituting the particles of the single-phase precursor powder. Provided is a method for producing a Ni-based alloy softened powder, which comprises a powder softening subhigh temperature-slow cooling heat treatment step for producing the Ni-based alloy softened powder in which the γ'phase is precipitated in an amount of 20% by volume or more. To do.

(IV) Yet another aspect of the present invention is a method for producing the above-mentioned Ni-based alloy softened powder.
The manufacturing method is
A single-phase precursor powder preparation step of preparing a single-phase precursor powder having the chemical composition and having powder particles composed of polycrystals of the γ-phase single-phase fine crystals.
The single-phase precursor powder is heated to a temperature equal to or higher than the solid solution temperature of the γ'phase and lower than the melting point of the γ phase, and then from that temperature to a temperature lower than the solid solution temperature of the γ'phase. By performing a high-temperature-slow cooling heat treatment in which the solid solution is slowly cooled at a cooling rate of ° C./h or less, the γ'phase is formed on the grain boundaries of the single-phase fine crystals of the γ-phase constituting the particles of the single-phase precursor powder. Provided is a method for producing a Ni-based alloy softened powder, which comprises a powder softening high temperature-slow cooling heat treatment step for producing the Ni-based alloy softened powder precipitated in an amount of 20% by volume or more.

In the present invention, the following improvements and changes can be made in the above-mentioned methods (II) to (IV) for producing a Ni-based alloy softened powder.
(V) The precursor powder preparation step or the single-phase precursor powder preparation step includes an atomizing elementary step.

In the present invention, the equilibrium precipitation amount of the γ'phase at 700 ° C., the solid dissolution temperature, and the melting point of the γ phase (solid phase line temperature) are the equilibrium obtained from the thermodynamic calculation based on the chemical composition of the Ni-based alloy material. The amount of precipitation and temperature can be used.

According to the present invention, a powder having better molding processability / molding processability than the conventional one while using a strong precipitation strengthened Ni-based alloy material, and a Ni-based alloy softened powder suitable for powder metallurgy technology and the softened powder. A manufacturing method can be provided. Further, by applying the powder metallurgy technique using the Ni-based alloy softened 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 the conventional one). ..

It is a schematic diagram showing the relationship between the γ phase and the γ'phase in the precipitation-strengthened Ni-based alloy material. When the γ'phase is precipitated in the crystal grains of (a) γ phase, (b) the crystal grains of γ phase This is the case where the γ'phase is precipitated on the grain boundaries of. It is a flow chart which shows the process example of the manufacturing method of the Ni-based alloy member using the Ni-based alloy softened powder which concerns on this invention. It is a schematic diagram which shows the change example of the microstructure of the Ni-based alloy powder in the manufacturing method which concerns on this invention. It is a flow chart which shows the other process example of the manufacturing method of the Ni-based alloy member using the Ni-based alloy softened powder which concerns on this invention. It is a schematic diagram which shows the change example of the microstructure of the Ni group alloy powder in the process of preparing a single-phase precursor powder-powder softening subhigh temperature-slow cooling heat treatment process. It is a flow chart which shows still another process example of the manufacturing method of the Ni-based alloy member which uses the Ni-based alloy softened powder which concerns on this invention.

[Basic Thought 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 view showing the relationship between the γ phase and the γ'phase in the precipitation-strengthened Ni-based alloy material. When the γ'phase is precipitated in the crystal grains of (a) 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 constituting the γ phase and the atom 2 forming the γ'phase form the matching interface 3. (The γ'phase is precipitated 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). Since the intragranular γ'phase constitutes the matching interface 3 with the γ phase, it is considered to hinder the movement of dislocations in the γ phase crystal grains, 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. 1 (a).

On the other hand, as shown in FIG. 1 (b), 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 constituting the γ phase 1 and the atom 2 that constitutes the γ'phase form an unmatched interface 4 (the γ'phase is precipitated in a state where it is not lattice-matched with the γ phase). Such a γ'phase is referred to as a grain boundary γ'phase (sometimes referred to as an intergranular γ'phase or an unmatched γ'phase). Since the grain boundary γ'phase forms an unmatched interface 4 with the γ phase, it does not hinder the movement of dislocations in the γ phase crystal grains. 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 precipitated instead of the intragranular γ'phase, the alloy material is in a softened state and the molding processability is dramatically improved. be able to.

In the present invention, the grain boundary γ'phase is not precipitated by hot forging the alloy ingot in the two-phase coexistence temperature region of the γ phase / γ'phase as in Patent Document 2. Forming a precursor powder / single-phase precursor powder of a Ni-based alloy in which the powder particles are composed of γ-phase fine crystals or polycrystals of single-phase fine crystals, and the precursor powder / single-phase precursor powder. A major feature is that 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 constituting the powder particles is produced by subjecting the powder particles to a predetermined heat treatment. The Ni-based alloy precursor powder / single-phase precursor powder can be said to be one of the key points.

Since the precipitation of the γ'phase basically requires the diffusion and rearrangement of the atoms forming the γ'phase, when the γ-phase crystal grains are large as in a cast material, the atoms are usually diffused and rearranged. It is considered that the γ'phase is preferentially precipitated in the γ-phase crystal grains that require a short rearrangement distance. It should be noted that even in the case of a cast material, it is not 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 grain boundaries becomes shorter and the grain boundary energy becomes higher than the volume energy of the crystal grains. Therefore, the γ'phase forming atoms are of the γ phase. It is considered that it is more energetically advantageous and more likely to occur by diffusing on the grain boundaries of the γ phase and rearranging on the grain boundaries than by solid-phase diffusion and rearrangement in the crystal grains. ..

Here, in order to promote the formation of the γ'phase on the grain boundaries of the γ phase, the γ phase is at least in a temperature region in which the γ'phase-forming atoms are likely to 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, to suppress the grain growth of the γ-phase crystal grains). Therefore, the present inventors have conducted intensive research on a technique for suppressing grain growth of γ-phase crystal grains even in a temperature range near the solid solution temperature of the γ'phase or above the solid solution temperature.

As a result, by forming a Ni-based alloy powder containing a predetermined amount of oxygen components in a controlled manner, the powder particles are composed of polycrystals of γ-phase fine crystals (a plurality of powder particles are present). (The grain boundary of the γ-phase fine crystal is present inside the powder particle, which is composed of the γ-phase fine crystal). Furthermore, such powder particles can suppress the grain growth of γ-phase fine crystals even if the temperature is raised to near the solid-melt temperature of the γ'phase or above the solid-melt temperature (single crystals in which the powder particles are in the γ-phase). It was found that the grain boundary γ'phase can be positively precipitated and grown on the grain boundary of the γ phase fine crystal by (maintaining the polycrystal without becoming) and slowly 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 a known technique or improved based on the known technique without departing from the technical idea of the invention. ..

[Manufacturing method of Ni-based alloy softened 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 softened powder according to the present invention. As shown in FIG. 2, the method for producing a Ni-based alloy member using the Ni-based alloy softened powder of the present invention generally has a predetermined chemical composition and the powder particles are polycrystals of γ-phase fine crystals. The grain boundary γ'phase is precipitated by 20% by volume or more by subjecting the precursor powder to a predetermined high temperature-slow cooling heat treatment in the precursor powder preparation step (S1) for preparing the precursor powder composed of the above. A powder softening high temperature-slow cooling heat treatment step (S2) for producing a softened Ni-based alloy powder, and a molding processing step (S3) for forming a molded product having a desired shape by powder metallurgy technology using the softened powder. , A solution heat treatment step in which the grain boundary γ'phase is solidified in the γ phase and an aging heat treatment for precipitating the intragranular γ'phase in the crystal grains of the γ phase is performed on the molded product. (S4) and. The precursor powder preparation step S1 and the powder softening high temperature-slow cooling heat treatment step S2 are methods for producing a Ni-based alloy softened powder according to the present invention.

The precursor powder is a state in which the powder particles are composed of polycrystals of γ-phase fine crystals, but the γ'phase is not precipitated on the grain boundaries of the γ-phase fine crystals (at least intentionally). A powder in which the grain boundary γ'phase is not precipitated). The softened 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 view showing an example of changes in the microstructure of the Ni-based alloy powder in the production method according to the present invention. First, the Ni-based alloy precursor powder prepared by the precursor powder preparation step is a powder having an average particle size of 500 μm or less, and the powder particles are composed of polycrystals of γ-phase fine crystals. Strictly speaking, it is strongly influenced by the temperature history (for example, cooling rate) of the process of forming the precursor powder, but the γ'phase (matched γ'phase) is not precipitated in the γ phase fine crystal. Fine crystals and γ-phase fine crystals in which an intragranular γ'phase is partially precipitated may coexist. The γ-phase fine crystal in which the intragranular γ'phase is not precipitated and the region in which the intragranular γ'phase is not precipitated in the γ-phase fine crystal are the composition before the hypersaturation state of the γ'phase or the formation of the γ'phase. It is considered to be in a fluctuating state.

Further, the particles of the precursor powder are basically composed of polycrystals in which one particle is composed of γ-phase fine crystals, but it does not deny that some particles are composed of γ-phase single crystals. .. In other words, the precursor powder is composed mostly of polycrystals of γ-phase fine crystals, but particles of γ-phase single crystals 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 becomes equal to or higher than the solid solution temperature of the γ'phase, all the γ'phases are solid-solved in the γ phase to become a single phase of the γ phase in thermal equilibrium. In the present invention, it is important to maintain the state in which the powder particles are composed of polycrystals of γ-phase fine crystals at this stage (prevent excessive coarsening of γ-phase fine crystals).

Next, when the powder is slowly cooled 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 can be obtained. .. Since the amount of precipitation of the γ'phase in the grains is sufficiently small in the softened powder, the mechanism of precipitation strengthening does not work, and the molding processability / molding processability is dramatically improved. Since the surface of the powder particles can be regarded as a kind of grain boundaries of γ phase fine crystals, the γ'phase precipitated on the surface of the powder particles is also regarded as the grain boundary γ'phase.

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

Then, the molded processed product having a desired shape is subjected to solution heat treatment in which most of the grain boundary γ'phase is solidified in the γ phase (for example, the grain boundary γ'phase is reduced to 10% by volume or less). Subsequently, aging heat treatment is performed to precipitate 30% by volume or more of the intragranular γ'phase in the crystal grains of the γ phase (solution hardening-aging heat treatment step S4). As a result, a strongly precipitation-strengthened Ni-based alloy member having a desired shape and being sufficiently precipitation-hardened can be obtained. The ease of the molding process by using the softened powder of the present invention leads to reduction of equipment cost, reduction of process cost, and improvement of manufacturing yield (that is, reduction of manufacturing cost of 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 deposits the unmatched γ'phase (grain boundary γ'phase, intergranular γ'phase) while intentionally leaving the matched γ'phase (intra-grain γ'phase). In order to produce a softened body, highly accurate control is required. On the other hand, the technique of the present invention produces a softened powder in which the intergranular γ'phase is once eliminated and then the grain boundary γ'phase is precipitated. In the present invention, since a softened powder can be obtained by combining a precursor powder forming step S1 having a low industrial difficulty and a powder softening high temperature-slow cooling heat treatment step S2 having a low industrial difficulty, it is more versatile than the technique of Patent Document 2. It has high characteristics and can reduce the cost of the entire manufacturing process. In particular, it is effective in producing a softened powder made of an ultra-strong precipitation-strengthened Ni-based alloy material having a volume fraction of γ'phase of 45% by volume or more.

Hereinafter, each step of S1 to S2 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 (particularly, 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 mother alloy ingot production element step (S1a) in which raw materials are mixed, melted, and cast so as to have a predetermined chemical composition to produce a mother alloy ingot (master ingot), and a precursor powder is formed from the mother alloy ingot. The atomizing elementary process (S1b) to be performed may be performed. Further, if necessary, a classification element step (S1c) for making the particle size of the precursor powder uniform may be performed.

The oxygen content is preferably controlled in the atomizing step S1b. As the atomizing method, conventional methods / methods can be used except for controlling the oxygen content in the Ni-based alloy. For example, a gas atomizing method or a centrifugal force atomizing method while controlling the amount of oxygen (oxygen partial pressure) in the atomizing atmosphere can be preferably used.

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

From the viewpoint of strengthening strong precipitation and improving the efficiency of grain boundary γ'phase grain formation, it is preferable to use a Ni-based alloy having a solid solution temperature of γ'phase of 1020 ° C. or higher. , It is more preferable to use the one having a temperature of 1050 ° C. or higher, and it is further preferable to use the one having a temperature of 1100 ° C. or higher. Details of the chemical composition other than the oxygen component 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, and further 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 handleability in the next step S2 is lowered, and the powder particles are easily coalesced during the next step S2, making it difficult to control the average particle size of the softened powder. If the average particle size of the precursor powder exceeds 500 μm, the shape controllability and shape accuracy of the molded product will deteriorate 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 are basically composed of polycrystals of γ-phase fine crystals, but the average crystal grain size of the γ-phase fine crystals in the powder particles is 5 μm or more and 50 μm or less. Is preferable. Further, when the precursor powder is formed by rapid solidification as in the atomizing method, the γ'phase (for example, the eutectic γ'phase directly crystallized from the liquid phase) is usually precipitated on the grain boundaries of the γ-phase fine crystals. do not.

(Powder softening high temperature-slow cooling heat treatment process 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 that temperature. This is a step of producing a softened powder by forming and increasing the grain boundary γ'phase by slow cooling. The slow cooling start temperature is preferably below the melting point of the γ phase (less than the solidus temperature), and is 35 ° C. above the solid dissolution temperature of the γ'phase in order to suppress unwanted coarsening of the γ phase fine crystals in this step. A high temperature or lower is more preferable, and a temperature 25 ° C. higher than the solidification temperature of the γ'phase is further preferable.

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", naturally "less than the melting point of the γ phase" is prioritized. ..

The heat treatment atmosphere is a non-oxidizing atmosphere (an atmosphere that does not contain oxygen at a partial pressure that causes oxidation) to prevent unwanted oxidation of the Ni-based alloy powder (oxidation exceeding the oxygen content controlled in the previous step S1). If so, there is no particular limitation, and a reducing atmosphere (for example, a hydrogen gas atmosphere) is more preferable.

Further, in this step S2, it cannot be denied that the intragranular γ'phase is not completely eliminated as a result of the high temperature-slow cooling heat treatment and is slightly present. For example, assuming that the grain boundary γ'phase is precipitated by 20% by volume or more, if the abundance of the intragranular γ'phase is 10% by volume or less, the molding processability in the subsequent molding process is strongly impaired. It is acceptable because it is not something to do. The abundance of the intragranular γ'phase 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 forged material obtained in 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 formed disappears, rapid coarsening of γ-phase crystal grains is likely to occur. As a result, even if the temperature is raised above the solid solution temperature of the γ'phase and then slowly cooled as in the present step S2, the precipitation and growth of the grain boundary γ'phase are hardly promoted.

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

The oxide formed at this time is considered to suppress the grain boundary movement of the γ-phase fine crystals (that is, the grain growth of the 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 the γ phase and the γ'phase contribute to strengthening by forming a matched interface, and the non-matched interface does not contribute to strengthening. It has excellent molding processability by reducing the amount of intragranular γ'phase (matched γ'phase) and increasing the amount of grain boundary γ'phase (intergranular γ'phase, unmatched γ'phase). A softened powder can be obtained.

Lowering the cooling rate in the slow cooling process is superior to the precipitation and growth of the grain boundary γ'phase. The cooling rate is preferably 100 ° C./h or less, more preferably 50 ° C./h or less, and 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 effects of the present invention cannot be sufficiently obtained.

Specifically, in order to ensure excellent molding processability / molding processability, it is preferable to slowly cool the grain boundary γ'phase to a temperature at which the precipitation amount of the grain boundary γ'phase is 20% by volume or more, and the grain boundary γ'phase 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, more preferably 5% by volume or less. The amount of γ'phase precipitated can be measured by microstructure observation and image analysis (eg, ImageJ, public domain software developed by the National Institutes of Health, USA).

As an example of the end temperature of the slow cooling process, when the γ'phase solidification temperature is relatively low, 1020 ° C. or higher and lower than 1100 ° C., the temperature preferably 50 ° C. or higher lower than the γ'phase solidification temperature is preferable. A temperature 100 ° C. or higher lower than the temperature is more preferable, and a temperature 150 ° C. or higher lower than the γ'phase solidification temperature is further preferable. When the γ'phase solidification temperature is relatively high at 1100 ° C. or higher, the end temperature of the slow cooling process is preferably 100 ° C. or higher lower than the γ'phase solidification temperature, and 150 ° C. from the γ'phase solidification temperature. A lower temperature is more preferable, and a temperature 200 ° C. or higher lower than the γ'phase solidification temperature is further preferable. More specifically, it is preferable to slowly cool to a temperature of 1000 ° C. or lower and 800 ° C. or higher.

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

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

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

Hereinafter, the differences between the above steps S1'to S2'(that is, other methods for producing the Ni-based alloy softened powder according to the present invention) from the above-mentioned steps S1 to S2 will be mainly focused on with reference to FIGS. 4 to 5. Explain to.

(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 having powder particles composed of polycrystals of single-phase fine crystals of γ-phase. In the present invention, the monophase precursor powder is 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 the level of rigor of a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM).

In this step S1', the same mother alloy ingot production elementary step (S1a) as in step S1 and the atomizing elementary step (S1'b) for forming the single-phase precursor powder are performed, and if necessary, the steps The same classification process (S1c) as S1 may be performed. The atomizing elementary step S1'b is the same atomizing method as the atomizing elementary step S1b of the step S1 except that the average cooling rate in the temperature region where the γ'phase is easily formed and precipitated (for example, 1100 ° C to 600 ° C) is controlled. Can be used. 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, and most preferably 2000 ° C./min or higher.

As a result of step S1'(in particular, atomizing elementary step S1'b), a single-phase precursor powder composed of polycrystals of γ-phase single-phase fine crystals is obtained as shown in FIG. The content of oxygen components in the single-phase precursor powder, the average particle size, and the average crystal particle size of the single-phase fine crystals are the same as those of the precursor powder obtained in step S1.

(Powder softening subhigh temperature-slow cooling heat treatment process S2')
In this step S2', a Ni-based alloy in which a grain boundary γ'phase is precipitated by 20% by volume or more by subjecting the single-phase precursor powder prepared in the previous step S1' to a predetermined subhigh temperature-slow cooling heat treatment. This is a step of producing a softened powder. Sub-high temperature-slow cooling heat treatment is heating to a temperature below the solid solution temperature at a temperature 80 ° C lower than the solid solution temperature of the γ'phase, and slowly cooling at a cooling rate of 100 ° C / h or less from the temperature. It is a heat treatment to be performed. The heating temperature (that is, the slow cooling start temperature) is more preferably 50 ° C. lower than the solid solution temperature of the γ'phase, and further preferably 30 ° C. or higher than the solid solution temperature of the γ'phase. The cooling rate in the slow cooling process is more preferably 50 ° C./h or less, still more preferably 10 ° C./h or less, as in step S2.

Since the single-phase precursor powder is used, the grain boundary γ'phase preferentially nucleates and grows grains even when the slow cooling start temperature is in the subhigh temperature range (see FIG. 5). Regarding the precipitation amount of the grain boundary γ'phase and the abundance of the intragranular γ'phase as a result of the slow cooling end temperature, cooling from the slow cooling end temperature, and the subhigh temperature-slow cooling heat treatment in step S2', the step Similar to those of the softened powder obtained with S2.

Here, the reason why a softened powder similar to the softened powder obtained in step S2 can be obtained by the sub-high temperature-slow cooling heat treatment on the single-phase precursor powder will be briefly considered. The exact mechanism has not been elucidated at this stage, but the single-phase precursor powder composed of polycrystals of γ-phase single-phase fine crystals may be an important point, and the following model Can be considered.

For a γ-phase single-phase crystal (in a situation where the γ'phase is substantially absent), a temperature above the solid-dissolving temperature of the γ'phase and below the solid-dissolving temperature (in the present invention, subhigh temperature). Is considered to be the temperature region where the degree of supercooling related to the precipitation of the γ'phase is small. Further, the precipitation of the γ'phase (that is, the 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, in the γ-phase single-phase crystal, the nucleation frequency of the intragranular γ'phase in the subhigh temperature region is considered to be very low.

On the other hand, it is considered that oxygen atoms are unevenly distributed or microoxides are formed at the grain boundaries of the γ-phase single-phase fine crystals 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 a thermodynamic point of view, it is known that inhomogeneous nucleation has a much lower activation energy than homogeneous nucleation, so that the nucleation frequency is sufficiently high even in a state of low supercooling. There is.

Taking these factors into consideration, sub-high temperature-slow cooling heat treatment for single-phase precursor powder is performed by competing homogeneous nucleation and heterogeneous nucleation in the temperature region where the supercooling degree of the γ'phase is small. It is considered that the heat treatment is performed to preferentially nucleate the grain boundary γ'phase caused by heterogeneous nucleation and then grow the nuclei generated in the supercooling process. It is considered that this consideration (model) can also be applied to "preferred 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.

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

(Chemical composition of Ni-based alloy softened 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 in which 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%, Cr of 5% or more and 25% or less, Co of more than 0% and 30% or less, Al of 1% or more and 8% or less, and the sum of Ti, Nb and Ta are 1% or more and 10% or less. , 10% or less Fe, 10% or less Mo, 8% or less W, 0.1% or less Zr, 0.1% or less B, 0.2% or less C, 2% or less Hf, and 5% or less Re, A chemical composition containing 0.003% or more and 0.05% or less of O, and the balance being Ni and unavoidable impurities is preferable. Hereinafter, each component will be described.

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

The Co component is an element close to Ni and dissolves in the γ phase in the form of replacing Ni, which has the effect of improving creep strength and corrosion resistance. Furthermore, it also has the effect of lowering the solid solution temperature of the γ'phase, improving high temperature ductility. However, since excessive addition promotes the formation of a harmful phase, it 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, forming an oxide film (Al ₂ O ₃ ) on the surface of the Ni-based alloy material in the actual use environment contributes to the improvement of oxidation resistance and corrosion resistance. It is preferably 1% by mass or more and 8% by mass or less, depending on the desired amount of γ'phase precipitation.

The Ti component, the Nb component, and the Ta component have the effect of forming a γ'phase and improving the high temperature strength in the same manner as the Al component. In addition, the Ti component and the Nb component also have the effect of improving corrosion resistance. However, since excessive addition promotes the formation of a harmful phase, the total sum of Ti, Nb and Ta components is preferably 1% by mass or more and 10% by mass or less.

By substituting the Fe component with the Co component or Ni component, there is an effect of reducing the material cost of the alloy. However, since excessive addition promotes the formation of a harmful phase, it is preferably 10% by mass or less.

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

The Zr component, B component, and C component have the effect of strengthening the grain boundaries of the γ phase (strengthening the tensile strength in the direction perpendicular to the grain boundaries of the γ phase) and improving high-temperature ductility and creep strength. There is. However, since excessive addition deteriorates molding processability, it is preferable that the Zr component is 0.1% by mass or less, B is 0.1% by mass or less, and C is 0.2% by 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 preferably 2% by mass or less.

The Re component has the effect of contributing to the enhancement of the solid solution of the γ phase and the improvement of corrosion resistance. However, excessive addition promotes the formation of harmful phases. Further, since Re is an expensive element, increasing the addition amount has a 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. However, in the present invention, as described above, the grain growth of γ-phase fine crystals is suppressed to form grain boundary γ'phase grains. It is an essential ingredient to promote. The O content is preferably 0.003% by mass or more and 0.05% by mass or less.

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

Hereinafter, the present invention will be described in more detail 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 raw materials of the Ni-based alloy. Melting was carried out by a vacuum induction heating melting method. Next, the obtained master ingot was redissolved to prepare a Ni-based alloy powder by a gas atomization method while controlling the partial pressure of oxygen in the atomizing atmosphere.

In the production of Ni-based alloy powder by the gas atomization method, it was confirmed that the average cooling rate of 1100 ° C to 600 ° C was 500 ° C / min or more for some alloy powders. In addition, when the fine structure of the powder particles was observed at a magnification of 1000 times using SEM-EDX for the alloy powder whose average cooling rate was confirmed to be 500 ° C / min or more, the γ'phase could not be detected and the γ phase could not be detected. It was judged to be monophasic. The fine structure of the powder particles was not observed for the powder for which the average cooling rate was not confirmed when the alloy powder was prepared by the gas atomization method.

Next, the obtained Ni-based alloy powder was 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 were prepared. .. The chemical compositions of the obtained powders PP1 to PP10 are shown in Table 1.

[Experiment 2]
(Preparation of softened Ni-based alloy powders of Examples 1 to 11 and Comparative Examples 1 to 12 and evaluation of moldability)
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, cooling rate in the slow cooling process) shown in Table 2 described later. The treatment was carried out to prepare Ni-based alloy softened powders of Examples 1 to 11 and Comparative Examples 1 to 12. The end temperature of the slow cooling process was 950 ° C. except for Comparative Examples 1 and 12. In Comparative Examples 1 and 12, the mixture was rapidly cooled by gas cooling from the slow cooling start temperature to room temperature.

For each of the obtained Ni-based alloy softened powders, microstructure observation (precipitation amount of grain boundary γ'phase) and room temperature Vickers hardness measurement were performed to evaluate moldability.

The amount of the grain boundary γ'phase precipitated was determined by electron microscope observation and image analysis (ImageJ) of the softened powder. The room temperature Vickers hardness of the softened powder was measured by randomly extracting 10 particles and using a micro Vickers hardness tester (Akashi Seisakusho Co., Ltd., model: MVK-E). The average value of the room temperature Vickers hardness of 8 particles excluding the maximum value and the minimum value among the room temperature Vickers hardness of 10 particles was taken as the room temperature Vickers hardness of the softened powder. In the moldability evaluation, the room temperature Vickers hardness of 370 Hv or less was judged as "pass", and the room temperature Vickers hardness of more than 370 Hv was judged as "fail".

Table 2 shows the specifications and evaluation results of the Ni-based alloy softened 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 were obtained from the alloy composition of Table 1 based on the thermodynamic calculation.

As shown in Table 2, the softened 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 deviates from the specification of the present invention are the precipitation amount of the grain boundary γ'phase. Is less than 20% by volume (instead, an increase in the amount of intragranular γ'phase precipitation is confirmed), and the room temperature Vickers hardness is over 370 Hv. As a result, it was determined that the molding processability was 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, so that sufficient molding is performed. It was confirmed that the sex could not be secured.

The softened powder of Comparative Example 8 using the precursor powder PP8 in which the equilibrium precipitation amount of the γ'phase at 700 ° C. is out of the specification of the present invention has an equilibrium precipitation amount of the γ'phase of less than 30% by volume. This does not apply to the target strong precipitation strengthened Ni-based alloy material. However, since the amount of γ'phase precipitation is absolutely small, there is no particular problem in molding processability / molding processability.

In contrast to these Comparative Examples 1 to 8, in each of 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 molding processability was judged to be acceptable. That is, the action and effect of the present invention were confirmed.

Further, the softened powders of Examples 8 to 9 using the single-phase precursor powders PP9 to PP10 have grains even in the sub-high temperature-slow cooling heat treatment in which the slow cooling start temperature is lower than the solid solution temperature of the γ'phase. The amount of boundary γ'phase precipitated is 20% by volume or more, and the room temperature Vickers hardness is 370 Hv or less. As a result, the molding processability was judged to be acceptable. That is, the action and effect of the present invention were 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 a grain boundary γ'phase precipitation amount of 20% by volume or more and were Vickers hardness at room temperature. The value is 370 Hv or less. As a result, the molding processability was judged to be acceptable. That is, the action and effect of the present invention were confirmed.

On the other hand, even if the single-phase precursor powders PP9 to PP10 are used, the softened powders of Comparative Examples 9 to 12 in which the start temperature or the cooling rate of the slow cooling process in the softening treatment deviates from the specification of the present invention are the precipitation of the grain boundary γ'phase. The amount is less than 20% by volume and the room temperature Vickers hardness is over 370 Hv. As a result, it was determined that the molding processability was 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, so that sufficient molding is performed. It was confirmed that workability could not be ensured.

From the above results, by applying the method for producing a Ni-based alloy softened powder according to the present invention, even a strong precipitation-strengthened Ni-based alloy material or an ultra-strong precipitation-strengthened Ni-based alloy material has good molding processability. It was shown that a softened powder exhibiting moldability can be provided. By applying powder metallurgy technology using the Ni-based alloy softened powder, it is expected that a strong precipitation strengthened Ni-based alloy member can be provided at low cost.

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

Atoms that make up 1 ... γ phase, atoms that make up 2 ... γ'phase, 3 ... matching interface between γ phase and γ'phase, 4 ... unmatched interface between γ phase and γ'phase.

Claims (13)

Ni-based alloy softened powder
The Ni-based alloy softened powder has a chemical composition in which the equilibrium precipitation amount of the γ'phase precipitated in the γ phase as the parent phase at 700 ° C. is 30% by volume or more and 80% by volume or less, and the average of the softened powders. The powder has a particle size of 5 μm or more and 500 μm or less, and the particles of the softened powder are composed of polycrystals of fine crystals of the γ phase.
20% by volume or more of the γ'phase is precipitated on the grain boundaries of the fine crystals of the γ phase constituting the particles.
A Ni-based alloy softened powder characterized in that the Vickers hardness of the particles at room temperature is 370 Hv or less. In the Ni-based alloy softened powder according to claim 1,
The chemical composition is
Cr of 5% by mass or more and 25% by mass or less,
Co with more than 0% by mass and less than 30% by mass,
Al of 1% by mass or more and 8% by mass or less,
Ti, Nb and Ta with a total of 1% by mass or more and 10% by mass or less,
Fe of 10% by mass or less and
Mo of 10% by mass or less and
W of 8% by mass or less and
Zr of 0.1% by mass or less and
B of 0.1% by mass or less and
C of 0.2% by mass or less and
Hf of 2% by mass or less and
Re of 5% by mass or less and
Contains O of 0.003% by mass or more and 0.05% by mass or less,
A Ni-based alloy softened powder characterized in that the balance consists of Ni and unavoidable impurities. In the Ni-based alloy softened powder according to claim 1 or 2.
The chemical composition is a Ni-based alloy softened powder having a chemical composition in which the solid solution temperature of the γ'phase is 1100 ° C. or higher. In the Ni-based alloy softened powder according to claim 3,
The Ni-based alloy softened powder is a Ni-based alloy softened powder having a chemical composition in which the equilibrium precipitation amount of the γ'phase at 700 ° C. is 45% by volume or more and 80% by volume or less. In the Ni-based alloy softened powder according to any one of claims 1 to 4.
A Ni-based alloy softened powder characterized in that the Vickers hardness of the particles at room temperature is 350 Hv or less. A method for producing softened Ni-based alloy powder.
The Ni-based alloy softened powder has a chemical composition in which the equilibrium precipitation amount of the γ'phase precipitated in the γ phase as the parent phase at 700 ° C. is 30% by volume or more and 80% by volume or less, and the average of the softened powders. The powder has a particle size of 5 μm or more and 500 μm or less, and the particles of the softened powder are composed of polycrystals of fine crystals of the γ phase.
The Vickers hardness of the particles at room temperature is 370 Hv or less.
The manufacturing method is
A precursor powder preparation step of preparing a precursor powder having the chemical composition and having powder particles composed of polycrystals of fine crystals of the γ phase.
The precursor powder is heated to a temperature equal to or higher than the solid dissolution temperature of the γ'phase and lower than the melting point of the γ phase to dissolve the γ'phase in the γ phase, and then the temperature is increased. The fine crystals of the γ phase constituting the particles of the precursor powder are subjected to a high-temperature-slow-cooling heat treatment in which the γ'phase is slowly cooled to a temperature lower than the solid solution temperature at a cooling rate of 100 ° C./h or less. A method for producing a Ni-based alloy softened powder, which comprises a powder softening high-temperature-slow-cooling heat treatment step for producing the Ni-based alloy softened powder in which 20% by volume or more of the γ'phase is precipitated on the grain boundary. A method for producing softened Ni-based alloy powder.
The Ni-based alloy softened powder has a chemical composition in which the equilibrium precipitation amount of the γ'phase precipitated in the γ phase as the parent phase at 700 ° C. is 30% by volume or more and 80% by volume or less, and the average of the softened powders. The powder has a particle size of 5 μm or more and 500 μm or less, and the particles of the softened powder are composed of polycrystals of fine crystals of the γ phase.
The Vickers hardness of the particles at room temperature is 370 Hv or less.
The manufacturing method is
A single-phase precursor powder preparation step of preparing a single-phase precursor powder having the chemical composition and having powder particles composed of polycrystals of the γ-phase single-phase fine crystals.
The single-phase precursor powder is heated to a temperature 80 ° C. lower than the solid solution temperature of the γ'phase and lower than the solid solution temperature, and at a cooling rate of 100 ° C./h or less from the temperature. By performing a sub-high temperature-slow cooling heat treatment for slow cooling, 20% by volume or more of the γ'phase is precipitated on the grain boundaries of the single phase fine crystals of the γ phase constituting the particles of the single phase precursor powder. A method for producing a Ni-based alloy softened powder, which comprises a powder softening subhigh temperature-slow cooling heat treatment step for producing a Ni-based alloy softened powder. A method for producing softened Ni-based alloy powder.
The Ni-based alloy softened powder has a chemical composition in which the equilibrium precipitation amount of the γ'phase precipitated in the γ phase as the parent phase at 700 ° C. is 30% by volume or more and 80% by volume or less, and the average of the softened powders. The powder has a particle size of 5 μm or more and 500 μm or less, and the particles of the softened powder are composed of polycrystals of fine crystals of the γ phase.
The Vickers hardness of the particles at room temperature is 370 Hv or less.
The manufacturing method is
A single-phase precursor powder preparation step of preparing a single-phase precursor powder having the chemical composition and having powder particles composed of polycrystals of the γ-phase single-phase fine crystals.
The single-phase precursor powder is heated to a temperature equal to or higher than the solid solution temperature of the γ'phase and lower than the melting point of the γ phase, and then from that temperature to a temperature lower than the solid solution temperature of the γ'phase. By performing a high-temperature-slow cooling heat treatment in which the solid solution is slowly cooled at a cooling rate of ° C./h or less, the γ'phase is formed on the grain boundaries of the single-phase fine crystals of the γ-phase constituting the particles of the single-phase precursor powder. A method for producing a Ni-based alloy softened powder, which comprises a powder softening high temperature-slow cooling heat treatment step for producing the Ni-based alloy softened powder precipitated in 20% by volume or more. The method for producing a Ni-based alloy softened powder according to any one of claims 6 to 8.
The chemical composition is
Cr of 5% by mass or more and 25% by mass or less,
Co with more than 0% by mass and less than 30% by mass,
Al of 1% by mass or more and 8% by mass or less,
Ti, Nb and Ta with a total of 1% by mass or more and 10% by mass or less,
Fe of 10% by mass or less and
Mo of 10% by mass or less and
W of 8% by mass or less and
Zr of 0.1% by mass or less and
B of 0.1% by mass or less and
C of 0.2% by mass or less and
Hf of 2% by mass or less and
Re of 5% by mass or less and
Contains O of 0.003% by mass or more and 0.05% by mass or less,
A method for producing a Ni-based alloy softened powder, wherein the balance is composed of Ni and unavoidable impurities. The method for producing a Ni-based alloy softened powder according to any one of claims 6 to 9.
The method for producing a Ni-based alloy softened powder, wherein the precursor powder preparation step or the single-phase precursor powder preparation step includes an atomizing element step. The method for producing a Ni-based alloy softened powder according to any one of claims 6 to 10.
The method for producing a Ni-based alloy softened powder, wherein the chemical composition is such that the solid solution temperature of the γ'phase is 1100 ° C. or higher. In the method for producing a Ni-based alloy softened powder according to claim 11.
A method for producing a Ni-based alloy softened powder, wherein the Ni-based alloy softened powder has a chemical composition in which the equilibrium precipitation amount of the γ'phase at 700 ° C. is 45% by volume or more and 80% by volume or less. The method for producing a Ni-based alloy softened powder according to any one of claims 6 to 12.
A method for producing a Ni-based alloy softened powder, wherein the Vickers hardness of the particles at room temperature is 350 Hv or less.

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