WO2018155446A1 - Ni-based super heat-resistant alloy and method for manufacturing same - Google Patents

Abstract

This Ni-based super heat-resistant alloy has a component composition in which the equilibrium precipitated amount of a gamma prime phase at 700°C is 35 mol% or greater, and has crystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure thereof. Also provided is a method for manufacturing this Ni-based super heat-resistant alloy. This method includes a preparation step for preparing a raw material of a Ni-based super heat-resistant alloy having a component composition in which the equilibrium precipitated amount of a gamma prime phase at 700°C is 35 mol% or greater, and a processing step for performing plastic processing of the raw material a plurality of times at a temperature of 500°C or less so as to obtain a cumulative processing rate of 30% or greater. Furthermore provided is a method for manufacturing a Ni-based super heat-resistant alloy, comprising preparing an alloy material having the abovementioned component composition, a hardness of 500 HV or greater, and crystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure thereof, performing plastic processing of the alloy material at a temperature of 500°C or less, and obtaining an alloy having a hardness of 500 HV or greater.

Description

Ni-base superalloy and manufacturing method thereof

The present invention relates to a Ni-base superalloy and a manufacturing method thereof.

As heat-resistant parts used in aircraft engines and gas turbines for power generation, for example, Ni-based super heat-resistant alloys such as Inconel (registered trademark) 718 alloy are often used. With the improvement in performance and fuel efficiency of gas turbines, heat-resistant parts having a high heat-resistant temperature are required. In order to improve the heat resistance (high temperature strength) of the Ni-base superalloy, it is also referred to as a gamma prime phase (hereinafter referred to as “γ ′” phase) which is a precipitation strengthening phase of an intermetallic compound mainly composed of Ni ₃ Al. ) Increasing the amount is most effective. The Ni-base superalloy can further improve the high-temperature strength of the Ni-base superalloy by including Al, Ti, and Nb that are γ′-generating elements. In the future, in order to satisfy high heat resistance and high strength, a Ni-base superalloy having a larger amount of γ ′ phase is required.

However, it is known that Ni-based superalloys are difficult to process because the deformation resistance of hot working increases as the γ 'phase increases. In particular, when the amount of γ ′ phase is 35 to 40 mol% or more of γ ′ mole ratio, the workability is particularly lowered. For example, alloys such as Inconel (registered trademark) 713C alloy, IN939, IN100, and Mar-M247 have a particularly large γ 'phase and are not capable of plastic working, and are usually as-cast as a cast alloy. Used in.

As a proposal for improving the hot plastic workability of such a Ni-base superalloy, in Patent Document 1, a Ni superbase heat-resistant alloy ingot having a composition with a γ ′ molar ratio of 40 mol% or more is processed at a processing rate of 5%. A manufacturing method is described in which after cold working at less than 30%, heat treatment is performed at a temperature exceeding the γ ′ solid solution temperature. This method obtains a recrystallization rate of 90% or higher that allows hot working to be applied to a Ni-base superalloy by combining a cold working process and a heat treatment process.

In recent years, there has been an increasing need for repairing the heat-resistant parts of the Ni-base superheat-resistant alloy having a large amount of the γ ′ phase described above or producing the heat-resistant parts themselves by three-dimensional molding. In this case, a Ni-based superheat-resistant alloy fine wire is required as a modeling material. This fine wire can also be used after being processed into a part shape such as a spring. The wire diameter (diameter) of the Ni-based superheat-resistant alloy is as thin as 5 mm or less, and further 3 mm or less, for example. For example, it is efficient to prepare such a thin wire by preparing a “wire” having a wire diameter of 10 mm or less as an intermediate product and subjecting this wire to plastic working. If this “intermediate product” “wire” can also be obtained by plastic working, Ni-based superalloys can be produced efficiently.
As a method for producing such a super heat-resistant alloy thin wire, a method has been proposed in which a cast wire having a wire diameter of 5 mm or more is used as a starting material, and a bundle of these cast wires is hot-extruded and then separated ( Patent Document 2).

International Publication No. 2016/129485 US Pat. No. 4,777,710

As described above, hot plastic workability of Ni-base superalloys decreases as the amount of γ ′ phase increases. The technique of Patent Document 2 is effective for the production of fine wires in a limited component composition, but can be applied only to the component composition, and the amount of γ ′ phase is “35 mol% or more” described later. When it becomes a Ni-based super heat-resistant alloy, it is very difficult to make it into a fine wire by hot plastic working. Further, the method of Patent Document 2 has problems such as a complicated process and an increase in manufacturing cost.
The method of Patent Document 1 is effective for Ni-base superalloys to which hot working is applied. However, for that purpose, it is necessary to further perform heat treatment after cold working the ingot at a working rate of 5% or more and less than 30%.

An object of the present invention is to provide a Ni-base superalloy having excellent plastic workability and a method for producing the same using a novel method that is completely different from the conventional one. Another object of the present invention is to provide a Ni-base superalloy capable of performing plastic working with a large working rate without performing hot working and a method for producing the same. Another object of the present invention is to provide a Ni-based superalloy and a method for producing the same that can perform plastic working with a large working rate without performing heat treatment in the middle. Another object of the present invention is to provide a new method for producing a Ni-base superalloy alloy wire or fine wire.

According to one aspect of the present invention, a Ni-based superalloy having a component composition in which the equilibrium precipitation amount of a gamma prime phase at 700 ° C. is 35 mol% or more and having crystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure. Is provided.

According to one specific example, the Ni-based superalloy is preferably 500 HV or higher.
Further, according to one specific example, it is preferable that five or more crystal grains having a maximum diameter of 75 nm or less exist per 1 μm ^{2 in the} cross-sectional structure.

According to one specific example, the Ni-base superalloy is, by mass, C: 0 to 0.25%, Cr: 8.0 to 25.0%, Al: 0.5 to 8.0%, Ti: 0.4 to 7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, W: 0 to 6.0%, Nb: 0 to 4.0%, Ta: 0 to 3 0.0%, Fe: 0 to 10.0%, V: 0 to 1.2%, Hf: 0 to 1.0%, B: 0 to 0.300%, Zr: 0 to 0.300% The balance is preferably made of Ni and impurities.

According to one specific example, this Ni-based superalloy preferably has a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 40 mol% or more.

According to one specific example, the Ni-base superalloy is, by mass, C: 0 to 0.03%, Cr: 8.0 to 22.0%, Al: 2.0 to 8.0%, Ti: 0.4-7.0%, Co: 0-28.0%, Mo: 2.0-7.0%, W: 0-6.0%, Nb: 0-4.0%, Ta : 0-3.0%, Fe: 0-10.0%, V: 0-1.2%, Hf: 0-1.0%, B: 0-0.300%, Zr: 0-0. It is preferable that 300% is included and the balance is made of Ni and impurities.

According to another aspect of the present invention, a method for producing the above Ni-base superalloy is provided. This manufacturing method is
A preparation step of preparing a Ni-based superalloy material having the above component composition;
This material includes a processing step of performing plastic processing a plurality of times at a temperature of 500 ° C. or less so that the cumulative processing rate is 30% or more.

According to a specific example, this plastic material has a shape of a bar, and a plurality of plastic processings in which the cumulative processing rate is 30% or more is a process of reducing the cross-sectional area of the bar.
This plastic working preferably includes a step of compressing from the peripheral surface of the bar toward the axis.

According to a specific example, it is preferable not to perform heat treatment between a plurality of plastic workings.

According to another aspect of the present invention, there is provided a method for manufacturing (or processing) a Ni-base superalloy having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more. This method
A preparation step of preparing an alloy material having a hardness of 500 HV or more and a crystal grain having a maximum diameter of 75 nm or less in a cross-sectional structure;
This alloy material is subjected to plastic working at a temperature of 500 ° C. or lower to obtain an alloy having a hardness of 500 HV or higher.

According to one specific example, it is preferable to repeat the above-described processing steps a plurality of times.
Further, it is preferable not to perform heat treatment during the plurality of processing steps.

According to a specific example, the alloy material and the alloy preferably include 5 or more crystal grains having a maximum diameter of 75 nm or less per 1 μm ^{2 in the} cross-sectional structure.

According to a specific example, the Ni-base superalloy preferably has a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 40 mol% or more.
Furthermore, it is preferable that this Ni-base superalloy has the component composition described above.

BRIEF DESCRIPTION OF THE DRAWINGS Advantages, features and details of the present invention will become apparent by reference to the following non-limiting example description and accompanying drawings.

Invention Example No. It is a figure which shows an example of the electron beam backscattering diffraction (EBSD) image of the cross-sectional microstructure of the 1-2 Ni-base superalloy. Invention Example No. It is a figure which shows an example of the EBSD image of the cross-sectional microstructure of 1-4 Ni-base superalloy. Invention Example No. It is a figure which shows an example of the EBSD image of the cross-sectional microstructure of 1-5 Ni-base superalloy. Invention Example No. FIG. 7 is a diagram showing an example of an EBSD image of a cross-sectional microstructure of a 1-7 Ni-base superalloy. Invention Example No. It is a figure which shows an example of the EBSD image of the cross-sectional microstructure of 1-9 Ni-base superalloy. Comparative Example No. It is a figure which shows an example of the EBSD image of the cross-sectional microstructure of 1-1 Ni-based superalloy.

The present invention is very novel that a Ni-based superalloy having excellent plastic workability can be provided by a new approach that does not rely on conventional hot plastic working.
The present inventor studied the plastic workability of a Ni-base superalloy having a large amount of γ ′ phase. As a result, the inventors have found a phenomenon in which the plastic workability of the Ni-based superalloy is dramatically improved by generating “nanocrystal grains” in the structure of the Ni-based superalloy. And it discovered that the production | generation of this nanocrystal grain could be achieved by "cold plastic working" of predetermined conditions, and came to this invention.

The Ni-base superalloy according to the present invention has a component composition in which the equilibrium precipitation amount of the gamma prime (γ ′) phase at 700 ° C. is 35 mol% or more, and has crystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure. Is. The Ni-base superalloy having crystal grains having a maximum diameter of 75 nm or less has excellent plastic workability. And regarding this plastic workability, the Ni-base superalloy according to the present invention is particularly excellent in cold plastic workability.

Here, the amount of the γ ′ phase of the Ni-base superalloy can be expressed by a numerical index such as “volume ratio” or “area ratio” of the γ ′ phase. In the present specification, the amount of the γ ′ phase is represented by a numerical index of “γ ′ molar ratio”. The γ ′ molar ratio is a stable gamma prime phase equilibrium precipitation amount in which the Ni-base superalloy can be precipitated in a thermodynamic equilibrium state. The value representing the equilibrium precipitation amount of the gamma prime phase in terms of “molar ratio” is determined by the component composition of the Ni-base superalloy. The value of mol% of the equilibrium precipitation amount can be obtained by analysis by thermodynamic equilibrium calculation. In the analysis by thermodynamic equilibrium calculation, it can be obtained accurately and easily by using various thermodynamic equilibrium calculation software.

In the present invention, the γ 'molar ratio of the Ni-base superalloy is defined as “equilibrium precipitation at 700 ° C.”. The high temperature strength of the Ni-base superalloy can be evaluated by the equilibrium precipitation amount of the gamma prime phase in the structure. The higher the high temperature strength, the more difficult the hot plastic working. In general, the equilibrium precipitation amount of the gamma prime phase in the tissue becomes generally constant at approximately 700 ° C. or less, and the temperature dependency becomes substantially constant. Therefore, the value at the above “700 ° C.” is used as a reference.

As described above, the hot plastic working is usually more difficult as the γ 'molar ratio of the Ni-base superalloy is larger. However, according to the present invention, increasing the γ 'molar ratio is greatly involved in improving the cold plastic workability of the Ni-base superalloy. In the Ni-base superalloy according to the present invention, having “nanocrystal grains” in the cross-sectional structure thereof, the cold plastic workability can be dramatically improved. The nanocrystal grains are most likely to be generated from the phase interface between the austenite phase (gamma (γ)), which is a matrix of the Ni-base superalloy, and the gamma prime phase. Therefore, increasing the γ 'molar ratio of the Ni-base superalloy will lead to an increase in the phase interface and contribute to the generation of nanocrystal grains. When the γ 'molar ratio reaches a level of 35%, the formation of the nanocrystal grains is promoted. A component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 40 mol% or more is more preferable. A more preferable equilibrium precipitation amount of the gamma prime phase is 50 mol% or more, and even more preferably 60 mol% or more. A particularly preferable equilibrium precipitation amount of the gamma prime phase is 63 mol% or more, more preferably 66 mol% or more, and still more preferably 68 mol% or more. The upper limit of the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is not particularly limited, but about 75 mol% is realistic.

The precipitation strengthened Ni-base superalloy having an equilibrium precipitation amount of gamma prime phase at 700 ° C. of 35 mol% or more, for example, in mass%, C: 0 to 0.25%, Cr: 8.0 to 25. 0%, Al: 0.5 to 8.0%, Ti: 0.4 to 7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, W: 0 to 6.0%, Nb: 0 to 4.0%, Ta: 0 to 3.0%, Fe: 0 to 10.0%, V: 0 to 1.2%, Hf: 0 to 1.0%, B: 0 to 0 .300%, Zr: 0 to 0.300%, with the balance being composed of Ni and impurities.

Alternatively, the Ni-base superalloy is in mass%, C: 0 to 0.03%, Cr: 8.0 to 22.0%, Al: 2.0 to 8.0%, Ti: 0.4 to 7.0%, Co: 0-28.0%, Mo: 2.0-7.0%, W: 0-6.0%, Nb: 0-4.0%, Ta: 0-3.0 %, Fe: 0 to 10.0%, V: 0 to 1.2%, Hf: 0 to 1.0%, B: 0 to 0.300%, Zr: 0 to 0.300%, the balance Preferably has a composition comprising Ni and impurities.

Hereinafter, each component having a preferable composition as an embodiment of the Ni-base superalloy according to the present invention will be described (the unit of the component composition is “mass%”).

Carbon (C)
C is conventionally contained as an element that enhances the castability of Ni-base superalloys. In particular, Ni-base superalloys with a large amount of γ ′ phase are difficult to be plastically processed, and are usually used as cast parts, and a certain amount of C is added. The added C remains as carbide in the cast structure, and a part thereof is formed as coarse eutectic carbide. Such coarse carbides serve as crack starting points and crack propagation paths when plastic processing of Ni-based superalloys, particularly at room temperature. It adversely affects plastic workability.

Therefore, for the present invention, which aims to provide a Ni-base superalloy having a large amount of γ 'phase as a Ni-base superheater alloy material excellent in plastic workability, not as a cast part, the Ni-base superheater alloy is provided. Reduction of C in the heat-resistant alloy is very important. On the other hand, in the Ni-base superalloy according to the present invention, the cold plastic workability is dramatically improved by having “nanocrystalline grains” in the cross-sectional structure. A C content comparable to the content in can be allowed. In the present invention, the C content is preferably 0.25% or less. More preferably, the order is 0.1% or less and 0.03% or less. More preferably, it is 0.025% or less, More preferably, it is 0.02% or less. Particularly preferably, it is less than 0.02%.
For the Ni-base superalloy according to the present invention, C is a regulating element and is preferably controlled to be lower. And when it is good also as C without addition (inevitable impurity level), the minimum of C can be made into 0 mass%. Usually, even if it is a Ni base superalloy without addition of C, when the component composition is analyzed, for example, a C content of about 0.001% can be recognized.

Chrome (Cr)
Cr is an element that improves oxidation resistance and corrosion resistance. However, when Cr is contained excessively, an embrittlement phase such as σ (sigma) phase is formed, and the strength and hot workability at the time of material preparation are lowered. Therefore, Cr is preferably 8.0 to 25.0%, for example. More preferably, it is 8.0 to 22.0%. A preferable lower limit is 9.0%, and more preferably 9.5%. More preferably, it is 10.0%. Moreover, a preferable upper limit is 18.0%, More preferably, it is 16.0%. More preferably, it is 14.0%. Particularly preferably, it is 12.5%.

Molybdenum (Mo)
Mo contributes to the solid solution strengthening of the matrix and has the effect of improving the high temperature strength. However, when Mo becomes excessive, an intermetallic compound phase is formed and high temperature strength is impaired. Therefore, Mo is preferably 0 to 8% (may be non-added (inevitable impurity level)). More preferably, it is 2.0 to 7.0%. A more preferable lower limit is 2.5%, and more preferably 3.0%. More preferably, it is 3.5%. Further, the upper limit is more preferably 6.0%, more preferably 5.0%.

Aluminum (Al)
Al is an element that forms a strengthening phase γ ′ (Ni ₃ Al) phase and improves high-temperature strength. However, excessive addition reduces the hot workability during material preparation and causes material defects such as cracks during processing. Therefore, Al is preferably 0.5 to 8.0%. More preferably, it is 2.0 to 8.0%. A more preferable lower limit is 2.5%, and more preferably 3.0%. More preferably, it is 4.0%, More preferably, it is 4.5%. Particularly preferably, it is 5.1%. Further, the upper limit is more preferably 7.5%, and more preferably 7.0%. More preferably, it is 6.5%.
In addition, in order to ensure the hot workability at the time of raw material preparation in relation to Cr mentioned above, when content of Cr is reduced, the content of Al of the reduced amount can be permitted. For example, when the upper limit of Cr is 13.5%, the lower limit of the Al content is preferably 3.5%.

Titanium (Ti)
Ti, like Al, is an element that forms a γ ′ phase and enhances the high temperature strength by solid solution strengthening of the γ ′ phase. However, excessive addition causes the γ ′ phase to become unstable at a high temperature, leading to coarsening at a high temperature, and forming a harmful η (eta) phase, thereby impairing hot workability during material preparation. Therefore, Ti is preferably, for example, 0.4 to 7.0%. Considering the balance with other γ′-forming elements and Ni matrix, the preferable lower limit of Ti is 0.6%, more preferably 0.7%. More preferably, it is 0.8%. Moreover, a preferable upper limit is 6.5%, More preferably, it is 6.0%. More preferably, it is 4.0%, and particularly preferably 2.0%.

Hereinafter, optional components that can be added to the Ni-base superalloy of the present invention will be described.

Cobalt (Co)
Co improves the stability of the structure and makes it possible to maintain the hot workability at the time of material preparation even if it contains a large amount of Ti as a strengthening element. On the other hand, since Co is expensive, the cost increases. Therefore, Co is one of optional elements that can be contained in a range of 28.0% or less, for example, in combination with other elements. A preferable lower limit in the case of adding Co is preferably 8.0%. More preferably, it is 10.0%. The preferable upper limit of Co is 18.0%. More preferably, it is 16.0%. In addition, when it is possible to set Co to the non-addition level (the inevitable impurity level of the raw material) due to the balance with the γ ′ generating element and the Ni matrix, the lower limit of Co is set to 0%.

Tungsten (W)
W, like Mo, is one of the selective elements that contribute to solid solution strengthening of the matrix. However, when W is excessive, a harmful intermetallic compound phase is formed and the high-temperature strength is impaired. For example, the upper limit is set to 6.0%. A preferable upper limit is 5.5%, and more preferably 5.0%. In order to exhibit the effect of W more reliably, the lower limit of W is preferably set to 1.0%. Moreover, the solid solution strengthening effect can be exhibited more by adding W and Mo in combination. In the case of composite addition, W is preferably 0.8% or more. In addition, when it is good also considering W as an additive-free level (inevitable impurity level of a raw material) by sufficient addition of Mo, the minimum of W shall be 0%.

Niobium (Nb)
Nb, like Al and Ti, is one of the selective elements that form a γ ′ phase and enhance the high temperature strength by solid solution strengthening of the γ ′ phase. However, excessive addition of Nb forms a harmful δ (delta) phase and impairs hot workability during material preparation. Therefore, the upper limit of Nb is, for example, 4.0%. A preferable upper limit is 3.5%, more preferably 2.5%. In order to exhibit the effect of Nb more reliably, the lower limit of Nb is preferably set to 1.0%. Preferably it is 2.0%. In the case where Nb is allowed to be at the non-addition level (inevitable impurity level) by adding other γ′-generating elements, the lower limit of Nb is set to 0%.

Tantalum (Ta)
Ta, like Al and Ti, is one of the selective elements that forms a γ ′ phase and strengthens the γ ′ phase by solid solution strengthening to increase the high-temperature strength. However, excessive addition of Ta causes the γ 'phase to become unstable at high temperatures, leading to coarsening at high temperatures, and forming a harmful η (eta) phase, thereby improving hot workability during material preparation. To lose. Therefore, Ta is set to 3.0% or less, for example. Preferably it is 2.5% or less. In order to exhibit the above Ta effect more reliably, the lower limit of Ta is preferably set to 0.3%. In the case where Ta is allowed to be a non-added level (inevitable impurity level) due to the addition of γ′-generating elements such as Ti and Nb and the balance with the matrix, the lower limit of Ta is set to 0%.

Iron (Fe)
Fe is one of the selective elements used as an alternative to expensive Ni and Co, and is effective in reducing alloy costs. In order to acquire this effect, it is good to determine whether to add in combination with other elements. However, if Fe is contained excessively, an embrittlement phase such as σ (sigma) phase is formed, and the strength and hot workability at the time of material preparation are lowered. Therefore, the upper limit of Fe is, for example, 10.0%. A preferable upper limit is 9.0%, more preferably 8.0%. On the other hand, when Fe may be made into an additive-free level (inevitable impurity level) due to the balance with the γ′-generating element and the Ni matrix, the lower limit of Fe is set to 0%.

Vanadium (V)
V is one of the selective elements useful for strengthening the solid solution of the matrix and strengthening the grain boundaries by forming carbides. However, excessive addition of V leads to the formation of a high-temperature unstable phase in the production process, which adversely affects manufacturability and high-temperature dynamic performance. Therefore, the upper limit of V is, for example, 1.2%. A preferable upper limit is 1.0%, and more preferably 0.8%. In order to exhibit the effect of V more reliably, the lower limit of V is preferably set to 0.5%. In the case where V may be made an additive-free level (inevitable impurity level) due to balance with other alloy elements in the alloy, the lower limit of V is set to 0%.

Hafnium (Hf)
Hf is one of the selective elements useful for improving the oxidation resistance of alloys and strengthening grain boundaries by forming carbides. However, excessive addition of Hf leads to production of oxides and high temperature unstable phases in the production process, and adversely affects manufacturability and high temperature dynamic performance. Therefore, the upper limit of Hf is, for example, 1.0%. In order to exhibit the effect of Hf more reliably, the lower limit of Hf is preferably set to 0.1%. In the case where Hf may be an additive-free level (inevitable impurity level) due to the balance with other alloy elements in the alloy, the lower limit of Hf is set to 0%.

Boron (B)
B is an element that improves the grain boundary strength and improves the creep strength and ductility. On the other hand, B does not exceed 0.300%, for example, because it has a large effect of lowering the melting point, and when a coarse boride is formed, hot workability during material preparation is hindered. It is good to control as follows. A preferable upper limit is 0.200%, and more preferably 0.100%. More preferably, it is 0.050%, Most preferably, it is 0.020%. In order to obtain the above effect, a content of at least 0.001% is preferable. A more preferred lower limit is 0.003%, and even more preferably 0.005%. Particularly preferred is 0.010%. In the case where B may be an additive-free level (inevitable impurity level) due to balance with other alloy elements in the alloy, the lower limit of B is set to 0%.

Zirconium (Zr)
Zr, like B, has the effect of improving the grain boundary strength. On the other hand, when Zr is excessive, the melting point is also lowered, and the high temperature strength and hot workability during material preparation are hindered. Therefore, the upper limit of Zr is, for example, 0.300%. A preferable upper limit is 0.250%, and more preferably 0.200%. More preferably, it is 0.100%, Most preferably, it is 0.050%. In order to obtain the above effect, a content of at least 0.001% is preferable. A more preferable lower limit is 0.005%, and further preferably 0.010%. In the case where Zr may be at an additive-free level (inevitable impurity level) due to balance with other alloy elements in the alloy, the lower limit of Zr is set to 0%.

The balance other than the elements described above is Ni, but may contain inevitable impurities.

The Ni-based superalloy according to the present invention has “nanocrystal grains” having a maximum diameter of 75 nm or less in the cross-sectional structure, thereby greatly improving the plastic workability in cold. This mechanism is not yet fully understood. However, as described above, the phase interface between the γ phase and the γ ′ phase seems to contribute to the formation of nanocrystal grains. The number of the generated nanocrystal grains increases as the plastic working rate increases, and this causes plastic deformation of the Ni-base superalloy by causing grain boundary sliding or crystal rotation. There is a possibility that the deformation mechanism is different from the conventional plastic deformation due to crystal slip due to the occurrence and growth of dislocations. One fact that suggests this possibility is that when the Ni-based superalloy is subjected to cold plastic processing, which will be described later, once nanocrystal grains begin to form, further plastic processing is performed (plastic processing). By increasing the rate, the number of nanocrystal grains increases, but the hardness of the alloy is “almost constant” regardless of an increase in the plastic working rate (including the case where it increases slightly) (for example, the above γ The inventor has confirmed that the molar ratio is 500 HV or more in the case of a Ni-base superalloy having a molar ratio of 35 mol% or more. This phenomenon suggests that no increase in dislocation density has occurred due to plastic working.

As described above, the size of the nanocrystal grains contributing to the improvement of plastic workability is “the maximum diameter is 75 nm or less” in the cross-sectional structure of the Ni-base superalloy. The crystal grain size having a maximum diameter of 75 nm or less can be distinguished from the crystal grain size found in the conventional normal process. At this time, for example, in the case of a wire rod, the above-described cross-sectional structure may be collected from a cross-section when it is divided in the longitudinal direction (that is, a cross-section including the central axis of the wire rod). And in this section, for example, the position of the surface of the wire, the position of 1 / 4D from the surface of the wire toward the central axis (D is the wire diameter), and the position of the central axis of the wire What is necessary is just to extract | collect from a cross section. And what is necessary is just to confirm that said nanocrystal grain exists in one or two or more cross-sectional structures of each of these cross sections.
In addition, it is only necessary to observe a cross-section when the shape other than the wire is halved in the longitudinal direction as described above.

As described above, the Ni-base superalloy according to the present invention has nanocrystal grains having a “maximum diameter of 75 nm or less” in the cross-sectional structure. It is preferable that 5 or more nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure exist per 1 μm ² of the cross-sectional structure. By increasing the number of nanocrystal grains, the number of media that play the role of plastic deformation increases, and the plastic workability is further improved. More preferably, there are 10 or more, more preferably 50 or more, and still more preferably 100 or more crystal grains having a maximum diameter of 75 nm or less per 1 μm ^{2 of} the cross-sectional structure. And it is still more preferable in order of 200 or more and 300 or more. The number density of the above-mentioned nanocrystal grains may be obtained by averaging the total number of nanocrystal grains confirmed in all observed cross-sectional structures divided by all observed visual field areas.
In addition, about the nanocrystal grain whose maximum diameter in a cross-sectional structure | tissue is 75 nm or less, the minimum of the maximum diameter does not need to set in particular. The presence / absence and number of nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure can be confirmed by, for example, an EBSD image. Nanocrystal grains having a maximum diameter of 75 nm or less among crystal grains that can be recognized when the measurement condition of EBSD is a scan step: 0.01 μm and the definition of crystal grains is a grain boundary having an orientation difference of 15 ° or more. Can be extracted and counted. As an example, the presence and number of nanocrystal grains having a maximum diameter of about 25 nm or more can be confirmed.
Such Ni-base superalloys preferably have a hardness of 500 HV or higher.

As described above, since the Ni-base superalloy according to the present invention is excellent in cold plastic workability, it can be made “for cold plastic working”.
Moreover, the Ni-base superalloy according to the present invention can be a “wire material” which is an intermediate product shape in which cold plastic working is performed. The wire has a thin wire diameter (diameter) of, for example, 10 mm or less, 8 mm or less, or 6 mm or less, and eventually 5 mm or less, 4 mm or less, 3 mm or less, or 2 mm or less. The length of the wire is, for example, 10 times or more, 50 times or more, or 100 times or more of the wire diameter of the wire.
Further, the Ni-base superalloy according to the present invention can be a “wire product” which is the final product shape obtained by the cold plastic working. The fine wire has a wire diameter (diameter) of, for example, 5 mm or less, 4 mm or less, 3 mm or less, and eventually 2 mm or less, 1 mm or less. The fine wire has a length that is longer than the wire diameter of the fine wire, for example, 50 times or more, 100 times or more, or 300 times or more.

Next, a manufacturing method for obtaining the Ni-based superalloy according to the present invention having the above component composition and having crystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure will be described. This manufacturing method includes a preparation step of preparing a raw material of a Ni-based superalloy having the above composition, and a cumulative processing rate of 30% or more at a temperature of 500 ° C. or less. And a processing step of performing plastic processing a plurality of times. It has been found that “nanocrystal grains” can be formed in the structure of the Ni-base superalloy material by increasing the “processing rate” of the compression processing.

This manufacturing method will be described.
The material for the Ni-base superalloy may be obtained by a melting method in which molten metal is poured into a mold to produce an ingot. And ingot manufacturing may be applied by combining vacuum melting and conventional methods such as vacuum arc remelting and electroslag remelting. Moreover, the raw material may be obtained by a powder metallurgy method. Then, the ingot or the alloy ingot produced by the powder metallurgy method is subjected to hot working or machining as necessary to obtain a predetermined shape such as a billet or a bar ( Bar material may be finished.

Next, plastic working with a cumulative working rate of 30% or more is performed at a temperature of 500 ° C. or lower. Unlike the conventional “hot” plastic working, the present invention can generate nanocrystal grains in the structure of a Ni-base superalloy by the “cold” plastic working. An excellent Ni-base superalloy can be obtained. In order to achieve this, the above-described cold plastic working needs to be in a low temperature region where recovery and recrystallization cannot occur during the plastic working. Therefore, it is preferable not to perform heat treatment during plastic working. The heat treatment here refers to a heat treatment in a high temperature region where recovery and recrystallization occur, and is a heat treatment for heating to a temperature exceeding 500 ° C., for example.
It is important that the plastic working temperature in the present invention is “500 ° C. or lower”. Preferably it is 300 degrees C or less, More preferably, it is 100 degrees C or less, More preferably, it is 50 degrees C or less (for example, room temperature).
It is clear that the production of the Ni-base superalloy described above can be applied to wire form, plate material, strip material and the like. At this time, the Ni-based superalloy according to the present invention has an intermediate product shape of a wire, a sheet material, and a strip material, as well as a thin wire, a sheet product, and a ribbon. It is also clear that the final product shape may be (strip product). Regarding the plate material (thin plate) and the strip material (thin strip), the dimensional relationship can be changed from the wire diameter of the above-described wire rod (thin wire) to the plate thickness or the strip thickness.

In particular, when the material of the Ni-base superalloy is a bar, in order to form the nanocrystal grains, the bar can be processed by compressing the cross-sectional area. In this case, starting from the “bar” of the Ni-base superalloy, the pressure can be uniformly applied to the bar as a mode of plastic working performed on this bar “vertical to the longitudinal direction of the bar” It is preferable to perform a process of compressing the cross-sectional area of the cross section. Then, the cross-sectional area (rod diameter) is plastically compressed to extend the length of the bar material. In particular, when obtaining a Ni-based superalloy alloy wire, it is efficient to produce a “bar” having a larger cross-sectional area (diameter) than the wire by plastic working. The cross-sectional area of the bar is compressed by performing plastic working with a cumulative working rate of 30% or more at a temperature of 500 ° C. or less from the peripheral surface of the bar to the axis. Such processing includes swaging, cassette roller die drawing, hole die drawing, and the like.
On the other hand, rolling can also be used for the production of a Ni-base superalloy alloy plate, strip, and the like.

In the present invention, in order to form nanocrystal grains, the cumulative processing rate of the plastic processing is increased to “30% or more”. Cumulative working ratio is preferably at least 40%, which is the number of cross-section per tissue 1 [mu] m ² of said nano-crystal grains, for example, preferred to generate 10 or more.
The cumulative processing rate is more preferably 60% or more, which is preferable for generating, for example, 50 or more nanocrystal grains. More preferably, it is 70% or more, and more preferably 80% or more. This is preferable for generating, for example, 100 or more nanocrystal grains. Still more preferably, it is 90% or more, particularly preferably 97% or more. These cumulative processing rates are preferable for generating the number of the above-mentioned nanocrystal grains, for example, 200 or more and 300 or more in order.
Here, the processing rate is expressed by the area reduction rate when swaging or die drawing a bar. The area reduction ratio is the relationship between the cross-sectional area A ₀ of the bar material before plastic working and the cross-sectional area A _{1 of the} wire or thin wire after plastic working.
[(A ₀ −A ₁ ) / A ₀ ] × 100 (%) (1)
It is calculated by the following formula.
On the other hand, when rolling, the processing rate is expressed as a reduction rate. The reduction ratio is defined as follows: t ₀ is the thickness of the material before plastic working, and t ₁ is the thickness of the plate or strip after plastic working.
[(T ₀ −t ₁ ) / t ₀ ] × 100 (%) (2)
It is calculated by the following formula.
The cumulative processing rate indicates the processing rate for the material of the final workpiece when plastic processing is performed a plurality of times or over a plurality of passes.

The mechanism by which nanocrystal grains are generated in the tissue has not yet been fully elucidated. However, it was experimentally confirmed that the above-mentioned processing rate is required to be at least about 30% in order to sufficiently generate nanocrystal grains (see Examples). In other words, when the above-described Ni-base superheat-resistant alloy bar is cold plastically processed and the cumulative processing rate reaches about 30%, the nanocrystal grains are first converted into γ phase and γ ′. It was observed that it was preferentially produced at the phase interface with the phase. Then, when the plastic processing by cold is further added to the Ni-based superalloy (for example, rod (wire)) once the nanocrystal grains are generated, the number of nanocrystal grains increases. The increase in grains further improves the plastic workability of Ni-based superalloys (eg, rods (wires)). By repeating this plastic working (by increasing the cumulative working rate), the plastic workability of Ni-base superalloys (for example, rods (wires)) is further improved, and heat treatment is performed during the plastic working. In addition, the "room temperature superplastic" plastic working phenomenon was confirmed, in which it was possible to perform plastic working with a cumulative working rate of 97% or more in the cold.

The above-described plastic processing with a processing rate of “30% or more” is not completed by a single plastic processing, but before the formation of nanocrystal grains in the structure, for example, cracks and wrinkles in the alloy. In order to suppress the occurrence of the like, it is preferable to complete by dividing into a plurality of plastic workings. By applying “large strain” with a processing rate of 30% or more to the material by dividing it into a plurality of plastic processing, the strain is moderately dispersed in the material, and the above-described intergranular sliding of nanocrystal grains It is effective in causing crystal rotation to occur uniformly in the material. As a result, the nanocrystal grains can be uniformly and uniformly formed in the material, and the occurrence of cracks, wrinkles and the like during the plastic working can be suppressed. When divided into a plurality of plastic workings, it is not necessary to perform a heat treatment between the plastic workings. The upper limit of the processing rate of 30% or more does not need to be set in particular, and may be set appropriately according to, for example, the shape of the intermediate product or the final product. And if the alloy material mentioned later is prepared, numerical values, such as 50%, 45%, 40%, 35%, can be set according to the specification etc., for example.

Also, when dividing into multiple times of plastic processing, the processing rate (area reduction) in a given plastic processing (pass) is larger than the processing rate (area reduction) in the previous plastic processing (pass) Thus, it is possible to increase the processing efficiency. The processing rate (area reduction rate) may be increased for each plastic processing (pass).
Regarding the “pass” in the present invention, when plastic processing is performed by one (or a pair) of dies or rolls in the types of plastic processing such as swaging, die drawing, and rolling described above, “one pass” is counted. be able to.

In particular, when the material of the Ni-base superalloy is a rod, it seems to be important to apply a uniform and even pressure to the rod by the above-described plastic working for the formation of nanocrystal grains. For this purpose, plastic working is effective in which the cross-sectional area of the bar is compressed from the circumferential surface of the bar toward the axis. At this time, there is no need to limit the plastic working method. However, a plastic working method in which pressure is evenly applied to the entire circumference of the rod to be plastic processed is advantageous. A specific example is swaging. Swaging is preferable for producing nanocrystal grains because the peripheral surface of the bar is forged while rotating a plurality of dies surrounding the entire circumference of the bar. In addition, other plastic processing such as cassette roller die drawing and hole die drawing is also applicable.

In the case of the present invention, a heat treatment may be performed in which a material (for example, a rod) before the plastic working is heated and held at a temperature Th equal to or higher than a γ ′ solid solution temperature (solvus temperature) Ts and cooled. By performing this heat treatment, the γ 'phase can be uniformly reprecipitated in the structure of the material. This facilitates the formation of nanocrystal grains in the structure after plastic working. This is thought to be due to the fact that the phase interface between the γ phase and the γ ′ phase of the Ni-base superheat-resistant alloy becomes uniform, thereby promoting the formation of nanocrystal grains.

The heating and holding temperature Th is preferably higher by 10 ° C. or more than the solvus temperature Ts. It is not necessary to provide an upper limit for the heating and holding temperature Th. The heated holding temperature Th is theoretically less than the temperature at which the Ni-based superalloy material starts to melt (solidus temperature). Moreover, it is preferable that the holding | maintenance time of the rod after reaching said heating holding temperature Th shall be 2 hours or more. And 10 hours or less is realistic. Preferably, it is 7 hours or less. More preferably, it is 4 hours or less. Thereby, there is an effect (soaking effect) also in equalizing the component composition.

According to another embodiment of the present invention, a method for producing a Ni-base superalloy having the above component composition is provided. This method includes a preparation step of preparing an alloy material having a hardness of 500 HV or more and a crystal grain having a maximum diameter of 75 nm or less in a cross-sectional structure, and plastic processing of the material at a temperature of 500 ° C. or less. And a processing step of obtaining an alloy having a hardness of 500 HV or higher. Here, the alloy material that is the starting material for processing is the Ni-base superalloy according to the present invention described above, and is, for example, the wire, plate, or strip described above. In the present invention, when the above-mentioned hardness is 500 HV or more and the Ni-based superalloy having a crystal grain having a maximum diameter of 75 nm or less in the cross-sectional structure is repeatedly subjected to plastic working at a temperature of 500 ° C. or less, The nanocrystal grains in the cross-sectional structure increased (continuously formed) along the way, and a phenomenon was observed in which plastic workability was maintained. At that time, the hardness of the alloy is maintained at 500 HV or higher or slightly increases. As a result, the Ni-base superalloy having “nanocrystal grains in the cross-sectional structure” of the present invention is excellent in the initial plastic workability, and the excellent plastic workability is maintained even in the subsequent plastic working. To go. And the Ni-based super heat-resistant alloy that has undergone all plastic working also has nanocrystal grains in the cross-sectional structure, which can be made into fine wires, thin plates, and ribbons of the final product shape. .

The Ni-base superalloy after plastic working has a linear structure in which the γ phase and the γ ′ phase extend in the stretching direction. However, a desired equiaxed crystal structure can be obtained by performing a heat treatment as necessary when plastic products are processed into predetermined dimensions and shapes and then supplied as final products. By this heat treatment, for example, the hardness can be adjusted to less than 500 HV, and it becomes easy to bend or cut the final product into a form suitable for a transportation form or a use form.

By this manufacturing method, for example, only by cold plastic working, various forms of Ni from intermediate product shapes such as wire, plate, and strip to final product shapes such as thin wire, thin plate, and strip. A base superalloy can also be provided.

The molten metal prepared by vacuum melting was cast to prepare a cylindrical Ni-based superalloy A having a diameter of 100 mm and a mass of 10 kg. Table 1 shows the composition (% by mass) of the Ni-base superalloy A. Table 1 also shows the “γ ′ molar ratio” and “γ ′ solid solution temperature (solvus temperature) Ts” of the ingot. These values were calculated using a commercially available thermodynamic equilibrium calculation software “JMatPro (Version 8.0.1, product of Senti Software Ltd.)”. The contents of each element listed in Table 1 were input to this thermodynamic equilibrium calculation software, and the above-mentioned “γ ′ molar ratio” and “γ ′ solid solution temperature Ts” were obtained. The ingot of this Ni-based superalloy A is subjected to a heat treatment at a holding temperature Th: 1200 ° C. and a holding time: 8 hours, cooled in a furnace, and then 6.0 mm in diameter and length in a direction parallel to the length direction of the ingot. A 60 mm bar was sampled and used as a material for plastic working. The bar had a hardness of 320 HV. This bar was subjected to “swaging process 1” (described in alloy 1-2 in Table 2) at room temperature (25 ° C.) and a processing rate of 31% to obtain a Ni-based superalloy according to Example 1 of the present invention. The wire (wire diameter 5.0 mm) was produced. The Ni-based superalloy alloy wire of Example 1 of the present invention could be produced while maintaining a good surface condition. And the hardness of the wire of the Ni-based superheat-resistant alloy of Invention Example 1 was 595 HV. In addition, the processing rate was calculated | required by Formula (1) demonstrated above.

FIG. 1 shows an alloy no. 2 shows an EBSD image of a cross-sectional microstructure of the wire 1-2. This cross-sectional microstructure is a structure taken from a cross-section at a position (position A) that is ¼D from the surface of the wire toward the central axis in the cross-section divided in the longitudinal direction of the wire (D is the wire of the wire) Indicates the diameter). And the measurement conditions of EBSD used the EBSD measurement system "OIM Version 5.3.1 (made by TSL Solution)" attached to the scanning electron microscope "ULTRA55 (made by Zeiss)", magnification: 10000 times. , Scan step: 0.01 μm, and the definition of the crystal grain was defined as a grain boundary having an orientation difference of 15 ° or more. At this time, the maximum diameter (maximum length) of the nanocrystal grains confirmed in the EBSD image was about 25 nm, which was small, and the presence and number of nanocrystal grains with the maximum diameter exceeding this value were confirmed. As shown in FIG. The wire No. 1-2 had nanocrystal grains having a maximum diameter of 75 nm or less (for example, a dark spot within a circle) in the cross-sectional structure. Alloy No. In the cross section of the wire rod halved in the longitudinal direction, the structure was also collected from the cross-section at the surface position (position B) of the wire rod and the cross-section at the position of the central axis of the wire rod (position C). Analysis by EBSD was performed. And about the total of six cross-sectional structures collected from two positions A, B, C, respectively, the total number of nanocrystal grains having a maximum diameter of 75 nm or less counted in the same visual field area (2 μm × 3 μm) as in FIG. The number density per unit area of the nanocrystal grains obtained by dividing by the total visual field area (6 μm ² × 6) was “8 particles / μm ² ”.

On the other hand, Alloy No. In 1-1, swaging was performed at room temperature (25 ° C.), but the wire diameter after processing was 5.5 mm, and the processing rate (area reduction rate) was 16.0%. This cross-sectional microstructure is designated as alloy no. When observed in the same manner as in 1-2, no nanocrystal grains having a maximum diameter of 75 nm or less were observed as shown in FIG. Moreover, the hardness was 480 HV.

Alloy No. of the present invention example For the wire No. 1-2, at the room temperature (25 ° C.), the “swinging processing 3 to 10” of the processing rates shown in Table 2 was sequentially accumulated while increasing the cumulative processing rate from the bar. Alloy No. 1-3 to Alloy No. Ni-base superalloy alloys up to 1-10 were prepared, respectively. Note that heat treatment is not performed between the swaging processes. Alloy No. 1-3 to Alloy No. All the wires up to 1-10 could be produced while maintaining a good surface condition. These wire rods also had nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure (visible as black grains in the figure). 2 to 5 show the alloy No. of the present invention. 1-4, no. 1-5, No. 1 1-7, No. 1 The EBSD images of the cross-sectional microstructure of 1-9 are shown in the respective order. The sampling position of the cross-sectional microstructure and the EBSD measurement conditions are the same as in FIG. And about these wires, alloy No. In the same manner as in 1-1, the number density per unit area of nanocrystal grains of 75 nm or less in the cross-sectional structure was measured. Moreover, the hardness of the wire was also measured. These measurement results are shown in Table 2 together with those of Example 1 of the present invention.

 

From the results shown in Table 2, it can be seen that the number of nanocrystal grains is increased by further applying cold plastic working to the Ni-based superalloy having nanocrystal grains once generated. However, while the number of nanocrystal grains increased, the hardness of the Ni-base superalloy was almost constant regardless of the increase in the plastic working rate. For this reason, this invention example No. whose wire diameter is 1.0 mm by swaging process. It was possible to carry out plastic working to 1-10 wires. This is referred to as Alloy No. When the 1-2 wire is used as a starting material (that is, an alloy material having a hardness of 500 HV or more and a crystal grain having a maximum diameter of 75 nm or less in the cross-sectional structure), the cumulative processing rate of the alloy material from the wire is 96. %, And if the cumulative processing rate from the original bar material, as much as 97% plastic working could be performed cold. Furthermore, alloy no. The wire of No. 1-10 was in a state where it could be further cold-worked after the plastic working with the large cumulative working rate. That is, the hardness of the alloy after working in the example of the present invention was almost constant (595 HV to 605 HV) regardless of the working rate, so that once the crystal grains having the maximum diameter of 75 nm or less were formed, the hardness of 500 HV or more was formed. It can be seen that the alloy material having a thickness can be subsequently cold worked.

The molten metal prepared by vacuum melting was cast to produce a cylindrical Ni-based superalloy B having a diameter of 100 mm and a mass of 10 kg. Table 3 shows the component composition (% by mass) of the Ni-base superalloy B. The “γ ′ molar ratio” and “γ ′ solid solution temperature Ts” shown in Table 3 were also calculated using a commercially available thermodynamic equilibrium calculation software “JMatPro (Version 8.0.1, product of Senté Software Ltd.). The ingot of the Ni-base superalloy B is subjected to a heat treatment with a holding temperature Th: 1250 ° C. and a holding time: 8 hours, cooled in the furnace, and then 6.0 mm in diameter and length in a direction parallel to the length direction of the ingot. A 60 mm bar was sampled and used as a raw material for plastic working, and the bar had a hardness of 381 HV, which was sequentially swaging in the same manner as in Example 1. Processing was performed to prepare wires Nos. 2-1 to 2-6.

From the results in Table 4, alloy no. The wire diameter of 2-1 was 5.5 mm after swaging, and the processing rate (area reduction rate) was 16.0%. No nanocrystal grains having a maximum diameter of 75 nm or less were observed in this cross-sectional microstructure. Further, the hardness was 494 HV.
On the other hand, Alloy No. No. 2-2 No. In the wires up to 2-6, the processing rate (area reduction rate) is 30% or more, and nanocrystal grains having a maximum diameter of 75 nm or less are observed in the cross-sectional structure of each wire. The number density of crystal grains also increased. The hardness of these alloys was 500 HV or more, but unlike the results of Example 1, there was a tendency for the hardness to increase slightly as the processing rate increased. The processed wire has a hardness of 600 HV or higher.

The molten metal prepared by vacuum melting was cast to prepare a cylindrical Ni-based superalloy C ingot having a diameter of 100 mm and a mass of 10 kg. Table 5 shows the component composition (mass%) of the Ni-base superalloy C. The “γ ′ molar ratio” and “γ ′ solid solution temperature Ts” shown in Table 5 were also calculated using a commercially available thermodynamic equilibrium calculation software “JMatPro (Version 8.0.1, product of Senté Software Ltd.). The ingot of the Ni-base superalloy C is subjected to a heat treatment of holding temperature Th: 1200 ° C. × holding time: 8 h, cooled in the furnace, and then 6.0 mm in diameter and 60 mm in length in a direction parallel to the length direction of the ingot. This bar was used as a raw material for plastic working, and the hardness of this bar was 389 HV, which was sequentially subjected to swaging as in Example 1. Accordingly, wires Nos. 3-1 to 3-10 were produced.

From the results in Table 6, alloy no. The wire diameter of 3-1 was 5.5 mm after swaging, and the processing rate (area reduction rate) was 16.0%. No nanocrystal grains having a maximum diameter of 75 nm or less were observed in this cross-sectional microstructure. The hardness was also 468HV.
Alloy No. No. 3-2 The wire rods up to 3-10 have a processing rate (area reduction rate) of 30% or more, and nanocrystal grains having a maximum diameter of 75 nm or less are observed in the cross-sectional structure. The number density of crystal grains also increased. The hardness of these alloys was 500 HV or more, but was almost constant (524 HV to 542 HV) regardless of the processing rate as in Example 1.

Alloy No. 1 of Example 1 A wire rod of 1-9 (wire diameter: 1.5 mm) was used as a starting material, and this was subjected to four-pass hole die drawing at room temperature (25 ° C.). 4-1 (wire diameter 1.35 mm), 4-2 (wire diameter 1.20 mm), 3-3 (wire diameter 1.05 mm), and finally, alloy no. A 4-4 wire (wire diameter: 0.95 mm) was produced. Processing could be performed without any problem even for a wire having a diameter of less than 1 mm. In addition, heat processing is not performed between each pass. The processing rate was obtained by the equation (1) described above.

In the middle of the above four passes, alloy no. The hardness of 4-1, 4-2, and 4-3 was 593HV, 602HV, and 598HV in order. In each of the wires, nanocrystal grains having a maximum diameter of 75 nm or less were observed in the cross-sectional structure, and the number density of the nanocrystal grains increased as the processing rate increased. And as shown in Table 7, the alloy No. obtained after finishing the four-pass die drawing was obtained. With respect to the wire 4-4, 620 nanocrystal grains having a maximum diameter of 75 nm or less were observed per 1 μm ² in the cross-sectional structure, and the hardness was 593 HV. And alloy no. The hardness of the wires from 4-1 to 4-4 was 500 HV or more, and was almost constant (593 HV to 602 HV) regardless of the processing rate, as in Example 1.

As described above, the Ni-base superalloys of each example are excellent in plastic workability, and the Ni-base superalloys of the examples of the present invention can be processed into a wire having an arbitrary wire diameter by plastic working in the cold. confirmed. Although the present Example was performed about manufacture of a wire, of course, these wires can also be handled as a fine wire of a final product shape. And since the Ni-base superalloy according to the present invention is excellent in plastic workability, it is clear that plastic working into shapes other than wires and fine wires is possible.

Claims (17)

1. A Ni-based superalloy having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more and having crystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure.
2. The Ni-base superalloy according to claim 1, wherein the Ni-base superalloy has a hardness of 500 HV or more.
3. 3. The Ni-base superalloy according to claim 1, wherein five or more crystal grains having a maximum diameter of 75 nm or less are present in a cross-sectional structure per 1 μm ² .
4. The Ni-based superalloy is mass%,
   C: 0 to 0.25%
   Cr: 8.0-25.0%,
   Al: 0.5 to 8.0%,
   Ti: 0.4 to 7.0%,
   Co: 0 to 28.0%,
   Mo: 0-8%,
   W: 0 to 6.0%,
   Nb: 0 to 4.0%,
   Ta: 0 to 3.0%,
   Fe: 0 to 10.0%,
   V: 0 to 1.2%
   Hf: 0 to 1.0%
   B: 0 to 0.300%,
   Zr: 0 to 0.300%
   The Ni-base superalloy according to any one of claims 1 to 3, wherein the balance is made of Ni and impurities.
5. The Ni-based superalloy according to any one of claims 1 to 4, which has a component composition in which an equilibrium precipitation amount of a gamma prime phase at 700 ° C is 40 mol% or more.
6. The Ni-based superalloy is mass%,
   C: 0 to 0.03%,
   Cr: 8.0-22.0%,
   Al: 2.0 to 8.0%,
   Ti: 0.4 to 7.0%,
   Co: 0 to 28.0%,
   Mo: 2.0 to 7.0%,
   W: 0 to 6.0%,
   Nb: 0 to 4.0%,
   Ta: 0 to 3.0%,
   Fe: 0 to 10.0%,
   V: 0 to 1.2%
   Hf: 0 to 1.0%
   B: 0 to 0.300%,
   Zr: 0 to 0.300%
   The Ni-base superalloy according to any one of claims 1 to 5, wherein the balance is made of Ni and impurities.
7. In the method for producing a Ni-base superalloy according to any one of claims 1 to 6,
   A preparation step of preparing a Ni-based superalloy material having the component composition;
   And a processing step of performing plastic processing a plurality of times so that the cumulative processing rate is 30% or more at a temperature of 500 ° C. or less.
8. The material has the shape of a bar;
   The method according to claim 7, wherein the plurality of times of plastic processing in which the cumulative processing rate is 30% or more is processing to reduce a cross-sectional area of the bar material.
9. The method according to claim 8, wherein the plastic working includes a step of compressing from a peripheral surface of the bar toward an axis.
10. The method according to any one of claims 7 to 9, wherein no heat treatment is performed during the plurality of plastic workings.
11. In a method for producing a Ni-base superalloy having a component composition in which the equilibrium precipitation amount of a gamma prime phase at 700 ° C. is 35 mol% or more,
    A preparation step of preparing an alloy material having a hardness of 500 HV or more and a crystal grain having a maximum diameter of 75 nm or less in a cross-sectional structure;
    And a processing step of performing plastic working on the alloy material at a temperature of 500 ° C. or lower to obtain an alloy having a hardness of 500 HV or higher.
12. The method according to claim 11, wherein the processing step is repeated a plurality of times.
13. The method according to claim 12, wherein no heat treatment is performed during the plurality of processing steps.
14. 14. The method according to claim 11, wherein the alloy material and the alloy have 5 or more crystal grains having a maximum diameter of 75 nm or less per 1 μm ^{2 in} a cross-sectional structure. .
15. The Ni-based superalloy is mass%,
    C: 0 to 0.25%
    Cr: 8.0-25.0%,
    Al: 0.5 to 8.0%,
    Ti: 0.4 to 7.0%,
    Co: 0 to 28.0%,
    Mo: 0-8%,
    W: 0 to 6.0%,
    Nb: 0 to 4.0%,
    Ta: 0 to 3.0%,
    Fe: 0 to 10.0%,
    V: 0 to 1.2%
    Hf: 0 to 1.0%
    B: 0 to 0.300%,
    Zr: 0 to 0.300%
    The method according to claim 11, wherein the balance is made of Ni and impurities.
16. The method according to any one of claims 11 to 15, wherein the equilibrium composition amount of the gamma prime phase at 700 ° C has a component composition of 40 mol% or more.
17. The Ni-based superalloy is mass%,
    C: 0 to 0.03%,
    Cr: 8.0-22.0%,
    Al: 2.0 to 8.0%,
    Ti: 0.4 to 7.0%,
    Co: 0 to 28.0%,
    Mo: 2.0 to 7.0%,
    W: 0 to 6.0%,
    Nb: 0 to 4.0%,
    Ta: 0 to 3.0%,
    Fe: 0 to 10.0%,
    V: 1.2% or less,
    Hf: 0 to 1.0%
    B: 0 to 0.300%,
    Zr: 0 to 0.300%
    The method according to claim 11, wherein the balance is made of Ni and impurities.
    

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