JP6826766B1 - Manufacturing method of Ni-based super heat-resistant alloy and Ni-based super heat-resistant alloy - Google Patents

Abstract

Provided are a method for producing a Ni-based superheat-resistant alloy having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more, and a Ni-based superheat-resistant alloy. The method of the present invention relates to (a) a material having a component composition having a carbon content of 0.05 to 0.25% by mass and an equilibrium precipitation amount of the gamma prime phase at 700 ° C. of 35 mol% or more. , The step of producing the first processed material by cooling after performing plastic working at a temperature of 900 ° C. or higher, and (b) heating the first processed material to a temperature of 900 ° C. or higher to perform heat treatment. The step of producing the first heat-treated material is included. Further, (c) further includes a step of plastically working the first heat-treated material at a temperature of 500 ° C. or lower to prepare a second processed material. The present invention is for cold plastic working, has the above-mentioned component composition, has an area ratio of M23C6 of 4.0 area% or less in a cross-sectional structure, and has an average particle size of the maximum diameter of crystal grains of 1. It is a Ni-based super heat-resistant alloy of 4 to 100 μm.

Description

The present invention relates to a method for producing a Ni-based superheat-resistant alloy and, specifically, a Ni-based superheated alloy having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more. It relates to a method for producing a heat-resistant alloy and a Ni-based super heat-resistant alloy.

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. Along with higher performance and lower fuel consumption 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 a Ni-based superheat-resistant alloy, the gamma prime (hereinafter, also referred to as "γ'") phase, which is a precipitation strengthening phase of an intermetallic compound having Ni ₃ Al as a main composition. It is most effective to increase the amount of. The Ni-based superheat-resistant alloy further contains the γ'forming elements Al, Ti, and Nb, so that the high-temperature strength of the Ni-based superheat-resistant alloy can be further improved. In the future, in order to satisfy high heat resistance and high strength, a Ni-based super heat resistant alloy having a larger amount of γ'phase will be required.

However, it is known that Ni-based superheat-resistant alloys are difficult to process because the deformation resistance of hot processing increases as the γ'phase increases. In particular, when the amount of the γ'phase is 35 to 40 mol% or more, the processability is particularly lowered. For example, alloys such as Inconel (registered trademark) 713C alloy, IN939, IN100, and Mar-M247 have a particularly large number of γ'phases, which makes plastic working impossible, and are usually cast as cast alloys (as-cast). Used in.

As a proposal for improving the hot plastic workability of such a Ni-based superheat-resistant alloy, in Patent Document 1, a Ni-based superheat-resistant alloy ingot having a composition having a γ'molar ratio of 40 mol% or more is processed at a processing rate of 5%. A manufacturing method is described in which cold working is performed at a temperature of less than 30% and then heat treatment is performed at a temperature exceeding the γ'solid solution temperature. In this method, a recrystallization rate of 90% or more, which enables hot working to be applied to a Ni-based superheat-resistant alloy, is obtained by combining a cold working step and a heat treatment step.

Further, in recent years, there is an increasing need for repairing heat-resistant parts of the above-mentioned Ni-based superheat-resistant alloy having a large amount of γ'phase, or manufacturing the heat-resistant parts themselves by three-dimensional molding. In that case, a fine wire of Ni-based super heat-resistant alloy is required as a modeling material. This thin wire can also be used by processing it into a component shape such as a spring. The wire diameter (diameter) of the thin wire of the Ni-based superheat-resistant alloy is, for example, as thin as 5 mm or less, further 3 mm or less. For such a thin wire, for example, it is efficient to prepare a "wire rod" having a wire diameter of 10 mm or less as an intermediate product and plastically process the wire rod to produce such a thin wire. If this intermediate product, "wire rod", can also be obtained by plastic working, it is possible to efficiently produce fine wires of Ni-based superheat-resistant alloys.
As a method for producing such a fine wire of a super heat-resistant alloy, 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, a bundle of these cast wires is hot-extruded, and then separated. Patent Document 2).

International Publication No. 2016/129485 U.S. Pat. No. 4777710

The method of Patent Document 1 is effective for Ni-based superheat-resistant alloys to which hot working is applied. However, as described above, the Ni-based superheat-resistant alloy has a decrease in hot plastic workability as the amount of the γ'phase increases. The method of Patent Document 2 is effective for producing 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 comes to a Ni-based super heat-resistant alloy, it is extremely difficult to hot-plasticize it to process fine wires. Further, the method of Patent Document 2 has a problem that the process is complicated and the manufacturing cost is high. Further, in producing thin wires and wire rods, there is a problem that if cracks occur in the middle of the process, the processing rate is limited and plastic working cannot be performed to a predetermined wire diameter.

An object of the present invention is to provide a method for producing a Ni-based superheat-resistant alloy having excellent plastic workability and a Ni-based superheat-resistant alloy, in particular, using a novel method completely different from the conventional one. It is to provide a new method capable of producing a fine wire of a super heat-resistant alloy and a Ni-based super heat-resistant alloy. Still another object of the present invention is to provide a method capable of producing a thin wire having few defects with a small number of man-hours at a reduced cost even with a Ni-based superheat-resistant alloy having a small wire diameter, and a Ni-based superheat-resistant alloy. ..

According to one aspect of the present invention, there is provided a method for producing a Ni-based superheat resistant alloy. This method
(A) A temperature of 900 ° C. or higher with respect to a material having a carbon content of 0.05 to 0.25% by mass and a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more. The process of producing the first processed material by cooling after performing plastic working in
(B) It includes a step of heating the first processed material to a temperature of 900 ° C. or higher to perform heat treatment to prepare the first heat-treated material.

According to one specific example, (c) the first heat-treated material includes a step of plastically working at a temperature of 500 ° C. or lower to produce a second processed material.

According to one specific example, it is preferable that (d) the second processed material further includes a step of performing a heat treatment at a temperature of 900 ° C. or higher.

Further, according to one specific example, the Ni-based superheat-resistant alloy is in mass%.
C: 0.05 to 0.25%,
Cr: 8.0-25.0%,
Al: 0.5-8.0%,
Ti: 0.4-7.0%,
Co: 0-28.0%,
Mo: 0-8.0%,
W: 0 to 15.0%,
Nb: 0-4.0%,
Ta: 0-5.0%,
Fe: 0 to 10.0%,
V: 0-1.2%,
Hf: 0-3.0%,
B: 0 to 0.300%,
Zr: 0 to 0.300%
It is preferable that the balance is composed of Ni and impurities.

Further, according to one aspect of the present invention, a Ni-based superheat resistant alloy is provided. This alloy is for cold plastic working and
It has a component composition having a carbon content of 0.05 to 0.25% by mass and an equilibrium precipitation amount of the gamma prime phase at 700 ° C. of 35 mol% or more.
In the cross-sectional structure, the area ratio of M ₂₃ C ₆ is 4.0 area% or less, and the average particle size of the maximum diameter of the crystal grains is 1.4 to 100 μm.

According to one specific example, the hardness of the Ni-based superheat-resistant alloy is preferably 460 HV or less.

Further, according to one specific example, the Ni-based superheat-resistant alloy is in mass%.
C: 0.05 to 0.25%,
Cr: 8.0-25.0%,
Al: 0.5-8.0%,
Ti: 0.4-7.0%,
Co: 0-28.0%,
Mo: 0-8.0%,
W: 0 to 15.0%,
Nb: 0-4.0%,
Ta: 0-5.0%,
Fe: 0 to 10.0%,
V: 0-1.2%,
Hf: 0-3.0%,
B: 0 to 0.300%,
Zr: 0 to 0.300%
It is preferable that the balance is composed of Ni and impurities.

The advantages, features and details of the present invention will become apparent by reference to the following non-limiting examples and accompanying drawings.

An electron backscatter diffraction (EBSD) image of a cross-sectional microstructure of a Ni-based superheat-resistant alloy subjected to plastic working with a surface reduction rate of 31%. The figure explaining the carbide in the structure when plastic working is performed on the 1st processed material which concerns on this invention. The figure explaining the cold plastic workability of the 1st heat-treated material (material) when the 1st processed material which concerns on this invention is heat-treated. Cross-sectional microstructure of material 1 (without heat treatment), EPMA mapping diagram of Cr and Nb, and EBSD image of Material 1 in Example 1. The cross-sectional microstructure of the material 2 (heat treatment temperature 1000 ° C.) in Example 1, the EPMA mapping diagram of Cr and Nb, and the EBSD image. Cross-sectional microstructure of material 3 (heat treatment temperature 1050 ° C.) in Example 1, EPMA mapping diagram of Cr and Nb, and EBSD image. The cross-sectional microstructure of the material 4 (heat treatment temperature 1100 ° C.) in Example 1, the EPMA mapping diagram of Cr and Nb, and the EBSD image. The cross-sectional microstructure of the material 5 (heat treatment temperature 1150 ° C.) in Example 1, the EPMA mapping diagram of Cr and Nb, and the EBSD image. The cross-sectional microstructure of the material 6 (heat treatment temperature 1200 ° C.) in Example 1, the EPMA mapping diagram of Cr and Nb, and the EBSD image. Cross-sectional microstructure of material 7 (heat treatment temperature 1200 ° C., air cooling) in Example 1, EPMA mapping diagram of Cr and Nb, and EBSD image. The figure which shows the relationship between the heat treatment temperature and the area ratio of a carbide when the 1st heat treatment material (material) is prepared by performing heat treatment on the 1st processed material in Example 1. FIG. FIG. 5 is a diagram showing the relationship between the heat treatment temperature and the number density of carbides when the first heat-treated material (material) is produced by heat-treating the first processed material in Example 1. The figure which shows the relationship between the heat treatment temperature and the crystal grain size when the first heat treatment material (material) was prepared by performing heat treatment on the 1st processed material in Example 1. FIG. The figure which shows the relationship between the heat treatment temperature and hardness at the time of producing the 1st heat treatment material (material) by performing heat treatment on the 1st processed material in Example 1. FIG.

The present invention provides a new method capable of producing a Ni-based super heat-resistant alloy having excellent plastic workability and a Ni-based super heat-resistant alloy by a new approach different from the conventional hot plastic working.
The present inventor studied the plastic workability of a Ni-based superheat-resistant alloy having a large amount of γ'phase. As a result, we found a phenomenon that it is possible to perform cold plastic working on a Ni-based super heat-resistant alloy that has been heat-treated by heating again after hot plastic working.
At that time, it was found that nanocrystal grains were generated in the structure of the Ni-based superheat-resistant alloy by cold plastic working at a processing rate of 30% or more. It is presumed that the formation of these nanocrystal grains contributes to the dramatic improvement in the plastic workability of the Ni-based superheat-resistant alloy.

Therefore, according to the present invention, the method for producing a Ni-based superheat-resistant alloy having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more is
(A) A temperature of 900 ° C. or higher with respect to a material having a carbon content of 0.05 to 0.25% by mass and a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more. The process of producing the first processed material by cooling after performing plastic working in
(B) It includes a step of heating the first processed material to a temperature of 900 ° C. or higher to perform heat treatment to prepare the first heat-treated material.
Then, in addition to the steps (a) and (b) described above,
(C) This material includes a step of plastically working the first heat-treated material at a temperature of 500 ° C. or lower to produce a second processed material.

The Ni-based superheat-resistant alloy targeted by the present invention is a component having a carbon content of 0.05 to 0.25% by mass and an equilibrium precipitation amount of the gamma prime (γ') phase at 700 ° C. of 35 mol% or more. Has a composition.
Here, the amount of the γ'phase of the Ni-based superheat-resistant alloy can be expressed by a numerical index such as "volume fraction" or "area fraction" of the γ'phase. In the present specification, the amount of the γ'phase is represented by a numerical index of “γ'molar rate”. The γ'molar ratio is a stable equilibrium precipitation amount of the gamma prime phase in which a Ni-based superheat resistant alloy can be precipitated in a thermodynamic equilibrium state. The value of the equilibrium precipitation amount of the gamma prime phase expressed in "molar ratio" is determined by the component composition of the Ni-based superheat-resistant alloy. The value of mol% of this 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'mol rate of the Ni-based superheat-resistant alloy is defined as "equilibrium precipitation amount at 700 ° C.". The high-temperature strength of the Ni-based superheat-resistant alloy can be evaluated by the equilibrium precipitation amount of the gamma prime phase in the structure, and the larger the high-temperature strength, the more difficult the hot plastic working. The equilibrium precipitation amount of the gamma prime phase in the structure is generally about 700 ° C. or lower, the temperature dependence becomes small and becomes almost constant. Therefore, the value at "700 ° C." is used as a reference.

As described above, hot plastic working is usually more difficult as the γ'molar ratio of the Ni-based superheat resistant alloy is larger. However, according to the present invention, increasing the γ'molar ratio greatly contributes to the improvement of the cold plastic workability of the Ni-based superheat-resistant alloy. By having "nanocrystal grains" in the cross-sectional structure of the Ni-based superheat-resistant alloy, the cold plastic workability can be dramatically improved. These nanocrystal grains are most likely to be generated from the phase interface between the austenite phase (gamma (γ) phase), which is a matrix of Ni-based superheat-resistant alloys, and the gamma prime phase. Therefore, increasing the γ'molar ratio of the Ni-based superheat-resistant alloy leads to an increase in the above-mentioned phase interface and contributes to the formation of nanocrystal grains. FIG. 1 shows an example of an EBSD image of a cross-sectional microstructure produced by cold plastic working of a wire rod in the manufacturing method of the present invention. The EBSD measurement conditions are as follows: Magnification: 10000 times, scanning using the EBSD measurement system "OIM Version 5.3.1 (manufactured by TSL Solution)" attached to the scanning electron microscope "ULTRA55 (manufactured by Zeiss)" Step: 0.01 μm, and the definition of crystal grains was defined as grain boundaries with an orientation difference of 15 ° or more. The maximum diameter (maximum length) of the nanocrystal grains (enclosed portion) confirmed in the EBSD image in FIG. 1 is as small as about 25 nm.

When the γ'mol ratio reaches the level of 35%, the formation of the above-mentioned 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. The equilibrium precipitation amount of the gamma prime phase is more preferably 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 even 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 is practically about 75 mol%.

As a precipitation-strengthening Ni-based superheat-resistant alloy in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more, for example, in mass%, C: 0.05 to 0.25%, Cr: 8.0 to 8.0 25.0%, Al: 0.5 to 8.0%, Ti: 0.4 to 7.0%, Co: 0 to 28.0%, Mo: 0 to 8.0%, W: 0 to 15 0.0%, Nb: 0-4.0%, Ta: 0-5.0%, Fe: 0-10.0%, V: 0-1.2%, Hf: 0-3.0%, B : 0 to 0.300%, Zr: 0 to 0.300%, and the balance preferably has a composition of Ni and impurities.

Hereinafter, each component having a preferable composition of the Ni-based superheat-resistant alloy of the present invention will be described (the unit of the component composition is "mass%").

Carbon (C)
Conventionally, C is contained as an element that enhances the castability of a Ni-based superheat-resistant alloy. In particular, Ni-based superheat-resistant alloys having a large amount of γ'phase are usually used as cast parts because plastic working is difficult, and a certain amount of C is added. This added C remains as a carbide in the cast structure, and a part of it is formed as a coarse eutectic carbide. Then, such coarse carbides serve as a crack starting point and a crack growth path when the Ni-based superheat-resistant alloy is plastic-worked, especially when the Ni-based superheat-resistant alloy is plastic-worked at room temperature. It has an adverse effect on sexuality.

Therefore, for the present invention in which a Ni-based superheat-resistant alloy having a large amount of γ'phase is produced by plastic working, not as a cast part, in the Ni-based superheat-resistant alloy. It is preferable to reduce C. In the case of the present invention, the C content is 0.25% or less. It is preferably 0.20% or less. More preferably, it is 0.15% or less.
However, C is also an element that enhances the strength of heat-resistant parts, and it is preferable that C is contained in consideration of producing or repairing such heat-resistant parts. According to the method for producing a Ni-based superheat-resistant alloy of the present invention, plastic working is possible even with an alloy having a high C content due to the effect of the nanocrystal grains described above. Even in that case, in the case of alloys with a high C content, when thin wires, wire rods, and other shaped products are manufactured by plastic working at room temperature, the above carbides can serve as crack origins and crack growth paths. The rate is limited. On the other hand, by using the Ni-based superheat-resistant alloy before plastic working as a "material" produced by the first hot plastic working and the first heat treatment, which will be described later, the cracks in the carbides can be cracked. Since the problem can be dealt with, for example, a C content similar to that in a cast part can be tolerated.
Therefore, in the method for producing a Ni-based superheat-resistant alloy according to the present invention, C is assumed to be contained in an amount of 0.05% or more. It is preferably 0.06% or more, more preferably 0.07% or more, still more preferably 0.1% or more. Furthermore, C may be contained in an amount of more than 0.1%.

Chromium (Cr)
Cr is an element that improves oxidation resistance and corrosion resistance. However, if Cr is excessively contained, an embrittled phase such as a σ (sigma) phase is formed, which reduces the strength and hot workability at the time of material preparation. Therefore, Cr is preferably set to 8.0 to 25.0%, for example. More preferably, it is 8.0 to 22.0%. The preferred lower limit is 9.0%, more preferably 9.5%. More preferably, it is 10.0%. The upper limit is preferably 18.0%, more preferably 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 the high temperature strength is impaired. Therefore, Mo is preferably 0 to 8.0% (addition-free (unavoidable impurity level) may be used). More preferably, it is 2.0 to 7.0%. A further preferred lower limit is 2.5%, 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 γ'(Ni ₃ Al) phase, which is a strengthening phase, and improves high-temperature strength. However, excessive addition reduces 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 further preferred lower limit is 2.5%, more preferably 3.0%. It is even more preferably 4.0% and even more preferably 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 relation to the above-mentioned Cr, when the Cr content is reduced in order to ensure hot workability at the time of material preparation, the reduced Al content can be allowed. Then, for example, when the upper limit of Cr is set to 13.5%, the lower limit of the Al content is preferably set to 3.5%.

Titanium (Ti)
Like Al, Ti is an element that forms a γ'phase and strengthens the γ'phase by solid solution to increase high-temperature strength. However, excessive addition causes the γ'phase to become unstable at high temperatures, leading to coarsening at high temperatures, forming a harmful η (eta) phase, and impairing hot workability during material preparation. Therefore, Ti is preferably 0.4 to 7.0%, for example. 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%. The upper limit is preferably 6.5%, more preferably 6.0%. It is more preferably 4.0%, and particularly preferably 2.0%.

Hereinafter, optional components that can be added to the Ni-based superheat-resistant alloy 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 a large amount of Ti, which is a reinforcing element, is contained. On the other hand, since Co is expensive, the cost increases. Therefore, Co is one of the arbitrary elements that can be contained in the range of 28.0% or less, for example, by combining with other elements. The preferable lower limit when 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%. If Co may be added-free (the level of unavoidable impurities in the raw material) depending on the balance with the γ'forming element and the Ni matrix, the lower limit of Co is set to 0%.

Tungsten (W)
Like Mo, W is one of the selective elements that contributes to the solid solution strengthening of the matrix. However, if W becomes excessive, a harmful intermetallic compound phase is formed and the high temperature strength is impaired. Therefore, for example, the upper limit is set to 15.0%. The preferred upper limit is 13.0%, more preferably 11.0%, and even more preferably 9.0%. In order to more reliably exert the effect of W described above, the lower limit of W is preferably 1.0%. Preferably, the lower limit of W can be set to 3.0%, 5.0%, 7.0%. Further, by adding W and Mo in combination, a more solid solution strengthening effect can be exhibited. In the case of composite addition, W is preferably added in an amount of 0.8% or more. If W can be set to a non-addition level (a level of unavoidable impurities in the raw material) by sufficiently adding Mo, the lower limit of W is set to 0%.

Niobium (Nb)
Like Al and Ti, Nb is one of the selective elements that forms the γ'phase and strengthens the γ'phase by solid solution to increase the high temperature strength. 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%. The preferred upper limit is 3.5%, more preferably 2.5%. In order to more reliably exert the effect of Nb, the lower limit of Nb is preferably 1.0%. It is preferably 2.0%. When Nb may be set to a non-addition level (unavoidable impurity level) by adding another γ'forming element, the lower limit of Nb is set to 0%.

Tantalum (Ta)
Like Al and Ti, Ta is one of the selective elements that forms the γ'phase and strengthens the γ'phase by solid solution 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, which improves hot workability during material preparation. To spoil. Therefore, Ta is set to 5.0% or less, for example. It is preferably 4.0% or less, more preferably 3.0% or less, still more preferably 2.5% or less. In order to more reliably exert the effect of Ta, the lower limit of Ta is preferably 0.3%. Preferably, the lower limit of Ta can be 0.8%, 1.5%, 2.0%. If Ta may be an additive-free level (unavoidable impurity level) due to the addition of γ'forming 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 a substitute for expensive Ni and Co, and is effective in reducing the alloy cost. To obtain this effect, it is advisable to decide whether or not to add in combination with other elements. However, if Fe is excessively contained, an embrittled phase such as a σ (sigma) phase is formed, which reduces the strength and hot workability at the time of material preparation. Therefore, the upper limit of Fe is, for example, 10.0%. The preferred upper limit is 9.0%, more preferably 8.0%. On the other hand, if Fe may be added-free level (unavoidable impurity level) depending on the balance with the γ'forming element and 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 manufacturing process, which adversely affects the manufacturability and high temperature mechanical performance. Therefore, the upper limit of V is, for example, 1.2%. The preferred upper limit is 1.0%, more preferably 0.8%. In order to more reliably exert the effect of V, the lower limit of V is preferably 0.5%. If V may be an additive-free level (unavoidable impurity level) due to the balance with other alloying 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 causes oxide formation in the manufacturing process and formation of a high temperature unstable phase, which adversely affects manufacturability and high temperature mechanical performance. Therefore, the upper limit of Hf is, for example, 3.0%, preferably 2.0%, and more preferably 1.5%. In order to more reliably exert the above-mentioned effect of Hf, the lower limit of Hf may be set to 0.1%. Preferably, the lower limit of Hf can be 0.5%, 0.7%, 1.0%. When Hf may be added-free level (unavoidable impurity level) depending on the balance with other alloying elements in the alloy, the lower limit of Hf is set to 0%.

Boron (B)
B is an element that improves grain boundary strength and improves creep strength and ductility. On the other hand, B has a large effect of lowering the melting point, and when a coarse boride is formed, the hot workability at the time of material preparation is hindered. Therefore, for example, it does not exceed 0.300%. It is good to control it like this. The preferred upper limit is 0.200%, more preferably 0.100%. It is more preferably 0.050%, and particularly preferably 0.020%. In order to obtain the above effect, the content is preferably at least 0.001%. A more preferable lower limit is 0.003%, and even more preferably 0.005%. Particularly preferably, it is 0.010%. If B may be added-free level (unavoidable impurity level) depending on the balance with other alloying elements in the alloy, the lower limit of B is set to 0%.

Zirconium (Zr)
Like B, Zr has the effect of improving the grain boundary strength. On the other hand, if Zr is excessive, the melting point is also lowered, and the high temperature strength and the hot workability at the time of material preparation are impaired. Therefore, the upper limit of Zr is, for example, 0.300%. The preferred upper limit is 0.250%, more preferably 0.200%. It is more preferably 0.100%, and particularly preferably 0.050%. In order to obtain the above effect, the content is preferably at least 0.001%. A more preferable lower limit is 0.005%, and even more preferably 0.010%. When Zr may be added-free level (unavoidable impurity level) depending on the balance with other alloying elements in the alloy, the lower limit of Zr is set to 0%.

The balance other than the elements described above is Ni, but unavoidable impurities may be contained.

Next, a specific example of the production method of the present invention for producing a Ni-based superheat-resistant alloy having the component composition described above and the Ni-based superheat-resistant alloy will be described.

(A) Step of Producing First Processed Material The method of producing the first processed material to be subjected to the heat treatment described later is not particularly limited. For example, the first processed material can be obtained by a melting method in which molten metal is poured into a mold to produce an ingot. Then, for the production of the ingot, for example, vacuum melting and conventional methods such as vacuum arc remelting and electroslag remelting may be combined and applied. Alternatively, the first processed material may be obtained by a powder metallurgy method. Then, the above-mentioned ingot or alloy ingot material produced by the powder metallurgy method is subjected to hot working such as hot forging, hot rolling, and hot extrusion, and then cooled to form a predetermined shape. Can be finished as a processed material. For example, it may be finished as a processed material in the shape of a bar material. The processing temperature (processing start temperature) in hot processing shall be 900 ° C. or higher. Further, in order to facilitate plastic working, the temperature is preferably 950 ° C. or higher, more preferably 1000 ° C. or higher, still more preferably 1050 ° C. or higher. And it is realistic that the temperature is 1250 ° C or lower at the highest.
In addition, heat treatment such as soaking can be performed between these operations. For example, soaking (for example, holding at 1100 ° C. to 1280 ° C. for 5 to 60 hours) may be performed to eliminate the elemental segregation of the ingot. Alternatively, for example, soaking may be performed after finishing the shape of a material (billet) to be subjected to hot extrusion.
The processed material after cooling can be machined (for example, cutting, polishing, grinding, etc. for dimensional adjustment and various maintenance), if necessary.

As an example of producing the first processed material, a case where the above material is hotly extruded to be finished as a material of a bar material having a predetermined shape will be described. The conditions for hot extrusion are preferably an extrusion temperature (heating temperature of the material) of 1050 ° C. to 1200 ° C., an extrusion ratio of 4 to 20, and an extrusion speed (stem speed) of 5 to 80 mm / s. The cross-sectional diameter of the extruded material) is, for example, 10 mm or more or more than 20 mm. And, for example, it is 200 mm or less. Then, when the bar material is manufactured, the surface of the extruded material can be finished by machining or the like, or the bar material having a predetermined size can be collected from the extruded material. In this case, the cross-sectional diameter of the bar can be set to, for example, 150 mm or less, 100 mm or less, 50 mm or less, 30 mm or less, 10 mm or less. Keeping the cross-sectional diameter of the bar small is that the number of plastic workings (number of passes) can be reduced when making wire rods, thin wires, etc. with even smaller cross-sectional diameters in cold plastic working, which will be described later. preferable.

(B) Step of Producing First Heat Treatment Material (Material) In the present invention, first, a first heat treatment material (referred to as “material”) having the component composition described above is prepared. Then, the Ni-based superheat-resistant alloy obtained by subjecting this material to strong processing (for example, processing having a processing rate of 30% or more) in the plastic working of (c) described later can be further processed. become. Therefore, cold working can be performed up to a larger working rate without performing heat treatment during plastic working.
However, the Ni-based superheat-resistant alloy targeted by the present invention contains 0.05 to 0.25% by mass of carbon. Various carbides typified by MC and M ₂₃ C ₆ are formed in the structure of the material produced by subjecting the material having this composition to hot working such as hot forging, hot rolling, and hot extrusion. There is. Then, coarse carbide 2 is precipitated in the structure of the material 1 (FIG. 2). After cold plastic working on material 1 and cold plastic working with a cumulative working rate of, for example, 40% or more, the processed material 3 of the Ni-based superheat-resistant alloy has a γ phase and a γ'phase. It becomes a linear structure extending in the stretching direction. The carbides are crushed by plastic working to become fine carbides 4, but the fine carbides are present in the processed structure as a carbide aggregate in which the fine carbides are connected in the extending direction of the structure. Material defects 5 (for example, gaps due to lack of material) are formed between the fine carbides. If plastic working is further performed as it is, the defects 5 between the fine carbides 4 may spread and combine with the adjacent defects 5 to become the starting point of cracking. Therefore, by adjusting the morphology of the carbides in the structure before the cold plastic working, it is possible to prevent the defect 5 from being generated in the cold plastic working. For example, in the cross-sectional structure in the stretching direction, the defect rate can be 0.5 area% or less. Therefore, it is possible to suppress the occurrence of cracks starting from material defects.

Then, in the adjustment of the form of the carbide, the temperature of 900 ° C. or higher is again applied to the material (referred to as "first processed material") that has been once cooled after the hot working. The first heat-treated material is obtained by heating the material to heat-treat it. The reason why the morphology of carbides in the material structure is adjusted by this heat treatment and the occurrence of cracks during plastic working is suppressed is that the first processed material (extruded material) before cold plastic working is shown in FIG. Using the relationship between the temperature of the heat treatment applied and the cold plastic workability (surface reduction rate), it can be considered as follows.

<Stage 1>
Coarse MC is formed in the structure of the first processed material produced by hot processing at the above processing temperature. Then, a "composite carbide" formed by contacting the MC and the M ₂₃ C ₆ is formed. When plastic working is performed on such a structure, it is considered that M ₂₃ C ₆ and MC are separated at the interface and cause material defects. Therefore, by heating the first processed material to a heat treatment temperature of 900 ° C. or higher, most of the MC reacts with the gamma phase and changes its form to M ₂₃ C ₆ , especially at the position of the surface layer described above. The proportion of complex carbides is reduced. As a result, the occurrence of cracks due to the above-mentioned carbides is suppressed in the vicinity of the surface layer of the first processed material, which is the starting point of cracks, and the basic plastic workability of the first heat-treated material is improved.

<Stage 2>
By heating the first processed material to a heat treatment temperature of 900 ° C. or higher, the proportion of the above-mentioned composite carbides decreases, but when the heat treatment temperature exceeds 1000 ° C., the solid solution of M ₂₃ C ₆ is formed. It seems to start moving forward. However, a part of M ₂₃ C ₆ reacts with the gamma prime phase and changes its morphology to MC, and as a result, in the structure of the "first heat treatment material" after the heat treatment, the morphologically changed MC is changed to M ₂₃ C ₆ The "composite" carbides that come into contact with the are formed again. Then, when the first heat-treated material having such a structure is subjected to plastic working, the above-mentioned composite carbide is separated at the interface between the MC and M ₂₃ C ₆ , like the above-mentioned first processed material. , It is considered that it is a factor that causes the above-mentioned material defects. As a result, the material under plastic working tends to be cracked due to carbides, and the plastic workability tends to be lower than that of the stage 1 material. However, in spite of this tendency, the crystal grain size of the first heat-treated material after the heat treatment grows from that of the first processed material, and the plastic workability of the first heat-treated material is the first. Can be superior to that of processed materials.

<Stage 3>
As described above, when the heat treatment temperature exceeds about 1000 ° C., the plastic workability of the first heat treatment material after the heat treatment tends to decrease, but when the heat treatment temperature exceeds 1150 ° C., the first heat treatment material becomes the first. The plastic workability of the heat-treated material is greatly improved. This is because the morphological change of M ₂₃ C ₆ to MC progresses, and the solid solution of M ₂₃ C ₆ further progresses. Then, when the heat treatment temperature reaches 1200 ° C., most of M ₂₃ C ₆ in the structure is solid-solved, and even if MC remains in the structure, the amount of the above-mentioned "composite" carbide is greatly reduced. To do. Then, the remarkable growth of the crystal grains also acts on this, and the plastic workability of the first heat-treated material is greatly improved.

Based on the above results, the first heat-treated material according to the present invention has an area ratio of M ₂₃ C ₆ of 4.0 area% or less, 3.0 area% or less, or 2 in its cross-sectional structure. It is less than 0.0 area%. Preferably, for example, it is 1.5 area% or less, 1.0 area% or less, 0.7 area% or less, 0.5 area% or less. And more preferably, it is 0.3 area% or less, 0.2 area% or less, and 0.1 area% or less (including the case of 0 area%).
Further, the first heat-treated material according to the present invention preferably has a number density of M ₂₃ C ₆ of 10.0 × ^10-2 / μm ² or less or 7.0 × in its cross-sectional structure. ^10-2 pieces / μm ² or less, 5.0 × ^10-2 pieces / μm ² or less, 3.0 × ^10-2 pieces / μm ² or less. Further, as the solid solution of M ₂₃ C ₆ progresses, more preferably, for example, 1.5 × ^10-2 pieces / μm ² or less, 1.3 × ^10-2 pieces / μm ² or less, 1. 0 × ^10-2 pieces / μm ² or less, 0.5 × ^10-2 pieces / μm ² or less. And more preferably, for example, 0.3 × ^10-2 pieces / μm ² or less, 0.2 × 10 ^-2 pieces / μm ² or less, 0.1 × ^10-2 pieces / μm ² or less ( Including the case of 0 pieces / μm ² ).

Further, the first heat-treated material according to the present invention preferably has an MC area ratio of 12.0 area% or less or 10.0 area% or less in its cross-sectional structure. And, for example, it is 8.0 area% or less, 6.0 area% or less, 5.0 area% or less. Further, for example, it is preferably 0.1 area% or more, 1.0 area% or more, and 2.0 area% or more. More preferably, for example, it is 2.5 area% or more, 3.1 area% or more, 3.2 area% or more, and 3.5 area% or more. And more preferably, it is 3.8 area% or more, 4.2 area% or more, and 4.5 area% or more.
Further, the first heat-treated material according to the present invention preferably has a cross-sectional structure in which the number density of MCs is, for example, 5.0 × ^10-2 / μm ² or less, or 3.0 × ^10-2. Pieces / μm ² or less, 2.5 × ^10-2 pieces / μm ² or less. More preferably, for example, 2.0 × ^10-2 pieces / μm ² or less, 1.7 × ^10-2 pieces / μm ² or less, 1.5 × ^10-2 pieces / μm ² or less. Further, for example, 0.1 × ^10-2 pieces / μm ² or more, 0.5 × ^10-2 pieces / μm ² or more, 1.0 × ^10-2 pieces / μm ² or more.

The upper limit of the heat treatment temperature is not particularly limited, but is about 1250 ° C. The heat treatment temperature is preferably a temperature exceeding 1150 ° C. The heat treatment time can be, for example, 30 minutes or more, 45 minutes or more, 60 minutes or more depending on the size and shape of the first processed material, and the upper limit is 180 minutes or less, 120 minutes or less, 90 minutes or less. It may be decided as appropriate. The heat treatment is preferably carried out in a vacuum, a reducing atmosphere, an inert atmosphere such as Ar, in order to avoid surface oxidation, but may be carried out in an oxidizing atmosphere (for example, an atmospheric atmosphere). When the heat treatment is performed in an oxidizing atmosphere, an oxidation scale is formed on the surface. If cold plastic working is performed with the oxide scale formed, it may become the starting point of cracks and defects. Therefore, it may be removed mechanically or chemically by, for example, polishing or grinding. In the case of wire rod production, it is preferable to remove the scale by using centerless polishing. When the heat treatment is performed in an oxidizing atmosphere, the heat treatment time is preferably completed in a short time, for example, 150 minutes or less, 100 minutes or less, 80 minutes or less.

In the present invention, the crystal grain size of the structure of the first heat-treated material (the average grain size of the maximum diameter of the crystal grains described later) can be set to 100 μm or less. It is preferably 80 μm or less, more preferably 60 μm or less, still more preferably 40 μm or less, still more preferably 20 μm or less. The refinement of crystal grains is effective for the production of nanocrystal grains. In addition, the crystal grains generated by recrystallization have less distortion in the grains, and the grain boundaries also increase by making the crystal grains finer. Therefore, if the cold plastic working described later is performed on this, the crystal grains can be increased. Processing strain is evenly applied to the entire structure. Therefore, by performing the above heat treatment, the deformation in the plastic working of the next step becomes more uniform, it is possible to avoid the occurrence of abnormal deformation and bending during the working, and the yield can be dramatically improved.
Then, the crystal grain size of the structure of the first heat-treated material can be made 1.4 μm or more. By growing the crystal grains, this acts on the adjustment of the distribution form of the carbides described above, and the plastic workability of the first heat-treated material is improved. It is preferably 1.5 μm or more, more preferably 1.8 μm or more. Then, as the heat treatment temperature rises, the crystal grain size of the first heat treatment material grows to, for example, 2.0 μm or more, 3.0 μm or more, 4.0 μm or more, 5.0 μm or more. For example, when the heat treatment temperature is a temperature exceeding 1150 ° C. or a temperature of 1200 ° C. or higher, it grows to a value of 7.0 μm or higher or 9.0 μm or higher.

In the present invention, the hardness of the first heat-treated material is not limited. Therefore, the cooling after the above heat treatment may be rapid cooling, air cooling, air cooling, furnace cooling, or the like. The hardness of the first heat-treated material can be, for example, 460 HV or less or 450 HV or less. More preferably, it is 430 HV or less. It is more preferably 400 HV or less, and even more preferably 380 HV or less. By setting the cooling rate after the heat treatment to a cooling rate slower than that of air cooling (for example, the cooling rate by furnace cooling), the hardness of the first heat treatment material can be made lower. Further, by slowing down the cooling rate after the heat treatment, it is preferable to suppress surface cracking of the first heat-treated material after cooling, and it is preferable for the smooth progress of the subsequent plastic working.
The lower limit of the hardness of the first heat-treated material is not particularly limited, but is realistically about 250 HV. Then, the hardness of the first heat-treated material can be set to 300 HV or more. The hardness of the first heat-treated material can be measured in cross section thereof.

As a result, it is possible to suppress a decrease in plastic workability due to carbides of the material (first heat-treated material) to be subjected to cold plastic working, so that the above-mentioned effect of forming nanocrystal grains is not hindered and is effective. It is possible to perform cold working up to a large working rate without heat-treating the material being plastically worked.

(C) Step of Producing Second Processed Material Next, cold plastic working is performed on the above material (first heat-treated material). Since the above-mentioned material is excellent in plastic working and is also excellent in plastic working during plastic working, it is possible to perform a plurality of cold plastic working in which the cumulative working rate from the material is 40% or more. The present invention produces a Ni-based superheat resistant alloy by "cold" plastic working, as opposed to conventional "hot" plastic working. In particular, in the case of a Ni-based superheat-resistant alloy having a γ'phase of 35 mol% or more, a cumulative working rate of 40% or more can be obtained by cold plastic working, and the alloy is processed by hot plastic working. The above-mentioned Ni-based superheat-resistant alloy, which has been difficult to achieve, can be processed into, for example, wire rods and fine wires in a relatively simple process and at low cost. In order to achieve this, it is necessary to carry out the above-mentioned cold plastic working in a low temperature region where recovery or recrystallization cannot occur during the plastic working.
Therefore, the plastic working temperature in the present invention is preferably "500 ° C. or lower". It is more preferably 300 ° C. or lower, still more preferably 100 ° C. or lower, and even more preferably 50 ° C. or lower (for example, room temperature).

The method for producing a Ni-based superheat-resistant alloy of the present invention can be applied to the production of various shapes. Although it is suitable for the wire rod form, it can also be applied to a plate material, a strip material, and the like. Therefore, the Ni-based superheat-resistant alloy produced by the production method of the present invention has an intermediate product shape of a wire material, a sheet material, and a strip material, and also has a wire material. It may be the final product shape of a product), a sheet product, or a strip product. Regarding the relationship between the dimensions of the plate material (thin plate) and the strip material (thin strip), the wire diameter (diameter) of the wire rod (thin wire) can be read as the plate thickness or the strip thickness.

In particular, when the hot-extruded material of the Ni-based superheat-resistant alloy is a bar, the bar can be processed to compress the cross-sectional area. In this case, using the Ni-based super heat-resistant alloy "bar" as a starting material, as a mode of plastic working performed on this bar, "vertical to the longitudinal direction of the bar" that can uniformly apply pressure to the bar. It is preferable to perform "processing to compress the cross-sectional area of the cross section". Then, the material of this bar material is processed by plastically compressing the cross-sectional area (bar diameter) to increase the length. In particular, when obtaining a wire rod made of a Ni-based superheat-resistant alloy, it is efficient to plastically process a "bar rod" having a cross-sectional area (diameter) larger than that of the wire rod. The cross-sectional area of the bar is compressed by performing plastic working with a cumulative working rate of 40% or more from the peripheral surface of the bar to the axis. Such processing includes swaging, cassette roller die wire drawing, hole type die wire drawing, and the like.
On the other hand, rolling processing can also be used for producing a plate material, a strip material, or the like of a Ni-based super heat-resistant alloy.

Here, the processing rate is expressed by the surface reduction rate when the bar is swaged or the die is drawn. The surface reduction rate is the relationship between the cross-sectional area A ₀ of the bar 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 ] x 100 (%) (1)
It is calculated by the formula of.
On the other hand, when rolling is performed, the processing rate is expressed as a rolling reduction rate. As for the reduction ratio, assuming that the thickness of the material before plastic working is t ₀ and the thickness of the plate or band after plastic working, or the thin plate or thin band is t ₁ ,
[(T _{0 −} t ₁ ) / t ₀ ] × 100 (%) (2)
It is calculated by the formula of.
The cumulative working rate indicates the working rate of the final work piece with respect to the material when plastic working is performed a plurality of times or over a plurality of passes.

In the present invention, for example, the cumulative working rate from the above-mentioned cold plastic working material is increased to 40% or more.
The plastic working at this working rate is not completed by one plastic working, but can be completed by dividing into a plurality of times of plastic working. No heat treatment is performed during multiple plastic workings. The heat treatment referred to here is a heat treatment in a high temperature region where recovery or recrystallization occurs, and is, for example, a heat treatment for heating to a temperature exceeding 500 ° C. As described above, heat treatment is not required between the cold working passes, and a plurality of cold strong working can be continuously performed to increase the cumulative working rate (cumulative surface reduction rate). In the strongly processed Ni-based superheat resistant alloy, the formation of nanocrystal grains can be observed in the structure. Although this mechanism has not been completely elucidated yet, it is considered that a plurality of cold strong processes can be continuously carried out by forming nanocrystal grains. At this time, if the processing rate is less than 40%, the effects of simplifying the manufacturing process and reducing the cost are reduced. That is, from the viewpoint of the practical benefit of performing cold plastic working, the cumulative working rate should be 40% or more. The cumulative processing rate is preferably 45% or more, more preferably 50% or more, still more preferably 55% or more. The upper limit of the cumulative processing rate is not particularly limited, but can be, for example, about 70%. Further, it can be about 80% and about 90%. It can exceed 90%. In the case of the method for producing a Ni-based superheat-resistant alloy of the present invention, despite the production of an alloy having a high C content, heat treatment is not performed during plastic working, and cold working is continued to a large working rate. Can be done. By these plastic workings, plastic working is performed up to the target dimensions (final product dimensions). The hardness of the material of the final product size can be 500 HV or more.
The processing rate (surface reduction rate) by one plastic working (pass) is preferably 30% at maximum. More preferably, it can be up to 28%. By not performing plastic working at a large machining rate once, it is more effective in suppressing cracks and defects in the material.
Regarding the term "pass" used in the present specification, in the above-mentioned types of plastic working such as swaging, die wire drawing, and rolling, when plastic working is performed by one (or a pair of) dies or rolls, "1" is used. It can be called a "pass". Hereinafter, when the term "1 pass" is used, it refers to the above-mentioned one-time "plastic working".

In particular, when the material of the Ni-based superheat-resistant alloy is a bar material, in order to improve the plastic workability, it is considered important to uniformly and evenly apply pressure to the bar material in the above plastic working. For this purpose, plastic working that compresses the cross-sectional area of the bar from the peripheral surface of the bar toward the axis is effective. At this time, it is not necessary to limit the plastic working method. However, a plastic working method in which pressure is evenly applied to the entire circumference of the bar to be plastic working is advantageous. A specific example of this is swaging. The swaging process is preferable for the formation of 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 working such as cassette roller die drawing and hole type die drawing can also be applied.

(D) Step of heat-treating (final heat-treating) the second processed material The alloy obtained by the above-mentioned cold plastic working can be used as the final product shape. For example, it can be a "thin line", a "thin plate", or a "thin band". The thin wire has a wire diameter (diameter) of 5 mm or less, 4 mm or less, 3 mm or less, and finally 2 mm or less and 1 mm or less. Further, the thin plate and the thin band have a thickness of, for example, 5 mm or less, 4 mm or less, 3 mm or less, and finally 2 mm or less and 1 mm or less. The thin wire, the thin plate, and the thin band are longer in length, for example, 50 times or more, 100 times or more, and 300 times or more with respect to the above wire diameter and thickness.

After plastic working to a predetermined size and shape, when it is supplied as a final product, it can be supplied as it is after the cold plastic working. The alloy in this case is, for example, a linear structure in which the γ phase and the γ'phase in the structure extend in the stretching direction. The hardness of the alloy is 500 HV or more. It is also possible that processing defects are present in the alloy. For example, in a cross-sectional structure including the central axis in the length direction (that is, the plastic working direction) of the alloy, the defect rate is a processing defect exceeding 0.5 area%. However, in reality, it is 1.0 area% or less. The existence of such processing defects does not cause any problem in that no further plastic working is performed.
Then, if necessary, a desired equiaxed crystal structure can be obtained by performing heat treatment at a temperature of 900 ° C. or higher (for example, holding at a temperature of 900 ° C. to 1200 ° C. for 30 minutes to 3 hours). By this heat treatment, for example, the hardness can be adjusted to less than 500 HV, 450 HV or less, and 420 HV or less. And, for example, the hardness is 300 HV or more or 350 HV or more. This makes it easy to bend or cut the final product into a form suitable for the transportation form and usage form. Further, the processing defect can be repaired by this heat treatment, and for example, the defect rate can be reduced to 0.5 area% or less in the cross-sectional structure including the central axis in the length direction (that is, the plastic working direction) of the alloy. Then, combined with the effect of the heat treatment performed in the state of the material before plastic working, the above defect rate can be further reduced to 0.4 area% or less, 0.3 area% or less, and 0.2 area% or less. This heat treatment can be performed when it is desired to reduce processing defects in the usage form of the Ni-based superheat resistant alloy.

It is considered that the crystal grains in the equiaxed crystal structure are grown by performing the above heat treatment. For example, the grain size of the crystal grains may reach the maximum wire diameter. Then, if the effect of suppressing the coarsening of the crystal grains (pinning effect) effectively functions by the carbide aggregates connected in the stretching direction, the growth of the crystal grains is suppressed. In this case, the size of the crystal grains after the heat treatment is the average particle size in the cross-sectional structure, for example, 100 μm or less, 75 μm or less, 50 μm or less, 25 μm or less, 10 μm or less.

The final heat treatment is preferably carried out in an inert atmosphere such as vacuum, reducing atmosphere or Ar in order to avoid surface oxidation, but may be carried out in an oxidizing atmosphere (for example, atmospheric atmosphere). When the heat treatment is performed in an oxidizing atmosphere, an oxidation scale is formed on the surface. If it may interfere with the quality of the product, the formed oxide scale may be removed mechanically or chemically, for example by polishing or grinding. In the case of wire rod production, it is preferable to remove the scale by using centerless polishing.
Further, regardless of the final heat treatment described above, the surface of the final product can be mechanically or chemically finished by, for example, polishing or grinding.

The Ni-based superheat resistant alloy according to the present invention has been described above. According to the present invention, since plastic working of a Ni-based superheat resistant alloy having a large cumulative working rate (for example, 40% or more) can be performed at a temperature of 500 ° C. or lower, it is complicated to repeat hot working and heat treatment. Strong cold plastic working is possible without the need for various manufacturing processes, and heat treatment between plastic working can be omitted. Therefore, the simplification of the process can be achieved and the manufacturing cost can be reduced. Further, if necessary, a product having a defect rate of 1.0 area% or less and few processing defects, particularly a wire rod, can be obtained. This effect is particularly remarkable for Ni-based superheat-resistant alloys having a large carbon content in which processing defects are likely to occur.

(A) Step of Producing First Processed Material A molten metal prepared by vacuum melting was cast to prepare a cylindrical Ni-based superheat-resistant alloy ingot A having a diameter of 100 mm and a mass of 10 kg. The component composition of Ingot A is shown in Table 1 (mass%). Table 1 also shows the "γ'mol rate" of Ingot A. This value was calculated using commercially available thermodynamic equilibrium calculation software "JMatPro (Version 8.0.1, a product of Center Software Ltd.)". The content of each element listed in Table 1 was input to this thermodynamic equilibrium calculation software, and the above "γ'mol rate" (%) was obtained.

Ingot A having this composition is heat-treated at a holding temperature of 1200 ° C. and a holding time of 8 hours, cooled in a furnace, and then a cylindrical material having a length of 150 mm and a diameter of 60 mm is collected in a direction parallel to the length of the ingot A. did. This cylindrical material was sealed in SUS304 capsules and subjected to hot extrusion. The conditions for hot extrusion were an extrusion temperature of 1100 ° C., an extrusion ratio of 10 (including capsules), and an extrusion stem speed of 15 mm / s. Hot extrusion was performed, the mixture was cooled to room temperature, and then the capsule material was removed to obtain an extruded material (first processed material) having a diameter of 27 mm.

(B) Step of Producing First Heat Treatment Material (Material) The above extruded material is heated to heat treatment temperatures of 1000 ° C., 1050 ° C., 1100 ° C., 1150 ° C., and 1200 ° C. in the air for heat treatment. (Holding time: 1 hour) and cooled in a furnace to obtain a first heat-treated material (hereinafter referred to as "material"). In addition, those having a heat treatment temperature of 1200 ° C. were also air-cooled. Then, in addition to the 6 types of materials obtained by performing the heat treatment under these 6 conditions, the materials that have not been heat-treated (as they are hot extruded) are added, and a total of 7 types of materials 1 to 7 [Material 1 (heat treatment). None), Material 2 (heat treatment temperature 1000 ° C), Material 3 (1050 ° C), Material 4 (1100 ° C), Material 5 (1150 ° C), Material 6 (1200 ° C), Material 7 (1200 ° C) However, after heat treatment, air cooling)] was prepared.

Materials 1 to 7 were cut in half parallel to the axial direction, and the microstructure (crystal grain size, carbide morphology) and hardness of the cut surface were evaluated.
The cross-sectional microstructure of the cut surface observed by scanning electron microscope (SEM image) of materials 1 to 7 is shown in the order of FIGS. 4 to 10. At this time, the magnification of the cross-sectional microstructure can be basically 2000 times. However, when the crystal grain size is large, the magnification can be reduced in order to confirm a larger number of crystal grains. For example, when the crystal grain size by EBSD described later exceeds 8 μm, the magnification is 1000 times. (Materials 6 and 7). The observation location was a position within a distance of D / 4 (D is the diameter of the extruded material) from the surface of the material toward the axis on the above-mentioned cut surface. Various carbide Each microstructure _{(MC, M} 23 _{C 6,} etc.) where it was observed (dispersion in the figure), the microstructure of the material 6, 7 of the heat treatment temperature is 1200 ° _{C., M 23} C No. ₆ was substantially not confirmed (0.1 × ^10-2 pieces / μm ² or less). The hardness was evaluated at a position within a distance of D / 2 from the surface of the material toward the axis (that is, the position of the axis) on the above-mentioned cut surface.

Regarding the distribution form of carbides, by analyzing the above observation location with EPMA (electron probe microanalyzer), the distribution form of MC is a mapping diagram of Nb, which is a metal element that composes it, and that of M ₂₃ C ₆ is It can also be confirmed in the Cr mapping diagram. The mapping diagram of Nb and the mapping diagram of Cr are shown in FIGS. 4 to 10 together. In the Cr mapping diagram of FIGS. 9 (material 6) and 10 (material 7), Cr is evenly distributed over the entire surface (that is, Cr is solid-solved in the base), and Cr is unevenly distributed. (Ie, no carbides of Cr) were found. Then, the mapping diagram of FIGS. 4 to 10 is set as one field of view (50 μm × 65 μm at 2000 times magnification, 100 μm × 130 μm at 1000 times magnification), and the area ratio and number density of carbides confirmed in this one field of view are shown in this one field of view. (That is, 100 μm × 130 μm at a magnification of 2000 times, 200 μm × 260 μm at a magnification of 1000 times), and the average value of these four fields of view is the value according to the present invention. It was determined as the carbide form of the heat treatment material of 1.

Then, at the above observation place, the crystal grain size of the materials 1 to 7 was evaluated by the EBSD image. The EBSD measurement conditions are as follows: Magnification: 2000 using the EBSD measurement system "Aztec Version 3.2 (Oxford Instruments)" attached to the above scanning electron microscope (JIB-4700F (JEOL Ltd.)). Double (1000 times for materials 6 and 7), scan step: 0.1 μm, and the definition of crystal grains was defined as grain boundaries with an orientation difference of 15 ° or more. The EBSD image at this time is also shown in FIGS. 4 to 10. Then, from the grains recognized by these measurement conditions and definitions, the grains excluding the MC carbides confirmed by the above EPMA are defined as crystal grains, and for these crystal grains, the maximum diameter (maximum length) of each crystal grain is used. ) And the number of crystals, the crystal grain size distribution was confirmed, and the average diameter of the maximum diameter of the crystal grains was determined. Then, the average diameter of the maximum diameters of the crystal grains obtained from the EBSD image of this one field of view is obtained in the same manner as in the case of the above-mentioned carbide form in another three fields of view vertically and horizontally adjacent to this one field of view. The average value of the values for the four fields of view was determined as the crystal grain size of the first heat treatment material according to the present invention.
The above results are shown in Table 2. Regarding this result, FIGS. 11 and 11 show the relationship between the heat treatment temperature and the carbide morphology (area ratio, number density), crystal grain size and hardness, except for the material 7 (air-cooled). 12, FIG. 13 and FIG. 14 are shown in this order. In FIGS. 11 and 12, when the heat treatment temperature rises, the area ratio and number density of MC and the area ratio and number density of M ₂₃ C ₆ are reversed between 1100 ° C. and 1150 ° C., and the MC However, the area ratio and the number density are high.

(C) Step of Producing Second Processed Material Next, a bar having a diameter of 6 mm and a length of 60 mm was cut out from the materials 1 to 7. The longitudinal direction of the bar was taken parallel to the axial direction of the extruded material.
Using a rotary swaging device, this bar is subjected to cold plastic working in multiple passes up to 12 passes at room temperature (about 25 ° C.), and the second processed materials 1 to 7 corresponding to each symbol are processed. Made. The processing rate (reduction rate) of each pass was set to 30% or less. In addition, no heat treatment was performed between each pass. The path schedule is shown in Table 3. Then, in this pass schedule, the diameter and the surface reduction rate that could be processed from the initial diameter of 6.0 mm (that is, the diameter and the surface reduction rate before the pass in which the processed material broke) were evaluated. In addition, the hardness at that time (the cross-sectional hardness at the position of the axial center when cut in half parallel to the axial direction) was also measured. The results are shown in Table 4.

Regarding the results in Table 4, the relationship between the temperature of the heat treatment applied to the extruded material before the cold plastic working and the cold plastic working (surface reduction rate) is shown in FIG. From FIG. 3, by heat-treating the extruded material, the workability of the material was dramatically improved (stage 1). Then, although the workability tends to decrease once when the heat treatment temperature exceeds 1000 ° C. (stage 2), the initial workability is maintained and the heat treatment temperature rises again when the heat treatment temperature exceeds 1150 ° C. The workability was further improved (stage 3).

As described above, it has been shown that a thin wire of a Ni-based superheat-resistant alloy can be produced by cold plastic working according to the examples. The Ni-based superheat-resistant alloy produced by the production method of the present invention can be processed into a wire rod having an arbitrary wire diameter by plastic working in the cold. Although this embodiment was performed on the production of wire rods, it can also be applied to the production of other shapes such as plate materials.

Claims (7)

It is a manufacturing method of Ni-based super heat-resistant alloy.
(A) A material having a carbon content of 0.05 to 0.25% by mass and a component composition having an equilibrium precipitation amount of the gamma prime phase at 700 ° C. of 35 mol% or more, plastically prepared at a temperature of 900 ° C. or higher. The process of producing the first processed material by cooling after processing and
(B) The first processed material is heated to a temperature of 900 ° C. or higher and 1250 ° C. or lower and heat-treated for 30 minutes or longer and 180 minutes or lower, and the area ratio of M ₂₃ C ₆ is 4.0 area% in the cross-sectional structure. Hereinafter, the number density of M ₂₃ C ₆ is 10.0 × ^10-2 pieces / μm ² or less, the area ratio of MC is 12.0 area% or less, and the number density of MC is 5.0 × ^10-2 pieces. / Μm ² or less, and the average value of the values for 4 visual fields of the average particle size obtained by confirming the maximum diameter of each crystal grain excluding the MC carbide in one visual field of the EBSD image is 1.4. A method for producing a Ni-based superheat -resistant alloy, which comprises a step of producing a first heat-treated material having a size of ~ 100 μm . (C) The production of the Ni-based superheat-resistant alloy according to claim 1, further comprising a step of plastically working the first heat-treated material at a temperature of 500 ° C. or lower to prepare a second processed material. Method. (D) The method for producing a Ni-based superheat-resistant alloy according to claim 2, further comprising a step of heat-treating the second processed material at a temperature of 900 ° C. or higher. The Ni-based super heat-resistant alloy is in mass%.
C: 0.05 to 0.25%,
Cr: 8.0-25.0%,
Al: 0.5-8.0%,
Ti: 0.4-7.0%,
Co: 0-28.0%,
Mo: 0-8.0%,
W: 0 to 15.0%,
Nb: 0-4.0%,
Ta: 0-5.0%,
Fe: 0 to 10.0%,
V: 0-1.2%,
Hf: 0-3.0%,
B: 0 to 0.300%,
Zr: 0 to 0.300%
The method for producing a Ni-based superheat-resistant alloy according to any one of claims 1 to 3, wherein the method comprises the above, and the balance is composed of Ni and impurities. A Ni-based super heat-resistant alloy for cold plastic working
It has a component composition having a carbon content of 0.05 to 0.25% by mass and an equilibrium precipitation amount of the gamma prime phase at 700 ° C. of 35 mol% or more.
In the cross-sectional structure, the area ratio of M ₂₃ C ₆ is 4.0 area% or less, the number density of M ₂₃ C ₆ is 10.0 × ^10-2 pieces / μm ² or less, and the area ratio of MC is 12.0. The area was% or less, the number density of MC was 5.0 × ^10-2 / μm ² or less, and the maximum diameter of each crystal grain excluding the MC carbide was confirmed and obtained in one field of view of the EBSD image. A Ni-based superheat-resistant alloy in which the average value of the values of the four visual fields of the average particle size is 1.4 to 100 μm. The Ni-based superheat-resistant alloy according to claim 5, which has a hardness of 460 HV or less. The Ni-based super heat-resistant alloy is based on mass%.
C: 0.05 to 0.25%,
Cr: 8.0-25.0%,
Al: 0.5-8.0%,
Ti: 0.4-7.0%,
Co: 0-28.0%,
Mo: 0-8.0%,
W: 0 to 15.0%,
Nb: 0-4.0%,
Ta: 0-5.0%,
Fe: 0 to 10.0%,
V: 0-1.2%,
Hf: 0-3.0%,
B: 0 to 0.300%,
Zr: 0 to 0.300%
The Ni-based superheat-resistant alloy according to claim 5 or 6, wherein the balance comprises Ni and impurities.

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