JPWO2020031579A1 - Method for producing Ni-base superheat-resistant alloy and Ni-base superheat-resistant alloy - Google Patents

Abstract

(EN) A method for producing a Ni-base superheat-resistant alloy having a component composition in which the equilibrium precipitation amount of a gamma prime phase at 700°C is 35 mol% or more, and a Ni-base superheat-resistant alloy. The method of the present invention is directed to (a) a material having a carbon content of 0.01 to 0.25% by mass, and an equilibrium precipitation amount of a gamma prime phase at 700° C. of 35 mol% or more. , A step of producing a first processed material by performing plastic working a plurality of times at a temperature of 500° C. or less so that the cumulative processing rate from the material becomes 40% or more, and (b) the first processed material A step of producing a first heat-treated material by performing heat treatment at a temperature of 900° C. or higher; and (c) a temperature of 500° C. or lower for the first heat-treated material, and further cumulative processing from the first heat-treated material. And the second working material is manufactured by performing the plastic working once or plural times so that the ratio becomes 10% or more. Further, the Ni-based superheat-resistant alloy of the present invention has the above-mentioned component composition, and the defect rate in the sectional structure is 0.5 area% or less.

Description

TECHNICAL FIELD The present invention relates to a method for producing a Ni-base superheat-resistant alloy and a Ni-base superheat-resistant alloy. The present invention relates to a method for producing a heat resistant alloy and a Ni-base super heat resistant alloy.

As a heat-resistant component used for an aircraft engine or a gas turbine for power generation, for example, a Ni-base super heat-resistant alloy such as Inconel (registered trademark) 718 alloy is often used. Along with the high performance and low 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 the Ni-base superalloy, a gamma prime (hereinafter, also referred to as “γ′”) phase which is a precipitation strengthening phase of an intermetallic compound mainly composed of Ni ₃ Al. It is most effective to increase the amount of. Further, the Ni-base superheat-resistant alloy further contains Al, Ti, and Nb which are γ′-forming elements, whereby the high temperature strength of the Ni-base superheat-resistant alloy can be further improved. In the future, in order to satisfy high heat resistance and high strength, a Ni-base super heat resistant alloy having a larger amount of γ'phase is required.

However, it is known that the Ni-base super heat-resistant alloy is difficult to work because the deformation resistance of hot working increases as the γ'phase increases. In particular, if the amount of the γ'phase is 35 to 40 mol% or more of the γ'molar ratio, the workability is particularly deteriorated. For example, alloys such as Inconel (registered trademark) 713C alloy, IN939, IN100, and Mar-M247 have a particularly large γ'phase, which makes plastic working impossible, and is usually as-cast as a casting alloy. Used in.

As a proposal for improving the hot plastic workability of such a Ni-based super heat-resistant alloy, in Patent Document 1, a Ni-based super heat-resistant alloy ingot having a composition with a γ'molar ratio of 40 mol% or more has a workability of 5%. A manufacturing method is described in which cold working is performed at less than 30% and then heat treatment is performed at a temperature higher than the γ'solid solution temperature. This method obtains a recrystallization rate of 90% or more that enables hot working to be applied to a Ni-base superalloy 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 Ni-based super heat-resistant alloys having a large amount of the γ'phase described above, or for manufacturing the heat-resistant parts themselves by three-dimensional molding. In this case, a Ni-based superheat-resistant alloy thin wire is required as a modeling material. This thin wire can also be processed into a component shape such as a spring and used. The wire diameter (diameter) of the thin wire of the Ni-base superalloy is, for example, 5 mm or less, and further, 3 mm or less. It is efficient to prepare such a thin wire, for example, by preparing a “wire material” having a wire diameter of 10 mm or less as an intermediate product and subjecting this wire material to plastic working. If the “wire material” which is this intermediate product can also be obtained by plastic working, the thin wire of the Ni-base superalloy can be efficiently manufactured.
As a method for producing such a super-heat-resistant alloy fine wire, a method has been proposed in which a casting wire having a wire diameter of 5 mm or more is used as a starting material, a bundle of these casting wires is hot extruded, and then separated ( Patent Document 2).

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

The method of Patent Document 1 is effective for Ni-base superalloys to which hot working is applied. However, as described above, in the Ni-base superalloy, the hot plastic workability decreases as the amount of the γ'phase increases. The method of Patent Document 2 is effective for producing a fine wire in a limited component composition, but can be applied only to the component composition, and the amount of the γ′ phase is “35 mol% or more” described later. When it becomes a Ni-base super heat-resistant alloy, it is extremely difficult to perform hot plastic working to work it into fine wires. Further, the method of Patent Document 2 has problems that the process is complicated and the manufacturing cost is increased. Further, in the production of thin wires and wire rods, there has been considered a problem that if a crack occurs in the middle of the process, the working rate is limited, and plastic working cannot be performed up to a predetermined wire diameter.

An object of the present invention is to provide a method for producing a Ni-base superheat-resistant alloy having excellent plastic workability by using a novel method which is completely different from the conventional one, and in particular, a fine wire of the Ni-base superheat-resistant alloy can be produced. It is to provide a new method. Another object of the present invention is to provide a method capable of producing a fine wire having few defects with a reduced number of man-hours and a reduced cost even with a Ni-base superheat-resistant alloy having a small wire diameter. And another object of the present invention is to provide a Ni-base superalloy with few defects.

According to one aspect of the present invention, a method for producing a Ni-base superalloy is provided. This method
(A) A carbon content of 0.01 to 0.25% by mass and a temperature of 500° C. or lower for a material having a component composition in which the equilibrium precipitation amount of a gamma prime phase at 700° C. is 35 mol% or more. A step of producing a first processed material by performing plastic working a plurality of times so that the cumulative processing rate from the material is 40% or more,
(B) a step of heat-treating the first processed material at a temperature of 900° C. or higher to produce a first heat-treated material,
(C) The first heat-treated material is subjected to plastic working at a temperature of 500° C. or lower and once or plural times so that the cumulative working rate from the first heat-treated material is 10% or more. And the step of producing the processed material of No. 2.

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

According to one specific example, after the step (c), it is preferable to perform the set of steps (b) and (c) once or a plurality of times to produce the second processed material.

According to one specific example, it is preferable that the working rate of one plastic working in the plastic working of the steps (a) and (c) is 30% or less.

Further, according to one specific example, it is preferable that the step (b) includes a step of removing the surface of the material after the heat treatment.

Further, according to one specific example, the Ni-base superalloy is, in mass%,
C: 0.01 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: 0-8.0%,
W: 0 to 15.0%,
Nb: 0 to 4.0%,
Ta: 0 to 5.0%,
Fe: 0 to 10.0%,
V: 0 to 1.2%,
Hf: 0 to 3.0%,
B: 0 to 0.300%,
Zr: 0 to 0.300%
And a balance of Ni and impurities.

Further, according to one aspect of the present invention, there is provided a method for producing a Ni-base superalloy. This method
(A) A material having a carbon content of 0.01 to 0.25% by mass and an equilibrium precipitation amount of a gamma prime phase at 700°C of 35 mol% or more at a temperature of 500°C or less, A step of performing a plastic working to produce a first processed material,
(B) a step of heat-treating the first processed material at a temperature of 900° C. or higher to produce a first heat-treated material,
(C) a step of performing plastic working on the first heat-treated material at a temperature of 500° C. or lower to produce a second worked material,
Perform the combination of the step (A) and the step (B) once or a plurality of times,
The dimension d in the direction perpendicular to the longitudinal direction of the first processed material subjected to the heat treatment of the last step (B) is not less than 1.5 times the dimension d _f of the final product, or the dimension d. The difference d−d _f between the final product size d _f and the final product size is more than 1 mm.

Further, according to another aspect of the present invention, a Ni-base superalloy is provided. This Ni-base super heat-resistant alloy has a carbon content of 0.01 to 0.25 mass %, and has a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700° C. is 35 mol% or more, and in the cross-sectional structure. The defect rate is 0.5 area% or less.

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

An electron backscatter diffraction (EBSD) image of a cross-sectional microstructure of a Ni-base super heat-resistant alloy that has undergone plastic working with an area reduction rate of 31%. The figure explaining the effect of the intermediate heat processing in this invention. Cross-sectional microstructure of rod (hot extruded material) (curling solution etching). Sectional microstructure before intermediate heat treatment (curling solution etching) of a wire rod having a cumulative working rate of 56% in Example 1. The cross-sectional microstructure (curling solution etching) after the intermediate heat treatment of the wire having a cumulative working rate of 56% in Example 1. The cross-sectional microstructure (curling solution etching) of the outer peripheral portion of the wire having a wire diameter of 1.0 mm in Example 1. The cross-sectional microstructure (curling solution etching) of the central part of the wire rod having a wire diameter of 1.0 mm in Example 1. The cross-sectional microstructure (curling solution etching) of the outer peripheral portion of the wire having a wire diameter of 2.5 mm in Example 3. Sectional microstructure (curling solution etching) of the central part of a wire rod having a wire diameter of 2.5 mm in Example 3. The EBSD image which shows an example of the cross-section structure of the hot extrusion material (raw material) in Example 4. The figure which shows the particle size distribution of the crystal grain recognized by the EBSD image of FIG. 7 is a microstructure photograph showing an example of a cross-sectional structure of a hot extruded material (raw material) in Example 4. The microstructure photograph of the material (diameter 4.5 mm) after the first plastic working in Example 4. The microstructure photograph of the material (diameter 4.5 mm) after the first heat treatment in Example 4. 7 is a microstructure photograph of the material (diameter 4.0 mm) after the fourth pass in the second plastic working in Example 4.

The present invention provides a new method capable of producing a Ni-base superalloy having excellent plastic workability by a new approach different from the conventional hot plastic working.
The present inventor has studied the plastic workability of a Ni-base superalloy having a large amount of γ'phase. As a result, the inventors have identified a phenomenon that cold plastic working can be performed on a Ni-base superalloy alloy material at a working rate of 40% or more.
At that time, it was discovered that cold plastic working at a working rate of 30% or more produced nano-crystal grains in the structure of the Ni-base superalloy. It is speculated that the formation of these nano-crystal grains contributes to the dramatic improvement in the plastic workability of the Ni-base superalloy.

Therefore, the method for producing a Ni-base superalloy according to the present invention, which has a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700°C is 35 mol% or more,
(A) A carbon content of 0.01 to 0.25 mass% and a temperature of 500° C. or lower for a material having a component composition in which the equilibrium precipitation amount of a gamma prime phase at 700° C. is 35 mol% or more. And a step of producing a first processed material by performing plastic working a plurality of times so that the cumulative processing rate from the material becomes 40% or more,
(B) a step of heat-treating the first processed material at a temperature of 900° C. or higher to produce a first heat-treated material,
(C) The first heat-treated material is subjected to plastic working once or a plurality of times at a temperature of 500° C. or less so that the cumulative working rate from the first heat-treated material is 10% or more. And a step of producing a second processed material.

The Ni-base superalloy according to the present invention has a carbon content of 0.01 to 0.25% by mass, and a component in which the equilibrium precipitation amount of the gamma prime (γ') phase at 700°C is 35 mol% or more. Having a composition.
Here, the amount of the γ'phase of the Ni-base superalloy can be represented 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 the stable equilibrium precipitation amount of the gamma prime phase, which allows the Ni-base superalloy to be precipitated in the thermodynamic equilibrium state. The value of the equilibrium precipitation amount of the gamma prime phase represented by "molar ratio" is determined by the component composition of the Ni-base superalloy. The value of mol% of this equilibrium precipitation amount can be obtained by analysis by thermodynamic equilibrium calculation. In the analysis by the thermodynamic equilibrium calculation, various thermodynamic equilibrium calculation software can be used to accurately and easily obtain.

In the present invention, the γ'molar ratio of the Ni-base superalloy is defined as "equilibrium precipitation amount 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 becomes. Generally, the equilibrium precipitation amount of the gamma prime phase in the structure becomes small and is almost constant at about 700° C. or less, and therefore the value at “700° C.” is used as a reference.

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

When the γ'molar ratio reaches the level of 35%, the formation of the above nano-grains is promoted. More preferably, the composition is such that the equilibrium precipitation amount of the gamma prime phase at 700° C. is 40 mol% or more. The more preferred equilibrium precipitation amount of the gamma prime phase is 50 mol% or more, and even more preferably 60 mol% or more. The particularly preferred 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 about 75 mol% is practical.

As a precipitation-strengthened Ni-base superheat-resistant alloy having an equilibrium precipitation amount of a gamma prime phase at 700° C. of 35 mol% or more, for example, in mass %, C: 0.01 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 to 4.0%, Ta:0 to 5.0%, Fe:0 to 10.0%, V:0 to 1.2%, Hf:0 to 3.0%, B :0 to 0.300% and Zr:0 to 0.300%, with the balance being Ni and impurities.

Hereinafter, each component of the preferable composition of the Ni-base superalloy according to 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 Ni-base superalloys. Since the Ni-base superheat-resistant alloy having a large amount of γ′ phase is difficult to plastically work, it is usually used as a cast part and a certain amount of C is added. The added C remains as carbide in the cast structure, and a part is formed as coarse eutectic carbide. Then, such a coarse carbide serves as a starting point of cracks and a crack propagation path when the Ni-base superheat-resistant alloy is plastically worked, particularly when the Ni-base superheat-resistant alloy is plastically worked at room temperature. Adversely affect sex.

Therefore, for the present invention aimed at producing a Ni-base superheat-resisting alloy by plastic working, not the Ni-base superheat-resisting alloy having a large amount of γ'phase, as a cast part, It is preferable to reduce C. In the present invention, the C content is 0.25% or less. It is preferably 0.20% or less. It is more preferably 0.15% or less.
However, C is also an element that enhances the strength of the heat-resistant component, and it is preferable that C is contained in consideration of producing and repairing such heat-resistant component. According to the method for producing a Ni-base 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 above-mentioned nano crystal grains. Even in that case, in the case of an alloy having a high C content, when a fine wire or a wire is manufactured by plastic working, the workability is limited due to the problem that the above-mentioned carbides can act as a crack starting point and a crack propagation path. On the other hand, the first and second intermediate heat treatments described later can also deal with the above-described problem of carbide cracking, so that, for example, a C content similar to the content in the cast component can be allowed. ..
Therefore, in the method for producing the Ni-base superalloy according to the present invention, C is contained at 0.01% or more. It is preferably 0.03% or more, more preferably 0.05% or more, still more preferably 0.07% or more. Furthermore, C may be contained in an amount of 0.1% or more.

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

Molybdenum (Mo)
Mo contributes to solid solution strengthening of the matrix and has an effect of improving high temperature strength. However, when Mo becomes excessive, an intermetallic compound phase is formed and the high temperature strength is impaired. Therefore, it is preferable to set Mo to 0 to 8.0% (there may be no addition (unavoidable impurity level)). More preferably, it is 2.0 to 7.0%. A more preferable lower limit is 2.5%, and a more preferable lower limit is 3.0%. A more preferable lower limit is 3.5%. Further, the more preferable upper limit is 6.0%, and the more preferable upper limit is 5.0%.

Aluminum (Al)
Al is an element that forms a γ'(Ni ₃ Al) phase that is a strengthening phase and improves the high temperature strength. However, excessive addition deteriorates 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 a more preferable lower limit is 3.0%. A more preferred lower limit is 4.0%, and an even more preferred lower limit is 4.5%. A particularly preferred lower limit is 5.1%. Further, the more preferable upper limit is 7.5%, and the more preferable upper limit is 7.0%. A more preferable upper limit is 6.5%.
Due to the above-described relationship with Cr, when the content of Cr is reduced in order to secure hot workability during material preparation, the reduced content of Al can be allowed. Then, for example, when the upper limit of Cr is 13.5%, the lower limit of the Al content is preferably 3.5%.

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

The optional components that can be added to the Ni-base superalloy according to the present invention will be described below.

Cobalt (Co)
Co improves the stability of the structure and makes it possible to maintain the hot workability at the time of preparing the material even if it contains a large amount of Ti, which is a strengthening element. On the other hand, since Co is expensive, the cost increases. Therefore, Co is one of the optional elements that can be contained in a range of, for example, 28.0% or less by combining with other elements. A preferable lower limit when Co is added is 8.0%. A more preferable lower limit is 10.0%. Moreover, the preferable upper limit of Co is 18.0%. A more preferable upper limit is 16.0%. In addition, when Co may be a non-added level (inevitable impurity level of 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)
W, like Mo, is one of the selective elements that contributes to solid solution strengthening of the matrix. However, if W is excessive, a harmful intermetallic compound phase is formed and the high temperature strength is impaired, so the upper limit is made 15.0%, for example. A preferred upper limit is 13.0%, a more preferred upper limit is 11.0%, and a still more preferred upper limit is 9.0%. In order to more reliably bring out the effect of W, the lower limit of W may be 1.0%. Preferably, the lower limit of W can be 3.0%, 5.0%, or 7.0%. Further, by adding W and Mo in combination, a solid solution strengthening effect can be more exerted. In the case of composite addition, W is preferably added at 0.8% or more. In addition, when W may be added to a non-added level (inevitable impurity level of 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 form a γ'phase and strengthen the solid solution of the γ'phase to enhance 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%. A preferable upper limit is 3.5%, and a more preferable upper limit is 2.5%. It should be noted that the lower limit of Nb may be set to 1.0% in order to more reliably bring out the effect of Nb. A preferable lower limit is 2.0%. When Nb may be made a non-added 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 a γ′ phase and strengthens the γ′ phase by solid solution to enhance the high temperature strength. However, excessive addition of Ta causes the γ'phase to become unstable at high temperature, leading to coarsening at high temperature, and forming a harmful η (eta) phase, which improves hot workability during material preparation. Spoil. Therefore, Ta is, for example, 5.0% or less. It is preferably 4.0% or less, more preferably 3.0% or less, and further preferably 2.5% or less. It should be noted that in order to more reliably bring out the effect of Ta, the lower limit of Ta may be set to 0.3%. Preferably, the lower limit of Ta can be 0.8%, 1.5%, or 2.0%. When Ta may be a non-added level (unavoidable impurity level) due to the addition of a γ′-forming element such as Ti or Nb or 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. In order to obtain this effect, it is advisable to decide 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 strength and hot workability at the time of material preparation are deteriorated. Therefore, the upper limit of Fe is, for example, 10.0%. A preferable upper limit is 9.0%, and a more preferable upper limit is 8.0%. On the other hand, in the case where Fe may be a non-added level (unavoidable 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 solid solution strengthening of the matrix and grain boundary strengthening due to carbide formation. However, excessive addition of V causes the formation of a high temperature unstable phase in the manufacturing process, which adversely affects the manufacturability and the high temperature mechanical performance. Therefore, the upper limit of V is, for example, 1.2%. A preferable upper limit is 1.0%, and a more preferable upper limit is 0.8%. It should be noted that the lower limit of V may be set to 0.5% in order to more reliably bring out the effect of V described above. If V may be a non-added level (unavoidable impurity level) due to the 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 the alloy and strengthening the grain boundaries by forming carbides. However, excessive addition of Hf leads to the formation of oxides in the manufacturing process and the formation of a high temperature unstable phase, which adversely affects the manufacturability and the high temperature mechanical performance. Therefore, the upper limit of Hf is, for example, 3.0%, preferably 2.0%, and more preferably 1.5%. It should be noted that in order to more reliably bring out the 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%, or 1.0%. When Hf may be set to a non-added level (unavoidable 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 has a large effect of lowering the melting point, and if a coarse boride is formed, the hot workability during the preparation of the raw material is impaired, so that it does not exceed 0.300%, for example. Control it. A preferable upper limit is 0.200%, and a more preferable upper limit is 0.100%. A more preferable upper limit is 0.050%, and a particularly preferable upper limit is 0.020%. In addition, in order to obtain the above effects, a minimum content of 0.001% is preferable. A more preferred lower limit is 0.003%, and a still more preferred lower limit is 0.005%. A particularly preferred lower limit is 0.010%. When it is possible to set B to a non-added level (unavoidable impurity level) due to the 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 high temperature strength and hot workability at the time of material preparation are impaired. Therefore, the upper limit of Zr is, for example, 0.300%. A preferable upper limit is 0.250%, and a more preferable upper limit is 0.200%. A more preferable upper limit is 0.100%, and a particularly preferable upper limit is 0.050%. The content is preferably 0.001% or more to obtain the above effects. A more preferable lower limit is 0.005%, and a still more preferable lower limit is 0.010%. When Zr may be a non-added level (unavoidable impurity level) depending on the 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 it may contain unavoidable impurities.

Next, a specific example of the manufacturing method of the present invention for manufacturing the Ni-base superalloy having the above-described component composition will be described.

Material In the present invention, first, a material having the above-described component composition is prepared. The method for producing this material is not particularly limited. For example, this material can be obtained by a melting method in which molten metal is poured into a mold to produce an ingot. Then, in the production of the ingot, for example, vacuum melting and a usual method such as vacuum arc remelting or electroslag remelting may be combined and applied. Alternatively, the material may be obtained by powder metallurgy. If necessary, hot working such as hot forging, hot rolling, hot extrusion or machining (for example, dimensional adjustment) is performed on the ingot or the alloy ingot produced by the powder metallurgy method. Or cutting for various kinds of care, polishing, grinding, etc.) to obtain a material having a predetermined shape, for example, a bar material. 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 element segregation in the ingot. Alternatively, for example, soaking may be performed after finishing the shape of a material (billet) to be subjected to hot extrusion. In the present invention, the structure of the material and the crystal grain size are not limited. Therefore, when the material is subjected to soaking or heat treatment, subsequent cooling may be any of rapid cooling, standing cooling, furnace cooling and the like.

As an example, a case will be described in which the above material is hot extruded to form a bar material having a predetermined shape. The conditions of hot extrusion are preferably extrusion temperature (heating temperature of material) 1050° C. to 1200° C., extrusion ratio 4 to 20 and extrusion speed (stem speed) 5 to 80 mm/s. The cross-sectional diameter of the extended material) is, for example, 10 mm or more, or more than 20 mm. And, for example, it is 200 mm or less. In the case of manufacturing a bar, it can be manufactured by finishing the surface of the extruded material by machining or by collecting a bar having a predetermined size from the extruded material. In this case, the cross-sectional diameter of the bar material 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. Moreover, the cross-sectional diameter of the rod may be set to, for example, 3 mm or more, 4 mm or more, and 5 mm or more. Keeping the cross-sectional diameter of the rod small is because it is possible to reduce the number of times of plastic working (number of passes) when producing wires and fine wires with a smaller cross-sectional diameter in cold plastic working described later. preferable.

In the present invention, the crystal grain size of the material is not limited. However, by performing the extrusion molding while hot, the crystal grain size of the material can be a recrystallized structure of, for example, 200 μm or less. The recrystallized structure is preferably 150 μm or less, more preferably 100 μm or less, still more preferably 50 μm or less. The recrystallized structure is preferably 0.1 μm or more, more preferably 0.5 μm or more, still more preferably 0.8 μm or more, still more preferably 1.5 μm or more. The crystal grains generated by recrystallization have less intragranular strain, and the grain boundaries also increase by making the crystal grains finer. Therefore, if cold plastic working described later is performed on this, the The processing strain is evenly applied to the entire structure. Further, the miniaturization of the crystal grains is also effective for the generation of nano crystal grains described later. Therefore, by performing this step, the deformation in the plastic working in the next step becomes more uniform, and it is possible to avoid the occurrence of abnormal deformation and bending during processing, and it is possible to dramatically improve the yield. In order to further improve this effect, the hot-extruded material may be subjected to a heat treatment for removing residual stress due to processing. The heat-treated material is cooled by cooling.

The crystal grain size of the material can be confirmed by an EBSD image of the cross section of the material (FIG. 7). The EBSD measurement condition is set to a scan step of 0.1 μm, and a crystal grain size distribution showing a relation between the maximum diameter and the number of each crystal grain that can be recognized at a grain boundary with an orientation difference of 15° or more. The average diameter of the maximum diameters of the crystal grains can be obtained from (FIG. 8). At this time, the crystal grain size distribution may be confirmed by the one recognized as a crystal grain under the above measurement conditions, and for example, the crystal grain having a maximum diameter of 0.2 μm or more can be confirmed. In the present invention, the crystal grain size of the raw material refers to the above-mentioned “average diameter of the maximum diameter of crystal grains”.
When the material contains a carbide, the carbide can also be recognized as a crystal grain defined by “a grain boundary having an orientation difference of 15° or more” in the above EBSD image (for example, an arrow in FIG. 7 ). In such a case, this carbide may also be included as crystal grains in the crystal grain size distribution.
By using the EBSD image, even when it is not easy to confirm the crystal grain boundaries of the cross-sectional structure of the material due to the presence of the γ'phase (for example, even when the crystal grain boundaries are not easily identified by observation with the above optical microscope), Since it is easy to unambiguously specify the crystal grain boundaries, it is suitable for determining the average diameter of the crystal grains of the Ni-base superalloy having a large amount of γ'phase. Moreover, even when the crystal grain size of the cross-sectional structure of the material is small (for example, even when the average diameter of the crystal grains is 30 μm or less, or 20 μm or less and 10 μm or less), the average diameter of the crystal grains can be obtained. It is suitable.

Alternatively, the crystal grain size of the material can be measured from the sectional structure of the material. First, the cross section of the material is corroded with a curling solution, and the cross-sectional structure after the corrosion is observed with an optical microscope at a predetermined magnification. Then, it can be evaluated by "grain size number G" according to JIS-G-0551 (ASTM-E112) and converted into "average grain diameter d of crystal grains" corresponding to the grain size number G. In the present invention, the crystal grain size of the material refers to the above-mentioned "average grain diameter d". When the crystal grain size of the cross-sectional structure of the material is large, the crystal grain size of the material can also be evaluated by the method according to the grain size number G.

The hardness of the material is not limited, but it is preferably low in order to secure the initial workability by cold plastic working in a state where nano-crystal grains described later are not formed in the structure. For example, it can be 550 HV or less or less than 500 HV. It is more preferably 470 HV or less, still more preferably 450 HV or less. The lower limit of the hardness of the material is not particularly limited, but about 250 HV is realistic. And, for example, it can be set to 300 HV or more or 350 HV or more. The hardness can exceed 400 HV. The hardness of a material can be measured on the cross section of the material.

First cold plastic working [step (a) [A]]
Next, cold plastic working is performed on the above material. More specifically, cold plastic working is performed a plurality of times so that the cumulative working rate from the material is 40% or more. The present invention, unlike conventional "hot" plastic working, produces a Ni-base superalloy by "cold" plastic working. In particular, in a Ni-base superalloy having a γ'phase amount of 35 mol% or more, cold plastic working can obtain a cumulative working rate of 40% or more, and the hot plastic working is performed. The above-mentioned Ni-base super heat-resistant alloy, which has been difficult to process, can be processed into, for example, wire rods and fine wires with a relatively simple process and at low cost. In order to achieve this, it is necessary to perform the cold plastic working in a low temperature region where recovery and recrystallization cannot occur during the plastic working.
Therefore, the plastic working temperature in the present invention is preferably set to “500° C. or lower”. The temperature is more preferably 300° C. or lower, further preferably 100° C. or lower, still more preferably 50° C. or lower (eg, room temperature).

The method for producing a Ni-base superheat-resistant alloy of the present invention is suitable for a wire rod form, but can also be applied to a plate material, a band material and the like. Therefore, the Ni-based super heat-resistant alloy manufactured by the manufacturing 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 thin wire. It may be a final product shape such as a product, a sheet product, or a strip product. Regarding the dimensional relationship of the plate material (thin plate) and the band material (thin band), the wire diameter (diameter) of the wire material (thin wire) can be read as the plate thickness or the band thickness.

In particular, when the hot-extruded material of the Ni-base super heat-resistant alloy is a bar, bar processing for compressing the cross-sectional area can be performed. In this case, by using the "bar material" of the Ni-based super heat-resistant alloy as a starting material, it is possible to apply a uniform pressure to the bar material as a mode of plastic working performed on the bar material "perpendicular to the longitudinal direction of the bar material. It is preferable to perform "processing for compressing the cross-sectional area of a large cross section". Then, the bar material is subjected to a process of plastically compressing the cross-sectional area (bar diameter) to extend the length. In particular, when obtaining a wire rod made of a Ni-base super heat-resistant alloy, it is efficient to plastically manufacture a "rod" having a larger cross-sectional area (diameter) than 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 toward the axis. Examples of such processing include swaging, cassette roller die wire drawing, and hole die drawing.
On the other hand, rolling can also be used for the production of the Ni-base superalloy alloy plate material, strip material and the like.

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

In the present invention, for example, the cumulative working rate from the cold plastic working material is increased to 40% or more.
The plastic working of this working rate can be completed not by one plastic working but by divided into plural plastic working. No heat treatment is performed between the multiple times of plastic working. The heat treatment mentioned here is a heat treatment in a high temperature region where recovery and recrystallization occur, and is, for example, a heat treatment of heating to a temperature exceeding 500°C. As described above, the heat treatment is not required between the cold working passes, and the plurality of cold strong workings can be continuously performed to increase the cumulative working ratio (cumulative area reduction ratio). In addition, in the Ni-base super heat-resistant alloy that has undergone heavy working, generation of nano-crystal grains can be observed in the structure. Although this mechanism has not been completely elucidated yet, it is considered that multiple cold strong workings can be continuously performed by the generation of nano crystal grains. At this time, if the processing rate is less than 40%, the effect of simplifying the manufacturing process and reducing the cost becomes small. That is, from the viewpoint of the actual 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 it is preferably about 80%. In the case of producing the alloy having a high C content according to the present invention, it is preferable to temporarily set the cumulative working rate to 80% or less in order to validate the material defect repairing effect by the first heat treatment described later. It is more preferably 75% or less, still more preferably 70% or less, still more preferably 65% or less. The processing rate (area reduction rate) for one plastic working (pass) is preferably 30% or less. More preferably, it can be 28% or less. This is because performing plastic working with a large working rate once may cause cracks or defects in the material.

When performing cold plastic working a plurality of times, if the number of times of plastic working (pass) is large, it is possible to further reduce the working rate by the above-mentioned single plastic working (pass). For example, when the number of times of plastic working (pass) is three or more, the processing rate by one plastic working (pass) can be set to 25% at the maximum. Further, when the number of plastic workings (passes) is four or more, the processing rate by one plastic working (pass) can be set to 23% at the maximum.
In addition, when performing cold plastic working multiple times, the working rate (area reduction rate) in a given arbitrary plastic working (pass) is calculated from the working rate (area reduction rate) in the previous plastic working (pass). It is also possible to increase the machining efficiency by increasing. The processing rate (area reduction rate) may be increased for each plastic processing (pass).
The term "pass" used in the present specification means "1" when the plastic working is performed by one (or a pair of) dies or rolls in the plastic working such as the above-mentioned swaging, die drawing, and rolling. Can be referred to as a "pass". Hereinafter, when the term "one pass" is used, it refers to the above-mentioned one-time "plastic working".

In particular, when the material of the Ni-base super heat-resistant alloy is a bar, it is considered important to apply a pressure uniformly and evenly to the bar in the above plastic working in order to improve the plastic workability. 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 plastically worked is advantageous. An example of this is swaging. The swaging process forges the peripheral surface of the rod while rotating a plurality of dies surrounding the entire circumference of the rod, and is therefore preferable for producing nano crystal grains. In addition, other plastic working such as cassette roller die wire drawing and hole die drawing is also applicable.

First heat treatment [step (b)[B]]
The processed material is heat-treated at a temperature of 900° C. or higher. The effect of this heat treatment will be described with reference to FIG.
As described above, the Ni-base super heat-resistant alloy that has undergone heavy working with a cumulative working rate of 40% or more is in a state where it can be further worked. Therefore, cold working can be performed up to a larger working rate without performing heat treatment during plastic working.
However, since the Ni-base superalloy according to the present invention contains 0.01 to 0.25 mass% of carbon, coarse carbides 2 are precipitated in the structure of the raw material 1. The processed material 3 of the Ni-base superheat-resistant alloy after the cold plastic working (i) with the cumulative working rate of 40% or more has a linear structure in which the γ phase and the γ′ phase extend in the stretching direction. The carbides are crushed by plastic working to form fine carbides 4, but the fine carbides are present in the worked structure as a carbide aggregate in which the fine carbides are continuous in the stretching direction of the structure. Material defects 6 (for example, gaps due to lack of material) are formed between the fine carbides. If the plastic working (ii) is further performed as it is, the defects 6 between the respective fine carbides 4 may spread to be bonded to the adjacent defects 6 and become a starting point of cracking. Therefore, at the stage where the carbide aggregates that are continuous in the stretching direction are formed, the heat treatment is performed to repair the material defects 6 formed between the fine carbides 4. For example, in the cross-section structure in the stretching direction, the defect rate can be 0.5 area% or less.
It is considered that this is because the material softens and the alloy component fills the gap due to the diffusion of the alloy component. Therefore, in the case where the plastic working is further performed after the heat treatment (iii), the crack does not occur starting from the material defect.
The time of heat treatment, that is, the stage at which a carbide aggregate is formed in the stretching direction, depends on the carbide content, the size and type of the carbide depending on the method of producing the material, and for example, the cumulative processing rate is 40% or more. For example, the target is 45% or more, 50% or more, 55% or more. However, as described above, the upper limit of the cumulative processing rate is preferably about 80%.
Further, the heat treatment is preferably performed at a time when the wire diameter does not become too small, though it varies depending on the carbide content, the size and type of the carbide depending on the method for producing the material, and the like. When the oxide scale or the like to be described later is removed after the heat treatment, if the wire diameter is too small, the removal rate of the material due to this removal increases, and the product yield may decrease. Then, for example, the case where the wire diameter is 2.7 mm or more is targeted. The wire diameter is preferably 3.0 mm or more, more preferably 3.3 mm or more, further preferably 3.6 mm or more, and still more preferably 3.9 mm or more. The upper limit can be set to about 4.5 mm, for example.

The heat treatment temperature is 900° C. or higher. If the temperature is lower than 900° C., it is insufficient for repairing the above-mentioned defects, that is, for the alloy components to diffuse enough to fill the defects. The upper limit of the temperature of the heat treatment is not particularly limited, but is about 1200°C. Since the heat treatment aims at repairing defects by processing as described above, it is sufficient that the defects can be repaired regardless of the solid solution of the γ'phase. The heat treatment time can be set to, for example, 10 minutes or more, 30 minutes or more, 60 minutes or more depending on the size and shape of the material, and the upper limit may be appropriately determined such as 120 minutes or less, 90 minutes or less. The heat treatment is preferably performed in a vacuum, a reducing atmosphere, or an inert atmosphere such as Ar in order to avoid surface oxidation, but may be performed in an oxidizing atmosphere (for example, an air atmosphere). When heat treatment is performed in an oxidizing atmosphere, oxide scale is formed on the surface. If cold plastic working is performed while the oxide scale is formed, it may become a starting point of cracks or defects. Therefore, it may be mechanically or chemically removed by, for example, polishing or grinding. In the case of manufacturing a wire rod, centerless polishing is preferably used to remove the scale. When the heat treatment is performed in an oxidizing atmosphere, the heat treatment time is preferably completed in a short time such as 100 minutes or less, 90 minutes or less, and 80 minutes or less.

Second plastic working [step (c) [C]]
The heat-treated material is further subjected to plastic working at a temperature of 500° C. or lower. More specifically, the plastic working is performed once or a plurality of times so that the cumulative working rate from the heat-treated material is 10% or more. Similar to the first plastic working, this plastic working may also be performed by rolling for manufacturing a wire rod, swaging, cassette roller die wire drawing, hole die wire drawing, etc. it can. By the first heat treatment, the work structure recrystallizes, but the material defects formed between the fine carbides are repaired. Therefore, even if cold plastic working is further performed, cracks may be generated from the material defects. There is no. By this plastic working, plastic working is performed up to the final product size. The hardness of the material of the final product size can be 500 HV or more, 550 HV or more, 600 HV or more.
The cumulative working rate of the second plastic working can be 10% or more. The upper limit of the cumulative working rate is not particularly limited, but a working rate similar to that of the first plastic working is aimed at. Then, considering that the cross-sectional diameter (wire diameter) is reduced by performing strong working with a cumulative working rate of, for example, 40% or more in the first plastic working, the cumulative working rate of the second plastic working is , The cumulative working rate of the first plastic working can be made smaller. The other processing conditions are the same as those of the first plastic working. For example, in the case of performing plastic working a plurality of times, it is possible to increase the working rate in a certain arbitrary pass to be higher than the working rate in the previous pass. The processing rate may be increased for each pass.

Second heat treatment and third plastic working [re-step (b)[B] and step (c)[C]]
When the final product size cannot be machined by the second plastic working, the first heat treatment and the second plastic working described above can be repeated once or more times to carry out the working up to the target size. The processing conditions, heat treatment conditions, etc. are as described above.
For example, for the second heat treatment, the temperature, time, atmosphere, etc. can be determined in the same manner as the first heat treatment. Further, when heat treatment is performed in an oxidizing atmosphere and oxide scale is formed on the surface, it can be removed. Then, the timing of performing the heat treatment can be determined, for example, by taking the cumulative processing rate of the second plastic working (that is, the immediately preceding plastic working) as a target.
In addition, the cumulative working rate of the third plastic working can be set to 10% or more. The upper limit of the cumulative working rate is not particularly limited, but a working rate similar to that of the first plastic working can be targeted. The cumulative working rate of the third plastic working can be made smaller than the cumulative working rate of the first plastic working. Further, when performing the plastic working a plurality of times in the third plastic working, it is possible to increase the working ratio in a certain arbitrary pass to be higher than the working ratio in the pass in the preceding round to improve the working efficiency. .. The processing rate may be increased for each pass.
The set of the second heat treatment and the third plastic working described above can be performed once or plural times depending on the final product size.
Here, when the combination of the step (A) and the step (B) is performed once or a plurality of times, the Ni-based super heat-resistant alloy (first processed material) to be subjected to the heat treatment of the last step (B) is performed. dimension d in the direction perpendicular to the longitudinal direction is preferably at least 1.5 times the final product dimensions d _f. Since the Ni-base super heat-resistant alloy (first processed material) is expanded by plastic working and becomes an elongated shape such as a linear shape, a plate shape, or a strip shape, the dimension d in the direction perpendicular to the longitudinal direction is the linear shape. The shape means the diameter, and the plate shape or the band shape means the thickness. The final product dimension d _f is a dimension in the above direction in the final product shape including the case of finishing and the case of no processing. As described above, when heat treatment (particularly, heat treatment in an oxidizing atmosphere such as an air atmosphere) is performed, oxide scale is formed on the surface, so mechanically or chemically removing it by polishing or grinding. Is preferred. The ratio of the amount of alloy lost due to such polishing increases as the alloy becomes thinner and thinner as the plastic working progresses, and the yield decreases. Therefore, it is preferable that the heat treatment between the plastic working and the plastic working be completed at a stage sufficiently larger than the finished dimension. From this point of view, the dimension d as described above is preferably 1.5 times or more of the final product dimensions d _f, more preferably not less than 1.8 times. Further, from the same viewpoint, it is preferably, more preferably the difference _{d-d f} 1.2 mm or more difference _{d-d f} of the dimensions d and final product size _{d f} as described above is 1mm greater. Then, the relationship between the dimensions d and d _f described above, it is preferable that meets when the heat treatment of any of the steps (B), in particular, it meets the time of the heat treatment of the last performed step (B) Is preferred. It is more preferable that the final product dimension d _f is 2 mm or less while satisfying these conditions.

Final heat treatment [step (d)]
The alloy obtained by the cold plastic working described above can be used as the final product shape such as "thin wire", "thin plate", or "thin band". The thin wire is a wire having a diameter (diameter) of, for example, 5 mm or less, 4 mm or less, 3 mm or less, and finally 2 mm or less, 1 mm or less. Further, the thin plate and the thin strip are those having a thickness of, for example, 5 mm or less, 4 mm or less, and 3 mm or less, and even 2 mm or less and 1 mm or less. The thin wire, the thin plate, and the thin strip are longer than the wire diameter and the thickness, for example, 50 times or more, 100 times or more, or 300 times or more.
After being plastically processed into a predetermined size and shape, when it is supplied as a final product, it can be supplied in a state where the cold plasticizing is completed. The alloy in this case has, 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 higher. It is also possible that there are processing defects in the alloy. For example, in a cross-sectional structure including the central axis of the alloy in the length direction (that is, the plastic working direction), the defect rate is a working defect exceeding 0.5 area %. However, in reality, it is 1.0 area% or less. The presence of such a processing defect does not cause any problem in that no further plastic working is performed.
Then, if necessary, heat treatment (for example, holding at 900° C. to 1200° C. for 30 minutes to 3 hours) can be performed to obtain a desired equiaxed crystal structure. 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. The hardness is, for example, 300 HV or higher, or 350 HV or higher. This makes it easy to bend or cut the final product into a form suitable for the form of transportation or use. Further, this heat treatment can also repair the work defect, and for example, in the cross-sectional structure including the central axis of the alloy in the length direction (that is, the plastic working direction), the defect rate can be 0.5% by area or less. Further, the effect of the heat treatment performed during the plastic working so far is also coupled, and the 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 pattern of the Ni-base superalloy.
It is considered that the crystal grains in the equiaxed crystal structure are grown by performing the heat treatment. For example, the maximum grain size of the crystal grains may reach the wire diameter. Then, if the carbide aggregates that are continuous in the stretching direction effectively function to suppress the coarsening of the crystal grains (pinning effect), the growth of the crystal grains is suppressed. In this case, the size of the crystal grains after the heat treatment is an average grain size in the cross-sectional structure, and is, for example, 100 μm or less, 75 μm or less, 50 μm or less, 25 μm or less, 10 μm or less.
Regardless of the above heat treatment, the surface of the final product can be mechanically or chemically finished by, for example, polishing or grinding.

The Ni-base superalloy according to the present invention has been described above. According to the present invention, since the Ni-based super heat-resistant alloy having a cumulative working rate of 40% or more is plastically worked at a temperature of 500° C. or less, a complicated manufacturing process such as repeated hot working and heat treatment is not necessary, Cold plastic working is possible, and the number of heat treatments during plastic working can be reduced. Therefore, the process can be simplified and the manufacturing cost can be reduced. 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 the Ni-base super heat-resistant alloy having a large carbon content, which easily causes processing defects.

The molten metal prepared by vacuum melting was cast to produce a cylindrical Ni-based super heat-resistant alloy A ingot having a diameter of 100 mm and a mass of 10 kg. Table 1 shows the composition of the Ni-base superheat-resistant alloy A (mass %). Table 1 also shows the "γ' molar ratio" of the above ingot. This value was calculated using a commercially available thermodynamic equilibrium calculation software "JMatPro (Version 8.0.1, product of Sent Software Ltd.)". The contents of the respective elements listed in Table 1 were input to this thermodynamic equilibrium calculation software, and the above "γ' molar ratio" (%) was obtained.

The ingot of this Ni-base super heat-resistant alloy A was heat-treated at a holding temperature of 1200° C. for a holding time of 8 hours, cooled in a furnace, and then formed into a cylindrical shape having a length of 150 mm and a diameter of 60 mm in a direction parallel to the length direction of the ingot. The material was collected. This cylindrical material was sealed in a SUS304 capsule and subjected to hot extrusion. The hot extrusion conditions were an extrusion temperature of 1150° C., an extrusion ratio of 10 (including capsules), and an extrusion stem speed of 15 mm/s. An extruded material having a diameter of 27 mm was obtained by hot extrusion. The crystal grain size (average crystal grain size) of the extruded material was 200 μm or less.

Next, a bar material having a diameter of 6 mm and a length of 60 mm was cut out from the extruded material. The longitudinal direction of the rod was taken parallel to the axial direction of the extruded material. FIG. 3 shows a cross-sectional microstructure of the central portion (axial portion) in the longitudinal direction of the bar material observed by an optical microscope. For observation, the cross section was polished and then etched with a curling solution. The γ'phase was uniformly precipitated in the γ structure, but carbides (MC, M ₂₃ C _6, etc.) of several microns to several tens of microns were observed. The hardness at this central portion was 449 HV.
This rod was subjected to cold plastic working in a plurality of passes at room temperature (about 25° C.) using a rotary swaging device (first plastic working). The processing rate (area reduction rate) of each pass was 30% or less. After the fourth pass (diameter 4.0 mm) when the cumulative processing rate from the material exceeded 55%, heat treatment (1150° C., 60 minutes) was performed in the atmosphere (first heat treatment) to form on the surface. The oxide scale was removed by centerless polishing. Therefore, the wire diameter was 3.8 mm. 4A and 4B show cross-sectional microstructures in the central portion in the longitudinal direction by an optical microscope before and after heat treatment. It can be seen that before the heat treatment (FIG. 4A), the γ phase and the γ′ phase have a linear structure extending in the stretching direction. As for the carbide, a carbide aggregate in which the carbide was continuous in the stretching direction was observed, and a defect portion (surrounding portion) starting from the carbide was observed. On the other hand, the structure after heat treatment (FIG. 4B) is a recrystallized structure in which the γ′ phase is uniformly precipitated in the granular γ phase. Although carbides that were continuous in the stretching direction also remained, the gaps between the carbide particles were widened and separated by the metallographic structure, and no defect was observed.

The material subjected to the first heat treatment was further subjected to two-pass cold plastic working (second plastic working), and when the cumulative working ratio of the material after the first heat treatment became 37.7%. Then, heat treatment and centerless polishing were performed again (second heat treatment). The material whose wire diameter became 2.8 mm by centerless polishing was further subjected to 4-pass cold plastic working (third plastic working), and the cumulative working ratio of the material after the second heat treatment was 49.0%. When this happens, heat treatment and centerless polishing were performed again (third heat treatment). Finally, the material whose wire diameter became 1.75 mm by centerless polishing was finally subjected to a 2-pass cold plastic working at which the cumulative working ratio from the material after the third heat treatment was 40.5% (fourth Plastic working), and the wire diameter was 1.35 mm. The wire rod having a wire diameter of 1.35 mm was finally subjected to centerless polishing to manufacture a wire rod having a final diameter of 1.0 mm and a length of about 1 m. 5A and 5B show the microstructures of the outer peripheral portion and the central portion by an optical microscope in a longitudinal cross section of a wire rod having a wire diameter of 1.0 mm, respectively. In each case, a linear structure in which the γ phase and the γ′ phase were extended in the stretching direction was obtained as in FIG. 4A. Although carbide aggregates that were continuous in the stretching direction were observed, no defect was observed between the carbide particles even when viewed in FIG. 5B in which the magnification was enlarged. The hardness of the central portion of the wire having a wire diameter of 1.0 mm was 570 HV. Further, the dimension d (2.0 mm) of the material used for the third heat treatment was 2.0 times the dimension d _f (1.0 mm) of the final product.

The wire material having a wire diameter of 1.35 mm obtained in Example 1 was subjected to a final heat treatment (1150° C., 60 minutes) in the air, and then subjected to centerless polishing for finishing to finally obtain a wire diameter of 1.0 mm, A wire having a final size of about 1 m was manufactured. In each of the microstructures of the outer peripheral portion and the central portion by the optical microscope in the longitudinal section of the wire having a wire diameter of 1.0 mm, the γ′ phase is uniformly precipitated in the granular γ phase as in FIG. 4B. A recrystallized structure was obtained. Although carbide aggregates that were continuous in the stretching direction were observed, no defect was observed between the carbide particles. The hardness of the central part of the wire having a wire diameter of 1.0 mm was 379 HV. The size of the crystal grains in the central microstructure of the cross section of the wire in the longitudinal direction was about 8 μm in terms of the average grain size excluding those of twin crystals.

A rod having a diameter of 6 mm and a length of 60 mm cut out from the hot-extruded Ni-base superalloy A produced under the method and conditions described in Example 1 was processed in the same manner as in Example 1 for multiple passes. Unlike Example 1, the intermediate heat treatment (that is, the first heat treatment) was performed at 1150° C. for 30 minutes, and thereafter, centerless polishing was not performed and plastic working was continuously performed with the oxide scale formed (Table 1). 3).
In Example 3, a wire rod having a wire diameter of 2.7 mm could be manufactured. The structure of this wire is a linear structure in which the γ phase and the γ′ phase extend in the drawing direction, as in FIG. 4A, and a carbide aggregate continuous in the drawing direction was observed. Then, a processing defect having a defect rate of 1.0 area% or less was recognized in the central cross-sectional structure of the wire in the length direction (that is, the plastic working direction).
The above-mentioned wire having a wire diameter of 2.7 mm was further subjected to plastic working at a working rate of 14.3% to manufacture a wire having a wire diameter of 2.5 mm. 6A and 6B show the microstructures of the outer peripheral portion and the central portion by an optical microscope in a longitudinal section, respectively. The structure of this wire is also a linear structure in which the γ phase and the γ′ phase extend in the drawing direction, as in FIG. 4A, and a carbide aggregate continuous in the drawing direction was observed. Although cracks were observed in the outer peripheral portion of this wire, it was confirmed that defective portions were suppressed inside. Further, the dimension d (4.0 mm) of the material subjected to the first heat treatment was 1.6 times the dimension d _f (2.5 mm) of the final product.
Further, from the results of Example 1 and Example 3, by performing an additional intermediate heat treatment, preferably by removing oxide scale on the surface, cracking of the outer peripheral portion of the wire is suppressed, and further plastic working is continued. It was confirmed that it was possible to manufacture a wire rod having a smaller wire diameter.

The molten metal prepared by vacuum melting was cast to produce a cylindrical Ni-based super heat-resistant alloy B ingot having a diameter of 80 mm and a mass of 10.5 kg. Table 4 shows the composition of the Ni-base superheat-resistant alloy B (% by mass). Table 4 also shows the “γ′ mole ratio” (%) of the above ingot, which was obtained in the same manner as in Example 1.

The Ni-based super heat-resistant alloy B was heat-treated at a holding temperature of 1200° C. for a holding time of 8 hours, cooled in a furnace, and then formed into a cylindrical shape having a length of 150 mm and a diameter of 66 mm in a direction parallel to the length direction of the ingot. The material was collected. This cylindrical material was sealed in a SUS304 capsule and subjected to hot extrusion. The hot extrusion conditions were an extrusion temperature of 1150° C., an extrusion ratio of 10 (including capsules), and an extrusion stem speed of 15 mm/s. An extruded material having a diameter of 27 mm was obtained by hot extrusion.

This extruded material was cut in half parallel to the axial direction of the extruded material, and the microstructure and hardness of the cut surface were evaluated. FIG. 9 shows a cross-sectional microstructure of the axial line portion of the cut surface observed by a scanning electron microscope (magnification: 2000 times). Various carbides (MC, M ₆ C, M ₂₃ C _6, etc.) were observed in the microstructure (dispersion in the figure). The hardness of the microstructure was 496 HV in the central portion (axial portion).

Then, the crystal grain size of the material was evaluated by an EBSD image. The measurement location was a position at a distance of D/4 (D is the diameter of the extruded material) from the surface of the extruded material toward the axis on the cut surface. EBSD measurement conditions are as follows: EBSD measurement system "Aztec Version 3.2 (manufactured by Oxford Instruments)" attached to the scanning electron microscope "JIB-4700F (manufactured by JEOL Ltd.)", magnification: 2000 times, Scan step: 0.1 μm, and the crystal grain was defined with a grain boundary of orientation difference of 15° or more. Then, for those (including carbides) recognized as crystal grains by these measurement conditions and definitions, the crystal grain size distribution was confirmed by the relationship between the maximum diameter (maximum length) and the number of individual crystal grains, and the crystal grain size was confirmed. The average diameter of the maximum diameter was calculated.
The EBSD image at this time is shown in FIG. 7, and the crystal grain size distribution is shown in FIG. In FIG. 8, the crystal grain size (maximum diameter of crystal grains) on the horizontal axis is collectively shown for each 0.2 μm. For example, a crystal grain having a maximum diameter of 0.2 μm or more and less than 0.4 μm is “0.4 μm”. The crystal grains having a maximum diameter of 0.6 μm or more and less than 0.8 μm are grouped in the “0.8 μm” group. The maximum value of the individual crystal grains was 6.43 μm. The smallest value was 0.36 μm. The average diameter of the maximum diameters of the crystal grains (that is, the crystal grain size of the material) was 1.1 μm.

Next, a bar material having a diameter of 6 mm and a length of 60 mm was cut out from the extruded material. The longitudinal direction of the rod was taken parallel to the axial direction of the extruded material. Similar to Example 1, the γ′ phase was uniformly precipitated in the γ structure in the cross-sectional microstructure of the bar of Ni-base superalloy B as well, and as described above, various carbides (MC, M ₆ C , M ₂₃ C ₆ ) was observed. The hardness of the bar of Ni-base superheat-resistant alloy B was 496 HV in the central portion in the longitudinal direction, as in the above case.

This rod was subjected to cold plastic working in a plurality of passes at room temperature (about 25° C.) using a rotary swaging device (first plastic working). The processing rate (area reduction rate) of each pass was 30% or less. After completion of the third pass (diameter 4.5 mm) when the cumulative processing rate from the material exceeded 40%, heat treatment (1150° C., 30 minutes) was performed in vacuum (first heat treatment). Then, the material subjected to the first heat treatment is not subjected to the centerless polishing of the surface, but is continuously subjected to two-pass cold plastic working (second plastic working) to remove the material after the first heat treatment. When the cumulative processing rate of No. 3 reached 39.5%, only the heat treatment was performed again (second heat treatment). Then, thereafter, as shown in Table 5, the third to sixth plastic workings and the third to fifth heat treatments (in vacuum, without centerless polishing) accompanying the plastic workings are performed to obtain a wire diameter of 1. A 3 mm wire rod was used. Then, after performing a final heat treatment (1150° C., 30 minutes) in the air on this wire having a wire diameter of 1.3 mm, centerless polishing for finishing is performed to remove oxide scale formed on the surface, Finally, a wire rod having a final diameter of 1.0 mm and a length of about 1 m was manufactured.
At this time, the hardness of the material at each time point is the hardness at the central portion, and after the material (diameter 5.5 mm) when the first pass was completed in the first plastic working was 563 HV, It was 500 HV or more when the plastic working was completed (it was about 610 HV). Further, it was less than 500 HV when the heat treatment was performed after the completion of each plastic working.

FIG. 10 shows a cross-sectional microstructure of the material (diameter 4.5 mm) after the first plastic working, which is observed by a scanning electron microscope (magnification: 1000 times). The cross-sectional microstructure of FIG. 10 was a linear processed structure in which the γ phase and the γ′ phase extended in the stretching direction (longitudinal direction of the material). In addition, there was a tendency that carbides also aggregate in the stretching direction. Then, although no defect portion originating from the carbide was found, the first heat treatment was performed at this point.
FIG. 11 shows a cross-sectional microstructure of the material (diameter 4.5 mm) after the first heat treatment, which was observed by a scanning electron microscope (magnification: 1000 times). The cross-sectional microstructure of FIG. 11 was an equiaxed crystal structure. Then, the above-mentioned equiaxed crystal structure has a structure having carbides linearly aggregated.
FIG. 12 shows a cross-sectional microstructure of the material (diameter 4.0 mm) after the completion of the fourth pass in the second plastic working, which was observed by a scanning electron microscope (magnification: 1000 times). The cross-sectional microstructure of FIG. 12 was a linear processed structure in which the γ phase and the γ′ phase extended in the stretching direction (longitudinal direction of the material). In addition, there was a tendency that carbides also aggregate in the stretching direction. Then, since the first heat treatment was performed at the time point after the first plastic working, no defect portion originating from the carbide was found.

Then, in each of the microstructures of the outer peripheral portion and the central portion by the optical microscope in the longitudinal cross section of the wire rod having the final dimension of 1.0 mm, the γ′ phase in the granular γ phase is the same as in FIG. 4B. A recrystallized structure with uniform precipitation was obtained. Although carbide aggregates that were continuous in the stretching direction were observed, no defect was observed between the carbide particles. The hardness of the central part of the wire having a wire diameter of 1.0 mm was 382 HV. Further, the dimension d (1.5 mm) of the material used for the fifth heat treatment was 1.5 times the dimension d _f (1.0 mm) of the final product.

As described above, it has been shown by the examples that the thin wires of Ni-base superalloys can be manufactured by cold plastic working. The Ni-base superheat-resistant alloy manufactured by the manufacturing method of the present invention can be processed into a wire rod having an arbitrary wire diameter by cold plastic working. Although the present embodiment was carried out for manufacturing a wire rod, it can be applied to manufacture of other shapes such as a plate material.

Claims (9)

A method for producing a Ni-base super heat-resistant alloy, comprising:
(A) a material having a carbon content of 0.01 to 0.25 mass% and an equilibrium precipitation amount of a gamma prime phase at 700° C. of 35 mol% or more at a temperature of 500° C. or less, A step of producing a first processed material by performing plastic working a plurality of times so that the cumulative processing rate from the material becomes 40% or more;
(B) a step of heat-treating the first processed material at a temperature of 900° C. or higher to produce a first heat-treated material,
(C) The first heat-treated material is subjected to plastic working at a temperature of 500° C. or lower and once or a plurality of times so that the cumulative working rate from the first heat-treated material is 10% or more. And a step of producing a second processed material, the method for producing a Ni-base superalloy. 2. The production of the Ni-base superalloy according to claim 1, wherein the step (b) and the step (c) are performed once or a plurality of times after the step (c) to produce the second processed material. Method. The method for producing a Ni-base superalloy according to claim 1 or 2, further comprising (d) a step of heat-treating the second processed material at a temperature of 900°C or higher. The Ni-base superheat-resistant alloy according to any one of claims 1 to 3, wherein a working ratio of one plastic working in the plastic workings of the steps (a) and (c) is 30% or less. Manufacturing method. The method for producing a Ni-base superalloy according to any one of claims 1 to 4, wherein the step (b) includes a step of removing the surface of the material after the heat treatment. The Ni-based super heat-resistant alloy, in mass%,
C: 0.01 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: 0-8.0%,
W: 0 to 15.0%,
Nb: 0 to 4.0%,
Ta: 0 to 5.0%,
Fe: 0 to 10.0%,
V: 0 to 1.2%,
Hf: 0 to 3.0%,
B: 0 to 0.300%,
Zr: 0 to 0.300%
The method for producing a Ni-base superheat-resistant alloy according to any one of claims 1 to 5, wherein the balance comprises Ni and impurities. A method for producing a Ni-base super heat-resistant alloy, comprising:
(A) A material having a carbon content of 0.01 to 0.25% by mass and an equilibrium precipitation amount of a gamma prime phase at 700°C of 35 mol% or more at a temperature of 500°C or less, A step of performing a plastic working to produce a first processed material,
(B) a step of heat-treating the first processed material at a temperature of 900° C. or higher to produce a first heat-treated material;
(C) a step of producing a second processed material by further performing plastic working on the first heat-treated material at a temperature of 500° C. or lower,
The combination of the step (A) and the step (B) is performed once or plural times,
Production method of the last performed step (B) Ni-base superalloy dimension d in the direction perpendicular to the longitudinal direction of the first workpiece subjected to the heat treatment is at least 1.5 times the final product dimensions d _f of .. A method for producing a Ni-base super heat-resistant alloy, comprising:
(A) A material having a carbon content of 0.01 to 0.25% by mass and an equilibrium precipitation amount of a gamma prime phase at 700°C of 35 mol% or more at a temperature of 500°C or less, A step of performing a plastic working to produce a first processed material,
(B) a step of heat-treating the first processed material at a temperature of 900° C. or higher to produce a first heat-treated material;
(C) a step of producing a second processed material by further performing plastic working on the first heat-treated material at a temperature of 500° C. or lower,
The combination of the step (A) and the step (B) is performed once or plural times,
The difference d−d _f between the dimension d _{f of} the first processed material in the direction perpendicular to the longitudinal direction and the final product dimension d _f to be subjected to the heat treatment of the finally performed step (B) is more than 1 mm. Alloy manufacturing method. The carbon content is 0.01 to 0.25 mass %, and the equilibrium precipitation amount of the gamma prime phase at 700° C. has a component composition of 35 mol% or more,
A Ni-base super heat-resistant alloy having a defect rate of 0.5 area% or less in a cross-sectional structure.