JP2019183263A - Ni BASED SUPERALLOY MATERIAL FOR COLD WORKING - Google Patents

Abstract

To provide a Ni based superalloy material suitable for cold working on the assumption that the manufacturing cost of a Ni based superalloy product is reduced by applying the cold working using a novel technical concept completely different from conventional one.SOLUTION: The Ni based superalloy material for cold working has a component composition having 35 mol% or more of a balance deposition amount of a gamma prime phase at 700°C, has a rod shape, has 200 μm or less of the average particle size of crystal grains in a cross sectional structure in the longitudinal direction of the rod shape, has an irregular shaped gamma prime phase having the maximum size of 2 μm or more and a gamma prime phase having the maximum size of 0.1 μm or more and 1 μm or less and has a tendency that the longitudinal direction of the irregular shaped gamma prime phase is oriented in that of the rod shape.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a Ni-base superheat-resistant alloy material for cold working, and more particularly to a Ni-base superheat-resistant alloy material having a component composition in which the equilibrium precipitation amount of gamma prime phase at 700 ° C. is 35 mol% or more. It is.

As heat-resistant parts used in aircraft engines and gas turbines for power generation, for example, Ni-based super heat-resistant alloys such as Inconel (registered trademark) 718 alloy are often used. With the improvement in performance and fuel efficiency of gas turbines, heat-resistant parts having a high heat-resistant temperature are required. In order to improve the heat resistance (high temperature strength) of the Ni-base superalloy, 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. The Ni-base superalloy can further improve the high-temperature strength of the Ni-base superalloy by including Al, Ti, and Nb that are γ′-generating elements. In the future, in order to satisfy high heat resistance and high strength, a Ni-base superalloy having a larger amount of γ ′ phase is required.

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

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

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

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

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

  The object of the present invention is suitable for such cold working on the premise that the manufacturing cost of Ni-base superalloy products is reduced by applying cold working using a novel technical idea completely different from the conventional one. It is to provide a Ni-based superalloy material.

  According to one aspect of the present invention, the composition of the gamma prime phase at 700 ° C. having a component composition of 35 mol% or more, having a bar shape, and having a cross-sectional structure along the longitudinal direction of the bar shape. The crystal grains have an average grain size of 200 μm or less, a deformed gamma prime phase having a maximum dimension of 2 μm or more, and a gamma prime phase having a maximum dimension of 0.1 μm or more and 1 μm or less, There is provided a Ni-based superalloy material for cold working having a tendency that the longitudinal direction of the prime phase is oriented in the longitudinal direction of the rod shape.

  According to another aspect of the present invention, the equilibrium precipitation amount of the gamma prime phase at 700 ° C. has a component composition of 35 mol% or more, has a rod shape, and has a cross-sectional structure along the longitudinal direction of the rod shape. The crystal grains have an average grain size of 200 μm or less, a deformed gamma prime phase having a maximum dimension of 2 μm or more, and a gamma prime phase having a maximum dimension of 0.1 μm or more and 1 μm or less, There is provided a Ni-based superalloy material for cold working having a divided structure in which the gamma prime phase is composed of a plurality of parts.

  According to a specific example, the rod-shaped diameter is preferably 3 to 20 mm.

  According to one specific example, it is preferable that the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 63 mol% or more.

  Further, according to one specific example, the component composition of the Ni-based superalloy for cold working is C% 0 to 0.25%, Cr: 8.0 to 25.0%, Al: 0.5 to 8.0%, Ti: 0.4 to 7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, W: 0 to 15.0%, Nb: 0 ~ 4.0%, Ta: 0 ~ 5.0%, Fe: 0 ~ 10.0%, V: 0 ~ 1.2%, Hf: 0 ~ 3.0%, B: 0 ~ 0.300% Zr: 0 to 0.300%, and the balance is preferably made of Ni and impurities.

Further, according to one specific example, the component composition of the Ni-based superalloy for cold working is C% 0 to 0.25%, Cr: 8.0 to 25.0%, Al: 0.5 to 8.0%, Ti: 0.4 to 7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, W: 0 to 6.0%, Nb: 0 ~ 4.0%, Ta: 0 ~ 3.0%, Fe: 0 ~ 10.0%, V: 0 ~ 1.2%, Hf: 0 ~ 1.0%, B: 0 ~ 0.300% Zr: 0 to 0.300%, and the balance is preferably made of Ni and impurities.
The above configurations can be combined as appropriate.

  According to the present invention, a Ni-based superalloy material suitable for cold working can be provided.

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

The schematic diagram which shows the shape change of the bar at the time of rolling a bar. The microstructure photograph which shows an example of the cross-sectional structure | tissue of the raw material extruded by the example of this invention. Alloy no. Microstructure photograph after swaging of 1-9 Ni-base superalloy. Alloy no. The EBSD image after the swaging process of the 1-9 Ni-base superalloy. Alloy no. The microstructure photograph after heat processing of the Ni-base superalloy 1-9. Alloy no. The drawing substitute photograph which shows the external appearance of the side surface after the roll rolling of 2-3 Ni-base superalloys. Alloy no. The drawing substitute photograph which shows the external appearance of the rolling surface after the roll rolling of 2-3 Ni-base superalloys. Alloy No. of Comparative Example The drawing substitute photograph which shows the external appearance of the side surface after roll rolling of 2-7 Ni-base superalloy. Alloy No. of Comparative Example The drawing substitute photograph which shows the external appearance of the rolling surface after roll-rolling of 2-7 Ni-base superalloy. A microstructure photograph showing an example of a cross-sectional structure of a hot-extruded material. A microstructure photograph showing an example of a cross-sectional structure of a hot-extruded material. A microstructure photograph showing an example of a cross-sectional structure of a raw material as it is homogenized. A microstructure photograph showing an example of a cross-sectional structure of a hot-extruded material.

The present invention relates to a new method capable of producing a Ni-base superalloy having excellent plastic workability by a new approach different from conventional hot plastic working, and is suitable for such a method. Is to provide.
The present inventor studied the plastic workability of a Ni-base superalloy having a large amount of γ ′ phase. As a result, the present inventors have found a phenomenon that the plastic workability of the Ni-base superalloy is dramatically improved by performing cold plastic working on the Ni-base superheater alloy material at a processing rate of 30% or more. At that time, it was found that nanocrystalline grains were generated in the structure of the Ni-base superalloy by cold plastic working at a working rate of 30% or more. It is speculated that the formation of the nanocrystal grains contributes to a dramatic improvement in the plastic workability of the Ni-base superalloy. And it discovered that the raw material which has a specific structure obtained by performing hot extrusion to the material of a Ni-base superalloy is suitable for such cold plastic working.

  That is, the Ni-based superalloy material for cold working according to the present invention has a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more, has a rod shape, In a cross-sectional structure along the longitudinal direction, the average grain size of the crystal grains is 200 μm or less, and a deformed gamma prime phase having a maximum dimension of 2 μm or more, and a gamma prime having a maximum dimension of 0.1 μm or more and 1 μm or less. And the longitudinal direction of the deformed gamma prime phase tends to be oriented in the longitudinal direction of the rod shape. According to another aspect, the Ni-based superalloy for cold working according to the present invention has a component composition in which the equilibrium precipitation amount of gamma prime phase at 700 ° C. is 35 mol% or more, and has a rod shape. And having a cross-sectional structure along the longitudinal direction of the rod shape, the crystal grain has an average grain size of 200 μm or less, a deformed gamma prime phase having a maximum dimension of 2 μm or more, and a maximum dimension of 0.1 μm or more And having a gamma prime phase of 1 μm or less, and the deformed gamma prime phase has a divided structure composed of a plurality of parts.

As described above, the Ni-base superheat-resistant alloy targeted by the present invention has a component composition in which the equilibrium precipitation amount of the gamma prime (γ ′) phase at 700 ° C. is 35 mol% or more.
Here, the amount of the γ ′ phase of the Ni-base superalloy can be expressed by a numerical index such as “volume ratio” or “area ratio” of the γ ′ phase. In the present specification, the amount of the γ ′ phase is represented by a numerical index of “γ ′ molar ratio”. The γ 'molar ratio is a stable equilibrium precipitation amount of the gamma prime phase in which the Ni-base superalloy can be precipitated in a thermodynamic equilibrium state. The value representing the equilibrium precipitation amount of the gamma prime phase in terms of “molar ratio” is determined by the component composition of the Ni-base superalloy. The value of mol% of the equilibrium precipitation amount can be obtained by analysis by thermodynamic equilibrium calculation. In the analysis by thermodynamic equilibrium calculation, it can be obtained accurately and easily by using various thermodynamic equilibrium calculation software.

  In the present invention, the γ ′ molar ratio of the Ni-base superalloy is defined as “equilibrium precipitation 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. In general, the equilibrium precipitation amount of the gamma prime phase in the tissue becomes generally constant at approximately 700 ° C. or less, and the temperature dependency becomes substantially constant. Therefore, the value at the above “700 ° C.” is used as a reference.

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

  As a precipitation strengthening type Ni-based superalloy material having an equilibrium precipitation amount of gamma prime phase at 700 ° C. of 35 mol% or more, for example, in mass%, C: 0 to 0.25%, Cr: 8.0 to 25 0.0%, Al: 0.5 to 8.0%, Ti: 0.4 to 7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, W: 0 to 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% It preferably contains 0.300%, Zr: 0 to 0.300%, with the balance being Ni and impurities.

  Alternatively, the Ni-base superalloy material is in mass%, C: 0 to 0.03%, Cr: 8.0 to 22.0%, Al: 2.0 to 8.0%, Ti: 0.4 -7.0%, Co: 0-28.0%, Mo: 2.0-7.0%, W: 0-6.0%, Nb: 0-4.0%, Ta: 0-3. 0%, Fe: 0 to 10.0%, V: 0 to 1.2%, Hf: 0 to 1.0%, B: 0 to 0.300%, Zr: 0 to 0.300%, The balance preferably has a composition comprising Ni and impurities.

  Hereinafter, each component of a composition preferable as one form of the Ni-based superalloy material according to the present invention will be described (the unit of the component composition is “mass%”).

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

Therefore, when it is intended to provide a Ni-base superalloy having a large amount of γ ′ phase as a Ni-base superalloy having excellent plastic workability rather than as a cast part, It is preferable to reduce C. On the other hand, in the cold plastic working using the Ni-based superalloy material of the present invention, the cold plastic workability can be drastically improved by having “nanocrystalline grains” in the cross-sectional structure. Therefore, for example, a C content comparable to the content in cast parts can be allowed. In the present invention, the C content is preferably 0.25% or less. More preferably, the order is 0.1% or less and 0.03% or less. More preferably, it is 0.025% or less, More preferably, it is 0.02% or less. Particularly preferably, it is less than 0.02%.
For the Ni-base superalloy material according to the present invention, C is a regulating element and is preferably managed lower. And when it is good also as C without addition (inevitable impurity level), the minimum of C can be made into 0 mass%. Usually, even if it is a Ni base superalloy without addition of C, when the component composition is analyzed, for example, a C content of about 0.001% can be recognized.

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

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

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

Titanium (Ti)
Ti, like Al, is an element that forms a γ ′ phase and enhances the high temperature strength by solid solution strengthening of the γ ′ phase. However, excessive addition causes the γ ′ phase to become unstable at a high temperature, leading to coarsening at a high temperature, and forming a harmful η (eta) phase, thereby impairing hot workability during material preparation. Therefore, Ti is preferably 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%. Moreover, a preferable upper limit is 6.5%, More preferably, it is 6.0%. More preferably, it is 4.0%, and particularly preferably 2.0%.

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

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

Tungsten (W)
W, like Mo, is one of the selective elements that contribute to solid solution strengthening of the matrix. However, if W is excessive, a harmful intermetallic compound phase is formed and the high-temperature strength is impaired. For example, the upper limit is set to 15.0%. A preferable upper limit is 13.0%, More preferably, it is 11.0%, More preferably, it is 9.0%. More preferably, the upper limit of W can be 6.0%, 5.5%, and 5.0%. In order to exhibit the effect of W more reliably, the lower limit of W is preferably set to 1.0%. Preferably, the lower limit of W can be set to 2.0%, 3.0%, 4.0%. Moreover, the solid solution strengthening effect can be exhibited more by adding W and Mo in combination. In the case of composite addition, W is preferably 0.8% or more. In addition, when it is good also considering W as an additive-free level (inevitable impurity level of a raw material) by sufficient addition of Mo, the minimum of W shall be 0%.

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

Tantalum (Ta)
Ta, like Al and Ti, is one of the selective elements that forms a γ ′ phase and strengthens the γ ′ phase by solid solution strengthening to increase the high-temperature strength. However, excessive addition of Ta causes the γ 'phase to become unstable at high temperatures, leading to coarsening at high temperatures, and forming a harmful η (eta) phase, thereby improving hot workability during material preparation. To lose. Therefore, Ta is set to 5.0% or less, for example. Preferably it is 4.0% or less, More preferably, it is 3.0% or less, More preferably, it is 2.5% or less. In order to exhibit the above Ta effect more reliably, the lower limit of Ta is preferably set to 0.3%. Preferably, the lower limit of Ta can be 0.8%, 1.5%, and 2.0%. In the case where Ta is allowed to be a non-addition level (inevitable impurity level) due to the addition of γ′-generating elements such as Ti and Nb and the balance with the matrix, the lower limit of Ta is set to 0%.

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

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

Hafnium (Hf)
Hf is one of the selective elements useful for improving the oxidation resistance of alloys and strengthening grain boundaries by forming carbides. However, excessive addition of Hf leads to production of oxides and high temperature unstable phases in the production process, and adversely affects manufacturability and high temperature dynamic performance. Therefore, the upper limit of Hf is, for example, 3.0%, preferably 2.0%, more preferably 1.5%, and still more preferably 1.0%. In order to exhibit the effect of Hf more reliably, the lower limit of Hf is preferably set to 0.1%. Preferably, the lower limit of Hf can be 0.5%, 0.7%, and 0.8%. In the case where Hf may be at an additive-free level (inevitable impurity level) due to 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 when a coarse boride is formed, hot workability at the time of preparing the material is hindered. For example, it does not exceed 0.300%. It is good to control as follows. A preferable upper limit is 0.200%, and more preferably 0.100%. More preferably, it is 0.050%, Most preferably, it is 0.020%. In order to obtain the above effect, a content of at least 0.001% is preferable. A more preferable lower limit is 0.003%, and further preferably 0.005%. Particularly preferred is 0.010%. In the case where B may be made an additive-free level (inevitable 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 the high temperature strength and hot workability during material preparation are hindered. Therefore, the upper limit of Zr is, for example, 0.300%. A preferable upper limit is 0.250%, and more preferably 0.200%. More preferably, it is 0.100%, Most preferably, it is 0.050%. In order to obtain the above effect, a content of at least 0.001% is preferable. A more preferable lower limit is 0.005%, and further preferably 0.010%. In the case where Zr may be at an additive-free level (inevitable impurity level) due to balance with other alloy elements in the alloy, the lower limit of Zr is set to 0%.

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

  Next, a specific example of a method for producing a cold-working Ni-base superalloy material having the above-described component composition will be described.

  In this specific example, a raw material having a crystal grain size of 200 μm or less is manufactured by hot extrusion. The material to be subjected to hot extrusion may be obtained, for example, by a melting method in which molten metal is poured into a mold to produce an ingot. For example, the ingot may be manufactured by combining vacuum melting and conventional methods such as vacuum arc remelting and electroslag remelting. In order to eliminate element segregation of the ingot, soaking (for example, holding at 1100 ° C. to 1280 ° C. for 5 to 60 hours) may be performed. This soaking may be performed after finishing the shape of the material to be subjected to hot extrusion. Alternatively, the material to be subjected to hot extrusion may be obtained by a powder metallurgy method for producing an alloy lump.

  And it extrudes with hot with respect to said material, and finishes it to the raw material of the bar material (bar material) of a predetermined shape. The conditions for hot extrusion are preferably performed at an extrusion temperature (material heating temperature) 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 diameter of the cross section in the direction orthogonal to the longitudinal direction of the extruded material is, for example, 10 mm or more and more than 20 mm. For example, it is 200 mm or less. In addition, when the cross section in the direction orthogonal to the longitudinal direction is not circular, the maximum diameter in the cross section is regarded as the above-mentioned diameter. And when manufacturing a bar, the surface of the extruded material is finished by machining such as cutting, or a bar-shaped material of a predetermined size is collected from the extruded material, and manufactured. Can do. In this case, the diameter of the rod-shaped material can be, for example, 150 mm or less, 100 mm or less, 50 mm or less, 30 mm or less, 20 mm or less, 10 mm or less. Further, the diameter of the rod-shaped material can be set to, for example, 3 mm or more, 4 mm or more, 5 mm or more. Keeping the diameter of the rod-shaped material small means that the number of plastic workings (number of passes) can be reduced when producing a wire or fine wire with a smaller diameter in cold plastic working, which will be described later. preferable. On the other hand, if the diameter of the rod-shaped material is excessively reduced, the number of hot extrusion processes and processing loss are increased. Therefore, the diameter of the rod-shaped material for cold working is preferably 3 mm or more.

  Extrusion is performed hot to make a recrystallized structure having a crystal grain size of 200 μm or less. The recrystallized structure is preferably 150 μm or less, more preferably 100 μm or less, and 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, and still more preferably 1.5 μm or more. The crystal grains produced by recrystallization are less strained in the grains, and the grain boundaries increase by making the grains finer. Processing strain is evenly applied to the entire tissue. In addition, the refinement of the crystal grains is effective for the generation of nanocrystal grains described later. Therefore, by carrying out this process, the deformation of the Ni-base super heat-resistant alloy material during cold plastic working becomes more uniform, and abnormal deformation and bending during processing can be avoided, resulting in a dramatic improvement in yield. Can be made. On the other hand, when plastic working is performed without passing through a hot extrusion step, deformation and bending occur during the processing, and the shape of the processed product tends to be poor, as will be described in the following examples. 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 crystal grain size of the material can be measured from the cross-sectional structure along the longitudinal direction of the rod shape. First, the cross section of the material is corroded with a curling liquid, and the cross-sectional structure after the corrosion is observed with an optical microscope having a predetermined magnification. And it can evaluate by "grain size number G" based on JIS-G-0551 (ASTM-E112), and can convert into "average diameter d of the crystal grain" corresponding to the grain size number G. In the present invention, the crystal grain size of the material refers to the above-mentioned “average diameter d of crystal grains”.

The raw material that has been subjected to hot extrusion has the following structure in a cross-sectional structure along the longitudinal direction of the rod shape. FIG. 8 shows a field emission scanning electron microscope (FE) of a rod-shaped Ni-based superalloy material obtained by homogenizing a 713C alloy ingot at 1200 ° C. and then hot-extrusion at 1100 ° C. -SEM) image (cross-sectional photograph). From the cross-sectional structure of FIG. 8, the deformed gamma prime phase 4 having a maximum dimension of 2 μm or more (phase that appears slightly dark in the figure. Hereinafter, also referred to as a coarse γ ′ phase), the maximum dimension is 0.1 μm or more, and A gamma prime phase 5 of 1 μm or less (a phase that appears bright in the figure, hereinafter also referred to as a minute γ ′ phase for convenience) can be confirmed. The irregular shape is an irregular shape different from a normal polygon. For example, in FIG. 8, it can be confirmed as an irregular shape including a curve and a dent. The minute γ ′ phase has a substantially polygonal shape, is mainly a quadrangular shape, and includes a triangular shape and those rounded. These fine γ ′ phases are dispersed so as to fill the space between the coarse γ ′ phases, and are precipitated exclusively in the crystal grains of the γ phase that is the matrix. Most of the fine γ ′ phases in FIG. 8 have a maximum dimension of 0.2 to 0.5 μm. In the cold plastic working described later, nanocrystal grains are generated at the phase interface between the γ phase and the γ ′ phase, and the plastic workability is improved as the number increases. Therefore, the Ni-based superalloy material for cold working having the fine γ ′ phase and the coarse γ ′ phase shown in FIG. 8 is suitable for cold plastic working. The maximum dimension can be evaluated by a cross-sectional structure.
In the cross-sectional structure, the area ratio of the minute γ ′ phase can be, for example, about 10 to 60%. In addition, a composition with a large amount of equilibrium precipitation of gamma prime phase at 700 ° C. is adopted.
It can also be about -60%.

  FIG. 9 shows an optical microscope image observed at a magnification lower than that of the FE-SEM image of FIG. For comparison, FIG. 10 shows an optical microscope image of a Ni-based superalloy material that has been homogenized at 1200 ° C. after casting. In the optical microscope image, the irregular coarse γ ′ phase 4 can be confirmed as a bright white phase. In FIG. 10, the longitudinal direction of the coarse γ ′ phase (the direction of the line to obtain the maximum dimension) is random, whereas in the Ni-based superalloy material subjected to hot extrusion shown in FIG. 9, the coarse γ ′ phase Have a tendency to be oriented in the rod-shaped longitudinal direction (left and right directions indicated by arrows in the figure). Here, “the tendency that the longitudinal direction of the coarse γ ′ phase is oriented in the longitudinal direction of the rod shape” means that all the longitudinal directions of the coarse γ ′ phase are oriented in the longitudinal direction of the rod shape. Even if the longitudinal direction of the coarse γ ′ phase is deviated from the longitudinal direction of the rod shape, or the coarse γ ′ phase close to the direction orthogonal to the longitudinal direction of the rod shape is present, the overall length of the rod shape This means that the proportion of coarse γ ′ phase having a longitudinal direction close to the direction is relatively high. Specifically, for example, the angle (acute angle) between the direction of the line for obtaining the maximum dimension (the maximum straight line that can be drawn at two points on the outer edge of the irregular coarse γ ′ phase) and the longitudinal direction of the rod shape is arbitrarily determined. When evaluated for several coarse γ ′ phases, it can be taken as a guide that 70% or more of the irregular coarse γ ′ phases are less than 45 degrees. In the Ni-base superalloy material shown in FIG. 9, approximately 97% of the irregular coarse γ ′ phase is less than 45 degrees.

  As described above, nanocrystal grains are generated at the phase interface between the γ phase and the γ ′ phase, and the plastic workability of the Ni-based superalloy material is improved as the number increases. Since it is considered that the nanocrystal grains are generated by applying cold working stress to the phase interface between the γ phase and the γ ′ phase, it is preferable that the stress is efficiently applied to the phase interface. In this respect, in cold working such as swaging and rolling, a large stress is applied in the radial direction of the rod-shaped Ni-based superalloy material, so the phase interface is perpendicular to this direction (the direction of the arrow in FIG. 9). The spreading state is more susceptible to cold working stress. Therefore, a configuration corresponding to such a state and showing a tendency that the longitudinal direction of the coarse γ ′ phase is oriented in the longitudinal direction of the rod shape is a configuration suitable for improving the cold plastic workability through the formation of nanocrystal grains. It is.

  FIG. 11 shows a scanning transmission electron observed at a higher magnification using a field emission transmission electron microscope (FE-TEM) with respect to the Ni-base superalloy material obtained through the hot extrusion shown in FIG. A microscope (STEM) image is shown. As shown in FIG. 11, the fine γ ′ phase 5 is precipitated in the grains of the γ phase that is a matrix, and a deformed coarse γ ′ phase 4 can be confirmed separately from the fine γ ′ phase. The irregular coarse γ ′ phase 4 shown in FIG. 11 is not integral but has a divided structure composed of a plurality of parts (individuals). Since the coarse γ 'phase has a split structure, the deformation resistance of the coarse γ' phase during cold working is reduced, so the structure in which the coarse γ 'phase has a split structure also improves cold plastic workability. It becomes a suitable structure. From the viewpoint of improving the cold workability, it is not necessary for all of the coarse γ ′ phases to have a divided structure, and at least a portion of the coarse γ ′ phase may have a divided structure. More preferably, 50% or more of the coarse γ ′ phases have a divided structure by observing a plurality of coarse γ ′ phases.

  The hardness of the Ni-based super heat-resistant alloy material for cold working is low in order to ensure the initial workability by cold plastic working in a state where the nanocrystal grains described later are not generated in the structure. preferable. For example, it is 550 HV or less or less than 500 HV, and more preferably 450 HV or less. More preferably, it is 400 HV or less, More preferably, it is 380 HV or less. Although the minimum of the hardness of a raw material is not specifically limited, About 250HV is realistic. The hardness of the material can be measured by the cross section of the material.

The Ni-based superalloy material for cold working obtained through the steps exemplified as described above is used for cold working. For example, cold plastic working with a working rate of 30% or more is performed. The above-mentioned Ni-based super heat-resistant alloy material is superior to conventional “hot” plastic working, and exhibits excellent workability in “cold” plastic working, and manufactures wires, fine wires, etc. by cold working It contributes to. In particular, in a Ni-base superalloy having an amount of γ ′ phase of 35 mol% or more, it is difficult to develop in hot plastic working by producing it by cold plastic working, which will be described later. "Increase action" of plastic workability due to the generation of nanocrystals from the phase interface (γ / γ 'interface) between the γ' (gamma prime) phase and the γ '(gamma prime) phase appears, making it difficult to process by hot plastic working The above Ni-base superalloy can be processed into a wire or a thin wire with a relatively simple process and low cost. In order to achieve this, it is necessary that the cold plastic working be performed in a low temperature region where it is considered that recovery and recrystallization cannot occur during the plastic working.
Therefore, the plastic processing temperature in the present invention is preferably set to “500 ° C. or lower”. More preferably, it is 300 degrees C or less, More preferably, it is 100 degrees C or less, More preferably, it is 50 degrees C or less (for example, room temperature).

  It is apparent that the production of Ni-base superalloy products by cold working using the Ni-base superheat-resistant alloy material described above can be applied to wire forms, plate materials, strips, and the like. At this time, the Ni-based superheat-resistant alloy material has an intermediate product shape of a wire material, a sheet material, and a strip material. Further, the Ni-based super heat-resistant alloy product by cold working may have such an intermediate product shape, or a final product shape of a wire product, a sheet product, or a strip product. It is also clear that it is good. Regarding the plate material (thin plate) and the strip material (thin strip), the dimensional relationship can be changed from the wire diameter (diameter) of the wire rod (thin wire) to the plate thickness or the strip thickness.

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

Here, the processing rate is expressed by the area reduction rate when swaging or die drawing a bar. The area reduction ratio is the relationship between the cross-sectional area A ₀ of the bar material before plastic working and the cross-sectional area A _{1 of the} wire or thin wire after plastic working.
[(A ₀ −A ₁ ) / A ₀ ] × 100 (%) (1)
It is calculated by the following formula.
On the other hand, when rolling, the processing rate is expressed as a reduction rate. The reduction ratio is defined as follows: t ₀ is the thickness of the material before plastic processing, and t ₁ is the thickness of the plate or strip after plastic processing.
[(T ₀ −t ₁ ) / t ₀ ] × 100 (%) (2)
It is calculated by the following formula.
The cumulative processing rate indicates the processing rate for the material of the final workpiece when plastic processing is performed a plurality of times or over a plurality of passes.

FIG. 1 is a schematic diagram showing a shape change of a bar when the bar is rolled in a plurality of passes (two passes in the figure). In the figure, reference numeral 1 denotes a rolling direction, reference numeral 2 denotes a rolling surface, and reference numeral 3 denotes a side surface. Although the bar which is a processing starting material has a substantially circular cross section, it receives a compressive force from the upper and lower sides in the rolling direction 1 by the rolling rolls, and the rolling surface 2 in contact with the rolling rolls has a flat and flat shape. When the diameter of the bar is t ₀ and the distance between the upper and lower rolling surfaces of the second pass, that is, the thickness is t ₁ , the processing rate by this two-pass rolling is expressed by the above formula (2).

In the present invention, the processing rate of the cold plastic processing (including “cumulative processing rate” as described below) is increased to “30% or more”. At this time, if the processing rate is less than 30%, the degree of processing is slight, and the actual benefit of performing cold plastic processing is lacking. The processing rate is preferably 40% or more. The processing rate is more preferably 60% or more. More preferably, it is 70% or more, More preferably, it is 80% or more, More preferably, it is 85% or more. And still more preferably 90% or more, particularly preferably 97% or more.
Such a Ni-based superalloy that has been subjected to strong processing with a processing rate of 30% or more is in a state where it can be further processed. Therefore, it is preferable not to perform heat treatment during plastic working (including non-heating). The heat treatment here refers to a heat treatment in a high temperature region where recovery and recrystallization occur, and is a heat treatment for heating to a temperature exceeding 500 ° C., for example. Thus, no heat treatment is required between passes of cold working, and a plurality of cold strong workings are continuously performed to increase the cumulative working rate (area reduction rate) as much as possible (approaching 100%). it can. At this time, the Ni-base superalloy that has been subjected to strong processing can be processed while being kept at a hardness of 500 HV or more, for example, even if plastic processing is performed. In addition, the Ni-based superalloy that has been subjected to strong processing can observe the formation of nanocrystal grains in the structure. Although this mechanism has not been fully elucidated, it is considered as follows.

  When cold working with a processing rate of 30% or more is applied to a Ni-based alloy, it will have a hardness of 500 HV or higher due to work hardening in the middle of the processing. When processed, nanocrystals are generated from the γ / γ ′ interface. It was experimentally confirmed that the above-described processing rate is required to be at least about 30% in order to sufficiently generate the nanocrystal grains (see Examples). That is, when cold-plastic processing is performed on the above-described Ni-base superheat-resistant alloy rod, and the cumulative processing rate reaches about 30%, the nanocrystal grains are first formed into γ phase and γ ′. It was observed that it was preferentially produced at the phase interface with the phase. And, when the plastic processing by cold is further added to the Ni-based super heat-resistant alloy (for example, rod (wire)) once the nanocrystal grains are generated, the number of nanocrystal grains increases. The increase in grains further improves the plastic workability of Ni-base superalloys (eg, rods (wires)). By repeating this plastic working (by increasing the cumulative working rate), the plastic workability of Ni-base superalloys (for example, rods (wires)) is further improved, and heat treatment is performed during the plastic working. In addition, the "room temperature superplastic" plastic working phenomenon was confirmed, in which it was possible to perform plastic working with a cumulative working rate of 97% or more in the cold.

  The cold plastic working with the processing rate of “30% or more” may be completed by a single plastic working. However, until the nanocrystal grains are formed in the structure, for example, the alloy is cracked. In order to prevent the occurrence of wrinkles and wrinkles, it is preferable to divide and complete a plurality of plastic workings. In this case, the processing rate of 30% or more is a cumulative processing rate. By applying “large strain” with a processing rate of 30% or more to the material divided into multiple plastic workings, the strain is moderately dispersed in the material, causing grain boundary slippage and crystal rotation of the nanocrystal grains. It is effective to uniformly generate in the material. As a result, the nanocrystal grains can be formed uniformly and evenly in the material, and the occurrence of cracks, wrinkles and the like during the plastic working can be suppressed. When divided into a plurality of plastic workings, it is not necessary to perform a heat treatment between the plastic workings.

  Note that the upper limit of the processing rate of 30% or more due to one time or accumulation is not particularly set, and may be appropriately set according to, for example, the shape of the intermediate product or the final product. For example, if a Ni-base superalloy that is further plastically processed is prepared as the intermediate product described above, for example, 50%, 45%, 40%, 35, depending on the specifications. A numerical value such as% can be set.

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

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

  The Ni-base superalloy material that performs cold plastic working can be manufactured by hot extrusion as described above. By performing hot extrusion, a recrystallized structure having a crystal grain size of 200 μm or less (for example, a cast structure) is formed. In a recrystallized structure having a crystal grain size of 200 μm or less, the γ ′ phase is uniformly reprecipitated in the structure of the material, and therefore nanocrystal grains are easily formed in the structure after the subsequent cold plastic working. This is thought to be due to the fact that the phase interface between the γ phase and the γ ′ phase of the Ni-base superheat-resistant alloy becomes uniform, thereby promoting the formation of nanocrystal grains.

  The Ni-base superalloy after the cold plastic working has a linear structure in which the γ phase and the γ ′ phase extend in the extending direction (see FIG. 3). Thus, the Ni-base superalloy after cold plastic working can have a linear structure of γ phase and γ ′ phase. However, after plastic processing to a predetermined size and shape, when supplying as a final product, heat treatment (for example, holding at 1000 ° C. to 1200 ° C. for 30 minutes to 3 hours) is performed to obtain the desired equiaxed shape. A crystal structure can be formed (see FIG. 5). By this heat treatment, for example, the hardness can be adjusted to less than 500 HV, 450 HV or less, or 420 HV or less. For example, the hardness is 300 HV or higher or 350 HV or higher. This makes it easy to bend or cut the final product into a form commensurate with the form of transportation and use.

  By this manufacturing method, Ni-base superalloys in various forms ranging from intermediate product shapes such as the above-mentioned wire rods, plate materials, and strips to final product shapes such as thin wires, thin plates, and strips are provided. You can also.

  The Ni-base superalloy manufactured by the manufacturing method related to the cold working described above has excellent plastic workability, and in particular, is excellent in cold plastic workability. As described above, this Ni-base superalloy can have a hardness of 500 HV or higher. Alternatively, the cross-sectional structure can have crystal grains having a maximum diameter of 75 nm or less.

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

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

It is preferable that 5 or more nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure of the Ni-base superalloy manufactured by the manufacturing method related to cold working exist per 1 μm ² of the cross-sectional structure. By increasing the number of nanocrystal grains, the number of media that play the role of plastic deformation increases, and the plastic workability is further improved. More preferably, there are 10 or more, more preferably 50 or more, and still more preferably 100 or more crystal grains having a maximum diameter of 75 nm or less per 1 μm ^{2 of} the cross-sectional structure. And it is still more preferable in order of 200 or more, 300 or more, and 400 or more. The number density of the above-mentioned nanocrystal grains may be obtained by averaging the total number of nanocrystal grains confirmed in all observed cross-sectional structures divided by all observed visual field areas.
In addition, about the nanocrystal grain whose maximum diameter in a cross-sectional structure | tissue is 75 nm or less, the minimum of the maximum diameter does not need to set in particular. The presence / absence and number of nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure can be confirmed by, for example, an EBSD image. Nanocrystal grains having a maximum diameter of 75 nm or less among crystal grains that can be recognized when the measurement condition of EBSD is scan step: 0.02 μm and the definition of crystal grains is a grain boundary having an orientation difference of 15 ° or more. Can be extracted and counted. As an example, the presence and number of nanocrystal grains having a maximum diameter of about 25 nm or more can be confirmed.

As described above, since the Ni-base superalloy manufactured by the manufacturing method related to cold working is excellent in cold plastic workability, this is further referred to as “for cold plastic working”. can do.
Further, the Ni-base superalloy material of the present invention can be an “intermediate product shape” in which cold plastic working is performed, such as “wire”, “plate”, and “strip”. The wire has a thin wire diameter (diameter) of, for example, 10 mm or less, 8 mm or less, or 6 mm or less, and eventually 5 mm or less, 4 mm or less, 3 mm or less, or 2 mm or less. Further, the thickness of the plate material and the band material is, for example, from 10 mm or less, 8 mm or less, 6 mm or less to 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less. The lengths of the wire material, the plate material, and the belt material are, for example, 10 times or more, 50 times or more, 100 times or more of the wire diameter or thickness.
Further, the final product shape obtained by the cold plastic working can be a “thin wire”, “thin plate”, or “thin strip”. The fine wire has a wire diameter (diameter) of, for example, 5 mm or less, 4 mm or less, 3 mm or less, and eventually 2 mm or less, 1 mm or less. Further, the thin plate and the thin strip are those having a thickness 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. The thin wires, thin plates, and ribbons are longer than the wire diameter and thickness, for example, 50 times or more, 100 times or more, or 300 times or more.

  The molten metal prepared by vacuum melting was cast to prepare a cylindrical Ni-based superalloy A having a diameter of 100 mm and a mass of 10 kg. The component composition of the Ni-base superalloy A is shown in Table 1 (% by mass). Table 1 also shows the “γ ′ molar ratio” of the ingot. This value was calculated using a commercially available thermodynamic equilibrium calculation software “JMatPro (Version 8.0.1, product of Senté Software Ltd.)”. The content of each element listed in Table 1 was input to this thermodynamic equilibrium calculation software, and the above-mentioned “γ ′ molar ratio” (%) was obtained.

  The ingot of this Ni-base superalloy A is subjected to a heat treatment at a holding temperature of 1200 ° C. and a holding time of 8 hours, cooled in a furnace, and then a cylindrical shape having a diameter of 60 mm and a length of 150 mm 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 4, 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. The measurement location was set at a position with a distance of D / 4 (D is the diameter of the extruded material) from the surface of the extruded material toward the axis. Then, the crystal grain size of five visual fields extracted from this position (an example of the structure of one visual field is shown in FIG. 2) is measured according to the above-mentioned procedure, and the average of the “average diameter d of crystal grains” of each visual field is determined as “material. Crystal grain size ". Moreover, the hardness of 5 points | pieces extracted from said position was measured, the average value was calculated | required, and it was set as the hardness of the raw material. The material measured by this method had a crystal grain size (average crystal grain size) of 38 μm (grain size number 6.5 according to ASTM-E112) and a hardness of 351 HV. As shown in FIG. 2, among the γ ′ phases, the longitudinal direction of the irregular γ ′ phase having a maximum dimension of 2 μm or more that can be confirmed as a bright white phase tends to be oriented in the longitudinal direction of the rod shape (left and right direction in the figure). You can see that it has. Evaluate the angle (acute angle) between the direction of the line to obtain the maximum dimension (the maximum straight line drawn at two points on the outer edge of the irregular coarse γ 'phase) and the longitudinal direction of the rod shape for 100 coarse γ' phases As a result, 90% of the irregular coarse γ ′ phase was less than 45 degrees.

  Next, a rod-shaped material (bar material) having a diameter of 6 mm and a length of 60 mm was cut out from the extruded material to prepare a Ni-based superalloy material for cold working. The longitudinal direction of the bar was taken parallel to the axial direction (extrusion direction) of the extruded material. The bar material was subjected to a plurality of passes of cold plastic working at room temperature (about 25 ° C.) using a rotary swaging device. It was performed continuously without performing heat treatment between the processing passes. Table 2 shows the details of each pass and the cumulative area reduction after multiple passes. The cumulative area reduction was obtained from the equation (1) described above.

  Alloy No. 1-1, the wire diameter after processing was 5.5 mm, and the processing rate (area reduction rate) was 16.0%. Alloy No. In 1-2, swaging was further cumulatively performed to a wire diameter of 5.0 mm (processing rate: 30.6%). Furthermore, alloy no. 1-3 to Alloy No. 1-9 is Alloy No. The wire (1-2) was subjected to the swaging process (pass rate) shown in Table 2 while accumulating sequentially. In this way, the alloy no. 1-1 to Alloy No. Ni-based superalloy alloys up to 1-9 were prepared respectively. Note that heat treatment is not performed between the swaging processes. All of the alloy samples could be processed while maintaining a good shape. In FIG. The optical micrograph (1000-times multiplication factor) of the cross-sectional structure | tissue of 1-9 is shown. This cross-sectional microstructure is a structure (D is the wire diameter of the wire) taken from the cross-section at a position (position A) that is 1 / 4D from the surface of the wire toward the central axis in the cross-section divided in the longitudinal direction of the wire. Etching was performed with a curling solution after polishing. From this figure, it can be seen that the γ phase and the γ ′ phase have a linear structure extending in the stretching direction.

Furthermore, the EBSD image of the cross-sectional microstructure of each of the above alloy samples was evaluated. This cross-sectional microstructure is a structure taken from the cross section at the position A. And the measurement conditions of EBSD used the EBSD measurement system "Aztec Version 3.2 (made by Oxford Instruments)" attached to the scanning electron microscope "JIB-4700F (made by JEOL Ltd.)", and magnification: 10000. Double, scan step: 0.02 μm, and the definition of crystal grains was defined as a grain boundary with an orientation difference of 15 ° or more. At this time, the maximum diameter (maximum length) of the nanocrystal grains confirmed in the EBSD image was about 25 nm, which was small, and the presence and number of nanocrystal grains with the maximum diameter exceeding this value were confirmed. Alloy no. The wire rod 1-2 had nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure.
Alloy No. In the cross section of the wire rod halved in the longitudinal direction, the structure is also collected from the cross section of the surface position (position B) of the wire rod and the cross section of the central axis position (position C) of the wire rod. Analysis by EBSD was performed. The total number of nanocrystal grains having a maximum diameter of 75 nm or less counted in the visual field area (2 μm × 3 μm) is obtained from the total visual field area (2 μm × 3 μm) for a total of six cross-sectional structures collected from two positions A, B, and C, respectively. The number density per unit area of the nanocrystal grains obtained by dividing by 6 μm ² × 6) was “21 particles / μm ² ”.
Moreover, the hardness in said position A of each alloy sample was also measured. And alloy no. The hardness of the 1-2 wire was 560 HV.

  On the other hand, Alloy No. 1-1, the cross-sectional microstructure of the alloy No. When observed in the same manner as in 1-2, nanocrystal grains having a maximum diameter of 75 nm or less were not observed. Further, the hardness was 492 HV.

  Alloy No. 1-3 to Alloy No. The wires up to 1-9 also had nanocrystal grains having a maximum diameter of 75 nm or less in the cross-sectional structure. As an example, FIG. 1-9 shows an EBSD image (position A) (in the figure, the nanocrystal grains are visible as individual fine grains that can be distinguished by the difference in color tone). And about these wires, alloy No. In the same manner as in 1-2, the number density per unit area of nanocrystal grains of 75 nm or less in the cross-sectional structure was measured. Moreover, the hardness of the wire was also measured. These measurement results are shown in Table 2.

From the results shown in Table 2, it can be seen that the number of nanocrystal grains increases by further applying cold plastic working to the Ni-based superalloy having nanocrystal grains once generated. However, while the number of nanocrystal grains increased, the hardness of the Ni-base superalloy was almost constant regardless of the increase in the plastic working rate. For this reason, this invention example No. which is 1.5 mm in wire diameter by swaging processing. It was possible to carry out plastic working cold to 1-9 wire. This is referred to as Alloy No. When the 1-2 wire is a starting material (that is, an alloy material having a hardness of 500 HV or more and a crystal grain having a maximum diameter of 75 nm or less in the cross-sectional structure), the cumulative processing rate of the alloy material from the wire is 91. %, And if it was the cumulative processing rate from the original bar material, it was possible to perform plastic working as much as 94% cold. Furthermore, alloy no. The wire 1-9 was in a state where it could be further cold-worked even after plastic working with the large cumulative working rate. That is, the hardness of the alloy after working in the example of the present invention was almost constant (558 HV to 620 HV) regardless of the working rate (the working rate was slightly lower when the working rate was 85% or more). Thus, it can be seen that once the crystal grains having the maximum diameter of 75 nm or less are formed and the alloy material having a hardness of 500 HV or more can be continuously cold worked.
In addition, after the cold working, the alloy No. 1-9 was heat-treated at 1200 ° C. for 30 minutes (furnace cooling). The hardness after the heat treatment was 365 HV. An optical micrograph (magnification 200 times) of the cross section is shown in FIG. The observation was performed at the position A, and the cross section was polished and then etched with a curling liquid. It can be seen that the processed structure can be made into an equiaxed crystal structure by this heat treatment.

From the hot extruded material (diameter 27 mm, average crystal grain size 38 μm, hardness 351 HV) of the Ni-based superalloy A prepared under the method and conditions described in Example 1, a rod shape having a diameter of 4 mm and a length of 60 mm was obtained. A material (bar material) was cut out to prepare a Ni-based superalloy material for cold working. The longitudinal direction of the bar was taken parallel to the axial direction (extrusion direction) of the extruded material. This bar was processed by a plurality of passes at room temperature (about 25 ° C.) with a roll mill (FIG. 1). It was performed continuously without performing heat treatment between the processing passes. Table 3 shows the details of each pass and the rolling reduction after multiple passes. The rolling reduction was obtained from the equation (2) described above.
As a comparative example, a bar-shaped material (bar material) having a diameter of 4 mm and a length of 60 mm was obtained by subjecting the ingot of the Ni-base superalloy A to a heat treatment with a holding temperature of 1200 ° C. and a holding time of 8 hours. It cut out and rolled by the same rolling mill as the example of this invention. That is, this material was subjected to rolling of the cast material without being subjected to hot extrusion. The crystal grain size (average crystal grain size) of the bar before rolling was 2.8 mm, and the hardness was 323 HV.

  Alloy No. No. 2-2 to Alloy No. In No. 2-5, any alloy sample could be processed while maintaining a good shape (see FIGS. 6A and 6B). However, alloy no. 2-6 and alloy no. No. 2-7 was distorted during rolling and did not have a good plate shape, but meandering and deformation occurred (see FIGS. 7A and 7B).

From the results in Table 3, alloy no. As for the plate material of 2-1, the plate | board thickness after a rolling process was 3.5 mm, the processing rate (rolling rate) was 12.5%, and the hardness was also 461HV. On the other hand, Alloy No. No. 2-2 to No. 2 The plate materials up to 2-5 had a processing rate (rolling rate) of 30% or more, and the hardness of these alloys was 500 HV or more, but unlike the results of Example 1, the processing rate increased. Accompanying this, hardness tended to increase slightly. The processed plate material had a hardness of 600 HV or higher.
From the above results, it can be seen that the Ni-based superalloy having a hardness of 500 HV or more can be continuously cold worked in the rolling process as in Example 1.
Alloy No. No. 2-2 to No. 2 In all of the plate materials up to 2-5, nanocrystal grains having a maximum diameter of 75 nm or less were observed in the cross-sectional microstructure, and the number density of the nanocrystal grains increased as the processing rate increased. On the other hand, Alloy No. No nanocrystal grains having a maximum diameter of 75 nm or less were observed in the cross-sectional microstructure of the wire 2-1.

As described above, it has been confirmed that the Ni-base superalloy material of each example is excellent in plastic workability and can be processed into a wire having an arbitrary wire diameter by cold plastic processing. Although the present Example performed about manufacture of a wire rod and a board | plate material, of course, these wire rods and board | plate materials can also be handled as a fine wire and a thin board of a final product shape. And since the Ni-base superalloy material of this invention is excellent in plastic workability, it is clear that plastic working to shapes other than these is also possible.

Claims (6)

Having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more,
Having a bar shape,
In the structure of the cross-section along the longitudinal direction of the rod shape,
The average grain size of the crystal grains is 200 μm or less,
An irregular gamma prime phase having a maximum dimension of 2 μm or more and a gamma prime phase having a maximum dimension of 0.1 μm or more and 1 μm or less;
A Ni-based super heat-resistant alloy material for cold working, in which the longitudinal direction of the deformed gamma prime phase tends to be oriented in the longitudinal direction of the rod shape. Having a component composition in which the equilibrium precipitation amount of the gamma prime phase at 700 ° C. is 35 mol% or more,
Having a bar shape,
In the structure of the cross-section along the longitudinal direction of the rod shape,
The average grain size of the crystal grains is 200 μm or less,
An irregular gamma prime phase having a maximum dimension of 2 μm or more and a gamma prime phase having a maximum dimension of 0.1 μm or more and 1 μm or less;
A Ni-based superalloy material for cold working having a split structure in which the deformed gamma prime phase is composed of a plurality of parts.   The Ni-based superalloy material for cold working according to claim 1 or 2, wherein the rod-shaped diameter is 3 to 20 mm.   The Ni-based superalloy material for cold working according to any one of claims 1 to 3, wherein the equilibrium precipitation amount of the gamma prime phase at 700 ° C is 63 mol% or more.   Component composition is mass%, C: 0-0.25%, Cr: 8.0-25.0%, Al: 0.5-8.0%, Ti: 0.4-7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, 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%, with the balance being Ni and impurities. The Ni-base superalloy material for cold working as described in any one of -4.   Component composition is mass%, C: 0-0.25%, Cr: 8.0-25.0%, Al: 0.5-8.0%, Ti: 0.4-7.0%, Co: 0 to 28.0%, Mo: 0 to 8%, W: 0 to 6.0%, Nb: 0 to 4.0%, Ta: 0 to 3.0%, Fe: 0 to 10.0 %, V: 0 to 1.2%, Hf: 0 to 1.0%, B: 0 to 0.300%, Zr: 0 to 0.300%, with the balance being Ni and impurities. Ni-based superalloy material for cold working as described in 1.