SHAPED ARTICLE MADE OF Ni-BASED ALLOY

Abstract

The purpose of the present invention is to provide a shaped article having high hardness realized in a short heat treatment time. The present invention provides a shaped article comprising a Ni-based alloy, wherein an α Cr phase and a γ phase and / or a γ' phase are lamellarly precipitated, and a granular precipitate having a particle diameter of 400 nm or more in terms of equivalent circle diameter is not included.

Description

Ni-based alloy molded objects

[0001] The present invention relates to a shaped object made of a Ni-based alloy produced by a manufacturing method such as three-dimensional additive manufacturing.

[0002] Conventionally, NiCrAl alloys have been used in engine parts and the like as Ni-based alloys that exhibit wear resistance and corrosion resistance. Examples of NiCrAl alloys include Ni-based high-strength heat-resistant alloys that contain, by mass %, 0.1% or less of C, 2.0% or less of Si, 2.0% or less of Mn, 30 to 45% of Cr, and 3.1 to 5% of Al, with the remainder consisting of unavoidable impurities and Ni, and that are strengthened by the composite precipitation of γ' and α phases (see Patent Document 1). This alloy material attempts to obtain hardness by precipitating lamellae of the α-Cr phase and the γ' phase.

[0003] In recent years, NiCrAl alloys have also been applied to metal additive manufacturing. Metal additive manufacturing products using NiCrAl alloys include, for example, Ni-based alloy products using Ni-based alloy powder containing 0.3 to 1.0% C, 36.0 to 50.0% Cr, 3.0 to 7.0% Al, and the remainder consisting of Ni and unavoidable impurities (see Patent Document 2). This alloy is an attempt to obtain hardness by adding C to the NiCrAl alloy to form carbides.

[0004] JP 2002-69557 A JP 2021-188069 A Electric Steel Manufacturing, Vol. 77, No. 2, p. 134, Fig. 1(a)

[0005] Although the NiCrAl alloys described in these documents aim for hardness and corrosion resistance, it takes time for the precipitation of a lamellar structure. For example, in Patent Document 2, an aging time of about 16 to 20 hours is required. Therefore, there is a manufacturing problem in that the heat treatment is time-consuming and costly.

[0006] Therefore, an object of the present invention is to provide a shaped article made of a Ni-based alloy such as a NiCrAl alloy, which has high hardness achieved by a short heat treatment time.

[0007] As a result of extensive research, the inventors have discovered that by directly aging a shaped article obtained by shaping using a Ni-based alloy powder such as NiCrAl alloy powder, without solution treatment, it is possible to obtain a shaped article made of a Ni-based alloy that does not contain granular precipitates with a circle equivalent diameter of 400 nm or more and has a lamellar structure of a γ phase and / or a γ' phase and an αCr phase, and have completed the present invention.

[0008] That is, the present invention provides the following shaped articles. [1] A shaped article made of a Ni-based alloy in which an αCr phase and a γ phase and / or a γ' phase are precipitated in layers, and which does not contain granular precipitates having a circle-equivalent diameter of 400 nm or more. [2] The shaped article according to [1], in which the prior γ grain size is 100 μm or less. [3] The shaped article according to [1] or [2], in which the Rockwell hardness is 50.0 HRC or more. [4] The shaped article according to any one of [1] to [3], in which the Vickers hardness is 513 HV or more. [5] The shaped article according to any one of [1] to [4], in which the Ni-based alloy has a composition, in mass %, of 30.0 to 45.0% Cr, 2.5 to 5.0% Al, 0 to 0.2% C, and the balance being Ni and unavoidable impurities. [6] The shaped object according to any one of [1] to [5], wherein the shaped object is a layered shaped object.

[0009] By subjecting a shaped article obtained by shaping using a Ni-based alloy powder (e.g., a NiCrAl alloy powder) to a short-term (e.g., 10 hours or less) aging treatment without solution treatment, it is possible to obtain a shaped article made of a Ni-based alloy (e.g., a NiCrAl alloy) with high hardness, such as a Rockwell hardness of 50.0 HRC or more (especially 59.5 HRC or more) and a Vickers hardness of 513 HV or more (especially 700 HV or more). Therefore, according to the present invention, it is possible to provide a shaped article that has high hardness but can be produced at low energy costs.

[0010] The shaped product of the present invention, in which the αCr phase and the γ phase and / or the γ' phase are precipitated in layers and which does not contain granular precipitates with a particle size of 400 nm or more in equivalent circle diameter, can achieve high hardness, such as a Rockwell hardness of 50.0 HRC or more (particularly 59.5 HRC or more) and a Vickers hardness of 513 HV or more (particularly 700 HV or more), without significantly impairing mechanical properties such as toughness.

[0011] Figure 1 is an SEM image of the microstructure of an additive manufacturing product of the present invention obtained by holding an unheated additive manufacturing product at 700°C for 4 hours and then air-cooling. Figure 2 is an SEM image of the microstructure of an additive manufacturing product of the present invention obtained by holding an unheated additive manufacturing product at 500°C for 8 hours and then air-cooling. Figure 3 is an SEM image of the microstructure of an additive manufacturing product obtained by solution-treating an unheated additive manufacturing product (holding at 1150°C for 30 minutes and then water-cooling), holding it at 500°C for 2 hours, and then air-cooling. The arrows indicate the direction of lamellar growth and show how the growth of the lamellar structure is stopped by granular precipitates.

[0012] The shaped object of the present invention will be described below.

[0013] [Components] The shaped article of the present invention is made of a Ni-based alloy. The Ni-based alloy used in the present invention preferably has a composition consisting of 30.0 to 45.0% Cr, 2.5 to 5.0% Al, 0 to 0.2% C, and the balance being Ni and unavoidable impurities. The types and contents of the added elements and the reasons for their limitations are as follows. Note that "%" for each component represents mass %.

[0014] First, the main constituent Ni and the essential additives Cr and Al will be described.

[0015] Ni Ni is a component that can provide a material with excellent corrosion resistance, strength, and toughness, and therefore the alloy used in the present invention is based on Ni.

[0016] Cr: 30.0 to 45.0% Cr is a forming element necessary for lamella formation. When a Ni-based alloy containing a certain amount of Cr is aged, the αCr phase and the γ phase and / or γ' phase precipitate in layers, contributing to increased strength and hardness. Furthermore, Cr forms a protective film on the material surface in various corrosive environments, greatly contributing to improved high-temperature corrosion resistance.

[0017] If the Cr content is too low, it will be impossible to stably form a lamellar structure throughout the entire structure by aging treatment, resulting in a decrease in hardness. Therefore, the Cr content is preferably 30.0% or more, more preferably 33.0% or more, and even more preferably 36.0% or more.

[0018] On the other hand, if the Cr content is excessive, the Ni content will be relatively small, resulting in an insufficient amount of γ' phase precipitation. Therefore, the Cr content is preferably 45.0% or less. The Cr content is more preferably 42.0% or less, and even more preferably 40.0% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0019] Al: 2.5 to 5.0% Al is a forming element necessary for lamella formation. Furthermore, Al forms Ni3Al (γ' phase) through aging treatment. In NiCrAl alloys, lamellar structures are formed by the precipitation of the αCr phase and the γ phase and / or γ' phase in layers, resulting in high hardness. Furthermore, Al contributes to improving high-temperature corrosion resistance and oxidation resistance. To achieve these effects, the Al content is preferably 2.5% or more. The Al content is more preferably 3.0% or more, and even more preferably 3.5% or more.

[0020] On the other hand, if the Al content is excessive, solidification cracking is likely to occur during molding. Therefore, the Al content is preferably 5.0% or less. The Al content is more preferably 4.5% or less, and even more preferably 4.0% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0021] C: 0-0.2% The Ni-based alloy used in the present invention may contain C as an additional component in addition to Ni, Cr, and Al. The C content may be 0% or more than 0%, but is preferably 0.2% or less. C is a component that forms carbides and contributes to increasing the hardness of the material, but if the C content is excessive, coarse carbides will occur, causing a deterioration in the toughness of the material. Therefore, even if C is contained as an impurity, the C content is preferably 0.2% or less. The C content is more preferably 0.1% or less, and even more preferably 0.03% or less.

[0022] The Ni-based alloy used in the present invention may contain one or more elements selected from C, Si, Mn, Fe, Co, Mo, P, S, O and N as unavoidable impurities.

[0023] [The αCr phase and the γ phase and / or the γ' phase are precipitated in a layered manner, and particulate precipitates with a diameter of 400 nm or more in equivalent circle diameter are not contained] The shaped article of the present invention is characterized in that the αCr phase and the γ phase and / or the γ' phase are precipitated in a layered manner, and particulate precipitates with a diameter of 400 nm or more in equivalent circle diameter are not contained. The fact that the αCr phase and the γ phase and / or the γ' phase are precipitated in a layered manner and that particulate precipitates with a diameter of 400 nm or more in equivalent circle diameter are not contained can be confirmed by the method described in the Examples.

[0024] High hardness is obtained by the precipitation of the αCr and γ phases, or the αCr and γ' phases, or the αCr and γ and γ' phases in layers, i.e., by growing into a lamellar structure. Furthermore, the finer the lamellar spacing, the higher the hardness, so a fine lamellar spacing is desirable.

[0025] The shaped product of the present invention is obtained by subjecting a shaped product (sometimes referred to herein as an "unheat-treated shaped product" or "unaged shaped product") obtained by shaping to an aging treatment. When the unheat-treated shaped product is subjected to an aging treatment, the αCr phase and the γ and / or γ' phase precipitate in layers, resulting in the growth of a lamellar structure. Because the growth of the lamellar structure is inhibited by contact with coarse granular precipitates, it is advantageous for the granular precipitates to be small in size. Therefore, it is desirable for the unheat-treated shaped product to be free of granular precipitates with a circle-equivalent diameter of 400 nm or greater. Since granular precipitates grow when the unheat-treated shaped product is subjected to a solution treatment, subjecting the unheat-treated shaped product to an aging treatment without a solution treatment can suppress the inhibition of lamellar structure growth caused by coarse granular precipitates, thereby achieving excellent aged hardness. Since the unheat-treated shaped product does not contain granular precipitates with a diameter of 400 nm or more in equivalent circle diameter, the shaped product of the present invention also does not contain granular precipitates with a diameter of 400 nm or more in equivalent circle diameter. In the shaped product of the present invention, the αCr phase and the γ phase and / or γ' phase are precipitated in layers, and granular precipitates with a diameter of 400 nm or more in equivalent circle diameter are not contained, so that high hardness such as a Rockwell hardness of 50.0 HRC or more (particularly 59.5 HRC or more) and a Vickers hardness of 513 HV or more (particularly 700 HV or more) can be achieved without significantly impairing mechanical properties such as toughness.

[0026] [Prior γ grain size of 100 μm or less] Conventionally, the prior γ grain size was approximately 400 μm (see Non-Patent Document 1). However, metal additive manufacturing and other manufacturing processes are suitable for obtaining a shaped product before aging treatment that has a fine prior γ grain size, and the prior γ grain size of the shaped product before aging treatment can be set to 100 μm or less. If the prior γ grain size of the shaped product before aging treatment is 100 μm or less, the time until the precipitation of a lamellar structure is completed during aging treatment can be shortened. Therefore, it is desirable that the prior γ grain size of the shaped product before aging treatment be 100 μm or less. The prior γ grain size of the shaped product before aging treatment is maintained even after aging treatment. Therefore, if the prior γ grain size of the shaped product before aging treatment is 100 μm or less, the prior γ grain size of the shaped product after aging treatment (i.e., the shaped product of the present invention) is also 100 μm or less.

[0027] [Powder] Molding is performed using Ni-based alloy powder. The Ni-based alloy constituting the Ni-based alloy powder has been described above. The Ni-based alloy powder used for molding is preferably gas-atomized powder, as it is nearly spherical, has excellent fluidity, and can be packed without gaps. The average particle diameter of the Ni-based alloy powder is preferably 10 to 100 μm in terms of volume-average particle diameter (D50). D50 is the particle diameter at the point where the cumulative volume is 50% on a volume-based cumulative frequency distribution curve calculated assuming the total volume of the powder is 100%. D50 is measured by a laser diffraction scattering method. An example of a suitable device for this measurement is Nikkiso's laser diffraction / scattering particle size distribution analyzer, the Microtrac MT3000. Powder is poured into the cell of this device together with pure water, and the particle diameter is detected based on the light scattering information of the particles.

[0028] [Shaping] The shaped object before aging treatment is produced by a process involving rapid melting, rapid cooling, and solidification using a Ni-based alloy powder containing Cr and Al. The material of the shaped object before aging treatment is a Ni-based alloy containing Cr and Al. By subjecting the shaped object before aging treatment to aging heat treatment, a lamellar structure in which the αCr phase and the γ phase and / or γ' phase are arranged in layers is obtained.

[0029] Examples of methods for producing a shaped object before aging include a rapid melting and rapid solidification process involving melting and solidifying a metal powder. Specific examples of this process include three-dimensional additive manufacturing (3D AM), thermal spraying, laser coating, and build-up welding. The shaped object before aging (and thus the shaped object after aging, i.e., the shaped object of the present invention) is preferably an additive manufactured by a 3D AM method. Specific examples of 3D AM methods include powder bed fusion (powder bed method) and directed energy deposition (powder deposition method). Specific examples of powder bed fusion (powder bed method) include selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM). In particular, the Ni-based alloy powder of the present invention is suitable for powder bed fusion 3D AM, allowing for the formation of large-sized, high-density objects.

[0030] The three-dimensional additive manufacturing method can be performed using, for example, a 3D printer. In the powder bed fusion (powder bed) additive manufacturing method, a laser beam or an electron beam is irradiated onto the spread Ni-based alloy powder of the present invention.

[0031] The particles are rapidly heated and melted by the irradiation. The melted particles then rapidly solidify. This melting and solidification process bonds the particles together. The irradiation is selectively performed on a portion of the spread Ni-based alloy powder. The portion of the spread powder that is not irradiated does not melt. A bonding layer is formed only in the irradiated portion.

[0032] A thin layer of Ni-based alloy powder is spread on top of the bonding layer. A laser beam or electron beam is irradiated onto a portion of this Ni-based alloy powder. The irradiation causes the particles to rapidly melt. The molten particles then rapidly solidify. This melting and solidification process bonds the particles in the powder together, forming a new bonding layer. The new bonding layer also bonds with the existing bonding layer.

[0033] Repeated bonding by irradiation gradually grows the aggregate of bonding layers. This growth results in a three-dimensional object. This additive manufacturing method makes it easy to obtain objects with complex shapes.

[0034] [Heat Treatment] The unheat-treated shaped object obtained by molding using Ni-based alloy powder is not used as is, but rather undergoes a process of aging treatment to obtain a shaped object of the present invention having the desired properties.

[0035] When NiCrAl alloys are used in conventional processes such as forging, they are generally solution-treated at temperatures of 1100° C. or higher. However, the present inventors have discovered that when an unheat-treated object is produced by a manufacturing method such as three-dimensional additive manufacturing, as in the present invention, excellent mechanical properties can be achieved by omitting the solution treatment of the unheat-treated object and directly subjecting the unheat-treated object to aging treatment.

[0036] When the unheat-treated shaped product is aged, the unheat-treated shaped product is heat-treated at 600°C or less, which reduces the lamellar spacing between the αCr phase and the γ and / or γ' phase, thereby obtaining a shaped product with high hardness. The aging temperature is preferably 600°C or less, more preferably 585°C or less, even more preferably 540°C or less, and most preferably 500°C or less. The lower limit is not particularly limited and may be, for example, 400°C or more or 450°C or more. Each of these lower limits may be combined with any of the above-mentioned upper limits.

[0037] When an unheat-treated shaped object is subjected to aging treatment, shortening the aging treatment time can reduce energy costs. The aging treatment time is preferably 10 hours or less, more preferably 8 hours or less, even more preferably 4 hours or less, and most preferably 2 hours or less. The lower limit is not particularly limited, and may be, for example, 0.5 hours or more or 1 hour or more. Each of these lower limits may be combined with any of the above-mentioned upper limits.

[0038] [Lamellar Morphology] Aging an unheat-treated layered object results in the precipitation of a lamellar structure of the αCr phase and the γ and / or γ' phase. Figure 1 shows an SEM image of the microstructure of an layered object of the present invention obtained by holding an unheat-treated layered object at 700°C for 4 hours and then air-cooling. It can be seen that lamellae on the scale of several tens of nanometers were formed when the object was aged at 700°C. Figure 2 shows an SEM image of the microstructure of an layered object of the present invention obtained by holding an unheat-treated layered object at 500°C for 8 hours and then air-cooling. It can be seen that when the object was aged at 500°C, the lamellar spacing was smaller, resulting in a very fine structure, compared to when the object was aged at 700°C.

[0039] Since the finer the lamellar spacing, the higher the hardness, it is preferable to perform aging treatment at a low temperature to precipitate fine lamellae.

[0040] [Area ratio of granular precipitates] Figure 3 shows an SEM image of the microstructure of an additive manufacturing product obtained by solution treatment of an unheated additive manufacturing product (holding at 1150°C for 30 minutes, followed by water cooling), then holding at 500°C for 2 hours, followed by air cooling. It can be seen that solution treatment resulted in the formation of coarse granular precipitates with a diameter of 400 nm or more. EDS analysis revealed that the granular precipitates were rich in Cr, suggesting that they were an α-Cr phase. It can be seen that the lamellae grow in the direction indicated by the arrows in the figure, but that lamellar growth is inhibited where the coarse granular precipitates come into contact with the tips of the grown lamellae.

[0041] Coarse granular precipitates inhibit the growth of lamellae and increase the time required for the precipitation reaction to be completed (lamellae precipitated over the entire surface), resulting in increased energy costs for heat treatment. Therefore, it is preferable that coarse granular precipitates do not precipitate. The occurrence of coarse granular precipitates can be avoided by avoiding solution treatment and / or long-term aging treatment. In the shaped product of the present invention, the area ratio of granular precipitates having a diameter of 400 nm or more in equivalent circle diameter is preferably 0.0%. The area ratio of granular precipitates having a diameter of 400 nm or more in equivalent circle diameter can be measured by the method described in the Examples.

[0042] [Prior γ Grain Size] Since lamellae of NiCrAl alloys precipitate in a cellular form from grain boundaries, a finer structure is preferable because the precipitation reaction is completed more quickly. The prior γ grain size of the shaped product before and after aging treatment (i.e., the shaped product of the present invention) is preferably 100 μm or less, more preferably 90 μm or less, even more preferably 80 μm or less, and most preferably 70 μm or less. The lower limit is not particularly limited, and may be, for example, 5 μm or more or 20 μm or more. Each of these lower limits may be combined with any of the above-mentioned upper limits. The prior γ grain size can be measured by the method described in the Examples. Since it is difficult to analyze the prior γ grain size by EBSD (electron backscatter diffraction) using the structure of the shaped product after aging treatment, in the Examples, the prior γ grain size was measured using the structure of the shaped product before aging treatment. Since the prior γ grain size of the shaped object before aging treatment is maintained after aging treatment, the prior γ grain size measured using the structure of the shaped object before aging treatment can be considered as the prior γ grain size of the shaped object after aging treatment.

[0043] [Hardness] NiCrAl alloys are desirably high in hardness because they are used in bearing parts and engine parts. Therefore, the Rockwell hardness of the shaped product of the present invention is preferably 50.0 HRC or higher, more preferably 60.0 HRC or higher, even more preferably 61.0 HRC or higher, and most preferably 62.0 HRC or higher. The upper limit is not particularly limited, and may be, for example, 65.0 HRC or lower. The Rockwell hardness can be measured by the method described in the Examples. The Vickers hardness of the shaped product of the present invention is preferably 513 HV or higher, more preferably 700 HV or higher, even more preferably 750 HV or higher, and most preferably 790 HV or higher. The upper limit is not particularly limited, and may be, for example, 850 HV or lower. The Vickers hardness can be measured by the method described in the Examples.

[0044] [Powder] Table 1 shows the chemical compositions of the Ni-based alloy powders used in the examples and comparative examples. After producing Ni-based alloy powder by vacuum melting inert gas atomization, the undersized powder obtained by classifying it through a sieve with a mesh size of -63 μm was used as the Ni-based alloy powder for additive manufacturing. "-63 μm" indicates that the mesh size is less than 63 μm. In the examples and comparative examples, argon was used as the inert gas. Note that C, Si, Mn, Fe, Co, Mo, P, S, O, and N in Table 1 are unavoidable impurities, and "Bal." in Table 1 represents the remainder.

[0045]

[0046] [Modeling] Using the Ni-based alloy powder for additive manufacturing as a raw material, additive manufacturing was performed using a three-dimensional additive manufacturing device (EOS-M290 manufactured by EOS Corporation) to form a 10 x 10 x 10 mm rectangular parallelepiped, which was used as a test piece for hardness and structure investigation. The modeling conditions were based on the standard device parameters HX (layer thickness 40 μm), with the output changed to 200 W, the scanning speed changed to 1200 mm / s, and the hatch width changed to 0.05 mm.

[0047] [Heat Treatment] Table 2 shows the heat treatment conditions for Examples 1 to 6, and Table 3 shows the heat treatment conditions for Comparative Examples 1 to 15. Solution treatment and aging treatment were carried out under the following conditions. Solution treatment: The specimens were held in an air atmosphere at the temperatures shown in Table 3 for 30 minutes, and then water-cooled. Note that, as shown in Table 2, no solution treatment was carried out in the Examples. Aging treatment: The specimens were held in an air atmosphere at the temperatures and times shown in Tables 2 and 3, respectively, and then air-cooled.

[0048] [Structural Observation: Determination of Area Ratio of Granular Precipitates] The heat-treated shaped product (10 × 10 × 10 mm) was cut along a plane parallel to the lamination direction, followed by mechanical polishing and ion milling. The center of the polished sample was observed with an FE-SEM (field emission scanning electron microscope). Observation was performed at 10,000x magnification, and images were taken of the areas shown in Figures 1 to 3. Image analysis was performed to determine the area ratio of granular precipitates with a particle size of 400 nm or more. Note that the particle size here refers to the circle-equivalent diameter, i.e., the diameter of a hypothetical circle having an area equal to the area of ​​the granular precipitates determined by image analysis.

[0049] [Structural Observation: Determination of Prior γ Grain Size] Samples before aging, prepared using the same procedure as for FE-SEM, were polished with colloidal silica and then subjected to electron backscatter diffraction (EBSD) measurement. The prior γ grain size was determined from the crystal orientation map obtained by the EBSD measurement. Note that a boundary with an orientation difference of 15° or more was defined as a grain boundary.

[0050]

[0051]

[0052] In Tables 2 and 3, the symbol "-" in the solution treatment temperature and solution treatment time columns indicates that solution treatment was not performed.

[0053] [Rockwell Hardness Measurement] The Rockwell hardness of the heat-treated test piece was measured on a surface perpendicular to the lamination direction using a Rockwell hardness tester in accordance with JIS Z 2245:2016.

[0054] [Vickers Hardness Measurement] The heat-treated test piece was embedded in resin, the surface of the test piece was polished, and then the Vickers hardness was measured using a micro Vickers hardness tester. The load was 1.96 N. The Vickers hardness measurement was performed in accordance with JIS Z2244-1:2020.

[0055] The obtained results were evaluated for the properties of the Examples and Comparative Examples using the following criteria. Aging time: If the aging time was within 10 hours, it was deemed good and marked with "good." If the aging time was longer than 10 hours, it was deemed poor and marked with "NG (not good)." Rockwell hardness: If the hardness was 59.5 HRC or higher, it was deemed excellent and rated with an "A." If it was between 50.0 and 59.5 HRC, it was deemed acceptable and rated with a "B." If it was less than 50.0 HRC, it was deemed unacceptable and rated with a "C." Vickers hardness: If it was 700 HV or higher, it was deemed excellent and rated with an "A." If it was between 513 and 700 HV, it was deemed acceptable and rated with a "B." If it was less than 513 HV, it was deemed unacceptable and rated with a "C." The results are shown in Tables 4 and 5.

[0056]

[0057]

[0058] As shown in Examples 1 to 6, when aging treatment was performed at low temperatures such as 500°C and 585°C, coarse granular precipitates were not generated, and it was confirmed that high hardness of Rockwell hardness of 59.5 HRC or more and Vickers hardness of 700 HV or more could be achieved.

[0059] In the examples of the present invention, high hardness can be achieved in a shorter time than the 16 hours required in the conventional methods disclosed in Patent Documents 1 and 2, and energy costs for production can be significantly reduced.

[0060] As an example closest to the examples of the present invention, Patent Document 2 describes "Ni-38Cr-3.8Al-0.1C, aged at 600°C for 16 hours (Comparative Example 2)", but Cr carbides are contained in the structure, and the hardness after aging is only 680 HV. The examples of the present invention do not contain coarse granular precipitates, have higher hardness, and have a short aging time, making them excellent in terms of energy cost.

[0061] Even if the hardness appears to be the same, the inclusion of coarse granular precipitates generally results in poor toughness, resulting in completely different mechanical properties. The examples of the present invention do not contain coarse granular precipitates, resulting in excellent mechanical properties, including toughness. On the other hand, for example, Non-Patent Document 1 is a wrought material, and therefore coarse granular precipitates are formed by solution treatment, resulting in inferior mechanical properties compared to the examples of the present invention.

[0062] As shown in Tables 3 and 5, Comparative Example 1 satisfies the hardness standard, but is inferior in terms of energy cost due to the long-term aging treatment. In addition, the long-term aging treatment causes the formation of granular precipitates with a particle size of 400 nm or more.

[0063] In Comparative Examples 2 to 5, aging treatment at 700°C resulted in the generation of granular precipitates with a particle size of 400 nm or more, and Cr was consumed by the granular precipitates, resulting in a decrease in the strengthening amount of the lamellar structure and a decrease in hardness.

[0064] In Comparative Examples 6 to 15, the solution treatment resulted in the generation of granular precipitates with a particle size of 400 nm or more, which reduced the hardness, or the lamellar precipitation rate decreased, which meant that it took longer to complete precipitation than in the case of direct aging treatment, making them inferior in terms of energy cost.

[0065] As can be seen from Table 3, the prior γ grain size decreases by solution treatment. This is because fine crystal grains are newly generated from the grain boundaries during solution treatment.

[0066] The prior γ grain size in the examples of the present invention is 100 μm or less, which is smaller than the prior γ grain size (approximately 400 μm) of the ingot material described in Non-Patent Document 1. The fine prior γ grain size specific to metal additive manufacturing in the examples of the present invention is thought to be effective in shortening the time to complete precipitation of a lamellar structure.

[0067] The shaped article (particularly the layered shaped article) of the present invention can be used for engine parts, bearing parts, molds, medical wires, and the like.

Claims

1. A shaped object made of a Ni-based alloy in which the αCr phase and the γ phase and / or the γ' phase are precipitated in layers, and which does not contain granular precipitates with an equivalent circle diameter of 400 nm or more.

2. The shaped object according to claim 1, wherein the prior γ grain size is 100 μm or less.

3. The shaped object according to claim 1, having a Rockwell hardness of 50.0 HRC or more.

4. The shaped object according to claim 1, having a Vickers hardness of 513 HV or more.

5. The shaped article according to any one of claims 1 to 4, wherein the Ni-based alloy has a composition, in mass%, of Cr: 30.0 to 45.0%, Al: 2.5 to 5.0%, C: 0 to 0.2%, and the balance: Ni and unavoidable impurities.

6. The object according to any one of claims 1 to 4, which is a layered object.

7. The object according to claim 5, which is an additively manufactured object.

Images