WO2024176728A1 - Sintered body and method for producing sintered body - Google Patents

Abstract

According to the present invention, when a calcined body is formed by heating and sintering an injection molded body, which contains a gamma-prime precipitation hardening alloy powder, after degreasing, a nitrogen gas is introduced into the furnace so that the N content ratio in the calcined body is 0.013% by mass to 0.064% by mass (preferably, 0.017% by mass to 0.059% by mass), and a sintered body that is obtained by further heating and sintering the calcined body is subjected to a precipitation hardening treatment, thereby obtaining a precipitation hardened sintered body that is formed of a gamma-prime precipitation hardening alloy and contains 0.011% by mass to 0.056% by mass (preferably, 0.016% by mass to 0.055% by mass) of N.

Description

Sintered body and method for producing the same

This invention relates to a sintered body and a method for manufacturing the sintered body, for example, a sintered body made of a gamma prime precipitation hardening type Ni-Cr-Fe alloy (such as ALLOY718) or a Ni-Cr-Mo-Al alloy (such as ALLOY713C or ALLOY713LC) and a method for manufacturing the sintered body.

Gamma prime precipitation hardening alloy materials, which have excellent high-temperature properties, are used in a variety of fields, such as aviation, space, and energy. Gamma prime precipitation hardening alloy materials have excellent high-temperature properties due to the formation of a gamma prime phase (γ' phase) in the alloy structure by precipitation hardening treatment. Precipitation hardening treatment generally consists of solution treatment (solution heat treatment) and age hardening treatment (precipitation heat treatment). Gamma prime precipitation hardening alloy materials are used in practice, for example, as a molten cast material disclosed in Japanese Patent No. 6610846, a forged material by powder solidification disclosed in Japanese Patent Publication No. 2007-277721, or a sintered material by powder injection molding disclosed in International Publication No. 2018-216067.

By the way, gamma prime precipitation hardening alloy materials are often used in products with aerodynamically complex shapes, such as gas turbine blades and turbocharger blades. Therefore, when mass-producing products with complex shapes using gamma prime precipitation hardening alloy materials, a manufacturing method that is easy to form in near net shape is preferred. As one manufacturing method that is easy to form in near net shape, the metal injection molding method (hereinafter referred to as "MIM") using metal powder disclosed in International Publication No. 2018-216067 is known. Gamma prime precipitation hardening alloy materials to which MIM can be applied can be easily mass-produced by high-precision near net shape molding, and can be provided to the market at low cost.

Patent No. 6610846 JP 2007-277721 A International Publication No. 2018-216067

A sintered body made of gamma prime precipitation hardening alloy powder to which MIM is applied (hereinafter simply referred to as "sintered body") is based on a solid-phase sintered structure formed by heating and sintering the alloy powder, and contains a gamma prime phase (γ' phase) generated by precipitation hardening treatment after sintering. Sintered bodies to which MIM is applied are prone to have fine voids in the sintered structure. Therefore, in order to make the sintered structure of the sintered body more dense and improve and stabilize its mechanical strength, HIP treatment (Hot Isostatic Pressing treatment) may be performed. During HIP treatment, when a sintered body is held for a long time under high temperature and pressure, the crystal grains that make up the sintered structure grow and become coarse. In addition, even if a precipitation hardening treatment is performed after HIP treatment, the crystal grains that have become coarse by the HIP treatment of the sintered body are difficult to reconstruct. The coarsening of the crystal grains of the sintered body is a factor that contributes to improving the high-temperature properties of the sintered body, such as creep properties and creep rupture properties. On the other hand, coarsening of the crystal grains of a sintered body leads to a decrease in the mechanical properties of the sintered body at room temperature and in high temperature environments, such as 0.2% proof stress, tensile strength, and elongation.

The object of the present invention is to provide a simple technical means for controlling the sintered structure of a sintered body after precipitation hardening to an appropriate form, and to provide a sintered body made of a gamma prime precipitation hardening alloy that has a specific mechanical strength in a room temperature environment of about 20°C and preferably in a high temperature environment of about 650°C, and a method for manufacturing the sintered body.

In this invention, the specific mechanical strength of the sintered body in a room temperature environment of about 20°C and in a high temperature environment of about 650°C is determined based on the descriptions of "Mechanical properties at 20°C (68°F)" and "Mechanical properties of parts at high temperatures (649°C, 1200°F)" in the material data sheet "NickelAlloy IN718" (10.2011 edition) provided by EOS GmbH-Electro Optical Systems. The details are described below. The Aerospace Material Specifications (AMS) mentioned later is an industrial standard issued by the Society of Automotive Engineers (SAE International), which is based in the United States.

The targeted mechanical strength of the sintered body in a room temperature environment of about 20° C. is as follows:
<0.2% yield strength of 1050 MPa or more>
The above-mentioned material data sheets state that the minimum required yield strength (0.2% proof stress) at room temperature is AMS5662 (1150±100 MPa, minimum value 1050 MPa) and AMS5664 (1240±100 MPa, minimum value 1140 MPa). Based on this description, the sintered body according to the present invention ensures a 0.2% proof stress of at least the minimum value (1050 MPa).
<Tensile strength of 1280 MPa or more>
The above-mentioned material data sheets state that the minimum required tensile strength at room temperature is AMS5662 (1400±100 MPa, minimum value 1300 MPa) and AMS5664 (1380±100 MPa, minimum value 1280 MPa). Based on this description, the sintered body according to the present invention ensures the minimum value (1280 MPa) or more.
<Growth of 12% or more>
The above-mentioned material data sheets state that the minimum required elongation (elongation at break) at room temperature is AMS5662 (15±3%, minimum value 12%) and AMS5664 (18±5%, minimum value 12%). Based on this description, the sintered body according to the present invention ensures the minimum value (12%) or more.

The mechanical strength of the sintered body in a targeted high-temperature environment of about 650° C. is as follows:
<0.2% yield strength of 870 MPa or more>
The above-mentioned material data sheets state that the minimum required yield strength (0.2% proof stress) at high temperatures is AMS5662 (970±50 MPa, minimum value 862 MPa) and AMS5664 (1010±50 MPa). Based on this description, the sintered body according to the present invention ensures a 0.2% proof stress of at least the minimum value (862 MPa rounded to 870 MPa).
<Tensile strength of 970 MPa or more>
The above-mentioned material data sheets state that the minimum tensile strength required at high temperatures is AMS5662 (1170±50 MPa, minimum value 965 MPa) and AMS5664 (1210±50 MPa). Based on this description, the sintered body according to the present invention ensures a tensile strength of at least the minimum value (965 MPa rounded to 970 MPa).
<Growth of 6% or more>
The above-mentioned material data sheets state that the minimum required elongation (elongation at break) at high temperatures is AMS5662 (16±3%, minimum value 6%) and AMS5664 (20±3%). Based on this description, the sintered body according to the present invention ensures elongation of the above-mentioned minimum value (6%) or more.

The inventors conducted numerous experiments to produce sintered bodies by MIM using alloy powder, which is a well-known type of gamma prime precipitation hardening alloy and has a chemical composition equivalent to Alloy 718 specified in AMS 5377G. They then investigated the manufacturing conditions and sintered structures of numerous sintered bodies and found that appropriate adjustment of the N (nitrogen) content ratio at the calcined body stage is important for controlling the sintered structure of the sintered body after precipitation hardening to an appropriate form. After further ingenuity, they came up with a means for easily adjusting the N content ratio of the calcined body. In detail, they obtained an experimental formula showing the relationship between the N content ratio of the calcined body and the N content ratio of the sintered body after precipitation hardening. Based on the experimental formula, they constructed a simple model (regression model) that can predict the mechanical properties of the sintered body after precipitation hardening from the N content ratio of the sintered body after precipitation hardening. Using the regression model, they finally found the appropriate range of the N content ratio of the sintered body after precipitation hardening and the N content ratio of the calcined body, leading to this invention.

The sintered body according to the present invention is made of a gamma prime precipitation hardening alloy and contains 0.011% to 0.056% by mass of N (nitrogen) after precipitation hardening. A sintered body having this configuration has a predetermined mechanical strength after precipitation hardening, i.e., a 0.2% yield strength of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature (approximately 20°C) environment.

The sintered body according to the present invention is preferably a sintered body containing 0.016% by mass or more and 0.055% by mass or less of N (nitrogen) after precipitation hardening. A sintered body having this configuration is a preferred sintered body that has a predetermined preferred mechanical strength after precipitation hardening, i.e., a tensile strength of 1280 MPa or more, a 0.2% yield strength of 1050 MPa or more, and an elongation of 12% or more in a room temperature (approximately 20°C) environment, and a 0.2% yield strength of 870 MPa or more, a tensile strength of 970 MPa or more, and an elongation of 6% or more in a high temperature (approximately 650°C) environment.

In the sintered body according to the present invention, the gamma prime precipitation hardening alloy may be a Ni-based alloy that contains, relative to the base Ni (nickel), the essential elements C (carbon), Cr (chromium), Mo (molybdenum), Nb (niobium), Ti (titanium), Al (aluminum), B (boron) and Zr (zirconium), and the possible elements Mn (manganese), Si (silicon), P (phosphorus), S (sulfur), Co (cobalt), Ta (tantalum), Fe (iron), Cu (copper) and Hf (hafnium), with the balance being N (nitrogen) and impurity elements.

The present invention also provides a method for producing a sintered body, the sintered body being made of a gamma prime precipitation hardening alloy and containing 0.011% by mass or more and 0.056% by mass or less of N after precipitation hardening, comprising:
a molded body preparation step of injection molding a kneaded product containing a gamma prime precipitation hardening type alloy powder and an organic component to prepare a molded body;
a degreased body preparation step of removing organic components constituting the compact to prepare a degreased body;
a calcined body producing step of sintering the alloy powder constituting the degreased body in a furnace by first heating to produce a calcined body;
a sintered body preparation step of sintering the alloy powder constituting the calcined body in a furnace by a second heating at a temperature higher than the first heating to prepare an actual sintered body;
A precipitation hardening step of precipitation hardening the actual sintered body,
In the calcination process, nitrogen gas is introduced into the furnace to adjust the N content of the calcination to 0.013% by mass or more and 0.064% by mass or less, and the sintered body is produced by the precipitation hardening process. This manufacturing method makes it possible to produce a sintered body having a predetermined mechanical strength after precipitation hardening, i.e., a 0.2% proof stress of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature (about 20°C) environment.

In the method for producing a sintered body according to the present invention, preferably, in the calcined body production step, nitrogen gas is introduced into the furnace to adjust the N content of the calcined body to 0.017% by mass or more and 0.059% by mass or less, and the precipitation hardening step produces the sintered body containing 0.016% by mass or more and 0.055% by mass or less of N. This production method makes it possible to produce a preferred sintered body that has a predetermined preferred mechanical strength after precipitation hardening, i.e., a 0.2% yield strength of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature (about 20°C) environment, and a 0.2% yield strength of 870 MPa or more, a tensile strength of 970 MPa or more, and an elongation of 6% or more in a high temperature (about 650°C) environment.

In the method for producing a sintered body according to the present invention, the gamma prime precipitation hardening type alloy powder may be a Ni-based alloy powder that contains, relative to the base Ni, essential elements including C, Cr, Mo, Nb, Ti, Al, B and Zr, and optionally contains one or more of Mn, Si, P, S, Co, Ta, Fe, Cu and Hf, with the remainder being impurity elements.

The method for producing a sintered body according to the present invention preferably further includes a HIP process in which the actual sintered body is held under high temperature and pressure, and the precipitation hardening process is carried out after the HIP process.

According to this invention, by the simple means of introducing nitrogen gas into the furnace in the calcined body preparation process to adjust the N contained in the calcined body to a specific range and then carrying out the precipitation hardening process, it is possible to provide a sintered body made of a gamma prime precipitation hardening type alloy that has a specific mechanical strength in a room temperature environment of about 20°C, and preferably also has a specific mechanical strength in a high temperature environment of about 650°C. This makes it possible to put into practical use a sintered body made of a gamma prime precipitation hardening type alloy that has a 0.2% yield strength of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature environment of about 20°C, and preferably also has a 0.2% yield strength of 870 MPa or more, a tensile strength of 970 MPa or more, and an elongation of 6% or more in a high temperature environment of about 650°C.

FIG. 2 is a diagram illustrating a process flow of a method for producing a sintered body according to the present invention. 1 is a graph (scatter plot) showing the measured values of the N content and 0.2% yield strength of a sintered body after precipitation hardening. 1 is a graph (scatter plot) showing the measured values of the N content and tensile strength of a sintered body after precipitation hardening. 1 is a graph (scatter plot) showing the measured values of the N content and elongation of a sintered body after precipitation hardening. 1 is a graph (scatter diagram) showing the measured values of the N content ratio of the sintered body after precipitation hardening, the N content ratio of the actual sintered body (silver body), and the N content ratio of the calcined body.

The sintered body and method for manufacturing a sintered body according to the present invention will be described with reference to the drawings as appropriate. Note that the sintered body and method for manufacturing a sintered body according to the present invention are not limited to the embodiments and examples exemplified herein, but are set forth in the claims, and it is appropriate to understand that all modifications within the meaning and scope equivalent to the claims are included. Note that the terms and symbols related to the sintered body and the method for manufacturing a sintered body may be shared in the description of the specification and drawings without special notice.

The sintered body according to the present invention is made of a gamma prime precipitation hardening alloy and contains 0.011% to 0.056% by mass of N (nitrogen) after precipitation hardening. The sintered body having this configuration has a predetermined mechanical strength after precipitation hardening, and can have the target room temperature strength, i.e., a 0.2% yield strength of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature (about 20°C) environment. The sintered body according to the present invention also preferably contains 0.016% to 0.055% by mass of N after precipitation hardening. The sintered body having this configuration has a predetermined preferred mechanical strength after precipitation hardening, and can have the target room temperature strength described above, and can also have the target preferred high temperature strength, i.e., a 0.2% yield strength of 870 MPa or more, a tensile strength of 970 MPa or more, and an elongation of 6% or more in a high temperature (about 650°C) environment.

In general, the growth of crystal grains is essential for sintered bodies made of gamma prime precipitation hardening alloys to ensure high-temperature strength. On the other hand, sintered bodies made of gamma prime precipitation hardening alloys may have reduced room-temperature strength due to excessive growth of crystal grains. In this regard, if the N content of the sintered body after precipitation hardening is 0.011 mass% or more and 0.056 mass% or less (preferably 0.016 mass% or more and 0.055 mass% or less), the sintered body after precipitation hardening has the above-mentioned specific room-temperature strength, and preferably has both the above-mentioned specific room-temperature strength and the above-mentioned specific high-temperature strength. In this case, it is considered that the sintered structure constituting the sintered body is controlled to an appropriate form during the sintering process, precipitation hardening process, and HIP process, etc., for producing a sintered body after precipitation hardening using a calcined body with an N content ratio adjusted to a specific range, and the sintered structure constituting the sintered body is controlled to an appropriate form during the high-temperature heating process exceeding 1000°C, and the sintered body contains N in the above-mentioned specific range after precipitation hardening.

If the N content of the sintered body after precipitation hardening is less than 0.011% by mass, the sintered body after precipitation hardening may not reach the target 0.2% yield strength under room temperature environment. In that case, considering the excessively small N content ratio of the sintered body after precipitation hardening, it is considered that the sintered structure constituting the sintered body was not controlled to an appropriate form during the above-mentioned high-temperature heat treatment, and as a result, the sintered body after precipitation hardening had insufficient 0.2% yield strength under room temperature environment. In addition, if the N content of the sintered body after precipitation hardening exceeds 0.056% by mass, the sintered body after precipitation hardening may not reach the target elongation under room temperature environment and high temperature environment. In that case, considering the excessively large N content ratio of the sintered body after precipitation hardening, it is considered that the sintered structure constituting the sintered body was not controlled to an appropriate form during the above-mentioned high-temperature heat treatment, and as a result, the sintered body after precipitation hardening had insufficient elongation under room temperature environment and high temperature environment. The relationship between the N content of the sintered body after precipitation hardening and the mechanical properties at room temperature and at high temperatures, which was confirmed through experiments, will be described later.

If the N content of the sintered body after precipitation hardening is 0.011% by mass or more but less than 0.016% by mass, the sintered body after precipitation hardening may reach the target 0.2% yield strength in a room temperature environment, but may not reach the target 0.2% yield strength in a high temperature environment. In that case, taking into consideration the relatively small N content of the sintered body after precipitation hardening, it is believed that the sintered structure constituting the sintered body is not controlled to a more appropriate and preferable form during the above-mentioned high-temperature heat treatment, and as a result, while the 0.2% yield strength in a room temperature environment reaches the target after precipitation hardening, the sintered body has insufficient 0.2% yield strength in a high temperature environment.

The sintered body according to the present invention is made of a gamma prime precipitation hardening alloy and contains N in the above-mentioned specific range after precipitation hardening. In a gamma prime precipitation hardening alloy, a gamma prime phase (γ' phase) that is a precipitation strengthening phase of fine intermetallic compounds is formed. This gamma prime phase (γ' phase) improves the mechanical strength of the alloy. Examples of gamma prime precipitation hardening alloys suitable for this invention include Ni-based alloys having chemical components equivalent to the Ni-Cr-Fe alloy ALLOY718 and the Ni-Cr-Mo-Al alloys ALLOY713C and ALLOY713LC. The gamma prime precipitation hardening Ni-based alloy suitable for this invention contains, in the base Ni (nickel), the essential elements C (carbon), Cr (chromium), Mo (molybdenum), Nb (niobium), Ti (titanium), Al (aluminum), B (boron), and Zr (zirconium). The gamma prime precipitation hardening Ni-based alloy suitable for this invention contains, in the base Ni, one or more of Mn (manganese), Si (silicon), P (phosphorus), S (sulfur), Co (cobalt), Ta (tantalum), Fe (iron), Cu (copper), and Hf (hafnium) as possible elements, with the remainder being composed of impurity elements.

The specific compositions (ranges of chemical components) of the above-mentioned Ni-based alloys are exemplified below in mass %. The above-mentioned Ni-based alloys contain, relative to the base Ni, the following essential elements: 0.002% to 0.08% C, 11.0% to 21.0% Cr, 2.8% to 5.2% Mo, 1.5% to 5.5% Nb, 0.50% to 1.2% Ti, 0.3% to 6.5% Al, 0.001% to 0.02% B, and 0.05% to 0.2% Zr. The Ni-based alloy may contain, for example, one or more of the following elements relative to the base Ni: 0.35% or less Mn, 0.5% or less Si, 0.015% or less P, 0.015% or less S, 1.0% or less Co, 0.15% or less Ta, 1.0% or less Fe, 0.5% or less Cu, and 2.0% or less Hf, with the remainder being impurity elements. The sintered body according to the present invention may be made of the gamma prime precipitation hardening type Ni-based alloy described above, and may contain the above-mentioned specific range of N after precipitation hardening.

In the case of the above-mentioned gamma prime precipitation hardening type Ni-based alloy, the gamma prime phase (γ' phase) has a face-centered cubic structure, and Al, Ti, Nb or Ta are regularly arranged at the corners, and Ni, Co, Fe or Mo are regularly arranged at the face center. Ni ₃ Al, which is a typical composition of the gamma prime phase (γ' phase), has high mechanical strength even at high temperatures, and contributes to improving the mechanical strength of the sintered body at high temperatures. In addition to the gamma prime phase (γ' phase), the mechanical strength of the sintered body at high temperatures is improved by solid solution strengthening in the parent phase (γ matrix phase) and precipitation strengthening in the grain boundaries. In this case, the solid solution strengthening elements are Cr and Mo among the essential elements and Co and Fe among the elements that can be contained. Cr also contributes to improving the corrosion resistance and oxidation resistance. In addition, the grain boundary strengthening elements are C, B, and Zr, which are essential elements. In particular, C forms carbides with Cr, Mo, Nb, Ti, Zr and Ta, and contributes to grain boundary strengthening. B forms borides with Zr, Cr, Ta, etc., and contributes to improving rupture strength. Among the elements that can be contained, Cu and Hf are beneficial if contained within the range exemplified above, while excessive content is likely to be harmful. Furthermore, Mn, Si, P and S are likely to be harmful if contained in excess beyond the range exemplified above. It is also possible to use W instead of Mo, but in that case, it is preferable to adjust the Mo equivalent (Mo+W/2) to 2.8% or more and 5.2% or less.

The method for producing a sintered body according to the present invention includes a molded body production step, a degreased body production step, a calcined body production step, a sintered body production step, and a precipitation hardening step, as shown in the process flow of Figure 1. It is also preferable that the method further includes a HIP treatment step. When the HIP treatment step is included, the precipitation hardening step is performed after the HIP treatment step.

<Molded body production process>
In the compact manufacturing process, a compact (green body) is manufactured using alloy powder and organic components, as shown in Fig. 1. Specifically, a mixture (compound) containing gamma prime precipitation hardening type alloy powder and organic components is injection molded to manufacture the compact.

In the injection molding of the kneaded material, MIM is preferably applied. The application of MIM makes it possible to mold the molded body into a near-net shape with high precision, facilitating the mass production of sintered bodies. Specifically, for example, the kneaded material heated to an appropriate temperature is injected into the mold cavity of an MIM-compatible injection molding device, and cooled at the appropriate time while being held at an appropriate pressure, after which the mold is opened and demolded. Such a molded body manufacturing process using MIM makes it easy to mass-produce molded bodies (green bodies). In this case, the shape of the mold cavity is preferably designed to correspond to the shape of the molded body (green body). The shape of the molded body (green body) is also preferably designed taking into consideration the amount of distortion of the degreased body and the amount of shrinkage of the sintered body, etc.

The organic components contained in the kneaded material are organic compounds that function as binders for the alloy powder. Binders that are mainly organic compounds can be made by combining waxes, polymeric resins, and other additives, for example. Waxes can be selected from paraffin wax, carnauba wax, and other materials as needed. Polymeric resins can be selected from polyethylene, polypropylene, acrylic resins, EVA (ethylene-vinyl acetate copolymer resin), styrene-based rubber, and other materials as needed. Other additives can be selected and added as needed to obtain a kneaded material suitable for MIM. In addition, when applying MIM, the compounding ratio of alloy powder in the kneaded material is preferably 55% to 70% by volume.

The gamma prime precipitation hardening type alloy powder is a metal powder made of a gamma prime precipitation hardening type alloy. The gamma prime precipitation hardening type alloy powder may be a Ni-based alloy powder, an Fe-based alloy powder, a Co-based alloy powder, or the like. For example, the gamma prime precipitation hardening type Ni-based alloy powder may contain, relative to the base Ni, essential elements such as C, Cr, Mo, Nb, Ti, Al, B, and Zr, and may contain, as possible elements, one or more of Mn, Si, P, S, Co, Ta, Fe, Cu, and Hf, with the remainder being composed of impurity elements.

The specific composition (range of chemical components) of gamma prime precipitation hardening type Ni-based alloy powder is shown below in mass %. Gamma prime precipitation hardening type Ni-based alloy powder contains, relative to the base Ni, essential elements such as 0.002% to 0.08% C, 11.0% to 21.0% Cr, 2.8% to 5.2% Mo, 1.5% to 5.5% Nb, 0.50% to 1.2% Ti, 0.3% to 6.5% Al, 0.001% to 0.02% B, and 0.05% to 0.2% Zr. And, the gamma prime precipitation hardening type Ni-based alloy powder contains, in relation to the base Ni, one or more of the following elements that can be contained, for example, 0.35% or less Mn, 0.5% or less Si, 0.015% or less P, 0.015% or less S, 1.0% or less Co, 0.15% or less Ta, 1.0% or less Fe, 0.5% or less Cu, and 2.0% or less Hf, with the remainder being made up of impurity elements.

In the case of Ni-based alloy powder, for example, in order to suppress a decrease in the mechanical strength of the sintered body due to the liquid phase that occurs during sintering, the Cr content is preferably set to 14.0% or less (11.0% or more) to suppress a decrease in the liquid phase formation temperature (melting point). Also, for example, in order to improve the mechanical strength of the sintered body by appropriately dispersing and forming grain boundary strengthening carbides during sintering, the C content is preferably set to 0.002% or more (0.07% or less) to appropriately disperse and form grain boundary strengthening carbides.

<Degreased body preparation process>
In the degreased body preparation process, as shown in Fig. 1, a degreased body (brown body) is prepared using a compact (green body). Specifically, the degreased body is prepared by removing the organic components that make up the compact. The process of removing the binder from the compact (green body) is called degreasing, and the organic components are removed by this degreasing.

Degreasing to remove organic components from a compact may be solvent degreasing, in which the compact is immersed in a solution to dissolve the organic components, or heat degreasing, in which the compact is heated to an appropriate temperature to dissolve and burn the organic components. Alternatively, combined degreasing may be performed in which solvent degreasing using a compact is followed by heat degreasing, in which the compact after solvent degreasing is heated to an appropriate temperature to dissolve and burn the remaining organic components. Combined degreasing of solvent degreasing and heat degreasing tends to suppress defects such as swelling, distortion, and cracking that tend to occur with sintering of alloy powder. Note that the compact after solvent degreasing is a solvent-degreased body composed of the remaining organic components and alloy powder, with some of the organic components removed. Note that the compact after heat degreasing or the solvent-degreased body after heat degreasing is a heat-degreased body composed of the alloy powder, with most of the organic components removed.

The heated degreased body can also be produced by heating in the calcined body production process, which is a process that combines part or all of the degreased body production process with the calcined body production process described below. For example, a solvent degreased body can be produced using a molded body (green body) in the degreased body production process, and the heated degreased body can be produced by heating the solvent degreased body in the calcined body production process. In this case, the calcined body can be produced by holding the temperature at a suitable temperature for thermal degreasing during the heating step in the calcined body production process for a suitable time, and then raising the temperature to a suitable temperature for producing the calcined body and holding it thereafter for a suitable time. Also, if the heating step in the calcined body production process is performed so that degreasing from the molded body (green body) gradually progresses to produce a heated degreased body, the heated degreased body can be produced on the way to a temperature suitable for producing the calcined body without going through the solvent degreased body. In this case, during the heating process for producing the calcined body, a step can be added to hold the temperature at a time suitable for thermal degreasing on the way to a temperature suitable for producing the calcined body.

<Preparation of calcined body>
In the calcined body preparation step, as shown in FIG. 1, a calcined body is prepared using a degreased body (Brown body). Specifically, the degreased body (Brown body) is placed in a furnace, and the gamma prime precipitation hardened alloy powder constituting the degreased body is lightly sintered by heating (hereinafter referred to as "first heating") at an appropriate temperature and time to prepare a calcined body. The degreased body (Brown body) used in the calcined body preparation step may be either a solvent degreased body or a heated degreased body. In addition, the calcined body can be prepared by using a molded body (green body) to make it into a heated degreased body during the temperature increase step of the first heating, and continuing the first heating from the heated degreased body state. In that case, the calcined body preparation step also serves as the degreased body preparation step.

The first heating step includes a step of heating and holding the gamma prime precipitation hardening type alloy powder constituting the degreased body (Brown body) at an appropriate temperature and for an appropriate time for slight sintering. For example, in the case of gamma prime precipitation hardening type Ni-based alloy powder, Fe-based alloy powder, or Co-based alloy powder, the first heating step preferably includes a step of heating and holding at a temperature of about 1000°C. In this case, if the holding temperature of the first heating step is excessively lower than 1000°C, the sintered structure of the calcined body formed by the first heating step (hereinafter referred to as the "calcined structure") becomes weak, and the calcined body is easily damaged due to handling errors, etc.

In the calcination process, it is important to introduce nitrogen gas into the furnace to adjust the N content of the calcination body to 0.013% by mass or more and 0.064% by mass or less. As mentioned above, while the coarsening of the crystal grains of the sintered body contributes to high-temperature properties, it also reduces the mechanical properties in room temperature and high-temperature environments. Therefore, even in the case of sintered bodies using gamma prime precipitation hardening alloy powder, it is considered important to control the sintered structure of the sintered body after precipitation hardening to an appropriate form. From this perspective, in this invention, the N content of the calcination body is adjusted to 0.013% by mass or more and 0.064% by mass or less. This is thought to allow the sintered structure constituting the sintered body to be controlled to an appropriate form during the high-temperature heat treatment described above. As a result, a sintered body having the above-mentioned specific room temperature strength after precipitation hardening can be easily produced. And the sintered body after precipitation hardening contains 0.011% by mass or more and 0.056% by mass or less of N.

In addition, in the calcined body preparation process, nitrogen gas is preferably introduced into the furnace to adjust the N content of the calcined body to 0.017% by mass or more and 0.059% by mass or less. This is believed to enable the sintered structure constituting the sintered body to be controlled to a more appropriate and preferable form during the high-temperature heat treatment described above. As a result, a preferable sintered body that has both the specific room-temperature strength and the specific high-temperature strength described above after precipitation hardening can be easily prepared. The sintered body after precipitation hardening then contains 0.016% by mass or more and 0.055% by mass or less of N.

If the N content of the calcined body is adjusted to less than 0.013 mass%, the sintered body after precipitation hardening may not reach the target 0.2% yield strength under room temperature environment. In that case, considering the excessively small N content ratio of the calcined body, it is considered that the sintered structure constituting the sintered body was not controlled to an appropriate form during the above-mentioned high-temperature heat treatment, and as a result, the sintered body after precipitation hardening had insufficient 0.2% yield strength under room temperature environment. In addition, if the N content of the calcined body exceeds 0.064 mass%, the sintered body after precipitation hardening may not reach the target elongation under room temperature environment and high temperature environment. In that case, considering the excessive N content ratio of the calcined body, it is considered that the sintered structure constituting the sintered body was not controlled to an appropriate form during the above-mentioned high-temperature heat treatment, and as a result, the sintered body after precipitation hardening had insufficient elongation under room temperature environment and high temperature environment. The relationship between the N content ratio of the sintered body after precipitation hardening and the N content ratio of the calcined body confirmed based on experiments will be described later.

If the N content of the calcined body is adjusted to less than 0.017% by mass even if it is 0.013% by mass or more, the sintered body after precipitation hardening may reach the target 0.2% yield strength in a room temperature environment, but may not reach the target 0.2% yield strength in a high-temperature environment. In that case, taking into account the relatively small N content of the calcined body, it is believed that the sintered structure constituting the sintered body is not controlled to a more appropriate and preferable form during the above-mentioned high-temperature heat treatment, and as a result, while the 0.2% yield strength in a room temperature environment reaches the target after precipitation hardening, the sintered body has insufficient 0.2% yield strength in a high-temperature environment.

<Sintered body production process>
In the sintered body preparation process, as shown in Fig. 1, the calcined body is used to prepare an actual sintered body (silver body). Specifically, the calcined body is placed in a furnace, and the gamma prime precipitation hardening alloy powder constituting the calcined body is sufficiently sintered by heating (hereinafter referred to as "second heating") at a temperature higher than the first heating and held for an appropriate time, to prepare an actual sintered body (silver body). In this invention, a sintered body that has not been subjected to the HIP treatment process and the precipitation hardening process is called an actual sintered body (silver body), and is distinguished from an actual sintered body that has been subjected to the HIP treatment process and a sintered body that has been subjected to the precipitation hardening process.

The second heating includes a step of heating and holding the gamma prime precipitation hardening alloy powder at an appropriate temperature and time for sufficient sintering (hereinafter referred to as "main sintering") to occur in the calcined structure of the calcined body, which has been lightly sintered by the first heating. For example, the holding temperature of the second heating is set to a temperature at or above which the calcined structure of the calcined body can be main sintered to form a sintered structure, and below the temperature at which the calcined structure of the calcined body begins to melt. When the gamma prime precipitation hardening alloy powder is Ni-based alloy powder, Fe-based alloy powder, or Co-based alloy powder, the holding temperature of the second heating can be set to, for example, 1250°C or higher and 1300°C or lower. In addition, the inside of the furnace in which the second heating is performed is set to a non-oxidizing atmosphere, preferably a non-oxidizing atmosphere that does not use nitrogen gas, to suppress excessive incorporation of N into the sintered structure of the actual sintered body (silver body).

<HIP treatment process>
In the HIP treatment process, as shown in FIG. 1, the actual sintered body (silver body) is subjected to HIP treatment (Hot Isostatic Pressing treatment) in which the actual sintered body is held under high temperature and high pressure. When the HIP treatment process is added, a precipitation hardening process is performed after the HIP treatment. The actual sintered body that has undergone the HIP treatment process is called a sintered body after the HIP treatment, and is distinguished from the actual sintered body (silver body) that has not undergone the HIP treatment process and the sintered body that has undergone the precipitation hardening process. In this invention, it is preferable to perform the HIP treatment on the actual sintered body (silver body) before the precipitation hardening treatment, thereby increasing the relative density (sintering density) of the actual sintered body (silver body) that is in a relatively soft state without precipitation hardening.

The sintered body after HIP treatment has a higher relative density (sintered density) than the actual sintered body (silver body) before HIP treatment, because the pores that existed in the sintered structure softened by holding at high temperature are crushed and densified by holding at high pressure. In general, the sintered structure of the sintered body before HIP treatment changes to a sintered structure containing relatively coarse crystal grains after HIP treatment due to the growth of crystal grains caused by holding at high temperature during HIP treatment. A sintered body with a sintered structure containing relatively coarse crystal grains may have high high-temperature strength but low room-temperature strength. In this regard, if the N content ratio of the calcined body is 0.013 mass% or more and 0.064 mass% or less (preferably 0.017 mass% or more and 0.059 mass% or less), the sintered structure is controlled to an appropriate form during HIP treatment due to the N contained in the actual sintered body (silver body), resulting in a sintered structure in which relatively coarse crystal grains are unlikely to exist, and it is thought that the decrease in room-temperature strength is easily suppressed.

<Precipitation hardening process>
In the precipitation hardening process, as shown in Fig. 1, the actual sintered body (silver body) or the sintered body after HIP treatment is precipitation hardened. As a result, the actual sintered body (silver body) or the sintered body after HIP treatment is made into a precipitation hardened sintered body containing 0.011 mass% to 0.056 mass% (preferably 0.016 mass% to 0.055 mass%) of N. As described above, the sintered body after precipitation hardening is considered to have a sintered structure constituting the sintered body controlled to an appropriate form during the high-temperature heat treatment, and as a result, it has the above-mentioned specific room temperature strength, and preferably has both the above-mentioned specific room temperature strength and the above-mentioned specific high temperature strength.

The precipitation hardening treatment carried out in the precipitation hardening step may be a treatment that is carried out by appropriately combining a solution treatment and an aging treatment. The precipitation hardening treatment preferably employs a heating step that maintains the temperature and time at an appropriate temperature that does not melt the matrix phase and that makes it difficult to promote the growth of the crystal grains that make up the sintered structure, making it easy for the gamma prime phase (γ' phase) and the carbide phase to dissolve in solid solution. The precipitation hardening treatment is preferably carried out in a non-oxidizing atmosphere, and more preferably in a non-oxidizing atmosphere that does not use nitrogen gas. This allows the precipitation strengthening phases, the gamma prime phase (γ' phase) and the carbide phase, to be more finely dispersed and precipitated at the crystal grain boundaries that make up the sintered structure, and the sintered structure can be reconstructed as a sintered body made of gamma prime precipitation hardening type alloy powder.

Here, the method of preventing the growth of the crystal grains that make up the sintered structure of the sintered body from being accelerated will be explained by comparing Experiments 1 to 8 and Experiments 9 to 11, which will be described later. Note that the alloy powders used in Experiments 1 to 11 had a maximum diameter of 53 μm or less and a d50 of 10 μm to 17 μm, as will be described later. The grain size numbers shown here are values specified in accordance with ASTM E112 (Standard Test Methods for Determining Average Grain Size), and the larger the grain size, the smaller the grain size number.

In the cases of Experiments 1 to 8, the N content of the sintered body after precipitation hardening was in the range of 0.011% by mass or more and 0.056% by mass or less, with the range of 0.016% by mass or more and 0.055% by mass or less being considered preferable). In the cases of Experiments 1 to 8, the actual sintered body obtained in the sintered body production process had a grain size number of about 8 to 9 (equivalent to a grain size of about 15 μm to 23 μm). The precipitation-hardened sintered body obtained by subjecting the actual sintered body to precipitation hardening treatment after HIP treatment had a grain size number of about 8 to 9 (equivalent to a grain size of about 15 μm to 23 μm). In other words, in the cases of Experiments 1 to 8, even when the actual sintered body was subjected to HIP treatment and precipitation hardening treatment, the precipitation-hardened sintered body still had a crystal size approximately equal to that of the actual sintered body. From this, it is believed that in sintered bodies in which the N content ratio after precipitation hardening is 0.011 mass% or more and 0.056 mass% or less (preferably 0.016 mass% or more and 0.055 mass% or less), the matrix phase does not melt due to the N content ratio, and the growth of the crystal grains that make up the sintered structure is not easily promoted, so the gamma prime phase (γ' phase) and carbide phase are suitably dissolved.

On the other hand, in the case of Experiments 9 to 11, the N content of the sintered body after precipitation hardening was outside the range of 0.011 mass% or more and 0.056 mass% or less. In the case of Experiments 9 to 11, the actual sintered body obtained in the sintered body production process had a grain size number of about 5.5 to 8.5 (equivalent to a grain size of about 18 μm to 55 μm). The precipitation-hardened sintered body obtained by subjecting the actual sintered body to HIP treatment followed by precipitation hardening treatment had a grain size number of about 3 to 6 (equivalent to a grain size of about 45 μm to 130 μm). In other words, in the case of Experiments 9 to 11, when the actual sintered body was subjected to HIP treatment and precipitation hardening treatment, the crystal grains that make up the sintered structure of the actual sintered body grew, and the crystal size of the sintered body after precipitation hardening became larger. From this, it is believed that in sintered bodies in which the N content falls outside the range of 0.011% by mass or more and 0.056% by mass or less after precipitation hardening, the growth of the crystal grains that make up the sintered structure is easily promoted due to the N content, and although the matrix phase does not melt, the gamma prime phase (γ' phase) and carbide phase are not suitably solid-dissolved.

Based on the fact that the particle size numbers according to ASTM E112 in the above cases of Experiments 1 to 8 are about 8 to 9 (approximately 15 μm to 23 μm in terms of particle size), it is believed that a sintered body having an N content ratio of 0.011 mass% to 0.056 mass% (preferably 0.016 mass% to 0.055 mass%) after precipitation hardening will have a crystal size that is approximately equal (1x) to the d50 (10 μm to 17 μm) of the alloy powder used and is approximately 2.5x or less. From this perspective, in this invention, a sintered body can be obtained in which the crystal grains that make up the sintered structure after precipitation hardening are 10 μm to 45 μm (equivalent circle diameter).

According to the process flow shown in Figure 1, the sintered body after precipitation hardening is made of a gamma prime precipitation hardening type alloy, contains 0.011 mass% to 0.056 mass% N, and has the specific room temperature strength described above. Alternatively, the sintered body after precipitation hardening is made of a gamma prime precipitation hardening type alloy, contains 0.016 mass% to 0.055 mass% N, and is a preferred sintered body that has both the specific room temperature strength and the specific high temperature strength described above. The sintered body after precipitation hardening according to this invention can be used as it is, or can be used after machining or the like.

Next, an experiment conducted to determine the N content ratio of the sintered body after precipitation hardening and the N content ratio of the calcined body according to the present invention will be described. In the experiment, a sintered body after precipitation hardening was produced using a gamma prime precipitation hardening type alloy powder by the manufacturing method shown in the process flow of Figure 1 using MIM, and the N content ratio and mechanical properties were measured. Based on the measurement data, a first empirical formula (experimental approximation formula) showing the relationship between the N content ratio of the sintered body after precipitation hardening and the mechanical properties of the sintered body after precipitation hardening and a second empirical formula (experimental approximation formula) showing the relationship between the N content ratio of the calcined body and the N content ratio of the sintered body after precipitation hardening were derived. Then, the first empirical formula was used to predict the range of the N content ratio of the sintered body after precipitation hardening in which the mechanical properties of the sintered body after precipitation hardening satisfy the target, and the second empirical formula was used to predict the range of the N content ratio of the calcined body in which the N content ratio of the sintered body after precipitation hardening falls within a specific range.

The first empirical formula described above is a model (regression model) for predicting the range of the N content of the sintered body after precipitation hardening in which the mechanical properties of the sintered body after precipitation hardening satisfy the target, and is referred to as the first model. The second empirical formula described above is a model (regression model) for predicting the range of the N content of the calcined body in which the N content of the sintered body after precipitation hardening falls within a specific range, and is referred to as the second model. In the first model, the mechanical properties of the sintered body after precipitation hardening are the dependent variable, and the N content of the sintered body after precipitation hardening is the independent variable. In the second model, the N content of the sintered body after precipitation hardening is the dependent variable, and the N content of the calcined body is the independent variable.

In the prediction by the first model, the dependent variable for each independent variable was obtained as a predicted value, and the overall average of the predicted values, the maximum value (Ymax) of the absolute values of the difference between the overall average and each predicted value, and the Mean Absolute Error (MAE) were obtained. The reliability of the first model was determined mainly based on the coefficient of determination (R ² ), taking into consideration Ymax and MAE, and referring to the Root Mean Square Error (RMSE) and Root Mean Squared Logarithmic Error (RMSLE). In addition, in the prediction by the second model, the dependent variable for the independent variable was obtained, and the range of the independent variable corresponding to a specific range (interval) of the dependent variable was calculated backwards as a predicted value. The reliability of the second model was determined mainly based on R ² , and referring to the RMSE and RMSLE.

In this invention, the main guideline for ^R2 in determining the reliability of a model was based on the concept of machine learning, and models with ^R2 ≧0.7 ( ^R2 ≦1) were unconditionally determined to be "reliable". Models with 0.6≦ ^R2 <0.7 were determined to be "reliable" under the condition that the independent variables were given a margin of about 30% in order to improve reliability. Models with 0.5≦ ^R2 <0.6 were determined to be "reliable" under the condition that the independent variables were given a margin of about 50% in order to sufficiently improve reliability. Models with ^R2 <0.5 were unconditionally determined to be "unreliable". The closer the coefficient of determination ( ^R2 ) is to 1, and the smaller the values of Ymax, MAE, RMSE, and RMSLE are, the more accurate the prediction.

Below, we will explain the details using Experiments 1 to 11.

In the compact manufacturing process carried out in Experiments 1 to 11, the kneaded material was injection molded to produce a compact (green body). The kneaded material used was a gamma prime precipitation hardening type alloy powder and a binder. The kneaded material was injection molded into the die cavity of an injection molding device to produce a cylindrical (round bar) compact (green body) with a diameter of approximately 8 mm and a length of approximately 50 mm. The gamma prime precipitation hardening type alloy powder was an alloy powder having a chemical composition equivalent to Alloy 718 as specified in AMS 5377G. The specifications of the chemical composition (mass%) of the alloy powder are detailed below. The base of the alloy powder was Ni in the range of 50.0% to 55.0%. The essential elements of the alloy powder are 0% to 0.08% C, 17.0% to 21.0% Cr, 2.80% to 3.30% Mo, 4.75% to 5.50% Nb, 0.75% to 1.15% Ti, 0.30% to 0.70% Al, 0% to 0.006% B, and 0% to 0.01% Zr. The elements that can be contained in the alloy powder are 0% to 0.35% Mn, 0% to 0.35% Si, 0% to 0.015% P, 0% to 0.015% S, 0% to 1.0% Co, 0% to 0.1% Ta, and 0% to 0.30% Cu, with the balance being Fe and impurity elements. The particle size distribution specifications of the alloy powder were determined from the cumulative volume distribution curve (laser diffraction scattering method) with a median diameter d50 of 10 μm to 17 μm, d10 of 3 μm to 9 μm, and d90 of 20 μm to 25 μm, with a maximum diameter of 53 μm or less. The binder was made by blending paraffin wax, polypropylene, polyolefin resin, and styrene resin containing organic components.

In the degreased body production process carried out in Experiments 1 to 11, a degreased body (brown body) was produced by performing solvent degreasing to mainly remove paraffin wax components, followed by thermal degreasing. Specifically, as a process combining the degreased body production process and the calcined body production process, the molded body (green body) was placed in the furnace used in the calcined body production process. Then, during the first heating carried out in the calcined body production process, the molded body (green body) was thermally degreased to produce a heated degreased body. Note that in the first heating carried out in the above-mentioned calcined body production process, the inside of the furnace during the thermal degreasing stage was a reduced pressure atmosphere with argon gas introduced.

In the calcination process carried out in Experiments 1 to 11, the calcination was carried out by the first heating. Specifically, the furnace was set to a specific atmosphere, and the molded body (green body) was heated and degreased during the first heating to form a degreased body (brown body), and then the calcination was carried out at a temperature suitable for the preparation of the calcination, to produce the calcination. Specifically, in Experiments 1 to 4, argon gas was introduced into the furnace and the temperature was raised while reducing the pressure, and when the temperature reached about 650°C, nitrogen gas was introduced while controlling the pressure (for two consecutive hours), and then argon gas was introduced while controlling the pressure, and when the temperature reached about 1100°C, the temperature was held for two hours. Similarly, in Experiments 5 and 6, nitrogen gas was introduced (for 0.75 consecutive hours) when the temperature reached about 650°C, and the temperature was held for two hours when the temperature reached about 1100°C. Similarly, in Experiments 7 and 8, nitrogen gas was introduced (for 0.5 consecutive hours) when the temperature reached about 650°C, and the temperature was held for two hours when the temperature reached about 1100°C. In contrast, in experiments 9 to 11, nitrogen gas was not introduced when the temperature reached approximately 650°C, and then heating was maintained for two hours when the temperature reached approximately 1000°C.

In the sintered body production process carried out in Experiments 1 to 11, the calcined body was used to produce an actual sintered body (silver body). Specifically, the calcined body was placed in a furnace and argon gas was introduced while controlling the pressure to perform the second heating, and the actual sintered body (silver body) was produced by heating and holding at a temperature at which the calcined structure of the calcined body could be sufficiently sintered to form a sintered structure. In Experiments 1 and 2, the temperature was held for 4 hours when it reached approximately 1260°C. In Experiments 3 to 8, the temperature was held for 4 hours when it reached approximately 1250°C. In Experiment 9, the temperature was held for 4 hours when it reached approximately 1220°C. In Experiment 10, the temperature was held for 4 hours when it reached approximately 1230°C. In Experiment 11, the temperature was held for 4 hours when it reached approximately 1210°C.

Next, in Experiments 3 to 8 and 10, the actual sintered body (silver body) was subjected to a HIP treatment process before the precipitation hardening process. In this case, the HIP treatment was performed by placing the actual sintered body (silver body) in a furnace, creating an argon gas atmosphere, setting the holding pressure to about 100 MPa, and heating and holding at about 1160°C for about 1 hour. Note that in Experiments 1, 2 and 9, the actual sintered body (silver body) was not subjected to HIP treatment.

In the precipitation hardening process carried out in Experiments 1 to 11, the actual sintered body (silver body) or the sintered body after HIP treatment was subjected to precipitation hardening treatment to produce a precipitation-hardened sintered body. In this case, the precipitation hardening treatment was a process in which the actual sintered body (silver body) or the sintered body after HIP treatment was subjected to solution treatment and then aging treatment. For the solution treatment, the actual sintered body (silver body) or the sintered body after HIP treatment was placed in a furnace, sufficiently reduced pressure to create a vacuum, and heated and held at approximately 1050°C for 1 hour. For the aging treatment, the sintered body after solution treatment was placed in a furnace, sufficiently reduced pressure to create a vacuum, heated and held at approximately 720°C for 8 hours, then cooled, and when it reached approximately 620°C, it was kept at that temperature for 8 hours.

The above process flow was used to obtain the calcined bodies, the actual sintered bodies (silver bodies), and the sintered bodies after precipitation hardening for Experiments 1 to 11. The N content ratio was then analyzed for the calcined bodies, the actual sintered bodies (silver bodies), and the sintered bodies after precipitation hardening for Experiments 1 to 11. The room temperature strength and high temperature strength were also measured for the sintered bodies after precipitation hardening for Experiments 1 to 11. The N content ratio was analyzed using an oxygen/nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.). The room temperature strength was measured with reference to JIS-Z2241:2011, and a tensile test was performed in an environment of approximately 20°C using a test piece with a central dimension of 3 mm in diameter and 7 mm in length, to measure the 0.2% yield strength, tensile strength, and elongation. The high temperature strength was measured with reference to JIS-G0567:2020, and a tensile test was performed in an environment of approximately 650°C using the same test piece as above, to measure the 0.2% yield strength, tensile strength, and elongation. The results are shown in Table 1.

Next, an empirical formula (empirical approximation formula) was derived based on the measurement data of the sintered body after precipitation hardening shown in Table 1. Specifically, taking into consideration practicality and ease, a general-purpose spreadsheet software (Microsoft Excel) was used to create a graph (scatter plot) of the N content ratio and mechanical properties of the sintered body after precipitation hardening, and a polynomial (quadratic) approximation formula was obtained using the graph's auxiliary functions. Then, the polynomial (quadratic) approximation formula was defined as an empirical formula (empirical approximation formula) and used as a regression model to predict the range of the N content ratio of the sintered body after precipitation hardening in which the mechanical properties meet the target. Table 2 shows the predicted values of the mechanical properties predicted by each of the first models described below using the actual measured values of the N content ratio of the sintered body after precipitation hardening in Experiments 1 to 11 (see Table 1).

<0.2% Yield Strength>
FIG. 2 is a graph (scatter diagram) created by a general-purpose spreadsheet using the measured values of the N content ratio and 0.2% yield strength of the sintered body after precipitation hardening. The horizontal axis of the graph is the N content ratio of the sintered body after precipitation hardening. The vertical axis of the graph is the 0.2% yield strength in a room temperature environment (hereinafter referred to as "room temperature yield strength") and the 0.2% yield strength in a high temperature environment (hereinafter referred to as "high temperature yield strength"). The room temperature yield strength is indicated by "●". The high temperature yield strength is indicated by "▲". One of the curves is a polynomial (quadratic) approximation equation showing the relationship between the N content ratio of the sintered body after precipitation hardening and the room temperature yield strength. The other of the curves is a polynomial (quadratic) approximation equation showing the relationship between the N content ratio of the sintered body after precipitation hardening and the high temperature yield strength.

In order to predict the range of the N content ratio of the sintered body after precipitation hardening in which the 0.2% proof stress satisfies the target, the polynomial (quadratic) approximation formula of the graph (scatter diagram) shown in FIG. 2 was defined as the first empirical formula, which was the first model y = Ax ² + Bx + C (A, B, and C are coefficients). Then, using the first model, the N content ratio of the sintered body after precipitation hardening was set as the independent variable x, and the predicted value of the 0.2% proof stress (see Table 2) which is the dependent variable y was obtained. Next, in the section of x≧0, the range of the N content ratio of the sintered body after precipitation hardening was predicted with the R ² of the first model as the main judgment, taking into consideration Ymax and MAE, and referring to RMSE and RMSLE. Note that the target of the room temperature proof stress in the first model is 1050 MPa or more, and the target of the high temperature proof stress is 870 MPa or more. The prediction results for the room temperature proof stress by the first model are shown in Table 3, and the prediction results for the high temperature proof stress are shown in Table 4.

As shown in Table 3, the prediction result by the first model for room temperature yield strength was 0.0110 or more and 0.0770 or less when y was 1050 or more and met the target in the range of x≧0. Also, when x was 0.0440, y was maximum. As a result, the prediction result was that the N content ratio of the sintered body after precipitation hardening when the room temperature yield strength of the sintered body after precipitation hardening becomes the target of 1050 MPa or more is 0.0110 mass% or more and 0.0770 mass% or less. This first model for room temperature yield strength has an ^R2 of about 0.73, which is larger than 0.7, which is the reliability benchmark. Also, with respect to the overall average of the predicted values shown in Table 2 (about 1122 MPa), the error estimated from MAE (about 27) is about 2.4%, and the deviation estimated from Ymax (about 96) is about 8.6%. In addition, both the RMSE (about 32) and the RMSLE (about 0.028) are not at a level that calls into question the reliability. From the above perspective, the prediction results of the first model for room temperature strength are unlikely to be significantly affected by outliers, and therefore can be judged to be "reliable."

As shown in Table 4, the prediction results of the first model for high temperature yield strength were such that, in the range of x≧0, when y was 870 or more and met the target, x was 0.0158 or more and 0.1308 or less. In addition, when x was 0.0733, y was maximum. As a result, the prediction result was that the N content ratio of the sintered body after precipitation hardening when the high temperature yield strength of the sintered body after precipitation hardening was the target of 870 MPa or more was 0.0158 mass% or more and 0.1308 mass% or less. This first model for high temperature yield strength has an ^R2 of about 0.81, which is sufficiently larger than 0.7, which was used as a guideline for reliability. In addition, the error estimated from MAE (about 18) was about 2% for the overall average of the predicted values shown in Table 2 (about 913 MPa), and the deviation estimated from Ymax (about 73) was about 8%. In addition, neither RMSE (about 20) nor RMSLE (about 0.022) was at a level that doubted reliability. From the above perspective, it is considered that the prediction results of the first model for high temperature resistance are unlikely to be significantly influenced by outliers, and therefore can be judged to be "reliable."

<Tensile strength>
FIG. 3 is a graph (scatter diagram) created by a general-purpose spreadsheet using the measured values of the N content ratio and tensile strength of the sintered body after precipitation hardening. The horizontal axis of the graph is the N content ratio of the sintered body after precipitation hardening. The vertical axis of the graph is the tensile strength in a room temperature environment (hereinafter referred to as "room temperature tensile strength") and the tensile strength in a high temperature environment (hereinafter referred to as "high temperature tensile strength"). The room temperature tensile strength is indicated by "●". The high temperature tensile strength is indicated by "▲". One of the curves is a polynomial (quadratic) approximation equation showing the relationship between the N content ratio of the sintered body after precipitation hardening and the room temperature tensile strength. The other of the curves is a polynomial (quadratic) approximation equation showing the relationship between the N content ratio of the sintered body after precipitation hardening and the high temperature tensile strength.

In order to predict the range of the N content ratio of the sintered body after precipitation hardening that satisfies the target tensile strength, the polynomial (quadratic) approximation formula of the graph (scatter diagram) shown in FIG. 3 was defined as the first empirical formula, which was the first model y = Ax ² + Bx + C (A, B, C are coefficients). Then, using the first model, the N content ratio of the sintered body after precipitation hardening was set as the independent variable x, and the predicted value of the tensile strength (see Table 2) that becomes the dependent variable y was obtained. Next, in the section of x ≧ 0, the range of the N content ratio of the sintered body after precipitation hardening was predicted with the R ² of the first model as the main judgment, taking into consideration Ymax and MAE, and referring to RMSE and RMSLE. Note that the target of the room temperature tensile strength in the first model is 1280 MPa or more, and the target of the high temperature tensile strength is 970 MPa or more. The prediction results for the room temperature tensile strength by the first model are shown in Table 5, and the prediction results for the high temperature tensile strength are shown in Table 6.

As shown in Table 5, the prediction result by the first model for room temperature tensile strength was 0.0071 or more and 0.0808 or less when y was 1280 or more and met the target in the range of x≧0. Also, when x was 0.0439, y was maximum. As a result, the predicted result was that the N content ratio of the sintered body after precipitation hardening when the room temperature tensile strength of the sintered body after precipitation hardening was the target 1280 MPa or more was 0.0071 mass% or more and 0.0808 mass% or less. This first model for room temperature tensile strength has an ^R2 of about 0.89, which is sufficiently larger than 0.7, which is the reliability benchmark. Also, with respect to the overall average of the predicted values shown in Table 2 (about 1362 MPa), the error estimated from MAE (about 14) was about 1%, and the deviation estimated from Ymax (about 86) was about 6.3%. In addition, both the RMSE (about 15) and the RMSLE (about 0.011) are not at a level that calls into question the reliability. From the above viewpoints, it is considered that the prediction result of the first model for the room temperature tensile strength is unlikely to be significantly affected by outliers, and therefore it can be judged to be "reliable."

As shown in Table 6, the prediction results of the first model for high temperature tensile strength were such that, in the range of x≧0, when y was 970 or more and met the target, x was 0.0000 or more and 0.1187 or less. Also, when x was 0.0585, y was maximum. As a result, the prediction result was that the N content ratio of the sintered body after precipitation hardening when the high temperature tensile strength of the sintered body after precipitation hardening was the target of 970 MPa or more was 0.0000 mass% or more and 0.1187 mass% or less. This first model for high temperature tensile strength has an ^R2 of about 0.81, which is sufficiently larger than 0.7, which is used as a guideline for reliability. Also, with respect to the overall average of the predicted values shown in Table 2 (about 1078 MPa), the error estimated from MAE (about 17) was about 1.6%, and the deviation estimated from Ymax (about 77) was about 7.1%. In addition, both the RMSE (about 19) and the RMSLE (about 0.017) are not at a level that calls into question the reliability. From the above viewpoints, it is considered that the prediction result of the first model for the high temperature tensile strength is unlikely to be significantly affected by outliers, and therefore it can be judged to be "reliable."

<Stretch>
FIG. 4 is a graph (scatter diagram) created by a general-purpose spreadsheet using the measured values of the N content ratio and elongation of the sintered body after precipitation hardening. The horizontal axis of the graph is the N content ratio of the sintered body after precipitation hardening. The vertical axis of the graph is the elongation in a room temperature environment (hereinafter referred to as "room temperature elongation") and the elongation in a high temperature environment (hereinafter referred to as "high temperature elongation"). The room temperature elongation is indicated by "●". The high temperature elongation is indicated by "▲". One of the curves is a polynomial (quadratic) approximation equation showing the relationship between the N content ratio of the sintered body after precipitation hardening and the room temperature elongation. The other of the curves is a polynomial (quadratic) approximation equation showing the relationship between the N content ratio of the sintered body after precipitation hardening and the high temperature elongation.

In order to predict the range of the N content ratio of the sintered body after precipitation hardening that satisfies the target elongation, the polynomial (quadratic) approximation formula of the graph (scatter diagram) shown in FIG. 4 was defined as the first empirical formula, which was the first model y = Ax ² + Bx + C (A, B, and C are coefficients). Then, using the first model, the N content ratio of the sintered body after precipitation hardening was set as the independent variable x, and the predicted value of elongation (see Table 2) that becomes the dependent variable y was obtained. Next, in the section of x ≧ 0, the range of the N content ratio of the sintered body after precipitation hardening was predicted with the R ² of the first model as the main judgment, taking into consideration Ymax and MAE, and referring to RMSE and RMSLE. Note that the target of the room temperature elongation in the first model is 1280 MPa or more, and the target of the high temperature elongation is 970 MPa or more. The prediction results for the room temperature elongation by the first model are shown in Table 7, and the prediction results for the high temperature elongation are shown in Table 8.

As shown in Table 7, the prediction results of the first model for room temperature elongation were such that, in the range of x≧0, when y was 12 or more and met the target, x was 0.0000 or more and 0.0606 or less. Also, when x was 0.0289, y was maximum. As a result, the predicted result was that the N content ratio of the sintered body after precipitation hardening when the room temperature elongation of the sintered body after precipitation hardening was the target of 12% or more was 0.0000 mass% or more and 0.0606 mass% or less. The first model for room temperature elongation had an ^R2 of about 0.68, which is slightly smaller than 0.7, which was used as a guideline for reliability. Also, compared to the overall average (about 22.3%) of the predicted values shown in Table 2, the error estimated from MAE (about 1.4) was about 6.3%, and the deviation estimated from Ymax (about 5.2) was about 23.3%, both of which were slightly large. In addition, both the RMSE (about 1.8) and the RMSLE (about 0.082) are not at a level that calls into question the reliability. From the above viewpoints, it was determined that the prediction results of the first model for room temperature elongation may be affected by outliers, and it was decided to provide a margin for the independent variables in order to improve the reliability.

Therefore, in the first model related to room temperature elongation that satisfies 0.6≦R ² <0.7, the condition of giving a margin of about 30% to the independent variable was applied as described above. Specifically, the independent variable x (0.0564) was obtained such that the dependent variable y was about 1.3 times (15.7) of 12.1 shown in Table 7, and the upper limit of the interval of the N content ratio of the sintered body after precipitation hardening was predicted based on the x value (0.0564). As a result, the predicted result was that the N content ratio of the sintered body after precipitation hardening when the room temperature elongation of the sintered body after precipitation hardening becomes the target 12% or more is 0.0000 mass% or more and 0.0564 mass% or less. From the above viewpoint, the predicted result of the first model related to room temperature elongation may be influenced by outliers, but it can be judged to be "reliable" by including a margin of about 30% in the upper limit of the interval.

As shown in Table 8, the prediction results of the first model for high-temperature elongation were such that, in the range of x≧0, when y was 6 or more and met the target, x was 0.0000 or more and 0.0608 or less. In addition, y tended to decrease without inflection with respect to an increase in x. As a result, the prediction result was that the N content ratio of the sintered body after precipitation hardening when the high-temperature elongation of the sintered body after precipitation hardening was the target of 12% or more was 0.0000 mass% or more and 0.0606 mass% or less. The first model for high-temperature elongation had an ^R2 of about 0.53, which is significantly smaller than 0.7, which was used as a guideline for reliability. In addition, the error estimated from MAE (about 3.0) was about 20%, and the deviation estimated from Ymax (about 8.1) was about 53%, compared to the overall average of the predicted values shown in Table 2 (about 15.2%), both of which were quite large. In addition, the RMSE (about 4.1) is not at a level that calls into question the reliability, but the RMSLE (about 0.274) is at a level that calls into question the reliability. From the above viewpoints, it was determined that the prediction results of the first model regarding high-temperature elongation may be affected by outliers, and it was decided to provide a margin to the independent variables in order to improve the reliability.

Therefore, in the first model related to high-temperature elongation that satisfies 0.5≦R ² <0.6, the condition of giving a margin of about 50% to the independent variable was applied as described above. Specifically, the independent variable x (0.0546) was obtained such that the dependent variable y was about 1.5 times (9.1) of 6.0 shown in Table 8, and the upper limit of the interval of the N content ratio of the sintered body after precipitation hardening was predicted based on the x value (0.0546). As a result, the N content ratio of the sintered body after precipitation hardening when the high-temperature elongation of the sintered body after precipitation hardening becomes the target 6% or more was predicted to be 0.0000 mass% or more and 0.0546 mass% or less. From the above viewpoint, the prediction result of the first model related to high-temperature elongation may be influenced by outliers, but it can be judged to be "reliable" by including a margin of about 50% in the upper limit of the interval.

As described above, the first model for each mechanical property constructed based on the measurement data shown in Table 1 was used to predict the range of N content of the sintered body after precipitation hardening in which each mechanical property meets the target. As a result, in the case of room temperature yield strength, it was 0.0110 mass% or more and 0.0770 mass% or less. In addition, in the case of room temperature tensile strength, it was 0.0071 mass% or more and 0.0808 mass% or less. In addition, in the case of room temperature elongation, it was 0.0000 mass% or more and 0.0564 mass% or less. From this, it can be seen that the range of N content of the sintered body after precipitation hardening is limited by the room temperature yield strength at the lower limit of the interval and limited by the room temperature elongation at the upper limit of the interval. It can also be seen that the range of N content of the sintered body after precipitation hardening that simultaneously meets the targets of 0.2% yield strength, tensile strength, and elongation in a room temperature (about 20°C) environment is 0.0110 mass% or more, which is the maximum value of the lower limit of the interval, and 0.0564 mass% or less, which is the minimum value of the upper limit of the interval. From this perspective, it can be determined that a sintered body made of a gamma prime precipitation hardening alloy containing 0.011% to 0.056% by mass (rounded to the nearest 4 decimal points) of N after precipitation hardening is highly likely to have a 0.2% yield strength of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature (approximately 20°C) environment.

Similarly, in the case of high-temperature yield strength, it was 0.0158 mass% or more and 0.1308 mass% or less. In the case of high-temperature tensile strength, it was 0.0000 mass% or more and 0.1187 mass% or less. In the case of high-temperature elongation, it was 0.0000 mass% or more and 0.0546 mass% or less. From this, it can be seen that the range of the N content of the sintered body after precipitation hardening is limited by the high-temperature yield strength at the lower limit of the interval and by the high-temperature elongation at the upper limit of the interval. It can also be seen that the range of the N content of the sintered body after precipitation hardening that simultaneously satisfies the targets of 0.2% yield strength, tensile strength, and elongation in a high-temperature (approximately 650°C) environment is equal to or more than the maximum value of the lower limit of the interval of 0.0158 mass% and equal to or less than the minimum value of the upper limit of the interval of 0.0546 mass%. From this perspective, it can be determined that a sintered body made of a gamma prime precipitation hardening alloy containing 0.016% to 0.055% by mass (rounded to the nearest tenth) of N after precipitation hardening is highly likely to have a 0.2% yield strength of 870 MPa or more, a tensile strength of 970 MPa or more, and an elongation of 6% or more in a high-temperature (approximately 650°C) environment.

Furthermore, the range of N content of the sintered body after precipitation hardening that satisfies the target high-temperature strength described above (0.016 mass% or more and 0.055 mass% or less) is included in the range of N content of the sintered body after precipitation hardening that satisfies the target room-temperature strength described above (0.011 mass% or more and 0.056 mass% or less). From this perspective, it can be determined that a sintered body made of a gamma prime precipitation hardening type alloy and containing 0.016 mass% or more and 0.055 mass% or less of N after precipitation hardening has a sufficiently high possibility of simultaneously satisfying the targets of room-temperature strength and high-temperature strength described above.

Next, a graph (scatter diagram) was created in the same manner as in constructing the first model, using the N content ratios (actual measurements) of the calcined body, the actual sintered body (silver body), and the sintered body after precipitation hardening shown in Table 1, and a polynomial (quadratic) approximation equation was obtained and defined as an empirical formula (experimental approximation equation). The empirical formula (experimental approximation equation) was then used as a regression model, with the N content ratio in the front-end process as the independent variable and the N content ratio in the rear-end process as the dependent variable, and the N content ratio in the rear-end process was predicted with a specific N content ratio in the front-end process as the target. In the combined model of the calcined body and the actual sintered body (silver body), the calcined body corresponds to the front-end process, and the actual sintered body corresponds to the rear-end process. In the combined model of the actual sintered body and the sintered body after precipitation hardening, the actual sintered body corresponds to the front-end process, and the sintered body after precipitation hardening corresponds to the rear-end process. In the combined model of the calcined body and the sintered body after precipitation hardening, the calcined body corresponds to the front-end process, and the sintered body after precipitation hardening corresponds to the rear-end process.

Figure 5 is a graph (scatter plot) showing a combination model of the calcined body and the actual sintered body, a combination model of the actual sintered body and the sintered body after precipitation hardening, and a combination model of the calcined body and the sintered body after precipitation hardening. The horizontal axis of the graph is the N content ratio in the previous process. The vertical axis of the graph is the N content ratio in the subsequent process. The combination model of the calcined body and the actual sintered body is indicated by "○". The combination model of the actual sintered body and the sintered body after precipitation hardening is indicated by "△". The combination model of the calcined body and the sintered body after precipitation hardening is indicated by "□". In Figure 5, one of the curves shown by the solid line is a polynomial (quadratic) approximation equation showing the relationship between the calcined body and the actual sintered body. The other curve shown by the solid line is a polynomial (quadratic) approximation equation showing the relationship between the actual sintered body and the sintered body after precipitation hardening. Additionally, the dashed curve is a polynomial (quadratic) approximation that shows the relationship between the calcined body and the sintered body after precipitation hardening.

<Prediction of N content of calcined body 1>
In order to predict the range of the N content ratio of the calcined body that makes the N content ratio of the sintered body after precipitation hardening in a specific range, a prediction 1 of the N content ratio of the calcined body was performed via the N content ratio of the actual sintered body. Specifically, the two polynomial (second-order) approximation formulas shown by solid lines in FIG. 5 were defined as the second experimental formula, the second experimental formula of the combination model of the calcined body and the actual sintered body was set as the second model q = Ap ² + Bp + C (A, B, C are coefficients), and the second experimental formula of the combination model of the actual sintered body and the sintered body after precipitation hardening was set as the second model r = Dq ² + Eq + F (D, E, F are coefficients). Then, by the second model q = Ap ² + Bp + C, the N content ratio of the calcined body was set as an independent variable p, and the p value was given to obtain the N content ratio (q value) of the actual sintered body that becomes the dependent variable q. Next, the N content ratio (r value) of the sintered body after precipitation hardening was obtained by using the second model r = Dq ² + Eq + F, with the N content ratio (q value) of the actual sintered body as the independent variable q, and the previously obtained q value was given as the dependent variable r. By this method, the range of p values corresponding to a specific range (section) of r values was predicted. The r value section is from 0.0110 (lower limit side) to 0.0564 (upper limit side) and from 0.0158 (lower limit side) to 0.0546 (upper limit side). The results of prediction 1 of the N content ratio of the calcined body by the second model via the N content ratio of the actual sintered body are shown in Table 9.

As shown in Table 9, in prediction 1, when the r value range is from 0.0110 to 0.0564, q at which r is 0.0110 is 0.0108, and p at which q is 0.0108 is 0.0132. Then, q at which r is 0.0564 is 0.0578, and p at which q is 0.0578 is 0.0639. Also, when the r value range is from 0.0158 to 0.0546, q at which r is 0.0158 is 0.0157, and p at which q is 0.0157 is 0.0167. Then, q at which r is 0.0546 is 0.0559, and p at which q is 0.0559 is 0.0595. From this, the range of p-values with the r-value interval from 0.0110 to 0.0564 was predicted to be 0.0132 to 0.0639. Moreover, the range of p-values with the r-value interval from 0.0158 to 0.0546 was predicted to be 0.0167 to 0.0595. Moreover, the second model related to prediction 1 has an ^R2 of about 0.98 and about 1.00, which is sufficiently larger than 0.7, which is a guideline for reliability, and is close to 1. Moreover, both RMSE and RMSLE are sufficiently small and are not at a level where reliability is doubted. From the above viewpoint, the prediction result of the second model related to prediction 1 is considered to be unlikely to be significantly influenced by outliers, so it can be judged to be "reliable".

<Prediction of N content of calcined body 2>
In order to predict the range of the N content of the calcined body that makes the N content of the sintered body after precipitation hardening fall within a specific range, prediction 2 of the N content of the calcined body without going through the N content of the actual sintered body was performed. Specifically, the polynomial (second-order) approximation shown by the dashed line in FIG. 5 was defined as the second experimental formula, and the second experimental formula of the combination model of the calcined body and the sintered body after precipitation hardening was set as the second model r = Ap ² + Bp + C (A, B, C are coefficients). Then, by the second model r = Ap ² + Bp + C, the N content of the calcined body was set as the independent variable p, and the N content of the sintered body after precipitation hardening was given a p value to obtain the N content (r value) that becomes the dependent variable r. By this method, the range of p values corresponding to the specific range (interval) of the r value was predicted. The interval of the r value is the same as the case of prediction 1 described above. The results of prediction 2 of the N content of the calcined body by the second model that does not go through the N content of the actual sintered body are shown in Table 10.

As shown in Table 10, in prediction 2, when the r value range is 0.0110 to 0.0564, p for r 0.0110 is 0.133, and p for r 0.0564 is 0.0635. When the r value range is 0.0158 to 0.0546, p for r 0.0158 is 0.0167, and p for r 0.0546 is 0.0593. As a result, the p value range for the r value range from 0.0110 to 0.0564 is predicted to be 0.0133 to 0.0635. The p value range for the r value range from 0.0158 to 0.0546 is predicted to be 0.0167 to 0.0593. In addition, the second model related to prediction 2 has an R ² of about 0.98, which is sufficiently larger than 0.7, which is used as a guideline for reliability, and is close to 1. In addition, both RMSE and RMSLE are sufficiently small and not at a level that calls into question the reliability. From the above viewpoint, it is considered that the prediction result of the second model related to prediction 2 is unlikely to be significantly affected by outliers, and therefore it can be judged to be "reliable."

As described above, the second model constructed based on the N content ratios (actual measurements) of the calcined body, the actual sintered body (silver body), and the sintered body after precipitation hardening shown in Table 1 was used to predict the range of the N content ratio of the calcined body in which the N content ratio of the sintered body after precipitation hardening is in a specific range. As a result, the range of the N content ratio of the calcined body in which the N content ratio of the sintered body after precipitation hardening is in the range of 0.0110 mass% to 0.0564 mass% was 0.0132 mass% to 0.0639 mass% in Prediction 1, and 0.0133 mass% to 0.0635 mass% in Prediction 2. From this, it can be seen that the range of the N content ratio of the calcined body in which the N content ratio of the sintered body after precipitation hardening is in the range of 0.0110 mass% to 0.0564 mass% is equal to or greater than the maximum value of the lower limit of the range, 0.0133 mass%, and equal to or less than the minimum value of the upper limit of the range, 0.0635 mass%.

In addition, the range of the N content of the calcined body that makes the N content of the sintered body after precipitation hardening in the preferred range of 0.0158 mass% or more and 0.0546 mass% or less is 0.0167 mass% or more and 0.0595 mass% or less for prediction 1, and 0.0167 mass% or more and 0.0593 mass% or less for prediction 2. From this, it can be seen that the range of the N content of the calcined body that makes the N content of the sintered body after precipitation hardening in the preferred range of 0.0158 mass% or more and 0.0546 mass% or less is equal to or greater than the maximum value of the lower limit of the interval, 0.0167 mass%, and equal to or less than the minimum value of the upper limit of the interval, 0.0593 mass%.

From the above viewpoints, it can be concluded that in order to produce a sintered body made of a gamma prime precipitation hardening alloy and containing 0.011 to 0.056 mass% N after precipitation hardening, nitrogen gas should be introduced into the furnace in the calcination body production process to adjust the calcined body to contain 0.013 to 0.064 mass% N (rounded to the nearest 4 decimal points). Also, in order to produce a preferred sintered body containing 0.016 to 0.055 mass% N after precipitation hardening, nitrogen gas should be introduced into the furnace in the calcination body production process to adjust the calcined body to contain 0.017 to 0.059 mass% N (rounded to the nearest 4 decimal points).

As described above, by using a simple manufacturing method such as adjusting the N content of the calcined body to 0.013% by mass or more and 0.064% by mass or less, it is possible to easily provide a sintered body made of a gamma prime precipitation hardening type alloy, which contains 0.011% by mass or more and 0.056% by mass or less of N after precipitation hardening, and which has a 0.2% yield strength of 1,050 MPa or more, a tensile strength of 1,280 MPa or more, and an elongation of 12% or more in a room temperature (about 20° C.) environment. Furthermore, by using a simple manufacturing method, such as adjusting the N content of the calcined body to 0.017% by mass or more and 0.059% by mass or less, it is possible to easily provide a preferred sintered body that is made of a gamma prime precipitation hardening type alloy, contains 0.016% by mass or more and 0.055% by mass or less of N after precipitation hardening, and has a 0.2% yield strength of 1050 MPa or more, a tensile strength of 1280 MPa or more, and an elongation of 12% or more in a room temperature (about 20° C.) environment, and has a 0.2% yield strength of 870 MPa or more, a tensile strength of 970 MPa or more, and an elongation of 6% or more in a high temperature (about 650° C.) environment.

Claims (7)

A sintered body made of a gamma prime precipitation hardening alloy containing 0.011% to 0.056% by mass of N after precipitation hardening. The sintered body according to claim 1, which is made of the alloy and contains 0.016% by mass or more and 0.055% by mass or less of N after precipitation hardening. The sintered body according to claim 1 or 2, wherein the gamma prime precipitation hardening alloy is a Ni-based alloy, containing, relative to the base Ni, the essential elements being C, Cr, Mo, Nb, Ti, Al, B and Zr, and the possible elements being one or more of Mn, Si, P, S, Co, Ta, Fe, Cu and Hf, with the balance being N and impurity elements. A method for producing a sintered body, comprising a gamma prime precipitation hardening alloy, the sintered body containing 0.011% by weight to 0.056% by weight of N after precipitation hardening, comprising:
a molded body preparation step of injection molding a kneaded product containing a gamma prime precipitation hardening type alloy powder and an organic component to prepare a molded body;
a degreased body preparation step of removing organic components constituting the compact to prepare a degreased body;
a calcined body producing step of sintering the alloy powder constituting the degreased body in a furnace by first heating to produce a calcined body;
a sintered body preparation step of sintering the alloy powder constituting the calcined body in a furnace by a second heating at a temperature higher than the first heating to prepare an actual sintered body;
A precipitation hardening step of precipitation hardening the actual sintered body,
In the calcined body preparation step, nitrogen gas is introduced into a furnace to adjust the N content of the calcined body to 0.013 mass% or more and 0.064 mass% or less, and the sintered body is prepared by the precipitation hardening step. The method for producing a sintered body according to claim 4, wherein in the calcined body production process, nitrogen gas is introduced into the furnace to adjust the N content of the calcined body to 0.017% by mass or more and 0.059% by mass or less, and the precipitation hardening process produces the sintered body containing 0.016% by mass or more and 0.055% by mass or less of N. The method for producing a sintered body according to claim 4 or 5, wherein the gamma prime precipitation hardening type alloy powder is a Ni-based alloy powder that contains, relative to the base Ni, the essential elements C, Cr, Mo, Nb, Ti, Al, B and Zr, and the possible elements Mn, Si, P, S, Co, Ta, Fe, Cu and Hf, and the remainder is composed of impurity elements. 6. The method for producing a sintered body according to claim 4, further comprising a HIP treatment step of holding the actual sintered body under high temperature and pressure, and carrying out the precipitation hardening step after the HIP treatment step.

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