Metal Sintered Body

Abstract

A metal sintered body contains: Ni in a content of 28.00 mass % or more and 32.00 mass % or less; Co in a content of 15.00 mass % or more and 20.00 mass % or less; and Si in a content of 0.01 mass % or more and 0.20 mass % or less, with a balance being Fe as a main component and impurities. The content of Si is preferably 0.05 mass % or more and 0.10 mass % or less.

Description

[0001] The present application is based on, and claims priority from JP Application Serial Number 2025-052411, filed Mar. 26, 2025, the disclosure of which is hereby incorporated by reference herein in its entirety.BACKGROUND1. Technical Field

[0002] The present disclosure relates to a metal sintered body.2. Related Art

[0003] JP-A-2002-026165 discloses a metal package for a semiconductor, which is a metal package molded into a box shape by metal powder injection molding and sintered, and is configured with a sintered body of Ni—Co—Fe alloy powder. The metal package has a composition of Ni: 28 mass % to 32 mass %, Co: 15 mass % to 20 mass %, B: 0.05 mass % to 0.8 mass %, with a balance being substantially Fe. Accordingly, a metal package having fewer micropores in a surface layer portion than in an inside can be achieved. As a result, it is possible to provide a semiconductor package that achieves densification of the surface layer portion without increasing the density by a hot isostatic pressing treatment and has airtightness and good Ni plating properties.

[0004] JP-A-2002-026165 is an example of the related art.

[0005] In recent years, metal packages for semiconductors used for optical communication and the like are required to have higher airtightness. The metal package described in JP-A-2002-026165 has room for further improvement from the viewpoint of inhibiting micropores. In order to achieve high airtightness, it is necessary to increase the density and strength of the sintered body.

[0006] In view of such a background, an object is to achieve a metal sintered body having good thermal expansion properties derived from the Ni-Co-Fe alloy and having high density and high strength.SUMMARY

[0007] A metal sintered body according to an application example of the present disclosure contains:

[0008] Ni in a content of 28.00 mass % or more and 32.00 mass % or less;

[0009] Co in a content of 15.00 mass % or more and 20.00 mass % or less; and

[0010] Si in a content of 0.01 mass % or more and 0.20 mass % or less,

[0011] with a balance being Fe as a main component and impurities.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic diagram showing an example of a cross section of a metal sintered body according to an embodiment.

[0013] FIG. 2 is a flowchart showing an example of a method for producing the metal sintered body.

[0014] FIG. 3 is Table 1 showing a configuration of a metal sintered body of each sample No.

[0015] FIG. 4 is Table 2 showing evaluation results of the metal sintered body of each sample No.

[0016] FIG. 5 is an electron microscope image obtained by observing a cross section of a metal sintered body of Sample No. 3 as an example.

[0017] FIG. 6 is an electron microscope image obtained by observing a cross section of a metal sintered body of sample No. 11 as a comparative example.

[0018] FIG. 7 is a photograph showing an appearance of the metal sintered body of sample No. 3 as the example after a neutral salt spray test is performed.

[0019] FIG. 8 is a photograph showing an appearance of the metal sintered body of sample No. 11 as the comparative example after the neutral salt spray test is performed.DESCRIPTION OF EMBODIMENTS

[0020] Hereinafter, a metal sintered body according to the present disclosure will be described in detail based on preferred embodiments shown in the accompanying drawings.

[0021] The metal sintered body according to the embodiment contains Ni in a content of 28.00 mass % or more and 32.00 mass % or less, Co in a content of 15.00 mass % or more and 20.00 mass % or less, and Si in a content of 0.01 mass % or more and 0.20 mass % or less, with a balance being Fe as a main component and impurities.

[0022] According to such a configuration, it is possible to achieve a metal sintered body having good thermal expansion properties derived from the Fe-Ni-Co alloy and having high density and high strength.1. Configuration

[0023] First, a configuration of the metal sintered body according to the embodiment will be described.1.1. Composition

[0024] The metal sintered body according to the embodiment contains Fe as a main component and contains Ni, Co, and Si. In addition, the metal sintered body inevitably contains impurities.

[0025] Fe (iron) is the main component of the metal sintered body. In the present specification, the main component refers to an element having the highest content in mass ratio.

[0026] The content of Fe is appropriately set according to the contents of other elements, and is preferably 50.00 mass % or more, and more preferably 52.00 mass % or more.

[0027] Ni (nickel) acts together with Co and contributes to the achievement of a metal sintered body having good thermal expansion properties. In addition, Ni imparts good toughness to the metal sintered body. On the other hand, when the toughness is too high, the machinability may be reduced. In contrast, powder metallurgy is near-net-shape processing, and therefore, cutting, grinding, and the like as secondary processing can be omitted or reduced for the metal sintered body.

[0028] The content of Ni is the second highest after Fe, and is 28.00 mass % or more and 32.00 mass % or less, preferably 28.30 mass % or more and 31.00 mass % or less, and more preferably 28.50 mass % or more and 30.0 mass % or less. When the content of Ni is within the above range, a metal sintered body having good thermal expansion properties and high density can be obtained.

[0029] Co (cobalt) acts together with Ni and contributes to the achievement of a metal sintered body having good thermal expansion properties.

[0030] The content of Co is the second highest after Ni, and is 15.00 mass % or more and 20.00 mass % or less, preferably 16.00 mass % or more and 19.00 mass % or less, and more preferably 16.50 mass % or more and 18.00 mass % or less. When the content of Co is within the above range, a metal sintered body having good thermal expansion properties and high density can be obtained.

[0031] Si (silicon) acts as a deoxidizing agent in an alloy melting process, and produces silicon oxide on surfaces of particles when made into powder.

[0032] The content of Si is 0.01 mass % or more and 0.20 mass % or less, preferably 0.03 mass % or more and 0.15 mass % or less, and more preferably 0.05 mass % or more and 0.10 mass % or less. When the content of Si is within the above range, the viscosity of molten metal can be optimized during powder production, and thus the metal powder for powder metallurgy can be spheroidized and a surface area thereof can be reduced. The amount of silicon oxide generated on the surfaces of the particles can be optimized. As a result, a metal sintered body having high density and high strength can be produced.

[0033] When the content of Si is less than the above lower limit, particularly when Cr is added to the molten metal, Cr is oxidized or the like, and an oxygen amount of the entire powder increases. In this case, the spheroidization and the reduction in surface area of the metal powder for powder metallurgy are insufficient, and the density of the metal sintered body decreases. On the other hand, when the content of Si is more than the above upper limit, the amount of Si becomes excessive, and thus the amount of silicon oxide generated on the surfaces of the particles becomes excessive. Therefore, the density of the metal sintered body decreases.

[0034] The metal sintered body according to the embodiment may contain Cr (chromium). The content of Cr is preferably more than 0 mass % and 0.05 mass % or less, and more preferably 0.01 mass % or more and 0.03 mass % or less. When the content of Cr is within the above range, chromium oxide is generated on the surfaces of the particles of the metal powder for powder metallurgy, and thus, the corrosion resistance of the metal sintered body can be further enhanced. When the content of Cr is within the above range, even when the content of Si is restricted to be relatively low, the spheroidization and the reduction in the surface area of the metal powder for powder metallurgy can be achieved, and thus the density of the metal sintered body can be increased.

[0035] When the content of Cr is less than the above lower limit, the corrosion resistance of the metal sintered body decreases, and the amount of oxide increases depending on the amount of Si, so that the density of the metal sintered body may decrease. On the other hand, when the content of Cr is more than the above upper limit, the balance of the composition of the metal sintered body is impaired, and the thermal expansion properties of the metal sintered body may deviate from a target range or the density of the metal sintered body may decrease.

[0036] In consideration of the quantitative balance between Si and Cr, a ratio Cr / Si of the content of Cr to the content of Si is preferably 0.05 or more and 0.60 or less, more preferably 0.10 or more and 0.50 or less, and still more preferably 0.20 or more and 0.40 or less. When the ratio Cr / Si is within the above range, the quantitative balance between Si and Cr can be optimized. Therefore, the corrosion resistance, the spheroidization, and the reduction in surface area of the metal powder for powder metallurgy can coexist, and the corrosion resistance and the density of the metal sintered body can be increased. When the ratio Cr / Si is within the above range, a metal sintered body having good adhesion of a plating film can be obtained. It is considered that the thickness, composition, and the like of an oxide film present on a surface of the metal sintered body affect the adhesion of the plating film. When the ratio Cr / Si is within the above range, a ratio between each oxide of Si and each oxide of Cr is optimized. Therefore, a metal sintered body having particularly good adhesion of a plating film can be obtained while achieving high corrosion resistance and high density in the metal sintered body.

[0037] When the ratio Cr / Si is less than the above lower limit, the amount of Cr is relatively too small with respect to the amount of Si, so that sufficient corrosion resistance may not be obtained depending on the amount of Si, and the spheroidization and the reduction in surface area of the metal powder for powder metallurgy are impaired. Therefore, the corrosion resistance and the density of the metal sintered body may decrease. The adhesion of the plating film to the metal sintered body may decrease. On the other hand, when the ratio Cr / Si is more than the above upper limit, the amount of Cr becomes relatively too large with respect to the amount of Si, so that the viscosity of the molten metal cannot be sufficiently optimized depending on the amount of Si, and the spheroidization and the reduction in surface area of the metal powder for powder metallurgy are impaired. Therefore, the density of the metal sintered body may decrease. The adhesion of the plating film to the metal sintered body may decrease.

[0038] The metal sintered body according to the embodiment may contain oxygen. Oxygen is contained, for example, as an oxide of each of the above elements. The oxygen content of the metal sintered body is preferably 0.002 mass % or more and 0.037 mass % or less, more preferably 0.003 mass % or more and 0.030 mass % or less, and still more preferably 0.007 mass % or more and 0.023 mass % or less. When the oxygen content is within the above range, the amount of oxides such as silicon oxide and chromium oxide can be optimized. Accordingly, the density and the corrosion resistance of the metal sintered body can be increased.

[0039] When the oxygen content is less than the above lower limit, the corrosion resistance of the metal sintered body may decrease. On the other hand, when the oxygen content is more than the above upper limit, the density of the metal sintered body may decrease.

[0040] The metal sintered body according to the embodiment may contain impurities containing other elements in addition to the elements described above. A total content of the impurities is preferably 1.00 mass % or less, more preferably 0.20 mass % or less, and still more preferably 0.10 mass % or less. The content of each element alone is preferably 0.20 mass % or less, more preferably 0.10 mass % or less, and still more preferably 0.05 mass % or less. When the content is within the range, an effect of the present disclosure is not inhibited by the other elements, and therefore, the content is acceptable.

[0041] The composition and impurities are identified by the following analysis method.

[0042] Examples of the analysis method include iron and steel-atomic absorption spectrometry defined in JIS G 1257:2000, iron and steel-ICP emission spectrometry defined in JIS G 1258:2007, iron and steel-spark discharge emission spectrometry defined in JIS G 1253:2002, iron and steel-fluorescent X-ray spectrometry defined in JIS G 1256:1997, and gravimetric, titration, and absorption spectrometric methods defined in JIS G 1211 to JIS G 1237.

[0043] Specifically, examples thereof include a solid-state optical emission spectrometer manufactured by SPECTRO, in particular a spark discharge optical emission spectrometer, model: SPECTROLAB, type: LAVMB08A, and an ICP device CIROS120 manufactured by Rigaku Corporation.

[0044] In particular, when identifying C (carbon) and S (sulfur), an infrared absorption method after combustion in a current of oxygen (combustion in high frequency induction furnace) defined in JIS G 1211:2011 is also used. Specifically, an example thereof is a carbon and sulfur analyzer CS-200 manufactured by LECO Corporation.

[0045] In particular, when N (nitrogen) and O (oxygen) are identified, methods for determination of nitrogen content for an iron and steel defined in JIS G 1228:1997 and general rules for determination of oxygen in metal materials defined in JIS Z 2613:2006 are also used. Specifically, examples thereof include an oxygen and nitrogen analyzer, TC-300 / EF-300, manufactured by LECO Corporation.1.2. Cross-sectional Structure

[0046] FIG. 1 is a schematic diagram showing an example of a cross section of a metal sintered body 1 according to an embodiment. Specifically, FIG. 1 illustrates a cut surface obtained by cutting the metal sintered body 1 perpendicularly to a surface 10. The metal sintered body 1 according to the embodiment includes metal portions 2 and non-metal portions 3 appearing on the cut surface. The metal portion 2 is a portion formed by sintering a metal powder for powder metallurgy and is a portion made of an alloy. Meanwhile, the non-metal portion 3 is a portion made of a non-metal material unlike the above-described alloy. Examples of the non-metal material include metal oxides and oxides such as silicon oxide in addition to cavities. These can be easily distinguished because they involve differences in brightness and color when the cut surface is observed in an enlarged manner. In the metal sintered body 1, the number of the non-metal portions 3 having a size of 1 μm or more, which are recognized in a predetermined range F, is preferably 120 or less, more preferably 100 or less, and still more preferably 80 or less. When the number of the non-metal portions 3 is within the above range, the metal sintered body 1 has high density, high strength, and high corrosion resistance.

[0047] When the number of the non-metal portions 3 is more than the upper limit, a proportion of the non-metal portions 3 having a relatively low specific gravity increases. Therefore, the density of the metal sintered body 1 may decrease. The non-metal portion 3 is likely to be a starting point of breakage, and therefore, there is a concern that the mechanical strength of the metal sintered body 1 may be reduced. When moisture or the like enters the non-metal portion 3, corrosion of the metal sintered body 1 may be likely to proceed.

[0048] The lower limit of the number of the non-metal portions 3 is not particularly limited, and is preferably 5 or more, and more preferably 10 or more, from the viewpoint of ensuring ease of production, production yield, and the like.

[0049] The number of the non-metal portions 3 is counted as follows.

[0050] First, the metal sintered body 1 is cut perpendicularly to the surface 10. Next, the obtained cut surface is subjected to mirror polishing.

[0051] Next, the cut surface subjected to the mirror polishing is observed with a digital microscope at a magnification of 500 times to acquire an observation image. Examples of the digital microscope include a digital microscope VHX-6000 manufactured by Keyence Corporation. The luminance during image capturing is set as a standard, and the threshold of binarization is set as −23.

[0052] Next, in the observation image, the range F of 300 μm square adjacent to the surface 10 is designated by the digital microscope. The term “adjacent” means that the minimum separation distance between the surface 10 and the range F is 50 μm or less. In the range F, the size and the number of the non-metal portions 3 are identified using differences in brightness and coloration. In this specific operation, the number of the non-metal portions 3 having a size of 1 μm or more is counted by using a foreign substance counting function of the digital microscope.

[0053] It is considered that the number of the non-metal portions 3 is mainly affected by the amount of Si and the amount of Cr in the metal powder for powder metallurgy. The number of the non-metal portions 3 can be reduced by optimizing the amount of Si, the amount of Cr, the ratio Cr / Si, and the like.1.3. Vickers Hardness of Cross Section

[0054] The Vickers hardness of the cross section of the metal sintered body according to the embodiment is preferably 150 or more and 200 or less, and more preferably 160 or more and 190 or less. When the Vickers hardness is within the above range, it is possible to achieve a metal sintered body in which scratches, dents, and the like are less likely to occur. A metal sintered body having good properties such as the tensile strength and the corrosion resistance can be achieved.

[0055] When the Vickers hardness is less than the above lower limit, a scratch, a dent, or the like may be likely to occur. On the other hand, when the Vickers hardness is more than the above upper limit, the tensile strength, the corrosion resistance, and the like may decrease.

[0056] A method for measuring the hardness is as follows.

[0057] First, the metal sintered body is cut perpendicularly to the surface. Next, the cut surface is subjected to mirror polishing, and then the hardness is measured by using a micro Vickers hardness tester. A measurement position is a position at a depth of 1 mm or more from the surface. An indentation load of an indenter during the measurement is set to 0.98 N.1.4. Relative Density

[0058] The relative density of the metal sintered body according to the embodiment is preferably 98.20% or more, more preferably 98.40% or more, and still more preferably 98.60% or more. When the relative density is within the above range, a metal sintered body having sufficiently high density and high strength can be obtained. When the relative density is within the above range, the airtightness of the metal sintered body can be sufficiently enhanced. Accordingly, for example, when the metal sintered body is applied to a hermetic sealing component, a sealing structure having good airtightness can be achieved. It should be noted that the reason why such high airtightness can be obtained is that there are few voids, foreign substances, and the like serving as leak paths inside or on the surface of the metal sintered body.

[0059] The relative density of the metal sintered body is calculated based on the volume and weight of the metal sintered body and the theoretical density determined based on the raw material of the metal sintered body.1.5. Tensile Strength

[0060] The tensile strength of the metal sintered body according to the embodiment is preferably 500 MPa or more, more preferably 515 MPa or more, and still more preferably 530 MPa. When the tensile strength is within the above range, a metal sintered body having sufficiently high strength and high reliability can be obtained.

[0061] An upper limit of the tensile strength may not be set, and the tensile strength is preferably 700 MPa or less, and more preferably 650 MPa or less in consideration of the possibility that the toughness decreases when the tensile strength is too high.

[0062] In a measurement of the tensile strength, first, a B-type tensile test piece defined in JIS Z 2551: 2021 is prepared as the metal sintered body according to the embodiment. Next, this B-type tensile test piece is subjected to a tensile test in accordance with a metal material tensile test method defined in JIS Z 2241: 2022, and the tensile strength is calculated.1.6. Thermal Expansion Properties

[0063] A linear expansion coefficient of the metal sintered body according to the embodiment is preferably 4.3×10−6 / ° C. or higher and 5.3×10−6 / ° C. or lower at 30° C. to 400° C. When the linear expansion coefficient is within the above range, in a case where the metal sintered body is joined to glass or ceramics, a difference in thermal expansion between them can be reduced. Accordingly, generation of stress in a joint portion can be prevented.

[0064] The linear expansion coefficient of the metal sintered body is measured by a thermal expansion measuring instrument.2. Use

[0065] The metal sintered body according to the embodiment has good thermal expansion properties, high density, and high strength, and therefore, the metal sintered body is preferably used as, for example, a component to be joined to glass or ceramics. Accordingly, a defect of a joint portion due to thermal expansion can be prevented.

[0066] Such a metal sintered body is used as a whole or a part of, for example, a component for an optical device, a component for an electronic device, a component for an electrical device, a component for a transport device, a component for a machine, a component for a plant, and a decorative article.3. Method for Producing Metal Sintered Body

[0067] FIG. 2 is a flowchart showing an example of a method for producing the metal sintered body.

[0068] The method for producing the metal sintered body shown in FIG. 2 includes a composition preparation step S102, a molding step S104, a degreasing step S106, and a sintering step S108. Hereinafter, the steps will be sequentially described.3.1. Composition Preparation Step

[0069] In the composition preparation step S102, a molding composition containing a metal powder for powder metallurgy and an organic binder is obtained. Examples of the form of the molding composition include a kneaded product and a granulated powder. The metal powder for powder metallurgy will be described in detail later.

[0070] As the organic binder, a resin that can be decomposed in a short time in a degreasing treatment and a sintering treatment is used. Examples of the resin include polyolefins such as polyethylene, polypropylene, and an ethylene-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene-based resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, polyether, polyvinyl alcohol, polyvinyl pyrrolidone, or copolymers thereof, various waxes, paraffins, higher fatty acids, higher alcohols, higher fatty acid esters, and higher fatty acid amides, and one type or a mixture of two or more types among these can be used.

[0071] A mixing ratio of the organic binder is preferably such an amount that a space factor of the metal powder for powder metallurgy in the molding composition is 55 volume % or more and 75 volume % or less.

[0072] In addition to these, various additives such as a plasticizer, a lubricant, an antioxidant, a degreasing accelerator, and a surfactant may be added to the molding composition.3.2. Molding Step

[0073] In the molding step S104, the molding composition is molded into an intended shape. Accordingly, a molded body can be obtained.

[0074] Examples of a molding method include an injection molding method, a compression molding method, an extrusion molding method, and an additive manufacturing method. Examples of the additive manufacturing method include a material extrusion deposition method and a binder jetting method. From the viewpoint of near net shaping and mass productivity, an injection molding method is preferably used.3.3. Degreasing Step

[0075] In the degreasing step S106, the molded body is degreased to obtain a degreased body.

[0076] Examples of the degreasing treatment include a method of decomposing the organic binder by heating the molded body, and a method of exposing the molded body to a gas that decomposes the organic binder. All or a part of the organic binder in the molded body is removed by the degreasing treatment.

[0077] When the method of heating the molded body is used, heating conditions for the molded body are preferably a temperature of 100° C. or higher and 750° C. or lower and a time of 0.1 hours or longer and 20 hours or shorter, and more preferably a temperature of 150° C. or higher and 600° C. or lower and a time of 0.5 hours or longer and 15 hours or shorter, although the heating conditions slightly vary depending on the composition and the blending amount of the organic binder.

[0078] An atmosphere for heating the molded body is not particularly limited, and examples thereof include an inert atmosphere such as nitrogen and argon, an oxidizing atmosphere such as air, and a reduced-pressure atmosphere obtained by reducing the pressure of these atmospheres.3.4. Sintering Step

[0079] In the sintering step S108, the degreased body is subjected to the sintering treatment to obtain a metal sintered body.

[0080] A sintering temperature varies depending on a composition ratio, a particle diameter, and the like of the metal powder for powder metallurgy, and is set to, for example, about 1000° C. or higher and 1450° C. or lower. The sintering temperature is preferably about 1300° C. or higher and 1400° C. or lower. A sintering time is set to 0.2 hours or longer and 7 hours or shorter, and is preferably set to about 1 hour or longer and 6 hours or shorter.

[0081] Examples of an atmosphere in the sintering treatment include a reducing atmosphere such as hydrogen, an inert atmosphere such as nitrogen and argon, and a reduced-pressure atmosphere obtained by reducing the pressure of these atmospheres. The pressure in the reduced-pressure atmosphere is not particularly limited as long as the pressure is lower than a normal pressure (100 kPa), and is preferably 10 kPa or less, and more preferably 1 kPa or less. Accordingly, the gas remaining in the degreased body can be particularly efficiently discharged, and the density of the finally obtained metal sintered body can be increased.

[0082] The produced metal sintered body may be subjected to an annealing treatment or the like as necessary. The annealing treatment is performed for the purpose of, for example, removing residual stress.4. Metal Powder for Powder Metallurgy

[0083] Next, an example of the metal powder for powder metallurgy used for the production of the metal sintered body will be described.

[0084] An average particle diameter of the metal powder for powder metallurgy used for the production of the metal sintered body is preferably 2.0 μm or more and 15.0 μm or less, more preferably 3.0 μm or more and 10.0 μm or less, and still more preferably 4.0 μm or more and 9.0 μm or less. When the average particle diameter is within the above range, the filling property can be further enhanced while ensuring the fluidity of the metal powder for powder metallurgy. When the average particle diameter is within the above range, the sinterability of the metal powder for powder metallurgy can be enhanced.

[0085] The average particle diameter of the metal powder for powder metallurgy is a particle diameter D50 at which a cumulative frequency is 50% from a small diameter side in a volume-based cumulative particle size distribution acquired using a laser diffraction particle size distribution measurement device.

[0086] A specific surface area of the metal powder for powder metallurgy used for the production of the metal sintered body is preferably 0.20 m2 / g or more and 0.70 m2 / g or less, more preferably 0.43 m2 / g or more and 0.65 m2 / g or less, and still more preferably 0.45 m2 / g or more and 0.60 m2 / g or less. When the specific surface area is within the above range, it is possible to approximate closest packing when the metal powder for powder metallurgy is molded. Accordingly, the filling property of the metal powder for powder metallurgy is particularly favorable.

[0087] The specific surface area of the metal powder for powder metallurgy is measured using, for example, a BET specific surface area measurement device HM1201-010 manufactured by Mountech Co., Ltd.

[0088] An average circularity of the metal powder for powder metallurgy used for the production of the metal sintered body is preferably 0.85 or more and 0.97 or less, more preferably 0.87 or more and 0.96 or less, and still more preferably 0.89 or more and 0.95 or less. When the average circularity is within the above range, the fluidity and the filling property of the metal powder for powder metallurgy is particularly favorable. Accordingly, a high-density molded body can be produced, and finally, a metal sintered body having high density and good mechanical properties can be produced.

[0089] The average circularity of the metal powder for powder metallurgy is acquired as follows.

[0090] First, an image (secondary electron image) of the metal powder for powder metallurgy is captured by a scanning electron microscope (SEM). Next, the obtained image is read into image processing software. As the image processing software, for example, image analysis type particle size distribution measurement software “Mac-View” manufactured by Mountech Co., Ltd. is used. Note that, an imaging magnification is adjusted such that 50 to 100 particles appear in one image. Then, a plurality of images are acquired to obtain images of a total of 300 or more particles.

[0091] Next, the circularity of images of 300 or more particles is calculated using software. When the circularity is represented by e, an area of the particle image is represented by S, and a perimeter of the particle image is represented by L, the circularity e is determined according to the following formula.e=4πS / L2

[0092] The tap density of the metal powder for powder metallurgy used for the production of the metal sintered body is preferably 4.10 g / cm3 or more and 4.80 g / cm3 or less, more preferably 4.20 g / cm3 or more and 4.70 g / cm3 or less, and still more preferably 4.30 g / cm3 or more and 4.60 g / cm3 or less. When the tap density is within the above range, the filling property of the metal powder for powder metallurgy is particularly favorable.

[0093] The tap density of the metal powder for powder metallurgy is measured by a powder property evaluation device, Powder Tester (registered trademark) PT-X manufactured by Hosokawa Micron Group. Note that, before the tap density is measured, the metal powder for powder metallurgy as a measurement target is preferably left to stand in an environment at a temperature of 25° C. and a relative humidity of 50% for 1 hour or longer.

[0094] A Hausner ratio of the metal powder for powder metallurgy used for the production of the metal sintered body is preferably 1.30 or more and 1.50 or less, more preferably 1.32 or more and 1.47 or less, and still more preferably 1.35 or more and 1.45 or less. The Hausner ratio is a ratio of a tap density to a bulk density, and is used as an index indicating the fluidity when an impact is intermittently applied. When the Hausner ratio is within the above range, the fluidity of the metal powder for powder metallurgy is particularly favorable.

[0095] The bulk density of the metal powder for powder metallurgy is measured by a powder property evaluation device, Powder Tester (registered trademark) PT-X manufactured by Hosokawa Micron Group. Note that, before the bulk density is measured, the metal powder for powder metallurgy as a measurement target is preferably left to stand in an environment at a temperature of 25° C. and a relative humidity of 50% for 1 hour or longer.5. Method for Producing Metal Powder for Powder Metallurgy

[0096] Next, an example of a method for producing a metal powder for powder metallurgy will be described.

[0097] The metal powder for powder metallurgy may be produced according to any production method, and is produced according to, for example, an atomization method. In the atomization method, a molten metal is caused to flow down from a crucible and collide with a fluid such as a liquid or a gas ejected at a high speed. The molten metal colliding with the fluid falls inertially, and therefore, at this time, becomes spherical droplets. As a result, it is possible to produce a metal powder for powder metallurgy, which has a high average circularity and a relatively small specific surface area despite a relatively small diameter.

[0098] Examples of the atomization method include a water atomization method, a gas atomization method, and a rotary water atomization method depending on the type of a cooling medium and a device configuration, and the water atomization method is preferably used from the viewpoint of easily achieving the average particle diameter, the average circularity, the specific surface area, and the like described above.

[0099] A flow-down amount of the molten metal varies depending on a device size and the like, and is preferably more than 1.0 kg / min and 20.0 kg / min or less, and more preferably 2.0 kg / min or more and 10.0 kg / min or less. Accordingly, it is possible to optimize the amount of molten metal flowing down during a certain time, and thus a metal powder for powder metallurgy, which has a narrow particle size distribution and in which each particle is sufficiently spherical can be efficiently produced. As a result, it is possible to produce a metal powder for powder metallurgy, which has a high average circularity and a relatively small specific surface area despite a relatively small diameter.

[0100] A temperature (casting temperature) of the molten metal in the crucible is preferably set, with respect to a melting point Tm [° C.] of a constituent material of the metal powder for powder metallurgy, to Tm+100° C. or higher and Tm+350° C. or lower, more preferably Tm+180° C. or higher and Tm+320° C. or lower, and still more preferably Tm+250° C. or higher and Tm+300° C. or lower. Accordingly, it is possible to ensure a time during which the molten metal is present longer than that in the related art when the molten metal is miniaturized and solidified using various atomization methods. As a result, it is possible to produce a metal powder for powder metallurgy, which has a high average circularity and a relatively small specific surface area despite a small diameter.

[0101] In the various atomization methods, an outer diameter of a fine flow when the molten metal flows down is not particularly limited, and is preferably 3.0 mm or less, and more preferably 0.3 mm or more and 2.0 mm or less. Accordingly, the fluid can be easily and uniformly applied to the molten metal, and thus liquid droplets having an appropriate size can be easily and uniformly scattered. As a result, a metal powder for powder metallurgy, which has an average particle diameter as described above and a good average circularity, can be produced with a relatively narrow particle size distribution.

[0102] Moreover, in the water atomization method, water injected at a high speed is injected in an inverted conical shape, and the molten metal is caused to collide with the vicinity of the apex. Accordingly, the vicinity of a collision point becomes a negative pressure due to a water film, and thus the molten metal becomes finer. In addition, oxidation of the molten metal can be reduced, and the spheroidization can be achieved even when the metal powder for powder metallurgy, which is to be produced, is fine. The negative pressure in the vicinity of the collision point is preferably 10 kPa or more and 150 kPa or less, and more preferably 30 kPa or more and 120 kPa or less. Accordingly, the metal powder for powder metallurgy, in which the particle diameter and the circularity are optimized, can be efficiently produced. In addition, when the negative pressure is increased within this range, the miniaturization and the spheroidization tend to be promoted.

[0103] When an apex angle of the injected water (an angle formed inside the apex of the inverted cone) is optimized, the pressure in the vicinity of the collision point formed by the water film can be further reduced, and the time until the molten metal flowing down reaches the collision point can be prolonged. Accordingly, even when the metal powder for powder metallurgy, which is to be produced, is fine, the spheroidization can be sufficiently achieved. The apex angle of the injected water is preferably 3° or more and 15° or less, and more preferably 5° or more and 10° or less. When the apex angle is reduced within this range, the miniaturization and the spheroidization tend to be promoted.

[0104] In addition, the produced metal powder for powder metallurgy may be classified as necessary. Examples of classification methods include dry classification such as sieving classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.6. Effects of Embodiment

[0105] As described above, the metal sintered body according to the embodiment contains Ni in a content of 28.00 mass % or more and 32.00 mass % or less, Co in a content of 15.00 mass % or more and 20.00 mass % or less, and Si in a content of 0.01 mass % or more and 0.20 mass % or less, with the balance being Fe as a main component and impurities.

[0106] According to such a configuration, a metal sintered body having good thermal expansion properties, high density, and high strength can be obtained.

[0107] In the metal sintered body according to the embodiment, the content of Si is preferably 0.05 mass % or more and 0.10 mass % or less.

[0108] According to such a configuration, it is possible to achieve the spheroidization and the reduction in surface area of the metal powder for powder metallurgy during powder production. The amount of silicon oxide generated on surfaces of particles can be optimized. Accordingly, a high-density molded body is obtained, and a high-density and high-strength metal sintered body can be obtained.

[0109] In the metal sintered body according to the embodiment, the content of Cr is preferably more than 0 mass % and 0.05 mass % or less.

[0110] According to such a configuration, chromium oxide is generated on the surfaces of the particles of the metal powder for powder metallurgy, and thus, the corrosion resistance of the metal sintered body can be further enhanced. When the content of Cr is within the above range, even when the content of Si is restricted to be relatively low, the spheroidization and the reduction in surface area of the metal powder for powder metallurgy can be achieved, and thus the density of the metal sintered body can be increased.

[0111] In the metal sintered body according to the embodiment, the ratio Cr / Si of the content of Cr to the content of Si is preferably 0.05 or more and 0.60 or less.

[0112] According to such a configuration, the quantitative balance between Si and Cr can be optimized, so that the corrosion resistance, the spheroidization, and the reduction in surface area of the metal powder for powder metallurgy can coexist, and the corrosion resistance and the density of the metal sintered body can be increased. When the ratio Cr / Si is within the above range, a metal sintered body having good adhesion of a plating film can be produced.

[0113] In the metal sintered body according to the embodiment, the relative density is preferably 98.20% or more.

[0114] According to such a configuration, a metal sintered body having sufficiently high density and high strength can be obtained. In addition, a metal sintered body having sufficiently high airtightness can be obtained.

[0115] In the metal sintered body according to the embodiment, the tensile strength is preferably 500 MPa or more.

[0116] According to such a configuration, a metal sintered body having sufficiently high strength and high reliability can be obtained.

[0117] In the metal sintered body 1 according to the embodiment, the number of the non-metal portions 3 in the predetermined range F is preferably 120 or less when mirror polishing is performed on a cut surface obtained by cutting the metal sintered body 1 perpendicularly to the surface 10, and an observation image is acquired by observing the cut surface subjected to the mirror polishing. The predetermined range F is a range F of 300 μm square adjacent to the surface 10 in the observation image. The cut surface is observed at a magnification of 500 times with a digital microscope, and the number of the non-metal portions 3 is counted for the range F. The non-metal portion 3 refers to a portion made of a component other than metal and having a size of 1 μm or more.

[0118] According to such a configuration, the metal sintered body 1 having high density, high strength, and high corrosion resistance can be obtained.

[0119] Although the metal sintered body according to the present disclosure has been described based on the preferred embodiment, the present disclosure is not limited thereto. For example, the metal sintered body according to the present disclosure may be subjected to secondary processing.Examples

[0120] Next, specific examples of the present disclosure will be described.7. Production of Metal Sintered Body

[0121] FIG. 3 is Table 1 showing a configuration of a metal sintered body of each sample No.

[0122] FIG. 4 is Table 2 showing evaluation results of the metal sintered body of each sample No.

[0123] First, raw materials having the compositions shown in Table 1 (FIG. 3) were melted in a high-frequency induction furnace and pulverized according to a water atomization method to obtain a metal powder for powder metallurgy. Various conditions in the water atomization method are as follows.

[0124] Outer diameter of fine flow of molten metal flowing down: 2.0 mm

[0125] Flow-down amount of molten metal: 5.0 kg / min

[0126] Casting temperature: Tm+270° C.

[0127] Negative pressure in the vicinity of the collision point of water: 50 kPa to 100 kPa

[0128] Apex angle of water: 5° to 10°

[0129] Next, the metal powder for powder metallurgy and an organic binder were kneaded to produce a compound for molding. The space factor of the metal powder for powder metallurgy in the compound for molding was 65 volume %. The organic binder is a mixture of a polymer made of polypropylene and polystyrene, a wax, and a plasticizer. A ratio of the polymer is 60 mass %, a ratio of the wax is 30 mass %, and a ratio of the plasticizer is 10 mass %.

[0130] Next, a molded body was produced according to a metal powder injection molding method (MIM method) using the obtained compound for molding. As a mold, a mold for a B-type tensile test piece defined in JIS Z 2551: 2021 was used. The molding pressure was 2000 kgf / cm2.

[0131] Next, the obtained molded body was subjected to a degreasing step and a sintering step to obtain a metal sintered body. Regarding the degreasing step, the temperature was 500° C., the time was 1 hour, and the atmosphere was N2. In addition, regarding the sintering step, the temperature was 1350° C., the time was 3 hours, and the atmosphere was Ar.

[0132] Table 1 shows a composition of the metal sintered body, an oxygen content, the number of non-metal portions in a predetermined range of a cross section, and the Vickers hardness of the cross section. The metal sintered body contained trace amounts of impurities such as C, P, Mn, Cu, and Zr, and the content of each impurity element was less than 0.01 mass %.

[0133] In addition, in Tables 1 and 2, when the metal sintered body of each sample No. corresponds to the present disclosure, the metal sintered body was described as “Example”, and when the metal sintered body of each sample No. does not correspond to the present disclosure, the metal sintered body was described as “Comparative Example”.

[0134] FIG. 5 is an electron microscope image obtained by observing the cross section of the metal sintered body 1 of Sample No. 3 as an Example.

[0135] FIG. 6 is an electron microscope image obtained by observing the cross section of a metal sintered body 1′ of Sample No. 11 as a Comparative Example.

[0136] In FIGS. 5 and 6, in the range F adjacent to the surface 10, the metal portion 2 is shown in a relatively light color, and the non-metal portion 3 is shown in a relatively dark color.

[0137] In FIG. 5 showing the metal sintered body 1 of the Example, it can be seen that the number of the non-metal portions 3 is smaller than that in FIG. 6 showing the metal sintered body 1′ of the Comparative example.8. Evaluation of Metal Sintered Body

[0138] The metal sintered body of each sample No. was evaluated as follows.8.1. Relative Density

[0139] The relative density of the metal sintered body of each sample No. was calculated from the volume, the weight, and the theoretical density. Then, the calculated relative density was evaluated in view of the following evaluation criteria. Evaluation results are shown in Table 2 (FIG. 4).

[0140] A: the relative density is 98.60% or more

[0141] B: the relative density is 98.40% or more and less than 98.60%

[0142] C: the relative density is 98.20% or more and less than 98.40%

[0143] D: the relative density is less than 98.20%8.2. Tensile Strength

[0144] The tensile strength of the metal sintered body of each sample No. was measured. The measurement of the tensile strength was performed according to a metal material tensile test method defined in JIS Z 2241: 2022. Then, measurement results were evaluated based on the following evaluation criteria. Evaluation results are shown in Table 2.

[0145] A: the tensile strength is 530 MPa or more

[0146] B: the tensile strength is 515 MPa or more and less than 530 MPa

[0147] C: the tensile strength is 500 MPa or more and less than 515 MPa

[0148] D: the tensile strength is less than 500 MPa8.3. Ni Plating Adhesion

[0149] The Ni plating adhesion of the metal sintered body of each sample No. was evaluated according to the following method.

[0150] First, an electrolytic Ni plating treatment was performed on the metal sintered body to form a Ni plating film. Next, the adhesion strength of the Ni plating film was measured by the “soldering test” defined in JIS H 8504: 1999. Then, the Ni plating adhesion was relatively evaluated by comparing measurement results with the following evaluation criteria. Evaluation results are shown in Table 2.

[0151] A: the adhesion strength of the Ni plating film is particularly high

[0152] B: the adhesion strength of the Ni plating film is slightly high

[0153] C: the adhesion strength of the Ni plating film is slightly low

[0154] D: the adhesion strength of the Ni plating film is particularly low8.4. Corrosion Resistance

[0155] The corrosion resistance of the metal sintered body of each sample No. was evaluated according to the following method.

[0156] First, the metal sintered body was subjected to a neutral salt spray test defined in JIS Z 2371: 2015. As the spray liquid, 5% neutral salt water was used, and the test was performed at 35° C. for 7 hours. Next, an appearance of the metal sintered body after the test was observed with a digital microscope, and an area ratio of a region discolored due to corrosion was calculated. Then, the corrosion resistance was relatively evaluated by comparing the calculated area ratio with the following evaluation criteria. Evaluation results are shown in Table 2.

[0157] A: the area ratio of the discolored region is less than 35%

[0158] B: the area ratio of the discolored region is 35% or more and less than 55%

[0159] C: the area ratio of the discolored region is 55% or more and less than 75%

[0160] D: the area ratio of the discolored region is 75% or more

[0161] FIG. 7 is a photograph showing the appearance of the metal sintered body 1 of Sample No. 3 as an Example after the neutral salt spray test.

[0162] FIG. 8 is a photograph showing the appearance of the metal sintered body 1′ of Sample No. 11 as a Comparative Example after the neutral salt spray test.

[0163] In FIGS. 7 and 8, the region discolored in the test is shown in a darker color than the surroundings. It can be seen that the area of the discolored region is smaller in FIG. 7 showing the metal sintered body 1 in the example than in FIG. 8 showing the metal sintered body 1′ of the comparative example.8.5. Thermal Expansion Properties

[0164] The thermal expansion properties of the metal sintered body of each sample No. were evaluated according to the following method.

[0165] First, a linear expansion coefficient of the metal sintered body at 30° C. to 400° C. was measured by a thermal expansion measurement device. Then, the thermal expansion properties were relatively evaluated by comparing measurement results with the following evaluation criteria. Evaluation results are shown in Table 2.

[0166] A: the linear expansion coefficient is 4.3×10−6 / ° C. to 5.3×10−6 / ° C.

[0167] C: the linear expansion coefficient is outside the above range of A 8.6. Consideration

[0168] From the above evaluation results, the following was revealed.

[0169] In the metal sintered body of each Example, good results were obtained in terms of the relative density and the tensile strength. These results are considered to be due to the fact that the fluidity and the filling property of the metal powder for powder metallurgy used for the production of the metal sintered body were good as a result of optimizing the composition such as the amount of Si, the ratio Cr / Si, and the oxygen content.

[0170] In the metal sintered body produced using the metal powder for powder metallurgy of each Example, the linear expansion coefficient was equal to that of glass or ceramics, and the thermal expansion properties were good.

[0171] The metal sintered body produced using the metal powder for powder metallurgy of each Example had good Ni plating adhesion and corrosion resistance. These results are considered to be caused by the optimization of the amount of Si and the ratio Cr / Si.

Claims

1. A metal sintered body comprising:Ni in a content of 28.00 mass % or more and 32.00 mass % or less;Co in a content of 15.00 mass % or more and 20.00 mass % or less; andSi in a content of 0.01 mass % or more and 0.20 mass % or less,with a balance being Fe as a main component and impurities.

2. The metal sintered body according to claim 1, whereinthe content of Si is 0.05 mass % or more and 0.10 mass % or less.

3. The metal sintered body according to claim 1, whereina content of Cr is more than 0 mass % and 0.05 mass % or less.

4. The metal sintered body according to claim 3, whereina ratio Cr / Si of the content of Cr to the content of Si is 0.05 or more and 0.60 or less.

5. The metal sintered body according to claim 1, which has a relative density of 98.20% or more.

6. The metal sintered body according to claim 1, which has a tensile strength of 500 MPa or more.

7. The metal sintered body according to claim 5, whereinwhen mirror polishing is performed on a cut surface obtained by cutting the metal sintered body perpendicularly to a surface, an observation image is acquired by observing the mirror-polished cut surface at a magnification of 500 times with a digital microscope, and the number of non-metal portions having a size of 1 μm or more and formed of a component other than a metal is counted in a range of 300 μm square adjacent to the surface in the observation image,the number of the non-metal portions is 120 or less.

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