Metal powder for injection molding and method for producing sintered body

Abstract

Provided are: a metal powder for injection molding, with which it is possible to produce an injection molded body having a low shrinkage rate during sintering and with which it is possible to produce a metal sintered body having high shape accuracy; and a method for producing a sintered body with which it is possible to produce a metal sintered body having high shape accuracy. The metal powder for injection molding is characterized in that in a volume-based cumulative particle size distribution curve obtained by a laser diffraction method, the particle size D50 is 1.0 [mu] m or more and less than 10.0 [mu] m when the cumulative value from the small diameter side is 50%, the average roundness is 0.86-0.95, and the particle size D50 is 1.0-10.0 [mu] m. When a composite for evaluation is prepared by kneading with an organic binder in such a manner that the melt viscosity measured using a capillary rheometer at a shear rate of 100 [s-1] and a temperature of 150 DEG C is 120 [Pas] (1200 [P]), the powder filling rate in the composite for evaluation is 63-75 vol% (inclusive).

Description

Technical Field

[0001] The present invention relates to a method for producing metal powder for injection molding and a sintered body. Background Art

[0002] Patent document 1 discloses a method for manufacturing a metal sintered body, which comprises: a molding step, in which metal powder with an average particle size of 0.1 to 40 μm manufactured by a gas atomization method or a water atomization method is molded by a metal powder injection molding method to obtain a molded body; a degreasing step, in which the molded body is degreased to obtain a degreased body; and a sintering step, in which the degreased body is sintered to obtain a sintered body.

[0003] According to such a production method, the sintering density can be increased, and a metal sintered body having high mechanical strength can be produced.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 11-181501.

[0007] However, during the firing process, the degreased body shrinks as sintering progresses. This shrinkage of the degreased body reduces the shape accuracy of the resulting metal sintered body. Therefore, a technical problem is to suppress the shrinkage during sintering and achieve a metal powder for injection molding that can produce metal sintered bodies with high shape accuracy. Summary of the Invention

[0008] Regarding the metal powder for injection molding according to the application example of the present invention, in a volume-based cumulative particle size distribution curve obtained by a laser diffraction method, the particle size D50 at which the cumulative value from the small diameter side is 50% is 1.0 μm or more and less than 10.0 μm, the average roundness is 0.86 or more and 0.95 or less, and when subjected to a capillary rheometer at a shear rate of 100 [s -1 When the evaluation composite is prepared by kneading with an organic binder so that the melt viscosity measured at 150°C is 120 [Pa･s] (1200 [P]), the powder filling rate in the evaluation composite is 63 volume % or more and 75 volume % or less.

[0009] The manufacturing method of the sintered body involved in the application example of the present invention includes: a kneading step, mixing the metal powder for injection molding involved in the application example of the present invention with an organic binder to prepare a composite; a molding step, injection molding the composite to obtain a molded body; and a sintering step, sintering the molded body to obtain a sintered body. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1It is a process diagram showing the configuration of a method for producing a sintered body according to the embodiment.

[0011] Description of Reference Numerals

[0012] S101: kneading process; S102: forming process; S103: degreasing process; S104: sintering process. DETAILED DESCRIPTION

[0013] Hereinafter, the method for producing the metal powder for injection molding and the sintered body according to the present invention will be described in detail based on the preferred embodiments shown in the drawings.

[0014] 1. Metal powder for injection molding

[0015] The metal powder for injection molding according to the embodiment is provided for molding by metal injection molding (MIM). The obtained molded body is degreased and sintered to obtain a metal sintered body.

[0016] 1.1. Powder filling rate in the evaluation compound

[0017] The metal powder for injection molding according to the embodiment has a particle size D50 of 1.0 μm or more and less than 10.0 μm at a cumulative value of 50% from the smaller diameter side in a volume-based cumulative particle size distribution curve obtained by laser diffraction.

[0018] Furthermore, the average circularity of the metal powder for injection molding according to the embodiment is 0.86 or more and 0.95 or less.

[0019] Furthermore, when a composite for evaluation is prepared using the metal powder for injection molding according to the embodiment, the metal powder for injection molding according to the embodiment is configured so that the composite for evaluation satisfies predetermined conditions.

[0020] Specifically, a composite for evaluation was prepared by kneading metal powder for injection molding with an organic binder. The organic binder used was a resin composition containing 26% by mass of polyethylene, 30% by mass of polystyrene, 28% by mass of paraffin wax, and 16% by mass of acetyl tributyl citrate (TBC).

[0021] Next, the evaluation compound was heated to 150°C and the shear rate was measured at 100 [s -1 ]. Viscosity was measured using a testing machine (capillary rheometer) that measures the melt viscosity of a sample containing a polymer material when shear flow is induced. The capillary rheometer has a capillary length of 10 mm, a die diameter of 1 mm, a furnace diameter of 9.55 mm, and a load cell capacity of 20 kN.

[0022] The order of measurement is as follows. First, add the evaluation compound into the furnace. Then, heat the evaluation compound to melt it. Then, measure the viscosity while squeezing the melt with a piston. The viscosity is measured when the piston extrusion speed is 0.5, 10, 20, 50, 100, 200, 500 [mm / min]. Then, plot the logarithm of the shear rate and viscosity corresponding to each extrusion speed. Then, perform a linear fit on the obtained flow curve. Then, calculate the viscosity when the shear rate is 100 [s -1 ]when the viscosity is 0.

[0023] The amount of organic binder used in the evaluation compound was set so that the viscosity measured as described above was 120 [Pa·s]. Furthermore, the metal powder for injection molding according to the embodiment, prepared so that the viscosity reached 120 [Pa·s], had a powder filling rate of 63% by volume or more and 75% by volume or less in the evaluation compound.

[0024] Even with a relatively small particle size D50, the aforementioned powder filling ratio can be considered a relatively high value. The ability to increase the powder filling ratio is associated with the ability to suppress the amount of organic binder used. Therefore, by using the metal powder for injection molding according to the embodiment, even when containing powders with a small diameter and a large specific surface area, a composite with a low organic binder content can be achieved, for example, when mass-producing sintered bodies. Furthermore, by using such a composite, it is possible to produce metal sintered bodies with high density and high surface accuracy. Furthermore, since the shrinkage associated with degreasing can be suppressed, the reduction in the shape accuracy of the metal sintered body associated with deformation during degreasing and sintering can be suppressed.

[0025] The powder filling rate in the evaluation composite material may be 63% by volume or more and 75% by volume or less, preferably 64% by volume or more and 72% by volume or less, and more preferably 65% ​​by volume or more and 70% by volume or less.

[0026] The powder filling rate is primarily controlled by the particle size, particle size distribution, roundness, and specific surface area of ​​the injection molding metal powder. For example, even if the particle size remains constant, increasing the average roundness or reducing the specific surface area can reduce the amount of organic binder required to achieve a desired viscosity. This can increase the powder filling rate in the evaluation composite. Furthermore, while also related to the specific surface area, optimizing the oxygen content of the injection molding metal powder to within a predetermined range can also improve the powder filling rate.

[0027] The powder filling rate in the evaluation compound was calculated by the following formula: In the following formula, the metal powder for injection molding is simply referred to as "powder."

[0028] Powder filling rate = Volume of powder contained in the evaluation compound × 100 / (Volume of organic binder contained in the evaluation compound + Volume of powder contained in the evaluation compound)

[0029] On the other hand, the binder filling rate in the evaluation compound is preferably 30% by volume or more and 36% by volume or less, more preferably 31% by volume or more and 35% by volume or less, and even more preferably 32% by volume or more and 34% by volume or less.

[0030] Even when the particle size D50 is relatively small, the binder filling rate can be said to be a relatively low value. Therefore, by using the metal powder for injection molding according to the embodiment, a composite material with a suppressed shrinkage rate during sintering can be realized.

[0031] The binder filling rate in the evaluation compound was calculated by the following formula.

[0032] Binder filling rate = Volume of organic binder contained in the evaluation compound × 100 / (Volume of organic binder contained in the evaluation compound + Volume of powder contained in the evaluation compound)

[0033] As previously mentioned, the particle size D50 of the metal powder for injection molding according to the embodiment is 1.0 μm or more and less than 10.0 μm, preferably 3.0 μm or more and 9.0 μm or less, and more preferably 5.0 μm or more and 8.0 μm or less. This provides a metal powder for injection molding with excellent filling and sintering properties.

[0034] The cumulative particle size distribution curve for deriving the particle size D50 of the injection molding metal powder can be obtained using a laser diffraction scattering particle size distribution measuring instrument. Examples of the laser diffraction scattering particle size distribution measuring instrument include Microtrac and HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[0035] It should be noted that if the particle size D50 of the injection molding metal powder is below the lower limit, the injection molding metal powder is too fine, resulting in reduced filling properties. This results in reduced shape accuracy and density of the sintered metal body. On the other hand, if the particle size D50 of the injection molding metal powder is above the upper limit, the injection molding metal powder is too coarse, resulting in reduced sinterability. This results in reduced shape accuracy and density of the sintered metal body.

[0036] As previously mentioned, the average roundness of the metal powder for injection molding according to the embodiment is 0.86 or higher and 0.95 or lower, preferably 0.88 or higher and 0.93 or lower, and more preferably 0.89 or higher and 0.92 or lower. It should be noted that if the average roundness is below the lower limit, the rotatability of the particles constituting the metal powder for injection molding decreases, and the specific surface area increases, thereby reducing the filling and flowability of the metal powder for injection molding. On the other hand, if the average roundness exceeds the upper limit, the production difficulty of the metal powder for injection molding increases, resulting in higher costs and reduced manufacturing efficiency.

[0037] The roundness of particles contained in the metal powder for injection molding is measured in the following manner.

[0038] First, use a scanning electron microscope (SEM) to capture an image (secondary electron image) of multiple particles. This image is then loaded into image processing software. For example, "Mac-View," an image analysis and particle size distribution measurement software manufactured by Mountech Co., Ltd., can be used. The imaging magnification is adjusted so that 50 to 100 particles are captured in one image. Multiple images are acquired to obtain a total of at least 300 particle images.

[0039] Next, the circularity of each particle image is calculated using software and the average value is obtained. The obtained average value is used as the average circularity calculated from the captured particle images.

[0040] 1.2. Materials Constituents of Metal Powder for Injection Molding

[0041] The material constituting the metal powder for injection molding is not particularly limited; any metal material can be used as long as it is sinterable. Examples include single elements such as Fe, Ni, Co, Cu, Ag, Al, Ti, Mo, W, Ta, and Zr, or alloys and intermetallic compounds containing these as primary components.

[0042] Examples of Fe-based alloys include stainless steels such as austenitic stainless steel, martensitic stainless steel, and precipitation-hardening stainless steel, low-carbon steel, carbon steel, heat-resistant steel, die steel, high-speed tool steel, Fe-Ni alloys, and Fe-Ni-Co alloys.

[0043] Examples of the Ni-based alloy include Ni—Cr—Fe-based alloys, Ni—Cr—Mo-based alloys, and Ni—Fe-based alloys.

[0044] Examples of the Co-based alloy include a Co-Cr-based alloy, a Co-Cr-Mo-based alloy, and a Co-Al-W-based alloy.

[0045] Examples of the Ti-based alloy include alloys of Ti and metal elements such as Al, V, Nb, Zr, Ta, and Mo. Specific examples include Ti-6Al-4V and Ti-6Al-7Nb.

[0046] It should be noted that the metal powder for injection molding can be an aggregate of particles having a single composition, or an aggregate of particles having different compositions, that is, an aggregate of two or more particles. The latter method can produce a metal powder for injection molding that can produce a metal sintered body that combines the properties of each composition.

[0047] Among them, the constituent material of the metal powder for injection molding is preferably precipitation-hardening stainless steel. Precipitation-hardening stainless steel has excellent mechanical strength and toughness due to the formation of precipitates.

[0048] Examples of precipitation-hardening stainless steel include SUS630 (17-4PH) and SUS631 (17-7PH).

[0049] 1.3. Various properties of metal powder for injection molding

[0050] The ratio of the tap density to the true density of the metal powder for injection molding is not particularly limited, but is preferably 0.610 to 0.640, and more preferably 0.615 to 0.630. When the ratio of the tap density to the true density is within this range, a metal powder for injection molding with fewer irregularly shaped particles and excellent filling properties and flowability can be obtained.

[0051] It should be noted that if the ratio of tap density to true density is below the lower limit, the filling rate of the injection molding metal powder in the composite may be reduced. This requires increasing the amount of organic binder used in the composite, which may reduce the shape accuracy of the metal sintered body. On the other hand, if the ratio of tap density to true density is above the upper limit, the production of the injection molding metal powder becomes more difficult, which may lead to higher costs and reduced manufacturing efficiency.

[0052] The tap density (closed bulk density) of the metal powder for injection molding was measured using a powder property evaluation device, POWDER TESTER (registered trademark), PT-X, manufactured by Hosokawa Micron Corporation.

[0053] The oxygen content of the metal powder for injection molding is preferably 1000 ppm to 6000 ppm by mass, more preferably 1500 ppm to 5000 ppm, and even more preferably 2000 ppm to 4000 ppm. If the oxygen content is within this range, both the filling and sintering properties of the metal powder for injection molding can be improved. Furthermore, although this depends on the type of steel used and other properties of the metal powder for injection molding, if the oxygen content is within this range, a metal powder for injection molding with excellent affinity for organic binders can be obtained. This makes it possible to achieve a metal powder for injection molding that achieves a predetermined melt viscosity while suppressing the amount of organic binder used.

[0054] It should be noted that if the oxygen content is below the lower limit, the affinity between the injection molding metal powder particles and the organic binder may be reduced, thereby reducing the filling capacity of the injection molding metal powder in the composite. Furthermore, the influence of the oxygen content is more likely to be apparent, potentially causing uneven density and shape in the sintered body. On the other hand, if the oxygen content is above the upper limit, the sinterability of the injection molding metal powder may be reduced. Furthermore, the affinity with the organic binder may be reduced.

[0055] The oxygen content of the metal powder for injection molding can be measured, for example, in accordance with the general rules for oxygen quantification of metallic materials specified in JIS Z2613:2006. Specifically, the measurement can be performed using an oxygen-nitrogen analyzer, TC-300 / EF-300, manufactured by LECO, or an oxygen-nitrogen-hydrogen analyzer, ONH836, manufactured by LECO.

[0056] The specific surface area of ​​the metal powder for injection molding is preferably 0.050 [m 2 / g] and above 0.250[m 2 / g] or less, more preferably 0.100 [m 2 / g] and above 0.240[m 2 / g] or less, more preferably 0.180 [m 2 / g] and above 0.230[m 2 When the specific surface area is within the above range, the sinterability of the metal powder for injection molding can be improved, and even if the particle size D50 is within the above range, the amount of organic binder used in the composite can be reduced.

[0057] 2. Method for manufacturing sintered body

[0058] Next, a method for producing a sintered body according to the embodiment will be described.

[0059] Figure 1It is a process diagram showing the configuration of a method for producing a sintered body according to the embodiment.

[0060] Figure 1 The method for producing a sintered body shown includes a kneading step S101 , a molding step S102 , a degreasing step S103 , and a sintering step S104 .

[0061] 2.1. Mixing process

[0062] In the kneading step S101, the metal powder for injection molding according to the embodiment is kneaded with an organic binder to prepare a composite. A solvent, various additives, etc. may be added to the composite.

[0063] The powder filling rate in the obtained composite is 63% by volume or more and 75% by volume or less, more preferably 64% by volume or more and 72% by volume or less, and even more preferably 65% ​​by volume or more and 70% by volume or less.

[0064] The metal powder for injection molding may be produced by any method. Examples of the production method include water atomization methods such as inverted cone water atomization method and rotary water atomization method, and various atomization methods such as gas atomization method.

[0065] It should be noted that the "inverted cone water atomization method" in this specification refers to a method of using water as a coolant to spray it into an inverted cone shape to gather it at one point, causing the molten metal to flow toward the gathering point and generate impact, thereby producing a method of producing metal powder.

[0066] The "swirling water atomization method" referred to in this specification is a method in which water is sprayed along the inner circumference of a cooling cylinder to create a swirling flow, thereby forming a water layer on the inner circumference and bringing the scattered molten metal into contact with this water layer. The micronized molten metal is drawn into the coolant layer and rapidly cooled, solidifying.

[0067] Water-atomized powder produced by water atomization is preferably used as the injection molding metal powder used in composite production. Contact with water forms an oxide film on the particle surface of water-atomized powder. This allows for the production of injection molding metal powder with an oxygen content within a predetermined range.

[0068] Examples of the organic binder include polyether resins, aliphatic carbonate resins, and polylactic acid resins, and these may be used alone or in combination of two or more.

[0069] Furthermore, the organic binder may contain polyethylene, polypropylene, ethylene-vinyl acetate copolymer, wax, higher fatty acid, higher alcohol, higher fatty acid ester, higher fatty acid amide, and the like in addition to the above-mentioned resins.

[0070] Examples of the additives include lubricants, antioxidants, degreasing accelerators, and surfactants.

[0071] The rate of molten metal flowing in the water atomization method is preferably greater than 1.0 [kg / min] and less than 20.0 [kg / min], and more preferably between 2.0 [kg / min] and less than 10.0 [kg / min]. This optimizes the amount of molten metal flowing within a given timeframe, enabling efficient production of metal powders with a small diameter and a sufficiently spherical shape. As a result, despite the small diameter, high average roundness and low specific surface area, metal powders for injection molding can be produced while minimizing the amount of organic binder used.

[0072] The molten metal temperature (pouring temperature) is preferably set to Tm + 100°C or higher and Tm + 350°C or lower, relative to the melting point Tm [°C] of the constituent material of the injection molding metal powder. It is more preferably set to Tm + 180°C or higher and Tm + 320°C or lower, and even more preferably set to Tm + 250°C or higher and Tm + 300°C or lower. This ensures that the molten metal remains as molten metal longer than before after being refined and solidified. As a result, it is possible to produce metal powders with a small diameter, high average roundness, and a relatively small specific surface area.

[0073] Furthermore, in the water atomization method, the outer diameter of the microstream of the molten metal as it flows is preferably 3.0 mm or less, more preferably 0.3 mm to 2.0 mm or less, and even more preferably 0.5 mm to 1.5 mm or less. This allows the molten metal to collide with the fluid, causing it to be finer, and allows droplets of appropriate size to be dispersed evenly. As a result, a metal powder with the aforementioned average particle size and good average roundness can be produced.

[0074] Furthermore, the produced metal powder may be classified as needed. Examples of the classification method include dry classification such as sieve classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.

[0075] Furthermore, as described above, the ratio of the tap density to the true density of the metal powder for injection molding is preferably 0.610 or more and 0.640 or less, and more preferably 0.615 or more and 0.630 or less.

[0076] Furthermore, as described above, the oxygen content of the metal powder for injection molding is preferably 1000 ppm to 6000 ppm, more preferably 1500 ppm to 5000 ppm, and even more preferably 2000 ppm to 4000 ppm, in terms of mass ratio.

[0077] This allows the preparation of a composite material with a high powder filling rate. As a result, since the shrinkage rate associated with degreasing can be suppressed, it is possible to suppress a decrease in the shape accuracy of the metal sintered body caused by deformation during degreasing and sintering.

[0078] 2.2. Molding process

[0079] In the molding step S102 , the compound is injection molded to obtain a molded body (injection molded body).

[0080] The molding conditions are not particularly limited, but the material temperature is approximately 80° C. or higher and 210° C. or lower, and the injection pressure is preferably approximately 10 MPa or higher and 500 MPa or lower.

[0081] 2.3. Degreasing process

[0082] In the degreasing step S103, the molded body is subjected to a degreasing treatment, thereby obtaining a degreased body.

[0083] The heating conditions in the degreasing treatment vary slightly depending on the type of steel and the composition and amount of the organic binder, but preferably the temperature is above 100°C and below 750°C and the time is above 0.1 hour and below 20 hours, and more preferably the temperature is above 150°C and below 600°C and the time is above 0.5 hour and below 15 hours.

[0084] It should be noted that this step may be omitted when the sintering process described later is combined with the degreasing process. In this case, the molded body may be subjected to the sintering process.

[0085] 2.4. Sintering process

[0086] In the sintering step S104 , the obtained degreased body is subjected to a sintering process, thereby obtaining a sintered body (metal sintered body).

[0087] The sintering temperature varies depending on the type of steel, the particle size of the powder, etc., but can be set to approximately 980° C. to 1450° C., as an example, and preferably approximately 1050° C. to 1400° C.

[0088] The sintering time is 0.2 hours to 7 hours, preferably about 1 hour to 6 hours.

[0089] Examples of the atmosphere for the sintering process include a reducing atmosphere such as hydrogen, an inert atmosphere such as nitrogen or argon, and a reduced pressure atmosphere obtained by reducing the pressure of these atmospheres.

[0090] Furthermore, the sintered body produced in this manner may be subjected to additional treatments as needed. Examples of additional treatments include solution treatment, age hardening treatment, double aging treatment, cryogenic treatment, tempering treatment, hot working treatment, cold working treatment, and the like, and any one or more of these treatments may be used in combination.

[0091] 3. Application of sintered metal

[0092] Metal sintered bodies manufactured using metal powder for injection molding can be used, for example, as components for transportation equipment such as automobile parts, bicycle parts, railway vehicle parts, ship parts, and aircraft parts; electronic equipment parts such as personal computer parts, portable phone terminal parts, tablet terminal parts, and wearable terminal parts; electrical equipment parts such as refrigerators, washing machines, and air conditioners; mechanical parts such as machine tools and semiconductor manufacturing equipment; factory parts such as nuclear power plants, thermal power plants, hydroelectric power plants, refineries, and chemical complexes; accessories such as watch parts, metal tableware, jewelry, and eyeglass frames; and the whole or part of medical instruments such as medical scalpels and forceps.

[0093] 4. Effects of the Implementation Methods

[0094] The metal powder for injection molding according to the embodiment has a particle size D50 of 1.0 μm or more and less than 10.0 μm when the cumulative value from the small diameter side is 50% in the volume-based cumulative particle size distribution curve obtained by laser diffraction. In addition, the metal powder for injection molding according to the embodiment has an average roundness of 0.86 or more and 0.95 or less. Moreover, the metal powder for injection molding according to the embodiment is a powder that, when subjected to a capillary rheometer at a shear rate of 100 [s -1 When the evaluation composite was prepared by kneading with an organic binder so that the melt viscosity measured at 150°C was 120 [Pa･s] (1200 [P]), the powder filling rate in the evaluation composite was 63 volume % or more and 75 volume % or less.

[0095] This configuration enables the production of injection-molded metal powders capable of producing injection-molded bodies with a low shrinkage ratio during sintering, that is, the shrinkage ratio of the sintered body relative to the internal volume of the mold cavity. Consequently, the use of this injection-molded metal powder suppresses dimensional deviations in the metal sintered body caused by shrinkage, enabling the production of metal sintered bodies with high shape accuracy.

[0096] The metal powder for injection molding according to the above embodiment is made of precipitation-hardening stainless steel.

[0097] According to such a configuration, a metal powder for injection molding capable of producing a metal sintered body having excellent mechanical strength and toughness can be obtained.

[0098] The particle size D50 of the metal powder for injection molding according to the embodiment is 5.0 μm or more and 8.0 μm or less.

[0099] According to such a configuration, a metal powder for injection molding having excellent filling properties and sintering properties can be obtained.

[0100] The binder filling rate in the compound for evaluation of the metal powder for injection molding according to the embodiment is 30% by volume or more and 36% by volume or less.

[0101] According to such a configuration, a metal powder for injection molding of a composite material capable of suppressing shrinkage during sintering can be obtained.

[0102] The ratio of the tap density to the true density of the metal powder for injection molding according to the embodiment is 0.610 or more and 0.640 or less.

[0103] According to such a configuration, a metal powder for injection molding can be obtained which has relatively few irregularly shaped particles and has excellent filling properties and flowability.

[0104] The specific surface area of ​​the metal powder for injection molding according to the embodiment is 0.050 [m 2 / g] and above 0.250[m 2 / g]or below.

[0105] According to such a configuration, it is possible to realize a metal powder for injection molding that can reduce the amount of organic binder used in the composite even when the particle size D50 is within the above range while improving sinterability.

[0106] The metal powder for injection molding according to the embodiment has an oxygen content of 1000 ppm or more and 6000 ppm or less in terms of mass ratio.

[0107] According to such a configuration, both the filling property and the sintering property of the metal powder for injection molding can be improved.

[0108] The method for producing a sintered body according to the embodiment includes a kneading step S101, a molding step S102, and a sintering step S104. In the kneading step S101, the metal powder for injection molding according to the embodiment is kneaded with an organic binder to prepare a composite. In the molding step S102, the composite is injection molded to obtain a molded body. In the sintering step S104, the molded body is sintered to obtain a sintered body.

[0109] According to such a configuration, a metal sintered body with high shape accuracy can be produced. In addition, a metal sintered body with high density and little variation in density and shape can be produced.

[0110] In the method for manufacturing a sintered body according to the embodiment, the metal powder for injection molding is produced by a water atomization method. Furthermore, the ratio of the tap density to the true density of the metal powder for injection molding is greater than or equal to 0.610 and less than or equal to 0.640. Furthermore, the oxygen content of the metal powder for injection molding is greater than or equal to 1000 ppm and less than or equal to 6000 ppm by mass. Furthermore, the kneading step S101 includes kneading the metal powder for injection molding with an organic binder to produce a composite material at a powder filling ratio of greater than or equal to 63% by volume and less than or equal to 75% by volume.

[0111] According to this structure, the shrinkage rate during sintering can be suppressed to a very low level, thereby making it possible to produce a metal sintered body with a particularly high shape accuracy. In addition, it is possible to produce a metal sintered body with a particularly high density and little variation in density and shape.

[0112] While the metal powder for injection molding and the method for producing a sintered body of the present invention have been described above based on preferred embodiments, the present invention is not limited thereto. For example, the metal powder for injection molding of the present invention may be a metal powder having any additional components added to the aforementioned embodiments.

[0113] Furthermore, the method for producing a sintered body of the present invention may be a method in which a step for any purpose is added to the above-described embodiment.

[0114] Example

[0115] Next, specific examples of the present invention will be described.

[0116] 5. Manufacturing of metal powder for injection molding

[0117] 5.1. Sample numbers 1 to 9

[0118] First, the raw materials were melted in a high-frequency induction furnace and powdered using water atomization (inverted cone water atomization) to produce metal powder for injection molding. The resulting metal powder was made of precipitation-hardened stainless steel 17-4PH (SUS630). The particle size, roundness, and specific surface area of ​​the injection molding metal powder were adjusted by adjusting the sulfidation level of the molten metal, pouring temperature, and the outer diameter of the flowing molten metal stream. This yielded the injection molding metal powders listed in Table 1 as Samples 1 to 9.

[0119] Table 1 shows the particle size D50, average circularity, powder filling rate and binder filling rate in the evaluation compound, specific surface area, ratio of tap density to true density, and oxygen content of the obtained metal powder for injection molding.

[0120] 5.2. Sample numbers 10-15

[0121] Metal powder for injection molding was obtained in the same manner as in Sample No. 1 except that the type of steel was changed to precipitation-hardening stainless steel 17-7PH (SUS631).

[0122] Table 2 shows the particle size D50, average circularity, powder filling rate and binder filling rate in the evaluation compound, specific surface area, ratio of tap density to true density, and oxygen content of the obtained metal powder for injection molding.

[0123] In Tables 1 and 2, among the metal powders for injection molding of each sample number, examples corresponding to the present invention are designated as “Examples,” and examples not corresponding to the present invention are designated as “Comparative Examples.”

[0124] 6. Evaluation of metal powder for injection molding

[0125] The following evaluations were performed on the metal powder for injection molding of each example and each comparative example.

[0126] 6.1. Density of the molded body

[0127] The injection molding metal powders of each Example and Comparative Example were injection molded at a material temperature of 180°C and an injection pressure of 11 MPa to produce cylindrical molded bodies with a diameter of 10 mm and a thickness of 5 mm. The weight and volume of the resulting molded bodies were measured, and the density was calculated. The calculated density was then evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0128] A: The density of the molded body is 5.50 g / cm 3 above

[0129] B: The density of the molded body is 5.40 g / cm 3 Above and less than 5.50g / cm 3

[0130] C: The density of the molded body is less than 5.40 g / cm 3

[0131] 6.2. Shrinkage of sintered body

[0132] The molded body was degreased and sintered to produce a sintered body. The sintering temperature was 1300°C and the sintering time was 3 hours. The volume of the sintered body was then measured, and the ratio of the volume of the sintered body to the internal volume of the cavity of the injection molding mold was calculated. The shrinkage of the sintered body was then evaluated by comparing the calculated results with the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0133] A: The ratio of the volume of the sintered body to the internal volume of the cavity is 12.0% or less

[0134] B: The ratio of the volume of the sintered body to the internal volume of the cavity is greater than 12.0% and less than 13.0%

[0135] C: The ratio of the volume of the sintered body to the internal volume of the cavity is greater than 13.0%

[0136] 6.3. Sintered body density unevenness

[0137] 100 sintered bodies were prepared. The density of each sintered body was calculated by dividing its weight by its volume. The standard deviation of the density was also calculated. The density variation of the sintered bodies was then evaluated by comparing the calculated standard deviation with the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0138] A: The standard deviation of the density of the sintered body is 0.06 g / cm 3 the following

[0139] B: The standard deviation of the density of the sintered body is greater than 0.06 g / cm 3 and 0.09g / cm 3 the following

[0140] C: The standard deviation of the density of the sintered body is greater than 0.09 g / cm 3

[0141] 6.4. Shape accuracy of sintered body

[0142] The length of each sintered body was measured, and the standard deviation of the length was calculated. The shape accuracy of the sintered body was then evaluated by comparing the calculated standard deviation with the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0143] A: The standard deviation of the length of the sintered body is 0.007 mm or less

[0144] B: The standard deviation of the length of the sintered body is greater than 0.007 mm and less than 0.011 mm

[0145] C: The standard deviation of the length of the sintered body is greater than 0.011 mm

[0146] 6.5. Extent of shrinkage cavities in sintered bodies

[0147] The surface deformation associated with shrinkage cavities in each of the sintered bodies was calculated. Shrinkage cavities are voids caused by inadequate filling of the metal powder. The calculated deformation was then compared with the following evaluation criteria to assess the extent of shrinkage cavities in the sintered bodies. The evaluation results are shown in Tables 1 and 2.

[0148] A: The surface deformation of the sintered body is 0.035 mm or less

[0149] B: The deformation amount of the surface of the sintered body is greater than 0.035 mm and less than 0.060 mm

[0150] C: The surface deformation of the sintered body is greater than 0.060 mm

[0151] 6.6. Surface roughness of sintered body

[0152] The surface roughness (arithmetic mean roughness Ra) of each sintered body was measured using a contact-type surface roughness measuring device (SURFCOM1400D, manufactured by Tokyo Seimitsu Co., Ltd.). The measured surface roughness was then evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0153] A: Surface roughness of sintered body is 0.750 μm or less

[0154] B: The surface roughness of the sintered body is greater than 0.750 μm and less than 0.850 μm

[0155] C: The surface roughness of the sintered body is greater than 0.850 μm

[0156] Table 1

[0157]

[0158] Table 2

[0159]

[0160] From the evaluation results shown in Tables 1 and 2, the following can be confirmed.

[0161] By using the metal powder for injection molding of each example, the density of the molded body can be increased.

[0162] By using the metal powder for injection molding of each example, the shrinkage rate, density unevenness, degree of shrinkage cavities, and surface roughness of the sintered body can be suppressed.

[0163] By using the metal powder for injection molding of each example, a sintered body with high shape accuracy can be obtained.

Claims

1. A metal powder for injection molding, characterized in that: In the volume-based cumulative particle size distribution curve obtained by the laser diffraction method, the particle size D50 at which the cumulative value from the small diameter side is 50% is 1.0 μm or more and less than 10.0 μm, The average roundness is 0.86 or more and 0.95 or less, When using a capillary rheometer with a shear rate of 100s -1 When a metal powder for injection molding is mixed with an organic binder so as to obtain a melt viscosity of 120 Pa·s (i.e., 1200 P) as measured at 150° C. to prepare an evaluation composite, the powder filling rate in the evaluation composite is 63% by volume or more and 75% by volume or less.

2. The metal powder for injection molding according to claim 1, characterized in that The metal powder for injection molding is composed of precipitation-hardening stainless steel.

3. The metal powder for injection molding according to claim 1 or 2, characterized in that The particle size D50 is 5.0 μm or more and 8.0 μm or less.

4. The metal powder for injection molding according to claim 1 or 2, characterized in that The binder filling rate in the evaluation compound is 30% by volume or more and 36% by volume or less.

5. The metal powder for injection molding according to claim 1 or 2, characterized in that The ratio of the tap density to the true density is 0.610 or more and 0.640 or less.

6. The metal powder for injection molding according to claim 1 or 2, characterized in that The specific surface area is 0.050m 2 / g or more and 0.250m 2 / g or less.

7. The metal powder for injection molding according to claim 1 or 2, characterized in that: The oxygen content is 1000 ppm or more and 6000 ppm or less in terms of mass ratio.

8. A method for producing a sintered body, characterized in that: have: a kneading step of kneading the metal powder for injection molding according to claim 1 or 2 with an organic binder to prepare a composite; a molding step of injection molding the composite to obtain a molded body; as well as The sintering step is to sinter the molded body to obtain a sintered body.

9. The method for producing a sintered body according to claim 8, wherein: The metal powder for injection molding is produced by water atomization. The ratio of the tap density to the true density of the metal powder for injection molding is 0.610 or more and 0.640 or less, The oxygen content of the metal powder for injection molding is 1000 ppm or more and 6000 ppm or less by mass ratio, The kneading step includes kneading the metal powder for injection molding with an organic binder so that the powder filling rate becomes 63 volume % or more and 75 volume % or less to prepare the composite.

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