Metal powder for injection molding and method for producing sintered body

Abstract

To provide metal powder for injection molding capable of producing an injection molded body having small shrinkage during sintering, and capable of producing a metal sinter with high form accuracy.SOLUTION: In a volume-based cumulative particle size distribution curve obtained by laser diffraction, when the cumulative value from the small-diameter side is 50%, the particle size D50 is 1.0 μm or more and less than 10.0 μm, the average circularity is 0.86 or more and 0.95 or less, and the molten viscosity measured using a capillary rheometer at a shear rate of 100 [s-1] and a temperature of 150°C is 120 [Pa s] (1200 [P]), when a preparation compound for evaluation is prepared by kneading with an organic binder to achieve these conditions, the metal powder for injection molding is characterized in that the powder packing density in the evaluation compound is 63 vol% or more and 75 vol% or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a method for producing a metal sintered body, which includes a molding step in which metal powder having an average particle size of 0.1 to 40 μm, produced by gas atomization or water atomization, is molded by metal powder injection molding to obtain a molded body, a degreasing step in which the molded body is degreased to obtain a degreased body, and a firing step in which the degreased body is sintered to obtain a sintered body.

[0003] According to this manufacturing method, it is possible to increase the sintering density and manufacture a metal sintered body having high mechanical strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-181501 Summary of the Invention [Problem to be solved by the invention]

[0005] However, during the firing process, the degreased body shrinks as the sintering process progresses. This shrinkage of the degreased body causes a decrease in the shape precision of the final metal sintered body. Therefore, it is a challenge to develop a metal powder for injection molding that can suppress the shrinkage rate during sintering and produce metal sintered bodies with high shape precision. [Means for solving the problem]

[0006] The metal powder for injection molding according to the application example of the present invention is In a volume-based cumulative particle size distribution curve obtained by a laser diffraction method, the particle size D50 when the cumulative value from the small diameter side is 50% is 1.0 μm or more and less than 10.0 μm, The average circularity is 0.86 or more and 0.95 or less, Using a capillary rheometer, the shear rate was 100 [s -1 ], and when the evaluation compound is prepared by kneading it with an organic binder so that the melt viscosity measured at a temperature of 150°C is 120 [Pa·s] (1200 [P]), the powder filling rate in the evaluation compound is 63% by volume or more and 75% by volume or less.

[0007] A method for producing a sintered body according to an application example of the present invention includes: a kneading step of kneading the metal powder for injection molding according to the application example of the present invention with an organic binder to prepare a compound; a molding step of injection molding the compound to obtain a molded body; a sintering step of sintering the compact to obtain a sintered body; It has. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a process diagram showing the configuration of a method for producing a sintered body according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The metal powder for injection molding and the method for producing a sintered body according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0010] 1. Metal powder for injection molding The metal powder for injection molding according to the embodiment is subjected to molding by metal powder injection molding (MIM), and the obtained compact is debound and sintered to obtain a metal sintered body.

[0011] 1.1. Powder filling rate of the evaluation compound 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 a volume-based cumulative particle size distribution curve obtained by laser diffraction.

[0012] Moreover, the metal powder for injection molding according to the embodiment has an average circularity of 0.86 or more and 0.95 or less.

[0013] Furthermore, when an evaluation compound is prepared using the metal powder for injection molding according to the embodiment, the metal powder for injection molding according to the embodiment is a powder that is configured so that this evaluation compound satisfies specified conditions.

[0014] Specifically, a compound for evaluation is prepared by kneading the metal powder for injection molding with an organic binder, which is a resin composition containing 26% by weight of polyethylene, 30% by weight of polystyrene, 28% by weight of paraffin wax, and 16% by weight of tributyl acetyl citrate (TBC).

[0015] Next, the evaluation compound was heated to 150°C and subjected to a shear rate of 100 [s -1 The viscosity is measured at a temperature of 100°C. A testing machine (capillary rheometer) is used to measure the melt viscosity when a sample containing a polymeric material is subjected to shear flow. The capillary length of the capillary rheometer is 10 mm, the die diameter is 1 mm, the furnace cylinder diameter is 9.55 mm, and the load cell load capacity is 20 kN.

[0016] The measurement procedure is as follows: First, the compound to be evaluated is placed in the furnace cylinder. Next, the compound to be evaluated is heated and melted. Next, the viscosity is measured while the molten material is extruded with the piston. Viscosity measurements are performed when the piston extrusion speeds are 0.5, 10, 20, 50, 100, 200, and 500 mm / min. Then, a logarithmic plot of the shear rate and viscosity corresponding to each extrusion speed is made. Next, a linear approximation is performed on the obtained flow curve. Next, when the shear rate is increased to 100 s -1 ] and calculate the viscosity when

[0017] The amount of organic binder used in the evaluation compound was set so that the viscosity measured as described above was 120 [Pa·s]. The metal powder for injection molding according to the embodiment is a powder in which the powder filling rate in the evaluation compound prepared to have a viscosity of 120 [Pa·s] is 63% by volume or more and 75% by volume or less.

[0018] The above powder filling rate can be said to be relatively high despite the relatively small particle size D50. Increasing the powder filling rate leads to a reduction in the amount of organic binder used. Therefore, by using the metal powder for injection molding according to the embodiment, a compound with a low organic binder content can be realized, even when mass-producing sintered bodies, despite containing powder with a small diameter and a large specific surface area. Furthermore, by using such a compound, metal sintered bodies with high density and surface precision can be manufactured. Furthermore, because the shrinkage rate associated with debinding can be reduced, the deterioration of the shape precision of the metal sintered body due to deformation during debinding and sintering can be suppressed.

[0019] The powder filling rate of the evaluation compound 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.

[0020] The powder packing rate is mainly controlled by the particle size, particle size distribution, circularity, specific surface area, etc. of the metal powder for injection molding. For example, even if the particle size is constant, if the average circularity can be increased or the specific surface area can be reduced, the amount of organic binder required to achieve a predetermined viscosity can be reduced. This can increase the powder packing rate of the evaluation compound. Furthermore, although this depends on the specific surface area, the powder packing rate can also be increased by optimizing the oxygen content of the metal powder for injection molding within a predetermined range.

[0021] The powder filling rate of the evaluation compound is calculated using the following formula: In the formula below, the metal powder for injection molding is simply referred to as "powder."

[0022] 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)

[0023] 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.

[0024] The binder filling rate is relatively low despite the relatively small particle size D50. Therefore, by using the metal powder for injection molding according to the embodiment, a compound can be realized that can suppress shrinkage during sintering.

[0025] The binder filling rate in the evaluation compound is calculated by the following formula. Binder filling rate = volume of organic binder contained in evaluation compound × 100 / (volume of organic binder contained in evaluation compound + volume of powder contained in evaluation compound)

[0026] As described above, the particle size D50 of the metal powder for injection molding according to the embodiment is set to be 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, thereby obtaining a metal powder for injection molding with good packing properties and sinterability.

[0027] The cumulative particle size distribution curve used to derive the particle size D50 of the metal powder for injection molding can be obtained using a laser diffraction / scattering particle size distribution analyzer, such as the Microtrac HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[0028] If the particle size D50 of the metal powder for injection molding is below the lower limit, the metal powder for injection molding becomes too fine, resulting in poor filling properties. This results in poor shape accuracy and density of the metal sintered body. On the other hand, if the particle size D50 of the metal powder for injection molding exceeds the upper limit, the metal powder for injection molding becomes too coarse, resulting in poor sinterability. This results in poor shape accuracy and density of the metal sintered body.

[0029] As described above, the average circularity of the metal powder for injection molding according to the embodiment is 0.86 to 0.95, preferably 0.88 to 0.93, and more preferably 0.89 to 0.92. If the average circularity is below the lower limit, the rolling ability of the particles constituting the metal powder for injection molding decreases and the specific surface area increases, resulting in decreased packing ability and flowability of the metal powder for injection molding. On the other hand, if the average circularity is above the upper limit, the metal powder for injection molding becomes more difficult to manufacture, resulting in increased costs and reduced manufacturing efficiency.

[0030] The circularity of the particles contained in the metal powder for injection molding is measured as follows. First, an image (secondary electron image) of multiple particles is captured using a scanning electron microscope (SEM). Next, the obtained image is loaded into image processing software. For example, image analysis particle size distribution measurement software "Mac-View" manufactured by Mountech Co., Ltd. is used as the image processing software. The imaging magnification is adjusted so that 50 to 100 particles are captured in one image. Then, multiple images are acquired so that a total of 300 or more particle images are obtained.

[0031] Next, the circularity of each particle image is calculated using software, and the average value is calculated. The average value thus obtained is the average circularity calculated from the captured particle images.

[0032] 1.2.Constituent materials of metal powder for injection molding The constituent material of the metal powder for injection molding is not particularly limited, and any sinterable metal material may be used, such as Fe, Ni, Co, Cu, Ag, Al, Ti, Mo, W, Ta, Zr, or an alloy or intermetallic compound containing these as the main component.

[0033] Among these, examples of Fe-based alloys include stainless steels such as austenitic stainless steel, martensitic stainless steel, and precipitation hardened stainless steel, low carbon steel, carbon steel, heat resistant steel, die steel, high speed tool steel, Fe-Ni based alloys, and Fe-Ni-Co based alloys.

[0034] Examples of Ni-based alloys include Ni-Cr-Fe-based alloys, Ni-Cr-Mo-based alloys, and Ni-Fe-based alloys.

[0035] Examples of Co-based alloys include Co-Cr-based alloys, Co-Cr-Mo-based alloys, and Co-Al-W-based alloys.

[0036] Examples of Ti-based alloys include alloys of Ti with metal elements such as Al, V, Nb, Zr, Ta, and Mo, and specific examples include Ti-6Al-4V and Ti-6Al-7Nb.

[0037] The metal powder for injection molding may be an aggregate of particles having a single composition, or may be an aggregate of particles having different compositions, i.e., two or more types of particles. In the latter case, the metal powder for injection molding can be used to produce a metal sintered body having the properties derived from each composition.

[0038] Of these, the constituent material of the metal powder for injection molding is preferably precipitation hardened stainless steel, which has excellent mechanical strength and toughness due to the formation of precipitates.

[0039] Examples of precipitation hardening stainless steel include SUS630 (17-4PH) and SUS631 (17-7PH).

[0040] 1.3.Various characteristics of metal powders for injection molding The ratio of tap density to 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. If the ratio of tap density to true density is within this range, the metal powder for injection molding will have relatively few irregularly shaped particles and will have good packing properties and flowability.

[0041] If the ratio of tap density to true density is below the lower limit, the filling rate of the metal powder for injection molding in the compound may decrease. This may require an increased amount of organic binder used in the compound, which may result in a decrease in the shape precision of the metal sintered body. On the other hand, if the ratio of tap density to true density is above the upper limit, the metal powder for injection molding may become more difficult to manufacture, which may result in higher costs and reduced manufacturing efficiency.

[0042] The tap density (packed bulk density) of the metal powder for injection molding is measured using a powder property evaluation device, Powder Tester (registered trademark) PT-X, manufactured by Hosokawa Micron Corporation.

[0043] 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 the above range, both the packing ability and sintering ability of the metal powder for injection molding can be improved. Furthermore, although this depends on the steel type and other properties of the metal powder for injection molding, if the oxygen content is within the above range, a metal powder for injection molding with excellent affinity with organic binders can be obtained. This makes it possible to realize a metal powder for injection molding that can achieve a predetermined melt viscosity while reducing the amount of organic binder used.

[0044] If the oxygen content is below the lower limit, the affinity between the particles of the metal powder for injection molding and the organic binder may decrease, which may reduce the packing ability of the metal powder for injection molding in the compound. Furthermore, the influence of the oxygen content may become more pronounced, which may lead to variations in the density and shape of the sintered body. On the other hand, if the oxygen content is above the upper limit, the sinterability of the metal powder for injection molding may decrease. Furthermore, the affinity with the organic binder may actually decrease.

[0045] The oxygen content of metal powder for injection molding is measured, for example, in accordance with the general rules for determining oxygen content in metallic materials as specified in JIS Z 2613: 2006. Specifically, the oxygen content can be measured using a LECO oxygen / nitrogen analyzer, TC-300 / EF-300, or a LECO oxygen / nitrogen / hydrogen analyzer, ONH836, or the like.

[0046] The specific surface area of ​​metal powder for injection molding is 0.050 [m 2 / g] or more 0.250[m 2 / g] or less, and 0.100 [m 2 / g] or more 0.240[m 2 / g] or less, and more preferably 0.180 [m 2 / g] or more 0.230[m 2 If the specific surface area is within this range, the sinterability of the metal powder for injection molding can be improved, and the amount of organic binder used in the compound can be reduced even if the particle size D50 is within the above range.

[0047] 2. Manufacturing method of sintered body Next, a method for producing a sintered body according to the embodiment will be described. FIG. 1 is a process diagram showing the configuration of a method for producing a sintered body according to an embodiment.

[0048] The method for producing a sintered body shown in FIG. 1 includes a kneading step S101, a molding step S102, a debinding step S103, and a sintering step S104.

[0049] 2.1.Mixing process In the kneading step S101, the metal powder for injection molding according to the embodiment is kneaded with an organic binder to prepare a compound. The compound may contain a solvent, various additives, and the like.

[0050] The powder filling rate in the obtained compound is from 63 to 75% by volume, more preferably from 64 to 72% by volume, and even more preferably from 65 to 70% by volume.

[0051] The metal powder for injection molding may be produced by any method, including, for example, water atomization methods such as inverted cone water atomization and rotary water atomization, and various atomization methods such as gas atomization.

[0052] In this specification, the term "inverted cone water jet atomization" refers to a method of producing metal powder by using water as a coolant, spraying it in an inverted cone shape that converges to one point, and then causing molten metal to flow down and collide with this convergence point.

[0053] The "rotary water atomization method" in this specification is a method in which water is jetted and supplied along the inner circumferential surface of a cooling cylinder, causing it to rotate, forming a water layer on the inner circumferential surface, and the molten metal that is scattered is brought into contact with this water layer. The finely powdered molten metal is taken into the cooling liquid layer and is rapidly cooled and solidified.

[0054] The metal powder for injection molding used to prepare the compound is preferably a water-atomized powder produced by the water atomization method. In the case of water-atomized powder, an oxide film is formed on the surface of the particles upon contact with water. This results in a metal powder for injection molding with an oxygen content within a specified range.

[0055] Examples of organic binders include polyether resins, aliphatic carbonate ester resins, and polylactic acid resins, and one or more of these can be used in combination.

[0056] In addition to the above resins, 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.

[0057] Examples of the additives include lubricants, antioxidants, degreasing accelerators, surfactants, and the like.

[0058] The flow rate of the molten metal in the water atomization method is preferably more than 1.0 kg / min and not more than 20.0 kg / min, and more preferably 2.0 kg / min or more and 10.0 kg / min or less. This allows the amount of molten metal flowing in a given period of time to be optimized, thereby efficiently producing metal powder with a relatively small diameter and sufficient spherical shape. As a result, metal powder for injection molding can be produced that has a high average circularity and a small specific surface area even with a small diameter, allowing for reduced use of organic binder.

[0059] The temperature of the molten metal (pouring temperature), where Tm [°C] is the melting point of the constituent material of the metal powder for injection molding, is preferably set to between Tm + 100°C and Tm + 350°C, more preferably between Tm + 180°C and Tm + 320°C, and even more preferably between Tm + 250°C and Tm + 300°C. This ensures that the molten metal remains in the form of molten metal for a longer period of time than conventional methods when it is atomized and solidifies. As a result, it is possible to produce metal powder with a high average circularity and a relatively small specific surface area, even if the diameter is small.

[0060] In addition, in the water atomization method, the outer diameter of the thin stream of molten metal when it is allowed to flow is preferably 3.0 mm or less, more preferably 0.3 mm to 2.0 mm, and even more preferably 0.5 mm to 1.5 mm. This makes it easier for droplets of appropriate size to be scattered uniformly when the molten metal is atomized by hitting it against a fluid. As a result, it is possible to produce metal powder with the above-mentioned average particle size and good average circularity.

[0061] The produced metal powder may be classified as needed by methods such as dry classification such as sieving classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.

[0062] As mentioned 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.

[0063] Furthermore, as mentioned above, the oxygen content of the metal powder for injection molding is preferably 1000 ppm or more and 6000 ppm or less by mass, more preferably 1500 ppm or more and 5000 ppm or less, and even more preferably 2000 ppm or more and 4000 ppm or less.

[0064] This allows the preparation of a compound with a high powder filling rate, which in turn reduces the shrinkage rate associated with debinding, thereby preventing the deterioration of the shape precision of the metal sintered body due to deformation during debinding and sintering.

[0065] 2.2. Molding process In the molding step S102, the compound is injection molded, thereby obtaining a molded body (injection molded body).

[0066] The molding conditions are not particularly limited, but it is preferable that the material temperature is about 80° C. or higher and 210° C. or lower, and the injection pressure is about 10 MPa or higher and 500 MPa or lower.

[0067] 2.3. Degreasing process In the degreasing step S103, the compact is subjected to a degreasing treatment, thereby obtaining a degreased body.

[0068] The heating conditions for the degreasing treatment vary slightly depending on the type of steel and the composition and amount of organic binder, but a temperature of 100°C or higher and 750°C or lower and a time of 0.1 hours or higher and 20 hours or lower are preferred, and a temperature of 150°C or higher and 600°C or lower and a time of 0.5 hours or higher and 15 hours or lower are even more preferred.

[0069] In addition, if the sintering treatment described later also serves as the degreasing treatment, this step may be omitted. In this case, the compact may be subjected to the sintering treatment.

[0070] 2.4.Sintering process In the sintering step S104, the obtained degreased body is subjected to a sintering process, thereby obtaining a sintered body (metal sintered body).

[0071] The sintering temperature varies depending on the type of steel, the particle size of the powder, etc., but is, for example, about 980° C. to 1450° C., and preferably about 1050° C. to 1400° C.

[0072] The sintering time is set to 0.2 hours or more and 7 hours or less, and preferably to about 1 hour or more and 6 hours or less.

[0073] The atmosphere for the sintering treatment may be, for example, a reducing atmosphere such as hydrogen, an inert atmosphere such as nitrogen or argon, or a reduced pressure atmosphere obtained by reducing the pressure of these atmospheres.

[0074] The sintered body thus produced may be subjected to additional treatments as needed, such as solution treatment, age hardening, double aging, sub-zero treatment, tempering, hot working, and cold working, and one or more of these may be used in combination.

[0075] 3. Uses of sintered metal Metal sintered bodies produced using metal powders for injection molding are used as materials for constituting all or part of, for example, transportation equipment parts such as automobile parts, bicycle parts, railway vehicle parts, ship parts, aircraft parts, and space transport vehicle parts; electronic equipment parts such as personal computer parts, mobile phone terminal parts, tablet terminal parts, and wearable terminal parts; electrical equipment parts such as refrigerators, washing machines, and air conditioners; machine parts such as machine tools and semiconductor manufacturing equipment; plant parts such as nuclear power plants, thermal power plants, hydroelectric power plants, refineries, and chemical complexes; watch parts; metal tableware, jewelry, ornaments such as eyeglass frames; and medical instruments such as medical scalpels and forceps.

[0076] 4. Effects of the above embodiment 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 a volume-based cumulative particle size distribution curve obtained by laser diffraction. The metal powder for injection molding according to the embodiment also has an average circularity of 0.86 or more and 0.95 or less. Furthermore, the metal powder for injection molding according to the embodiment has a shear rate of 100 [s ] measured using a capillary rheometer. -1 ], and when the compound for evaluation is prepared by kneading it with an organic binder so that the melt viscosity measured at a temperature of 150°C is 120 [Pa·s] (1200 [P]), the powder filling rate in the compound for evaluation is 63% by volume or more and 75% by volume or less.

[0077] This configuration makes it possible to realize a metal powder for injection molding that can produce injection-molded bodies with a small shrinkage rate during sintering, i.e., a small shrinkage rate of the sintered body relative to the internal volume of the mold cavity. Therefore, by using this metal powder for injection molding, dimensional deviation of the metal sintered body due to shrinkage is suppressed, making it possible to produce metal sintered bodies with high shape precision.

[0078] The metal powder for injection molding according to the embodiment is made of precipitation hardening stainless steel.

[0079] According to this configuration, a metal powder for injection molding can be obtained that can be used to produce a metal sintered body that is excellent in mechanical strength and toughness.

[0080] The metal powder for injection molding according to the embodiment has a particle size D50 of 5.0 μm or more and 8.0 μm or less.

[0081] According to this configuration, a metal powder for injection molding having good packing properties and sintering properties can be obtained.

[0082] In the metal powder for injection molding according to the embodiment, the binder filling rate in the evaluation compound is 30% by volume or more and 36% by volume or less.

[0083] According to this configuration, a metal powder for injection molding can be obtained that can realize a compound that can suppress the shrinkage rate during sintering.

[0084] The metal powder for injection molding according to the embodiment has a ratio of tap density to true density of 0.610 or more and 0.640 or less.

[0085] According to this configuration, a metal powder for injection molding can be obtained that contains relatively few irregularly shaped particles and has good filling properties and flowability.

[0086] The metal powder for injection molding according to the embodiment has a specific surface area of ​​0.050 [m 2 / g] or more 0.250[m 2 / g or less.

[0087] According to this configuration, it is possible to realize a metal powder for injection molding that has improved sinterability and allows the amount of organic binder used in the compound to be reduced even if the particle size D50 is within the above range.

[0088] The metal powder for injection molding according to the embodiment has an oxygen content of 1000 ppm or more and 6000 ppm or less by mass ratio.

[0089] This configuration can improve both the packing ability and sintering ability of the metal powder for injection molding.

[0090] 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 and an organic binder are kneaded to prepare a compound. In the molding step S102, the compound is injection molded to obtain a molded body. In the sintering step S104, the molded body is sintered to obtain a sintered body.

[0091] According to this configuration, it is possible to manufacture a metal sintered body with high shape accuracy, and also to manufacture a metal sintered body with high density and little variation in density and shape.

[0092] In the method for producing a sintered body according to the embodiment, the metal powder for injection molding is a powder 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. Furthermore, the oxygen content of the metal powder for injection molding is 1000 ppm or more and 6000 ppm or less by mass. The kneading step S101 includes kneading the metal powder for injection molding with an organic binder to prepare a compound with a powder filling rate of 63 vol. % or more and 75 vol. % or less.

[0093] This configuration allows the shrinkage rate during sintering to be kept particularly low, making it possible to produce a metal sintered body with particularly high shape accuracy, and also to produce a metal sintered body with particularly high density and little variation in density and shape.

[0094] While the metal powder for injection molding and the method for manufacturing a sintered body according to 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 according to the present invention may be one in which any component is added to the above-described embodiment.

[0095] Furthermore, the method for producing a sintered body of the present invention may be such that any step for any purpose is added to the above-described embodiment. [Example]

[0096] Next, specific examples of the present invention will be described. 5. Manufacturing of metal powder for injection molding 5.1. Samples No. 1 to 9 First, the raw materials were melted in a high-frequency induction furnace and pulverized by water atomization (inverted cone water flow atomization) to obtain metal powder for injection molding. The steel type used for the obtained metal powder for injection molding was precipitation hardened stainless steel 17-4PH (SUS630). In addition, the particle size, circularity, specific surface area, etc. of the metal powder for injection molding were adjusted by adjusting the amount of sulfurization of the molten metal, the pouring temperature, the outer diameter of the thin stream of molten metal to be poured, etc. In this way, metal powder for injection molding samples 1 to 9 shown in Table 1 were obtained.

[0097] 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.

[0098] 5.2. Samples No. 10-15 A metal powder for injection molding was obtained in the same manner as Sample No. 1, except that the steel type was changed to precipitation hardened stainless steel 17-7PH (SUS631).

[0099] 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.

[0100] In Tables 1 and 2, among the metal powders for injection molding of each sample number, those that correspond to the present invention are labeled "Examples," and those that do not correspond to the present invention are labeled "Comparative Examples."

[0101] 6. Evaluation of metal powders for injection molding The metal powders for injection molding of each of the Examples and Comparative Examples were evaluated as follows.

[0102] 6.1. Density of the compact The metal powders for injection molding of each Example and Comparative Example were injection molded at a material temperature of 180°C and an injection pressure of 11 MPa to obtain cylindrical molded bodies with a diameter of 10 mm and a thickness of 5 mm. The weight and volume of the obtained molded bodies were measured, and the density was calculated. The calculated densities were then evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0103] A: The density of the molded body is 5.50 g / cm 3 That's all B: Density of the molded body is 5.40 g / cm 3 More than 5.50g / cm 3 is less than C: Density of the molded body is 5.40 g / cm 3 is less than

[0104] 6.2. Shrinkage rate of sintered body The above-mentioned compact 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 mold cavity used for injection molding was calculated. The calculated results were then compared with the following evaluation criteria to evaluate the shrinkage rate of the sintered body. The evaluation results are shown in Tables 1 and 2.

[0105] A: The ratio of the volume of the sintered body to the internal volume of the cavity is 12.0% or less B: The ratio of the volume of the sintered body to the internal volume of the cavity is more than 12.0% and 13.0% or less. C: The ratio of the volume of the sintered body to the internal volume of the cavity is more than 13.0%

[0106] 6.3. Density variation of sintered body One hundred of the above sintered bodies were prepared, and the weight of each sintered body was divided by the volume to calculate the density, and the standard deviation of the density was also calculated. The calculated standard deviation was then used to evaluate the density variation of the sintered bodies according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0107] A: The standard deviation of the density of the sintered body is 0.06 g / cm 3 is B: The standard deviation of the density of the sintered body is 0.06 g / cm 3 Super 0.09g / cm 3 is C: The standard deviation of the density of the sintered body is 0.09 g / cm 3 It is super

[0108] 6.4. Shape accuracy of sintered body The length of each sintered body was measured and the standard deviation of the length was calculated. The calculated standard deviation was then used to evaluate the shape accuracy of the sintered body according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0109] A: The standard deviation of the length of the sintered body is 0.007 mm or less B: The standard deviation of the length of the sintered body is more than 0.007 mm and 0.011 mm or less C: The standard deviation of the length of the sintered body is more than 0.011 mm.

[0110] 6.5. Degree of Shrinkage Porosity in Sintered Body The amount of surface deformation associated with shrinkage cavities for each of the above sintered bodies was calculated. Shrinkage cavities refer to voids caused by improper filling of the metal powder. The calculated amount of deformation was then compared with the following evaluation criteria to evaluate the degree of shrinkage cavities for the sintered bodies. The evaluation results are shown in Tables 1 and 2.

[0111] A: The deformation of the surface of the sintered body is 0.035 mm or less. B: The deformation amount of the surface of the sintered body is more than 0.035 mm and 0.060 mm or less C: The deformation of the surface of the sintered body is more than 0.060 mm.

[0112] 6.6.Surface roughness of sintered body The surface roughness (arithmetic mean roughness Ra) of each of the sintered bodies was measured. A contact-type surface roughness measuring device (SURFCOM1400D, manufactured by Tokyo Seimitsu Co., Ltd.) was used for the measurement. The measured surface roughness was then evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0113] A: The surface roughness of the sintered body is 0.750 μm or less B: The surface roughness of the sintered body is more than 0.750 μm and not more than 0.850 μm C: The surface roughness of the sintered body is more than 0.850 μm

[0114] [Table 1]

[0115] [Table 2]

[0116] From the evaluation results shown in Tables 1 and 2, the following was recognized. By using the metal powder for injection molding of each example, the density of the molded body could be increased.

[0117] By using the metal powder for injection molding of each example, it was possible to suppress the shrinkage rate of the sintered body, the variation in density, the degree of shrinkage cavities, and the surface roughness.

[0118] By using the metal powder for injection molding of each example, sintered bodies with high shape accuracy were obtained. [Explanation of symbols]

[0119] S101: Mixing process, S102: Molding process, S103: Degreasing process, S104: Sintering process

Claims

1. 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 circularity is 0.86 or more and 0.95 or less, Using a capillary rheometer, the shear rate was 100 [s －１ ] and an organic binder so that the melt viscosity measured at a temperature of 150°C is 120 [Pa s] (1200 [P]), the powder filling rate of the evaluation compound is 63 volume % or more and 75 volume % or less.

2. 2. The metal powder for injection molding according to claim 1, which is made of precipitation hardening stainless steel.

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

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

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

6. The specific surface area is 0.050 [m ２ / g] or more 0.250[m ２ 3. The metal powder for injection molding according to claim 1, wherein the powder has a viscosity of 1 / 2 g or less.

7. 3. The metal powder for injection molding according to claim 1, wherein the oxygen content is 1000 ppm or more and 6000 ppm or less by mass ratio.

8. a kneading step of kneading the metal powder for injection molding according to claim 1 or 2 with an organic binder to prepare a compound; a molding step of injection molding the compound to obtain a molded body; a sintering step of sintering the compact to obtain a sintered body; A method for producing a sintered body, comprising:

9. The metal powder for injection molding is a powder produced by a water atomization method, 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, 9. The method for producing a sintered body according to claim 8, wherein the kneading step includes an operation of kneading the metal powder for injection molding and an organic binder to prepare the compound so that the powder filling rate is 63% by volume or more and 75% by volume or less.

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