JP2015224379A - Mixed powder for powder metallurgy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mixed powder for powder metallurgy which allows reduction of variation of the weight of a molding by improving the packing capacity of a mold.SOLUTION: A mixed powder for powder metallurgy is obtained by mixing a graphite powder of an average particle size D50 of 1.0-3.0 μm and an average particle size D90 of 10 μm or smaller with an iron-based powder under shear force, without addition of a binder. The mixed powder for powder metallurgy thus obtained contains an iron-based powder and a graphite powder present collectively in concave parts of the iron-based powder.

Description

  The present invention relates to a powder metallurgy technique for producing a sintered body by molding and sintering a mixed powder whose main raw material is an iron-based powder, and in particular, a molded body obtained by improving the filling property of the mixed powder into a mold. The present invention relates to a powder mixture for powder metallurgy that can reduce the weight variation of the powder.

  In powder metallurgy for producing a sintered body using iron powder or copper powder as a main raw material, usually powder of the main raw material, graphite powder for improving the physical properties of the sintered body, auxiliary raw material powder such as an alloy component, A mixed powder containing a lubricant or the like is used. In particular, in order to improve the mechanical properties of the sintered body, such as strength and hardness, a carbon supply component such as graphite (that is, a carbon source) is added and molded, followed by carbon during the heating and sintering process. It is common to diffuse and penetrate the source into the iron powder.

  However, since graphite has a smaller specific gravity and smaller particle size than iron powder, there is a problem that graphite and iron powder are separated largely by simply mixing them, and graphite is segregated and cannot be mixed uniformly. In the powder metallurgy method, in order to mass-produce sintered bodies, the mixed powder is usually stored in a storage hopper in advance. In storage hoppers, graphite with a low specific gravity tends to segregate in the upper layer of the hopper, and when the mixed powder is discharged from the hopper, the concentration of graphite increases at the end of the hopper discharge, and the graphite concentration in the sintered body is high. A cementite structure is deposited on the part, and the mechanical properties are lowered. If the carbon content in the sintered body varies due to the segregation of graphite, it becomes difficult to produce a component with stable quality. Further, in the mixing process and the molding process, graphite powder is generated due to the segregation of graphite, which causes problems such as deterioration of the workplace environment and deterioration of the handleability of the mixed powder. The above-mentioned segregation occurs not only in graphite but also in various other powders mixed with iron powder, and prevention of segregation has been demanded.

  In order to prevent the above-mentioned segregation and dust generation, three methods have been proposed in the past. The first method is a method in which a liquid additive such as tall oil is added to the mixed powder as described in Patent Documents 1 and 2, for example. Although this method has the advantage that a mixed powder can be produced with simple equipment, if a liquid additive is added in an amount necessary for the effect of preventing segregation, the liquid crosslinking force acts between the iron powder particles, and the However, there is a problem that the flowability deteriorates. The second method is a method in which a solid binder such as a polymer is dissolved in a solvent and uniformly mixed, and then the solvent is evaporated and graphite is adhered to the surface of the iron powder, as in Patent Documents 3 and 4. is there. This method has the advantage that graphite can be reliably attached and the choice of lubricant to be used is wide, but depending on the amount and type, the flowability of the mixed powder is insufficient or the compressibility is low. There is a problem of lowering. The third method is a so-called hot melt method in which a relatively low molecular weight lubricant such as a fatty acid is heated and melted during mixing with iron powder as disclosed in Patent Document 5 and the like. In this method, since the melted lubricant is uniformly fixed on the surface of the iron powder, the temperature control during mixing is very important, and there are disadvantages that the choice of the lubricant that can be used is limited. In the third method, it is necessary to wait until the lubricant cools, and there is a problem in productivity.

  In Patent Document 6 filed by the present applicant, unlike the above-described three methods, graphite having a controlled average particle diameter is mixed with iron-based powder while applying a shearing force without adding a binder. Discloses a technique for suppressing segregation of graphite powder. The technique describes that the fluidity of the mixed powder is also excellent. In the powder metallurgy method, when the mixed powder is discharged from the storage hopper and filled into the mold, the flowability of the mixed powder is one of the important characteristics. In Patent Document 6, as the fluidity index, for example, the fluidity of the mixed powder defined in JIS Z2502 is used. In addition to such fluidity, the mixed powder is discharged from the hopper through the hose, and the mold is used. Is also an important characteristic. When the filling property of the mold is lowered, the weight variation of the molded body is caused.

JP-A-60-502158 JP-A-6-49503 JP-A-5-86403 JP-A-7-173503 JP-A-1-219101 JP 2012-102355 A

  An object of the present invention is to provide a powder mixture for powder metallurgy that can improve the filling property of a mold and reduce the weight variation of a molded body.

  The mixed powder for powder metallurgy according to the present invention that has achieved the above-mentioned problems is obtained by adding graphite powder having an average particle diameter D50 of 1.0 μm or more and 3.0 μm or less and D90 of 10 μm or less without adding a binder, It is obtained by mixing with iron-based powder while applying a shearing force. The mixed powder for powder metallurgy of the present invention thus obtained is a mixed powder for powder metallurgy characterized by including an iron-based powder and a graphite powder that is present in the recesses of the iron-based powder. is there.

  In this invention, it is preferable that the average particle diameter D50 of the said graphite powder is 1.6 micrometers or more and 2.7 micrometers or less, and it is also preferable that the said iron base powder is atomized iron powder or reduced iron powder.

  According to the present invention, since the graphite powder having D50 and D90 in a predetermined range is mixed with the iron-based powder while applying a shearing force without adding a binder, the graphite powder is in the recess of the iron-based powder. As a result, it is possible to ensure good mold filling properties and reduce the weight variation of the molded body.

FIG. 1 is a schematic view of a mold filling property evaluation apparatus used in Examples described later, FIG. 1 (a) is a front view, and FIGS. 1 (b) to 1 (d) are sectional views showing operating states. It is. FIG. 2 is a scanning electron micrograph of the mixed powder of the present invention observed in the examples described later. FIG. 3 is a scanning electron micrograph of the mixed powder of the present invention observed in the examples described later.

  Based on the technique of the above-mentioned Patent Document 6, the present inventors examine the relationship between the particle size of graphite and the weight variation of the molded body in order to reduce the weight variation of the molded body, which was not noted in Patent Document 6. The following experiment was conducted. Commercially available natural graphite (manufactured by Nippon Graphite, CPB, average particle size 22.6 μm) was pulverized by a dry jet mill so as to have an average particle size D50 shown in Table 1 below. Graphite powder obtained by grinding, iron powder (manufactured by Kobe Steel, Atmel 300M, particle size: 180 μm or less, average particle size: 70 μm), copper powder (manufactured by Fukuda Metal, CuAtw-250), and lubricant Zinc stearate (manufactured by ADEKA, ZNS-730) was mixed to obtain a mixed powder. The mixing ratio is 0.8 parts by mass of graphite powder, 2 parts by mass of copper powder, and 0.75 parts by mass of lubricant with respect to 97.2 parts by mass of iron powder. Mixing was performed at 300 rpm for 4 minutes using a high-speed mixer having a stirring blade.

  Using the obtained mixed powder, 300 test pieces with a target weight of 51 g were continuously formed with a mechanical powder forming press, and the weight variation of the obtained formed body was evaluated. The weight variation was evaluated by the difference R (g) between the maximum weight and the minimum weight among the 300 molded bodies. The results are shown in Table 1.

  The weight variation of Reference Example 1 in which no graphite powder was added in the above mixing was 1.35 g, whereas the weight variation of Reference Examples 2 to 11 in which graphite powder was added was larger than that of Reference Example 1. I understand. In addition, although there is an approximate tendency that the weight variation becomes smaller as the average particle diameter D50 of the graphite powder becomes finer, particularly when the Reference Examples 6 to 11 are viewed, only the average particle diameter D50 of the graphite powder becomes the weight variation. We cannot conclude that it is affecting. Moreover, the target that the variation with respect to the target weight is about 4% or less (that is, about 2 g or less) cannot be achieved only by controlling the average particle diameter of the graphite powder.

  Therefore, the present inventors conceived of adjusting not only the average particle diameter D50 of the graphite powder proposed in Patent Document 6, but also D90. As shown in the examples to be described later, the graphite powder adjusted for D50 and D90 is mixed with the iron-based powder while applying a shearing force, so that the graphite powder can be rubbed into the recesses existing on the surface of the iron-based powder. The mold filling property can be improved, and the weight variation of the molded product can be reduced.

  In order to sufficiently exhibit the above-mentioned rubbing effect, the D50 of the graphite powder is set to 3.0 μm or less. D50 is preferably 2.7 μm or less, and more preferably 2.5 μm or less. From the viewpoint of the rubbing effect, it is preferable that the D50 of the graphite powder is small. However, if the D50 is too small, the weight variation can be reduced, but the density of the compact at the time of press molding is significantly reduced, and the compact is sintered. The strength of the parts obtained in this way cannot be secured. Therefore, the D50 of the graphite powder is set to 1.0 μm or more. The D50 of the graphite powder is preferably 1.1 μm or more, more preferably 1.6 μm or more. From the viewpoint of achieving all of the reduction in the variation in the weight of the compact, the improvement of the mold filling property, and the improvement in the density of the compact, the D50 of the graphite powder may be 1.6 μm or more and 2.7 μm or less. preferable. In addition, when D50 of graphite powder is less than 1.0 micrometer, it is thought that the reason for the density reduction of the compact is that the layered structure of graphite is broken by excessive grinding and the lubricity of graphite is impaired.

  The graphite powder of the present invention in which D50 is adjusted to the above range can be obtained by pulverizing commercially available natural graphite or artificial graphite, and an ordinary pulverizer may be used for pulverization. The atmosphere of pulverization is not particularly limited, and the pulverization atmosphere may be dry or pulverized wet. As the pulverizer, a normal pulverizer can be used, and examples thereof include a roll crusher, a cutter mill, a rotary crusher, a hammer crusher, a jet mill, a vibration mill, a pin mill, a wing mill, a ball mill, and a planetary mill.

  The pulverized graphite powder has a large specific surface area, and it is considered that a physical force such as static electricity acts as well as a chemical force. That is, it is considered that the finely pulverized graphite pulverized surface contains a lot of functional groups such as hydrogen groups, and intermolecular force is generated between the iron powder and the graphite powder via the functional groups, It is thought that adhesion between graphite powder and iron-based powder increases. The presence or absence of the functional group and the content thereof can be grasped to some extent by heating the graphite powder in a nitrogen atmosphere and measuring the weight change rate from room temperature to 950 ° C. The rate of temperature increase when the temperature is raised from room temperature to 950 ° C. is preferably about 10 ° C./min. Normally, the type of gas generated from the graphite powder differs for each heating temperature range, and the type of functional group removed in that temperature range can be estimated from the type of generated gas. A carboxyl group (—COOH) and a hydroxy group (—OH) are removed at 150 to 500 ° C., an oxo group (═O) is removed at 500 to 900 ° C., and a hydrogen group (—H) is removed at 900 ° C. and above. It is generally known. By examining the weight loss from 150 to 950 ° C., it is possible to remove the influence of the weight reduction of moisture that can be removed at temperatures lower than 150 ° C., and to know the type and content of functional groups contained in the graphite powder. it can.

  In the present invention, it is important not only to adjust D50 of the graphite powder to a predetermined range, but also to set D90 to 10 μm or less. By setting D90 to 10 μm or less, the amount of graphite powder that is not rubbed into the recesses of the iron-based powder can be reduced. D90 of the graphite powder is preferably 9.5 μm or less, more preferably 9.0 μm or less, and particularly preferably 8.5 μm or less. The lower D90 of the graphite powder is preferable, but the lower limit is usually about 3.5 μm. In order to set the D90 of the graphite powder within the above range, airflow classification may be performed after pulverization by the above pulverizer.

  In addition, both D50 and D90 of graphite powder can be measured by a laser diffraction particle size distribution measuring device, D50 means a volume-based cumulative particle size equivalent to 50%, and D90 means a volume-based cumulative particle size equivalent to 90%. Means.

  The content of the graphite powder is usually 0.1 to 2.5 parts by mass with respect to 100 parts by mass of the total amount of the iron-based powder, the graphite powder, and the strength improver described later. When applied to machine structural parts, a blending ratio of 0.2 to 1.2 parts by mass is often used, and is preferably used within this range.

  In order to achieve good mold filling properties, it is important to mix the graphite powder and the iron-based powder while applying a shearing force without adding a binder. By giving a shearing force, graphite powder can be rubbed into the recesses of the iron-based powder, and since no binder is added, it is possible to suppress the graphite powder from adhering to other than the recesses of the iron-based powder (for example, protrusions), The graphite powder gathers in the recesses of the iron-based powder and exists. When a large amount of graphite powder is present other than the recesses of the iron-based powder, the fluidity of the mixed powder is deteriorated and the mold filling property is deteriorated. In a method (described later) different from the method of adding a binder or the method of applying a shearing force (to be described later), many graphite powders exist in addition to the recesses of the iron-based powder, and good mold filling properties cannot be achieved.

  Also, the absence of a binder means that the density of the molded body when molded at the same molding pressure and the density of the sintered body obtained by sintering the molded body are higher than when the binder is added. There is also an effect that the strength of the bonded body is improved. Furthermore, the mixed powder of the present invention to which no binder is added can omit or simplify the dewaxing process performed between the molding process and the sintering process, contributing to improved productivity of sintered parts and environmental measures. To do.

  The mixing method which gives a shearing force is a method different from a convection mixing method represented by a V-type mixer or a double cone mixer, a mixing method using a vibration mill such as a vibro mill or an electromagnetic mill, or a ball mill. Mixing that gives a shearing force can be realized, for example, by using a mixer equipped with a stirring blade. The stirring blade is preferably one that moves so as to cut powder, and examples of the shape include a paddle, a turbine, a ribbon, a screw, a multistage blade, an anchor type, a horseshoe type, and a gate type. As long as the stirring blade is provided, the container of the mixer may be a fixed type or a rotary type. Specific examples of the mixer equipped with the stirring blade include a high-speed mixer (such as Henschel), a plow-type mixer, and a nauter mixer. The mixing time is generally 1 to 20 minutes, although it depends on the type of the mixer used and the amount of the mixed powder.

  Mixing of the graphite powder and the iron-based powder may be performed dry or wet. The mixing procedure of the graphite powder and the iron-based powder is not particularly limited, and these powders may be simultaneously mixed in a mixer, or one of the powders may be first charged in the mixer and the other powder. May be added later. The mixing of the graphite powder and the iron-based powder is not performed by heating to a temperature at which the lubricant or the like melts as in the so-called hot melt method, but may be performed at room temperature, for example. Moreover, the atmosphere of mixing is not specifically limited, For example, it is in air | atmosphere.

  The powder for powder metallurgy according to the present invention contains at least one of a lubricant and a physical property improver (for example, a strength improver, an abrasion resistance improver, a machinability improver, etc.) in addition to the graphite powder and the iron-based powder. You may contain. These may be added at the time of mixing the graphite powder and the iron-base powder, and the order of addition is not particularly limited. For example, the graphite powder and the iron-base powder may be added to the mixer at the same time and mixed. In addition, the graphite powder and the iron-based powder are mixed first, and then the above-mentioned lubricant and physical property improver are added to the mixer one by one or two or more while mixing (for example, while operating the stirring blade). May be.

Examples of the lubricant include metal soap, alkylene bis fatty acid amide, fatty acid and the like, and these may be used alone or in combination of two or more. For the metal soap, a fatty acid salt can be used. For example, a fatty acid salt having 12 or more carbon atoms, particularly zinc stearate is preferably used. Specific examples of the alkylene bis fatty acid amide include C _2-6 alkylene bis C _12-24 carboxylic acid amide, and ethylene bisstearyl amide is preferably used. As the fatty acid, for example, a compound exemplified as R ₁ COOH (R ₁ is a hydrocarbon group) can be used, preferably a carboxylic acid having about 16 to 22 carbon atoms, and stearic acid and oleic acid are particularly preferably used. It is done. The content of the lubricant is, for example, 0.3 parts by mass or more and 1.5 parts by mass or less, more preferably 0.1 parts by mass or less with respect to 100 parts by mass of the total amount of iron-based powder, graphite powder, and strength improver. 5 parts by mass or more and 1.0 part by mass or less.

  Examples of the strength improver include powders containing at least one of copper, nickel, chromium, molybdenum, manganese, and silicon. Specifically, copper powder, nickel powder, chromium-containing powder, molybdenum powder, manganese-containing powder And silicon-containing powder. A strength improver may be used independently and may use 2 or more types together. The addition amount of the strength improver is, for example, 0.2 parts by mass or more and 5 parts by mass or less, more preferably 0. 3 parts by mass or more and 3 parts by mass or less.

  Examples of the wear resistance improver include hard particles such as carbide, silicide, and nitride, and these may be used alone or in combination of two or more.

  Examples of the machinability improver include manganese sulfide, talc, calcium fluoride, and the like. These may be used alone or in combination of two or more.

  The iron-based powder used in the present invention may be either pure iron powder or iron alloy powder. The iron alloy powder may be a partial alloy powder in which an alloy powder (for example, copper, nickel, chromium, molybdenum, etc.) is diffusely adhered to the surface of the iron-based powder, or an alloy component (the same component as the above alloy powder). It may be a pre-alloy powder obtained from molten iron (or molten steel). The iron-based powder may be atomized iron powder obtained by atomizing molten iron or steel, or reduced iron powder obtained by reducing iron ore or mill scale. As the iron-based powder, an iron powder usually used for machine parts can be used. Specifically, the average particle diameter D50 is 70 to 100 μm, and the maximum particle diameter is 250 μm or less (preferably 180 μm or less). ) Is preferred. The average particle size of the iron-based powder is the particle size of 50% of the cumulative sieving amount when the particle size distribution is measured according to Japan Powder Metallurgy Industry Association Standard JPMA P 02-1992. means.

  According to the present invention, the mold filling property can be improved and the weight variation of the molded body can be reduced. The weight variation evaluated by the maximum value and the minimum value of the molded body weight when a plurality of molded bodies are molded using the mixed powder of the present invention can be 4% or less with respect to the target weight.

  In addition, the present invention can stabilize quality by minimizing dimensional change by miniaturizing graphite powder, and realizes energy saving and cost saving in the production of sintered parts such as reduction of sintering temperature and shortening of sintering time. it can. The mixed powder of the present invention can be applied to sintered parts for machine structures and the like, and particularly applicable to complicated and thin-walled parts. And since it can be reduced in weight, it is suitable also for a high-strength material.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can of course be implemented with appropriate modifications within a range that can be adapted to the above-described gist. Included in the range.

  Commercially available natural graphite (manufactured by Nippon Graphite Co., Ltd., CPB, average particle size 22.6 μm) was pulverized by a dry jet mill so as to have an average particle size D50 shown in Tables 4 to 6 below, and D90 was pulverized or by air classification. It was adjusted. Graphite powder obtained by pulverization, iron powder (manufactured by Kobe Steel, Atmel 300M, 300NH, or 250M), copper powder (made by Fukuda Metal, CuAtw-250), and zinc stearate (manufactured by ADEKA) as a lubricant. , ZNS-730) to obtain a mixed powder. The mixing ratio is 0.8 parts by mass of graphite powder, 2 parts by mass of copper powder, and 0.75 parts by mass of lubricant with respect to 97.2 parts by mass of iron powder. Mixing was performed at 300 rpm for 4 minutes using a high-speed mixer having a stirring blade. The following (1) to (3) were evaluated using the obtained mixed powder.

(1) Measurement of weight variation of molded body Using the obtained mixed powder, 300 ring-shaped test pieces having a target weight of 51 g, an outer diameter of 30 mm, and an inner diameter of 10 mm were continuously molded using a mechanical powder molding press. The weight variation of the molded body was evaluated. The weight variation was evaluated by the difference R (g) between the maximum weight and the minimum weight among the 300 molded bodies.

(2) Measurement of mold filling property The mold filling property was evaluated using the evaluation apparatus shown in FIG. FIG. 1 shows a base 1 that accommodates a cavity container 3, an air cylinder 5 that is fixed on the base on the other side of the cavity container 3, and a tip of a rod 4 of the air cylinder 5. This is a powder mold filling property evaluation apparatus composed of a powder supply box 2. The powder supply box 2 is a bottomless box, and reciprocates on the cavity container 3 by the operation of the air cylinder 5 with the upper surface of the base 1 being almost airtight. Further, the cavity container 3 has a slit-like cavity having a width of several mm that is elongated in a direction perpendicular to the reciprocating direction of the powder supply box 2. Fig.1 (a) is a front view of this evaluation apparatus, (b)-(d) is sectional drawing showing the state during the movement of the powder supply box.

The measurement procedure is as follows. First, a predetermined amount of powder is charged into the powder supply box 2 with the rod 4 of the air cylinder 5 extended (FIG. 1B). Next, the rod 4 of the air cylinder 5 is shortened, and the powder supply box 2 is passed over the slit-shaped cavity of the cavity container 3 at a predetermined speed. By this passage, the powder in the powder supply box 2 falls into the cavity container 3 (FIG. 1C). Then, after passing through the powder supply box 2, the cavity container 3 is filled with powder (FIG. 1 (d)). The size of the powder supply box 2 is 80 × 80 × 70 mm, the size of the cavity container 3 is 80 × 60 × 55 mm, the slit size is 2 × 60 mm, and the shoe speed (passing speed of the powder supply box 2) is 100 mm / s. Each experiment No. The amount of powder (mg) filled for each test was divided by the area of the slit-shaped cavity (120 mm ² ), and the average of these values was determined for each No. 1 test. Mold filling property (mg / mm ² ).

(3) Measurement of molded body density The obtained mixed powder was put into a predetermined mold and molded at a press pressure of 490 MPa and 686 MPa to produce a tablet-shaped test piece of φ11.28 mm, and the obtained molding Body density was measured.

  The characteristics of the iron-based powder used (Atmel 300M, 300NH, or 250M) are as shown in Tables 2 and 3. The apparent density described in Tables 2 and 3 is a method specified by JIS Z2504 (metal powder-apparent density test method), and the fluidity is a method specified by JIS Z2502 (metal powder flow rate test method). It is the result measured by. Based on Atmel 300M, 300NH has a large apparent density and 250M has a small apparent density. That is, based on the Atmel 300M, 300NH has less irregularities on the surface of the iron powder and has a lower irregularity, and 250M has more irregularities and a higher irregularity. In addition, the apparent density of 250M is substantially equivalent to the apparent density of the reduced iron powder.

The results of the above (1) to (3) are shown in Tables 4 to 6. In Table 4, Atmel 300M (average particle size: about 70 μm) is used as the iron-based powder. In Table 5, Atmel 300NH (apparent density is 3.10 g / cm ³ , average particle size: about 90 μm). Atmel 250M (apparent density was 2.42 g / cm ³ , average particle size: about 85 μm) was used.

  From Tables 4 to 6, it is shown in Experiment No. of the present invention that D50 of graphite powder is 3.0 μm or less and D90 is 10 μm or less. 1-9, 1-11, 1-12, 1-14 to 1-16, 2-3, 2-4, 3-3, 3-4, the weight variation R is 2.0 g or less (that is, the target weight) 4% or less), and the compact density was also good. FIG. It is the scanning electron micrograph which observed 2-3. It can be seen from FIG. 2 that the graphite powder is gathered in the recesses of the iron powder. Also, FIG. FIG. 3 is a scanning electron micrograph of 3-3, and in FIG. 3, it can be observed that graphite powder is gathered and present in the recesses.

  Moreover, the invention example of Table 4 (No. 1-9, 1-11, 1-12, 1-14 to 1-16) using Atmel 300M, and the invention example of Table 5 using Atmel 300NH (2- When comparing 3 and 2-4), the weight variation R is further reduced in the invention example of Table 5. As described above, Atmel 300NH has less irregularities on the surface of the iron powder and lower irregularity than Atmel 300M, but the ratio of large particles is high and the width of the recesses is large. It is thought that it was possible to enter.

  On the other hand, D50 of graphite powder was over 3.0 μm, or D90 was over 10 μm. 1-1 to 1-8, 1-10, 1-13, Experiment No. 2-1, 2-2, Experiment No. In 3-1, 3-2, the weight variation R became large. In addition, Experiment No. In Nos. 1-17, 2-5, and 3-5, since D50 was less than 1.0 μm, the weight variation R was 2.0 g or less, but the molded body density was compared with each experimental example of the present invention. Became smaller. In addition, since a molded object density is influenced also by the shape of an iron-based powder, it is appropriate to evaluate a molded object density for every kind of iron-based powder. That is, no. No. 1-17 is No.1. Compared to 1-9, 1-11, 1-12, and 1-14 to 1-16, the molded body density is small. 2-5 is No.2. Compared with 2-3 and 2-4, the compact density is small. 3-5 is No.3. It can be evaluated that the density of the molded body is small as compared with 3-3 and 3-4.

1: Base 2: Powder supply box 3: Cavity container 4: Rod 5: Air cylinder

Claims (4)

A graphite powder having an average particle diameter D50 of 1.0 μm or more and 3.0 μm or less and D90 of 10 μm or less,
Without adding binder
A mixed powder for powder metallurgy obtained by mixing with an iron-based powder while applying a shearing force. Iron-based powder,
A mixed powder for powder metallurgy, characterized by comprising graphite powder that collects and exists in the recesses of the iron-based powder.   The mixed powder for powder metallurgy according to claim 1, wherein an average particle diameter D50 of the graphite powder is 1.6 µm or more and 2.7 µm or less. The mixed powder for powder metallurgy according to any one of claims 1 to 3, wherein the iron-based powder is atomized iron powder or reduced iron powder.