JP2010106296A - Powder mixture for powder metallurgy and method of manufacturing the same - Google Patents

Abstract

Disclosed is a powder mixture for powder metallurgy that is less susceptible to segregation of alloy powders and the like, has excellent fluidity, and has excellent lubricity with a mold interface during molding.
In a powder mixture for powder metallurgy in which an alloy powder 30 is adhered to an iron-based powder 1 via an organic binder 31, a coating layer 2 with a wetting improver is formed on the surface of the iron-based powder in order from the lower layer side. And a coating layer 3 containing an alloy powder and an organic binder, and a coating layer 4 made of a surface modifier. The surface of the iron-based powder can be uniformly coated with the coating layer of the alloy powder / organic binder by the action of the coating layer of the wetting improver, so that segregation of the alloy powder can be prevented and the lubricity with the mold can be improved. Furthermore, high fluidity can be obtained by the action of the coating layer of the surface modifier.
[Selection] Figure 1

Description

  The present invention relates to a powder mixture for powder metallurgy mainly composed of iron-based powder and a method for producing the same.

Conventionally, a powder mixture for powder metallurgy mainly composed of an iron-based powder includes an iron-based powder such as iron powder, an alloy powder such as copper powder, graphite powder, and iron phosphide powder, and zinc stearate or lithium stearate. In general, a lubricant such as MnS is mixed, and if necessary, a powder for improving machinability such as MnS is mixed.
However, such a powder mixture is a mixture of a plurality of types of powders having different sizes, shapes, and densities, so when transporting after mixing, when charging into the hopper, when discharging from the hopper, and even when using a mold At the time of filling or the like, there is a problem that the powder is not uniformly distributed in the mixture and segregation is likely to occur.

The segregated powder mixture is pressed (compressed) using a mold to form a molded body (hereinafter referred to as “green compact”), and the green compact is sintered to obtain a final product. In such a case, the composition, as well as the size and strength of each product vary greatly, and defective products frequently occur. In particular, many of the alloy powders mixed with the iron-based powder are finer than the iron-based powders, and therefore, when such alloy powders are mixed, the degree of variation described above is further increased.
In order to prevent the segregation of such powder mixture for powder metallurgy, a technique (segregation prevention treatment) for adhering the alloy powder to the iron-based powder surface with an organic binder is known. Since the (intermolecular force) is large, the fluidity of the powder mixture becomes small, and there is a problem that the dischargeability from the hopper and the filling property into the cavity at the time of molding deteriorate.

In order to solve this problem, nanoparticles such as metal oxide and carbon black are added to a powder mixture that has been subjected to segregation prevention treatment with an organic binder, and the adhesion between the particles is enhanced by the effect of the rolls of these nanoparticles. Techniques for reducing the flowability of the powder mixture have been proposed (for example, Patent Documents 1 to 3).
Special table 2008-505249 gazette Special table 2003-508635 gazette JP-T-2002-515542

However, when nanoparticles are added to the powder mixture as in Patent Documents 1 to 3, the fluidity is improved, but on the other hand, the lubricity with the mold interface at the time of molding is reduced. In addition, it is necessary to increase the extraction force after molding, and defects are particularly likely to occur in parts having a particularly large and complicated shape.
Accordingly, an object of the present invention is to provide a powder mixture for powder metallurgy that is less likely to cause segregation of alloy powder and the like, has excellent fluidity, and has excellent lubricity with a mold interface during molding.
Moreover, the other object of this invention is to provide the manufacturing method which can manufacture such a powder mixture for powder metallurgy stably.

As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
(A) When using an organic binder to add an additive powder such as an alloy powder to the surface of the iron-based powder (segregation prevention treatment), the organic bond is poor due to poor wettability between the organic binder and the iron-based powder surface. There is a tendency for the agent to be unevenly distributed in the recesses on the surface of the iron-based powder with unevenness, and as a result, a portion that is not covered with the organic binder (the portion where the ground iron is exposed) occurs, and an appropriate segregation preventing effect cannot be obtained. . For such a problem, it is effective to treat the surface of the iron-based powder with a wetting improver in advance, so that the surface of the iron-based powder can be uniformly coated with an organic binder.

(B) On the other hand, when the iron-based powder surface is uniformly coated with an organic binder, the adhesion between particles is increased and the fluidity is reduced (more than the conventional technique in which the organic binder is coated unevenly). For this reason, the dischargeability from the popper and the filling property into the cavity during molding are deteriorated. For such problems, it is effective to coat the surface of the iron-based powder with an organic binder containing an alloy powder and then coat with a surface modifier. Reduce and effectively improve fluidity.
(C) Uniform coating of the iron-based powder surface with an organic binder not only prevents segregation of the alloy powder, but also improves lubricity with the mold interface during molding, thus reducing the molding pressure. Further, it is possible to reduce the extraction force from the metal mold, and it is possible to reduce the occurrence of component defects. In addition, since it is not necessary to add nanoparticles as used in the prior art in order to improve fluidity, it is easy to ensure lubricity during molding from this point.
(D) By the above, a powder mixture for powder metallurgy is obtained in which segregation of an alloy powder or the like is unlikely to occur, excellent in fluidity, and excellent in lubricity with a mold interface during molding.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] In a powder mixture for powder metallurgy in which an alloy powder is adhered to an iron-based powder via an organic binder, a coating layer formed by a wetting improver, an alloy powder, A powder mixture for powder metallurgy comprising a coating layer containing an organic binder and a coating layer made of a surface modifier.
[2] The powder mixture for powder metallurgy according to [1], wherein the wetting improver is at least one selected from a coupling agent and a nonionic surfactant. .
[3] In the powder mixture for powder metallurgy according to [1] or [2] above, the surface modifier is at least one selected from a coupling agent, a nonionic surfactant, and a siloxane coating agent. A powder mixture for powder metallurgy.

[4] In the powder mixture for powder metallurgy according to [2] or [3] above, the coupling agent is an aluminate coupling agent, a silane coupling agent, a titanate coupling agent, or a zirconium coupling agent. A powder mixture for powder metallurgy, wherein the powder mixture is one or more selected from the group consisting of:
[5] In the powder mixture for powder metallurgy according to [2] or [3] above, the nonionic surfactant is acetylene alcohol, an ethylene oxide adduct of acetylene alcohol, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, A powder mixture for powder metallurgy, wherein the powder mixture is one or more selected from polyoxyalkylene alkyl ethers and polyoxyethylene alkyl amines.
[6] In the powder mixture for powder metallurgy according to [3], the siloxane coating agent is hexamethyldisiloxane, hexaethyldisiloxane, siloxane-modified polyurethane, organopolysiloxane, acrylic-modified polysiloxane, or polyether-modified polydimethylsiloxane. A powder mixture for powder metallurgy, wherein the powder mixture is one or more selected from among them.
[7] A powder mixture for powder metallurgy, wherein the powder mixture for powder metallurgy according to any one of [1] to [6] further includes a lubricant released from the iron-based powder.

[8] A step (A) of forming a coating layer with a wettability improver on the surface of the iron-based powder by adding a solution containing the wettability improver to the iron-based powder, mixing and drying, and the step (A) The alloy powder and the organic binder are added to the iron-based powder that has undergone A), and the mixture is heated while being heated to a temperature equal to or higher than the melting point of the organic binder, and then cooled to form a coating layer on the wetting improver. The step (B) of forming the coating layer containing the powder for alloy and the organic binder, the solution containing the surface modifier added to and mixed with the iron-based powder that has undergone the step (B), and then dried. A process for producing a powder mixture for powder metallurgy, comprising a step (C) of forming a coating layer with a surface modifier on a coating layer containing the alloy powder and an organic binder.
[9] In the manufacturing method of [8] above, the lubricant is released from the iron-based powder by adding and mixing the lubricant to the iron-based powder in step (C) or after completion of step (C). A method for producing a powder mixture for powder metallurgy, characterized in that it is included in a state.

  The powder mixture for powder metallurgy according to the present invention is less susceptible to segregation of powders for alloys, etc., so that it is possible to produce parts with a uniform composition and strength, and because it has excellent fluidity, it can be discharged from a hopper. In addition, it has excellent filling properties in the mold during molding and also has excellent lubricity with the mold interface during molding, so it is possible to reduce molding pressure and extraction force from the mold. Even a large and complicated part can be manufactured without causing defects. Moreover, according to the manufacturing method of this invention, the powder mixture for powder metallurgy which has such outstanding performance can be manufactured stably.

The powder mixture for powder metallurgy of the present invention (hereinafter, simply referred to as “powder mixture”) is a powder mixture in which an alloy powder is attached to an iron-based powder via an organic binder, and the iron-based powder surface is exposed from the lower layer side. In order, a coating layer with a wetting improver (hereinafter referred to as “wetting improver layer” for convenience of description), a coating layer containing an alloy powder and an organic binder (hereinafter referred to as “alloy powder / organic binder layer for convenience of description”). )), And a coating layer with a surface modifier (hereinafter referred to as “surface modifier layer” for convenience of explanation).
Examples of the iron-based powder constituting the powder mixture of the present invention include pure iron powder, alloy steel powder, and partially diffused alloyed steel powder obtained by partially diffusing and adhering alloy components to pure iron powder. One or more of these can be used.

  FIG. 1 schematically shows a cross section of the powder mixture of the present invention (iron-based powder particles and substances adhering thereto), wherein 1 is an iron-based powder and 2 is formed on the surface of the iron-based powder 1. 3 is an alloy powder / organic binder layer (30 is an alloy powder, 31 is an organic binder) and 4 is an alloy powder / organic. It is a surface modifier layer formed on the upper layer of the binder layer 3. On the other hand, FIG. 2 schematically shows a cross section of a conventional powder mixture for powder metallurgy (iron-based powder particles and substances adhering thereto), and an alloy powder and an organic bond are formed on the surface of the iron-based powder 1. Coating 5 (50 is an alloy powder, 51 is an organic binder), but this coating 5 is unevenly distributed in the concave portion of the surface of the iron-based powder, and the convex portion is exposed to ground iron. ing.

Examples of the wetting improver constituting the wetting improver layer 2 include coupling agents such as aluminate coupling agents, silane coupling agents, titanate coupling agents, and zirconium coupling agents; acetylene alcohol, Nonionic surfactants such as ethylene oxide adduct of acetylene alcohol, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyalkylene alkyl ether, polyoxyethylene alkylamine, polyoxyethylene oleyl ether, etc. One or more of these can be used.
The wetting improver layer 2 can be usually formed by adding a solution containing the above wetting improver to the iron-based powder and mixing it, followed by drying.

By providing such a wetting improver layer 2 on the surface of the iron-based powder 1, the wettability with the organic binder is improved, and the alloy powder / organic binder layer 3 is uniform over the entire surface of the iron-based powder 1. (The iron-base powder surface can be uniformly segregated to prevent segregation). As a result, segregation of the alloy powder or the like can be prevented, the lubricity during molding can be improved, and the molding pressure can be reduced and the extraction force from the mold can be reduced.
If the content of the wettability improving agent in the powder mixture is too small, the uniform wettability improving agent layer 2 cannot be formed. If the content is too high, the density of the green compact and the strength of the sintered body are reduced. For this reason, the content of the wetting improver is 0.01 to 0.2 mass% with respect to the total mass of the iron-based powder + alloy powder (that is, 0% relative to the total 100 parts by mass of the iron-based powder + alloy powder). .01-0.2 parts by mass) is appropriate.

Examples of the alloy powder (secondary material) constituting the alloy powder / organic binder layer 3 include powders containing alloy components such as copper powder, graphite powder, iron phosphide powder, Ni, Mo, Cr, and Mn. One or more of these can be used.
The content of the alloy powder in the powder mixture is usually about 0.1 to 10 mass% as a ratio in the iron-base powder + alloy powder. For example, when the iron-base powder is pure iron powder The alloy powder generally contains about 1 to 3% by mass of copper powder and about 0.3 to 1.0% by mass of graphite powder in the ratio of iron-based powder + alloy powder.

Similarly, examples of the organic binder include metal soaps such as zinc stearate, manganese stearate, and lithium stearate; fatty acid amides including bisamides such as ethylene bisstearic acid amide; stearic acid monoamide, erucic acid amide, and the like. Fatty acid amides including monoamides such as: fatty acids such as oleic acid and stearic acid; thermoplastic resins such as polyamide, polyethylene, polyacetal, etc., and one or more of these can be used.
The organic binder may be added in an amount sufficient to allow the alloy powder to adhere to the iron-based powder, and the content in the powder mixture is generally 0.00% relative to the total mass of the iron-based powder + alloy powder. In general, the amount is set to about 05 to 0.8% by mass.
In the alloy powder / organic binder layer 3, the alloy powder and the organic binder are added to the iron-based powder (iron-based powder 1 having the wetting improving agent layer 2) and heated to a temperature equal to or higher than the melting point of the organic binder. The mixture can be formed by cooling while mixing.

Examples of the surface modifier constituting the surface modifier layer 4 include coupling agents such as aluminate coupling agents, silane coupling agents, titanate coupling agents, and zirconium coupling agents; acetylene Nonionic surfactants such as alcohol, ethylene oxide adduct of acetylene alcohol, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyalkylene alkyl ether, polyoxyethylene alkylamine, polyoxyethylene oleyl ether; hexamethyl Siloxane coating agents such as disiloxane, hexaethyldisiloxane, siloxane-modified polyurethane, organopolysiloxane, acrylic-modified polysiloxane, polyether-modified polydimethylsiloxane Etc. it includes, can be used at least one of the foregoing.
The surface modifier layer 4 is usually obtained by applying a solution containing the surface modifier as described above to an iron-based powder 1 (iron-based powder 1 having a wetting improving agent layer 2 and an alloy powder / organic binder layer 3). After adding and mixing, it can be formed by drying.

When the iron-based powder 1 is uniformly coated with the alloy powder / organic binder layer 3, the adhesion between the particles increases and the fluidity decreases, and the discharge from the popper and the filling ability into the cavity during molding are achieved. Gets worse. On the other hand, in the present invention, by providing the surface modifier layer 4 on the upper layer of the alloy powder / organic binder layer 3, high fluidity can be obtained by reducing the adhesion between particles. That is, the surfactant, coupling agent, and siloxane coating agent constituting the surface modifier have a hydrophobic group and a hydrophilic group in one molecule, but the surface of the organic binder covering the iron-based powder surface. Since the hydrophobic part of them coordinates, the surface modifier layer 4 has hydrophilicity. In particular, when a coupling agent is used, the hydrophilic group (silanol group, titanol group, etc.) reacts with H ₂ O and changes to SiO ₂ or TiO _2. Reduces intermolecular forces, thereby increasing fluidity and improving evacuation from the hopper and filling into the cavity.

On the other hand, when the iron-based powder is not uniformly coated with the alloy powder / organic binder layer, the portion with the organic binder reduces the intermolecular force as described above, but the portion without the organic binder. Is hydrophilic, when the outermost layer corresponding to the surface modifier layer 4 is provided, the hydrophilic groups in the molecules of the surfactant and coupling agent constituting this coordinate to the iron surface, The outermost layer becomes a hydrophobic organic layer. In this case, as in the conventional powder mixture, the intermolecular force increases, and the effects of the surfactant and the coupling agent are counteracted. Therefore, the surface of the iron-based powder 1 needs to be uniformly coated with the alloy powder / organic binder layer 3.
If the content of the surface modifier in the powder mixture is too small, the uniform surface modifier layer 4 cannot be formed. If the content is too large, the density of the green compact and the strength of the sintered body are reduced. For this reason, the content of the surface modifier is suitably about 0.01 to 0.2 mass% with respect to the total mass of the iron-based powder and the alloy powder.

As described above, by forming the wetting improver layer 2, the alloy powder / organic binder layer 3, and the surface modifier layer 4 in this order from the lower layer side on the surface of the iron-based powder 1, (1) alloy (2) High fluidity, excellent evacuation from the hopper and excellent mold filling capability, (3) Excellent lubricity during molding, molding pressure , Reduction of the extraction force from the mold, and the occurrence of component defects can be reduced.
In the present invention, addition of nanoparticles (for example, metal oxide, carbon black, etc.) as used in the prior art is not excluded, but the powder mixture of the present invention does not contain nanoparticles. On the other hand, when the nanoparticles are added, the lubricity with the mold interface at the time of molding is lowered, so it is preferable not to add the nanoparticles.

The powder mixture of the present invention further contains an additive released from the iron-based powder such as a lubricant and a cutting improver (not an additive attached to the iron-based powder such as an alloy powder or an organic binder). Can do.
A lubricant is added to reduce the pulling force during molding. Examples of the lubricant include metal soaps such as zinc stearate, manganese stearate, and lithium stearate; fatty acid amides including bisamides such as ethylene bis stearamide; stearic acid monoamide, erucic acid amide, and the like. Fatty acid amides including such monoamides; fatty acids such as oleic acid and stearic acid; thermoplastic resins such as polyamide, polyethylene, polyacetal, and the like, and one or more of these can be used.
The content of the lubricant in the powder mixture is usually about 0.1 to 2 mass% with respect to the total mass of the iron-based powder and the alloy powder.

Next, the manufacturing method of the powder mixture of this invention is demonstrated.
First, a solution containing a wettability improver is added to and mixed with the iron-based powder 1 and then dried at an appropriate temperature (usually about 100 ° C.) to produce a reaction product between the wettability improver solvent and the wettability improver and water. The wetting improver layer 2 is formed by evaporating alcohols (for example, a solvent in the case of a surfactant, an alcohol that is a reaction product of a solvent and water in the case of a coupling agent) and the like. (Step A).
Subsequently, an alloy powder (for example, graphite powder, copper powder) as an auxiliary material is added together with an organic binder to the iron-based powder (iron-based powder 1 having the wetting-improving agent layer 2) subjected to the wetting improvement treatment, The mixture is stirred and mixed while being heated to a temperature equal to or higher than the melting point of the organic binder, and then cooled to solidify the organic binder (step B). Thereby, the alloy powder / organic binder layer 3 in which the alloy powder adheres to the upper layer of the wettability improving agent layer 2 via the organic binder is formed. Here, since the organic binder uniformly coats the entire iron-based powder by the action of the wettability improving agent layer 2, the alloy powder / organic binder layer 3 covering the entire iron-based powder is formed.

After adding and mixing the solution containing the surface modifier to the iron-based powder 1 with the alloy powder / organic binder layer 3 formed in this way, an appropriate temperature (usually about 100 ° C.) And the alcohols that are the reaction product of the surface modifier solvent and the surface modifier with water (for example, a solvent in the case of a surfactant and a solvent and water in the case of a coupling agent). The surface modifier layer 4 is formed by evaporating (alcohol, which is a reaction product) or the like (step C). In the case of a siloxane coating agent, the surface is cured by irradiation with UV while heating.
When the lubricant is added, it may be added at the same time as the surface modifier in Step C, or may be added after the surface modifier layer 4 is formed (after completion of Step C). When a lubricant is added, mixing is performed by a stirring blade type mixer such as a Henschel mixer, a container rotating type mixer such as a V-type blender or a double cone mixer, and the like.

The powder mixture of the present invention can be used for the production of machine parts by applying a general method in powder metallurgy. Specifically, after the powder mixture is filled into a mold and compression-molded, sizing is performed as necessary and sintered to obtain a sintered body. After sintering, heat treatment such as carburizing quenching, bright quenching and induction quenching is performed to obtain a product (machine part).
In the production of such mechanical parts, the powder mixture of the present invention has no segregation such as powder for alloys, so that a product having a uniform composition and strength without variation can be obtained, and also has high fluidity. Since it is excellent in filling into the mold and excellent in moldability during molding and extraction from the mold, even a large and complicated part can be easily manufactured.

[Example of the present invention]
Pure iron powder is used as the iron-based powder, and the alloy powder (subsidiary raw material), organic binder, wetting improver, surface modifier and lubricant shown in Table 1 are blended in accordance with the manufacturing method described above. A powder mixture of the inventive example was produced.
Further, pure iron powder was used as the iron-based powder, and the powder for alloy (sub-material), organic binder and lubricant shown in Table 2 were blended therein to produce a powder mixture of a comparative example. In this production process, the alloy powder and the organic binder are added to the iron-based powder, and after stirring and mixing while heating to a temperature equal to or higher than the melting point of the organic binder, the organic binder is solidified by cooling. Lubricant was added and mixed.

About the powder mixture of this invention example and comparative example which were obtained in this way, the filling property and the compacting property were evaluated by the following methods.
(1) Evaluation of filling property Using the filling tester shown in FIG. 3, filling rate and filling variation were measured as follows. The test powder was filled into a cavity having a length of 20 mm, a depth of 40 mm, and a width of 0.5 mm. The powder box moved in the direction of the arrow in the figure, and the moving speed was 200 mm / second. The holding time of the powder box on the cavity was 0.5 seconds. The filling density after filling (filling mass / cavity volume) expressed as a percentage of the apparent density before filling was defined as the filling rate (complete filling at a filling rate of 100%). Moreover, the same test was repeated 10 times, and the variation in the filling rate was represented by the standard deviation of the filling rate.
(2) Evaluation of compacting properties The test powder was formed into a cylindrical molded product of 11 mmφ × 11 mmH by pressure molding at room temperature and 588 MPa, and the extraction force when the resulting molded product was extracted from the mold was measured. The density of the molded product was measured.

  The above evaluation results are shown in Table 1 and Table 2 together. According to this, the powder mixture of the comparative example shown in Table 2 is extremely inferior in filling properties. On the other hand, the powder mixture of the example of the present invention shown in Table 1 has very good results in both filling properties and compacting properties (density and extraction output).

Explanatory drawing which shows typically the cross section of the powder mixture for powder metallurgy of this invention (iron-based powder particle and the substance adhering to this) Explanatory drawing which shows typically the cross section of the powder mixture for conventional powder metallurgy (iron-based powder particle and the substance adhering to this) Explanatory drawing which shows the filling test machine used for the evaluation test of a filling property in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Iron-based powder 2 Wetting improving agent layer 3 Powder / organic binder layer for alloy 4 Surface modifier layer 30 Powder for alloy 31 Organic binder

Claims (9)

In a powder mixture for powder metallurgy in which an alloy powder is adhered to an iron-based powder via an organic binder,
Powder for metallurgy characterized by having, on the surface of the iron-based powder, in order from the lower layer side, a coating layer with a wetting improver, a coating layer containing an alloy powder and an organic binder, and a coating layer with a surface modifier. blend.   The powder mixture for powder metallurgy according to claim 1, wherein the wetting improver is at least one selected from a coupling agent and a nonionic surfactant.   The powder mixture for powder metallurgy according to claim 1 or 2, wherein the surface modifier is at least one selected from a coupling agent, a nonionic surfactant, and a siloxane coating agent.   The coupling agent according to claim 2 or 3, wherein the coupling agent is at least one selected from an aluminate coupling agent, a silane coupling agent, a titanate coupling agent, and a zirconium coupling agent. The powder mixture for powder metallurgy as described.   The nonionic surfactant is one or more selected from acetylene alcohol, an ethylene oxide adduct of acetylene alcohol, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyalkylene alkyl ether, and polyoxyethylene alkylamine. The powder mixture for powder metallurgy according to claim 2 or 3, characterized in that:   The siloxane coating agent is one or more selected from hexamethyldisiloxane, hexaethyldisiloxane, siloxane-modified polyurethane, organopolysiloxane, acrylic-modified polysiloxane, and polyether-modified polydimethylsiloxane. Item 4. A powder mixture for powder metallurgy according to Item 3.   The powder mixture for powder metallurgy according to any one of claims 1 to 6, further comprising a lubricant released from the iron-based powder. A step (A) of forming a coating layer with a wetting improver on the surface of the iron-based powder by adding and mixing a solution containing the wetting-improving agent to the iron-based powder and then drying;
The powder for alloying and the organic binder are added to the iron-based powder that has undergone the step (A), mixed with heating to a temperature equal to or higher than the melting point of the organic binder, and then cooled, whereby the coating layer by the wetting improver A step (B) of forming a coating layer containing an alloy powder and an organic binder on
A solution containing a surface modifier is added to and mixed with the iron-based powder that has undergone the step (B), and then dried, whereby the surface modification is performed on the coating layer containing the alloy powder and the organic binder. A method for producing a powder mixture for powder metallurgy, comprising the step (C) of forming a coating layer with a quality agent.   The lubricant is contained in a state free from the iron-based powder by adding and mixing the lubricant to the iron-based powder in the step (C) or after the completion of the step (C). A method for producing a powder mixture for powder metallurgy described in 1.

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