JP2010001516A - Metal powder for powder metallurgy, and method for producing sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide metal powder for powder metallurgy which has excellent packing properties upon compacting in powder metallurgy and can produce a sintered compact having high density and excellent dimensional precision, and to provide a method for producing a sintered compact using the metal powder for powder metallurgy. <P>SOLUTION: The metal powder 1 for powder metallurgy is composed of: metal powder 2; and a film 3 covering the surfaces of the respective grains thereof. The film 3 is composed of a material comprising water-soluble organic amines. In this way, the frictional resistance among the respective grains of the metal powder 2 is relaxed with the water soluble organic amines, so as to reduce the resistance of the surface. As a result, the fluidity of the metal powder 1 for powder metallurgy is made excellent. Further, kneaded material comprising the metal powder 1 for powder metallurgy can securely flow to all the corners of the cavity of a molding die, and, a molded body thereby is made into the one to which the shape of the cavity is faithfully transferred. Further, the obtained molded body is made into the one homogeneous and having a reduced individual difference. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a metal powder for powder metallurgy and a method for producing a sintered body.

  In the powder metallurgy method, a metal powder and an organic binder are mixed, formed into a predetermined shape to obtain a formed body, and then the formed body is degreased and fired to obtain a sintered body. The sintered body thus obtained is close to the target shape even if it has a relatively complicated shape, and the amount of post-processing is small. Moreover, since it molds using a metal mold | die, the sintered body of uniform quality can be efficiently produced in large quantities. Thereby, reduction of production cost can be aimed at easily.

However, in the mixture of the metal powder and the organic binder, the fluidity of the mixture is influenced by the lubricity between the metal powders. And when the fluidity | liquidity of a mixture is low, the filling property of the mixture at the time of shaping | molding will fall, and the fall of the density of a molded object will be caused.
In order to solve such a problem, Patent Document 1 discloses a method in which fatty acid metal salt particles are added to a mixture to thereby improve the fluidity of the mixture.

However, since it is difficult for the method disclosed in Patent Document 1 to uniformly disperse the metal powder and the fatty acid metal salt particles in the mixture, it is expected that the lubricity between the metal powders will be improved uniformly. Can not. Therefore, it is difficult to sufficiently improve the fluidity of the mixture, and the filling property at the time of molding is lowered, so that it is difficult to obtain a high-density sintered body.
In addition, a large amount of fatty acid metal salt decomposition products remain in the sintered body. In particular, since the fatty acid metal salt contains a metal atom, there is a concern that it adversely affects various properties of the sintered body.

JP 2000-273502 A

  An object of the present invention is to provide a metal powder for powder metallurgy capable of producing a sintered body having excellent filling properties at the time of molding in powder metallurgy, high density and excellent dimensional accuracy, and sintering using such metal powder for powder metallurgy. It is in providing the manufacturing method of a zygote.

The above object is achieved by the present invention described below.
The metal powder for powder metallurgy according to the present invention is a metal powder for powder metallurgy formed by coating a metal powder having an average particle diameter of 1 to 30 μm with a coating composed of a material mainly composed of water-soluble organic amines. ,
When the tap density of the metal powder for powder metallurgy is A and the tap density of the metal powder is B, A> B is satisfied.
Thereby, the metal powder for powder metallurgy which can manufacture the sintered compact which was excellent in the filling property at the time of shaping | molding in powder metallurgy, was excellent in the high density and the dimensional accuracy is obtained.

In the metal powder for powder metallurgy according to the present invention, the tap density A of the metal powder for powder metallurgy is preferably 1.05 times or more the tap density B of the metal powder.
A compact formed using such a metal powder for powder metallurgy having a tap density has a high filling property and a high density as compared with a compact formed only with a metal powder before film formation. This is because a coating having a relatively low specific gravity is added compared to the specific gravity of the metal powder before forming the coating, which may reduce the density of the molded body. This is because there is a surplus.

In the metal powder for powder metallurgy according to the present invention, the metal powder is an Fe-based alloy powder,
The tap density of the metal powder for powder metallurgy is preferably 4.5 g / cm ³ or more.
It can be said that the metal powder for powder metallurgy having such a tap density has particularly sufficient fluidity even if irregularly shaped particles are contained in the metal powder before film formation. Therefore, when a metal powder for powder metallurgy having such a tap density is filled in a mold, a compact with high dimensional accuracy and density can be produced stably regardless of the properties of the metal powder before film formation. Finally, a sintered body with high dimensional accuracy and high density can be manufactured.

In the metal powder for powder metallurgy of the present invention, the water-soluble organic amine is preferably at least one of alkylamine, cycloalkylamine, alkanolamine and derivatives thereof.
These amines can form a film having sufficient water solubility and sufficient oxidation resistance.

In the metal powder for powder metallurgy according to the present invention, the organic amine derivative is preferably any one of organic amine nitrites, organic amine carboxylates, and organic amine chromates.
These amines can form a film having sufficient water solubility and sufficient oxidation resistance.

In the metal powder for powder metallurgy according to the present invention, the average thickness of the coating is preferably 1 to 20 nm.
Thereby, the coating has a necessary and sufficient thickness from the viewpoint of smoothness and oxidation resistance.
In the metal powder for powder metallurgy according to the present invention, the coating film preferably has a hydrophobic surface.
Thereby, the metal powder for powder metallurgy can suppress adhesion and penetration of moisture, and can suppress oxidation of the metal powder by moisture. As a result, the metal powder for powder metallurgy has particularly excellent oxidation resistance.

In the metal powder for powder metallurgy according to the present invention, the metal powder for powder metallurgy is preferably used for powder metallurgy by metal powder injection molding.
In the metal powder injection molding method, the lubricity between particles of metal powder and the lubricity between particles and an organic binder generally have a great influence on the dimensional accuracy and molding density of the molded body. The metal powder for powder metallurgy of the present invention has high surface smoothness of individual particles due to the action of the coating film, so that the lubricity between particles and between the particles and the organic binder is high, and the fluidity of the whole powder is excellent. ing. For this reason, the kneaded material containing the metal powder for powder metallurgy can surely flow to every corner of the cavity of the mold, and the shape of the molded body is faithfully transferred. Further, due to the high fluidity, the kneaded material can flow uniformly in the cavity. As a result, it is possible to efficiently produce a molded body that is homogeneous and has few individual differences.

The method for producing a sintered body of the present invention is characterized in that the metal powder for powder metallurgy of the present invention and an organic binder are mixed and a sintered body is obtained by a powder metallurgy method using the obtained mixture.
Thereby, the sintered compact with high density and excellent dimensional accuracy can be manufactured.
In the method for producing a sintered body according to the present invention, it is preferable that the surface of the coating provided in the metal powder for powder metallurgy has affinity for the organic binder.
Thereby, the mixture (kneaded material) of the metal powder for powder metallurgy and the organic binder has high fluidity based on the affinity. For this reason, it is possible to produce a molded body with high shape transferability and high fillability, and consequently a sintered body.
In the method for producing a sintered body according to the present invention, it is preferable that the coating film is decomposed at a temperature equal to or lower than a heating temperature in the firing.
Thereby, a particularly high-density sintered body is obtained.

Hereinafter, the metal powder for powder metallurgy and the method for producing a sintered body of the present invention will be described based on preferred embodiments shown in the accompanying drawings.
<Metal powder for powder metallurgy>
First, the metal powder for powder metallurgy according to the present invention will be described.
The metal powder for powder metallurgy of the present invention exhibits high fluidity because the surface of each particle is covered with a coating.

FIG. 1 is a cross-sectional view showing an embodiment of the metal powder for powder metallurgy of the present invention, and FIG. 2 is a front view showing the configuration of a mixer used for producing the metal powder for powder metallurgy of the present invention. In the following description, the upper side in FIG. 2 is referred to as “upper”, the lower side as “lower”, the right side as “right”, and the left side as “left”.
A metal powder 1 for powder metallurgy shown in FIG. 1 includes a metal powder 2 and a coating 3 that covers the surface of each particle. Hereinafter, each part is explained in full detail.

The metal powder 2 may be any metal material powder.
Specifically, as a metal material used for the metal powder 2, for example, Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Pd, Ag , In, Sn, Sn, Ta, W, or alloys thereof.
Among these, as the metal powder 2, powders of various Fe-based alloys such as stainless steel, die steel, high-speed tool steel, low carbon steel, Fe—Ni alloy, Fe—Ni—Co alloy and the like are preferably used. Since such an Fe-based alloy has excellent mechanical properties, a sintered body obtained using this Fe-based alloy powder has excellent mechanical properties and can be used for a wide range of applications.

Examples of the stainless steel include SUS304, SUS316, SUS317, SUS329, SUS410, SUS430, SUS440, and SUS630.
The average particle size of the metal powder 2 is 1 to 30 μm, preferably 3 to 20 μm. Such a metal powder 2 having a relatively small particle diameter has a very large specific surface area, so that the particles are likely to aggregate and inherently have low fluidity. However, in the metal powder 1 for powder metallurgy, the flow is caused by the action of the coating 3. The sex can be enhanced sufficiently. Therefore, according to the metal powder 1 for powder metallurgy obtained by coating the surface of the metal powder 2 having such a particle size with the coating 3, it is possible to fill a small particle size powder with a high density. A sintered body can be easily manufactured. Moreover, it is empirically known that the mechanical strength of the metal material increases in inverse proportion to the 1/2 power of the crystal grain size. That is, by using the metal powder 1 for powder metallurgy having a small particle size, the crystal particle size in the sintered body is reduced, and the mechanical strength can be dramatically increased.

In addition, it is difficult to manufacture the metal powder 2 having an average particle size smaller than the lower limit. Further, when the average particle size of the metal powder 2 exceeds the upper limit, the ratio of the influence of the surface state on the fluidity of the metal powder 2 decreases, so that the fluidity improvement effect by the coating 3 is almost obtained. There is a risk of being lost.
The coating 3 can reduce the surface frictional resistance by relaxing the surface friction of each particle of the metal powder 2. Thereby, the metal powder 1 for powder metallurgy is excellent in fluidity. And the lubricity of each particle | grain, the lubricity of the metal powder 2 and an organic binder, and the lubricity of the metal powder 2 and the inner wall face of a shaping | molding die can each be improved.

In addition to the improvement in fluidity and lubricity as described above, the coating 3 can prevent the metal powder 2 from directly contacting oxygen, moisture, and the like. For this reason, the metal powder 1 for powder metallurgy is excellent in oxidation resistance and weather resistance. That is, the metal powder 1 for powder metallurgy can reliably prevent alteration and deterioration due to oxidation before being subjected to powder metallurgy.
Such a coating 3 is made of a material containing water-soluble organic amines.

Here, the water-soluble organic amines will be described in detail.
These organic amines contain an amino group in each molecule, but since this amino group is a polar group, this amino group is quickly adsorbed on the surface of each particle of the metal powder 2 particularly under the condition of an aqueous solution. can do. This is presumed that the organic aminos and the metal powder 2 are efficiently adsorbed by the interaction between the lone electron pair of the polar group and the adsorption site on the surface of each particle of the metal powder 2. As a result, organic amines can form a dense and strong coating 3 on the surface of each particle.

  The film 3 thus formed can reduce the surface frictional resistance by relaxing the surface friction of each particle of the metal powder 2. Thereby, the lubricity of each particle | grain becomes high and the metal powder 1 for powder metallurgy becomes what was excellent in fluidity | liquidity. In addition, the coating 3 prevents the metal powder 2 from coming into direct contact with oxygen, moisture, etc., so that the metal powder 1 for powder metallurgy is excellent in oxidation resistance and weather resistance.

  Examples of such water-soluble organic amines include water-soluble alkylamines, cycloalkylamines, alkanolamines, allylamines, arylamines, alkoxyamines, or derivatives thereof. Among them, in particular, at least one of alkylamines, cycloalkylamines, alkanolamines and derivatives thereof is preferably used. These amines can form the coating 3 having sufficient water solubility and sufficient oxidation resistance.

Examples of alkylamines include n-hexylamine, n-heptylamine, n-octylamine (normal octylamine), monoalkylamines such as 2-ethylhexylamine, dialkylamines such as diisobutylamine, diisopropyl And trialkylamines such as ethylamine.
Examples of cycloalkylamines include cyclohexylamine and dicyclohexylamine.

  Examples of the alkanolamines include monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine, N, N-dimethylethanolamine, N, N-diethylethanolamine, N- Examples include aminoethylethanolamine, N-methylethanolamine, N-methyldiethanolamine.

Further, the derivatives of these organic amines are not particularly limited, but preferably, organic amine nitrites, organic amine carboxylates, organic amine chromates and the like can be used. Such amines can also form the coating 3 having sufficient water solubility and sufficient oxidation resistance.
Moreover, it is preferable that the average thickness of the film 3 is about 1-20 nm, and it is more preferable that it is about 1-5 nm. Such a coating 3 has a necessary and sufficient thickness from the viewpoint of lubricity and oxidation resistance. Although the average thickness may exceed the upper limit, for example, when a metal powder sintered body is produced using the metal powder 1 for powder metallurgy as in the present embodiment, a large amount of the coating 3 Can remain in the sintered body or the density of the sintered body can be prevented from decreasing.

  When the polar group of the organic amine is adsorbed on the surface of the metal powder 2, the hydrophobic group of the organic amine is exposed on the opposite side. This tendency is particularly remarkable in the alkylamines and cycloalkylamines as described above. In this case, the surface of the powder metallurgy powder 1 (coating 3) exhibits hydrophobicity. For this reason, the metal powder 1 for powder metallurgy can suppress adhesion and penetration of moisture, and can suppress oxidation of the metal powder 2 due to moisture. For these reasons, the metal powder 1 for powder metallurgy has particularly excellent oxidation resistance.

Such metal powder 1 for powder metallurgy exhibits high fluidity as described above, and the fluidity of such powder can be quantitatively evaluated by the tap density.
Specifically, when the tap density of the metal powder 1 for powder metallurgy (the metal powder for powder metallurgy of the present invention) is A and the tap density of the metal powder 2 before being covered with the coating 3 is B, A> B Satisfy the relationship. Thus, even if the metal powder 1 for powder metallurgy is reduced in density by the amount of the coating 3 due to the addition of the coating 3, the improvement in the filling property accompanying the improvement in fluidity reduces the density. There is more to supplement. For this reason, the sintered compact which was finally high-density and excellent in the dimensional accuracy can be manufactured.

  More specifically, the tap density A of the metal powder 1 for powder metallurgy is preferably 1.05 times or more, and more preferably 1.1 times or more the tap density B of the metal powder 2. When the tap density A exceeds the tap density B as described above, the compact formed using the metal powder 1 for powder metallurgy has a higher filling property and higher than the compact formed only of the metal powder 2. It becomes density. This is because the coating 3 having a relatively low specific gravity compared to the specific gravity of the metal powder 2 is added, which may lower the density of the molded body. However, the improvement in the filling property described above compensates for the decrease in the density. This is because there are too many. That is, if the tap density A is within the above range, the density of the sintered body can be dramatically increased as compared with the conventional case.

Further, when the metal powder 2 is an Fe-based alloy powder, the tap density A of the metal powder 1 for powder metallurgy is preferably 4.5 g / cm ³ or more, more preferably 4.7 g / cm ³ or more. preferable. It can be said that such metal powder 1 for powder metallurgy has particularly sufficient fluidity even if the metal powder 2 includes particles having irregular shapes. Therefore, when the metal mold 1 for powder metallurgy having a tap density A within the above range is filled in a mold, a compact with high dimensional accuracy and density can be manufactured stably regardless of the properties of the metal powder 2. Finally, a sintered body with high dimensional accuracy and high density can be manufactured.

Next, a method for producing the metal powder 1 for powder metallurgy shown in FIG. 1 will be described.
In the manufacturing method of the metal powder 1 for powder metallurgy, the metal powder 2 and a water-soluble organic amine are brought into contact with each other, whereby the coating 3 is formed so that the molecules of the organic amine cover the surface of the metal powder 2. Is used.
Specifically, this manufacturing method includes [1] preparing metal powder 2, suspending the metal powder 2 in water to obtain suspension water 4, and [2] water-soluble organic in suspension water 4. After adding the additive 5 containing amines, it has the process of drying the suspension water 4 and obtaining the metal powder 1 for powder metallurgy formed by coating each particle of the metal powder 2 with the component of the additive 5. Hereinafter, each process will be described sequentially.

[1] First, a metal powder 2 is prepared.
The metal powder 2 may be produced by any method. Examples of the method include an atomizing method (for example, a water atomizing method, a gas atomizing method, a high-speed rotating water atomizing method, etc.), a reduction method, a carbonyl method, and a pulverizing method. Etc.
Among these, the metal powder 2 is particularly preferably prepared by various atomizing methods, more preferably a water atomizing method or a high-speed rotating water atomizing method. The atomizing method is a method in which a molten metal obtained by melting a raw material of the metal powder 2 is made to collide with a gas jet or a water jet so that the molten metal is scattered and cooled and solidified to produce a metal powder. According to such an atomizing method, it is possible to efficiently produce a fine metal powder 2 having a narrow particle size distribution (uniform particle size).

  In particular, according to the water atomizing method or the high-speed rotating water stream atomizing method, in addition to the advantages of the atomizing method, a water jet having a higher specific gravity than a gas jet is used, so that the molten metal is severely divided. Thereby, the metal powder 2 containing many irregular shaped particles is obtained. Such metal powder 2 has low lubricity between particles and inherently low fluidity. For this reason, when only the metal powder 2 not covered with the coating 3 is subjected to powder metallurgy, the moldability (fillability into the mold) is low, and the obtained sintered body has low dimensional accuracy and density. Conventionally, it has been a problem.

On the other hand, in the metal powder 1 for powder metallurgy, the fluidity can be sufficiently enhanced by the action of the coating 3. For this reason, according to the metal powder 1 for powder metallurgy, even if the metal powder 2 produced by the water atomization method is used, the moldability is improved, and a high-quality sintered body can be finally obtained.
Further, in the metal powder 1 for powder metallurgy 1 in which the metal powder 2 containing a large number of irregularly shaped particles described above is coated with the coating 3, the irregularly shaped particles are entangled with each other by being pressed during molding. To be molded. For this reason, the shape of the obtained molded body is less likely to collapse, and the shape retainability (shape retention) is excellent. Therefore, according to the metal powder 2 containing many irregularly shaped particles, a sintered body having excellent dimensional accuracy can be reliably produced.

Here, as an example, a method for producing the metal powder 2 by the water atomization method will be described in detail.
First, the raw material of the metal powder 2 is melted to obtain a molten metal.
Next, the molten metal is pulverized by a water atomizing method and cooled and solidified to obtain a metal powder 2. The obtained metal powder 2 is recovered in the state of the suspended water 4 together with the cooling water (water jet) injected by the water atomization method.

[2] Next, an additive containing water-soluble organic amines is added to the obtained suspension water 4, and then the suspension water 4 is dehydrated and dried. Thereby, the metal powder 1 for powder metallurgy obtained by coating each particle of the metal powder 2 with the component of the additive 5 is obtained.
Since the additive 5 contains water-soluble organic amines, the organic amines dissolve in the suspended water 4 and diffuse quickly throughout. Thereby, since organic amines can be spread over the entire suspension water 4 and the organic amines are uniformly in contact with the entire metal powder 2, a uniform coating 3 can be formed.

  Water-soluble organic amines are dissolved in the suspension water 4 and the molecules are dispersed apart. Each molecule contains an amino group, and since this amino group is a polar group, it can be quickly adsorbed on the surface of each particle of the metal powder 2. This is presumed that the organic aminos and the metal powder 2 are efficiently adsorbed by the interaction between the lone electron pair of the polar group and the adsorption site on the surface of each particle of the metal powder 2. As a result, organic amines can form a dense and strong coating 3 on the surface of each particle.

  As described above, the coating film 3 formed in this way can improve the surface smoothness by relaxing the unevenness on the surface of each particle of the metal powder 2. Thereby, the lubricity of each particle | grain becomes high and the metal powder 1 for powder metallurgy becomes what was excellent in fluidity | liquidity. In addition, the coating 3 prevents the metal powder 2 from coming into direct contact with oxygen, moisture, etc., so that the metal powder 1 for powder metallurgy is excellent in oxidation resistance and weather resistance.

  The amount of additive 5 added to suspension water 4 is set based on the amount of organic amines. Specifically, the additive 5 is preferably added in an amount of 0.005 to 10% by mass with respect to the mass of the metal powder 2 and about 0.01 to 5% by mass. It is more preferable that the amount is small. Thereby, the coating 3 having a necessary and sufficient thickness can be formed. As a result, sufficient lubricity is imparted to the coating 3, and the oxidation resistance and weather resistance of the metal powder 2 can be improved by the coating 3.

In addition, by adding the additive 5 to the suspension water 4 in the dehydration step, the coating 3 can be efficiently formed as long as the minimum amount of the additive 5 necessary for forming the coating 3 is added. Is done. That is, the consumption of the additive 5 can be suppressed. As a result, the environmental load due to the additive 5 can be reduced.
In addition, water-soluble organic amines having a boiling point exceeding 100 ° C. are preferably used. Such organic amines are prevented from being vaporized during dehydration and drying described below. As a result, the organic amines reliably remain in dehydration and drying, and the coating 3 is reliably formed.

The additive 5 may contain components other than the organic amines as described above. Examples of such components include surfactants and organic solvents.
As the surfactant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant and the like can be used.
Moreover, the additive 5 can be mixed with the metal powder 2 uniformly by adding the additive 5 and then stirring the suspension water 4. As a result, a more uniform coating 3 can be formed on each particle of the metal powder 2.
Stirring of the suspension 4 can be performed by various types of mixers such as a batch type and a continuous type, and the batch type mixers include a forced type and a gravity type, but preferably a batch type as shown in FIG. The forced mixer 200 is used.

The mixer 200 shown in FIG. 2 includes a pedestal 201, a column 202 provided on the pedestal 201 along the vertical direction, and a support unit 203 that extends from the upper end of the column 202 to the left and right of the column 202.
The mixer 200 includes a container 204, a lid 205 of the container 204, and two stirring blades 206 and 206 that rotate inside the container 204 and stir the contents in the container 204. The lid portion 205 is fixed to the left end of the support portion 203. On the other hand, the lid 205 and the container 204 are separable, and the container 204 can move up and down along the support column 202. Accordingly, the lid 205 can be opened and closed with respect to the container 204 by moving the container 204 up and down.

  A motor 207 is provided on the right side of the support portion 203. Further, a rotating shaft (not shown) is inserted so as to penetrate the lid portion 205. The lower part of this rotating shaft is fixed to each stirring blade 206, 206, while the upper part of the rotating shaft receives the power of the motor 207 via a power transmission mechanism (not shown). With such a mechanism, the stirring blades 206 and 206 can be rotated by the motor 207. Thus, the contents in the container 204 can be stirred by rotating the stirring blades 206 and 206.

A flow path 208 through which steam (water vapor) passes is adjacent to the outer surface of the container 204. By flowing steam through the flow path 208, the suspended water 4 can be dried by utilizing heat exchange between the container 204 and the steam.
Suspended water 4 is put into the container 204 of such a mixer 200. Subsequently, the additive 5 is also added into the container 204.

When such an additive 5 is added to the suspended water 4, water-soluble organic amine molecules are adsorbed on the surface of each particle of the metal powder 2, thereby forming a coating 3 on the surface of each particle. .
Then, the metal powder 1 for powder metallurgy is obtained by dehydrating and drying the suspension water 4.
Moreover, since the suspension water 4 is agitated by the mixer 200, it is suitable for uniformly mixing raw materials having a large difference in the mixing ratio, such as the metal powder 2 and the additive 5, so that the coating 3 can be more uniform. Can be achieved.

  In addition, it is preferable that the content rate of the water in the suspension water 4 is about 3-30 mass%, and it is more preferable that it is about 5-20 mass%. By setting the amount of water within the above range, the water in which the organic amines are dissolved can be reliably turned to the entire metal powder 2. Thereby, the emitted-heat amount accompanying stirring can fully be suppressed, and the quality change and deterioration of the metal powder 2 and the additive 5 by heat | fever can be prevented.

In addition, when a content rate is less than the said lower limit, not only the water does not spread over the whole metal powder 2, but also there is a possibility that the amount of heat generated by friction when the suspended water 4 is stirred increases significantly. On the other hand, when the content rate exceeds the upper limit, the amount of water to be removed becomes enormous, and there is a possibility that it takes a long time for dehydration and drying.
The metal powder 1 for powder metallurgy is obtained as described above.

<Method for producing sintered body>
Next, a method for producing a sintered body using the metal powder 1 for powder metallurgy as described above (a method for producing a sintered body of the present invention) will be described.
As shown in FIG. 3, the method for producing a sintered body of the present invention comprises [A] a metal powder 1 for powder metallurgy mixed with an organic binder 6, and molding the mixture to obtain a molded body 7. [B] A degreasing step of degreasing the molded body 7 to obtain a degreased body 8 and [C] a firing step of firing the degreased body 8 to obtain a sintered body 9. Hereinafter, each process will be described sequentially.

[A] Molding process First, the metal powder 1 for powder metallurgy and the organic binder 6 are mixed.
Next, the obtained mixture is molded into a predetermined shape to obtain a molded body 7.
The production method (molding method) of the molded body is not particularly limited, and examples thereof include a metal powder injection molding (MIM) method, a compression molding (compact molding) method, and an extrusion molding method.
Among these, the MIM method can manufacture a relatively small-sized product or a complex and fine-shaped molded body with a near net (a shape close to the final shape).

Hereinafter, as an example of the molding method, the production of the molded body 7 by the MIM method will be described.
First, the metal powder 1 for powder metallurgy and the organic binder 6 are kneaded to obtain a kneaded product (or a pellet of this kneaded product). Next, the kneaded product is injected into a mold using an injection molding machine, and a molded body 7 having a desired shape is manufactured.
The molded body 7 thus obtained is in a state where the metal powder 1 for powder metallurgy is dispersed almost uniformly in the organic binder 6.

  Here, since the metal powder 1 for powder metallurgy is excellent in fluidity, the kneaded material also has excellent fluidity. In particular, in the MIM method, the lubricity between metal powder particles and the lubricity between the particles and the organic binder generally have a great influence on the dimensional accuracy and molding density of the molded body. As described above, since the metal powder 1 for powder metallurgy has high surface smoothness of individual particles due to the action of the coating 3, the lubricity between particles and the lubricity between particles and organic binder is high, Excellent fluidity. For this reason, the kneaded material containing the metal powder 1 for powder metallurgy can surely flow to every corner of the cavity of the molding die, and the shape of the cavity of the molded body 7 is faithfully transferred. Further, due to the high fluidity, the kneaded material can flow uniformly in the cavity. As a result, it is possible to efficiently produce a molded body 7 that is homogeneous and has few individual differences.

The shape and size of the molded body 7 to be manufactured are determined in consideration of the shrinkage of the molded body 7 due to the subsequent degreasing and firing.
The conditions for injection molding vary depending on various conditions such as the metal composition and particle size of the metal powder 1 for powder metallurgy used, the composition of the organic binder 6 and the blending amount thereof. For example, the material temperature is preferably Is about 80 to 200 ° C., and the injection pressure is preferably about ^{2 to} 30 MPa (20 to 300 kgf / cm ² ).

  Further, as described above, when the polar group of the organic amine is adsorbed on the surface of the metal powder 2, the hydrophobic group of the organic amine is exposed on the opposite side. To do. Therefore, the surface of the metal powder 1 for powder metallurgy is oleophilic and has a high affinity (wetability) for the organic binder 6. As a result, since the mixture (kneaded material) of the metal powder 1 for powder metallurgy and the organic binder 6 has high fluidity based on the above-described affinity, the compact 7 having high shape transferability and high filling properties. Can be obtained.

[B] Degreasing step Degreasing treatment (debinding treatment) is performed on the molded body 7 obtained in the molding step. Thereby, the degreased body 8 is obtained.
In the degreasing process, the molded body 7 is heated to remove the organic binder 6 in the molded body 7 by thermal decomposition.

The heating temperature in the degreasing treatment varies slightly depending on the composition of the organic binder 6 and the like, but is preferably about 100 to 750 ° C, more preferably about 150 to 600 ° C. The organic binder 6 in the molded body 7 can be efficiently removed.
Further, the coating 3 of the metal powder 1 for powder metallurgy in the compact 7 is preferably decomposed (or volatilized) and removed in this degreasing step. By appropriately setting the composition and the like so that the film 3 has such decomposability (or volatility), it is ensured that the components of the film 3 remain in the finally obtained sintered body 9. Can be prevented.

Moreover, although the heating time in a degreasing process changes according to the volume and heating temperature of the molded object 7, when heating temperature is in the said range, it is preferable to set it as about 0.1 to 20 hours, 0.5 More preferably, it is about 15 hours. Thereby, degreasing | defatting of the molded object 7 can be performed sufficiently and necessary.
Further, examples of the atmosphere in the degreasing treatment include an inert gas atmosphere such as nitrogen gas and argon gas, a reducing gas atmosphere such as hydrogen gas, or a reduced pressure (vacuum) atmosphere obtained by reducing these.
In this degreasing step, not all of the organic binder 6 in the molded body 7 may be removed, but a part thereof may be left.

Further, as the water-soluble organic amines which are the main components of the coating 3, it is preferable to use those having a decomposition temperature (or volatilization temperature) lower than that of the organic binder 6. Thereby, the film 3 is removed before the organic binder 6 in the degreasing step. As a result, holes are formed in the portion where the coating 3 was present. Since these holes inevitably communicate with the outside of the molded body 7, the decomposition product of the organic binder 6 is now discharged to the outside of the molded body 7 through the holes as the temperature rises. . In this way, the molded body 7 can be degreased more efficiently while reliably preventing the molded body 7 from cracking due to the sudden volatilization of the organic binder 6.
Since the coating 3 covers the surface of the metal powder 2 and is uniformly dispersed throughout the formed body 7, the above-described pores are also formed uniformly throughout the entire formed body 7. Therefore, the molded body 7 is uniformly degreased, and finally a homogeneous sintered body 9 can be obtained.

When the coating 3 is removed first, this degreasing step may be performed in a plurality of steps (steps) having different degreasing conditions. That is, after holding for a certain time at a heating temperature at which the coating 3 is removed and the organic binder 6 is not removed, this time, if the holding temperature is kept at a heating temperature at which the organic binder 6 is removed, the above-mentioned The removal of the organic binder 6 through such holes is promoted. As a result, efficient and reliable degreasing treatment is possible.
The organic binder 6 preferably contains water-soluble organic amines that are the main components of the coating 3 described above. Thereby, along with the decomposition of the coating 3, the organic binder 6 is also partially decomposed. As a result, degreasing of the organic binder 6 can be further promoted in this degreasing step.

[C] Firing step The degreased body 8 obtained in the degreasing step is fired in a firing furnace. Due to this sintering, the metal powder 2 in the degreased body 8 is diffused at the interface between the particles and becomes a crystal structure. As a result, a sintered body 9 is obtained.
For example, when the metal powder 2 is an Fe-based alloy powder, the firing temperature is preferably about 1000 to 1400 ° C., and about 1100 to 1350 ° C. More preferably. By baking the degreased body 8 at such a temperature, it is possible to prevent the crystal structure from becoming larger than necessary. As a result, it is possible to obtain a sintered body 9 that includes a fine crystal structure and is excellent in mechanical properties and chemical properties.

The firing time is preferably about 0.2 to 7 hours and more preferably about 1 to 4 hours when the firing temperature is within the above range. By setting the firing time within the above range, it is possible to further optimize the sintering of the degreased body 8 and to sinter while reliably preventing the enlargement of the crystal structure.
The atmosphere at the time of firing is not particularly limited, and examples thereof include a reducing atmosphere such as hydrogen, an inert atmosphere such as nitrogen, helium, and argon, and a reduced pressure atmosphere obtained by decompressing each of these atmospheres.
The sintered body 9 can be obtained as described above.

The sintered body 9 obtained in this way has high fluidity of the metal powder 1 for powder metallurgy, so that the shape transferability and filling property of the molded body 7 are improved, and as a result, the dimensional accuracy is high. It will be of density.
Further, according to the present invention, even if the metal powder 2 is fine (small particle size) with an average particle diameter of 1 to 30 μm and contains a lot of irregularly shaped particles, the inherent fluidity seems to be particularly low. Even if it is a thing, by the effect | action of the film 3, the metal powder 1 for powder metallurgy with high fluidity | liquidity is obtained. By using this metal powder 1 for powder metallurgy, a high-density and high-strength sintered body 9 can be obtained.

Further, the coating 3 provided in each particle of the metal powder 1 for powder metallurgy can protect the metal powder 2 and prevent oxidation of the metal powder 2. For this reason, the metal powder 1 for powder metallurgy is excellent in oxidation resistance and weather resistance. And the sintered compact 9 manufactured using this metal powder 1 for powder metallurgy has a low oxygen content, and in addition to chemical characteristics such as oxidation resistance and weather resistance, it also has electromagnetic characteristics and mechanical characteristics. Excellent high-quality products can be obtained.
As mentioned above, although the manufacturing method of the metal powder for powder metallurgy and the sintered compact of this invention was demonstrated based on suitable embodiment, this invention is not limited to this.
For example, in the manufacturing method of a sintered compact, arbitrary processes can also be added as needed.

Next, specific examples of the present invention will be described.
1. Production of metal powder for powder metallurgy and sintered body (Example 1)
[1] First, a metal powder was obtained by a water atomization method using an Fe-based alloy (AISI 4340) as a raw material.
The composition (steel type) of AISI 4340 is as follows: C: 0.38 to 0.43 mass%, Si: 0.15 to 0.30 mass%, Mn: 0.60 to 0.80 mass%, P: 0 0.035% by mass or less, S: 0.040% by mass or less, Ni: 1.65 to 2.00% by mass, Cr: 0.70 to 0.90% by mass, Mo: 0.20 to 0.30% by mass , Fe: the balance.

The obtained metal powder is recovered in the state of suspension water together with the cooling water used in the water atomization method.
Further, when the average particle size of the obtained metal powder was measured by a laser diffraction type particle size distribution measuring device (Microtrack, manufactured by Nikkiso Co., Ltd., HRA9320-X100), the average particle size was 10 μm.

[2] Next, the suspended water was put into the mixer shown in FIG. The water content in the suspension water charged into the mixer was 15% by mass.
Next, an alkylamine derivative was further added as an additive to the mixer. The amount of alkylamine derivative added was 0.045% by mass relative to the mass of the metal powder.

Then, the suspended water was dried while stirring. Thereby, metal powder for powder metallurgy obtained by coating each particle of metal powder with a coating of alkylamine derivative was obtained.
Moreover, when qualitative analysis was performed about the obtained metal powder for powder metallurgy, presence of the alkylamine derivative has been confirmed. From this, it is guessed that the alkylamine derivative mentioned above has coat | covered each particle | grains of metal powder as a film, without volatilizing by drying.
In addition, when the average thickness of the coating film of the metal powder for powder metallurgy was calculated from the specific surface area of the metal powder and the addition amount of the additive, the average thickness of the coating film was 3 nm.
[3] Next, a metal powder for powder metallurgy and a mixture of polypropylene and wax (organic binder) were weighed so as to have a mass ratio of 9: 1 to obtain a mixed raw material.
Next, the mixed raw material was kneaded with a kneader to obtain a compound.

[4] Next, this compound was molded under the molding conditions shown below to produce a molded body.
<Molding conditions>
・ Molding method: injection molding method ・ Molding shape: 20 mm square cube shape ・ Material temperature: 150 ° C.
Injection pressure: 11 MPa (110 kgf / cm ² )

[5] Next, the obtained molded body was subjected to heat treatment (degreasing treatment) under the following degreasing conditions to obtain a degreased body.
<Degreasing conditions>
・ Degreasing temperature: 520 ° C.
・ Degreasing time: 5 hours ・ Degreasing atmosphere: Nitrogen gas atmosphere

[6] Next, the obtained degreased body was fired under the firing conditions shown below. In this way, 10 sintered bodies were produced.
<Baking conditions>
・ Baking temperature: 1200 ℃
-Firing time: 2.5 hours-Firing atmosphere: reduced pressure Ar atmosphere-Atmospheric pressure: 1.3 kPa (10 Torr)

(Example 2)
A metal powder for powder metallurgy and sintered bodies (10 pieces) were obtained in the same manner as in Example 1 except that the additive was changed to a cycloalkylamine derivative.
(Example 3)
A metal powder for powder metallurgy and a sintered body (10 pieces) were obtained in the same manner as in Example 1 except that the additive was changed to an alkanolamine derivative.

Example 4
A water atomized powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 1 except that the raw material was changed to an Fe-based alloy (2% Ni—Fe).
The composition of 2% Ni—Fe is as follows: C: 0.4 to 0.6 mass%, Si: 0.35 mass% or less, Mn: 0.8 mass% or less, P: 0.03 mass% or less, S: 0.045% by mass or less, Ni: 1.5 to 2.5% by mass, Cr: 0.2% by mass or less, Fe: remainder.
The obtained metal powder had an average particle size of 6 μm.

(Example 5)
A water atomized powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 1 except that the raw material was changed to an Fe-based alloy (SUS-316L) and the conditions of the water atomization method were changed.
The average particle size of the obtained metal powder was 4 μm.

(Example 6)
A water atomized powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 1 except that the raw material was changed to an Fe-based alloy (SUS-316L) and the conditions of the water atomization method were changed.
The average particle size of the obtained metal powder was 8 μm.

(Example 7)
A water atomized powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 1 except that the raw material was changed to 9.5Cr-3Si and the conditions of the water atomization method were changed.
In addition, the composition of 9.5Cr-3Si is C: 0.015 mass% or less, Si: 2.90-3.30 mass%, Mn: 0.20 mass% or less, P: 0.040 mass% or less, S: 0.020% by mass or less, Ni: 2.00% by mass or less, Cr: 9.10-9.70% by mass, Mo: 0.20% by mass or less, Fe: remainder.
The obtained metal powder had an average particle size of 23 μm.

(Comparative Example 1)
A metal powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 1 except that the addition of the additive was omitted.
(Comparative Example 2)
A metal powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 4 except that the addition of the additive was omitted.

(Comparative Example 3)
A metal powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 5 except that the addition of the additive was omitted.
(Comparative Example 4)
A metal powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 6 except that the addition of the additive was omitted.

(Comparative Example 5)
A metal powder and sintered bodies (10 pieces) were obtained in the same manner as in Example 7 except that the addition of the additive was omitted.
(Comparative Example 6)
The water atomized powder and sintered body were the same as in Example 1 except that the raw material was changed to Ni-20Cr-LC, the conditions of the water atomization method were changed, and the additive was changed to an alkanolamine derivative. (10 pieces) were obtained.

The composition of Ni-20Cr-LC is as follows: C: 0.03 mass% or less, Si: 0.50-1.20 mass%, Mn: 0.50 mass% or less, P: 0.035 mass% or less, S: 0.030 mass% or less, Fe: 0.50 mass% or less, Cr: 19.00-21.00 mass%, Ni: balance.
The obtained metal powder had an average particle size of 33 μm.

(Comparative Example 7)
A water atomized powder and sintered bodies (10 pieces) were obtained in the same manner as in Comparative Example 6 except that the addition of the additive was omitted.
(Comparative Example 8)
While omitting the addition of the additive to the suspension water and adding the non-water-soluble zinc stearate (fatty acid metal salt) in the compound at a ratio of 0.01% by mass, the same as in Example 1 above. Metal powder and sintered bodies (10 pieces) were obtained.

(Comparative Example 9)
In the same manner as in Example 4 except that the addition of the additive to the suspension water was omitted, and water-insoluble zinc stearate (fatty acid metal salt) was added to the compound at a ratio of 0.01% by mass. Metal powder and sintered bodies (10 pieces) were obtained.
(Comparative Example 10)
The metal powder and sintering were performed in the same manner as in Example 1 except that the addition of the additive to the suspension water was omitted and the water-insoluble stearamide was added to the compound at a ratio of 0.01% by mass. Body (10) was obtained.
(Comparative Example 11)
Metal powder and sintering were performed in the same manner as in Example 4 except that addition of the additive to the suspension water was omitted and water-insoluble stearamide was added to the compound at a ratio of 0.01% by mass. Body (10) was obtained.

2. Evaluation 2.1 Evaluation of powder flowability In order to evaluate the fluidity of the metal powder obtained in each Example and each Comparative Example, the tap density of the metal powder for powder metallurgy was measured based on the method prescribed in JIS Z 2512. did.

2.2 Evaluation of dimensional accuracy of sintered body The dimensional accuracy of the sintered bodies obtained in each of Examples and Comparative Examples was evaluated. In evaluating the dimensional accuracy, the evaluation was performed based on the general tolerance (± 0.5%) in the powder metallurgy field using the metal powder injection molding method and the following evaluation criteria.
<Evaluation criteria for dimensional accuracy>
◎: All sintered bodies are within general tolerance. ○: One sintered body deviated from general tolerance. △: Two to four sintered bodies deviated from general tolerance. X: From general tolerance. There are 5 or more detached sintered bodies

2.3 Evaluation of Relative Density of Sintered Body The sintered body obtained in each Example and each Comparative Example was measured for density by Archimedes method. And the relative density was computed from the true density of each raw material.
2.4 Measurement of Oxygen Content in Sintered Body The oxygen content of the sintered body obtained in each Example and each Comparative Example was measured with an oxygen-nitrogen simultaneous analyzer (type TC-300, manufactured by LECO). did.
The measurement results of 2.1 to 2.4 are shown in Table 1.

As is clear from Table 1, the metal powder (metal powder for powder metallurgy) obtained in each example had a higher tap density than the metal powder obtained in each comparative example. For this reason, it became clear that the metal powder for powder metallurgy obtained in each Example has high fluidity.
In each of the examples, a high-quality sintered body having high dimensional accuracy and relative density and low oxygen content was obtained as compared with each comparative example.

In Comparative Example 6, when compared with Comparative Example 7, sufficient improvement in tap density was not recognized.
In addition, in the sintered bodies obtained in Comparative Examples 8 to 11, a slight improvement in relative density was observed by using a water-insoluble additive, but this did not reach Examples 1-4. It was. In addition, the sintered bodies obtained in Comparative Examples 8 to 11 had a high oxygen content. This is presumably because the metal powder was oxidized after the production of the metal powder and before the production of the compound.

It is sectional drawing which shows embodiment of the metal powder for powder metallurgy of this invention. It is a front view which shows the structure of the mixer used for manufacture of the metal powder for powder metallurgy of this invention. It is a figure for demonstrating embodiment of the manufacturing method of the sintered compact of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Metal powder for metallurgy 2 ... Metal powder 3 ... Coating 4 ... Suspended water 5 ... Additive 6 ... Organic binder 7 ... Molded body 8 ... Degreased body 9 ... Sintered body 200 ... ... Mixer 201 …… Pedestal 202 …… Stand 203 …… Supporting part 204 …… Container 205 …… Cover part 206 …… Agitating blade 207 …… Motor 208 …… Flow path

Claims (11)

It is a metal powder for powder metallurgy obtained by coating a metal powder having an average particle size of 1 to 30 μm with a film composed of a material mainly composed of water-soluble organic amines,
A metal powder for powder metallurgy satisfying A> B, where A is a tap density of the metal powder for powder metallurgy and B is a tap density of the metal powder.   The metal powder for powder metallurgy according to claim 1, wherein the tap density A of the metal powder for powder metallurgy is 1.05 times or more of the tap density B of the metal powder. The metal powder is an Fe-based alloy powder,
The tap density of the powder metallurgical metal powder for powder metallurgy metal powder according to claim 1 or 2 is 4.5 g / cm ³ or more.   The metal powder for powder metallurgy according to any one of claims 1 to 3, wherein the water-soluble organic amine is at least one of alkylamine, cycloalkylamine, alkanolamine, and derivatives thereof.   The metal powder for powder metallurgy according to claim 4, wherein the derivative of the organic amine is any one of nitrites of organic amines, carboxylates of organic amines, and chromates of organic amines.   The metal powder for powder metallurgy according to any one of claims 1 to 5, wherein an average thickness of the coating is 1 to 20 nm.   The metal powder for powder metallurgy according to any one of claims 1 to 6, wherein the coating has a hydrophobic surface.   The metal powder for powder metallurgy according to any one of claims 1 to 7, wherein the metal powder for powder metallurgy is used for powder metallurgy by a metal powder injection molding method.   The metal powder for powder metallurgy according to any one of claims 1 to 8 and an organic binder are mixed, and a sintered body is obtained by a powder metallurgy method using the obtained mixture. Method.   The method for producing a sintered body according to claim 9, wherein a surface of the coating provided on the metal powder for powder metallurgy has an affinity for the organic binder.   The method for producing a sintered body according to claim 9 or 10, wherein the coating is decomposed at a temperature equal to or lower than a heating temperature during the firing.

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