JPH06228607A - Production of sintered metallic part by injection molding of metal powder - Google Patents

Abstract

PURPOSE:To produce a sintered metallic part increased in strength, hardness, etc., and excellent in dimensional accuracy by mixing a resin in a metal powder as a binder, compacting the mixture, degreasing the compact under specified conditions and sintering the compact. CONSTITUTION:Thermoplastic resin such as PE as a binder, wax as a low-mol. wt. org. matter, etc., are added to the powder of steel copper and other metals and alloys having <=100mum grain diameter and mixed to produce an injection- molding green compound. The compound is molded into a desired shape by an injection-molding machine, and the compact is heated to about 300 deg.C in a closed furnace contg. an inert gas or hydrogen atmosphere to volatilize off the low-mol.wt. component such as wax, and then heated to 600-1000 deg.C to decompose the resin into hydrocarbons. The compact is carburized by the hydrocarbons to remove oxides and then sintered at 800-2000 deg.C, and a sintered metallic part increased in strength and hardness and excellent in dimensional accuracy is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sintered metal part by a metal powder injection molding method.

[0002]

2. Description of the Related Art The metal powder injection molding method is a technique used as a method for mass-producing small and complicated metal parts. In this method, first, a metal powder as a raw material and a binder are kneaded to obtain a raw material compound for injection molding. This compound has thermoplasticity and is molded into a desired shape by an injection molding machine. This molding process is essentially the same as molding of plastic materials, and mass molding is possible. Next, unnecessary binder is removed from the obtained molded body. This process is called degreasing. As the degreasing method, a method of heating to evaporate or flow out the binder from the molded body, a method of holding the molded body in a solvent to extract the binder, a method of combining the two, etc. are known. The degreasing method is selected according to the type. Finally, the degreased body is sintered to obtain a metal part.

The metal powder injection molding method is characterized in that it can mold fine metal powders having a high sintered density. Conventionally,
Fine powders having an average particle diameter of 10 μm or less were difficult to mold by a press due to problems of poor fluidity and problems of galling of molds, but this method enables easy molding of fine powders. Moreover, it is possible to form a three-dimensional complex shape. Due to these advantages, the metal powder injection molding method has recently been often used in the production of stainless parts and the like, and its application is expanding to magnetic materials and superhard materials.

By the way, the characteristics of the sintered metal part are greatly affected by the amount of carbon (C) contained therein. For example, Fe-N
The strength and hardness of parts for mechanical structures such as i-type are largely controlled by the C content, and in stainless steel, not only the mechanical properties but also the corrosion resistance are affected by the C content. The same applies to the amount of oxygen (O) in the sintered body. Therefore, also in the production of sintered parts, a technique for controlling the C and O amounts to desired amounts is required. In the metal powder injection molding method, the C and O contents of the final sintered body are influenced by the C and O contents of the powder, the type of binder, the degreasing method, the sintering method, and the shape of the parts.
As a method for adjusting the amounts of C and O, not only a method of adjusting the amount of C and O of the powder but also a method of adding an oxide (Japanese Patent Laid-Open No. 2-57607) is disclosed as a method of adjusting the O amount. . Regarding the amount of C, in the case of reducing the amount of C, a method of decarbonizing by introducing hydrogen gas during degreasing (JP-A-3-45566), and in the case of positively containing C, A method of adding graphite to the raw material powder (Japanese Patent Laid-Open No. 2-39402) is disclosed.

[0005]

However, in the method of adding graphite, the problem that the graphite and the metal powder are difficult to mix uniformly and segregation occurs, and the graphite powder is in the form of flakes, the method of flowing the raw material during injection molding However, there is a problem that the dimensional accuracy of the sintered body is reduced as a result of causing uneven contraction of the sintered body.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the present invention is a firing method capable of appropriately adjusting the C content of a sintered body produced by a metal powder injection molding to improve the dimensional accuracy. The present invention has been completed by finding a method for manufacturing a bonded metal part.

That is, according to the present invention, in order to adjust the C content of the sintered body, part of the degreasing process is performed at 600 ° C.
Provided is a method for producing a sintered metal part, which is characterized in that the heat treatment is carried out at a temperature of ℃ or less and the heat treatment at that time is carried out in a closed heating furnace.

According to the present invention, a desired amount of C can be added in the degreasing step, and the amount of C in the sintered body can be controlled.

[0009]

The present invention will be described in more detail below. In the metal powder injection molding method, a raw material compound obtained by kneading a raw metal powder with an organic binder is molded into a component shape by the injection molding method. Since the binder is an auxiliary agent for molding, it needs to be removed in the degreasing step. The binder usually contains a thermoplastic resin, which is 300 to 5
It is removed by thermal decomposition at 00 ° C. The features of the present invention are:
The heat treatment in the degreasing process during the decomposition of the resin should be 600 ° C or higher.
It is to perform the heat treatment at a temperature range of 000 ° C. or less in a closed heating furnace.

A polymer compound such as a thermoplastic resin is decomposed by heat into a low-molecular gas (decomposition gas). The decomposition behavior varies depending on the type of resin, but the decomposition gas generated by decomposition is considered to be essentially C _{1 to} C ₆ hydrocarbons. Such hydrocarbons generally have a carburizing effect on metals at high temperatures. For example, in methane (CH ₄ ), the metal is carburized by the reaction of CH ₄ → C + 2H ₂ (formula 1), or C is present as free carbon on the metal surface. This reaction behavior is the same for hydrocarbons having a large number of carbons. Therefore, at the time of degreasing, it is possible to leave C in the degreased body if the temperature is raised to a temperature sufficient for the carburization reaction to occur. On the other hand, in the conventional degreasing process for injection-molded articles, it was usual to degrease in the temperature range required for the resin to decompose, and to flow an inert gas such as nitrogen so as to promptly remove the decomposed gas. . However, in the present invention, the purpose is to positively utilize the decomposed gas as the C source, so it is essential to seal the furnace during degreasing.

According to the present invention, the C content of the degreased body after the treatment can be made larger than that of the raw material powder, but the increase amount can be controlled by the heating temperature and the treatment time during the heat treatment. That is, the higher the heating temperature and the longer the treatment time, the greater the amount of C in the degreased body. The absolute value of the amount of increase in the amount of C depends on the steel type of the powder, the characteristics of the powder, and the type of binder, but it can be controlled by the temperature and the processing time.

Further, according to the present invention, C can be uniformly distributed in the degreased body. Therefore, segregation of C and the above-mentioned non-uniform shrinkage, which are problems of the method of adding graphite, do not occur.

As described above, part of the degreasing process is
By performing the heat treatment at a temperature of 00 ° C. or more and 1000 ° C. or less and performing the heat treatment at that time in a closed heating furnace, it is possible to uniformly increase the desired amount of C in the degreased body, and moreover, a dimension without distortion. It is possible to manufacture a sintered body with excellent accuracy.

The injection-molded article used in the present invention contains a metal powder and an organic binder.

Metal powders usable in the present invention include iron, copper,
Examples thereof include powders of titanium, tungsten, nickel, molybdenum and chromium, or alloy powders such as stainless steel and Fe—Ni based alloys. Moreover, when it mentions according to the manufacturing method of powder, carbonyl powder, water atomized powder, gas atomized powder, pulverized powder, etc. can be mentioned. Furthermore, it is also possible to use a mixed powder of two or more of these.
The particle size of the powder can be in the range of 0.01 to 1000 μm, but it is preferable to use the powder of 100 μm or less in view of the fluidity of the compound or the sinterability of the powder.
A more preferable range of particle size is 0.1 to 50 μm.

Examples of components of the organic binder that can be used in the present invention include thermoplastic resins, waxes, plasticizers and lubricants. The resin, as a main component of the binder, imparts plasticity to the raw material compound and also has strength of the molded body at room temperature. As the resin component, polyethylene, polypropylene, polystyrene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polymethacrylic acid alkyl ester, polyamide and the like are known. 1 or 2
Used in combination of two or more species.

Further, in order to improve degreasing property and fluidity,
Wax or plasticizer, which is an organic substance having a lower molecular weight than the resin, is added. As the component having a lower molecular weight than the resin, one kind or a combination of two or more kinds of paraffin wax, higher fatty acid, higher alcohol, higher fatty acid ester, higher fatty acid amide, phthalic acid ester such as diethyl phthalate, dibutyl phthalate and the like can be used. Used. As described above, the raw material compound for metal powder injection molding is generally a mixture of metal powder and several kinds of organic substances such as resin, wax and plasticizer.

The compounding ratio of the organic binder and the metal powder is preferably 3 to 20 parts by weight of the organic binder with respect to 100 parts by weight of the metal powder. If the amount is less than 3 parts by weight, the amount of the binder is insufficient with respect to the metal powder, the fluidity of the compound is poor, and injection molding becomes difficult. On the other hand, if it exceeds 20 parts by weight, injection molding is possible, but shape retention during degreasing cannot be maintained, which is not preferable.

An injection molding compound is manufactured by kneading these metal powders and an organic binder. As the kneader, a Henschel mixer, a plastomill, a pressure kneader, a Banbury mixer, a roll mill, a single screw kneader, a twin screw kneader, or the like can be used, and two or more kinds of these may be combined and kneaded.

The kneaded compound is ground or granulated to obtain a molding material. A general injection molding machine for thermoplastics can be used as the injection molding machine. The injection molding is performed at an injection temperature in the range of 100 ° C to 250 ° C. However, if the injection temperature is too high, the deterioration of the binder component becomes remarkable and the moldability and degreasing property of the recycled material are changed. Is preferably in the range of 100 ° C to 180 ° C.
Degreasing is performed by heating in a degreasing furnace.

The degreasing process carried out in the present invention comprises a pretreatment process for removing low-molecular components other than the resin, and a process for adjusting the C content of the molded product.

As a pretreatment step, in order to obtain a degreased body free from defects and shape deformation, it is necessary to gradually remove low-molecular components other than the resin at a resin decomposition temperature or lower. This is performed under the atmosphere of an atmosphere, an inert gas such as nitrogen or argon, a reducing gas such as hydrogen, and a temperature rising rate of 10 ° C / h to 10 ° C.
It is performed by raising the temperature in the range of 0 ° C./h. Also, a vacuum can be used as the atmosphere. This pretreatment is 3
It is preferably carried out at a temperature of 00 ° C or lower. Moreover, you may use the method of extracting a part of binder component with a solvent.

In the present invention, a part of the degreasing step after the pretreatment is carried out at 600 ° C. or higher in order to control the C content of the molded product.
It is carried out at a temperature of 000 ° C. or lower, and at that time, it is carried out in a closed heating furnace.

Specifically, after removing low-molecular components,
When the reducing or inert gas has been introduced, after the introduction of the gas is stopped, the valve of the conduit for exhausting gas is also closed to close the inside of the heating furnace. Preferably, after stopping the introduction of the reducing or inert gas, the pressure in the heating furnace is set to 10 To.
It is advisable to seal the inside of the heating furnace after adjusting the temperature to rr or less. This is to suppress an increase in pressure during the subsequent temperature rise. After sealing the heating furnace, the temperature is raised to decompose the resin. The amount of C in the degreased body is increased by the generated decomposition gas.

After removing the low-molecular component, 600
Even after the temperature is raised to ˜1000 ° C. and the inside of the heating furnace is closed by the same method, the same effect as the present invention can be obtained.

The treatment temperature and treatment time are selected according to the composition and powder characteristics of the metal powder, the binder species and the amount of C to be increased. However, the processing temperature is preferably in the range of 600 to 1000 ° C. If the treatment temperature is less than 600 ° C, the amount of C does not increase efficiently, and 1000 ° C
If it exceeds, the sintering of the powder proceeds, the gas is not evenly distributed in the degreased body, and a non-uniform distribution of the C content is generated, which is not preferable. Further, as the sintering progresses, the decomposed gas may be trapped in the degreased body, which may adversely affect the characteristics of the sintered body. Therefore, the processing temperature is 600 ℃ or more, 1000 ℃
Hereafter, it is preferably carried out in the range of 700 to 900 ° C.

The sintering step may be carried out subsequently in the same furnace after the degreasing step is completed, or may be carried out in a different furnace after taking out the degreased body from the degreasing furnace. When performing in the same furnace,
It is preferable to raise the temperature after exhausting the inside of the furnace. Sintering is
The sintering is performed at a temperature of 800 ° C. to 2000 ° C. for 10 minutes to 6 hours, and the sintering conditions and the sintering atmosphere are appropriately selected and determined according to the material of the metal powder used and the powder characteristics.

[0028]

【Example】

(Example 1) Average particle size 8.5 μm, C content: 0.03
A water atomized powder of SUS316 composition of wt% and O content: 0.70 wt% was prepared. Add this to polyethylene 4
0 wt%, polybutyl methacrylate 10 wt%, paraffin wax 30 wt%, dibutyl phthalate 20 w
A binder of t% was added in an amount of 10 parts by weight to 100 parts by weight of the metal powder, and the mixture was kneaded using a pressure kneader to produce an injection molding compound. This compound was molded into a rectangular parallelepiped test piece of 4 mm × 10 mm × 50 mm by an injection molding machine.

This test piece (molded body) was degreased and sintered as follows. As a pretreatment step for degreasing, in a nitrogen stream,
The temperature was raised from room temperature to 250 ° C. in 40 hours to remove most of the paraffin wax and dibutyl phthalate. After that, the introduction of nitrogen was stopped, the valve on the exhaust side was closed, and the inside of the furnace was set to 1
The pressure was reduced to Torr and the furnace was closed. Then, the maximum temperature of the degreasing treatment was changed from 550 ° C to 1050 ° C to produce degreased bodies, and the degreased bodies of Invention Examples 1 to 6 were obtained. Specifically, the degreased body was obtained by raising the temperature to the maximum temperature in 1 hour, holding at the maximum temperature of each invention example for 1 hour, and then exhausting and cooling the inside of the furnace. Table 1 shows the results of analyzing the C content of the degreased body when the maximum temperature was changed from 550 ° C to 1050 ° C. As the heating temperature becomes higher, the carbon content of the degreased body increases due to the carburizing action of the decomposition gas generated from the organic binder. A range of 0.30 to 0.45% as a C amount is suitable for removing oxygen in the powder by a reduction reaction with C during sintering, and a sintered body also has preferable characteristics (C: 0 to 0.05%). , O:
0 to 0.30%) is obtained. Here, the sintered body was evaluated under Example 1 in which the maximum heating temperature was 850 ° C. under degreasing conditions (Invention Example 4).

Sintering is carried out under vacuum at 10 ° C. up to 1320 ° C.
The temperature was raised at a rate of 1 minute / minute, the temperature was maintained for 2 hours, and then cooled. This sintered body is referred to as the sintered body of Example 1. As an evaluation of the sintered body,
The dimensions in the width direction and the length direction were measured, and C and O were chemically analyzed. The results are shown in Table 2. When a degreased body having a maximum degreasing temperature exceeding 1000 ° C. was sintered, the C content of the sintered body increased, and a preferable sintered body could not be obtained. Further, if the degreasing temperature is lower than 600 ° C., the O content of the sintered body is not reduced, and a preferable sintered body cannot be obtained.

(Comparative Example 1) SUS3 used in Example 1
16 atomized water atomized powder and 0.3 graphite powder
Kneading and molding were performed in the same manner as in Example 1 except that a powder obtained by mixing 5 wt% was used as the raw material powder. In the degreasing, the temperature was raised from normal temperature to 250 ° C. in 40 hours in a nitrogen stream, then raised to 500 ° C. over 1 hour, and kept at 500 ° C. for 1 hour. The degreasing process was performed in a nitrogen stream while flowing nitrogen. Sintering was performed and evaluated in the same manner as in Example 1.

Comparative Example 2 Using water atomized powder of SUS316 composition mixed with graphite used in Comparative Example 1, a sintered body was manufactured in the same process as in Example 1 and evaluated.

(Comparative Example 3) A sintered body was produced in the same process as in Example 1 except that degreasing was carried out in a nitrogen stream while flowing nitrogen, and the evaluation was made. went.

Table 2 shows the evaluation results of the sintered bodies of Example 1 and Comparative Examples 1 and 2.

In Example 1, since the degreasing treatment according to the present invention was carried out, C increased after degreasing, and the characteristics of the sintered body were favorable. In Comparative Example 1, a graphite powder was added to the raw material powder for the same purpose to produce a sintered body. Although the characteristics are preferable as in Example 1, the difference in shrinkage ratio between the length direction and the width direction is 2.5.
% And 0.5% in Example 1, and the dimensional accuracy was poor. In Comparative Example 2, the C content of the degreased body was excessive, and a sintered body having favorable characteristics could not be obtained. Furthermore, the difference in shrinkage between the length direction and the width direction was 3.2%, which was not good in dimensional accuracy. In Comparative Example 3, since the degreasing step of Example 1 was all performed in a nitrogen stream, the increase of C in the degreasing step was small, the O content of the sintered body was large, and a preferable sintered body could not be obtained.

[0036]

[Table 1]

[0037]

[Table 2]

Example 2 A mixed powder of Fe-4% Ni composition was prepared from carbonyl iron powder and carbonyl nickel powder as raw materials. The average particle size of the mixed powder is 5.5 μm, C
The content was 0.05 wt% and the O content was 0.25 wt%. To this mixed powder, 9 parts by weight of an organic binder having the same composition as in Example 1 was added, and kneading, molding, degreasing and sintering were carried out in the same manner as in Example 1 to evaluate the sintered body.

(Comparative Example 4) Kneading and molding were carried out in the same manner as in Example 2 except that 0.5 wt% of graphite powder was added to the mixed powder of Fe-4% Ni composition of Example 2. Degreasing is performed by raising the temperature from room temperature to 250 ° C. in 40 hours in a nitrogen stream in 40 hours, and then raising the temperature to 500 ° C. in 1 hour.
Hold at 1 ° C for 1 hour. The degreasing process was performed in a nitrogen stream while flowing nitrogen. Sintering was performed in the same manner as in Example 1, and the degreased body and the sintered body were evaluated.

Table 3 shows the evaluation results of the sintered bodies of Example 2 and Comparative Example 3.

By the method according to the present invention and the method in which graphite is added, a sintered body having a high density and controlled C content could be obtained. However, in the method of adding graphite, the difference in shrinkage between the length direction and the width direction is large, and it is understood that the sintered body according to the present invention is superior in dimensional accuracy.

[0042]

[Table 3]

[0043]

According to the manufacturing method of the present invention, a part of the degreasing step of the metal powder injection molding method is performed at 600 ° C. or higher and 1000 ° C.
By performing the heat treatment at the following temperature and performing the heat treatment at that time in a closed heating furnace, it was possible to appropriately adjust the C content after degreasing and improve the dimensional accuracy of the sintered body.

Claims (1)

[Claims] 1. In the step of producing a sintered metal part by a metal powder injection molding method, at least part of the degreasing step is
A method for manufacturing a sintered metal component, which is performed at a temperature of 00 ° C. or higher and 1000 ° C. or lower, and the heat treatment at that time is performed in a closed heating furnace.