JPH0543906A - Production of sintered material - Google Patents

Abstract

(57) [Summary] [Structure] The method for producing a sintered material according to the present invention comprises sintering a molded body obtained by molding a sintering powder made of various metal powders or alloy powders, and having a dew point of -20 ° C. It is characterized in that it is carried out together with a carbonaceous agent such as graphite powder while supplying the following hydrogen gas. [Effect] The carbon can be effectively distributed uniformly in the sintered body, and the carbon content can be effectively controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder metallurgical method for producing a sintered material by sintering a metal or alloy powder, and more particularly to a sintered material having a controlled carbon content. It relates to a powder metallurgical process that can be manufactured.

[0002]

2. Description of the Related Art Currently, as a powder metallurgy method for producing a sintered product, a binder is mixed with a sintering powder such as metal, injection molding is performed, and then a binder obtained by debinding is sintered. There is known an injection molding method for carrying out the above, a press molding method for carrying out press molding of sintering powder without using a binder, and sintering the resulting press molded body.

In these powder metallurgy methods, for example, SUS3
When obtaining a sintered body of 04, SUS304L is used as the sintering powder, and a powder having an extremely low carbon content is used. When trying to obtain a sintered body containing carbon, for example, when trying to obtain a sintered body of S50C,
Pure iron powder is used as a sintering powder, and graphite powder is mixed therein so that the carbon content in the sintered body is 0.5% by weight, followed by molding and sintering.

[0004]

However, in the above-mentioned conventional powder metallurgy method, it is difficult to control the carbon content, and there is a problem that it is not suitable for producing a sintered material containing carbon. is there. For example, when graphite is blended as described above, in the injection molding method, there is a binder as a carbon supply source in addition to the graphite. That is, in the injection molding method, since this binder is used in an amount of about 30 to 70% by volume, it is difficult to control the amount of carbon after sintering. Further, since carbon mixed with the sintering powder reacts with oxygen at a high temperature, even in a press molding method that does not use a binder, it is possible to adjust the amount of carbon in balance with the amount of oxygen contained in the raw material powder. It has become difficult.

Therefore, an object of the present invention is to provide a sintered material having a desired carbon content, in which carbon is uniformly distributed in the sintered body in the injection molding method or the press molding method and the carbon content can be effectively controlled. Another object of the present invention is to provide a method for producing a sintered material capable of obtaining

[0006]

According to the present invention, a compact obtained by compacting a sintering powder made of one or more of metals and alloys is used as a carbonaceous material in hydrogen or a hydrogen-containing atmosphere. A method for producing a sintered material is provided, which comprises subjecting the material to sintering together with an agent.

[0007]

In other words, in the present invention, together with the carbonaceous agent,
By performing the sintering in hydrogen or a hydrogen-containing atmosphere, for example, the reaction between carbon and oxygen during sintering is effectively suppressed, and the density of the compact is low, and hydrogen and carbon are porous in the compact. As a result, the molded body is efficiently carburized and sintered. Therefore, according to the present invention, carbon can be uniformly distributed in the sintered body, and the carbon content can be effectively controlled.

Powder for Sintering In the present invention, as the powder for sintering, at least one kind of various metals and alloys thereof, for example, pure iron, stainless steel, carbonyl iron, pure cobalt, etc. is used, but generally, its average grain size is used. The diameter is preferably in the range of 3-40 μm. The sintering powder can also be used as a mixture with a part of the carbonaceous agent described later.

Molding In the present invention, the above-mentioned powder for sintering is molded, but this molding may be press molding or injection molding. In the case of press molding, the sintering powder is filled in a press die, and the press pressure is generally 10 to 1000.
It is performed under the condition of MPa. In the case of injection molding, a binder is mixed with the sintering powder to prepare a kneaded product for injection molding, and then injection molding is performed using the kneaded product. As the binder used in the preparation of the kneaded material for injection molding,
Known per se, for example, thermoplastic resins such as polyvinyl alcohol, polyethylene, polypropylene, ethylene vinyl acetate copolymer, waxes such as polyethylene wax and paraffin wax, and higher fatty acids such as stearic acid can be used. Can be used alone or in combination of two or more. In general, these binders are preferably used in a proportion of 30 to 70% by volume based on the total amount with the sintering powder on a volume basis. The injection molding is performed, for example, under the conditions of an injection temperature of 80 to 200 ° C. and an injection pressure of 50 to 200 MPa.

In injection molding, the binder in the molded body is removed by debinding after molding. This debinding is performed by heating the molded body to a temperature above the thermal decomposition temperature of the binder used.

Sintering According to the method of the present invention, the molded body obtained above is
Sintering is performed in a hydrogen or hydrogen containing atmosphere with a carbonaceous agent.

Any carbonaceous agent may be used as long as it contains carbon, but graphite (particularly 100% graphite) is preferably used in practice. This carbonaceous agent can be used in powder form or plate form, but in the case of plate form, the reaction rate tends to be slow, so generally use it in powder form. Is preferable, and a powder of 100 mesh under is preferably used. Further, the carbonaceous agent is used in an appropriate amount according to the carbon content of the target sintered material, but as described above, a part thereof can be mixed with the sintering powder and used.

Sintering is carried out under conventionally known conditions except that it is carried out in hydrogen or an atmosphere containing hydrogen.
1100 to 13 depending on the type of sintering powder used
It is carried out by holding the compact at a temperature of 00 ° C for 0.5 to 5 hours.

Sintering in hydrogen or a hydrogen-containing atmosphere
It is carried out while supplying hydrogen gas. At this time, the hydrogen gas used is preferably dry hydrogen gas having a dew point of -20 ° C or lower. If the hydrogen gas contains excessive water, oxygen in the water reacts with carbon, so that the carburizing effect becomes weak, and oxygen remains in the sintered body, causing the generation of oxide inclusions. Become.

The above-mentioned supply of hydrogen gas at the time of sintering is 11
It is preferable to carry out at 00 ° C or higher. When hydrogen gas is supplied from a stage of a temperature that is too low, the action of hydrogen that does not allow carbon to react with oxygen in the molded body is weak, and the sintering also tends to stop. On the other hand, too high temperature, for example 1300 ℃
If it is performed over the range, sintering proceeds before the above-mentioned action of hydrogen is exhibited, and carburization becomes insufficient and non-uniform.
Further, the carbon content in the sintered body tends to increase in proportion to the hydrogen supply time. Further, the supply of hydrogen does not have to be performed until the sintering is completed, and may be stopped in the middle of the sintering as long as the carburization is performed sufficiently uniformly as intended. Thus, according to the present invention, it is possible to obtain a sintered material in which carbon is sufficiently uniformly distributed and the carbon content is effectively controlled.

[0016]

EXAMPLES Examples 1 to 4 Pure iron (carbonyl iron powder) having an average particle size of 6 μm was used as a powder for sintering (carbon content in powder: 0%), and a binder was kneaded and injected. A kneaded product for molding was prepared.
As the binder, low density polyethylene, ethylene vinyl acetate copolymer and stearic acid are used in a ratio of 3: 1: 1.
A blending ratio of (weight ratio) was used, and the compounding ratio of this binder and carbonyl iron powder was 8:92 (weight ratio).

The kneaded product for injection molding was granulated into pellets, and a test piece having a thickness of 5 mm was molded using an injection molding machine (injection pressure: 100 MPa, injection temperature: 160 ° C.). The test piece was heated to 450 ° C. in a nitrogen atmosphere at a temperature rising rate of 20 ° C./hr (furnace internal volume: 200 liters) to remove the binder by thermal decomposition.

Next, 100 g of graphite powder (100 mesh under) was placed in an oven box (50 mm × 50 mm × 50) of alumina.
mm) and place it 100 mm away from the test piece,
The inside of the furnace is evacuated and heated to 700 ° C at a heating rate of 30 ° C / min, and further heated to 1300 ° C at a heating rate of 10 ° C / min,
The temperature of 1300 ° C was maintained for 1 hour.

At this time, in Example 1, hydrogen gas having a dew point of −79 ° C. was supplied for 30 minutes at a rate of 20 liters / minute from the time when the temperature in the furnace reached 1300 ° C. In Example 2, the hydrogen gas was supplied at a rate of 20 liters / minute for 60 minutes from the time when the temperature in the furnace reached 1300 ° C. In Example 3, the inside of the furnace is 1100.
From the time when the temperature reached ℃, the hydrogen gas was supplied for 20 minutes at a rate of 20 liters / minute (temperature at the end of hydrogen supply: 1300
C). In Example 4, from the time when the temperature in the furnace reached 1100 ° C, the hydrogen gas was supplied at a rate of 20 liters / minute for 80 minutes (temperature at the end of hydrogen supply: 1300 ° C).

After the holding at the temperature of 1300 ° C. was completed, the furnace was cooled to 1100 ° C., and then nitrogen was introduced into the furnace for forced cooling. Table 1 shows the carbon content, relative density, etc. of the obtained sintered body.
Shown in. The carbon content was measured for 10 samples and shown as the average value. In each of the examples, the variation in carbon content was extremely small and was within the range of 2.1 to 3.3%.

The sintered bodies obtained in each of the above examples are
When a sample obtained by corroding this with Nital was examined under an optical microscope, it was confirmed that iron carbide was uniformly dispersed. Further, when the sintered body was examined by X-ray, no defect was recognized.

Examples 5 and 6 A sintered body was manufactured in the same manner as in Example 1 except that graphite powder having an average particle size of 20 μm was mixed with pure iron (graphite content 0.15% by weight). Was carried out (Example 5). Further, as a sintering powder, a sintered body was manufactured in exactly the same manner as in Example 2 except that graphite powder having an average particle size of 20 μm was mixed with pure iron (graphite content: 0.15 wt%) (Example 6). ).
Table 1 shows the carbon content, relative density, etc. of the obtained sintered body. Further, in these sintered bodies, iron carbide was uniformly dispersed, and no defects were observed, as in the above-mentioned examples.

[0023]

[Table 1]

Comparative Examples 1 to 6 Sintered bodies were manufactured in the same manner as in each of Examples 1 to 6 except that the hydrogen gas supplied had a dew point of + 10 ° C. Table 2 shows the carbon content, relative density, etc. of the obtained sintered body.

In Comparative Examples 1, 3, and 5, the carbon content of the sintered body was remarkably varied, for example, the variation of the data of 10 pieces was 17 to 22%, and it was difficult to adjust the carbon content. Met. Further, in Comparative Examples 2, 4, and 6, many oxide inclusions were observed in the sintered body (the oxide inclusions were confirmed by observation with an optical microscope and EPMA).

[0026]

[Table 2]

[0027]

According to the present invention, when the sintered material is manufactured by the powder metallurgy method, the carbon content of the sintered material can be easily adjusted.

Claims (3)

[Claims] 1. A compact obtained by compacting a sintering powder made of one or more of metals and alloys is subjected to a sintering treatment together with a carbonaceous agent in hydrogen or a hydrogen-containing atmosphere. A method for producing a characteristic sintered material. 2. The manufacturing method according to claim 1, wherein hydrogen gas having a dew point of −20 ° C. or lower is used as the atmosphere for sintering. 3. The manufacturing method according to claim 1, wherein the sintering is performed at a temperature of 1100 ° C. or higher.