JPS6144105A - Production of sinter-forged member - Google Patents

Abstract

PURPOSE:To produce a sinter-forged member having excellent tensile strength and fatigue strength in the stage of producing the sinter-forged member by coating a mixture composed of raw material metallic powder and graphite powder to the surface ot the part where the required strength in a molding of a powder raw material is high to penetrate said mixture into such part then supplying the raw material powder. CONSTITUTION:The powder mixture mixed with 1-4% copper powder, 0.2- 1.0% graphite powder and 0.5-1.0wt% zinc stearate powder as a lubricating agent and consisting of the balance iron powder is molded. Such molding is subjected to a dewaxing treatment to dissipate the zinc stearate and thereafter the mixture composed of the Fe powder and graphite powder similar to the above-mentioned Fe powder is coated to the part where the required strength is high. The molding is then heated and sintered, by which the surface in the part of the large required strength is subjected to a carburization treatment and the sinter-forged member having mechanical properties such as tensile strength and fatigue strength is inexpensively produced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a sintered forged member, and in detail,
In the production of sintered forged parts, graphite is added to the surface part of the compacted compact, which is the area where the required strength of the sintered forged part is high, in a fine powder made of a material similar to the gold mud powder raw material for powder metallurgy of the sintered forged part. By coating and infiltrating the mixed powder and then performing a heating sintering process, mechanical properties such as tensile strength and fatigue strength can be significantly improved, and surface carburization can be performed at low cost. The present invention relates to a method for producing a sintered forged member.

[Conventional technology]

Recently, as a resource-saving and energy-saving manufacturing method for gold mud parts, hot forging of fully bent powder after sintering has been developed.
The strength of the sintered member is improved by crushing the pores inherent in the surface of the sintered body, and the elongated material is maintained at a strength comparable to that of a steel member manufactured by hot forging. can be done,
The sinter forging method is widely used.

In particular, in recent years, automobile parts, office machine parts,
Metal members such as agricultural machinery parts are manufactured by sintering and forging.

Now, in the conventional sinter-forging method, there are two steps: forming a powder compact by compacting the metal powder raw material for powder metallurgy, heating and sintering the powder compact, and heating and sintering the powder compact. A sintered forged member is manufactured by hot forging a sintered body at a high temperature.

In such a conventional method for manufacturing sintered forged parts,
The density of the powder compact formed by compaction is 5.5
It was ~1.5 g/cra', and was in a porous state.

For this reason, when a sintered body sintered in a heated sintering furnace in a non-oxidizing atmosphere is taken out of the heated sintering furnace into the atmosphere, the sintered body will penetrate from the surface of the sintered body considerably into the inside through the pores of the sintered body. The air is halogenated, and as a result, the surface of the sintered body is often oxidized or decarburized.

Further, since the surface portion of the sintered body is in direct contact with the forging die during hot forging, the surface portion of the sintered body, which has been heated to a high temperature by heat sintering, is cooled by the weir-forming die.

The surface of the cooled sintered body is less compacted by the subsequent hot forging process than the inside of the uncooled sintered body, and therefore residual pores remain on the surface. Cheap.

For these reasons, in the conventional manufacturing method of sintered forged parts, defects such as an oxidized layer, a decarburized layer, or an increase in pores are created on the surface of the sintered body. It was easy to occur.

For this reason, sintered forged parts manufactured by the conventional sintered forging method have sufficient mechanical properties such as fatigue strength and tensile strength.
At present, it is difficult to use sintered forged parts for gold-plated parts that require high strength.

[Problem that the invention seeks to solve]

In view of the current state of the conventional technology as described above, the problem to be solved by the present invention is that in the conventional method for manufacturing a sintered forged member, the problem is that it is formed by powder forming. Since the compacted compact is in a fairly porous state, when the sintered compact is sintered in a heated sintering furnace in a non-oxidizing atmosphere and taken out from the heated sintering furnace into the atmosphere,
Air penetrates considerably from the surface of the sintered body to the interior through the pores of the sintered body, and as a result, the surface of the sintered body is oxidized and decarburized, resulting in mechanical problems such as tensile strength and fatigue strength. In addition, as mentioned above, the compacted powder has a low density, so in a carburizing atmosphere, it will carburize to the inside in a short time, making it difficult to carburize the surface in the heating sintering furnace. If this is not possible and the sintered forged member is surface carburized, it is necessary to add another carburizing step after sintering and forging, which significantly increases the manufacturing cost of the surface carburized sintered forged member.

Therefore, the technical problem of the present invention is that in a method for manufacturing a sintered forged member, the powder of the sintered forged member is Mechanical properties such as tensile strength and fatigue strength are improved by coating and infiltrating a mixed powder made by mixing graphite powder with a fine powder made of a similar material to metallurgical metal powder raw materials, and then performing a process of heating and sintering. In addition to being extremely superior, for the parts of sintered forged parts that require high strength,
The object of the present invention is to enable surface carburization in a heating sintering furnace, and to significantly reduce the manufacturing cost of surface-carburized sintered forged members.

[Means for solving problems]

In view of such problems in the conventional technology, in the present invention, a means for solving the problems in the conventional technology is to form a compact by compacting a metal powder raw material for powder metallurgy. a step of heating the powder compact to perform a dewaxing treatment; a step of heating and sintering the dewaxed powder compact at a temperature range in which the sintering reaction sufficiently proceeds; A method for manufacturing a sintered forged member, comprising a step of hot forging a heated and sintered sintered body at a high temperature to form a sintered forged member, the method comprising: After the compacting process or after the dewaxing process, a mixture of graphite powder and fine powder made of a similar material to the metal powder raw material for powder metallurgy used to manufacture the sintered forged part is added to the surface of the compacted compact. The method of manufacturing a sintered forged member is characterized by coating and infiltrating the powder and then performing the heating and sintering steps described above.

[Effect]

The effects of the present invention will be explained below.

In the present invention, the gold mud powder raw material for powder metallurgy is not particularly limited (although conventional metal powder raw materials for powder metallurgy used for manufacturing ordinary sintered forged parts can be used).

In particular, iron-based metal powder raw materials for powder metallurgy are used in the method for producing a sintered forged member of the present invention.

Furthermore, specifically, a mixed powder consisting of iron powder, copper powder, and graphite powder is used as a metal powder raw material for powder metallurgy.
It is used a lot.

The blending ratio of copper powder is 1°0 to 4.0% by weight (hereinafter, weight% is simply referred to as %), the blending ratio of graphite powder is 0.2 to 1.0%, and the balance is substantially It is common to use iron powder.

To this mixed powder, 0.5 to 1.0% of zinc stearate powder, which is a lubricant, is added and mixed.

Copper powder and graphite powder are dissolved in iron powder during the heating and sintering process, and the rigidity of the sintered and forged parts that are formed.

It has the effect of improving strength etc.

In addition, in the present invention, dewaxing the powder compact before the heat sintering process of the powder compact causes rapid loss of lubricant (zinc stearate powder) in the subsequent heat sintering process. This is to prevent the atmosphere in the sintering furnace from becoming unstable due to dissipation.

In addition, in the process of heating and sintering, the powder compact whose surface is coated and infiltrated with a mixed powder made of fine powder of the same type of material as the compact and graphite powder is placed in a non-oxidizing atmosphere. This is a process of heating and promoting a sintering reaction between gold mud powder raw materials for powder metallurgy to integrate them.

In addition, in the present invention, metal powder for powder metallurgy of the sintered forged member is added to the surface portion of the compacted body, which is a region with high required strength of the sintered forged member, after the compacting process or after the dewaxing process. The reason why a mixed powder of graphite powder is coated and infiltrated into a fine powder made of a material similar to the raw material is as follows. , in the surface depressions and powder grain boundaries that occur during the powder compaction process and the dewaxing process,
Prevents oxidation and decarburization after taking out the sintered body from the heating sintering furnace.

(2) By using fine powder, the sintering reaction of the surface layer is promoted to reduce residual pores in the hot forging process.

(2) Using the mixed graphite powder, only the surface layer is carburized in a sintering furnace to form a predetermined carburized layer after sintering and forging.

This is because it has the following effects.

In addition, in the coating/penetration process of fine powder, coating/? fi
It is desirable that the average particle size of the fine powder and graphite powder is 1/10 or less of the average particle size of the main powder metallurgy raw material.

This is because if the average particle size of the fine powder exceeds 1/10 of the coarse powder raw material for main powder metallurgy, it becomes difficult to infiltrate the fine powder into the surface recesses of the compacted compact. It is.

In addition, a mixed powder of fine powder and graphite powder is coated and infiltrated into the surface of the compact.
The solvent that is made into a slurry to facilitate penetration is not particularly limited, but a quick-drying organic solvent or the like is preferable.

Furthermore, the method of coating and infiltrating the surface of the compacted body with the mixed powder of fine powder and graphite powder is not particularly limited.
Mechanical methods such as spraying can also be applied.

Furthermore, it is desirable that the amount of the mixed powder of fine powder and graphite powder applied to the surface of the compacted body (receiving FR thickness) is 0.51 or less. 5t
This is because Jtit is likely to fall off.

Further, the amount of graphite powder added to the fine powder to be coated and infiltrated into the surface of the compacted compact can be set as desired depending on the carburizing depth required after sintering 2I2.

Additionally, the process of coating and infiltrating the mixed powder of fine powder and graphite powder may be carried out after pressure, molding, or after the dewaxing process, but it is easier to perform the process of coating and infiltrating after the dewaxing process. desirable.

Furthermore, sintering conditions such as sintering temperature and sintering atmosphere can be arbitrarily selected depending on the type of metal powder raw material for powder metallurgy used.

In addition, when the metal powder raw material for powder metallurgy is an iron powder raw material, the atmospheric gas in the heating sintering furnace is so-called R
An endothermic gas known as X-gas is preferred.

Further, the sintering temperature is preferably about 1150°C and the sintering time is preferably about 20 minutes.

In addition, when the metal powder raw material for powder metallurgy consists of iron, copper 2gA lead powder, the iron powder is sintered together by this heating sintering process, and the copper and graphite are diffused into the sintered iron and metal. Convert to solid solution.

Next, the process of manufacturing a sintered forged member by hot forging at a high temperature involves inserting the high-temperature sintered body formed in the heating sintering process into a forging die, and performing hot forging with the forging die. This is the process of

This process is basically the same as the conventional sintering process (ν), and when iron-based metal powder raw materials are used for powder metallurgy, the forging die is made of alloy tool steel. Assuming a forging die and a pressure force during hot forging, it is 8 tons/
The pressing force is usually about cm'.

In that case, if an iron-based metal is used as the metal powder raw material for powder metallurgy, a sintered forged member with a density of about 7.80 g/cm' can be manufactured.

It goes without saying that after the sintering and forging process, the sintering and forging member can be subjected to heat treatment and machining as necessary.

〔Example〕

One embodiment of the present invention will be described below.

In terms of weight ratio, 96.8% pure iron powder with a particle size of 80μ, 2% copper powder with a particle size of 20μ, 0.6% graphite powder with a particle size of about 10μ, and a? 0.6% of zinc stearate powder as a Pt agent was added and mixed for 20 minutes using a ■ type mixer.

Using this mixed powder, the plate thickness was 5 yen and the length of the parallel part was 2 yen.
A powder compact for a 0 mm plate bending test piece was manufactured.

The compacting pressure at that time was 4 ton/cm, and the density of the formed compact was about 6.8 g/cm.
It was Cm'.

Then, the compact was heated in nitrogen gas at 500°C for 30 minutes to perform a dewaxing treatment.

Next, a coating material made by mixing 97% pure iron powder with a grain size of 5μ and graphite powder with a grain size of 1μ and slurry with alcohol was applied to the surface of the parallel part of the test piece with a brush to a thickness of approximately Q, l mm. It was applied to a thickness of .

In addition, when the cross section was observed after coating and drying, it was found that the fine powder covered the surface of the powder compact and also formed into the concavities on the surface. :
I have confirmed that it is transparent.

After that, fine powder of pure iron powder and graphite powder are applied to the surface of the green compact, which is a part of the sintered forged part that requires high strength. A powder compact made by coating and infiltrating a powder mixture with graphite powder is heated to carbon potential (CP-0,6
%) in an endothermic gas atmosphere for 20 minutes at 1150°C, then taken out from the heating sintering furnace, transferred to a forging mold placed in the atmosphere, and immediately subjected to a pressing force of 8 ton/am'. After hot forging, it was cooled by forced air cooling.

It should be noted that it took about 8 seconds to take out the sintered body from the heating sintering furnace and forge and pressurize it with a forge die.

In order to investigate the characteristics of the sintered forged member formed as described above, the forged member was cut and the ``maximum oxidation phase distance depth'', ``topmost surface layer porosity'', and ``charcoal depth'' were measured.

Incidentally, FIG. 1 shows microscopic photographs of the cross-sectional fully bent structures of sintered forged members sintered and forged by the method (a) of the present invention and the conventional method fbl.

As is clear from this figure, the formation of a decarburized layer is observed in the sintered forged member manufactured by the conventional method (Fig. 1 (5)), whereas the sintered forged member manufactured by the method of the present invention is found to have a decarburized layer. In FIG. 1(b), no decarburized layer is observed; rather, it is understood that the surface is slightly carburized.

Furthermore, the "tensile strength" and "107 times fatigue strength" of the forged members were measured.

The measurement results of those characteristics are shown in the table below.

For comparison, a mixed powder made by mixing graphite powder with a fine powder made of a material similar to the total bending powder raw material for powder metallurgy of sintered 9[2-manufactured members] was coated for comparison.・
A sintered forged member was manufactured using the conventional method, except for the infiltration step, with the other steps being completely the same as those of the example.

The various properties of the sintered forged parts manufactured by the conventional method were measured in the same manner as in the examples of the method of the present invention, and the measurement results are also shown in the above table.

As is clear from the table above, the "maximum oxide layer depth" is
While it is 95μ in the conventional method, it is reduced to 15μ in the method of the present invention.

In addition, the "top layer porosity" is 3.2% in the conventional method.
In contrast, the method of the present invention has fewer defects in the outermost surface layer at 0.9% (the "decarburization depth" is also 0.23% in the conventional method, compared to 0.23% in the conventional method). .

In addition, the "tensile strength" was 74.6 (H
/mm', whereas in the method of the present invention, 75.7 Kg/m
It was m'.

Furthermore, "107 times fatigue strength" is 23 times in the conventional method.
．． 2 Kg/mm", the method of the present invention yielded 31°1 Kg/mm".

Moreover, FIG. 2 shows the cross-sectional hardness distribution in the surface portion of the sintered forged member manufactured by the method of the present invention and the sintered forged member manufactured by the conventional method.

As is clear from this figure, in the sintered forged member manufactured by the method of the present invention, an increase in hardness near the surface is observed due to surface carburization, whereas in the sintered forged member manufactured by the conventional method, an increase in hardness is observed in the vicinity of the surface due to surface carburization. A decrease in hardness near the surface is observed due to the influence of the surface decarburized layer.

As mentioned above, according to the method of the present invention, the "maximum oxide layer depth", "topmost surface layer porosity", "decarburization depth", "tensile strength J, rlo 7 times fatigue strength" are all It is understood that this method also shows superior characteristics compared to the conventional method.

〔Effect of the invention〕

As is clear from the above, according to the method for manufacturing a sintered forged member according to the present invention, in the method for manufacturing a sintered forged member, the surface portion of the powder compact, which is a portion with a high required strength of the sintered forged member, Then, by coating and infiltrating a mixed powder made by mixing graphite powder with a fine powder made of a material similar to the total bending powder raw material for powder metallurgy of the product sintered forged part, and then carrying out a process of heating and sintering, In addition to significantly superior mechanical properties such as tensile strength and fatigue strength, it also enables surface carburization in a heated sintering furnace for parts of sintered forged parts that require high strength. There is an advantage that the manufacturing cost of the sintered forged member can be significantly reduced.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional BQ microscopic photograph of a sintered & E2 manufactured member metal structure sintered and forged by the present invention method (al) and the conventional method (bl). Sintering: [2] This is a diagram showing the cross-sectional hardness distribution of the back surface of the manufactured sintered forged member.

Claims (1)

[Claims] 1. A step of compacting a metal powder raw material for powder metallurgy to form a compact; a step of heating the compact to dewax; and a step of dewaxing the powder compact; A step of heating and sintering the compacted compact at a temperature range where the sintering reaction sufficiently proceeds, and hot forging the heated and sintered sintered compact at a high temperature to form a sintered forged member. A method for producing a sintered forged member, the method comprising: applying the relevant material to the surface of the powder compact, which is a region with high required strength of the sintered forging member, after the powder compaction step or after the dewaxing treatment step. A fine powder made of a material similar to the metal powder raw material for powder metallurgy used to manufacture sintered forged parts is coated and infiltrated with a mixed powder containing graphite powder, and then the above-mentioned heating and sintering process is carried out. A method for producing a sintered forged member.