JPS62256903A - Production of sintered member - Google Patents

Abstract

PURPOSE:To produce a sintered member having improved tensile strength and resistance to fatigue by subjecting ferrous metallic powder to two stages of compression molding under specific conditions to increase the density thereof and sintering the molding in a nonoxidizing atmosphere. CONSTITUTION:The ferrous metallic powder is compressively molded to form the primary compression molding having 80-90% density ratio. After the primary molding is heated to 800-1,000 deg.C, the molding is again subjected to compression molding to form the secondary compression molding having >=95% density ratio. The secondary stage is preferably executed in the nonoxidizing atmosphere. The compacted compression molding is sintered by heating to 1,100-1,300 deg.C in the nonoxidizing atmosphere and the sintered body is cooled down to an ordinary temp. the sintered member having no defects in the surface part and having the high resistance to fatigue is obtd. by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a manufacturing method for manufacturing a sintered member that is dense and has excellent tensile strength and fatigue strength while saving energy.

[Prior Art] A conventional method for manufacturing a sintered member includes a compression step in which a ferrous metal powder is compression-molded to obtain a compression-molded body, and a compression-molded body is heated at 1100 to 1300°C in a heating sintering furnace. A sintering process of heating and sintering to form a sintered body, a process of cooling the sintered body, and a process of reheating the cooled sintered body to 800 to 1,100°C and forming a bowl mold in the reheated state. A recompression process in which the sintered body is recompressed and densified using the sintered body, and a cooling process in which the sintered body is cooled to room temperature are sequentially carried out (Comparative Example 1, which will be described later).

The tensile strength of the sintered body manufactured using this conventional sintered member manufacturing method is close to that of ingot material, but its fatigue strength is significantly lower than that of ingot material. The reason is assumed to be as follows.

That is, the sintered body is porous. For this reason,
When the sintered body is taken out of the non-oxidizing heating sintering furnace into the atmosphere and subjected to the recompression process, air enters from the surface to a considerable part of the interior through the pores of the sintered body, which causes the surface area to become oxidized. be done. Furthermore, since the surface portion of the sintered body is in direct contact with the forging die used in the recompression step, the surface portion of the sintered body, which has been heated to a high temperature during thermal sintering, is cooled by the forging die.

This cooled surface portion is less likely to be consolidated during recompression than the uncooled interior, and therefore residual pores are likely to remain in the surface portion. For these reasons, in the conventional method for manufacturing a sintered member, defects, mainly linear defects, are likely to occur on the surface of the obtained sintered member. Therefore, the obtained sintered member had problems such as low fatigue strength.

In order to improve problems such as low fatigue strength, it is necessary to carry out a compression process in which iron-based metal powder is compression-molded to obtain a compression-molded body, and the resulting compression-molded body is placed in a heating sintering furnace to a temperature of 1100 to 13
a sintering step of heating and sintering at 00°C to form a sintered body;
The step of cooling the sintered body and the cooling of the cooled sintered body from 800 to
A recompression process in which the sintered body is reheated to 1100°C and in the reheated state is recompressed and densified using a forging die, a cooling process in which the sintered body is cooled to room temperature, and then sintering 100 body
It is possible to perform a heating process to eliminate linear defects by heating to 0 to 1200°C three times (corresponding to Comparative Example 2 described later), but this will improve the fatigue strength, but the repeated heating will cause a large amount of damage. energy is wasted and costs increase. In addition, as a method to improve fatigue strength,
A method of bombarding a compression molded body with solid particles by shot blasting or the like (Japanese Unexamined Patent Publication No. 162701/1983)
has also been developed.

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide a method for manufacturing a dense sintered member that improves fatigue strength while saving energy. .

[Means for Solving the Problems] The method for producing a sintered member of the present invention includes a compression step of compression molding iron-based metal powder to obtain a compression molded body, and a compression molding step of compressing the obtained compression molded body in a non-oxidizing atmosphere. In a method for manufacturing a sintered member, the method includes a sintering step of heating and sintering at 1100 to 1300° C. to form a sintered body, and a cooling step of cooling the heated and sintered sintered body to room temperature, In the above compression process, iron-based metal powder is compression-molded and the density ratio is 8.
A first step of obtaining a primary compression molded product having a density ratio of 0 to 90%, and a second step of heating and recompression molding the primary compression molded product at 800 to 1000°C to form a secondary compression molded product having a density ratio of 95% or more. It is characterized by consisting of two steps.

In the method for manufacturing a sintered member of the present invention, the compression molded body before the sintering step has a density ratio of 95% or more, the surface thereof is compacted, and the pores in the surface portion are closed. Here, the density ratio refers to the ratio to true density. Therefore, during the sintering process, there is less possibility that air will penetrate into the compression molded body.

This makes it difficult to form oxides or a decarburized layer on the surface of the sintered body. Therefore, a sintered member with excellent fatigue tensile properties and tensile strength properties can be manufactured.

The compression step is a step in which iron-based metal powder is pressurized in a compression mold, and is compacted by pressure to obtain a compression molded body having a certain shape. The iron-based metal powder is not particularly limited, and conventional iron-based sintering table ffI powder raw materials used for ordinary sintered members can be used. More specifically, a mixed powder consisting of iron powder, copper powder, and graphite powder is often used as a raw material for iron-based metal powder. In addition, alloyed, prealloyed, or premixed low alloy steel powder can be used as a raw material. For example, commercially available A
There are powders equivalent to l5I4100 and powders equivalent to Al5I4600. In this case, alloying elements such as Ni, Mo, Cr, Mn, and Co1C effectively act to improve the strength. The blending ratio of copper powder is 0.5 to 10% by weight (hereinafter % means ff!M%), and the blending ratio of graphite powder is 0.3 to 10%.
%, the balance being iron powder. To this, 0.5 to 1.0% of zinc stearin, which is a lubricant, is added and mixed.

Here, copper powder and graphite powder are usually dissolved in iron powder during the sintering process, and play the role of improving the rigidity, strength, etc. of the obtained sintered body.

In the first step of the compression process, the density ratio of the primary compression molded body is set to 8.
Consolidate from 0 to 90%. The first step is usually performed at room temperature. When the density ratio of the primary compression molded product is less than 80%, the strength of the primary compression molded product is insufficient, and problems such as peeling of the surface portion and chipping of corners and corners are likely to occur.

On the other hand, if the density ratio of the primary compression molded product exceeds 90%, the compression force during compression molding becomes extremely large. This is disadvantageous in terms of the life of the mold.

In the second step of the compression process, the above-mentioned primary compression molded product is
After heating to 00 to 1000°C, recompression molding is performed to form a secondary compression molded product having a density ratio of 95% or more. In this case 8
If the temperature is less than 00°C, the pressure applied when obtaining a secondary compression molded body having a density ratio of 95% or more becomes excessive. Moreover, if the temperature exceeds 1000°C, the secondary compression molded product will be easily oxidized, which is disadvantageous in terms of energy saving.

The second step of the compression step described above is preferably carried out in a protective atmosphere, that is, a non-melting atmosphere such as an inert gas atmosphere, a reducing atmosphere, or a nitrogen atmosphere, but may be carried out in the air depending on the case. This is because if the sintering step is performed in a reducing atmosphere, even if the secondary compression molded body is slightly oxidized during the compression step, it can be reduced.

The sintering process is a process in which the secondary compression molded body is heated in a non-oxidizing atmosphere to sinter and integrate the iron-based powder particles. Conditions such as sintering temperature and sintering atmosphere can be arbitrarily selected depending on the type of iron-based metal powder used. The atmospheric gas is preferably an endothermic gas generally known as RX gas, decomposed ammonia gas commonly known as Ax gas, or the like. Sintering temperature is 110
The temperature is 0 to 1300°C. Here, if it is below 1100°C, sintering will be insufficient. Specifically, about 1150 degrees is good, but it varies depending on the steel type, and for F13-CIJ-C series it is about 1120 degrees
1150℃, 4600 series 1150-1200℃, 41
00 series is preferably about 1200 to 1250°C. The sintering time is preferably about 20 minutes.

The cooling process can be performed under the same conditions as conventional ones.

[Example 1] First, in the first step of the compression process, commercially available 0.6 graphite powder for powder metallurgy (ACPi made by Nippon Graphite Co., Ltd., commercially available
3 parts by weight of electrolytic copper powder (GE-25) manufactured by Kashi Metals Co., Ltd. and 0.7 parts by weight of zinc stearate powder as a lubricant were blended to form a mixture of Fe-3%Cu-0.6%Gr-0.7%Zn. -5t
The mixture was mixed for 20 minutes using a mold mixer.

Next, the first mold is used to create a plate with a thickness t7 as shown in Figure 2.
~8■, the width D1 of the parallel part is 9.5I@Ill, the arc R1 of the parallel part is 1811℃, the entire length D2 is 98III11
A primary compression molded body for a test piece having a width D3 of 221 was manufactured. Note that the density ratio of the primary compression molded body in the first step was about 81.5%.

Next, in the second step of the compression process, the primary compression molded body is inserted into a heating furnace with an RX gas atmosphere, heated at 900°C for 20 minutes, and the primary compression molded body taken out from the heating furnace is placed in a second mold. Recompression molding was performed to form a secondary compression molded body having a density ratio of 97.5%. The secondary compression molded body is shown in Fig. 3, and has a plate thickness of 7711, a width L1 of the parallel part of 101, an arc R2 of the parallel part of 1711, and an overall length L2 of 1100.
A secondary compression molded body for a test piece with a width of 13 and a width of 231111 was manufactured. Colloidal graphite diluted with water was applied as a lubricant to the cavity of the second mold.

Immediately after completing the compression process described above, the secondary compression molded body with a density ratio of 97.5% is inserted into a heating furnace with an RX gas atmosphere, and the sintering process is performed by sintering it at 1120°C for 20 minutes. The sintered body was taken out of the simulated heating furnace and placed in the atmosphere, and the sintered body was cooled down to room temperature at a rate of 0° C./min for a cooling process.

Example 2] The composition was the same as in Example 1, the first and second steps of the compression process were performed under the same conditions, and the density ratio was 97.5.
% of the secondary compression molded body was formed, and a sintering process was further performed. In the cold fJI step, cooling was performed at a lower cooling section speed than in Example 1, that is, at a rate of 0° C./min. Cooling process: After heating and holding in vacuum at 900°C for 30 minutes, the sintered body is placed in oil and quenched, and then heated and held at 550°C in a nitrogen atmosphere for 60 minutes, thereby quenching and tempering. Processed.

[Example 31] First, in the first step of the compression step, commercially available spray alloy powder equivalent to AIS 14600 (Fe-1,8Vi-0,
5Mo), commercially available graphite powder 0.6% and lubricant 0.7%
Fe-1,8N i-0,5Mo-0,7%G
Powders having the composition of r-0.7% Zn-5t were mixed for 20 minutes using a type mixer. Next, a primary compression molded body was manufactured using the first mold. The density ratio of the obtained primary compression molded product was about 84% (higher than Example 1)
.

Next, in the second step of the compression process, the primary compression molded body is inserted into a heating furnace with an RX gas atmosphere, heated at 950°C for 20 minutes, and then recompression molded using a second mold to achieve a density ratio of 9765%. Next, a compression molded body was formed.

Immediately after completing the above compression process, the secondary compression molded body was inserted into a heating furnace with an IIX gas atmosphere, and heated to 1150°C for 2 hours.
The sintering process was performed by sintering for 0 minutes to form a sintered body. Next, the sintered body was heated from 900°C to 300°C at 0°C/min.
The cooling process was performed by cooling at a rate of .

[Comparative Example 1] From iron-based metal powder blended to have the same composition as in Example 1, a compression molded body was formed as shown in FIG. 1
The density ratio of the compressed compact was approximately 81.5% (
(same density ratio as the primary compression molded product of Example 1).

Next, the compression molded body is inserted into a heating furnace with an RX gas atmosphere, and
A sintering process was performed by sintering at 120° C. for 20 minutes to form a sintered body. Next, the sintered body was cooled to room temperature and a cooling process was performed. After that, the sintered body was inserted into a heating furnace with an RX gas atmosphere and reheated, and after being heated and held at 1000°C for 15 minutes,
The sintered body is recompressed (forged) using an R mold to achieve a density ratio of 97.5%.
And so.

The sintered body was cooled well.

[Comparative Example 2] Using the sintered body with a density ratio of 97.5% formed in Comparative Example 1, the sintered body was further inserted into a heating furnace in an RX gas atmosphere,
After heating and holding at 1120°C for 20 minutes, it was cooled from 900 to 300°C at a cooling rate of -40°C/min.

[Comparative Example 3] A compression molded body shown in FIG. 2 was formed from a wheat-based gold FF powder having the same composition as in Example 1. The density ratio of the compression molded product obtained was about 8165%.

Next, the compression molded body is inserted into a heating furnace with an RX gas atmosphere, and
Local sintering was performed at 120° C. for 20 minutes to form a sintered body. Thereafter, it was gradually cooled by furnace cooling. However, in the process of furnace cooling, 9
The sintered body was recompressed with a forging die at 50°C and the density ratio was 97.
It was set at 5%. After that, heat from 900 to 300℃ at -40℃/
Cooling was performed at a cooling rate of min.

[Evaluation] Figure 4 shows the number of heating times in Example 1 and Comparative Examples 1 to 3;
Energy dissipation [t, respectively indicates the time of recompression.

In order to examine the characteristics of the test pieces of the obtained sintered members of Examples and Comparative Examples, tensile strength and fatigue strength were measured. The tensile strength was measured using a universal tester at a crosshead speed of 2111111/min. Fatigue strength was determined by Sienck type plate bending (plane bending) fatigue testing machine.
This was done by creating Diagram 13J. The test results are shown in Figure 1.

As is clear from Fig. 1, the tensile strength was 73 to 75 kgf/1lIIz in Comparative Examples 1 to 3, whereas
In Examples 1 to 3, it was 73 to 77kc+f/1llt, and a slight increase was observed. On the other hand, the fatigue strength of Comparative Example 1
In Comparative Example 3, it is about 15kOf/mm2, and in Comparative Example 3, it is 18kOf/mm2.
It is about kOf/a+m2, and in comparative example 2 it is 25 k
g f/nv2, whereas in Examples 1 to 3 it was 24 to 26 kof/mm2, 1, and Comparative Examples 1 to 3
Although the composition of the sintered member of Example 1 was the same as that of the sintered member of Example 1, a significant increase was observed. As is clear from the above test results, the fatigue strength of Examples 1 to 3 is significantly increased. The fatigue strength of Examples 1 to 3 is different from that of Comparative Example 2 (because the heating process of compression process - sintering process - cooling process - heating process - recompression process - cooling process - reheating process - cooling process is repeated many times) uses a lot of energy to
It has a fatigue strength comparable to or higher than that of other manufacturing methods (which increase costs). Therefore, in Examples 1 to 3, fatigue strength and tensile strength can be ensured while saving energy.

It is clear from the comparison in Figure 4 that the aim is to save energy.

The reason why the above-mentioned test binding is obtained is that in Examples 1 to 3, the density ratio of the secondary compression molded product is 95% or more, so the surface portion thereof is consolidated and the pores on the surface are closed. For this reason, even during the sintering process, air is difficult to penetrate into the interior through the pores in the surface portion.

Therefore, an oxide layer or a decarburized layer is less likely to form inside the secondary compression molded body. In addition, even if linear defects occur on the surface by continuing the sintering process in a protective atmosphere after the secondary compression, they are easily reduced, resulting in surface modification and fatigue. This is thought to be because it can prevent a decrease in strength. For this reason, it is estimated that 1 g of sintered member with high fatigue strength and high tensile strength is required.

〔Effect of the invention〕

In the method for manufacturing a sintered member according to the present invention, a sintered member with high fatigue strength can be obtained. The reason for this is presumed to be as follows. That is, the density ratio of the secondary compression molded product is 95
% or more, the surface is consolidated and the pores on the surface are crushed. For this reason, even during the sintering process, air is difficult to penetrate into the interior through the pores in the surface portion. Therefore, it is presumed that this is because an oxide layer or a decarburized layer is less likely to form inside the secondary compression molded body, and thus defects are less likely to occur on the surface.

[Brief explanation of drawings]

FIG. 1 is a graph showing the test results of tensile strength and fatigue strength of Examples and Comparative Examples. FIG. 2 is a plan view of the primary compression molded product, FIG. 3 is a plan view of the secondary compression molded product, and FIG. 4 is a graph showing the number of times of heating and energy consumption in Examples and Comparative Examples. Patent Applicant: Toyota Self-Help Co., Ltd. Agent: Patent Attorney: Hirodo Okawa Patent Attorney: Akio Maruyama Figure 1 (kgt/mrn”) (kc]f/
mm2) Figure 4

Claims (3)

[Claims] (1) A compression step of compressing iron-based metal powder to obtain a compression molded body, and placing the obtained compression molded body in a non-oxidizing atmosphere at 110°C.
a sintering process of heating and sintering at 0 to 1300°C to form a sintered body; a cooling process of cooling the heated and sintered sintered body to room temperature;
In the method for manufacturing a sintered member, the compression step includes:
A first step of compression molding iron-based metal powder to obtain a primary compression molded body with a density ratio of 80 to 90%, and heating the primary compression molded body to 800 to 1000°C and then recompression molding to obtain a density ratio of 95. % or more of a secondary compression molded body. (2) In the second step, a second compression molded body having a density ratio of 97.5% or more is formed.
Manufacturing method described in section. (3) The manufacturing method according to claim 1, wherein the second step is performed in a non-oxidizing atmosphere.