JPH0768568B2 - Method for manufacturing high strength and high ductility sintered body - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-strength processed material obtained by swaging a sintered body made of a W-Fe-Ni alloy or the like at a warm temperature. The present invention relates to a method for manufacturing a highly ductile sintered body.

[0002]

2. Description of the Related Art A W-Fe-Ni alloy, which is one of sintered bodies, is used as a high-strength, high-ductility material by utilizing the property of W for applications such as weights and radiation shielding. ing. When manufacturing this sintered body, generally, as shown in FIG. 4, 90% to 97% by weight of W powder and the remaining Fe and Ni powders are prepared and mixed, and this is mixed with CIP ( Cold isostatic pressing) to form a green compact into a predetermined shape, and then heat the green compact to a temperature above the liquidus temperature of the Fe-Ni alloy to convert the W powder to the Fe powder. -Sintering with Ni alloy bonding (pre-sintering and main sintering). The obtained sintered body is subjected to mechanical processing such as machining after heat treatment, and further preheated to 400 to 600 ° C. in order to give predetermined mechanical characteristics (improvement of strength, etc.) depending on the application. Perform warm processing such as swaging. After that, post heat treatment is performed to obtain a sintered body.

[0003]

However, in the above swaging, when the plastic working rate exceeds 20%, the ductility of the obtained sintered body is drastically lowered. . Moreover, this phenomenon tends to be more remarkable as the preheating temperature is higher. Therefore, it is difficult to perform swage processing on a sintered body with a processing rate of more than 20% with a material requiring good ductility, and therefore swage processing provides sufficient mechanical properties. There is a problem that it cannot be improved.

The inventors of the present invention have variously investigated and investigated the decrease in ductility in the swaging, and as a result,
Fe that becomes a binder with W particles during swaging
-It is thought that this may be because the Ni alloy causes plastic flow having a different aspect. That is, the W-Fe-Ni alloy sintered body has a structure in which a high-strength, high-ductility Ni / Fe phase is melted around W particles, and when this is swaged, it is sintered with a processing tool. It was thought that either W particles or Ni / Fe would preferentially flow due to the frictional force at the contact surface with the body, resulting in the W particles contacting each other. In particular, it was confirmed that when the sintered body was processed at a processing rate of more than 20%, the number of contact portions was extremely large. At this contact portion, the contact portion is brittle, and it is considered that this may cause a decrease in ductility.

When the above points are verified in terms of the hardness of the sintered body, as shown in FIG. 3, the processed material (comparative material) manufactured by the conventional method has a surface layer contacting the center part with the processing tool. The hardness of the side is high, which is due to W particles and Fe-Ni.
As a result of the difference in plastic flow from the alloy, the flow of the Fe-Ni alloy increases and the hardness increases, and it is considered that the decrease in ductility is due to the contact of W particles with it. The present invention has been made in the background of the above circumstances, and W
Provided is a method for producing a high-strength and high-ductility sintered body, which can obtain a high-strength and high-ductility sintered body by preventing the occurrence of a contact portion between particles as much as possible and preventing a decrease in ductility. The purpose is to do.

In order to solve the above problems, a method for producing a high-strength and high-ductility sintered body according to the present invention is a method of sintering high-strength powder.
When swaging the body, at least
Is characterized in that a metal film mainly composed of Cu is formed on the surface in contact with the working tool, and then the sintered body is swaged at a warm temperature.

Examples of the high-strength powder include W powder, but the present invention is not limited to this, and other high-strength particles such as WC may be used. With respect to the high-strength powder, in the W particles, a binder is added so that an Fe-Ni alloy is used, and further, if necessary, other additives are mixed,
Sinter. The process until obtaining a sintered body is not particularly limited in the present invention, and a sintered body obtained by a conventional method or the like is used.

The metal film formed on the surface of the sintered body is
It can be done by plating, metal spraying, etc.
The method is not limited to these methods, and the point is that the method can be used as long as a required metal film can be formed, and the forming method is not limited. The metal coating may be mainly Cu, and more preferably pure copper. Further, the metal film does not necessarily have to be formed on the entire surface of the sintered body, and may be formed on at least the necessary surface of the contact surface with the processing tool. For the film thickness,
If it is too thin, the film may break, and if it is too thick, the lubrication performance deteriorates, so a thickness of 5 μm to 50 μm is desirable.

After the film is formed, the sintered body is preheated in order to perform swaging at a warm temperature. The preheating temperature is not particularly limited, but it can be heated to a higher temperature than the conventional method, and the temperature is preferably 450 to 650 ° C. The reason is that if the temperature is lower than 450 ° C., the deformability of the sintered body decreases, and there is a risk that work cracks may occur.
This is because if the temperature exceeds 50 ° C., transformation occurs in the sintered body and ductility decreases. After the swaging at this temperature , a post heat treatment is performed if necessary.

[0010]

In other words, according to the present invention, the metal coating formed on the surface of the sintered body has a lubricating property peculiar to Cu-based metal, and by warm working the sintered body in this state. The lubricity between the processing tool and the surface of the sintered body is improved, and the frictional force between them is reduced. As a result, the high-strength particles and the binder in the sintered body structure evenly plastically flow, and aggregation of the high-strength particles and an increase in the contact portion between the high-strength particles are prevented as much as possible, and a decrease in ductility is prevented. The obtained sintered body is sufficiently processed to increase its strength, and the decrease in ductility is prevented, so that a high-strength and highly ductile sintered body can be obtained.

[0011]

EXAMPLE According to the process of FIG. 1, W having an average particle size of about 5 μm
93% by weight of the powder and 7% by weight of Ni and Fe powder having an average particle size of about 5 μm (however, the Ni: Fe weight ratio is 7/3) are mixed and filled in a rubber bag having a predetermined shape, It was compressed by hydraulic molding to obtain a rod-shaped green compact with a diameter of 50 mm.
If necessary, this green compact is machined, and then
Pre-sintering and main sintering were performed. For pre-sintering, 13
The sintering is performed by heating to 00 to 1400 ° C. and holding for 4 hours. The main sintering is 1460 to 15 for the pre-sintered green compact.
It heated at 50 degreeC and hold | maintained for 1 hour, and performed. The obtained sintered body was heat-treated at 1100 ° C. for 10 hours, and then subjected to necessary milling in the cold.

Then, pure copper was plated on the entire side surface of the sintered body to a thickness of 5 μm or more. Furthermore, after applying a molybdenum disulfide-based lubricant to the surface of this sintered body,
The invention material was obtained by performing swaging for compressing the side surface of the sintered body by preheating by heating to 600 ° C. at processing rates of 10%, 20%, and 25%, respectively. Further, as a comparative example, a comparative material was obtained by heating the above lubricant-coated sintered body to 550 to 600 ° C. without performing plating with pure copper and performing swaging in the same manner as above. The above-mentioned invention material and comparative material were post-heat-treated at 400 to 600 ° C. A tensile test was conducted on the above-mentioned invention material and comparative material, and the test results, elongation and tensile strength, are shown in FIG. Further, using the same sintered body as the above-mentioned sintered body, an oily graphite lubricant was applied to the sintered body, and the invention method and the comparative example were swaged at a processing rate of 10% in the same manner as above. The Rockwell hardness of each of the obtained invention material and comparative material was measured while changing the depth in the radial direction, and the results are shown in FIG.

As is clear from FIG. 2, the invention material has excellent ductility, whereas the comparative material has a sharp decrease in elongation at a processing rate of more than 20%, and thus has a sufficient ductility. I couldn't get it. Further, as is clear from FIG. 3, the invention material obtained almost uniform hardness irrespective of the depth, but the comparative material had a particularly high hardness in the surface layer portion. It seems that W particles are condensed in the surface layer. Note that this invention material also had excellent ductility. Although molybdenum disulfide-based lubricants and oil-based graphite-based lubricants are used as the lubricants in the above-described examples, the lubricants are not limited to these, and other lubricants may be used.

[0014]

As described above, the method for producing a high-strength and high-ductility sintered body of the present invention is performed by sintering high-strength powder.
When swaging the body, at least
Also , since a metal film mainly composed of Cu is formed on the surface contacting the processing tool, and then the sintered body is swaged at a warm temperature, it is possible to prevent a decrease in ductility at the time of swaging. As a result, it is possible to perform processing with a sufficient processing rate, and as a result, it is possible to obtain a sintered body having high strength and high ductility.

[Brief description of drawings]

FIG. 1 is a chart showing steps of a manufacturing method of an example.

FIG. 2 is a graph showing a tensile strength-elongation relationship of sintered bodies of Examples and Comparative Examples.

FIG. 3 is a graph showing hardness distributions in radial depths of sintered bodies of Examples and Comparative Examples.

FIG. 4 is a chart showing steps of a conventional manufacturing method.

Claims (2)

[Claims] 1. A sintered body obtained by sintering high-strength powder is swaged.
At the time of machining , at least the processing tool of the sintered body
A metal film mainly composed of Cu is formed on the contact surface,
Thereafter, the sintered body is swaged warmly, and a method for producing a high-strength and high-ductility sintered body, the method comprising: 2. The sintered body is made of a W—Fe—Ni alloy,
Pure copper is plated on the surface of this sintered body to form a metal film,
After that, the sintered body is preheated to 450 to 650 ° C.
A method for producing a high-strength and high-ductility sintered body according to claim 1, characterized in that