JPH05117719A - Production of sintered body having high strength and ductility - Google Patents

Abstract

PURPOSE:To work a high-strength sintered body at a high working rate without lowering its ductility. CONSTITUTION:A metallic film consisting essentially of Cu is formed on the surface of the sintered body of a high-strength powder, and then the sintered body is hot-worked. Consequently, the ductility is not lowered when worked, the sintered body is worked at a high working rate, and a sintered body having high strength and ductility is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength and high-ductility product which is obtained by hot working a sintered body made of a W-Fe-Ni alloy or the like to obtain a processed material having high strength and high ductility. The present invention relates to a method for manufacturing a sintered body.

[0002]

2. Description of the Related Art A W-Fe-Ni alloy, which is one of the 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 ( Using a cold isostatic press, etc., the green compact is pressed into a predetermined shape to obtain a green compact, and then the green compact is heated to the liquidus temperature of the Fe-Ni alloy or higher, and the W powder is converted into the Fe powder. -Sintering with Ni alloy bonding (pre-sintering and main sintering). After the heat treatment, the obtained sintered body is subjected to machining such as machining, and further preheated to 400 to 600 ° C. in order to give predetermined mechanical properties (improvement of strength, etc.) depending on the application. Perform warm processing such as swaging. After that, a post heat treatment is performed to obtain a sintered body.

[0003]

However, in the above swaging, when the plastic working rate exceeds 20%, there is a problem that the ductility of the obtained sintered body sharply decreases. .. 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 that requires good ductility. Therefore, swage processing provides sufficient mechanical properties. There is a problem that it cannot be improved.

The inventors of the present invention have conducted various research studies on the reduction of ductility in the swaging process, and as a result,
Fe that becomes a binder with W particles during swaging
-It is thought that it 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 considered that one of W particles and Ni / Fe would preferentially flow due to the frictional force on 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 higher, 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 between the W particles. The present invention has been made against the background of the above circumstances, and W
Provided is a method for producing a high-strength and high-ductility sintered body, which is capable of obtaining a high-strength and high-ductility sintered body by preventing generation of a contact portion between particles as much as possible and preventing a decrease in ductility. The purpose is to do.

[0006]

In order to solve the above-mentioned problems, a method for producing a high-strength and high-ductility sintered body according to the present invention is such that a metal mainly containing Cu is formed on the surface of the sintered body obtained by sintering high-strength powder. A film is formed, and then the sintered body is warm-worked.

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 up to 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 coating 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 required metal film can be formed, and the forming method is not limited. The above-mentioned metal film may be mainly composed of 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 for warm working. The preheating temperature is not particularly limited, but it can be heated to a higher temperature than the conventional method,
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,
This is because there is a risk that work cracking will occur, and if the temperature exceeds 650 ° C., transformation will occur in the sintered body and ductility will decrease. The type of warm working is not particularly limited, but generally swaging is performed. After the warm working, 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 the lubrication performance peculiar to Cu-based metal, and the sintered body is warm-worked 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 binder in the structure of the sintered body uniformly plastically flow, and the aggregation of the high-strength particles and the increase in the contact portion between the high-strength particles are prevented as much as possible, and the decrease in ductility is prevented. The obtained sintered body is sufficiently processed to increase its strength and is prevented from being reduced in ductility, 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 of 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. Further, after applying a molybdenum disulfide-based lubricant to the surface of this sintered body,
The invention material was obtained by performing pre-heating by heating to 600 ° C. and swaging for compressing the side surface of the sintered body 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, the same sintered body as the above-mentioned sintered body was used, and an oily graphite lubricant was applied thereto, and in the same manner as above, the invention method and the comparative example were swaged at a processing rate of 10%. The Rockwell hardness of each of the obtained invention material and comparative material was measured while changing the radial depth, 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 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 at the surface layer. The 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 the W-
Since a metal film mainly composed of Cu is formed on the surface of a sintered body such as an Fe-Ni alloy by plating, and then the sintered body is warm-worked, the ductility during warm-working is reduced. It is possible to prevent this and 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 surface of a sintered body obtained by sintering high-strength powder,
A method for producing a high-strength and high-ductility sintered body, which comprises forming a metal film mainly composed of Cu and then hot working the sintered body. 2. The sintered body is made of a W—Fe—Ni alloy,
The method for producing a high-strength and high-ductility sintered body according to claim 1, wherein pure copper is plated on the surface of the sintered body to form a metal film.