JPH09194908A - Sintered and forged product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce decarburizing layers in the surface part of a sintered and forged product without executing machining after forging by subjecting the surface part of a sintered body to cold mechanical sealing treatment and thereafter executing hot forging. SOLUTION: Decarburization is not generated by cold sealing treatment, but, by crushing pores in the surface part of the sintered body prior to forging, when the sintered body is heated by reheating in hot forging, decarburization in the surface part of the sintered body is made small. Namely, the depth of the decarburizing layers after the forging is made shallow of <=0.1mm. Furthermore, the strength of the surface part of the forged body sufficiently increases because pores therein are mechanically crushed by sealing treatment. Thus, there is no need of executing machining after the forging for removing decarburizing layers. As the sealing treatment, a shot peening treatment or a shot blasting method can be used. By the above, pores over the whole body of the surface can securely be crushed even in a sintered body having an exceedingly complicated surface shape.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a sintered forged product and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a conventional sinter forging method, a green compact is heated and sintered, and a sintered body is reheated as it is before forging. However, in this conventional method, decarburization occurs on the surface of the sintered body during heating before forging, and a decarburized layer having a depth of about 0.5 mm remains in the sintered forged product after forging. The reason for such decarburization is that the sintered body has a large number of pores. This decarburized layer weakens the strength and durability of the sintered forged product. In the forging, the surface of the sintered body comes into contact with the mold and cools, so the density does not increase,
It is difficult to increase the strength of the surface of the sintered body.

Therefore, conventionally, the size of the sintered forged product after forging is set to be slightly larger than the final product shape, and the surface portion of the sintered forged product is cut by about 0.7 mm to remove the decarburized layer. I was doing. However, in this conventional method, a large amount of raw material is wastefully used for cutting, and the cutting process requires a processing cost, and thus the cost is high. In addition, in Japanese Examined Patent Publication No. 6-23403, in order to increase the fatigue strength of the sintered forged connecting rod which is a sintered forged product, the surface of the sintered forged connecting rod is subjected to shot blasting after the forging. It is described that the density of parts is increased. However, in the method described in this Japanese Patent Publication No. 6-23403, the decarburized layer remains as it is, which causes the strength to decrease.

[0004]

As described above, in the conventional sintering forging method, a deep decarburized layer is formed on the surface of the sintered forged product, and the decarburized layer is removed by cutting. There was a problem that the cost was high. The present invention
The present invention is intended to solve such a problem, and an object thereof is to reduce the decarburized layer on the surface portion of the sintered forged product without performing cutting after the forging.

[0005]

In order to achieve the above-mentioned object, a sintered forged product according to a first aspect of the present invention presses a raw material powder to form a green compact, and heats the green compact. Sintering, the surface of the sintered body after this sintering is mechanically sealed cold,
The sintered body after the sealing treatment is hot forged.

In the sintered forged product thus obtained, the decarburized layer on the surface portion is reduced without cutting after forging. In addition to that, it has high strength because the density of the surface portion is increased by the mechanical sealing treatment. According to a second aspect of the invention, in the sintered forged product of the first aspect of the invention, the depth of the decarburized layer on the surface portion after the hot forging is 0.1 mm or less.

That is, the decarburization layer depth after forging can be reduced to 0.1 mm or less by the sealing treatment before forging.
Sufficient strength can be obtained. In order to achieve the above-mentioned object, the method for manufacturing a sintered forged product according to the invention of claim 3 comprises a powder molding step of pressurizing a raw material powder to form a powder compact, and a powder compact obtained by this powder molding step. A sintering step of heating and sintering the body, a sealing step of mechanically sealing the surface portion of the sintered body obtained by the sintering step in the cold, and a firing step after the sealing step. And a forging step of hot forging the united body.

Although decarburization does not occur in the cold sealing step, the pores on the surface of the sintered body are crushed prior to forging, so that when the sintered body is heated during forging, Decarburization of the surface portion of this sintered body is reduced. According to a fourth aspect of the invention, in the method for manufacturing a sintered forged product according to the third aspect of the invention, the sealing step is a step of performing a sealing treatment by a shot peening method or a shot blast method.

That is, by hitting the shot on the surface of the sintered body, the density of the surface portion of the sintered body is increased and the pores thereof are crushed. Even a sintered body having a considerably complicated surface shape can be applied if the shot peening method or the shot blasting method is used.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a sintered forged product and a manufacturing method thereof according to the present invention will be described below with reference to the drawings. FIG. 2 shows a work (compacted powder, sintered body, forged body) 1.
3 shows an example of the shape of. The work 1 has a circular ring shape. FIG. 3 shows another example of the shape of the work 1A. The work 1A has a gear shape.

At the time of manufacture, as shown in FIG. 1, for example, an iron-based raw material powder is pressed by a powder molding press to mold a green compact (powder molding step). Next, this green compact is heated and sintered in a sintering furnace (sintering step). Then
The surface portion of the sintered body after the sintering is mechanically sealed in the cold (sealing step). Next, the sintered body is reheated to perform hot forging (reheating step), and then the sintered body is pressed by a forging press to forge (forging step). And
As the sealing step, for example, a shot peening method or a shot blast method is used.

Although decarburization does not occur in the cold sealing step, when the sintered body is heated in the reheating step by crushing the pores on the surface of the sintered body prior to forging, Decarburization of the surface portion of this sintered body is reduced. That is, the depth of the decarburized layer on the surface portion of the forged body (sintered forged product) after forging is as shallow as 0.1 mm or less. Moreover, the surface portion of the forged body has a high density due to the mechanical crushing of the pores in the sealing step, so that the strength of the forged body is sufficiently increased. Therefore, it is not necessary to perform a cutting process after the forging process to remove the decarburized layer, and the cost can be reduced.

In the sealing step by the shot peening method or the shot blasting method, shots (steel balls) are hit on the surface of the sintered body to increase the density of the surface portion of the sintered body and crush the pores. . Therefore,
In addition to the simple shaped sintered body shown in FIG.
Even a gear-shaped sintered body as shown in (4) or a sintered body with a more complicated shape can surely collapse the pores on the entire surface. Further, the shot peening method and the shot blasting method can be efficiently performed at a lower cost than cutting processing.

The means for sealing treatment is not limited to the one using shots, but various means such as surface rolling for rolling the surface of the sintered body or burnishing can be used. For example, in rolling, by rolling a roller on the surface of the sintered body, the surface of the sintered body is rolled,
The pores on this surface are crushed. This is an effective means when only a specific portion such as an end surface portion or an outer peripheral surface portion of the sintered body needs to be sealed. Further, it is possible to carry out carburizing and quenching after forging.

[0015]

EXAMPLES Here, the shot peening method applied during the sintering step and the reheating step before forging and its function and effect will be described with reference to specific examples. Shot peening method includes table shot and rotation (apron)
There are shots and straight shots, both of which can be used, but here, the results when using a table shot are shown. First, in order to clarify the conditions of the shot peening method in this example, the measurement results of arc height (according to JIS B 0130) are shown in FIG. The arc height is the amount of deflection of the test piece when a shot is applied, and the greater the value, the greater the energy of the shot peening method. The shot diameter is 1.5 mm, and the results are shown for two cases where the output of the shot machine was changed. In the figure,
The black circles and the solid line graphs are the results for the test piece of the standard piece Almen strip A, and the white circles and the broken line graph are the results for the sintered test piece.

The target sintered body is the one shown in FIG. 2, which has an outer diameter of about 110 mm and a thickness (axial length) of about 15 mm.
It is. 5 to 7 show micrographs of the cross section of the sintered body showing the distribution of pores before forging. In these figures, (A) is the part A shown in FIG. 2 (b), and (B) is the same part B.
It is a photograph of the department. FIG. 5 shows the shot peening method not applied, FIG. 6 shows the shot peening method applied for 15 minutes, and FIG. 7 shows the shot peening method applied for 30 minutes. In these photographs, the portions that appear to be black in a granular form are pores. Apparently, the shot peened method has fewer pores on the surface portion (upper portion in the figure) than the shot peened method. The shot peening method applied for 30 minutes had fewer pores on the surface than the application applied for 15 minutes.

Further, FIGS. 8 to 13 show micrographs of the cross section of the forged body showing the metal structure. In these figures, FIGS. 8, 10 and 12 are photographs of the A portion, and FIGS. 9, 11 and 13 are photographs of the B portion. Further, FIGS. 8 and 9 show that the shot peening method is not applied,
10 and 11 show the shot peening method applied for 15 minutes, and FIGS. 12 and 13 show the shot peening method applied for 30 minutes. In these photographs, the brightly visible part is ferrite. In both photographs, the surface of the forged body (the upper part in the figure)
A decarburized layer, in which almost only ferrite has been formed by decarburization, is seen in Fig. However, the decarburized layer is much shallower in the shot peened method than in the non-shot peened method. Further, it can be seen that the decarburized layer is further shallower in the case where the shot peening method is applied for 30 minutes than in the case where it is applied for 15 minutes.

Further, FIG. 14 shows the sintered body before forging and the one not subjected to the shot peening method, the one subjected to the shot peening method for 15 minutes, and the one subjected to the shot peening method for 30 minutes. The measurement result of the density of each part of the forged body after forging is shown. In the figure, the broken line graph shows the density of the sintered body, and the solid line graph shows the density of the forged body. In addition, the triangular mark indicates the density of the part a (one end face part) shown in FIG. 2B, the circular mark indicates the density of the part b (intermediate part), and the square mark indicates the same part c (the other end face part). ) Shows the density. In addition, in FIG.
In order to clarify the regions of the parts b and c, the parts a and c are cross-hatched. In general, the density of the shot peened material is higher than that of the non-shot peened material. In particular, the portions a and c which are the surface portions are more important than the central portion b.
In the part, the density is remarkably increased by applying the shot peening method.

In FIG. 15, shot peening is not applied, shot peening is applied for 10 minutes, shot peening is applied for 20 minutes, and shot peening is applied for 30 minutes. The measurement results of the H _R C surface hardness of the forged body are shown for each of the above. In the figure, white circles indicate the value of each sample, and black circles indicate the sample average. This also applies to FIG. 16 described later.
The one subjected to the shot peening method has a higher surface hardness than the one not subjected to the shot peening method, and the longer the time of the shot peening method, the higher the surface hardness tends to be. Harder surface hardness indicates higher density and shallower decarburization depth.

Further, in FIG. 16, the shot peening method is not applied, the shot peening method is applied for 10 minutes, the shot peening method is applied for 20 minutes, and the shot peening method is applied for 30 minutes. The results of measuring the radial crushing strength (according to JIS Z 2507) of the forged body are shown. The radial crushing strength is obtained from the load when the forged body is pressed by two surfaces parallel to its axis and cracking starts to occur. Apparently, the radial crushing strength of the one subjected to the shot peening method is stronger than that of the non-shot peening method, and the radial crushing strength is stronger as the time of the shot peening method is longer. In the case of this sintered forged product, the desired radial crushing strength is 3000 kg.
Although it is f or more, in the case where the shot peening method is not applied, the radial crushing strength is less than 3000 kgf, whereas
Approximately 3000 kgf if shot peening method is applied for 10 minutes or more
The above radial crushing strength is obtained.

From the above results, by subjecting the sintered body to the shot peening method before forging, the pores in the surface portion of the sintered body are crushed and the density of the surface portion of the sintered body and the forged body is increased, It is clear that the decarburized layer on the surface of the forged body is reduced and the strength of the forged body is increased.

[0022]

According to the invention of claim 1, the surface of the sintered body is mechanically sealed in the cold state, and then the sintered body is hot forged. The density of the part is high, the decarburized layer is few, and the strength is high. Further, since the cutting process after forging is unnecessary, it can be manufactured at a low cost.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, the decarburized layer depth of the surface portion after the forging step is 0.
Since it is 1 mm or less, sufficient strength can be obtained without cutting after forging. According to the invention of claim 3, in the method of manufacturing a sintered forged product, a sealing step of cold mechanically sealing the surface portion of the sintered body is performed between the sintering step and the forging step. Since it is added, the density of the surface portion of the sintered body is increased, decarburization that occurs during the forging step is reduced, and the strength of the sintered forged product is improved. Therefore, it is not necessary to perform cutting work after forging, and the cost can be reduced.

According to the invention of claim 4, in addition to the effect of the invention of claim 3, since the sealing step is a step of performing the sealing treatment by the shot peening method or the shot blasting method, a considerably complicated surface shape is burnt. Even with a tie, the pores on the surface can be reliably collapsed.

[Brief description of the drawings]

FIG. 1 is a flow chart of steps showing a sintering forging method of the present invention.

FIG. 2 shows an example of a work, (a) is a plan view,
(B) is a partial cross-sectional view.

FIG. 3 is a plan view showing another example of the work.

FIG. 4 is a graph showing arc height in the shot peening method.

FIG. 5 is a photograph of a cross section of a sintered body not subjected to the shot peening method.

FIG. 6 is a photograph of a cross section of a sintered body that has been subjected to the shot peening method for 15 minutes.

FIG. 7 is a photograph of a cross section of a sintered body that has been subjected to the shot peening method for 30 minutes.

FIG. 8 is a photograph of a cross section of a portion A of a forged body not subjected to the shot peening method.

FIG. 9 is a photograph of a cross section of a B part of a forged body not subjected to the shot peening method.

FIG. 10 is a photograph of a cross section of an A portion of a forged body that has been subjected to the shot peening method for 15 minutes.

FIG. 11 is a photograph of a cross section of a B portion of a forged body that has been subjected to the shot peening method for 15 minutes.

FIG. 12 is a photograph of a cross section of part A of a forged body that has been subjected to the shot peening method for 30 minutes.

FIG. 13 is a photograph of a cross section of a B part of a forged body that has been subjected to the shot peening method for 30 minutes.

FIG. 14 is a graph showing the densities of a sintered body and a forged body.

FIG. 15 is a graph showing the surface hardness of a forged body.

FIG. 16 is a graph showing radial crushing strength of a forged body.

[Explanation of symbols]

 1,1A work (green compact, sintered compact, forged compact)

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[Procedure amendment]

[Submission date] April 15, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a flow chart of steps showing a sintering forging method of the present invention.

FIG. 2 shows an example of a work, (a) is a plan view,
(B) is a partial cross-sectional view.

FIG. 3 is a plan view showing another example of the work.

FIG. 4 is a graph showing arc height in the shot peening method.

FIG. 5 is a micrograph of a cross section of a sintered body that is not subjected to the shot peening method.

FIG. 6 is a micrograph of a cross section of a sintered body that has been subjected to the shot peening method for 15 minutes.

FIG. 7 is a micrograph of a cross section of a sintered body that has been subjected to the shot peening method for 30 minutes.

FIG. 8 is a micrograph showing a metal structure of a section A of a forged body that is not subjected to the shot peening method.

FIG. 9 is a micrograph showing a metal structure of a cross section of a B portion of a forged body not subjected to the shot peening method.

FIG. 10 is a micrograph showing a metal structure of a section A of a forged body subjected to a shot peening method for 15 minutes.

FIG. 11 is a micrograph showing a metal structure of a section B of a forged body that has been subjected to the shot peening method for 15 minutes.

FIG. 12 is a micrograph showing a metal structure of a section A of a forged body that has been subjected to the shot peening method for 30 minutes.

FIG. 13 is a micrograph showing a metal structure of a section B of a forged body that has been subjected to the shot peening method for 30 minutes.

FIG. 14 is a graph showing the densities of a sintered body and a forged body.

FIG. 15 is a graph showing the surface hardness of a forged body.

FIG. 16 is a graph showing radial crushing strength of a forged body.

[Explanation of code] 1,1A work (compacted powder, sintered body, forged body)

Claims (4)

[Claims] 1. A raw material powder is pressed to form a green compact, the green compact is heated and sintered, and the surface of the sintered body after the sintering is mechanically sealed in a cold state. A sintered forged product, characterized in that it is obtained by hot forging the sintered body after the treatment and the sealing treatment. 2. The depth of the decarburized layer on the surface portion after the hot forging is
The sintered forged product according to claim 1, which has a diameter of 0.1 mm or less. 3. A powder forming step of pressurizing a raw material powder to form a green compact, a sintering step of heating and sintering the green compact obtained by the powder forming step, and a sintering step of It is characterized by including a sealing step of mechanically sealing the surface portion of the obtained sintered body in a cold state, and a forging step of hot forging the sintered body after the sealing step. A method for manufacturing a sintered forged product. 4. The method for producing a sintered forged product according to claim 3, wherein the sealing step is a step of performing a sealing treatment by a shot peening method or a shot blasting method.