JPH03232903A - Manufacture of high carbon sintered parts - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing high-carbon sintered parts, and more specifically, the present invention relates to a method for manufacturing high-carbon sintered parts, and more specifically, the present invention relates to a method for manufacturing high-carbon sintered parts. The present invention relates to a method of manufacturing carbon sintered parts.

[Prior Art] Conventionally, iron-based sintered parts that require wear resistance and high strength are produced by molding a molded product into a predetermined shape from a metal powder made of metal powder and graphite, that is, carbon, and then sintering it. ,
It is manufactured by quenching and tempering a sintered product. Quenching and tempering may be performed in a carburizing atmosphere in order to further improve wear resistance. When manufacturing sintered parts such as gears that require high dimensional accuracy, the sintered product is usually machined to a predetermined size.

[Problem to be solved by the invention] For example, if a sintered gear is to be manufactured, a metal raw material powder containing as much as 0.5% by weight or more of carbon is generally used to provide the desired strength. Needs to be shaped and sintered.

Furthermore, since high dimensional accuracy is required, it is necessary to perform a shaving process or the like after sintering. However, since the sintered body has a hard structure with a high carbon content as a whole, it has poor machinability during shaving, etc., and cannot be manufactured with good productivity. In addition, due to poor machinability, there was a problem in that machining accuracy deteriorated due to wear of the shearing cutter and the like. Conversely, if the carbon content of the metal raw material powder is less than 0.5% by weight, the machinability of the sintered product can be improved. However, even when heat treated in a carburizing atmosphere,
The inside of the sintered gear lacks strength due to low carbon content. Also,
Since low carbon sintered products have a high specific gravity before heat treatment, their volume tends to swell due to heat treatment, which increases the amount of dimensional change and deteriorates dimensional accuracy.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide a method for manufacturing high-precision, high-carbon sintered parts with good productivity.

[Means for Solving the Problems] The method for producing a high carbon sintered part of the present invention includes the steps of molding a molded product from metal raw material powder containing 0.5% by weight or more of carbon, and decarburizing the molded product. A step of obtaining a sintered product with a low carbon surface layer by sintering in an atmosphere, a step of obtaining a rough-shaped product by machining the sintered product, and a step of obtaining a rough-shaped product in a carburizing atmosphere. The method is characterized by comprising a step of heat treatment.

The metal raw material powder refers to powder of iron or iron-based alloy containing 0.5% by weight or more of carbon. If the carbon content is less than 0.5% by weight, the strength of the sintered parts will be insufficient.

As the molding method, mold molding or the like can be adopted.

Sintering can be performed in a decarburizing atmosphere during the latter half of the sintering process. As the decarburizing atmosphere, RX gas with adjusted decarburizing ability can be used. It is desirable that the surface layer of the sintered product is reduced in carbon by sintering in such a decarburizing atmosphere to a depth that slightly exceeds the machining allowance for machining. This is because machining can be performed with good layer productivity.

As the machining process, for example, when manufacturing a sintered gear, shaving process, rolling process, etc. can be performed.

Heat treatment is performed in a carburizing atmosphere. The carburizing atmosphere can be carried out by quenching and tempering using RX gas in which carburizing has been adjusted.

[Function] In the method for manufacturing high-carbon sintered parts of the present invention, only the surface layer of the sintered body is removed by keeping the molded product made of metal raw material powder containing a large amount of carbon in a decarburizing atmosphere during sintering. is decarburized to obtain a sintered product with a soft structure with a low carbon surface layer and a hard structure with a high carbon content inside except for the surface layer. By performing machining on the surface layer of the soft structure of the sintered product, machinability during machining is improved, and high-precision rough-formed products can be produced without inducing wear on the mating material, such as the cutter. obtain. After this, high-carbon sintered parts are obtained by heat-treating the high-precision rough-shaped parts in a carburizing atmosphere.The surface layer of the soft structure of high-carbon sintered parts becomes highly carbonized and hardens, resulting in high-carbon The internal hard structure ensures wear resistance and high strength.

Further, at this time, since the high-carbon rough-shaped product has a low specific gravity before heat treatment, it is difficult for the volume to expand due to heat treatment, and the amount of dimensional change is small. This ensures high precision for high carbon sintered parts.

[Example] Hereinafter, an example in which the present invention is embodied in a method for manufacturing a gear will be described together with a comparative example.

(Example) First, a metal raw material powder consisting of 99.0 wt% of 4600 series alloy powder and graphite 'l, Qwt% was prepared, and the compacting density was 7. Oq/cm", number of teeth 40, module 1.9
A molded article of an involute helical gear having a helix angle of 20 degrees, a face width of 16 #, and an inner diameter of 50 # was molded by a mold molding method.

A sintered product was obtained by sintering this molded product. Sintering conditions were temperature increase, 1130'C x 25 minutes (C.

P, = 1.0%), 1 in a decarburizing atmosphere using RX dregs
Slow cooling was performed at 130°C for 15 minutes (C, P, -0.2%).

Then, cutter rotation speed 2001', l), m,
Cutter feed rate 0.6m/min, machining allowance (0, B, D>0.2
A rough-shaped product was obtained by shaving under the processing conditions of #5 and cutter material of 5KH53.

A gear was obtained by heat-treating this rough shape.

The heat treatment conditions were 920°C in a carburizing atmosphere using RX gas.
°CX150 minutes (C, P, -1.0%), quenching (6
(in 0'C oil) and tempered at 180'C x 60 minutes).

(Comparative Example 1) In order to compare machinability during shaving processing with the method of the example, sintering was performed under conditions other than a decarburizing atmosphere to obtain a gear. That is, the sintering conditions were: temperature increase, 1130'C x 40 minutes (C
, P, = 1.0%) and slow cooling. Note that the other conditions were the same as in the examples.

(Comparative Example 2) In order to compare the gear accuracy before and after heat treatment with the method of the example,
Gears were obtained by reducing the amount of carbon in the metal raw material powder and sintering in an atmosphere that does not cause decarburization or carburization. That is, 99°8wt% of 4600 series alloy powder and 0 graphite.
．． A metal raw material powder consisting of 2wt% was used. In addition, the sintering conditions were: temperature increase, 1130'CX 40 minutes (C, P, -
0.2%) and slow cooling. Note that the other conditions were the same as in the examples.

(Evaluation) In order to compare the machinability during shaving processing, 2000 gears were manufactured using the methods of Example and Comparative Example 1, and the cutting edge 1, which is the corner between the serrations and the tooth surface of the shaving cutter, was manufactured using the methods of Example and Comparative Example 1. The amount of wear (μm) was measured (see Figure 1). The results are shown in Figure 2.

In the method of the example, since sintering was performed in a decarburizing atmosphere, a sintered product having a soft structure with a low carbon surface layer was subjected to shaving processing. On the other hand, in the method of Comparative Example 1, sintering was performed under conditions other than a decarburizing atmosphere, so a sintered product with a hard structure in the surface layer was subjected to shaving processing. Therefore, as shown in FIG. 2, it can be seen that the method of the example enables shaving with a smaller amount of wear than the method of comparative example 1.

In addition, in order to compare gear accuracy before and after heat treatment, the tooth profile error (μm> and tooth line error (μ'rrL) of 20 gears manufactured by the method of Example and Comparative Example 2 were measured. The amount of change and variation during heat treatment were investigated.The results are shown in the table.

In the method of the example, the amount of carbon in the metal raw material powder is large, whereas in the method of Comparative Example 2, the amount of carbon in the metal powder is small.

Therefore, as shown in the table, compared to the method of Comparative Example 2, the method of the example has smaller variations and variations in tooth profile error and tooth line error, and can manufacture gears with high precision.

In the above embodiments, the case where the shaving process is performed has been described, but the present invention can also exhibit its effects when the rolling process is performed. In this case as well, as in the above embodiment, by reducing the carbon content of the surface layer portion, the plastic deformability during rolling processing is improved, and the productivity and processing accuracy of the high carbon sintered part are improved. Further, the wear resistance of the high carbon sintered parts can be further improved by increasing the density by rolling.

Furthermore, although the method for manufacturing gears has been described in the above embodiments, the present invention can also be applied to methods for manufacturing other parts as long as they are high carbon sintered parts that require wear resistance and high strength. Of course.

[Effects of the Invention] As detailed above, in the method for manufacturing high-carbon sintered parts of the present invention, sintering is performed in a decarburizing atmosphere, so that the surface layer of the sintered product has a soft structure with less carbon. . In addition, the interior, excluding the surface layer, maintains strength due to high carbon content. Then, the surface layer of the soft structure of the sintered product is machined, and the surface layer of the soft structure of the obtained rough-shaped product is hardened by heat treatment.

Further, at this time, since the high-carbon coarse-shaped product has a low specific gravity before heat treatment, it is difficult to expand its volume by heat treatment, and the amount of dimensional change is small.

Therefore, according to the manufacturing method of the present invention, it is possible to improve machinability and to manufacture high-carbon sintered parts with high productivity.

In addition, it does not induce wear of the cutter, etc., which is the mating material, and the amount of dimensional change during heat treatment is small, so it is possible to obtain high carbon sintered parts that have high precision as well as wear resistance and high strength. can.

Furthermore, according to the method for manufacturing high carbon sintered parts of the present invention,
Since it is possible to increase the proportion of carbon, it is possible to manufacture high-carbon sintered parts that do not undergo hardening and have high internal base material strength.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a cutting edge portion of a shaving cutter. FIG. 2 is a graph showing a comparison of the amount of wear on the cutting edge between the example and the comparative example. 1...Cutting blade part

Claims (1)

[Claims] (1) A process of molding a molded product from metal raw material powder containing 0.5% by weight or more of carbon, and a sintered product whose surface layer has a low carbon content by sintering the molded product in a decarburizing atmosphere. manufacturing a high carbon sintered part, comprising the steps of: obtaining a rough-shaped product by machining the sintered product; and heat-treating the rough-shaped product in a carburizing atmosphere. Method.