JPH062013A - Production of powder sintered part - Google Patents

Abstract

(57) [Summary] [Purpose] There are few restrictions on materials and there are no process inconveniences.
It is also an object of the present invention to provide a method for producing a powder sintered part having high strength, high hardness and high precision, which has a low processing cost. [Composition] A step of preparing a powder sintered body (steps 1 to 3),
A step (step 4) of nitriding the powder sintered body to form a nitride layer on the surface layer portion, and a step of sizing or reaming the powder sintered body on which the nitride layer is formed to obtain a powder sintered part. And a step (step 5) of obtaining the above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a powder sintered part which requires high strength, high hardness and high accuracy.

[0002]

2. Description of the Related Art As a method for producing a high-strength, high-hardness powder-sintered component, a powder-sintered body is conventionally sized by carburizing and quenching to produce a retained austenite structure. After that, a method has been proposed in which deep-cooling treatment is performed to obtain a martensite structure and then tempering (Japanese Patent Laid-Open No. 63-195202). The manufacturing process of the powder sintered part at this time is shown in FIG.

However, this method is limited to products containing elements that easily generate retained austenite, such as high Ni products and products containing Mn and Co. Further, there are inconveniences in the process such that quenching and tempering cannot be continuously carried out and special treatment such as deep-chill treatment (subzero treatment) is required.

Further, even in the case of general materials, carburizing and tempering are used as heat treatments to obtain powder-sintered parts having high strength and high hardness. b) Strain due to residual stress when cooling from high temperature, and (c) Volume expansion when transforming from austenite structure to martensite structure. It is necessary to remove the above deformations (a) to (c) by machining.

However, since carburizing and quenching is performed by gas carburizing,
Since the hardened layer is formed inside the product through the pores in the product, the hardness is high and it is difficult to correct the deformation due to quenching by sizing and one-time machining. Therefore, FIG.
It is manufactured by the manufacturing process shown in. That is, after mixing, shaping, and sintering the powder to form a sintered body, the strain due to sintering is removed by reaming to reduce the cutting allowance after quenching, and then carburizing and tempering are performed. After that, rough finishing is performed by grinding with a grindstone to remove distortion due to quenching, and finally lapping or honing is performed to obtain a high precision product with a tolerance of several microns. Since three machining processes are required in this way, the processing cost becomes high, resulting in an extremely high product cost.

The present invention has been made in view of the above circumstances, and is a high-strength, high-hardness, high-accuracy powder-sintered part with few restrictions on materials, no inconvenience in the process, and low processing cost. It aims at providing the manufacturing method of.

[0007]

In order to solve the above problems, the present invention provides a step of preparing a powder sintered body and a nitriding treatment of the powder sintered body to form a nitride layer on the surface layer portion thereof. There is provided a method for producing a powder sintered part, comprising: a forming step; and a step of sizing or reaming the powder sintered body on which a nitride layer is formed to obtain a powder sintered part.

As a result of various studies to solve the above problems, the present inventor has found that the above problems can be solved by forming a nitride layer on the powder sintered body. That is, by performing nitriding treatment on the powder sintered body to form a nitride layer, it is possible to obtain by the carburizing and tempering treatment while maintaining the hardness and strength equivalent to the carburizing and tempering treatment. The inventors have found that it is possible to obtain difficult machinability and workability, and have completed the present invention having the above-described structure. In this way, it is possible to obtain good machinability and workability by nitriding treatment, which is different from carburizing and tempering treatment, in that a hardened layer made of nitride can be formed only on the surface layer portion. Because you can. According to the invention,

(1) Not limited to, for example, high Ni steel as in the technique disclosed in JP-A-63-195202, general iron-based products in general (carbon steel, structural alloy steel, tool steel,
It can be applied to stainless steel, low alloy steel, etc.). (2) Quenching and tempering processes are unnecessary. (3) No special sub-zero processing is required.

(4) While the reamer processing, grindstone polishing, and lapping or honing processing were required three times, highly accurate powder sintered products can be obtained by one sizing or inexpensive reamer processing. Therefore, the processing cost can be remarkably reduced. Hereinafter, the present invention will be described in detail.

According to the present invention, as shown in FIG.
The starting materials are mixed (step 1), this is molded (step 2), and the molded body is further sintered (step 3) to obtain a sintered body. In this case, molding and sintering may be performed simultaneously by hot pressing or the like. It should be noted that the material to be applied is not limited as long as it is an iron-based material as described above. For example, C is 0 to 1.0% and Cu is 0 to 30 by weight.
%, Ni is 0 to 10%, and the balance is Fe. The molding pressure during molding is ^{2 to} 8 ton / cm ^2.
Is appropriate. Moreover, sintering can be suitably performed in a reducing atmosphere or vacuum in the range of 1050 to 1300 ° C.

Then, the sintered body thus obtained is subjected to a nitriding treatment (step 4) to form a nitride layer on the surface portion of the sintered body to a thickness of about 2 to 20 μm, and then sizing. Alternatively, reaming is performed (step 5) to obtain a desired powder sintered product. The reason why the thickness of the nitride layer is set in this range is that if the thickness is larger than this range, the nitride layer is likely to be chipped, and if it is smaller than this range, the nitride layer may not be formed in the corner portion. The most preferable range of the thickness of the nitride layer is 4 to 7 μm.

In this case, as the nitriding treatment, for example, a salt bath nitriding treatment described in JP-A-54-161516 can be adopted. The salt bath nitriding treatment in this publication is carried out in order to improve the wear resistance, galling resistance, contact fatigue resistance and lubricity of the member, but the nitriding treatment in the present invention has high hardness as described above. And to improve machinability and workability while maintaining high strength, and the purpose is different.

This salt bath nitriding treatment is performed by the steps shown in FIG. First, the sintered body is degreased (step 6), and then preheated (step 7). Thereafter, salt bath nitriding is performed (step 8), cooling (step 9), washing (step 10),
After drying (step 11), a shot blast treatment is finally performed (step 12). This salt bath treatment is KCNO, KC
Using a salt such as N, Na ₂ CO ₃ , for example, 550 ±
It is performed at a temperature of about 50 ° C. The salt bath treatment time is 10 to 10.
It is set to 180 minutes. The nitriding method is not limited to such salt bath nitriding, and any conventionally used nitriding such as gas nitriding or ion nitriding may be applied.

As described above, the nitride layer is formed on the surface layer portion of the sintered body to a thickness of about 2 to 20 μm by the nitriding treatment, so that the large diameter portion is 5 to 50 mmφ and the small diameter portion is 1 mm, for example.
A powder sintered product having a shape of ˜30 mmφ and a height of 10 to 30 mmφ can be obtained with a tolerance of several microns only by performing sizing or reaming. The sizing at this time is 1 to 10 ton / cm ^2. Can be done with pressure.

[0016]

EXAMPLES Examples of the present invention will be described below.

Here, in weight display, C is 0.8%, C
An iron-based material containing 2% u, 1% Ni, and the balance Fe was used. First, the powders of the respective components were mixed so as to have such a composition, and the resulting mixed powder was mixed at 6 ton / cm ² Molded at a molding pressure of 1130 ° C in a reducing atmosphere or vacuum
And sintered.

After that, KCNO is 32-40%, KCN
Is 55% and the balance is Na ₂ CO ₃ , and the salt bath temperature is 5
A salt bath treatment was performed at 70 ° C. for 120 minutes. This allows
Decomposition of KCNO → KCN + O ₂ occurred, N and C penetrated into the sintered body, and a nitride layer of 7 μm was formed in the surface layer portion.

The sintered body having the nitride layer thus formed is subjected to sizing or reamer processing to obtain a powder sintered product having a large diameter portion of 30 mmφ, a small diameter portion of 3 mmφ and a height of 10 mmφ. Obtained. The sizing at this time is 6ton /
cm ² I went there. As a result, a highly accurate product with a tolerance of 2 to 9 μm was obtained.

As a result of examining the drill life and the reamer life of the sizing treatment at this time, both the drill life and the reamer life were about 3000 times / piece in the case of the above-mentioned embodiment. When the tempering process was performed, it was about 300 times / piece. That is, it was confirmed that the tool life of the present invention was increased 10 times that of the conventional one, and that the nitriding treatment of the present invention significantly improved the machinability and workability.

A product produced according to the present invention,
As a result of measuring the Vickers hardness of the conventional carburized and tempered product, as shown in Table 1, the product of the present invention has a higher value than the conventional product.

[0022]

[Table 1]

Furthermore, according to the present invention, after the nitride layer is formed, the sizing or the low-cost reaming process can be performed once to obtain the highly accurate product as described above, so that the processing cost is significantly lower than the conventional one. I found that I could do it. By the way, by using the method of the present invention,
Approximately 1/8 of the conventional method shown in FIG.
A product could be obtained at a processing cost that was about 11% lower than that of the method described in Japanese Patent No. 5202.

[0024]

According to the present invention, there are few restrictions on the material,
Provided is a method for producing a high-strength, high-hardness, high-precision powder-sintered component which has no process inconvenience and is low in processing cost.

[Brief description of drawings]

FIG. 1 is a view for explaining the steps of a method for manufacturing a powder sintered component according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of a nitriding treatment used in the present invention.

FIG. 3 is a view for explaining an example of steps of a conventional method for manufacturing a powder sintered component.

FIG. 4 is a view for explaining another example of the steps of the conventional method for manufacturing a powder sintered part.

Claims (2)

[Claims] 1. A step of preparing a powder sintered body, a step of subjecting the powder sintered body to a nitriding treatment to form a nitride layer on a surface layer portion thereof, and a powder sintered body on which the nitride layer is formed. Sizing or reaming to obtain a powder sintered part. 2. The method for producing a powder sintered part according to claim 1, wherein the thickness of the nitrided layer is in the range of 2 to 20 μm.