JPH0397845A - Borided sliding member and production thereof - Google Patents

Abstract

PURPOSE:To produce the borided sliding member having excellent surface characteristics, strength and load resistance by pressurizing the surface of a sintered material internally having holes to decrease the porosity on the surface side and forming a boride on the extreme surface thereof. CONSTITUTION:The sintered material internally having the holes is prepd. by using a material, such as steel, The porosity thereof is preferably about 6 to 30%. The surface to be treated of the sintered member is subjected to a pressurization treatment to decrease the porosity on the surface side and to constitute the extreme surface region where the porosity is smaller than the inside and is <=5% and the porous inner region which maintains the as- sintered porosity on the inner side thereof. At least the extreme surface region is then brought into contact with a boriding agent to form the boride layer only on this surface. The extreme surface region is preferably formed to about 0.05 to 2mm thickness and the boride layer to about 10 to 150mum thickness. The borided sliding member which is excellent in the surface characteristics, such as wear resistance, oxidation resistance and corrosion resistance, as well as in the strength, load resistance and fatigue resistance is obtd. in this way.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a boron-treated sliding member and a method for manufacturing the same. This invention relates to a sintered sliding member and its manufacturing method.

(Conventional technology) Boring treatment of steel materials targets materials that have undergone conventional melting processes such as rolling, forging, extrusion, and casting, and improves wear resistance,
It has been widely used as a surface treatment to improve oxidation resistance, corrosion resistance, etc. Although boron immersion treatment exhibits these excellent properties, its weakness is that it causes embrittlement due to the hardness and brittleness of the boride. In particular, the surface of the treated layer contains Fe.
A very brittle layer of B is likely to form. This FeB easily cracks or becomes brittle, so if FeB occurs, it is problematic to use it as a sliding material. Sintered materials are generally used as they are, but post-treatments such as rolling, wire drawing, swaging, forging, sizing, or coining (a method of rerolling the sintered material in a mold) are performed as additional treatments for the sintered materials. (Revised and expanded Powder Metallurgy, Standard Metals Course, Corona Publishing, 1980, 12th edition,
(pages 105-106), surface treatment of sintered materials is not common.

An overview of the conventional technology for surface treatment of sintered materials is MPIP.
(Metal Powder Institute F
There are materials that can be case hardened, such as material standard FN-0200-T (2nd revised edition, Metal Data Book, published by Maruzen Co., Ltd., January 30, 1980, 2nd edition).
32-233). This material is characterized by the addition of Ni and a relatively high density of 7.2 to 7.6. Furthermore, SMF type 2 of the Japanese Powder Metallurgy Association standard JPMA 1 is a material that can be carburized (cited above, Metal Data Book, p. 236). This material has carburizability because the Cu added in an amount of 3% or less eliminates pores.

On the other hand, as a patent document related to boron treatment, there is Japanese Patent Application Laid-Open No. 60-21371, but this technology pressurizes a metal container containing Cr powder and controls the manufacturing conditions when sintering the Cr powder. A sintered body with true density without bottle holes is formed, and then a material obtained by machining the container of the sintered body and the like, that is, a material without pores, is subjected to boron immersion treatment, This is not a method in which a Cr sintered material with holes is directly subjected to boron treatment.

(Problem to be solved by the invention) Conventionally, sintered materials capable of case hardening, carburizing, etc. have been known.
If such a material is subjected to case hardening, the entire surface will be hardened, and the treatment cannot be applied to partial surfaces such as the inner surface of a cylindrical part. Furthermore, it is not known that boron immersion treatment is applied to iron-based sintered materials or sintered materials with pores, and of course it is only applied to a part of the surface of the sintered material. There is no known boron treatment method. The present inventors performed direct immersion boron treatment on the inner surface of a tubular sintered material. Naturally, the desired treatment layer could not be formed on the inner surface because the plating itself could not be carried out. In addition, when a large amount of gas is generated or the entire sintered body is treated with boron, boronization occurs not only on the surface but also inside the sintered body. Very brittle FeB on the surface of the pores
It was found that the entire sintered material was embrittled due to boronization, as a considerable amount of was generated.

Therefore, an object of the present invention is to provide a boron-treated sintered sliding member in which a boride layer is formed only on desired surfaces, and which has excellent strength and load resistance as well as surface characteristics. Another object of the present invention is to provide a method for manufacturing such a sliding member.

(Means for Solving the Problems) A boron-treated sintered sliding member according to the present invention is a sliding member in which only a part of a surface of a sintered material having holes inside is boron-treated. comprising a porous inner region provided inside the surface to be subjected to the boron immersion treatment, and an outermost surface region provided on the surface side and having a porosity smaller than that of the inner region and 5% or less. , a boride is formed at least on the surface side of the outermost surface region, and the inner region is substantially free of boride and has a higher porosity than the outermost surface region.

The method according to the present invention includes a step of preparing a sintered material having pores inside, and applying pressure to the surface of the sintered material to be treated with boron to reduce the porosity on the surface side. an outermost surface region and a region where the porosity is smaller than the interior and 5% or less;
A region forming step of forming a porous inner region that substantially maintains the porosity when sintered on the inner side;
At least the outermost surface region is brought into contact with a boron treatment agent to form a boride on at least the surface of the outermost surface region, and the inner region having a higher porosity than the outermost surface region is substantially free of boride. It is characterized by comprising each step of forming a boron-treated layer without forming it.

Hereinafter, the configuration of the present invention will be explained in detail.

The base material to be subjected to the boron treatment of the present invention is sintered iron, iron-carbon system, iron-carbon-copper system, iron-nickel system, iron-nickel-copper system, iron-manganese system, iron-carbon-system. Various materials may be used, such as manganese-based sintered materials and sintered materials with sulfur added thereto. Boron treatment methods include solid method, liquid method,
Any known method such as the gas method can be adopted, but
Solid state methods are particularly preferred. The boride phase formed by the boron treatment is formed in a thin layer on surfaces where it is necessary to impart wear resistance, such as the inner or outer surface of a tubular member or one surface of a plate. It is best not to form a boride layer on the surface of a sintered material that does not slide with the mating material and where sliding properties are not required, to minimize the reduction in fatigue strength caused by the presence of a brittle boride layer. The outermost surface region of the present invention has a smaller porosity than the inner region and is set to 5% or less. This is because if the porosity of the outermost surface area exceeds 5%, the processing gas will leak into the internal area, and the desired surface may not be boronized, or the boronization may extend deep into the internal area or extend to the entire internal area. This is to avoid embrittlement of the sliding member due to the formation of brittle FeB over a wide area inside. In addition, if the porosity of the outermost surface area and the porosity of the internal area are the same, when used as a sliding material, stress tends to concentrate on the boron-treated area, resulting in insufficient load-bearing capacity. Depending on the porosity, embrittlement may occur in the internal region. In other words, the porosity of the outermost surface region is smaller than that of the inner region and is 5%.
Both of the following must be satisfied.

Here, it is preferable from another point of view that the porosity of the outermost surface region is 2% or more. This is because when the porosity is in the range of 2 to 5%, the amount of gas leaking is small and boronization is possible as described above, and at the same time, this leaked gas fills the pores near the outermost surface.
This is because the boron treatment speed can be sped up at the initial stage. Moreover, since the boronization process involves some expansion of the sintered material due to the formation of borides, the pores tend to gradually become narrower in the later stages of the boronation process, resulting in even less leakage and more leakage in the internal region. It starts to suppress elementalization. Of course, in the present invention, since the porosity of the inner region is higher than that of the outermost surface region, gas leaking from the outermost surface region to the inner region can be discharged from the inner region to the outside of the sintered body. This means that boronization can be suppressed. At this time, the thickness of the outermost surface area is set to 0.05 to 2}, preferably 0.
．． The thickness is preferably 1 to 1 mo+, more preferably 0.2 to 0.6 mm. In particular, it is preferable to set it to around 0.5 mm.

In addition, when the porosity is set to 2% or more, an advantage in manufacturing the outermost surface region is that less pressure is required in the region forming process, and the porosity can be reduced without the need for complicated and expensive equipment. can be easily done. In the present invention, it is preferable to form an inner region having a porosity set to be between the outermost layer and the inner region between the outermost surface layer and the inner region. In addition, the inner region has a porosity close to that of the outermost surface region on the outermost surface side, a porosity of the inner region on the inner region side, and a porosity that continuously decreases in the middle toward the outermost surface region. Such a structure is preferable in terms of bondability, load absorption capacity, gas discharge properties, etc., contributes to improvement in sliding characteristics, and is also preferable in terms of manufacturing.

Further, the inner region can cooperate with the inner region to further improve the load-bearing capacity. The thickness of this inner region is 0.5
It is preferable to set it to 1.5 mm.

Also, the total thickness of the outermost surface area and the inner area is 2lII1
It is recommended to do the following. It is best to form the boride in the outermost surface area as much as possible by dipping the boron treatment, but if the outermost surface area is thin, the boride should be formed until it reaches a part of the surface side of this internal area. You may.

The porosity of the inner region is higher than that of the outermost surface region, which prevents boronization by increasing the number of pores.The porosity of the pores acts as a load-absorbing cushion, which reduces stress on the surface boron-treated layer. It is set to avoid concentration, improve the load bearing capacity of the sliding member as a whole, and exhibit excellent sliding characteristics. On the other hand, if boride occurs in the internal region, not only will boride be formed in undesired areas that are not the original purpose of surface treatment, but also the brittle FeB formed on the surface of the pores in the internal region will be removed by polishing. Since this is not possible, embrittlement progresses. In this way, the pore surface is FeB
When a sliding member that is made of aluminum is subjected to a load, the surface of the pores will be chipped and the load bearing capacity will decrease. Therefore, it is preferable to configure the outermost surface region to have a high porosity.

The porosity of the inner region is preferably 6% or more. If the porosity is less than 6%, the cushioning effect will be insufficient and the powder metallurgical conditions for obtaining a high-density sintered material will become severe. On the other hand, if the porosity exceeds 30%, which corresponds to the lowest density of ordinary sintered industrial products, the strength decreases and the material becomes unsuitable for use as a sliding member. The porosity of the internal region mentioned above refers to the average porosity from the boundary in contact with the outermost surface region to the opposite surface to the boron treatment. It is preferable that the porosity of the inner region is small in the inner region in contact with the outermost surface region and larger in the inner region. In particular, when the porosity of the inner region is large, the inner region where the porosity is between the above average value and the outermost surface region is actively used in order to average stress in the inner region.

The inner region preferably has a thickness of, for example, 0.5 to 1.5 mm, and a porosity of, for example, 6 to 15%.

When the load applied to the sliding member is low, the boride may be formed to penetrate into the inner region by a few tens of micrometers, but preferably the boride is thinner than the outermost surface region so that no boride is formed. Control the depth of boride formation so that the outermost surface area remains. In this way, when a sliding member whose layer structure is controlled so that the boride phase, the outermost surface area where no boride is formed (hereinafter referred to as the intermediate layer), and the internal area are arranged in order from the surface is subjected to load, the intermediate layer The layers as a whole evenly transfer loads to the interior areas, increasing load carrying capacity and strength. That is, since the intermediate layer is dense, it does not have low-strength areas that would cause stress concentration, and the entire body takes the load and transmits it to the internal region. On the other hand, since the interface between the outermost surface region and the inner region is a place where the former, which is a brittle layer, and the latter, which is a low-strength layer, are in contact, stress concentration tends to occur when exposed to a load, and the latter is locally loaded. is transmitted and can easily cause its destruction.

In the boride layer, a portion of the brittle FeB formed on the outermost surface is usually removed by several micrometers by polishing or the like, and then the boron-treated sintered material is used as a sliding member. Furthermore, as proposed by the present applicant in Japanese Patent Application No. 181671/1983, FeB may be removed by polishing or the like to reveal a two-phase mixed structure of FetB and FesB. The thickness of the boride layer is 10~
Preferably it is 150LLm. This thickness is 10μ
If it is less than 1 m, the wear resistance of the sliding member will not be sufficient;
If it exceeds 50 ILm, a large amount of brittle FeB will be generated,
The treatment may cause deformation of the shape of the sliding member, making it easier for strength to deteriorate inside the boride layer. Particularly preferred boride layer thicknesses are between 30 and 100 microns.

If the thickness of the outermost surface region is increased relative to the thickness of the boride layer, a residual portion free of boride will be formed in the outermost surface region, and the outermost surface region containing boride will become substantially integrated. This avoids stress concentration and distributes the stress to the internal region with high porosity.

In order to create a sintered material with different porosity in the outermost region and the inner region as described above, sintering is performed using the usual method to create a sintered material with approximately uniform porosity as a whole. Claim 2
Perform the method described. Specific pore reduction means may be any method such as rolls, molds, rotating disk dies, etc.
Sizing is the most common method based on the life of the jig. Sizing is preferably performed to reduce the dimensions of the workpiece by about 3 to 10%. When the size reduction due to sizing is less than 3%, the effect of reducing pores is small;
If it exceeds 100%, processing becomes difficult. The processing method for sizing differs depending on the shape of the workpiece. For example, when reducing the pores on the inner surface of a cylindrical object, the inner surface of the workpiece is pressed with a mandrel-like mold with a tapered tip, and then When processing the outside surface, use a cylindrical die to squeeze the outside surface.

(Function) By setting the porosity of the outermost surface region and the inner region as described above, it becomes possible to perform boron treatment on the sintered material, and it also avoids the general drawbacks of boron treatment and the porosity of the sintered material. embrittlement, which can be particularly harmful in

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example) JPMA machine structural parts sintered material standards, 3 types of iron-carbon type,
SMF3030 was sintered in a conventional manner to prepare sintered materials with different porosities. The density of the sintered material is 7. 0g/cm”
(corresponding to a porosity of 16%), a cylindrical sintered body having an inner diameter of 20 mm and an outer diameter of 40 mm was produced. The inner surface of this sintered body was sized to have an inner diameter of 19.2 mm. In other words, the sizing fee is 0.8+++m, and the sizing rate is 4%.
Met. Thereafter, the sintered material was subjected to boron treatment at 900°C for 1 hour. The boron treatment agent is 84C: 3 to 20 parts, S
A mixed powder consisting of 50 to 80 parts of iC, 30 to 30 parts of C, and 205 to 7 parts of potassium fluoride was used. This mixed powder was brought into contact only with the surface to be treated, and boron treatment was performed. After this treatment, the state of the pores and the boride layer after polishing a portion of the outermost surface of FeB is schematically shown in FIG. In the figure, 1 is the outermost surface area (thickness is 0.5 mm),
2 is an internal region, 3 is a hole, and the hatched portion is a boride layer 1a. The boride layer 1a had a jagged interface with the base material, and the thickness was measured at the average position of the unevenness.

Example 1 The porosity of the outermost surface region 1 (0.5 mm) was 4%, the porosity of the inner region 2b was 16%, and the inner region 2a (thickness 1.0
The porosity at the center of mm) was 7%. In areas affected by sizing, the pores were either compressed or deformed into elongated shapes. As a result, the porosity decreased in the outermost region 1 and the inner region 2a. The average thickness of the boride layer was 50 microns.

Figure 2 (100
(magnification) and Figure 3 (magnification 400x). It is clear that a boride layer is formed on the surface of the sintered material.

Example 2 The porosity of the outermost surface region 1 (0.5 mm) was 2%, the porosity of the inner region 2b was 16%, and the inner region 2a (thickness 1 ml)
The porosity of 1) was set to 6 to 15%, and a boride layer 1a having a thickness of 80 μm was formed.

Moreover, the boron immersion treatment was carried out under the above-mentioned preferable conditions, and the desired results could be obtained.

(Effects of the Invention) According to the present invention, a part of the surface of the sintered material can be subjected to boron treatment, and the sintered material has excellent wear resistance, oxidation resistance, load resistance, and fatigue resistance. A sliding member can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the boron-treated surface of the sintered sliding member of Example 1 of the present invention, and FIGS. 2 and 3 are photographs of the metallurgical microstructure of the boron-treated surface of Example 1. .

Claims (2)

[Claims] 1. A sliding member in which only a part of the surface of a sintered material having holes inside is subjected to boron treatment, and a porous internal region provided inside the surface to be subjected to the boron treatment. , an outermost surface region provided on the surface side and having a porosity smaller than the inner region and 5% or less, a boride is formed at least on the surface side of the outermost surface region, and the inner region is substantially A boron-treated sliding member characterized in that no boride is formed and the porosity is higher than that of the outermost surface region. 2. A step of preparing a sintered material having pores inside, pressurizing the surface of the sintered material to be boronized to reduce the porosity on the surface side so that the porosity is smaller than the inside and 5 % or less, and a porous inner region that substantially maintains the porosity when sintered, followed by soaking at least the outermost surface region. Formation of a boron treatment layer in which boride is formed on at least the surface of the outermost surface region by contact with a raw treatment agent, and substantially no boride is formed in the inner region having a higher porosity than the outermost surface region. 1. A method for manufacturing a boron-treated sliding member, comprising the following steps.