JPH11189859A - Sliding member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sliding member excellent in sliding property and wear resistance with a simple equipment without using a salt bath by providing a solid lubricant coating film of a sulfide or a multiple compound consisting essentially of the sulfide on the surface of an iron based metallic base material and nitriding the sulfide by a gas equal to or above one time. SOLUTION: MoS2 and WS2 individually or in combination or further mixed with a solid lubricant such as graphite, BN are dispersed in an organic or inorganic solvent to be made colloidal and applied on the iron based metallic base material, which is desirably dried and after that, nitrided. Though the nitridation is optional if performed in the gas, a gas soft nitcidation is most suitable and is performed by housing the iron base metallic base material in a nitridation furnace heated to and kept at 500-600 deg.C, introducing gaseous ammonia and RX gas in the nitridation furnace to react and generating activated nascent nitrogen (2N) and carbon (C) to infiltrate into the iron base metallic base material. As a result, the sliding member having a 3 layer structure of the solid lubricant coating film, a porous layer and a nitride layer is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding member used for a component that slides with a mating component such as a bearing, and a method of manufacturing the same. The present invention relates to a technique for effectively reducing wear of a mating part as well as improving wearability.

[0002]

2. Description of the Related Art Bearings are required to have excellent wear resistance and low frictional resistance (sliding characteristics), and improvements have been made to enhance these two characteristics. From the viewpoint of improving wear resistance, the hardness and strength of the base metal material itself are increased by heat treatment, or only the surface layer of the base material is hardened by induction hardening. In addition, a hard layer is formed on the surface of the base material by gas-phase plating such as plasma spraying, PVD, or CVD, or the surface layer is cured by nitriding. They are used properly. Among these, in addition to the conventional gas nitriding method (hard nitriding method), a nitrocarburizing method using a salt bath and a gas nitrocarburizing method have been used as the nitriding method.

In the gas nitrocarburizing method, an iron-based material such as pure iron, mild steel, cast iron and alloy steel is heated to 500 to 600 ° C. in an atmosphere of ammonia gas and RX gas, and a Fe—N This treatment forms a compound layer. By this treatment, a material having excellent wear resistance, corrosion resistance and fatigue strength of the base material can be obtained.

[0004] However, in the above-described method, although the wear resistance and the fatigue strength of the base material are improved, there are problems in that the sliding characteristics are not taken into consideration and that the aggressiveness to the mating member is increased. . In other words, when sliding characteristics are required, the use of oil or grease as a lubricant is indispensable, but when the lubricant is exhausted, metal contact occurs between the bearing and the shaft, and This can lead to serious damage such as scuffing and burning.

[0005] As a surface treatment method that simultaneously satisfies wear resistance and sliding characteristics, a sulfonitriding method developed by the Hydromechanical Wear Institute (HEF) in France in 1972 and put to practical use. Is also known as the sulf method). In this sulphonitriding method, an alkali metal salt containing sulfur is kept at about 565 ° C., and a treatment agent is immersed in a molten salt bath to form iron sulfide (FeS, etc.) and iron nitride on the surface layer of the treatment agent. This is a method in which a porous layer (sulfur-nitrided layer) mainly composed of (Fe ₃ N, Fe ₄ N, etc.) is formed, and a layer in which nitrogen is diffused in ferrite is formed inside the porous layer. . According to such a sulphonitriding method, the lubricant is retained on the sliding surface by the presence of the porous layer containing iron sulfide, which is rich in lipophilicity, and the porous layer functions as a solid lubricant. There is an advantage that the porous layer has a certain degree of plastic fluidity, has good compatibility with the shaft, and has good wear resistance.

[0006]

However, in the sulphonitriding method described above, since a cyanide is used in a salt bath, strict treatment and management of wastewater are required, which has been a major obstacle to implementation. In addition, the sliding characteristics of the bearing treated by the nitrosulphurizing method cannot be said to be sufficient as compared with those using a solid lubricant as described above, so that there is a problem that the use is restricted. . Therefore, the present invention has been made in view of the above circumstances, and can be implemented with simple equipment without using a salt bath, and can manufacture a sliding member having high sliding characteristics. A method of manufacturing the member,
It is an object of the present invention to provide a sliding member excellent in both sliding characteristics and wear resistance.

[0007]

When a solid lubricant such as molybdenum disulfide is provided in the bearing material, the bearing material is immersed in molybdenum disulfide-dispersed colloidal oil, and then maintained in an atmosphere at about 180 ° C. The liquid component is volatilized to fix the molybdenum disulfide film on the surface of the bearing. The present inventors have conducted studies to increase the bonding strength, and as a result, have found that when gas nitrocarburizing is performed after forming a molybdenum disulfide coating, the bonding strength of the coating to the bearing material is significantly increased. The reason is not clear, but is presumed as follows.

That is, S contained in molybdenum disulfide diffuses into the bearing base material due to the gas nitrocarburizing atmosphere temperature, and S in molybdenum disulfide is reduced by the nascent [H] present in the atmosphere. As a result, a Mo-rich phase is formed on the molybdenum disulfide film. And
The Mo-rich phase Mo interdiffuses with Fe in the bearing base material to form a bonding state similar to diffusion bonding, or
It is presumed that the rich phase and the bearing base material may be in a bonding state similar to metal bonding. However, this is merely a guess, and it goes without saying that the present invention is not limited by the presence or absence of such an action.

The method of manufacturing a sliding member according to the present invention is based on the above findings, and comprises forming a solid lubricant film of sulfide or a composite compound mainly composed of sulfide on the surface of an iron-based metal base material. Gas nitriding treatment once or two times.
It is characterized by being applied more than once.

In the above-described manufacturing method, nitrogen and / or carbon penetrates from the surface of the iron-based metal base material into the inside by the nitriding treatment, and a nitride layer or a carbonitride layer (hereinafter referred to simply as a nitride layer) ), And S contained in the solid lubricant film penetrates into the iron-based metal base material to form a porous layer made of iron sulfide and iron nitride or iron carbonitride.
That is, an oxynitrided layer is formed. FIG. 1 shows an example of a sectional structure of a sliding member after a nitriding treatment. As shown in FIG. 1, the internal structure of the iron-based metal base material is ferrite + pearlite, and it can be seen that a nitride layer (white layer) is formed on the surface layer. In addition, it can be seen that a porous layer is formed on the surface side from the nitride layer, and the surface of the sliding member is covered with the solid lubricant film.

Thus, the sliding member of the present invention having a three-layer structure of a solid lubricant film, a porous layer and a nitride layer can be obtained. That is, the sliding member of the present invention is provided with a nitride layer on the surface layer of the iron-based metal base material, and on the surface side of the nitride layer, a porous layer mainly composed of iron sulfide and iron nitride or iron carbonitride. Further, a solid lubricant film of iron sulfide or a composite compound mainly composed of iron sulfide is provided on the surface of the porous layer.

In the sliding member having the above structure, the sliding characteristics can be improved by the presence of the solid lubricant film.
Further, by using a lubricant such as grease, maximum sliding characteristics can be exhibited. In addition, since the solid lubricant or grease is retained on the surface of the porous layer, even if the solid lubricant is worn, the solid lubricant or grease retained on the surface of the porous layer is lubricated. Is carried out, and the porous layer itself containing iron sulfide acts as a solid lubricant. Further, even when the porous layer is worn, the performance as a sliding member is maintained because the lower nitride layer is present. Therefore, not only the sliding characteristics can be improved, but also the life of the sliding member can be greatly extended.

As described above, according to the method for manufacturing a sliding member of the present invention, a sliding member having significantly improved sliding characteristics and life can be obtained. In addition, since a nitrosulphurized layer can be formed by a nitriding furnace, simple equipment that does not require consideration of wastewater treatment etc. is sufficient, and the manufacturing process involves applying a solid lubricant to the iron-based metal base material. Since only the nitriding treatment is performed, the manufacturing cost can be reduced.

The sliding member of the present invention can be manufactured by a method other than the above-described manufacturing method of the present invention. For example, after a nitriding layer is formed on the surface of an iron-based metal base material by a nitriding treatment, a nitrosulphurizing layer is formed by a salt bath sulphating method (sul-sulfur method). An agent film can also be provided. However, in consideration of the adhesion strength between the solid lubricant film and the iron-based metal base material, it is preferable to use the manufacturing method of the present invention, which can increase the adhesion strength and further extend the life. Hereinafter, preferred embodiments of the present invention will be described.

[0015]

DETAILED DESCRIPTION OF THE INVENTION A. Formation of Solid Lubricant Film The solid lubricant is composed of sulfide or a composite compound mainly composed of sulfide. For example, molybdenum disulfide (MoS
₂ ) and tungsten disulfide (WS ₂ ) can be used alone or in combination, and further, a solid lubricant such as graphite, boron nitride (BN), or PTFE can be mixed. These solid lubricants are dispersed in a suitable organic or inorganic solvent to form a colloid, and are applied to the iron-based metal base material by brushing or dipping. To facilitate handling after coating, it is desirable to heat and dry the material to volatilize the solvent, but it is also possible to omit the heating and drying step by performing a nitriding treatment as it is after coating.

B. Nitriding The nitriding treatment is optional as long as it is performed in a gas, and a gas nitriding method, a gas nitrocarburizing method, an ion nitriding method, or the like can be applied. The gas nitrocarburizing method is most preferable. In addition,
In the ion nitriding method, a glow discharge is generated between a furnace body as an anode and a workpiece as a cathode in a low-pressure nitrogen gas atmosphere, and nitrogen ions collide with the workpiece and penetrate into the workpiece. It is a way to make it.

In the gas nitrocarburizing method, an iron-based metal base material is housed in a nitriding furnace heated and held at 500 ° C. to 600 ° C., and ammonia gas and RX gas are introduced into the nitriding furnace to perform a reaction represented by the following equation (1). Generated and activated nascent nitrogen [2N]
And carbon [C] are generated and permeate the iron-based metal base material.

## EQU1 ## 2NH ₃ → [2N] + 3H ₂ (1) CO ₂ + H ₂ → CO + H ₂ O (2) 2CO → [C] + CO ₂ (3)

The activated element as described above penetrates from the surface of the iron-based metal base material to the inside thereof, whereby the surface layer of the iron-based metal base material is formed of a hard Fe—N—C carbonitride. A nitride layer is formed. This nitrided layer has a thickness of 5 to 15 μm and a hardness of 400 to 700 Hmv. At the same time, S contained in the solid lubricant also penetrates the iron-based metal material to form a porous layer made of iron sulfide and iron carbonitride. This porous layer functions as a solid lubricant, and has a thickness of 5 to 15 μm and a hardness of 300 to 500 Hmv. Then, this porous layer firmly adheres to the solid lubricant film as described above.

C. Other Manufacturing Method In the present invention, the nitriding treatment is performed once or twice on the iron-based metal base material before the solid lubricant film of sulfide or a complex compound mainly containing sulfide is provided on the iron-based metal base material. Good results are obtained when applied. FIG. 2 shows an example of the cross-sectional structure of the sliding member thus obtained. As is clear from comparison with FIG. 1, it can be seen that the nitrided layer (white layer) has expanded to the lower layer by the two nitriding treatments. Further, the thickness of the porous layer and the thickness of the nitride layer are increased. in this way,
By performing the nitriding treatment first, the thickness of the porous layer and the thickness of the nitrided layer can be increased, so that the life of the sliding member can be further extended.

The reason why the nitriding treatment after the solid lubricant film is provided in a gas is that in the salt bath nitrocarburizing method, S in the solid lubricant film is changed to the surrounding nascent stage [H] or H ions. This is because they do not permeate into the iron-based metal base material by reacting. Therefore, the nitriding treatment performed before providing the solid lubricant film may be a salt bath nitrocarburizing method in addition to the nitriding method performed in the gas described above.

[0021]

The present invention will be described below in more detail with reference to specific examples. Example 1 An S45C disk having a diameter of 60 mm and a thickness of 10 mm was prepared as an iron-based metal base material (hereinafter, simply referred to as a base material). First, this base material was heated to 580 ° C. in a furnace, and NH ₃ gas of a nitriding source, CO ₂ gas of a carburizing source, and N ₂ gas were introduced, and after holding for 80 minutes, oil-cooling treatment was performed. As a result, a nitride layer mainly composed of iron carbonitride was formed to a thickness of 15 to 20 μm on the base material surface layer. Next, this material was immersed in molybdenum disulfide dispersed colloidal oil and taken out.
For 30 minutes to form a solid lubricant film. Next, this material is heated again to 580 ° C. in a furnace, and N 2 as a nitriding
After H ₃ gas, CO ₂ gas of carburizing source and N ₂ gas were introduced and maintained for 80 minutes, the furnace was cooled and the treatment was completed. By this final nitriding treatment, a porous layer containing porosity mainly composed of iron sulfide and iron carbonitride was formed on the initially formed carbonitride-based nitrided layer. The solid lubricant film provided on the outermost surface of the base material has a surface hardness Hmv
A thin film of 53 molybdenum disulfide was obtained.

Next, the sliding characteristics of this material were investigated using a ball-on-disk friction tester. In the test, a SUJ steel ball having a diameter of 5 mm was selected as a ball, and dry friction was performed under the conditions of a load of 0.5 kg, a speed of 10 m / min, and a friction time of 10 minutes. Further, as Comparative Example 1, a material having a nitrided layer by performing only the gas soft nitriding treatment (surface hardness Hmv519),
As Comparative Example 2, mainly F
eS porous material (surface hardness Hmv
463), and a friction test was performed on these under the same conditions as described above. Table 1 shows the results.

[0023]

[Table 1]

Next, several drops of mineral oil were dropped on the sliding surface of each material, and then wiped lightly with absorbent cotton. A friction test was performed under the conditions of a load of 0.5 kg, a speed of 10 m / min, and a friction time of 20 hours under the wet condition of the thin oil film. Table 2 shows the results.
Shown in

As is evident from Tables 1 and 2, the sliding properties of the Example materials showed excellent results under both dry friction and wet friction conditions. In particular, in the friction test using a ball-on-disk tester, point contact occurs at the start of the test, which is a severe condition for the material surface test. The material was compared with the wear amount in Comparative Example 1.
About 56 times that of Comparative Example 2 and about 4.6 times that of Comparative Example 2. In the results of the wet friction test, the material of the example showed about 7.2 times the performance of the comparative example 1 and about 12.7 times the performance of the comparative example 2. In each friction test, no peeling or abrasion of the solid lubricant film of the example material occurred.

[0026]

[Table 2]

Example 2 The condition of the first nitriding treatment was set to 50
The material of Example 2 was produced under the same conditions as Example 1 except that the temperature was set to 0 ° C. and the holding time was set to 60 minutes. The hardness of the solid lubricant film of the produced material was Hmv48. Using this material, a dry friction test and a wet friction test were performed under the same conditions as in Example 1. For comparison, the material 1 used in Example 1 was used.
A dry rub test and a wet rub test were performed using Material 2 and Material 2 under the same conditions. Tables 3 and 4 show the results of these friction tests, respectively.

[0028]

[Table 3]

[0029]

[Table 4]

As is clear from Tables 3 and 4, the material of the present invention also exhibited excellent sliding performance in this example. In the dry friction test, the material of the example showed about 136 times the abrasion amount of Comparative Example 1. , About 11 times the performance of Comparative Example 2. Further, according to the results of the wet friction test, the material of Example was Comparative Example 1
About 18.6 times that of Comparative Example 2 and about 10.5 times that of Comparative Example 2. Also in this example, the solid lubricant film of the example material did not peel or wear.

[0031]

As described above, according to the present invention, a sliding member having a sulfided nitrided layer can be manufactured with simple equipment without using a salt bath. By increasing the adhesion strength to the material, a sliding member excellent in both sliding characteristics and wear resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a sliding member obtained by applying a molybdenum disulfide to an iron-based metal base material and then performing a nitriding treatment.

FIG. 2 is a view showing a structure of a sliding member which is obtained by applying a molybdenum disulfide to a ferrous metal base material after a nitriding treatment, and then performing a nitriding treatment.

Continued on the front page (72) Inventor Saburo Yamagata 2-25-1, Nishi-Nippori, Arakawa-ku, Tokyo Oriental Engineering Co., Ltd. (72) Inventor Yasuo Takahashi 2- 25-1, Nishi-Nippori, Arakawa-ku, Tokyo Riental Engineering Co., Ltd.

Claims (3)

[Claims] 1. A solid lubricant film of sulfide or a composite compound mainly composed of sulfide is provided on a surface of an iron-based metal base material,
A method for manufacturing a sliding member, wherein a nitriding treatment with a gas is performed once or twice or more. 2. The ferrous metal base material is subjected to nitriding once or twice.
Applying a solid lubricant film of sulfide or a composite compound mainly composed of sulfide on the surface of the iron-based metal base material, and performing gas nitriding once or twice. A method for manufacturing a sliding member, comprising: 3. A nitride or carbonitride layer is provided on the surface of the iron-based metal base material, and a porous layer mainly composed of iron sulfide and iron nitride or iron carbonitride is provided on the surface side of the nitride or carbonitride layer. A sliding member, comprising: a porous layer; and a solid lubricant film of sulfide or a complex compound mainly composed of sulfide on the surface of the porous layer.