JPH1047334A - Rolling slide parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure durability and wear resistance by regulating the quantity of carbide in a surface layer, hardness, the decomposition ratio of residual austenite associated with surface reinforcing work and surface roughness respectively to the specific value. SOLUTION: This rolling slide part is used in the state of coming in rolling contact or sliding contact with another opposed part. In the case where a range of 0-50μm in depth from the surface is made a surface layer part, the rate of carbide contained in this surface layer is 10-25vol%, the decomposition ratio of residual austenite of the surface layer part to the initial value is 1/10-3/10, the hardness of the surface layer part is Hv830-Hv960, and surface roughness is 25μm. Sufficient durability and wear resistance can thereby be ensured even under such a severe condition as to be lubricated only by lubricating oil with soot and other insoluble components mixed therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION A rolling sliding part according to the present invention is used as a shaft of a cam follower constituting a valve train of various engines such as a diesel engine.

[0002]

2. Description of the Related Art A cam follower is incorporated in a valve mechanism for transmitting the movement of a cam fixed to a camshaft that rotates together with the crankshaft of an engine to a valve, and the friction during operation of the valve mechanism is reduced from sliding friction. By changing to friction, it is possible to reduce the friction loss of the relevant part,
In recent years, it has been widely practiced. Also, to improve the durability of the surface of rolling and sliding parts, such as the outer ring and shaft used for such cam followers, which come into rolling or sliding contact with the mating part during use, the surface texture has been conventionally improved. Various inventions relating to the improvement of are known.

In order to improve the durability and abrasion resistance of the surface of the rolling sliding part as described above, it is necessary to increase the amount of carbide on the surface of the rolling sliding part or to increase the surface hardness. Has been known to be effective. Also, a method for increasing the amount of carbide is described in, for example, The Japan Institute of Metals Society Vol. 32, No. 12 (1993), 888-8.
As described in Toru Arai's paper "Improvement of Wear Resistance of Steel by Metallurgical Means" on page 97, it is conventionally known. Further, a method for increasing the surface hardness has been conventionally known, as described in many documents such as Japanese Patent Application Laid-Open No. 5-195070.

On the other hand, as a technique for improving the durability by changing the surface properties, for example, Japanese Patent Publication No. 1-3000
The 8 discloses, on the surface of the rolling surface R _max is 0.3 to 1.5
Patent Document 1 discloses an invention relating to a bearing rolling element in which a scratch in a random direction is formed at μm and a residual stress layer of 50 kgf / mm ² or more is formed on a surface layer. Also, JP-A-3-1177
No. 23-5 discloses an invention in which a number of dents are randomly formed on the surface by barrel processing to increase the hardness of the surface layer compared to the internal hardness and to generate a compressive residual stress in the surface layer. ing. Also, JP-A-3-199716
Japanese Patent Application Laid-Open Publication No. H11-15064 discloses a bearing in which a surface hardened layer is provided on a surface in contact with a mating member, and the depth of the peak value of the compressive residual stress and the depth of the peak value of the shear stress distribution are matched. Further, JP-A-4-54312, by shot peening, the compressive residual stress and 100 kgf / mm ² or more in the surface portion, the invention relates to bearing component was 40 kgf / mm ² or more at a portion of the subsurface 300μm Have been described. Further, JP-A-5-288257 discloses that when the depth from the surface is in the range of 0 to 50 μm, the maximum compressive residual stress of the surface layer is 50 to 11 μm.
0 kgf / mm ² , and the hardness of the surface layer is also Hv 830 to Hv
960, wherein the average wavelength of the surface roughness is 25 μm or less, and the ratio of the retained austenite in the surface layer portion exceeds 7% by volume. In addition, for example, Japanese Patent Application Laid-Open No. 5-239
The technique described in No. 550 and the like is known.

[0005]

In the case of the above-mentioned known invention, excellent durability can be obtained depending on use conditions, but sufficient durability may not always be obtained in a specific use condition. . For example, in the case of a cam follower device incorporated in a diesel engine, soot (carbon soot) generated by the combustion of the diesel engine and other insoluble components are mixed in the lubricating oil supplied to the cam follower device. When these soots and other insoluble components intervene on the rolling surface or sliding surface, these soots and other insoluble components act like abrasives and damage the rolling surface or sliding surface. Cause. In particular, abnormal wear may occur on the shaft of the cam follower having a high contact surface pressure with the mating surface. When the wear generated on the shaft of the cam follower progresses in this way, stepped wear occurs on the contact surface of the part of the shaft with the rolling surface of the needle supporting the cam follower. And flaking based on stress concentration occurs at a portion in contact with the end of the rolling surface of the needle at the width direction end of the inner raceway present on the outer peripheral surface of the shaft,
The durability of the rotation support portion of the cam follower is impaired.

[0006] With respect to such deterioration of durability due to insoluble components such as soot mixed into the lubricating oil, the above-described conventional technology cannot always provide a sufficient effect of improving durability. For example, if the amount of carbide is simply increased to improve the wear resistance, the amount of retained austenite on the surface increases,
The surface life is reduced and the fatigue life is reduced in situations involving rolling contact. If the surface is subjected to a strengthening process such as shot peening using a steel ball or the like in order to prevent a decrease in fatigue life due to such a cause, residual austenite (γ _R ) on the surface is excessively decomposed. As a result, embrittlement occurs due to distortion of the surface shape, and sufficient durability and wear resistance cannot be obtained. That is, to simply prevent wear, the surface hardness may be increased. However, if the hardness is simply increased, cracks are easily generated on the surface due to embrittlement of the surface due to decomposition of residual austenite. Become.

[0007] In view of such circumstances, the rolling sliding component of the present invention is intended to ensure sufficient durability and wear resistance.
It regulates the amount and hardness of carbide contained in the surface layer, the decomposition rate of retained austenite accompanying the surface strengthening process, and the surface roughness.

[0008]

The rolling sliding component of the present invention is used in a state of rolling contact or sliding contact with another facing component. In particular, in the rolling sliding part of the present invention, when the depth from the surface is in the range of 0 to 50 μm as the surface layer, the ratio of the carbide contained in the surface layer is 10 to 25% by volume. The decomposition rate of the retained austenite in the surface layer with respect to the initial value is 1/10 to 3/10.
Similarly, the hardness of the surface layer is Hv830 to Hv960, and the average wavelength of the surface roughness is 25 μm or less.

[0009] It is impossible to simultaneously obtain the above-mentioned specifications in terms of the amount of carbide and the hardness by ordinary heat treatment using a bearing steel and performing quenching and tempering. Therefore, in order to realize the above specifications, for example, with respect to carbide, the amount of carbide on the surface of the bearing steel is increased by subjecting the bearing steel constituting the rolling sliding component to carbonitriding. Regarding the hardness and the decomposition rate of the retained austenite, the surface hardness of the bearing steel is increased by suppressing the decomposition of the retained austenite, and the surface roughness is adjusted to a desired value while suppressing the decomposition of the retained austenite by a kind of hard shot peening. To That is, by using light and fine shot grains used for the hard shot peening, the surface hardness, the decomposition rate, and the surface roughness are regulated to desired values.

[0010]

In the case of the rolling sliding part of the present invention configured as described above, as in the case of a cam follower shaft of a diesel engine, soot and other insoluble components are mixed in the lubricating oil. The wear resistance and durability of the components used can be sufficiently ensured. That is, in the case of the rolling sliding part of the present invention, the amount of carbide in the surface layer is regulated to 10 to 25% by volume, so that the surface wear is suppressed and the rolling fatigue life is prevented from being reduced (the rolling fatigue life). Can be secured). When the amount of the carbide is less than 10% by volume, the amount of the thermally stable carbide is insufficient in the surface layer portion, and wear is remarkable. Conversely, when the amount of the carbide exceeds 25% by volume, the surface layer becomes brittle, and the rolling fatigue life is reduced.

The hardness of the surface layer is Hv830 to Hv96.
Since it is restricted to the range of 0, it is possible to prevent the occurrence of cracks associated with peeling while suppressing wear. The above hardness is Hv
If it is less than 830, cracks do not occur but wear becomes remarkable. Conversely, if the hardness exceeds Hv 960, cracks tend to occur instead of suppressing wear, and in any case, the life is shortened. Come.

As described above, in order to control the amount of the carbide and the hardness of the surface portion, the strength of the shot peening is controlled. And the decomposition rate of retained austenite is 1 /
By controlling the strength of the shot peening process so as to be 10/3/10, the amount and hardness of the carbide in the surface layer portion can be controlled to a desired range, and the surface can be prevented from becoming brittle. Thereby, wear resistance and fatigue life are improved.

The surface roughness affects the ability to form an oil film between the surface of the rolling sliding component and the surface of the mating component. The finer the pitch (wavelength) of the roughness, the better the ability to form an oil film. It was confirmed by experiments conducted by the present inventors that the oil film forming ability was remarkably improved when the particle size was 25 μm or less. Therefore, the average wavelength of the roughness is regulated to 25 μm or less. Incidentally, in the present specification, the mean wavelength lambda _a surface roughness, expressed by _{λ a = 2π · R a /} θ a. Where _Ra
The average roughness of the surface, the theta _a is the average of the absolute value of the inclination angle of the minute protrusions on the surface. As a result of shortening the mean wavelength lambda _a surface roughness as improves the ability to retain lubricant between the large number of fine projections on the surface, between the rolling slide member surface and the mating part surface Oil film forming ability is improved, and wear resistance and fatigue life are improved.

[0014]

Next, in order to manufacture the rolling sliding part of the present invention,
An example of a method of processing a surface into a predetermined property and an experiment performed by the present inventor to confirm the effect of the present invention will be described. As shown in the table below, 4
A total of 13 types of test specimens of the present invention and 9 types of comparative products were prepared. All test piece materials are bearing steel (SUJ
2), depending on the specifications of the test piece, tempering after carbonitriding and quenching, and tempering (150 to 850 ° C., oil cooling) followed by tempering (150 to (200 ° C.). In the table below, those without the carbonitriding treatment have been subjected to ordinary quenching and tempering treatment. The size of the test piece is a cylindrical shaft having an outer diameter of 8.8 mm and a length of 25 mm.

[0015]

[Table 1]

Among the comparative products, the test pieces 1 and 2 were not polished by polishing the surface with a polishing cloth, and thus were not subjected to shot peening for hardening the surface. As with the invention described in Japanese Patent Application Laid-Open No. 4-54312, all 11 types of test pieces 3 to 13 belonging to the comparative product and the product of the present invention are shown in FIG. The surface was hardened by performing shot peening using an apparatus as shown in FIG. 1, and a large compressive residual stress was generated in the surface layer.

The structure and operation of the shot peening apparatus shown in FIG. 1 will be briefly described. The fine shot particles 3 put into the pressurized tank 2 from the hopper 1 are pushed into the mixer 5 by compressed air sent from the air supply pipe 4 into the pressurized tank 2. Then, the shot grains 3 are sent to the nozzle 7 by compressed air sent to the mixer 5 through the branch pipe 6, and are blasted from the nozzle 7 toward the surface to be processed. As a result, the surface to be processed is hardened, a compressive residual stress is generated on the surface to be processed, and minute irregularities are formed on the surface to be processed.

The shot grains 3 include test pieces 3 to 1
In any of the three, ceramic particles (metal oxide particles and the like) having an average particle diameter of 0.03 to 0.1 mm were used. The projection speed of the shot particles 3 (initial speed of the shot particles 3 ejected from the nozzle 7) was set to 32 to 120 m / sec (average projection speed = 80 m / sec). The adjustment of the projection speed is performed by adjusting the opening of the adjustment valve 8 provided in the middle of the branch pipe 6, and based on the adjustment of the projection speed, each of the test pieces 3 to 3 is adjusted.
The residual compression stress generated on the surface of No. 13 was adjusted.

Further, the test pieces 10 to 13 of the present invention.
After performing shot peening with ceramic particles such as the above metal oxide particles, the second stage shot peening using glass beads or ceramic beads, which are lighter shot particles. Was performed. The average grain size of the shot grains used in the shot peening in the second stage was 0.05 mm or less. Thus, the second stage shot peening using light shot grains is performed by changing only the surface roughness without changing the hardness of the surface layer and the compressive residual stress (roughening). To shorten the average wavelength).

The shot peening process is performed eight times at a time, and the hardness of the surface layer, the residual stress of the surface layer, the amount of retained austenite in the surface layer, and the average wavelength of the roughness are almost the same. Were made eight at a time. A total of 104 test pieces 1 to 8 of 13 types obtained in this way were obtained.
A durability test was performed on all of the test samples 13 using a test apparatus as shown in FIG.

In this test apparatus, two mating rings 10 and 10 are fixed at two positions on the outer peripheral surface of a rotating shaft 9 which is driven to rotate by a motor, with an interval therebetween. One pair of supporting pieces 12, 12 provided on one surface of the pressing piece 11 in accordance with the intervals between the mating rings 10, 10 respectively support one test piece 13, 13. ,
The outer races 15 constituting a cam follower are rotatably supported by needles 13 via needle bearings 14. The outer peripheral surfaces of the outer races 15 and 15 and the outer peripheral surfaces of the mating rings 10 and 10 are in rolling contact with each other. As a result, each of the outer races 1 is rotated with the rotation of the rotation shaft 9.
5, 15 rotate. Therefore, in the test device shown in FIG. 2, the durability test of the two test pieces 13, 13 supporting the two outer rings 15, 15 can be performed at the same time.

The rotation speed of the rotating shaft 9 is controlled by the outer ring 1
The rotation speeds of 5, 15 were adjusted so as to be 1000 rpm. The pressing piece 11 is 356 kg toward the rotating shaft 9.
Pressed with force f. Therefore, a radial load of 178 kgf is applied to the contact portions between the outer peripheral surfaces of the outer races 15, 15 and the outer peripheral surfaces of the mating rings 10, 10, respectively. In addition, the lubrication of the supporting portions of the outer rings 15, 15 by the test pieces 13, 13 is performed by splashing degraded oil (lubricant mixed with soot and other insoluble components) of 10W-30 heated to 120 ° C. It was done by running.

The test was discontinued for 200 hours, and was interrupted a plurality of times (50 hours, 100 hours, and 150 hours after the start of the test).
The radial clearance between the radial needle bearings 14 and 14 supporting the bearings 15 and the outer races 15 and 1
The sensation (hand sensation) when turning 5 by hand was examined.
When the bearing gap exceeded 50 μm, or when a feeling of turning (feeling uncomfortable with vibration) was felt, the durability test on the test piece was terminated at that time.

As a result, in each of the test pieces 1 to 13,
The bearing clearance did not increase until 200 hours elapsed for all eight test pieces, and no scumming occurred. The result is indicated by ◎. When the feeling was felt, the result was ○, and the bearing clearance was increased with 4 to 7 pieces, or when the feeling of scraping was felt, Δ, and the bearing gap was increased with all eight pieces, or the feeling of scraping was generated. The result was indicated as x and described in the column of evaluation in the above table.

As is evident from the above table showing the results of the durability test, the rolling sliding parts of the present invention do not have a large bearing clearance and do not have a feeling of rubbing even under severe lubrication conditions. In addition, among the signs described after each numerical value in the above table, （(excluding the column of evaluation) indicates that the numerical value is included in the limited range of the present invention, and x (excluding the column of evaluation) indicates The numerical values deviate from the limited range of the present invention, respectively.

[0026]

The rolling sliding part of the present invention has sufficient durability and abrasion resistance even under severe lubricating conditions in which lubricating oil containing only soot and other insoluble components can be obtained. Can be secured. As a result, it is possible to achieve excellent effects that are extremely useful in industry, such as extending the inspection time of the mechanical device such as a diesel engine and achieving maintenance-free operation.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a shot peening apparatus.

FIG. 2 is a half vertical sectional view of the durability test apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hopper 2 Pressurized tank 3 Shot grain 4 Air supply pipe 5 Mixer 6 Branch pipe 7 Nozzle 8 Adjustment valve 9 Rotating shaft 10 Mating ring 11 Pressing piece 12 Supporting piece 13 Test piece 14 Needle bearing 15 Outer ring

Claims (1)

[Claims] In a rolling sliding part used in a state of rolling or sliding contact with another opposing part, when the surface layer has a depth of 0 to 50 μm from the surface, The ratio of carbide contained in the surface layer is 10
-25% by volume, the decomposition rate of the retained austenite in the surface layer portion with respect to the initial value is 1/10 to 3/10, and the hardness of the surface layer portion is also Hv830 to Hv960.
A rolling sliding part characterized in that the average wavelength of the surface roughness is 25 μm or less.