JPH09125203A - High damping rolling bearing made of graphite steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high damping rolling bearing effectively reduced in the generation of vibration and noise by forming at least any of inner ring, outer ring, and rolling element by the use of a graphite steel, providing the surface with carbo-nitrided layer, and also providing the inner part with graphite-precipitated structure. SOLUTION: In a rolling bearing consisting of bearing ring of inner ring and outer ring and a rolling element attached between the inner ring and the outer ring, the inner ring, the outer ring, or the rolling element is formed of graphite steel. Carbo-nitriding treatment is applied to the surface to form a hardened carbo-nitrided layer of high carbon and high nitrogen in the surface, and surface hardness is regulated to ∞ about HRC 58 and the structure in the inner part is formed into graphite-precipitated structure. Further, a graphite steel, having a composition consisting of, by weight ratio, 0.5-2.0% C, 0.5-2.0% Si, 0.3-1.5% Mn, and the balance Fe with inevitable impurities, is preferred as the graphite steel. By this method, the inexpensive rolling bearing, capable of combining the hardness and wear resistance at the surface with the damping characteristic in the inner part, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing made of graphite steel having vibration damping properties and soundproof properties.

[0002]

2. Description of the Related Art Rolling bearings used in highly precise machines and devices, and rolling bearings used in machines used in a quiet environment, generate abnormal noise and vibration during operation. Is required, and from this point,
In terms of bearing design, measures such as dimensional accuracy, surface hardness, and protection methods against foreign matter in the bearing are taken, but there is a limit to structural improvement. Attempts have been made to provide soundproofing.

Conventionally, as a damping material that can be used for bearings, 13% Cr martensitic stainless steel and 5-10% Cr-containing high chromium steel (0.6 to 0.8) which is an improvement of this steel type. % C) has been proposed (Japanese Patent Laid-Open No. 2-
93041, JP-A-5-125488),
These are to impart excellent vibration damping properties by utilizing the internal friction phenomenon due to the addition of a large amount of Cr, and at the same time ensure the required hardness and wear resistance by quenching and tempering or carbonitriding.

Further, as vibration damping steel, 0.05 to 1.0
There is known a graphite steel in which graphite is precipitated in low / medium carbon steel containing C in a small amount and containing a small amount of B (Japanese Patent Laid-Open No. 3-75331). This steel is used as a vibration damping material by hot-rolling / hot-forging followed by graphitization annealing to precipitate graphite.

In order to construct a member of the bearing with vibration-damping steel,
It is necessary that the heat treatment results in a high hardness of HRC58 or more and is excellent in wear resistance, the bearing has a long fatigue life, and the heat treatment does not lower the vibration damping property. Since the above-mentioned conventional 5-10% Cr steel contains a large amount of Cr, it is excellent in hardenability, but it is considerably more expensive than ordinary SUJ2 steel and is not general. Also, the latter low / medium carbon graphite steel cannot be added in a large amount of Cr that hinders graphitization, so that it has a low quench hardening ability and cannot sufficiently secure the surface hardness HRC58 or higher required for bearing rings and rolling elements. There was a problem. Further, when quenching, there is a problem that graphite easily remains near the surface of the bearing ring and the like, and the graphite particles near the surface serve as a stress concentration source, which reduces the rolling life.

In view of the above problems, the present invention provides a low-priced rolling bearing which is molded from graphite steel and is capable of achieving both surface hardness / wear resistance and vibration damping in the internal portion. Is what you are trying to do.

[0007]

A rolling bearing of the present invention is a rolling bearing including race rings of an inner ring and an outer ring and rolling elements interposed between the inner ring and the outer ring, and the features thereof are at least the inner ring, the outer ring, Alternatively, one of the rolling elements is formed of graphite steel and has a carbonitriding layer on the surface thereof, and the internal part thereof has a graphite precipitation structure to impart vibration damping properties.

In the rolling bearing made of graphite steel of the present invention, the material of the bearing ring or rolling element is formed of graphite steel.
This is to make the graphite precipitate structure in the internal part after heat treatment, which allows the graphite particles to be dispersed in the internal part that occupies most of the volume of the bearing ring and rolling elements to absorb vibration energy and suppress vibration. Is given.

On the other surface of the bearing ring, rolling element, etc., a carbonitriding treatment is performed to form a carbonitriding layer of high carbon / high nitrogen which has been hardened by quenching and hardened, so that the surface hardness becomes HRC.
The wear resistance and the rolling fatigue life are secured at 58 or more, preferably HRC 60 or more.

Further, the carbonitriding treatment reduces the concentration of stress in the surface layer portion below the rolling surface due to the graphite particles, because the graphite particles of the carbonitriding layer dissolve and disappear in the matrix. Further, N is increased in the carbonitrided layer, whereby the amount of retained austenite becomes higher than that in the internal portion, and the toughness of the surface layer is increased. In this way, the formation of the carbonitriding layer is effective for prolonging the rolling fatigue life of graphite steel. On the other hand, if the carburized layer is simply used, a large amount of granular graphite remains on the surface layer, so that the rolling fatigue life is low.

Thus, the rolling bearing of the present invention is
By carbonitriding the graphite steel, it has both high hardness and high wear resistance on the surface and vibration control at the internal part.

The present invention relates to a method for manufacturing a bearing ring, which is produced by molding graphite steel which has been graphitized into a ring for a bearing ring.
Then, after forming the raceway groove by cold rolling,
The ring is carbonitrided and quenched in a cooling agent, 150-2
A method of manufacturing a bearing ring for a vibration-damping rolling bearing that is tempered at 50 ° C is included.

In this method, when a ring is formed from a graphitized graphite steel material, and a raceway groove is formed by cold rolling, the ring peripheral surface, particularly,
At the surface layer of the raceway groove, plastic flow occurs due to the reduction, and the graphite particles are stretched and become flat. When carbonitriding this, the graphite particles are easily dissolved in the mother phase in the carbonitriding process, and the graphite particles in the carbonitriding layer can be almost eliminated.

In the present invention, the graphite steel broadly covers carbon steel type steel in which graphite is precipitated by heating near the A ₁ point. In particular, as graphite steel, C0.
5 to 2.0%, Si 0.5 to 2.0%, and Mn 0.3
.About.1.5%, with the balance being Fe and unavoidable impurities.

In this composition, C is necessary for determining the amount of graphite deposited on the core and ensuring the strength of the core, but if it is higher than 2.0% C, the amount of graphite is too large, Even by carbonitriding, it becomes difficult to completely extinguish graphite in the carbonitriding layer on the surface layer. On the other hand, if it is lower than 0.5% C, it is difficult to secure the hardness of the surface layer even by carbonitriding processing.

Si is necessary as a deoxidizing agent in the steelmaking stage, and is used as a graphitization accelerator in the present invention. S
If i is higher than 2.0% Si, cold workability is significantly impaired and carbonitriding becomes difficult, while 0.5% Si
If it is lower, graphitization becomes difficult.

Mn is the quench-hardenability of steel, in this case,
It is necessary to enhance the quench-hardenability of the carbonitrided layer, but on the other hand, addition of a large amount of Mn hinders workability, so
It is necessary to set it in the range of 0.3 to 1.5% Mn.

[0018] Cr is preferable in that it enhances the quench-hardening ability, but since it significantly inhibits graphitization, it is not usually added positively. It is mixed to the extent of mixing with the raw materials in the steelmaking stage, usually 0.3% Cr or less.

In the present invention, Al is necessary as a deoxidizing agent in the steelmaking stage, but it can be used as a graphitization accelerator like Si. B (boron) can also be used as a graphitization accelerator, and its addition amount is 0.0005-
The range is 0.0050% B. It is necessary to reduce other impurities, especially P, S and O as much as possible.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The rolling bearing of the present invention is formed into the shape of an inner ring, an outer ring or a rolling element from the above graphite steel, and is carbonitrided and tempered at a low temperature, whereby the surface layer is made into a carbonitride layer. The internal part has a graphite precipitation structure. The process is graphitization annealing of a graphite steel rod-shaped material (billet), external cutting and track groove formation, carbonitriding and immediate cooling. Especially after quenching in oil and tempering, precision finishing (grinding + super finishing) is performed.

The graphitization annealing can be carried out by heating and holding the raw material near the A ₁ point of the steel, for example, at 600 to 700 ° C. for 10 hours or more and gradually cooling. This makes it possible to decompose cementite and pearlite in the steel and deposit graphite in the form of particles to form a ferrite structure in which graphite is deposited.

Carbonitriding treatment is carried out by heating graphite steel having such a graphite precipitation structure to form a carbonitriding layer enriched with C and N only in the surface layer and quenching in a cooling agent such as oil. The carbonitriding layer has a quenched structure.
Solid carbonitriding, liquid carbonitriding, and gas carbonitriding are all possible. In the case of gas carbonitriding, heating and holding is performed in an austenite region, for example, 850 to 1000 ° C. for a long time in a furnace prepared in a carburizing and nitriding atmosphere, followed by rapid cooling into oil. The carbonitriding atmosphere may be adjusted in the same manner as in the normal carbonitriding method when the graphite steel is about 0.5 to 1.0% C. For example, RX gas or N 2 may be used.
The carbon potential CP of the X gas is adjusted to 1.2 to 1.5% CP by adding propane or the like if necessary, and ammonia is added in an amount of 5 to 15% by volume to make it nitriding.
When the carbonitriding treatment is difficult because of the high Si content, steam treatment or thermal oxidation treatment is performed as a pretreatment to leave the surface in a black skin state, which promotes the subsequent carbonitriding treatment. It will be possible. Further, secondary quenching may be performed in order to make the microstructure finer after the graphite in the surface layer is extinguished by carbonitriding.

After carbonitriding, tempering is performed at 150 to 250 ° C.
The heating is performed for 1 to 5 hours within the range. As a result, the surface hardness of the carbonitrided layer after tempering is set to HRC 58 or more, and the residual austenite is partially decomposed. At this time, the amount of retained austenite in the carbonitrided layer was set to 1 by setting the tempering temperature and time.
It is adjusted to 5% or more, preferably 20 to 30%.

In the method for manufacturing a bearing ring of the present invention, a ring is formed by using a rod-shaped material or a tube material on which graphite is already deposited by graphitization annealing. The outer shape of the ring and the formation of the raceway groove are performed by cold rolling, but the ring has a rectangular cross section (a suitable chamfer may be provided), and the rolling is performed by the mandrel on the inner circumference side of the ring and the ring. Outer dimensions in which a groove for forming a raceway groove is provided on one of the outer peripheral side main roll and the groove forming roll, and the ring is pinched between the mandrel and the main roll and the ring leaves a grinding allowance for the bearing ring. Rolled into. At this time, the orbital groove forming ridges of the groove forming roll come into contact with the corresponding week surface and roll down, so that the plastic deformation around the orbital groove becomes particularly large, and the elongation and flatness of the graphite particles at that portion is large. When this ring is carbonitrided,
In the carbonitriding layer of the raceway groove, the graphite particles flattened as the concentration of C and N melts well in the matrix and can be almost completely eliminated.
The carbonitrided layer with a high concentration has a high hardness.

[0025]

Example A graphite sample having a composition shown in Table 1 and preliminarily graphitized was used to form a cylindrical sample having a diameter of 12 mm.
Carbonitriding treatment was performed at 0 ° C. for 2 hours. The conditions for the carbonitriding treatment were as follows: RX gas was added with CP 1.2% and 10% ammonia was added, and the mixture was heated and held, and then put into oil at 90 ° C.

[0026]

[Table 1]

FIGS. 1 (A) and 1 (B) show microstructure photographs near the surface of graphite steel after carbonitriding and tempering. Before carbonitriding treatment, graphite particles are dispersed in ferrite, but after carbonitriding treatment (A, B), graphite particles disappear in the surface layer portion, and a quenched carbonitriding structure is obtained. . FIG. 2 is a microstructure photograph of the internal portion of the graphite steel after carbonitriding treatment. In the internal portion, graphite remains,
The matrix has a graphite precipitation structure with martensite. As described above, by carbonitriding, graphite can be left in the internal portion and the surface layer can be a carbonitriding layer without graphite.

In FIG. 3, the outer diameter of the graphite steel of Table 1 is 38
mm × Inner diameter 34 mm, Width 20 mm is formed and carbonitrided (RX gas, CP1.2%, ammonia 10% mixed, heated at 950 ° C. for 2 h, and then put in oil at 90 ° C. and allowed to cool).
And about the sample that was tempered (180 ° C x 2h),
The hardness distribution from the surface of the carbon steel after carbonitriding is shown, but the surface has a sufficiently high hardness of Hv 700 or more,
A decrease in hardness is observed toward the inner part.

(Vibration damping characteristics) A ring having an outer diameter of 38 mm x an inner diameter of 34 mm and a width of 20 mm was formed from graphite steel having the composition shown in Table 1 above, and the same carbonitriding treatment (RX gas, CP1.
2%, 10% ammonia mixed, heated at 950 ° C for 2h 9
Put into oil at 0 ° C and let it cool down, and temper (180 ° C x 2h)
The vibration damping test was performed using the above as a ring sample. The comparative example is a similar ring sample obtained by quenching and tempering SUJ2 steel (composition is shown in Table 1). In the heat treatment of the comparative example, quenching was performed by heating at 850 ° C. for 50 minutes, then rapidly cooling in oil at 90 ° C., and tempering was performed at 180 ° C. for 2 hours.

In the vibration damping test, a strain gauge was attached to the surface of the ring sample, suspended with a thread, the ring was hit with a hammer, and the strain vibration was detected by the strain gauge and recorded in a recorder. .

FIG. 4 shows the vibration curve (A) of the example and the vibration curve (B) of the comparative example. When the logarithmic damping coefficient δ is obtained from this figure, δ = for SUJ2 steel of the comparative example. 0.0
In contrast, in the graphite steel of the example, δ =
It is 0.0163, and the vibration damping property is recognized in the examples.

(Rolling life) Diameter 12 m from the above graphite steel
m columnar sample was cut out and subjected to the same carbonitriding treatment (RX gas, CP1.2%, ammonia 10% mixture, 9
After heating at 50 ° C. for 2 hours, it was put into 90 ° C. oil and allowed to cool, and tempered (180 ° C. × 2 hours) to perform a rolling life test.

The method and conditions for the rolling fatigue life test are shown below. Tester ； Point contact type life tester Specimen ； Diameter 12mm Length 22mm Opposite Specimen ； 3 / 4inch steel ball Contact stress ； Pmax 5.9GPa Load speed ； 46240rpm

The results of the rolling life test are shown in Table 2. The comparative examples are a sample obtained by quenching and tempering the above graphite steel without carbonitriding and a sample obtained by quenching and tempering SUJ2 steel (composition is shown in Table 1). In each of the comparative examples, quenching was performed by heating at 850 ° C. for 50 minutes, then rapidly cooling in oil at 90 ° C., and tempering was performed at 180 ° C. for 2 hours.

[0035]

[Table 2]

Rolling fatigue life (L ₁₀ ) of Examples and Comparative Examples
Table 2 shows that the hardened graphite steel has an extremely short rolling fatigue life, but the carbonitriding process extends the life of the product, resulting in a rolling life comparable to that of the conventional SUJ2 steel. It turns out that it can be obtained.

When carbon steel is subjected to carbonitriding treatment, the surface layer becomes high carbon / nitrogen, and in this carbonitrided layer, the graphite is dissolved and disappears in the carbonitriding process, but it is said that graphite remains on the surface layer. It is considered that the graphite particles can be the starting point of cracking and peeling. However, even if a small amount of graphite particles remain in this layer, it has been confirmed that due to contact stress, the graphite particles disappear in the surface layer below the rolling surface due to rolling under high surface pressure. The disappearance of graphite is considered to be due to the fact that graphite dissolves in the matrix and becomes solid solution carbon in the matrix.

FIGS. 5 (A) and 5 (B) are photomicrographs of a cross section near the rolling surface of the cylindrical sample used in the above life test. This sample has graphite particles on the surface by grinding after carbonitriding. It was exposed and a fatigue life test was conducted. From this micrograph, a region where graphite disappeared is clearly observed below the rolling surface. When the amount of graphite in this region is small in the surface pressure of the rolling surface (Fig. 5 (A), Pmax = 4.9GP
Compared with a), when the surface pressure on the rolling surface is large (Fig. 5)
It can be seen that (B) and Pmax = 5.9 GPa) are greatly reduced.

FIG. 6 shows the relationship between the amount of retained austenite in the surface layer and the rolling life when carbonitriding a material having surface defects such as graphite steel. Long life can be achieved by securing a relatively large amount of about 30%.

Generally, when a high stress load is applied to the surface layer due to rolling due to high surface pressure, the retained austenite is
The stress concentration acting around the material defect is relaxed by its plastic deformation to delay the initiation of cracks, but even in the case of carbonitriding of graphite steel, the stress concentration acting around the remaining graphite particles is softened. The relaxation of the retained austenite has the effect of preventing the occurrence of cracks.

[0041]

EFFECTS OF THE INVENTION The rolling bearing of the present invention utilizes the vibration damping property of graphite steel and has its surface layer hardened by carbonitriding, so that it can exhibit the fatigue life at the level of conventional bearing steel. It can be used for bearings of machinery / equipment to effectively reduce the generation of vibration and noise caused by the bearings themselves.

[Brief description of the drawings]

FIG. 1 shows micrographs of a metal structure of a surface layer portion of a sample formed of carbon steel and carbonitrided (A, B) (nital corrosion).

FIG. 2 shows a micrograph of the metal structure of the internal portion of a sample formed of carbon steel and carbonitrided (nital corrosion).

FIG. 3 is a diagram showing a cross-sectional hardness distribution from a surface of a sample formed of carbon steel and subjected to carbonitriding treatment.

FIG. 4 is a diagram showing a vibration curve of time-amplitude in a vibration damping test of a ring-shaped sample, (A) is a sample of carbon steel subjected to carbonitriding treatment, and (B) is a comparative example of SUJ2 steel. The samples subjected to quenching treatment are shown below.

FIG. 5 shows a micrograph of a metal structure of a cross section near a rolling surface of a cylindrical sample used in a life test (nital corrosion).
(A) is the surface pressure Pmax 4.9 GPa, (B) is the surface pressure Pma
x Tested at 5.9 GPa.

FIG. 6 is a graph showing the relationship between the amount of retained austenite in the surface layer and rolling fatigue life (L ₁₀ ).

Claims (5)

[Claims] 1. A rolling bearing comprising inner and outer ring raceways and rolling elements interposed between the inner and outer rings, wherein the inner ring, outer ring or rolling element is made of graphite steel and has a surface layer. A vibration-damping rolling bearing, characterized in that it has a carbonitrided layer on its inside and has a graphite precipitate structure in its internal part. 2. The graphite steel has a weight ratio of C0.5 to
2.0%, Si 0.5-2.0%, Mn 0.3-1.5
%, And the balance Fe and unavoidable impurities, and the vibration-damping rolling bearing according to claim 1. 3. The vibration-damping rolling bearing according to claim 1, wherein the carbonitrided layer contains a residual austenite amount of 15 to 30%. 4. A ring for a bearing ring having a raceway groove on the ring peripheral surface is formed from graphitized graphite steel, and then the ring is carbonitrided and rapidly cooled in a cooling agent.
A method for manufacturing a bearing ring for a vibration-damping rolling bearing, which is tempered at 250 ° C. 5. A ring for a bearing ring is formed from graphitized graphite steel, and then a ring groove is formed on the ring circumferential surface by cold rolling, and then the ring is carbonitrided to form a cooling agent. A method for manufacturing a bearing ring for a vibration-damping rolling bearing, which is rapidly cooled in the medium and tempered at 150 to 250 ° C.