JP2734704B2 - Rolling bearing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rolling bearing used for an automobile, an agricultural machine, a construction machine, a steel machine, and the like, and is particularly required for a jet engine and a gas turbine engine. Related to long-life rolling bearings.

[Conventional technology]

Conventionally, various alloy steels such as bearing steel class II (SUJ-2) exist as steels used for rolling bearings. However, in recent years, the surface pressure applied to the bearing tends to increase due to an increase in load and a reduction in the size of the bearing. The use conditions are becoming severe, such as insufficient formation of an oil film for bearing lubrication, and there is a need to improve the durability life. Particularly, rolling bearings used in jet engines and gas turbine engines are required to have high reliability because their use conditions are high temperature and high speed.

Therefore, in order to improve the durability life of bearings used under high temperature and high speed conditions, various alloy steels have been applied. For example, in order to improve the durability life of a rolling bearing used in a jet engine or the like, a high-speed steel having good tempering hardness, high-temperature hardness, and wear resistance is used. As this high-speed steel for bearings, for example, a precipitation hardening type steel such as M50 containing Cr, Mo, V and the like has been provided.

High speed steels are often made by powder sintering in recent years. For example, JP-A-61-19756 discloses a sintered high-speed steel obtained by sintering and solidifying a carbide powder of a carbide forming element selected from Cr, Mo, W, and V and soft Fe and carbon powders. ing. Also, Japanese Patent Application Laid-Open No. 60-67644 discloses a method of sintering an alloy powder.
Particles that do not react with the matrix metal during heat treatment (unreacted particles) and react with the matrix metal during sintering to form a solid solution, and those that precipitate during heat treatment (reactive particles) are sintered and solidified. A high speed steel is disclosed.

These conventional examples provide a high-speed steel with good wear resistance by sintering a powdered high-speed steel having fine crystallized carbides and increasing the hardness of a large carbide-free steel by precipitation hardening. .

[Problems to be solved by the invention]

According to the inventor's intensive studies, the rolling fatigue life (hereinafter referred to as life) of a rolling bearing depends on the hardness and the size of carbides. It has been found that the value part has a maximum value. Therefore, in order to improve the life of the rolling bearing, it is necessary to find an optimum range of the hardness of the alloy steel and the grain size of the carbide. There is a problem that a long life rolling bearing cannot always be provided only by using a sintered high-speed steel.

Accordingly, it is an object of the present invention to provide a long-life rolling bearing by finding the optimum range of the hardness of alloy steel and the particle size of carbide.

[Means for solving the problem]

In order to achieve such an object, the present invention provides a rolling bearing composed of a bearing ring and a rolling element, wherein at least the rolling element is
Due to high temperature tempering, hardness is in the range of HRC 62 to 70,
In addition, the carbide is made of an alloy steel having a diameter of 12 μm or less in terms of a perfect circle.

It is desirable that the hardness of the rolling elements be equal to or greater than the hardness of the bearing ring. Further, it is desirable that at least the rolling elements are made of sintered alloy steel powder. Furthermore, high temperature tempering
It is desirable to carry out at 450 to 600 ° C. Further, it is desirable that at least the amount of carbides in the rolling elements is 20 to 50 vol%.

[Action]

The present inventor quenched and tempered various low- and high-alloy steels in order to search for alloy steels having a long life, prepared test pieces, and performed a rolling fatigue life test. As a result, regarding the relationship between the life and hardness of the rolling bearing, the calculated life (= 1.
Some test pieces have a long life exceeding 100 times that of 25 × 10 ⁶ cycles (calculated by JIS B 1518), but their life varies greatly with hardness, and only controlling hardness improves the life of the bearing. Found it difficult to do so.

The inventors of the present invention have examined the relationship between hardness and life at a tempering temperature which can be a parameter of the carbide grain size and the toughness of the matrix, which is a problem depending on whether it can be a starting point of flaking. The result was as follows.

The life test was performed on a disc-shaped test piece (composition is the same as that of sample 1 described later) in “Special Steel Handbook (1st edition) edited by Denki Steel Research Institute, Science and Engineering Building, May 25, 1965, No. 10 ~twenty one
The test was performed using the tester described in the section. The test conditions are as follows.

Maximum contact surface pressure _{(P max) = 578kgf / mm} 2, the rotational speed (N) = 3
000Cpm, lubricants = VG68 turbine oil the first figure the particle size distribution of carbides present in the alloy steel, divided by four times the value of the perfect circle equivalent diameter (the area of the carbides in the inspection area 165mm ² in π The maximum value is 6 μm or less, more than 6 μm 12 μm or less, more than 12 μm 18 μm
Divide into the following three groups and further divide each group into 160
It is divided into two groups: low temperature tempering at ~ 200 ° C and high temperature tempering at 450-600 ° C.
L ₁₀ life those (90% remaining life, the release to at least one of the raceway surface of the disk-shaped test piece displayed in revolutions until occur) showing the relationship between.

Examining FIG. 1 in detail, the life depends on the hardness, and the diameter of the carbide converted to a perfect circle is 6 μm or less and 6 μm or less.
It can be seen that the life and hardness are particularly well correlated in the two groups of more than μm and less than 12 μm. That is, the hardness is constant (HRC62) in two groups in which the equivalent circle diameter of carbide is 6 μm or less and more than 6 μm and 12 μm or less.
It can be seen that the lifetime has a maximum value (within the range of ~ 70) (Figs. 1A to 1D). Therefore, the equivalent circle diameter of carbide is
By setting the hardness after hardening to 12 μm or less and the hardness after hardening to HRC 62 to 70, a long-life rolling bearing can be obtained.

In order to obtain a long-life rolling bearing, it is effective to perform high-temperature tempering (for example, 450 to 600 ° C.) as shown in FIG. Perform high temperature tempering to reduce the carbide equivalent circular diameter to 12
and μm or less, life by a further stiffness and HRC62~70 (L ₁₀₎ can be 10 ⁷ cycles or longer life. In particular, the diameter of the carbide produced by subjecting the alloy steel to high temperature tempering and hardening is 6 μm or less.
By setting the hardness to HRC 62 to 69, it is possible to obtain a bearing having a long life of 100 times or more the calculated life.

For high temperature tempering, low temperature tempering (for example, 160 to 200
C), the toughness of the matrix is low and the life is shorter than in the case of the high temperature tempering. Therefore, it is more desirable to perform the high temperature tempering in order to obtain a long life.

To improve bearing life, the carbide equivalent circular diameter is 12
It is preferably at most μm, particularly preferably at most 6 μm. When the carbide becomes finer, the stress concentration is reduced and the peeling resistance is improved. Therefore, when the carbide diameter exceeds 12 μm, the life is shortened due to the stress concentration.

In order to refine the carbide, it is preferable to use an alloy steel obtained by a powder sintering method. Needless to say, this does not hinder the use of the alloy steel obtained by a normal melting method or the like.

As the high-temperature tempering temperature of the alloy steel, 450 to 600 ° C. is usually preferable. If the temperature is lower than 450 ° C., no remarkable effect is observed, and if the temperature is higher than 600 ° C., the carbides are agglomerated by tempering and the toughness of the matrix tends to decrease.

When producing a rolling bearing, at least the rolling elements must be made of the alloy steel. This is because when the bearing is used under conditions of high surface pressure, insufficient oil film formation, or when both radial and thrust forces are applied, or when lubrication with contaminants is involved, the rolling elements precede the bearing rings. This is because flaking occurs and the life of the bearing is determined, and such use conditions are actually large. However, it is natural that it is more effective to make both the rolling element and the raceway from the alloy steel in order to improve the life of the rolling bearing.

The present inventor further studied and found from the following experiments that the fact that the hardness of the rolling elements is equal to or higher than the hardness of the bearing ring is more effective in improving the life of the rolling bearing. Was.

Bearing outer diameter 62 mm, width 16 mm, bearing inner diameter 30 using the alloy steel
mm single-row deep groove ball bearings (6206). At that time, the heat treatment is adjusted so that the hardness difference between the rolling elements and the races (inner and outer rings) (however, the hardness of the inner and outer rings is the same) HR)
It formed in a range of -7 to + 7 C, L ₁₀ running life test
The relationship between the life (hours) and ΔHRC (HRC of the rolling elements−HRC of the inner and outer rings) was determined. The result is shown in FIG. DerutaHRC but becomes the L ₁₀ as increased long L ₁₀ is substantially saturated constant in the range of ΔHRC ≧ 0. On the other hand, in the range of ΔHRC <0, the rolling elements are separated and the life is shortened. From the above results, it was confirmed that it is necessary to make the hardness of the rolling elements higher than that of the bearing ring in order to improve the life of the bearing.

The life test described in FIG. 2 was performed using an oil bath lubricated bearing durability life tester described in “Nippon Seiko Co., Ltd., Technical Journal No. 646, page 20”.

FIG. 3 (1) is a front view of the tester, and FIG. 3 (2) is a sectional view taken along the line AA of FIG. 3 (1). In the figure, 70 is a test axis, 71 is a vibration detecting unit, 72 is a thermocouple,
73 is an oil level and 74 is a support bearing. As shown in FIG.
A radial load is applied to the test bearing. The test conditions of this tester are as follows.

Radial load Fr = 1410kgf, Maximum contact pressure ( _Pmax ) = 35
0 kgf / mm ² , lubricating oil = VG68 turbine oil, rotation speed (inner ring rotation, outer ring stationary) = 3000 rpm Examples of the alloy steel used in the present invention include high alloy steel such as high speed steel. As an example of a specific composition, C: 1.2 to 2.5% by weight, Cr; 3.5 to 18.5% by weight,
Mo; 2.0 to 6.0% by weight, W; 7.0% by weight, V; 0.5 to 5.0% by weight, with the balance being Fe.

C is an element necessary for improving the hardness after quenching and tempering. However, excessive addition increases the size of the crystallized carbides and shortens the life. Further, if the content is insufficient, the hardenability and the tempering hardness become insufficient. Cr is an element that improves temper softening resistance. Further, by forming fine carbides and performing precipitation hardening, sufficient hardness can be obtained even if high-temperature tempering is performed. Further, since hard and fine Cr carbides are precipitated, wear resistance is also improved. Insufficient Cr content results in insufficient hardenability, wear resistance and oxidation resistance during quenching. Further, if added more than necessary, a giant crystallized carbide is easily formed, which causes a reduction in life. Mo is Cr
Is an element effective for improving the tempering softening resistance.
In addition, it is an element that improves hardenability. However, the shortage of the content makes it impossible to obtain the required secondary hardening hardness, and at the same time, lowers the crystal grain coarsening temperature, resulting in heat sensitivity. In addition, excessive addition lowers the high-temperature workability. V has a remarkable effect on improving the tempering softening resistance, and also precipitates at the crystal grain boundaries to suppress the coarsening of the crystal grains, to achieve the refinement, and to combine with carbon in the steel to produce fine carbides. Is added because the addition increases the hardness and improves the wear resistance. Insufficiency in the amount of addition lowers the secondary hardening hardness and high-temperature hardness, and adding more than necessary is disadvantageous in cost. W is contained in a necessary amount because it is effective in improving quenching hardness and abrasion resistance.

In the alloy steel of the present invention, in order to reduce the generation of nonmetallic oxide-based inclusions, the oxygen content in the steel should be 200 ppm or less for sintered steel, and 15 ppm or less in other cases. Is preferred. The upper limit in the case of sintered steel is high because the size of the inclusions is small. The oxide may be a starting point of the occurrence of flaking, and may shorten the life of the bearing. Therefore, it is necessary to reduce the amount of oxide generated as much as possible. The inventor made an alloy steel by changing the oxygen content in the steel (the content of other elements was fixed) and formed a single-row deep groove ball bearing (6206) using this alloy steel. When the life was examined using a test machine, FIG. 4 was obtained for the sintered steel, and the other, that is, for the steel obtained by melt casting,
The result of the characteristic as shown in FIG. 5 was obtained. As a result, it can be seen that the improvement of the bearing life is remarkable when the oxygen content is 200 ppm or less in the case of sintered steel and 15 ppm or less in the case of other steel such as steel by melt casting.

In order to improve the life of the bearing, it is necessary to reduce the content of other impurity elements as much as possible. Such elements include, for example, P and S. P and S are
It is preferable that P is 0.02% by weight or less and S is 0.008% by weight or less.

In addition, it is preferable to contain 0.04% by weight or less of Si as a deoxidizing agent at the time of steel making and as a hardenability improving element.

As described above, in order to obtain a long-life rolling bearing, the invention according to claim (1) is directed to a rolling bearing comprising a race and a rolling element, wherein at least the rolling element has a hardness of HRC62 or higher due to high temperature tempering. 70, and is made of an alloy steel having a carbide size of 12 μm or less in terms of a perfect circle. By performing a hardening heat treatment (particularly quenching → high-temperature tempering), the retained austenite is converted to martensite, and carbides are precipitated and hardened in the matrix. By changing the retained austenite to martensite, a dimensional change can be prevented and dimensional stability in a high-temperature environment can be improved.

This carbide is hard and has excellent wear resistance, and as a result, has the function of improving the rolling fatigue resistance of the bearing. When the carbide is fine, stress concentration based on the applied load does not occur, so that the life of the bearing can be improved.

The carbide referred to in the present invention is, for example, M ₆ C, M ₇ C ₃ , Mo ₂ C, W ₂
C, V ₄ C ₃ , VC, and M ₃ C.

In the present invention, if the hardness is less than HRC62 or more than HRC70, the bearing life deviates from the maximum value, and sufficient rolling fatigue resistance cannot be obtained. If the size of the carbide exceeds 12 μm in terms of a perfect circle, the carbide becomes a starting point of crack generation due to stress concentration as shown in FIG. 1, and the life of the bearing is reduced.

In the present invention, the amount of carbide present in the surface layer of the bearing is preferably 20 to 50 vol%. If the amount of carbide is less than 20 vol%, it tends to be disadvantageous in obtaining the HRC required in the present invention, and if it exceeds 50 vol%, fine carbides are bonded to each other to cause coarsening of the carbide. This is because stress concentration tends to occur.

〔Example〕

Metal powders having the compositions shown in the following Table 1 were produced by a water spray method, and only fine powders passing through 100 mesh were collected. This powder was mixed with a high energy ball mill. The mixing of the metal powders may be performed by a method of mixing metal powders of the respective elements (premixing) or a method of mixing alloy powders (prealloy). These samples No1,
No. 2 shows an example of a sintered high-speed steel or a powdered die steel suitable for the present invention.

Each of these powder samples was sized at a pressure of 7 ton / cm ²
It was press-formed into a columnar shape of 100 mm x 100 mm length, canned, and sintered in a vacuum at 1150 ° C for 2 hours.

After that, it is sealed in a vacuum, and 1
HIP (hot isostatic pressing) treatment was performed for a time. Next, the steel ingot thus formed was rolled to produce a steel bar. In order to produce the 6206 single-row deep groove ball bearing, the bar was formed into an inner ring and an outer ring by hot forging and cutting. Then, as shown in FIGS. 6 and 7, the inner and outer rings thus processed were preheated using a high-temperature salt bath for 850 ° C. for 15 minutes.
About 1170 ° C. for 30 minutes and oil quenching, immediately subject this inner and outer ring to sub-zero treatment for sample No. 1 at −80 ° C. for 90 minutes, and then temper the inner and outer ring at 520 ° C. × 1 hour × 2 times For sample No. 2, the inner and outer rings were tempered at 550 ° C. × 1 hour × 3 times. Then, heat-treated inner ring,
The outer ring was polished and adjusted to standard dimensions to obtain a finished inner and outer ring.

On the other hand, the rolling elements (steel balls) were prepared as follows.
After the HIP treatment, hot extrusion was performed, and a wire rod was obtained through a heating wire rod rolling process. The wire rod was subjected to header processing and deburred to obtain elementary balls. This elementary ball is attached to the sixth and seventh
Heat treatment shown in the figure (When the quenching temperature is the inner and outer rings, sample No. 1
070 ° C. and Sample No. 2 were 1170 ° C., whereas in the case of a rolling element, Sample No. 1 was 1100 ° C. and Sample 2 was 1200 ° C.). After that, a rolling element which is a perfect sphere was obtained through a polishing lappig process. The reason that the quenching temperature is higher in rolling element creation than in inner and outer ring creation is that rolling elements are more likely to cause flaking earlier than inner and outer rings (see above), To prevent this.

Next, for each of the inner and outer races and the rolling elements thus obtained, the particle size of the carbide that contributed to hardening was measured. The measurement of the carbide particle size was performed as follows. The inner ring, outer ring, and part of the rolling elements were mirror-polished, and the carbide was analyzed using an electron microscope image analyzer. This analyzer consists of a combination of a TV camera, a TV screen, and a counter. An image from a microscope is transferred to a TV camera, which is scanned with an electron beam to convert light and dark on the screen into an electric signal. I asked. The following Table 2 shows the maximum values of the diameters of the inner ring, the outer ring, and the rolling elements in terms of the perfect circle at the carbide test area of 165 mm ² together with the hardness (HRC) measurement results. For comparison, a conventional bearing steel class II (C; 1.02, Si; 0.28, Mn; 0.3) having a carbide diameter and hardness as shown in Table 2 was used.
The inner and outer races and rolling elements of the single row deep groove ball bearing were prepared using a smelting material of (6, Cr; 1.47, O; 11 ppm). As shown in FIG. 9, the heat treatment conditions are oil quenching by holding at 840 ° C. × 30 minutes, tempering at 180 ° C. × 2 hours (inner and outer rings) and 160 ° C. × 2 hours (rolling element).

Next, the single-row deep groove ball bearing was assembled using the inner and outer races and rolling elements made of Sample 1, Sample 2 and bearing steel class II, respectively, and the oil-lubricated bearing durability life tester was used. _Ten
The life (hour) was measured. The life was determined based on the elapsed time at which scaly peeling due to flaking occurred on one of the raceway surfaces of the inner and outer rings and the raceway surface of the rolling elements. In addition, the quality of the life was determined to be "longer life" as the ratio of the measured life to the calculated life was higher. The results of the life test are shown in FIG. 8 and the following Table 3. In FIG. 8, the vertical axis represents the occurrence rate (defect occurrence rate) of bearings that are determined to be unusable due to flaking, and the horizontal axis represents elapsed time.

As can be seen from Tables 2 and 3, the inner and outer races and rolling elements made of samples 1 and 2 are within the scope of the present invention in terms of tempering temperature, carbide particle size, and hardness. The bearing (FIGS. 8F and G) has a long life. On the other hand, a rolling bearing formed of bearing steel class II (Fig. 8E)
Although the carbide particle size and hardness are within the range of the present invention, since the tempering temperature is lower than within the range of the present invention, the service life is shorter than that of the bearings made of samples 1 and 2.

In addition, if the tempering temperature, hardness and carbide particle size within the range of the present invention can be adjusted to the raceway and rolling elements of the rolling bearing without using the powder sintering method, the alloy steel is melted by ordinary melting. It is also possible to produce by a manufacturing method and a sintering forging method.

In this embodiment, the hot isostatic pressing (HIP) process is used, but a cold isostatic pressing (CIP) process may be used.

In this embodiment, both the bearing ring and the rolling element are made of the alloy steel in the range of the present invention. However, if at least the rolling element is made of the alloy steel in the range of the present invention, the object of the present invention can be achieved. It is possible.

Alloy steels that can be used in the present invention include powder die steel,
In addition to powdered high-speed steel, the present invention is not limited to those described in the Examples, and it is possible to control the adjustment of carbide particle size and hardness even after high-temperature tempering by heat treatment such as carburizing or carbonitriding so as to be within the scope of the present invention. For example, various alloy steels can be used. For example, carburized steel obtained by adding 3 to 18% by weight of Cr to JIS SCr may be used.

〔The invention's effect〕

As described above, according to the invention described in claim (1), at least the rolling element has a hardness of HR by high-temperature tempering.
Since it is made of an alloy steel having a range of C62 to 70 and a carbide particle diameter of 12 μm or less in terms of a perfect circle, a long-life rolling bearing can be provided.

According to the invention described in claim (2), since the hardness of the rolling elements is equal to or greater than the hardness of the bearing ring, it is possible to provide a rolling bearing having a longer life.

According to the invention described in claim (3), since at least the rolling elements are made of alloy steel obtained by the powder sintering method, carbides are further refined, thereby providing a rolling bearing having a longer life. be able to.

Further, since the invention according to claim (4) performs high-temperature tempering at 450 to 600 ° C., it is possible to provide a rolling bearing having a longer life.

According to the invention described in claim (5), while the desired hardness can be obtained, the coarsening of the carbide can be prevented, so that stress concentration does not occur at least in the rolling elements.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the relationship between the maximum value of the hardness and the roundness equivalent diameter of carbide and the bearing life, and FIG. 2 shows the relationship between (rolling element HRC-inner / outer ring HRC) = ΔHRC and the bearing life. 3 is a characteristic diagram showing the relationship between the oxygen content in the sintered alloy steel and the bearing life, and FIG. 5 is a molten and cast alloy steel. 6 and 7 are heat treatment process diagrams showing heat treatment conditions of the embodiment, and FIG. 8 is a graph showing the relationship between the defect occurrence rate of the rolling bearing and the elapsed time. FIG. 9 is a heat treatment process chart showing heat treatment conditions of a steel material which is a reference in the embodiment.

Claims (5)

(57) [Claims] 1. A rolling bearing comprising a race and a rolling element, wherein at least the rolling element is C: 1.2-2.5% by weight, Cr: 3.5% by weight.
~ 18.5% by weight, Mo: 2.0 ~ 6.0% by weight, V: 0.5 ~ 5.0% by weight, W: 7% or less, and after quenching,
A rolling bearing having a hardness in the range of HRC 62 to 70 by high-temperature tempering and a carbide size of 12 μm or less in terms of a perfect circle. 2. The rolling bearing according to claim 1, wherein the hardness of the rolling element is not less than the hardness of the race. 3. The rolling bearing according to claim 1, wherein at least the rolling element is made of sintered alloy steel powder. 4. The rolling bearing according to claim 1, wherein the high-temperature tempering is performed at 450 to 600 ° C. 5. The method according to claim 5, wherein at least the amount of carbides in said rolling elements is
The rolling bearing according to claim 1, wherein the content is 20 to 50 vol%.