JPH07110988B2 - Rolling bearing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rolling bearing used in automobiles, agricultural machines, construction machines, steel machines, etc., and in particular, it has a long service life required for transmissions and engines. Regarding rolling bearings.

[Conventional technology]

Rolling bearings are used in a severe manner that they are repeatedly subjected to shear stress under high surface pressure. Therefore, in order to withstand the shear stress and secure a rolling fatigue life (hereinafter, also referred to as rolling life or life), high carbon chromium is used. Using a steel bearing (SUJ2), it was quenched and tempered to have a Rockwell hardness of HRC58-64. Also, in case of rolling bearings using case hardening steel, it is necessary to set the hardness curve according to the internal shear stress distribution due to the contact surface pressure, so low carbon case hardening steel SCR420H, SCM420H with good hardenability , SAE8620H, SAE
Carburizing or carbonitriding, quenching, and tempering of 4320H etc., the surface hardness of the inner and outer rings and rolling elements is HRC58-64, and the core hardness is HRC30.
We have ensured the required life by making it ~ 48.

However, in today's demand for extended bearing life, rolling elements and inner and outer races may be damaged by more severe conditions, for example, foreign matter mixed in the bearing lubricating oil, and the above conventional bearing hardness is not sufficient. There were enough cases. Therefore, it is necessary to improve the surface hardness of the bearing.

As a conventional example for improving the bearing surface hardness, for example,
There is a conventional example in which a bearing is manufactured using a precipitation hardening type tool steel (SKH, SKD) in which a large amount of carbide is precipitated by adding an oxide forming element (Handbook of Metals, edited by the Japan Institute of Metals, 3rd revised edition,
Pp. 780-797).

[Problems to be Solved by the Invention]

However, the bearing manufactured using the above-mentioned conventional tool steel,
Although the rolling surface hardness is high and the indentation due to foreign matter in the lubricating oil is less likely to occur, on the other hand, depending on the content of alloying elements that form carbides, precipitated carbides become coarse, so carbides There is a drawback that stress concentration occurs around the circumference, flaking occurs from that portion as a starting point, and conversely the life is shortened.

Also, by setting the amount of retained austenite on the bearing surface within a predetermined range, stress concentration at the edge of the foreign matter indentation can be relaxed and the life can be extended (Japanese Patent Application No. 62-209167).
However, for example, in a high surface pressure state required for automobiles, further improvement in life is required as compared with the conventional case.

An object of the present invention is to provide a rolling bearing having a longer life than that of a conventional rolling bearing in order to solve such an unsolved problem of the prior art.

[Means for solving problems]

According to the invention of claim (1) for achieving the above object,
In a rolling bearing consisting of a bearing ring and a rolling element, at least one of the bearing ring and the rolling element is C: 0.3 to 0.6% by weight,
Cr: made of an alloy steel containing at least 3 to 14% by weight, and having a surface layer portion carburized or carbonitrided and subjected to hardening heat treatment, and present in at least one surface layer portion of the bearing ring and the rolling element. The amount of fine carbide is 20 to 50 vol%,
The amount of retained austenite in the surface layer is 10 to 25 vol%
Is characterized in that.

Further, in claim (2), the average grain size of the fine carbides present in the surface layer portion is 0.5 to 1.0 μm.

Further, in claim (3), the surface hardness of the surface layer portion is set to HrC.65 to 70.

Further, as in the invention of claim (4), at least one of the bearing ring and the rolling element is C: 0.3 to 0.6 wt% Cr: 3 to 14 wt% Ti: 40 ppm or less O: 12 ppm or less P: 200 ppm or less S: 80 ppm or less The balance consists of Fe alloy steel, and at least one of the bearing ring and the rolling element has a surface layer portion which is carburized or carbonitrided and hardened and is present in the surface layer portion. It is also possible that the fine carbide is 20 to 50 vol% and the residual austenite amount is 10 to 25 vol%.

Also in this invention, as in claim (5), the average particle size of the fine carbide in the surface layer portion is 0.5 to 1.0 μm, and, as in claim (6), the race and the rolling elements are The surface hardness of at least one of the surface layer portions may be HrC65 to 70.

Further, as in the invention of claim (7), in a rolling bearing composed of a raceway ring and rolling elements, at least one of the raceway ring and the rolling elements is C: 0.3 to 0.6 wt% Cr: 3 to 14 wt% Ti. : 40ppm or less Si: 0.9wt% or less Mo: 0.4 to 2.0wt% Mn: 2.0wt% or less O: 12ppm or less P: 200ppm or less S: 80ppm or less The balance consists of alloy steel of Fe, At least one of which has a surface layer portion which is subjected to carburizing or carbonitriding and hardening heat treatment, the fine carbide present in the surface layer portion is 20 to 50 vol%, and residual austenite is 1
It was set to 0 to 25 vol%.

Also in this invention, as in claim (8), the average particle size of the fine carbides present in the surface layer portion can be 0.5 to 1.0 μm, and as in claim (9), the bearing ring is The surface hardness of at least one of the surface layer part of the
Sometimes C65-70.

Further, as in the invention of claim (10), in a rolling bearing consisting of a bearing ring and a rolling element, at least one of the bearing ring and the rolling element is C: 0.3 to 0.6% by weight Cr: 3 to 14% by weight. Ti: 40ppm or less Si: 0.9wt% or less Mn: 2.0wt% or less V: 0.03 to 1wt% O: 12ppm or less P: 200ppm or less S: 80ppm or less The balance consists of Fe alloy steel, and the bearing ring and rolling elements At least one of which has a surface layer portion which is subjected to carburizing or carbonitriding and hardening heat treatment, the fine carbide present in the surface layer portion is 20 to 50 vol%, and the retained austenite is 1
It can be 0 to 25 vol%.

Also in this invention, as in claim (11), the average particle size of the fine carbides present in the surface layer portion is 0.5 to 1.0 μm, or as in claim (12), the race and the rolling element. The surface hardness of at least one of the surface layer part of HrC65-70
There is also a mode.

Further, as in the invention of claim (13), in a rolling bearing consisting of a bearing ring and a rolling element, at least one of the bearing ring and the rolling element is C: 0.3 to 0.6% by weight Cr: 3 to 14% by weight. Ti: 40ppm or less Si: 0.9wt% or less Mo: 0.4 to 2.4wt% Mn: 2.0wt% or less V: 0.03 to 1wt% O: 12ppm or less P: 200ppm or less S: 80ppm or less The balance consists of Fe alloy steel At least one of the bearing ring and the rolling element has a surface layer portion that is subjected to carburizing or carbonitriding and hardening heat treatment, and a fine carbide present in the surface layer portion is 20 to 50 vol% and remains. Austenite 1
It can be 0 to 25 vol%.

Also in this invention, as in claim (14), the average particle diameter of the fine carbides present in the surface layer portion is 0.5 to 1.0 μm,
Further, as claimed in claim (15), the surface hardness of at least one of the surface layer portions of the bearing ring and the rolling element is HrC65 to 70.
There is also an embodiment.

Furthermore, as in the invention of claim (16), in a rolling bearing comprising a raceway ring and rolling elements, at least one of the raceway ring and the rolling elements is C: 0.3-0.6 wt% Cr: 3-14 % By weight Si: 0.9% by weight or less Mn: 2.0% by weight or less Ti: 40 ppm or less O: 12 ppm or less P: 200 ppm or less S: 80 ppm or less The balance is made of an alloy steel of Fe, and at least one of the raceway and the rolling element is , Has a surface layer part which is carburized or carbonitrided, and is subjected to hardening heat treatment, and the fine carbides present in the surface layer part are 20 to 50 vol% and the residual austenite is 1
It may be 0 to 25 vol%.

Also in the case of the present invention, as in claim (17), the average particle size of the fine carbides present in the surface layer portion is 0.5 to 1.0 μm.
And the surface hardness of at least one of the surface layer portions of the bearing ring and the rolling element is Hr.
Can be C65-70.

[Action]

The inventors of the present application conducted various studies on extending the life of a rolling bearing manufactured using a high-cleanliness steel that is an alloy steel having a low content of impurities, and as a result, refined carbide in the bearing surface layer portion, and Various knowledge has been obtained regarding the amount of the austenite, the relationship between the amount of retained austenite in the bearing surface layer and the life, and the relationship between the S content and the crack occurrence rate during forging, and the claims are based on this finding. The invention has been reached as described.

The action of the element contained in the present invention and the critical significance of the content will be described.

C: 0.3 to 0.6 wt% C is an element necessary for improving the hardness after quenching and tempering.

If the carbon content concentration exceeds 0.6% by weight, the toughness at the core portion is reduced and the fracture strength is reduced.

On the other hand, if it is less than 0.3% by weight, the carburizing or carbonitriding treatment time becomes long and the heat treatment productivity decreases, so the carbon content was limited to the above range. Especially 0.35-0.45% by weight
Is preferred.

Cr: 3 to 14% by weight The rolling bearing according to the present invention is intended to form a hard carbide on the surface layer portion of the bearing to improve the bearing surface hardness. At this time, Cr is necessary as a carbide forming element, and Cr combines with C to form fine carbide.

When the Cr content is less than 3% by weight, the required surface hardness (HR
The amount of carbides for obtaining C65-70) decreases. On the other hand, 1
If the content exceeds 4% by weight, huge carbides will be formed at the material stage, stress concentration will occur around this carbide, and the life will be shortened. Therefore, the Cr content is limited to the above range. did. It is particularly preferably 11.0 to 13.0% by weight.

Ti: 40 ppm or less Ti appears as a non-metallic compound in the form of TiN. This TiN
Has a high hardness and a small plastic deformability, so it becomes a source of stress concentration and shortens the life. As a result, it is necessary to reduce the Ti content as much as possible. Therefore, the Ti content is limited to the above value.

Si; 0.9 wt% or less Si in steel is effective for solid solution strengthening and improving temper softening resistance. However, when the content increases, decarburization due to heat treatment becomes remarkable and the surface hardness decreases, so the upper limit of the content is limited to the above value. Therefore, Si
By containing, the solid solution strengthening and the temper softening resistance are improved.

Mo; 0.4 to 2.0 wt% Mo is effective because it is necessary to form carbides on the bearing surface and improves hardenability, as in the case of Cr.

The effect of forming fine carbides by Mo becomes remarkable when Mo is contained in an amount of 0.4% by weight or more within the Cr content range, so the lower limit of the Mo content is set to this value.

On the other hand, when the content of Mo exceeds 2.0% by weight, similarly to Cr, giant carbides are formed at the stage of the material and the life of the bearing is shortened. Therefore, the upper limit and the above value are set. Especially 1.5-2.0
It is preferably in the weight%.

Therefore, by containing Mo, a carbide of molybdenum is generated to further improve the surface hardness of the bearing.

Mn: 2.0 wt% or less Mn in steel has a large role in improving hardenability and is contained at a low price.

However, when the content thereof is large, a large amount of non-metallic inclusions are likely to occur, the hardness is improved, and the machinability such as forgeability and machinability deteriorates. Therefore, the upper limit of the Mn content is set to the above value.

Therefore, the inclusion of Mn here is intended to improve the hardenability.

V: 0.03 to 1 wt% V is an element that precipitates at the grain boundaries and suppresses the coarsening of the crystal grains to make it finer and to combine with carbon in steel to form fine carbides. , The hardness of the bearing surface layer is improved and the wear resistance is improved, so that it is added.

Since the effect becomes remarkable when the V content is 0.03% by weight or more, the lower limit of the content is set to this value.

On the other hand, if the upper limit of the content exceeds 1% by weight, carbides of V are precipitated at the grain boundaries, deteriorating the workability and various mechanical properties. Therefore, the upper limit of the content is limited to the above value. In particular, it is preferably 0.8 to 1% by weight.

Therefore, by containing V, the surface hardness of the bearing is further improved.

O; 12 ppm or less O is an element that generates oxide-based non-metallic inclusions (especially Al ₂ O ₃ ), and in order to reduce rolling fatigue life, its content must be reduced as much as possible, so the upper limit is 12 ppm. did.

P: 200 ppm or less P is an element that reduces the impact resistance of alloy steel. Therefore, it is necessary to reduce its content, and the upper limit is 20
It was set to 0 ppm.

S: 80 ppm or less S causes sulfide-based non-metallic inclusions such as MnS. Since MnS has low hardness and high plastic deformability, it acts as a starting point for cracking during pre-processing such as rolling and forging. Therefore, it is necessary to reduce the S content in order to prevent the occurrence of cracks during pre-processing such as forging and enable stronger processing, and the upper limit was set to 80 ppm.

A cylindrical sample of φ20 × 30 mm was prepared using the alloy steel having such a composition, cold working (forging) was carried out at an upsetting rate of 80%, and the crack occurrence rate was investigated. FIG. 2 shows the relationship between the S content in steel and the crack generation rate. It can be seen from FIG. 2 that the crack generation rate decreases as the S content in the test material decreases, and that the crack generation rate is 0% when the S content is 80 ppm or less. Therefore, if the S content is 80 ppm or less, stronger working becomes possible.

Next, the action of retained austenite, which is a feature of the present invention, and the critical significance of its abundance will be described.

When the bearing is used under the condition that foreign matter is mixed and lubricated, concave indentations are generated on the rolling surfaces of the inner and outer races and the rolling elements due to repeated contact with the foreign matter. The indentation has an edge portion.

Retained austenite is soft, for example, about Hv300 (however, it depends on the carbon content of the material)
Unlike low-carbon martensite, which is simply low in hardness, martensite is formed, that is, hardens while undergoing work-induced transformation. Therefore, the retained austenite present in an appropriate amount on the bearing surface layer portion is martensite due to the deformation energy applied to the surface after a predetermined number of relative passages of the mating member (for example, the race ring to the rolling element) that passes through the indentation during rolling. It becomes a site and hardens. In the process, the rolling load concentrated on the edge portion of the indentation due to the foreign matter mixed in the lubricating oil is alleviated to prevent the generation of microcracks and improve the life.

The life of a bearing material in a lubrication test with foreign matter mixed is 1st
Bearing life and retained austenite γ shown in the graph
_{As is} clear from the relationship with _R (vol%), the life L ₁₀ indicated by the stress repetition number changes according to the change in the amount of retained austenite.

That is, in the range where the amount of retained austenite is 40% or less, as the amount increases, the life under lubrication with foreign matter becomes longer.

On the other hand, by setting the amount of carbide in the surface layer to 20 to 50 vol% in order to improve the hardness of the rolling surface, if the residual austenite amount exceeds 25 vol%, the mechanical strength of the material decreases and it becomes practical. I can't stand it. In addition, since carbide forming elements such as Cr, Mo and V are added, the solid solution of C in the matrix is small and the residual austenite is 25 vol%.
Is difficult to cross.

If the amount of retained austenite is less than 10 vol%, life extension hardening under foreign matter-mixed lubrication is small, so the amount of retained austenite was set to 10 to 25 vol%.

In FIG. 1, curves and indicate lifespans L ₁₀ and L ₅₀ under clean lubrication, respectively. Also, the curves and are
Shows the life L ₁₀ and L ₅₀ under contaminated lubrication respectively.

The experimental conditions in FIG. 1 are as follows.

"Special Steel Handbook (1st edition), Electric Steel Research Laboratory, R & D, 1
965, May 25, pp. 10-21, using a test machine,
Using turbine oil [FBK oil RO68 manufactured by Nippon Oil Co., Ltd.] with steel powder (hardness HRC66.3, Fe ₃ C with a powder diameter of 80 to 160 μm) at a mixing ratio of 300 ppm, a maximum surface pressure of 500 kgf / mm ^2, was tested in a stress repetition rate 3000cpm.

Next, the action of the carbide existing in the bearing surface layer portion and the content thereof will be described for their critical significance.

In the present invention, at least one surface layer portion of the bearing ring and the rolling element is subjected to carburizing or carbonitriding treatment, quenching, and tempering treatment to generate fine carbides.

This carbide is hard and has excellent wear resistance, and as a result, improves the life of the bearing. Moreover, since the size thereof is minute, the life of the bearing can be improved without causing stress concentration due to the applied load.

In the present invention, the carbide is, for example, Cr ₇ C ₃ , Cr ₃ C ₆ , Mo
₂ C, VC, V ₄ C ₃ and Fe ₃ C or their double carbides are mentioned.

In the present invention, the size of the carbide (1/2 of the maximum diameter and the minimum diameter) is preferably 0.5 to 1.0 μm.

In the present invention, the amount of carbides present in the surface layer portion of the bearing is 20 to 50 vol%, and the critical significance is as follows.

The surface hardness is HRC65-70 to achieve long bearing life.
Is desirable, but the amount of carbides present is 20 vol%
If it is less than the above range, the desired hardness cannot be obtained. On the other hand, if it exceeds 50 vol%, fine carbides are bound to each other and the carbides are coarsened to cause stress concentration, which is not preferable. Therefore, the amount of carbides present in the surface layer portion is set within the above range.

By allowing fine carbides to exist in the surface layer portion of the bearing within the above range, it is possible to obtain a bearing having a high surface hardness of HRC65 to 70.

In the present invention, the alloy steel having the composition described in the claims is subjected to carburizing or carbonitriding so that the solid solution carbon or solid solution carbon nitrogen content is 0.6 or less as shown in FIG.
The amount of retained austenite in the surface layer portion can be reduced to 10 to 25 vol% by quenching and tempering this to 0.8 wt% (total carbon concentration on the surface is 2.5 to 3.8 wt%).

Further, in the above heat treatment process, carbide nuclei are generated when heated above the A ₁ transformation point, and fine spherical carbides can be precipitated in the surface layer portion in the subsequent quenching and tempering processes. Moreover, the amount of solute carbon is 0.6 to 0.8.
By adjusting the weight ratio (total carbon concentration on the surface to 2.5 to 3.8% by weight), the amount of carbides in the surface layer portion can be set to 20 to 50% by volume.

〔Example〕

 Next, examples of the present invention will be described.

The alloy steels of the test pieces shown in the following Table 1 are carburized, and then subjected to soaking, quenching, and tempering to obtain specimens 1 to 1.
Twelve created.

Next, heat treatment conditions in this example will be described.

Of the carburizing heat treatment, the direct quenching type heat treatment is
As shown in the graph in FIG. 4, carburizing heat treatment is performed at 920 to 960 ° C. for about 3 to 5 hours in an atmosphere of Rx gas and enriched gas, then 680 ° C. × 1 hour soaking treatment, then 8
Oil quenching was performed at 40 ° C for 1 hour, and further tempering was performed at 180 ° C for 2 hours. Further, as for the carbonitriding heat treatment, as shown in the graph of FIG. 5, Rx gas + enriched gas +
830-8 for about 3-5 hours in an atmosphere of 5% ammonia gas
Carbonitriding heat treatment was performed at 70 ° C., and then the same treatment as in the case of the above carburizing treatment was performed. In Fig. 4 and 5, the A ₁ transformation point (about 726
(° C), carbide nuclei are generated, and thereafter, fine spherical carbides are deposited around the nuclei on the surface layer of the test piece.

Then, for each test piece, the surface hardness (HRC), the abundance (vol%) of carbides present in the surface layer portion, the amount of retained austenite present in the surface layer portion, and the average grain size of the carbides were measured. Further, using each of the test pieces subjected to the carburizing heat treatment, a disk-shaped test piece which can be applied to any one of the raceway ring of the rolling bearing, that is, the inner ring and the outer ring is prepared, and the stress repetition number for each disk-shaped test piece ( The rolling life (L ₁₀ ) indicated by cycle was measured. The results are also shown in Table 1 above.

Further, FIG. 6 shows the relationship between hardness (HRC) and rolling life (L ₁₀ ), and FIG. 7 shows the relationship between residual austenite amount (vol%) and rolling life (L ₁₀ ).

The measurement of the life was based on the following conditions.

The bearing life test is carried out by using a thrust tester described in "Special Steel Handbook, (First Edition) Electric Steel Research Laboratory, edited by Science and Engineering, 25th May 1965, pp. 10-21" (stock)
Made FBK oil RO68] to steel powder (hardness, HRC66.3, powder diameter 80-160
using a lubricant in which (μm Fe ₃ C) was added at a mixing ratio of 300 ppm,
The maximum surface pressure of 500 kgf / mm ² was tested at a stress repetition rate of 3000 cpm. Then, the life was determined when flaking occurred on the surface.

In Table 1 above, the test piece 1 corresponds to the embodiment of the invention described in claim (4), and the surface carbide concentration in the surface layer portion is also a good value of 22 vol%, so that the surface hardness It also has a good value of HRC66, and a good rolling life can be achieved even under lubrication with foreign matter mixed. Although it is inevitable that Si and Mn are contained as inevitable impurities in the test piece 1,
Even if the contents of Si and Mn are reduced as much as possible and the contents are made 0, good surface hardness and rolling life can be obtained as in the case of the test piece 1.

The test pieces 2 and 3 are examples of the invention of claim (16),
It is possible to achieve good surface hardness and rolling life.

Specimen 4 is an embodiment of the invention described in claim (7), specimen 5 is an embodiment of the invention described in claim (10), and specimens 6 and 7 are claimed (13). ) Is an embodiment of the described invention,
Good surface hardness and rolling life can be achieved as in the case of each of the test pieces.

The comparative example (SUJ-2) of the invention according to claim (16), wherein the content of C in the test piece 8 exceeds the range of the present invention and the content of Cr falls below the range of the present invention. Is.

In this test piece 8, since the Cr content was small, the amount of Cr carbide generated in the surface layer portion was reduced to 8 vol%, and as a result, the improvement of the surface hardness was insufficient and it was less than about HRC62. Therefore, the L ₁₀ life is a small value of 1 × 10 ^{6 as} compared with each of the above-mentioned test pieces. Further, since the C content is large, the toughness in the deep portion is lowered and the fracture strength is lowered.

Specimen 9 is a comparative example of the invention according to claim (16), in which the content of Cr is below the range of the present invention, as is the case with specimen 8.

In this test piece 9, as in the case of the test piece 8, the amount of Cr carbide generated in the surface layer portion was reduced to 11 vol%, and as a result, the surface hardness was insufficiently improved to about HRC64. Therefore, the L ₁₀ life is 3.5 × 10 in comparison with each of the above specimens.
It becomes a small value of ⁶ .

The test piece 10 is a comparative example of the invention described in claim (7), which is characterized in that the Mo content exceeds the range of the present invention. In this test piece 10, even if the content of Mo exceeds the range of the present invention, there is no great difference in the effect of forming fine Mo carbide on the rolling surface of the bearing and the cost becomes high, and the carbide becomes huge. As compared with the test piece 4 which is the embodiment of the invention described in claim (7), the rolling life tends to be shortened.

The test piece 11 is a comparative example of the invention according to claim (10), which is characterized in that the V content exceeds the range of the present invention. In this test piece 11, even if the V content exceeds the range of the present invention, there is no difference in the grain refining effect, the cost increases, and the workability and various mechanical properties deteriorate, which is not preferable.

The test piece 12 is a comparative example of the invention described in claim (13), which is characterized in that the contents of Mo and V exceed the range of the present invention. In this test piece 12, even if the Mo and V contents exceed the range of the present invention, there is no difference in the effect of forming fine carbide on the surface layer portion of the bearing, and the V content of the present invention is Even if the range is exceeded, there is no difference in the effect of refining the crystal grains, and in any case, there is a cost disadvantage. Further, the carbide tends to become huge and the rolling life is shortened, which is not preferable.

For each of the above-mentioned test pieces 1 to 7, ten cylindrical samples each having a diameter of 20 × 30 mm were prepared, cold-worked (forged) at an upsetting rate of 80, and crack occurrence rates were examined. The crack occurrence rate of the test piece was 0%.

Next, a small ball bearing (686) having an inner diameter of 6 mm was prototyped using each of the test pieces 1, 2, 4 to 6, 8 and a wear resistance test was performed on this bearing. The test conditions are as follows.

Preload… 2kgf, swing angle… 8 °, speed… 20HZ, grease lubrication, evaluation cycle… 2 × 10 ⁷ times, temperature… room temperature, number of prototypes…
Eight pieces The results of this abrasion resistance test are shown in the following Tables 2 and 3 for explanation.

(Presence or absence of fretting) As shown in Tables 2 and 3 above, the test pieces 1 and 2 have surface carbide concentrations of 22 vol% and 22 vol% respectively, which are within the scope of the present invention. The number of fretting occurrences is smaller and the wear amount is smaller than that of the test piece 8 lower than the range.

Further, in the test pieces 4 to 6 in which the surface carbide concentration is higher than the test pieces 1 and 2, both the number of fretting occurrences and the wear amount are smaller.

Next, 20 small ball bearings (686) with an inner diameter of 6 mm that were prototyped from the test piece were tested to confirm that the indentation was not likely to occur and that the acoustic characteristics were good.
_The impression was made at ₀ , and the test was performed according to JIS B 1548. The test results are shown in FIG.

As can be seen from FIG. 8, all of the test pieces 1, 2, 4 to 6 have lower average sound pressure (dB) values ‖ than the test piece 8. This is because the test pieces 1, 2, 4 to 6 have a higher surface carbide concentration and a higher rolling surface hardness than the test piece 8, so that it is difficult for the indentation to adhere to the surface. Particularly, the sound pressure levels of the test pieces 4 to 6 having the surface carbide concentration higher than those of the test pieces 1 and 2 are lower.

The surface layer portion referred to in the present invention can be calculated from the contact pressure applied to the contact surfaces of the inner ring, the outer ring, and the raceway surfaces of the rolling elements that form the rolling bearing. That is, when the maximum shear stress position (depth from the surface) is Z ₀ , it means a portion from the surface to a depth of Z _{0 to} 2Z ₀ . As an order, for example 0 from the surface.
The depth is about 2 to 0.5 mm.

In the rolling life test shown in Table 1 above, the life of a disc-shaped test piece applicable to any of the inner ring and the outer ring was shown, but rolling elements were formed from the same material, and the rolling life test The same result can be obtained by performing.

Furthermore, in the wear resistance test and the acoustic characteristic test, the entire rolling bearing, that is, the inner and outer races and the rolling elements were prepared from the test piece, but at least one of the inner race, the outer race and the rolling element is an alloy according to the present invention. If it is made of steel, it becomes possible to obtain good wear resistance and acoustic characteristics as in the above-mentioned embodiment.

〔The invention's effect〕

As described above, according to the rolling bearing of the present invention, an appropriate amount of fine carbide is formed on at least one surface layer portion of the inner ring, the outer ring and the rolling element to improve the surface hardness, and The presence of an appropriate amount of retained austenite prevents the generation of microcracks under lubrication containing foreign matter.

Therefore, when the bearing is used under clean lubrication, it has a much longer life than the conventional bearing,
In addition, when the bearing is used under lubrication containing foreign matter, it has a much longer life than the conventional bearing.

As a result, in any of the cases where the bearing is used under both of the above lubrication conditions, it is possible to improve the life of the bearing under a high rolling load.

[Brief description of drawings]

Fig. 1 shows bearing life and retained austenite γ _R (vol%)
FIG. 2 is a characteristic diagram showing the relationship between the S content in steel and the crack generation rate, and FIG. 3 is a solid solution carbon or solid solution carbon nitrogen content and residual austenite content. 4 and 5 are process diagrams explaining the heat treatment conditions for manufacturing the rolling bearing according to the present invention, and FIG. 6 is the surface hardness (HRC) and stress of the test piece. Fig. 7 is a characteristic diagram showing the relationship with the bearing life L ₁₀ indicated by the number of repetitions, Fig. 7 is a characteristic diagram showing the relationship between the amount of retained austenite and the stress repetition number of the fatigue life of the bearing, and Fig. 8 is a graph of each test piece. It is a characteristic view which shows an acoustic characteristic.

Claims (18)

[Claims] Claim: What is claimed is: 1. In a rolling bearing consisting of a bearing ring and a rolling element, at least one of the bearing ring and the rolling element is C: 0.
3 to 0.6% by weight, Cr: made of an alloy steel containing at least 3 to 14% by weight, and having a surface layer portion subjected to carburizing or carbonitriding and hardening heat treatment, at least the race and the rolling element. The amount of fine carbides present in one surface layer is 20 ~
A rolling bearing, characterized in that it is 50 vol% and the amount of retained austenite in the surface layer portion is 10 to 25 vol%. 2. The rolling bearing according to claim 1, wherein the fine carbide particles present in the surface layer portion have an average particle diameter of 0.5 to 1.0 μm. 3. The rolling bearing according to claim 1, wherein the surface hardness of the surface layer portion is HrC65 to 70. 4. A rolling bearing comprising a raceway ring and rolling elements, wherein at least one of the raceway ring and rolling elements is C: 0.3 to 0.6% by weight Cr: 3 to 14% by weight Ti: 40 ppm or less O: 12 ppm Below P: 200 ppm or less S: 80 ppm or less The remainder is made of an alloy steel of Fe, at least one of the bearing ring and the rolling element has a surface layer portion that is subjected to carburizing or carbonitriding and hardening heat treatment, A rolling bearing, wherein the amount of fine carbides present in the surface layer portion is 20 to 50 vol% and the amount of retained austenite is 10 to 25 vol%. 5. The rolling bearing according to claim 4, wherein the fine carbide particles present in the surface layer portion have an average particle diameter of 0.5 to 1.0 μm. 6. The surface hardness of at least one of the surface layer portions of the bearing ring and the rolling element is HrC65 to 70.
Rolling bearing described. 7. A rolling bearing comprising a raceway ring and rolling elements, wherein at least one of the raceway ring and rolling elements is C: 0.3 to 0.6 wt% Cr: 3 to 14 wt% Ti: 40 ppm or less Si: 0.9 Weight% or less Mo: 0.4 to 2.0 weight% Mn: 2.0 weight% or less O: 12 ppm or less P: 200 ppm or less S: 80 ppm or less The balance is made of an alloy steel of Fe, and at least one of the bearing ring and the rolling element is carburized. Or having a surface layer portion carbonitrided and subjected to a hardening heat treatment, the amount of fine carbide present in the surface layer portion is 20 to 50 vol%, and the residual austenite amount is 10 to 25 vol% A rolling bearing. 8. The rolling bearing according to claim 7, wherein the fine carbide particles present in the surface layer portion have an average particle diameter of 0.5 to 1.0 μm. 9. The surface hardness of at least one of the surface layer portions of the bearing ring and the rolling element is HrC65 to 70.
Rolling bearing described. 10. A rolling bearing comprising a bearing ring and a rolling element, wherein at least one of the bearing ring and the rolling element is C: 0.3 to 0.6% by weight Cr: 3 to 14% by weight Ti: 40 ppm or less Si: 0.9 Weight% or less Mn: 2.0 weight% or less V: 0.03 to 1 weight% O: 12 ppm or less P: 200 ppm or less S: 80 ppm or less The balance is made of alloy steel of Fe, and at least one of the bearing ring and the rolling element is carburized. Or having a surface layer portion carbonitrided and subjected to a hardening heat treatment, the amount of fine carbide present in the surface layer portion is 20 to 50 vol%, and the residual austenite amount is 10 to 25 vol% A rolling bearing. 11. The rolling bearing according to claim 10, wherein the average particle size of the fine carbide present in the surface layer portion is 0.5 to 1.0 μm. 12. The surface hardness of at least one of the surface layer portions of the bearing ring and the rolling elements is HrC65 to 70.
Rolling bearing described in 0. 13. A rolling bearing comprising a bearing ring and a rolling element, wherein at least one of the bearing ring and the rolling element is C: 0.3 to 0.6 wt% Cr: 3 to 14 wt% Ti: 40 ppm or less Si: 0.9 Weight% or less Mo: 0.4 to 2.4 weight% Mn: 2.0 weight% or less V: 0.03 to 1 weight% O: 12ppm or less P: 200ppm or less S: 80ppm or less The balance is made of Fe alloy steel and the bearing ring and rolling elements are used. At least one of which has a surface layer portion which is subjected to carburizing or carbonitriding and hardening heat treatment, the amount of fine carbide present in the surface layer portion is 20 to 50 vol%, and the residual austenite amount is 10 to 25 vol. Rolling bearing, characterized in that it is%. 14. The rolling bearing according to claim 13, wherein the fine carbide particles present in the surface layer portion have an average particle diameter of 0.5 to 1.0 μm. 15. The surface hardness of at least one of the surface layer portions of the bearing ring and the rolling element is HrC65 to 70.
Rolling bearing described in 3. 16. A rolling bearing comprising a bearing ring and a rolling element, wherein at least one of the bearing ring and the rolling element is C: 0.3 to 0.6% by weight Cr: 3 to 14% by weight Si: 0.9% by weight or less Mn. : 2.0 wt% or less Ti: 40 ppm or less O: 12 ppm or less P: 200 ppm or less S: 80 ppm or less The balance is made of an Fe alloy steel, and at least one of the bearing ring and the rolling element is carburized or carbonitrided and hardened by heat treatment. A rolling bearing, which has a surface layer portion formed thereon, wherein the amount of fine carbide present in the surface layer portion is 20 to 50 vol% and the amount of retained austenite is 10 to 25 vol%. 17. The rolling bearing according to claim 16, wherein the fine carbides present in the surface layer portion have an average particle diameter of 0.5 to 1.0 μm. 18. The surface hardness of at least one of the surface layer portions of the bearing ring and the rolling element is HrC65 to 70.
Rolling bearing described in 6.