JP2624337B2 - Rolling bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an outer ring made of steel for rolling members used in automobiles, agricultural machines, construction machines, steel machines, and the like.
The present invention relates to a rolling bearing including an inner ring and a rolling element, and particularly to a long-life rolling bearing required for a transmission or an engine.

[Conventional technology]

Rolling bearings, which consist of an inner ring, an outer ring, and rolling elements, are subjected to severe use under repeated high shear stress under high surface pressure, so they withstand the shear stress and secure the rolling fatigue life (hereinafter referred to as life). There is a need.

Therefore, conventionally, inner ring, a high carbon chromium bearing steel rolling member material is an outer ring or rolling elements (SUJ2), it by applying quenching and tempering, Rockwell hardness H _R C58~64 In order to secure the necessary life span.

There is also a conventional example in which the life is improved by using case hardening steel. In this conventional example, since it is necessary to set a hardness curve in accordance with the internal shear stress distribution caused by the contact surface pressure, a low carbon case hardened steel SCR420H, SCM420H, with good hardenability.
SAE8620H, using SAE4320H like, by subjecting the carburized or carbonitrided heat treatment → quenching → tempering thereto, a surface portion hardness H _R C58～64 of the inner and outer rings and rolling elements, and the core hardness is H _The required life span has been ensured by setting the RC to 30 to 48.

By the way, as the load using and the speeding up of the machine using the rolling bearings increase, the operating conditions of the bearings become severe, and the following problems arise when the rolling bearings are used in a range of quasi-high temperature to high temperature. Had occurred.

First, when the operating temperature of the rolling bearing increases, the hardness of the bearing decreases, which causes plastic deformation and shortens the service life. Secondly, when used at high temperatures, the oil film on the outer ring, inner ring and rolling elements of the bearing may be cut off. As a result, boundary lubrication is likely to occur and the wear of the bearing member is promoted. Further, as a third problem, since some retained austenite remains in the rolling member, the retained austenite is transformed into martensite at a high temperature, and as a result, a dimensional change occurs, impairing dimensional stability.

Therefore, conventionally, high-temperature chrome bearing steel (SUJ2) and case-hardened steel have been subjected to high-temperature tempering in order to prioritize and solve the dimensional stability of rolling bearings used at sub-high to high temperatures.
A high-temperature tempered product having improved dimensional stability by converting retained austenite into martensite in advance has been provided.

In addition to the high-temperature tempered products, precipitation hardening steels such as M50, which is a high-speed steel for high-temperature bearings containing Cr, Mo, and V, are provided as rolling member materials for sub-high to high temperatures.

This M50 is such that, by being subjected to high-temperature tempering, alloy carbides are precipitated and the rolling bearing exerts its strength when used at high temperatures.

In addition, in order to improve the life of a rolling bearing whose operating temperature may reach a high temperature to a high temperature, for example, Japanese Patent Application Laid-Open No.
The wear-resistant carburized steel described in 37518 and the carburized wear-resistant steel described in JP-A-54-75420 can be used as the material for the rolling member.

[Problems to be solved by the invention]

In the high-temperature tempered product, the dimensional stability can be improved, but on the other hand, the hardness is reduced by the high-temperature temper, and the plastic deformation at the time of use at a high temperature to a high temperature is further increased, so that the life of the bearing is rather shortened. In addition, since the wear resistance is not sufficient, there is a possibility that the wear may significantly progress under boundary lubrication when the bearing is used at a high temperature.

In the case of the precipitation hardening type M50, the C concentration is high, and the large carbides of Cr, Mo, and V are present at the material stage, so that the workability of the pretreatment is poor, and the presence of the large carbides causes stress around the carbides. There is a problem that concentration occurs, flaking occurs from that part as a starting point, and the life may be shortened. Therefore, solution treatment at high temperature (about 11
(00 ° C.), and a special heat treatment for refining the carbide after the huge carbide is dissolved in the matrix is required. However, this requires a special heat treatment facility and has a problem that heat treatment productivity is reduced.

In addition, in the wear-resistant steel described in JP-A-53-37518, giant carbides may be generated, and the life is shortened. Further, even in the wear-resistant steel for carburizing described in the above-mentioned JP-A-54-75420, giant carbides may be generated. In particular, when the content of C is large, the tendency becomes large.

Therefore, the present invention can form fine carbides without performing a special heat treatment in order to solve the above problems,
Even if high-temperature tempering is performed to improve dimensional stability at high temperatures, the hardness does not decrease, and the generation of oxide inclusions is extremely small. It is an object to provide a long-life rolling bearing having excellent dimensional stability even when used under high temperatures.

[Means for solving the problem]

In order to solve the above-mentioned problems, in the first invention described in the claims, at least one of the inner ring, the outer ring, and the rolling element of the rolling bearing has C: 0.2 to 0.6% by weight, Si: 0.5 to 2.
0% by weight, Cr: 1.8 to 2.5% by weight, Mo: 3.0% by weight or less, Mn:
1.6% by weight or less, O: 12ppm or less, balance Fe and alloy steel of unavoidable impurities, further subjected to carburizing or carbonitriding heat treatment, then tempered at 240 ° C to 550 ° C after quenching, and the surface layer Is characterized in that carbide having an average diameter of 0.5 to 1.0 μm is precipitated and the amount thereof is 20 to 50 vol%.

In the second invention described in the claims,
At least one of the inner ring, the outer ring and the rolling element of the rolling bearing has C: 0.2 to 0.6% by weight, Si: 0.5 to 2.0% by weight, Cr: 1.8 to
2.5% by weight, Mo: 3.0% by weight or less, Mn: 1.6% by weight or less, O: 1
2ppm or less, V: 0.1-1.0% by weight, balance Fe and alloy steel of unavoidable impurities, further subjected to carburizing or carbonitriding heat treatment, then tempered at 240 ° C-550 ° C after quenching, The layer is characterized in that carbide having an average diameter of 0.5 to 1.0 μm is precipitated and its amount is 20 to 50 vol%.

[Action]

The rolling member steel in the rolling bearing according to the present invention is characterized in that low-medium carbon steel is added with Si, Cr, Mo, V and the like. Si, C
The addition of r, Mo, and V improves the tempering softening resistance, and thus the steel for rolling members is tempered, especially when subjected to high-temperature tempering to reduce the amount of retained austenite, which has an adverse effect on dimensional stability. A decrease in hardness due to tempering can be suppressed. Therefore, it is possible to reduce the degree of softening at a high temperature.

Further, in the rolling member steel in the rolling bearing of the present invention, since the matrix is a low-medium carbon steel, a huge carbide is unlikely to be generated at the material stage. Therefore, there is no need for complicated heat treatment for solution treatment of huge carbides, and no special high-temperature treatment equipment such as a salt bath is required.

In the process of performing carburizing heat treatment or carbonitriding heat treatment on the rolling member steel and quenching and tempering, fine Cr, Mo, V carbides are precipitated on the surface layer.

The required hardness at a high temperature can be obtained by the precipitation hardening in the carbonization, and as a result, it is possible to secure the required hardness at a high temperature to a high temperature. As a result, plastic deformation can be significantly reduced, and tempering softening can be avoided. When the carbides are fine, stress concentration is low, so that damage such as flaking cracks and plastic deformation hardly occur in the rolling bearing of the present invention, and as a result, the life is improved. Furthermore, the presence of fine carbides in the surface layer also improves wear resistance.

Further, the amount of oxygen in the steel can be reduced as much as possible to suppress the generation of oxide-based inclusions.

The rolling bearing of the present invention is made of such rolling member steel, and is formed by subjecting the steel to carburizing or carbonitriding heat treatment, quenching and tempering. Due to the formation of a suitable carbide, there is no decrease in hardness even when used at sub-high temperature to high temperature, and since it has excellent wear resistance, it has a long life not only at normal temperature but also at sub-high temperature to high temperature, and oxidizes. Since the generation of physical inclusions is suppressed as much as possible, the life becomes longer.

Further, in the rolling bearing of the present invention, since the tempering is performed at a high temperature, the average amount of retained austenite from the surface layer of the bearing to the core is 3% or less. As a result, the dimensional stability at the time of use from a quasi-high temperature to a high temperature is excellent.
Even if high temperature tempering is performed, tempering softening does not occur, so that even if high temperature tempering is performed, a long life can be maintained.

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

C: 0.2 to 0.6% by weight C is an element necessary for improving the hardness after quenching and tempering. When the rolling bearing is formed, the carbon concentration on the bearing surface is increased by carburizing or carbonitriding the rolling member steel according to the present invention.
Content.

When the content of C exceeds 0.6% by weight, huge carbides are generated at the stage of the material, so that the toughness is reduced and the breaking strength is also reduced. On the other hand, when the content of C is high, the amount of retained austenite increases, and dimensional changes occur at high temperatures, which hinders dimensional stability.

On the other hand, if it is less than 0.2% by weight, the time for carburizing or carbonitriding becomes long, and the heat treatment productivity decreases.

Si: 0.5 to 2.0% by weight Si in the steel is effective for solid solution strengthening and improvement of tempering softening resistance. In order to exhibit the effect, the content needs to be 0.5% by weight or more. However, an increase in the content causes a decrease in mechanical strength. Further, the upper limit of the content is set to 2.0% by weight because Si is an element having carburization inhibiting properties.

Cr: 1.8 to 2.5% by weight Cr is an element that improves temper softening resistance. Also, by forming and hardening fine carbides,
Even if high temperature tempering is performed, sufficient hardness can be obtained.

Furthermore, since hard and fine Cr carbides are precipitated, wear resistance is improved.

And since Cr is a carbide forming element, it has the effect of increasing the C concentration of the carburized layer, thereby increasing the carburizing property of a material containing a large amount of Si having carburizing inhibition.

These effects, is effective, the required surface hardness (preferably, H _R C61~70) was 1.8 wt% the lower limit of the Cr content in order to ensure.

On the other hand, if the upper limit of the Cr content exceeds 2.5% by weight, giant carbide is formed at the material stage, stress concentration occurs around the carbide, and the rolling bearing life may be shortened. In addition, quenching at a high temperature is required to reduce the size of the carbide, and the heat treatment productivity is reduced. Therefore, the upper limit of the Cr content is set to the above value.

Mo: 3.0% by weight or less Mo is an element effective for improving the temper softening resistance like Cr, and is an element necessary for forming carbides on the surface layer. In addition, it is an element that improves hardenability.

However, even if Mo is contained in excess of 3.0% by weight, the above effect does not increase so much, and conversely, there is a risk that a giant carbide is formed at the stage of the raw material and the life is reduced, which is disadvantageous in terms of cost, The upper limit of the Mo content was 3.0% by weight.

Mn: 1.6% by weight or less Mn in steel has a large role in improving hardenability and is included because it is inexpensive.

However, when the content is large, non-metallic inclusions are generated in large amounts, so that the life of the bearing is shortened, and the hardness is improved, and the machinability such as forgeability and machinability is reduced. The upper limit of the amount was the above value.

O: 12ppm O must be reduced as much as possible in order to reduce its life as an element generating oxide-based nonmetallic inclusions (especially Al ₂ O ₃ ), so the upper limit of the content is 12 ppm or less. And In particular, the content is preferably 9 ppm or less.

V: 0.1 to 1.0% by weight 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 miniaturization, and to reduce the content in the steel. An element that combines with carbon to form fine carbides, and is added additionally because the addition improves the hardness of the bearing surface layer and improves the wear resistance. , (5), (6).

Since the effect becomes remarkable when the V content is 0.1% 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 1.0% by weight, carbides of V precipitate at the 19 grain boundaries, not only deteriorating workability and various mechanical properties, but also V is expensive and cost-effective. Therefore, the upper limit of the content is limited to the above value.

In the present invention, unavoidable impurity elements may be contained in addition to the various elements described above. The inevitable impurity elements include, for example, Ti, S, and P.

Ti appears as a nonmetallic compound in the form of TiN. This T
Since iN has a high hardness and a low plastic deformability, it becomes a source of stress concentration and shortens the service life. As a result, it is necessary to reduce the Ti content as much as possible. Desirably its content
Make it 40ppm or less.

P is an element that reduces impact resistance. Therefore it is necessary to reduce the content, desirably 200p
pm or less.

S causes formation of sulfide-based nonmetallic inclusions such as MnS. Since MnS has a low hardness and a large plastic deformation ability, it acts as a starting point of crack generation during pre-processing such as rolling and forging. Therefore, it is necessary to reduce the S content as much as possible in order to prevent the occurrence of cracks at the time of pre-processing such as forging and to enable stronger processing, and it is desirable that the S content be 80 ppm or less.

In the present invention, at least one surface layer of the inner ring, the outer ring, and the rolling elements generates fine carbides by carburizing or carbonitriding, quenching, and tempering.

This carbide is hard and has excellent wear resistance. As a result, the required hardness of the bearing can be ensured when the operating temperature is in a quasi-high temperature to a high temperature. Moreover, since the size is minute, the life of the rolling bearing can be improved without causing stress concentration based on 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 double carbides thereof.

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

In the present invention, the amount of carbide present in the surface layer of the bearing is preferably 20 to 50 vol%.

To achieve a longer bearing life, the surface hardness must be H _R C61
It is desirable to have ~ 70, but the carbide abundance is 20vo
If it is less than 1%, the above-mentioned desired hardness cannot be obtained. On the other hand, if the content exceeds 50 vol%, fine carbides are bonded to each other, and the carbides are coarsened and stress concentration occurs, which is not preferable.

Fine carbides by the presence in the surface layer of the bearing within the above range, it is possible to surface hardness to obtain a bearing of high hardness H _R C61~70.

In the above carburizing or carbonitriding heat treatment, by generating carbides nuclei when heated beyond the A ₁ transformation point, it is possible to precipitate fine carbides in the surface layer portion in the course of the subsequent quenching and tempering . Moreover, the amount of solute carbon
By setting the surface carbon content to 0.6 to 0.8% by weight (total surface carbon concentration of 2.5 to 3.8% by weight), the amount of carbides in
l%.

In the present invention, by performing carburizing or carbonitriding on the alloy steel for rolling members having the composition described in the claims, the amount of solid solution carbon or solid solution carbon nitrogen is set to 0.6 to 0.8% by weight (of the surface). By quenching and then tempering at a high temperature, the fine carbide can be precipitated on the surface layer and the amount of retained austenite can be reduced to 3 vol% or less.

The retained austenite is transformed into martensite at a high temperature and a dimensional change occurs at this time. Therefore, the average retained austenite amount is desirably 3 vol% or less.

The tempering temperature at this time is from about 240 to 550 ° C., preferably from 240 to 350 ° C., from the viewpoint that if the tempering temperature is low, it is insufficient to transform the retained austenite into martensite.
It is desirable that

〔Example〕

 Next, examples of the present invention will be described.

The alloy steels (test materials) A to H having the compositions shown in the following Table 1 are subjected to carburizing or carbonitriding heat treatment, and then quenching and tempering, so that any of the inner ring and the outer ring, which are the rolling wheels of the rolling thrust bearing, is obtained. Disc-shaped test pieces 1 to 14 which can also be applied to were prepared.

Table 2 shows the heat treatment conditions for preparing each test piece. The heat treatment conditions for the test piece 1 will be described below. .

Direct quenching (direct quenching) among carburizing treatments is performed in an atmosphere of Rx gas + enriched gas for about 3 hours.
Carburizing heat treatment at 950 ° C. is performed, then oil quenching is performed from this state, and high-temperature tempering is further performed at 300 ° C. × 2 hours × 1 time.

Test pieces 5 and 13 were quenched without carburizing or carbonitriding, and the other test pieces were subjected to heat treatment under different carburizing or carbonitriding conditions or tempering temperatures.

Test pieces 1 to 10 were subjected to high-temperature tempering to reduce the amount of retained austenite. Test pieces 11 to 14 were tempered at normal temperatures.

When performing carbonitriding instead of carburizing, the atmosphere is Rx gas + enriched gas + ammonia gas 5%.

For each of the test pieces, the surface hardness (H _R C) and the amount of retained austenite were measured. The results are shown in Table 2 above.

For the test pieces 1 to 14, the number of stress repetitions (cycl
The life (L ₁₀ ) shown in e) was measured.

In measuring the life, the life was measured at 130 ° C. and at normal temperature (about 50 to 60 ° C.) in order to check the life characteristics at high temperatures. Test pieces 1 to 10 measured the life under 130 ° C., and test pieces 11 to 14 measured the life under normal temperature. The measurement of the life was performed under the following conditions.

In addition, the time when the visible flaking occurred for each test piece was determined as the life.

Test machine: Thrust test machine described in “Special Steel Handbook (1st Edition), edited by Electric Steel Research Institute, Science and Engineering Building, May 25, 1965, pp. 10-21” Lubricating oil: FKB oil RO 150 (130 ℃ test)… FKB oil RO 80 (normal temperature test) Maximum surface pressure… 560kg / mm ² (130 ℃ test)… 530kg / mm ² (normal temperature test) Number of stress repetitions… 3000cpm Life of each test piece Are shown in Table 2 above.

Then, using a plurality of the respective disc-shaped test pieces of the test pieces 1 to 14, at 130 ° C. or at room temperature, flaking occurs in the disc-shaped test piece due to the number of stress repetitions and the repetitive stress, and the disc-shaped test piece is The relationship with the probability of failure was investigated.
The results are shown in FIGS.

FIG. 1 shows test pieces 1 to 10 whose life was measured at 130 ° C.
FIG. 2 shows the results of the test pieces 11 to 14 whose life was measured at room temperature.

In FIGS. 1 and 2, the numerical values in the figures indicate the numbers of the test pieces.

The test piece 1 is composed of the test material A which is an embodiment of the invention described in claim (1), and corresponds to the embodiment of the invention described in claim (5), and the fine carbide is formed on the surface layer portion. for various elements to enhance the resistance to temper softening is contained together are precipitated, as shown in table 2, also the surface hardness by performing high-temperature tempering is as H _R C61.2 It is a high value. Further, since the amount of retained austenite is reduced to 2-3% by weight by high temperature tempering,
Good dimensional stability during life test at ℃.

Since the hardness is good and the carbide is fine, the result of the life test at 130 ° C. is a good value. Accordingly, as shown in FIG. 1, the probability of failure with respect to the number of stress repetitions at high temperatures is small.

The test piece 2 is made of the test material A similarly to the test piece 1. The only difference from the test piece 1 is that carbonitriding is performed instead of carburizing.

Like the test piece 1, the test piece 2 has a good value of H _R C, a small amount of retained austenite, and 130
The life at ℃ is also good. As shown in FIG. 1, the characteristics of the probability of breakage with respect to the number of repeated stresses are also good.

The test piece 3 is made of a test material B which is an embodiment of the invention described in claim (2), and corresponds to an embodiment of the invention described in claim (6).

Specimen B can improve tempering softening resistance as compared with Specimen A, and forms a V carbide and contains an appropriate amount of V having a carbide refining action.

This test material B also contains various elements for improving the provision of temper softening in the same manner as the test material A, and fine carbides are precipitated on the surface layer. Both hardness and life are improved compared to
It is a good value like 1,2. As a result of the high-temperature tempering, the amount of retained austenite was
Less like 2

The test piece 4 is also formed from the test material B, and is similar to the test piece 3 in that only carbonitriding is performed instead of carburizing.

The test piece 5 corresponds to a comparative example formed from a test material C which is SUJ2 of a conventional high carbon chromium bearing steel.

Although the amount of retained austenite of test sample C decreases with high-temperature tempering, it is effective in improving temper softening resistance.
Since the contents of various elements such as Si and the like are lower than the lower limit of the present invention, the amount of carbide in the surface layer is small and the hardness is not sufficient. Then, as the operating temperature of the bearing rises, the hardness increases greatly as shown in FIG.

Test piece 6 corresponds to a comparative example formed from test material D, which is SCr420 of conventional case hardening steel.

This test material D is effective in improving temper softening resistance.
Since the content of Si and Cr, which have the effects of improving temper softening resistance and forming carbides, is small, the hardness after high-temperature tempering is reduced, and the life is also low. As shown in FIG. 1, the probability of breakage also increases.

The test piece 7 is formed from the test material E in which the content of Cr is less than the lower limit of the present invention. Therefore, the lower the Cr content, the lower the tempering softening resistance and the lower the amount of carbide formed in the surface layer. Therefore, the hardness after high-temperature tempering is also lower than that of the test piece 1, and the life is accordingly reduced. Then, the probability of damage increases (FIG. 1).

The test piece 8 is formed from a test piece F containing no Mo. Therefore, since Mo is not contained, the tempering softening resistance is reduced, and the amount of carbide formed on the surface layer is also reduced. Therefore, similarly to the test piece 7, the hardness after the high-temperature tempering is not sufficient, and the life is not sufficient. Then, as shown in FIG. 1, the probability of breakage is lower than that of the test piece 1.

The test piece 9 is formed of the test agent G in which the contents of Cr and Mo exceed the upper limits of the present invention. If the contents of Mo and Cr are increased, carbides may be enlarged. Therefore, as compared with the test piece 1, the test piece 9 has a large degree of stress concentration due to the large amount of carbide, so that the life of the test piece 9 is slightly reduced. However, addition of Cr and Mo exceeding the upper limit of the present invention is not only less effective but also disadvantageous in cost.

The test piece 10 is formed from a test material H having a V content exceeding the upper limit of the present invention. However, even if the content of V increases, the hardness and life of the test piece 10 are substantially the same as those of the test piece 1 and the like as shown in Table 2. The same applies to the breakage probability. However, addition of V exceeding the upper limit of the present invention is disadvantageous in cost.

The test piece 11 corresponds to one embodiment of the invention described in claim (3). The test piece 11 is formed from the test material A as in the test 1, but unlike the test piece 1,
Tempering is performed at a normal temperature in place of high temperature tempering.

The amount of retained austenite of the test piece 11 is larger than that of the test piece 1 and the like because the high temperature tempering is not performed. Has a good value.
And, even at normal temperature, its life is a good value. As shown in FIG. 2, the characteristics of the breakage probability are also good.

The test piece 12 corresponds to an embodiment of the invention described in claim (5). The test piece 12 is formed from the test material B in the same manner as the test piece 3, but is different from the test piece 3 in that normal tempering is performed instead of high-temperature tempering. Therefore, the test piece 12 has good values for both hardness and life, similarly to the test piece 11. However, the hardness and life after tempering are better than that of the test piece 11 because V is further contained. The same applies to the breakage probability.

Specimen 13 is made of conventional high chromium bearing steel
The difference is that the test piece 5 is made of SUJ-2 and is subjected to high temperature tempering, whereas the test piece 13 is tempered at normal temperature.

In the test piece 13, the tempering softening occurs similarly to the test piece 5, and the fine carbide is not sufficiently precipitated on the surface layer portion. Therefore, the hardness is lower than the test pieces 11 and 12, In addition, the life at room temperature also decreases. The same applies to the probability of breakage (FIG. 2).

The test piece 14 is made of a conventional case hardened steel SCr4 similarly to the test piece 6.
20 is formed by carburizing. The difference between the test piece 14 and the test piece 6 is that tempering at normal temperature is performed instead of high-temperature tempering.

Since the content of Si, which is effective for improving the temper softening resistance, and Cr, which is effective for improving the temper softening resistance and forming fine carbides, is less than the lower limit of the present invention,
The hardness and the life are inferior to those of the test pieces 11 and 12. The same applies to the breakage probability (FIG. 2).

The surface layer portion in the present invention is obtained by calculation from the contact pressure applied to the contact surfaces of the raceway surfaces of the inner ring, the outer ring and the rolling elements constituting the rolling bearing. That refers maximum shearing stress position (depth from the surface) When Z _0, the portion from the surface up to a depth of Z ₀ ~2Z _0. As an order, for example, 0.
The depth is about 2 to 0.5 mm.

Further, in the above-described embodiment, an example in which the life test shown in Table 2 was performed at 130 ° C. is shown.
Even at a high temperature of about 200 to 500 ° C., good results can be obtained as in the case of Table 2.

Furthermore, in the life test shown in Table 2, the life of a disc-shaped test piece applicable to both the inner ring and the outer ring was shown. However, a rolling element was formed from the same material, and a life test was performed on the rolling element. Can obtain a similar result.

In addition, the inner ring and the outer ring in the present invention are not limited to the exclusive inner ring and the outer ring as bearing parts. For example, as in a thrust needle roller bearing, the exclusive inner ring or the outer ring is omitted, and the shaft or the housing is omitted. It is needless to say that the present invention also includes a case in which each is also used as an inner ring or an outer ring.

〔The invention's effect〕

As described above, according to the first invention, when tempering,
Even in the case of high-temperature tempering to improve the dimensional stability in a range of quasi-high temperature to high temperature, fine carbide can be formed on the surface layer without tempering softening and without special heat treatment. it can. Therefore, it is necessary to provide a rolling bearing that has sufficient hardness without a decrease in hardness at high temperatures, has good wear resistance, and has a long life not only at room temperature but also at high temperatures. Can be.

Further, according to the second invention, since the carbide in the surface layer portion is further refined, the hardness of the surface layer portion is improved, the wear resistance is further improved, and the improvement in temper softening resistance is also remarkable. A rolling bearing having an effect can be provided.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the results of a thrust life test expressed by the relationship between the number of stress repetitions in a rolling bearing at 130 ° C. and the probability of failure, and FIG. 2 is the number of stress repetitions in a rolling bearing at room temperature. FIG. 9 is a characteristic diagram illustrating a thrust life test result indicated by a relationship of a breakage probability.

Continued on the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location F16C 33/30 F16C 33/30

Claims (4)

(57) [Claims] 1. A rolling bearing comprising an inner ring, an outer ring and a rolling element, wherein at least one of the inner ring, the outer ring and the rolling element comprises 0.2 to 0.6% by weight of C, 0.5 to 2.0% by weight of Si, and 1.8 to 1.8% of Cr.
2.5% by weight, Mo: 3.0% by weight or less, Mn: 1.6% by weight or less, O: 1
2ppm or less, the balance is made of alloy steel of Fe and unavoidable impurities, further subjected to carburizing or carbonitriding heat treatment,
After quenching, tempering is performed at 240 ° C to 550 ° C, and on the surface layer, carbide having an average diameter of 0.5 to 1.0 μm precipitates and the amount thereof is reduced.
20 to 50 vol%, the rolling bearing characterized by the above-mentioned. Wherein the average surface hardness retained austenite amount is not more than 3 vol% is H _R C61~70, rolling bearing according to claim (1), wherein a. 3. A rolling bearing comprising an inner ring, an outer ring and a rolling element, wherein at least one of the inner ring, the outer ring and the rolling element has C: 0.2-0.6% by weight, Si: 0.5-2.0% by weight, Cr: 1.8-1.8%.
2.5% by weight, Mo: 3.0% by weight or less, Mn: 1.6% by weight or less, O: 1
2 ppm or less, V: 0.1 to 1.0% by weight, balance Fe and alloy steel of unavoidable impurities, further subjected to a carburizing or carbonitriding heat treatment, then tempered at 240 ° C to 550 ° C after quenching, A rolling bearing characterized in that carbide having an average diameter of 0.5 to 1.0 μm is precipitated on the surface layer and the amount thereof is 20 to 50 vol%. Wherein the average surface hardness retained austenite amount is not more than 3 vol% is H _R C61~70, rolling bearing according to claim (3), wherein a.