JP2016008327A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing with a long service life by suppressing structure change type peeling caused by peeling infiltrated into an alloy steel forming a bearing member.SOLUTION: Provided is a rolling bearing obtained by subjecting an alloy steel in which at least one of an inner ring and an outer ring contains specified amounts of C, Si, Mn, Cr and Mo, and the balance iron with inevitable impurities is subjected to carburization treatment or carbonitriding treatment to form a hardened layer on the surface, also having a specified surface hardness, and in which a chromium chemical film with a thickness of 0.1 μm or higher is formed on the outermost surface.

Description

  The present invention relates to a long-life rolling bearing that suppresses delamination accompanied by a structural change caused by hydrogen, and is particularly used to support a main shaft of a wind power generator and a rotating shaft constituting a transmission, a construction machine, and an industrial robot. It is suitable as a rolling bearing.

  Various types of rolling bearings are used to support the main shaft of the wind turbine generator and the rotating shafts that make up the various machines described above. When large radial loads are applied, tapered rollers or cylindrical rollers are used as rolling elements. The used radial tapered roller bearing or radial cylindrical roller bearing may be used.

  In rolling bearings, metal fatigue occurs due to long-term use in a state where a load is applied, and the surfaces of the raceway surface and the rolling surface may peel off. Specifically, in the alloy steel that constitutes the bearing member, internal origin type delamination that originates from non-metallic inclusions such as oxides and nitrides and leads to delamination, and foreign matter enters the lubricating oil. Indentation-origin-type delamination is known in which fatigue cracks occur and delamination starts from indentations generated on the raceway surface.

  Also, in some applications where the usage conditions are severe, the metal structure of the alloy steel base itself constituting the rolling bearing changes from a martensite structure to fine ferrite grains called white structure, and fatigue cracks start from the change in structure. It is also known that tissue change-type peeling that leads to peeling occurs. In this structure change-type peeling, the new surface that appears when the raceway surface and the rolling element come into contact with each other is used as a catalyst under conditions of use such that the lubricating film formed on the raceway surface is partially broken. Is considered to be caused by the accumulation of hydrogen generated by the tribochemical reaction in the stress concentration part in the alloy steel.

  In particular, in a rolling bearing using a roller as a rolling element, or a rolling bearing having a rolling element with a diameter of 30 mm or more, the contact area between the race and the rolling element is large, so that the lubricating film is difficult to be formed stably. Therefore, metal contact is likely to occur locally, and the lubricant is easily decomposed by the above tribochemical reaction to generate hydrogen.

  Also, in applications where the shaft of a transmission that transmits power with a gear is supported and the direction of the torque acting on the shaft changes temporarily, a large slip occurs between the rolling elements and the raceway. Easy to cut. Therefore, metal contact is likely to occur locally, and the lubricant is easily decomposed by the above tribochemical reaction to generate hydrogen.

  Furthermore, even in applications where the rotation direction of the rolling bearing changes frequently, the lubricating film between the rolling element and the raceway tends to break. Therefore, metal contact is likely to occur locally, and the lubricant is easily decomposed by the above tribochemical reaction to generate hydrogen.

  As a countermeasure against such a structural change caused by hydrogen, as in Patent Documents 1 to 3, a layer of iron tetroxide is formed on the transfer surface (black dyeing treatment) to prevent generation of a new surface. Yes. In addition, as in Patent Document 4, an iron phosphate coating is formed on the transfer surface to prevent the formation of a new surface.

JP-A-2-190615 JP-A-10-176718 JP 2013-96448 A JP 2003-97560 A

  However, the coating treatment as described above is worn over time in a use environment where metal contact is likely to occur and a new surface is likely to be generated, and the coating may disappear relatively early.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a long-life rolling bearing that suppresses structure change-type separation due to hydrogen entering the alloy steel forming the bearing member over a long period of time. To do.

  As a result of intensive studies, the present inventors have found that it is effective to make the surface specific hardness and to form a chromium conversion coating with a thickness of 0.1 μm or more in order to solve the above problems. Has been found to be effective, and the present invention has been completed. That is, the present invention provides the following rolling bearing.

(1) In a rolling bearing including a rolling element provided between an inner ring and an outer ring so as to be freely rollable,
At least one of the inner ring and the outer ring,
C: 0.08 to 0.38% by mass,
Si: 0.16-0.5% by mass,
Mn: 0.18 to 1.2% by mass,
Cr: 2.5-4.5 mass%,
Mo: 0.09 to 0.4 mass%,
An alloy steel containing iron and inevitable impurities in the balance, carburized or carbonitrided to form a hardened layer on the surface, and
The surface hardness is Hv653-804,
A rolling bearing characterized in that a chromium conversion coating having a thickness of 0.1 μm or more is formed on the outermost surface.
(2) The rolling bearing according to (1), wherein the following formula (1) is satisfied.
Formula (1): [Cr] -5 ([C] -0.02 [γR]) ≧ −0.3
[Cr] in formula: Cr amount in alloy steel (mass%)
[C]: C amount (mass%) at a position of 0.01D from the surface of the contact surface with the rolling element
[ΓR]: γR amount (volume%) at a position of 0.01D from the surface of the contact surface with the rolling element

  According to the present invention, the steel material composition constituting each part is specified, the surface is set to a specific hardness, and further, a chromic conversion film is formed to prevent the generation of a new surface and further the invasion of hydrogen. It is possible to provide a rolling bearing having a long life by suppressing the structure change type separation.

It is a figure which shows an example of the heat processing pattern at the time of manufacturing the rolling bearing of this invention. It is a figure which shows the other example of the heat processing pattern at the time of manufacturing the rolling bearing of this invention. It is a figure which shows the further another example of the heat processing pattern at the time of manufacturing the rolling bearing of this invention. It is a figure for demonstrating the rotation mode in the rolling life evaluation test of an Example. It is a graph which shows the relationship between Cr amount and lifetime ratio obtained in the Example. It is a graph which shows the relationship between the thickness of a trivalent chromium chemical conversion film obtained in the Example, and a lifetime ratio.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

In the rolling bearing of the present invention, at least one of the inner ring and the outer ring, preferably both, is made of an alloy steel containing the following elements, the balance containing iron and inevitable impurities, and further carburized or carbonitrided on the surface. A cured layer is formed.
C: 0.08 to 0.38% by mass,
Si: 0.16-0.5% by mass,
Mn: 0.18 to 1.2% by mass,
Cr: 2.5-4.5 mass%,
Mo: 0.09 to 0.4 mass%,

[C: 0.08 to 0.38 mass%]
C is an element that dissolves in the base structure of the alloy steel by quenching and improves the hardenability. The content is 0.08 to 0.33 mass%, preferably 0.10 to 0.30. When the C content is less than 0.08% by mass, the hardness in the core is insufficient and the rigidity is lowered. On the other hand, when the C content exceeds 0.38% by mass, the toughness of the core part is lowered. In addition, when carburizing treatment or carbonitriding treatment is performed, the surface is hard and the hardness decreases toward the inside. However, in the present invention, the portion where the hardness is reduced and becomes constant is defined as the core portion.

[Si: 0.16-0.5% by mass]
Si is an element that improves the hardenability by dissolving in the base structure of the alloy steel. Moreover, in order to stabilize the martensite of a base organization, the composition group change by hydrogen is delayed and it brings about the effect of extending the lifetime of each component. The content is 0.16 to 0.5 mass%, preferably 0.2 to 0.5 mass%. When the Si content is less than 0.16% by mass, the effect of delaying the tissue change cannot be sufficiently obtained. On the other hand, when Si content exceeds 0.5 mass%, carburizing property and carbonitriding property may deteriorate.

[Mn: 0.18 to 1.2% by mass]
Mn is an element that improves the hardenability by dissolving in the matrix structure in the alloy steel. Moreover, in order to stabilize the martensite of a base organization, the composition group change by hydrogen is delayed and it brings about the effect of extending the lifetime of each component. Furthermore, the effect of facilitating generation of retained austenite after heat treatment is brought about. The produced retained austenite delays the diffusion and accumulation of hydrogen in the alloy steel, thereby delaying the local occurrence of structural changes and extending the life of each component. The content is 0.18 to 1.2% by mass, preferably 0.6 to 1.2% by mass. When the Mn content is less than 0.18% by mass, the effect of easily generating retained austenite cannot be obtained. On the other hand, when the Mn content exceeds 1.2% by mass, the prior austenite grains become coarse or the residual austenite amount becomes excessive, and the dimensional stability decreases.

[Cr: 2.5-4, 5% by mass]
Cr is an element that improves the hardenability by dissolving in the base structure of the alloy steel. Moreover, it combines with C to form carbides in the steel and brings about an effect of improving wear resistance. Furthermore, in order to stabilize the carbonaceous material and the martensite of the base structure, the structural change caused by hydrogen is delayed, thereby bringing about an effect of extending the life of each part. Its content is 2.5-4.5% by mass, preferably 2.6-4.5% by mass. When the Cr content is less than 2.5% by mass, the effect of delaying the structural change cannot be obtained sufficiently. On the other hand, if the Cr content exceeds 4.5% by mass, the toughness of each part may decrease, and the carburizing property and carbonitriding property may decrease. In addition, the cost of the material is increased, and unless the quenching temperature is increased, a predetermined hardness cannot be obtained, resulting in an increase in production cost.

[Mo: 0.09 to 0.4 mass%]
Mo is an element that improves the hardenability and temper softening resistance by dissolving in the base structure of the alloy steel. In addition, since the carbide, martensite and austenite of the base structure are stabilized, the structural change caused by hydrogen is delayed, and the life of each part is extended. The content is 0.09 to 0.4 mass%, preferably 0.1 to 0.4 mass%. When the Mo content is less than 0.09% by mass, the effect of delaying the change in structure cannot be sufficiently obtained. On the other hand, if the Mo content exceeds 0.4% by mass, the cost of the material is increased or the machinability is lowered, so that productivity is lowered.

[Other alloy components]
The alloy steel contains the above-mentioned elements as essential components, but can contain Ni, Cu, S, P, O, and the like, but it is preferable that the content is small.

[Surface hardness: Hv 653-804]
In order for the bearing to realize a smooth rolling motion, the inner ring or the outer ring and the rolling element are in contact with each other in a minute region, and high contact pressure is generated on the contact surface. Therefore, in order to prevent plastic deformation of the contact surface and ensure a sufficient rolling fatigue life, the alloy steel is subjected to carburizing or carbonitriding, and the surface hardness after quenching is set to Hv (Vickers hardness). 653 to 804, preferably Hv 653 to 800. If it is less than Hv653, such an effect cannot be obtained and the rolling fatigue life is reduced. On the other hand, if it exceeds Hv 804, the toughness of each part will decrease. To achieve such surface hardness, the amount of (C + N) and quenching and tempering conditions are controlled along with the control of the alloy composition.

[Chromium conversion coating]
The chromium conversion coating is composed mainly of Cr—O and is chemically stable because it is in a passive state. Therefore, it is possible to prevent a tribochemical reaction with the lubricant from occurring even under use conditions where the lubricating film is partially broken, and to suppress generation of hydrogen. Moreover, even if the coating is thinned by metal contact, it can maintain a film-forming state for a long time because it has a certain degree of self-healing ability. The purpose of forming the chrome conversion coating in the present invention is to prevent the formation of a new surface, and the effect of the present invention is basically obtained regardless of the form of the chromic conversion coating such as trivalent chromium or hexavalent chromium. It is done. However, for the purpose of environmental protection, it is preferable to perform trivalent chromium conversion treatment. Specifically, a film made of chromium oxide (Cr ₂ O ₃ ) or chromium hydroxide (Cr (OH) ₃ ) is formed by immersing each part in an acidic solution based on a trivalent chromium salt. Film.

  This chromium conversion coating has a Cr content of 1.3% as in ordinary bearing steel (JIS-SUJ2) when the film is formed on steel having a Cr content of 2.5 to 4.5% by mass. It was found that the bond between the steel and the coating became stronger and the film formation state could be maintained for a longer time than when the film was formed on steel of ˜1.6% by mass. For this reason, the chrome conversion coating is generally carried out in order to ensure corrosion resistance on the plating treatment trace, but in the present invention, it is directly formed on the steel surface.

  The film thickness of the chrome conversion coating is 0.1 μm or more, preferably 0.1 to 2.1 μm, and more preferably 0.1 to 2.0 μm. If the film thickness is less than 0.1 μm, a sufficient film effect cannot be obtained. On the other hand, if the coating becomes too thick, the gap provided between the inner ring or the outer ring and the rolling element becomes small, and smooth rolling motion may be hindered. Therefore, the upper limit is preferably set to 2.1 μm. .

[More preferred quality]
In order to further enhance the life extension effect, when the rolling element diameter is D, the amount of C and the amount of retained austenite (γR amount) at a depth of 0.01 D from the surface of the raceway surface, and the amount of Cr in the steel, It is preferable that the following formula (1) is satisfied.
Formula (1): [Cr] -5 ([C] -0.02 [γR]) ≧ −0.3
[Cr] in formula: Cr amount in alloy steel (mass%)
[C]: C amount (mass%) at a position of 0.01D from the surface of the contact surface with the rolling element
[ΓR]: γR amount (volume%) at a position of 0.01D from the surface of the contact surface with the rolling element

[Position 0.01D from the surface]
In rolling bearings, the contact stress between the bearing ring (inner ring and outer ring) and the rolling element generates a shear stress inside the contact surface. This shear stress causes metal fatigue, leading to separation of the contact surface. There is. Since the distribution of the shear stress is determined by the contact stress and the contact area between the race and the rolling element, the diameter of the rolling element greatly affects the distribution of the shear stress. Under normal conditions of use, the shear stress increases at a depth of about 1% of the rolling element diameter (D) (depth 0.01D), and peeling occurs from that region. Similarly, it has been clarified that the structural change caused by hydrogen increases in shear stress and easily occurs at the depth of 0.01D. For these reasons, it is preferable that the expression (1) is satisfied at a depth of 0.01D.

[Definition of Formula (1)]
When the carbide is generated, Cr dissolved in the base structure is taken up by the carbide. For this reason, the distribution of alloy components is non-uniform in the vicinity of the carbide and other places, and the effect of firmly bonding the chromium conversion coating may not be obtained in places where Cr is sparse. This phenomenon is particularly noticeable in alloy steels with a large amount of Cr. Accordingly, the relationship between the amount of Cr in the steel material, the amount of C at the position of depth of 0.01D and the amount of retained austenite (γR amount) satisfies the formula (1), thereby suppressing the formation of carbides and the base structure. It was found that a large amount of the alloying element can be uniformly dissolved.

  The value of equation (1) increases as the Cr content increases. In addition, when the amount of C is large, C that cannot be completely dissolved in the base structure is combined with Cr to form carbides, and therefore the value of formula (1) increases as the amount of C decreases. Furthermore, generally, if the amount of C dissolved in the base tissue is increased by increasing the amount of C or increasing the quenching temperature, the amount of γR increases. Therefore, when the amount of γR is large, the amount of dissolved C increases and the generation of carbides decreases, so the value of the formula (1) increases. And when the value of Formula (1) is -0.3 or more, the balance of Cr amount, C amount, and γR amount is good, and the formation of carbides is suppressed, and a large amount of alloy elements are uniformly dissolved in the base structure. The effect of extending the life can be further increased. A more preferable value of the formula (1) is 1 or more.

[Amount of retained austenite at a depth of 0.01D]
The retained austenite in the metal structure has a crystal structure different from that of martensite, which is the base structure of the alloy steel, and has an effect of reducing the hydrogen diffusion constant due to the crystal structure. Therefore, there is an effect of delaying the local accumulation of hydrogen at a position of depth 0.01D and delaying the occurrence of tissue change at this position. In order to sufficiently obtain this effect, the amount of retained austenite at a depth of 0.01 D is preferably 20 to 45% by volume. If it is less than 20% by volume, the effect of delaying the tissue change is not sufficient, and if it exceeds 45% by volume, the dimensional stability of each part decreases. Moreover, in order to make the amount of retained austenite at a depth of 0.01D within this range, the components of the alloy steel are controlled, and the (C + N) amount and quenching / tempering conditions are controlled.

[Compressive residual stress at a depth of 0.01D]
In addition to satisfying the formula (1), it is more preferable that the compressive residual stress at a depth of 0.01D is 50 to 300 MPa. The compressive residual stress at this position where hydrogen is likely to accumulate has the effect of suppressing the generation of cracks and their propagation from structural changes. If the compressive residual stress at this position is less than 50 MPa, the effect of delaying this structural change cannot be obtained sufficiently. On the other hand, if the compressive residual stress at this position exceeds 300 MPa, the value of the tensile residual stress generated inside the material in order to achieve equilibrium with this compressive residual stress increases, and conversely, there is a possibility of accelerating the progress of cracks. is there.

[Heat treatment conditions]
In producing the rolling bearing of the present invention, the following heat treatment may be performed, for example, in order to satisfy the above-described formula (1) and further the compressive residual stress at a depth of 0.01D.

  As shown in FIG. 1, first, a carburizing process or a carbonitriding process, preferably a carbonitriding process that is held at 880 to 1000 ° C. for a predetermined time is performed. When N is dissolved in the base structure by carbonitriding, the hardness and the amount of γR can be kept high even when the C content is low. More preferably, the N content is 0.05 to 0.50 mass%. If it is less than 880 degreeC, since sufficient diffusion rate of C and N cannot be obtained and processing time becomes long, productivity will be reduced. On the other hand, when the temperature exceeds 1000 ° C., the prior austenite grains become coarse. The gas concentration in the furnace needs to be adjusted to obtain the optimum (C + N) content. For example, the C concentration can be controlled by controlling the flow rate of hydrocarbon gas such as propane or butane, and the gas flow rate of ammonia. The N concentration is adjusted by controlling. About holding time, it adjusts so that it may become the optimal depth of carburizing or carbonitriding according to the size of an inner ring and an outer ring.

  After the carburizing process or carbonitriding process, it is allowed to cool. Moreover, as shown in FIG. 2, you may cool rapidly. Alternatively, as shown in FIG. 3, after the carburizing process or the carbonitriding process, holding at 800 to 880 ° C. for a predetermined time may be followed by rapid cooling. When kept below 800 ° C., carbides due to precipitate C are generated from the base structure. On the other hand, when the holding temperature exceeds 880 ° C., the coarsened prior austenite grains affect the quenching process in the next step, and the structure becomes rough. The holding time is adjusted so as to obtain the optimum carburizing or carbonitriding depth according to the size of the inner ring and the outer ring.

  Next, a quenching process is performed. At that time, the inner ring and the outer ring are held at 820 to 900 ° C. for a predetermined time and then cooled with oil. When the quenching temperature is less than 820 ° C., the hardness after quenching is insufficient. More preferably, it is performed at 860 ° C. or higher in order to facilitate the melting of the alloy element into the base structure. On the other hand, if the quenching temperature exceeds 900 ° C., the amount of retained austenite becomes excessive or coarsening of prior austenite grains occurs, resulting in a decrease in toughness. The quenching time is adjusted so as to obtain an optimum carburizing or carbonitriding depth according to the size of the inner ring and outer ring.

  However, this quenching process does not need to be carried out when it is kept at 800 to 880 ° C. for a predetermined time after the carburizing process or the carbonitriding process.

  Next, a tempering process is performed. At that time, air cooling or furnace cooling is performed after a predetermined time in which the inner ring and the outer ring are held at 160 to 240 ° C. If the tempering temperature is less than 160 ° C, the toughness is reduced. The structure of the alloy steel becomes sensitive to hydrogen, and the structure changes easily due to hydrogen. On the other hand, when the quenching temperature exceeds 240 ° C., the retained austenite is decomposed and solid solution C is precipitated, so that the effect of delaying the structural change due to hydrogen cannot be sufficiently obtained. The tempering time is adjusted so as to obtain the optimum carburization or carbonitriding depth according to the size of the inner ring or outer ring.

  In the present invention, the type of rolling bearing is not limited, and ball bearings such as deep groove ball bearings, angular ball bearings, thrust ball bearings, roller bearings such as cylindrical roller bearings, tapered roller bearings, and self-aligning roller bearings, or needles Applicable to bearings and the like. The rolling bearing of the present invention is filled with a lubricant or supplied from the outside, but the lubricant may be a lubricating oil or a grease.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereby.

(Examples 1-14, Comparative Examples 1-13)
In this example, the inner ring of the ball bearing 6317 was manufactured using a steel material made of the steel types shown in Table 1 (however, the steel type H was JIS-SUJ2), and the outer ring and balls were manufactured by JIS-SUJ2. This is because the inner ring is easily peeled off in the life evaluation test described later.

  The inner ring was subjected to the heat treatment shown in Table 2 after cutting the steel material of the steel type shown in Table 1 into a predetermined size and performing hot rolling and turning. Carburizing treatment or carbonitriding treatment was held at 880 to 1000 ° C. for 14 hours. In addition, the carburizing process starts with a mixed gas atmosphere of RX gas and enriched gas from the beginning, and the carbonitriding process starts with a mixed gas atmosphere of RX gas, enriched gas, and ammonia gas, and the CP value is adjusted to the C concentration in Table 2. Adjusted. When holding at the time of cooling after carbonitriding, oil cooling was carried out after holding at 860-880 degreeC for 1.5 hours. Then, it hardened after hold | maintaining at 800-900 degreeC for 1.5 hours, and tempered at 160-240 degreeC after that.

  After heat treatment, after grinding and finishing, fully degreased and washed, immersed in an acidic solution based on 30 ° C. trivalent chromium salt for 20 to 120 seconds, and then washed and dried. As a result, a trivalent chromium conversion coating was formed on the surface. Finally, using the inner ring produced in this way, it was assembled together with the outer ring, ball and cage to obtain a ball bearing 6317 (inner diameter 85 mm, outer diameter 180 mm, width 41 mm, ball diameter 30.2 mm). And this bearing was used for the life evaluation test shown below.

(Life evaluation test)
High traction oil (synthetic oil for transmission) with a radial load of 53.2N
As shown in FIG. 4, the rotation direction was reversed every 10 seconds to continuously rotate, and the time until the end of the service life was measured. The life was due to the occurrence of delamination. All delamination occurred on the inner ring side, and a white structure was observed in the delamination area. The number of samples was 3, and the average value was obtained. The results are shown in Table 2, and are relative values with respect to the life of Comparative Example 1 made of JIS-SUJ2, which is a general bearing steel. Table 2 also shows the steel types used, heat treatment conditions, surface hardness, depth 0.01D quality (C content, N content, retained austenite content, compression residual effect), and the film thickness of the chrome conversion coating. Show.

  As shown in Table 2 and FIG. 6, in Examples 1 to 14, the alloy composition, the heat treatment quality, and the thickness of the chromic conversion coating are within the ranges defined by the present invention, and the standard JIS-SUJ2 of Comparative Example 1 is used. In comparison with the product, the lifetime is extended 10 times or more in Examples 1 to 9, and 5.5 to 6.9 times in Examples 10 to 14.

  On the other hand, in Comparative Examples 2 to 13, the lifetime was shorter than that of the Example, and in the observation of the metal structure of the inner ring cross section after the test, a structural change due to hydrogen was observed. The reason is considered as follows.

  In Comparative Examples 2, 11, and 12, the alloy composition is out of the scope of the present invention, or the heat treatment quality is out of the scope of the present invention, so the life is shortened.

  In Comparative Examples 3 to 9, since the chrome conversion coating is not formed, the lifetime is shortened. However, since the alloy composition and the heat treatment quality are within the scope of the present invention, the structural change due to hydrogen is delayed, and the life is extended 4 to 5 times compared with Comparative Example 1.

  Since the thickness of the chromic conversion coating is outside the scope of the present invention, the life of the comparative example 10 is shortened.

  Moreover, in order to evaluate the durability of the chrome conversion coating, the relationship between the amount of Cr in the alloy steel and the life ratio of Examples 1 to 7 and 11 and Comparative Examples 2 and 13 in which the chrome conversion coating was formed. Asked. As shown in FIG. The steel types are A to G, H, K, and N, and everything except for the amount of Cr is within the scope of the present invention. Therefore, the life ratio is considered to indicate the durability of the chromium conversion coating. And as shown in FIG. 5, when the amount of Cr is 2.5 mass% or more, the lifetime becomes remarkably long.

Claims (2)

In a rolling bearing comprising a rolling element provided between an inner ring and an outer ring so as to be freely rollable,
At least one of the inner ring and the outer ring,
C: 0.08 to 0.38% by mass,
Si: 0.16-0.5% by mass,
Mn: 0.18 to 1.2% by mass,
Cr: 2.5-4.5 mass%,
Mo: 0.09 to 0.4 mass%,
An alloy steel containing iron and inevitable impurities in the balance, carburized or carbonitrided to form a hardened layer on the surface, and
The surface hardness is Hv653-804,
A rolling bearing characterized in that a chromium conversion coating having a thickness of 0.1 μm or more is formed on the outermost surface. The rolling bearing according to claim 1, wherein the following formula (1) is satisfied.
Formula (1): [Cr] -5 ([C] -0.02 [γR]) ≧ −0.3
[Cr] in formula: Cr amount in alloy steel (mass%)
[C]: C amount (mass%) at a position of 0.01D from the surface of the contact surface with the rolling element
[ΓR]: γR amount (volume%) at a position of 0.01D from the surface of the contact surface with the rolling element

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