JP2014101896A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing capable of securing sufficient durability even under a severe use condition.SOLUTION: Outer and inner rings 3 and 5 are made of alloy steel that suppresses a structural change, caused by hydrogen, to some extent. In addition, outer-ring and inner-ring raceways 2 and 4 of the outer and the inner rings 3 and 5, and rolling surfaces of respective balls 6 and 6 have properties that make surface roughness hardly worse. Furthermore, RSm crowning a roughness curve of a raceway surface is set to be a great value such as 8 μm or more. These restrain a newly formed surface from being formed by metal contact, suppress hydrogen generation in itself, and suppress structural change-type separation.

Description

  The present invention is a relatively large and large load during operation used to support a rolling bearing, in particular, a main shaft of a wind power generator or a rotating shaft constituting a transmission, a construction machine, an industrial robot, or the like. The present invention relates to improvements in rolling bearings that support

  For example, a radial ball bearing 1 as shown in FIG. 1 is incorporated in a rotation support portion of various rotary machine devices. The radial ball bearing 1 includes an outer ring 3 having an outer ring raceway 2 on an inner peripheral surface, an inner ring 5 having an inner ring raceway 4 on an outer peripheral surface, and an outer ring raceway 2 and an inner ring raceway 4 provided between the outer ring raceway 2 and the inner ring raceway 4. A plurality of balls 6 and 6 which are moving bodies are provided. These balls 6, 6 are held by a cage 7 so as to be able to roll while being arranged at equal intervals in the circumferential direction.

  Further, a radial cylindrical roller bearing 8 as shown in FIG. 2, for example, is incorporated in the rotation support portion to which a large radial load is applied. The radial cylindrical roller bearing 8 includes an outer ring 3a having a cylindrical concave outer ring raceway 2a on an inner peripheral surface, an inner ring 5a having a cylindrical convex inner ring raceway 4a on an outer peripheral face, the outer ring raceway 2a and the inner ring raceway 4a. In between, there are provided a plurality of cylindrical rollers 9, 9 each being a rolling element provided so as to be able to roll while being held by the cage 7 a. Further, inward flange portions 10 and 10 are formed at both ends of the inner peripheral surface of the outer ring 3a, and an outward flange portion 11 is formed at one end portion of the outer peripheral surface of the inner ring 5a.

  Further, a radial tapered roller bearing 12 using a tapered roller as a rolling element, for example, as shown in FIG. 3 is incorporated in a rotation support portion to which a large radial load and a thrust load are applied. The radial tapered roller bearing 12 includes an outer ring 3b having a conical concave outer ring raceway 2b on an inner peripheral surface, an inner ring 5b having a conical convex inner ring raceway 4b on an outer peripheral surface, the outer ring raceway 2b and the inner ring raceway 4b. Are provided with a plurality of tapered rollers 13 and 13 each of which is a rolling element provided so as to be able to roll while being held by the cage 7b. Further, out of both ends of the outer peripheral surface of the inner ring 5b, a large-diameter side flange 14 is formed at the large-diameter end, and a small-diameter flange 15 is formed at the small-diameter end. The small diameter side flange 15 may be omitted.

  Rolling bearings such as the radial ball bearing 1, the radial cylindrical roller bearing 8, the radial tapered roller bearing 12 and the like as described above fix the inner ring 5, 3a, 3b to the housing, and fix the inner ring 5, 5a, 5b. Is externally fixed to the rotation shaft, thereby rotatably supporting the rotation shaft with respect to the housing. When the rolling bearing used in such a state is operated while supporting a large load, the raceway surfaces of the outer ring raceways 2, 2a, 2b and the inner ring raceways 4, 4a, 4b, etc. 6, 6, a large surface pressure is repeatedly applied to the rolling contact surface, which is a portion in rolling contact with the raceway surface, among the surfaces of the rolling elements such as the cylindrical rollers 9, 9 and the tapered rollers 13, 13.

  Thus, in a rolling bearing used under severe conditions for supporting a large load, metal fatigue may occur due to operation for a long time, and the surfaces of the raceway surface and the rolling surface may be peeled off. As such a peeling mode, internal origin type peeling, indentation origin type peeling, tissue change type peeling, and the like are known. Of these, the internal starting type peeling constitutes rolling elements of balls 6 and 6, cylindrical rollers 9 and 9, tapered rollers 13 and 13, and race rings such as outer rings 3, 3a and 3b, inner rings 5, 5a and 5b. Fatigue cracks are generated starting from non-metallic inclusions such as oxides and nitrides present in alloy steels such as bearing steels, resulting in delamination. Indentation starting type peeling is a process in which fatigue cracks start from the indentation generated on the raceway surface by hard foreign matter mixed in the lubricating oil, leading to peeling.

  Furthermore, the structure change type delamination occurs in some applications where the conditions of use are severe, and the metal structure of the base of the alloy steel constituting the rolling bearing itself changes from a martensite structure to fine ferrite grains called a white structure. It changes, and fatigue cracks are generated starting from the structure change portion, leading to peeling. Such a structure change type peeling is an active new surface that appears when the raceway surface and the rolling surface come into contact with each other under use conditions where the oil film (lubricant film) formed on the raceway surface is partially broken. This is considered to be caused by the fact that hydrogen generated by the tribochemical reaction between the nascent surface and the lubricant accumulates in the stress concentration part in the steel. Such a structure change type peeling is likely to occur in the case of a cylindrical roller bearing or a tapered roller bearing using a cylindrical roller or a tapered roller as a rolling element, or a large ball bearing having a ball diameter of 30 mm or more. The reason for this is that since the contact area of the rolling contact portion between the raceway surface and the rolling surface is large, it is difficult for a lubricating film to be stably formed on this rolling contact portion, and local metal contact tends to occur locally at this rolling contact portion. This is because hydrogen is easily generated by the above-described tribochemical reaction.

  In the case of a rolling bearing for supporting a rotating shaft whose direction or magnitude of transmission torque changes momentarily or temporarily, such as a rotating shaft of a transmission that transmits power by gears, At the moment when the torque changes, a large slip occurs at the rolling contact portion between the rolling surface and the raceway surface, and the lubricating film is easily cut. When the lubricating film is cut, metal contact locally occurs at the rolling contact portion, and hydrogen is easily generated by a tribochemical reaction. Further, even in a usage mode in which the direction in which the pair of race rings rotate relative to each other frequently changes, the lubricating film easily breaks at the rolling contact portion, and hydrogen is easily generated due to the decomposition of the lubricating oil.

For example, techniques described in Patent Documents 1 to 6 are known as techniques for suppressing such structure change-type peeling caused by hydrogen.
Among these, the prior arts described in Patent Documents 1 and 2 suppress the generation of hydrogen based on the decomposition of the base oil in the grease by devising the composition of the grease sealed as a lubricant in the rolling bearing, and the structure The company intends to extend the life of rolling bearings by suppressing variable peeling.
However, depending on the application of the rolling bearing, lubricating oil may be used without using grease as a lubricant. In particular, relatively large rolling bearings often use lubricating oil rather than grease. In such a case, as described in Patent Documents 1 and 2, the structure change type peeling due to the improvement of the grease is performed. It cannot be suppressed.

In addition, the prior arts described in Patent Documents 3 and 4 apply a coating treatment to the surface of a rolling bearing part such as a rolling element or a bearing ring, so that the rolling surface or the raceway surface, which is the surface of the rolling bearing part, is applied. Makes new surfaces less likely to occur. Then, the generation of hydrogen based on the tribochemical reaction between the new surface and the lubricant is suppressed, and the change in structure change type is suppressed, thereby extending the life of the rolling bearing.
In the case of such conventional techniques described in Patent Documents 3 and 4, the surface coating may be peeled off under severe use conditions such as long-term operation under a high load. The occurrence of tissue change-type peeling cannot be suppressed. In addition, the product cost increases due to the increase in the coating process.

Furthermore, the prior art described in Patent Documents 5 and 6 regulates the components of alloy steel constituting the bearing parts, specifically, by increasing the Cr content and further restricting the heat treatment process, the white structure It is going to delay the occurrence of change.
In the case of the prior arts described in Patent Documents 5 and 6 as described above, a certain degree of effect can be obtained, but only with that, under a high load, for example, a rotation support portion for a main shaft of a wind power generator. It is difficult to obtain a sufficiently satisfactory effect under extremely severe use conditions that require extremely long-term maintenance-free operation. If the Cr content is sufficiently increased, durability can be improved, but instead, it becomes difficult to process the components of the rolling bearing, resulting in an increase in cost due to a decrease in productivity.

JP 2002-327758 A JP 2003-106338 A JP-A-10-176718 JP 2001-221310 A JP 2005-314794 A JP 2012-031457 A

The present invention has been invented in order to realize a rolling bearing capable of ensuring sufficient durability even under severe use conditions in view of the circumstances as described above.
Specifically, alloy steel that suppresses structural changes caused by hydrogen to some extent is used, and the formation of new surfaces due to metal contact is suppressed to suppress the generation of hydrogen itself. The present invention provides a technology that can sufficiently extend the life of a rolling bearing.

The rolling bearing of the present invention comprises a first alloy ring having a first raceway surface on any surface and a second alloy steel having a second raceway surface facing the first raceway surface. A bearing ring and a plurality of rolling elements each provided between the first and second raceway surfaces so as to be freely rollable and each made of alloy steel are provided.
In particular, in the rolling bearing of the present invention, each rolling element is subjected to carbonitriding or nitriding. The N concentration of the surface layer of each rolling element is 0.2% by mass or more, the residual austenite amount is 30% by volume or less, and the hardness is Hv780 or more. And the area ratio of the nitride of the surface layer of each said rolling element is 1% or more and less than 10%.
Further, at least one of the two race rings (for example, inner ring having strict conditions, preferably both), C is 0.10 to 0.30 mass%, Si is 0.2 to 0.9 mass%. , Mn is 0.2 to 1.2% by mass, Cr is 2.6 to 4.5% by mass, Mo is 0.1 to 0.9% by mass, Ni is 0.9% by mass or less, and Cu is 0.2% by mass. 20% by mass or less, S is 0.020% by mass or less, P is 0.020% by mass or less, and the balance is made of an alloy steel composed of Fe and inevitable impurities. Further, the surface of the at least one raceway ring made of the alloy steel is subjected to carburizing treatment or carbonitriding treatment. Then, from the surface of the raceway surface provided on the raceway, the hardness at the depth position (1% position) of 1% of the diameter of each rolling element is Hv720 to 832, and the content of C and the content of N are also the same. The amount of C + N that is the sum of the amount is 0.8 to 1.2% by mass, the amount of retained austenite is 20 to 45% by volume, and the compressive residual stress is also 50 to 300 MPa.
In addition, regarding the roughness curve of the surface of the raceway surface provided on the raceway, RSm indicating the interval between adjacent peaks is set to 8 μm or more.

Furthermore, in the case of the rolling bearing of the present invention, each rolling element is composed of 0.3 to 1.2% by mass of C, 0.3 to 2.2% by mass of Si, and 0.3 to 2% of Mn. Carbonitriding and quenching to alloy steels containing 0% by mass and 0.5 to 2.0% by mass of Cr, respectively, and having a Si / Mn ratio of 5 or less, which is the ratio of the Si content to the Mn content It is made by processing and tempering. Then, 100 or more nitrides having an average particle diameter of 0.05 to 1 μm are contained in the surface of each rolling element in an area of 375 μm ² .

In carrying out the present invention, for example, as in the invention described in claim 2, each of the rolling elements is a roller such as a cylindrical roller, a tapered roller, a spherical roller, or the like. As in the invention described above, the ball has a diameter of 30 mm or more.
Furthermore, as a form of use, it can be used in a state where it is incorporated in a rotation support portion of a wind power generator as in the invention described in claim 4, or a construction machine can be used as in the invention described in claim 5. Used in a state where it is incorporated in the rotation support section.

  The rolling bearing of the present invention configured as described above is used for rolling bearings by defining the N concentration of the surface layer, the amount of retained austenite, the hardness, and the area ratio of nitride on the surface for each rolling element. The accompanying deterioration of the roughness of the rolling surface of each rolling element can be suppressed. In addition, with respect to the raceway, since RSm indicating the distance between adjacent peaks of the raceway surface roughness curve is increased, metal contact is caused at the rolling contact portion between the raceway surface and the rolling surface of each rolling element. Reduce the total number of mountains that come into contact when you wake up. In short, even if metal contact occurs at the rolling contact portion by improving the surface roughness of the rolling contact surface and reducing the number of peaks existing on the raceway surface that contacts the rolling contact surface. Therefore, the area of the nascent surface formed based on this can be reduced (can be reduced), and the amount of hydrogen generated by the action of the nascent surface can be reduced.

In addition, the composition of the alloy steel constituting the bearing ring is devised, and the position where the shear stress is high and the structure is likely to change is the depth position (1% position) of the diameter of each rolling element from the surface. The hardness, the amount of C + N, the amount of retained austenite, and the compressive residual stress are appropriately regulated. For this reason, it is possible to suppress the structural change of the alloy steel when hydrogen enters the alloy steel constituting the race.
Accordingly, it is possible to sufficiently extend the life of the rolling bearing even under severe use conditions in which the lubricating film is easily cut.

Furthermore, since the composition of the alloy steel constituting each rolling element and the nitride existing on the surface of each rolling element are appropriately regulated, the surface of each rolling element can be used even for a long period of use. The deterioration of properties can be suppressed (the rolling surface can be kept smooth). Further, it is possible to more effectively reduce the frequency of occurrence of metal contact at the rolling contact portion and the area of the metal contact surface.
Hereinafter, the reasons for adopting the requirements of the present invention and the reasons for limiting these requirements will be described.

“Regarding the requirements of the invention described in claim 1”
[N concentration on the surface of each rolling element: 0.2% by mass or more]
The alloy steel constituting each of these rolling elements uses an alloy steel containing Si and Mn in order to give the rolling surface the necessary hardness. When the N concentration in such an alloy steel is increased, fine and hard Si—Mn nitride is precipitated, and the rolling surface as the surface layer portion is strengthened. In order to sufficiently strengthen this rolling surface, in order to deposit a sufficient amount of fine and hard Si-Mn nitride on the surface layer portion of each rolling element, the N concentration of this surface layer portion is set to It is necessary to be 0.2% by mass or more. On the other hand, when the N concentration of the surface layer portion exceeds 2% by mass, the toughness of the surface layer portion decreases. Therefore, the upper limit value of the N concentration in the surface layer portion of each rolling element is suppressed to 2% by mass or less.

“Nitride area ratio of each rolling element surface: 1% or more and less than 10%]
In order to obtain the effect of strengthening the rolling surface of each rolling element sufficiently stably, the Si-Mn nitride deposited on the surface layer portion of each rolling element that becomes this rolling surface It is necessary to secure a certain amount. When the area ratio of nitride on the surface of each rolling element is less than 1%, the rolling surface cannot be sufficiently strengthened. On the other hand, if the amount of Si-Mn nitride deposited on the surface layer portion of each rolling element is too large, the hardness of the surface layer portion of each rolling element becomes too high and After heat-treating the rolling elements, the grindability when finishing the rolling surfaces of these rolling elements is reduced, and not only the processing cost is increased, but also the toughness of the surface layer portion of each rolling element is increased. It becomes easy to generate | occur | produce damages, such as a crack, in this surface layer part. The inconvenience due to a decrease in grindability and a decrease in toughness becomes significant when the area ratio of nitride on the surface of each rolling element is 10% or more. Therefore, the area ratio of nitride on the surface of each rolling element is set to 1% or more and less than 10%.

[Amount of retained austenite in the surface layer portion of each rolling element: 30% by volume or less]
Since the retained austenite is a soft structure, it affects the shape of the indentation on the rolling surface of each rolling element, and alleviates stress concentration on the indentation edge. Therefore, by securing a certain amount of retained austenite in the surface layer portion of each rolling element, it is possible to obtain an effect of suppressing peeling due to the scratches and indentations. However, if the amount of retained austenite in the surface layer portion of each rolling element is too large, the hardness of the rolling surface of each rolling element decreases, and it is difficult to ensure the rolling fatigue life of the rolling surface of each rolling element. Become. Therefore, the amount of retained austenite in the surface layer portion of each rolling element is suppressed to 30% by volume or less, more preferably 15% by volume or less. On the other hand, when the amount of retained austenite in the surface layer portion of each rolling element is less than 2% by volume, the above-described effect cannot be obtained. Therefore, the lower limit of the amount of retained austenite in the surface layer portion of each rolling element is set to 2% by volume or more.

[Hardness of surface layer portion of each rolling element: Hv780 or more]
If the hardness of the surface layer portion of each rolling element is low, scratches and indentations are likely to be made on the rolling surface, and if there are scratches or indentations, the roughness of the rolling surface is reduced. And not only the noise and vibration which generate | occur | produce at the time of operation | movement of a rolling bearing become large, but a metal contact becomes easy to occur between the said rolling surface and the said track surface. When metal contact occurs, as described above, a new surface that induces generation of hydrogen tends to occur. Therefore, the hardness of the surface layer portion of each rolling element is set to Hv 780 or more so that scratches and indentations are hardly attached to the rolling surface. On the other hand, if the hardness of the surface layer portion of each rolling element exceeds Hv1050, the grindability of the rolling surface of each rolling element deteriorates. Therefore, the upper limit value of the hardness is set to Hv1050 or less.

[C content in alloy steel constituting raceway ring: 0.10 to 0.30 mass%]
C is an element that dissolves in the base of the alloy steel by quenching and improves the hardness. When the content of C in the alloy steel constituting the bearing ring is less than 0.10% by mass, the hardness of the core of the obtained bearing ring is insufficient, and the rigidity of the bearing ring is insufficient. Become. On the other hand, when the content of C in the alloy steel constituting the raceway exceeds 0.30% by mass, the core part of the obtained raceway ring becomes too hard, and the toughness of this core part is too high. It will decline. Therefore, the C content in the alloy steel constituting the race is set to 0.10 to 0.30 mass%. In the case of the present invention, in order to ensure the hardness of the raceway surface, the raceway is subjected to carburizing treatment or carbonitriding treatment. In this case, when carburizing treatment or carbonitriding treatment is performed on the alloy ring raceway, the surface is hard, the hardness decreases toward the inside, and after reaching a certain depth from the surface, Hardness does not decrease even if deeper than that. The core portion is a portion where the hardness is lowered and becomes constant in this way.

[Si content in alloy steel constituting the bearing ring: 0.2 to 0.9 mass%]
Si has the effect of improving the hardenability and temper softening resistance by solid solution in the base of the alloy steel, so it is added to ensure the necessary hardness for the race. In addition, Si has the effect of stabilizing martensite in the base structure, delaying the structural change caused by hydrogen, which is an important object of the present invention, and suppressing the occurrence of white tissue peeling. The effect of extending the life due to the white structure change delay is not sufficiently obtained when the Si content is less than 0.2% by mass. On the other hand, when the Si content exceeds 0.9 mass%, the carburizing property and the carbonitriding property are deteriorated, and the effect of heat treatment for obtaining the necessary hardness for the raceway surface is hindered. Therefore, the Si content in the alloy steel constituting the race is set to 0.2 to 0.9 mass%.

[Mn content in alloy steel constituting the bearing ring: 0.2 to 1.2% by mass]
Mn has the effect of improving the hardenability by dissolving in the base of the alloy steel, so Mn is added to ensure the necessary hardness for the race. Further, Mn has an effect of stabilizing austenite, and makes it easy to generate retained austenite after heat treatment. Residual austenite has the effect of delaying the diffusion and accumulation of hydrogen in the metal structure. Therefore, by adding Mn, the local structure change caused by hydrogen can be delayed to extend the life. Such an effect cannot be sufficiently obtained unless the amount of Mn added is 0.2% by mass or more. On the other hand, if the content of Mn exceeds 1.2% by mass, the prior austenite grain size becomes coarse, the deformation resistance during hot forging increases, the hot forgeability decreases, and the mass productivity decreases. . Further, the retained austenite in the alloy steel constituting the bearing component is decomposed little by little with the use of the rolling bearing, and the volume expands, albeit slightly, with the decomposition. For this reason, when the amount of retained austenite becomes excessive by increasing the content of Mn, the stability of the shape and dimensions of the bearing component is lowered. Therefore, the amount of Mn in the steel constituting this bearing part is set to a range of 0.2 to 1.2% by mass. In order to further stabilize the hot forgeability and dimensional stability, the Mn content is preferably suppressed to 0.8% by mass or less. However, in order to sufficiently obtain the above effects, the lower limit value of the Mn content is preferably 0.6% by mass.

[Cr content in alloy steel constituting the bearing ring: 2.6 to 4.5% by mass]
Cr has the effect of improving the hardenability by dissolving in the base of the alloy steel. Moreover, it combines with C to form carbides and has the effect of improving wear resistance. Furthermore, in order to stabilize the carbide and martensite in the base structure, there is an effect of delaying the structural change caused by hydrogen, delaying the formation of the white structure, and extending the life of the bearing component. When the Cr content is less than 2.6% by mass, such an effect cannot be sufficiently obtained. On the other hand, if the Cr content exceeds 4.5 mass%, the toughness of the raceway ring is reduced, and the carburizing ability and carbonitriding ability are reduced. In addition, since Cr is an expensive element, the inclusion of a large amount increases the procurement cost of alloy steel used as a material for the race. Furthermore, if the quenching temperature is not increased, a predetermined hardness cannot be obtained, so that the productivity of the race is reduced. Therefore, the content of Cr in the alloy steel constituting the bearing ring is set to 2.6 to 4.5 mass%.

[Mo content in alloy steel constituting raceway ring: 0.1 to 0.9 mass%]
Mo dissolves in the base of the alloy steel to improve the hardenability and temper softening resistance and to secure the hardness of the raceway surface of the raceway. That is, Mo functions as a carbonitride-forming element and improves the wear resistance and rolling fatigue life of this raceway surface. Furthermore, since Mo stabilizes martensite in the base structure, it has an effect of delaying the structure change (white structure generation) due to hydrogen, which is important in the present invention. Such an effect (for example, a structure change delay effect) cannot be sufficiently obtained when the Mo content is less than 0.1% by mass. On the other hand, if the Mo content in the alloy steel exceeds 0.9 mass%, the toughness of the raceway will be reduced. Moreover, since Mo is also an expensive element, the procurement cost of the alloy steel used as the material for the bearing ring increases when it is contained in a large amount. Furthermore, the machinability of the manufactured raceway is reduced, and the productivity of this raceway is reduced. Therefore, the Mo content in the alloy steel constituting the bearing ring is set to 0.1 to 0.9 mass%, preferably 0.1 to 0.4 mass%.

[Ni content in alloy steel constituting raceway ring: 0.9 mass% or less]
Ni is an element mixed from scrap as a raw material, and has the effect of improving hardenability, the effect of stabilizing retained austenite, and the effect of improving toughness. However, when a large amount is mixed, the amount of retained austenite becomes excessive, and the stability of the shape and dimensions of the bearing part is lowered. Moreover, since Ni is also an expensive element, the procurement cost of the alloy steel used as the material of the bearing ring increases when it is contained in a large amount. Therefore, Ni is not actively added, and the Ni content is 0.9 mass% or less, preferably 0.2 mass% or less.

[Cu content in alloy steel constituting raceway ring: 0.20 mass% or less]
Cu is an element mixed from scrap, and has an effect of improving hardenability and an effect of improving grain boundary strength. However, when the Cu content increases, hot forgeability decreases. Therefore, Cu is not actively added, and its content is set to 0.20% by mass or less.

[S content in alloy steel constituting raceway ring: 0.020 mass% or less]
Since S forms MnS and acts as an inclusion, the smaller the amount of S contained in the steel, the better. However, S is an element that exists abundantly in the natural world, and trying to keep the S content extremely low reduces the productivity of the steel material and increases the manufacturing cost of the steel material, so it can be widely used industrially. It becomes difficult. On the other hand, even if S is contained in an amount of about 0.020% by mass, durability required for bearing parts can be ensured by making the content of other elements and the heat treatment method appropriate. Therefore, the upper limit of the S content is set to 0.020% by mass.

[1% depth position (1% position) of the diameter of each rolling element from the raceway surface]
The present invention regulates the hardness, C + N amount, retained austenite amount, and compressive residual stress for the 1% position. The reason why these parameters are regulated at the 1% position is as follows.
In rolling bearings, due to the contact pressure between the raceway surface of each bearing ring and the rolling surface of each rolling element, a shear stress is applied directly below the rolling contact surface inside each bearing ring and the bearing component that is each rolling element. It is known that this shear stress generates metal fatigue, which leads to peeling of the surface of the rolling contact surface. Since this shear stress distribution is determined by the contact stress and the contact area between the raceway surface and the rolling surface, the rolling element diameter greatly affects the shear stress distribution. Under normal conditions of use, the shear stress becomes maximum at a position (depth 0.01D) that is about 1% of the rolling element diameter (D) from the raceway surface and the rolling surface. Delamination occurs. It has been found that the structural change caused by hydrogen is also likely to occur at the 1% position where the shear stress is similarly maximized.
Therefore, the present invention regulates the hardness, C + N amount, retained austenite amount, and compressive residual stress at the 1% position as follows in order to make it difficult for the phenomenon that leads to peeling at the 1% position. doing.

[Hardness of raceway at 1% position: Hv 720-832]
Hydrogen that has entered the alloy steel constituting the race ring from the raceway surface moves around in the alloy steel and has a property of being easily accumulated in a region where stress is high. The region where the stress increases during the operation of the rolling bearing is at the 1% position as described above. Since the shear stress inside the raceway is maximized at the 1% position, hydrogen tends to accumulate at the 1% position. According to the study by the present inventors, the structural change caused by hydrogen is caused by local plastic deformation, and in order to delay the occurrence of this structural change, the hardness at the 1% position is improved, It has been found that improving the resistance value against plastic deformation is effective. Therefore, the hardness at the 1% position of the raceway is regulated to Hv720-2032 (HRC61-65). When the hardness at the 1% position is less than Hv720, the plastic deformation at the 1% position cannot be sufficiently suppressed under severe use conditions such that a large load is repeatedly applied to the raceway surface. The occurrence of structural changes cannot be sufficiently suppressed, and the rolling fatigue life of the races cannot be sufficiently ensured. On the other hand, if the hardness at the 1% position exceeds Hv832, the toughness of the raceway is insufficient. The hardness at the 1% position can be properly regulated by regulating the composition of the alloy steel constituting the race and controlling the amount of C + N and the conditions of quenching and tempering. .

[Amount of C + N in alloy steel at 1% position: 0.8 to 1.2% by mass]
If the amount of C or N dissolved in the base structure of the alloy steel is large, the strength of the base structure becomes high, and the structural change is less likely to occur. Such an effect cannot be sufficiently obtained when the amount of C + N at the 1% position is less than 0.8% by mass. On the other hand, when the amount of C + N at the 1% position exceeds 1.2% by mass, a large carbide or nitride is generated, stress concentration is generated in the vicinity thereof, and the structure is likely to change. . That is, the above-described internal origin type peeling is likely to occur. Therefore, the amount of C + N in the alloy steel at the 1% position is set to 0.8 to 1.2% by mass.

[Amount of retained austenite in alloy steel at 1% position: 20 to 45% by volume]
The retained austenite in the metal structure has a crystal structure different from that of martensite, which is a base structure of the alloy steel, and has an effect of lowering the hydrogen diffusion constant due to the crystal structure. For this reason, the residual austenite existing at the 1% position has an effect of delaying the local accumulation of hydrogen at the 1% position and delaying the occurrence of the structural change at the 1% position. Such an effect cannot be sufficiently obtained when the amount of retained austenite at the 1% position is less than 20% by volume. On the other hand, if the amount of retained austenite at the 1% position exceeds 45% by volume, the dimensional stability of the bearing ring is lowered. Therefore, the amount of retained austenite at the 1% position was restricted to a range of 20 to 45% by volume. The amount of retained austenite at the 1% position can be regulated by controlling the components of the alloy steel and controlling the above-mentioned C + N amount and quenching and tempering conditions.

[Compressive residual stress of raceway at 1% position: 50 to 300 MPa]
As described above, the structure change type peeling to be suppressed in the present invention occurs based on the occurrence of cracks starting from the structure change caused by hydrogen at the 1% position. On the other hand, the compressive residual stress acts to suppress the occurrence of cracks and suppress the spread of cracks even if they occur. The compressive residual stress existing at the 1% position where hydrogen is likely to accumulate and the structure change due to hydrogen is likely to occur. This structure change suppresses the generation of cracks and their propagation. Fulfill. The effect of preventing the structure change type peeling based on such a function cannot be sufficiently obtained when the compressive residual stress at the 1% position is less than 50 MPa. On the other hand, when the compressive residual stress at the 1% position exceeds 300 MPa, the value of the tensile residual stress generated inside the raceway ring increases in order to balance the compressive residual stress. There is a possibility that cracks are generated and propagated in the portion where the stress is increased. Therefore, in the case of the present invention, the value of the compressive residual stress at the 1% position is regulated within the range of 50 to 300 MPa. This compressive residual stress at the 1% position regulates the alloy steel components and adjusts the carburizing time or carbonitriding time, so that a C + N gradient from the surface of the raceway to the core (carburizing treatment). Alternatively, it can be regulated by controlling the expansion amount of the surface layer portion based on the carbonitriding process.

[RSm indicating the distance between adjacent peaks in the roughness curve of the raceway surface: 8 μm or more]
This requirement is necessary to minimize the area of the new surface that promotes the decomposition of the lubricating oil. As described above, hydrogen is generated by decomposing lubricating oil by a tribochemical reaction in which a new surface formed by metal contact between the raceway surface and the rolling surface functions as a catalyst. In order to suppress the generation of hydrogen by such a mechanism, it is conceivable to reduce the amount (area) of a new surface formed by a single metal contact. Based on this idea, the present inventors focused on RSm, which is a value indicating the interval between adjacent peaks, in the roughness curve related to the raceway surface, and reduced the amount (area) of the new surface to reduce the amount of hydrogen. Reduced the occurrence and the progress of the structure change type peeling, and extended the life of the rolling bearing.

  Generally, the surface roughness of the raceway surface of the bearing ring constituting the rolling bearing is a roughness curve such as arithmetic average roughness (Ra), maximum height (Ry), and ten-point average roughness (Rz). Is evaluated with the vertical parameter (height of peaks and valleys). Actually, the ease of metal contact at the rolling contact portion between the raceway surface of each raceway and the rolling surface of each rolling element constituting the rolling bearing is determined by the roughness of the raceway surface and the rolling surface in the vertical direction. The RSm, which can be calculated from the relationship between the parameter and the thickness of the lubricating film, and is a lateral roughness parameter is not involved. On the other hand, in the present invention, as shown in FIGS. 4A to 4B, by increasing this RSm, which is a roughness parameter in the lateral direction, metal contact easily occurs at the rolling contact portion. Instead, the number of ridges to be contacted by one metal contact was reduced, and the amount (area) of a new surface formed by this metal contact was suppressed. If the area of the new surface formed by a single metal contact can be reduced, the decomposition of the lubricating oil due to the catalytic action of this new surface can be suppressed, and the amount of hydrogen generated by this decomposition can be suppressed. Progress can be suppressed. Such an effect becomes more prominent as the RSm is larger. When the RSm is less than 8 μm, this effect cannot be obtained sufficiently. Preferably, this RSm is 21 μm or more. On the other hand, as the RSm is larger, the amount (area) of the new surface is reduced and the progress of the tissue change type peeling is suppressed, so the upper limit value of the RSm is not particularly defined. That is, as the value of RSm is larger, the area of the new surface is reduced, and the progress of tissue type peeling can be suppressed. However, if this RSm becomes excessive, the number of ridges in contact with the rolling surface of each rolling element in the raceway surface becomes too small, and depending on the load condition when using a rolling bearing, the local surface pressure Becomes excessive and wear resistance decreases. In consideration of such circumstances, the upper limit value of the RSm is suppressed to 100 μm or less, more preferably 50 μm or less.

[C content in alloy steel constituting each rolling element: 0.3 to 1.2% by mass]
C is an element that dissolves in the base of the alloy steel by quenching and improves the hardness. When the content of C in the alloy steel constituting the rolling element is less than 0.3% by mass, not only sufficient strength cannot be obtained, but also to obtain the necessary hardened layer depth by carbonitriding. The required heat treatment time is increased, leading to an increase in heat treatment cost. For this reason, the content of C in the alloy steel constituting the rolling element is 0.3% by mass or more, preferably 0.5% by mass or more, and more preferably 0.95% by mass or more. On the other hand, if the content of C in the alloy steel constituting the rolling element is too large, giant carbides are produced during steelmaking, which adversely affects the subsequent quenching characteristics and rolling fatigue life, and the rod-shaped material is not rolled. Ease of processing (header property) for plastic processing of a moving body is reduced, and processing costs are increased. Therefore, the upper limit of the C content in the alloy steel constituting the rolling element is set to 1.2 mass%, preferably 1.10 mass%.

[Si content in alloy steel constituting each rolling element: 0.3 to 2.2% by mass]
With the carbonitriding process, Si stably precipitates a sufficient amount of Si-Mn nitride on the surface layer portion of each rolling element, and the hardness required for the rolling surface of each rolling element Add to give Such an effect is not always sufficiently obtained when the Si content in the alloy steel is less than 0.3% by mass. On the other hand, when Si is added in excess of 2.2% by mass, the toughness of the obtained rolling elements is reduced, or the diffusion of N into the core of each rolling element is inhibited, and each rolling element is inhibited. In some cases, the hardness of the entire moving body cannot always be sufficiently high. Therefore, the content of Si in the alloy steel constituting the rolling elements is regulated to 0.3 to 2.2% by mass.

[Mn content in alloy steel constituting each rolling element: 0.3 to 2.0 mass%]
Mn, together with Si described above, stably deposits a sufficient amount of Si-Mn nitride on the surface layer portion of each rolling element, and has the hardness required for the rolling surface of each rolling element. Add to make it. In order to acquire such an effect, it is so preferable that there is much content of Mn in alloy steel, and specifically, it is preferable to contain 0.3 mass% or more of Mn. On the other hand, if the content of Mn is too large, the forgeability and machinability of the alloy steel are reduced, or it is combined with impurities such as S and P contained in the alloy steel to cause internal origin type peeling. It becomes easy to form the hard inclusion which causes. Therefore, the content of Mn in the alloy steel constituting each rolling element is preferably set to 2.0% by mass or less.

[Cr content in alloy steel constituting each rolling element: 0.5 to 2.0 mass%]
Cr functions to improve hardenability, and at the same time, is a carbide forming element and promotes precipitation of carbides that strengthen the material and further refines it. Such an effect is obtained as the Cr content in the alloy steel increases, and when the content is less than 0.5% by mass, the hardenability is lowered and sufficient hardness cannot be obtained. Or the carbides become coarse during the carbonitriding process. On the other hand, if the content of Cr in the alloy steel exceeds 2.0% by mass, a Cr oxide film is formed on the surface of each rolling element during the carbonitriding process. Inhibits diffusion. Therefore, the content of Cr in the alloy steel constituting each rolling element is preferably 0.5 to 2.0 mass% or less, more preferably 0.9 to 1.2 mass%.

[Ratio of Si and Mn in alloy steel constituting each rolling element: 5 or less]
Unlike nitrides produced by tempering, Si—Mn nitride is formed by reacting N with Si while taking Mn. Therefore, if the Mn content is less than the Si content in the alloy steel, precipitation of Si—Mn nitride is not promoted even if N is sufficiently diffused. For the reasons described above, the area ratio is 1% or more on the surface of the alloy steel in which the Si content is 0.3 to 2.2 mass% and the Mn content is 0.3 to 2.0 mass%. In order to deposit less than 10% of Si—Mn nitride, Si / Mn is preferably 5 or less (Mn is contained by 1/5 or more of Si). The lower limit value of the ratio Si / Mn is a value determined from the above-described limit value of the content of Si and Mn (the ratio between the lower limit value of Si and the upper limit value of Mn, 0.3 / 2.0 = 0. 15).

[Size and number of nitrides in alloy steel constituting each rolling element: 100 or more nitrides having an average particle size of 0.05 to 1 μm in an area of 375 μm ² ]
The presence of nitride on the surface (rolling surface) of each rolling element can strengthen this rolling surface, but relatively large nitrides with an average particle size exceeding 1 μm It does not contribute much to strengthening, and it is strengthened more when fine nitrides are dispersed. This is because, in theory of precipitation strengthening, the smaller the distance between the precipitate particles, the better the strengthening ability. Therefore, even if the area ratio of the Si—Mn nitride is the same, the number of precipitated particles is large. This is because the distance between the particles becomes relatively short and the degree to which the rolling surface is strengthened becomes remarkable. In consideration of these matters, the area ratio of the Si—Mn nitride deposited on the rolling surface of each rolling element is in the range of 1 to 10%, and the average particle size is 0.05 to 1 μm. It is preferable to increase the number of nitrides. Specifically, it is preferable that the number of Si—Mn nitrides of 0.05 to ¹ μm is 100 or more in an area of 375 μm ² . On the other hand, when the number of Si—Mn nitrides of 0.05 to 1 μm in the area described above exceeds 2000, the grindability of the surface of each rolling element is deteriorated. Therefore, the upper limit of the number of nitrides is 2000, more preferably 1000.

1 is a partially cut perspective view of a radial ball bearing which is a kind of rolling bearing that is an object of the present invention. FIG. The partial cutaway perspective view of a radial cylindrical roller bearing. The partial cut perspective view of a radial tapered roller bearing. The schematic diagram of the surface part of a track surface for demonstrating the influence which the space | interval of adjacent mountains exerts on generation | occurrence | production of a new surface regarding a roughness curve.

  The feature of the present invention is that, for each rolling element and bearing ring constituting the rolling bearing, the composition of the alloy steel, the N concentration of the surface layer, the amount of retained austenite, the hardness, the area ratio of nitride on the surface, and the compression residual It is the point which suppresses white structure | tissue peeling by specifying a stress appropriately. As for the structure appearing in the drawings, the radial ball bearing 1 shown in FIG. 1, the radial cylindrical roller bearing 8 shown in FIG. 2, and the radial tapered roller bearing 12 shown in FIG. Since it is the same as that of the rolling bearing of a structure, the overlapping description is abbreviate | omitted.

The rolling life evaluation test conducted for confirming the effect of the present invention will be described.
In order to carry out this rolling life test, a single-row deep groove type ball bearing 1 (inner diameter) as shown in FIG. The outer ring 3 and the inner ring 5 constituting the ball bearing 1 having the same reference number 6317 are used for the balls 6 and 6 constituting 85 mm, outer diameter 180 mm, width 41 mm) using 16 kinds of alloy steels shown in Table 2. These balls 6, 6 and the outer ring 3 and the inner ring 5 were assembled into a ball bearing 1, and the ball bearing 1 was subjected to an evaluation test for rolling life.

  The balls 6, 6 and the outer ring 3 and the inner ring 5 were made by the following manufacturing process using 25 types of alloy steels whose compositions were listed in Tables 1 and 2. The numerical values with parentheses in Tables 1 and 2 indicate that they are outside the range defined in the claims (Claims 1 and 2). Further, in steel types 1-D and 1-F in Table 1, Si / Mn is out of the range of claim 2. Further, Comparative Example 1 among the samples described in Table 3 to be described later is a high carbon chromium bearing steel that is generally used for making bearing parts for the balls 6 and 6 and the outer ring 3 and the inner ring 5. Two types (SUJ2, JIS G 4805) were used.

“Manufacturing process of balls 6 and 6”
Each of these balls 6, 6 is a material obtained by cutting a wire made of alloy steel having the composition shown in Table 1 into a predetermined length, and then subjecting it to a ball by sequentially performing header processing and rough grinding processing, then carburizing. Nitriding treatment was performed. In this carbonitriding process, the temperature was held at 800 to 870 ° C. for 8 hours. When the holding temperature exceeds 870 ° C., the nitride of the surface layer portion of the balls 6 and 6 becomes coarse, and the number of fine Si—Mn nitrides decreases. Further, since the solid solubility limit of nitrogen is increased, the amount of nitride is reduced, and a desired area ratio (1 to 10%) cannot be obtained. In the carbonitriding process, a mixed gas atmosphere of Rx gas, enriched gas, and ammonia gas was initially set, the CP value was 1.2 or more, and the flow rate of ammonia gas was 1/5 or more of the flow rate of Rx gas. Further, after the carbonitriding treatment, quenching was performed as it is at 800 to 870 ° C., and then tempering was performed at a temperature in the range of 160 to 270 ° C.

"Manufacturing process of outer ring 3 and inner ring 5"
The outer ring 3 and the inner ring 5 are obtained by cutting a material made of alloy steel having the composition shown in Table 2 into a predetermined size and subjecting it to hot rolling, spheroidizing annealing, and turning, as the outer ring 3 or the inner ring 5. After the shape was adjusted, carbonitriding was performed. In this carbonitriding process, the temperature was maintained at 900 to 980 ° C. for 14 hours. In the carbonitriding process, a mixed gas atmosphere of Rx gas, enriched gas and ammonia gas was used from the beginning, and the CP value was 1.0 or more. Further, after carbonitriding, the steel was kept at 860 to 880 ° C. for 1.5 hours and then quenched, and then tempered in the range of 160 to 200 ° C.

  For any of the balls 6, 6, the outer ring 3, and the inner ring 5, after the heat treatment (quenching and tempering), grinding and finishing were performed. Then, the balls 6, 6, the outer ring 3 and the inner ring 5 obtained in this way are assembled together with the cage 7, and each ball bearing 1 as shown in FIG. 1 is a sample of a rolling life evaluation test. It was. In addition, three samples of the same kind are included in 13 types (Examples 1 to 13) belonging to the technical scope of the present invention (the invention described in claim 2), and 15 types out of the technical scope of the present invention ( A total of 84 samples of 28 types with Comparative Examples 1 to 15) were prepared.

The test conditions of the rolling life evaluation test are as follows.
Load load: Pure radial load of 53.2 kN Rotational speed: 500 to 2000 min ⁻¹ (Rotational speed fluctuation)
Lubricant: High traction oil (synthetic oil for transmission)
The results of experiments conducted under such conditions are shown in Table 3 below along with the properties of the balls 6 and 6, the outer ring 3, and the inner ring 5. The life ratio shown in Table 3 is the ratio of the average life of each example and each comparative example when the average life of Comparative Example 1 is 1.0. Further, as a result of the life evaluation test, in the ball bearing in which peeling occurred, all peeling occurred on the inner ring raceway, and a white structure was observed in the peeling portion. Note that all the race rings in Table 3 are inner rings. This is because the inner ring easily peels preferentially in the rolling life test under the above-described conditions (all the inner ring raceways were peeled even in the actual test). The properties and life of each part described in Table 3 are the average values of three samples of the same kind.

  As is apparent from the results shown in Table 3, Examples 1 to 13 are made of alloy steel having the composition defined in the present invention for any bearing parts of the balls 6 and 6 and the outer ring 3 and the inner ring 5. Because it is manufactured and the properties after heat treatment are within the range specified in the present invention, any ball bearing 1 has a lifespan five times longer than that of a standard SUJ2 ball bearing 1. Extending to the above, no peeling occurred. Furthermore, since Examples 1-8 and 11-13 were in a more preferable range of the composition of the alloy steel constituting the outer ring 3 and the inner ring 5, the effect of delaying the structural change due to hydrogen became particularly excellent. Even when the metal structure of the inner ring cross section after the test was observed, no change in the structure was observed.

  On the other hand, all of Comparative Examples 2 to 15 that deviate from the technical scope of the present invention in any one of the composition of the alloy steel and the properties after the heat treatment are all ball bearings 1 made of SUJ2 (Comparative Example). Even though the life was extended from 1), the rolling life was shorter than in Examples 1-13. Further, in the observation of the metal structure of the inner ring cross section after the test, a change in structure due to hydrogen was observed. The reasons are considered as follows.

First, in Comparative Examples 2 to 5, the composition of alloy steel or Si / Mn constituting the balls 6 and 6 is outside the scope of the present invention. For this reason, a fine and high-hardness Si—Mn nitride that prevents the deterioration of the roughness of the rolling surfaces of the balls 6 and 6 cannot be stably obtained.
Next, in Comparative Example 6, the N concentration of the surface layers of the balls 6 and 6 is low, and the number of fine nitrides having an average particle diameter of 0.05 to 1 μm is small. For this reason, the effect which prevents the deterioration of the roughness of the rolling surface of each said balls 6 and 6 is small.
In Comparative Examples 7 and 8, the hardness of the surface layers of the balls 6 and 6 is low. For this reason, the effect which prevents the deterioration of the roughness of the rolling surface of each of these balls 6 and 6 is small.
In Comparative Example 9, the number of fine nitrides having an average particle size of 0.05 to 1 μm is small. For this reason, the effect which prevents the deterioration of the roughness of a rolling element is small.
As a result, in any of Comparative Examples 2 to 9, the formation of a new surface by the metal contact progressed to the inner ring raceway 4 due to the deterioration of the rolling surfaces of the balls 6 and 6, and the life was shortened. Conceivable.

On the other hand, since the RSm regarding the roughness curves of the outer ring raceway 2 and the inner ring raceway 4 is small, the effect of suppressing the generation of hydrogen due to the reduction of the new surface cannot be obtained and the life of the comparative example 10 is considered to be short. .
Furthermore, in Comparative Examples 11 to 15, the composition of the alloy steel constituting the outer ring 3 and the inner ring 5 is outside the scope of the present invention, and in Comparative Examples 11, 12, 14, and 15, the properties after heat treatment Is also outside the scope of the present invention. For this reason, it is considered that the effect of delaying the change in structure due to hydrogen cannot be sufficiently obtained and the life is short.

The type of the rolling bearing in the case of carrying out the present invention is not particularly limited (the thrust bearing is also an object), but the contact area of the rolling contact portion between the raceway surface and the rolling surface is large, and a lubricating film is formed on the rolling contact portion. As described above, a rolling bearing that is difficult to be stably formed is liable to cause metal contact locally at the rolling contact portion and easily generate hydrogen due to a tribochemical reaction. Is obtained. As such a rolling bearing, each rolling element is a roller bearing such as a cylindrical roller, a tapered roller, or a spherical roller (the invention described in claim 2), or a large-sized ball having a diameter of 30 mm or more. There is a ball bearing (in the case of the invention described in claim 3).
Further, as in the invention described in claim 4, the rolling bearing used in a state incorporated in the rotation support portion of the wind power generator, or the rotation support of the construction machine as in the invention described in claim 5. Since the rolling bearing used in the state incorporated in the part is used under severe conditions such that the rotation speed or the rotation direction frequently changes, the life extension effect according to the present invention can be remarkably obtained.

DESCRIPTION OF SYMBOLS 1 Radial ball bearing 2, 2a, 2b Outer ring raceway 3, 3a, 3b Outer ring 4, 4a, 4b Inner ring raceway 5, 5a, 5b Inner ring 6 Ball 7, 7a, 7b Cage 8 Radial cylindrical roller bearing 9 Cylindrical roller 10 Inward facing Part 11 Outward flange 12 Radial tapered roller bearing 13 Tapered roller 14 Large diameter flange 15 Small diameter flange

Claims (5)

A first race ring made of alloy steel having a first raceway surface on any surface, a second race ring made of alloy steel having a second raceway surface facing the first raceway surface, and the first In a rolling bearing provided with a plurality of rolling elements, each of which is made of alloy steel, and is provided between the second raceway surfaces so as to be freely rollable.
Each rolling element is subjected to carbonitriding or nitriding treatment. The surface layer of each rolling element has an N concentration of 0.2% by mass or more, a residual austenite amount of 30% capacity or less, and a hardness of Hv780. And the area ratio of the nitride of the surface layer of each rolling element is 1% or more and less than 10%,
At least one of the two race rings is 0.10 to 0.30 mass% for C, 0.2 to 0.9 mass% for Si, 0.2 to 1.2 mass% for Mn, Cr is 2.6 to 4.5% by mass, Mo is 0.1 to 0.9% by mass, Ni is 0.9% by mass or less, Cu is 0.20% by mass or less, and S is 0.020% by mass or less. , P each containing 0.020% by mass or less, the balance being made of an alloy steel composed of Fe and inevitable impurities, the surface of which is carburized or carbonitrided, and provided on the raceway. From the surface, the hardness at a depth position of 1% of the diameter of each rolling element is Hv720-832, and the C + N amount, which is the sum of the C content and the N content, is 0.8- 1.2 mass%, the amount of retained austenite is 20 to 45% by volume, and the compressive residual stress is 5 Is ~300MPa,
Regarding the roughness curve of the surface of the raceway surface provided on the raceway, RSm indicating the interval between adjacent peaks is 8 μm or more,
Each said rolling element is 0.3-1.2 mass% for C, 0.3-2.2 mass% for Si, 0.3-2.0 mass% for Mn, and 0.5-2. It is formed by carbonitriding and quenching treatment and tempering treatment on an alloy steel containing 0 mass%, each containing Si / Mn, which is a ratio of Si content and Mn content, of 5 or less, A rolling bearing comprising 100 or more nitrides having an average particle size of 0.05 to 1 μm in an area of 375 μm ² on the surface.   The rolling bearing according to claim 1, wherein each of the rolling elements is a roller.   The rolling bearing according to claim 1, wherein the rolling element is a ball having a diameter of 30 mm or more.   The rolling bearing as described in any one of Claims 1-3 used in the state integrated in the rotation support part of the wind power generator.   The rolling bearing according to any one of claims 1 to 3, wherein the rolling bearing is used in a state of being incorporated in a rotation support portion of a construction machine.

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