JP2015017661A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing for suppressing white tissue separation while reducing its cost, even when used under conditions that current flows between an outer ring 3 and an inner ring 5.SOLUTION: The outer ring 3 as part of a ball bearing 1 is formed of steel containing 0.2-0.6 mass% C, 0.1-0.6 mass% Si, 0.6-1.5 mass% Mn, 0.6-1.8 Cr, and Fe and inevitable impurities for the rest, and subjected to either carburizing or nitrocarburizing treatment and tempering treatment. A residual austenite amount on the top surface of an outer ring raceway 2 is 20-45 vol.%, a C+N amount at a position of a depth X being 1% of the diameter of each of balls 6 and 6 is 0.80-2.00 mass%, and compressive residual stress at the position of the depth X with respect to the peripheral direction of the outer ring 3 and that with respect to the axial direction thereof are 100-500 MPa and 50-500 MPa, respectively.

Description

  The present invention is intended to improve the durability of various rolling bearings, including general rolling bearings such as radial bearings and thrust bearings, and special rolling bearings such as linear motion bearings (linear guides) and ball screws. More specifically, such as a rolling bearing for rotatably supporting the rotating shaft of a rotating electrical apparatus having a rotating shaft such as an electric motor such as a generator, a three-phase motor, or a servo motor, or a generator. Even under severe use conditions where a potential difference is generated between a pair of bearing ring members constituting the rolling bearing and a current flows between these two bearing ring members, It is intended to improve the durability of the rolling bearing including the bearing component by suppressing the structural change of the steel constituting the bearing component including the rolling element (particularly the raceway having severe conditions).

  A radial ball bearing 1 as shown in FIG. 1, which is one type of rolling bearing that is an object of the present invention, is incorporated in a rotation support portion of various rotating electrical 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, the rotary support portion to which a large radial load is applied is also a kind of a rolling bearing which is a subject of the present invention, for example, a radial cylindrical roller using cylindrical rollers 8 and 8 as rolling elements as shown in FIG. A bearing 9 is incorporated. The radial cylindrical roller bearing 9 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 surface, the outer ring raceway 2a and the inner ring raceway 4a. In between, each said cylindrical roller 8 and 8 each provided as a rolling element was provided so that rolling was possible in the state hold | maintained at the holder | retainer 7a. Further, inward flange portions 10 and 10 are formed on the inner peripheral surfaces of both ends of the outer ring 3a, and outward flange portions 11 are formed on the outer peripheral surface of one end portion of the inner ring 5a.

  In addition, the rotating support portion to which a thrust load is applied in addition to a large radial load is also a kind of rolling bearing that is a subject of the present invention, for example, tapered rollers 12 and 12 as rolling elements as shown in FIG. The used radial tapered roller bearing 13 is incorporated. The radial tapered roller bearing 13 includes an outer ring 3b having a tapered outer ring raceway 2b on the inner peripheral surface, an inner ring 5b having a tapered outer ring raceway 4b on the outer peripheral surface, the outer ring raceway 2b and the inner ring raceway 4b. In the meantime, the tapered rollers 12 and 12 are 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.

  Furthermore, under the condition that it is operated in a state of receiving a large radial load and it is difficult to keep the center axis of the outer ring and the center axis of the inner ring in exact agreement, the rolling bearing that is the subject of the present invention is also used. One type of self-aligning roller bearing 16 as shown in FIG. 4 is used. In this self-aligning roller bearing 16, spherical rollers 17 and 17 are used as rolling elements, the bus bar shape of which is a partial arc shape, and the whole is a beer barrel type. Further, the outer ring raceway 2c provided on the inner peripheral surface of the outer ring 3c has a partially spherical concave surface with a point on the central axis of the outer ring 3c as the center of curvature. In addition, double-row inner ring raceways 4c and 4c are provided on the outer peripheral surface of the inner ring 5c. The generatrix shape of both the inner ring raceways 4c and 4c is symmetric with respect to the generatrix shape of the outer ring raceway 2c with respect to the rotation center axis of the spherical rollers 17 and 17. Further, each of the spherical rollers 17 and 17 is rotatably provided between the outer ring raceway 2c and the inner ring raceways 4c and 4c while being held by the cages 7c and 7c, respectively.

  When the various rolling bearings 1, 9, 13, and 16 as shown in FIGS. 1 to 4 are used in the rotation support portion of the rotary electric device as described above, the outer rings 3, 3a that are the pair of bearing ring members. 3b, 3c and the inner rings 5, 5a, 5b, 5c may flow a stray current that is a minute current. When such a stray current flows, the outer ring raceways 2, 2a, 2b, which are the raceways of the outer races 3, 3a, 3b, 3c and the inner races 5, 5a, 5b, 5c, which are both raceway members, 2c, the inner ring raceways 4, 4a, 4b, 4c, and the balls 6, 6, the cylindrical rollers 8, 8, the tapered rollers 12, 12, and the spherical surfaces. Of the surfaces of the rollers 17 and 17, metal is electrochemically melted on the rolling surface which is a portion in rolling contact with the outer ring raceways 2, 2a, 2b and 2c and the inner ring raceways 4, 4a, 4b and 4c. Electric corrosion, which is a form of corrosion that occurs, may occur. The electrolytic corrosion generated in this manner deteriorates the surface roughness of each raceway surface and each rolling surface (rather than a smooth surface) and induces “surface-initiated peeling”. In addition, energization is not always performed stably between the surfaces that are in rolling contact with each other, that is, at a plurality of rolling contact portions existing inside the rolling bearing, and is often performed with sparks. And when a spark generate | occur | produces in any rolling contact part, hydrogen (especially hydrogen atom) will generate | occur | produce based on decomposition | disassembly of the hydrocarbon-type lubricating oil which comprises the lubricant which intervenes in the said rolling contact part. When the hydrogen generated in this way enters the metal material (steel) constituting each bearing component at each rolling contact portion, specifically on the surface portion of the bearing component, specifically, the raceway surface and the rolling element. It is widely known in the technical field of rolling bearings at a depth of about 1% of the rolling element diameter where the shear stress based on the circumferential frictional force generated based on the rolling contact with the rolling surface is maximized. As shown, a “white tissue change” occurs in which the portion changes to white. Hydrogen embrittlement occurs in the white structure portion generated based on such a change, and early exfoliation called white structure exfoliation is likely to occur starting from this white structure.

  The cause of the early peeling of the surface of the bearing part is not only the surface-origin type peeling or white structure peeling as described above, but also “inclusion-origin-type peeling that occurs from the inclusion in the material constituting the bearing part. Is known. In addition, it is known that even when surface-origin type peeling is performed, an indentation in which foreign matter such as dust is bitten is generated as a starting point. Since each of these peelings occurs by different mechanisms, different measures are required for each. The present invention is mainly intended to suppress surface-origin-type peeling caused by surface roughness based on electric corrosion and white structure peeling, and surface roughness and white peeling based on these electric corrosion. In order to suppress this, it is effective to prevent current from flowing through the rolling bearing. For this reason, for example, as described in Patent Document 1, any of the race rings is assembled to a housing or a rotating shaft via an insulating layer. However, the machining of the race rings is troublesome and costly. Is bulky. Also, as described in Patent Documents 2 to 3, a lubricant that fills the rolling bearing and a seal ring that is assembled to the rolling bearing are used, and the gap is generated between a pair of race rings. A large proportion of the current based on the potential difference is allowed to flow through the conductive lubricant or seal ring, and the ratio of the current flowing through the rolling contact portion where the surfaces of the steel bearing parts come into contact with each other can be kept low. Has been done. However, with such a countermeasure, the potential difference generated between a pair of race rings becomes large like the rolling bearing for supporting the rotating shaft of the rotating electrical device described above, and the current flows between the two race rings. Under severe use conditions in which the absolute value of the current increases, white tissue peeling as described above cannot be sufficiently suppressed. For example, in the case of a rolling bearing incorporated in a rotation support portion of a wind power generator, a large potential difference is likely to occur between the inner ring and the outer ring, and the required durability (maintenance-free operation time) is also 20 to 30 years. For this reason, it is not sufficient to take only measures using the lubricant and the seal ring.

JP 2009-287658 A JP 2009-210079 A JP 2009-264401 A

  In view of the circumstances as described above, the present invention is used under severe conditions in which a potential difference generated between a pair of race rings becomes large, such as a rolling bearing for supporting a rotating shaft of an electric device. Even in this case, the present invention has been invented to realize a rolling bearing capable of sufficiently suppressing surface-origin type peeling and white structure peeling based on electrolytic corrosion while suppressing cost.

  The rolling bearing according to the present invention includes the radial ball bearing 1, the radial cylindrical roller bearing 9, the radial tapered roller bearing 13, and the self-aligning roller bearing 16 shown in FIGS. As with the bearing, a first race ring having a first raceway surface on any surface, a second race ring having a second raceway surface on a surface opposite to the first raceway surface, and these A plurality of rolling elements provided between the first and second raceway surfaces so as to be freely rollable. Moreover, each of these rolling elements is hold | maintained so that rolling is possible with a holder | retainer as needed.

  In particular, in the rolling bearing of the present invention, at least one of the first and second bearing rings has C of 0.20 to 0.60 mass% and Si of 0.10 to 0. .60 mass%, Mn 0.60 to 1.50 mass%, Cr 0.60 to 1.80 mass%, Mo 0.00 to 0.40 mass%, Ni 0.00 to 0.20 The steel is made of steel containing 0.00% to 0.20% by mass of Cu and the balance being Fe and inevitable impurities. Among the inevitable impurities, the content of S, P and O is preferably regulated. Specifically, it is preferable to regulate S to 0.020 mass% or less, P to 0.020 mass% or less, and O to 15 massppm or less.

Then, the outermost surface of the raceway surface provided on the at least one raceway by subjecting the at least one raceway to quenching treatment and tempering treatment which are either carburizing treatment or carbonitriding treatment. The amount of retained austenite is 20 to 45% by volume.
Further, when X is a length of 1% of the diameter of each rolling element (the maximum diameter in the case of balls, the diameter of the rolling contact portion in the case of rollers), the at least one of the raceways The C + N amount, which is the sum of the C content and the N content at the position of depth X from the surface of the raceway surface provided in the ring, is 0.80 to 2.00% by mass.
Further, the compressive residual stress in the circumferential direction of the raceway at the position of the depth X from the surface of the raceway surface provided on the at least one raceway is set to 100 to 500 MPa, and the compressive residual stress in the axial direction is also set to 50. ˜500 MPa.

  When carrying out the present invention as described above, preferably, as in the invention described in claim 2, each of the rolling elements is composed of 0.80 to 1.20% by mass of C and 0.10 to 0 of Si. 70 mass%, Mn 0.20 to 1.20 mass%, Cr 0.90 to 1.80 mass%, Mo 0.00 to 0.25 mass%, Ni 0.00 to 0.20 The steel is made of steel containing Fe and unavoidable impurities. Among the inevitable impurities, the content of S, P and O is preferably regulated. Specifically, it is preferable to regulate S to 0.020 mass% or less, P to 0.020 mass% or less, and O to 10 mass ppm or less.

  And by subjecting each rolling element made of steel having such a composition to carbonitriding and quenching treatment and tempering treatment, the surface hardness of the rolling surface of each rolling element is set to HRC 63 to 67. At the same time, the amount of retained austenite on the outermost surface of each rolling element is set to 20 to 40% by volume. Further, when the length of 1% of the diameter of each rolling element is X, the N amount at the position of the depth X from the surface of each rolling element is 0.05 to 2.00% by mass. The compressive residual stress at the position X is set to 500 to 900 MP.

  Moreover, when implementing this invention, Preferably the grease which is a lubrication agent is filled into the bearing internal space in which each said rolling element was installed. The thickener of this grease is a diurea compound, the rust inhibitor is one or more selected from naphthenate, succinic acid, and derivatives thereof, and the antioxidant is also phenolic. One or more selected from a compound and an amine compound, and the extreme pressure additive is an organometallic salt of a dialkyldithiocarbamic acid (DTC) compound and a dialkyldithiophosphate (DTP) compound It is set as 1 type or 2 types or more selected from.

In carrying out the present invention, it is preferable that carbon black having an average particle diameter of 10 to 300 nm, which is a conductive substance, is used as a lubricant that fills the bearing internal space in which the rolling elements are installed. A grease composition containing ˜20% by weight is used.
In carrying out the present invention, preferably, in order to close the opening end of the bearing internal space where the rolling elements are installed, a conductive sealing plate is used between the first and second raceways. It is installed in a state where it is hung between them, and these both race rings can be energized through the seal plate.

  As described above, the rolling bearing of the present invention performs carburizing or carbonitriding on at least one of the bearing rings, and determines the amount of retained austenite on the outermost surface of the bearing ring and the diameter of the rolling element from the surface of the bearing ring. Since the compressive residual stress at the depth of 1% is increased, the surface starting point starting from this rough surface after the occurrence of rough surface and white structure due to electrolytic corrosion while suppressing the increase in production cost. The mold peeling and white texture peeling starting from the white texture can be suppressed, and the life of the entire rolling bearing can be extended.

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 partial cutaway perspective view of a self-aligning roller bearing.

  The inventors of the present invention have repeated a number of experiments and comparatively verified the respective results to thereby determine the surface of the raceway, which is subjected to shear stress based on repeated rolling contact, from the rolling surfaces of a plurality of rolling elements. Increasing the amount of retained austenite on the outermost surface of the steel has the effect of alleviating metal fatigue at the outermost surface, making it difficult for “surface-origin-type delamination” to occur. I found that I can extend Further, of the surface portion of the raceway, the depth position of 1% of the diameter of the rolling element from the raceway surface (the depth from the raceway surface when X is the length of 1% of the diameter of each rolling element) When high compressive residual stress is applied to the X position, it has the effect of suppressing the progress of cracks generated from the white structure change that occurred internally due to electrolytic corrosion, extending the life of rolling bearings related to white structure peeling. I found what I could do.

  Specifically, by controlling the amount of retained austenite on the outermost surface of the raceway surface to 20 to 45% by volume by carburizing treatment or carbonitriding treatment, Life can be extended. Further, the C + N amount (content of C and N) at a depth position of 1% of the diameter of the rolling element from the surface of the raceway surface in the surface portion of the raceway is 0.80 to 2.00% by mass. At the same time, if the compressive residual stress at this position is set to 100 to 500 MPa in the circumferential direction of the race, and similarly set to 50 to 500 MPa in the axial direction, the life of the rolling bearing related to the white tissue peeling can be extended.

  In addition, such surface-origin type peeling and white structure peeling that lead to a reduction in the life of the rolling bearing, as long as the usage conditions of the rolling bearing are the same, a plurality of rolling elements whose rolling contact surface changes (especially the rotating shaft is Compared with the rolling surface of the changing ball), the raceway surfaces of both the raceways that are in rolling contact with the rolling surface of each of these rolling elements at the same part (the entire circumferential surface where the axial position is constant) (in particular, The shape in the circumferential direction is a convex surface and is likely to occur in an inner ring raceway where the surface pressure of the rolling contact portion increases. Therefore, as in the present invention, a bearing part that adjusts the amount of retained austenite on the outermost surface and the value of the compressive residual stress on the surface portion can obtain a remarkable effect by using a bearing ring rather than a rolling element.

  However, the electrolytic corrosion that leads to the surface-origin peeling and the white tissue peeling also occurs on the surface (rolling surface) of a plurality of rolling elements, and when it occurs, it is the same as when it occurs on the raceway surface of the raceway ring. The mechanism may reduce the life of the rolling bearing. In order to suppress such a decrease in the life of the rolling bearing due to the electrolytic corrosion of the rolling surface, it is effective to give the rolling elements the same properties as the raceway. That is, even if each of these rolling elements is subjected to a heat treatment including a carbonitriding quenching process and a tempering process to adjust the properties of the rolling surface, the life of the rolling bearing can be further extended. Specifically, as in the invention described in claim 2, the steel rolling elements having a predetermined composition are subjected to the heat treatment, and the surface hardness of each of these rolling elements is set to HRC 63 to 67. The amount of retained austenite on the outermost surface is 20-40% by volume, and the depth position of 1% of the diameter of the rolling element from the surface of each rolling element (when the length of 1% of the diameter of each rolling element is X) The N amount (the content of N) at the depth X from the surface of each rolling element is preferably 0.05 to 2.00% by mass, and the compressive residual stress at the same position is preferably 500 to 900 MPa. .

  Furthermore, the hydrogen that causes white structure peeling is decomposed by the sparks generated at the rolling contact portions of the base oil and other components of the grease existing in the rolling contact portions in a state where the rolling bearing is filled. Therefore, it is also preferable to use a stable grease that is difficult to be decomposed by this spark as the grease, from the viewpoint of suppressing a decrease in the life of the rolling bearing due to electrolytic corrosion of the raceway surface and the rolling surface. . Specifically, as an additive for the grease, a thickener composed of a diurea compound, a rust preventive material composed of one or more selected from naphthenates, succinates and derivatives thereof, phenolic One or more antioxidants selected from among compounds and amine compounds, one selected from dialkyldithiocarbamic acid compounds and dialkyldithiophosphate compounds that are organometallic salts, or A mixture of two or more extreme pressure additives is used. By using such a grease as a lubricant, generation of hydrogen from the lubricant can be suppressed, and a rolling bearing having a longer life can be provided.

  Further, since the spark is generated based on a potential difference existing between the two race rings, the potential difference existing between the two race rings is obtained by electrically connecting the two race rings. Reduction or elimination is also preferable from the viewpoint of suppressing a decrease in the life of the rolling bearing due to the electric corrosion of the raceway surface and the rolling surface. Specifically, a grease composition containing 0.5 to 20% by mass of carbon black having an average particle diameter of 10 to 300 nm is used as a lubricant as a conductive material. Alternatively, a conductive seal plate is used to enable energization between the inner ring and the outer ring.

  Hereinafter, the present invention will be described in more detail. The feature of the present invention is that, as described above, at least of the bearing parts constituting the rolling bearing, the steel constituting the bearing ring is used. By appropriately regulating the composition, the amount of retained austenite on the outermost surface of the raceway surface, the amount of C + N at a predetermined position on the raceway surface, and the value of compressive residual stress, the white tissue peeling that occurs from the white structure based on hydrogen penetration It is in the point to suppress. On the other hand, the structures appearing in the drawings include the radial ball bearing 1, the radial cylindrical roller bearing 9, the radial tapered roller bearing 13, and the self-aligning roller bearing 16 shown in FIGS. Since it is the same as that of various rolling bearings, the overlapping description is omitted.

(1) Regarding both races First, the races corresponding to the first aspect of the invention will be described.

[Amount of retained austenite on the outermost surface of the raceway: 20 to 45% by volume]
Residual austenite is usually a soft structure. For this reason, it has the effect of relieving the stress concentration generated at the edge portion around the scratches and indentations on the raceway surface and suppressing the occurrence of cracks. Such an effect can be obtained not only in the case of mechanically generated scratches and indentations, but also on the raceway surface roughened by the electrolytic corrosion marks which are minute dents caused by electrochemical corrosion. In this case, the greater the amount of retained austenite, the greater the effect of suppressing surface-origin separation. When the amount of retained austenite on the outermost surface of the raceway surface is less than 20% by volume, the effect of relaxing the stress concentration generated at the edge portion is insufficient as described above. For example, wind power generation as described above In the case of a rolling bearing incorporated in the rotary support portion of the machine, sufficient durability cannot be obtained. In contrast, when the amount of retained austenite on the outermost surface of the raceway surface exceeds 45% by volume, not only the effect of relaxing the stress concentration is saturated, but also the hardness of the raceway surface is excessively reduced. Therefore, it is difficult to secure a rolling fatigue life, and it is difficult to ensure the durability of the rolling bearing. Therefore, the amount of retained austenite on the outermost surface of the raceway surface after performing the quenching process which is one of the carburizing process or the carbonitriding process is restricted to a range of 20 to 45% by volume.
In the present invention, the amount of retained austenite on the outermost surface of the raceway surface is a value obtained by measuring the amount of retained austenite from the outermost surface of the orbital surface to 10 μm using an X-ray diffractometer. means.

[Amount of C + N from the surface of the raceway surface to a 1% depth position of the diameter of the rolling element: 0.80 to 2.00% by mass]
The amount of C + N in this portion is regulated to ensure the hardness of this portion and to make the amount of retained austenite in this portion an appropriate value. That is, the hardness and residual austenite amount of the raceway surface of the raceway after the carburizing treatment or carbonitriding treatment and tempering treatment, which is a quenching treatment, are applied to the steel raceway. The amount of C + N penetrated into the steel by nitriding treatment is affected. In particular, a depth position of 1% of the diameter of the rolling element from the surface of the raceway surface (hereinafter referred to as “1% depth position”) is generated based on the rolling contact between the raceway surface and the rolling surface of the rolling element. The shear stress based on the circumferential frictional force is substantially maximized. If the hardness at the maximum shear stress position is insufficient, the rolling fatigue life of the raceway surface of the raceway is reduced.
Further, by setting the amount of C + N at the 1% depth position to 0.80 to 2.00% by mass, it is possible to make the amount of retained austenite at the 1% depth position suitable. That is, the amount of retained austenite at the 1% depth position can be set to a preferable value of 15 to 40% by volume. The retained austenite at the 1% depth position has an effect of trapping hydrogen to prevent local accumulation and suppressing the generation of white structure.

  In addition, when the amount of C + N at the 1% depth position is less than 0.80% by mass, the hardness becomes insufficient, and it is difficult to ensure the rolling fatigue life of the raceway surface. It becomes difficult to ensure the amount of retained austenite at the 1% depth position. On the other hand, when the amount of C + N at the 1% depth exceeds 2.00% by mass, not only the effect is saturated, but also the time required for the carburizing process or the carbonitriding process becomes long, and the trajectory The surface becomes unnecessarily hard, and the finishing of the raceway surface becomes troublesome, which causes an increase in cost. Therefore, the C + N amount at the 1% depth position is restricted to a range of 0.80 to 2.00% by mass, preferably 0.80 to 1.10% by mass.

[Regarding the compressive residual stress of the surface portion of the bearing ring, the circumferential value of the bearing ring at the 1% depth position: 100 to 500 MPa, also the axial value: 50 to 500 MPa]
As described above, hydrogen penetrates locally into the steel constituting the raceway based on electrolytic corrosion, so that the white structure is generated on the surface portion of the raceway. When this white structure is generated, microcracks are generated from the interface with the normal structure. However, if compressive residual stress exists on the surface portion of the raceway, including the boundary between the white tissue and normal tissue, the compressive residual stress suppresses the progress (increase) of the crack, and the raceway ring There is an effect of remarkably extending the time from the white texture existing on the surface portion of the raceway surface to the white texture peeling.
In general, cracks occur on the raceway surface and rolling surface of the bearing parts that make up the rolling bearing, including the white texture separation, and the growth is generally due to the shear stress associated with the movement of the rolling element (revolution motion). By change. Therefore, it is effective to secure (increase) the compressive residual stress in the circumferential direction of the race. However, cracks with white texture changes partially develop in random directions, and in order to sufficiently suppress white texture peeling in all directions, the axial residual compressive stress is also This is necessary.

  Of the compressive residual stress in each direction, the compressive residual stress in the circumferential direction of the raceway is gradient between the surface and the interior to the solid solution concentration of C in the base structure of the raceway surface by carburizing or carbonitriding. (By increasing the surface C concentration and increasing the volume) can be applied. Therefore, the magnitude of the compressive residual stress in the circumferential direction changes the concentration gradient of the solute carbon by changing one or both of the holding temperature and time during the heat treatment that is carburizing or carbonitriding. Can be adjusted by. In any case, if the value of the compressive residual stress in the circumferential direction is less than 100 MPa, the effect of suppressing the white tissue peeling cannot be sufficiently obtained. On the other hand, if the compressive residual stress generated in the raceway surface portion based on the heat treatment is too high, it means that this raceway surface portion is over-carburized. When the raceway surface portion is overcarburized, the grindability and toughness of the raceway surface are lowered, which causes an increase in manufacturing cost and a decrease in durability. Therefore, the maximum value of the compressive residual stress in the circumferential direction is set to 500 MPa that can be applied in a range in which the raceway surface portion does not become overcarburized.

On the other hand, also regarding the magnitude of the compressive residual stress in the axial direction, one or both of the holding temperature and time during the heat treatment that is carburizing treatment or carbonitriding treatment is changed to change the concentration gradient of solute carbon. It can be adjusted by things. The axial compressive residual stress need not be as large as the circumferential compressive residual stress value. However, when the value of the compressive residual stress in the axial direction is less than 50 MPa, the effect from the aspect of sufficiently suppressing white tissue peeling in all directions becomes insufficient. On the other hand, when the axial compressive residual stress is too high, the same problem occurs as when the circumferential compressive residual stress is too high. Therefore, the maximum value of the axial compressive residual stress is set to 500 MPa. It was.
From the viewpoint of more effectively suppressing white tissue peeling, it is preferable to set the compressive residual stress in the circumferential direction of the raceway to 300 to 500 MPa and the axial compressive residual stress to 300 to 500 MPa.

Hereinafter, an essential additive component of steel constituting the bearing ring of the present invention, specifically, an additive amount (content) of C, Si, Mn and Cr will be described.
[C content in steel constituting the bearing ring: 0.20 to 0.60 mass%]
C is an element that dissolves in the base by quenching and improves the hardness, and is added to ensure the hardness required for the bearing parts. If the C content in the steel is less than 0.20% by mass, the hardness of the core after quenching is insufficient, and the rigidity of the raceway is reduced (insufficient). Therefore, C is contained in an amount of 0.20% by mass or more, preferably 0.25% by mass or more. On the other hand, if the C content in the steel exceeds 0.60% by mass, the resulting bearing part becomes too hard, resulting in a decrease in grindability and a decrease in fracture toughness value due to insufficient toughness of the core. . Therefore, the C content is set to 0.60% by mass or less, preferably 0.55% by mass or less. In addition, although the surface is hard when carburizing or carbonitriding is performed, the hardness decreases toward the inside, but in this specification, the portion where the hardness is reduced and becomes constant is defined as the core.

[Si content in steel constituting the bearing ring: 0.10 to 0.60 mass%]
Si has the effect of improving the hardenability and temper softening resistance by dissolving in the base and is added to ensure the necessary hardness for the bearing parts. In addition, Si stabilizes martensite in the base structure, delays the white texture change of the raceway surface portion of the front raceway due to hydrogen, delays the occurrence of the white tissue peeling, and incorporates this raceway. Contributes to extending the life of rolling bearings. Such a life extension effect due to the delay of the white structure change cannot be sufficiently obtained when the Si content is less than 0.10% by mass. On the other hand, when the Si content exceeds 0.60% by mass, not only carburization and carbonitriding properties are deteriorated, but also the hardness after spheroidizing annealing is increased, so that turning properties and cold workability are reduced. To do. In order to suppress the hardness after carburizing, carbonitriding, and spheroidizing annealing to an appropriate range, and to obtain stable turning and cold workability, the Si content is preferably 0.50% by mass or less. suppress.

[Mn content in steel constituting the raceway: 0.60 to 1.50 mass%]
Mn has the effect of improving the hardenability by dissolving in the base, so it is added to ensure the necessary hardness for the race. Mn also has the effect of suppressing the occurrence of white tissue peeling, which is an important object of the present invention, as in the case of Si described above. That is, Mn also stabilizes the martensite in the base structure, delays the white structure change that occurs around the non-metallic inclusions, suppresses the occurrence of white structure peeling on the track ring, and incorporates this track ring. Contributes to extending the life of rolling bearings. Further, Mn has an effect of easily generating retained austenite after heat treatment. Residual austenite is a relatively soft structure, and suppresses the above-described surface-origin type peeling, and contributes to extending the life of the rolling bearing incorporating the raceway from another viewpoint. Such an effect cannot be sufficiently obtained when the Mn content is less than 0.60 mass%. On the other hand, when the content of Mn exceeds 1.50% by mass, the deformation resistance during hot forging increases, and the hot forgeability at the time of manufacturing the raceway is reduced. In addition, the retained austenite in the steel is a relatively soft structure, and the presence of excess austenite is disadvantageous in terms of ensuring the rolling fatigue life of the raceway surface in the raceway. Furthermore, the retained austenite in the steel constituting the bearing ring is gradually decomposed with the use of the rolling bearing, and the volume expands, albeit slightly, with the decomposition. For this reason, if the amount of retained austenite becomes excessive by increasing the content of Mn, not only will it be difficult to ensure the rolling fatigue life of the raceway surface, but the stability of the shape and dimensions of the raceway will be reduced. Therefore, the content of Mn in the steel constituting the race is set to a range of 0.60 to 1.50% by mass, preferably 0.70 to 1.40% by mass.

[Cr content in steel constituting the raceway: 0.60 to 1.80 mass%]
Cr is distributed into a part that dissolves in the base martensite and a part that dissolves in the spheroidized carbide. Cr dissolved in the martensite at the base has the effect of improving the hardenability and ensuring the hardness of the raceway surface of the raceway. Moreover, it combines with C to form carbides, and has the effect of improving wear resistance and rolling fatigue life. Furthermore, Cr also has the effect of extending the life by delaying the structural change caused by hydrogen in order to stabilize the carbide and martensite of the base structure, as in the case of Si and Mn. Such an effect cannot be sufficiently obtained when the Cr content is less than 0.60 mass%. On the other hand, if the Cr content exceeds 1.80% by mass, the carburizing properties and carbonitriding properties decrease, the temperature required to ensure the hardness of the raceway surface increases, and the productivity of the raceway decreases. In addition to increasing the hardness after spheroidizing annealing, the turning and cold workability are reduced. Therefore, the Cr content in the steel constituting the bearing ring is set to a range of 0.60 to 1.80 mass%. In order to further stabilize the turning property and the cold workability, the Cr content is preferably 1.70% by mass or less.

Subsequently, among the contents of selective additive components (Mo, Ni, Cu) of steel constituting the bearing ring of the present invention, and the inevitable impurities, it is particularly preferable to regulate the content (S, The content of P, O) will be described.
[Mo content in steel constituting the bearing ring: 0.00 to 0.40 mass%]
Mo is dissolved in the base and has the effect of improving the hardenability and temper softening resistance and ensuring the hardness of the raceway surface of the raceway. Further, Mo also has an effect of suppressing the occurrence of white tissue peeling as in the case of Si, Mn, and Cr described above. That is, Mo also has an effect of stabilizing martensite in the base structure and delaying the white structure change due to hydrogen. In addition, by delaying the butterfly structure change that occurs around oxide inclusions and sulfide inclusions, it is possible to suppress the occurrence of inclusion-origin separation on the bearing ring, and the life of rolling bearings incorporating this bearing ring Contributes to extension. However, if the Mo content exceeds 0.40% by mass, a part of Mo forms a hard carbide, which reduces grindability. Moreover, since it is an expensive element, it causes an increase in the manufacturing cost of the rolling bearing including the raceway. Therefore, the Mo content was regulated to 0.00 to 0.40 mass%. In addition, it is preferable to make content of Mo into 0.01-0.15 mass% from a viewpoint of acquiring the said effect fully, suppressing manufacturing cost.

[Ni content in steel constituting the bearing ring: 0.00 to 0.20% by mass]
Ni is an element having an effect of improving hardenability and an effect of stabilizing austenite. Further, when added in a large amount, Ni improves toughness. However, since it is an expensive element, it causes an increase in the manufacturing cost of the rolling bearing including the raceway. Therefore, the Ni content is regulated to 0.00 to 0.20 mass%. In addition, it is preferable that content of Ni shall be 0.01-0.18 mass% from a viewpoint which fully obtains the said effect, suppressing manufacturing cost.

[Cu content in steel constituting the bearing ring: 0.20 mass% or less]
Cu has the effect of improving the hardenability and the effect of improving the grain boundary strength. However, when the Cu content increases, hot forgeability decreases. Therefore, the Cu content was regulated to 0.00 to 0.20 mass%. In addition, in order to acquire the said effect fully, it is necessary to make Cu content 0.01 mass% or more.

[S content in steel constituting raceway ring: 0.020 mass% or less]
Since S forms MnS, and this MnS acts as an inclusion and becomes the starting point of inclusion starting type peeling, the smaller the amount of S contained in the steel, the better. However, S is an element that exists abundantly in nature, and trying to keep the S content extremely low reduces the productivity of steel materials (steel materials) for making bearing rings, and the manufacturing costs of steel materials. Increases, making it difficult to use widely in industry. On the other hand, even if S is contained in an amount of about 0.020% by mass, the content of other elements and the heat treatment method can be made appropriate to suppress the occurrence of the inclusion-origin-type separation, and the durability required for the bearing ring can be improved. It can be secured. Therefore, the upper limit of the S content is set to 0.020% by mass.

[P content in steel constituting the bearing ring: 0.020 mass% or less]
P is preferably as small as possible because it segregates at the grain boundaries and lowers the grain boundary strength and fracture toughness value. However, P is also an element that exists in a large amount in nature. If an attempt is made to keep the P content extremely low, the manufacturing cost of the steel material will increase. On the other hand, even if P is contained in an amount of about 0.020% by mass, durability required for the race can be ensured by making the content of other elements and the heat treatment method appropriate. Therefore, the upper limit of the P content is set to 0.020% by mass.

[Content of O in steel constituting raceway ring: 15 mass ppm or less]
O forms oxide inclusions such as Al ₂ O ₃ in the steel. Oxide inclusions are hard and serve as starting points for inclusion-origin separation, and have a great adverse effect on the rolling fatigue life of the raceway surface. Therefore, the smaller the O content, the better. However, with regard to O as well, the steel material cost increases when the content is extremely reduced. On the other hand, even if O is contained in an amount of about 15 mass ppm, the content of other elements and the heat treatment method can be made appropriate. The required durability can be ensured. Therefore, the upper limit of the O content was set to 15 ppm by mass.

(2) About each rolling element Next, it respond | corresponds to the invention described in Claim 2, and demonstrates each said rolling element.
For each of these rolling elements, basically, a general high-carbon chromium bearing steel type 2 (SUJ2, JIS G 4805) material subjected to general quenching (tempering) treatment and tempering treatment. Can be used. However, in order to extend the life of the rolling bearing as a whole under severe conditions such as the rolling contact surfaces of these rolling contact surfaces do not change, the rolling elements can be sufficiently expanded. It is preferable that the composition of the steel constituting the steel is limited as in the invention described in claim 2, and the steel material is further subjected to carbonitriding and quenching to have the properties defined in claim 2. . The specific matters of the invention described in claim 2 will be described below.

[Surface hardness of rolling elements: HRC63-67]
In the white structure, hydrogen in the steel constituting the steel bearing parts (the bearing ring and the rolling elements) causes local plastic deformation, so that the martensite of the base structure of the steel becomes ultrafine particles. It has changed to a ferrite structure. Therefore, in order to delay the formation of the white texture on the surface of each rolling element, it is effective to increase the surface hardness of each rolling element to make it difficult to plastically deform. Such an effect cannot be sufficiently obtained when the surface hardness is less than HRC63. In order to obtain the effect of stably delaying the formation of the white structure, more preferably, the surface hardness of each rolling element is set to HRC 64.5 or more. However, if the surface hardness exceeds HRC67, the toughness of the rolling surface of each rolling element is reduced, and the rolling surface of each rolling element is likely to be damaged, such as a crack. This is disadvantageous in terms of ensuring durability. Therefore, the surface hardness of the rolling elements was set to HRC63-67.
The surface hardness of each rolling element can be adjusted by the carbon and nitrogen concentrations, the quenching temperature, the tempering temperature, and the ball peening processing conditions by the carbonitriding and quenching treatment.

[Amount of retained austenite on the outermost surface of the rolling element: 20 to 40% by volume]
As described in the previous section of the raceway, retained austenite is usually a soft structure, so it exists on the rolling surface that is roughened by electrolytic corrosion, as well as scratches and indentations on the rolling surface that is the outermost surface of the rolling element. The stress concentration generated at the edge portion around the galvanic corrosion mark is alleviated and the generation of cracks is suppressed. Such an effect cannot be sufficiently obtained when the amount of retained austenite is less than 20% by volume, as in the case of the raceway. On the other hand, since each rolling element requires higher rigidity than the raceway, the core is hardened using a material containing a large amount of carbon. Therefore, if the amount of retained austenite on the outermost surface exceeds 40% by volume, the amount of retained austenite inside also increases, and for the reason explained in the above-mentioned raceway part, dimensional stability and shape stability are lowered. May end up.
In addition, it is preferable to make the said retained austenite amount into 30-40 volume% from a viewpoint of suppressing generation | occurrence | production of a crack more effectively.
In the present invention, the amount of retained austenite on the outermost surface of the rolling element is a value obtained by measuring the amount of retained austenite from the outermost surface of the rolling element to 10 μm using an X-ray diffractometer. means.

[N content at 1% depth from the rolling element surface: 0.05 to 2.00% by mass]
By carbonitriding and quenching for hardening the rolling surface of each rolling element, N that has entered and diffused from the surface of each rolling element has a higher concentration on the surface and lowers toward the inside. . High concentration of N near the surface forms Si-Mn nitride. On the other hand, the low concentration of N diffused inside has an effect of stabilizing the retained austenite. Therefore, by diffusing a small amount of N up to the 1% depth position, the retained austenite at that position can be stabilized, and the effect of delaying the white structure change due to the retained austenite as described above can be enhanced. Such an effect cannot be sufficiently obtained when the N amount at the 1% depth position is less than 0.05 mass%. For this reason, the N amount at the 1% depth position is set to 0.05% by mass or more. On the other hand, when the N amount at the 1% depth position exceeds 2.00% by mass, the effect is saturated. For this reason, the N amount at the 1% depth position is 2.00% by mass or less, preferably 0.30% by mass or less.
The N amount (concentration) at the 1% depth position is obtained by changing at least one of the nitrogen potential and the holding time in the atmospheric gas when the rolling elements are subjected to carbonitriding and quenching. Can be adjusted.

[Compressive residual stress at 1% depth from the rolling element surface: 500 to 900 MPa]
As for the rolling surfaces of the rolling elements, as in the case of the raceway surface of the raceway, cracks are formed at the boundary between the white structure and the normal structure by causing a compressive residual stress to exist at the 1% depth position. This has the effect of suppressing the progress of the above and extending the time until the white tissue is peeled off starting from the white tissue existing on the surface portion of the rolling surface of each rolling element.
In the case of each rolling element, the compressive residual stress can be imparted also by the effect of plastic working by ball peening performed after polishing of the respective rolling surfaces. For this reason, the value of the compressive residual stress that can be applied to the rolling surface portion of each rolling element is higher than the compressive residual stress that can be applied to the raceway surface of the raceway. In addition to changing the concentration gradient of the solute carbon by changing at least one of the holding temperature and time during the carbonitriding and quenching treatment, the magnitude of this compressive residual stress is also the drum during ball peening processing. It can also be adjusted by changing at least one of the rotation speed and the machining time. As described above, the development of the microcrack generated from the interface between the white structure and the normal structure can be suppressed by causing a compressive residual stress to exist at the 1% depth position. However, when the value of this compressive residual stress is less than 500 MPa, the effect of suppressing the crack propagation cannot be sufficiently obtained as far as the rolling surface of each rolling element is concerned. On the other hand, when the value of the compressive residual stress exceeds 900 MPa, cracks are caused by the action of tensile stress generated in each of the rolling elements with a size that balances the compressive residual stress at the 1% depth position. There is a possibility that progress will be promoted. Therefore, the compressive residual stress at the 1% depth position of each rolling element is set to 500 to 900 MPa, preferably 600 to 850 MPa. The reason why the value of the compressive residual stress at the 1% depth position of each rolling element is higher than that in the case of the raceway is that each rolling element is in a non-load zone, In order to support a load from a state where it does not rotate at a speed corresponding to the revolution speed, and to receive a large slip locally when entering a load zone that needs to rotate at a speed corresponding to the revolution speed. This is because cracks tend to develop.

Hereinafter, an essential additive component of steel constituting each rolling element of the present invention, specifically, an additive amount (content) of C, Si, Mn, and Cr will be described.
[C content in steel constituting each rolling element: 0.80 to 1.20 mass%]
C is an element that improves the hardness by solid solution by quenching as described above in the raceway part, but when the C content in the steel is less than 0.80% by mass. However, the hardness of the rolling surface of each rolling element cannot be sufficiently ensured, and it becomes difficult to secure the wear resistance and rolling fatigue life of the rolling surface of each rolling element. Further, when the carbonitriding and quenching treatment is performed on each of these rolling elements, the time required for the carbonitriding and quenching process becomes long, and the productivity of these rolling elements is reduced. On the other hand, when C is added excessively (exceeding 1.20% by mass), the respective rolling elements become too hard, and the grindability and fracture toughness value of these rolling elements are reduced. In consideration of these matters, the C content in the steel constituting each rolling element is 0.80 to 1.20% by mass (in order to stably obtain the above-described effect, more preferably 0.90). To 1.10% by mass).

[Si content in steel constituting each rolling element: 0.10 to 0.70 mass%]
Si is added to secure the necessary hardness for bearing parts because it has the effect of improving the hardenability and temper softening resistance by dissolving in the base as described above in the race. To do. And Si stabilizes the martensite in the base structure, delays the white texture change of the rolling surface portion of each rolling element due to hydrogen, delays the occurrence of the white tissue peeling, these rolling elements Contributes to extending the life of the built-in rolling bearing. Such a life extension effect due to the delay of the white structure change cannot be sufficiently obtained when the Si content is less than 0.10% by mass. On the other hand, when the Si content exceeds 0.70% by mass, turning properties and cold workability are deteriorated. Therefore, the Si content is set to 0.10 to 0.70 mass%, preferably 0.20 to 0.60 mass%.

[Mn content in steel constituting each rolling element: 0.20 to 1.20 mass%]
Mn is added to secure the necessary hardness for each rolling element because it has the effect of improving the hardenability by dissolving in the base as described in the above-mentioned raceway part. Mn also has the effect of suppressing the occurrence of white tissue peeling, which is an important object of the present invention, as in the case of Si described above. That is, Mn also stabilizes the martensite in the base structure, delays the white structure change that occurs around the non-metallic inclusions, and suppresses the occurrence of white tissue peeling on each of the rolling elements. Contributes to extending the life of rolling bearings incorporating Further, Mn has an effect of easily generating retained austenite after heat treatment. Residual austenite is a relatively soft structure, and suppresses the above-described surface-originating separation, and contributes to extending the life of the rolling bearing incorporating the rolling elements from another viewpoint. Such an effect cannot be sufficiently obtained when the Mn content is less than 0.20% by mass. On the other hand, if the content of Mn exceeds 1.20% by mass and the amount of retained austenite becomes excessive, it is difficult not only to ensure the rolling fatigue life of the rolling surface of each rolling element, but also the shape of each rolling element. And dimensional stability is reduced. Therefore, the Mn content in the steel constituting each of the rolling elements is set to a range of 0.20 to 1.20 mass%.

[Cr content in steel constituting each rolling element: 0.90 to 1.80 mass%]
As described in the above-mentioned raceway part, Cr is also dissolved in the martensite of the base, improving the hardenability and ensuring the hardness of the rolling surface of each rolling element. . Moreover, it combines with C to form carbides, and has the effect of improving wear resistance and rolling fatigue life. Furthermore, Cr also has the effect of extending the life by delaying the structural change caused by hydrogen in order to stabilize the carbide and martensite of the base structure, as in the case of Si and Mn. Such an effect cannot be sufficiently obtained when the Cr content is less than 0.90 mass%. On the other hand, when the content of Cr exceeds 1.80% by mass, the turning property and the cold workability are deteriorated. Therefore, the Cr content in the steel constituting each rolling element is set to a range of 0.90 to 1.80 mass%. In order to further stabilize the turning property and the cold workability, the Cr content is preferably 1.70% by mass or less.

Subsequently, among the contents of selective additive components (Mo, Ni, Cu) of steel constituting each rolling element of the present invention and unavoidable impurities, it is particularly preferable to regulate the content (S , P, O) will be described.
[Mo content in steel constituting each rolling element: 0.00 to 0.25% by mass]
As described in the above-mentioned raceway part, Mo is also dissolved in the base to improve the hardenability and temper softening resistance and to ensure the hardness of the rolling surface of each rolling element. There is. Mo also has the effect of stabilizing martensite in the base structure and delaying the change in white structure due to hydrogen. However, when the content of Mo exceeds 0.25% by mass, a part of Mo forms a hard carbide and reduces grindability. Moreover, since it is an expensive element, it causes an increase in the manufacturing cost of the rolling bearing including the rolling elements. Therefore, the Mo content was regulated to 0.00 to 0.25% by mass. In addition, it is preferable to make content of Mo into 0.01-0.15 mass% from a viewpoint of acquiring the said effect fully, suppressing manufacturing cost.

[Ni content in steel constituting each rolling element: 0.00 to 0.20 mass%]
Ni is an element having the effect of improving the hardenability and the effect of stabilizing the retained austenite as described in the above-described raceway ring portion. Further, when added in a large amount, Ni improves the toughness. However, since it is an expensive element, it causes an increase in the manufacturing cost of the rolling bearing including the rolling elements. Therefore, the content of Ni is regulated to 0.00 to 0.20% by mass. In addition, it is preferable that content of Ni shall be 0.01-0.18 mass% from a viewpoint which fully obtains the said effect, suppressing manufacturing cost.

[Cu content in steel constituting each rolling element: 0.00 to 0.20 mass%]
Cu has the effect of improving the hardenability and the effect of improving the grain boundary strength, as described above for the raceway part. However, when the Cu content increases, hot forgeability decreases. Therefore, the Cu content was regulated to 0.00 to 0.20 mass%. In addition, in order to acquire the said effect fully, it is necessary to make Cu content 0.01 mass% or more.

[S content in steel constituting each rolling element: 0.020% by mass or less]
As described in the above-described raceway portion, S forms MnS that acts as an inclusion, so the smaller the amount of S contained in the steel, the better. However, S is an element that exists abundantly in nature. If the content of S is to be suppressed to an extremely low level, the productivity of steel materials (steel materials) for producing the rolling elements will be reduced. Since the manufacturing cost rises, it becomes difficult to use it widely industrially. On the other hand, even if S is contained in an amount of about 0.020% by mass, the durability required for each rolling element 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.

[P content in steel constituting each rolling element: 0.020 mass% or less]
As described above with respect to the raceway part, P is segregated at the crystal grain boundaries and lowers the grain boundary strength and fracture toughness value. However, P is also an element that exists in a large amount in nature. If an attempt is made to keep the P content extremely low, the manufacturing cost of the steel material will increase. On the other hand, even if P is contained in an amount of about 0.020% by mass, the durability required for each rolling element can be secured by making the content of other elements and the heat treatment method appropriate. Therefore, the upper limit of the P content is set to 0.020% by mass.

[O content in steel constituting each rolling element: 10 mass ppm or less]
O also forms oxide inclusions such as Al ₂ O ₃ in the steel, as described above for the raceway portion. Oxide inclusions are hard and serve as starting points for inclusion-origin separation, and have a significant adverse effect on the rolling fatigue life of the rolling surface. Therefore, the smaller the O content, the better. However, regarding O, if the content is extremely reduced, the steel material cost increases, but even if O is contained in an amount of about 10 ppm by mass, the content of other elements and the heat treatment method can be made appropriate. The durability required for the rolling elements can be secured. Therefore, the upper limit of the O content was set to 10 mass ppm.

(3) Regarding Grease Next, the composition of grease filled in the bearing internal space where the rolling elements are installed will be described. That is, when the rolling bearing according to the present invention is carried out, the grease is added with an appropriate additive as described below, thereby stably protecting the raceway surface and each rolling surface. A coating is formed to suppress the intrusion of hydrogen into the steel constituting the race and the rolling elements, and the progress of white structure peeling can be suppressed.

[Thickener: Diurea compound]
The diurea compound is added as a thickener to the grease and has excellent heat resistance, so that the operating environment temperature of the rolling bearing is high, and the rolling contact portion between the raceway surface and each rolling surface is Even when the temperature rises, a stable protective film (oil film) can be formed on each of the rolling contact portions. The blending ratio of the thickener is preferably 5 to 25% by mass with respect to the total amount of the grease composition. If the blending ratio of the thickener exceeds 25% by mass, the grease composition becomes excessively hard and it becomes difficult to obtain sufficient lubrication performance. On the other hand, when the blending ratio of the thickener is less than 5% by mass, the grease cannot be made sufficiently grease-like (necessary for forming a strong protective film on each rolling contact portion. Viscosity cannot be ensured).

  Preferred examples of the diurea compound that can be suitably used as a thickener include those represented by the following chemical formulas: [Chemical Formula 1] to [Chemical Formula 3].

In the above [Chemical Formula 1] to [Chemical Formula 3], R ₁ contains an aromatic ring-containing hydrocarbon group (7 to 12 carbon atoms in total), and R ₂ contains a divalent aromatic ring. A hydrocarbon group (the number of carbon atoms is 6 to 15 in total), and R ₃ is a cyclohexyl group or an alkylcyclohexyl group (the number of carbon atoms is 7 to 12 in total).

[Rust preventive: Naphthenate, succinic acid or derivatives thereof]
Naphthenic acid salt, succinic acid or derivatives thereof are added as a rust preventive agent in grease, and the raceway surfaces and the rolling elements are the surfaces of steel constituting the bearing rings and the rolling elements. Adsorb to the moving surface to form a protective coating. And about each of these surfaces, while exhibiting a rust prevention effect, the effect which suppresses generation | occurrence | production and penetration | invasion of hydrogen in these each surface is exhibited. These substances that function as rust inhibitors may be used alone or in combination of two or more. In order to stably obtain the above effects, the total amount of naphthenic acid salt, succinic acid or a derivative thereof is preferably 0.25 to 5% by mass based on the total amount of the grease composition.

The naphthenic acid salt is not particularly limited as long as it is a carboxylate having a naphthene nucleus, but a saturated carboxylate having a naphthene nucleus is preferable. Examples of such naphthenates include saturated monocyclic carboxylates (C _n H _2n-1 COOM), saturated bicyclic carboxylates (C _n H _2n-3 COOM), and derivatives thereof. For example, preferable examples of the saturated monocyclic carboxylate include those represented by the following chemical formula: [Chemical Formula 4] or [Chemical Formula 5].

In the above [Chemical Formula 4] and [Chemical Formula 5], R ₄ represents a hydrocarbon group, and specific examples include an alkyl group, an alkenyl group, an aryl group, an alkaryl group, and an aralkyl group. M represents a metal element, and specifically includes Co, Mn, Zn, Al, Ca, Ba, Li, Mg, Cu and the like. Examples of succinic acid or derivatives thereof include succinic acid, alkyl succinic acid, alkyl succinic acid half ester, alkenyl succinic acid, alkenyl succinic acid half ester, and succinimide.

[Antioxidants: phenolic compounds or amine compounds]
A phenolic compound or an amine compound is added to the grease as an antioxidant, and prevents the base oil of the grease from being oxidized, and at the same time, adsorbs to the surface of the steel constituting the race and the rolling elements. By forming a protective coating on the raceway surface and each rolling surface, hydrogen is generated on the raceway surface and each rolling surface portion, and hydrogen enters the raceway surface and each rolling surface. Demonstrate the effect. In order to obtain these effects, one selected from a phenol compound and an amine compound may be used alone, or two or more may be used in combination. In order to stably obtain the above effect, the total amount of one or more antioxidants selected from phenolic compounds and amine compounds is 2 to 2 with respect to the total amount of grease. It is preferable to set it as 10 mass%.

(A) Phenol-based compound As the phenol-based compound, any alkylphenol-based compound used as an antioxidant for lubricating oil can be used, and in particular, an alkylphenol compound represented by the following chemical formula: Can be used for

In the above [Chemical Formula 6], R ₅ is an alkyl group having 1 to 4 carbon atoms, R ₆ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₇ is a hydrogen atom, 4 represents an alkyl group or a group represented by the following chemical formula:

In the above [Chemical Formula 7], R ₈ represents an alkylene group or sulfur atom having 1 to 6 carbon atoms, R ₉ represents an alkyl group having 1 to 4 carbon atoms, and R ₁₀ represents a hydrogen atom or 1 carbon atom. Represents an alkyl group of ˜4, respectively. K represents 0 or 1.

In the above [Chemical Formula 6], examples of the compound when R ₇ is alkyl having 1 to 4 carbon atoms include 2,6-di-tert-butyl-p-cresol, 2,6-di-tert. -Butyl-4-ethylphenol can be mentioned.
In the above [Chemical Formula 6], examples of the compound in which R ₇ is a group represented by the above [Chemical Formula 7] include bis (3,5-di-tert-butyl-4-hydroxyphenyl), Bis (3,5-di-tert-butyl-4-hydroxyphenyl) methane, 1,1-bis (3,5-di-tert-butyl-4-hydroxyphenyl) ethane, 1,2-bis (3 5-di-tert-butyl-4-hydroxyphenyl) ethane, 1,1-bis (3,5-di-tert-butyl-4-hydroxyphenyl) propane, 1,2-bis (3,5-di-) tert-butyl-4-hydroxyphenyl) propane, 1,3-bis (3,5-di-tert-butyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-di-tert-butyl- 4-hydroxyphenyl) Propane and the like, such as 4,4-thiobis (3-methyl -6-tert-butylphenol) and mixtures thereof.

(B) Amine-based compound As the amine-based compound, any aromatic amine-based compound used as an antioxidant for lubricating oil can be used, and in particular, α-- represented by the following chemical formula: Preferred examples include one or more aromatic amines selected from naphthylamines and diphenylamines represented by [Chemical Formula 10].

In the above [Chemical Formula 8], R ₁₁ represents a hydrogen atom or a group represented by the following chemical formula: [Chemical Formula 9]. Of these, R ₁₁ is preferably a group represented by the following [Chemical 9].

In the above [Chemical Formula 9], R ₁₂ represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms.
Examples of the alkyl group having 1 to 16 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, Examples include a tetradecyl group, a pentadecyl group, and a hexadecyl group. These alkyl groups may be linear or branched. Among these, a branched alkyl group having 8 to 16 carbon atoms is preferable.

In the above [Chemical Formula 10], R ₁₃ in the same molecule may be the same or different. As R < ₁₃ >, a hydrogen atom or a C1-C16 alkyl group can be mentioned, Among these, a C1-C16 alkyl group is preferable. Specific examples of the alkyl group represented by R ₁₃ include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl. Group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group and the like. These alkyl groups may be linear or branched. Among these, a branched alkyl group having 3 to 16 carbon atoms is preferable.
Examples of amine antioxidants include Nn-butyl-paminophenol, 4,4′-tetramethyl-di-, as well as amine compounds represented by the above [Chemical Formula 8] and [Chemical Formula 10]. Aminodiphenylmethane, N, N′-disalicylidene-1,2-propylenediamine and the like can be used.

[Extreme pressure additive: DTC compound or DTP compound]
A dialkyldithiocarbamic acid (DTC) -based compound or a dialkyldithiophosphoric acid (DTP) -based compound, which is an organic metal salt, is added as an extreme pressure additive to grease, and the raceway is moved along with the operation of the rolling bearing. When the raceway surface of the ring and the rolling contact surface of each rolling element make metal contact, it chemically reacts with the metal surface to form a protective film on the raceway surface and each rolling surface. It exhibits the effect of suppressing the generation of hydrogen at the moving surface portion and the entry of hydrogen into the raceway surface and each rolling surface. Further, the wear resistance and seizure resistance of the raceway surfaces and the respective rolling surfaces are also improved. In order to obtain these effects, the DTC compound and the DTP compound may be used alone or in combination. In order to stably obtain the above effect, the amount of addition of one or more selected from DTC compounds and DTP compounds is preferably 0.5 to 10% by mass with respect to the total amount of grease. Is preferable.

  As the DTC-based compound, an organic metal salt represented by the following chemical formula: [Chemical Formula 11] is preferably used, and as the DTP-based compound, an organic metal salt represented by the following chemical formula: [Chemical Formula 12] is preferably used. it can.

In the above [Chemical Formula 11] and [Chemical Formula 12], M represents a metal atom, and specifically includes Sb, Bi, Sn, Ni, Te, Se, Fe, Cu, Mo, Zn, and the like. It is done. Also, R ₁₄ represents a hydrocarbon group having 1 to 18 carbon atoms, R ₁₄ in the same molecule may be the same or different. Examples of the hydrocarbon group represented by R ₁₄ include an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, an alkylaryl group, and an arylalkyl group. Among these, 1,1,3,3-tetramethylbutyl group, 1,1,3,3-tetramethylhexyl group, 1,1,3-trimethylhexyl group, 1,3-dimethylbutyl group, 1-methyl Undecane group, 1-methylhexyl group, 1-methylpentyl group, 2-ethylbutyl group, 2-ethylhexyl group, 2-methylcyclohexyl group, 3-heptyl group, 4-methylcyclohexyl group, n-butyl group, isobutyl group, Isopropyl group, isoheptyl group, isopentyl group, undecyl group, eicosyl group, ethyl group, octadecyl group, octyl group, cyclooctyl group, cyclododecyl group, cyclopentyl group, dimethylcyclohexyl group, decyl group, tetradecyl group, docosyl group, dodecyl group , Tridecyl group, trimethylcyclohexyl group, nonyl group, propyl , Hexadecyl group, hexyl group, henicosyl group, heptadecyl group, heptyl group, pentadecyl group, pentyl group, methyl group, tert-butylcyclohexyl group, tert-butyl group, 2-hexenyl group, 2-methallyl group, allyl group, undecenyl Group, oleyl group, decenyl group, vinyl group, butenyl group, hexenyl group, heptadecenyl group, tolyl group, ethylphenyl group, isopropylphenyl group, tert-butylphenyl group, Sec-pentylphenyl group, n-hexylphenyl group, 3-octylphenyl group, isononylphenyl group, n-dodecylphenyl group, phenyl group, benzyl group, 1-phenylmethyl group, 2-phenylethyl group, 3-phenylpropyl group, 1,1-dimethylbenzyl group, 2- Phenylisopropyl group, 3-phenylhexyl group, benzhydride Group, biphenyl group. These hydrocarbon groups may have an ether bond.

[Conductive substance: Carbon black]
By containing a conductive substance in the grease, a current is always passed between the pair of race rings, and a discharge (spark) is generated between the two race rings at the rolling contact portions. It is possible to suppress the occurrence of a potential difference that is sufficient to cause the That is, as described above, normally, during the rotation of the rolling bearing, an oil film by grease exists between the raceway ring and each of the rolling surfaces, so that the two raceways are in an insulated state. It has become. In such a state, when a potential difference is generated between these two race rings, an oil film is momentarily cut by vibration or slip, and a metal contact is produced in which the raceway surface and each rolling surface are in direct contact with each other. A discharge is generated at the contact portion, and electrolytic corrosion is generated on the raceway surface and each rolling surface. At the same time, the decomposition of the lubricant and water is accelerated by the discharge (spark), and the generation of hydrogen is accelerated. On the other hand, by adding carbon black, which is a conductive substance, to the grease, the potential difference between the two races can be made small or zero, making it difficult for discharge to occur at each rolling contact portion. , Can suppress the generation of electrolytic corrosion and hydrogen. As a result, the penetration of hydrogen into the steel constituting the race and the rolling elements can be suppressed, and the progress of white structure peeling can be suppressed.

The content of carbon black is preferably 0.5 to 20% by mass with respect to the total amount of the grease composition, from the viewpoint of securing the necessary amount of electricity while securing the amount of other additives to be added. 1.0 to 15% by mass is more preferable. The particle size of the carbon black is preferably 10 to 300 nm, more preferably 10 to 200 nm in terms of average particle size, from the viewpoint of dispersibility in the grease composition and acoustic characteristics.
In addition, as the grease filled in the bearing internal space when the present invention is carried out, grease added with various additives can be used as long as the effects of the various additives described above are not impaired.

(4) Conductive Seal Plate Next, the case where a conductive seal plate is used as a seal plate that closes the end opening of the bearing internal space where the rolling elements are installed will be described. That is, when carrying out the rolling bearing of the present invention, by using a conductive material as the sealing plate, it is possible to suppress the occurrence of discharge at the rolling contact portion between the race and the rolling elements, The generation of hydrogen at the rolling contact portion and the penetration of hydrogen into the steel constituting the race and the rolling elements can be suppressed, and the progress of white structure peeling can be suppressed.

  That is, when carrying out the rolling bearing of the present invention, by using a conductive material as the seal plate, as in the case of using a conductive material as the grease, between the two race rings. The potential difference between them can be made small or zero, and it is difficult for electric discharge to occur at the respective rolling contact portions, and generation of electrolytic corrosion and hydrogen can be suppressed. In addition, as a sealing plate which has electroconductivity, it describes by the above-mentioned patent document 2, etc., various things conventionally known, for example, metal metal cores and electroconductive elastomer seal lips, for example Can be used in combination.

  A plurality of experiments conducted in the course of making the present invention and confirming the effects of the present invention will be described. In each of these experiments, a pair of race rings (inner ring and outer ring) and a plurality of balls, each of which is a rolling element, are made of steel having a predetermined composition and subjected to a predetermined heat treatment. Examining [Prototype and heat treatment quality test], and obtaining the life related to white tissue peeling of a rolling bearing (single-row deep groove type radial ball bearing) formed by assembling the prototype raceway and rolling element [White tissue peeling life test] Two types of tests were conducted.

[Prototype and heat treatment quality test]
As materials (steel) for making the both race rings, 10 types of steel having the compositions shown in A to J of Table 1 are used as materials (steel) for making the rolling elements. Ten types of steel having the composition shown in T were prepared. The numerical values in Tables 1 and 2 represent mass% excluding O (O is mass ppm). The numerical value shown in parentheses indicates that the numerical value is out of the range defined in the claims.

[Regarding the bearing ring]
The single row deep groove type ball bearing as shown in FIG. 1 described above, which has a nominal number of 6303 by subjecting the ten types of steel shown in Table 1 to predetermined forging, cutting and polishing. Seven outer rings 3 and inner rings 5 of 1 (outer diameter: 47 mm, inner diameter 17 mm, width 14 mm) were made for each steel having each composition (N = 7). Next, after carbonitriding at 900 to 960 ° C., the outer ring 3 and the inner ring 5, each of which is a race, are subjected to oil quenching in a state where the temperature is decreased to 820 to 860 ° C., and then 160 Tempering was performed at ˜200 ° C. When the cross-sectional structures of the outer ring 3 and the inner ring 5, which were the manufactured test pieces, were observed, precipitation of carbide and nitride was confirmed in the surface layer portion. Moreover, when the crystal grain size of the austenite grain was measured, it was crystal grain size number 9-10. In addition, the steel type J in Table 1 is a high carbon chromium bearing steel corresponding to SUJ2 defined in JIS G 4805.

  After the outer ring 3 and the inner ring 5 which are test pieces are made of the ten kinds of steels having different compositions from each other, the heat treatment quality of each of the test pieces, that is, the outer ring raceway 2 and the inner ring which are raceway surfaces is then obtained. The amount of retained austenite on the outermost surface of the track 4, the residual stress in the circumferential direction and axial direction of the track ring at the 1% depth position, and the C + N amount at the same position were measured. Among these, the amount of retained austenite was measured by measuring the amount of retained austenite on the outermost surface of the outer ring raceway 2 and the inner ring raceway 4 as the raceway surface with an X-ray diffractometer. The residual stress is measured by electropolishing the surface of the raceway surface (the outer ring raceway 2 or the inner ring raceway 4) of each test piece to a depth of 85 to 90 μm (the 1% depth position). The measurement was performed by measuring the residual stress of the exposed surface with an X-ray diffractometer. Further, the amount of C + N at the 1% depth position is the electron with respect to the surface exposed by electropolishing the surfaces of the outer ring raceway 2 and the inner ring raceway 4 to a depth of 85 to 90 μm (the 1% depth position). Using an electron microanalyzer (EPMA), the acceleration voltage was measured at 15 kV. The measurement results regarding these heat treatment qualities are shown in Table 3 below. A residual stress value of negative (-) indicates that the residual stress is a compressive stress.

[Regarding each rolling element (ball 6)]
Ten types of steel shown in Table 2 above are subjected to predetermined cutting and forging processes, each of which is processed into balls having a diameter of 8.731 mm, and each of these balls is subjected to carbonitriding and quenching at 820 to 860 ° C. Then, after tempering at 160 to 200 ° C., ball peening and finish grinding are performed, and the balls 6 and 6 for the ball bearing 1 shown in FIG. It was subjected to the required test. However, regarding the steel type P in Table 2, the Si content and the Cr content regarding the steel type R are out of the scope of the invention described in claim 2, respectively, and the steel material is spheroidized. Hardness after annealing from the raw material (intermediate material cut to a predetermined length into a spherical shape) is high, and it is difficult to process balls 6 and 6 having the required dimensional accuracy and shape accuracy. Therefore, it was excluded from the subject of the white peel life test. Observation of the cross-sectional structure of the balls 6 and 6 made of the remaining steel types K to O, Q, and S to T confirmed that carbide and nitride were deposited on the surface layer. Moreover, when the crystal grain size of the austenite grain was measured, it was crystal grain size number 9-10. In addition, the component of the steel type K in the said Table 2 is high-carbon chromium bearing steel equivalent to SUJ2 prescribed | regulated to JISG4805.

  Next, the heat treatment quality of each of the balls 6 and 6 was measured. The hardness of the surface (rolling surface) of each ball 6, 6 was measured by pressing an indenter from the surface of each ball 6, 6 using the Rockwell hardness C scale. In this measurement, a correction value is obtained according to the method for correcting the hardness of the spherical test surface described in Annex D of JIS Z 2245, and the correction value is added to the measurement value. The hardness of the rolling surface that is the surface.

  Next, the amount of retained austenite on the outermost surface of the rolling surfaces of the balls 6 and 6 and the residual stress at the 1% depth position were measured. Among these, the amount of retained austenite was measured by measuring the amount of retained austenite on the outermost surface of the rolling surfaces of the balls 6 and 6 with an X-ray diffractometer. The residual stress is measured by measuring the residual stress on the surface exposed by electrolytic polishing by a depth of 85 to 90 μm (the 1% depth position) from the rolling surfaces of the balls 6 and 6. It was done by measuring by. The measurement results regarding the heat treatment quality are shown in Table 3. A residual stress value of negative (-) indicates that the residual stress is a compressive stress.

[White tissue peeling life test]
The outer ring 3 and the inner ring 5 made of the steel shown in Table 1 and the balls 6 and 6 made of the steel shown in Table 2 were assembled to obtain a test bearing for use in bearing life. This test bearing includes the balls 6 between the outer ring raceway 3 provided on the inner peripheral surface of the outer ring 3 and the inner ring raceway 4 provided on the outer peripheral surface of the inner ring 5 made of steel described in Table 1. 6, each of these balls 6 and 6 is held by a crown-shaped cage made of polyamide resin so as to be freely rollable. In addition, grease is filled in the bearing inner space in which the balls 6, 6 are incorporated between the inner peripheral surface of the outer ring 3 and the outer peripheral surface of the inner ring 5, and both ends of the bearing inner space are formed by a pair of seal rings. Each of the test bearings was formed by closing the opening. The grease is blended with a thickening agent composed of a diurea compound in a PAO base oil in order to evaluate the white structure peeling resistance of each steel type described in Tables 1 and 2 above. An unblended grease was used. (In Table 3 above, this grease is described as “no additive grease”.)

  The tester for measuring the white tissue peeling life is an improved alternator simulation tester disclosed in “NSK Technical Journal No.679, p.28” published by the applicant company. It was. Specifically, a positive electrode is attached to the outer ring that does not rotate among the test bearings, and a negative electrode is attached to the end of the metal shaft that rotates with the inner ring of the test bearing fitted and fixed. During the test, a radial load (about 1300 N) in a predetermined direction (the operation direction is constant and does not change) is applied to the shaft while a current of 0.5 A is passed between the outer ring and the inner ring from a DC stabilized power supply. The life test was then continued. Therefore, a load is repeatedly applied to the inner ring raceway 4 over the entire circumference, but a load is continuously applied to the outer ring raceway 2 only in a part in the circumferential direction. Therefore, among the outer ring raceway 2, the inner ring raceway 4, and the respective rolling surfaces, which are the both raceways, the outer ring raceway 2 is in the most severe state with respect to the peeling life. This testing machine uses a plurality of rolling elements (balls 6.6) between a pair of bearing rings constituting the rolling bearing (between the outer ring 1 and the inner ring 5) during the life test of the rolling bearing. In this way, the rolling bearing as the test bearing is subjected to conditions that are liable to cause deterioration of surface properties due to electrolytic corrosion and generation of hydrogen due to decomposition of grease. Using such a testing machine, seven (N = 7) white structures were used for each of the 23 types of test bearings of Examples 1 to 17 and Comparative Examples 18 to 19 and 21 to 24 shown in Table 3. A peel life test was conducted to determine the life at which the cumulative failure probability was 50%. The results of the white tissue peeling life performed in this manner are shown in Table 3.

  As is clear from the results of the white tissue peeling life test whose results are shown in Table 3, the results of Examples 1 to 5 having the specific matters of the invention described in claim 1 in the claims are as follows. In the bearing manufactured under the conditions, no separation occurred on the raceway surfaces (the outer ring raceway 2 and the inner ring raceway 4) of the pair of raceways (the outer ring raceway 3 and the inner ring raceway 5). Regarding Examples 1 to 5, the composition of the steel constituting the both races and the residual austenite on the outermost surfaces of these races (the outermost surfaces of the raceway 3 and the inner raceway 4 which are raceway surfaces). This is because the amount, the C + N amount at the 1% depth position, and the value of the compressive residual stress in each direction were appropriate. However, regarding Examples 1 to 5, the balls 6 and 6 are specified matters of the invention described in claim 2 in the claims (N amount at the 1% depth position: 0.05 mass) % Or more), the rolling surfaces of any of the balls 6 and 6 were peeled in 200 to 280 hours.

  Next, the bearing manufactured under the conditions of Examples 6 to 9 including the specific matters of the invention described in claim 1 is the raceway surface of a pair of race rings (outer ring 3 and inner ring 5). No peeling occurred on the outer ring raceway 2 and the inner ring raceway 4. However, with regard to Examples 6 to 9, the balls 6 and 6 are specified matters of the invention described in claim 2 in the claims (steel composition, surface hardness: HRC 63 to 67, 1 % Depth position N amount: 0.05% by mass or more, and the value of residual tensile stress: 500 to 900 MPa) was not provided. The rolling surfaces of 6 and 6 were peeled off. That is, in each of the above Examples 6 to 9, the rolling elements (balls 6) were compared with the test bearings incorporating the bearing rings made of the steel type E that had good quality in the above Examples 1 to 5. 6) The heat treatment applied to 6) was varied (submerged quenching → carbonitriding). However, in the case of Example 6, the compressive residual stress at the 1% depth position, in the case of Example 7, the content of Mn in the steel, the surface hardness, the content of Si and Mn in the steel In the case of Example 8, the surface hardness, the amount of residual austenite on the outermost surface, the amount of N at the 1% depth position, and the compressive residual stress are in the case of Example 9. The contents of Si and Cr in the steel are not appropriate, and the resistance to structural change of this steel is insufficient, so that the rolling surfaces of any of the balls 6 and 6 peeled off relatively early.

  Next, the test bearing manufactured under the conditions of Examples 10 to 13 having the specific matters of the invention described in claims 1 and 2 of the claims has a raceway surface of the raceway of 450 to 520 h. It peeled and peeling did not generate | occur | produce on the rolling surface of each rolling element. In each of Examples 10 to 13, the composition of steel constituting the race, the amount of retained austenite on the raceway surface, the amount of C + N at the 1% depth position, and the value of compressive residual stress in each direction are appropriate. Further, since the hardness of the surface (rolling surface) of each rolling element, the amount of retained austenite on the outermost surface, the amount of N at the 1% depth position and the compressive residual stress are appropriate, the rolling bearing The lifespan of has increased.

  Further, the grease includes the specific matters of the invention described in claims 1 and 2 in the claims, and further, as grease to be filled in the inner space of the bearing, in the grease, zinc naphthenate as a rust preventive agent, The test bearing of Example 14 using benzotriazole as an antioxidant and zinc dithiocarbamine sanate added as an extreme pressure additive (described as “improved grease” in Table 3) continued the durability test. During 1000 hours, which was the time, no peeling occurred on the raceway surfaces of the both race rings and the rolling surfaces of the rolling elements, so the durability test was terminated at 1000 hours. However, when the unpeeled raceway was cut and the cross section was observed, a white structure was generated.

  Further, the grease having the specific matters of the invention described in claims 1 and 2 in the claims, and having an average particle diameter of 10 to 10 as a conductive substance in the grease as the grease filling the bearing internal space. Example 15 using at least one of carbon black of 300 nm added in an amount of 5.0% by mass or more (described as “conductive grease” in Table 3) and a conductive sealing plate In the test bearings No. 17 to No. 1000, which is the duration of the endurance test, neither the raceway surfaces of the raceways nor the rolling surfaces of the rolling elements are separated, and the endurance test is conducted at 1000 hours. Censored. In Examples 15 to 17, the action of the conductive grease and / or the conductive seal plate delays the occurrence of electrolytic corrosion on the raceway surfaces of the raceways and the rolling surfaces of the rolling elements. The life of the test bearing has been extended. Moreover, when the unpeeled raceway was cut and the cross section was observed, no white structure was generated.

On the other hand, in the case of the test bearings of Comparative Examples 18 to 24 having a pair of raceways whose steel composition deviates from the scope of the present invention, a total of 7 test bearings for each test bearing. The outer ring raceway separated. Further, when the cross section of the outer ring after the test was observed, a white structure was generated in the outer ring raceway portion.
In Comparative Example 18 out of the test bearings of Comparative Examples 18 to 24, the heat treatment quality of the both races is substantially within the range defined by the present invention (the specific matter of the invention described in Claim 1). Since the Si content in the steel is small, the base structure is easily changed by hydrogen, and the life of each test bearing is shortened.

Further, in Comparative Example 19, the heat treatment quality of both the races was outside the range defined by the present invention (departed from the invention specific matters). Specifically, the amount of retained austenite in the raceway surface portion is insufficient, and the effect of relaxing the stress concentration on the surface cannot be obtained sufficiently, and the life of the test bearing is shortened.
Further, in Comparative Example 20, the heat treatment quality of both the races was outside the range defined by the present invention (departed from the invention specific matters). Specifically, the amount of retained austenite at the raceway surface is excessive, it is difficult to ensure the rolling fatigue life of the raceway surface, and the dimensional stability and shape stability of the raceway surface cannot be ensured. For this reason, in Comparative Example 20, a test bearing was not prototyped and a life test of the test bearing was not performed.
Further, in Comparative Example 21, with respect to the race, the circumferential compressive residual stress at the 1% depth position was outside the range defined by the present invention (departed from the invention specific matters). Specifically, because the compressive residual stress in the circumferential direction at the 1% depth position was insufficient, the hydrogen generated at the rolling contact portion of the test bearing caused a structural change of the base structure, and the generated cracks progressed. The life of the test bearing was shortened.
Further, in Comparative Example 22, the axial compressive residual stress at the 1% depth position was out of the range defined by the present invention with respect to the raceway (excluded from the invention specific matters). Specifically, since the compressive residual stress in the axial direction at the 1% depth position is insufficient, the structure change of the base structure occurs due to the hydrogen generated at the rolling contact portion of the test bearing, and the generated crack progresses. The life of the test bearing was shortened.
Further, in Comparative Example 23, the properties after heat treatment of both the races were within the range specified in the present invention. However, since the Cr content in the steel constituting these races is small, The base structure was easily changed by hydrogen generated at the rolling contact portion, and the life of the test bearing was shortened.
Furthermore, in Comparative Example 24, a material corresponding to SUJ2 specified in JIS was used for a bearing ring and a rolling element in a normal heat treatment (for an extremely general single row radial ball bearing). It is a result. By comparing the life of the test bearing with respect to the comparative example 24 and the life of the test bearing with respect to each of the examples 14 to 17, the life of the test bearing with respect to each of the examples 14 to 17 is extremely common. It can be seen that there is more than 10 times the life of the row radial ball bearing.

  As is apparent from the results of the experiments described above, the rolling bearing incorporating the bearing ring having the specific matters of the invention described in claim 1 out of the inventions described in the claims, It can be used for applications where the air flows, ensuring durability. In particular, according to the invention in which a rolling element having the specific matters defined in claim 2 is used and a conductive grease or a conductive seal plate is added, a certain amount of current flows inside the rolling bearing. Even when used in a harsh environment, the raceway surfaces of the raceways and the rolling surfaces of the rolling elements constitute the rolling contact portions by the conductive grease and the conductive seal plate. In addition, the occurrence of electric corrosion that occurs and the occurrence of white tissue based on this electric corrosion is suppressed. In addition, according to the present invention, erosion occurs on the raceway surfaces of the raceways and the rolling surfaces of the rolling elements, and the raceway surfaces of the raceways and the rolling surfaces of the rolling bodies become rough. Even in this case, the remaining austenite on the outermost surfaces of these surfaces can suppress the occurrence of cracks on the surfaces of these surfaces, and the decrease in the rolling fatigue life of each of the rolling contact portions can be suppressed. Furthermore, even if hydrogen is generated by the decomposition of the lubricant by discharge (spark) and a white structure is generated on the raceway surfaces of the both race rings and the rolling surfaces of the rolling elements, the boundary between the white structures is generated. By suppressing the progress of cracks generated in the portion by compressive residual stress, it is possible to suppress the rolling bearing life reduction based on the presence of the white structure.

In the present invention, a current flows during operation, and the electric corrosion may occur on the pair of raceway surfaces and the respective rolling surfaces due to the current. The two raceways and the respective rolling elements are made of steel. Applicable to rolling bearings. For example, in various types of electric motor bearings, a small amount of current from the electric motor flows into the bearing through the rotating shaft, and deterioration of surface roughness due to electrolytic corrosion or generation of hydrogen due to decomposition of lubricating oil is promoted. Accordingly, the effect of extending the life of the rolling bearing by implementing the present invention is great.
The bearing life test described above was performed when the present invention was applied to a deep groove type radial ball bearing. However, the present invention is not limited to other ball bearings such as angular ball bearings and thrust ball bearings, and wind power generators. The same effects can be obtained when applied to cylindrical roller bearings, tapered roller bearings, spherical roller bearings, roller bearings such as needle bearings, and special rolling bearings such as ball screws and linear guides. It is done.

DESCRIPTION OF SYMBOLS 1 Radial ball bearing 2, 2a, 2b, 2c Outer ring raceway 3, 3a, 3b, 3c Outer ring 4, 4a, 4b, 4c Inner ring raceway 5, 5a, 5b, 5c Inner ring 6 Ball 7, 7a, 7b, 7c Cage 8 Cylindrical roller 9 Radial cylindrical roller bearing 10 Inward flange 11 Outward flange 12 Tapered roller 13 Radial tapered roller bearing 14 Large diameter flange 15 Small diameter flange 16 Spherical roller bearing 17 Spherical roller

Claims (4)

A first raceway having a first raceway surface on any surface, a second raceway having a second raceway surface on a surface opposite to the first raceway surface, and the first and second In a rolling bearing provided with a plurality of rolling elements provided between the raceway surfaces of the two rolling elements,
At least one of the first and second bearing rings has C of 0.20 to 0.60 mass%, Si of 0.10 to 0.60 mass%, and Mn of 0.60 to 1. .50 mass%, Cr 0.60 to 1.80 mass%, Mo 0.00 to 0.40 mass%, Ni 0.00 to 0.20 mass%, Cu 0.00 to 0.20 It is made of steel containing the mass%, the balance being Fe and inevitable impurities,
By applying a quenching process and a tempering process, which is one of a carburizing process and a carbonitriding process, to the at least one raceway ring,
The amount of retained austenite on the outermost surface of the raceway provided on the at least one raceway is 20 to 45% by volume,
When the length of 1% of the diameter of each rolling element (the diameter of the portion in rolling contact with the raceway surface) is X,
The C + N amount at a position of depth X from the surface of the raceway surface provided on the at least one raceway is 0.80 mass% or more and 2.00 mass% or less,
The compressive residual stress in the circumferential direction of the raceway at a position of a depth X from the surface of the raceway surface provided on the at least one raceway is 100 to 500 MPa, and the compressive residual stress in the axial direction is also 50 to 500 MPa. Rolling bearing characterized by that.   The rolling bearing according to claim 1, wherein the bearing ring is made of steel having S of 0.020 mass% or less, P of 0.020 mass% or less, and O of 15 mass ppm or less. In each of the rolling elements, C is 0.80 to 1.20 mass%, Si is 0.10 to 0.70 mass%, Mn is 0.20 to 1.20 mass%, and Cr is 0.90 to 1. 80% by mass, Mo: 0.00-0.25% by mass, Ni: 0.00-0.20% by mass, Cu: 0.00-0.20% by mass, the balance being Fe and inevitable impurities Made of steel,
By applying a carbonitriding quenching treatment and a tempering treatment to the rolling elements made of steel, the surface hardness of the rolling surfaces of these rolling elements is HRC63 to 67,
The amount of retained austenite on the outermost surface of each rolling element is 20 to 40% by volume,
When the length of 1% of the diameter of each rolling element is X,
N amount of the position of the depth X from each rolling element surface is 0.05 mass% or more and 2.00 mass% or less,
And the rolling bearing of Claim 1 or 2 whose compressive residual stress of the position of the depth X from each said rolling element surface is 500-900 MPa.   4. The rolling bearing according to claim 3, wherein each rolling element is made of steel having S of 0.020 mass% or less, P of 0.020 mass% or less, and O of 10 mass ppm or less.

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