Rolling bearing device

Abstract

To provide a rolling bearing device having a longer service life by suppressing micro-spalling.SOLUTION: Each of the plurality of needle rollers 2 has a hardness not lower than 05mm at a depth not smaller than 0. 20mm and not greater than 0. 733HV from a first contact surface which is a surface in contact with another component. Each of the plurality of needle rollers 2 has a first contact surface having a surface roughness Ra of 0.01 μm or more and 0.05 μm or less. A nitrogen concentration of a first surface layer portion including the first contact surface of each of the plurality of needle rollers 2 is not lower than 0.20 mass% and not higher than 0.60 mass%. The hardness at a depth of 0. 05mm or more and 0. 20mm or less from a second contact surface, which is a surface where the shaft member 1 comes into contact with another component, is 720HV or more. The surface roughness Ra of the second contact surface of the shaft member 1 is 0.01 μm or more and 0.05 μm or less. The nitrogen concentration of the second surface layer area including the second contact surface of the shaft member 1 is 0.20 mass% or more and 1.20 mass% or less. The carbon concentration of the second surface layer area is 0.60 mass% or more and 1.20 mass% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing device. [Background technology]

[0002] In recent years, the environments in which rolling bearings (rolling bearing devices) are used have become more diverse. Specifically, for example, rolling bearings are used in conditions where the viscosity of lubricating oil has decreased, the amount of lubricating oil has been reduced, and the entire bearing is exposed to high temperatures. Furthermore, as automobiles use more and more automatic transmissions (ATs), rolling bearings are used in conditions where they rotate at higher speeds. Furthermore, rolling bearings are used in conditions where foreign matter has been mixed into the lubricating oil, so-called contaminated lubrication. In each of these environments, rolling bearing components can develop spalling. In many cases, this spalling is not internal spalling originating from inclusions in the material, but rather surface spalling resulting from micro-spalling. Micro-spalling occurs, for example, in the planetary pinion of a planetary gear device.

[0003] The rolling members and shaft members of rolling bearings attached to planetary pinions are required to have physical properties that allow them to be used under harsh conditions such as high temperatures, high rotational speeds, and lubrication with foreign matter. For example, Japanese Patent Application Laid-Open No. 2010-001521 (Patent Document 1) proposes improving the rolling fatigue characteristics of shaft members attached to planetary pinions under the above-mentioned harsh environments and suppressing plastic deformation of the shaft members. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-001521 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the rolling fatigue life is extended by carbo-nitriding the shaft member and enriching the amount of retained austenite in the surface layer. Patent Document 1 also describes forming the shaft member from case-hardened steel and reducing the amount of retained austenite in the core, which is located inside the surface layer, to zero, thereby suppressing plastic deformation of the shaft member. However, Patent Document 1 does not mention optimizing both the hardness and surface roughness of the surface layer of the shaft member. Therefore, from the perspective of suppressing micro-spalling, the technology in Patent Document 1 has limited effect on extending life.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a rolling bearing device that can have a long life by suppressing micro-spalling. [Means for solving the problem]

[0007] A rolling bearing device according to the present disclosure includes a plurality of rolling members and a shaft member. The shaft member supports the plurality of rolling members rotatably and in direct contact with the plurality of rolling members. Each of the plurality of rolling members is made of steel containing 0.95% to 1.10% by mass of carbon, 0.5% to 0.008% by mass of manganese, 0.008% to 0.35% by mass of sulfur, 0.15% to 0.35% by mass of silicon, 1.30% to 1.60% by mass of chromium, and the balance being iron and impurities. Each of the plurality of rolling members has a hardness of 733 HV or higher at a depth of 0.05 mm to 0.20 mm from a first contact surface, which is a surface that comes into contact with other components. The surface roughness Ra of each of the plurality of rolling members is 0.01 μm to 0.05 μm. The nitrogen concentration of the first surface layer portion including the first contact surface of each of the plurality of rolling members is 0.20% by mass or more and 0.60% by mass or less. The shaft member is made of steel containing 0.10% by mass or more and 0.40% by mass or less of carbon, 0.10% by mass or more and 2.50% by mass or less of silicon, 0.30% by mass or more and 1.20% by mass or less of manganese, 0.40% by mass or more and less than 3.00% by mass of chromium, and 1.00% by mass or less of molybdenum, with the balance being iron and impurities. The hardness at a depth of 0.05 mm to 0.20 mm from the second contact surface, which is the surface of the shaft member that comes into contact with other components, is 720 HV or more. The surface roughness Ra of the second contact surface of the shaft member is 0.01 μm to 0.05 μm or less. The nitrogen concentration of the second surface layer portion including the second contact surface of the shaft member is 0.20% by mass or more and 1.20% by mass or less. The carbon concentration of the second surface layer portion is 0.60 mass % or more and 1.20 mass % or less. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a rolling bearing device that can have a longer life by suppressing micro-spalling. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a front view of the planetary gear device. [Figure 2] 1 is a partially cutaway perspective view showing a planetary gear and its support structure in a planetary transmission, with the planetary gear cut away. FIG. [Figure 3] FIG. 3 is a cross-sectional view of the planetary gear and its support structure shown in FIG. 2. [Figure 4] 3 is a flowchart showing an outline of a manufacturing method for the rolling bearing device according to the present embodiment. [Figure 5] 10 is a flowchart showing the procedure of a heat treatment step (S20) for a steel material to be made into a needle roller. [Figure 6] 10 is a flowchart showing the procedure of a heat treatment step (S20) for a steel material to be made into a shaft member. [Figure 7] FIG. 2 is a schematic cross-sectional view showing the configuration of a radial load tester used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment will be described with reference to the drawings. <Basic configuration> Fig. 1 is a front view of a planetary gear device. Referring to Fig. 1, the planetary gear device 1000 has a shaft member 1, a planetary gear 4, an internal gear 6, a sun gear 7, a sun gear shaft 11, and a carrier (not shown in Fig. 1). The planetary gear device 1000 is used, for example, in a reducer for an automobile transmission.

[0011] The internal gear 6 has an annular shape. The internal gear 6 has an inner peripheral surface and an outer peripheral surface. A plurality of teeth are formed on the inner peripheral surface of the internal gear 6 along the circumferential direction of the internal gear 6. The teeth of the internal gear 6 protrude from the inner peripheral surface of the internal gear 6 toward the radially inward direction of the internal gear 6.

[0012] The sun gear shaft 11 has a cylindrical shape. The position of the central axis of the sun gear shaft 11 coincides with the position of the central axis of the internal gear 6. The sun gear 7 has an inner peripheral surface and an outer peripheral surface. A plurality of teeth are formed on the outer peripheral surface of the sun gear 7 along the circumferential direction of the sun gear 7. The teeth of the sun gear 7 protrude from the outer peripheral surface of the sun gear 7 toward the radially outward direction of the sun gear 7. A central hole is formed in the center of the sun gear 7, penetrating the sun gear 7 in the thickness direction. The sun gear shaft 11 is attached to the sun gear 7 by fitting into the central hole of the sun gear 7.

[0013] The shaft member 1 has a cylindrical shape. The shaft member 1 has an outer circumferential surface. A detailed configuration of the shaft member 1 will be described later. The planetary gear 4 is a planetary pinion part of the planetary gear device. The planetary gear 4 is disposed between the internal gear 6 and the sun gear 7. A center hole is formed in the center of the planetary gear 4, penetrating the planetary gear 4 in the thickness direction.

[0014] The planetary gear 4 has an inner peripheral surface and an outer peripheral surface. A plurality of teeth (teeth 4a shown in FIG. 2 described later) are formed on the outer peripheral surface of the planetary gear 4 along the circumferential direction of the planetary gear 4. The teeth of the planetary gear 4 protrude from the outer peripheral surface toward the radially outward direction of the planetary gear 4. The teeth of the planetary gear 4 mesh with the teeth of the internal gear 6 and the teeth of the sun gear 7.

[0015] The shaft member 1 is inserted into the through hole of the planetary gear 4. In other words, the shaft member 1 is a so-called pinion shaft. The shaft member 1 is rotatably supported by the inner peripheral surface of the planetary gear 4. More specifically, a plurality of rolling elements, which will be described later, are arranged between the outer peripheral surface of the shaft member 1 and the inner peripheral surface of the planetary gear 4. From another perspective, the outer peripheral surface of the shaft member 1 is the surface of the shaft member 1 that comes into contact with the rolling elements. The rolling elements are, for example, needle rollers. The carrier is fixed to one end of the shaft member 1 in the axial direction (the direction in which the shaft member 1 extends).

[0016] By rotating the sun gear shaft 11, which serves as the input shaft, around its central axis, the sun gear 7 rotates around the central axis of the sun gear shaft 11. Because the teeth of the planetary gears 4 mesh with the teeth of the sun gear 7 and the teeth of the internal gear 6, the planetary gears 4 revolve around the sun gear 7 as the sun gear 7 rotates. The revolution of the planetary gears 4 is transmitted to the carrier via the shaft member 1, causing an output shaft (not shown) fixed to the carrier to rotate around its central axis. In this way, according to the planetary gear set 1000, the rotation of the input shaft is decelerated and then transmitted to the output shaft.

[0017] Fig. 2 is a partially cutaway perspective view showing the planetary gears and their supporting structure in a planetary transmission, with the planetary gears cut away. Fig. 3 is a cross-sectional view of the planetary gears and their supporting structure shown in Fig. 2. With reference to Figs. 1, 2 and 3, the planetary transmission has a rolling bearing device 12 that rotatably supports a planetary gear 4. The rolling bearing device 12 has a shaft member 1 and a plurality of needle rollers 2. The rolling bearing device 12 may have a cage 3. The rolling bearing device 12 may also include a planetary gear 4.

[0018] The planetary gears 4 are formed with a plurality of teeth 4a. Wall surfaces 4b defining the through holes of the planetary gears 4 form the inner peripheral surfaces of the planetary gears 4. The planetary gears 4 surround the outer periphery of the shaft member 1. The shaft member 1 has an oil passage 1a inside. The shaft member 1 corresponds to the inner member of the rolling bearing device 12, and the planetary gears 4 correspond to the outer member of the rolling bearing device 12. A needle roller bearing with a cage is arranged between the outer peripheral surface (raceway surface 1b) of the shaft member 1 and the inner peripheral surface (wall surface 4b) of the planetary gears 4.

[0019] The needle roller and cage bearing has a plurality of needle rollers 2 as rolling members, and a cage 3. The cage 3 has an annular shape and surrounds the outer peripheral surface of the shaft member 1. The cage 3 has a plurality of pockets 3a. The plurality of pockets 3a are arranged at approximately equal intervals along the circumferential direction. A needle roller 2 is held in each of the plurality of pockets 3a so that it can roll freely.

[0020] 2, each of the multiple needle rollers 2 is arranged to roll on the outer peripheral surface that forms the raceway surface 1b of the shaft member 1 and the inner peripheral surface that forms the wall surface 4b of the planetary gear 4. The planetary gear 4 is rotatably supported relative to the shaft member 1 by the needle roller bearing with cage.

[0021] As shown in Figure 3, a carbo-nitrided layer 2c is formed on the surface of each of the multiple needle rollers 2 and in areas very close to (very shallow) the surface. A carbo-nitrided layer 1c is formed on the surface of the shaft member 1 and in areas very close to (very shallow) the surface. This is formed by subjecting the needle rollers 2 and shaft member 1 to a carbonitriding treatment (carbonitriding treatment). In the shaft member 1 and needle rollers 2, the carbo-nitrided layers 1c, 2c are harder than other areas.

[0022] While a gear transmission has been described as an example of application of the shaft member 1, the present invention can also be applied to belt-type, toroidal-type, and hydraulic-type transmissions. Hereinafter, the rolling bearing device 12 according to this embodiment is assumed to include a plurality of needle rollers 2, which are rolling members, and the shaft member 1. However, the rolling bearing device 12 may also include, in addition to the above-described components, a cage 3 in which the plurality of needle rollers 2 are mounted. In other words, the rolling bearing device 12 may also include a needle roller bearing with cage and the shaft member 1. The portion of the rolling bearing device 12 consisting of the shaft member 1 and the needle roller bearing with cage is attached to a planetary gear 4 (planetary pinion portion) as shown in FIGS. 1 and 2.

[0023] <Material> The needle rollers 2 constituting the rolling bearing device 12 of this embodiment are made of high carbon chromium bearing steel (SUJ material). The cage 3 is made of carbon steel for machine structures. The shaft member 1 is made of chromium molybdenum steel (SCM material). From the viewpoint of suppressing the occurrence of micro-spalling in the rolling bearing device 12, it is preferable to use the above materials. However, the constituent materials of each member are not limited to the above. The material of the shaft member 1 may be any of SCr, SNC, and SNCM.

[0024] <Action and effect> Here, the features, functions and effects of the rolling bearing device according to this embodiment will be described.

[0025] The rolling bearing device according to this embodiment includes a plurality of rolling members (needle rollers 2) and a shaft member 1. The shaft member 1 supports the plurality of needle rollers 2 rotatably and in direct contact with the plurality of needle rollers 2. Each of the plurality of needle rollers 2 is made of steel containing 0.95% to 1.10% by mass of carbon, 0.5% to 1.10% by mass of manganese, 0.008% to 0.008% by mass of sulfur, 0.15% to 0.35% by mass of silicon, and 1.30% to 1.60% by mass of chromium, with the remainder being iron and impurities. The hardness of each of the plurality of needle rollers 2 at a depth of 0.05 mm to 0.20 mm from its first contact surface (outermost surface), which is the surface that comes into contact with other components, is 733 HV or higher. The surface roughness Ra of the first contact surface of each of the plurality of needle rollers 2 is 0.01 μm to 0.05 μm. The nitrogen concentration of the first surface layer portion, including the first contact surface of each of the multiple needle rollers (2), is 0.20% by mass or more and 0.60% by mass or less. The shaft member (1) is made of steel containing 0.10% by mass or more and 0.40% by mass or less of carbon, 0.10% by mass or more and 2.50% by mass or less of silicon, 0.30% by mass or more and 1.20% by mass or less of manganese, 0.40% by mass or more and less than 3.00% by mass of chromium, and 1.00% by mass or less of molybdenum, with the balance being iron and impurities. The hardness at a depth of 0.05 mm to 0.20 mm from the second contact surface (outermost surface), which is the surface of the shaft member (1) that comes into contact with other parts, is 720 HV or more. The surface roughness Ra of the second contact surface of the shaft member (1) is 0.01 μm to 0.05 μm or less. The nitrogen concentration of the second surface layer portion, including the second contact surface of the shaft member (1), is 0.20% by mass or more and 1.20% by mass or less. The carbon concentration of the second surface layer portion is 0.60 mass % or more and 1.20 mass % or less.

[0026] In the above, "the hardness of the needle roller 2 is 733 HV or more" means that the hardness is 733 HV or more throughout the entire region from 0.05 mm to 0.20 mm deep from the first contact surface. "The first surface layer portion" means the region within 0.05 mm (50 μm) deep from the first contact surface. "The nitrogen concentration of the first surface layer portion is 0.20 mass% to 0.60 mass%" means that the nitrogen concentration is within the above numerical range throughout the entire first surface layer portion. "The hardness of the shaft member 1 is 720 HV or more" means that the hardness is 720 HV or more throughout the entire region from 0.05 mm to 0.20 mm deep from the second contact surface. "The second surface layer portion" means the region within 0.05 mm (50 μm) deep from the second contact surface. "The nitrogen concentration of the second surface layer portion is 0.20 mass% to 1.20 mass%" means that the nitrogen concentration is within the above numerical range throughout the entire second surface layer portion. The carbon concentration of the second surface layer portion being 0.60 mass% or more and 1.20 mass% or less means that the carbon concentration of the entire second surface layer portion is 0.60 mass% or more and 1.20 mass% or less. Furthermore, the surface roughness Ra in this specification means the arithmetic mean roughness Ra specified in JIS B 0601.

[0027] As described above, the rolling bearing device of this embodiment is characterized by the hardness, surface roughness, and nitrogen concentration (and carbon concentration) of the needle rollers 2 and shaft member 1. The hardness of the depth region from the first contact surface of the needle rollers 2 to a depth of 0.05 mm or more and 0.20 mm or less is set to 733 HV or more. In other words, the hardness of the region close to the first contact surface is maintained high. This suppresses the occurrence of micro-spalling in the needle rollers 2. Of the above, it is particularly preferable that the hardness of the depth region from the first contact surface of the needle rollers 2 to a depth of 0.05 mm or more and 0.20 mm or less is 759 HV or more.

[0028] The surface roughness Ra of the first contact surface of needle roller 2 is set to 0.01 μm or more and 0.05 μm or less. By making the surface roughness smooth in this way, a sufficient oil film can be formed even in a lean lubrication environment. Among the above, it is particularly preferable that the surface roughness Ra of the first contact surface of needle roller 2 be set to 0.01 μm or more and 0.03 μm or less.

[0029] If the nitrogen concentration in the first surface layer portion of the needle roller 2 is 0.20 mass% or more, the needle roller 2 is less likely to soften after tempering, improving temper softening resistance. If the nitrogen concentration in the first surface layer portion is 0.20 mass% or more, solid solution strengthening and precipitation hardening by nitrogen are possible. If the nitrogen concentration is 0.60 mass% or less, the risk of carbides and carbonitrides in the steel material disappearing can be reduced. Among the above, it is particularly preferable that the nitrogen concentration in the first surface layer portion of the needle roller 2 be 0.20 mass% or more and 0.30 mass% or less.

[0030] The hardness of the region of the shaft member 1 that is 0.05 mm to 0.20 mm deep from the second contact surface is set to 720 HV or higher. In other words, the hardness of the region close to the second contact surface is maintained high. This suppresses the occurrence of micro-spalling in the shaft member 1. The region less than 0.05 mm deep from the first and second contact surfaces is a region that wears with use and loses properties such as hardness. For this reason, it is preferable to set the hardness of the region 0.05 mm or deeper from the first and second contact surfaces as described above.

[0031] The surface roughness Ra of the second contact surface of the shaft member 1 is set to 0.01 μm or more and 0.05 μm or less. By smoothing the surface roughness in this way, a sufficient oil film can be formed even in a lean lubrication environment. However, if the surface roughness Ra is set to less than 0.01 μm, the cost of surface processing will increase. For this reason, a surface roughness Ra of 0.01 μm or more is preferable. Among the above, it is particularly preferable that the surface roughness Ra of the second contact surface of the shaft member 1 be set to 0.01 μm or more and 0.03 μm or less.

[0032] If the nitrogen concentration of the second surface layer portion of the shaft member 1 is 0.20 mass% or more, temper softening resistance is improved. If the nitrogen concentration of the second surface layer portion is 0.20 mass% or more, solid solution strengthening and precipitation hardening by nitrogen are possible. If the nitrogen concentration is 1.20 mass% or less, a decrease in hardness of the surface layer caused by an excessive amount of retained austenite can be suppressed. Among the above, it is particularly preferable that the nitrogen concentration of the second surface layer portion of the shaft member 1 be 0.30 mass% or more and 0.80 mass% or less.

[0033] If the carbon concentration of the second surface layer portion of the shaft member 1 is 0.60% by mass or more, carbides can be obtained inside the steel material, and the steel material can have an appropriate hardness. If the carbon concentration is 1.20% by mass or less, the risk of abnormal structures such as reticulated cementite occurring in the surface layer of the steel material can be reduced. Generally, case-hardened steels often have a carbon concentration of 0.20% by mass or less to facilitate carburizing and carbonitriding processes. However, in this embodiment, the carbon concentration is set to 0.60% by mass or more and 1.20% by mass or less, which is higher than that of ordinary case-hardened steels, from the viewpoint of spalling resistance.

[0034] From the viewpoint of suppressing the occurrence of micro-spalling, it is preferable that the materials constituting the needle rollers 2 and the shaft member 1 have the following numerical content ranges. Other effects resulting from the material compositions of the needle rollers 2 and the shaft member 1 are as follows: The carbon content of the needle rollers 2 is set to 0.95 mass% or more and 1.10 mass% or less. If the carbon content of the needle rollers 2 is set to 0.95 mass% or more, the amount of carbides in the steel constituting the needle rollers 2 can be sufficiently increased and the hardness of the steel can be sufficiently increased without introducing a large amount of carbon through heat treatment. If the carbon content of the needle rollers 2 is set to 1.10 mass% or less, the risk of large carbide lumps forming in the steel constituting the needle rollers 2 during its manufacturing stage can be reduced.

[0035] If the manganese content of the needle roller 2 is 0.5 mass % or less, the hardness of the material of the needle roller 2 before heat treatment can be reduced, thereby improving the workability of the needle roller 2 in the cold working process.

[0036] If the sulfur content of the needle rollers 2 is 0.008 mass % or less, the risk that the steel material constituting the needle rollers 2 will chemically bond with manganese or the like to form non-metallic inclusions such as manganese sulfide can be reduced.

[0037] If the silicon content of needle roller 2 is 0.15 mass% or more, nitrides are more likely to precipitate during heat treatment, increasing hardness. If the silicon content of needle roller 2 is 0.35 mass% or less, it is possible to suppress an increase in the amount of hydrogen absorbed into the steel material that constitutes needle roller 2. This reduces the risk of peeling of the steel material that constitutes needle roller 2 due to hydrogen embrittlement.

[0038] Setting the chromium content of needle roller 2 to 1.30 mass % or more and 1.60 mass % improves the hardenability of the steel material that constitutes needle roller 2. In other words, needle roller 2 as a whole can be sufficiently hardened by quenching.

[0039] By setting the carbon content of the shaft member 1 to 0.10 mass % or more and 0.40 mass % or less, it is possible to reduce the amount of retained austenite in the core away from the surface of the shaft member 1. This makes it possible to suppress creep deformation of the shaft member 1. Note that creep deformation refers to the phenomenon in which a material undergoes plastic deformation even when a small stress below the yield point is applied as a result of a load being continuously applied to the material over time.

[0040] Nitride precipitation is promoted by setting the silicon content of the shaft member 1 to 0.10 mass % or more and 2.50 mass % or less, and as a result, temper softening resistance is improved by precipitation hardening.

[0041] By setting the manganese content of the shaft member 1 to 0.30% by mass or more and 1.20% by mass or less, the hardenability of the steel material constituting the shaft member 1 can be improved. In other words, the entire shaft member 1 can be sufficiently quench-hardened. By setting the manganese content of the shaft member 1 to 0.30% by mass or more and 1.20% by mass or less, the hardenability of the steel material constituting the shaft member 1 can be improved.

[0042] By setting the chromium content of the shaft member 1 to 0.40 mass % or more and less than 3.00 mass %, the hardenability of the members constituting the shaft member 1 can be improved, and the temper softening resistance can be improved.

[0043] By setting the molybdenum content of the shaft member 1 to 1.00 mass % or less, the hardenability of the members constituting the shaft member 1 can be improved, and the temper softening resistance can be improved.

[0044] In the rolling bearing device 12, the amount of retained austenite in the first and second surface layer portions may be 25% by volume or more and 35% by volume or less. By setting the amount of retained austenite to 25% by volume or more, crack propagation can be reduced even if foreign matter gets caught in the rolling bearing device 12 under operating conditions with lubrication containing foreign matter. This is because the presence of relatively soft retained austenite at positions 0.05 mm (50 μm) from the first and second contact surfaces relieves stress at these positions. Setting the amount of retained austenite at these positions to 35% by volume or less prevents excessive reduction in hardness of the first and second surface layer portions.

[0045] The amount of retained austenite at a position 0.05 mm deep from the first contact surface and at a position 0.05 mm deep from the second contact surface may be 25% by volume or more and 35% by volume or less. The amount of retained austenite in the entire first surface layer portion and / or second surface layer portion (all regions) may be 25% by volume or more and 35% by volume or less, or the average amount of retained austenite in the entire first surface layer portion and / or second surface layer portion may be 25% by volume or more and 35% by volume or less.

[0046] In the above-described rolling bearing device 12, the grain size number of the prior austenite crystals in the needle rollers 2 is equal to or greater than 9 and equal to or less than 11, and the grain size number of the prior austenite crystals in the shaft member 1 is equal to or greater than 7 and equal to or less than 11. By making the crystal grains in the needle rollers 2 and the shaft member 1 dense, it is possible to slow the propagation of cracks when micro-spalling occurs.

[0047] In the rolling bearing device 12, the amount of retained austenite in the core, which is a region farther from the second contact surface than the second surface layer portion of the shaft member 1, is preferably 0.5% by volume or more and 3.0% by volume or less. Here, the core refers to a region whose distance from the center of a cross section (e.g., a circle) intersecting the extension direction of the shaft member 1 is within 20% of the radius of the circular cross section. This makes it possible to suppress creep deformation of the shaft member 1.

[0048] <Measurement method> The hardness (cross-sectional hardness) of the needle rollers 2 and shaft member 1, for example, in a region from the outermost surface to a depth of 0.05 mm or more and 0.20 mm or less, is measured using a Vickers hardness tester, from the outermost surface, first surface layer portion, and second surface layer portion to the inner part (core portion). The surface roughness Ra of the first contact surface and second contact surface is measured using a contact-type roughness measuring device. That is, the surface roughness Ra is measured by moving the measuring device along the axial direction while contacting the outer diameter surfaces of the needle rollers 2 and shaft member 1. The nitrogen concentration and carbon concentration of the first surface layer portion and second surface layer portion can be measured using an electron probe microanalyzer (EPMA). The amount of retained austenite at a certain depth position or surface layer portion is measured using an X-ray analyzer.

[0049] The grain size numbers of the prior austenite crystals in the needle rollers 2 and the shaft member 1 are obtained by corroding the actual objects with a nitric acid ethanol solution to reveal the crystal grains, which are then magnified and observed under a microscope, and measuring the grain size. For example, in this specification, the grain size numbers of the prior austenite crystals in the needle rollers 2 and the shaft member 1 are measured at a position 50 μm deep from the surface (first contact surface and second contact surface) that has been revealed. However, the depth position is not limited to the above, as it is sufficient to measure the grain size number of the prior austenite crystals for the crystal grains revealed as described above. The grain size number may also be measured at any position within a depth of 50 μm from the surface (first contact surface and second contact surface).

[0050] <Method for manufacturing rolling bearing device> FIG. 4 is a flowchart showing an outline of a manufacturing method for a rolling bearing device according to this embodiment. Referring to FIG. 4, a steel material preparation step (S10) is first performed. In step (S10), a high-carbon chromium bearing steel material (SUJ material) for forming needle roller 2 and a chromium-molybdenum steel material (SCM material) for forming shaft member 1 are prepared. The SUJ material contains 0.95% by mass to 1.10% by mass of carbon, 0.5% by mass to 1.10% by mass of manganese, 0.008% by mass to 0.15% by mass to 0.35% by mass of silicon, and 1.30% by mass to 1.60% by mass of chromium, with the remainder consisting of iron and impurities. A wire material is prepared by, for example, subjecting such steel material to multiple wiredrawing processes. The wire material is then subjected to processes such as cutting, forging, and turning. This results in a steel material formed into the general shape of needle roller 2. SCM material contains 0.10% to 0.40% by mass of carbon, 0.10% to 2.50% by mass of silicon, 0.30% to 1.20% by mass of manganese, 0.40% to 3.00% by mass of chromium, and 1.00% or less by mass of molybdenum, with the balance being iron and impurities. Such steel material, such as a steel bar or steel wire, is used as a raw material, and the steel bar or steel wire is subjected to processing such as cutting, forging, and turning. This results in a steel material formed into the general shape of the shaft member 1.

[0051] Next, in step (S20), a heat treatment step is carried out. Fig. 5 is a flowchart showing the procedure of the heat treatment step (S20) for the steel material to be made into a needle roller. Referring to Fig. 5, the steel material formed into the general shape of needle roller 2 is first subjected to a heating step (S21) as a preparation stage. In the heating step (S21), the steel material is heated to, for example, 850°C or higher and 940°C or lower.

[0052] In the heat treatment process (S20) for a steel material to be made into a needle roller, a heating process (S21) is followed by a carbo-nitriding process (S22A). In the carbo-nitriding process (S22A), the steel material is heated to or above the A1 transformation point in a heat treatment gas and maintained at that temperature. Specifically, an enriched gas serving as a carbon source and ammonia gas serving as a nitrogen source are added as an endothermic conversion gas (RX gas). The enriched gas may be propane gas, butane gas, or the like. The steel material is placed in this atmosphere and heated to a temperature between 850°C and 940°C. When the heating temperature exceeds 940°C, the decomposition of ammonia gas is promoted, and undecomposed ammonia is reduced. As a result, the nitrogen concentration in the first surface layer portion, including the first contact surface of the steel material, is likely to be lower than the desired value. For this reason, the heating temperature is preferably 940°C or lower.

[0053] In the heat treatment step (S20) of the steel material to be made into needle rollers, a carbo-nitriding step (S22) is followed by a quenching step (S23). In the quenching step (S23), the steel material, which has been maintained at or above the A1 transformation point, is immersed in oil (oil quenching) to be rapidly cooled to a temperature below the Ms point (martensitic transformation start point). In the quenching step (S23), instead of oil quenching, the steel material may be immersed in water to be cooled (water quenching).

[0054] In the heat treatment step (S20) of the steel material to be made into needle rollers, a quenching step (S23) is followed by a tempering step (S24). In the tempering step (S24), the steel material that has been quench-hardened in the quenching step (S23) is subjected to heat treatment at a temperature below the A1 transformation point. More specifically, after step (S23) is completed, the steel material is heated to a temperature below the A1 transformation point, between 160°C and 200°C. The steel material is subjected to tempering treatment by being held at this temperature for a predetermined time. Thereafter, the steel material is cooled in air at room temperature (air cooling). The toughness of the steel material can be improved by the tempering treatment (S24). As a result of the above, a steel material is formed that has a cross section intersecting the extension direction that is, for example, a circle with a diameter of 1.5 mm to 5.5 mm and that has the desired hardness and toughness.

[0055] Fig. 6 is a flow chart showing the procedure of the heat treatment step (S20) for the steel material to be made into the shaft member. Referring to Fig. 6, the steel material formed into the general shape of the shaft member 1 is first subjected to a heating step (S21) as a preparation stage. This is the same as the heating step (S21) for the needle roller 2 described above, and therefore the description thereof will not be repeated.

[0056] In the heat treatment process (S20) for steel material to be used as a shaft member, a heating process (S21) is followed by a carburizing process (S22B). In the carburizing process (S22B), the steel material is heated to or above the A1 transformation point in a heat treatment gas and maintained at that temperature. Specifically, an enriched gas serving as a carbon source is added as an endothermic transformation gas (RX gas). The enriched gas is, for example, propane gas or butane gas. The steel material is placed in this atmosphere and heated to 850°C or higher and 940°C or lower. The carburizing process (S22B) may be omitted.

[0057] The steel material to be used as the shaft member is then subjected to a carbonitriding step (S22C). The carbonitriding step (S22C) is similar to the carbonitriding step (S22A) described above, and therefore a detailed description thereof will not be repeated. The temperature at which the steel material is held in the carbonitriding step (S22C) is preferably the same as the temperature at which the steel material is held in the carburizing step (S22B).

[0058] Thereafter, the steel material to be used as the shaft member is subjected to a quenching step (S23) and a tempering step (S24). These steps are similar to those for the needle rollers, and therefore the description thereof will not be repeated.

[0059] Referring again to Figure 4, the steel material to become the needle rollers and the steel material to become the shaft member that have been subjected to the heat treatment step (S20) as shown in Figures 5 and 6 are subjected to a grinding step (S30). This results in needle rollers 2 and shaft member 1 with their final dimensions and shape. These are combined to form the rolling bearing device 12 shown in Figures 2 and 3. [Example]

[0060] A test was conducted to compare the life of needle rollers 2 constituting rolling bearing device 12 according to this embodiment with that of needle rollers 2 according to a comparative example.

[0061] FIG. 7 is a schematic cross-sectional view showing the configuration of a radial load tester used in the examples. Referring to FIG. 7, the radial load tester used in the examples has an aspect that imitates the planetary gear 4 and its support structure shown in FIG. 2. That is, the radial load tester used in the examples includes an aspect that imitates the rolling bearing device 12 according to this embodiment shown in FIG. 2. Specifically, the radial load tester 200 in FIG. 7 includes a shaft 10, rollers 20, a cage 30, and an outer ring 40. The shaft 10 corresponds to the shaft member 1 in FIG. 2. The rollers 20 correspond to the needle rollers 2 in FIG. 2. The cage 30 corresponds to the cage 3 in FIG. 2. The outer ring 40 corresponds to the planetary gear 4 in FIG. 2. Therefore, the shaft 10 and rollers 20 (and cage 30) in FIG. 7 together correspond to the rolling bearing device 12 according to this embodiment.

[0062] In Example 1, a radial load testing machine 200 (designated testing machine B1) was prepared, which combined a shaft 10 (designated shaft B1) formed under the conditions for the rolling bearing device 12 of this embodiment with a roller 20 (designated roller B1) formed under the conditions for the rolling bearing device 12 of this embodiment. For comparison, a radial load testing machine 200 (designated testing machine A1) was prepared, which combined the shaft B1 with a roller 20 (designated roller A1) formed under conditions other than those for the rolling bearing device 12 of this embodiment. Testing machines A1 and B1 were rotated in the same manner as the actual product of the planetary gear 4 and its support structure shown in FIG. 2, and a test was conducted to compare the life ratios of both. The verified life ratio was the L50 life, i.e., the time required for the cumulative failure probability to reach 50% (confidence level 50%). From the viewpoint of investigating the L50 life, six rollers A1 and six shafts B1 were used for the test machine A1, and seven rollers B1 and seven shafts B1 were used for the test machine B1.

[0063] The rotational drive conditions for the testing machines A1 and B1 were as follows: The rotational speed of the shaft 10 was a constant 9,000 revolutions per minute. The radial load was 8,400 N. The radial load refers to the load applied radially to the shaft 10 from the outside of the rotating shaft 10, as indicated by arrow F in Figure 7. The lubrication conditions for the testing machines A1 and B1 were a clean oil core oil bath. A core oil bath refers to a form in which the lubricant is supplied centered on the shaft 10. The surface roughness Ra of the outer ring 40 was 0.4 μm or more and 0.5 μm or less. The surface roughness Ra of the outer ring raceway surface 40a of the outer ring 40, which faces the rollers 20 and cage 30 in the radial direction, is shown here.

[0064] The conditions for each component of each testing machine A1, B1, and the resulting L50 life values ​​are shown in Table 1. The items in Table 1 are as follows: "Cross-section hardness" is the cross-section depth in the region 0.05 mm to 0.20 mm deep from the surface (contact surface) of each component. "Surface layer" refers to the first surface layer (needle roller) or second surface layer (shaft member) described above. "Core" refers to the region as defined above. The "core" of needle roller 2 is the same as the "core" of shaft member 1, and is the region whose distance from the center of a cross section (for example, a circle) intersecting the extension direction of needle roller 2 is within 20% of the radius of the circular cross section. "Grain size number" refers to those at a position 0.05 mm deep from the surface (contact surface) of each component.

[0065] [Table 1]

[0066] From Table 1, it can be seen that the L50 life was longer (1.7 times) when rollers formed under the cross-sectional hardness, surface roughness Ra, and surface layer nitrogen concentration conditions according to this embodiment were used than the comparative example in which rollers formed under the above conditions were used. This confirmed the effectiveness of this embodiment over the comparative example. [Example]

[0067] A test was conducted to compare the lifespan of the shaft member 1 constituting the rolling bearing device 12 according to this embodiment with that of a shaft member 1 according to a comparative example. This test was conducted using the radial load testing machine 200 shown in Fig. 7, as in Example 1 (however, as will be described later, there are differences in the roughness of the outer ring raceway surface, etc.).

[0068] In Example 2, a radial load testing machine 200 (designated testing machine B2) was prepared, which combined a shaft 10 (designated shaft B2) formed under the conditions for the rolling bearing device 12 of this embodiment with a roller 20 (designated roller B1) formed under the conditions for the rolling bearing device 12 of this embodiment. For comparison, a radial load testing machine 200 (designated testing machine A2) was prepared, which combined the roller B1 with a shaft 10 (designated shaft A1) formed under conditions other than those for the rolling bearing device 12 of this embodiment. Testing machines A2 and B2 were rotated in the same manner as the actual product of the planetary gear 4 and its support structure shown in FIG. 2, and a test was conducted to compare the life ratios of both. The verified life ratio was the L10 life, i.e., the time required for the cumulative failure probability to reach 10% (90% confidence). In order to investigate the L10 life, six rollers B1 and six shafts A1 were used for the test machine A2, and 14 rollers B1 and six shafts B2 were used for the test machine B2.

[0069] The rotational drive conditions for testing machines A2 and B2 were as follows: The rotational speed of the outer ring 40 was a constant 9,000 revolutions per minute. The radial load was 6,670 N, and the moment load was 13.5 N·m. The moment load refers to the load indicated by arrow M in Figure 7 acting on the fixed shaft 10. The lubrication conditions for testing machines A2 and B2 were clean oil circulating. Circulating lubrication means that lubrication is provided by circulating unused clean lubricating oil within testing machines A2 and B2. The surface roughness Ra of the outer ring raceway surface 40a of the outer ring 40 was 0.2 μm.

[0070] The conditions for each member of each test machine A2, B2 and the obtained L10 life values ​​are as shown in Table 2. Each item in Table 2 is defined in the same way as each item in Table 1.

[0071] [Table 2]

[0072] From Table 2, it can be seen that the L10 life was longer (1.3 times) when rollers formed under the cross-sectional hardness, surface roughness Ra, nitrogen concentration and carbon concentration conditions of the surface layer according to this embodiment were used than the comparative example in which rollers formed under the above conditions were used. This confirmed the effectiveness of this embodiment over the comparative example.

[0073] The features described in the above-described embodiments and examples may be applied in appropriate combinations within the scope of technical compatibility.

[0074] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0075] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A plurality of rolling members; a shaft member that supports the plurality of rolling members rotatably and in direct contact with the plurality of rolling members, each of the plurality of rolling contact members is made of steel containing 0.95% by mass or more and 1.10% by mass or less of carbon, 0.5% by mass or less of manganese, 0.008% by mass or less of sulfur, 0.15% by mass or more and 0.35% by mass or less of silicon, 1.30% by mass or more and less than 1.60% by mass of chromium, with the remainder being iron and impurities; the hardness at a depth of 0.05 mm or more and 0.20 mm or less from a first contact surface, which is a surface of each of the plurality of rolling members that comes into contact with other components, is 733 HV or more; the surface roughness Ra of the first contact surface of each of the plurality of rolling members is 0.01 μm or more and 0.05 μm or less; a nitrogen concentration in a first surface layer portion including the first contact surface of each of the plurality of rolling members is 0.20% by mass or more and 0.60% by mass or less; the shaft member is made of steel containing 0.10% by mass or more and 0.40% by mass or less of carbon, 0.10% by mass or more and 2.50% by mass or less of silicon, 0.30% by mass or more and 1.20% by mass or less of manganese, 0.40% by mass or more and less than 3.00% by mass of chromium, and 1.00% by mass or less of molybdenum, with the remainder being iron and impurities; The hardness at a depth of 0.05 mm or more and 0.20 mm or less from a second contact surface, which is a surface where the shaft member comes into contact with another part, is 720 HV or more, the surface roughness Ra of the second contact surface of the shaft member is 0.01 μm or more and 0.05 μm or less; a nitrogen concentration in a second surface layer portion including the second contact surface of the shaft member is 0.20 mass % or more and 1.20 mass % or less; The rolling bearing device, wherein the carbon concentration of the second surface layer portion is 0.60 mass % or more and 1.20 mass % or less.

[0076] (Appendix 2) 2. The rolling bearing device according to claim 1, wherein the first surface layer portion and the second surface layer portion have an amount of retained austenite of 25% by volume or more and 35% by volume or less.

[0077] (Appendix 3) The grain size number of the prior austenite crystals of the rolling members is 9 or more and 11 or less, 3. The rolling bearing device according to claim 1, wherein the grain size number of the prior austenite crystals of the shaft member is 7 or more and 11 or less.

[0078] (Appendix 4) A rolling bearing device as described in any one of Appendices 1 to 3, wherein the amount of retained austenite in the core portion, which is a region of the shaft member farther from the second contact surface than the second surface layer portion, is 0.5 volume % or more and 3.0 volume % or less.

[0079] (Appendix 5) 5. The rolling bearing device according to any one of claims 1 to 4, including a planetary pinion portion of a planetary gear device. [Explanation of symbols]

[0080] 1 shaft member, 1a oil passage, 1b raceway surface, 1c, 2c carbo-nitrided layer, 2 needle roller (rolling member), 3, 30 cage, 3a pocket, 4 planetary gear, 4a tooth, 4b wall surface, 6 internal gear, 7 sun gear, 10 shaft, 11 sun gear shaft, 12 rolling bearing device, 20 roller, 40 outer ring, 40a outer ring raceway surface, 200 radial load testing machine, 1000 planetary gear device.

Claims

1. A plurality of rolling members; a shaft member that supports the plurality of rolling members rotatably and in direct contact with the plurality of rolling members, each of the plurality of rolling members is made of steel containing 0.95% by mass or more and 1.10% by mass or less of carbon, 0.5% by mass or less of manganese, 0.008% by mass or less of sulfur, 0.15% by mass or more and 0.35% by mass or less of silicon, 1.30% by mass or more and less than 1.60% by mass of chromium, with the balance being iron and impurities; the hardness at a depth of 0.05 mm or more and 0.20 mm or less from a first contact surface, which is a surface of each of the plurality of rolling members that comes into contact with another component, is 733 HV or more; a surface roughness Ra of the first contact surface of each of the plurality of rolling members is 0.01 μm or more and 0.05 μm or less; a nitrogen concentration in a first surface layer portion including the first contact surface of each of the plurality of rolling members is 0.20 mass % or more and 0.60 mass % or less; the shaft member is made of steel containing 0.10% by mass or more and 0.40% by mass or less of carbon, 0.10% by mass or more and 2.50% by mass or less of silicon, 0.30% by mass or more and 1.20% by mass or less of manganese, 0.40% by mass or more and less than 3.00% by mass of chromium, and 1.00% by mass or less of molybdenum, with the remainder being iron and impurities; The hardness at a depth of 0.05 mm to 0.20 mm from a second contact surface, which is a surface of the shaft member that comes into contact with another component, is 720 HV or more, the surface roughness Ra of the second contact surface of the shaft member is 0.01 μm or more and 0.05 μm or less; a nitrogen concentration in a second surface layer portion including the second contact surface of the shaft member is 0.20 mass % or more and 1.20 mass % or less; The rolling bearing device, wherein the carbon concentration of the second surface layer portion is 0.60 mass % or more and 1.20 mass % or less.

2. 2. The rolling bearing device according to claim 1, wherein the amount of retained austenite in the first surface layer portion and the second surface layer portion is 25% by volume or more and 35% by volume or less.

3. the grain size number of the prior austenite crystals of the rolling members is 9 or more and 11 or less, 3. The rolling bearing device according to claim 1, wherein the grain size number of the prior austenite crystals of said shaft member is 7 or more and 11 or less.

4. 3. The rolling bearing device according to claim 1, wherein the amount of retained austenite in the core portion, which is a region of the shaft member farther from the second contact surface than the second surface layer portion, is 0.5% by volume or more and 3.0% by volume or less.

5. 3. The rolling bearing device according to claim 1, further comprising a planetary pinion portion of a planetary gear device.

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