Rolling member

Abstract

To provide a rolling member capable of prolonging the service life by suppressing micro-spalling.SOLUTION: The hardness at a depth of 0. 05mm or more and 0. 20mm or less from a contact surface, which is a surface where needle roller 2 comes into contact with another component, is 733HV or more. The contact surface has a surface roughness Ra of 0.01 μm or more and 0.05 μm or less. The nitrogen concentration of the surface layer portion including the contact surface is 0.20 mass% or more and 0.60 mass% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rolling member. [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 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 mixed in. For example, Japanese Patent Application Laid-Open No. 2007-332390 (Patent Document 1) proposes improving the wear resistance and seizure resistance of rolling members under lubricated conditions where foreign matter is mixed in or in an environment with insufficient lubrication. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-332390 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, rolling contact members made of SUJ3 bearing steel are subjected to carbonitriding treatment to increase the nitrogen concentration in the surface layer and precipitate appropriate amounts of carbides or carbonitrides containing silicon and manganese. This improves the wear resistance and seizure resistance of the rolling contact members and extends their rolling fatigue life. 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 member that can have a long life by suppressing micro-spalling. [Means for solving the problem]

[0007] The rolling contact member according to the present disclosure is made of steel. The steel contains 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, and the remainder being iron and impurities. The hardness at a depth of 0.05 mm to 0.20 mm from the contact surface, which is the surface of the rolling contact member that comes into contact with other components, is 733 HV or more. The surface roughness Ra of the contact surface is 0.01 μm to 0.05 μm. The nitrogen concentration of the surface layer including the contact surface is 0.20% by mass to 0.60% by mass. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a rolling member that can have a long 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 method for manufacturing a rolling bearing device including needle rollers 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-type 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, a rolling bearing device 12 is assumed to include a plurality of needle rollers 2, which are the rolling members according to this embodiment, and the shaft member 1. However, the rolling bearing device 12 may also include a cage 3 in which the plurality of needle rollers 2 are mounted, in addition to the above-mentioned components. That is, 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 . The rolling members according to this embodiment are the plurality of needle rollers 2 included in the needle roller bearing with cage.

[0023] <Material> The needle rollers 2 of this embodiment that make up the rolling bearing device 12 are made of high carbon chromium bearing steel (SUJ material). The needle rollers 2 are made of SUJ2, which is particularly easy to procure. The cage 3 is made of carbon steel for mechanical 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, actions and effects of the rolling member (needle roller 2) according to this embodiment will be described.

[0025] The rolling member (needle roller 2) according to this embodiment 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, and the remainder being iron and impurities. The hardness of the needle roller 2 at a depth of 0.05 mm to 0.20 mm from the contact surface (outermost surface) that is the surface that comes into contact with other parts is 733 HV or more. The surface roughness Ra of the contact surface is 0.01 μm to 0.05 μm. The nitrogen concentration of the surface layer including the contact surface is 0.20% by mass to 0.60% by mass.

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

[0027] As described above, the needle roller 2 of this embodiment is characterized by its hardness, surface roughness, and nitrogen concentration. The hardness of the depth region from the contact surface of the needle roller 2 to 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 contact surface is maintained high. This suppresses the occurrence of micro-spalling in the needle roller 2. Among the above, it is particularly preferable that the hardness of the depth region from the contact surface of the needle roller 2 to 0.05 mm or more and 0.20 mm or less is 759 HV or more.

[0028] The surface roughness Ra of the contact surface of the 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 contact surface of the needle roller 2 be set to 0.01 μm or more and 0.03 μm or less.

[0029] If the nitrogen concentration in the surface layer 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 surface layer 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 surface layer of the needle roller 2 be 0.20 mass% or more and 0.30 mass% or less.

[0030] From the viewpoint of suppressing the occurrence of micro-spalling, it is preferable that each material constituting the needle roller 2 has the following numerical content range. Other effects resulting from the material composition of the needle roller 2 are as follows: The carbon content of the needle roller 2 is set to 0.95 mass% or more and 1.10 mass% or less. If the carbon content of the needle roller 2 is set to 0.95 mass% or more, the amount of carbide in the steel constituting the needle roller 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 roller 2 is set to 1.10 mass% or less, the risk of large carbide lumps forming in the steel constituting the needle roller 2 during its manufacturing stage can be reduced.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In the needle roller 2, the amount of retained austenite in the surface layer may be 25% by volume or more and 35% by volume or less. By making the amount of retained austenite 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 contaminated foreign matter. This is because having relatively soft retained austenite at a position 0.05 mm (50 μm) from the contact surface relieves stress at that position. By making the amount of retained austenite at that position 35% by volume or less, excessive reduction in hardness of the surface layer can be prevented.

[0036] The amount of retained austenite at a depth of 0.05 mm from the contact surface may be 25% by volume or more and 35% by volume or less. The amount of retained austenite in the entire 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 surface layer portion may be 25% by volume or more and 35% by volume or less.

[0037] In the needle roller 2, the grain size number of the prior austenite crystals is equal to or greater than 9 and equal to or less than 11. By making the crystal grains of the needle roller 2 dense, it is possible to retard the propagation of cracks when micro-spalling occurs.

[0038] <Measurement method> The hardness (cross-sectional hardness) of a region of the needle roller 2, for example, 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, the surface layer, to the inner part (core). The surface roughness Ra of the contact surface is measured using a contact-type roughness measuring instrument. That is, the surface roughness Ra is measured by moving the measuring instrument in the axial direction while contacting the outer diameter surface of the needle roller 2. The nitrogen concentration and carbon concentration in the surface layer can be measured using an electron probe micro analyzer (EPMA). The amount of retained austenite at a certain depth position or in the surface layer is measured using an X-ray analyzer.

[0039] The grain size number of the prior austenite crystals of the needle roller 2 is obtained by corroding the actual product with a nitric acid ethanol solution to expose the crystal grains, observing them under a microscope to enlarge them, and measuring the grain size. For example, in this specification, the grain size number of the prior austenite crystals of the needle roller 2 is measured at a position that is 50 μm deep from the surface (contact surface) that has been exposed. However, since it is sufficient to measure the grain size number of the prior austenite crystals for the crystal grains that have been exposed as described above, the depth position is not limited to the above. The grain size number may also be measured at any position within a depth of 50 μm from the surface (contact surface).

[0040] <Method for manufacturing rolling bearing device> FIG. 4 is a flowchart showing an outline of a manufacturing method for a rolling bearing device including a needle roller 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 the needle roller 2 and a chromium-molybdenum steel material (SCM material) for forming the 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 0.008% by mass of manganese, 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 from such a steel material by, for example, 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 the 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.

[0041] 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.

[0042] In the heat treatment process (S20) for steel material to be formed into needle rollers, 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 surface layer, including the contact surface of the steel material, tends to be lower than the desired value. For this reason, a heating temperature of 940°C or lower is preferred.

[0043] 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).

[0044] 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 heat-treated 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 tempered by holding it at this temperature for a predetermined time. The steel material is then cooled in air at room temperature (air cooling). The tempering treatment (S24) can improve the toughness of the steel material. As a result, 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. The needle roller 2, which is the steel material formed in the above manner, is ultimately incorporated into the previously described needle roller and cage bearing. However, the needle rollers 2 may be incorporated into either a drawn cup needle roller bearing or a solid needle roller bearing.

[0045] 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.

[0046] In the heat treatment step (S20) of the steel material to be made into the shaft member, a heating step (S21) is followed by a carburizing step (S22B). In the carburizing step (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 may be propane gas, butane gas, or the like. The steel material may be placed in such an atmosphere and heated to 850°C or higher and 940°C or lower.

[0047] 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).

[0048] 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.

[0049] 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]

[0050] A test was conducted to compare the life of needle roller 2 according to this embodiment with that of needle roller 2 according to a comparative example.

[0051] 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 embodiment 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 embodiment that imitates the rolling bearing device 12 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, rollers 20 (and cage 30) in FIG. 7 together correspond to the rolling bearing device 12. The rollers 20 in FIG. 7 correspond to the rolling members of this embodiment.

[0052] In Example 1, a radial load testing machine 200 (designated testing machine B1) was prepared, which was comprised of a shaft 10 (designated shaft B1) and a roller 20 (designated roller B1) formed under the conditions of this embodiment. For comparison, a radial load testing machine 200 (designated testing machine A1) was prepared, which was comprised of a shaft 10 and a roller 20 (designated roller A1) formed under conditions other than those of this embodiment. Testing machines A1 and B1 were rotated and driven in the same manner as the actual planetary gear 4 and its support structure shown in FIG. 2 , and a test was conducted to compare the life ratios of the two. The verified life ratio was the L50 life, i.e., the time required for the cumulative failure probability to reach 50% (50% confidence). To investigate the L50 life, six rollers A1 and six shafts B1 were used for testing machine A1, and seven rollers B1 and seven shafts B1 were used for testing machine B1.

[0053] 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.

[0054] 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 region within 0.05 mm (50 μm) deep from the contact surface (surface) for both needle roller 2 and shaft member 1, as described above. "Core" refers to the region within 20% of the radius of the circular cross-section from the center of a cross-section (for example, a circle) that intersects with the extension direction of needle roller 2 or shaft member 1. "Grain size number" refers to those at a position 0.05 mm deep from the surface (contact surface) of each component.

[0055] [Table 1]

[0056] 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.

[0057] The features described in the above-described embodiments and examples may be applied in appropriate combinations within the scope of technical compatibility.

[0058] 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.

[0059] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A rolling member, The steel contains 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, and the balance being iron and impurities; The hardness of the rolling member is 733 HV or more at a depth of 0.05 mm or more and 0.20 mm or less from the contact surface, which is the surface where the rolling member comes into contact with other parts, The surface roughness Ra of the contact surface is 0.01 μm or more and 0.05 μm or less, A rolling member in which the nitrogen concentration in the surface layer portion including the contact surface is 0.20% by mass or more and 0.60% by mass or less.

[0060] (Appendix 2) 2. The rolling contact member according to claim 1, wherein the amount of retained austenite in the surface layer portion is 25% by volume or more and 35% by volume or less.

[0061] (Appendix 3) 3. The rolling contact member according to claim 1 or 2, wherein the prior austenite crystals have a grain size number of 9 or more and 11 or less.

[0062] (Appendix 4) 4. The rolling member according to any one of claims 1 to 3, wherein a plurality of the rolling members are included in a needle roller and cage bearing attached to a planetary pinion portion of a planetary gear device. [Explanation of symbols]

[0063] 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 rolling member, The steel contains 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, and the balance being iron and impurities; The hardness of the rolling member is 733 HV or more at a depth of 0.05 mm or more and 0.20 mm or less from the contact surface, which is the surface where the rolling member comes into contact with another part, the surface roughness Ra of the contact surface is 0.01 μm or more and 0.05 μm or less; A rolling member, wherein the nitrogen concentration in a surface layer portion including the contact surface is 0.20 mass % or more and 0.60 mass % or less.

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

3. 3. The rolling contact member according to claim 1, wherein the prior austenite crystals have a grain size number of 9 or more and 11 or less.

4. 3. The rolling member according to claim 1, wherein a plurality of the rolling members are included in a needle roller and cage bearing attached to a planetary pinion portion of a planetary gear device.

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