JP6294620B2 - Rolling bearing for transmission - Google Patents

Description

  The present invention relates to a rolling bearing used in a transmission such as a CVT.

  An automobile transmission is a device that changes the engine power to an optimal torque and rotational speed and transmits it to the axle. The rolling bearings used therein have a large load capacity and high rotational performance, especially the rotational speed associated with the speed change. Designed to follow rapid changes. Furthermore, since the bearing bites foreign matter in the transmission case, it is possible to prevent entry of foreign matter and improve durability by applying a seal seal or special heat treatment. Although it has a hermetic seal, the main purpose of the hermetic seal is to prevent foreign matter from entering, and since it does not have a function to stop the intrusion of fluid, the oil filled in the transmission is removed from the gap of the hermetic seal. Enter the bearing. Until the oil enters the inside of the bearing, lubrication is performed with grease previously enclosed in the bearing.

  In recent years, in an environment where low-viscosity lubricating oil is used as a transmission oil, such as CVT (continuously variable transmission), separation occurs much earlier on the bearing race than fatigue and foreign matter biting. (Early peeling) came to be seen. The surface layer of the peeled portion is characterized by running innumerable cracks that are microscopically changed, which was not seen in conventional peeling. This separation causes slippage between the race and the rolling elements, and the grease generated inside the bearing and the hydrogen generated by the decomposition of the components of the transmission oil that has entered the bearing enter the steel and cause the steel to become brittle. It is thought that peeling occurred. As the viscosity of the lubricating oil component is lower, slipping is more likely to occur, so that the component is more likely to decompose and early peeling due to the hydrogen embrittlement is likely to occur.

  In general, it has been proposed to use bearing steel having an increased Cr content to prevent such early peeling (see Patent Document 1). This is because Cr whose content is increased in the steel material combines with oxygen on the surface of the rolling surface, and forms an oxide film (passive film) of Cr on the surface of the rolling surface. This prevents hydrogen from entering, and thus prevents early peeling due to hydrogen embrittlement.

JP 2000-282178 A

  However, in the steel material of Patent Document 1, carbide is coarsened by adding a large amount of Cr, which may cause early peeling due to a stress concentration source. Moreover, the passive film has the effect of slowing the diffusion of hydrogen, but also has the effect of promoting the adsorption of the generated hydrogen on the steel surface. When rolling bearings are used intermittently, hydrogen can be dissipated when stopped, so delaying the entry of hydrogen into the steel may be effective in preventing early delamination. However, when used continuously in a transmission, the amount of hydrogen that penetrates into the steel increases as the passive film adsorbs much hydrogen, so that early delamination occurs. Also, special steel materials are expensive and difficult to procure overseas. For these reasons, the steel material of Patent Document 1 cannot sufficiently suppress early separation in a rolling bearing for transmission, and its application is difficult.

  The present invention has been made to cope with such problems, and it is an object of the present invention to provide a rolling bearing for a transmission that can effectively prevent early separation on a rolling surface due to hydrogen embrittlement when used in a transmission. To do.

  The transmission rolling bearing according to the present invention is disposed in a transmission that transmits the rotation of the input shaft and the rotation of the output shaft while shifting, and rotates the input shaft, the output shaft, or a member that rotates in accordance with the rotation. A rolling bearing for transmission that freely supports, the rolling bearing having an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner and outer rings, the inner ring, the outer ring, and the rolling element The at least one bearing member selected from the above is made of steel, and at least a part of the oxide inclusions contained in the steel is covered with MnS, and the maximum diameter in the steel is 3 μm or more. The ratio of the number of oxide inclusions covered with MnS to the total number exceeds 40%. The “maximum diameter” means that the oxide inclusions are substantially spherical, and mainly mean their diameter. When the oxide inclusions are stretched in any direction (for example, the rolling direction), the maximum diameter Means.

  The composition of the steel material is as follows: C: 0.95 mass% or more and 1.1 mass% or less, Si: less than 0.35 mass%, Mn: less than 0.5 mass%, S: less than 0.025 mass%, Cr : 1.4% by mass or more and less than 1.6% by mass, the balance being iron and impurities.

  The bearing member is characterized in that the surface layer is subjected to nitriding treatment, and the surface nitrogen concentration is 0.05 to 0.6% by weight. Further, the Vickers hardness difference ΔHV between the portion having a depth of 0.05 mm from the surface of the bearing member and the portion having a depth not containing nitrogen is 60 or more.

  The transmission is a continuously variable transmission system in which the rotation of the input shaft and the rotation of the output shaft are shifted and transmitted in a continuously variable manner.

  The transmission rolling bearing according to the present invention is disposed in a transmission that transmits the rotation of the input shaft and the rotation of the output shaft while shifting, and rotates the input shaft, the output shaft, or a member that rotates in accordance with the rotation. A rolling bearing for transmission that is freely supported. The rolling bearing includes an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner and outer rings, and the inner ring, the outer ring, and the rolling element. The at least one bearing member selected is made of a steel material, and at least a part of oxide inclusions contained in the steel material is covered with MnS, and the maximum diameter in the steel material is 3 μm or more. In the physical inclusions, the ratio of the number of the inclusions covered with MnS to the total number exceeds 40%. Thus, since most of the oxide inclusions inevitably contained in the steel material of the bearing member are covered with the soft MnS, the tensile stress field formed around the oxide inclusions is alleviated. . For this reason, when used in the transmission, hydrogen is less likely to accumulate inside the steel material, and early peeling due to hydrogen embrittlement can be prevented. In particular, even in an environment where a low-viscosity lubricating oil is used as a transmission oil, such as CVT, the early peeling can be prevented.

It is sectional drawing of the deep groove ball bearing which shows an example of the rolling bearing for transmissions of this invention. It is sectional drawing which shows an example of the transmission (CVT) using the rolling bearing for transmissions of this invention. It is a photograph which shows the representative example (Comparative example 1 and Example 1) of an inclusion inspection result. It is a photograph which shows the representative example (Example 2 and Example 3) of an inclusion inspection result. It is a figure which shows the shape of an ultrasonic axial load fatigue test piece. It is a figure which shows an ultrasonic axial load fatigue test result. It is a figure which shows a rapid acceleration / deceleration operation pattern. It is a figure which shows the cross-sectional hardness distribution of the depth direction from a rolling surface. It is a figure which shows the cross-sectional nitrogen concentration distribution of the depth direction from a rolling surface.

  In order to improve hydrogen embrittlement resistance in a rolling bearing for transmission, attention was focused on oxide inclusions inevitably contained in steel materials constituting bearing members such as inner rings, outer rings, and rolling elements. If the bearing member is worn due to slipping or the like, a new surface is formed, water and lubricant mixed therein are decomposed, and hydrogen is generated. Part of the generated hydrogen penetrates into the steel. A tensile stress field is formed around the oxide inclusions. Hydrogen has the property of accumulating in the tensile stress field. On the other hand, most of the oxide inclusions were covered with soft MnS (over 40%) (about 150 HV) to relax the tensile stress field and make it difficult to accumulate hydrogen. As a result, it has been found that hydrogen embrittlement resistance is improved. The present invention is based on such knowledge.

  In particular, diffusible hydrogen is considered to be a cause of hydrogen embrittlement among hydrogen that penetrates into steel materials. Diffusible hydrogen refers to hydrogen that is not trapped in a grain boundary or the like and can move relatively freely. This diffusible hydrogen is released out of the steel material with time at room temperature. For example, diffusible hydrogen can be defined as hydrogen released by heating up to 200 ° C., and non-diffusible hydrogen can be defined as hydrogen released from steel material only at a heating temperature exceeding 200 ° C. The total amount of non-diffusible hydrogen is the total amount of hydrogen that has penetrated into the steel material.

In the steel material constituting the bearing member, oxide inclusions are inevitably included. In the rolling bearing for transmission according to the present invention, at least one bearing member selected from an inner ring, an outer ring, and a rolling element is covered with MnS with respect to the total number of oxide inclusions having a maximum diameter of 3 μm or more in steel. It is essential that the ratio of the number of objects (coverage) exceeds 40%. The coverage is represented by the following formula.

Coverage (%) = (number of oxide inclusions covered with MnS among oxide inclusions having a maximum diameter of 3 μm or more) / (total number of oxide inclusions having a maximum diameter of 3 μm or more) ) × 100

Moreover, the one where a coverage is high is preferable, 50% or more is more preferable, and 90% or more is further more preferable. Here, being covered with MnS means a state in which MnS is precipitated with oxide inclusions as nuclei and wound around the oxide inclusions. This includes not only the case of being completely covered but also the case of being partially covered. Further, MnS has a linear shape drawn in the rolling direction.

  In the calculation of the coverage, the target oxide inclusions have a maximum diameter of 3 μm or more. The presence state of fine oxide inclusions having a maximum diameter of less than 3 μm (covering state of MnS) hardly contributes to early peeling due to hydrogen embrittlement. The presence of oxide inclusions having a maximum diameter of 3 μm or more can be easily measured with an optical microscope.

  Moreover, the lower limit value of the maximum diameter of the target oxide inclusions may be increased, for example, 5 μm or more and 10 μm or more. In the case of an oxide-based inclusion having a maximum diameter of 3 μm or more, the coverage is substantially the same even if the lower limit of the maximum diameter is increased.

  There is no particular limitation on the production method or the like in which the oxide inclusion inclusion coverage with MnS is within the above range. In general, when the cooling rate is high as in the case of continuous casting of steel, oxide inclusions and soft inclusions MnS precipitate separately, and the coverage tends to be low. On the other hand, when the cooling rate is slow as in the case of ingot casting of steel, the oxide inclusions become the core of precipitation of MnS, which is a soft inclusion, and the coverage tends to increase.

  In the present invention, the component composition of the steel material used for at least one bearing member selected from an inner ring, an outer ring, and a rolling element is C: 0.95 mass% to 1.1 mass%, Si: less than 0.35 mass% Mn: Less than 0.5% by mass, S: Less than 0.025% by mass, Cr: 1.4% by mass or more and less than 1.6% by mass, and the balance is preferably iron and impurities. The detail of the said component composition is demonstrated below.

C: 0.95 mass% or more and 1.1 mass% or less C (carbon) is an element required for ensuring the strength of the steel material. In addition, the hardenability is greatly affected, and the hardness and depth of the hardened hardened layer is increased to contribute to the improvement of fatigue strength. Within the above range, these effects can be sufficiently obtained.

Si: Less than 0.35% by mass Si (silicon) is originally intended to be added positively in order to suppress austenite grain growth during quenching heating, but forgeability and machinability are significantly degraded by the addition of Si. From these viewpoints, the content is less than 0.35% by mass.

Mn: Less than 0.5% by mass Mn (manganese) is an element that contributes effectively to improving strength and hardenability. Further, if Mn is excessive, it is considered that segregation occurs at the grain boundary and causes grain boundary cracking, and therefore, less than 0.5% by mass is appropriate.

S: Less than 0.025 mass% S (sulfur) is an element that forms MnS in a steel material. On the other hand, it segregates at the grain boundaries of austenite, which may reduce the grain boundary strength and reduce the fatigue strength. From these viewpoints, the content is less than 0.025% by mass.

Cr: 1.4% by mass or more and less than 1.6% by mass Cr (chromium) is an element that forms stable carbides and improves hardenability and contributes to improvement in strength, wear resistance, and fatigue strength. It is. On the other hand, if Cr is excessively contained, forgeability and machinability are lowered. In order to sufficiently obtain these effects, the above range is appropriate.

  As the steel material having the above component composition, for example, high carbon chromium bearing steel SUJ2 (JIS standard), SUJ2 equivalent material 52100 (AISI or SAE standard), 100Cr6 (DIN standard), GCr15 (GSB standard), etc. There are things. Even steel materials satisfying the above component composition cannot be used in the rolling bearing for transmission of the present invention if they do not satisfy the above-mentioned predetermined coverage (%). In the rolling bearing for a transmission according to the present invention, it is preferable to use a steel material that satisfies the above-described predetermined coverage (%) and satisfies the above component composition.

  In the present invention, the steel material used for at least one bearing member selected from the inner ring, the outer ring, and the rolling element is preferably subjected to nitriding treatment on the surface layer. For the inner and outer rings (race rings), nitriding treatment is applied to the rolling surfaces of the races. The nitriding treatment is performed, for example, in an atmosphere in which ammonia gas is added to RX gas at a temperature of 850 ° C. By performing nitriding treatment on the rolling surface and quenching, the raceway is less likely to be plastically deformed and the hydrogen embrittlement resistance is improved. The surface nitrogen concentration on the rolling surface is preferably 0.05 to 0.6% by weight. If it is less than 0.05% by weight, the effect of improving the life by nitriding may not be obtained. On the other hand, when the surface nitrogen concentration exceeds 0.6% by weight, a large amount of Cr carbonitride is produced, so that the amount of Cr contributing to hardenability is deficient and sufficient hardenability may not be ensured.

  Quenching is performed after nitriding, and then tempering. The heat treatment (quenching / tempering conditions) is not particularly limited, and known conditions can be adopted. For example, first, the steel material is heated to a predetermined temperature of point A1 or higher and held for a predetermined time. At this time, the steel material is heated in an atmosphere in which ammonia gas is added to RX gas or the like, thereby nitriding the steel material surface layer. Then, by immersing the steel material in oil or the like, the steel material is cooled from a temperature of A1 point or higher to a temperature of MS point or lower, and the quench hardening process is completed. Furthermore, the tempering process is completed by heating the quench-hardened steel material to a predetermined temperature which is a temperature of A1 or lower, holding the steel material for a predetermined time, and then air-cooling it to room temperature, for example. Through the above steps, the heat treatment is completed.

  Rolling bearings are used under conditions where metal contact occurs between the contact elements due to their motion and causes slippage.For example, hydrogen easily penetrates into the steel due to exposure of the new metal surface on the steel member surface. It is a sensitive component. In particular, in a rolling bearing for a transmission, in an environment where a low-viscosity lubricating oil is used as a transmission oil, such as CVT described later, slip is likely to occur and is easily affected by hydrogen. Further, when moisture such as air is mixed in the transmission oil, hydrogen is generated due to decomposition of the mixed water, and the penetration into the steel material is promoted.

  An example of a rolling bearing for transmission according to the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a rolling bearing (deep groove ball bearing). In the rolling bearing 1, an inner ring 2 having an inner ring rolling surface 2a on the outer peripheral surface and an outer ring 3 having an outer ring rolling surface 3a on the inner peripheral surface are arranged concentrically, and the inner ring rolling surface 2a and the outer ring rolling surface 3a A plurality of rolling elements 4 are arranged between the two. The rolling element 4 is held by a cage 5. If necessary, the axially opposite end openings 8 a and 8 b of the inner and outer rings are sealed by the seal member 6, and the grease 7 is sealed around the rolling element 4. At least one of the inner ring 2, the outer ring 3, and the rolling element 4 is made of the above-described predetermined steel material.

  A lubricant such as grease 7 is lubricated by being interposed on the rolling surfaces of the inner ring 2 and the outer ring 3 and the rolling elements 4. As the lubricant, any lubricating oil or grease can be used. Transmission oil filled in the transmission enters the bearing through the gap of the seal member 6. Until the transmission oil enters the inside of the bearing, lubrication is performed with the grease 7 previously enclosed in the bearing.

  In the above rolling bearing, the rolling element 4 can be made of silicon nitride which does not show hydrogen embrittlement, although the cost increases. In addition, the cage 5 is less likely to cause early peeling due to hydrogen embrittlement than a resin cage in the case of a metal cage made of steel or copper alloy under conditions where energization occurs.

  The seal member 6 may be made of a metal or a rubber molded body alone, or may be a composite of a rubber molded body and a metal plate, a plastic plate, a ceramic plate, or the like. From the viewpoint of durability and ease of fixing, a composite of a rubber molded body and a metal plate is preferable.

  The ball bearing is exemplified as the transmission rolling bearing of the present invention, but rolling bearings such as cylindrical roller bearings, tapered roller bearings, and needle roller bearings other than those described above can also be used.

  An example of a transmission using the rolling bearing for transmission of the present invention will be described with reference to FIG. FIG. 2 is a sectional view of the transmission (CVT). As shown in FIG. 2, this transmission shifts the rotation of the input shaft 11 in a stepless manner and transmits it to the rotation of the output shaft 14.

  The input shaft 11 is rotationally driven via a torque converter 20 and a planetary mechanism 21 by a drive source (not shown) such as an engine. A driving pulley 12 that rotates synchronously with the input shaft 11 is provided on the input shaft 11, and the groove width of the driving pulley 12 is controlled by a driving actuator 13 so as to be freely expanded and contracted. A driven pulley 15 that rotates synchronously with the output shaft 14 is provided on the output shaft 14, and the groove width of the driven pulley 15 is controlled by a driven actuator 16 so as to be freely expanded and contracted. Further, the driven pulley 15 and the driving pulley 12 rotate at a speed corresponding to each diameter via an endless belt 17 spanned by a diameter corresponding to the selected groove width, and input. The power transmitted to the shaft 11 is transmitted from the driving pulley 12 to the driven pulley 15 via the endless belt 17. The power transmitted to the driven pulley 15 is transmitted from the output shaft 14 to drive wheels (not shown) via the reduction gear train 18 and the differential 19. As the rolling bearing 10 that rotatably supports the input shaft 11 and the output shaft 14, the above-described transmission rolling bearing of the present invention is used.

  When accelerating the output shaft 14 relative to the input shaft 11, the endless belt 17 is stretched by reducing the groove width of the driving pulley 12 and increasing the groove width of the driven pulley 15. The diameter of the portion is large at the driving pulley 12 portion and small at the driven pulley 15 portion, and the output shaft 14 is accelerated relative to the input shaft 11. When the output shaft 14 is decelerated with respect to the input shaft 11, the groove spanned on the endless belt 17 is increased by increasing the groove width of the driving pulley 12 and decreasing the groove width of the driven pulley 15. Is smaller at the driving pulley 12 and larger at the driven pulley 15, and the output shaft 14 is decelerated with respect to the input shaft 11.

  Transmission oil is circulated in the transmission by an oil pump (not shown). As described above, the transmission oil enters the bearing through the gap between the seal members. For example, in CVT, a lubricating oil having a low kinematic viscosity is used as a transmission oil.

  The rolling bearing for transmission of the present invention will be specifically described with reference to examples, but is not limited to these examples.

<Chemical component analysis>
Table 1 shows chemical components of the steel materials of Examples and Comparative Examples. The steel material of Comparative Example 1 was manufactured by continuous casting, and the steel materials of Examples 1 to 3 were manufactured by ingot casting. The coverage in the table is the ratio (%) in which the oxidized inclusions were covered with MnS in the inclusion inspection results described later. There is no significant difference in the chemical composition itself between Comparative Example 1 (conventional steel) and Examples 1 to 3 (developed steel), but the coverage is different.

<Inclusion inspection>
In the inclusion inspection, each of the oxide inclusions (with a maximum diameter of 3 μm or more) detected by observing a 30 mm × 30 mm area (test area 900 mm ² ) of the steel cross section is covered with MnS. Judged whether or not. Here, the oxide inclusions detected by observing the steel material cross section (surface) are oxide inclusions exposed on the cross section (surface). A photograph of a representative example of Comparative Example 1 (upper figure) and Example 1 (lower figure) is shown in FIG. 3, and a photograph of a representative example of Example 2 (upper figure) and Example 3 (lower figure) is shown in FIG. . In each figure, the black spot at the approximate center of each sample or a stretched one is an oxide inclusion, and the thin line covering the periphery is MnS.

  Comparative Example 1 is 988 out of 4071 (coverage 24%), Example 1 is 1620 out of 3985 (coverage 41%), and Example 2 is 2137 out of 4103 (coverage 52%). 3 was covered with MnS in 4005 out of 4267 (coverage 94%).

<Ultrasonic axial load fatigue test>
The ultrasonic axial load fatigue test is a fatigue test in which a test piece is brought into a resonance state by ultrasonic vibration, repeated stress is generated, and the fatigue strength of the test piece can be obtained in a short time. For this reason, it is possible to fatigue before the hydrogen which penetrate | invaded in steel materials dissipates, and the influence of hydrogen can be rationally evaluated. Using the steel materials of Comparative Example 1 and Examples 1 to 3, ultrasonic axial load fatigue test pieces having the shape shown in FIG. 5 were manufactured. The numerical unit in FIG. 5 is mm. In each of the heat treatments, heating was performed in an RX gas atmosphere at 850 ° C. for 50 minutes, followed by quenching in oil at 80 ° C., followed by tempering at 180 ° C. for 120 minutes.

  Before starting the ultrasonic axial load fatigue test, a cathode electrolytic hydrogen charge was applied for 20 hours at a current density at which the hydrogen content in the steel was 5 mass-ppm, and then the test was conducted 10 minutes later (with charge). A test without hydrogen charge was also conducted (no charge). FIG. 6 shows the results of the ultrasonic axial load fatigue test. In FIG. 6, the horizontal axis represents the number of loads, and the vertical axis represents the stress amplitude (MPa). In comparison example 1 (conventional steel), the fatigue strength was clearly reduced by charging, while in examples 1 to 3 (development steel) was slightly lower than that without hydrogen charging. From these results, it can be said that Examples 1 to 3 (developed steel) have characteristics that hydrogen is less likely to accumulate around oxide inclusions that are the starting points of fracture, as compared with Comparative Example 1 (conventional steel).

<Thrust type life test (rolling fatigue test)>
Under rolling contact conditions where water is mixed into transmission oil or the like, water is decomposed to generate hydrogen, which penetrates into the steel and causes early peeling. Therefore, a rolling fatigue test was performed in water-mixed oil. Using the steel materials of Comparative Example 1 and Example 1, the inner and outer rings of the thrust bearing 51106 were manufactured. Test piece 1 (Comparative Example 1) and test piece 2 (Example 1) are used. In each heat treatment, heating was performed in an RX gas atmosphere at 850 ° C. for 50 minutes, and after quenching with oil at 80 ° C., tempering was performed at 180 ° C. for 120 minutes. Moreover, about the steel material of Example 1, what added ammonia gas in 850 degreeC RX gas atmosphere was also manufactured. This is designated as test piece 3 (Example 1 + nitriding treatment).

VG150 polyglycol synthetic oil (density 1.073 g / cm ³ , kinematic viscosity at 40 ° C. 150 mm ² / s, kinematic viscosity at 100 ° C. 23.6 mm ² / s) with 40 ± 0.01 wt% pure water It was mixed. After making the water-mixed oil, seal with a thin film for food packaging so that water does not evaporate, stir with a stirrer for 30 minutes or more, and then use the inner and outer rings of the above test piece in a 200 mL water-mixed oil bath A test for rotating the thrust bearing 51106 was performed. Here, 12 balls made of SUS440C were used. A cage made of resin that holds 12 balls at equal intervals was used. Only the axial load Fa = 5.10 kN was applied, and the inner ring was suddenly accelerated or decelerated at 0 to 2500 min ⁻¹ . FIG. 7 shows an operation pattern. The maximum contact surface pressure between the race surface and the steel ball in the elastic Hertz contact calculation under this load condition is 2.3 GPa. In the elastic Hertz contact calculation, the Young's modulus and Poisson's ratio of 51106 and SUS440C steel balls were E = 204 GPa and ν = 0.29, respectively. The peeling was detected with a vibrometer.

  The test was performed by preparing five pieces of each of the test piece 2 (Example 1), the test piece 3 (Example 1 + nitriding treatment), and the test piece 1 (Comparative Example 1). All peeling occurred on the race surface of the inner ring or outer ring 51106, and all peeling was characterized by hydrogen.

Table 2 shows L ₁₀ , L ₅₀ , and Weibull slope (shape parameter) e obtained by applying the peel life of each test piece to the 2-parameter Weibull distribution. Test piece 1 (Comparative Example 1) had L ₁₀ = 38.5 hours. On the other hand, the test piece 2 (Example 1) had L ₁₀ = 118.8 hours, which was about three times as long as the test piece 1 (Comparative Example 1). From this, it can be said that the rolling bearing of the present invention has an effect of making it difficult to cause early peeling due to hydrogen embrittlement. Further, the test piece 3 (Example 1 + nitriding) _is L 10 = 183.4 hours, showed about 5 times longer life to the test piece 1 (Comparative Example 1). From this, it can be said that adding nitriding treatment to the test piece 2 (Example 1) has an effect of making it difficult to cause early peeling due to hydrogen embrittlement.

  Test piece 3 (Example 1 + nitriding treatment) was tempered at 500 ° C. for 1 hour. FIG. 8 shows the cross-sectional hardness distribution (Vickers hardness HV) in the depth direction from the rolling surface of the test piece 3. The measurement was performed at 50 μm intervals using a Vickers hardness meter. As shown in FIG. 8, the hardness difference ΔHV between the rolling surface of 0.05 mm and the non-nitrided depth (0.2 mm or more) was 60.

  FIG. 9 shows the cross-sectional nitrogen concentration distribution in the depth direction from the rolling surface of the test piece. Measurement was performed using an Electron Probe Micro Analyzer (EPMA) at an acceleration voltage of 15 kV, a spot diameter of 2 μm, a measurement interval of 2 μm, and a measurement time of 1 sec (seconds). The nitrogen concentration distribution in the steel material was measured by EPMA in the direction from the rolling surface side to the inside of the test piece. As shown in FIG. 9, the surface nitrogen concentration was 0.05% by weight. The “surface” in the surface nitrogen concentration is a range where the depth from the surface is 0 to 0.01 mm. As the nitrogen concentration in the surface layer increases, ΔHV increases.

  Since the rolling bearing for transmission of the present invention can effectively prevent early peeling at the rolling surface due to hydrogen embrittlement without using special steel material with an increased Cr content, etc., it is used as a bearing used in automobile transmissions. It can be suitably used.

DESCRIPTION OF SYMBOLS 1 Rolling bearing 2 Inner ring 3 Outer ring 4 Rolling body 5 Cage 6 Seal member 7 Grease 8a, 8b Opening part 10 Rolling bearing 11 Input shaft 12 Drive side pulley 13 Drive side actuator 14 Output shaft 15 Drive side pulley 16 Drive side actuator 17 Endless Belt 18 Reduction gear train 19 Differential 20 Torque converter 21 Planetary mechanism

Claims (4)

A rolling bearing for a transmission that is disposed in a transmission that transmits the rotation of the input shaft and the rotation of the output shaft while shifting, and rotatably supports the input shaft, the output shaft, or a member that rotates along with the rotation. There,
The rolling bearing has an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner and outer rings,
At least one bearing member selected from the inner ring, the outer ring, and the rolling element is made of steel, and the composition of the steel is C: 0.95% by mass to 1.1% by mass, Si: 0. Less than 35% by mass, Mn: less than 0.5% by mass, S: less than 0.025% by mass, Cr: 1.4% by mass or more and less than 1.6% by mass, the balance being iron and impurities,
At least a part of the oxide inclusions contained in the steel material is covered with MnS, and the oxide inclusions having a maximum diameter of 3 μm or more in the steel material are covered with MnS for the total number thereof. Rolling bearing for transmission, characterized in that the ratio of the number of broken parts exceeds 40%.   The rolling bearing for a transmission according to claim 1, wherein the bearing member has a surface layer subjected to nitriding treatment, and has a surface nitrogen concentration of 0.05 to 0.6% by weight. The rolling bearing for a transmission according to claim 2 , wherein a Vickers hardness difference ΔHV between a portion having a depth of 0.05 mm from a surface of the bearing member and a portion having a depth not containing nitrogen is 60 or more. . The transmission is according to any one of claims claims 1-3, characterized in that the rotation of the rotating and the output shaft of the input shaft is continuously variable method for transmitting and shift steplessly change Rolling bearing for transmission.