JP2006329268A - Rolling bearing for planetary gear mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing highly strong corresponding to severe working conditions, of a long life to surface damage such as surface starting separation or inside starting separation, and easy to caulk at the end. <P>SOLUTION: The rolling bearing 20 for a planetary gear mechanism comprises an inward member 17 and an outward member 13 arranged in a concentric manner, and rolling elements laid between both members. At least one of the inward member 17 and the outward member 13 has a nitrogen enriched layer. At least one member has an austenite crystal grain size of No.11 or more and hardness of HV653 or more at the surface layer portion in a rolling surface region where the rolling elements 18 roll. It has a hardness of HV550 or more at the sectional center of a rolling surface central portion. The inward member has a hardness of HV300 or less at the end. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling bearing for a planetary gear mechanism, and more particularly to a rolling bearing for supporting a planetary gear of a planetary gear mechanism.

  Among recent rolling bearings, for example, a rolling bearing used in a planetary gear mechanism is a full-roller type bearing that does not use a cage, but there is an increasing demand for high-speed and high-load applications. In the following, all roller bearings and other rolling bearings are not particularly distinguished, and all are described as rolling bearings. In a rolling bearing without a cage, interference between the rollers is unavoidable, and the lubricant may not be supplied well into the bearing, which may cause separation from the surface of the roller or the rolling surface.

  Further, when the rotation speed of the roller becomes high, surface damage is likely to occur on the roller due to the effects of assembly errors and offset load, and the roller position is not controlled smoothly and skew is likely to occur. For this reason, surface origin separation due to slipping or internal origin separation due to local increase in surface pressure may occur. As a result, sliding heat generation and local surface pressure increase occurred, and surface damage such as peeling, smearing, and surface-origin separation, and load-dependent internal origin delamination were likely to occur.

The inner member of the planetary gear mechanism requires high strength on the rolling surface of the roller, but the end is preferably soft so that it can be crimped. Many developments that take this into account have also been made (see Patent Documents 1 and 2).
JP 2003-301933 A JP 2004-003627 A

  In the future, planetary gear mechanisms such as A / T transmissions for automobiles will inevitably become more severe due to acceleration of higher speed and higher load and lower viscosity of lubricating oil. In a rolling bearing placed under such usage conditions, it is required to increase the rolling life and achieve high strength or high crack fatigue strength.

  The main object of the present invention is to increase the strength in response to severe use conditions, to have a long life against surface damage such as surface-origination peeling and internal origin peeling, and to perform caulking at the end. It is to provide an easy rolling bearing.

  A rolling bearing for a planetary gear mechanism according to the present invention comprises an inner member and an outer member arranged concentrically and a rolling element interposed between the two members, and at least one of the inner member and the outer member is The austenite grain size of the surface layer portion of the rolling surface region where the rolling element rolls is 11 or more and the hardness is HV653 or more in the at least one member. The hardness of the central portion of the cross section of the running surface central portion is HV550 or more, and the hardness of the end portion of the inner member is HV300 or less.

  With this configuration, it is possible to realize a long life by suppressing surface damage such as surface-initiated separation and internal origin separation at the surface layer portion in the region of the rolling surface. Moreover, since the hardness is limited as described above at the end portion of the inner member, it is easy to perform caulking. Furthermore, for example, it is possible to increase the strength of the inner member and the outer member to improve the crack fatigue strength. If the austenite grain size of the surface layer portion of the rolling surface is less than 11, the rolling fatigue life under severe use conditions cannot be increased, so the austenite grain size of the surface layer portion is 11 or more. The reason why the nitrogen-enriched layer is disposed is that the microstructure is refined and toughened by induction hardening the nitrogen-enriched layer. The austenite crystal grains are austenite crystal grains that have undergone phase transformation during quenching and heating, and that remain as past history even after transformation to martensite by cooling. The austenite crystal grain may be a grain boundary that can be observed by performing a process of revealing the grain boundary, such as etching, on the gold phase sample of the target member. In the sense that it is a grain boundary at the time of heating just before quenching, it may be referred to as prior austenite grains. The measurement may be obtained by converting the average value of the JIS standard particle size number to the average particle size as described above, or while the random direction straight line superimposed on the metal phase structure by the intercept method or the like is associated with the grain boundary. An average value of the interval lengths may be taken, and a two-dimensional to three-dimensional interval length may be obtained by applying a correction coefficient.

  The nitrogen-enriched layer is formed by carbonitriding as will be described later. However, the nitrogen-enriched layer may or may not be enriched with carbon.

  In a region other than the surface layer portion of the rolling surface region, a region in which the microstructure includes ferrite and carbide may be included (claim 2).

  Here, the ferrite is an α phase of iron and refers to a ferrite that does not contain dislocations at a high density such as martensite. Corresponding to this is ferrite formed by slow cooling from the austenite (γ) phase, and ferrite that has been quenched and sufficiently tempered. Carbides such as cementite corresponding to ferrite having such a low dislocation density are dispersed in an agglomerated and coarsened state. Thus, the microstructure with the ferrite and carbide described above corresponds to a typical softened state. The softened microstructure may be present in a region other than the surface layer portion of the rolling surface region. In particular, since the hardness at the end of the inner member is premised on HV300 or less, the softened tissue is arranged at the end of the inner member.

Carbide mainly refers to cementite Fe ₃ C, but in a nitrogen-enriched layer, it contains much nitrogen but not carbon, so it should be called carbonitride like Fe ₃ (C, N). However, for the sake of simplicity, the term “carbide” includes carbonitride. Moreover, since steel materials usually contain Mn and the like, they are dissolved in carbides and take a form such as (Fe, Mn) ₃ (C, N), but such a form is also naturally included. Further, when tempering is performed at a high temperature, not only M ₃ C type carbides but also M ₂₃ C ₆ type carbides and other carbides are included, and the above carbides include such carbides.

  The rolling surface region can be formed by induction hardening (Claim 3). With this configuration, a fine grained hardened structure can be obtained in a short processing step. As a result, high bearing strength or high crack fatigue strength can be realized at low cost without deteriorating surface damage resistance, rolling fatigue life resistance, and the like.

  The hardness of the surface layer portion of the rolling surface can be HV653 or more, and the hardness of the central portion of the cross section of the rolling surface region can be HV550 or more. With this configuration, long life is achieved by reliably suppressing surface damage and internal origin separation at the surface layer portion of the rolling surface, and the strength of the central portion of the cross section of the rolling surface is increased, or an inner member, High crack fatigue strength of the outer member can be obtained. If the hardness of the surface part of the rolling surface is less than HV653, it is difficult to extend the life under the above conditions, and if the hardness of the center part of the cross section of the rolling surface is less than HV550, the planetary gear mechanism needs to be increased in speed and load. High strength that meets the requirements cannot be obtained.

  Residual austenite may occupy 10 volume% or more and 50 volume% or less in the surface layer part of the area of the rolling surface, and residual austenite may exist in the center of the cross section of the rolling surface. With this configuration, the surface layer portion can suppress the crack propagation in the surface-origination separation and the internal origin separation, and the strength level can be increased in the center portion of the cross section due to the induction hardening. If the retained austenite in the surface layer is less than 10% by volume, a long life under severe use conditions cannot be obtained, and if it exceeds 50% by volume, it does not become fine retained austenite. To shorten. Moreover, since it hardens | cures by induction hardening in the center part of a cross section, although it is not so much as a surface layer part, a retained austenite produces | generates. That is, residual austenite exists because it is cured to the center of the cross section.

  The residual austenite can be measured by a known method such as X-ray diffraction or transmission electron microscopy (TEM). Austenite can be measured using a magnetic measuring device such as a magnetic balance by utilizing the fact that austenite is not a ferromagnetic material unlike ferrite and cementite.

The inner member, the outer member, that is, at least one of the above members, is subjected to carbonitriding at A ₁ or higher and then gradually cooled to less than A ₁ and then subjected to induction hardening of the rolling surface region. (Claim 5). The above A ₁ point corresponds to the eutectoid temperature is 723 ° C. In example Fe-C system. Further, the point A _{1 of a} steel material usually used for a rolling bearing is also a temperature in the vicinity thereof.

  According to said process, since it is hard to receive a damage in a surface layer part, it is long-life, and it can obtain the member which is easy to caulk in another part. In the part to be induction hardened, the austenite grain size (JIS standard) is No. 11 or more, the residual austenite is 10% by volume or more and 50% by volume or less, and the hardness is HV653 or more. This is because induction hardening is performed on the region to be included. In addition, the hardness of HV300 or less at a part not affected by induction hardening, such as the end of the inner member, is that the steel is gradually cooled after carbonitriding or is tempered (tempered) even when quenched. It is.

  According to this invention, at least one of the outer member and the inner member has the nitrogen-enriched layer, and the end portion of the inner member is softened, so that excellent damage resistance and caulking are achieved. Sex can be obtained. Furthermore, by performing induction hardening, high crack fatigue strength and rolling fatigue strength and surface damage resistance in the inner member and the outer member can be ensured in a short time with a simple treatment process. In particular, having a predetermined range of retained austenite in the surface layer portion effectively acts to suppress cracks generated and propagated by repeated loading.

  Embodiments of the present invention will be described below with reference to the drawings. Here, FIG. 1 schematically shows the configuration of the planetary gear mechanism, and FIG. 2 schematically shows the configuration of the automatic transmission incorporating the planetary gear mechanism.

  As shown in FIGS. 1 and 2, the planetary gear mechanism 10 is located between a sun gear shaft 11 and an internal gear shaft 16 in an automatic transmission, and includes a sun gear 12, an internal gear 15, and a plurality of planetary gears 13. Contains. The sun gear 12 has teeth formed on the outer periphery and is in an integral relationship with the sun gear shaft 11. The internal gear 15 has teeth formed on the inner peripheral surface, and is in an integral relationship with the internal gear shaft 16. Each planetary gear 13 is located between the sun gear 12 and the internal gear 15, meshes with both the sun gear 12 and the internal gear 15, and can revolve the outer periphery of the sun gear 12 while rotating. The gears of the planetary gear mechanism 10 are always meshed, and by applying a driving force to one of the sun gear 12, the planetary frame 14, or the internal gear 15, or by locking any of them, the internal teeth for the sun gear shaft 11 can be locked. The rotation speed, rotation direction, torque, and the like of the gear shaft 16 can be changed.

  The planetary gear 13 is rotatably supported with respect to the planetary gear shaft 17 by the rolling bearing 20 of the planetary gear mechanism 10. The planetary gear shaft 17 is supported by the planetary frame 14 so as to be rotatable through the shaft. As is well known, a rolling bearing is composed of an inner ring (inner member), an outer ring (outer member), and a rolling element, and the rolling element rolls between the outer raceway of the inner ring and the inner raceway of the outer ring. ing. In this embodiment, the rolling bearing 20 is a radial needle roller bearing as shown in FIG. 3, and a plurality of needle rollers 18 are held at correct positions by a cage 19 at regular intervals. The outer peripheral surface of the planetary gear shaft 17 provides an inner track, and the inner peripheral surface of the planetary gear 13 provides an outer track. Therefore, in this case, the planetary gear shaft 17 and the planetary gear 13 constitute an inner member and an outer member of the rolling bearing 20.

  Note that an inner ring fixed to the outer periphery of the planetary gear shaft 17, which is separate from the planetary gear shaft 17, may be used as the inner member of the rolling bearing 20. Similarly, an outer ring fixed to the inner periphery of the planetary gear 13, which is separate from the planetary gear 13, may be used as the outer member of the rolling bearing 20.

  Among the components constituting the rolling bearing 20, that is, the bearing components, the planetary gear shaft 17 as an inner member is subjected to heat treatment to be described below, and the surface layer portion thereof is made of ultrafine austenite grains.

  In the rolling bearing in this embodiment, the planetary gear shaft 17 which is an inner member has a nitrogen-enriched layer, and induction hardening is applied to the surface layer portion in the region of the rolling surface on which the rolling element rolls to austenite crystals. The particle size is 11 or more (according to the JIS standard) and is very fine, and the hardness is HV653 or more. Except for the region of the rolling surface (surface layer portion and axial center portion), the austenite grain size is relatively coarse as 10 or less, and there is a portion where the hardness of the end portion is particularly low and HV300 or less. Since induction hardening is performed in the region of the rolling surface on which the rolling elements roll, the retained austenite is 10% by volume or more and 50% by volume or less in the surface layer portion. At the center of the axis of the rolling surface, both are induction-heated and hardened during induction hardening of the surface layer, so that they are hardened and residual austenite is generated. As a result, both surface damage and load-dependent internal origin separation are less likely to occur in the surface layer portion, and at least the rolling surface has increased hardness from the axial center portion to the surface layer portion, thereby improving crack fatigue strength. On the other hand, it is easy to caulk because other parts such as the end have low hardness. For this reason, both ends of the planetary gear shaft are caulked and a caulking fixed portion is formed at the chamfered portion of the planetary gear shaft support portion.

  Next, heat treatment including carbonitriding treatment performed on the planetary gear shaft 17 will be described. FIG. 4 shows a heat treatment pattern in which carbonitriding is performed at a point A1 or higher and then gradually cooled, and FIG. This is a heat treatment pattern to be performed. The slow cooling process in the heat treatment pattern of FIG. 4 and the tempering process in FIG. 5 correspond to each other and contribute to reducing the hardness of the entire inner member. Both of the heat treatment patterns of FIGS. 4 and 5 are thereafter subjected to induction hardening in the region of the rolling surface (surface layer portion to shaft center portion), and then subjected to low temperature tempering.

  Any of the above heat treatments can be applied to the inner member of the bearing. Then, by any of the heat treatments described above, a nitrogen-enriched layer that is a “carbonitriding layer” is formed by carbonitriding treatment therein. Since the carbon concentration of steel used as a material in the carbonitriding process is high, carbon may not easily enter the steel surface from the normal carbonitriding process atmosphere. For example, in the case of steel having a high carbon concentration, a carburized layer having a higher carbon concentration may be generated, or a carburized layer having a higher carbon concentration may be difficult to generate. However, although the nitrogen concentration depends on the Cr concentration, etc., it is as low as about 0.025% by weight or less for normal steel, so the nitrogen-enriched layer is clear regardless of the carbon concentration of the steel. Generated.

  Next, how the microstructure is generated for each process of FIGS. 4 and 5 will be described. First, for example, carbonitriding is performed at a point A1 or higher. In this carbonitriding process, a nitrogen-enriched layer is formed on the planetary gear shaft 17 which is an inner member of the bearing component, here. In this nitrogen-enriched layer, C and N, which are interstitial elements for iron atom Fe, invade hypereutectoid, for example, carbide is precipitated in austenite (two-phase coexistence). That is, the nitrogen-enriched layer is hypereutectoid steel. Further, inside the carbonitriding process, an austenite phase is formed due to the composition of the original steel material. Further, the carbonitriding treatment may be performed at a temperature at which the steel material as a raw material coexists with two phases of ferrite and austenite, or two phases of austenite and cementite.

Next, when cooling, in the pattern of FIG. 4 (referred to as heat pattern H ₁ ), cooling is gradually performed from the carbonitriding temperature. The purpose of this slow cooling is to soften the tissue and improve the caulking processability. During this slow cooling, pearlite composed of ferrite and cementite is produced from the above-mentioned austenite inside, but softening is promoted by agglomerating and coarsening the cementite in the pearlite without layering. Therefore, the temperature range for slow cooling may be from the carbonitriding temperature to about (A ₁ point-100 ° C.). Even if it is gradually cooled to a temperature lower than this, agglomeration and coarsening of cementite cannot be expected, and it takes time and efficiency is lowered. As a guide, it may be up to about 620 ° C. Thereafter, air cooling may be performed to shorten the time, or water cooling or oil cooling may be performed.

  In the nitrogen-enriched layer, pearlite is generated from austenite having a carbide + austenite structure, and the carbide in the aggregate is coarsened.

In the pattern of FIG. 5 (referred to as heat pattern H ₂ ), quenching is performed from the carbonitriding temperature, for example, by oil cooling. In this case, martensite and the like are generated from austenite inside due to the composition of the original steel material. This martensite structure is hard. Since the caulking process is difficult as it is, the tempering process (tempering process) is performed. Tempering is desirably performed within a range of A ₁ point to 680 ° C. By this tempering, the high dislocation density in the martensite structure disappears, and a structure of ferrite having a low dislocation density and aggregated and coarsened cementite is obtained.

  In the nitrogen-enriched layer, martensite is generated from austenite of the structure (carbide + austenite) generated during heating by quenching such as oil cooling. Martensite is similarly softened by the above tempering. The original carbides agglomerate. In the above description of the microstructure, as described above, secondary factors in nitrogen and a more complicated actual microstructure are ignored.

Next, induction hardening is performed on both the heat patterns H ₁ and H ₂ . In the previous stage of induction hardening, the nitrogen-enriched layer had a structure in which agglomerated carbides (large ratio) and ferrite were mixed. In the induction hardening, rapid heating is performed, and at this time, austenite is nucleated while the carbide is dissolved. Since the density of the dispersed carbide is very high, the austenite nucleus generation density is very high, and the austenite structure crystal grains formed by associating the generated austenite with each other are ultrafine. In addition, since the nitrogen-enriched layer is a hypereutectoid steel, carbides coexist, and the carbides are just formed, preventing the growth of ultrafine austenite grains. For this reason, ultrafine austenite grains can be obtained in the nitrogen-enriched layer. As the temperature for rapid heating increases, the carbide dissolves, and many carbons of ultrafine austenite are dissolved. In addition, the shaft center portion is affected by the fact that it is not a nitrogen-enriched layer, but basically changes in the same manner as the change in the surface layer portion.

  Next, when induction hardening is performed, that is, quenching is performed after rapid heating, austenite is transformed into martensite. At this time, since a large amount of carbon is dissolved, austenite is stabilized, and untransformed austenite is left behind in a fine region between martensites. This is retained austenite. This retained austenite is very fine because it is formed between martensite. In terms of volume ratio, the retained austenite is 10% by volume or more and 50% by volume or less.

  Thereafter, tempering is performed at a temperature of about 180 ° C. so as not to significantly reduce the hardness. In this tempering at about 180 ° C., high-density dislocations are maintained with almost no loss. This tempering is performed to stabilize the structure. In this tempering, cementite does not aggregate and hardly softens. The induction-quenched structure containing the above retained austenite is tough and can realize a long life under severe use conditions.

  By performing the above heat treatment, the austenite grain size in the region of the rolling surface (surface layer part and axial center part) can be changed to 11 or more ultrafine grains. Further, the hardness of the surface layer portion can be HV653 or more, and the retained austenite can be in the range of 10 to 50% by volume, preferably 15 to 35% by volume. Further, the hardness of the shaft center portion can be set to HV550 or more so that residual austenite exists. On the other hand, the hardness of the portion other than the region of the rolling surface, for example, the end can be set to HV300 or less. Therefore, the inner member subjected to the above heat treatment has high strength or high crack fatigue strength, has a long rolling fatigue characteristic, and is easily caulked.

  Heat treatment of heat pattern H1 (corresponding to FIG. 4) shown in FIG. 6 and heat pattern H2 (corresponding to FIG. 5) shown in FIG. 7 was performed using the bearing steel SUJ2. That is, the steel pipe or the cold-worked steel material is first subjected to carbonitriding at A1 or higher, and then gradually cooled (furnace cooling) to (A1) or lower (heat pattern H1) according to the heat pattern H1 or H2. Or (heat pattern H2) tempering (tempering) after quenching to A1 point or less. Then, induction hardening is performed to the area | region (surface layer part-axial center part) corresponding to a rolling surface. The temperatures in the heat patterns H1 and H2 are as shown in FIGS.

  In the specimen prepared by the above heat treatment using the planetary gear shaft 17 as a sample, the retained austenite is 10% by volume or more and 50% by volume or less, more preferably 15% by volume or more and 35% by volume or less in the surface layer portion. The particle size is 11th or more and ultrafine. Moreover, in the axial center part of the area | region of a rolling surface, it is induction-heated and quenched with the said surface layer surface, and a retained austenite remains. The hardness of this specimen was measured. For comparison, the hardness of the conventional specimen J, in which only surface induction hardening was performed on the surface, was also measured. Table 1 shows the measurement results. The shape and hardness measurement position of each specimen are shown in FIG. FIG. 8A is a front view of the test body, and FIG. 8B is a cross-sectional view of the center of the test body (through point A). In FIG. 8, the area | region of the rolling surface 32 of a test body has the part 31 by which induction hardening hardening was carried out over the surface layer part-axial center part.

  According to Table 1, in the specimens 1 and 2 of the present invention, in the region of the rolling surface 32 (surface layer portion to shaft center portion), the hardness is HV 790 to 800 in the surface layer portions A and B, and the shaft center portion E. (Refer to FIG. 8 (b)), it is very high as HV710 to 730, and HV250 to 270 in C and D other than the region of the rolling surface. The hardness at the portions C and D is appropriate for caulking. On the other hand, in the test body J of the conventional example, in the region of the rolling surface, the hardness is 735 to 780 in the surface layer portions A and B, and HV215 is very low in the shaft center portion E. Moreover, the hardness of the measurement positions C and D where the influence of induction hardening does not reach is HV210-220.

  Further, as shown in Table 2, the specimens 1 and 2 of the present invention have a very fine austenite grain size number of 12, but the conventional specimen J is slightly coarser at 10.5. Further, the retained austenite at the point A is in an appropriate range of 24.7% by volume in the specimen 1 of the present invention and 25.5% by volume in the specimen 2. On the other hand, the test piece J of the conventional example is 7.5% by volume, which is out of the range where surface damage or the like can be prevented.

  A crack fatigue test was performed on the test bodies 1 and 2 of the present invention and the test body J of the conventional example to verify the increase in strength. As shown in FIG. 9, the test method is a method in which a load is repeatedly applied to the central portion of the test body 30 by the load load section 28 in a state where both ends of the test body 30 are supported by the fulcrum 27. The test conditions are as shown in Table 3. The number of repetitions until the load was changed to breakage was plotted to obtain a load load-breakage number line. The test results are shown in Table 4.

In Table 4, the load load that breaks at a load count of 10 ⁶ is shown as a ratio with a value of 1 in the test specimen J of the conventional example as 1. In the specimen 1 of the product of the present invention, it is 1.32, an increase of 32% compared to the conventional example. Moreover, in the test body 2 of the product of the present invention, it is 1.28, an increase of 28% compared to the conventional example. As a result, it was confirmed that high crack fatigue strength was achieved.

  Next, an outer ring rotation type fatigue life test was performed on the above-described specimens 1 and 2. Table 2 shows the austenite grain size number and retained austenite at point A (surface layer part) of the test specimen, and Table 5 shows the test conditions. FIG. 10 shows a test apparatus for the outer ring rotation type fatigue life test. In this test apparatus, a roller 35 is disposed so as to be sandwiched from the upper and lower sides of the test body 30, and the roller 35 rotates while applying close pressure to the surface layer portion of the test body 30 while applying external pressure. Is done.

  According to the above test conditions, surface damage or internal origin delamination occurs during the test. Therefore, by carrying out this test, the lifetimes of both surface damage and internal origin peeling can be confirmed. The results of this fatigue test are shown in Table 6.

  According to Table 6, the specimens 1 and 2 of the present invention have a lifespan that is 3.3 to 3.8 times longer than that of the specimen J of the conventional example. In the specimen J of the conventional example, the fatigue life is due to the metal structure (austenite grain size, residual austenite amount) resulting from not performing the carbonitriding process and not performing the induction hardening process from the surface layer part to the shaft center part. It is considered short.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

(A) is a front view of a planetary gear mechanism, (b) is a longitudinal sectional view, and (c) is a perspective view. It is a longitudinal cross-sectional view of an automatic transmission. It is the perspective view which fractured | ruptured a part of needle roller bearing. It is a heat pattern figure. It is a heat pattern figure. It is a heat pattern figure. It is a heat pattern figure. (A) is the longitudinal cross-sectional view of a test body, (b) is a cross-sectional view similarly. It is the schematic for demonstrating the crack fatigue test method. It is a longitudinal cross-sectional view of a fatigue life test apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Planetary gear mechanism 11 Sun gear shaft 12 Sun gear 13 Planet gear 14 Planetary frame 15 Internal gear 16 Internal gear shaft 17 Planetary gear shaft 18 Needle roller 19 Cage 20 Needle roller bearing (Rolling bearing for planetary gear mechanism)

Claims (5)

  A concentric inner member and an outer member, and a rolling element interposed between the two members, wherein at least one of the inner member and the outer member has a nitrogen-enriched layer, In one member, the austenite grain size of the surface layer portion of the rolling surface area where the rolling element rolls is 11 or more, the hardness is HV653 or more, and the hardness of the central portion of the cross section of the rolling surface center portion Is a rolling bearing for a planetary gear mechanism, wherein HV550 or higher and the hardness of the end portion of the inner member is HV300 or lower.   The rolling bearing for a planetary gear mechanism according to claim 1, wherein a region having a microstructure including ferrite and carbide is included in a portion other than a surface layer portion of the rolling surface region and a central portion of the cross section of the rolling surface central portion.   The rolling bearing for a planetary gear mechanism according to claim 1 or 2, wherein the rolling surface region is induction-hardened.   The planetary gear according to any one of claims 1 to 3, wherein residual austenite occupies 10% by volume or more and 50% by volume or less in a surface layer portion of the rolling surface region, and residual austenite is present in a central portion of a cross section of the central portion of the rolling surface. Rolling bearing for mechanism. Wherein at least one of the members, and cooled to less than A ₁ point after the carbonitriding process by A ₁ point or more, then the rolling surface area was induction hardening, the rolling bearing for one of the planetary gear mechanism of claims 1 to 4 .

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