JP2006145012A - Component part of planetary gear mechanism and rollingly supporting mechanism of planetary gear mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a component part of a planetary gear mechanism and a bearing member of the planetary gear mechanism having advanced cracking resistant strength and dimensional stability and excellent in fatigue characteristics (rolling fatigue characteristics for bearing member). <P>SOLUTION: This planetary gear mechanism 10 comprises a sun gear 12, an internal gear 15 surrounding the outer periphery of the sun gear 12, and a planetary gear 13 meshed with both of the sun gear 12 and the internal gear 15. The component part of the planetary gear mechanism 10 comprises a nitrogen-enriched layer having an austenitic grain size of 10 in grain number. A residual austenite in the nitrogen-enriched layer comes within the range of 11 to 25%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a component of a planetary gear mechanism such as an A / T transmission (Automatic / Transmission) of an automobile and a rolling support mechanism of the planetary gear mechanism. More specifically, the present invention relates to rolling fatigue life characteristics and smearing strength characteristics. The present invention relates to an improved long-life planetary gear mechanism component and a rolling support mechanism for the planetary gear mechanism.

  Among recent rolling bearings, there are an increasing number of bearings used for high-speed and high-load applications, such as bearings used in planetary gear mechanisms of A / T missions for automobiles. In particular, in a full-roller type bearing, heat is generated due to relative sliding between the rollers, or the roller position is not controlled smoothly, and roller skew occurs. Further, insufficient lubrication occurs when the lubricating oil is not sufficiently supplied into the bearing. As a result, sliding heat generation, local surface pressure increase, or insufficient lubrication occurs, so the surface has damage (peeling, smearing, In many cases, surface-origin type peeling) or internal-origin type peeling occurs and does not function as a bearing.

As a heat treatment method that gives a long life against rolling fatigue of a bearing component, a method of performing a carbonitriding process on the surface layer portion of the bearing component by adding ammonia gas to the atmosphere RX gas during quenching heating, etc. Yes (see Patent Documents 1 and 2). By using this carbonitriding treatment method, the surface layer portion can be hardened, retained austenite can be generated in the microstructure, and the rolling fatigue life can be improved.
JP-A-8-4774 Japanese Patent Laid-Open No. 11-101247

  In future planetary gear mechanism bearing parts, with higher loads and higher temperatures during use, and due to demands for smaller and more compact planetary gear mechanisms, the bearing parts will be under higher load conditions and at higher temperatures. It is required to have characteristics that can be used. For this reason, a bearing component having high strength, a long rolling fatigue life, and high crack resistance strength and dimensional stability is required.

  However, since the carbonitriding method described above is a method of diffusing carbon and nitrogen, it is necessary to keep the temperature high for a long time. For this reason, it is difficult to improve the cracking resistance due to the coarsening of the structure. In addition, an increase in the dimensional change rate due to increase in retained austenite is also a problem.

  On the other hand, it is possible to cope with rolling fatigue by adjusting the composition in the alloy design of steel in order to ensure a long life, improve crack strength, and prevent an increase in the rate of dimensional change over time. However, the alloy design causes problems such as an increase in raw material costs.

  The present invention provides a planetary gear mechanism component having a high degree of cracking resistance and dimensional stability and excellent fatigue life (rolling fatigue life in the case of a rolling support mechanism) and the rolling support mechanism of the planetary gear mechanism. The purpose is to provide.

  The components of the planetary gear mechanism of the present invention are incorporated in a planetary gear mechanism having a sun gear, an internal gear that surrounds the outer periphery of the sun gear, and a planetary gear that meshes with both the sun gear and the internal gear. Further, in the component parts of the planetary gear mechanism, the above-described component part has a nitrogen-enriched layer, the grain size number of the austenite crystal grain of the component part exceeds 10, and the residual austenite in the nitrogen-enriched layer is It is in the range of 11 volume% or more and 25 volume% or less.

  The rolling support mechanism of the planetary gear mechanism of the present invention rotatably supports a planetary gear that meshes with both a sun gear and an internal gear that surrounds the outer periphery of the sun gear. An inner member, an outer member, and a rolling element having an inner member positioned inside the outer member, and a plurality of rolling elements interposed between the outer member and the inner member. At least one of the members has a nitrogen-enriched layer, the austenite grain size number of the member exceeds 10, and the residual austenite in the nitrogen-enriched layer is 11 volume% or more and 25 volume% or less It is characterized by being in the range of.

  According to the planetary gear mechanism component and the rolling support mechanism of the present invention, the rolling fatigue life can be greatly improved because the austenite grain size number is very fine exceeding 10th. . When the austenite grain size number is 10 or less, the degree of improvement in rolling fatigue life is small, so the grain size number is in a range exceeding 10th. Usually 11 or more. The finer austenite grains are desirable, but it is usually difficult to obtain a grain number exceeding 13th. The above-mentioned austenite crystal grains do not change so much in the surface layer portion where the nitrogen-enriched layer is located or in the inner part thereof. Therefore, the target position of the above crystal grain size number range is the surface layer portion and the inside. Here, the austenite crystal grain is a crystal grain based on the trace of the grain boundary of the austenite crystal grain immediately before quenching after the quenching treatment.

  In the planetary gear mechanism component and rolling support mechanism of the present invention, the amount of retained austenite in the nitrogen-enriched layer is in the range of 11% by volume to 25% by volume. Balance with characteristics. When the amount of retained austenite is 11% by volume or more, the surface damage life can be greatly improved. If the amount of retained austenite is less than 11% volume, the surface damage life is not greatly improved. However, if the amount of retained austenite exceeds 25% by volume, there is no difference from the amount of retained austenite in a normal carbonitrided product, and the dimensional change over time increases, so it is desirably in the range of 11% to 25% by volume. . The amount of retained austenite is a value at the surface layer of 50 μm of the rolling surface after grinding, and can be measured, for example, by comparing the diffraction intensities of martensite α (211) and retained austenite γ (220) by X-ray diffraction. . The comparison of diffraction intensities may be made using a peak value, or may be made using an area value in the vicinity including the peak. α represents body-centered cubic iron, and γ represents face-centered cubic iron. Usually, martensite has a body-centered tetragonal structure in a state where carbon is dissolved, but carbon moves by tempering and changes from a body-centered tetragonal structure to a body-centered cubic structure. From the comparison of diffraction intensities, volume% of the retained austenite amount is obtained. Since the density difference between α iron and γ iron is small, there is no significant difference between volume% and mass%.

  In at least one of the constituent parts of the planetary gear mechanism of the present invention and the rolling support mechanism, the nitrogen content of the nitrogen-enriched layer can be in the range of 0.1 mass% to 0.7 mass%. . The nitrogen-enriched layer is a layer formed on the surface layer and having an increased nitrogen content, and can be formed, for example, by a process such as carbonitriding, nitriding, or nitriding. When the nitrogen content in the nitrogen-enriched layer is lower than 0.1% by mass, the surface damage resistance is lowered and the life is shortened. On the other hand, if the nitrogen content is more than 0.7% by mass, voids called voids are formed, or the amount of retained austenite increases so much that the hardness cannot be ensured, resulting in a short life. The nitrogen content of the nitrogen-enriched layer is a value at the surface layer of 50 μm of the rolling surface after grinding, and can be measured by, for example, EPMA (wavelength dispersion type X-ray microanalyzer).

  In at least one of the components of the planetary gear mechanism of the present invention and the rolling support mechanism, the surface hardness of the nitrogen-enriched layer can be HV653 or more. As described above, the rolling fatigue life can be significantly improved by increasing the surface hardness to HV653 or higher. If the surface hardness is less than HV653, the rolling fatigue life cannot be greatly improved, but rather deteriorates. Usually, the range of surface hardness is HV720-800. A higher surface hardness is desirable, but it is usually difficult to obtain a surface hardness exceeding HV900.

  In at least one of the components of the planetary gear mechanism of the present invention and the rolling support mechanism, the area ratio of the spheroidized carbide in the nitrogen-enriched layer can be in the range of 10% to 25%. By setting the area ratio of the spheroidized carbide to 10% or more, the rolling fatigue life can be greatly improved. If the area ratio of the spheroidized carbide is less than 10%, the rolling fatigue life is not greatly improved. When the area ratio of the spheroidized carbide exceeds 25%, the toughness of the material deteriorates due to coarsening and aggregation of the spheroidized carbide. Therefore, the area ratio is desirably 10% or more and 25% or less. The area ratio of the spheroidized carbide is a value in the surface layer of 50 μm of the rolling surface after grinding, and after corroding with a picric acid alcohol solution (picral), it can be observed with an optical microscope (400 times). Here, although it is simply expressed as spheroidized carbide, it is actually a combination of carbide / nitride.

  The rolling support mechanism of the planetary gear mechanism of the present invention may be a bearing that constitutes one of a needle roller with cage, a full roller type needle roller, and a shell type needle roller.

  In the planetary gear mechanism component and the rolling support mechanism of the present invention, the carbonitrided layer, ultrafine austenite grains, and an appropriate residual austenite amount range that balances the surface damage resistance and aging resistance characteristics By doing so, it is possible to improve both the normal load-dependent rolling fatigue life and the surface damage life due to metal contact caused by slipping or oil film breakage. Further, in the nitrogen-enriched layer, the durability can be improved more reliably by setting the nitrogen content, surface hardness and spheroidized carbide area ratio within the above ranges, and the rolling support mechanism can be made compact. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a configuration of an automatic transmission incorporating components of a planetary gear mechanism according to an embodiment of the present invention. 2 is a front view (a), a cross-sectional view (b), and a perspective view (c) schematically showing the configuration of the planetary gear mechanism of the P portion in FIG.

  Referring to FIGS. 1 and 2 (a) to 2 (c), this planetary gear mechanism 10 includes a sun gear shaft (hereinafter referred to as a sun gear shaft) 11 in an automatic transmission (A / T), for example. And a ring gear shaft (hereinafter referred to as an internal gear shaft) 16. This planetary gear mechanism includes a sun gear (hereinafter referred to as a sun gear) 12, a ring gear (hereinafter referred to as an internal gear) 15, and a plurality of planet pinion gears (hereinafter referred to as planetary gears) 13. Has mainly.

  The sun gear 12 is provided on the outer periphery of the sun gear shaft 11. The internal gear 15 surrounds the outer periphery of the sun gear 12, a gear is engraved on the inner peripheral surface, and is fixed to the internal gear shaft 16. Each of the plurality of planetary gears 13 is disposed between the sun gear 12 and the internal gear 15 and meshes with both the sun gear 12 and the internal gear 15.

  Each of the plurality of planetary gears 13 is rotatably supported with respect to the planetary gear shaft 17 by the rolling support mechanism 20 of the planetary gear mechanism 10. The rolling support mechanism 20 of the planetary gear mechanism 10 includes, for example, an inner member, an outer member, and a plurality of rolling elements interposed between the inner member and the outer member. In the present embodiment, the rolling support mechanism 20 of the planetary gear mechanism 10 is a radial needle roller bearing as shown in FIG. Therefore, the inner member of the rolling support mechanism 20 of the planetary gear mechanism 10 is the planetary gear shaft 17, the outer member is the planetary gear 13, and the rolling elements are needle rollers 18.

  Each of the plurality of needle rollers 18 is held at a correct position by a holder 19 at a constant interval. The planetary gear shaft 17 is pivotally supported by a planet pinion carrier (hereinafter referred to as a planetary frame) 14.

  Further, the inner member may be an inner ring provided separately from the planetary gear shaft 17 and fixed to the outer periphery of the planetary gear shaft 17. The outer member may be the planetary gear 13. May be an outer ring provided separately and fixed to the inner periphery of the planetary gear 13.

  With such a structure, each of the plurality of planetary gears 13 can mesh with the sun gear 12 and the internal gear 15 and revolve the outer periphery of the sun gear 12 while rotating along the circumference. is there.

  The gears of the planetary gear mechanism 10 are always in mesh with each other, and by applying driving force to either the sun gear 12 or the planetary frame 14 or the internal gear 15 or locking any one of them, The rotation speed, rotation direction, torque, and the like of the internal gear shaft 16 with respect to the gear shaft 11 can be changed.

  The outer member of the rolling support mechanism 20 of the planetary gear mechanism 10 (the planetary gear 13 or the outer ring fixed to the inner periphery of the planetary gear 13), the inner member (the planetary gear shaft 17 or the planetary gear shaft 17) At least one member of the fixed inner ring) and the rolling element (needle roller 18) has a nitrogen-enriched layer, the austenite grain size number of the member exceeds 10, and the nitrogen The retained austenite in the enriched layer is in the range of 11-25%.

  Further, the component parts of the planetary gear mechanism 10 (at least one of the sun gear shaft 11, the sun gear 12, the planetary frame 14, the internal gear 15, and the internal gear shaft 16) have a nitrogen-enriched layer, The austenite grain size number of the component exceeds 10 and the residual austenite in the nitrogen-enriched layer is in the range of 11-25%.

  Components of the planetary gear mechanism 10 of the present invention (at least one of the sun gear shaft 11, the sun gear 12, the planetary frame 14, the internal gear 15, and the internal gear shaft 16), or the rolling of the planetary gear mechanism 10 The outer member of the support mechanism 20 (the planetary gear 13 or the outer ring fixed to the inner periphery of the planetary gear 13), the inner member (the planetary gear shaft 17 or the inner ring fixed to the outer periphery of the planetary gear shaft 17) and the rolling member. At least one member of the moving body (needle roller 18) has a nitrogen content of the nitrogen-enriched layer in the range of 0.1% by mass to 0.7% by mass.

  The planetary gear mechanism 10 according to the present invention (at least one of the sun gear shaft 11, the sun gear 12, the planetary frame 14, the internal gear 15, and the internal gear shaft 16) or the planetary gear mechanism 10 The outer member of the rolling support mechanism 20 (the planetary gear 13 or the outer ring fixed to the inner periphery of the planetary gear 13), the inner member (the planetary gear shaft 17 or the inner ring fixed to the outer periphery of the planetary gear shaft 17). At least one member of the rolling elements (needle rollers 18) has a surface hardness of HV653 or more in the nitrogen-enriched layer.

  The planetary gear mechanism 10 according to the present invention (at least one of the sun gear shaft 11, the sun gear 12, the planetary frame 14, the internal gear 15, and the internal gear shaft 16) or the planetary gear mechanism 10 The outer member of the rolling support mechanism 20 (the planetary gear 13 or the outer ring fixed to the inner periphery of the planetary gear 13), the inner member (the planetary gear shaft 17 or the inner ring fixed to the outer periphery of the planetary gear shaft 17). At least one member of the rolling elements (needle rollers 18) has an area ratio of spheroidized carbide in the nitrogen-enriched layer in the range of 10% to 25%.

  In the above description, the needle roller bearing with a cage has been described as the rolling support mechanism 20 of the planetary gear mechanism 10 as shown in FIG. 3, but the rolling support mechanism 20 of the planetary gear mechanism 10 is not limited to this. A type needle roller bearing, a shell type needle roller bearing, or the like may be used.

  Next, the heat treatment including the carbonitriding process performed on the components of the planetary gear mechanism 10 and the rolling support mechanism 20 in the present embodiment will be described.

4 and 5 show a heat treatment method according to an embodiment of the present invention. FIG. 4 is a heat treatment pattern showing a method of performing primary quenching and secondary quenching, and FIG. 5 shows a method of cooling the material to below the A ₁ transformation point temperature during quenching and then reheating and finally quenching. It is the heat processing pattern shown. Both are exemplary embodiments of the present invention.

Referring to FIG. 4, first, for example, steel for bearing parts is heated to a carbonitriding temperature (for example, 845 ° C.) exceeding the A ₁ transformation point, and carbon for the bearing parts is subjected to carbonitriding at that temperature. The In the temperature treatment T ₁ , carbon and nitrogen are diffused in the steel base, and the carbon is sufficiently dissolved in the steel. Thereafter, the steel for bearing parts is subjected to oil quenching from the temperature of treatment T ₁ and cooled to a temperature below the A ₁ transformation point. Tempering is then performed at 180 ° C., but this tempering can be omitted.

Thereafter, the steel for the bearing component is reheated to a temperature lower than the temperature of the carbonitriding process (for example, 800 ° C.) at a temperature equal to or higher than the A ₁ transformation point, and the process T ₂ is performed by holding at that temperature. After that, oil quenching is performed from the temperature of the treatment T ₂ , and it is cooled to a temperature below the A ₁ transformation point. Tempering is then performed at 180 ° C.

Referring to FIG. 5, first, for example, steel for bearing parts is heated to a carbonitriding temperature (for example, 845 ° C.) exceeding the A ₁ transformation point, and carbon for the bearing parts is subjected to carbonitriding at that temperature. The In the temperature treatment T ₁ , carbon and nitrogen are diffused in the steel base, and the carbon is sufficiently dissolved in the steel. Thereafter, the steel for bearing parts is not quenched and cooled to a temperature below the A ₁ transformation point. Thereafter, the steel for the bearing component is reheated to a temperature lower than the temperature of the carbonitriding process (for example, 800 ° C.) at a temperature equal to or higher than the A ₁ transformation point, and the process T ₂ is performed by holding at that temperature. After that, oil quenching is performed from the temperature of the treatment T ₂ , and it is cooled to a temperature below the A ₁ transformation point. Tempering is then performed at 180 ° C.

  The above heat treatment can improve the cracking strength and reduce the aging dimensional change rate while carbonitriding the surface layer portion, rather than normal quenching (ie, quenching as it is after the carbonitriding process). As described above, according to the above heat treatment method, it is possible to obtain a microstructure in which the grain size of austenite crystal grains is ½ or less of the conventional one. The bearing parts subjected to the above heat treatment have a long rolling fatigue characteristic, can improve the cracking strength, and can also reduce the rate of dimensional change over time.

“Normal quenching” refers to quenching that does not perform the “carbonitriding process” described in FIG. 4 or FIG. Further, “primary quenching” described in FIG. 4 refers to the first quenching that is heated to the heating temperature T ₁ for the carbonitriding process and rapidly cooled by oil cooling. The “secondary quenching” described in FIG. 4 is the second quenching in which the primary quenching illustrated in FIG. 4 is performed and then heated to a heating temperature T ₂ for normal quenching and rapidly cooled by oil cooling. Say.

  FIG. 6A shows the austenite grain size of the bearing steel to which the heat treatment pattern shown in FIG. 4 is applied. For comparison, FIG. 6B shows the austenite grain size of the bearing steel obtained by the conventional heat treatment method. FIGS. 7 (a) and 7 (b) show the austenite grain sizes illustrating FIGS. 6 (a) and 6 (b). From the structure showing these austenite crystal grain sizes, the conventional austenite grain size is No. 10 in the grain size number of JIS (Japanese Industrial Standard) standard, and according to the heat treatment method of the present invention, No. 12 fine grains can be obtained. . Moreover, the average particle diameter of Fig.6 (a) was 5.6 micrometers as a result of measuring by the intercept method.

  Next, examples of the present invention will be described.

Example 1
A bearing for a rolling fatigue test was manufactured using JIS standard SUJ2. The inner ring had an outer diameter φ14.64 mm × width L 17.3 mm, and the outer ring had an inner diameter φ18.64 mm × outer diameter φ24 mm × width L6.9 mm. The rollers used were 26 rollers with an outer diameter of φ2 mm and a length of L6.8 mm, and had a full roller type configuration without using a cage. The basic dynamic load rating of this bearing is 8.6 kN, and the basic static load rating is 12.9 kN.

  The manufacturing history of each test bearing is as follows.

  Test bearing No. 1-3 (examples of the present invention): In the heat treatment pattern shown in FIG. 4, the carbonitriding temperature was 850 ° C. (845 ° C. in FIG. 4), and the holding time was 150 minutes. The atmosphere at that time was a mixed gas of RX gas and ammonia gas. At that time, test bearing No. The processing was performed by changing the mixing ratio of RX gas and ammonia gas in 1 to 3. Thereafter, in the heat treatment pattern shown in FIG. 4, primary quenching is performed from a carbonitriding temperature of 850 ° C., followed by secondary quenching by heating at a temperature 800 ° C. lower than the carbonitriding temperature, and then at 180 ° C. Tempering was performed for 90 minutes.

  Test bearing No. 4 (Comparative example): Standard heat treatment was performed. That is, in an RX gas atmosphere, heating was performed at a heating temperature of 840 ° C. and a holding time of 20 minutes, followed by quenching, and then tempering at 180 ° C. for 90 minutes.

  Test bearing No. 5, 6 (comparative example): Carbonitriding was performed. That is, heating was performed in a mixed gas atmosphere of RX gas and ammonia gas at a heating temperature of 850 ° C. and a holding time of 150 minutes. At that time, test bearing No. 5 and 6 were performed by changing the mixing ratio of RX gas and ammonia gas. Then, it hardened from 850 degreeC and then tempered at 180 degreeC for 90 minutes.

  Test bearing No. manufactured by each manufacturing method described above. Table 1 shows the material investigation results and function evaluation test results of the inner rings 1-6.

  Next, a material investigation method and a function evaluation test method will be described.

(1) Austenite grain size The austenite grain size was measured based on the austenite grain size test method for steel of JIS G 0551.

(2) Amount of retained austenite The amount of retained austenite was measured by comparing the diffraction intensities of martensite α (211) and retained austenite γ (220) by X-ray diffraction. As the amount of retained austenite, the value at the surface layer of 50 μm of the rolling surface after grinding was adopted.

(3) Nitrogen content The nitrogen content was measured using EPMA. For the nitrogen content, the value at the surface layer of 50 μm of the rolling surface after grinding was adopted.

(4) Surface hardness The surface hardness was measured using a Vickers hardness meter (1 kgf).

(5) Area ratio of spheroidized carbide The area ratio of spheroidized carbide was measured by observation with an optical microscope (400 times) after corrosion using a picric acid alcohol solution (picral). As the area ratio of the spheroidized carbide, the value at the surface layer of 50 μm of the rolling surface after grinding was adopted. The spheroidized carbide is not necessarily a sphere, and may be any carbide that can be identified as black in the microscope field of view, and is automatically measured.

(6) Rolling fatigue life test The rolling fatigue life was performed under the test conditions shown in Table 2 using the test test apparatus shown in FIG. The test apparatus shown in FIG. 8 is an outer ring rotating test apparatus. Referring to FIG. 8, a configuration in which a plurality of needle rollers 53 (3) are arranged so as to roll between an inner ring 52 (2) and an outer ring 54 (4) incorporated in a test machine is used. A rolling fatigue test was performed by rotating the outer ring 54 at a predetermined speed while applying a radial load by the members 55 and 56.

(7) Static crack strength test Using the outer ring of the test bearing, a static crack strength test was performed by applying a load with an Amsler tester alone.

(8) Crack fatigue strength test A crack fatigue strength test was conducted under the test conditions shown in Table 3 using the outer ring of the test bearing.

  The results of the rolling fatigue life test, static crack strength test, and crack fatigue strength test are shown in the standard heat-treated product No. The value of 4 was set to 1, and the result of each test bearing was expressed as a ratio.

  The test results shown in Table 1 will be described.

(1) Austenite crystal grain size 1-3 are remarkably refined with a grain size number of 11-12. Standard heat treated product and conventional carbonitrided product No. Nos. 4 to 6 are austenite grains having a grain size number of 8 to 9 and coarser than those of the present invention.

(2) Amount of retained austenite The amount of retained austenite of 1 to 3 is 12 to 24%, and an appropriate amount of austenite is present in these samples. Standard heat treatment No. The amount of retained austenite of 4 is 8%, which is less than that of the present invention. In addition, the conventional carbonitriding product No. The amount of retained austenite of 5 and 6 is 29% and 36%, which is larger than that of the present invention. The austenite amount of the product of the present invention is the amount of retained austenite between the standard heat treated product and the conventional carbonitrided product.

(3) Nitrogen content Product No. The nitrogen content of 1 to 3 is 0.12 to 0.62% by mass. Standard heat treatment No. Since no carbonitriding treatment was performed on No. 4, the nitrogen content was 0%. In addition, the conventional carbonitriding product No. The nitrogen contents of 5 and 6 were 0.31% by mass and 0.70% by mass. The nitrogen content of the product of the present invention tended to be slightly lower than that of the conventional carbonitrided product. This is considered to be because the product of the present invention is subjected to secondary quenching at a temperature of 800 ° C. lower than the carbonitriding temperature after the conventional carbonitriding treatment.

(4) Surface hardness This product No. The surface hardness of 1-3 is HV730-780. Standard heat treatment No. 4 is HV740. In addition, the conventional carbonitriding product No. Nos. 5 and 6 are HV760 and HV650. Regarding No. 6, the amount of retained austenite is too large and the hardness is not obtained.

(5) Area ratio of spheroidized carbide The area ratio of the spheroidized carbides in 1 to 3 is 11.4 to 13.6%. Standard heat treated product and conventional carbonitrided product No. The area ratios of spheroidized carbides in 4, 5, and 6 are 7.9%, 9.6%, and 8.8%. Compared with the standard heat-treated product and the conventional carbonitrided product, the product of the present invention has a larger area ratio of the spheroidized carbide, is refined, and has a larger amount. This is because the product of the present invention performs secondary quenching at a temperature of 800 ° C. lower than the carbonitriding temperature after conventional carbonitriding.

(6) Rolling fatigue life test No. 1-3 are standard heat-treated products No. Compared with No. 4, it has a rolling fatigue life of 3 times or more. Compared with 5, 6, it has a rolling fatigue life of 1.5 times or more. In addition, carbonitrided product No. Nos. 5 and 6 are standard heat treated product Nos. Compared to 4, it has a rolling fatigue life slightly less than twice.

(7) Static crack strength test The static crack strength of Nos. 1 to 3 is the standard heat treated product No. Compared to 4, it is equivalent or slightly improved. In addition, carbonitrided product No. In Nos. 5 and 6, the standard heat treatment product No. Compared to 4, the static crack strength is reduced. This is considered to be due to the coarsening of the nitrogen-enriched layer and austenite crystal grains in the surface layer portion.

(8) Crack fatigue strength test 1-3 are standard heat-treated products No. Compared to 4, it is improved by 20% or more. In addition, carbonitrided product No. Nos. 5 and 6 are standard heat-treated product Nos. Compared to 4, it is improved by 20% or more. This is considered to be caused by the formation of compressive residual stress in the surface layer due to the penetration of nitrogen into the surface.

  In summary, the product No. 1 to 3 have a nitrogen-enriched layer in the surface layer portion, have austenite crystals refined to a particle size number of 11 or more (greater than 10), have moderately retained austenite, and have an appropriate surface Since it has hardness and the area ratio of spheroidized carbide is large, the usual load-dependent rolling fatigue life and crack fatigue strength are improved.

(Example 2)
Peeling and smearing specimens were manufactured using JIS standard SUJ2 steel. The test piece has an outer diameter of φ40 mm and a width of L12 mm. The manufacturing history of each test bearing is as follows.

  Test bearing No. 1 (Example of the present invention): In the heat treatment pattern shown in FIG. 4, the carbonitriding temperature was 850 ° C. and the holding time was 150 minutes. The atmosphere at that time was a mixed gas of RX gas and ammonia gas. Thereafter, in the heat treatment pattern shown in FIG. 4, primary quenching is performed from a carbonitriding temperature of 850 ° C., followed by secondary quenching by heating at a temperature 800 ° C. lower than the carbonitriding temperature, and then at 180 ° C. Tempering was performed for 90 minutes.

  Test bearing No. 2 (Comparative example): Standard heat treatment was performed. That is, in an RX gas atmosphere, heating was performed at a heating temperature of 840 ° C. and a holding time of 20 minutes, followed by quenching, and then tempering at 180 ° C. for 90 minutes.

  Test bearing No. 3 (Comparative example): Carbonitriding was performed. That is, after heating in a mixed gas atmosphere of RX gas and ammonia gas at a heating temperature of 850 ° C. and a holding time of 150 minutes, quenching was performed from 850 ° C., and then tempering was performed at 180 ° C. for 90 minutes.

  Table 4 shows the material investigation results, the peeling test, and the smearing test results of the test pieces manufactured by the manufacturing method.

  Next, the function evaluation test method will be described.

(1) Peeling test Generated on the test piece when the test piece and the counterpart test piece are brought into rolling contact under the test conditions shown in Table 5 with a standard heat treatment product of JIS standard SUJ2 having a rough surface as the counterpart test piece. The area ratio of peeling (aggregate of fine peeling) to be measured was measured as peeling strength. The peel strength ratio is the standard heat treatment product No. The value of 2 was set to 1, and the result of each test bearing was represented by the reciprocal of the ratio.

(2) Smearing test Under the test conditions shown in Table 6, both the test piece and the counterpart test piece were made of the same material in rolling contact with each other, and the rotational speed of only the test piece was increased at a constant rate. In this case, the relative rotation speed between the test pieces at the moment when the generated sound became larger than a certain value was defined as the smearing strength. The smearing strength ratio is the standard heat treatment product no. The value of 2 was set to 1, and the result of each test bearing was expressed as a ratio.

  The test results shown in Table 4 will be described.

(1) Peeling test Product No. No. 1 is a standard heat treatment product No. Compared with No. 2, it has a peeling strength of 1.8 times. Compared to 3, it is the same or slightly improved. This has a nitrogen-enriched layer in the surface layer part, the austenite crystal is refined to a grain size number of 11 or more, the amount of retained austenite is moderately, it has an appropriate surface hardness, and the area of spheroidized carbide A large ratio is considered to have increased toughness and resistance to crack initiation and propagation.

(2) Smearing test Product No. No. 1 is a standard heat treatment product No. Compared with No. 2, it has 1.7 times the smearing strength. Compared to 3, it is the same or slightly improved. This has a nitrogen-enriched layer in the surface layer part, the austenite crystal is refined to a grain size number of 11 or more, the amount of retained austenite is moderately, it has an appropriate surface hardness, and the area of spheroidized carbide A large ratio is considered to suppress the plastic flow of the surface layer under large sliding conditions and to improve the seizure resistance.

  In summary, the product No. No. 1 is better than the conventional heat-treated product in both peeling test and smearing test.

  In addition, the lubrication conditions are poor, the rollers interfere with each other, the roller position is not controlled smoothly, and the surface damage life due to roller skew is improved.

  The product of the present invention has a nitrogen-enriched layer in the surface layer part, the austenite crystal is refined to a particle size number of 11 or more, the amount of retained austenite is moderately, the surface hardness is appropriate, and the spheroidized carbide Therefore, the resistance to the occurrence and development of cracks is very large, and the generation of surface cracks due to surface heat generation and tangential force due to sliding can be suppressed.

(Example 3)
Using JIS standard SUJ2 material (1.0% by mass C-0.25% by mass Si-0.4% by mass Mn-1.5% by mass Cr), (1) measurement of hydrogen content, (2) crystal grain size (3) Charpy impact test, (4) Fracture stress value measurement, and (5) Rolling fatigue test. Table 7 shows the results.

  The manufacturing history of each sample is as follows.

  Samples A to D (examples of the present invention): In the heat treatment pattern shown in FIG. 4, the carbonitriding temperature was 850 ° C., and the holding time was 150 minutes. The atmosphere at that time was a mixed gas of RX gas and ammonia gas. In the heat treatment pattern shown in FIG. 4, primary quenching was performed from a carbonitriding temperature of 850 ° C., followed by secondary quenching by heating to a temperature range of 780 ° C. to 830 ° C. lower than the carbonitriding temperature. However, Sample A having a secondary quenching temperature of 780 ° C. was excluded from the test because of insufficient quenching.

  Samples E and F (comparative examples): The carbonitriding treatment was carried out with the same history as the invention examples A to D, and the secondary quenching temperature was 850 ° C to 870 ° C, which is a carbonitriding temperature of 850 ° C or higher.

  Conventional carbonitrided product (comparative example): Carbonitriding was performed. That is, after heating at a heating temperature of 850 ° C. and a holding time of 150 minutes in a mixed gas atmosphere of RX gas and ammonia gas, quenching was performed as it was from the carbonitriding temperature of 850 ° C., and secondary quenching was not performed.

  Normal quenching product (comparative example): without any carbonitriding treatment, it was quenched by heating to 850 ° C. Secondary quenching was not performed.

  Next, the test method will be described.

(1) Measurement of hydrogen amount The amount of hydrogen was determined by analyzing the amount of non-diffusible hydrogen in the steel using a DH-103 type hydrogen analyzer manufactured by LECO. The amount of diffusible hydrogen is not measured. The specification of this LECO DH-103 type hydrogen analyzer is shown below.

Analysis range: 0.01 to 50.00 ppm
Analysis accuracy: ± 0.1 ppm or ± 3% H (whichever is greater)
Analysis sensitivity: 0.01ppm
Detection method: Thermal conductivity method Sample weight size: 10 mg to 35 mg (maximum: diameter 12 mm × length 100 mm)
Heating furnace temperature range: 50 ° C to 1100 ° C
Reagents: Anhydrone Mg (ClO ₄ ) ₂ , Ascarite NaOH
Carrier gas: nitrogen gas, gas dosing gas: hydrogen gas, both gases have a purity of 99.99% or more and a pressure of 40 psi (2.8 kgf / cm ² ).

  The outline of the measurement procedure is as follows. A sample collected with a dedicated sampler is inserted into the hydrogen analyzer together with the sampler. Internal diffusible hydrogen is directed to the thermal conductivity detector by a nitrogen carrier gas. This diffusible hydrogen is not measured in this example. Next, a sample is taken out from the sampler, heated in a resistance heating furnace, and non-diffusible hydrogen is guided to the thermal conductivity detector by nitrogen carrier gas. The amount of non-diffusible hydrogen can be known by measuring the thermal conductivity with a thermal conductivity detector.

(2) Measurement of crystal grain size The crystal grain size was measured based on the JIS G 0551 steel austenite grain size test method.

(3) Charpy impact test The Charpy impact test was performed based on the Charpy impact test method of the metal material of JIS Z2242. As a test piece, a U-notch test piece (JIS No. 3 test piece) shown in JIS Z 2202 was used.

(4) Measurement of Fracture Stress Value FIG. 9 is a diagram showing a test piece of a static crush strength test (measurement of a fracture stress value). The load until it is broken by applying a load in the P direction in the figure is measured. Thereafter, the obtained fracture load is converted into a stress value by the following bending beam stress calculation formula. In addition, a test piece is not restricted to the test piece shown in FIG. 9, You may use the test piece of another shape.

Assuming that the fiber stress on the convex surface of the test piece of FIG. 9 is σ ₁ and the fiber stress on the concave surface is σ ₂ , σ ₁ and σ ₂ are obtained by the following formulas (Mechanical Engineering Manual A4 Knitting Material Dynamics A4-40) . Here, N is the axial force of the cross section including the axis of the annular specimen, A is the cross-sectional area, e ₁ is the outer radius, and e ₂ is the inner radius. Further, κ is a section modulus of the curved beam.

σ ₁ = (N / A) + {M / (Aρ ₀ )} [1 + e ₁ / {κ (ρ ₀ + e ₁ )}]
σ ₂ = (N / A) + {M / (Aρ ₀ )} [1-e ₂ / {κ (ρ ₀ −e ₂ )}]
κ = − (1 / A) ∫A {η / (ρ ₀ + η)} dA
(5) Rolling fatigue life Table 8 shows the test conditions for the rolling fatigue life test. FIG. 10 is a schematic view of a rolling fatigue life tester. FIG. 10A is a front view, and FIG. 10B is a side view. 10 (a) and 10 (b), the rolling fatigue life test piece 31 is driven by the drive roll 21 and rotates in contact with the ball 23. The ball 23 is a 3/4 inch ball and is guided by the guide roll 22 to roll while exerting a high surface pressure with the rolling fatigue life test piece 31.

  The test results shown in Table 7 will be described as follows.

(1) Amount of hydrogen Conventional carbonitrided products that have undergone carbonitriding have a very high value of 0.72 ppm. This is thought to be because ammonia (NH ₃ ) contained in the carbonitriding atmosphere decomposed and hydrogen entered the steel. On the other hand, in Samples B to D, the hydrogen content is reduced to almost half of 0.37 to 0.40 ppm. This amount of hydrogen is at the same level as that of ordinary hardened products.

  By reducing the amount of hydrogen described above, embrittlement of steel due to hydrogen solid solution can be reduced. That is, the reduction in the amount of hydrogen greatly improves the Charpy impact value of Samples B to D of the present invention example.

(2) Crystal grain size When the secondary quenching temperature is lower than the quenching (primary quenching) temperature during carbonitriding, that is, in the case of Samples B to D, the austenite grains are prominent as the grain size numbers 11 to 12. Has been refined. The austenite grains of the samples E and F, the conventional carbonitrided product and the normal quenching product have a crystal grain size number 10, and are coarser than the samples B to D of the examples of the present invention.

(3) Charpy impact test According to Table 7, the Charpy impact value of the samples B to D of the present invention example is 6 compared to the Charpy impact value of the conventional carbonitrided product being 5.33 J / cm ^2. A high value of .30 to 6.65 J / cm ² is obtained. Among these, the one where secondary quenching temperature is low shows the tendency for a Charpy impact value to become high. The normally hardened product has a high Charpy impact value of 6.70 J / cm ² .

(4) Measurement of fracture stress value The fracture stress value corresponds to the crack resistance strength. According to Table 7, the conventional carbonitrided product has a fracture stress value of 2330 MPa. Compared to this, the fracture stress values of Samples B to D were improved to 2650 to 2840 MPa. The fracture stress value of the normal quenching product is 2770 MPa, and the improved cracking resistance strength of Samples B to D is estimated to have a great effect by reducing the hydrogen content, along with the refinement of austenite crystal grains.

(5) According to the rolling contact fatigue test table 7, normally quenched sample has to reflect that do not have a carbonitrided layer in the surface portion, the rolling fatigue life L ₁₀ is the lowest. Compared to this, the rolling fatigue life of the conventional carbonitrided product is 3.1 times. The rolling fatigue life of Samples B to D is significantly improved as compared with the conventional carbonitrided product. Samples E and F are almost equivalent to conventional carbonitrided products.

  In summary, Samples B to D of the present invention have a reduced hydrogen content, an austenite crystal grain size of 11 or more, and improved Charpy impact value, crack resistance strength and rolling fatigue life. .

Example 4
Next, Example 4 will be described. A series of tests were performed on the following X material, Y material, and Z material. JIS standard SUJ2 material (1.0% by mass C-0.25% by mass Si-0.4% by mass Mn-1.5% by mass Cr) is used for the material for heat treatment, which is common to X material to Z material. did. The manufacturing history of the X material to the Z material is as follows.

  X material (comparative example): Only normal quenching (not carbonitriding).

  Y material (comparative example): quenching directly after carbonitriding (conventional carbonitriding quenching). The carbonitriding temperature was 845 ° C. and the holding time was 150 minutes. The atmosphere of the carbonitriding process was a mixed gas of RX gas and ammonia gas.

  Z material (example of the present invention): bearing steel subjected to the heat treatment pattern of FIG. The carbonitriding temperature was 845 ° C. and the holding time was 150 minutes. The carbonitriding atmosphere was a mixed gas of RX gas and ammonia gas. The final quenching temperature was 800 ° C.

(1) Rolling fatigue life Test conditions and test equipment for rolling fatigue life are as shown in Table 8 and FIG. The rolling fatigue life test results are shown in Table 9.

According to Table 9, the Y material of the comparative example shows 3.1 times the L ₁₀ life of the X material that has been subjected only to normal quenching in the comparative example (the life that one of the 10 test pieces breaks), The effect of extending the life by carbonitriding is recognized. On the other hand, the Z material of the example of the present invention has a long life of 1.74 times that of the Y material and 5.4 times that of the X material. The main reason for this improvement is thought to be the refinement of the microstructure.

(2) Charpy impact test The Charpy impact test was performed by the method according to the above-mentioned JIS Z 2242 using the U notch test piece. The test results are shown in Table 10.

  The Charpy impact value of the Y material (comparative example) subjected to carbonitriding was not higher than that of the normal quenching X material (comparative example), but the Z material obtained the same value as the X material.

(3) Test of Static Fracture Toughness Value FIG. 11 is a diagram showing a test piece of a static fracture toughness test. About 1 mm of pre-crack was introduced into the notch portion of the test piece, and then a static load by three-point bending was applied to determine the fracture load P. The following formula (I) was used for calculation of the fracture toughness value (K ₁ c value). The test results are shown in Table 11.

K ₁ c = (PL√a / BW ² ) {5.8−9.2 (a / W) +43.6 (a / W) ² −75.3 (a / W) ³ +77.5 (a / W) ⁴ } (I)

  Since the precrack depth is larger than the carbonitrided layer depth, there is no difference between the X material and the Y material of the comparative example. However, the Z material of the present invention example was able to obtain a value about 1.2 times that of the comparative example.

(4) Static Crushing Strength Test The static crushing strength test piece having the shape shown in FIG. 9 was used as described above. In the figure, a static crushing strength test was performed by applying a load in the P direction. The test results are shown in Table 12.

  The Y material subjected to carbonitriding has a slightly lower value than the normal quenching X material. However, the Z material of the present invention has higher static crushing strength than the Y material, and a level comparable to that of the X material is obtained.

(5) Aged dimensional change rate The measurement results of the aged dimensional change rate at a holding temperature of 130 ° C. and a holding time of 500 hours are shown in Table 13 together with the surface hardness and the retained austenite amount (50 μm depth).

  It can be seen that the Z material of the example of the present invention is suppressed by about 40% compared to the dimensional change rate of the Y material having a large amount of retained austenite.

(6) Rolling life test under the presence of foreign matter Using a ball bearing 6206, the rolling fatigue life under the presence of foreign matter mixed with a predetermined amount of standard foreign matter was evaluated. Table 14 shows the test conditions and Table 15 shows the test results.

  Compared to the X material, the Y material subjected to the conventional carbonitriding treatment is about 2.5 times longer, and the Z material of the present invention example has a long life of about 2.3 times. Although the Z material of the present invention has less retained austenite than the Y material of the comparative example, a substantially equivalent long life is obtained due to the intrusion of nitrogen and the effect of the refined microstructure.

  From the above results, the Z material, that is, the present invention example, simultaneously satisfies the three items of the rolling fatigue life extension, crack strength improvement, and reduction of aging dimensional change rate, which were difficult in the conventional carbonitriding process. I found out that I can do it.

  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.

  The present invention improves durability by improving the load-dependent rolling fatigue life and the surface damage life due to metal contact, and the components of planetary gear mechanisms such as automobile A / T missions and rolling of planetary gear mechanisms. It can be applied particularly advantageously to the support mechanism.

It is a schematic sectional drawing which shows the structure of the automatic transmission incorporating the component of the planetary gear mechanism in one embodiment of this invention. It is the front view (a) which shows the structure of the planetary gear mechanism of the P section of FIG. It is a partially broken perspective view which shows roughly the structure of a rolling bearing as a rolling support mechanism in the planetary gear mechanism of FIG. It is a figure explaining the heat processing method in embodiment of this invention. It is a figure explaining the modification of the heat processing method in embodiment of this invention. It is a figure which shows the microstructure of a bearing component, especially an austenite grain. (a) is a bearing part of the example of the present invention, and (b) is a conventional bearing part. (A) shows the austenite grain boundary illustrated in FIG. 6 (a), and (b) shows the austenite grain boundary illustrated in FIG. 6 (b). It is a figure which shows the rolling fatigue testing machine of outer ring | wheel rotation. It is a figure which shows the test piece of a static crushing strength test (measurement of a fracture stress value). It is the schematic of a rolling fatigue life tester. (A) is a front view, (b) is a side view. It is a figure which shows the test piece of a static fracture toughness test.

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 Planet gear shaft, 18 Needle roller, 19 Cage, 20 Rolling support Mechanism, 21 Drive roll, 22 Guide roll, 23 Ball, 31 Rolling fatigue life test piece, 52 Inner ring, 53
Needle roller (test object), 54 outer ring, 55, 56 Test equipment members.

Claims (11)

In a component part of a planetary gear mechanism incorporated in a planetary gear mechanism having a sun gear, an internal gear surrounding the outer periphery of the sun gear, and a planetary gear meshing with both the sun gear and the internal gear. ,
The component has a nitrogen-enriched layer, the austenite grain size number of the component exceeds 10 and the retained austenite in the nitrogen-enriched layer is in the range of 11% to 25%. Components of the planetary gear mechanism.   2. The planetary gear mechanism component according to claim 1, wherein the nitrogen content of the nitrogen-enriched layer is in the range of 0.1% by mass to 0.7% by mass.   The planetary gear mechanism component according to claim 1 or 2, wherein a surface hardness of the nitrogen-enriched layer is HV653 or more.   The component part of the planetary gear mechanism according to any one of claims 1 to 3, wherein an area ratio of the spheroidized carbide in the nitrogen-enriched layer is in a range of 10% to 25%. In the rolling support mechanism of the planetary gear mechanism that rotatably supports the planetary gear meshing with both the sun gear and the internal gear surrounding the outer periphery of the sun gear,
The rolling support mechanism includes an outer member, an inner member located inside the outer member, and a plurality of rolling elements interposed between the outer member and the inner member,
At least any one member of the inner member, the outer member, and the rolling element of the rolling support mechanism has a nitrogen-enriched layer, and the grain number number of the austenite crystal grains of the member exceeds # 10, And a rolling support mechanism of a planetary gear mechanism in which the retained austenite in the nitrogen-enriched layer is in the range of 11% to 25%.   The rolling support mechanism of the planetary gear mechanism according to claim 5, wherein the nitrogen content of the nitrogen-enriched layer is in the range of 0.1 mass% or more and 0.7 mass% or less.   The rolling support mechanism for a planetary gear mechanism according to claim 5 or 6, wherein the surface hardness of the nitrogen-enriched layer is HV653 or more.   The rolling support mechanism of the planetary gear mechanism according to any one of claims 5 to 7, wherein an area ratio of the spheroidized carbide in the nitrogen-enriched layer is in a range of 10% to 25%.   The rolling support mechanism of the planetary gear mechanism according to any one of claims 5 to 8, wherein the rolling support mechanism constitutes a needle roller with a cage.   The rolling support mechanism of the planetary gear mechanism according to any one of claims 5 to 8, wherein the rolling support mechanism constitutes a full roller type needle roller.   The rolling support mechanism of the planetary gear mechanism according to any one of claims 5 to 8, wherein the rolling support mechanism constitutes a shell-type needle roller.

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