JP2006112558A - Tapered roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tapered roller bearing having high crack-proof strength and dimensional stability and excellent in fatigue life. <P>SOLUTION: At least one component part of an inner ring 10, an outer ring 20 and tapered rollers 30 of the tapered roller bearing has a nitrogen enrichment layer in a surface layer part. Grain size numbers of austenite crystal grains in the nitrogen enrichment layer exceed 10. Crowning is formed on opposite end portions of a raceway surface 12 of the inner ring 10. A width Wc at each end portion is set at 20% or less of a raceway surface width W of the inner race 10. A value R/R<SB>BASE</SB>of a ratio of a curvature radius R of large end faces 32 of the tapered rollers 30 to a distance R<SB>BASE</SB>from cone apexes of the tapered rollers 30 to a cone back face rib surface 18 of the inner ring 10 is set to be not less than 0.75 nor more than 0.87. Side run-out with outside surface at the large end faces 32 of the tapered rollers 30 is set at 3μm or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tapered roller bearing.

  The tapered roller bearing is a radial bearing using a tapered roller as a rolling element, and includes an inner ring 10, an outer ring 20, a tapered roller 30, and a cage 40 as shown in FIG. The inner ring 10 has a conical track 12 on the outer periphery, and includes a small brim 14 and a large brim 16 on both sides of the track 12. The outer ring 20 has a conical track 22 on the inner periphery. The tapered roller 30 is interposed between the raceways 12 and 22 of the inner and outer rings 10 and 20 so as to roll freely. The cage 40 has a plurality of pockets arranged at predetermined intervals in the circumferential direction, and the tapered rollers 30 are accommodated in the respective pockets.

  In the tapered roller bearing, the tapered roller 30 and the raceways 12 and 22 of the inner and outer rings 10 and 20 are in line contact, and as shown in FIG. 2, the raceways 12 and 22 of the inner and outer rings 10 and 20 and the tapered roller 30 are tapered. The apex is designed to gather at one point O on the bearing central axis, and can receive a radial load and an axial load in one direction. Since the conical angle is different between the raceway 12 of the inner ring 10 and the raceway 22 of the outer ring 20, the resultant force of the load applied to the tapered roller 30 from each race acts in the direction of pushing the tapered roller 30 toward the collar 16 of the inner ring 10. For this reason, the tapered roller 30 is guided in a state in which the large end surface 32 is pressed against the large collar 16 of the inner ring 10 and is brought into sliding contact therewith. Specifically, as shown in FIG. 16, the large collar surface 18 is a flat surface in which the generatrix y forms a predetermined angle with respect to the central axis of the bearing, and the large end surface 32 of the tapered roller 30 is in sliding contact with the flat surface. .

  Tapered roller bearings are suitable for carrying radial loads, axial loads, and their combined loads, and because they have a large load capacity, tapered rollers are used in power transmission devices such as differentials and transmissions in automobiles and construction machinery. A support device in which a gear shaft is supported by a bearing is used. There are two types of automobile transmissions: manual type and automatic type. Depending on the vehicle drive system, front wheel drive (FWD) transaxle, rear wheel drive (RWD) transmission, and four wheel drive (4WD) transfer ( Sub transmission). In either case, the driving force from the engine is shifted and transmitted to a drive shaft or the like.

  FIG. 17 shows a configuration example of an automobile transmission. This transmission is of a synchronous mesh type, and the left side of the figure is the engine side and the right side is the drive wheel side. A tapered roller bearing 43 is interposed between the main shaft 41 and the main drive gear 42. In this example, the outer ring raceway surface of the tapered roller bearing 43 is formed directly on the inner periphery of the main drive gear 42. The main drive gear 42 is rotatably supported with respect to the casing 45 by a tapered roller bearing 44. A clutch gear 46 is engaged and connected to the main drive gear 42, and a synchronization mechanism 47 is disposed in the vicinity of the clutch gear 46.

  The synchronizer 47 includes a sleeve 48 that moves in the axial direction (left and right in FIG. 17) by the operation of a selector (not shown), a synchronizer key 49 that is mounted on the inner periphery of the sleeve 48 so as to be axially movable, and a main shaft. The hub 50 engaged and connected to the outer periphery of 41, the synchronizer ring 51 slidably mounted on the outer periphery (cone portion) of the clutch gear 46, and the synchronizer key 49 are elastically pressed against the inner periphery of the sleeve 48. A pressing pin 52 and a spring 53 are provided.

  In the state shown in FIG. 17, the sleeve 48 and the synchronizer key 49 are held in the neutral position by the pressing pin 52. At this time, the main drive gear 42 idles with respect to the main shaft 41. On the other hand, when the sleeve 48 is moved to the left side in the axial direction, for example, by the operation of the selector, the synchronizer key 49 is moved to the left side in the axial direction following the sleeve 48, and the synchronizer ring 51 is moved to the clutch gear 46. Press against the inclined surface of the cone. As a result, the rotational speed of the clutch gear 46 decreases, and conversely, the rotational speed on the synchro mechanism 47 side increases. When the rotational speeds of the two are synchronized, the sleeve 48 further moves to the left in the axial direction, engages with the clutch gear 46, and the main shaft 41 and the main drive gear 42 are connected via the sync mechanism 47. . Thereby, the main shaft 41 and the main drive gear 42 rotate synchronously.

  By the way, in recent years, low-viscosity oil tends to be used in automobile transmissions for mission AT, CVT, fuel efficiency, and the like. In an environment where low-viscosity oil is used, a surface-origin type that has a very short life due to poor lubrication when the oil temperature is high, the amount of oil is low, preload loss occurs, etc. Peeling may occur.

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. (For example, JP-A-8-4774, JP-A-11-101247). 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

  However, since the carbonitriding method described above is a diffusion treatment that diffuses carbon and nitrogen, it must be kept at a high temperature 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, in order to secure a long life against rolling fatigue, improve crack strength, and prevent an increase in the rate of dimensional change over time, it is possible to cope with the problem by adjusting the structure by the steel alloy design. However, the alloy design causes problems such as high raw material costs.

  Bearing parts in future transmissions will be used under higher load conditions and higher temperatures than ever before, as the usage environment increases in load and temperature, and in response to demands for smaller and more compact transmissions. It is required to have characteristics that can be achieved. For this reason, a bearing component having high strength, long rolling fatigue characteristics, high cracking strength and dimensional stability is required.

  An object of the present invention is to provide a tapered roller bearing having high cracking resistance and dimensional stability and excellent in rolling fatigue life.

The tapered roller bearing of the present invention includes an inner ring having a tapered surface raceway on the outer periphery and formed with large and small collars on both sides of the track, an outer ring having a tapered surface raceway on the inner periphery, and an inner ring raceway. A plurality of tapered rollers interposed between the outer ring raceway and a retainer for keeping the tapered rollers at a predetermined interval in the circumferential direction, and at least one component of the inner ring, outer ring, and tapered roller Has a nitrogen-enriched layer in the surface layer part, the austenite grain size number in the nitrogen-enriched layer exceeds 10, and forms crowning at both ends of the raceway surface of the inner ring, at each of these end parts The width of the crowning is 20% or less of the raceway surface width of the inner ring, and the ratio R / of the radius R of curvature of the large end face of the tapered roller to the distance R _BASE from the top of the tapered ring of the tapered roller to the large collar surface of the inner ring the R _BASE 0.75 And above 0.87 or less, it is characterized in that the runout end surface of the large end face of the tapered rollers and 3μm or less.

  According to the present invention, since the austenite grain size of at least one of the inner ring, the outer ring, and the tapered roller is fine, the crack resistance strength, dimensional stability, and rolling fatigue life are greatly improved. If the austenite grain size number is 10 or less, the rolling fatigue life is not greatly improved. Usually 11 or more. Although it is desirable that the austenite particle size is finer, it is usually difficult to obtain a particle size number exceeding # 13. Note that the austenite grains of the inner ring, outer ring, and rolling elements of the shaft support structure in the transmission do not change either in the surface layer part that is greatly affected by the carbonitriding process 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.

  The inner ring or the outer ring in this specification may be integrated with members such as a shaft and a housing, or may be provided separately.

  In the case of austenite grains, traces are left in the ferrite phase such as martensite and bainite after being quenched. In some cases, “old” is added to emphasize the austenite grain boundary before quenching. That is, the austenite grains and the prior austenite grains represent the same thing.

  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 low-temperature quenching, it may be referred to as prior austenite grains as described above. The measurement may be obtained by converting the average value of the particle size number of JIS standard to the average particle size, or the length of the interval between the straight lines in the random direction superimposed on the gold phase structure by the intercept method or the like and associated with the grain boundary. You may take the average value of.

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

The structure having the nitrogen-enriched layer as described above can be formed by the following heat treatment process. That is, after carbonitriding steel for the bearing parts carbonitriding temperature exceeding the A ₁ transformation points, and cooled to a temperature lower than the A ₁ transformation points, then less than the temperature of the carbonitriding process by A ₁ transformation temperature or more Reheat to the quenching temperature range and quench. Since the final quenching is performed after cooling to a temperature below the A ₁ transformation point after carbonitriding, the austenite grain size can be made fine. As a result, it is possible to improve the Charpy impact value, fracture toughness value, crack strength, fatigue life (rolling fatigue life when the component is a rolling bearing or rolling bearing component), and the like.

  Further, for example, by cooling to a temperature at which austenite transforms, the austenite grain boundary during carbonitriding and the austenite grain boundary during final quenching can be made irrelevant. Furthermore, since the heating temperature at the time of final quenching is lower than the heating temperature at the time of carbonitriding, the amount of undissolved cementite in the surface layer portion to which the effect of carbonitriding is exerted is greater than that at the time of carbonitriding. For this reason, at the heating temperature of the final quenching, the ratio of the amount of undissolved cementite increases and the ratio of the austenite amount decreases compared to the carbonitriding process. Moreover, in the iron-carbon binary phase diagram, in the coexistence region of cementite and austenite, the concentration of carbon that dissolves in austenite also decreases as the quenching temperature decreases.

  When heated to the final quenching temperature, the austenite grains become fine due to the large amount of undissolved cementite that hinders the growth of austenite grains. In addition, the structure transformed from austenite to martensite or bainite by quenching has a low carbon concentration, and therefore has a structure rich in toughness as compared with the structure quenched from the carbonitriding temperature.

  In the above method for producing a tapered roller bearing, the quenching temperature range is preferably a temperature range of 790 ° C to 830 ° C. Thereby, since it reheats and quenches to the temperature which austenite crystal grain growth does not produce easily, an austenite grain size can be made fine.

  The reason why the crowning is formed at both ends of the raceway surface of the inner ring is to prevent the occurrence of excessive edge load on the raceway surface of the roller and the inner ring, and the width of these crownings is 20% or less of the raceway width of the inner ring. This is because the contact surface pressure at the center portion of the raceway surface becomes excessive when it exceeds 20%.

The ratio R / R _BASE between the radius of curvature R of the tapered end of the tapered roller and the distance R _BASE from the top of the tapered angle of the tapered roller to the collar of the inner ring is in the range of 0.75 to 0.87. Because of the reason.
Conventionally, the radius of curvature R of the roller large end face was 0.90 ≦ R / R _BASE ≦ 0.97. In this case, the minimum oil film thickness ratio between the large brim surface and the tapered roller large end face is 0. .9 or less, which is not always a satisfactory value for high-speed rotation. Based on experiments, the present inventors have found that the optimum value of R that enables the minimum oil film thickness ratio to be 0.95 or more is 0.75 ≦ R / R _BASE ≦ 0.87, and realizes this. It has been made.

FIG. 5 shows the result of calculating the oil film thickness t formed between the inner ring large collar surface and the tapered roller large end surface using Karna's equation. In the figure, the horizontal axis represents R / R _BASE , and the vertical axis represents the ratio t / t ₀ of the ratio of the oil film thickness t to the oil film thickness t ₀ when R / R _BASE = 0.76. . As is apparent from the figure, the oil film thickness t becomes maximum when R / R _BASE = 0.76, and decreases rapidly when R / R _BASE exceeds 0.9.

FIG. 6 shows the result of calculating the maximum Hertz stress p between the inner ring large collar surface and the tapered roller large end surface. In the figure, the horizontal axis represents R / R _BASE , and the vertical axis represents the value p of the ratio of the maximum Hertz stress p to the maximum Hertz stress p ₀ when R / R _BASE = 0.76 as in FIG. / P ₀ is represented. As is clear from the figure, the maximum Hertz stress p monotonously decreases as R / R _BASE increases.

In order to reduce torque loss and heat generation due to sliding friction between the inner ring large collar surface and the tapered end surface of the tapered roller, it is desirable to increase the oil film thickness t and decrease the maximum Hertz stress p. The inventors determined the appropriate range of R / R _BASE to 0.75 to 0.87 based on the seizure resistance test results shown in Table 1 later with reference to the calculation results of FIGS. 5 and 6. .

  Further, conventionally, the allowable value of the end face deflection is 4 μm even in the case of the smallest grade 1 (the nominal diameter Dw of the tapered roller is 3 mm or more and 10 mm or less). By setting the end face runout of the large end face of the tapered roller to 3 μm or less, the fluctuation of the contact stress between the tapered end face of the tapered roller and the large collar face of the inner ring is reduced, and the factors that hinder oil film formation are reduced.

According to a second aspect of the present invention, in the tapered roller bearing of the first aspect, the component component has a fracture stress value of 2650 MPa or more. The present inventors, after was carbonitrided in carbonitriding temperature exceeding the A ₁ transformation point of steel is cooled to a temperature below the A ₁ transformation point, then reheated to a quenching temperature range of not lower than the A ₁ transformation point It has been found that by performing quenching and quenching, the fracture stress value of the steel having a nitrogen-enriched layer can be 2650 MPa or more, which has not been obtained conventionally. Thereby, it is possible to obtain a tapered roller bearing which has an excellent fracture stress value as compared with the conventional one and thereby has a high strength.

  According to a third aspect of the invention, in the tapered roller bearing of the first aspect, the hydrogen content of the component is 0.5 ppm or less. Thereby, embrittlement of steel due to hydrogen can be reduced. When the hydrogen content of steel exceeds 0.5 ppm, the crack strength of steel decreases. Therefore, such a steel is not very suitable for a support structure for a hub to which a severe load is applied. A lower hydrogen content is desirable. However, in order to reduce it to less than 0.3 ppm, heating for a long time is required, the austenite grain size becomes coarse, and on the contrary, the toughness is lowered. For this reason, a more desirable hydrogen content is in the range of 0.3 to 0.5 ppm. More desirably, it is in the range of 0.35 to 0.45 ppm.

  Note that the above hydrogen content does not measure diffusible hydrogen, but only measures non-diffusible hydrogen released from steel at a predetermined temperature or higher. If the sample size is small, it will be released and dissipated from the sample even at room temperature, so the amount of diffusible hydrogen is excluded from the measurement. Non-diffusible hydrogen is trapped in a defective portion or the like in steel and is released from a sample only after a predetermined heating temperature or higher. Even if limited to this non-diffusible hydrogen, the hydrogen content varies greatly depending on the measurement method. The above hydrogen content range is a range determined by a measurement method using a thermal conductivity method. Furthermore, as will be described later, it is desirable to measure using a DH-103 type hydrogen analyzer manufactured by LECO or a measuring device according to it.

  According to a fourth aspect of the present invention, in the tapered roller bearing of the first aspect, a crown having a gentle curvature is formed in a portion excluding both ends where the crowning of the inner ring raceway surface is formed. is there. By adopting such a configuration, the surface pressure distribution on the raceway surface can be made more uniform.

  According to a fifth aspect of the present invention, in the tapered roller bearing of the first aspect, the surface roughness of the large end face of the tapered roller is 0.02 μmRa or less. By adopting such a configuration, the surface roughness is reduced with respect to the oil film thickness, and the factors that hinder oil film formation are reduced. More specifically, if the surface roughness is large with respect to the oil film thickness, metal contact is made, but if the surface roughness is small, metal contact is not made and the oil film is not broken.

  By using the tapered roller bearing of the present invention, an excellent fracture stress value that has never been obtained can be obtained after forming a nitrogen-enriched layer.

  In addition, edge crowning having a width of 20% or less of the width of the raceway surface is formed at both ends of the inner ring raceway surface, the contact surface pressure on the raceway surface is made uniform, and seizure is prevented. The carbonitrided layer can be stably maintained in a material having an appropriate toughness, and the durability life under foreign matter mixing can be remarkably improved.

Further, the ratio R / R _BASE of the radius of curvature R of the large end face of the tapered roller to the distance R _BASE from the apex of the tapered roller to the large brim surface of the inner ring is 0.75 or more and 0.87 or less, and By controlling the end face runout of the tapered roller's large end face to 3 μm or less, it promotes the formation of an optimal oil film between the inner ring's large brim and the tapered roller's large end face, and improves seizure resistance and preload resistance. It is. As is well known, the preload loss is a phenomenon in which the preload gradually decreases due to wear or the like.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the tapered roller bearing includes an inner ring 10, an outer ring 20, a tapered roller 30, and a cage 40. The inner ring 10 has a conical track 12 on the outer periphery, and includes a small brim 14 and a large brim 16 on both sides of the track 12. Reference numeral 18 represents a large collar surface of the inner ring 10, that is, a surface in contact with the large end surface 32 of the tapered roller 30. The outer ring 20 has a conical track 22 on the inner periphery. The tapered roller 30 is interposed between the raceways 12 and 22 of the inner and outer rings 10 and 20 so as to roll freely. The cage 40 has a plurality of pockets arranged at predetermined intervals in the circumferential direction, and the tapered rollers 30 are accommodated in the respective pockets.

  As shown in FIGS. 1 and 2, the tapered rollers 30 and the raceways 12 and 22 of the inner and outer rings 10 and 20 are in line contact, and the raceways 12 and 22 of the inner and outer rings 10 and 20 and the tapered rollers 30 are conical (conical). The apex (O) of the angle: β) is designed to gather at one point O on the bearing center axis. Since the conical angle is different between the raceway 12 of the inner ring 10 and the raceway 22 of the outer ring 20, the resultant force of the load applied from each of the raceways 12 and 22 to the tapered roller 30 acts in the direction of pushing the tapered roller 30 toward the large collar 16 of the inner ring 10. To do. For this reason, the tapered roller 30 is guided in a state in which the large end surface 32 is pressed against the large collar surface 18 of the inner ring 10, and both are in sliding contact.

As shown in FIG. 4, at both end portions of the raceway surface 12 of the inner ring 10, the width Wc edge crowning C ₂ of less than 20% of the width W of the raceway surface 12 is formed, between each of these crowning C ₂ A center crowning C ₁ having a very gentle curvature is formed at the center. Incidentally, the drop amount d ₂ of crowning C ₂ is turned 20 [mu] m, on the outside of crowning C ₂ parts of relief portion 19 is provided.

The radius of curvature R of the large end surface 32 of the tapered roller 30 is in the range of 0.75 ≦ R / R _BASE ≦ 0.87, where R _BASE is the distance from the apex (O) of the tapered roller to the large collar surface 18 of the inner ring 10. It is set in. In other words, the value R / R _BASE of the ratio of the radius of curvature R of the large end surface 32 of the tapered roller 30 to the distance R _BASE from the top (O) of the cone to the large collar surface 18 of the inner ring 10 is 0.75 or more and 0.87. It is as follows.

FIG. 5 is a graph showing the effect of the radius of curvature R of the large end surface 32 of the tapered roller 30 on the oil film thickness, as already mentioned above, from the KARNA equation. As is apparent from the figure, the oil film is relatively thin in the conventional range of 0.90 ≦ R / R _BASE ≦ 0.97. The oil film thickness ratio is 0.95 or more in the range of 0.65 ≦ R / R _BASE ≦ 0.87. Among these ranges, R / R _BASE <0.75 has a large end face 32. As a result, the contact area was relatively small, and as a result, the contact surface pressure was increased, and it was confirmed by experiments that it was disadvantageous for seizure resistance. For this reason, it turned out that the optimal value of the curvature radius R is the range of 0.75 <= R / _RBASE <= 0.87 after all.

FIG. 7 is an experimental result showing that the R / R _BASE value is disadvantageous for seizure resistance regardless of whether the R / R _BASE value is too small or too large, and this experiment uses a bearing (model number M86649 / 10). However, when the value of the radius of curvature R of the tapered roller 30 is four types, that is, expressed as R / R _BASE , two tapered rollers having different values of 0.72, 0.78, 0.90, and 0.97 are used. Each set was assembled into a total of eight bearings, placed under conditions of a rotational speed of 7000 rpm and a load of 650 kgf, and the temperature rise of the outer ring outer peripheral surface was measured under the action of lubricating oil. From the experimental results, it is confirmed that the ranges of R / R _BASE <0.75 and 0.87 <R / R _BASE are areas where the temperature rise tendency becomes clear, which is disadvantageous for seizure resistance. It was done.

FIG. 8 shows the result of the seizure test of the tapered roller bearing, where the horizontal axis represents the axial clearance and the vertical axis represents the seizure time (minutes). In this test, a bearing in which the radius of curvature R of the tapered roller large end face is changed is used. That is, R / R _BASE was set to 0.97 for Comparative Example 1, 0.90 for Comparative Example 2, and 0.78 for the Example. In Comparative Examples 1 and 2, seizure occurred within 5 minutes even when the axial clearance was increased to about 100 μm, but the bearings of the examples had an axial clearance of about 90 μm and the temperature was stable and no seizure was observed.

  The large end face 32 of the tapered roller 30 has an end face runout of 3 μm or less, more preferably 1 μm or less. The end face runout is measured by a method defined in JIS B 1506. Specifically, as shown in FIG. 9, the tapered roller 30 is placed on the support base 5, and is brought into point contact with the stopper 6 near the periphery of the large end surface 32, and the contact point and the center of the tapered roller 30 are at the end surface. The probe 7 is applied to a position symmetrical with respect to the axis, and the tapered roller 30 is rotated. The end face runout of the tapered roller 30 is obtained as a difference between the maximum value and the minimum value of the reading of the measuring instrument when the tapered roller 30 is rotated once.

  Furthermore, the large end surface 32 of the tapered roller 30 is honed and the surface roughness is 0.020 μmRa or less. Incidentally, it was conventionally 0.063 μmRa or less. Note that the surface roughness of the large end face 32 of the tapered roller 30 is, for example, 0.01 μm as a lower limit as a processing limit.

In order to confirm the influence of the radius of curvature R of the large end face 32 of the tapered roller 30 on the seizure resistance, a seizure test was performed. The test conditions are as follows.
Test bearing: 30206
R / R _BASE (%): 80 (Example) / 95 (Comparative example)
Edge runout: 1 μm
Surface roughness: 0.02 μm Ra
Rotational speed: 5000 rpm (V = 6.2 m / s)
The results of the seizure test are shown in Table 1. In Table 1, o indicates no seizure, x indicates seizure generation, and-indicates untested.

As apparent from Table 1, when R / R _BASE was 80% (Example), seizure did not occur even when the contact surface pressure of the inner ring large collar surface was 7.0 kgf / mm ² . On the other hand, when the R / R _BASE was 95% (Comparative Example), seizure occurred even when the contact surface pressure of the inner ring large collar surface was lowered to 5.5. From this, it can be seen that good seizure resistance can be obtained within the range of R / R _BASE 0.75 or more and 0.87 or less.

  At least one member among the inner ring, outer ring, and tapered roller of the tapered roller bearing includes steel having a nitrogen-enriched layer in the surface layer portion, and the grain size number of the austenite crystal grain of the member exceeds ten. Is in range.

  Moreover, at least any one member of the inner ring, the outer ring, and the tapered roller of the tapered roller bearing includes steel having a nitrogen-enriched layer, and the fracture stress value is 2650 MPa or more.

Moreover, at least any one member of the inner ring, the outer ring, and the tapered roller of the tapered roller bearing includes steel having a nitrogen-enriched layer, and the hydrogen content in the steel is 0.5 ppm or less.
Next, heat treatment including carbonitriding performed on the components of the tapered roller bearing according to the present embodiment will be described.

10 and 11 show a heat treatment method according to the embodiment of the present invention. FIG. 10 is a heat treatment pattern showing a method of performing primary quenching and secondary quenching, and FIG. 11 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. 10, first, steel for bearing parts is heated to a carbonitriding temperature (845 ° C.) exceeding the A ₁ transformation point, and carbonitriding is performed on the steel for bearing parts at that temperature. Carbon and nitrogen in the matrix of the treated T ₁ steel is diffused, also carbon is dissolve sufficiently 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. Next, tempering is performed at 180 ° C.

Referring to FIG. 11, first, steel for bearing parts is heated to a carbonitriding temperature (845 ° C.) exceeding the A ₁ transformation point, and carbonitriding is performed on the steel for bearing parts at that temperature. Carbon and nitrogen in the matrix of the treated T ₁ steel is diffused, also carbon is dissolve sufficiently 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 was 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 T2 was performed by holding at that temperature. Thereafter, oil quenching is performed from the temperature of the treatment T2, and the temperature is cooled to a temperature lower than the A ₁ transformation point. Next, tempering is 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 less than half of the conventional one. The tapered roller bearing components subjected to the heat treatment described above have a long fatigue life characteristic (or rolling fatigue life characteristics when the component is a rolling bearing or a rolling bearing part), improving crack strength, The rate of change over time can also be reduced.

  In both of the above heat treatments, 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 with a high carbon concentration (steel of about 1% by weight), a carburized layer with a higher carbon concentration may be generated, or a carburized layer with 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 in normal steel, so a nitrogen-enriched layer is clearly formed regardless of the carbon concentration of the raw steel. The Needless to say, the nitrogen-enriched layer may be enriched with carbon.

  FIG. 12A shows the austenite grain size of the bearing steel to which the heat treatment pattern shown in FIG. 10 is applied. For comparison, FIG. 12B shows the austenite grain size of the bearing steel obtained by the conventional heat treatment method. FIGS. 13 (a) and 13 (b) show the austenite grain sizes illustrating FIGS. 12 (a) and 12 (b). From the structure showing the austenite crystal grain size, the conventional austenite grain size is 10 according to the JIS (Japanese Industrial Standard) standard grain size number, and according to the heat treatment method of the present invention, 12th fine grain can be obtained. it can. Moreover, the average particle diameter of Fig.12 (a) was 5.6 micrometers as a result of measuring by the cutting method.

Examples Next, examples of the present invention will be described.

Example 1
Example 1 of the present invention was performed using JIS standard SUJ2 material (1.0 wt% C-0.25 wt% Si-0.4 wt% Mn-1.5 wt% Cr). The manufacturing history of each sample shown in Table 2 is shown below.

(Samples A to D: Examples of the present invention)
Carbonitriding was performed by holding at a temperature of 850 ° C. for 150 minutes. The atmosphere during the carbonitriding process was a mixed gas of RX gas and ammonia gas. In the heat treatment pattern shown in FIG. 10, 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 due to insufficient quenching hardness.
(Samples E and F: Examples of the present invention)
The carbonitriding process was performed with the same history as A to D in the examples of the present invention, and the secondary quenching temperature was 850 ° C. to 870 ° C., which is equal to or higher than the carbonitriding temperature (850 ° C.).
(Conventional carbonitrided product: Comparative example)
Carbonitriding was performed by holding at a temperature of 850 ° C. for 150 minutes. The atmosphere during the carbonitriding process was a mixed gas of RX gas and ammonia gas. Quenching was performed as it was from the temperature during the carbonitriding treatment, and secondary quenching was not performed.
(Normally hardened product: comparative example)
Without performing the carbonitriding process, it was quenched by heating to 850 ° C. Secondary quenching was not performed.

  For each of the above samples, (1) measurement of hydrogen content, (2) measurement of crystal grain size, (3) Charpy impact test, (4) measurement of fracture stress value, (5) rolling fatigue test Was done. The results are also shown in Table 1.

Next, these measurement methods and test methods 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 g (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), all gas purity 99.99% or more, pressure 40 PSI (2.8 kgf · cm ² )

  The outline of the measurement procedure is as follows. Samples collected with a dedicated sampler are inserted into the hydrogen analyzer for each 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 and heated in a resistance heating furnace, and non-diffusible hydrogen is guided to a 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. The Charpy impact value is a value obtained by dividing the absorbed energy E of the following formula by the cross-sectional area (0.8 cm ² ).
Absorbed energy: E = WgR (cosβ-cosα)
W: Hammer weight (= 25.438 kg)
g: Gravitational acceleration (= 9.80665 m / sec ² )
R: Distance from the center of rotation of the hammer to the center of gravity (= 0.6569m)
α: Hammer lifting angle (= 146 °)
β: Hammer descending angle

(4) Measurement of Fracture Stress Value FIG. 14 shows a test piece used for measurement of the fracture stress value. Using an Amsler universal testing machine, load is applied in the direction P in the figure and the load until the test piece is broken 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. 14, You may use the test piece of another shape.

When the fiber stress σ _{1 on} the convex surface of the test piece of FIG. 14 and the fiber stress on the concave surface are σ ₂ , σ ₁ and σ ₂ are obtained by the following equations (Mechanical Engineering Handbook 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 / (Aρo)} [1 + e ₁ / {κ (ρo + e ₁ )}]
σ ₂ = (N / A) + {M / (Aρo)} [1 + e ₂ / {κ (ρo−e ₂ )}]
κ = − (1 / A) ∫ _A {η / (ρo + η)} dA

(5) Rolling fatigue test Table 2 and FIG. 15 show the test conditions of the rolling fatigue life test and a schematic diagram of the test apparatus. In FIG. 15, the rolling fatigue life test piece 118 is driven by the driving roll 112 and rotates in contact with the ball 116. The ball 116 is a 3/4 inch ball and is guided by the guide roll 114 to roll while exerting a high surface pressure with the rolling fatigue life test piece 118.

  Next, the measurement results and test results will be described.

(1) Hydrogen content From Table 2, the hydrogen content in steel of the conventional carbonitrided product as it is carbonitrided is 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, the amount of hydrogen in steel of Samples B to F is 0.37 to 0.42 ppm, which is reduced to nearly half that of the conventional carbonitrided product. The amount of hydrogen in this steel is at the same level as that of ordinary quenched products.

  By reducing the amount of hydrogen in the steel, embrittlement of the steel due to hydrogen solid solution can be reduced. That is, by reducing the amount of hydrogen, the Charpy impact value and the fracture stress value of the samples BF of the present invention example are greatly improved.

(2) Crystal grain size From Table 2, the crystal grain size is the grain size number 11 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. It is remarkably miniaturized with ~ 12. The austenite grains of Samples E and F, as well as the conventional carbonitrided product and normal quenching product have a crystal grain size number 10, and are coarser than Samples B to D.

(3) Charpy impact value According to Table 2, the Charpy impact value of the samples BF of the present invention is 6 compared to the Charpy impact value of the conventional carbonitrided product, which is 5.33 J / cm ^2. A high value of .20 to 6.65 J / cm ² is obtained. Among these, the lower the secondary quenching temperature, the higher the Charpy impact value tends to be. In addition, the Charpy impact value of the normally quenched product is as high as 6.70 J / cm ² .

(4) Fracture stress value The above-mentioned fracture stress value corresponds to the crack resistance strength. According to Table 2, the conventional carbonitrided product has a fracture stress value of 2330 MPa. Compared to this, the fracture stress values of Samples B to F are improved to 2650 to 2840 MPa. The fracture stress value of the normally quenched product is 2770 MPa, which is equivalent to the fracture stress values of Samples B to F. Such improved crack resistance strength of Samples B to F is presumed 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 2, usually quenched sample will reflect that no has a nitriding layer at the surface layer portion, the rolling fatigue life L ₁₀ 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 were almost equivalent to conventional carbonitrided products.

  In summary, in Samples B to F of the present invention example, the amount of hydrogen in the steel is lowered, and the fracture stress value and Charpy impact value are improved. However, what can be improved including the rolling fatigue life is the samples B to D in which the austenite crystal grain size is further refined to about 11 or more in the grain size number. Therefore, samples B to F correspond to the examples of the present invention, but a more preferable range of the present invention is sample B in which the secondary quenching temperature is made lower than the carbonitriding temperature to further refine crystal grains. It is the range of -D.

(Example 2)
Next, Example 2 will be described.

A series of tests were performed on the following A material, B material, and C material. JIS standard SUJ2 material (1.0% by weight C-0.25% by weight Si-0.4% by weight Mn-1.5% by weight Cr) is used for the material for heat treatment, which is common to materials A to C. did. The manufacturing histories of the A material to the C material are as follows.
A material (comparative example): Only normal quenching was performed (without carbonitriding).
B material (comparative example): It quenched as it was after carbonitriding (conventional carbonitriding quenching). The temperature of carbonitriding was 845 ° C., and the holding time was 150 minutes. The atmosphere of carbonitriding was RX gas + ammonia gas.
Material C (Example of the present invention): The heat treatment pattern of FIG. 11 was applied to the bearing steel. The carbonitriding temperature was 845 ° C., the holding time was 150 minutes, and the atmosphere was RX gas + ammonia gas. The final quenching temperature was 800 ° C.

(1) Rolling fatigue life The above-described apparatus shown in FIG. 15 was used as a rolling fatigue life test apparatus, and the test conditions were as shown in Table 3. The results of this rolling fatigue life test are shown in Table 4.

According to Table 4, L ₁₀ life of B material subjected to carbonitriding treatment (comparative example), normally hardened only alms was A material (Comparative Example) of L ₁₀ life (the test piece 10 in one damaged Life) is 3.1 times longer, and the effect of extending the life by carbonitriding is recognized. On the other hand, the C material of the present invention example has a long life of 1.74 times that of the B material and 5.4 times that of the A 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 5.

  In the C material of the present invention example, a Charpy impact value equivalent to that of the A material (comparative example) subjected only to normal tempering and higher than that of the B material (comparative example) subjected to carbonitriding was obtained.

(3) Test of static fracture toughness value The test piece shown in FIG. 16 was used as a test piece for the static fracture toughness test. After introducing a crack of about 1 mm in advance, a static load P by three-point bending was applied, The breaking load was determined. The following equation was used to calculate the fracture toughness value (K _IC value). The test results are shown in Table 6.
K _IC = (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 }

Since the depth of cracks introduced in advance is larger than the depth of the nitrogen-enriched layer, there is no difference between the A material and the B material of the comparative example. However, in the C material of the present invention, a fracture toughness value (K _IC value) about 1.2 times that of the A material and B material of the comparative example could be obtained.

(4) Static crush strength test (measurement of fracture stress)
As the static crushing strength test piece, one having the shape shown in FIG. 16 was used as described above. In the figure, a load was applied in the P direction, and a static crushing strength test was performed in the same manner as described above. The test results are shown in Table 7.

  The static crushing strength of the B material (comparative example) subjected to the carbonitriding treatment is slightly lower than the static crushing strength of the A material (comparative example) subjected only to normal quenching. However, the static crushing strength of the C material of the present invention example is higher than the static crushing strength of the B material, and is slightly higher than the static crushing strength of the A material.

(5) Aged dimensional change rate Aged dimensional change rate was measured at a temperature of 130 ° C. for 500 hours. The measurement results are shown in Table 8 together with the surface hardness and the amount of retained austenite (at a depth of 0.1 mm from the surface).

  Compared to the dimensional change rate of the B material having a large amount of retained austenite, the dimensional change rate of the C material of the example of the present invention is kept low.

(6) Life test under lubrication mixed with foreign matter Using a ball bearing 6206, the rolling fatigue life was evaluated under lubrication mixed with foreign matter in which a predetermined amount of standard foreign matter was mixed. Table 9 shows the test conditions, and Table 10 shows the test results.

  Compared to the A material, a long life was obtained about 2.5 times longer for the B material (comparative example) subjected to carbonitriding, and about 3.7 times longer for the C material of the present invention example. In the C material of the present invention example, the retained austenite is less than the B material of the comparative example, but a long life is obtained due to the intrusion of nitrogen and the influence of the refined microstructure.

  From the above results, the C material of the present invention example, that is, the bearing part forming the support structure in the transmission manufactured by the heat treatment method of the present invention, has a long rolling fatigue life that was difficult with the conventional carbonitriding process. It was found that the three items of improvement in crack strength and reduction in aging dimensional change can be satisfied simultaneously.

  The austenite crystal grains in the present specification are austenite crystal grains that have undergone phase transformation during quenching heating, and this is what remains as a past history after transformation to martensite by cooling. Say.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be variously modified. For example, the present invention can be applied to a double row tapered roller bearing having two or more rows.

  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.

It is a longitudinal cross-sectional view of the tapered roller bearing which shows embodiment of this invention. It is sectional drawing for demonstrating the design specification of a tapered roller bearing. FIG. 2 is an enlarged view of a large collar surface portion of an inner ring in the tapered roller bearing of FIG. 1. It is an enlarged view of the raceway surface of the inner ring in the tapered roller bearing of FIG. It is a graph which shows the relationship between the curvature radius of a tapered roller large end surface, and an oil film thickness. It is a graph which shows the relationship between the curvature radius of a tapered roller large end surface, and the maximum Hertz stress. It is a graph which shows the relationship between the curvature radius R of a tapered roller large end surface, and a bearing temperature rise. It is a graph which shows the relationship between an axial clearance gap and seizing time. An end face run-out measuring device is shown, (a) is a front view and (b) is a side view. It is a diagram which shows the heat processing pattern in embodiment of this invention. It is a diagram which shows the heat processing pattern in embodiment of this invention. It is a figure which shows the microstructure of steel, especially an austenite grain, Comprising: (a) is an example of this invention, (b) is conventional. (A) is a schematic diagram of FIG. 12 (a), (b) is a schematic diagram of FIG.12 (b). It is sectional drawing of the test piece of a static crushing strength test (measurement of a fracture stress value). It is the schematic of a rolling fatigue life test machine, (a) is a front view, (b) is a side view. It is a figure which shows the test point of a static fracture toughness test. It is a principal part longitudinal cross-sectional view of a transmission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inner ring 12 Track 14 Small brim 16 Large brim 18 Large brim surface 19 Nuts C ₁ , C ₂ Crowning 20 Outer ring 22 Track 30 Tapered roller 32 Large end surface 40 Cage

Claims (5)

An inner ring having a conical track on the outer periphery and having a large and small brim on both sides of the track, an outer ring having a conical track on the inner periphery, and an inner ring and an outer ring A plurality of tapered rollers, and a retainer for keeping the tapered rollers at a predetermined interval in the circumferential direction,
At least one component of the inner ring, the outer ring, and the tapered roller has a nitrogen-enriched layer in a surface layer part, and the austenite grain size number in the nitrogen-enriched layer exceeds 10,
The crowning is formed at both ends of the raceway surface of the inner ring, and the width of the crowning at each end thereof is 20% or less of the raceway width of the inner ring,
The ratio R / R _BASE of the radius of curvature R of the large end surface of the tapered roller to the distance R _BASE from the top of the tapered roller of the tapered roller to the large collar surface of the inner ring is 0.75 or more and 0.87 or less,
A tapered roller bearing characterized in that the end face runout of the large end face of the tapered roller is 3 μm or less.   The tapered roller bearing according to claim 1, wherein the component has a breaking stress value of 2650 MPa or more.   The tapered roller bearing according to claim 1, wherein the hydrogen content of the component is 0.5 ppm or less.   2. The tapered roller bearing according to claim 1, wherein a crowning having a gentle curvature is formed in a portion excluding both ends where the crowning of the inner ring raceway surface is formed.   2. The tapered roller bearing according to claim 1, wherein a surface roughness of the large end face of the tapered roller is 0.02 [mu] mRa or less.

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