JP2007297676A - Method for manufacturing shaft, and shaft manufactured by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To extend the service life of a shaft having the surface functioning as an inner ring orbit of a rolling bearing and to excellently fix its edge part by calking. <P>SOLUTION: Either one of steel materials of SUJ1 to SUJ5 is used and is carbo-nitridedand. Then, a spheroidizing annealing is performed at Ac<SB>1</SB>transforming point or avobe and Ac<SB>m</SB>transforming point or below. Successively, an induction-hardening is performed, and then a low temperature tempering is performed so that the depth (d) of the hardened layer becomes 3.0 to 15% of the diameter (D) of the shaft. The total content ratio of carbide and carbo-nitride precipitated in the surface layer part of the orbital surface is defined as 15-40 area% and the maximum grain diameter corresponding to the circle is defined as ≤3μm. The hardness of the surface layer is defined as Hv650 to 900, and the retained austenite is defined as 5-20 vol%. In the core part and the end part of the orbital surface, the hardness are defined as Hv150 to 250 and the retained austenite are defined as 0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a shaft that has a surface that functions as an inner ring raceway of a rolling bearing and that is used with its ends fixed by “caulking”.

  In radial needle bearings, the surface of the shaft often functions as an inner ring raceway (that is, needle rollers that are rolling elements are brought into rolling contact with the shaft). For example, in a planetary gear mechanism (planetary gear device) of an automatic transmission (AT) or a continuously variable transmission (CVT) of an automobile, the outer peripheral surface at the center in the length direction of the pinion shaft is the inner raceway surface, and the inner peripheral surface of the pinion gear is It is an outer ring raceway surface, and a large number of needle rollers are arranged between the pinion shaft and the pinion gear. As a bearing for a rocker arm of an automobile engine, a radial needle bearing having an inner ring raceway surface is used.

The shafts of such radial needle bearings have the problems of improving rolling fatigue characteristics and making plastic deformation difficult to occur even when the impact load is large.
In order to solve this problem, in Patent Document 1 below, a shaft (rolling shaft) that also serves as an inner ring of a radial needle bearing is made of steel containing 0.5 to 1.2 wt% carbon, The amount of retained austenite in the core is 0, the nitrogen content of the surface layer is 0.05 to 0.4 wt%, the hardness of the surface layer is Hv650 or more, and the amount of retained austenite in the surface layer is 15 to 40 vol%. It is disclosed.

  In addition, in this document, as a manufacturing method of the shaft having the above-described structure, quenching / tempering (high temperature tempering) is performed after carbonitriding, and the entire hardness of the shaft is set to Hv 300 to 500 (preferably Hv 400 to 500). Subsequently, a method is described in which induction hardening and tempering are performed to make the hardness of the surface layer portion Hv650 or higher. In this method, the amount of retained austenite in the core is 0, and the hardness of the core is Hv 300 to 500 (preferably Hv 400 to 500).

  In Patent Document 2 below, carbon is 0.2 to 0.3 mass%, chromium is 2.5 to 7 mass%, manganese is 0.5 to 2 mass%, and silicon is 0.1 to 1. mass%. 5% by mass, alloy steel containing 05-2% by mass of molybdenum, subjected to heat treatment consisting of carburizing or carbonitriding, quenching and tempering, and the surface layer part of the pinion shaft (planetary shaft) is the sum of carbon and nitrogen It is described that the content is 1 to 2.5% by mass, the hardness is HRC60 or more, the amount of retained austenite is 15 to 45% by volume, and the average value of the amount of retained austenite from the surface to the core is 8% by volume or less. Has been.

Furthermore, in Patent Document 3 below, as a method for fixing the pinion shaft to the carrier, instead of the conventional pin fixing method, a fixing method by “caulking” is adopted in order to meet the demand for reduction in size and weight. In correspondence with this case, it is described that the surface hardness of the end portion of the pinion shaft is set to Hv 200 to 300.
Japanese Patent Laid-Open No. 2002-4003 JP 2005-291342 A JP 2004-340221 A

In recent years, the planetary gear mechanism has been used under the following conditions: high load (for example, 4000 N or more), high speed rotation (for example, 8000 min ⁻¹ or more), high temperature (for example, 120 ° C. or more), low lubricating oil amount (for example, supply amount per pinion 30 ml / However, the techniques described in Patent Documents 1 to 3 are not sufficient, although it is demanded that the service life be long under such severe conditions.
The problem of the present invention is that it has a surface that functions as an inner ring raceway of a rolling bearing, and has a long life under such severe conditions as a shaft that is used with its end fixed by “caulking”. The object is to provide a material that can be fixed well.

  In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a shaft having a surface (track surface) that functions as an inner ring raceway of a rolling bearing and having an end portion fixed by “caulking”. After processing any of the steel materials SUJ1 to SUJ5 defined in 4805 "into a predetermined shape, as a heat treatment, the following processes (1) and (2) are performed by any one of the following four combinations. An induction hardening process for the raceway surface) and 4) a low-temperature tempering process are performed in this order to satisfy the following configurations (A) to (F).

First combination: 1) Treatment after carbonitriding at a temperature (T ₁ ) equal to or higher than Ac ₁ point (temperature at which austenite begins to form), and 2) Ac ₁ point to Ac _m point (during heating) Spheroidizing annealing treatment in which the cementite in the hypereutectoid steel is maintained at a temperature (T ₂₁ ) or lower (cooling to room temperature by furnace cooling or slow cooling).
Second combination: 1) carbonitriding at a temperature of Ac ₁ point or higher (T ₁ ), and 2) furnace temperature or slow cooling after holding at a temperature of Ac ₁ point or higher and Ac _m point or lower (T ₂₁ ). Spheroidizing annealing treatment to cool to room temperature.

Third combination: 1) a process of cooling after carbonitriding at Ac ₁ point or more temperature (T _1), after holding the 2) Ac ₁ point or more Ac _m point below the temperature (T _21), Ac ₁ A spheroidizing annealing treatment in which the temperature is kept at a temperature (T ₂₂ ) of “Ac ₁ point temperature−200 ° C.” or higher after cooling to room temperature by air cooling. Fourth combination: 1) a process of cooling after carbonitriding at Ac ₁ point or more temperature (T _1), 2) Ac ₁ point after holding the Ac ₁ point or more Ac ₁ point below the temperature (T ₂₁₎ Less than “Ac ₁ point temperature−200 ° C.” or higher (T ₂₂ ) is repeated a plurality of times and then cooled to room temperature by air cooling.

(A) The sum of the carbon content and the nitrogen content of the surface layer after the treatment in 1) is 1.0% by mass or more and 2.0% by mass or less.
(B) The total of the carbon content and the nitrogen content dissolved in the matrix of the surface layer part after the treatment in 2) is 0.6% by mass or more and 1.2% by mass or less.
(C) The total content of carbides and carbonitrides deposited on the surface layer of the raceway surface after the treatment of 3) is set to 15 area% or more and 40 area% or less, and the maximum equivalent to the circle of the carbides and carbonitrides The particle size is 3 μm or less.
(D) By the treatment of 3), the depth (d) of the hardened layer on the raceway surface becomes 3.0% to 15% of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015). To meet).
(E) The hardness of the surface layer portion of the raceway surface is 650 to 900 in terms of Vickers hardness (Hv), and the amount of retained austenite of the surface layer portion of the surface is 5 volume% to 20 volume%.
(F) The hardness of the core portion and the end portion of the raceway surface is set to 150 to 250 in terms of Vickers hardness (Hv), and the retained austenite of the core portion and the end portion of the raceway surface is set to zero.

According to the shaft manufacturing method of the present invention, after carbonitriding, the total carbon and nitrogen content of the matrix is increased by performing spheroidizing annealing at a temperature not lower than Ac ₁ point and not higher than Ac _m point. Precipitation of carbides and carbonitrides in the matrix increases the wear resistance of the shaft. Holding temperature of spheroidizing annealing is longer processing time to be Ac less than ₁ point, the particle size of the precipitated carbides and carbonitrides become coarse easily. When the holding temperature for spheroidizing annealing exceeds the Ac _m point, the precipitated carbide and carbonitride are dissolved in the matrix, and therefore the carbide and carbonitride precipitates are less likely to be present in the matrix.

In the spheroidizing annealing treatment of the first and second combinations in the method of the present invention, by maintaining the temperature at T ₂₁ , carbon and nitrogen dissolved in a supersaturated state in the austenite phase are formed on the grain boundary with Fe ₃ C or It precipitates as Fe ₃ (C, N), and these become the cores of spherical carbide and spherical carbonitride. And these nuclei are made to adhere to each other and grow by being cooled to room temperature by furnace cooling or slow cooling.

Comparing the first combination and the second combination, in the second combination, by performing spheroidizing annealing without performing cooling after carbonitriding (such as slow cooling to a temperature lower than the martensite transformation point), The processing time can be shortened compared with the case where the first combination is employed.
In the third combination spheroidizing annealing treatment, carbon and nitrogen dissolved in a supersaturated state in the austenite phase as Fe ₃ C and Fe ₃ (C, N) precipitate on the grain boundary by maintaining the temperature at T _21. These serve as nuclei for spherical carbides and spherical carbonitrides. Next, by maintaining the temperature at T ₂₂ , these nuclei are attached to each other and grown. Therefore, when the third combination is employed, the diameters of the precipitated carbides and carbonitrides are larger than when the first and second combinations are employed, but the content of these precipitates is increased.

When the fourth combination is employed, the diameter of the precipitated carbide or carbonitride is reduced as compared with the case where the third combination is employed.
Moreover, when cooling to room temperature after carbonitriding with each combination, carbonitriding and spheroidizing annealing can be processed in separate furnaces, so the degree of freedom in production can be increased. In addition, as cooling after carbonitriding, slow cooling and quenching can be mentioned, but when slow cooling is performed, cracks are less likely to occur compared to quenching, and cleaning can be omitted. In the case of quenching, the processing time can be shortened compared to the case of performing slow cooling.

FIG. 1 shows the surface layer of carbide and charcoal when heat treatment is performed in the first combination using SUJ2 by the method of the present invention, and the treatment (spheroidizing annealing) temperature (T ₂₁ ) of 2) is 780 ° C. It is a microscope picture which shows the distribution state of nitride. 2, using the SUJ2, when other than performing the high-temperature tempering at instead of spheroidizing annealing 700 ° C. (temperature lower than the Ac ₁ point) is subjected to the same heat treatment, the surface layer of the carbide and carbonitride It is a microscope picture which shows a distribution state.

From comparison of these figures, the heat treatment after the carbonitriding process is performed at a temperature not lower than Ac ₁ point and not higher than Ac _m point (FIG. 1), so that it is performed at a temperature lower than Ac ₁ point (FIG. 2). It can be seen that the precipitated carbides and carbonitrides become finer and the precipitation density increases.
In the method of the present invention, the carbonitriding temperature (T ₁ ) is preferably 830 to 860 ° C., and the holding time is preferably 2 to 4 hours. Temperature T ₂₁ in the process of 2) is set to from 750 to 790 ° C., the temperature T ₂₂ is preferably set to six hundred and fifty to seven hundred and ten ° C.. Also, when the first and second combination, it is preferable that the holding time at a temperature T ₂₁ in the process of 2) is to be 1 to 3 hours, more preferably 2 to 3 hours.

In the third combination, the retention time at the temperature T ₂₁ in the process of 2) and 1 to 3 hours, it is preferable that the 1-4 hours retention time at the temperature T _22. More preferably, the holding time at the temperature T ₂₁ and 2-3 hours, and 3-4 hours retention time at the temperature T _22. For the fourth combination, the retention time at the temperature T ₂₁ in the process of 2) is set to 1 to 2 hours, the retention time at the temperature T ₂₂ is preferably set to 1 to 2 hours.

Moreover, it is preferable to perform induction hardening at 850-900 degreeC, and to perform low temperature tempering by hold | maintaining at 150-170 degreeC for 1.5 to 2 hours.
In the method of the present invention, carbides and carbonitrides are likely to be spheroidized and precipitated by using any of the steel materials SUJ1 to SUJ5 defined in “JIS G 4805”.
Further, by satisfying the configurations (A) and (B), the configurations (C) to (F) can be achieved.

  When the composition (A) is not satisfied, that is, when [C + N] (total of carbon content and nitrogen content) of the surface layer after the treatment of 1) is less than 1.0% by mass, the treatment of 3) In some cases, the total content of carbides and carbonitrides deposited on the surface layer portion of the later raceway surface cannot be made 15 area% or more, or the hardness of the surface layer portion cannot be made Hv 650 or more. . When [C + N] of the surface layer portion after the treatment of 1) exceeds 2.0% by mass, the spherical carbide and carbonitride after the treatment of 2) are easily coarsened.

  When the composition (B) is not satisfied, that is, when [C + N] dissolved in the matrix of the surface layer portion after the treatment of 2) is less than 0.6 mass%, the raceway surface after the treatment of 3) In some cases, the amount of retained austenite in the surface layer cannot be 5% by mass or more. When [C + N] dissolved in the matrix of the surface layer after the treatment of 2) exceeds 1.2% by mass, the amount of retained austenite in the surface layer of the raceway surface after the treatment of 3) exceeds 20% by mass There is a case.

Further, by satisfying the above-mentioned configuration (C), that is, by the presence of fine carbides and carbonitrides on the surface layer portion of the raceway surface, the shaft seizure resistance, abrasion resistance, and galling resistance are obtained. In addition, pressure scar resistance and white peel resistance are remarkably increased.
In the case of white peeling, when the raceway surface of the shaft and the rolling element come into metal contact, the active surface is formed in the sliding part, so that the lubricant is decomposed to generate hydrogen, and this hydrogen is activated. It is thought that it occurs by diffusing from the surface to the inside and concentrating around the maximum shear stress position and non-metallic inclusions. Therefore, in order to prevent white peeling, it is effective to improve the wear resistance of the raceway surface of the shaft and suppress the generation of the active surface.

  When the composition (C) is not satisfied, that is, when the total content of carbides and carbonitrides precipitated in the surface layer portion of the raceway surface after the treatment of 3) is less than 15% by area, these precipitations The above-mentioned action by the object is not substantially obtained. If the total content of these precipitates exceeds 40% by area, the abundance of the coarsened material may increase, or the amount of retained austenite may not be 5% by mass or more. When the maximum equivalent-circle particle size of these precipitates is larger than 3 μm, the probability of causing internal origin type peeling such as white peeling increases.

Further, since the configuration (E) is provided, the rolling life of the obtained shaft is increased.
When the configuration (E) is not satisfied, that is, when the amount of retained austenite in the surface layer portion of the raceway surface is less than 5% by volume, the effect of increasing the rolling life due to retained austenite cannot be substantially obtained. Further, if the amount of retained austenite in the surface layer portion of the raceway surface exceeds 20% by volume, the bending deformation and the expansion of the diameter may increase, and the rolling life may be reduced due to edge loading. In addition, the pressure scar resistance is significantly reduced. In particular, when these are used at high temperatures, these drawbacks become prominent. Therefore, it is preferable that the amount of retained austenite in the surface layer portion of the raceway surface is set to not more than volume%.
If the hardness of the surface layer portion of the raceway surface exceeds 900 in terms of Vickers hardness (Hv), the amount of retained austenite may not be able to be increased to volume% or more. In addition, in order to achieve hardness exceeding Hv900, it is necessary to increase the temperature during induction hardening, and as a result, crystal grains become coarse and toughness decreases.

In addition, since the configuration (D) is provided, the mechanical strength of the obtained shaft is high, and the plastic deformation bending of the raceway surface and the expansion of the diameter are suppressed.
When the configuration (D) is not satisfied, that is, when the depth (d) of the hardened layer is less than 3.0% of the diameter (D) of the shaft, a hardened layer with a sufficient depth cannot be obtained, and the track Insufficient surface strength. If the depth (d) of the hardened layer exceeds 15% of the shaft diameter (D), the abundance of retained austenite in the shaft diameter direction increases, and therefore plastic deformation due to decomposition of the retained austenite increases. The depth (d) of the hardened layer is the depth from the shaft surface to the position where the amount of retained austenite is greater than zero.

Further, since the structure (F) is provided, the end portion of the obtained shaft can be easily fixed by “caulking”, and plastic deformation accompanying decomposition of retained austenite during use can be prevented.
When the configuration (F) is not satisfied, that is, when the hardness of the end portion of the shaft is less than 150 in terms of Vickers hardness (Hv), the fixing strength of the shaft due to “caulking” becomes insufficient. If it exceeds Hv250, the toughness is insufficient and cracks and cracks are likely to occur during fixing by “caulking”. Further, if the retained austenite at the core portion and the end portion of the raceway surface is not 0, plastic deformation accompanying decomposition of the retained austenite occurs during use.

The present invention is also a shaft that has a surface (track surface) that functions as an inner ring raceway of a rolling bearing and is used by fixing an end portion thereof by “caulking”, and is manufactured by the method of the present invention. Provided is a shaft characterized by comprising configurations (1) to (4).
(1) The total content of carbides and carbonitrides deposited on the surface layer of the raceway surface is 15 area% or more and 40 area% or less, and the maximum equivalent circle diameter is 3 μm or less.
(2) The depth (d) of the hardened layer formed by induction hardening is 3.0% to 15% of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015 is satisfied). .
(3) The hardness of the surface layer portion of the raceway surface is 650 or more and 900 or less in terms of Vickers hardness (Hv), and the amount of retained austenite of the surface layer portion of the raceway surface is 5% by volume or more and 20% by volume or less.
(4) The hardness of the core portion of the raceway surface and the end portion is 150 to 250 in terms of Vickers hardness (Hv), and the retained austenite of the core portion of the raceway surface and the end portion is zero.

  According to the shaft of the present invention, the rolling life is increased because of the configuration (3). The reason for limitation of the configuration (3) is the same as the reason for limitation of the configuration (E) in the above-described method of the present invention. Further, since the configuration (2) is provided, the mechanical strength of the shaft is high, and the plastic deformation bending and the diameter expansion of the raceway surface are suppressed. The reason for limitation of the configuration (2) is the same as the reason for limitation of the configuration (D) in the above-described method of the present invention.

  In addition, since the configuration (1) is provided, the seizure resistance, the wear resistance, the galling resistance, the pressure scar resistance, and the white peel resistance are remarkably increased. The reason for limitation of the configuration (1) is the same as the reason for limitation of the configuration (C) in the above-described method of the present invention. In addition, since the configuration (4) is provided, the end portion of the shaft can be easily fixed by “caulking”, and plastic deformation accompanying decomposition of retained austenite during use can be prevented. The reason for limitation of the configuration (4) is the same as the reason for limitation of the configuration (F) in the above-described method of the present invention.

  According to the present invention, as a shaft that has a surface that functions as an inner ring raceway of a rolling bearing and is used by fixing an end portion thereof by “caulking”, compared to the rolling shafts described in Patent Documents 1 to 3, The service life is long under harsh conditions, and fixing by “caulking” is performed well.

Hereinafter, embodiments of the present invention will be described.
As a material for the pinion shaft, a rod-shaped material composed of SUJ2 and SUJ3 was prepared, and these were processed to obtain a shaft having a diameter of 15.61 mm and a length of 65 mm. As shown in FIG. 3, the shaft (pinion shaft) 1 is an oil composed of a parallel path 21 extending along the axis, and a vertical path 22 extending along the radial direction of the shaft at the center position in the longitudinal direction of the shaft. It has a hole 2. Moreover, the recessed parts 31 and 32 are formed in the both end surfaces of the axis | shaft 1, and the recessed part 31 connected to the parallel path 21 of the oil hole 2 is a supply port of lubricating oil.

Next, as shown in Table 1 below, each of the axes was subjected to any one of the following heat treatments in samples No. 1 to 16 and Nos. 18 to 29. Sample No. 17 was “baked” at 820 ° C. and then tempered at 160 ° C. 4A to 4E are graphs showing the relationship between the temperature (T) and time (t) of each heat treatment of a to e.
The Ac ₁ point of SUJ2 is around 760 ° C., and the Ac _m point is around 850 ° C. Ac ₁ point of SUJ3 is around 750 ° C., Ac _m point is around 840 ° C..

[Heat treatment a]
1) treatment: quenching after carbonitriding at temperature T ₁ (temperature of Ac ₁ point or higher), 2) treatment: after holding at temperature T ₂₁ (temperature of Ac ₁ point or higher and Ac _m point or lower) spheroidizing annealing to cool to room temperature by furnace cooling, 3) of the process: the high-frequency quenching treatment to the surface (raceway surface) of the central portion 11 at a temperature T _3, 4) of the process: the low temperature tempering treatment at a temperature T ₄ this Do in order.

[Heat treatment b]
1) treatment: carbonitriding at temperature T ₁ (ac ₁ point or more), 2) treatment: temperature T ₂₁ (ac _{1 to} ac _m point), and then kept at room temperature by furnace cooling spheroidizing annealing cooling to 3 process): induction hardening process on the surface (raceway surface) of the central portion 11 at a temperature T _3, 4 treatment): performing low temperature tempering treatment at a temperature T ₄ in this order.

[Heat treatment c]
Treatment 1): quenching after carbonitriding at temperature T ₁ (temperature of Ac ₁ point or higher), treatment of 2): holding at temperature T ₂₁ (temperature of Ac ₁ point or higher and Ac _m point or lower), then temperature T ₂₂ (A temperature of less than Ac ₁ point 650 ° C. or more, “650 ° C. or more” corresponds to “Ac ₁ point temperature −200 ° C. or more”), and then cooled to room temperature by air cooling, 3) Treatment: induction hardening treatment for the surface (orbital surface) of the central portion 11 at the temperature T ₃ , 4) treatment: low temperature tempering treatment at the temperature T ₄ is performed in this order.

[Heat treatment d]
Treatment of 1): quenching after carbonitriding at temperature T ₁ (temperature of Ac ₁ point or higher), treatment of 2): temperature T ₂₂ after holding at temperature T ₂₁ (temperature of Ac ₁ point or higher and Ac _m point or lower) (A temperature of less than Ac ₁ point 650 ° C. or higher, “650 ° C. or higher” is equivalent to “Ac ₁ point temperature −200 ° C. or higher”) 3 times, and then cooled to room temperature by air cooling annealing treatment, 3 process): induction hardening process on the surface (raceway surface) of the central portion 11 at a temperature T _3, 4 treatment): performing low temperature tempering treatment at a temperature T ₄ in this order.

[Heat treatment e]
1) treatment: quenching after carbonitriding at temperature T ₁ (temperature of Ac ₁ point or higher), 2) treatment: air cooling after holding at temperature T ₂₂ (temperature less than Ac ₁ point 650 ° C. or higher) tempered at high temperatures to 3 process): induction hardening process on the surface (raceway surface) of the central portion 11 at a temperature T _3, 4 treatment): performing low temperature tempering treatment at a temperature T ₄ in this order.

In addition, Tables 1 and 2 below show the temperatures T ₂₁ and T ₂₂ and the holding time of the treatment of 2) for each sample. The holding time is the holding time for the entire processing of 2), and is the total time when holding at the temperature T ₂₂ after holding at the temperature T ₂₁ .
For all samples (other than No. 17 not subjected to carbonitriding), the carbonitriding atmosphere is Rx gas + enrich gas + ammonia gas (ammonia gas concentration 1-7 vol%), and the carbonitriding holding temperature T ₁ is The temperature was 840 ° C. and the holding time was 3 hours.

Further, in the heat treatment b, since the spheroidizing annealing process is performed without cooling after the carbonitriding process, both processes are performed in the same furnace. That is, after carbonitriding, ammonia gas in the furnace was discharged, and the spheroidizing annealing treatment was performed by lowering the carbon potential to the extent that decarburization was not performed.
Induction hardening was performed under conditions of a temperature (T ₃ ) 850 ° C., a frequency of 100 to 400 kHz, a voltage of 12 kV, a current of 5 A, a feed rate of 8 to 15 mm / second, and a cooling water amount of 35 liters / minute. Further, the ratio (d / D) to the shaft diameter (D) was changed by changing the induction hardening depth (d) in each sample. The induction hardening depth (d) was changed by changing the frequency.

Low temperature tempering was performed by holding at a temperature (T ₄ ) of 160 ° C. for 1.5 hours and then cooling (furnace cooling) in the furnace.
For the pinion shaft of sample Nos. 1 to 29, after the processing of 1), the total value [C + N] of the carbon content and nitrogen content of the surface layer part (part from the surface to a depth of 100 μm) 11a of the central part 11 is measured. did. Further, after the treatment of 2), the total value [C + N] of the carbon content and the nitrogen content dissolved in the matrix of the surface layer portion 11a of the central portion 11 was measured.
Further, after all the heat treatments are finished, the hardness (Hv) and the retained austenite amount (γ _R ) of the surface layer portion 11a of the central portion 11, the hardness (Hv) of the end portion 12, and the core portion of the central portion 11 The amount of retained austenite (γ _R ) of 11b was measured. Moreover, the depth (d) of the hardened layer was measured, and the ratio (d / D) to the diameter (D) of the shaft was calculated.

These results are also shown in Tables 1 and 2 below.
Moreover, the following test was done using the pinion shaft of each obtained sample.
[Test to examine the surface condition when rotating to the calculated life under high speed and low load conditions]
The planetary gear device incorporating the pinion shaft of each sample was rotated on an NSK testing machine under the following conditions, and then the surface state of the pinion shaft was examined. The results are shown in Tables 1 and 2 below. In Tables 1 and 2, “◯” indicates that the surface is not damaged, “Δ” indicates that smearing has occurred on the surface, and “×” indicates that peeling or seizing has occurred on the surface. Show.

The pinion gears and needle rollers were made of SUJ2 and used normal products that had been tempered after soaking. The diameter of the needle roller was 3.5 mm. The lubricating oil was supplied between the pinion shaft and the pinion gear via the oil passage 2 of the pinion shaft 1.
<Rotational test conditions>
Spinning speed of pinion shaft: 13000 min ^-1
Basic dynamic load rating (C): 17500N
Basic static load rating (C0): 16500N
Radial load: 3000N
Rotation time: 460 hours which is the calculated life (L ₁₀ ) Dm · n value = 248000
Lubricating oil: ATF
Oil temperature: 100 ° C
Lubricating oil supply amount: 30 ml / min

[Test to investigate rolling fatigue life when rotating under high speed, high load and low lubrication conditions]
The planetary gear device incorporating the pinion shaft of each sample is run on an NSK testing machine under the following conditions, and the rotation time until the point when any of the pinion shaft, pinion gear, or needle roller is damaged "Fatigue life". The life ratio was calculated when the “rolling fatigue life” was “1” when the No. 17 pinion shaft was used. Further, the surface state of the pinion shaft after the test was observed to examine the presence or absence of white peeling. These results are also shown in Tables 1 and 2 below.
<Rotational test conditions>
Spinning speed of pinion shaft: 10000 min ^-1
Basic dynamic load rating (C): 17500N
Basic static load rating (C0): 16500N
Radial load: 7000N
Calculated life: L ₁₀ = 36 hours P / C = 0.4
Lubricating oil: ATF
Oil temperature: 100 ° C
Lubricating oil supply amount: 10 ml / min

(Bending creep test)
The pinion shaft of each sample was subjected to a three-point bending creep test under the conditions of a temperature of 160 ° C., a load of 3000 N, and a holding time of 20 hours, and the maximum bending amount in the direction perpendicular to the axis was measured.
These results are also shown in Tables 1 and 2 below.
[End part caulking resistance test]
The end of the pinion shaft of each sample was put on a press machine and pressed at a load of 2.0 tons and at a speed of 40 mm / second, and then it was examined whether the end was damaged or cracked.
These results are also shown in Tables 1 and 2 below.

  From the results of these tables, the pinion shafts of Sample Nos. 1 to 16 corresponding to the examples of the present invention have a good surface condition under high speed and low load conditions, and a rolling fatigue life ratio of 5.1 to 9.2. It can be seen that white peeling does not occur even under high speed, high load, and low lubrication conditions, the bending amount by the bending creep test is as small as 1 to 5 μm, and the end portion has high caulking resistance.

On the other hand, the pinion shafts of Nos. 17 to 29 corresponding to the comparative examples of the present invention have a rolling fatigue life ratio of 1 to 4.6, the surface condition under high speed and low load conditions, high speed, high load, A defect occurred in any of the following points: white peeling under low lubrication conditions, bending amount of 10 μm or more by bending creep test, and insufficient caulking resistance at the end.
Specifically, the pinion shaft of No. 17 was not so good in any of the test results because the heat treatment was “sukiyaki”.

The pinion shaft of No. 18 was subjected to heat treatment a, but did not satisfy “(d / D) ≦ 15%” and “residual austenite amount of the surface layer portion of the raceway surface of 20 volume% or less”, so the bending amount was 10 μm. The rolling fatigue life ratio was 2.9, which was lower than Sample Nos. 1-16.
The pinion shaft of No. 19 was subjected to heat treatment b, but [C + N] ≦ 2.0 mass% after the treatment of “1” and carbide and carbonitride of the surface layer portion after the treatment of “3) Is not more than 40 area%, the maximum particle size is 3 μm or less, “the amount of retained austenite of the surface layer portion of the raceway surface is 5 vol% or more”, and “the hardness of the core and end portions is Hv 150 or more”. The end portion was damaged, and the rolling fatigue life ratio was as low as 1.1.

The pinion shaft of No. 20 was subjected to the heat treatment c, but satisfyed “[C + N] ≦ 2.0 mass%” after the process of “1” and “the amount of retained austenite of the surface layer portion of the raceway surface is 5 volume% or more”. Therefore, the rolling fatigue life ratio was as low as 1.3.
The pinion shaft of No. 21 was heat-treated d, but did not satisfy the “remaining austenite amount of the surface layer portion of the raceway surface of 20 volume% or less”, so the bending amount was as large as 12 μm and the rolling fatigue life ratio was 3.1. And lower than Sample Nos. 1-16.

The pinion shafts of No. 22 to 24 and 27 to 29 are samples that have been subjected to high temperature tempering as the treatment of 2), and “the amount of retained austenite in the surface layer portion of the raceway surface is 20% by volume or less” and “ Since it does not satisfy "Hv 250 or less", the bending amount was as large as 12 to 16 µm, and the rolling fatigue life ratio was 1.2 to 4.6, which was lower than those of Sample Nos. 1 to 16.
In particular, since the pinion shafts of No. 24 and 29 do not satisfy the abundance ratio of carbide and carbonitride in the surface layer after the treatment of “3” is 15 area% or more ”, the surface condition under high speed and low load conditions And white peeling occurred under high speed, high load and low lubrication conditions. Moreover, since the hardness of the end portion was extremely hard as Hv312,328, a crack occurred in the caulking resistance test.

  The pinion shafts of No. 25 and No. 26 have a surface layer portion carbide and carbonitride content of 15 area% or more after the treatment of “the amount of retained austenite of the surface layer portion of the raceway surface is 20 volume% or less” and “3). ”, The bending amount is as large as 12 to 15 μm, the rolling fatigue life ratio is as low as 1.2 to 1.4, the surface condition is poor under high speed and low load conditions, and the high speed, high load and low lubrication conditions are And white peeling occurred.

It is a microscope picture which shows the distribution state of the carbide | carbonized_material and carbonitride of a surface layer part at the time of performing the heat processing by the method of this invention using SUJ2. It is a microscope picture which shows the distribution state of the carbide | carbonized_material and carbonitride of a surface layer part at the time of replacing with spheroidizing annealing and performing high temperature tempering at 700 degreeC using SUJ2. It is sectional drawing which shows the pinion shaft produced in embodiment. It is a figure explaining the heat processing performed in embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pinion shaft 11 Center part of pinion shaft 11a Surface layer part of raceway surface 11b Core part of raceway surface 12 End part of pinion shaft 2 Oil hole 21 Parallel path 22 Vertical path 31 Recess 32 Recess

Claims (5)

In a method of manufacturing a shaft that has a surface that functions as an inner ring raceway of a rolling bearing and that is used with its end fixed by `` caulking ''
After processing any of the steel materials SUJ1 to SUJ5 defined in “JIS G 4805” into a predetermined shape,
As the heat treatment, 1) Ac <sub>1</sub> point (during heating, the process of cooling after carbonitriding at austenite begins to generate temperature) or higher temperatures, 2) Ac <sub>1</sub> point or more Ac <sub>m</sub> points (when heated in the over-eutectoid steel The temperature at which the cementite is completely dissolved) is maintained at a temperature equal to or lower than the temperature, and then spheroidizing annealing is performed to cool to room temperature by furnace cooling or slow cooling.
The total of the carbon content and nitrogen content of the surface layer part after the treatment of 1) is 1.0% by mass or more and 2.0% by mass or less,
The total of the carbon content and nitrogen content dissolved in the matrix of the surface layer after the treatment of 2) is 0.6 mass% or more and 1.2 mass% or less,
The total content of carbides and carbonitrides precipitated on the surface layer portion of the surface after the treatment of 3) is set to 15 area% or more and 40 area% or less, and the maximum equivalent circle diameter of the carbides and carbonitrides is set to 3 μm or less,
By the treatment of 3), the hardened layer is formed so that the depth (d) is not less than 3.0% and not more than 15% of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015 is satisfied). And
The surface layer portion of the surface has a Vickers hardness (Hv) of 650 or more and 900 or less, and the amount of retained austenite of the surface layer portion of the surface is 5 volume% or more and 20 volume% or less,
The shaft is characterized in that the core of the surface and the end have a Vickers hardness (Hv) of 150 to 250, and the retained austenite of the core and the end of the surface is 0. Method. In a method of manufacturing a shaft that has a surface that functions as an inner ring raceway of a rolling bearing and that is used with its end fixed by `` caulking ''
After processing any of the steel materials SUJ1 to SUJ5 defined in “JIS G 4805” into a predetermined shape,
As heat treatment, 1) carbonitriding at a temperature equal to or higher than Ac ₁ point (temperature at which austenite begins to form), 2) Ac ₁ point to Ac _m point (when heated, cementite in the hypereutectoid steel is completely 3) Spheroidizing annealing treatment which is cooled to room temperature by furnace cooling or slow cooling after being held at the following temperature, 3) Induction hardening treatment for the surface, 4) Low temperature tempering treatment in this order,
The total of the carbon content and nitrogen content of the surface layer part after the treatment of 1) is 1.0% by mass or more and 2.0% by mass or less,
The total of the carbon content and nitrogen content dissolved in the matrix of the surface layer after the treatment of 2) is 0.6 mass% or more and 1.2 mass% or less,
The total content of carbides and carbonitrides precipitated on the surface layer portion of the surface after the treatment of 3) is set to 15 area% or more and 40 area% or less, and the maximum equivalent circle diameter of the carbides and carbonitrides is set to 3 μm or less,
By the treatment of 3), the hardened layer is formed so that the depth (d) is not less than 3.0% and not more than 15% of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015 is satisfied). And
The surface layer portion of the surface has a Vickers hardness (Hv) of 650 or more and 900 or less, and the amount of retained austenite of the surface layer portion of the surface is 5 volume% or more and 20 volume% or less,
The shaft is characterized in that the core of the surface and the end have a Vickers hardness (Hv) of 150 to 250, and the retained austenite of the core and the end of the surface is 0. Method. In a method of manufacturing a shaft that has a surface that functions as an inner ring raceway of a rolling bearing and that is used with its end fixed by `` caulking ''
After processing any of the steel materials SUJ1 to SUJ5 defined in “JIS G 4805” into a predetermined shape,
As the heat treatment, 1) Ac <sub>1</sub> point (during heating, the process of cooling after carbonitriding at austenite begins to generate temperature) or higher temperatures, 2) Ac <sub>1</sub> point or more Ac <sub>m</sub> points (when heated in the over-eutectoid steel after the cementite is held in complete dissolution temperature) below the temperature, after holding the Ac less than <sub>1</sub> point "Ac <sub>1</sub> point temperature -200 ° C." or higher temperatures, spheroidizing annealing to cool to room temperature by air cooling, 3) Induction hardening treatment for the surface, 4) low temperature tempering treatment in this order,
The total of the carbon content and nitrogen content of the surface layer part after the treatment of 1) is 1.0% by mass or more and 2.0% by mass or less,
The total of the carbon content and nitrogen content dissolved in the matrix of the surface layer after the treatment of 2) is 0.6 mass% or more and 1.2 mass% or less,
The total content of carbides and carbonitrides precipitated on the surface layer portion of the surface after the treatment of 3) is set to 15 area% or more and 40 area% or less, and the maximum equivalent circle diameter of the carbides and carbonitrides is set to 3 μm or less,
By the treatment of 3), the hardened layer is formed so that the depth (d) is not less than 3.0% and not more than 15% of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015 is satisfied). And
The surface layer portion of the surface has a Vickers hardness (Hv) of 650 or more and 900 or less, and the amount of retained austenite of the surface layer portion of the surface is 5 volume% or more and 20 volume% or less,
The shaft is characterized in that the core of the surface and the end have a Vickers hardness (Hv) of 150 to 250, and the retained austenite of the core and the end of the surface is 0. Method. In a method of manufacturing a shaft that has a surface that functions as an inner ring raceway of a rolling bearing and that is used with its end fixed by `` caulking ''
After processing any of the steel materials SUJ1 to SUJ5 defined in “JIS G 4805” into a predetermined shape,
As the heat treatment, 1) Ac ₁ point (during heating, the process of cooling after carbonitriding at austenite begins to generate temperature) or higher temperatures, 2) Ac ₁ point or more Ac _m points (when heated in the over-eutectoid steel after repeating several times that cementite holds the complete dissolution temperature) below Ac less than ₁ point after holding at a temperature of "Ac ₁ point temperature -200 ° C." or higher temperatures, spheronization cooling to room temperature by air cooling An annealing treatment, 3) induction hardening treatment for the surface, 4) low temperature tempering treatment in this order,
The total of the carbon content and nitrogen content of the surface layer part after the treatment of 1) is 1.0% by mass or more and 2.0% by mass or less,
The total of the carbon content and nitrogen content dissolved in the matrix of the surface layer after the treatment of 2) is 0.6 mass% or more and 1.2 mass% or less,
The total content of carbides and carbonitrides precipitated on the surface layer portion of the surface after the treatment of 3) is set to 15 area% or more and 40 area% or less, and the maximum equivalent circle diameter of the carbides and carbonitrides is set to 3 μm or less,
By the treatment of 3), the hardened layer is formed so that the depth (d) is not less than 3.0% and not more than 15% of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015 is satisfied). And
The surface layer portion of the surface has a Vickers hardness (Hv) of 650 or more and 900 or less, and the amount of retained austenite of the surface layer portion of the surface is 5 volume% or more and 20 volume% or less,
The shaft is characterized in that the core of the surface and the end have a Vickers hardness (Hv) of 150 to 250, and the retained austenite of the core and the end of the surface is 0. Method. A shaft that has a surface that functions as an inner ring raceway of a rolling bearing, and that is used with its end fixed by “caulking”,
Manufactured by any one of claims 1 to 4,
The total content of carbides and carbonitrides precipitated on the surface portion of the surface is 15 area% or more and 40 area% or less, and the maximum equivalent circle particle diameter is 3 μm or less,
The depth (d) of the hardened layer formed by induction hardening is 3.0% or more and 15% or less of the shaft diameter (D) (0.030 ≦ d / D ≦ 0.015 is satisfied),
The hardness of the surface layer portion of the surface is 650 or more and 900 or less in terms of Vickers hardness (Hv), and the amount of retained austenite of the surface layer portion of the surface is 5 volume% or more and 20 volume% or less,
The core of the surface and the hardness of the end are 150 to 250 in terms of Vickers hardness (Hv), and the retained austenite of the core and the end of the surface is 0 .