JP2014005526A - Method for manufacturing bearing ring of rolling bearing and bearing ring of rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a bearing ring of a rolling bearing, capable of reducing deformation at the time of heat treatment and enhancing a lifetime under foreign matter contamination or lubrication, and having excellent dimensional stability and high production efficiency.SOLUTION: A method for manufacturing the bearing ring of a rolling bearing comprises: heating and carbonitriding an inner ring 7 at a temperature exceeding an Atransformation point and cooling it to less than the Atransformation point in a carbonitriding/cooling chamber 1; induction-heating the inner ring at a heating temperature or more of carbonitriding and less than the heating temperature+100°C in an induction heating coil 22 of an induction heating part 2; hardening and reforming the inner ring in a cooling/reforming part 3; cooling the inner ring 7 until it is put into an outer diameter restraining form 34 and a cooling temperature becomes equal to or less than an Mpoint in the middle of the cooling before reaching the Mpoint; annealing the inner ring at a high frequency and reforming it by an outer diameter restraining ceramic form 42 in an annealing/reforming part 4; and removing an oxide film formed on the surface of the inner ring in an oxide film removing chamber 5.

Description

  The present invention relates to a method of manufacturing a rolling bearing race having characteristics in a heat treatment process.

In recent years, in rolling bearings, it has been required to reduce the thickness of the bearing rings. A thin bearing ring is greatly deformed during heat treatment. The raceway whose roundness has deteriorated due to deformation during heat treatment is likely to cause black skin residue in the grinding process. Productivity is reduced by repeating the grinding process to remove the black skin. If the deformation during heat treatment is very large, the roundness is not within the set range even if the grinding process is repeated, resulting in a defective product. As described above, it is required for the bearing ring of the rolling bearing to reduce deformation during heat treatment.
Patent Document 1 discloses a straightening and quenching apparatus capable of efficiently performing straightening and quenching of the annular body regardless of changes in the thickness of the annular body and greatly reducing post-processing work such as polishing. Describes a straightening and quenching device that corrects the outer diameter after quenching of an annular body with martensitic transformation expansion.

This device includes an annular heating coil for heating the annular body, an annular cooling jacket for cooling by injecting cooling water onto the inner and outer circumferences of the annular body, and an annular jacket that press-fits and corrects the outer circumference of the annular body. The outer diameter restraining type is arranged coaxially in the vertical direction. This device rotates an annular body moved into the heating coil, and an elevating mechanism for moving the annular body coaxially into the annular space of the heating coil, the annular space of the cooling jacket, and the outer diameter restraining type. And rotating means.
Patent Document 2 includes a correction die that restrains at least one of the outer peripheral surface and the end surface of the annular member after quench hardening, and a heating unit that induction-heats the annular member restricted by the correction die to a desired tempering temperature. As a deformation correction device for an annular member, a deformation correction device in which at least a portion of the correction mold that comes into contact with the annular member is made of conductive ceramics is described.

On the other hand, along with demands for reducing fuel consumption of automobiles and the like, miniaturization and high efficiency of machine parts have been performed. For this reason, the use environment of machine parts is under more severe conditions such as poor lubrication and contamination with foreign matter.
In order to extend the life of the rolling bearing used under the contamination with foreign matter, it is necessary to alleviate the concentration of stress on the periphery of the indentation generated on the raceway surface due to the foreign matter being caught. As a method for achieving such relaxation of stress concentration, there is a method for increasing the amount of retained austenite on the raceway surface. By performing carburization or carbonitriding on the raceway surface, the amount of retained austenite on the raceway surface can be increased.

In Patent Document 3, as a heat treatment for bearing parts (at least one of an inner ring, an outer ring, and a rolling element), after carbonitriding by heating to a temperature (T1) exceeding the A ₁ transformation point (austenite transformation temperature). a carbonitriding and cooling step of cooling to below the a ₁ transformation point, the carbonitriding-bearing rings after the cooling step, the heating temperature of the carbonitriding and cooling step comprising at a ₁ transformation point or above (T1) lower than the temperature A method is described in which a quenching step of cooling after heating (secondary heating) to (T2 <T1) is performed in this order.

According to Patent Document 3, according to this method, a microstructure in which the grain size of the austenite crystal grain size is less than or equal to the conventional one can be obtained. Therefore, the primary heating (carbonitriding treatment) is performed once as it is. There is a description that it is possible to improve the cracking strength and reduce the aging dimensional change rate while carbonitriding the surface layer portion, compared with the usual carbonitriding / quenching method without quenching and secondary heating. .
Patent Document 3 also discloses that the balance between surface damage resistance and aging dimensional change characteristics is achieved by setting the amount of retained austenite in the nitrogen-enriched layer of the bearing component in the range of 11% to 25% by this method. Is described.

In Patent Documents 4 and 5, a primary heat treatment apparatus for heating a steel part to a temperature exceeding the A ₁ transformation point (T1) and then cooling to a temperature below the A ₁ transformation point to form a nitrogen-enriched layer on the surface; The steel part after the primary heat treatment is heated to a temperature exceeding the A ₁ transformation point (T2) and then cooled to below the A ₁ transformation point, and the secondary heat treatment device is heated by induction heating. In addition to being an apparatus, it is described that mold hardening is performed with a secondary heat treatment apparatus.
And patent document 4 describes that the austenite grain in steel is refined | miniaturized by making the relationship of the heating temperature in a primary heat processing apparatus and a secondary heat processing apparatus into T2 <T1. Patent Document 5 describes that T2 <T1 or T2 ≧ T1 may be satisfied.

  Patent Document 6 discloses a method in which the surface temperature of the raceway is higher than the martensite transformation start temperature by injecting the coolant toward the rotating raceway after induction heating the raceway to an austenite transformation temperature or higher. To a temperature range of from 500 to 500 ° C., followed by a quenching step of gas cooling until the temperature falls below the martensite transformation start temperature. During the water cooling or gas cooling, the raceway ring is formed into a cylindrical outer diameter correction mold. A method of manufacturing a rolling bearing race is described, which includes inserting and restraining and correcting the outer dimensions of the race.

Japanese Patent No. 4539164 JP 2001-64721 A JP 2006-316821 A JP 2005-113213 A JP 2005-133212 A JP 2009-203522 A

  An object of the present invention is a method for producing a bearing ring for a rolling bearing that has a high roundness after heat treatment, can increase the life under foreign matter-mixed lubrication, and can provide a bearing ring with excellent dimensional stability. Is to provide.

In order to solve the above-described problems, a method for manufacturing a rolling bearing race of the present invention is a method in which a steel bearing ring (inner ring or outer ring) constituting a rolling bearing exceeds a temperature exceeding the A ₁ transformation point (austenite transformation temperature) ( after the carbonitriding was heated to T1), and carbonitriding-cooling step of cooling to below the a ₁ transformation point, the carbonitriding-bearing rings after the cooling step, or the heating temperature of the carbonitriding and cooling process The heating temperature is a step of induction heating to a temperature lower than 100 ° C. (T2; T1 + 100 ° C.> T2 ≧ T1) and then cooling to a temperature below the M _S point (martensitic transformation start temperature), and M _{S during} cooling Before reaching the point, the raceway is placed in the outer diameter restraint type, and induction hardening and straightening process for quenching and straightening, and the raceway after the induction hardening and straightening process are restrained with a ceramic straightening die. Induction heating in this state, induction tempering / correction process for tempering and correction, and oxide film removal process for removing the oxide film formed on the surface of the raceway after the induction tempering / correction process in this order It is characterized by performing.

In the method of the present invention, in the induction hardening / correction step, not only is the correction performed by putting the race ring into an outer diameter constrained type during cooling during quenching, but also the correction is performed during induction tempering, thereby correcting the race ring. The deformation during the heat treatment can be reduced, and the roundness of the race after the heat treatment can be increased.
In addition, since ceramic is a non-magnetic material and is not easily magnetized by an external magnetic field, the temperature is difficult to increase by induction heating. For this reason, by using a ceramic correction die in the induction tempering / correction step, the temperature rise of the correction die can be suppressed. Therefore, the dimensional change of the correction mold is smaller than when a correction mold other than ceramics is used, and the correction accuracy in the induction tempering / correction process is increased.

In addition, the correction at the time of induction hardening is correction using the expansion | swelling at the time of the martensitic transformation of the metal which comprises a bearing ring, and is performed, cooling. Examples of the straightening mold used in the induction hardening and straightening process include those made of high carbon steel.
Furthermore, in the method of the present invention, the secondary heating performed after the primary heating (heating during carbonitriding) is performed by induction heating at a temperature (T1) that is equal to or higher than the temperature (T1) during primary heating and lower than T1 + 100 ° C. While increasing the amount of retained austenite in the surface layer portion, the amount of retained austenite in the core portion can be decreased. As a specific example, according to the method of the present invention, the amount of retained austenite in the surface layer portion (in the depth range from the surface to 50 μm) of the raceway surface is set to 20% by volume or more and 45% by volume or less, and the amount of retained austenite in the core portion is set. It can be made into 15 volume% or less.

A rolling bearing having a bearing ring in which the amount of retained austenite in the surface layer portion of the raceway surface is 20% by volume or more and 45% by volume or less and the amount of retained austenite in the core portion is 15% by volume or less has a life under lubrication mixed with foreign matter. Is long and excellent in dimensional stability.
When the amount of retained austenite in the surface layer portion of the raceway surface is less than 20% by volume, rolling fatigue characteristics are insufficient under the contamination with foreign matter. When the amount of retained austenite in the surface layer portion of the raceway surface exceeds 45% by volume, sufficient hardness of the raceway surface cannot be obtained, and rolling fatigue characteristics are insufficient. When the amount of retained austenite in the core exceeds 15% by volume, the amount of expansion due to aging deformation is large, and the dimensional stability is insufficient.

  In the method of the present invention, correction is performed during induction quenching by performing the correction by placing the bearing ring in an outer diameter constrained mold during the induction quenching after the carbonitriding / cooling step (performing the induction quenching / correction step). Since the roundness of the raceway is higher than in the case where no rounding is performed, it is possible to reduce the amount of grinding for setting the roundness of the raceway within a set range in the grinding process. And the effect which can reduce this grinding amount is so high that the change rate of the roundness of the said bearing ring before and behind the said induction hardening and correction process is large. For example, when the change rate of the roundness of the raceway before and after the induction hardening / correction process is 40% or more, the grinding process can be efficiently performed by reducing the grinding amount.

  In the method of the present invention, after the raceway is corrected in the induction hardening / correction step, it is further corrected in the induction tempering / correction step. That is, the roundness of the raceway improved by the induction hardening / correction process is changed by the induction tempering / correction process. When the rate of change in the roundness of the raceway before and after the induction tempering / correction process exceeds ± 30%, it is necessary to perform an additional correction process after the induction tempering / correction process, resulting in reduced production efficiency. To do. Therefore, it is preferable that the change rate of the roundness of the raceway before and after the induction tempering / correction step is within ± 30%.

The change rate Ch of roundness before and after the straightening process (induction hardening / correction process or induction tempering / correction process) is expressed by the following formula, where Cb is the roundness immediately before the straightening process and Ca is the roundness immediately after the straightening process. Calculated in (1).
Ch (%) = ((Cb−Ca) / Cb) × 100 (1)

  The method of the present invention is a method of manufacturing a bearing ring for a rolling bearing, which has a high roundness after heat treatment, can extend the life under foreign matter-mixed lubrication, and has excellent dimensional stability. Is the method.

It is a schematic block diagram which shows the processing line which can implement the method of embodiment. It is a figure which shows the state which is heating the inner ring | wheel by the induction heating part which comprises the processing line of FIG. It is a figure which shows the state which is correct | amending while cooling the inner ring | wheel in the cooling and correction part which comprises the processing line of FIG. It is a figure which shows the state which is correcting, heating the inner ring | wheel in the tempering / correcting part which comprises the processing line of FIG.

Embodiments of the present invention will be described below.
In the method of this embodiment, the processing line shown in FIG. 1 is used to perform processing on the inner ring (race ring) of the rolling bearing.
This processing line includes a carbonitriding / cooling chamber 1, an induction heating unit 2, a cooling / correcting unit 3, a tempering / correcting unit 4, an oxide film removing chamber 5, and a conveyor 6. The inner ring 7 is conveyed by a conveyor 6 between each chamber and part.

The carbonitriding / cooling chamber 1 has a heating furnace and a cooling chamber. The heating furnace is a furnace in which an atmosphere gas for carbonitriding can be introduced and the inside can be heated to the A ₁ transformation point or higher. A device capable of air cooling, oil cooling, and water cooling is installed in the cooling chamber.
In the induction heating unit 2, a rotary table 21, an annular induction heating coil 22, and a piston 23 are arranged. The rotary table 21 has a rotary shaft 21a extending downward, and is configured to be movable up and down along the rotary shaft 21a. The rotary table 21 stands by at a position substantially the same height as the conveyor 6.

The induction heating coil 22 is arranged at a position higher than the conveyor 6 with the rotation axis 21 a of the turntable 21 being centered. As the induction heating coil 22, an induction heating coil having an inner diameter that produces a constant interval outside the inner ring 7 to be processed is used.
The piston 23 has a disc-shaped presser plate 23a and a shaft 23b extending upward, and is configured to be movable up and down along the shaft 23b. The piston 23 is arranged at a position higher than the induction heating coil 22 so as to be aligned with the rotation shaft 21 a of the turntable 21.

When the inner ring 7 is heated by the induction heating unit 2, the rotary table 21 on which the inner ring 7 is placed is raised, and the inner ring 7 is disposed in the induction heating coil 22 as shown in FIG. Then, the inner ring 7 is pressed from above with the presser plate 23a. In this state, the rotary table 21 is rotated and the induction heating coil 22 is energized.
The cooling / correcting unit 3 includes a rotary table 31, an annular cooling jacket 32, an internal cooling device 33, a cylindrical outer diameter correcting die 34, and a piston 35. The rotary table 31 has a rotary shaft 31a extending downward, and is configured to be movable up and down along the rotary shaft 31a. The rotary table 31 stands by at a position substantially the same height as the conveyor 6.

  The cooling jacket 32 is made of an annular body having an inner diameter and an axial dimension larger than those of the outer diameter correcting die 34. A large number of nozzles are arranged inside the cooling jacket 32. A cooling liquid supply device that supplies a cooling liquid to the cooling jacket 32 is connected to the cooling jacket 32. By this coolant supply device, a predetermined amount of coolant is injected from the nozzle of the cooling jacket 32 at a predetermined timing. The cooling jacket 32 is arranged at a position higher than the conveyor 6 so as to be aligned with the rotation shaft 31 a of the turntable 31.

  The internal cooling device 33 is fixed to the lower part of the piston 35. A large number of nozzles are arranged outside the internal cooling device 33. A coolant supply device that supplies coolant to the internal cooling device 33 is connected to the internal cooling device 33 via the piston 35. By this coolant supply device, a predetermined amount of coolant is injected from the nozzle of the internal cooling device 33 toward the inner ring 7 at a predetermined timing.

The outer diameter correction die 34 is arranged on the upper side inside the cooling jacket 32 so as to be aligned with the rotation shaft 31 a of the rotary table 31.
The piston 35 has a disc-shaped presser plate 35a and a shaft 35b extending upward, and is configured to be movable up and down along the shaft 35b. An internal cooling device 33 is fixed to the central portion of the lower surface of the presser plate 35a. The piston 35 is arranged on the upper side of the outer diameter correction die 34 so as to align with the rotation shaft 31a of the rotary table 31.

  When the inner ring 7 is cooled by the cooling / correcting unit 3, the rotary table 31 on which the inner ring 7 is placed is raised, and the lower side of the inner diameter correcting die 34 in the cooling jacket 32 as shown in FIG. The inner ring 7 is disposed on the inner side. Further, the piston 35 is lowered and the inner ring 7 is pressed from above by the pressing plate 34a. Thereby, the internal cooling device 33 enters the inner ring 7. In this state, the cooling jacket 32 and the internal cooling device 33 are operated to rotate the rotary table 31.

When the inner ring 7 is corrected by the cooling / correcting unit 3, the rotary table 31 on which the inner ring 7 is placed is further raised from the state shown in FIG. 3A, and as shown in FIG. Is pressed into the outer diameter correction die 34. In this state, the cooling jacket 32 and the internal cooling device 33 are operated to rotate the rotary table 31.
In the tempering / correcting unit 4, a rotary table 41, a cylindrical outer diameter correcting die 42, a piston 43, and an annular induction heating coil 44 are arranged. The rotary table 41 has a rotary shaft 41a extending downward, and is configured to be movable up and down along the rotary shaft 41a. The rotary table 41 stands by at a position almost the same height as the conveyor 6.

The outer diameter correction die 42 is arranged at a position higher than the conveyor 6 with the rotation axis 31a of the turntable 31 being aligned with the center.
The piston 43 has a disc-shaped pressing plate 43a and a shaft 43b extending upward, and is configured to be movable up and down along the shaft 43b. The piston 43 is arranged on the upper side of the outer diameter correction die 42 so as to align with the rotation shaft 41 a of the rotary table 41.

The induction heating coil 44 is arranged outside the lower portion of the outer diameter correction mold 42 so as to be aligned with the outer diameter correction mold 42 and the rotation shaft 41 a of the rotary table 41. As the induction heating coil 44, an induction heating coil having an inner diameter that produces a constant interval outside the outer diameter correction mold 42 is used.
When the inner ring 7 is heated and corrected by the tempering / correcting section 4, the rotary table 41 on which the inner ring 7 is placed is raised, and the inner ring is placed below the inside of the outer diameter correcting die 42 as shown in FIG. 7 is press-fitted, and an induction heating coil 44 is disposed outside the lower portion of the outer diameter correction die 42. Further, the piston 43 is lowered and the inner ring 7 is pressed from above by the pressing plate 43a. In this state, the rotary table 41 is rotated and the induction heating coil 44 is energized.

When the inner ring 7 is heated without being corrected by the tempering / correcting unit 4, the rotary table 41 on which the inner ring 7 is placed is lifted while the outer diameter correcting die 42 and the piston 43 are retracted upward to guide the inner ring 7. The inner ring 7 is disposed in the heating coil 44. In this state, the rotary table 41 is rotated and the induction heating coil 44 is energized.
A shot blasting device is disposed in the oxide film removal chamber 5.

Using the processing line of FIG. 1, the steel inner ring 7 is processed by the following method.
First, the inner ring 7 is put in the heating furnace of the carbonitriding / cooling chamber 1, the inside of the heating furnace is maintained in a carbonitriding atmosphere, and the temperature inside the heating furnace is set to a temperature T1 (the temperature exceeding the A ₁ transformation point (726 ° C.)). 800-900 ° C) for a predetermined time. Thereby, the carbonitriding process for the inner ring 7 is performed. Next, the inner ring 7 is moved to the cooling chamber and cooled to a temperature equal to or lower than the M _S point, whereby the inner ring 7 is primarily quenched.

  Next, the inner ring 7 is placed on the conveyor 6, conveyed to the induction heating unit 2, and placed on the rotary table 21. Next, the rotary table 21 on which the inner ring 7 is placed is raised to the state shown in FIG. 2, the rotary table 21 is rotated, and a high frequency (5 to 15 kHz) is applied to the induction heating coil 22 for a short time (2 to 5 seconds). Energize. Thereby, the raceway surface 71 of the inner ring 7 is heated to a temperature T2 that is equal to or higher than the heating temperature T1 in the carbonitriding / cooling step and is lower than T1 + 100 ° C. (for example, 800 to 900 ° C. depending on the temperature of T1). After the energization is completed, heat from the raceway surface 71 is transmitted to the surface of the inner ring 7 other than the raceway surface 71 and the core, and a temperature gradient is formed in the depth direction of the raceway surface 71.

  Next, the rotary table 21 is lowered to the height of the conveyor 6, and the inner ring 7 is placed on the conveyor 6 and conveyed to the cooling / correcting unit 3. Next, the inner ring 7 on the conveyor 6 is placed on the rotary table 31, the rotary table 31 is raised, and the piston 35 is lowered to the state shown in FIG. In this state, the inner ring 7 is cooled by operating the cooling jacket 32 and the internal cooling device 33 and rotating the rotary table 31.

By this cooling, when the inner ring 7 reaches a temperature slightly higher than the point M _S , the rotary table 31 is further raised and the inner ring 7 is press-fitted into the outer diameter correction die 34 as shown in FIG. . In this state, cooling is performed until the temperature is equal to or lower than the M _S point. Thereby, the outer diameter of the inner ring 7 is corrected at the time of quenching. Further, secondary quenching of the inner ring 7 is performed by the steps of FIGS. 3 (a) and 3 (b).

  Next, the rotary table 31 is lowered to the height of the conveyor 6, and the inner ring 7 is placed on the conveyor 6 and conveyed to the tempering / correcting unit 4. Next, the inner ring 7 on the conveyor 6 is placed on the rotary table 41 and the rotary table 41 is raised, so that the inner ring 7 is press-fitted into the outer diameter correction die 42 as shown in FIG. In this state, the rotary table 41 is rotated and the induction heating coil 44 is energized with a high frequency (3 to 10 kHz) for a short time (1 to 10 seconds), whereby the raceway surface 71 of the inner ring 7 is tempered and heated (180). After heating to ˜320 ° C., it is left for a predetermined time (10 seconds to 1 minute). Thereby, tempering of the inner ring 7 and correction of the outer diameter are performed.

Next, the rotary table 41 is lowered to the height of the conveyor 6, and the inner ring 7 is placed on the conveyor 6 and conveyed to the oxide film removing chamber 5. In the oxide film removal chamber 5, the inner ring 7 is applied to a shot blasting apparatus to remove the oxide film on the surface.
According to the method of this embodiment, by correcting the outer diameter of the inner ring 7 at the time of secondary quenching and tempering, deformation during the heat treatment of the inner ring 7 is reduced, and the perfect circle of the outer diameter of the inner ring 7 after the heat treatment is reduced. The degree can be increased.

In the method of this embodiment, the secondary heating (heating at the time of secondary quenching) performed after primary heating (heating at the time of carbonitriding) is performed at a temperature not lower than T1 + 100 ° C. at a temperature (T1) at the time of primary heating in the induction heating unit 2. By performing in (T2), the amount of retained austenite in the core portion can be decreased while the amount of retained austenite in the surface layer portion is increased.
In the method of this embodiment, the cooling temperature of the carbonitriding and cooling process although the M _S point below the temperature may be a temperature higher than M _S point, if a temperature lower than the A ₁ transformation point. In that case, quenching is performed only by induction quenching / correction process.
Further, the oxide film removal step may not be shot blasting. Examples of the oxide film removing process other than the shot blasting include a bright barrel process and a honing process.

Examples of the present invention will be described below.
SUJ2 (M _S point: 275 ° C.) by turning the material consisting of, by processing a predetermined size (OD 101.3Mm, inner diameter 94.6Mm, width 13 mm, groove bottom thickness 2 mm) to the inner ring of. 16 × 200 inner rings were prepared, and the following processing was performed on 200 inner rings of sample Nos. 1-16.

In sample Nos. 1 to 13, the carbonitriding / cooling step, induction hardening / correction step, induction tempering / correction step, and oxide film removal step are performed based on the method of the above-described embodiment using the processing line of FIG. It was.
In sample No. 14, the same process as sample No. 1-13 was performed except that correction was not performed in the induction tempering process. In sample No. 15, the same process as sample No. 1-13 was performed except that correction was not performed in the induction hardening process. Sample No. 16 was subjected to the same steps as Sample Nos. 1 to 13 except that correction was not performed in both the induction hardening step and the induction tempering step.

The heating conditions in the carbonitriding / cooling step were the same for all samples. That is, the same carbonitriding gas atmosphere was used, and the temperature in the heating furnace was the same 850 ° C., and each inner ring was held at this temperature for 3 hours. As shown in Table 1, cooling in the carbonitriding / cooling process should be performed for each sample until it reaches 275 ° C. (temperature below the M _S point) by any one of air cooling, oil cooling, and water cooling. Thus, primary quenching was performed on the inner ring 7. Air cooling, oil cooling, and water cooling were performed in the same manner.
In No. 1-6 and No. 13-16, the heating condition in the induction heating unit 2 was performed at a high frequency (frequency: 10 kHz) for 2 seconds, so that the temperature of the track surface 71 (measured with a radiation thermometer at the groove bottom position). The temperature was 850 ° C. In Nos. 7 and 9, the temperature of the raceway surface 71 was set to 880 ° C. by performing induction heating in the induction hardening / correction process at a high frequency (frequency 10 kHz) for 3 seconds.

In Nos. 8 and 10, the temperature of the raceway surface 71 was set to 900 ° C. by performing induction heating in the induction hardening / correction process for 4 seconds at a high frequency (frequency 10 kHz). In No. 11, the temperature of the raceway surface was set to 950 ° C. by performing induction heating in the induction hardening / correction process at a high frequency (frequency 10 kHz) for 5 seconds. In No. 12, the temperature of the track surface 71 was set to 820 ° C. by performing induction heating in the induction hardening / correction process for 1 second at a high frequency (frequency 10 kHz).
For all samples, after the energization to the induction heating coil 22 is finished, the state shown in FIG. 2 is held for 3 seconds, so that heat from the raceway surface 71 is conducted to a portion other than the raceway surface 71 to the inner ring 7. A temperature gradient was formed.

Next, in No. 1-14, the cooling in the cooling / correcting unit 3 is performed for 2 seconds in the state of FIG. 3A, so that the surface temperature of the inner ring 7 (radiation thermometer at the groove bottom position of the raceway surface 71). 3), the surface temperature of the inner ring 7 was set to 30 ° C. by further cooling for 10 seconds. As the outer diameter correcting die 34, a high carbon steel one was used.
In Nos. 15 and 16, the surface temperature of the inner ring 7 was set to 30 ° C. by performing cooling in the cooling / correcting unit 3 for 12 seconds in the state of FIG.

Next, in No. 1, 2, 4-8, 11-13, 15, as shown in FIG. 4, the inner ring 7 is press-fitted into the outer diameter correction die 42 by the tempering / correcting section 4, and the high frequency (frequency 5 kHz) was applied to the induction heating coil 44 for 5 seconds to heat the raceway surface 71 of the inner ring 7 to 180 ° C. (temperature measured with a radiation thermometer at the groove bottom position) and left for 10 seconds. As a result, induction tempering and correction for the inner ring 7 were performed.
In No. 3, as shown in FIG. 4, with the inner ring 7 being press-fitted into the outer diameter correction die 42 in the tempering / correcting section 4, a high frequency (frequency 5 kHz) was passed through the induction heating coil 44 for 6 seconds, The raceway surface 71 of the inner ring 7 was heated to 200 ° C. and left for 10 seconds. As a result, induction tempering and correction for the inner ring 7 were performed.

  In No. 9, as shown in FIG. 4, with the inner ring 7 being press-fitted into the outer diameter correction die 42 in the tempering / correcting section 4, a high frequency (frequency 5 kHz) was passed through the induction heating coil 44 for 7 seconds, The raceway surface 71 of the inner ring 7 was heated to 240 ° C. and left for 10 seconds. As a result, induction tempering and correction for the inner ring 7 were performed. In No. 10, as shown in FIG. 4, with the inner ring 7 being press-fitted into the outer diameter correction die 42 in the tempering / correcting section 4, a high frequency (frequency 5 kHz) was passed through the induction heating coil 44 for 10 seconds, The raceway surface 71 of the inner ring 7 was heated to 320 ° C. and left for 10 seconds. As a result, induction tempering and correction for the inner ring 7 were performed.

In Nos. 1 to 12 and 15, the outer diameter correcting die 42 made of silicon nitride (ceramics) (correcting die A) was used. In No. 13, the outer diameter correction mold 42 was made of the same material as the outer diameter correction mold 34 of the cooling / correcting section 3 (correction mold B).
In Nos. 14 and 16, when only the induction heating coil 44 is arranged outside the inner ring 7 in the tempering / correcting section 4, a high frequency (frequency 5 kHz) is energized to the induction heating coil 44 for 5 seconds to track the inner ring 7. The surface 71 was heated to 180 ° C. and left for 10 seconds. Thereby, induction tempering for the inner ring 7 was performed.

Finally, the oxide film removal process was performed under the same conditions for all samples. That is, the oxide film formed on the surface of the inner ring 7 was removed by performing a shot blasting process in which SiC particles were projected with compressed air of 49 to 196 kPa.
For each sample, the amount of retained austenite in the surface layer portion and the core portion of the raceway surface 71 of the inner ring 7, the rate of change in the roundness of the inner ring 7 before and after the induction hardening / correction process, and before and after the induction tempering / correction process, It was measured.

  The amount of retained austenite was measured for all 200 inner rings of Nos. 1 to 16 using an X-ray diffractometer (XRD) at a depth of 150 μm and a depth of 1 mm from the surface. And it computed from the diffraction intensity of the martensite alpha (211) plane and austenite gamma (220) plane of each diffraction pattern. And the value obtained from the measurement result at a depth of 150 μm from the surface is the amount of retained austenite in the surface layer part, and the value obtained from the measurement result at the position of 1 mm depth from the surface is the amount of retained austenite at the core part. . From each value, an average value of 200 inner rings subjected to the same treatment was calculated, and the amount of retained austenite No. 1 to 16 was obtained.

The change rate of the roundness of the inner ring was measured by the following method. First, immediately before and after each correction step, the diameter at the groove bottom position on the raceway surface was measured over the entire circumference for all 200 inner rings of No. 1 to No. 16. Next, the difference (δ) between the minimum value and the maximum value of the diameter measured for each inner ring was calculated, and the average value of 200 δ subjected to the same processing was calculated. This average value was introduced into equation (1) as the roundness Cb immediately before each correction step and the roundness immediately after it as Ca, and the change rate Ch of roundness was calculated.
Table 1 shows the difference between these results and the heat treatment method of each sample.

  From this result, in No. 1-10 which implemented the method included in the method of this invention, the amount of retained austenite of the surface layer part of an inner ring raceway surface is 21-43 volume%, and the amount of retained austenite of a core part is 5-14. It is volume%. That is, “the amount of retained austenite in the surface layer part is 20% by volume or more and 45% by volume or less, and the amount of retained austenite in the core part is 15% by volume or less” is satisfied.

  On the other hand, a method in which the heating temperature in the induction hardening / correction process is outside the range of the method of the present invention (the heating temperature in the carbonitriding / cooling process is 850 ° C., which is 850 ° C. or more and less than 950 ° C.) In Nos. 11 and 12, the retained austenite amounts in the surface layer portion of the raceway surface are 17% by volume and 47% by volume, and the retained austenite amounts in the core portion are 19% by volume and 6% by volume. That is, it does not satisfy “the amount of retained austenite in the surface layer part is 20% by volume or more and 45% by volume or less and the amount of retained austenite in the core part is 15% by volume or less”.

  Further, in No. 13, the straightening mold used in the induction tempering / correction process was not made of ceramics, so the rate of change in the roundness of the inner ring before and after the induction tempering / correction process was as large as -40%. In No. 14, since correction was not performed during induction tempering, the rate of change in the roundness of the inner ring before and after induction tempering was as high as -35%. In Nos. 15 and 16, since no correction was performed during induction hardening, the rate of change in the roundness of the inner ring before and after the induction hardening process was as large as -10%.

  Accordingly, the rolling bearing having the inner rings of No. 1 to 10 has a longer life under foreign matter-mixed lubrication and excellent dimensional stability compared to the rolling bearings having the inner rings of No. 11 and No. 12. Become. In addition, the inner rings of No. 1 to 10 have higher roundness after the heat treatment than the inner rings of No. 13 to 16, so there is no need to perform an additional correction process after the induction tempering / correction process. Since the amount of grinding in the process is reduced, the production efficiency is improved.

DESCRIPTION OF SYMBOLS 1 Carbonitriding / cooling chamber 2 Induction heating part 21 Rotary table 21a Rotating shaft 22 Induction heating coil 23 Piston 23a Holding plate 23b Shaft 3 Cooling / correcting part 31 Rotating table 31a Rotating shaft 32 Cooling jacket 33 Internal cooling device 34 Outer diameter correction type 35 Piston 35a Presser plate 35b Shaft 4 Tempering / correcting part 41 Rotary table 41a Rotating shaft 42 Outer diameter correction type 44 Induction heating coil 43 Piston 43a Presser plate 43b Shaft 5 Oxide film removal chamber 6 Conveyor 7 Inner ring (Race ring)
71 Track surface

Claims (4)

A carbonitriding / cooling step in which a steel bearing ring constituting the rolling bearing is heated to a temperature exceeding the A ₁ transformation point and subjected to carbonitriding and then cooled to below the A ₁ transformation point;
Wherein the bearing ring after carbonitriding and cooling step, after the induction heating to the carbonitriding and cooling temperature of the heating temperature of less than + 100 ° C. or higher heating temperature of step, a step of cooling until below M _S point, Induction quenching and straightening process in which quenching and correction are performed by placing the raceway in an outer diameter constrained type before reaching the M _S point during cooling,
An induction tempering / correction process for performing tempering and correction by induction heating in a state where the raceway ring after the induction hardening / correction process is constrained by a ceramic correction mold;
An oxide film removing step for removing an oxide film formed on the surface of the raceway after the induction tempering / correcting step;
A rolling bearing bearing ring manufacturing method characterized by performing the steps in this order.   The amount of retained austenite in the surface layer portion of the raceway surface is 20% by volume or more and 45% by volume or less, and the amount of retained austenite in the core part is 15% by volume or less. Rolling bearing raceway.   2. The method of manufacturing a rolling bearing race according to claim 1, wherein a rate of change of the roundness of the raceway before and after the induction hardening / correction step is 40% or more.   The method of manufacturing a rolling bearing race according to claim 1, wherein a rate of change of the roundness of the raceway before and after the induction tempering / correction step is within ± 30%.

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