JP2013124416A - Method for manufacturing bearing ring of rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, as the method for manufacturing the bearing ring of a rolling bearing, a method for obtaining a bearing ring, with which the deformation in heat treatment can be made small and the service life under foreign matter mixing lubrication can be made long, and which is also excellent in the stability of size.SOLUTION: To an inner ring 7, at first, heating is performed until the temperature exceeding an Atransformation point to perform carbonitriding treatment and then cooling is performed until the temperature lower than the Atransformation point in a carbonitriding treatment chamber 1. Next, induction heating is performed until the temperature at the heating temperature of carbonitriding or more in an induction-heating coil 20 of an induction-heating part 2. Next, a quenching and a reformation are performed in a cooling and reforming part 3. Before reaching the Mpoint on the way of the cooling, the inner ring 7 is inserted into an outer-diameter constraint mold 34, and is cooled until reaching the Mpoint or lower. Next, a high-frequency tempering is performed by a tempering part 4. Next, the oxidized film formed on the surface thereof is removed in an oxidized 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.

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 1, 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). The carbonitriding step for cooling below the A ₁ transformation point and the raceway after the carbonitriding step are set to a temperature (T2 <T1) that is equal to or higher than the A ₁ transformation point and less than the heating temperature (T1) of the carbonitriding step. A method is described in which a quenching step of cooling after heating (secondary heating) is performed in this order.

  According to Patent Document 1, according to this method, a microstructure in which the grain size of 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 1 also discloses that the balance between surface damage resistance and secular dimensional change characteristics can be 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.
Patent Documents 2 and 3 include a primary heat treatment apparatus in which a steel part is heated to a temperature exceeding the A ₁ transformation point (T1) and then cooled to less than 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 2 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 3 describes that T2 <T1 or T2 ≧ T1 may be satisfied.
Patent Document 4 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 the 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.

JP 2006-316821 A JP 2005-113213 A JP 2005-133212 A JP 2009-203522 A

  The subject of this invention is a method for producing a bearing ring for a rolling bearing, in which the deformation during heat treatment can be reduced, the life under lubrication mixed with foreign matter can be extended, and a bearing ring having excellent dimensional stability can be obtained. Is to provide.

In order to solve the above-mentioned problems, the rolling bearing raceway manufacturing method of the present invention has a bearing ring (inner ring or outer ring) constituting the rolling bearing at a temperature (T1) exceeding the A ₁ transformation point (austenite transformation temperature). after heating to subjected to carbonitriding and carbonitriding step of cooling to below the a ₁ transformation point, the carburization after nitriding step the raceway of, a ₁ equal to or more than the transformation point above the heating temperature of the carbonitriding process Cool after induction heating to a temperature (T2 ≧ T1) and before reaching the M _S point (martensitic transformation start temperature) in the middle of cooling, put it in the outer diameter constrained mold and cool it to below the M _S point. Induction hardening and straightening process for quenching and straightening, induction tempering process for induction tempering by induction heating of the raceway after the induction hardening and straightening process, and formation on the surface of the raceway after the induction tempering process Oxidation The oxide film removing step for removing the film is performed in this order.

In the method of the present invention, in the induction hardening / correction step, the raceway can be reduced during heat treatment by performing the straightening by putting the raceway into an outer diameter constrained mold during cooling during quenching.
In the method of the present invention, secondary heating (holding temperature during quenching) performed after cooling after primary heating (carbonitriding) is performed by induction heating at a temperature (T2) equal to or higher than temperature (T1) during primary heating. By doing so, 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. 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.

  The method of the present invention is a method of manufacturing a bearing ring for a rolling bearing, which can reduce deformation during heat treatment, can extend the life under the contamination with foreign matter, and can provide a bearing ring with 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 cooling and correct | amending 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 heating the inner ring | wheel in the tempering 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 treatment line includes a carbonitriding treatment chamber 1, an induction heating unit 2, a cooling / correcting unit 3, a tempering 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 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 lifted, and 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 unit 4, a rotary table 41 and an annular induction heating coil 42 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 induction heating coil 42 is arranged at a position higher than the conveyor 6 with the rotation axis 41 a of the turntable 41 being centered. As the induction heating coil 42, an induction heating coil having an inner diameter that generates a constant interval outside the inner ring 7 to be processed is used.
When the inner ring 7 is heated by the tempering unit 4, the rotary table 41 on which the inner ring 7 is placed is raised, and the inner ring 7 is disposed in the induction heating coil 42 as shown in FIG. 4. In this state, the rotary table 21 is rotated and the induction heating coil 42 is energized.

A shot blasting device is disposed in the oxide film removal chamber 5.
Using the processing line shown in FIG. 1, the inner ring 7 is processed by the following method.
First, the inner ring 7 is placed in the heating furnace of the carbonitriding 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 (800 ° C.) exceeding the A ₁ transformation point (726 ° C.). ˜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 3 seconds). Energize. Thereby, the raceway surface 71 of the inner ring 7 is heated to a temperature T2 (800 to 900 ° C.) that is equal to or higher than the A ₁ transformation point and higher than the heating temperature T1 in the carbonitriding step. 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 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 to obtain the state shown in FIG. In this state, the rotary table 31 is rotated, and the induction heating coil 42 is energized with a high frequency (3 to 10 kHz) for a short time (1 to 2 seconds). Thereby, the raceway surface 71 of the inner ring 7 is heated to a tempering heating temperature (180 to 300 ° C.).

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, the deformation of the inner ring 7 during heat treatment can be reduced by correcting the outer diameter of the inner ring 7 during quenching.

In the method of this embodiment, secondary heating performed after cooling after the carbonitriding process is performed at a temperature equal to or higher than the heating temperature of the carbonitriding process in the induction heating unit 2, thereby increasing the amount of retained austenite in the surface layer part, The amount of retained austenite in the core can be reduced.
In the method of this embodiment, the cooling temperature of the carbonitriding process is set to 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. With respect to this inner ring, in sample Nos. 1 to 5, using the processing line of FIG. 1, the carbonitriding step, induction hardening / correction step, induction tempering step, oxide film removal step based on the method of the above-described embodiment Went. In sample Nos. 6 to 10, instead of the induction hardening / correction process and the induction tempering process, oil quenching for oil cooling after furnace heating and tempering by furnace heating were performed.

The heating conditions for the carbonitriding process 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, the cooling method was performed by air cooling, oil cooling, or water cooling for each sample. Air cooling, oil cooling, and water cooling were performed in the same manner.
In Nos. 1 to 3, the temperature of the raceway surface was set to 850 ° C. by performing the heating conditions in the induction heating unit 2 at a high frequency (frequency 10 kHz) for 2 seconds. In No. 4, the temperature of the raceway surface 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 No. 5, the temperature of the raceway surface was set to 820 ° C. by performing induction heating in the induction hardening / correction process at a high frequency (frequency 10 kHz) for 1 second.

  Next, in Nos. 1 to 5, after the energization to the induction heating coil 22 is finished, the state shown in FIG. 2 is held for 3 seconds to conduct the heat from the raceway surface to a portion other than the raceway surface, thereby causing a temperature gradient. Formed. Next, in No. 1-5, after cooling in the cooling / correcting section 3 for 2 seconds in the state of FIG. 3A, the surface temperature of the inner ring is set to 300 ° C., and then in FIG. As a state, the surface temperature of the inner ring was set to 30 ° C. by further cooling for 10 minutes.

In No. 6, the temperature in the heating furnace was kept at 820 ° C. and heated for 1 hour, and then cooled with oil. In Nos. 7-9, the temperature in the heating furnace was kept at 850 ° C. and heated for 1 hour, and then oil-cooled. In No. 10, the temperature in the heating furnace was kept at 880 ° C. and heated for 1 hour, and then cooled with oil.
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 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 core portion of the raceway surface was measured. The amount of retained austenite in the surface layer portion was calculated as an average value in a range from the surface to a depth of 50 μm. The amount of retained austenite in the core was calculated as an average value in a range of 1 mm from the surface. Table 1 shows the difference between the results and the heat treatment method of each sample.

  From this result, in No. 1-4 which implemented the method included in the method of this invention, the amount of retained austenite of the surface layer part of a raceway surface is 26-36 volume%, and the amount of retained austenite of a core part is 8-12 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, in No. 5-10 which implemented the method which is outside the range of the method of this invention, the amount of retained austenite of the surface layer part of a raceway surface is 26-36 volume%, and the amount of retained austenite of a core part is 8 It is ˜12% 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”.

  Therefore, the rolling bearings having the inner rings of No. 1 to 4 have a longer life under lubrication mixed with foreign matters than the rolling bearings having the inner rings of No. 5 to 10, and the inner rings of No. 1 to 4 Dimensional stability is better than 5-10 inner rings.

DESCRIPTION OF SYMBOLS 1 Carbonitriding process 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 correcting type 35 Piston 35a Presser plate 35b Shaft 4 Tempering part 41 Rotating table 41a Rotating shaft 42 Induction heating coil 5 Oxide film removal chamber 6 Conveyor 7 Inner ring (track ring)
71 Track surface

Claims (2)

A carbonitriding step in which the 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 a temperature below the A ₁ transformation point;
The bearing ring after the carbonitriding step, before cooling after induction heating comprising at A ₁ transformation point or above to a temperature above the heating temperature in the carbonitriding process, reaches the M _S point of the middle cooling, the outer diameter constraining Induction hardening and straightening process to quench and straighten by cooling into the mold and below the M _S point,
An induction tempering step in which tempering is performed by induction heating of the raceway after the induction hardening and correction step;
A method of manufacturing a rolling bearing bearing ring, comprising performing an oxide film removing process for removing an oxide film formed on a surface of the bearing ring after the induction tempering process 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.

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