JP2007186760A - Manufacturing method of bearing ring for rolling bearing, and rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing ring manufacturing method capable of obtaining the requested rolling fatigue life of a bearing ring even when the bearing ring is thin-walled. <P>SOLUTION: At least one of an inner ring 1 and an outer ring 2 for a ball bearing formed of steel is worked in a predetermined shape. The steel is subjected to carbo-nitriding at the temperature higher than the A<SB>c1</SB>transformation point, and cooled to the temperature lower than the A<SB>r1</SB>transformation point; and then, heated and maintained at the temperature higher than the A<SB>c1</SB>transformation point, and subjected to the corrective hardening and tempered. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing rolling bearing race rings (inner and outer rings) and a rolling bearing.

  Rolling bearings used in automobile parts such as reduction gears, transmissions (transmissions), and engines are often used under lubrication conditions in which foreign matter is mixed (hereinafter referred to as “under foreign matter mixed lubrication”). . In this type of rolling bearing, indentations due to foreign matter are formed on the raceway (inner and outer rings) and the rolling surfaces (raceways and rolling surfaces) of the rolling elements, and stress is concentrated on the edges (edges) of the indentations. As a result, there is a problem that surface peeling occurs from the edge portion. In order to suppress this surface peeling, stress concentration at the edge portion of the indentation is eased by making the retained austenite softer than martensite in the surface layer portion forming the rolling surface.

  In Patent Document 1, at least one of an inner ring, an outer ring, and a rolling element is produced by carburizing or carbonitriding a medium carbon manganese steel processed into a predetermined shape, and the surface layer forming the rolling surface thereof It has been proposed that the amount of retained austenite in the part is 25 to 40% by volume. Here, in order to secure the amount of retained austenite in the surface layer portion forming the rolling surface, it is preferable to perform carbonitriding.

By the way, in recent years, with the miniaturization and weight reduction of automobile parts, there is a tendency to reduce the thickness (wall thickness) of the bearing ring of the rolling bearing used in these parts. The bearing ring is usually produced by subjecting steel processed into a predetermined shape to hardening treatment such as quenching and tempering. However, if the thickness of the bearing ring is reduced, deformation may increase during the hardening treatment. . In order to suppress the deformation after the curing process, it is necessary to reheat and perform a correction process such as press quench (correction quenching) or sizing temper (correction tempering) after the curing process.
Japanese Patent No. 2885829

However, in the rolling bearing described in Patent Document 1 described above, if it is attempted to reduce the wall thickness of the bearing ring, it is necessary to perform a correction process after the carbonitriding process, so that a sufficient amount of retained austenite cannot be obtained in the surface layer portion. In some cases, the required rolling fatigue life cannot be obtained.
Therefore, an object of the present invention is to produce a rolling ring having a small thickness so that a necessary rolling fatigue life can be obtained.

In order to solve such a problem, the present invention includes a pair of race rings having raceway surfaces arranged to face each other, and a plurality of rolling elements arranged to roll between the pair of race rings, In the method of manufacturing the bearing ring of the rolling bearing provided with the above, after carbonitriding the steel processed into a predetermined shape at a temperature higher than the A _c1 transformation point, to a temperature lower than the A _r1 transformation point Provided is a method for manufacturing a bearing ring for a rolling bearing, characterized by performing cooling and tempering after cooling and then heating and holding at a temperature higher than the A _c1 transformation point.

That is, the rolling bearing race according to the present invention is manufactured by performing the following heat treatment on steel processed into a predetermined shape.
<Steel used as material>
The steel used in the present invention is not particularly limited as long as it can provide the rolling fatigue life required for the bearing ring for rolling bearings, but it is preferable to use a bearing steel such as SUJ2 (high carbon chromium bearing steel type 2). .

<About heat treatment>
First, carbonitriding is performed on steel processed into a predetermined shape at a temperature (for example, 840 to 880 ° C.) higher than the A _c1 transformation point. The carbonitriding is performed by heating and holding for a predetermined time (for example, 2 to 4 hours) in a carbonitriding atmosphere (for example, a mixed gas atmosphere of RX gas, enriched gas, and ammonia gas).
Next, it is cooled to a temperature (for example, room temperature to 500 ° C.) lower than the A _r1 transformation point. In order to reduce the heat treatment deformation after carbonitriding and suppress the occurrence of cracking, for example, this cooling is preferably performed by cooling such as gas cooling or air cooling, furnace cooling, or cooling.
Next, after heating and holding again at a temperature higher than the A _c1 transformation point, straightening and tempering are performed.

Here, the heating retention temperature after carbonitriding, higher than transformation point A _c1 and, as to a temperature close to the transformation point A _c1, austenite grains become fine, the rolling fatigue life and impact resistance However, when the austenite grain size is 9 or more in terms of the austenite grain size specified in JIS G 0551, the effect of improving rolling fatigue life and impact resistance is saturated. Further, the necessary hardness (for example, Hv 700 or more) and the residue remain on the surface layer portion (the portion from the surface to a predetermined depth, for example, 50 μm) that forms the raceway surface after reheating after carbonitriding and quenching and tempering. It is necessary to ensure the amount of austenite (for example, 25 volume% or more and 40 volume% or less). For this reason, it is preferable to perform the reheating after carbonitriding at 840-900 degreeC.

Further, the heating and holding time after carbonitriding is preferably 5 minutes or more after the race ring is soaked in order to sufficiently dissolve the carbon and nitrogen of the matrix.
Further, after the carbonitriding and heating, straightening and quenching is performed in order to improve the dimensional accuracy after the heat treatment. In order to improve roundness, straightening quenching is preferably performed by using a die without slits and press-fitted in the axial direction. In order to suppress deformation during press-fitting and to improve roundness, a race ring It is preferable to start correction in the austenite state.

Furthermore, tempering after straightening and quenching is preferably normal tempering from the viewpoint of cost, but straightening and tempering may be used to further improve the roundness.
According to such a method of manufacturing a race, even if carbon steel is carbonitrided and then heated and held again and then subjected to straightening and tempering, the amount of retained austenite necessary for the surface layer portion forming the raceway surface can be obtained. Therefore, even a thin raceway ring can be manufactured so as to obtain a necessary rolling fatigue life under lubrication mixed with foreign matter.

The present invention also provides a rolling bearing comprising a pair of raceways having raceway surfaces arranged opposite to each other, and a plurality of rolling elements that are slidably arranged between the pair of raceways. At least one of the bearing rings is subjected to carbonitriding at a temperature higher than the A _c1 transformation point on steel processed into a predetermined shape, and then cooled to a temperature lower than the A _r1 transformation point. After that, it is obtained by heating and holding at a temperature higher than the A _c1 transformation point, followed by straightening quenching and tempering. The hardness of the surface layer portion forming the raceway surface is Hv 700 or more, and the amount of retained austenite in the surface layer portion is Provided is a rolling bearing characterized by an austenite crystal grain size of 25 vol% or more and 40 vol% or less and a surface layer portion of 9 or more.

  Here, if the hardness of the surface layer portion forming the raceway surface is less than Hv700, indentations due to foreign matter are easily formed, and the necessary rolling fatigue life cannot be obtained under the foreign matter mixed lubrication. Further, if the amount of retained austenite in the surface layer portion forming the raceway surface is less than 25% by volume, it becomes impossible to alleviate the stress concentration at the edge portion of the indentation under the contamination with foreign matter. On the other hand, if the amount of retained austenite in the surface layer portion forming the raceway surface is larger than 40% by volume, the true contact area between the rolling members increases, and the rolling fatigue life necessary for the surface layer portion cannot be obtained. Furthermore, if the austenite grain size of the surface layer portion forming the raceway is less than 9, the necessary rolling fatigue life and impact resistance cannot be obtained.

According to the method for manufacturing a bearing ring for rolling bearings according to the present invention, a steel processed into a predetermined shape is subjected to carbonitriding at a temperature higher than the A _c1 transformation point, and then a temperature lower than the A _r1 transformation point. The amount of retained austenite required for the surface layer even when straightening quenching and tempering is performed after heating and holding at a temperature higher than the A _c1 transformation point, followed by carbonitriding. Is obtained. Therefore, even a thin bearing ring can be manufactured so as to obtain a necessary rolling fatigue life.
That is, by using the rolling bearing bearing ring obtained by this manufacturing method in a rolling bearing used in automobile parts, a necessary rolling fatigue life can be obtained under the contamination with foreign matter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a ball bearing as an example of a rolling bearing according to the present invention.
As shown in FIG. 1, the ball bearing includes an inner ring 1 and an outer ring 2 having raceway surfaces 1 a and 2 a that are arranged to face each other, and a plurality of balls (not shown) that are arranged to roll between the inner ring 1 and the outer ring 2 ( Rolling element) 3 and a cage 4 for holding the ball 3 so as to roll freely.

The inner ring 1 and the outer ring 2 were produced by the following procedure.
First, a material made of SUJ2 was processed into the shape of the inner ring 1 (outer diameter: 41 mm, inner diameter 30 mm, width 16 mm) and the outer ring 2 (outer diameter 62 mm, inner diameter 52 mm, width 16 mm) for the ball bearing No. 6206. Then, carbonitriding was performed by heating and holding at 840 to 880 ° C. for 2 to 4 hours in a carbonitriding atmosphere (mixed gas atmosphere of RX gas, enriched gas, and ammonia gas). Next, it was cooled to room temperature. Next, after reheating to 840-900 degreeC, straightening hardening was performed. Next, it tempered by hold | maintaining at 180-220 degreeC for 2 hours. Next, grinding finishing was performed on the raceway surfaces 1a and 2a.

Thereby, in the surface layer portion (portion from the surface to 50 μm) forming the raceway surfaces 1a and 2a of the inner ring 1 and the outer ring 2, the hardness is Hv 700 or more, the residual austenite amount is 25 volume% or more and 40 volume% or less, and austenite The crystal grain size was 9 or more.
After processing the material which consists of SUJ2 into a predetermined shape, the ball 3 is quenched by heating and holding at 840 to 900 ° C. for 0.5 to 1.0 hour, and then heated and held at 180 to 220 ° C. for 2 hours. It produced by performing tempering.

  According to the ball bearing of the present embodiment, in the surface layer portion forming the raceways 1a and 2a of the inner ring 1 and the outer ring 2, the hardness is Hv 700 or more, the residual austenite amount is 25% by volume or more and 40% by volume or less, and the austenite crystal grain size is set. By setting it to 9 or more, the necessary rolling fatigue life can be obtained even when used under the contamination with foreign matter.

<Example>
Hereinafter, the result of verifying the effect of the present invention will be described.
The outer ring of the ball bearing described above was produced by the following procedure. First, after processing into a predetermined shape using a material made of SUJ2, heat treatments A and B were performed as shown below. As the heat treatment A, after carbonitriding at a temperature shown in Table 1 (temperature higher than the A _c1 transformation point), it was cooled to room temperature (temperature below the A _r1 transformation point), and then re-heated to the temperature shown in Table 1. After heating, straightening quenching and tempering by heating at 180 to 240 ° C. for 2 hours were performed. As the heat treatment B, tempering similar to the heat treatment A was performed after performing quenching by heating and holding at 840 ° C. for 0.5 to 1.0 hours without performing carbonitriding.

The hardness of the surface layer portion (portion from the surface to 50 μm), the amount of retained austenite, and the austenite grain size were measured using a sample for fracture test among the outer rings thus obtained. These results are also shown in Table 1.
In addition, the hardness of the surface layer part was measured using the Vickers hardness test method prescribed | regulated to JISZ2211. The amount of retained austenite in the surface layer was measured using a known X-ray diffractometer. Furthermore, the austenite crystal grain size of the surface layer part is determined by first polishing the raceway surface and corroding the polished surface with an etching solution to reveal austenite crystal grains, and then measuring the size of the austenite crystal grains with an optical microscope. Observed at (100 times), the crystal grain size based on the standard grain size diagram defined in JIS G 0551 was calculated.

Further, the inner ring and the ball of the ball bearing described above are subjected to carbonitriding by heating and holding at 840 to 900 ° C., and quenching and tempering similar to heat treatment B after processing a material made of SUJ2 into a predetermined shape. Made.
And using the life test sample among the obtained outer ring, inner ring, and ball, the above-mentioned ball bearing was assembled, and a life test was performed under the conditions shown below assuming that it would be used under foreign matter-mixed lubrication. . In this life test, the time until the value of the vibrometer attached to the ball bearing tripled from the start of the test was measured as the life, and the L ₁₀ life based on the Weibull distribution curve was calculated. This result is shown in No. 8 of L ₁₀ life ratio when a 1, also shown in Table 1.
<Life test conditions>
Surface pressure: 4900 MPa
Rotational speed: 3000min ^-1
Lubricating oil: Turbine oil (VG68)
Foreign matter: Fe ₃ C (hardness: HRC52, particle size: 74 to 147 μm) mixed to 300 ppm with respect to the entire lubricating oil

As shown in Table 1, as a heat treatment, after carbonitriding at a temperature higher than the A _c1 transformation point, cooling to a temperature lower than the _{Ar 1} transformation point, and then heating again at a temperature higher than the A _c1 transformation point No. 1 was prepared by performing straightening quenching and tempering after holding, and specifying the hardness of the surface layer portion, the amount of retained austenite, and the austenite grain size. 1-No. In No. 6, the other No. 7-No. Compared with 9, a long life was obtained.

On the other hand, no. In No. 7, since the reheating temperature after carbonitriding was lower than the A _c1 transformation point, a sufficient amount of retained austenite was not obtained in the surface layer portion, and the life was short.
No. In No. 8, since carbonitriding was not performed, a sufficient amount of retained austenite was not obtained in the surface layer portion, and the life was short.
Furthermore, no. In No. 9, since the tempering temperature was high, a sufficient amount of retained austenite and hardness were not obtained in the surface layer portion, and the life was short.

  From the above results, the inner ring 1 and the outer ring 2 were no. 1-No. No. 6 was prepared by performing the same heat treatment as in No. 6, and the structure of the surface layer portion forming the raceway surfaces 1a and 2a was described above. 1-No. In the same manner as in No. 6, it was confirmed that even when the inner ring 1 and the outer ring 2 were made thinner, the necessary rolling fatigue life could be obtained under the contamination with foreign matter.

It is sectional drawing which shows a ball bearing as an example of the rolling bearing which concerns on this invention.

Explanation of symbols

1 Inner ring (Raceway)
1a Raceway surface 2 Outer ring (Raceway)
2a Raceway surface 3 ball (rolling element)
4 Cage

Claims (3)

In a method for manufacturing the raceway of a rolling bearing comprising a pair of raceways having raceway surfaces arranged opposite to each other, and a plurality of rolling elements that are freely rollable between the pair of raceways. ,
Steel that has been processed into a predetermined shape is carbonitrided at a temperature higher than the A _c1 transformation point, cooled to a temperature lower than the _{Ar 1} transformation point, and then heated at a temperature higher than the A _c1 transformation point. A method of manufacturing a bearing ring for a rolling bearing, wherein straightening and tempering are performed after the holding.   2. The method for manufacturing a bearing ring for a rolling bearing according to claim 1, wherein the temperature maintained by heating after the carbonitriding is 840 to 900 ° C. 3. In a rolling bearing provided with a pair of raceways having raceway surfaces arranged to face each other, and a plurality of rolling elements arranged to roll between the pair of raceways,
At least one of the pair of race rings is subjected to carbonitriding at a temperature higher than the A _c1 transformation point on steel processed into a predetermined shape, and then cooled to a temperature lower than the A _r1 transformation point. And then heated and held at a temperature higher than the A _c1 transformation point, followed by straightening and tempering,
The hardness of the surface layer part forming the raceway surface is Hv 700 or more, the amount of retained austenite of the surface layer part is 25% by volume or more and 40% by volume or less, and the austenite grain size of the surface layer part is 9 or more. Rolling bearing.

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