JPH11257357A - Race for rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress manufacturing cost without impairing quality for a finished product, as for a race for a rolling bearing of steel to be ground after heat treatment. SOLUTION: Without turning an outer diameter part of an outer ring and an inner diameter part of an inner ring at the time of turning process (S6) after CRF working (S4), a decarbonized layer having a surface decarbonization ratio of not less than 10% and not more than 50% and the maximum decarbonization depth of 0.4 mm or less is reserved on the inner diameter part of the inner ring in a race. A decarbonized layer having a surface decarbonization ratio of not less than 10% and not more than 70% and the maximum decarbonization depth of 0.5 mm or less is reserved on the outer diameter of the outer ring, and no decarbonized layer is reserved on a race surface of the race.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a motorcycle, an automobile,
The present invention relates to rolling bearings used everywhere such as agricultural machines and construction machines, and in particular, to rolling bearings effective as bearing rings for rolling bearings such as deep groove ball bearings manufactured by using cold rolling (CRF processing). It relates to a bearing ring.

[0002]

2. Description of the Related Art Generally, inner and outer rings (track rings) of a deep groove ball bearing manufactured by grinding after heat treatment are manufactured in the following manner in consideration of manufacturing costs. This will be described with reference to FIG.

As the bearing material, a rolled round bar steel material is used (S1). First, as shown in FIG. 2A, a round bar steel material 21 is formed by using a multi-stage former. Hot forging is performed to form rough rings 22, 23 as inner and outer rings as shown in FIG. 2 (B) (S2). Next, the hardness is reduced or the microstructure is improved by softening annealing (S3).

Subsequently, cold rolling (hereinafter referred to as CR)
F processing) (S4). As shown in FIG. 3, which is a simplified diagram, CRF processing refers to roughing rings 22, 23.
Is thinned by rolling with a load W while being pressed between the rotating forming roll 11 and the mandrel 12, thereby increasing the ring diameter.

[0005] Here, when the CRF processing is not used, a forging process as shown in FIG. 4 is conventionally employed. When the rough rings a1 and b1 to be the outer ring and the inner ring are formed in the forging process, The portions denoted by reference numerals c1 and c2 are discarded as scrap. On the other hand, when performing the above-mentioned CRF processing, small rough rings 22 and 23 shown in FIG. 2B are made by hot forging, and two rings 31 and 32 shown in FIG. Since the diameter can be increased, the portion denoted by reference numeral c2 in FIG. 4 does not occur.
Since the size can be reduced as shown in c3, the scrap amount is small. Further, when the diameter of the ring is expanded by CRF processing, the raceway surface is formed to have grooves 31b, 32a, etc., so that the machining allowance can be reduced as much as possible, and the material yield is greatly improved. Therefore, as described above, CRF processing is adopted in consideration of manufacturing costs.

Next, sizing (S5) is performed. Then, in order to remove the oxidized layer and decarburized layer generated during forging and annealing, and to form into the shape required for the raceway of the deep groove ball bearing after heat treatment and grinding, the rough ring after CRF processing (hereinafter referred to as CRF ring) Turning (S6) is performed on the entire surface of the ring. In some cases, burrs and the like formed during hot forging before turning may be removed by grinding.

Next, quenching and tempering are performed to obtain the hardness required for the bearing (S7). Then, the inner and outer races as finished products are manufactured by grinding the raceway surface and the mating surface (S8).

[0008] Conventionally, Japanese Patent Publication No. 6-838
As described in Japanese Patent Publication No. 72, as a pre-process of CRF processing, the entire surface of the rough ring is subjected to turning processing to make the shape and weight constant, and then, by precise CRF processing, a raceway surface groove required as a deep groove ball bearing. There is disclosed an apparatus in which a shape having seal grooves or the like is completely finished so that subsequent turning is omitted and cost is reduced.

[0009] Regardless of which manufacturing method is adopted, conventionally, the decarburized layer is processed so as not to remain on the entire surface of the inner and outer rings as a finished product.

[0010]

Here, as described above, the CRF process is a process of forming a rough ring in order to expand its diameter. Therefore, although the radial thickness and the diameter expansion amount of the ring can be adjusted, the width of the ring cannot be controlled because the width is free. As a result, protrusion occurs in the width direction.

[0011] Therefore, in the raceway manufactured by the manufacturing method described in Japanese Patent Publication No. 6-83872, which performs precise CRF processing, it is easy for the raceway to protrude in the width direction.
Since strong pressure is applied by CRF processing without a decarburized layer, there is a possibility that minute cracks may occur at the edges of seal grooves and race grooves that need to be formed into complicated shapes.

As a result, it is necessary to turn the entire surface before the CRF processing in order to adjust the dimensions before the CRF processing and to keep the volume and the like constant. Would. In addition, precise CRF processing of a complex shape requires a long processing time.
This is a factor that increases the cost of RF processing. In other words, the bearing ring is disadvantageous in manufacturing cost.

On the other hand, in a raceway manufactured by the above-mentioned conventional method in which turning is not performed before CRF processing, a groove shape (31b, 32 in FIG. 2) is formed on the raceway surface when the diameter is increased by CRF processing.
By shaping a) or the like, the subsequent machining allowance can be reduced as much as possible. However, if decarburization generated during hot forging or soft annealing remains, uneven hardness and surface cracks are likely to occur, which may cause problems in bearing function. Later, the entire surface of the CRF rings 31 and 32 was turned,
As will be described later, there is still room for pursuit with respect to the reduction of manufacturing costs by omitting steps.

The present invention has been made in accordance with the above-mentioned knowledge, and it is possible to reduce the manufacturing cost of a steel rolling bearing ring which is subjected to grinding after heat treatment without impairing the quality as a finished product. An object of the present invention is to provide a bearing ring of a rolling bearing that can perform the rolling operation.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a raceway of a rolling bearing manufactured by performing a grinding process after a heat treatment. A decarburized layer with a decarburization rate of 10% or more and 50% or less and a maximum decarburization depth of 0.4 mm or less remains.
A decarburized layer with a surface decarburization rate of 10% or more and 70% or less and a maximum decarburization depth of 0.5 mm or less remains on the outer ring outer diameter, and no decarburized layer remains on the raceway surface. The present invention provides a rolling bearing race ring.

Here, the surface decarburization rate (D) is a rate of change of the carbon content of the finished product surface with respect to the carbon content of the bearing material, and is a value represented by the following equation (1). However, the above surface carbon amount is the carbon amount in the portion where decarburization occurs most in the entire circumferential direction.

The present invention is based on the idea that the decarbonized layer is positively left in the outer ring outer diameter portion and the inner ring inner diameter portion as a finished product by changing the idea from the conventional one, so that the CRF processing can be performed at a high pressure during the production of the bearing ring. This prevents fine cracks at the groove shoulder and the like, and significantly reduces the amount of cutting, thereby improving the machinability. Here, as described later, in the rough ring after the CRF processing, the decarburized layer exists most on the outer surface portion of the outer diameter, and the other portions are few.

As a result, a bearing ring whose manufacturing cost can be reduced as compared with the prior art is obtained. Furthermore, by limiting the surface decarburization rate and the decarburization depth of the inner ring inner diameter portion and the outer ring outer diameter portion in the finished product to the above ranges, even if a decarburized layer remains in the inner ring inner diameter portion and the outer ring outer diameter portion. The fretting resistance characteristics of the inner ring inner diameter portion and the outer ring outer diameter portion can be set to the same performance as that of a conventional bearing ring from which the decarburized layer is completely removed.

Although the raceway surface greatly affects the bearing life, in the present invention, the decarburized layer does not remain on the raceway surface as in the prior art, so there is no adverse effect on the bearing life. Next, the basis of the present invention will be described.

The present inventors have investigated the effect of the decarburized layer on the bearing function depending on the amount and depth thereof, and have obtained the following results. If the amount of decarburization on the bearing raceway surface increases, the hardness after quenching decreases and the retained austenite decreases, and the life of the bearing decreases. In particular, in the bearing life due to damage to the surface starting point simulating a failure in the market, the bearing life is reduced even if a small amount of decarburization remains on the raceway surface.

The inner diameter of the inner ring and the outer diameter of the outer ring to be fitted to the shaft or the housing may be liable to cause abrasion or fretting due to a decrease in hardness after quenching when the amount of decarburization increases, but is more remarkable as the life of the bearing increases. In addition, it has been found that there is a limit to the amount and depth of decarburization in which the above-mentioned effects of wear and fretting occur.

In addition, the seal groove and the chamfer
There was no significant effect of decarburization. Furthermore, the influence of the amount and depth of the decarburized layer on the processing characteristics was investigated, and the following results were obtained.

In the CRF processing, it has been found that normally, if the surface is decarburized, the hardness is reduced, so that the deformation resistance is reduced and good processing can be performed. It has also been found that in turning, workability is improved by the presence of an appropriate amount of decarburization.

From the above, it is better that the decarburized layer remains in an appropriate amount on the raceway surface other than the raceway surface which directly affects the rolling life, thereby improving the workability at the time of manufacturing, lowering the manufacturing cost, and reducing the cost at each position of the bearing inner and outer rings. It has been found that adjusting the decarburization amount to an appropriate value does not impair the bearing function. That is, it has been found that there is an optimum decarburization amount at each position of the bearing inner and outer rings.

Next, the reason for limiting the numerical value of the finished bearing product of the present invention will be described. A decarburized layer with a surface decarburization rate of 10% or more and 50% or less and a decarburization depth of 0.4 mm or less at the inner ring inner diameter part of the completed bearing. The inner diameter surface of the bearing inner ring is fitted with shafts as a necessary function. Anti-fretting properties.

If the surface decarburization rate is too high, the hardness will be too low, and the deeper the decarburization depth, the wider the range of the maximum decarburization position, and the fretting resistance will deteriorate. The decarburization amount was investigated for the optimum range that exhibits the same anti-fretting characteristics as the raceway where decarburization does not remain. (See Table 1 below). In addition, the product of the present invention retains an appropriate amount of decarburization, thereby lowering the surface hardness, improving the cold workability, and extending the life of the CRF and the cutting tool.

For the above reasons, the decarburized layer remaining on the inner ring inner diameter portion of the finished product has a surface decarburization rate of 10%.
The maximum decarburization depth is limited to not more than 50% and not more than 0.4 mm.

However, as can be seen from Table 1, the surface decarburization rate tends to be worse as the surface decarburization amount increases.
% And the decarburization depth is preferably within 0.3 mm. In addition,
Even if the decarburization amount is smaller than the range of the present invention, the anti-fretting property is good, but the cold workability is deteriorated as compared with the present invention, so that a raceway whose production cost is higher than that of the present invention is obtained.

The outer surface of the outer ring has a decarburization rate of 10% or more and 70% or less and a decarburization layer having a decarburization depth of 0.5 mm or less. And fretting resistance to the fit.

As described above, if the surface decarburization rate is too high, the hardness is too low, and as the decarburization depth increases, the range of the maximum decarburization position increases and the fretting resistance increases. The characteristics deteriorate.

With respect to the amount of decarburization, an optimum range for exhibiting fretting resistance equivalent to that of a bearing ring in which decarburization does not remain was investigated, and no decarburization remained in the range of decarburization of the product of the present invention. It has been found that it exhibits anti-fretting properties equivalent to those shown in Table 2 below. In addition, the product of the present invention retains an appropriate amount of decarburization, thereby lowering the surface hardness, improving the cold workability, and extending the life of the CRF and the cutting tool.

From the above, as the decarburized layer remaining on the outer diameter of the outer ring, the surface decarburization rate% was limited to 10% or more and 70% or less, and the maximum decarburization depth was limited to 0.5 mm or less. However, as can be seen from Table 2, since the surface decarburization amount tends to become worse as the surface decarburization amount increases, it is desirable that the surface decarburization rate is 50% or less and the decarburization depth is 0.4 mm or less.

Although the fretting resistance is good even if the amount of decarburization is smaller than the range of the present invention, the cold workability is deteriorated as compared with the present invention, and the raceway whose production cost is higher than that of the present invention. Becomes

Here, since the surface decarburization ratio is a value larger than 0, the decarburization depth of the inner ring inner diameter portion and the outer ring outer diameter portion is a value larger than 0. Here, the rolling wheel is, for example, a hot forging step of hot forging a round bar material to form a rough ring, a step of performing a soft annealing to spheroidize the carbide with respect to the rough ring, and after the soft annealing A cold rolling process to increase the diameter of the rough ring to form the inner ring and the outer ring, and a finish turning process to finish the shape of the rough ring after the cold rolling process to the required shape as a raceway ring. Manufactured by a quenching and tempering process to obtain the required hardness as a bearing by performing quenching and tempering, and a grinding process to grind the raceway surface and the mating surface.In the finish turning process, the inner ring inner diameter and outer ring outer diameter are manufactured. Not to be turned, leaving a decarburized layer with a surface decarburization rate of 10% or more and 50% or less and a maximum decarburization depth of 0.4 mm or less on the inner ring inner diameter of the finished bearing, and a surface decarburization on the outer ring outer diameter. The largest charcoal percentage is 10% or more and 70% or less As coal depth to leave the decarburized layer within 0.5 mm, it can be produced by adjusting up mainly annealing.

[0035]

Next, embodiments of the present invention will be described with reference to the drawings. In this embodiment, an inner and outer ring of a deep groove ball bearing will be described as an example.

First, the manufacturing method will be described. Manufacturing is performed by the following steps as shown in FIG.
As the bearing material, a rolled steel bar is used as it is (S1). The material is, for example, bearing steel (SUJ2), which has been most frequently used in bearings and almost used in deep groove ball bearings.

First, as shown in FIG.
1 is subjected to hot forging using a multi-stage former to form rough rings 22 and 23 serving as inner and outer rings (S2). Next, the rough rings 22 and 23 are subjected to softening annealing for spheroidizing carbides to lower the hardness and improve the microstructure (S3). In the steps so far, a decarburized layer is formed.

Subsequently, CRF processing is performed (S4). At the time of this CRF processing, the grooves 31b and 32a are formed. This reduces the machining allowance on the raceway surface. Further, by performing the high pressure processing in a state where the decarburized layer is present, even if the groove or the like is formed, there is no possibility that a fine crack is generated in a groove shoulder or the like.

Next, sizing (S5), that is, correction of the outer diameter is performed. Then, CRF ring 3 after CRF processing
Turning (S6) is performed to remove the oxidized and decarburized layers generated at the time of forging and annealing on at least the raceway surfaces of the first and second raceways. In some cases, burrs and the like formed during hot forging before turning are removed by grinding.

At this time, the inner ring inner diameter portion 32b and the outer ring outer diameter portion 31a are not subjected to turning but leave a decarburized layer for optimization. Thereby, the turning workability is improved.

Next, quenching and tempering are performed to obtain the hardness required for the bearing (S7). Then, the inner and outer races as finished products are manufactured by grinding the raceway surface and the mating surface (S8).

Here, in the inner ring inner diameter portion as a finished product,
A decarburized layer having a surface decarburization rate of 10% or more and 50% or less and a maximum decarburization depth of 0.4 mm or less remains, and a surface decarburization rate of 10% or more and 70% in the outer diameter portion of the outer ring. In the following, a decarburized layer having a maximum decarburization depth of 0.5 mm or less is left.

Since the decarburized layer is mainly generated up to the annealing step, particularly in the annealing step, the decarburized amount within the above range is determined as follows.
This can be mainly achieved by adjusting the annealing conditions in the annealing step. When the inner and outer races, which are races, are manufactured as described above, the manufacturing cost can be reduced by omitting the turning of the inner race inner diameter portion 32b and the outer race outer diameter portion 31a in the finishing turning process. Here, as will be described later, the outermost portion of the outer ring 31a has the largest amount of decarburized layer, which is particularly effective because the turning of that portion is omitted. In addition, the decarburization amount of the outer ring outer diameter portion 31a can also be adjusted at the time of grinding.

Furthermore, by leaving decarburization in an appropriate amount, the CRF workability, the finish of the raceway surface shape, the finish turning work for forming the seal groove and adjusting the end face are improved, and the cost can be further reduced.

In other words, for a raceway which is fully turned after CRF processing, a decarburized layer is left in an appropriate amount on the raceway surface other than the raceway surface which directly affects the rolling life. In this case, the workability can be improved, and the bearing ring of the rolling bearing whose manufacturing cost is reduced can be provided. Moreover, by optimizing the remaining decarburized layer,
Deterioration of anti-fretting characteristics at the outer ring outer diameter portion and the inner ring inner diameter portion required for a rolling bearing is prevented. Further, as described above, the optimization of the decarburized layer leads to the improvement of the workability described above and the improvement of the life of the cutting tool.

That is, the bearing ring of this embodiment can greatly reduce the manufacturing cost without deteriorating the quality as a bearing function. Here, among the steel rolling bearings that are subjected to grinding after heat treatment, the present inventors took an example of the inner and outer rings of a deep groove ball bearing, and investigated the material and each manufacturing process in detail regarding the manufacturing cost thereof, and described the following. The result was obtained.

Most of the deep groove ball bearings have an outer ring outer diameter of about 20 mm to about 200 mm, which is generally called a parallel diameter, and are produced in large quantities at low cost. Therefore, compared to heat treatment, shots, and the like that can simultaneously process many bearings, the reduction in the number of steps of grinding and turning for each bearing has a large cost reduction effect.

In order to perform mass production, it is also important to reduce the cost due to the yield of materials. Forging blanks (scraps) can be reduced by using CRF processing, or grooves can be formed on the raceway surface. It is effective to reduce the turning allowance.

In the conventional precision CRF processing for completely finishing the raceway groove and seal groove shape, the cost of full-turning before CRF processing, the problem of cracking due to high pressure without a decarburized layer, and the cost of extending the processing time of CRF processing In consideration of the increase, it is cheaper to perform the turning after the CRF processing.

From the above, from the viewpoint of reducing the manufacturing cost of the bearing ring, it is most preferable to adopt the CRF processing and to minimize the number of turning steps after the CRF processing without performing the turning processing before the CRF processing. Found to be effective.

Next, the findings obtained by the present inventors regarding the optimization of the remaining decarburization amount will be described. When hot forging is applied in the manufacturing process of the inner and outer rings of deep groove ball bearings, depending on the cooling rate and the alloy composition of the bearing material, in most cases, a pearlite structure appears, adversely affecting the subsequent processing such as turning . Therefore, the hardness must be reduced by annealing and the mouth structure must be improved. Conventionally, spheroidizing annealing is generally employed in bearing steel (SUJ2) having a carbon content of 1% as a material most commonly used for bearings.

Then, a heat treatment step before the CRF processing, that is, hot forging to be heated to 1100 to 1200 ° C. and upsetting, and 10 to 10 to 750 to 800 ° C.
By performing annealing for about 20 hours,
An oxidized layer and a decarburized layer are generated on the surface of the rough ring. Then, the CR before turning enlarged in diameter by the subsequent CRF processing
The oxidized layer and the decarburized layer remain almost as they are on the surface of the F ring. If an oxidized layer or decarburized layer remains on the surface of the finished bearing, the function of the bearing, such as life or wear, may be reduced. The coal seam had been removed.

First, the CRF of a general deep groove ball bearing is used.
The amount of decarburization in each manufacturing process was investigated in detail from the raw material by the manufacturing method of processing (in the case of manufacturing in the process shown in FIG. 1).
Here, as a material, a bearing steel (SUJ2), which has been most frequently used for a bearing in the past and most of a deep groove ball bearing has been used. To determine the amount of decarburization, use a cross
This was performed by measuring characteristic X-rays of carbon by X-ray analysis. Note that an X-ray measuring device (trade name: EPMA-1600) manufactured by Shimadzu Corporation was used for the measurement.

In general, as-rolled round bar steel is used because of its advantageous material cost. Therefore, a certain degree of decarburization has already occurred from the steelmaking to the rolling process. Next, FIG. 6 shows the measurement results of the maximum decarburization amount after hot forging.

In FIG. 6, the horizontal axis represents the distance (m) from the surface.
m), and the vertical axis indicates the carbon concentration (% by weight) (the same applies to FIGS. 7 and 8 described later). Also, during hot forging, about 1
Decarburization is increasing during upset molding by heating to 100-1200 ° C.

Also, as a result of measuring the amount of decarburization of the rough ring (forged ring) after hot forging, there was a variation in the amount of decarburization depending on the measurement position, and the end surfaces of the outer ring outer diameter and the inner ring outer diameter (FIG. 2).
Since the decarburization is large in (B) 22a and 23a), one of the causes is considered to be the accumulation of the decarburization amount from the raw material. Here, FIG. 2 shows a hot forging process in the case where the CRF processing is adopted. According to an investigation, the outer diameter portion 21a of the round bar material 21 shown in FIG. In addition, when the material 21 is hot forged, the outer diameter surfaces 22a and 23a of the forged ring in FIG. In particular, it was confirmed that a large amount of decarburization tended to remain in the widthwise center of a portion 22a corresponding to the outer ring outer diameter portion 31a.

Further, the present inventors conducted an investigation of the decarburization amount at each position on the circumference, and confirmed that even in the maximum decarburization portion (the center position of 22a), there was also variation in the circumferential direction. .

Next, the amount of decarburization after annealing in a nitrogen atmosphere, which is generally performed with a bearing generally called a parallel diameter, was measured, and the result shown in FIG. 7 was obtained. In the annealing process, the heating temperature is 7
It is as low as 50-800 ° C, but it is about 10-
Since the treatment was performed for about 20 hours, the maximum decarburization amount was greatly increased even in a nitrogen atmosphere. In other words, it became clear that the main cause of decarburization was the annealing process. However, the amount greatly depends on the annealing conditions, mainly the annealing atmosphere. That is, the desired decarburization amount can be set by appropriately setting the annealing conditions.

In some cases, annealing after forging is performed in the air without using an atmosphere. In such a case, the surface is violently oxidized and decarburized to a rough state, and the surface is oxidized by shot peening or shot blasting. After the layer is removed, further turning with a large allowance including the decarburized layer is required. That is, in the air annealing, the removal step of the surface oxide layer by shot blasting or the like and the allowance for the turning work increase, and as a result, the cost increases. For this reason, in a bearing generally called a uniform diameter, atmospheric annealing is hardly performed in order to reduce a cutting allowance.

In order to extremely reduce the amount of decarburization, vacuum annealing or annealing in a carburizing atmosphere may be adopted. However, significant costs are required for equipment setting, control technology, equipment maintenance, and the like.

Therefore, a method in which an appropriate amount of an inert gas such as nitrogen is introduced into a furnace to perform annealing is advantageous from the viewpoint of reducing manufacturing costs. Here, as a result of measuring the decarburization amount of the rough ring (forged ring) after annealing, there is a variation in the decarburization amount depending on the measurement position as in the case of forging, but the decarburization is particularly large in the outer ring outer diameter portion 31a. In addition, the amount of decarburization tended to increase from the raw material, and the variation further increased.

Next, when the decarburization amount at each position after the CRF processing was measured, the results shown in FIG. 8 were obtained. Here, FIG.
(A) is the maximum value of the outer diameter 31a of the outer ring, which is almost the same as the maximum decarburization amount after annealing in FIG. 7, but is slightly reduced in depth by rolling by CRF processing. On the other hand, FIG. 8 (B) shows the maximum value in the outer ring groove 31b, but the outer ring groove has a relatively small decarburization amount, and has been subjected to the strong processing for the CRF groove processing, so that the decarburized layer has a shallow depth. Is running low. FIG. 8 (C) shows the maximum value in the inner raceway groove 32a. The inner raceway groove is a position where the decarburization amount is relatively large, but the decarburization layer is shallow and small due to the heavy working. FIG. 8 (C) shows the maximum value at the inner ring inner diameter 32b. The inner ring inner diameter is a position where the decarburization amount is small, but the processing degree is low.
Somewhat deep.

From the above, when a forged ring manufactured by hot forging is subjected to CRF processing after annealing, large decarburization remains in the outer ring outer diameter portion 31a, but a small amount of decarburization in other positions. Was. This means that, as in the present invention, in a raceway in which an appropriate amount of decarburized layer is positively left in the outer ring outer diameter portion 31a, the amount of cutting is greatly reduced as compared with the case where the entire surface is cut. It greatly contributes to the improvement of cutting life and the life of cutting tools. However, for the other raceway surface shape finishing, seal groove forming, and end face adjustment, a minimum necessary finish turning is required.

Here, the measured decarburization amount is the maximum value of the position in the circumferential direction, and is present not partially but entirely. On the other hand, as a result of investigating the state of use of the parallel-diameter ball bearings in the market, most of them showed the fatigue state of the surface damage type.

Then, when the surface decarburization rate of the raceway surface was changed and a foreign matter mixed lubrication test in which damage was caused at the starting point of the surface was performed, the result shown in FIG. 9 was obtained. The test conditions in FIG. 9 will be described later.

As can be seen from FIG. 9, if even a small amount of decarburization remains on the raceway surface, the life is sharply reduced, so that decarburization cannot be left on the raceway surface. However, in the manufacturing method of the present embodiment, since the turning is performed to finish the shape of the raceway surface, the decarburized layer can be sufficiently removed together with the grinding after the heat treatment. That is,
The bearing life is equivalent to that of conventional bearings.

In the above description, a basic experiment was conducted using SUJ2 as a material, but this is not a limitation as long as the required quality as a bearing can be obtained by quenching and tempering. By setting the components of the bearing material as follows, the quality required for the bearing can be obtained.

That is, carbon is an important element for obtaining hardness and carbide necessary for bearings, and at least 0.8 to obtain sufficient hardness and carbide area ratio necessary for life.
% Or more is necessary. However, when the content exceeds 1.2%, generation and segregation of giant carbides during steelmaking become strong.
In the soaking treatment performed with two materials, giant carbides and segregation may not be sufficiently adjusted, so that carbide refinement in subsequent warm rolling becomes insufficient.

For the above reasons, the carbon content of the material is 0.8%
It is desirable that the amount is not less than the amount% and not more than 1.2% by weight. Si
Is an element that acts as a deoxidizer during steelmaking of the material, improves hardenability and strengthens base martensite, and is an effective element for extending the life of bearings. 0.1% by weight is required. But,
If the Si content is too large, the workability including machinability and forgeability deteriorates, so the upper limit is desirably 0.5% by weight or less.

For the above reasons, the Si content of the material is 0.1%
It is desirable that the content be not less than 0.5% by weight and not more than 0.5% by weight. Mn
Is an element that improves the hardenability, but at least 0.2% by weight is necessary to achieve the effect. However, Mn
Is also an element that strengthens the ferrite of the material, and particularly when the carbon content of the material is 0.8% or more, the cold workability is remarkably reduced when the Mn content exceeds 1.1%. It is desirable to set it to 1.1%.

Cr is an element that strengthens the matrix, such as improving hardenability and tempering softening resistance, and requires at least 0.1% by weight to exert its effect. However, when the content exceeds 1.8% by weight, the generation and segregation of giant carbides during steelmaking become strong, and the giant carbides and segregation cannot be sufficiently adjusted by the soaking process which is usually performed with SUJ2 material. Carbide refinement in the subsequent warm rolling becomes insufficient.

For the above reasons, the Cr content of the material is desirably 1.0% by weight or more and 1.8% by weight or less.

[0073]

Next, examples showing the validity of the present invention will be described. About the surface decarburization rate and life of the raceway surface The present inventors have conducted a detailed investigation of the usage of the ball bearings in the market, and as a result, it is generally considered to be a clean environment except for some pure clean environments. Most of the grease-filled ball bearings with seals also showed surface damage type fatigue.

Therefore, in order for a bearing to have a sufficient durable life, it must have a sufficient life to damage the surface starting point. Therefore, we conducted a lubrication test under contaminant contamination, which damages the surface starting point, by changing the surface decarburization rate of the raceway surface.

Here, the material is SUJ2, and the bearing manufactured and evaluated for its function is a deep groove ball bearing 6304 or a thrust test piece. The conditions are as follows.・ Heat treatment condition of thrust test piece: temperature 810 ° C or higher to 8
After holding for 0.5 to 1 hour at 50 ° C or less, quenching is performed,
Next, tempering was performed at 160 to 200 ° C. for 2 hours.

-Life test conditions under lubrication with foreign substances mixed therein: "Special Steel Handbook" 1st edition (edited by Denki Steel Research Institute, Rigakusha, 1969)
May 25, 2013) Using a thrust type bearing steel life tester described on pages 10 to 21 and using SUJ2 balls as rolling elements, cumulative stress repetition up to the time when flaking occurred in each sample A Weibull plot is created by investigating the number of times (life), and each L is calculated from the result of each Weibull distribution.
Ten lifetimes were determined.

The test conditions are as follows. Test surface pressure: Maximum 4900 MPa Revolution: 3000 C.I. P. M. Lubricating oil: # 68 turbine oil Contaminating foreign matter: Composition: Stainless steel powder Hardness: HRC50 Particle size: 65 to 120 μm Contaminated amount: 300 ppm in lubricating oil The results of the test are as shown in FIG.

As shown in FIG. 9, if even a small amount of decarburized remains on the raceway surface, the life is sharply reduced, so that decarburization cannot be left on the raceway surface. However, in the manufacturing method based on the embodiment for manufacturing the bearing ring of the present invention,
Turning is performed to finish the raceway surface. As a result, the decarburized layer is sufficiently removed together with the grinding after the heat treatment.

Regarding the surface decarburization rate and anti-fretting characteristics of the inner ring inner diameter and outer ring outer diameter, the inner diameter surface of the bearing inner ring has a required function of anti-fretting characteristics against fitting with shafts, and the outer ring outer diameter surface is a housing. Fretting resistance to fitting with other types.

Thus, the anti-fretting characteristics were evaluated by changing the surface decarburization rate of the inner ring inner diameter portion and the outer ring outer diameter portion. The bearing was a deep groove ball bearing 6304. In the test, 20 bearings under each condition were evaluated, and the occurrence of fretting was confirmed at each test time to show the occurrence rate. Each condition is as follows.

Heat treatment conditions of 6304: After holding at a temperature of 810 ° C. to 850 ° C. for 0.5 to 1 hour, quenching was performed, and then tempering was performed at 160 to 200 ° C. for 2 hours.

Evaluation conditions for anti-fretting characteristics: The outline of the tester and the fluctuation pattern of the rotation speed were as shown in FIG. FIG. 10 shows a testing machine, and in FIG.
Reference numeral 1 denotes a test bearing, reference numeral 3 denotes a shaft to which an inner ring is fitted, and reference numeral 2 denotes a housing to which an outer ring is fitted. Then, the rotation of the motor 7 is transmitted from the pulley 5 to the belt 6, the pulley 4, and the shaft 3, and the inner ring of the test bearing 1 is rotated. The number of rotations is repeated by changing the number of rotations of the motor 7 as shown in the pattern of FIG. A load is applied to the test bearing 1 from the motor 7 via the pulley 5 through the belt 6, the pulley 4, and the shaft 3 when the air cylinder 9 pushes down the motor base 10.

The test conditions are as follows. Test load: 3200 MPa Rotation speed: 5000-8000 rpm Fluctuation Lubricating oil: Albania grease 2 (manufactured by Showa Shell Sekiyu) Fit: 1) In the case of the inner ring inner diameter evaluation test, the test is performed with the shaft 3 lightly pressed up to a clearance of -10 to 20 μm. .

2) In the case of the outer ring outer diameter evaluation test, the test is performed in a state of being lightly pressed into the aluminum housing 2 at ± 0. Table 1 shows the results of evaluating the anti-fretting properties with respect to the surface decarburization rate and decarburization depth of the inner ring inner diameter of the finished product.

[0085]

[Table 1]

In Table 1, the products of the present invention exhibited the same anti-fretting characteristics as those in which no decarburization remained. That is, as can be seen from Table 1, by setting the amount of decarburization within the range of the present invention, anti-fretting characteristics equivalent to those in which decarburization did not remain were exhibited.

On the other hand, if the decarburization rate is higher than the range of the present invention, the hardness is too low, and if the decarburization depth is deep, the range of the maximum decarburization position is widened, and the fretting resistance is deteriorated. Resulting in.

That is, even if the surface decarburization rate is within the range of the present invention, if the decarburization depth exceeds the present invention as in No. 6, the anti-fretting property is deteriorated. . In addition, even if the decarburized layer falls within the range of the present invention, when the surface decarburization rate becomes larger than the range of the present invention as in No. 5, the anti-fretting characteristics deteriorate.

In addition, when conventional turning is performed to prevent decarburization from remaining on the surface of the finished product, the cost increases.
Further, if carburizing treatment or the like is performed in the annealing step in order to reduce the decarburized layer without turning, the cold workability is deteriorated as in NO. 7 and NO. 8 shown in Table 1. That is, NO. 7 and NO. 8 are out of the range of the present invention, but the fretting resistance is good due to the small amount of decarburization, but the cold workability deteriorates as described later, The cost is higher than the race of the present invention.

As described above, the inner ring inner diameter of the finished product which can reduce the production cost most requires a decarburized layer with a surface decarburization rate of 10% to 50% and a decarburization depth of 0.4 mm or less. It turns out that it becomes.

However, from Table 1 above, since the surface decarburization amount tends to become worse as the surface decarburization amount increases, it is desirable that the surface decarburization rate is 40% or less and the decarburization depth is 0.3 mm or less. Next, Table 2 shows the results of evaluating the anti-fretting characteristics with respect to the surface decarburization rate and the decarburization depth in the outer ring outer diameter of the finished product.

[0092]

[Table 2]

As can be seen from Table 2, by setting the amount of decarburization within the range of the present invention, the same anti-fretting characteristics as those without residual decarburization were exhibited. . On the other hand, those having a decarburization rate and decarburization depth outside the range of the present invention have deteriorated fretting resistance, and those having no decarburization remaining on the finished product surface have deteriorated cold workability. Would.

That is, even if the surface decarburization rate is within the range of the present invention, if the decarburization depth exceeds the present invention as in No. 6, the anti-fretting characteristics are deteriorated. . In addition, even if the decarburized layer falls within the range of the present invention, when the surface decarburization rate becomes larger than the range of the present invention as in No. 5, the anti-fretting characteristics deteriorate.

Further, in the case of conventional turning in order to prevent decarburization from remaining on the surface of the finished product, the cost increases.
Further, if carburizing treatment or the like is performed in the annealing step in order to reduce the decarburized layer without turning, the cold workability is deteriorated as in Nos. 7 and 8 shown in Table 2. That is, NO. 7 and NO. 8 are out of the range of the present invention, but the fretting resistance is good because the amount of decarburization is small, but the cold workability is deteriorated as described later, The cost is higher than the race of the present invention.

As described above, the outer diameter of the outer ring is such that the surface decarburization rate% is 10% or more and 70% or less and the decarburization depth is 0.5 mm
The decarburized layer within is required. However, as shown in Table 2, since the amount of surface decarburization tends to deteriorate as the amount of surface decarburization increases, it is desirable that the surface decarburization rate is 50% or less and the decarburization depth is 0.4 mm or less.

Regarding CRF tool life evaluation In the CRF processing, the mandrel shown at 12 in FIG. 5 is liable to wear and damage, and is greatly reflected in the processing cost as a consumable part.

From this viewpoint, the evaluation was made in the case where the wear of the mandrel was 0.2 mm or more, the mandrel had a step in the case of the inner ring, and the shape of 32b in FIG.
In the case of the outer ring, the life was defined as the case where the groove shape indicated by 31b in FIG.

Next, the test conditions will be described. CRF tool life evaluation condition: Processing machine: CRF70 manufactured by Kyoei Seiko Processing load: 5 to 7 ton Lubricant: Press Homer PZ13 (manufactured by Sanko Chemical) Diameter expansion ratio: outer ring = 1.4 to 2.0 times, inner ring = 1. 1 to 1.4 times Processing speed: 600 to 800 pieces / hour The test results are as shown in Tables 1 and 2 above.

Those with much decarburization and low hardness showed a long life. However, although Nos. 5 and 6 in Tables 1 and 2 show a long life, the anti-fretting characteristics are low. No. 7 and 8 shown in Tables 1 and 2 having a decarburization rate lower than the range of the present invention.
Is too high in hardness to degrade cold workability.

Turning Tool Life Evaluation Here, in high-speed turning, tool wear is severe, and this is largely reflected in the machining cost as a consumable part.

From this viewpoint, the evaluation was that the tool wear was 0.2%.
mm or more, the roughness of the turning surface is deteriorated, the tool chatters, and the cutting resistance is increased. The test conditions are as follows.

Turning tool life evaluation condition: Processing machine: High-speed lathe Tool: P10 (JIS B4053) Cutting speed: 200 to 250 m / min Feeding amount: 0.2 to 0.3 mm / rotation Cutting depth: 0.6 to 1.0mm Lubrication: Koshiro oil NO. 3 (manufactured by Koshiro Chemical Co., Ltd.) The test results are as shown in Tables 1 and 2 above.

As can be seen from this table, those with a large amount of decarburization and a decrease in hardness exhibited a long life.
NO. 5 had too low hardness and became sticky, and did not have a long life for the hardness. However, although No. 6 in Tables 1 and 2 shows a long life, the anti-fretting property is low.

Further, in Nos. 7 and 8 shown in Tables 1 and 2 where the decarburization rate is lower than the range of the present invention, the hardness is too high and the cold workability deteriorates.

[0106]

As described above, according to the present invention,
By leaving an appropriate amount of decarburized layer on the inner ring inner diameter and outer ring outer diameter on the raceway ring of rolling bearings manufactured by grinding after heat treatment, CRF workability, raceway surface finish, seal groove formation and end surface adjustment This has the effect of improving the finish turning workability and the like, and providing a bearing ring that can reduce the manufacturing cost as compared with the prior art.

Further, by optimizing the decarburized layer,
Even if the decarburized layer is left unlike the conventional case, the deterioration of the fretting resistance of the outer ring outer diameter portion and the inner ring inner diameter portion is suppressed, and since the decarburization does not remain on the raceway surface, the bearing life is the same as the conventional one.

[Brief description of the drawings]

FIG. 1 is a view showing a conventional manufacturing process.

FIG. 2 is a view for explaining manufacturing employing CRF processing.

FIG. 3 is a diagram for explaining CRF processing.

FIG. 4 is an explanatory view of forging when CRF processing is not adopted.

FIG. 5 is a diagram showing a manufacturing process according to the embodiment of the present invention.

FIG. 6 is a diagram showing the amount of decarburization after conventional hot forging.

FIG. 7 is a diagram showing the amount of decarburization after conventional softening annealing.

FIG. 8 is a view showing a decarburization amount of the conventional CRF processing,
(A) at the outer ring outer diameter portion, (B) at the outer ring groove, (C)
Indicates an inner ring groove, and (D) indicates an inner ring inner diameter portion.

FIG. 9 is a diagram showing a relationship between decarburization on a raceway surface and life.

FIG. 10 is a view showing a test machine.

FIG. 11 is a diagram showing a test pattern.

[Explanation of symbols]

 21 Material 22, 23 Rough Ring 31, 32 CRF Ring (Rough Ring) 31a Outer Ring Outer Diameter 31b Outer Ring Groove 32a Inner Ring Groove 32b Inner Ring Inner Diameter

Claims (1)

[Claims] In a bearing ring of a rolling bearing manufactured by performing a grinding process after a heat treatment, the inner surface of an inner ring of a completed bearing ring has a maximum decarburization depth of 10% or more and 50% or less at a surface decarburization rate. A decarburized layer of less than 0.4 mm
A decarburized layer with a surface decarburization rate of 10% or more and 70% or less and a maximum decarburization depth of 0.5 mm or less remains on the outer ring outer diameter, and no decarburized layer remains on the raceway surface. Rolling bearing raceway features. However, the surface decarburization rate (D) is a change rate of the carbon content of the finished product surface with respect to the carbon content of the bearing material, and is a value represented by the following equation (1). However, the above surface carbon amount is the carbon amount in the portion where decarburization occurs most in the entire circumferential direction.