JPH11347673A - Roller bearing, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost by hot-forging a round bar stock to form coarse rings of inner and outer rings, and effecting the hot ring rolling of the coarse rings without spheroidizing annealing to roll into the inner and other rings to omit the softening annealing and to reduce a turning margin. SOLUTION: A stock is hot forged to form coarse rings, and not CRF working but the WRF working is effected to the coarse rings to form inner and outer rings of a bearing. Annealing can be omitted, and the decarburizing quantity can be reduced to greatly reduce the turning margin 13d by the subsequent turning. After the hot forging of the stock, the WRF working is effected. Since the carbide is grain refined by the heating in a high temperature range, the spheroidizing speed of the carbide is remarkably increased, and when the heating to the specified working temperature is completed, the ring rolling is immediately started, and due to the subsequent gradual cooling, the conventional long annealing time can be reduced by half including the ring rolling time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing used in various places such as a motorcycle, an automobile, an agricultural machine, a construction machine and the like, and a method of manufacturing the rolling bearing. Related to rolling bearings such as bearings and self-aligning bearings.

[0002]

2. Description of the Related Art With regard to a method of manufacturing inner and outer rings of a deep groove ball bearing in which a grinding process is performed after a heat treatment, a ring rolling process (hereinafter referred to as CR) in a cold state is conventionally generally performed in consideration of a manufacturing cost.
F processing). For example,
No. 83872 discloses that by performing full-scale turning before CRF processing to make the shape and weight constant, and then to complete the shape of raceway surface grooves and seal grooves necessary for a deep groove ball bearing by precise CRF processing. There is disclosed an apparatus which can omit subsequent turning to further reduce the cost.

[0003] Also, in Japanese Patent Publication No. 2524156,
The ring is heated and subjected to roughing by hot rolling, and when the temperature drops as it is, precision warm rolling and forging are performed, resulting in good workability, no cracking, and good dimensional accuracy. The ring is said to be obtained. Further, there is disclosed a structure in which the structure is refined during subsequent quenching and heating to increase the toughness due to processing strain during warm working.

Japanese Patent Application Laid-Open No. Hei 9-176740 discloses that a ring-shaped material is expanded while forming ball grooves by hot ring rolling, and is immediately heated to a quenching temperature to adjust the outer diameter (sizing). There is disclosed a method in which quenching is performed by restricting the inner diameter of the mold or by restricting the inner diameter, that is, by combining corrective quenching with hot working with low dimensional accuracy, thereby achieving a cost reduction effect by omitting steps.

[0005]

Here, the ring rolling process will be briefly described with reference to the simplified diagram of FIG. 5. The rough ring 13 sandwiched between the forming roll 11 and the mandrel 12 is rolled by a load W. Then, the cross section becomes thinner, while the ring diameter increases. Thus, the diameter of a rough ring such as a forged ring or a turning ring is increased to form a rolled ring. Therefore, the thickness and the diameter expansion amount can be adjusted, but they are not constrained in the width direction, so that the lateral dimension control cannot be performed. Therefore, as shown in the cross-sectional view of the rolled ring 13 subjected to the ring rolling shown in FIG. 6, a protrusion 13a (portion shown by a mesh line) is formed in the ring width direction. In addition, in FIG. 6, 13n is an inner diameter surface of the ring to be rolled including a margin by the subsequent machining. The two-dot chain line shows the shape after machining, 13b is a race groove of the inner and outer rings, 13c is a seal groove, and the space between the ring inner diameter surface 13n and the shape of the two-dot chain line is used during machining. 13d of allowance
It is.

In the case of Japanese Patent Publication No. 6-83872, in which the ring rolling is performed in a cold state, in addition to such protrusion in the width direction, the edge of a seal groove or a race groove for forming a complicated shape is formed in a cold state. Minute cracks due to processing are likely to occur. Therefore, there is a problem that, before performing the precise CRF processing, the entire surface must be turned in order to adjust the dimensions in advance and to keep the volume constant, and further, after the CRF processing, the finish turning is required to remove cracks and the like. There is. In addition, when a complicated shape is precisely subjected to CRF processing, a long processing time is required, and there is a problem that the cost of ring rolling tends to increase.

In Japanese Patent Publication No. 2524156, processing is performed in the hot temperature range. However, in the hot temperature range, the degree of deformation of the material is reduced due to the reduced deformation resistance, and the structure is refined by the processing. The effect is considered to be small. Also,
Once heated sufficiently to the hot temperature range, the carbides melt and become small and spherical. Then, even if the subsequent warm working is performed, there is no effect particularly on the refinement of carbides, but only the austenite grains are refined by recrystallization at the time of quenching and reheating due to the working strain of the warm working. That is, in this case, it is not possible to extend the life of the bearing by making the structure, particularly the carbides, finer by working, and there is still room for improvement in that respect.

In Japanese Patent Application Laid-Open No. Hei 9-176740, since the working is performed in the hot region in the same manner as described above, it is considered that the effect of making the structure fine is small. Further, a method is disclosed in which quenching is performed as it is after hot working, but in that case, the structure is rather coarsened, and the spheroidization of the carbide may be insufficient. In addition, the rolling ring obtained by hot rolling and straightening and quenching the material ring must then be turned and finished one by one,
There is still room for improvement in terms of cost reduction.

The present invention has been made in view of the above-mentioned conventional unsolved problem relating to a method of manufacturing a bearing made of high carbon steel, which is subjected to grinding after heat treatment, and particularly to a method of manufacturing inner and outer rings. It is an object of the present invention to provide a rolling bearing and a method of manufacturing the rolling bearing, in which the carbide is refined by processing (hereinafter, referred to as WRF processing) to thereby excel in the function of the bearing and to reduce the manufacturing cost as compared with the related art.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the invention of a bearing manufacturing method according to the first aspect of the present invention is directed to a method of manufacturing a rolling bearing in which high carbon steel is hardened and heat-treated for grinding. In, to make a rough ring to be processed into an inner ring and an outer ring by hot forging from a round bar material, and then form and roll the crude ring as it is by warm ring rolling without spheroidizing annealing It is characterized by an inner ring and an outer ring.

According to a second aspect of the present invention, there is provided a rolling bearing, wherein the carbide on the surface of the finished product of the inner ring and the outer ring produced by the manufacturing method of the first aspect has an area ratio of 5% or more and 15% or less. And carbides having an average particle size of 0.5 μm or less with respect to the total carbides have an area ratio of 50% or more, and carbides having an average particle size of 1 μm or more have a total area ratio of 2% or less with respect to the total carbides. And the surface hardness is HV730 or more and 90.
0 or less.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (1) Regarding miniaturization of spherical carbides:
When high-carbon steel containing about 1.0% by weight of carbon, such as SUJ2 material, is hot-worked as it is after hot-working, most of the spherical carbide is 0.5 μm unlike the case where the high-carbon steel is spheroidized and annealed. The present inventors have found that the present invention is miniaturized, and have accomplished the present invention.

That is, in the case of high carbon steel containing about 1.0% by weight of carbon, such as SUJ2 material, which has been conventionally most frequently used as a material for bearing inner and outer rings, it is known that hot rolling is performed. If it is cooled later, it becomes a network cementite (carbide) and a pearlite structure. In this state, it is hard and difficult to work, so that it adversely affects subsequent machining processes such as turning. Therefore, softening annealing is performed before machining to lower the hardness and improve the microstructure. SUJ2
In the case of soft annealing in the case of a material, spheroidizing annealing is generally performed. For example, when manufacturing the inner and outer rings of a deep groove ball bearing, conventionally, a rough ring formed by hot forging at 1100 to 1200 ° C is formed at 760 to 820 ° C in an N ₂ gas atmosphere at 10 to 10 ° C.
Anneal for as long as 20 hours. When heated around the A1 transformation point in this general spheroidizing annealing treatment, a part of the network carbide is dissolved, the layered structure of pearlite is broken, and the carbide is spheroidized. As a result, the high carbon steel after the completion of the treatment has a structure in which spherical carbides are present in the ferrite base, and the carbides have an area ratio of at least half of which has an average particle size of 0.5 μm or more, and in some cases, 2 μm or more.
m or less. An oxide layer and a decarburized layer are generated on the surface of the rough ring.

As described above, the high carbon steel material is subjected to spheroidizing annealing after hot rolling or hot forging (hot working), and then to warm working or cold working such as ring rolling. Normally, carbides hardly become fine during the warm or cold working in that case. Further, even if cold working is performed without spheroidizing annealing or hot working is repeated after hot rolling or hot forging, the effect is hardly obtained. In addition, the oxidized layer and the decarburized layer generated on the surface of the rough ring remain as they are on the surface of the rolling ring subjected to the ring rolling. If the oxidized layer and the decarburized layer remain on the bearing surface, the bearing function such as life and wear may be deteriorated. Therefore, it is necessary to turn the entire surface of the rolling ring to remove the decarburized layer.

On the other hand, the bearing manufacturing method according to the present invention is characterized in that after hot working of a material, warm working is performed without performing spheroidizing annealing. This warm working promotes spheroidization of carbides and at the same time adds strong working, so that network cementite (carbide) and plate-like cementite in the pearlite structure are spheroidized while being refined, and after cooling, the carbide is finely spheroidized. Become an organization.
In other words, even if the already spheroidized structure is processed, the carbides hardly become finer, and even if spheroidizing annealing for softening is subsequently performed, the spheroidized structure is merely almost a normal spheroidized structure. Does not become fine even when cold-worked, but when the pearlite structure is warm-rolled as in the present invention, carbides can be made finer and finer and spheroidized.

Thus, in the bearing manufacturing method of the present invention, when performing the hot working as it is after the hot working of the material, the heating condition and the subsequent cooling rate are gradually cooled so that the temperature does not rise again. However, since it is sufficient to appropriately maintain the annealing temperature, it is possible to omit the conventional softening annealing performed after hot working. Here, first, in order to increase the spheroidization ratio of the steel structure, it is necessary to set heating conditions for warm working. 600 to prevent undissolved pearlite from remaining
On the other hand, in order to prevent a situation in which the austenite transformation amount becomes too large when the temperature is too high and pearlite is regenerated, it is necessary to carry out 820 ° C.
It is necessary to warm work below. For better softening, the spheroidization rate of the carbide is high, 680 ° C. or higher and 800 ° C.
The following is preferred. Furthermore, in order to lower the hardness after cooling, it is necessary to gradually control the cooling rate after warm working. The cooling rate is preferably as low as possible,
It is necessary to set the temperature to 5 ° C./Sec or less in order to sufficiently soften. However, considering the productivity and cost, 1 ° C /
Since it is necessary to set the cooling rate to Sec or higher, an appropriate cooling rate is in the range of 1 ° C./Sec to 5 ° C./Sec. For better softening, 3 ° C./Sec or less is desirable.

(2) Decarburization of the ring surface:
The inventors of the present application believe that it is necessary to consider the removal of the oxidized layer and the decarburized layer remaining on the rolling ring surface by the conventional general CRF processing, and therefore, the ring rolling processing of the general deep groove ball bearing is considered. The amount of decarburization in each production process in the production method incorporating the method was investigated in detail. The material used was bearing steel (SUJ2) which is most frequently used for bearings, and particularly used for most of deep groove ball bearings. The method for examining the decarburization amount was to measure the characteristic X-ray of carbon by X-ray analysis of the cross section. Note that an X-ray measuring device (trade name: EPMA-1600) manufactured by Shimadzu Corporation was used for the measurement. Since a rolled round bar material, which is generally advantageous in terms of material cost, is used as the material, a certain degree of decarburization has already occurred in the rolling process from steelmaking.

FIG. 7 shows the measurement results of the maximum decarburization amount after hot forging.
Shown in In FIG. 7, the horizontal axis is the distance from the surface (mm).
The vertical axis indicates the carbon concentration (% by weight) (the same applies to FIGS. 8 to 10 described later). About 1100-1 during hot forging
It can be seen that the surface was slightly decarburized during upsetting by heating to 200 ° C. FIG. 8 shows the results of measurement of the amount of decarburization after annealing in a generally performed nitrogen (N ₂ ) atmosphere. As will be described later, in the annealing step, the heating temperature is as low as about 760 to 820 ° C.
In order to perform a long-time soft annealing treatment up to 20 hours,
The maximum decarburization amount had increased significantly. From this result, it became clear that the main cause of decarburization was the annealing process. FIG.
Fig. 7 shows the measurement results of the amount of decarburization after CRF rolling in the next step of hot rolling. Although the depth becomes slightly shallower due to the rolling by the CRF, the decarburization result which is almost the same as the maximum decarburization amount after annealing shown in FIG. 8 appears. From these results, in the forged ring manufactured by hot forging, the decarburization greatly increases in the subsequent long annealing process of 10 to 20 hours, which is conventionally performed. It can be said that full turning with a sufficient turning amount is inevitable.

On the other hand, in the bearing manufacturing method according to the present invention, the raw material is hot forged to form a rough ring, and the rough ring is subjected to WRF processing instead of CRF processing. By forming the inner and outer rings, annealing can be omitted to reduce the amount of decarburization.
As shown in FIG. 0, the turning allowance 1 by the subsequent turning process
3d can be greatly reduced compared to the conventional one.

FIG. 1 shows a process diagram of a method for manufacturing a rolling bearing according to the present invention.
Perform F processing. Since the carbides are refined by heating in the warm temperature range in the processing, the spheroidizing speed of the carbides is remarkably increased, and as soon as the heating to the predetermined processing temperature is completed, the ring rolling processing is started, and thereafter, the cooling is gradually performed. Because
It is possible to halve the long-time annealing treatment in the conventional softening annealing, including the processing time for rolling and forming the ring. Thus, according to the method for manufacturing a rolling bearing of the present invention,
In the spheroidizing annealing process, the annealing time can be reduced by half and the ring rolling can be completed at the same time. For comparison, FIG. 2 shows a process chart for performing conventional CRF processing.

In the process of the present invention, since the soft annealing step in FIG. 2 is omitted, a situation in which decarburization increases due to long-time holding during annealing does not occur. FIG. 11 shows the measurement results of the decarburization amount after the WRF processing of the present invention. It is almost equal to the maximum decarburization amount after hot forging in FIG. 7, and the increase in decarburization can be extremely suppressed in the WRF processing. In addition, hot working has higher deformability than cold working, and relatively precise working can be performed in a short period of time. Especially, it is possible to form the bearing groove precisely without cracking. Accordingly, it becomes possible to extremely reduce the machining of the groove portion where the machining time is long in the turning process.

Further, the decarburization amount shown in FIG. 7 is the outer diameter portion of the outer ring which is the maximum, and the decarburization amount is further reduced in the groove portion. In some cases, only the grinding after the heat treatment is performed without turning the groove portion. It is also possible to finish with. (3) Manufacturing costs: In recent years, rolling bearings
While demands for high load and light weight are strong and the use environment is severe, demand for low cost is also increasing. Therefore, the inventors of the present application performed a workability evaluation that has an important relationship with cost, in addition to a function evaluation assuming a condition in which a use environment is relatively severe. A description will be given of a study performed by the inventors of the present invention on “the manufacturing cost of a steel bearing inner and outer ring in which grinding is performed after heat treatment”.

That is, the inventors of the present application have described the inner and outer rings of a bearing manufactured from a steel material by various conventional manufacturing methods.
Each manufacturing process was investigated in detail and the following results were obtained. Generally, bearings having an outer ring outer diameter of about 20 mm to about 200 mm, which is a so-called parallel diameter, are mass-produced in large quantities at low cost. Therefore, compared to heat treatment that can process many bearings at once at the same time or subsequent shot peening process, reducing the number of grinding and turning processes to process each bearing after heat treatment is more cost effective. large.

Since mass production is performed, it is also important to reduce the cost by reducing the material yield. Forging blanks can be made smaller (reduce scrap) by ring rolling, and grooves can be formed on the inner and outer raceway surfaces. It is effective to add a shape or the like to reduce the turning allowance.

The complete finishing of the race grooves and seal groove shapes by precise ring rolling processing involves the cost and cracking problem of full-turning before rolling processing, and the cost increase due to prolonged time for precision processing. Not very advantageous when considered. Rather, turning after ring rolling is less costly. In other words, it has been found that when manufacturing costs are reduced, it is optimal to reduce the number of turning steps after ring rolling as much as possible without performing turning before ring rolling to make the blank constant.

The critical significance of limiting the numerical values of the inner and outer rings of the rolling bearing manufactured by the method of the present invention will be described below. (A) [Carbide area ratio on finished product surface: 5% or more and 15% or less]: In ball bearings and especially spherical roller bearings, contact wear occurs on the inner and outer races due to insufficient lubrication and sliding of rolling elements. It is generally known that the higher the hardness of the surface, and the greater the amount of carbide present on the wear surface, the more effective the wear resistance. FIG. 3 shows the relationship between the wear resistance assuming a poor lubrication state and the area ratio of carbide. When the area ratio of carbide on the surface is 5% or more, the wear resistance is improved. On the other hand, the inner and outer rings are roll-formed by WRF processing, but the mandrel 12 shown in FIG. 5 shown above is worn or damaged. FIG. 4 shows the relationship between the workability and the area ratio of carbide. When the area ratio of carbide on the surface is 15% or more, the life of the mandrel is reduced. From the above, the carbide area ratio on the surface of the finished product is set to 5% or more and 15% or less. However,
In order to sufficiently obtain both wear resistance and workability, the carbide area ratio on the surface of the finished product is desirably from 9% to 12%. (B) [Area ratio of carbide having an average particle diameter of 0.5 μm or less on the surface of the finished product; 50% or more] Surface damage such as sliding wear and peeling that occurs on bearings due to poor lubrication or abrasion is included. It is considered that the cause is that the inner and outer races and the rolling elements come into metallic contact due to a shortage of an oil film during use of the bearing. As described above, in the case of abrasion, it is simply determined by the area ratio of the carbide. In the case of surface damage, there is a tendency that good wear characteristics are sufficient, but it cannot be solved by itself. The present inventors have observed a state of surface damage in a bearing test, and as a result, confirmed a state in which fine cracks were generated on the surface due to sliding contact of the rollers, and the cracks were advanced and the surface layer was scuffed. .

Fine precipitation of carbides not only strengthens the matrix, such as micronizing the structure, but can also reduce the gap in the base material on which no carbides are precipitated. In addition, a hardness measuring device such as Vickers hardness converts the plastic deformability of an object to be pressed into hardness, and the hardness measures a state in which carbides are precipitated on a substrate. . However, since the surface damage is caused by micro metal contact, it may come into contact with the gap of the base material where carbide is not precipitated,
The wear resistance and peeling resistance are low in the microscopic part, and the possibility of generation of a fine crack increases.

That is, in the present invention, a long service life is achieved by minimizing the gap in which surface damage is likely to occur due to fine precipitation of carbide. In order to achieve a long life effect against surface damage as described above, the area ratio of fine carbide having an average particle size of 0.5 μm or less on the surface of the finished product needs to be 50% or more of the total carbide area ratio. In order to obtain a further sufficient long-life effect, 70% or more is desirable. (C) [Area ratio of carbide having an average particle size of 1 μm or more on the finished product surface: 2% or less] By making the area ratio of fine carbide having an average particle size of 0.5 μm or less 50% or more of the total carbide area ratio, The gap where surface damage is likely to occur is made as small as possible, but depending on the quenching conditions, fine carbides may partially aggregate and become relatively large carbides. The life will be rapidly reduced. In order to obtain a long service life against surface damage, it is necessary to adjust the quenching conditions so that the area ratio of carbide having an average particle diameter of 1 μm or more on the surface of the finished product is 2% or less of the total carbide area ratio. In order to further obtain a sufficient long life effect, the content is preferably 1% or less. (D) [Surface hardness is HV730 or more and 900 or less] Fine precipitation of carbides tends to increase the surface hardness because the matrix is strengthened, such as finer structure. Inventive bearings have higher hardness. In the bearing of the present invention, it is possible to simultaneously reduce the size of the carbide and increase the hardness. On the other hand, the surface hardness is an important factor for abrasion resistance and peeling resistance,
Even if carbide is finely precipitated, if the overall surface hardness is reduced, the bearing life will be extremely reduced. In a life test assuming poor lubrication and mixing of wear, the surface hardness was HV730.
If less than this, a long life cannot be obtained. Therefore, the surface hardness is H
Vs 730 or more is required. However, increasing the hardness while maintaining the fine precipitate structure of carbides under heat treatment conditions (for example, rapid heating, high-frequency heating), cooling methods (for example, water quenching, sub-zero treatment), and the like tend to have a long life. When the hardness exceeds HV900, the toughness of the base material is rapidly reduced and the life of the bearing is reduced. Therefore, the surface hardness needs to be HV900 or less. In addition, in order to stably obtain the strengthening of the base, HV 770 or more and HV 850
The following is preferred.

In the present invention, a basic experiment using SUJ2 as a material is performed. However, the present invention is not limited to this as long as the required quality as a bearing is obtained by quenching and tempering. The components are as follows.

[C: 0.8 to 1.2% by weight] Carbon is an important element for obtaining hardness and carbide necessary for bearings.
At least 0.8% by weight or more is required to obtain sufficient hardness and carbide area ratio necessary for the life. But,
If the content exceeds 1.2% by weight, the generation and segregation of giant carbides during steelmaking become strong. In the case of soaking treatment, giant carbides and segregation may not be sufficiently controlled, and therefore, carbide refinement in subsequent warm rolling becomes insufficient. For the above reasons, the carbon content of the material is set to 0.8% by weight or more and 1.2% by weight or less.

[Si: 0.1 to 0.5% by weight] Silicon acts as a deoxidizing agent during steelmaking of the material, improving hardenability and strengthening the base martensite, thereby extending the life of the bearing. Is an effective element, and at least 0.1% by weight is necessary to obtain the effect. However, Si
If the content is too large, the workability including machinability and forgeability deteriorates, so the upper limit was made 0.5% by weight or less. For the above reasons, the Si content of the material is set to 0.1% by weight or more and 0.5% by weight or less.

[Mn: 0.2-0.8% by weight] Manganese is an element for improving the hardenability, but at least 0.2% by weight is necessary to obtain its 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% by weight or more, the cold workability becomes remarkable when the content of Mn exceeds 1.1% by weight. The lower limit is set to 1.1% by weight.

[Cr: 0.1 to 1.8% by weight] Chromium is an element that strengthens the matrix, such as improving hardenability and resistance to tempering softening. %is necessary. However, when the content exceeds 1.8% by weight, the generation and segregation of giant carbides are increased during steelmaking, and the giant carbides and segregation cannot be sufficiently adjusted by the soaking process 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 1.0% by weight or more and 1.8% by weight.
The following is assumed.

Here, when components that greatly affect the formation of carbides and the transformation temperature, such as the carbon content and the Cr content, are adjusted in the component range of the present invention, a subtle change naturally appears in the optimum warm working region. <Example> Subsequently, a comparative experiment between an example and a comparative example, which was performed to specifically explain the effect of the present invention, will be described.

In this experiment, as a sample, a material obtained by miniaturizing a carbide by performing WRF processing on a bearing inner / outer ring material made of a hot-forged high-carbon steel without performing softening annealing was used. Then, according to the difference in the area ratio of the carbide on the surface of the finished inner and outer rings, a comparative study was conducted by classifying into Examples and Comparative Examples. In order to directly measure the area ratio of the carbide, the structure of the bearing surface is photographed with an electron microscope, and only the carbide is taken out of the electron microscope image base material by an image analyzer, and the shape, area, number, etc. are further measured. Then, the area ratio was calculated.

Electron microscope: JSM-T220A, manufactured by JEOL Ltd. Image analyzer: IBAS2000, manufactured by Carl Zeiss [A: Abrasion characteristic test] A test method for abrasion characteristics is shown. The abrasion test was performed using a two-cylinder abrasion tester (FIG. 12), and a test piece S was mounted on each of a pair of cylinders 10 facing each other up and down. The test pieces S were rotated at a low speed in the opposite direction, the slip rate was set according to the difference in the number of revolutions, and the wear rates (g
/ M). Particularly, in order to reproduce the wear characteristics in a poor lubrication state, a low-viscosity lubricating oil that easily breaks the oil film during rotation was used.

(Abrasion test conditions) Test machine: Two-cylindrical abrasion test machine Load: 100 kgf Rotation speed: 10 rpm Slip ratio: 30% Lubricating oil: SIO Oil temperature: 60 ° C [B: WRF workability test] Processing related to WRF processing This shows the test method for sex. In order to improve the wear resistance, it is necessary to increase the carbide area on the surface. However, the carbide area ratio of the raw material is higher than the carbide area ratio of the finished product after the heat treatment, because the carbide is not dissolved in the base material. If the carbide area ratio of the raw material is higher, the workability naturally declines.
In the WRF processing, the mandrel 12 shown in FIG. 5 is easily worn and damaged, and is largely reflected on the processing cost as a consumable part.

(WRF tool life evaluation conditions) Processing machine: KRF70 manufactured by Kyoei Seiko Processing load: 5-7 ton Lubricants: Press former PZ13 manufactured by Sanko Chemical Co., Ltd. Diameter expansion ratio: outer ring = 1.4-2.0 times, inner ring = 1.1-1.
4 times Processing speed: 500-700 parts / hour Test bearing processing start temperature: 720-780 ° C Evaluation: Wear of the mandrel is 0.2 mm or more, and in the case of the inner ring, the mandrel has a step and the inner diameter is wavy when the shape is wavy. And Further, in the case of the outer ring, the life was defined as the case where the groove shape collapsed due to wear or the mandrel was cracked or damaged due to thermal fatigue. Table 1 and FIG. 3,
FIG. 4 shows the carbide area ratio of the finished product surface, the wear rate by a wear test, and the test results of the WRF workability of the material.

[0039]

[Table 1]

As the carbide area ratio increases, the wear rate tends to decrease, and the wear characteristics are improved. Conversely, WRF
Workability decreases. No. in the comparative example. In Nos. 7, 8, and 9, the carbide area ratio is less than 5%, so that the wear rate sharply increases and the wear resistance decreases. On the other hand, in Comparative Example NO. In Nos. 10 and 11, the carbide area ratio exceeds 15%, and the WRF processability is remarkably reduced. Among the examples, the carbide area ratio is particularly 9%.
No. of not less than 12% or more. 3 and 4 are wear resistance and WRF
Compatible with workability.

(Heat treatment conditions) The heat treatment was carried out under the conditions of quenching and tempering treatments usually performed in SUJ2. quenching,
Tempering treatment conditions: 0.1 at temperatures from 830 ° C to 860 ° C.
After holding for 5 to 1 hour, quenching is performed, and then 160 to
Tempering was performed at 200 ° C. for 2 hours.

[C: Life Test of Finished Bearing] A life test method for a bearing is shown below. This service life test is conducted with ball bearings and spherical roller bearings, etc., in which fine foreign substances are mixed to reproduce metal contact between the rolling element and inner and outer rings due to poor lubrication and surface damage due to sliding of the rolling element. evaluated.

The test object was a deep groove ball bearing having a nominal number of 6206, and the rolling element was a SUJ2 ball, and the vibration was measured at the load position. When vibrations more than three times the initial vibration value occur, test bearings are examined, and if there is peeling or abnormal wear, a Weibull plot is created based on the endurance time as the life, and each result is obtained from the results of the Weibull distribution. to determine the L ₁₀ life.

(Peeling life condition) Test surface pressure: Max. 260 MPa Rotational speed: 3000 rPm Lubricating oil: No. 68 turbine oil Contaminant foreign matter: Composition: Stainless steel powder Hardness: HRC52 Particle size: 30 μm or less Mixed amount: in lubricating oil To 500 ppm area ratio of carbide having an average particle size of 1 μm or more, average particle size of 0.5
Table 2 shows the life evaluation results of the finished bearings with respect to the area ratio and the surface hardness of carbides of um or less.

[0045]

[Table 2]

Embodiments 12 to 22 having inner and outer rings of the present invention
Showed a long life tendency against surface damage by uniformly refining granular carbide unique to SUJ2. On the other hand, in Comparative Example No. In Nos. 23 and 25, the area ratio of the carbide having an average particle diameter of 1 μm or more exceeds 2%, the portion where the carbide is partially agglomerated increases, and there is almost no microscopic fine carbide in the portion. Therefore, the life is sharply shortened against surface damage. Further, the area ratio of carbide having an average particle size of 0.5 μm or less has a large effect on surface damage. In Nos. 24 and 25, the area ratio of carbide having an average particle size of 0.5 μm or less is less than 50%, so that the portion where surface damage is likely to occur increases, and the life is sharply reduced.

Although the surface hardness is also effective against surface damage, the improvement in hardness due to finer carbides is effective against surface damage. However, in Comparative Example No. 26 is
This is the case where only the hardness is reduced by the heat treatment condition or the like. However, when the surface hardness is less than HV750, the life is sharply reduced with respect to the surface damage. Comparative Example No. No. 27 increased the hardness as the carbide was refined, but when the hardness exceeded HV900, the toughness of the base material was reduced, and the life was conversely reduced with respect to surface damage.

Among the rolling bearings of the present invention, those having an area ratio of carbides having an average particle diameter of 1 μm or more and 1% or less (Examples Nos. 12 to 16), an average particle diameter of 0.5 μm
The following carbides have an area ratio of 70% or more (Example N
o. 12-14 and 17-19), and the surface hardness is HV
750 or more and HV850 or less (Example No. 12,
13, 15 to 17 and 19 to 21) show a tendency to have a longer life. 12 showed the longest life.

[0049]

As described above, the rolling bearing according to the present invention is a conventional rolling bearing having an inner and outer ring manufactured by rolling and expanding the inner and outer rings by cold rolling after hot forging of the material. Unlike the hot forging, the inner and outer rings manufactured by performing a ring rolling process (WRF process) warm after hot forging can be used, so that the softening annealing for the inner and outer rings can be omitted and the amount of decarburization is reduced to reduce the machining allowance. This has the effect of being able to reduce the cost and providing it at low cost. In addition, the granular carbide specific to the high carbon bearing steel, which is the material of the inner and outer rings, is uniformly refined, and it is possible to enhance the function against surface damage, thereby providing a long rolling bearing life.

The function of the rolling bearing according to the present invention is improved by controlling the structure and the amount and distribution of carbides of the constituent materials. The rolling bearing includes surface treatments such as carburizing and carbonitriding.
And surface treatment such as barrel and shot peening,
By adjusting the surface hardness, the surface compressive residual stress, and the surface roughness, the effect is added. Therefore, better results can be obtained than those obtained by applying them to conventional materials.

[Brief description of the drawings]

FIG. 1A is a block diagram of a manufacturing process of the inner and outer races of the rolling bearing according to the present invention, FIG. 1B is a graph showing a change in temperature with time in the hot forging process, and FIG. 5 is a graph of the change over time.

2 (a) is a block diagram of a manufacturing process of the inner and outer races of the conventional rolling bearing as compared with FIG. 1, (b) is a graph of a change over time in temperature in the hot forging process, and (c) is a graph thereof. FIG. 4 is a graph showing a change in temperature over time in the soft annealing step, and FIG. 4D is a graph showing the temperature in the CRF processing step.

FIG. 3 is a graph showing a relationship between a carbide area ratio and a wear rate in a wear test of inner and outer rings.

FIG. 4 is a graph showing a relationship between a carbide area ratio and a tool (mandrel) life in a WRF workability test of a material.

FIG. 5 is a schematic diagram illustrating ring rolling processing.

FIG. 6 is a radial cross-sectional view of a conventional CRF-processed enlarged-diameter ring, in which a mesh is a protruding portion formed by the process.

FIG. 7 is a graph showing a decarburized state of a raw material after hot forging in a conventional method for manufacturing an inner and outer ring of a rolling bearing.

8 is a graph showing a decarburized state after annealing in a general nitrogen atmosphere performed on the hot forged material of FIG. 7;

FIG. 9 is a graph showing a decarburized state of a conventional enlarged ring subjected to CRF processing.

FIG. 10 is a radial cross-sectional view of a WRF-processed enlarged ring according to the present invention, in which a mesh is a protruding portion formed by the process.

FIG. 11 is a graph showing a decarburized state of the expanded ring after WRF processing in the present invention.

FIG. 12 is a schematic explanatory view of a two-cylinder abrasion tester, in which (a)
Is a front view, and (b) is a side view.

Claims (2)

[Claims] 1. In the production of rolling bearings, especially inner and outer rings, which are made by hardening and heat-treating high-carbon steel for grinding, a rough ring is formed by hot forging from a round bar material and processed into inner and outer rings. A method of manufacturing a bearing, comprising forming and rolling an inner ring and an outer ring by subjecting the rough ring to ring rolling in a warm state without performing spheroidizing annealing. 2. The carbide on the surface of the finished product of the inner ring and the outer ring produced by the method of claim 1 is present in an area ratio of 5% or more and 15% or less, and has an average particle size of 0.5 μm.
The following carbides have an area ratio of 50% or more with respect to all carbides, and the carbides having an average particle size of 1 μm or more have an area ratio of 2% or less with respect to all carbides, and have a surface hardness of HV730.
A rolling bearing having a value of not less than 900 and not more than 900.