JPH10141379A - Bearing ring for bearing and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressed steel bearing ring prevented from the generation of an oil film break so as to be excellent in lubricating ability and also improved in strength by forming a uniform nitride layer. SOLUTION: In a bearing ring 2 for a bearing, an oxide on the surface of a bearing ring 2 formed by pressing is eliminated by substituting a metal fluoride film for the oxide by fluroridizing treatment. The metal fluoride film prevents oxide formation. The oxide can be positively eliminated from the surface, and this surface is nitrified. A nitride layer N of 1μm or less in average grain diameter is formed on the surface of the bearing ring minutely, uniformly and sufficiently so as to maintain smoothness of the surface, thereby preventing an oil film break of the bearing ring 2. The minute, uniform and smooth nitride layer N can therefore be formed stably, and the strength of the bearing ring can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing ring for steel bearings and a method of manufacturing the same. In particular, it relates to a press-formed race.

[0002]

2. Description of the Related Art Conventionally, some bearing rings for bearings are manufactured by press-forming a thin steel plate (see Japanese Patent Application Laid-Open No. 8-4757). It is assumed that such a race is used for a simple bearing in a situation where sufficient lubrication cannot be expected.
In addition, since a press-formed raceway uses a soft material that can be press-formed, it is required to improve strength and prevent wear.

In order to improve strength and prevent wear,
2. Description of the Related Art Conventionally, a surface treatment including a nitriding treatment such as salt bath nitriding and gas nitriding, which is called a so-called tuftride treatment, may be applied to the surface of a raceway of a rolling bearing. By performing the nitriding treatment, there is also an advantage that the lubricity can be improved. For this reason, it is conceivable that the nitriding-processed ring is used in a situation where lubrication conditions are not very good.

[0004] Therefore, assuming that such a nitriding treatment is applied to the above-mentioned press-formed raceway, it is considered that such raceway is used in a situation where lubrication conditions are not so good. Therefore, even in the bearing ring whose lubricating property is enhanced by the nitriding treatment as described above, the oil film may be broken, and in some cases, there is a possibility that seizure may occur between the bearing ring and the rolling element. You.

The following may be considered as causes of the oil film shortage. That is, the oxide on the surface is removed in the pretreatment before the nitriding treatment. However, not only is it difficult to completely remove the oxide, but also after the removal, oxygen adsorption and oxidization work again, so that the oxide on the surface cannot be completely removed. In this state, when the nitriding treatment is performed, the nitrided layer is sufficiently formed in the portion where the oxide is removed.
The remaining portion of the oxide was insufficiently formed, and as a result, the nitrided layer was uneven and many cracks were formed. On the surface of the insufficient nitrided layer, the smoothness is originally insufficient, and there are cracks, and it is difficult for the lubricating oil to be retained on the outermost surface of the nitrided layer, so that the oil film is easily cut,
It is considered that lubrication is insufficient.

Accordingly, it is a main object of the present invention to solve the above-mentioned technical problems, and to provide a uniform nitrided layer, which is less likely to cause oil film breakage, has good lubricity, and has improved strength. Is to provide a bearing ring. Another object of the present invention is to provide a manufacturing method capable of stably manufacturing the above-described race.

[0007]

In order to achieve the above object, a bearing ring for a steel bearing according to the first aspect of the present invention is a steel bearing ring formed by press forming, and the surface of the bearing ring is made of nitride. A dense nitride layer having an average particle diameter of 1 μm or less is formed. According to this configuration, the nitride layer can be formed densely, uniformly, and sufficiently on the surface.
In the bearing ring on which such a nitrided layer is formed, it is possible to maintain good lubricity without breaking the oil film.

[0008] In addition, since soft steel is usually used for press forming, it has been considered difficult to use under heavy load due to peeling of the raceway surface. Due to the softness of the inside of the press-formed bearing ring, a two-layer structure can be formed, so that a bearing ring having excellent strength can be obtained, and the application range of the bearing having the press-formed bearing ring can be expanded. it can.

This bearing ring can be manufactured, for example, by the following method for manufacturing a bearing ring according to the second aspect of the present invention. The method for manufacturing a bearing race according to the invention according to claim 2 is a method for manufacturing a bearing race which is press-molded and has a nitrided layer formed on the surface thereof. It is characterized by including a fluoride treatment for replacing the oxide with a metal fluoride film.

[0010] According to this structure, the activated fluorine atoms used in the fluoridation process destroy foreign substances such as processing aids attached to the surface of the steel of the press-formed base material by being broken and removed. At the same time as the surface is purified, a passive film such as an oxide film on the steel surface is replaced by a metal fluoride film. By being replaced in this way, the surface of the steel is covered and protected by the metal fluoride film, and the generation of oxide is prevented until the subsequent nitriding treatment, so that the oxide can be surely removed. Therefore, the surface is dense and uniform,
In addition, a sufficient nitride layer can be formed.

Conventionally, when the nitriding treatment is carried out at 480 ° C.
In the temperature range of 700 ° C., Cr, Mn, Si, A
Metal elements such as 1 are easily oxidized. However, in the above-mentioned temperature range, since it is difficult to create an atmosphere for maintaining these metal elements completely neutral or reducing, the metal elements are almost oxidized in the above-mentioned temperature range,
As a result, a grain boundary oxide is formed on the surface of the steel material during the nitriding treatment, and the grain boundary oxide hinders the nitriding treatment. As a result, a nitrided layer could not be stably formed on the surface of the steel material.

On the other hand, according to the present invention, since the oxide can be reliably removed, a constant nitrided layer can be stably formed. That is, at the time of the nitriding treatment,
At a temperature of about 0 ° C., a gas having a nitrogen source (eg, NH ₃
By introducing a mixed gas of (gas) and H ₂ gas into the furnace, the metal fluoride film covering and protecting the steel material surface is broken and removed by the H ₂ gas. This allows
A purified and activated metal matrix appears, and N atoms in a nitriding gas (for example, NH ₃ gas) act on the activated metal matrix to quickly permeate and diffuse into the inside to form a deep nitride layer uniformly. . That is, from the surface of steel to the inside, Cr
An ultra-hard compound layer (nitride layer) containing nitrides such as N, Fe ₂ N, Fe ₃ N, and Fe ₄ N is formed uniformly and deeply, followed by a hard N atom diffusion layer. The above compound layer + diffusion layer constitutes a fully nitrided layer. The hardness of the nitrided layer is the same as that of the conventional tufftrided product, and the surface hardness is Vickers hardness 450 HV (test load 50 gf).
Has been maintained.

As the fluorine-based gas used in the fluorination treatment of the present invention, NF ₃ , BF ₃ , CF ₄ , HF, SF ₆ , F
The fluorine source component comprising ₂ alone or a mixture was contained in an inert gas such as N ₂ gas is preferably used.
Among them, NF ₃ is the most excellent in terms of safety, reactivity, controllability, handleability and the like, and is practical. In such a fluorine-based gas, a fluorine source component such as NF ₃ is contained in an amount of 0.05% to 20% (weight basis, the same applies hereinafter) from the viewpoint of the effect.
Is set to the density of Preferred is in the range of 3% to 5%.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a bearing ring according to an embodiment of the present invention; First, the bearing ring of the present invention will be described. FIG. 1 is a perspective view of a ball bearing to which the bearing ring according to the present invention is applied. FIG. 2 is a sectional view of the ball bearing of FIG. Please refer to FIG. 1 and FIG.

The bearing 1 includes a bearing ring 2 as an outer ring, and a plurality of spherical rolling elements 3 held in the bearing ring 2. An inner annular space 4 is formed inside the bearing ring 2, in which the rolling elements 3 are accommodated and arranged in an annular shape. The rotating shaft 5 is inserted into the center of this ring, and its outer peripheral surface is in contact with the rolling element 3. That is, in the bearing 1, the inner ring is also used on the outer peripheral surface of the rotating shaft 5.

The race 2 is made of, for example, JIS cold rolled steel plate (SPCC) or Japanese bearing industry standard SPB2.
It has a one-piece structure in which a steel plate or the like is press-formed into an annular U-shaped cross section. The bearing ring 2 has a pair of substantially flat side walls 21 that are opposed to each other in the axial direction in parallel with each other, and a substantially flat cylindrical part 22 that connects the outer circumferences of the side walls 21 in a bridge-like manner. A cylindrical portion 22 and a pair of side wall portions 21
And the inner annular space 4 is partitioned. Further, the inner periphery of the side wall portion 21, that is, the inner periphery side opening of the bearing ring 2, is inclined and extends with respect to the side wall portion 21 so that the opening width is slightly smaller than the ball diameter of the rolling element 3. A pair of flat flanges 23 are provided. The flange 23 is formed along the tangent of the rolling element 3 housed and held in the internal annular space 4.

The rolling element 3 is press-fitted into an inner annular space 4 (here, grease is applied) from an inner peripheral opening of the bearing ring 2. The rolling elements 3 housed in the inner annular space 4 are received by the pair of flanges 23 and do not fall out therefrom. Further, the rolling element 3 is brought into contact with two points a and b of the cylindrical portion 22 of the bearing ring 2 and one of the side wall portions 21 in a state where the rotating shaft 5 is inserted, and is guided to roll. .

The above-described structure of the bearing 1 is the same as that disclosed in the prior application of the applicant of the present invention (Japanese Patent Application Laid-Open No. H8-4747). However, in the present invention, the following nitrided layer N is formed. This is different from the prior application described above. In the bearing ring 2 of the present invention,
Over the entire surface, a nitride layer N in a state where nitrides mainly composed of Fe ₃ N are densely and uniformly laminated so that the average particle diameter is 1 μm or less is formed by a manufacturing method described later. (See the section of Examples described later). In addition, the nitrided layer N may be formed at least in a portion that becomes a raceway groove of the raceway ring 2, for example, in the above-described bearing 1, a portion of the raceway ring 2 that guides the rolling elements 3 to roll. That is, the nitrided layer N may be formed only on the inner peripheral surface that divides the inner annular space 4 of the bearing ring 2, or may be formed on the inner peripheral surface and other portions.

The race 2 is manufactured, for example, as follows. That is, FIG. 3 is a schematic process diagram of the manufacturing method of the present invention. Hereinafter, the manufacturing method according to the present invention will be described with reference to FIG. This manufacturing method includes a forming step 11 for forming the bearing ring 2, a fluoride treatment 12 for replacing the oxide on the surface of the formed bearing ring 2 with a metal fluoride film, and a nitriding treatment 13 for forming a nitrided layer N. It has. Thereafter, an assembling step 14 of assembling the bearing ring 1 on which the nitrided layer N is formed into the bearing 1 is performed.

In the forming step 11, a steel plate, for example, SPCC
The material is press-formed to form a molded product having the shape of the bearing ring 2. In the fluoridation treatment 12, a molded article to be treated is placed in a mixture of nitrogen trifluoride (NF ₃ ) and nitrogen at a predetermined fluorination temperature T1, for example, 300 ° C. to 400 ° C.
For a predetermined time (10 minutes to 120 minutes). as a result,
Foreign matter and the like on the surface of the molded article are removed by being destroyed by activated fluorine atoms used in the fluoridation treatment, and the surface is purified.At the same time, a passivation film such as an oxide film on the steel surface becomes a metal. Replaced by a fluoride film. At this time, since the metal fluoride film formed on the surface is a passive film, it prevents the adsorption and oxidation of oxygen on the surface and prevents the next nitriding treatment.
Generation of oxides is prevented up to 3, and as a result, oxides can be reliably removed.

In the nitriding treatment 13, gas nitriding is performed.
The fluorinated molded article (the surface of which is covered with a metal fluoride film), which is the article to be treated here, has a predetermined reaction gas,
For example in the NH ₃ made from a single piece gas or NH ₃ and a mixed gas consisting of a carbon source (e.g. RX gas), to a predetermined nitriding temperature T2, the predetermined time (0.5 hour to 5 hours) it is maintained.

In the process of raising the temperature from the fluoride temperature T1 to the nitriding temperature T2, the metal fluoride film on the surface of the article to be processed becomes an activated film. As a result, in the nitriding treatment 13, nitrogen quickly penetrates deeply into the metal, and a nitrided layer N is formed. Thereafter, it is cooled for a predetermined time. The article to be processed is kept in the nitrogen gas until the cooling is completed, so that generation of oxide on the surface is prevented.

The nitriding temperature T2 and the holding time in the nitriding process 13 are preferably set to predetermined values according to the depth of the nitride layer N formed in the nitriding process 13. Nitriding temperature T2
If the temperature is 480 ° C. to 700 ° C., a hard nitrided layer can be formed on the surface. Therefore, lubricity can be improved. Further, since the surface of the article to be treated is activated by the fluoridation treatment 12, the nitriding temperature T2 can be made lower than the temperature at which the article to be treated is held when a conventional nitride layer is formed. As the nitriding temperature T2 decreases, the surface of the nitrided layer N tends to be formed more smoothly. In particular, when the nitriding temperature T2 is 480 ° C. to 700 ° C. as described above, the nitrided layer N is formed at this nitriding temperature T2. The surface of the nitrided layer N becomes smoother than the surface of the nitrided layer of a conventionally formed tufted product.
The surface roughness of the nitrided layer N is an untreated product, that is, the roughness of the polished surface (center line average roughness Ra = 0.7 μm to 1.0 μm).
μm, ten-point average roughness Rz = 4.0 μm to 7.0 μm, and maximum height Rmax = 4.5 μm to 7.5 μm). The surface roughness of the conventional tufftrided product is Ra = 1.5 μm to 2.0 μm, Rz = 10.0 μm
m-15.0 μm, Rmax = 14.0 μm-18.0
Since the thickness is μm, the nitrided layer N of the present invention has a smaller surface roughness than that of a conventional tuftride-treated product, and has considerably increased smoothness.

Furthermore, since the nitrided layer N is smooth and dense as described above, and has almost no cracks, it has a good lubricating oil holding property on the outermost surface of the nitrided layer N (see the column of Examples described later). In this respect, the seizure resistance is also improved (see the column of Example). In the nitride layer N,
Since there is no possibility of friction increasing, oil film breakage is unlikely to occur,
Seizure can be made even more difficult. Incidentally, the coefficient of friction in a non-lubricated state is 0.24, which is less than half of 0.54 of the conventional tuftride-treated product. The test conditions were as follows. A test piece (SPCC material) was loaded with a ball (SUJ2 material) on a test piece (SPCC material) at a load of 200 gf, a speed of 100 mm / sec, and a distance of 20 mm using an HRIDON abrasion tester.
Zero reciprocation was performed, and the dynamic friction coefficient at that time was measured, and the average of the maximum values of the measured values was determined.

In the assembling step 14, the rolling elements 3 are accommodated in the inner annular space 4 of the race 2 in which the nitride layer N is formed, and assembled into the bearing 1. As described above, according to the bearing ring 2 of the present embodiment, the following operation and effect can be obtained. The bearing ring 2 has a simple structure by being press-formed, and can be manufactured at low cost.

Further, as described in detail below, the nitride layer N
In addition to improvement in strength and prevention of wear, there is an advantage that lubricity can be improved. In particular, since the nitrided layer N of the present embodiment is formed uniformly and densely, it has a harder surface and better wear resistance than a conventional nitrided layer having a porous portion.

Further, in the bearing ring 2, a hard nitride layer N
Not only improves the mechanical strength of the steel plate, but also maintains the flexibility and toughness of the non-nitrided steel plate inside, so it has impact resistance and further improves the strength as a bearing ring . Therefore, when the bearing 1 provided with the bearing ring 2 rotates, the bearing ring 2 can withstand an impact even if it receives an impact from the rolling element 3 and is not likely to be damaged. can do. In particular, the nitrided layer N formed by the manufacturing method of the present invention has a lower hardness at the center portion of the material as compared with the conventional tufftrided product (see the section of Examples described later), and as a result, the internal flexibility In addition, the toughness can be further improved to withstand impact. Here, the strength of the bearing ring is not the mechanical strength of the material itself obtained by measuring a test piece having a simple shape, but the strength when the bearing ring is actually used. This is a strength in which flexibility, toughness, impact resistance and the like are added to the strength of the above.

In particular, since soft steel is usually used for press forming, it has been considered difficult to use it under heavy load because the raceway surface is peeled off. Since the above-described two-layer structure can be formed by the softness of the inside of the press-formed bearing ring 2, the bearing ring 2 having excellent strength can be obtained. Therefore,
The range of application of the bearing having the press-formed bearing ring can be expanded.

Further, in the present embodiment, the nitride layer N is formed on the surface from which the oxide has been surely removed by the fluoridation treatment 12.
Since it is formed densely, uniformly and uniformly, the lubricating oil can be held on the surface, the oil film does not break, and good lubricity can be maintained. On the other hand, the nitride layer formed by the conventional tuftride treatment is formed on the surface on which the oxide remains, and is not sufficiently formed on the surface on which the oxide remains, so that the nitride layer is an insufficient nitride layer and has a crack. , The oil film was sometimes broken (see the column of Examples below).

Further, in the bearing ring 2 of the present invention, the effect of improving the lubricity of the nitride layer on the surface itself can be further improved by forming a dense, uniform and sufficient nitride layer N. Therefore, even in a situation where lubrication is difficult to be performed, the above-described effect can be maintained at a high level. Therefore, when this bearing ring 2 is applied to an application in which a situation in which lubrication is difficult to occur is likely to occur, for example, a bearing related to a two-cycle engine for a motorcycle, there is a remarkable effect. By the way, even in the case of improving lubricity, when a concave portion serving as an oil reservoir is formed on the surface and the lubricant held in the concave portion improves the lubricity, the effect is maintained in a situation where lubrication is difficult to be performed. It is difficult.

According to the method of manufacturing a bearing ring of the present embodiment, the following operation and effect can be obtained. Since the nitriding treatment 13 is gas nitriding, there is no concern about environmental pollution such as salt bath nitriding. Further, according to the conventional manufacturing method, in the temperature range of 480 ° C. to 700 ° C. during the nitriding treatment, Cr,
Metal elements such as Mn, Si, and Al were almost oxidized, and grain boundary oxides were formed on the surface of the steel material. This grain boundary oxide hinders the nitriding treatment, and as a result, a nitrided layer cannot be stably formed on the surface of the steel material. On the other hand, in the present invention, since the oxide can be reliably removed by the fluoridation treatment 12, a constant nitrided layer N can be formed stably. The hardness of the nitrided layer is also the same as that of the conventional tufftrided product, and the surface hardness is maintained at Vickers hardness of 450 HV (see Examples described later).

In addition, since the nitriding treatment 13 is gas nitriding, the reaction gas actively moves around, and the nitrogen molecules are spread all over the surface of the article to be treated, and the nitride layer N
Can be formed uniformly. For example, the nitrided layer N is also formed on the inner peripheral surface defining the inner annular space 4 of the bearing ring 2, the inside of the flange 23, the edge portion, and the like. Accordingly, the wear resistance of the entire race is good.

Conventionally, in the case of gas nitriding, heat transfer is slow, and it sometimes takes a long time for the surface of the article to be processed to be sufficiently activated. On the other hand, in the method of the present invention, the metal fluoride film formed on the surface of the article to be treated is sufficiently activated at the nitriding temperature T2, so that the nitrogen quickly penetrates into the metal, and it takes a long time. A sufficient nitride layer N is formed without being applied.

Further, as described above, since the nitriding temperature T2 can be made lower than the temperature at which the article to be processed is held during the conventional formation of the nitride layer, the influence of heat such as thermal deformation can be reduced. . In particular, in press molding, a thin sheet material that is easily thermally deformed is often used. Therefore, the nitriding treatment 13 is preferable for the press-formed bearing ring 2 because the influence of heat such as thermal deformation can be reduced.

The bearing ring and the method of manufacturing the same according to the present invention are not limited to the bearing ring 2 constituting the outer ring of the bearing 1 described above. For example, as the inner ring of the bearing 1 as shown in the sectional view of FIG. It can be applied to the bearing ring 6. That is, the bearing 1 includes the above-described race 6 and the race 2 as an outer race,
And a plurality of rolling elements 3 disposed therebetween. The bearing ring 6 is an annular member formed in an M-shaped cross section, and has a concave orbit groove on its outer peripheral surface capable of rollingly guiding the rolling element 3, and is located radially inward from both ends of the outer peripheral surface. The flange portions are respectively extended. The flange part can function as a mounting part with the rotating shaft 5. In addition,
The bearing 1 shown in FIG.
No. 8523).

Further, the bearing ring of the present invention and the method of manufacturing the same are not limited to the one-piece bearing ring 2.
The present invention can also be applied to a raceway 2 having a two-piece structure as shown in the sectional view of FIG. That is, the bearing 1 shown in FIG. 5 includes an inner ring 7, a press-made orbital ring 2 that forms an outer ring by the first and second wheels 25 and 26, and a plurality of orbits arranged between the orbital ring 2 and the inner ring 7. Rolling element 3. First wheel 25
And the second wheel 26 each have a cylindrical portion and a side wall portion that is bent from one end of the cylindrical portion toward the radial inner diameter. The outer peripheral surface of the cylindrical portion of the second wheel 26 is press-fitted into the inner peripheral surface of the cylindrical portion of the first wheel 25 such that the side walls of the two wheels are opposed to each other to form the internal annular space 4 therebetween. . In this case, in the forming step 11, the first wheel 25 and the second
The two rings with the ring 26 are formed, and when the bearing is assembled, the two rings are combined to be assembled as the raceway ring 2. Also, after the forming step 11, the two rings may be press-fitted to assemble a raceway, and then the assembled raceway may be subjected to a fluoridation treatment 12 and a nitriding treatment 13 as an article to be processed. The bearing 1 shown in FIG. 5 is similar to that according to the prior application of the present applicant (Japanese Utility Model Laid-Open No. 5-79040).

The race of the present invention and its manufacturing method can also be applied to a shielded angular contact ball bearing as shown in the sectional view of FIG. That is, the bearing 1 of FIG. 6 includes a raceway 2 as a steel outer race having a curved portion serving as a raceway surface formed by pressing at a substantially central portion in the axial direction, and the raceway 2.
Similarly, a track ring 6 as a steel inner ring in which a curved portion serving as a track surface is press-formed at a substantially central portion in the axial direction, and a plurality of track rings disposed between the curved portions of the track ring 6 and the track ring 2. It has a rolling element 3 and an annular seal member 8 made of steel and having a substantially U-shaped cross section, which is press-fitted into the inner peripheral surface of one end of the bearing ring 2.
In the case of such a bearing, the nitrided layer N according to the present invention may be formed only on the bearing ring 2 as the outer ring and the bearing ring 6 as the inner ring. The layer N may be formed. Such a shielded angular ball bearing is used for a starter of an automobile and the like.

Further, the material of the bearing ring 2 is not limited to the above-mentioned carbon steel, but may be, for example, stainless steel. In addition to the ball bearings described above, the bearing race of the present invention can be used in various shapes for various rolling bearings such as cylindrical roller bearings, tapered roller bearings, spherical roller bearings, and needle roller bearings. Can be applied to

In addition, various design changes can be made without changing the gist of the present invention.

[0040]

EXAMPLE An analysis and test of the bearing ring 2 manufactured by the above-described method for manufacturing a bearing ring of the present invention were performed. The results will be described. In addition, as a comparative example, analysis and test of a conventional race were similarly performed. The bearing ring of the comparative example is a bearing ring which has been subjected to salt bath nitriding by removing the oxide by a conventional method without performing a fluoridation treatment.

Surface Condition Analysis Method As shown in the perspective view of FIG. 11, the surface S1 (the portion in contact with the rolling elements) of the raceway ring 2 forming the raceway groove and the cross section S2 near the surface are scanned with the scanning electron beam. Analysis was performed using a microscope (JSM # 5400, manufactured by JEOL Ltd.).

Microscopic images obtained as a result are shown in FIGS. FIG. 7 is a photograph showing the metallographic structure on the surface of the nitrided layer N of the bearing ring 2 of the example. FIG. 8 is a photograph showing the metallographic structure of the surface of the nitrided layer of the bearing ring of the comparative example. FIG. 9 shows the nitride layer N of the bearing ring 2 of the embodiment.
3 is a photograph showing a metal structure of a cross section of FIG. FIG. 10 is a photograph showing the metallographic structure of the cross section of the nitrided layer of the bearing ring of the comparative example.
7 to 10 show images obtained at a magnification of 5000 times, and a scale indicating the size is imprinted on each figure. In FIGS. 9 and 10, a white portion shown below the center portion is a track ring, and a black portion shown above it is a photographing member.

As shown in FIG. 7, the particles on the surface of the nitrided layer N in the embodiment are fine particles having an average particle diameter of 1 μm or less. The size of the particles is also substantially uniform.
No large undulation is observed on the surface. These are also shown in FIG. Also, from the situation near the surface shown in FIG. 9, it can be seen that the surface is densely formed.

On the other hand, on the surface of the nitrided layer of the comparative example, as shown in FIG.
Some of about μm are also observed. In addition, the unevenness of the surface is larger than that of the example, and cracks are recognized from the surface to the inside in FIG. Surface Hardness The surface hardness of the bearing ring of the example was measured by Vickers hardness. The measurement position is the surface S1 of the portion forming the raceway groove of the raceway shown in FIG.

Results Average Hardness of Example 619 HV (Test Load 25 gf) Average Hardness 451 HV (Test Load 50 gf) Average Hardness 370 HV (Test Load 100 gf) Cross-sectional Hardness Were measured at a plurality of cross-sectional positions having different distances. Similarly, the measurement was performed for the comparative example. The test load of Vickers hardness was 100
gf.

Results FIG. 16 is a graph showing the relationship between the hardness of the bearing ring and the distance from the surface. In FIG. 16, the example is shown by a line Ha (─), the comparative example is shown by a line Hb (、), the hardness is shown by the Vickers hardness (HV) on the vertical axis, and the surface is shown by the horizontal axis from the surface. Is shown as the distance (μm).

The nitride layer N of the embodiment has a hardness of about 4 near the surface.
50 HV, which is almost the same as the nitride layer of the comparative example. Further, the nitrided layer N of the embodiment is a portion closer to the inside from the surface,
Hardness is lower than the nitrided layer of the comparative example. This indicates that the nitrided layer N of the example has a two-layer hardness distribution with a hard surface and a soft inside, and that the example has a larger difference in hardness between the surface and the inside than the comparative example.

Therefore, it is considered that the examples have better impact resistance than the comparative examples. Oil Retaining Property Test Method The oil retaining properties of the bearing ring surfaces of the examples and comparative examples were tested. That is, a plate-shaped test piece was prepared, and a nitride layer similar to that formed in the example and a nitride layer similar to the comparative example were formed on the surface of the prepared test piece. 0.01 cc of lubricating oil is dropped on the surface of the nitrided layer of each test piece. The surface before the dropping and the surface one hour after the dropping at a temperature of 150 ° C. are compared with a laser microscope, and the state of the oil film on the surface is measured.

Microscopic images observed as a result are shown in FIGS. FIG.
Is a photograph showing the metallographic structure on the surface of the nitrided layer N in the example, which is a state before oil dripping. FIG. 13 is a photograph showing a metallographic structure on the surface of the nitrided layer N of the example, and shows a state after oil dropping. FIG. 14 is a photograph showing the metal structure on the surface of the nitrided layer of the comparative example, which is in a state before oil dripping. FIG. 15 is a photograph showing the metal structure on the surface of the nitrided layer of the comparative example, which is in a state after oil dropping. 12 to 15 show images obtained at a magnification of 500 times.

In the nitrided layer N of the example, as shown in FIG. 13, a stripe pattern indicating the presence of the lubricating oil is recognized on the whole, and it can be seen that the oil film is retained on the surface. This is clearer from the comparison between FIG. 12 before dropping and FIG. 13 after dropping. On the other hand, in the nitride layer of the comparative example,
The difference between FIG. 14 and FIG. 15 is small, and the stripe pattern is also small in FIG. 15, indicating that the oil film is not sufficiently held.

Accordingly, it can be seen that the nitrided layer N of the example is superior in the lubricating oil holding property as compared with the comparative example. Seizure Resistance (A) Next, the results of the seizure resistance test will be described. The above-mentioned bearing ring 2 was applied to a bearing, and the life was measured under the following conditions.
Here, the life is a time required for the seizure to occur when lubrication is stopped.

As a comparative example, the life of a conventional race was measured in the same manner. Before the bearing radial load 200Kgf rotational speed 11000rpm lubrication conditions rotated using rolling elements of the test conditions applied bearing deep groove shape ball bearing (bearing number 6305), a lubricating oil for two-cycle engines 0.01cc drop test results invention embodiment sample Average life: 38.5 minutes Comparative example Average life: 18.6 minutes As described above, the bearing ring of the present invention has a life twice as long as that of the conventional product even under harsh conditions near almost no lubrication. I have. . The service life of the bearing with anti-seizure (B) was measured under more severe conditions.

Test conditions Radial load 400 Kgf Rotational speed 11400 rpm Lubrication conditions Lubricating oil for two-cycle engine was dropped 0.005 cc before rotation Test result Product of the present invention Average life 6.1 minutes Comparative example Average life 3.9 minutes In addition, the bearing ring of the present invention has a service life that is about 1.6 times that of the conventional product even under severer conditions.

Note that these tests are acceleration tests in which severe conditions are assumed that are not assumed in normal use. Therefore, the bearing ring of the present invention does not seize in normal use.

[0055]

According to the first aspect of the present invention, an oil film is not broken in a bearing ring having a dense, uniform, and sufficiently formed nitrided layer formed on its surface. Lubricity can be maintained. Further, the hard nitride layer can form a two-layer structure depending on the softness of the inside of the race, so that a race with excellent strength can be obtained. Therefore,
The range of application of the bearing having the press-formed bearing ring can be expanded.

According to the second aspect of the present invention, the oxide on the surface can be surely removed by the fluoridation treatment.
In addition, a uniform and sufficient nitride layer can be formed.
In addition, since the oxide can be reliably removed, a certain nitrided layer can be stably formed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a bearing provided with a bearing race according to the present invention.

FIG. 2 is a sectional view of the bearing of FIG. 1;

FIG. 3 is a schematic process drawing of a method for manufacturing a bearing race for a bearing according to the present invention.

FIG. 4 is a cross-sectional view of another bearing provided with a bearing ring to which the present invention can be applied.

FIG. 5 is a sectional view of another bearing provided with a bearing ring to which the present invention can be applied.

FIG. 6 is a sectional view of still another bearing provided with a bearing ring to which the present invention can be applied.

FIG. 7 is a photograph showing the metallographic structure of the surface of the nitrided layer of the bearing ring of the present invention.

FIG. 8 is a photograph showing the metallographic structure of the nitrided layer surface of the bearing ring of the comparative example.

FIG. 9 is a photograph showing a metal structure of a cross section of a nitrided layer of a bearing ring of the present invention.

FIG. 10 is a photograph showing a metal structure of a cross section of a nitrided layer of a bearing ring of a comparative example.

FIG. 11 is a perspective view of a bearing ring for explaining an observation position in FIGS. 7 to 10;

FIG. 12 is a photograph showing a metallographic structure on the surface of a nitrided layer of an example, showing a state before oil dripping.

FIG. 13 is a photograph showing the metallographic structure of the surface of the nitrided layer in the example, showing the state after oil dropping.

FIG. 14 is a photograph showing a metal structure on the surface of a nitrided layer of a comparative example, showing a state before oil dripping.

FIG. 15 is a photograph showing a metallographic structure on the surface of a nitrided layer of a comparative example, showing a state after oil dripping.

FIG. 16 is a graph showing the relationship between the hardness of the bearing ring of the example and the comparative example and the distance from the surface, wherein the ordinate represents the hardness in Vickers hardness (HV), and the abscissa represents the difference from the surface. Distance (μ
m), line Ha shows the case of the example, and line Hb shows the case of the comparative example.

[Explanation of symbols]

 2 raceway ring 6 raceway ring 12 fluoridation treatment 13 nitriding treatment N nitride layer

Claims (2)

[Claims] 1. A press-formed steel race, wherein a dense nitride layer having an average particle diameter of nitride of 1 μm or less is formed on the surface of the race. 2. A method of manufacturing a bearing ring having a nitrided layer formed on a surface thereof, which is press-molded, wherein the oxide on the surface of the ring is replaced with a metal fluoride film before nitriding. A method for producing a bearing ring for a bearing, comprising a treatment.