JP2004347129A - Retainer for bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a retainer made of a steel sheet often has an imperfect nitriding layer because the nitriding is carried out in the state that oxide existing on the surface of the retainer has not been completely removed, the nitriding layer can not satisfactorily hold lubricating oil, and the lubricating oil film is often broken because the nitriding layer has imperfect portions and the nitriding layer itself is inferior in smoothness, has cracks, etc. <P>SOLUTION: In the retainer 1 for a bearing, the oxide existing on the surface of an annular sheet 1a formed by press working is removed by converting the oxide into a metal fluoride film by a fluorination treatment 12. The metal fluoride film prevents forming of the oxide, and the surface is fluorinated by surely removing the oxide from the surface. A nitriding layer N is closely, uniformly, and sufficiently formed on the surface of the annular sheet 1a. As a result, smoothness of the surface is maintained and the breakage of the oil film existing on the retainer 1 is prevented. The close, uniform, and smooth nitriding layer N can be stably formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a steel bearing retainer.

  2. Description of the Related Art Conventionally, steel bearing cages have problems of improving strength and preventing wear. In order to solve this problem, for example, a so-called corrugated press retainer is used in a deep groove type ball bearing for a crank bearing of a motorcycle engine, particularly a two-cycle engine, and a so-called tuft ride is provided on the surface of the corrugated press retainer. Surface treatment including nitriding such as salt bath nitriding and gas nitriding has been performed. Further, when the nitriding treatment is performed, there is an advantage that lubricity can be improved.

However, the crank bearing of the two-stroke engine is lubricated with lubricating oil mixed with gasoline, so that a constant amount of lubricating oil is not always supplied. For this reason, even in the cage having improved lubricity by the nitriding treatment as described above, the oil film may be broken, and in some cases, seizure may occur between the cage and the rolling elements.
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, the shape of the corrugated press retainer is complicated, oxides are apt to remain, and in addition, the oxygen adsorption and oxidizing action again works after the removal, so that the oxides on the surface cannot be completely removed. In this state, when the nitriding treatment is performed, the nitrided layer is formed sufficiently in the portion where the oxide has been removed, and insufficiently in the portion where the oxide remains, and as a result, the nitrided layer has unevenness. A number of cracks were formed. On the surface of the insufficiency nitrided layer, the smoothness was originally insufficient, cracks were present, and it was difficult for the lubricating oil to be retained on the outermost surface of the nitrided layer. Can be

  Therefore, an object of the present invention is to solve the above-mentioned technical problems and to provide a steel bearing retainer which is less likely to cause oil film breakage and has good lubricity due to a uniform nitrided layer.

In order to achieve the above object, the steel bearing retainer of the present invention has a structure in which a dense nitride layer having an average particle diameter of nitride of 1 μm or less is formed inward from the steel surface, As for the roughness, the center line average roughness Ra = 0.7 μm to 1.0 μm, the ten-point average roughness Rz = 4.0 μm to 7.0 μm, and the maximum height Rmax = 4.5 μm to 7.5 μm. Features.
According to this configuration, the nitride layer can be formed densely, uniformly, and sufficiently on the surface. In the cage in which such a nitride layer is formed, the oil film is not broken, and good lubricity can be maintained.

This cage can be manufactured, for example, by the following method for manufacturing a steel bearing cage.
The manufacturing method includes, in the method for manufacturing a steel bearing retainer having a nitrided layer formed on a surface thereof, a fluorine treatment for replacing an oxide on the surface of the retainer with a metal fluoride film before the nitriding treatment.
Activated fluorine atoms used in the fluoride treatment destroy and remove foreign substances such as processing aids attached to the surface of the base metal steel, thereby purifying the surface and simultaneously oxidizing the steel surface. Passive films, such as films, are replaced by metal fluoride films. By being replaced in this manner, 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, a dense, uniform, and sufficient nitride layer can be formed on the surface.

  Conventionally, in a temperature range of 480 ° C. to 700 ° C., metal elements such as Cr, Mn, Si, and Al in a steel material are easily oxidized during nitriding. However, in the above temperature range, it is difficult to create an atmosphere in which these metal elements are kept completely neutral or reducible. Therefore, the above metal elements are almost oxidized in the above temperature range. Grain boundary oxides are formed on the surface of the steel material, and the grain boundary oxides hinder 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, in the above-described manufacturing method, the oxide can be surely removed, so that a constant nitrided layer can be formed stably. That is, when the nitriding treatment at a temperature of about 480 ° C. to 700 ° C., by introducing a mixed gas of the H ₂ gas gas (e.g. NH ₃ gas) into a furnace having a nitrogen source, by the H ₂ gas The metal fluoride film covering and protecting the surface of the steel material is destroyed and removed. As a result, 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 penetrate and diffuse into the inside to uniformly form a deep nitride layer. Formed. That is, an ultra-hard compound layer (nitride layer) containing nitrides such as CrN, Fe ₂ N, Fe ₃ N, and Fe ₄ N is formed uniformly and deeply from the surface of the steel toward the inside. A hard diffusion layer of N atoms is formed, and the compound layer + diffusion layer constitutes a fully nitrided layer. Also, the hardness of the nitrided layer is equivalent to that of the conventional tuftride-treated product, and the surface hardness is maintained at Vickers hardness 450 HV (test load 50 gf).

As the fluorine-based gas used for the fluoridation treatment in the above-described production method, a fluorine source component consisting of NF ₃ , BF ₃ , CF ₃ , HF, SF ₆ , or F ₂ alone or in a mixture of inert gas such as N ₂ Is preferably used. Among them, NF ₃ is the best in terms of safety, reactivity, controllability, handleability and the like, and is practical. In such a fluorine-based gas, the concentration of the fluorine source component such as NF ₃ is set to 0.05% to 20% (weight basis, the same applies hereinafter) from the viewpoint of the effect. Preferred is in the range of 3% to 5%.

Hereinafter, a bearing retainer and a method of manufacturing the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
First, the cage of the present invention will be described. FIG. 1 is a perspective view of a retainer according to the present invention. FIG. 2 is a sectional view of a ball bearing which is a bearing provided with the retainer of FIG. Please refer to FIG. 1 and FIG.

  The retainer 1 includes a pair of ring plates 1a formed by press-forming a low carbon steel plate such as an SPCC material, and studs 2 for fixing the pair of ring plates 1a to each other. The pair of ring plates 1a are arranged to face each other, and constitute a substantially annular holder 1. A plurality of recessed portions 1b are formed at equal intervals in the ring plate 1a, and between the recessed portions 1b, rivet holes (not shown) for rivet fixing are formed. The concave bay portions 1b are arranged to face each other, and form pockets P for accommodating the spherical rolling elements 3 of the bearing A.

The retainer 1 is provided between the outer peripheral surface of the inner race 4 of the bearing A and the inner peripheral surface of the outer race 5 together with the rolling elements 3 held in the pockets P, and supports the inner and outer races so as to be relatively rotatable. And the bearing A.
In addition, the cage 1 of the present invention is dense and dense by a manufacturing method described below such that the nitride mainly composed of Fe ₃ N has an average particle diameter of 1 μm or less over the entire surface of the annular plate 1a. The nitride layer N in a state of being uniformly laminated is formed (see column (1) of the embodiment described later). Note that the nitride layer N may be formed at least in a portion where the pocket P of the annular plate 1a is formed. That is, the nitrided layer N may be formed only on the inner peripheral surface of the concave portion 1b, or may be formed on the inner peripheral surface and other portions.

The retainer 1 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 a ring plate 1a, a fluoridation treatment 12 for replacing an oxide on the surface of the formed ring plate 1a with a metal fluoride film, and a nitriding treatment 13 for forming a nitrided layer N. And an assembling step 14 for assembling the ring plate 1a into the retainer 1.

In the forming step 11, a molded product having the shape of the annular plate 1a is formed by press-molding a steel plate, for example, an SPCC material.
In the fluoride treatment 12, the article to be treated is placed in a mixture of nitrogen trifluoride (NF ₃ ) and nitrogen at a predetermined fluoride temperature T1, for example, 300 ° C. to 400 ° C. for a predetermined time (10 ° C.). Min-120 min). As a result, foreign substances and the like on the surface of the molded product are destroyed by activated fluorine atoms used in the fluoridation treatment and removed, and the surface is purified, and at the same time, a passive film such as an oxide film on the steel surface is removed. Is replaced by a metal fluoride film. At this time, since the metal fluoride film formed on the surface is a passive film, it prevents adsorption and oxidation of oxygen to the surface and prevents oxide formation until the next nitriding treatment 13. As a result, the oxide 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, is made of a predetermined reaction gas, for example, a gas consisting of NH ₃ alone or NH ₃ and a carbon source. In a mixed gas (for example, RX gas), a predetermined nitriding temperature T2 is maintained for a predetermined time (0.5 to 5 hours).
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 over 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 treatment 13 are preferably set to predetermined values according to the depth of the nitrided layer N formed in the nitriding treatment 13 and the like.
If the nitriding temperature T2 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 during the conventional formation of a nitride layer. As the nitriding temperature T2 becomes lower, 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 surface is formed at this nitriding temperature T2. The surface of the nitrided layer N becomes smoother than the surface of the nitrided layer of the conventionally formed tuftride-treated 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, ten point average roughness Rz = 4.0 μm to 7.0 μm). 0 μm and the maximum height Rmax = 4.5 μm to 7.5 μm). The surface roughness of the conventional tuftride-treated product is Ra = 1.5 μm to 2.0 μm, Rz = 10.0 μm to 15.0 μm, and Rmax = 14.0 μm to 18.0 μm. Has a surface roughness smaller than that of a conventional tuftride-treated product, and has considerably increased smoothness.

Furthermore, in addition to the fact that the nitrided layer N is smooth and dense as described above and that there are almost no cracks, the retention of the lubricating oil on the outermost surface of the nitrided layer N is good (see the column (4) in Examples described later). Also in this respect, the seizure resistance is improved (see columns (5) and (6) of the embodiment).
Further, in the nitrided layer N, there is no possibility that the friction is increased, so that the oil film is less likely to break, and the seizure can be made more difficult. Incidentally, the coefficient of friction in the non-lubricated state is 0.24, which is less than half that of 0.54 of the conventional tuftride-treated product. The experimental conditions were as follows: a ball (SUJ2 material) was reciprocated 10 times at a load of 200 gf, a speed of 100 mm / sec, and a distance of 20 mm on a test piece (SPCC material) using an HRIDON abrasion tester, and the dynamic friction coefficient at that time was measured. The average of the maximum values of the measured values was determined.

In the assembling step 14, the pair of annular plates 1 a on which the nitrided layer N is formed are fixedly fastened with the studs 2, and are assembled to the holder 1.
As described above, according to the cage 1 of the present embodiment, the following operation and effect can be obtained.
Since the retainer 1 is made of a steel plate, it can be used more safely even in a high temperature environment than a synthetic resin retainer. For example, a bearing used in an engine or the like can be used.

Further, as described in detail below, the nitrided layer N has an advantage that it can improve the strength and prevent abrasion and can also improve lubricity.
In particular, since the nitrided layer N of the present embodiment is formed uniformly and densely, the surface is much harder and the abrasion resistance is better than a conventional nitrided layer having a porous portion.
Further, in the cage 1, the mechanical strength of the steel sheet is improved by the hard nitrided layer N on the surface, and the flexibility and toughness are maintained by the non-nitrided steel sheet portion inside, so that the impact resistance is improved. In addition, the strength as a retainer is further improved. Therefore, when the bearing A provided with the cage 1 rotates, the cage 1 can withstand an impact even if it receives an impact from the rolling element 3 and there is no risk of breakage. can do. In particular, the nitrided layer N formed by the manufacturing method of the present invention has a lower hardness at the central portion of the material as compared with the conventional tufftrided product (see column (3) of the embodiment described later). Can further improve the flexibility and toughness to withstand impact. The strength of the cage here is not the mechanical strength of the material itself obtained by measuring a test piece having a simple shape, but the strength when the cage is actually used. This is a strength in which flexibility, toughness, impact resistance and the like are added to the strength of the above.

  Further, in the present embodiment, since the nitrided layer N is formed densely, uniformly and sufficiently on the surface from which the oxide has been surely removed by the fluoridation treatment 12, the lubricating oil is used. Good lubricity can be maintained without breaking the oil film on the surface. On the other hand, the nitride layer formed by the conventional tuftride treatment is formed on the surface where the oxide remains, and is not formed sufficiently on the surface where the oxide remains. , The oil film was sometimes broken (see columns (1) and (4) in Examples described later).

  In addition, in the cage 1 of the present invention, the effect of improving the lubricity of the nitrided layer itself on the surface can be further improved by forming a dense, uniform, and sufficient nitrided layer N. The above-mentioned effect can be maintained high even in a situation where it is difficult to perform. Therefore, when the cage 1 is applied to an application in which lubrication is difficult to occur, for example, to a crank bearing of 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.

Further, according to the method for manufacturing a cage 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.
In the conventional manufacturing method, metal elements such as Cr, Mn, Si, and Al in the steel material are almost oxidized in a temperature range of 480 ° C. to 700 ° C. during the nitriding treatment, and the grain boundary oxide is formed on the surface of the steel material. Was formed. 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 tuftride-treated product, and the surface hardness maintains the Vickers hardness of 450 HV (see Example (2) described later).

In addition, since the nitriding treatment 13 is gas nitriding, the reactive gas actively moves around, and the nitrogen molecules are evenly distributed on the surface of the article to be treated, and the nitrided layer N can be formed even in the portion where the nitrogen gas enters. . For example, the nitride layer N is also formed on the inner peripheral surface, the edge, and the like of the concave bay portion 1b. Therefore, the wear resistance of the cage as a whole is good.
Conventionally, in the case of gas nitriding, heat transfer is slow, and it sometimes takes a long time to sufficiently activate the surface of the article to be treated. 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 nitrogen penetrates into the metal promptly, and a long period of time. A sufficient nitrided layer N is formed without being applied.

Further, as described above, since the nitriding temperature T2 can be lower than the temperature at which the workpiece is held during the conventional formation of the nitride layer, the influence of heat such as thermal deformation can be reduced.
The cage and the method for manufacturing the same according to the present invention can be applied to a machined cage, a crown-shaped punched cage, and the like, in addition to the press-formed corrugated cage. Further, the material is not limited to carbon steel, but can be applied to stainless steel, tool steel, chrome steel, and chromium molybdenum steel.

Further, in the above-described embodiment, the assembly as the retainer is performed after the annular plate 1a is subjected to the nitriding treatment, but is not limited to this. For example, an assembling step 14 may be performed after the forming step 11, and thereafter, the fluoride treatment 12 and the nitriding treatment 13 may be performed using the assembled retainer as an article to be processed.
In addition, the bearing retainer of the present invention and the method of manufacturing the same are not limited to the above-described ball bearings, but may be any shape for various rolling bearings such as cylindrical roller bearings, tapered roller bearings, spherical roller bearings, and needle roller bearings. Can be applied to the cage.

  In addition, various design changes can be made within the scope of the claims of the present invention.

The cage 1 manufactured by the above-described method for manufacturing a bearing cage of the present invention was analyzed and tested. The results will be described. In addition, as a comparative example, analysis and test of a conventional cage were performed in the same manner. The cage of the comparative example is a cage obtained by removing the oxide by a conventional method without performing a fluoridation treatment and performing salt bath nitriding.
(1) Surface condition [Analysis method]
As shown in the perspective view of FIG. 8, the surface S1 (portion in contact with the rolling element) of the portion forming the pocket P of the cage 1 and the cross section S2 near the surface are scanned with a scanning electron microscope (manufactured by JEOL Ltd.). (JSM # 5400).

[result]
The obtained microscope images are shown in FIGS. FIG. 4 is a photograph showing the metal structure on the surface of the nitrided layer N of the cage 1 of the example. FIG. 5 is a photograph showing the metal structure of the nitride layer surface of the cage of the comparative example. FIG. 6 is a photograph showing a metal structure of a cross section of the nitride layer N of the cage 1 of the example. FIG. 7 is a photograph showing the metal structure of the cross section of the nitride layer of the cage of the comparative example. 4 to 7 show images obtained at a magnification of 5000 times, and a scale indicating the size is imprinted on each figure. In FIGS. 6 and 7, the white portion shown below the center is the retainer, and the black portion shown above it is the photographing member.

The particles on the surface of the nitrided layer N in the example are fine particles having an average particle diameter of 1 μm or less, as shown in FIG. Also, the size of the particles is almost uniform. No large undulation is observed on the surface. These are also shown in FIG. In addition, the situation near the surface shown in FIG. 6 indicates 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. 5, particles having various sizes and a particle diameter of about 5 μm are also observed. In addition, the unevenness of the surface is larger than that of the example, and cracks are observed from the surface to the inside in FIG.

(2) Surface hardness:
The surface hardness of the cage of the example was measured by Vickers hardness. The measurement position is the surface S1 of the portion forming the pocket P of the cage shown in FIG.
[result]
Average hardness of the examples: 619 HV (test load 25 gf).
Average hardness: 451 HV (test load 50 gf).
Average hardness: 370 HV (test load 100 gf).

(3) Section hardness:
The hardness of the cage of the example was measured at a plurality of cross-sectional positions at different distances from the surface. Similarly, the measurement was performed for the comparative example. The test load of the Vickers hardness is 100 gf.

[result]
FIG. 13 is a graph showing the relationship between the hardness of the cage and the distance from the surface. In FIG. 13, an example is shown by a line Ha (─), a comparative example is shown by a line Hb (─ ■ ─), the hardness is shown by Vickers hardness (HV) on the vertical axis, and the surface is shown by the horizontal axis. Is shown (μm).
The nitrided layer N of the example has a hardness of about 450 HV near the surface, which is almost the same as the nitrided layer of the comparative example. The hardness of the nitrided layer N of the example is lower than that of the nitrided layer of the comparative example at a portion closer to the inside from the surface. From this, it can be seen 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.
(4) Oil retention [Test method]
The oil retaining properties of the cage surfaces of the examples and comparative examples were tested. That is, a flat test piece was prepared, and a nitride layer similar to that formed in the example and a nitride layer similar to that of 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 nitride layer of each test piece. The surface before dropping and the surface at 1 hour after dropping at a temperature of 150 ° C. are compared with a laser microscope to measure the state of the oil film on the surface.

[result]
The observed microscope images are shown in FIGS. FIG. 9 is a photograph showing the metallographic structure on the surface of the nitrided layer N in the example, and shows a state before oil dripping. FIG. 10 is a photograph showing the metallographic structure on the surface of the nitrided layer N in the example, and shows a state after oil dropping. FIG. 11 is a photograph showing the metallographic structure on the surface of the nitrided layer of the comparative example, which is a state before oil dropping. FIG. 12 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. 9 to 12 show images obtained at a magnification of 500 times.

In the nitrided layer N of the example, as shown in FIG. 10, a stripe pattern indicating the presence of the lubricating oil is recognized throughout, which indicates that the oil film is retained on the surface. This is clearer when FIG. 9 before dropping is compared with FIG. 10 after dropping.
On the other hand, in the nitride layer of the comparative example, the difference between FIG. 11 and FIG. 12 is small, and the stripe pattern is also small in FIG. 12, indicating that the oil film is not sufficiently retained.

Therefore, it can be seen that the nitrided layer N of the example is superior in the retention of lubricating oil as compared with the comparative example.
(5) Seizure resistance (A):
Next, the test result of the seizure resistance will be described.
The cage 1 described above 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 the conventional cage was measured in the same manner.
[Test condition]
Applied bearing: deep groove ball bearing (nominal number 6305).
Radial load: 200 kgf.
Rotation speed: 11000 rpm.
Lubrication condition: Before rotation, 0.01 cc of lubricating oil for two-cycle engine was dropped.

[Test results]
Inventive product: average life 38.5 minutes.
Comparative example: average life 18.6 minutes.
As described above, the cage of the present invention has a service life approximately twice as long as that of the conventional product even under severe conditions that are almost lubricated.

(6) Seizure resistance (B):
The life of the bearing of (5) was measured under more severe conditions.
[Test condition]
Radial load: 400 kgf.
Rotation speed: 11400 rpm.
Lubrication condition: 0.005 cc of 2-cycle engine lubricating oil was dropped before rotation.

[Test results]
The product of the present invention: average life of 6.1 minutes.
Comparative example: average life 3.9 minutes.
As described above, the cage of the present invention has a life that is about 1.6 times that of the conventional product even under severer conditions.

  Note that these tests (5) and (6) are acceleration tests in which severe conditions that are not assumed in normal use are imposed. Therefore, the retainer of the present invention does not burn during normal use.

1 is a perspective view of a bearing retainer according to the present invention. It is sectional drawing of the bearing provided with the cage for bearings of FIG. It is a schematic process drawing of the manufacturing method of the bearing cage for the present invention. 5 is a photograph showing a metallographic structure on the surface of a nitride layer of the cage of the present invention. It is a photograph showing the metallographic structure of the nitride layer surface of the cage of the comparative example. 5 is a photograph showing a metal structure of a cross section of a nitride layer of the cage of the present invention. It is a photograph showing the metal structure of a section of a nitride layer of a cage of a comparative example. FIG. 8 is a perspective view of the retainer for explaining the observation positions in FIGS. 4 to 7. It is a photograph showing the metallographic structure of the nitrided layer surface of an Example, and shows the state before oil dripping. It is a photograph showing the metal structure of the nitride layer surface of an example, and shows the state after oil dripping. 4 is a photograph showing a metal structure on the surface of a nitride layer of a comparative example, showing a state before oil dripping. 5 is a photograph showing a metal structure on the surface of a nitride layer of a comparative example, showing a state after oil dropping. It is a graph which shows the relationship between the hardness of the cage | basket of an Example and a comparative example, and distance from a surface, hardness is shown by Vickers hardness (HV) on a vertical axis | shaft, and distance from a surface (micrometer) is shown on a horizontal axis. , The line Ha shows the case of the embodiment, and the line Hb shows the case of the comparative example.

Explanation of reference numerals

1 cage N nitride layer

Claims (1)

A dense nitride layer having an average particle diameter of nitride of 1 μm or less is formed inward from the surface of the steel, and the surface roughness of the nitride layer is center line average roughness Ra = 0.7 μm to 1.0 μm, A steel bearing retainer characterized by having a ten-point average roughness Rz = 4.0 μm to 7.0 μm and a maximum height Rmax = 4.5 μm to 7.5 μm.