JP2003222138A - Rolling bearing and material for rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing and a material for the rolling bearing having a superior low-noise capability, a corrosion-resistance and a long life. <P>SOLUTION: A plurality of rolling bodies 3 are provided between an inner ring 2 and an outer ring 1. The rolling body 3 is made of high carbon chromium bearing steel, and at least one of the inner ring 2 and outer ring 1 is made of martensitic stainless steel. An area rate of eutectic carbide contained in this stainless steel is from 2 to 7%, a longer diameter of the eutectic carbide is 30 μm or less, an average value of a circle-equivalent diameter of the eutectic carbide is from 1.0 to 1.6 μm, and an average area of the eutectic carbide is from 0.8 to 2 μm<SP>2</SP>. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing and a material for a rolling bearing, and more particularly to a rolling bearing and a material for a rolling bearing suitable for a rotating part of precision equipment such as VTR and computer peripheral equipment. is there.

[0002]

2. Description of the Related Art Conventionally used bearing steels are those described below.

Rolling bearings such as ball bearings and roller bearings, which have contact surface pressures of 1000 to 1300 MPa, and in some cases 3000 to 4000 MPa, are carburized with high carbon chromium bearing steel having a high carbon content and the surface thereof. Hardened steel is used. High carbon chrome bearing steel is 1.
The main component is 1% C-1 to 1.5% Cr, and the hardenability is changed depending on the addition amounts of Mn and Mo. This steel type is quenched from a temperature of 1050 to 1120K,
It is tempered at 420 to 470K and used as a structure in which 7 to 8% of spherical cementite is dispersed in martensite. The hardness after tempering is high at HRC 58 to 64. It is desirable to have a clean steel with a small amount of carbon, and nowadays, it is manufactured mostly by utilizing carbon deoxidation by vacuum degassing, and if necessary, special melting methods such as electroslag remelting and vacuum arc remelting are combined to make A material with reduced metal inclusions and miniaturization is used.

Since the carburized bearing is made by carburizing case hardened steel, it has a high surface hardness and a flexible core.
Especially suitable for applications subject to impact loads.

Further, in a bearing used in an environment exceeding 390K, a low temperature deoxidizing type steel cannot be used because it causes a structural change, softening and dimensional change. Therefore, high-temperature tempered high carbon high alloy steels such as M50 (0.8C-4Cr-4.3Mo-1V) and T1 (0.7C-4Cr-18W-1V) are used.

However, each of the conventional bearing steels has the following drawbacks.

That is, the case-hardening steel is less likely to lower the oxygen content in melting and refining as compared with the high carbon chromium bearing steel, is likely to generate oxide-based non-metallic inclusions, and becomes a factor to reduce the rolling life. .

In addition, high carbon and high alloy steels are also liable to form huge carbides which reduce the rolling life.

In this respect, the high carbon chrome bearing steel does not have such drawbacks and can obtain a high processing accuracy, so that it is used in the rotating part of precision equipment which is required to be quiet during rotation. Suitable for However, high carbon chrome bearing steel is prone to rust, and it is necessary to apply rust preventive oil to the outer surface, and gasification of this rust preventive oil may cause malfunction of precision equipment.

Therefore, martensitic stainless steel equivalent to SUS440C steel, which is excellent in corrosion resistance and wear resistance, is used for the bearing used in a corrosive atmosphere. However, this stainless steel has non-metallic inclusions such as eutectic carbides that are generated by eutectic reaction when molten steel solidifies and alumina that is generated by chemical changes of impurities in the raw materials in the molten steel. When machining, a difference in machinability occurs between the eutectic carbides and non-metallic inclusions and the microstructure of the steel material, making it impossible to perform high-precision cutting.In particular, in rolling bearings, the rolling of the inner and outer rings Since the moving groove cannot be processed with high precision, noise generated due to vibration during rotation is large and it cannot be used in the rotating part of precision equipment.

Therefore, as a rolling bearing excellent in quietness, wear resistance and corrosion resistance, Japanese Patent Laid-Open No. 6-11743 has been proposed.
No. 9 discloses that "a plurality of balls made of high carbon chromium bearing steel are provided between the inner and outer rings, and at least one of the inner ring and the outer ring has a hardness of HRC58 or more and a eutectic carbide diameter of 10 μm or less. Ball bearings composed of martensitic stainless steel "have been proposed.

Further, Japanese Patent Publication No. 5-2734 discloses that
"In a stainless steel rolling bearing in which a plurality of rolling elements are interposed between the outer race and the inner race,
The above stainless steel has a weight ratio of C: 0.6 to 0.75.
%, Si: 0.1 to 0.8%, Mn: 0.3 to 0.8
%, Cr: 10.5-13.5%, balance Fe and inevitably mixed impurities, and the eutectic carbide contained therein has a major axis of 20 μm or less and an area ratio of 10% or less. Bearings "have been proposed.

[0013]

When the eutectic carbide grows into a huge size, and a huge carbide appears on the surface of the bearing, as described above, the difference in machinability between the carbide and the surrounding matrix is correct. It is difficult to make a finished surface shape, and there is a problem in quietness during rotation. Further, the giant carbide causes a difference in wear resistance with the surrounding base during use as a bearing, cracks and falls off the surface, disturbs the surface shape, and significantly reduces quietness. Therefore, it is preferable to reduce the size of the carbides as much as possible because the carbides are less likely to appear on the bearing surface. As described in the above patent publication, it is quiet to reduce the diameter of the carbides to 20 μm or less or 10 μm or less. Effective in improving sex. However, it is not possible to obtain a satisfactory level of quietness simply by suppressing the size of the carbide. On the other hand, in order to reduce the diameter of the carbide as such, an additional step in manufacturing technology is required, which causes a large increase in manufacturing cost and is not a practical means.

The present invention has been made in view of the above problems of the prior art, and its object is to have excellent quietness and to have corrosion resistance and life resistance (corresponding to wear resistance). To provide a low-cost rolling bearing and a material for a rolling bearing.

[0015]

The present inventor pays particular attention to the size of the maximum major axis of eutectic carbide in stainless steel, the average circle equivalent diameter of eutectic carbide and the average area of eutectic carbide, This result was obtained as a result of diligent research on the relationship between these numerical values and machinability (workability), quietness as a rolling bearing, durability, and manufacturing cost.

That is, it is clear that reducing the maximum major axis of the eutectic carbide has the effect of improving the quietness of the rolling bearing, but in reality, the number of eutectic carbides having a maximum major axis of more than 20 μm will be increased. It is extremely small, and the probability that the large eutectic carbide appears on the surface in contact with the rolling element is extremely low. In addition, it is difficult to reduce the generation of eutectic carbides whose maximum major axis is larger than 20 μm to zero by a general manufacturing technique for mass production process, and an extra additional process is required, which significantly increases the manufacturing cost. To raise. In this respect,
Considering the manufacturing cost, the major axis of the eutectic carbide should be 30μ.
It is preferable that the thickness is not more than m, since a certain effect can be obtained in improving the machinability and the manufacturing cost is not increased.

The average equivalent circle diameter of the eutectic carbide is generally about 2.0 to 2.8 μm, but reducing the average equivalent circle diameter improves machinability. Is effective, and the thickness is preferably 1.0 to 1.6 μm.
The average value of the equivalent circle diameters means the average value of the diameters when the area of each eutectic carbide is obtained by an image analyzer and the area is converted into a circle.

Further, the average area of the eutectic carbide is generally about 3.0 to 6.0 μm ² , and reducing the average area is effective in improving machinability, 8
It is preferable to be set to ² μm ² .

Further, in order to improve the machinability, it is preferable to limit the absolute amount of eutectic carbide, and therefore, the area ratio of eutectic carbide is preferably 2 to 7%. The area ratio means the ratio (percentage) of the total area of the eutectic carbide to the total measured area of the visual field.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION That is, according to the present invention, in a rolling bearing having a plurality of rolling elements between an inner ring and an outer ring, the rolling elements are made of high carbon chromium bearing steel, and at least one of the inner ring and the outer ring is used. Is a martensitic stainless steel, the area ratio of the eutectic carbide contained in this stainless steel is 2 to 7%, the major axis of the eutectic carbide is 30 μm or less, and the average value of the circle equivalent diameters of the eutectic carbide is 1.0 ~
1.6 μm, and the average area of the eutectic carbide is 0.8 to 2
A rolling bearing having a diameter of μm ² is defined as the first invention, a rolling groove is formed on the outer circumference of the shaft, and a plurality of rolling elements are provided between the rolling groove and the rolling groove on the inner circumference of the outer ring. In a rolling bearing comprising: a rolling element made of high carbon chromium bearing steel, at least one of the shaft and the outer ring made of martensitic stainless steel, and the area ratio of the eutectic carbide contained in the stainless steel is 2 to 7 %, The major axis of the eutectic carbide is 30 μm or less, the average equivalent circle diameter of the eutectic carbide is 1.0 to 1.6 μm, and the average area of the eutectic carbide is 0.8 to ² μm ² . A rolling bearing characterized by being present is the second invention, and C is 0.6 to 0.75 in weight ratio.
%, Si 1% or less, Mn 1% or less, P 0.03%
Hereinafter, S is 0.02% or less and Cr is 11.5 to 13.5.
%, Mo is 0.3% or less, V is 0.15% or less, Ti is 15 ppm or less, O is 35 ppm or less, and the balance is Fe and unavoidably mixed impurities. The area ratio of the eutectic carbide contained in the steel is 2 to 7%, and the major axis of the eutectic carbide is 30 μm.
m or less, and the average equivalent circle diameter of the eutectic carbide is 1.
0 to 1.6 μm, the average area of eutectic carbide is 0.8
A rolling bearing material having a thickness of ² μm ² is a third invention.

Since the rolling elements are made of high carbon chrome bearing steel, in the rolling element production by cold working, it is possible to perform high-precision processing more easily than in the case of processing stainless steel, so that quietness can be improved. . In the present invention,
"Quietness" means "a metal material out of the noise generated by a precision metal device when it is processed into a rolling element or an inner ring or an outer ring and assembled into a rolling bearing, and that bearing is incorporated into a precision device for operation. Low noise caused by
Say. The noise is due to the vibration generated during the rolling operation of the rolling bearing, and the vibration greatly depends on the shape accuracy of the rolling elements, the inner ring and the outer ring as described above. In a relatively small rolling bearing used in the field of precision equipment, quietness is an important issue which is not a problem in other applications. Therefore, quietness can be improved by using high carbon chromium bearing steel for the rolling elements.

By using martensitic stainless steel for at least one of the inner ring and the outer ring, rust is less likely to occur, and corrosion resistance and life resistance can be improved.

By setting the major axis of the eutectic carbide contained in the stainless steel to 30 μm or less, the machinability can be improved without increasing the manufacturing cost.

Further, by making the area ratio of the eutectic carbide 7% or less, the average equivalent circle diameter of the eutectic carbide 1.6 μm or less, and the average area of the eutectic carbide 2 μm ² or less, The machinability can be further improved, and the quietness can be greatly improved.

However, the area ratio of the eutectic carbide and the equivalent circle diameter
To reduce the average value and average area of
It requires a special manufacturing process for
It leads to the rise. Therefore, the area ratio of eutectic carbide
Is 2% or more, the average value of equivalent circle diameters of eutectic carbide is 1.
The average area of eutectic carbide is 0.8 μm when it is 0 μm or more.² Since
Within the above range, it can be manufactured according to almost normal manufacturing process.
Can be done without increasing the manufacturing cost,
An economical manufacturing system can be achieved.

The reasons for limiting the components (% by weight) of the stainless steel of the present invention are as follows.

C is an essential constituent element for imparting high temperature strength and wear resistance, and is required to be 0.6% or more, but if it is too much, a large eutectic carbide is formed and machinability is improved. Since it lowers and corrosion resistance deteriorates, it is preferably 0.75% or less.

Si less than 1%, Mn less than 1%, P less than 0.03%, S less than 0.02%, Mo less than 0.3%.
Below, V is 0.15% or less, Ti is 15 ppm or less, and O is 35 ppm or less. If too many of these elements are used, work hardening is promoted and machinability deteriorates. In addition, in order to suppress the formation of non-metallic inclusions, these elements are suppressed below the above numerical values. Furthermore, if the amount of these elements is too large, there is a disadvantage that the hardenability is lowered and the martensite conversion rate is lowered.

Cr is combined with C to form a carbide, which enhances the life resistance and Cr dissolved in the matrix as a solid solution increases the corrosion resistance, so 11.5% or more is necessary. However, if too much, the quenching hardness decreases, so it is preferable to set Cr to 13.5% or less in relation to the C content.

[0030]

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments.

In FIG. 1, 1 is an outer ring, 2 is an inner ring, and 3 is a rolling element. A plurality of rolling elements 3 made of high carbon chromium bearing steel (SUJ2) are filled between the rolling groove 4 on the inner circumference of the outer ring 1 and the rolling groove 5 on the outer circumference of the inner ring 2. When martensitic stainless steel having the composition (% by weight) shown in Table 1 is used as the material for the outer ring 1 and the inner ring 2 (Example 1),
A eutectic carbide contained in the stainless steel when the outer ring 1 is made of martensitic stainless steel having the composition shown in Table 1 and the inner ring 2 is a high carbon chromium bearing steel (SUJ2) (Example 2). The area ratio, the maximum major axis, the average value of the equivalent circle diameters, and the average area are as shown in Table 2.

In FIG. 2, a plurality of rolling elements made of high carbon chromium bearing steel (SUJ2) are provided between the rolling groove 7 formed on the outer circumference of the shaft 6 and the rolling groove 4 on the inner circumference of the outer ring 1. 3 is filled (Example 3). In the third embodiment, the outer ring 1 and the shaft 6 are made of martensite stainless steel having the composition shown in Table 1, and the rolling elements 3 are made of high carbon chromium bearing steel (SUJ2). In this case, the area ratio of the eutectic carbide contained in the stainless steel, the maximum major axis, the average value of the equivalent circle diameters and the average area are shown in Table 2.
In Example 3, both the outer ring 1 and the shaft 6 are made of martensitic stainless steel, but depending on the use conditions, only one that requires corrosion resistance and high temperature strength can be made of martensitic stainless steel.

In obtaining the above-mentioned martensitic stainless steel, after water quenching from 1025 ° C., subzero treatment (-80 ° C.) was performed and tempering to 170 ° C. was carried out.

[0034]

[Table 1]

[0035]

[Table 2]

The area ratio of eutectic carbides in stainless steel, the maximum major axis, the average value of the equivalent circle diameters and the average area are the production conditions in the production steps such as control of impurity elements, preparation of raw materials and refining, and ingot making. For example, it can be controlled by refining time, degassing conditions, solution heat treatment conditions, diffusion heat treatment step insertion, working degree conditions in cold working, and the like).

AFBMA (The Anti-Friction) was applied to the vibration and noise evaluation tests of the rolling bearings of Examples 1 to 3.
Table 2 shows the results (Anderon value) according to the standards of the Bearing Manufacturers Association, Inc., and the machinability (machinability), life resistance and cost of these rolling bearings as an index. .

In Table 2, the evaluation results of Comparative Examples 1 to 3 and Conventional Examples 1 and 2 are also shown at the same time. In Comparative Examples 1 to 3, the rolling elements 3 were high carbon as in Example 1. A chromium bearing steel, in which martensitic stainless steel having the composition shown in Table 1 is used as the material of the outer ring 1 and the inner ring 2, and the area ratio of the eutectic carbide contained in the stainless steel, the maximum major axis, and the average value of the equivalent circle diameters And at least one characteristic value in the average area is outside the scope of the present invention. Further, in Conventional Examples 1 and 2, all of the materials of the outer ring 1, the inner ring 2 and the rolling elements 3 are martensitic stainless steels having the compositions shown in Table 1, and the area ratio and the maximum major axis of the eutectic carbide contained in the stainless steels. At least one characteristic value among the average value of the equivalent circle diameters and the average area is outside the scope of the present invention.

In Table 2, M and H of Anderon values are
Each is a division of the measurement frequency band, M is a medium frequency band (300-1800 Hz), H is a high frequency band (180
0-10000 Hz) is shown. In the same frequency band, the lower the Anderon value, the better the quietness.

The workability, the durability and the cost are indicated by indexes with the value of Conventional Example 1 being 100, and the smaller the value is, the better the characteristics are. It should be noted that the workability is evaluated by performing peripheral cutting and parting-off cutting with a precision lathe and comparing the additional current increments, and the life resistance is evaluated at 20 ° C. based on the specifications determined by the use location.
It was performed by heating at a temperature of 80 ° C., 100 ° C., etc. for a certain period of time, rotating for a total of about 1000 hours, and then comparing the rotational tone (acoustic, vibration, etc.) and the grease state. Table 2
The following points can be pointed out. (1) The Anderon value is the lowest because the area ratio, the maximum major axis, the average value of the equivalent circle diameters, and the average area of the carbides of Comparative Example 2 are the smallest. However, a special manufacturing process is required to reduce these values, and the manufacturing cost for that is extremely high, and it cannot be said to be an economical material. (2) In Comparative Example 1 and Conventional Examples 1 and 2, the maximum major axis of carbides is shorter than that of Examples 1 to 3, but the average value and average area of equivalent circle diameters are outside the range of the present invention. Anderon value is larger than ~ 3. Further, Comparative Example 1 and Conventional Examples 1 and 2 are higher in cost than Examples 1 to 3 in order to reduce the maximum major axis of carbides, and in particular, the maximum major axis of carbides of Conventional Example 2 and Comparative Example 1 is 8 μm and 12 μm respectively
Since the average value of the equivalent circle diameters is relatively small, the manufacturing cost therefor is extremely high. (3) In Comparative Example 3, the area ratio of carbide, the maximum major axis, the average value of the equivalent circle diameters, and the average area are all outside the range of the present invention, and the Anderon value is extremely large. (4) Examples 1 to 3 compared to the above comparative examples and conventional examples
Has an appropriate area ratio, maximum longest diameter, average value of circle equivalent diameters and average area within the scope of the present invention regarding carbides, and therefore the Anderon value is at a level comparable to that of Comparative Example 2, and processability, All of the durability and cost are at a better level than the conventional example.

The relationship between the average value of these circle equivalent diameters and the Anderon value (M) is shown in FIG. 3, and the relationship between the maximum major axis and the cost index is shown in FIG. In FIGS. 3 and 4, “⊚” indicates the example,
“▲” indicates a comparative example, and “●” indicates a conventional example. 3 and 4
Can be said to clearly show the feature of the present invention that the Anderon value is low and the cost is low. In FIG. 4, Comparative Example 3 has the lowest cost, but Comparative Example 3 has an extremely high Anderon value, as shown in FIG. Further, in FIG. 3, the Anderon value of Comparative Example 2 is the lowest, but in Comparative Example 2, the cost is extremely high as shown in FIG.

The area ratio of carbides, the maximum major axis, the average value of the equivalent circle diameters and the average area in Table 2 were obtained by embedding a stainless steel measurement sample in resin, polishing and finishing, and observing with a metallographic microscope. It is the result of taking a photograph and measuring with an image analyzer.

Since it is rarely expected that the eutectic carbide having the maximum major axis will appear on the polished surface, the rolling bearing is dissolved in the acid solution by constant current electrolysis, the carbide is filtered by a filter, and scanning is performed. FIG. 5 shows the result (2000 times) of the structure observed with an electron microscope (SEM). In FIG. 5, white lump portions indicate carbides.

[0044]

The present invention is configured as described above,
It is possible to provide a low-cost rolling bearing and a material for a rolling bearing which are excellent in quietness and have corrosion resistance and life resistance. In particular, the present invention is an invention with a great industrial effect that contributes to cost reduction and quietness improvement of precision equipment such as VTRs and computer peripherals.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of a rolling bearing of the present invention.

FIG. 2 is a vertical sectional view of another embodiment of the rolling bearing of the present invention.

FIG. 3 is a diagram showing a relationship between an average value (μm) of circle-equivalent diameters of eutectic carbides and an Anderon value (M).

FIG. 4 is a diagram showing the relationship between the maximum major axis (μm) of eutectic carbide and the cost index.

FIG. 5 is a view showing an SEM image of carbide deposited on stainless steel.

[Explanation of symbols]

1 ... Outer ring 2 ... Inner ring 3 ... rolling elements 4, 5, 7 ... Rolling groove 6 ... axis

Claims (3)

[Claims] 1. A rolling bearing comprising a plurality of rolling elements between an inner ring and an outer ring, wherein the rolling elements are high carbon chrome bearing steel, and at least one of the inner ring and the outer ring is martensitic stainless steel. The area ratio of the eutectic carbide contained in this stainless steel is 2 to 7%, the major axis of the eutectic carbide is 30 μm or less, and the average equivalent circle diameter of the eutectic carbide is 1.0 to 1.6 μm. And a eutectic carbide having an average area of 0.8 to ² μm ² . 2. A rolling bearing in which a rolling groove is formed on the outer circumference of a shaft, and a plurality of rolling elements are provided between the rolling groove and the rolling groove on the inner circumference of the outer ring. Carbon chrome bearing steel, at least one of the shaft and outer ring is martensitic stainless steel, the area ratio of eutectic carbide contained in this stainless steel is 2 to 7%, and the major axis of eutectic carbide is 30 μm or less. The rolling bearing is characterized in that the eutectic carbide has an average circle equivalent diameter of 1.0 to 1.6 μm and the eutectic carbide has an average area of 0.8 to ² μm ² . 3. By weight ratio, C is 0.6 to 0.75%, and S
i is 1% or less, Mn is 1% or less, P is 0.03% or less,
S is 0.02% or less, Cr is 11.5 to 13.5%, M
o is 0.3% or less, V is 0.15% or less, Ti is 15 pp
A martensitic stainless steel consisting of m or less, O of 35 ppm or less, and balance of Fe and impurities inevitably mixed. The area ratio of eutectic carbide contained in this stainless steel is 2 to 7%. The major axis of the carbide is 30 μm or less, and the average equivalent circle diameter of the eutectic carbide is 1.0 to
1.6 μm, and the average area of the eutectic carbide is 0.8 to 2
A material for rolling bearings characterized by having a size of μm ² .