JPH11100647A - Rolling bearing and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of an indentation caused by high temp. holding for long time and dropping and shock by composing at least either one of a bearing ring and a rolling element of a steel forming stainless steel power and forming it from the steel material composed of ferrite and cementite in the micro structure. SOLUTION: This rolling bearing is produced at the following. Molten steel is dripped down and the power composed of the stainless steel by blowing gas to these drips. The powder is incorporated into a carbon steel pipe and closely sealed, and after compacting into the high density with a hot extrusion, etc., the steel pipe is removed by cutting off. Successively, the green compact is finished to a prescribed size by rolling. Then, a tempering is executed at the temp. or higher in the third step of quenching and tempering of the steel. The quenching treatment can be adopted in the ordinary method, but the high nitrogen structure can be formed just below the surface by executing a carbon- nitriding quenching. By this method, the hardness on the surface layer even after completing the third step of the tempering can be made to >58 HRC and the resistance to the deterioration of sound performance and the rolling fatigue service life can further be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing suitable for use as a rotary spindle bearing used in information processing equipment such as a hard disk drive, and a method for manufacturing the same. And a method for manufacturing the same.

[0002]

2. Description of the Related Art For example, bearings for a hard disk drive motor used for information processing equipment such as a hard disk device as a magnetic recording medium and bearings for a polygon mirror motor of a laser beam printer are small and used with relatively light load. However, it is required that vibration and sound generated from the bearing itself when the spindle rotating at high speed is supported and driven is as low as possible. To meet these demands,
Conventionally, bearing steel has been quenched and tempered to ensure a predetermined surface hardness and surface dimensional accuracy.

[0003] In recent years, information processing equipment has tended to be miniaturized, and as portable and portable types have become widespread, the usage environment has also been diversified. After the bearings are used more frequently. When the environmental temperature of the bearing increases,
Mechanical and acoustic vibrations from rolling bearings tend to increase significantly. Also, in portable or portable devices, there are cases where the device is dropped or hit against something in the middle of carrying, and the sound generated from the bearings when used thereafter may increase. In the case of bearings used in precision equipment such as information processing equipment, the life is determined by the sound generated from the bearing exceeding the user's tolerance limit rather than the rolling fatigue life of the bearing,
It is necessary to make improvements so that the above-described acoustic performance degradation does not occur.

It is considered that the deterioration of the acoustic performance in the rolling bearing is caused by the following phenomenon. For example, when the bearing is left in a stopped state at a high temperature of 60 to 90 ° C. for as long as 100 hours, a rolling element (for example, a steel ball) inserted between the inner and outer races, and the two races Due to the concentrated stress on the contact surface of the rolling element, extremely shallow but concave indents are formed on the transfer surface between the raceway ring and the rolling elements by the number of rolling elements, and the steel balls rotate and simultaneously pass through multiple indents while the bearing is operating. It is thought that acoustic vibrations are generated by doing this. Also, when a drop or impact is applied, the same concave indentation as described above may be generated at the contact position with the rolling element, which also causes deterioration of the acoustic performance during operation of the bearing.

As described above, the indentation that causes the deterioration of the acoustic performance is due to the concentrated stress caused by the contact between the race and the rolling element, and the concentrated stress is 1 / the elastic limit of the steel material constituting the bearing. Normally, a stress of 2 or less should not be formed in theory. Also, the impact force when the device hits an object is about 1/3 or less compared to the static load capacity of the bearing, and cannot be said to be a large impact force. However, the formation of minute indentations by such minute pressures that would not normally be a problem,
In information processing equipment that requires a high degree of precision, there is a problem as acoustic performance degradation.

[0006]

SUMMARY OF THE INVENTION
For high-carbon chromium steel, a bearing has been proposed in which the microstructure is composed of ferrite and cementite (hereinafter, referred to as “ferrite + cementite” structure) to increase the resistance to indentation formation, and a method of manufacturing the same. . On the other hand, information equipment often requires rust resistance. Conventionally, 440C steel and 13% Cr-containing stainless steel have been used for corrosion-resistant bearings. However, when these stainless steels are subjected to a heat treatment for forming the above “ferrite + cementite” structure, the hardness becomes H _R C56. It will be smaller.

Also, 440C steel and 13% Cr-containing stainless steel have a disadvantage that large carbides are present and the surface roughness of the transfer surface is not reduced. The small surface roughness is extremely important for improving the sound and vibration performance of such a precision bearing for information equipment.

[0008] Therefore, an object of the present invention is to prevent the occurrence of indentations caused by holding at a high temperature for a long time, and to prevent the occurrence of indentations due to dropping or impact, to provide excellent resistance to acoustic performance deterioration, and to provide excellent hardness and rust resistance. An object of the present invention is to provide a rolling bearing having a small surface roughness on a transfer surface and optimal for information processing equipment and a method for manufacturing the same.

[0009]

Means for Solving the Problems The inventor of the present invention has conducted intensive studies to increase the resistance to deterioration of acoustic performance and obtain high hardness. As a result, in a rolling bearing, the raceway is made of a steel material having a microstructure of "ferrite + cementite". By making use of the fact that at least one of the ring (inner and outer rings) and the rolling element can increase the resistance to acoustic performance deterioration, the hardness is increased by manufacturing the structure using powder made of stainless steel. The inventors have found that H _R C can be 56 or more and completed the present invention.

[0010] Therefore, in the rolling bearing of the present invention, at least one of the race and the rolling element is made of a steel formed by molding a powder of stainless steel, and the microstructure is made of a steel material made of ferrite and cementite. .

In the rolling bearing of the present invention, at least one of the rolling element and the bearing ring is made of a steel material having a "ferrite + cementite" structure. The generation of indentation can be prevented, and excellent resistance to acoustic performance deterioration can be obtained.

Further, since such a “ferrite + cementite” structure is obtained by molding a powder made of stainless steel, even if a heat treatment for obtaining the “ferrite + cementite” structure is performed, the structure in the structure is not affected. The carbides are finely and uniformly distributed, and high hardness can be obtained.

In addition, the carbide in the structure becomes fine and uniform, and unlike the case of ordinary smelted steel, there is no coarsening of the carbide, so that the surface roughness of the transfer surface also becomes small.

Further, since at least one of the rolling elements and the bearing ring is manufactured using powder made of stainless steel, it has excellent rust resistance.

[0015] Preferably, in the above aspect, the hardness of the surface layer portion is 56 or more in Rockwell hardness (H _R C).

A method for manufacturing a rolling bearing according to the present invention includes the following steps in a method for manufacturing a rolling bearing having a bearing ring and a rolling element.

First, a powder made of stainless steel is prepared. Then, the powder is molded to form a molded body. Then, after quenching the formed body, by performing the tempering at a temperature of the third stage of the tempering of the steel or more, at least one of the raceway ring and the rolling element made of a steel material having a microstructure of ferrite and cementite are formed. It is formed.

In the method for manufacturing a rolling bearing of the present invention, since powder made of stainless steel is used, even if heat treatment for obtaining a “ferrite + cementite” structure is performed, carbide in the structure is finely and uniformly distributed. And high hardness can be obtained.

Since the carbide in the structure is fine and uniform, the surface roughness of the transfer surface is also reduced. Furthermore, since at least one of the rolling elements and the bearing ring is manufactured using a powder made of stainless steel, it has excellent rust resistance.

Further, the above-mentioned “ferrite + cementite”
The structure is obtained by quenching the powdered stainless steel and then tempering at a temperature equal to or higher than the third stage of tempering. If tempering is performed at a temperature equal to or higher than the temperature of the third stage of tempering, the microstructure is formed by decomposition of residual cementite (also referred to as “spherical cementite”) existing immediately after quenching and quenched martensite by tempering. Ferrite and fine cementite (this mixed structure is called "tempered troostite"), and ferrite and fine cementite generated by decomposition of tempered austenite during tempering by tempering. That is, the microstructure of the steel material is composed of spherical cementite, ferrite, and fine cementite (substantially two-layered structure of ferrite and cementite), and most of the microstructure is ferrite.

As described above, the martensite in the quenched structure is decomposed by the high-temperature tempering at or above the temperature of the third stage of tempering to become a mixed structure of ferrite and cementite (ie, a “ferrite + cementite” structure). . As a result, the structure is further stabilized and softened in hardness measurement. However, when a very small amount of plastic deformation is a problem as in the present invention, the stabilization of the structure is rather small stress. It is considered that the resistance to the plastic deformation below is increased. As a result, it is possible to prevent the occurrence of indentations caused by holding the high temperature for a long period of time and to prevent indentations caused by dropping or impact, and to obtain excellent resistance to deterioration in acoustic performance.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION At least one of the rolling elements and races constituting the rolling bearing of the present invention is made of a steel formed by molding a powder of stainless steel, and has a microstructure of ferrite and cementite. Has become. The difference in the metal structure between the steel formed from the powdered stainless steel and the molten stainless steel is clear. That is, as can be seen from the phase diagram, giant carbide M ₇ C ₃ generated by the eutectic reaction exists in the smelted stainless steel, and this M ₇ C ₃ cannot be eliminated by the subsequent heat treatment.

On the other hand, when the powdered stainless steel is formed from powdered stainless steel, the powder changes from a liquid to a solid very quickly, so that the carbide M ₇ C ₃ has no time to grow and becomes very fine. Therefore, M ₇ C ₃ is finely and uniformly distributed, and the microstructure of this steel material is substantially S in the distribution state of carbide.
It is the same as UJ2.

Considering the cost, the composition of the steel material is preferably 440C. Further, in order to reduce the decrease in hardness due to high temperature tempering, Mo (molybdenum),
It is desirable to add V (vanadium).

In the rolling bearing of the present invention, it is specified that at least one of the race and the rolling element is made of a steel material which satisfies the above requirements. However, at least a steel material which satisfies the above requirements is used for the race. If so, the object of the present invention can be achieved. However, it is effective to use a steel material that satisfies the above requirements also for the rolling elements. As a result, the formation of indentations on the surface of the rolling element can be prevented, and the resistance to acoustic performance deterioration can be further increased.

However, it is effective to use not only steel but also ceramics. If a ceramic rolling element is used, even if the rolling bearing is left at a high temperature, the rolling element itself hardly forms an indentation due to contact with the bearing ring, and has excellent wear resistance. Become. As the ceramics that can be used for such rolling elements, those usually used for rolling bearings can be used as they are, and examples thereof include silicon nitride, silicon carbide, alumina, and zirconia.

FIG. 1 is a process chart showing a method for manufacturing a rolling bearing according to the present invention. Referring to FIG. 1, in the method for manufacturing a rolling bearing of the present invention, first, a powder made of stainless steel is prepared (Step 1: S1). Then, a molded body is formed by molding the powder (Step 2: S2). Then, the molded body is quenched (Step 3: S3). After this quenching, tempering is performed at a temperature equal to or higher than the temperature of the third stage of tempering of the steel (step 4: S
4) At least one of a raceway and a rolling element made of a steel material having a microstructure of ferrite and cementite is formed.

The specific method for producing the steel formed from the powdered stainless steel in the above is as follows.

First, a molten steel is dropped, and a gas is blown onto the molten steel to blow off the powder, and the powder is collected to produce a powder made of stainless steel. Then, the powder is put into a carbon steel pipe and sealed. Thereafter, the density is increased by hot extrusion or HIP (Hot Isostatic Pressing). Then, after the carbon steel pipe is removed by cutting, it is finished to predetermined dimensions by rolling.

After the above processing, quenching and tempering (steps 3, 4: S3, S4) are performed as described above.

As the quenching treatment (quenching and hardening treatment) performed in the manufacturing method of the present invention, ordinary quenching (subbing quenching) may be employed, but carbonitriding and quenching and quenching may be employed instead. Alternatively, a high nitrogen tissue may be formed just below the surface.
By making the nitrogen concentration just below the surface in this way,
The third stage ends after the surface layer hardness tempering H _R C58 or higher that can be can be assumed that further excellent with rolling fatigue life resistance to acoustic performance degradation.

[0032]

EXAMPLES Example 1 440C steel, which was formed by melting a 440C steel and a stainless steel powder by a conventional method, was quenched and then tempered. Then, a change in hardness when the tempering temperature was changed was examined. The result is shown in FIG.

Referring to FIG. 1, the results show that the 440C steel obtained by forming the powder into a steel material was obtained, as compared with the 440C steel obtained by smelting.
It was found that steel had higher hardness at each tempering temperature. The tempering hardness sharply decreased when the tempering temperature was 500 ° C. or higher. This is because the microstructure changes to ferrite and cementite by the third stage of tempering. Compared to the ingot 440C steel, the steel formed from powdered stainless steel has the same composition, but has a hardness of H _R C60 or more in tempering at 500 ° C. or less. This is because carbides are finely and uniformly distributed. Although the hardness sharply decreases after the third stage of tempering, the steel formed from powdered stainless steel still maintained higher hardness than the smelted steel.

Example 2 An acoustic test was performed using a rolling bearing. As a sample, a miniature ball bearing 696 was produced using 440C steel (steel B) produced by an ordinary method and steel (steel A) obtained by turning a powder steel of the same composition into a steel material by HIP treatment. Table 1 shows the chemical composition of the steels A and B used at this time.

[0035]

[Table 1] Next, the inventor conducted an acoustic test to investigate the acoustic degradation of the test bearing before and after heating. First, a rolling bearing composed of an inner ring, an outer ring and a rolling element was manufactured using each of steels A and B. At this time, after heating at 1100 ° C. for 0.5 hour, quenching treatment is performed by rapidly cooling in oil, and after cooling, 12 ° C. in a temperature range of 180 to 600 ° C. as shown in Table 2 below.
Tempering for 0 minutes, polishing and bearing number 696
The test bearing was assembled by assembling into a small bearing.

In the acoustic test, two test bearings were assembled so that a predetermined surface pressure was applied, and the axial vibration velocity of the bearing alone was measured as the sound emitted from the bearing. The measuring device used for the vibration measurement had a built-in detector for measuring the axial vibration velocity on the rotating shaft, and the measurement was performed by lightly pressing the rotating shaft of the measuring device against the side surface of the inner ring of the bearing. The measurement conditions at this time were as follows: the maximum contact surface pressure between the rolling elements and the inner and outer rings was 1.3 GPa, the rotation speed was 2200 rpm, and the measurement frequency range was an audible sound range of 300 to 6300 Hz.

Using the above-mentioned ball bearings, an acoustic test was conducted under the above-mentioned measuring method and conditions before leaving at high temperature,
After being heated to 0 ° C. and allowed to stand for 120 hours, an acoustic test was performed again to measure the vibration speed. Ratio Vh / Vc between measured vibration velocity Vh after heating and measured vibration velocity Vc before heating
Is the amount of sound deterioration and is expressed in decibels (20 log
[Vh / Vc]).

Table 2 shows the results of the acoustic test together with the amount of retained austenite and the hardness of the surface layer.

[0039]

[Table 2] From this result, the higher the tempering temperature of both steel A and steel B, the smaller the acoustic degradation. However, in the case of steel B produced by melting, which is a normal steel making method, the hardness tempered at 500 ° C. or more is H.
Becomes smaller than _R C56.0, easily scratched in the bearing manufacturing process, the initial sound is larger as the acoustic degradation amount is small, which is not preferable.

As is evident from the results shown in Table 2, the tempering temperature was further increased as compared with the case where tempering was simply performed in the second stage of tempering to reduce the amount of retained austenite to substantially 0%. It is certain that the higher the tempering temperature is, the smaller the acoustic deterioration is because there is an effect other than the amount of retained austenite. It is considered that it has greatly contributed to prevention of occurrence.

Example 3 Metallurgical microscope of 440C steel tempered at the temperature of the third stage of tempering after quenching a steel material formed of powdered stainless steel and 440C steel melted by a conventional method. The tissue was examined. As a result, powdered stainless steel was formed 4
FIG. 3 shows the 40C steel, and FIG. 4 shows the 440C steel produced by melting.

FIGS. 3 and 4 show a metallographic structure at 400 × magnification. As is clear from FIG. 3, the steel manufactured by the method of the present invention has a microstructure constituted by a steel material having a mixed structure of ferrite and cementite, and has a carbide M ₇ C ₃ finely and uniformly distributed. I was

On the other hand, in the melted 440C, a giant carbide M ₇ C ₃ was present as shown in FIG.

The embodiments and examples disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0045]

According to the rolling bearing of the present invention, at least one of the rolling element and the bearing ring is made of a steel material made of ferrite and cementite. The generation of indentation can be prevented, and excellent resistance to acoustic performance deterioration can be obtained.

Further, since such a structure is obtained by molding a powder of stainless steel, even if heat treatment for obtaining the structure is performed, carbides in the structure will be finely and uniformly distributed. High hardness can be obtained.

Further, the carbide in the structure is fine and uniform, and the surface roughness of the transfer surface is also reduced. Furthermore, since at least one of the rolling elements and the races is manufactured using powdered stainless steel, it has excellent rust resistance.

In the method for manufacturing a rolling bearing of the present invention, since the structure composed of ferrite and cementite is obtained by molding a powder of stainless steel, heat treatment for obtaining the structure composed of ferrite and cementite is performed. Even if it is performed, carbides in the structure are finely and uniformly distributed, so that high hardness can be obtained.

Further, since a "ferrite + cementite" structure is obtained by high-temperature tempering at a temperature higher than the third stage of tempering, it is possible to prevent the formation of indentations caused by holding at a high temperature for a long period of time and indentations caused by falling or impact. And excellent resistance to deterioration of acoustic performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for manufacturing a rolling bearing of the present invention.

FIG. 2 is a graph showing a change in hardness when a tempering temperature is changed between a melted 440C steel and a 440C steel formed by molding a powder made of stainless steel.

FIG. 3 is a photograph showing a metallographic microstructure of a rolling bearing of the present invention.

FIG. 4 is a photograph showing a metal microstructure of a smelted steel.

Claims (3)

[Claims] 1. A rolling bearing having a race and a rolling element, wherein at least one of the race and the rolling element comprises:
A rolling bearing comprising a steel formed by molding a powder of a stainless steel and a microstructure comprising a steel material comprising ferrite and cementite. 2. The hardness of the surface layer is determined by the Rockwell hardness (H _R).
The rolling bearing according to claim 1, wherein C) is 56 or more. 3. A method for manufacturing a rolling bearing having a bearing ring and a rolling element, comprising the steps of: preparing a powder made of stainless steel, forming the powder to form a compact; After quenching, a step of performing tempering at a temperature equal to or higher than the third stage of tempering the steel to form at least one of the bearing ring and the rolling element made of a steel material having a microstructure of ferrite and cementite. With,
A method for manufacturing rolling bearings.