JPH1193955A - Rolling bearing and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of a surface origin damage and also suppress the generation of a stamp flaw or frosting by using a bearing steel having a specified maximum grain size or less of a carbide in the surface layer and a specified surface hardness or more for either one of a race and a rolling body. SOLUTION: Since this rolling bearing has a surface hardness of HRC 60 or more, a high-temperature hardness equal to or higher than M50 can be provided. Since the maximum grain size of a carbide in the surface layer can be set to 8 μm or less which is smaller than M50, the dropping-out of a carbide or the occurrence of a surface origin damage with the carbide as a stress collecting source can be prevented under a high-temperature condition causing the deterioration of lubricating characteristic is deteriorated or a condition causing the biting of foreign matter. Since the maximum grain size of the carbide can be set smaller than M50, a counter object can be prevented from being damaged even if the metal contact with the counter object is caused in rolling because of a poor lubricating characteristic, and a so-called stamp flaw or frosting can be prevented.

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 method for manufacturing the same, and more particularly, to a high-temperature (up to 300
C), a rolling bearing which can be used under a high-speed lean lubrication condition or a foreign matter biting condition, and a method for producing the same.

[0002]

2. Description of the Related Art With the miniaturization, high performance, and high efficiency of machines, the use conditions of rolling bearings have been diversified, and the conditions have become increasingly severe in each direction. One of the problems is an increase in the operating temperature. For rolling bearing steel used at high temperatures (up to 300 ° C), M
There are 50. Although this material has excellent high-temperature hardness properties, it contains large carbides.Therefore, under conditions where lubricating properties at high temperatures deteriorate or when foreign matter is caught, the carbides may fall off and the carbides may be used as a stress concentration source. Origin-type damage (peeling) could occur. Further, since this carbide does not deform during rolling contact, it has poor lubricating properties, and when the metal comes into contact with the counterpart object, it damages the counterpart object, which is considered to cause so-called stamp damage and frosting.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has excellent high-temperature hardness, can suppress the occurrence of surface-initiated damage, and can suppress the occurrence of stamp scratches and frosting. An object of the present invention is to provide a bearing and a method for manufacturing the bearing.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies from the viewpoint of high-temperature hardness and carbide particle size, and
By subjecting the bearing steel containing carbonitriding to carbonitriding and sintering a compact of high alloy steel powder, the maximum grain size of carbide in the surface layer is 8 μm or less,
Further, it has been found that a raceway or a rolling element having a surface hardness of HRC60 or more can be obtained.

Therefore, a rolling bearing according to the present invention is a rolling bearing having a race and a rolling element, wherein at least one of the race and the rolling element has a maximum grain size of carbide in the surface layer of 8 μm or less. Yes and surface hardness is HRC
Made of more than 60 bearing steels.

Here, the surface layer has a depth of about 0.1 mm from the surface, and in this case, means the surface after polishing after heat treatment.

[0007] In the rolling bearing of the present invention, the surface hardness is HR
Since it is C60 or more, a high-temperature hardness equal to or more than M50 can be obtained. In addition, since the maximum particle size of the carbide in the surface layer can be smaller than M50 of 8 μm or less, under conditions where the lubricating properties at high temperatures deteriorate or under conditions where foreign matter is caught, the carbide may fall off or the carbide may be used as a stress concentration source. The occurrence of surface-originated damage can be prevented. In addition, since the maximum particle size of the carbide can be made smaller than M50, lubrication characteristics are poor, and even when metal contact occurs with a counterpart object during rolling, damage to the counterpart object is prevented, and so-called stamp damage and frosting are prevented. can do.

Here, the steel for bearing includes carburized steel and carbonitrided steel, and steels generally used for rolling bearings can be used.

M50 is a steel containing 4% of chromium (Cr), 4% of molybdenum (Mo) and 1% of vanadium (V). Carbonitrided steel is obtained by increasing the carbon concentration in the surface layer and injecting an appropriate amount of nitrogen.

In the above rolling bearing, it is preferable that at least one of the bearing ring and the rolling element is made of carbonitrided steel containing 1% by weight or more and 2% by weight or less of Si or Al.

In the above-mentioned rolling bearing, it is preferable that at least one of the race and the rolling element is formed by sintering a compact of a high alloy steel powder.

A method of manufacturing a rolling bearing according to the present invention is a method of manufacturing a rolling bearing having a rolling element and a bearing ring, and includes the following steps.

First, carbonitriding treatment is performed on a bearing steel containing 1% by weight or more and 2% by weight or less of Si so that the maximum grain size of carbide in the surface layer is 8 μm or less. Then, the carbonitrided bearing steel is tempered to obtain at least one of a bearing ring and a rolling element made of bearing steel having a surface hardness of HRC60 or more.

In the method for manufacturing a rolling bearing of the present invention, since carbonitriding is performed, a high hardness of HRC 60 or more can be obtained even after high-temperature tempering. Further, since Si or Al, which is an element which gives heat resistance by being dissolved in steel, is contained, excellent heat resistance can be obtained.

When the amount of Si exceeds 2% by weight, heat resistance is improved, but adverse effects such as rusting and carbonization of carbon are easily caused. When the amount of Si added is 1
When the amount is less than the weight percentage, improvement in heat resistance and rolling life cannot be obtained. Al also gives heat resistance similarly to Si, but if it is too much, it forms inclusions and shortens the life. Therefore, Si
Alternatively, the addition amount of Al is 1% by weight or more and 2% by weight or less.

A method of manufacturing a rolling bearing according to another aspect of the present invention is a method of manufacturing a rolling bearing having a bearing ring and a rolling element. The method includes a step of forming at least one of a wheel and a rolling element.

In a method for manufacturing a rolling bearing according to another aspect of the present invention, a compact of high alloy steel powder is sintered to have a maximum carbide grain size of 8 μm or less and a surface hardness of HRC 60 or more. At least one of a bearing ring and a rolling element can be obtained.

JP-A-64-83625 discloses that long life can be obtained even after high-temperature tempering by carbonitriding high Si bearing steel. However,
The invention described in this publication is based on Cr which is a carbide forming element.
(Chromium), Mo (molybdenum), V (vanadium), and the like, the carbides increase after carbonitriding, and the maximum particle size of the carbides in the surface layer exceeds 8 μm.

On the other hand, the material of the present invention does not contain such carbide forming elements such as Cr, Mo, and V,
Even after carbonitriding, the carbide is unlikely to become large, and the maximum particle size of the carbide can be reduced to 8 μm or less. Therefore, even when lubrication conditions such as slippage and metal contact are severe, carbides do not fall off. Also, since the particle size of the carbide after carbonitriding does not become too large, the surface finish surface roughness can be reduced.
For this reason, frosting and stamp flaws are not made on the mating member, and a bearing with high temperature and little change in sound over time can be obtained.

[0020]

EXAMPLES A test piece and a mating test piece were prepared from the materials shown in Table 1 below, and the test piece and the mating test piece were rolled under conditions (Table 2) where metal contact occurred. Thereafter, the formation of pits (including the removal of carbides) on the steel of the test piece and the counter sample, the indentation on the counter sample, the formation of frosting, and the state of peeling were observed. Table 1 shows the results.

[0021]

[Table 1]

[0022]

[Table 2]

According to the results shown in Table 1, M50s or M50s
In the case of the combination of 50 and SUJ2, etc., it was found that a large amount of surface damage occurred on the test piece or the counter specimen, but the surface damage was hardly generated between the steels of the present invention or the combination of the steel of the present invention and SUJ2.

Next, for the steel of the present invention and a comparative steel such as M50 material, the maximum grain size of carbide in the surface layer was 400 ° C.
Hardness, peeling resistance and frosting resistance after tempering were examined. Table 3 shows the results.

[0025]

[Table 3]

As is evident from the results in Table 3, when the diameter of the carbide in the surface layer is small and tempering resistance is obtained, it is found that the surface layer has excellent surface damage resistance. Therefore, when there is no carbide having a diameter of 8 μm or more below the surface due to a combination of chemical components and surface modification, and there is no decrease in hardness during use,
It can be said that cracks and pits formed at the starting point of the carbide and indentation and frosting on the mating surface due to the swelling of the carbide are unlikely to occur.

On the other hand, with respect to peeling damage, M50 steel is excellent in peeling resistance, but peeling is apt to occur in a mating member. This is also because the carbide acts as a rough surface or the mating member is damaged by the dropped carbide, so that surface cracks and surface pits are generated on the mating surface starting from the mating member. When the carbide is reduced and the surface hardness is controlled appropriately, peeling damage is least likely to occur. That is, under the following conditions, it is possible to provide a bearing that is unlikely to cause surface deterioration or surface damage under severe conditions.

(1) Elements (Si, Al) which give heat resistance by being dissolved in steel to form a solid solution are contained in an amount of 1.0% by weight to 2.0% by weight.
The following steel is carbonitrided, and the maximum grain size of carbide in the surface layer is 8 μm or less, and the material that secures HRC 60 or more by tempering at 350 ° C or more and 400 ° C or less. The tempering temperature is 350 ° C or more and 400 ° C or less. The reason is that if the temperature is not within this temperature range, the surface hardness after carbonitriding is HRC60.
This is because it is not possible to do so.

(2) A material having both the above-mentioned carbide particle size and hardness, which is manufactured by sintering a powder of high alloy steel such as M50 material. The embodiment disclosed herein is an example in all respects and is limited. Should not be considered as a matter of course. 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.

[0030]

As described above, according to the present invention, when foreign matter is mixed or the oil film breaks, the formation of pits on the surface and the dropout of carbides are small, and a long life and high precision at high temperatures (up to 300 ° C.). A rolling bearing can be obtained. Also,
Since the carbide is fine, deterioration of dimensional accuracy and deterioration of acoustic characteristics over time can be prevented. In addition, carbonitrided products of high Si steel can provide the above characteristics at low cost.

Claims (5)

[Claims] 1. A rolling bearing having a race and a rolling element, wherein at least one of the race and the rolling element comprises:
The maximum particle size of the carbide in the surface layer is 8 μm or less,
A rolling bearing comprising a bearing steel having a surface hardness of HRC60 or more. 2. The method according to claim 1, wherein at least one of said race and said rolling element contains 1% by weight or more and 2% by weight of Si or Al.
The rolling bearing according to claim 1, wherein the rolling bearing is made of carbonitrided steel containing: 3. The rolling bearing according to claim 1, wherein at least one of the bearing ring and the rolling element is formed by sintering a compact of a high alloy steel powder. . 4. A method of manufacturing a rolling bearing having a bearing ring and a rolling element, comprising: a bearing steel containing 1% by weight or more and 2% by weight or less of Si or Al; Applying a carbonitriding treatment to a thickness of 8 μm or less; and performing a tempering treatment on the carbonitrided bearing steel to form a bearing ring and a rolling element of the bearing steel having a surface hardness of HRC60 or more. A method for manufacturing a rolling bearing, comprising: obtaining at least one of the above. 5. A method for manufacturing a rolling bearing having a bearing ring and a rolling element, wherein at least one of the bearing ring and the rolling element is formed by sintering a compact of high alloy steel powder. A method for manufacturing a rolling bearing.