JP2003342710A - Rolling bearing parts and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a nitrided layer of sufficient depth on a surface layer of a stainless steel rolling bearing parts. <P>SOLUTION: Bearing parts, i.e., an inner ring 1 and an outer ring 2 and balls 3 of a ball bearing are formed of stainless steel containing ≥12 mass % Cr. A nitrided layer of its surface layer is formed by performing heating diffusion of nitrogen contained in a nitrided part through nitridation before hardening, and hardened at a temperature lower than 1,050°C. By exerting high compressive residual stresses to a deep position of the surface layer, and setting the hardness from the surface to an inner part to be Vickers hardness ≥Hv 650, rolling fatigue life characteristic and wear resistance are excellent. This nitrided layer is applicable to the rolling bearing under high loads. <P>COPYRIGHT: (C)2004,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 part made of stainless steel and a method for manufacturing the same.

[0002]

2. Description of the Related Art Inner rings, outer rings, which require special corrosion resistance,
The material of rolling bearing parts such as rolling elements is SUS440C.
For example, stainless steel for bearings is used. Since such a bearing component has a large Cr content of 12 mass% or more, huge carbides are present, and there is a problem that the rolling contact fatigue life is shorter than that of a bearing component using a normal bearing steel such as SUJ2. .
Therefore, its application is limited to rolling bearings with a relatively low load where rolling fatigue life does not matter.

Damage due to rolling contact fatigue is an internal-origin type delamination starting from the depth position where the maximum shear stress near the rolling surface of the bearing component acts, and in order to prolong the rolling contact fatigue life, this damage is caused. Deeper than the position where the maximum shear stress acts,
It is known that it is effective to form a compressive residual stress in the surface layer and to secure sufficient hardness of this surface layer. As a means for forming a compressive residual stress in such a surface layer and sufficiently securing its hardness, there is a method of forming a nitride layer or a carbonitriding layer in the surface layer. That is, the nitriding layer and the carbonitriding layer not only increase the hardness of the surface layer but also have a large specific volume, so that a compressive residual stress is formed in the surface layer. Further, the surface hardness needs to be sufficiently high in order to secure wear resistance which is a basic characteristic of the bearing component.

Therefore, in a bearing component using a normal bearing steel such as SUJ2, a nitriding layer or a carbonitriding layer having a sufficient depth is formed on the surface layer by gas nitriding treatment or gas carbonitriding treatment in a high temperature atmosphere. Many have been formed. However, in a bearing component made of stainless steel for bearings, a gas nitriding treatment or a gas carbonitriding treatment cannot be applied because a passivation film is formed on the surface of the bearing component to prevent the infiltration of nitrogen and carbon.

On the other hand, as a nitriding treatment method for stainless steel, an ion nitriding treatment capable of nitriding while removing the passivation film, and a method of nitriding treatment by substituting and removing the passivation film with fluorine are known. . However, in these nitriding methods, the processing temperature is limited to as low as about 500 ° C., so that it is not possible to form a sufficiently deep nitrided layer required for bearing parts.

[0006]

An object of the present invention is to form a nitride layer having a sufficient depth on the surface layer of a stainless steel rolling bearing component.

[0007]

In order to solve the above problems, the rolling bearing component of the present invention has a Cr content of 12%.
In rolling bearing parts that are made of stainless steel with a mass% or more and have a nitrided layer on the surface, either inner ring, outer ring or rolling element, the nitrided layer is heated and diffused before quenching nitrogen that has been nitrified. It is formed by diffusing by the treatment, and the bearing component is
A structure was adopted in which the hardness from the surface to the inside was Vickers hardness Hv 650 or more by quenching at a temperature lower than 50 ° C.

The rolling bearing component manufacturing method of the present invention uses, as a raw material, stainless steel having a Cr content of 12% by mass or more, and any one of the inner ring, the outer ring, or the rolling element on which a nitride layer is formed is formed. In the method of manufacturing a bearing component, after the material is subjected to a nitriding treatment, nitrogen nitrified by the nitriding treatment is diffused by a heat diffusion treatment to form the nitride layer. A method of quenching at a low temperature was adopted.

That is, after a stainless steel material having a Cr content of 12% by mass or more is subjected to a nitriding treatment, nitrogen nitrified by this nitriding treatment is diffused by a heat diffusion treatment to form a nitride layer, and this heating is performed. By quenching at a temperature lower than 1050 ° C. after the diffusion treatment, the depth of the nitride layer initially formed by the nitriding treatment can be increased by the heat diffusion treatment, and a nitride layer having a sufficient depth as a bearing component can be formed. I did it.
By forming a nitride layer having such a depth, a compressive residual stress can be formed on the surface layer of the bearing component, and the hardness from the surface to a sufficiently deep inside should be Vickers hardness Hv 650 or more. You can

The quenching temperature is set to a temperature lower than 1050 ° C. The reason is that at a normal quenching temperature of 1050 ° C. or higher, the amount of retained austenite increases, and the hardness from the surface to the inside becomes Vickers hardness Hv 650 or higher. Because you cannot do it. As a nitriding treatment means for forming an initial nitriding layer on the stainless steel material, an ion nitriding treatment method or a method of nitriding treatment by substituting and removing the passivation film with fluorine can be adopted.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows a ball bearing used for a special corrosion resistance using a rolling bearing part according to the present invention, and includes a plurality of rolling elements in an annular space between an inner ring 1 and an outer ring 2. A ball 3 is held by a cage 4. Each of the rolling bearing parts of the inner ring 1, the outer ring 2 and the balls 3 is SUS440C (Cr content: 16.
0 to 18.0 mass%).

The rolling bearing parts are made of SUS440C.
Ion nitriding treatment at 500 ° C. for 20 hours to form an initial nitriding layer on the surface layer, and then heat diffusion treatment at 1050 ° C. for 2 hours in vacuum,
Nitrogen in the initial nitride layer was diffused, then heated again in vacuum at 1000 ° C for 20 minutes to perform oil quenching at room temperature, and finally 180 ° C for 2 hours to perform tempering treatment. is there.

Examples and comparative examples will be given below.

[0014]

Example A sample of a bearing component manufactured by the manufacturing method described above using SUS440C as a raw material and a test piece for a line contact life test described later were prepared.

[0015]

[Comparative Example] As Comparative Examples 1 to 4, the same SUS4 as the example
Using 40C as a raw material, a sample of a bearing component manufactured by the following manufacturing method and a test piece for a line contact life test were prepared.
In Comparative Example 1, only the ion nitriding treatment was performed at 500 ° C. for 20 hours. Comparative Examples 2 and 3 are obtained by omitting the above heat diffusion treatment, and each of Comparative Example 1 is heated in a vacuum, oil-quenched to room temperature, and tempered under the same conditions as in the Examples. is there. The heating conditions for quenching are 1050, which is the standard of SUS440C in Comparative Example 2.
℃ × 20 minutes, Comparative Example 3 is lower than this 1000 ℃ ×
20 minutes. Comparative Example 4 is the standard heat treatment of SUS440C that is subjected to only the quenching and tempering treatments, and the quenching and tempering conditions are the same as those of Comparative Example 2.

With respect to each of the samples of the above-mentioned Examples and Comparative Examples, the cross-sectional hardness distribution and residual stress distribution of the surface layer were measured, and the corrosion resistance test was conducted. The cross-sectional hardness distribution and the residual stress distribution were measured up to a depth of 1 mm from the surface, which is sufficiently deeper than the position where the maximum shear stress acts. In the corrosion resistance test, the sample was exposed to an atmosphere of a temperature of 50 ° C. and a humidity of 95% for 20 hours, and then exposed to the atmosphere for 4 hours. The cycle was repeated until red rust was generated on the surface of the sample. Was evaluated. The corrosion resistance test was conducted on the example, the comparative example 4 which is a conventional product, and the sample which was subjected to standard heat treatment of SUJ2 which is a normal bearing steel.

FIG. 2 is a graph showing the measurement results of the cross-sectional hardness distribution of the surface layer. The examples and the comparative examples 3 and 4 all exhibit a sufficiently high hardness distribution, and their Vickers hardness Hv is in the range of 680 to 720. on the other hand,
In Comparative Example 1 in which only the ion nitriding treatment was performed, it was found that the surface area was 0.
Although it has a very high hardness up to about 05 mm, the Vickers hardness Hv inside thereof is sharply reduced to about 250 to 280. From this result, it is estimated that the depth of the nitrided layer formed by the ion nitriding treatment is only about 0.05 mm. In addition, 1050 which is the standard of SUS440C
Comparative Example 2 quenched at 0 ° C. has a hardness sufficiently higher than 0.3 mm from the surface, but on the surface side than this, the Vickers hardness Hv is lower than 650 due to the increase in the amount of retained austenite. Has become.

FIG. 3 is a graph showing the measurement result of the residual stress distribution of the surface layer. The residual stress distribution was measured only for Examples and Comparative Examples 3 and 4 in which a sufficient cross-sectional hardness distribution was obtained. In the case of the example in which the heat diffusion treatment is performed before quenching, a large compressive residual stress is formed up to about 0.6 mm from the surface, which is deeper than the position where the maximum shear stress acts, and gradually decreases inside this. is doing. From this result, it can be seen that the initial nitrided layer formed by the ion nitriding treatment is diffused to a considerable depth by the diffusion of nitrogen by the heat diffusion treatment. On the other hand, in Comparative Example 3 which was quenched and tempered without heat diffusion treatment, a large compressive residual stress was formed up to about 0.2 mm from the surface, but a maximum shear stress deeper than this was applied. At the position, sufficient compressive residual stress is not formed. In Comparative Example 4 which was not subjected to the nitriding treatment, no compressive residual stress was formed.

FIG. 4 is a graph showing the results of the corrosion resistance test. The example shows excellent corrosion resistance equivalent to that of the comparative heat treatment product of SUS440C, which is a standard heat treatment product, and the number of cycles until the occurrence of red rust is five times that of the standard heat treatment product of SUJ2 which is a normal bearing steel. .

Using the test pieces of the above-mentioned Examples and Comparative Examples,
A line contact life test was conducted. Also in this line contact life test, Examples and Comparative Examples 3 and 4 in which a sufficient cross-sectional hardness distribution was obtained.
Only about. For the line contact life test, a cylindrical test piece with a diameter of 12 mm and a length of 12 mm attached to the drive rotation shaft was attached to the driven rotation shaft, and a diameter of 20 m manufactured by SUJ2 was used.
The rolling fatigue life is evaluated by L10 life (90% of the test piece can be used without being damaged) by rolling it in line contact with a cylinder having a length of m and a length of 20 mm. The test conditions are as follows.・ Maximum contact pressure Pmax: 4.2 GPa ・ Load speed: 20400 times / min ・ Lubricating oil: Turbine oil VG68

[0021]

[Table 1]

Table 1 shows the test results. In the table, the life ratio based on the L10 life of Comparative Example 4 is also shown. The example has a L10 life that is at least twice as long as that of the comparative example 4, which is a standard heat-treated product of SUS440C. From this result,
As shown in FIG. 3, it can be seen that forming a large compressive residual stress from the surface to a sufficiently deep position was effective in improving the rolling contact fatigue life. The L10 life of Comparative Example 3 in which the formation depth of the compressive residual stress was shallower than the position where the maximum shear stress acts was almost the same as that of Comparative Example 4.

In the above-mentioned embodiments, the material of each bearing component is SUS440C, but the material of the bearing component according to the present invention may be other stainless steel for bearings having a Cr content of 12% by mass or more. Further, the bearing component and the method for manufacturing the same according to the present invention are not limited to those for ball bearings, and can of course be applied to those for other types of rolling bearings such as roller bearings.

[0024]

INDUSTRIAL APPLICABILITY As described above, the rolling bearing component of the present invention is made of stainless steel having a Cr content of 12% by mass or more, and the nitride layer of the surface layer thereof is made of nitrogen that has been nitrified by nitriding treatment. Before hardening, it is formed by diffusing it with a heating diffusion process,
After this heat diffusion treatment, quenching is performed at a temperature lower than 1050 ° C., a large compressive residual stress is formed to a deep position of the surface layer, and the hardness from the surface to the inside is Vickers hardness Hv 650 or more, which is excellent. It has rolling fatigue life characteristics and wear resistance, and can be applied to rolling bearings that require special corrosion resistance and under high load.

In the rolling bearing component manufacturing method of the present invention, a nitriding treatment is performed using stainless steel having a Cr content of 12 mass% or more as a raw material, and then nitrogen diffused by the nitriding treatment is heated and diffused. To form a nitride layer,
After this heat diffusion treatment, quenching was performed at a temperature lower than 1050 ° C, so that a large compressive residual stress can be formed deep in the surface layer of the bearing component, and the hardness from the surface to the inside is Vickers hardness Hv 650 or more. Therefore, it is possible to manufacture a bearing component suitable for a rolling bearing that requires special corrosion resistance and is subject to a high load.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a ball bearing adopting a bearing component of an embodiment.

FIG. 2 is a graph showing cross-sectional hardness distributions of surface layers in Examples and Comparative Examples.

FIG. 3 is a graph showing residual compressive stress distributions of surface layers in Examples and Comparative Examples.

FIG. 4 is a graph showing the results of the corrosion resistance test of Examples and Comparative Examples.

[Explanation of symbols]

1 inner ring 2 outer ring 3 balls 4 cage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F16C 33/58 F16C 33/58 F term (reference) 3J101 AA02 AA62 BA01 BA53 BA54 DA02 EA06 FA08 FA15 4K028 BA02 BA12 4K042 AA22 BA03 BA04 CA07 DA06

Claims (2)

[Claims] 1. In a rolling bearing component, which is formed of stainless steel having a Cr content of 12% by mass or more and has a nitride layer on the surface, which is an inner ring, an outer ring or a rolling element, the nitride layer is immersed in a nitriding treatment. It is formed by diffusing the nitrogen that has been nitrified by a heat diffusion treatment before quenching, and the bearing component is quenched at a temperature lower than 1050 ° C. after this heat diffusion treatment, so that the hardness from the surface to the inside is reduced. A rolling bearing part characterized by having a Vickers hardness Hv of 650 or more. 2. An inner ring formed of a stainless steel having a Cr content of 12% by mass or more and having a nitride layer formed on the surface thereof,
In a method for manufacturing either a rolling bearing component of an outer ring or a rolling element, after the material is subjected to a nitriding treatment, nitrogen nitrided by this nitriding treatment is diffused by a heat diffusion treatment to form the nitrided layer, After this heat diffusion treatment, 1050 ° C
A method for manufacturing a rolling bearing component, characterized by quenching at a temperature lower than that.