JP2022135966A - Race ring for rolling bearing, manufacturing method thereof, and rolling bearing using race ring for rolling bearing - Google Patents

Abstract

To provide a race ring for a rolling bearing capable of maintaining fitting performance with a shaft under a quasi-high temperature environment close to 150°C for a long period while securing resistance to foreign matter, a manufacturing method thereof, and a rolling bearing using the race ring.SOLUTION: In a race ring for a rolling bearing made of high carbon chromium bearing steel, a carbonitriding layer is formed on a raceway surface that comes in contact with a rolling element. A residual austenite quantity at a position away from a surface side of the carbonitriding layer in a depth direction by 50 μm is caused to be in the range of 15-25% by an area ratio, and a residual austenite quantity at a position away from the surface side of the carbonitriding layer in the depth direction at least by 800 μm is caused to be less than 10% by an area ratio.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a bearing ring (inner ring and outer ring) for a rolling bearing made of high-carbon chromium bearing steel, a method for manufacturing the same, and a rolling bearing using the bearing ring.

Rolling bearings with carbonitrided layers formed on the surfaces of the inner and outer rings and rolling elements made of high-carbon chromium bearing steel (SUJ2) have improved wear resistance and impression resistance on the raceway surface, resulting in longer rolling bearing life. known to promote

In addition, Patent Documents 1 and 2 disclose that by setting the amount of retained austenite in the carbonitrided layer to a predetermined range, it has characteristics that damage and peeling phenomenon (flaking) are unlikely to occur due to foreign matter contamination from the outside. is disclosed.

JP-A-2006-71022 JP 2017-150640 A

However, in order to increase the resistance to foreign matter, SUJ2 rolling bearings must be subjected to heat treatment under special conditions such as carbonitriding in order to increase the amount of retained austenite in the surface layer.

When heat treatment is performed under such special conditions, not only the amount of retained austenite in the surface layer but also the amount of retained austenite in the interior is maintained at the same time. The inner diameter expands. As a result, there was a problem that the fitting performance with the shaft on the machine side could not be maintained, resulting in creep and deterioration in transmission characteristics between the shaft and the bearing.

On the other hand, when trying to improve the dimensional stability of rolling bearings, there is a method of reducing the amount of retained austenite in the steel by high-temperature tempering. Another problem arises in that the amount of retained austenite in the surface layer portion, which contributes to foreign matter resistance, also decreases.

In particular, in so-called thick-walled products, where the thickness of the inner ring (based on the center of the raceway surface) is 6 mm or more, the cooling rate during quenching decreases, so in the case of carbonitrided products, the amount of retained austenite in the surface layer is higher As a result, there is a problem that the surface layer portion cannot sufficiently obtain a predetermined hardness.

Accordingly, the present invention provides a bearing ring for a rolling bearing that can maintain the fitting performance with a shaft for a long period of time in a semi-high temperature environment of about 150° C. while ensuring foreign matter resistance, a method for manufacturing the bearing ring, and a use thereof. An object of the present invention is to provide a smooth rolling bearing.

In the rolling bearing ring made of high-carbon chromium bearing steel (SUJ2) of the present invention, a carbonitrided layer is formed on the raceway (surface) in contact with the rolling element, and the surface side of the carbonitrided layer is separated from the surface side by 50 μm in the depth direction. The area ratio of the retained austenite at the position where the carbonitrided layer is located is set to be in the range of 15% or more and 25% or less, and the area ratio of the retained austenite immediately below the carbonitrided layer (high carbon chromium bearing steel) is set to less than 10%.

Here, the term "immediately below the carbonitrided layer" refers to a region of the high-carbon chromium bearing steel, which is the base material, and refers to a position at least 800 μm or more in the depth direction from the surface side of the carbonitrided layer.

In the manufacturing method of the bearing ring for the rolling bearing, high-carbon chromium bearing steel is heated to 800°C in an atmosphere of hydrocarbon-based gas (enriched gas) such as LPG (liquefied propane gas), endothermic transformation gas (RX gas) and ammonia. A first heat treatment (carbonitriding treatment) for heating in the range of ~ 850 ° C. After the first heat treatment, the high carbon chromium bearing steel is treated with a hydrocarbon gas such as LPG (enriched gas) and an endothermic transformation gas (RX gas). ), and the third heat treatment (tempering treatment), first to third heat treatments.

Further, the invention of the rolling bearing having the above-described rolling bearing ring and rolling elements made of high carbon chromium bearing steel (SUJ2) forms a carbonitrided layer on the surface of the rolling element, and the surface layer of the carbonitrided layer is The hardness is in the range of 780 HV or more and 900 HV or less in Vickers hardness, the amount of retained austenite in the carbonitrided layer is in the range of 25% or more and 45% or less in area ratio, and the carbonitride on the surface of the carbonitrided layer is The particle diameter shall be 5 μm or less.

The bearing ring for a rolling bearing of the present invention maintains a constant amount of retained austenite in the carbonitrided layer provided on the surface layer, and reduces the amount of retained austenite in the base material (high-carbon chromium bearing steel). is maintained, and the fitting performance with the shaft can be maintained for a long period of time even in a semi-high temperature environment of about 150°C.

1 is a photograph of a cross-sectional structure of a bearing ring (inner ring) for a rolling bearing; It shows the heat treatment conditions for the inventive materials of the examples and the comparative materials. 1 is a list of retained austenite amounts and the like of inventive materials of examples and comparative materials. It is a dimension measurement result of Example 1. FIG. 2 shows the results of life test in foreign oil in Example 2. FIG.

One embodiment of the rolling bearing race according to the present invention will be described below with reference to the drawings. FIG. 1 shows a photograph of a cross-sectional structure of a bearing ring (inner ring) for a rolling bearing that is one embodiment of the present invention. As shown in FIG. 1, the bearing ring for rolling bearing has a carbonitrided layer formed on the surface of high-carbon chromium bearing steel, which is a base material. The surface of the carbonitrided layer is also a contact surface (raceway surface) with a rolling element (not shown).

In addition, although the thickness of the carbonitrided layer shown in FIG. If there is, it can correspond to various thicknesses depending on the size (dimension) of the rolling bearing ring. The hardness of the surface layer of the carbonitrided layer is desirably in the range of 700 HV or more and 850 HV or less in terms of Vickers hardness.

The matrix structure of this carbonitrided layer is mainly formed of martensite and retained austenite, and the ratio of martensite and retained austenite (ratio of area ratio) changes depending on the depth direction of the carbonitrided layer. For example, the amount (area ratio) of martensite on the surface of the carbonitrided layer exceeds the area ratio of retained austenite, but as the carbonitrided layer progresses in the depth direction, the area ratio of martensite gradually increases, Conversely, the area ratio of retained austenite gradually decreases.

In particular, the amount of retained austenite at a position 50 μm (0.05 mm) away from the surface side of the carbonitrided layer in the depth direction is in the range of 15% or more and 25% or less in area ratio, and the amount of retained austenite in the carbonitrided layer has the highest area ratio. Also, the amount of N (nitrogen amount) contained in the carbonitrided layer is at least 0.05% by mass.

On the other hand, immediately below the carbonitrided layer, that is, in the high-carbon chromium bearing steel that is the base material, the area ratio of the retained austenite amount is even smaller than the area ratio of the retained austenite amount in the carbonitrided layer. For example, the amount of retained austenite at a position (the base material only region) at least 800 μm (0.8 mm) away from the surface side of the carbonitrided layer in the depth direction is less than 10% in terms of area ratio.

Next, a method for manufacturing the above-described high-carbon chromium bearing steel rolling bearing ring will be described. The manufacturing method is roughly divided into a first heat treatment (carbonitriding treatment), a second heat treatment (diffusion treatment), and a third heat treatment (tempering treatment). Each of these heat treatments is described below.

First, a carbonitriding treatment is performed on the high-carbon chromium bearing steel (SUJ2), which is the base material. This treatment forms a carbonitrided layer on the surface of the high carbon chromium bearing steel. A high-carbon chromium bearing steel is placed in a heat treatment furnace, and a hydrocarbon-based gas (enriched gas) such as LPG, an endothermic transformation gas (RX gas), and ammonia are enclosed in the heat treatment furnace. Heat to temperature range. This state is maintained for at least 2 hours. At this time, the CP value is in the range of 1.0 to 1.5%, and the ammonia concentration is in the range of 1.0 to 3.0%.

After completion of the carbonitriding treatment, the rolling bearing ring is subjected to a diffusion treatment. In the diffusion treatment, the rolling bearing ring placed in the heat treatment furnace is again heated to 800 to 850° C. and held for at least 30 minutes. At this time, only a hydrocarbon-based gas (enriched gas) such as LPG and an endothermic transformation gas (RX gas) are charged into the heat treatment furnace (the CP value is 0.6 to 2.0%). Finally, after the diffusion treatment is completed, a tempering treatment is performed in a temperature range of 180-230° C. for at least one hour.

Next, an embodiment of a rolling bearing using the rolling bearing ring described above will be described below. The rolling bearing is formed from the aforementioned rolling bearing ring and rolling elements made of high-carbon chromium bearing steel. A carbonitrided layer is formed on the surface of this rolling element, and the surface layer hardness of the carbonitrided layer is in the range of 780 HV to 900 HV in terms of Vickers hardness.

Further, the amount of retained austenite in the carbonitrided layer of the rolling element is in the range of 25% or more and 45% or less in terms of area ratio, and the grain size of the carbonitride on the surface of the carbonitrided layer is 5 μm or less.

(Example 1)
Using a bearing ring (inner ring) for a rolling bearing according to the present invention and a bearing ring (inner ring) for a bearing outside the present invention, changes in dimensions over time at a predetermined temperature were measured. The test results will be explained using drawings. do. Hereinafter, the test piece of the rolling bearing ring (inner ring) according to the present invention used in this example is referred to as "inventive material", and the test piece of the bearing ring (inner ring) other than the present invention is referred to as "comparative material". .

All the test pieces used in this example were made of high carbon chromium bearing steel (SUJ2), and the carbonitrided layer (position 50 μm away from the surface side of the carbonitrided layer in the depth direction) and immediately below the carbonitrided layer (carbonitrided layer Inventive material (2 levels) and comparative material (3 levels) according to the amount of retained austenite at a position 800 μm away from the surface side in the depth direction). FIG. 2 shows the heat treatment conditions of the inventive materials used in Example 1 and comparative materials 1 to 3, and FIG.

In this example, the inventive material and the comparative material were placed and held in a constant temperature bath set at a predetermined temperature (150° C.). After that, the inventive material and the comparative material were taken out from the thermostatic chamber each time a predetermined time had passed since they were placed in the thermostatic chamber, and after slowly cooling to room temperature, the inventive material and the comparative material were measured using a three-dimensional measuring machine. of the inner diameter was measured.

FIG. 4 shows the measurement results of the dimensions of Inventive Materials 1 and 2 and Comparative Materials 1 to 3 in this example. After setting the test piece in the constant temperature bath, take out the test piece every time 50, 100, 150, 300, 400, 500, 1000 times have passed, measure the dimension, / initial inner diameter x 100) was calculated.

As shown in FIG. 4, the test pieces taken out after 1000 hours from being placed in the constant temperature bath are arranged in descending order of dimensional change rate: 0.005% for comparative material 1, 0.023% for inventive material 1, 0.023% for The material 2 was 0.028%, the comparative material 2 was 0.061%, and the comparative material 3 was 0.088%. From this result, it was found that the smaller the amount of retained austenite inside, the smaller the dimensional change rate.

In particular, invention materials 1 and 2 and comparative material 1, in which the amount of internal retained austenite is less than 10%, obtained results superior to those of comparative materials 2 and 3. In other words, it was found that by setting the amount of retained austenite in the base metal (SUJ2) immediately below the carbonitrided layer to less than 10%, the fitting performance with the shaft can be maintained for a long period of time in a semi-high temperature environment of around 150°C.

(Example 2: Life test in foreign oil)
Next, using the same test piece (inner ring) used in Example 1, the impression resistance of the raceway surface against foreign matter mixed in the lubricating oil was evaluated. In this example, test specimens were obtained by assembling single-row deep groove ball bearings (hereinafter referred to as ball bearings) using inventive materials 1 and 2, comparative materials 1 to 3, and an outer ring made of SUJ2.

In the test method of this embodiment, the above-mentioned ball bearings, which serve as test pieces, are attached to both ends of the shaft, and another bearing is attached to the center of the shaft. While injecting lubricating oil (oil temperature: 100° C.), the shaft was rotated at a rotation speed of 3500 rpm while applying a radial load (14 kN).

In this example, the sensor was set to detect vibration and automatically stop the rotation of the shaft when the test piece, the ball bearing, was damaged. The basic rated life ( _L10 life) was calculated using the time from the start of this test until the rotation of the shaft stopped as the test time. FIG. 5 shows the results of the basic rating life test of Inventive Materials 1 and 2 and Comparative Materials 1-3.

As shown in FIG. 5, comparing the basic rating life (L ₁₀ life), that is, the length of the test time at a cumulative failure rate of 10%, Comparative material 1 is 36.1 hours, Comparative material 2 is 14.3 hours, Comparative material 3 was 33.4 hours. In contrast, the inventive material 1 lasted 86.7 hours, and the inventive material 2 lasted 65.7 hours. In other words, it was found that even when the amount of retained austenite inside is low, the service life can be extended while maintaining dimensional stability by increasing the amount of retained austenite in the surface layer. From the above test results, Inventive Materials 1 and 2 have foreign matter resistance performance as compared with Comparative Materials 1-3.

Claims (4)

In a rolling bearing ring made of high-carbon chromium bearing steel, a carbonitrided layer is formed on the raceway surface in contact with the rolling elements, and residual The amount of austenite is in the range of 15% or more and 25% or less in area ratio, and the amount of retained austenite at a position at least 800 μm away from the surface side of the carbonitrided layer in the depth direction is less than 10% in area ratio. A bearing ring for a rolling bearing characterized by: 2. The rolling bearing ring according to claim 1, wherein the rolling bearing ring is an inner ring for a rolling bearing having a thickness of 6 mm or more and 12 mm or less at the central portion of the raceway surface. a first heat treatment in which the high carbon chromium bearing steel is heated in a hydrocarbon gas and ammonia atmosphere in the range of 800 to 850 ° C., and after the first heat treatment, the high carbon chromium bearing steel is heated to a hydrocarbon gas. and a third heat treatment for heating the high carbon chromium bearing steel to 180 to 230° C. after the second heat treatment. A method for manufacturing a bearing ring for a rolling bearing, characterized by: A rolling bearing comprising the rolling bearing ring according to claim 1 or 2 and a rolling element made of high carbon chromium bearing steel, wherein a carbonitrided layer is formed on the surface of the rolling element, The surface hardness of the carbonitrided layer of the rolling element is in the range of 780 HV or more and 900 HV or less in terms of Vickers hardness, and the amount of retained austenite in the carbonitrided layer of the rolling element is in the range of 25% or more and 45% or less in area ratio. and a carbonitride particle diameter of 5 μm or less on the surface of the carbonitrided layer of the rolling element.

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