Rolling bearing and method for manufacturing rolling element

Abstract

The invention provides a rolling bearing capable of prolonging peeling life and a method for manufacturing a rolling body. A rolling bearing is provided with an inner ring (2), an outer ring (3), and rolling elements (4), the rolling elements (4) having a hardness of HRC 61.1 or more and a retained austenite amount of 31 vol% or less, and the ratio of the hardness of the rolling elements (4) to the hardness of the inner ring (2) and the outer ring (3) being 1 or more.

Description

Technical Field

[0001] The invention relates to a rolling bearing and a method for manufacturing a rolling element. Background Art

[0002] In recent years, the trend towards further extending the life of bearings has intensified in the entire bearing industry. With the advancement of steelmaking technology, the cleanliness of bearing steel has been greatly improved, so the life problems caused by internal starting point peeling have been reduced, and the life reduction caused by surface starting point peeling caused by indentations caused by foreign matter biting into the lubricating oil has become a problem.

[0003] In order to improve such peeling life, for example, the following rolling bearing is disclosed in Patent Document 1: at least one component among the outer ring, inner ring, and rolling element is obtained by performing quenching and tempering treatment, the hardness of the surface portion is greater than HRC60 and less than HRC65, and the retained austenite on the raceway surface is greater than 15 volume % and less than 24 volume %.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-41652 Summary of the invention

[0007] Problems to be solved by the invention

[0008] According to the method disclosed in Patent Document 1, the amount of retained austenite can be increased by quenching and tempering without performing special heat treatment such as carbonitriding, and the peeling life can be improved. However, further improvement of the peeling life is required.

[0009] Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a rolling bearing and a method for manufacturing a rolling element that can improve the peeling life.

[0010] Means for solving problems

[0011] According to one embodiment of the present invention, a rolling bearing is provided, which comprises an inner ring, an outer ring and a rolling element, wherein the hardness of the rolling element is greater than HRC61.1, the amount of retained austenite is less than 31 vol%, and the ratio of the hardness of the rolling element to the hardness of the inner ring and the outer ring is greater than 1.

[0012] According to one aspect of the present invention, there is provided a method for manufacturing a rolling element, which is used in a rolling bearing, wherein the method for manufacturing a rolling element comprises: a quenching process, in which after being processed into a specified shape in a manner to become the rolling element, the heated raw material is immersed in oil or water at a temperature of not less than 60°C and not more than 120°C, the raw material is kept immersed in the oil or the water, and the temperature of the raw material is kept at not less than 60°C and not more than 120°C for more than 20 minutes; a first low-temperature holding process, in which after the quenching process, the raw material is cooled, and the raw material is kept at a temperature of not less than 5°C and not more than 35°C for more than 30 minutes; a vacuum cleaning process, in which after the first low-temperature holding process, the raw material is vacuum cleaned at a temperature of not less than 100°C and not more than 140°C for more than 40 minutes; and a second low-temperature holding process, in which after the vacuum cleaning process, the raw material is cooled, and the temperature of the raw material is kept below 35°C.

[0013] Effects of the Invention

[0014] According to one aspect of the present invention, there is provided a rolling bearing and a method for manufacturing a rolling element capable of improving the peeling life. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view showing a rolling bearing according to one embodiment of the present invention.

[0016] Figure 2 This is a graph showing the relationship between the amount of retained austenite and the dimensional change rate.

[0017] Figure 3 It is an explanatory diagram showing a method of heat treatment of a rolling element. DETAILED DESCRIPTION

[0018] In the following detailed description, embodiments of the present invention are described with reference to the accompanying drawings. In the description of the accompanying drawings, the same or similar parts are marked with the same or similar figure marks and repeated descriptions are omitted. Each drawing is a schematic diagram, including situations that are different from reality. In addition, the embodiments shown below illustrate devices and methods for concretizing the technical ideas of the present invention, but the technical ideas of the present invention do not limit the materials, structures, configurations, etc. of the constituent parts to the following contents. The technical ideas of the present invention can be subjected to various changes within the technical scope specified by the claims recorded in the claims.

[0019] <Rolling bearings>

[0020] Reference Figure 1 , a rolling bearing 1 according to an embodiment of the present invention will be described. Figure 1As shown, the rolling bearing 1 includes an inner ring 2, an outer ring 3, a plurality of rolling elements 4, and a cage 5. The inner ring 2 and the outer ring 3 are also collectively referred to as a raceway ring.

[0021] The ratio of the hardness of the rolling element 4 to the hardness of the inner ring 2 and the outer ring 3 is greater than or equal to 1. In other words, the hardness of the rolling element 4 is greater than or equal to the hardness of the inner ring 2 and the outer ring 3.

[0022] It is known that the cause of early peeling under the foreign matter mixed lubrication is the tangential force acting on the rolling surface of the raceway ring and the rolling element 4. Factors affecting the tangential force include the surface shape and surface roughness of the rolling surface. When a rolling device such as a rolling bearing is used in an environment where the oil film formation in the rolling portion is insufficient, a protrusion interference of the surface roughness is generated between the two rolling surfaces. It is known that in the protrusion interference portion where this protrusion interference occurs, the life of the rolling device is reduced due to the increase in the friction coefficient and the increase in the local contact stress, which causes the generation of surface damage. When the tangential force acting on the raceway ring increases due to Mindrin Slip and the like, damage to the inner ring 2 and the outer ring 3 caused by rotation is likely to occur. Therefore, by making the surface hardness of the rolling element 4 harder than the raceway surface, an appropriate hardness difference is given to the contacting parts, thereby improving the surface roughness and suppressing the damage to the rolling element 4 as much as possible.

[0023] In this embodiment, the rolling element 4 is a roller. In addition, the hardness of the rolling element 4 is HRC61.1 or more, and the amount of retained austenite is 31 vol% or less. Moreover, preferably, the residual compressive stress on the surface of the rolling element 4 is 100 MPa or less. The amount of retained austenite and the dimensional change rate have Figure 2 As shown in the correlation, there is a tendency that the greater the initial retained austenite amount, the greater the dimensional change. When the retained austenite amount increases, the gap between the rolling element 4 and the raceway ring becomes narrower, causing sintering, etc., which easily shortens the life. Therefore, by setting the upper limit of the retained austenite amount to 31vol%, the dimensional stability is improved, and the increase in surface pressure and sintering caused by the change in size over time can be suppressed, thereby increasing the life of the rolling bearing. In addition, by making the hardness of the rolling element 4 above HRC61.1, a rolling element 4 that is harder than the inner ring 2 and the outer ring 3 can be formed.

[0024] The inner ring 2 and the outer ring 3 are not particularly limited as long as they satisfy the hardness ratio with the rolling element 4, and the manufacturing method, materials, etc. are not particularly limited. In addition, the inner ring 2, the outer ring 3 and the rolling element 4 are preferably made of the same material of SUJ2 or SUJ3, which is a high carbon chromium bearing steel specified in JIS G4805.

[0025] <Method for manufacturing rolling element>

[0026] Next, a method for manufacturing the rolling element 4 of this embodiment will be described. Figure 3 The rolling element 4 is manufactured by the heat treatment mode shown. Figure 3 As shown, first, the following high temperature holding step is performed: the raw material (also referred to as the processed material or workpiece) processed into a predetermined shape to become the rolling element 4 is heated and held at a temperature of 800° C. to 900° C. for a certain period of time. In the high temperature holding step, the time of holding at a temperature of 800° C. to 900° C. is preferably set to 30 minutes to 90 minutes.

[0027] After the high temperature holding process, a quenching process is performed on the heated raw material to perform quenching treatment. In the quenching process, the raw material is immersed in oil or water at a temperature of 60°C or more and 120°C or less (quenching treatment). Then, in a state where the raw material is immersed in oil or water, the temperature of the raw material is maintained at 60°C or more and 120°C or less, preferably at 90°C. In addition, in a state where the raw material is immersed in oil or water, the temperature of the raw material is maintained at 60°C or more and 120°C or less for more than 20 minutes, preferably more than 24 minutes. In addition, when the temperature of the raw material is lower than 60°C, the retained austenite is unstable. In addition, when the temperature of the raw material exceeds 120°C, energy is wasted and manufacturing costs increase.

[0028] After the quenching process, the first low temperature holding process is performed to cool the raw material and keep the raw material at a temperature of 5°C or more and 35°C or less for more than 30 minutes. In the first low temperature holding process, the raw material after the quenching treatment is placed at room temperature and left to stand for cooling. At this time, air cooling can also be performed using a fan or the like. In addition, in the first low temperature holding process, the retained austenite can be further stabilized by keeping the raw material at a temperature of 5°C or more and 35°C or less.

[0029] After the first low temperature holding step, a vacuum cleaning step is performed in which the raw materials are vacuum cleaned at a temperature of 100°C to 140°C, preferably 120°C, for more than 40 minutes. In the vacuum cleaning step, it is preferred to use a vacuum cleaning machine that can be heated and set the temperature. In addition, the vacuum cleaning time is preferably more than 40 minutes. Vacuum cleaning not only has excellent cleaning power, but also removes bubbles, and the cleaning liquid contacts the raw materials to every corner of the raw materials, thereby the raw materials are heated evenly and quickly. Furthermore, the solvent loss in vacuum cleaning is also small, and the environmental load is also reduced.

[0030] After the vacuum cleaning process, a second low-temperature holding process is performed to cool the raw material and keep the temperature of the raw material below 35°C. In the second low-temperature holding process, the raw material can be cooled in the same way as the first low-temperature holding process, and oil cooling or water cooling can be used when cooling to a low temperature of about 0°C to 10°C. In addition, the temperature of the raw material can be made below 0°C, but it is not preferred because of the waste of energy. By performing the second low-temperature holding process, the retained austenite can be further stabilized. In addition, in the second low-temperature holding process, when the temperature of the raw material exceeds 35°C, the stabilization effect of the retained austenite is reduced. In addition, in the second low-temperature holding process, it is preferred to keep the temperature of the raw material below 35°C for more than 15 minutes.

[0031] After the second low temperature holding step, a tempering step is performed in which the raw material is held at a temperature of 160° C. to 180° C. for 90 minutes to 150 minutes. The tempering step is not essential, but the toughness and dimensional stability can be improved by performing the tempering treatment.

[0032] In the manufacturing method of the rolling element 4 of the present embodiment, at least a quenching step, a first low temperature holding step, a vacuum cleaning step, and a second low temperature holding step are performed. Thus, the rolling element 4 having a retained austenite amount of 31 vol% or less, a hardness of HRC61.1 or more, and a surface residual compressive stress of 100 MPa or less can be manufactured without excessive processing and with low energy consumption. In addition, the residual compressive stress is an average value in the circumferential direction at a depth of 100 μm.

[0033] In addition, in the manufacturing method of the rolling element 4 of the present embodiment, no special equipment is required, and general equipment can be used to optimize the heat treatment conditions. Therefore, there is no need to install new equipment, and the life of the rolling bearing can be extended at a low cost. Furthermore, since nitriding treatment used in the surface treatment of the bearing is not required, CO2 is also reduced.

[0034] Furthermore, in the rolling bearing of the present embodiment, there is no restriction on the hardness of the inner ring 2 and the outer ring 3 , so there are few restrictions on the materials used, and the bearing can be manufactured easily.

[0035] <Modification>

[0036] The present invention has been described above with reference to specific embodiments, but it is not intended to limit the invention by these descriptions. By referring to the description of the present invention, other embodiments of the present invention including the disclosed embodiments and various modifications are also obvious to those skilled in the art. Therefore, it should be understood that the embodiments of the invention described in the claims also include embodiments that include these modifications described in this specification alone or in combination.

[0037] For example, in the above-mentioned embodiment, the inner ring 2, the outer ring 3, and the rolling element 4 are made of the same material of SUJ2 or SUJ3, which is a high carbon chromium bearing steel specified in JIS G4805, but the present invention is not limited to this example. The inner ring 2, the outer ring 3, and the rolling element 4 may be made of materials other than SUJ2 and SUJ3, or may be made of different materials.

[0038] <Effects of Implementation Methods>

[0039] (1) A rolling bearing 1 according to one embodiment of the present invention comprises an inner ring 2, an outer ring 3 and rolling elements 4, wherein the hardness of the rolling elements 4 is greater than HRC 61.1, the amount of retained austenite is less than 31 vol%, and the ratio of the hardness of the rolling elements 4 to the hardness of the inner ring 2 and the outer ring 3 is greater than 1.

[0040] According to the structure of (1) above, the surface hardness of the rolling element 4 is made harder than the hardness of the raceway surfaces of the inner ring 2 and the outer ring 3, and the surface roughness is improved by an appropriate hardness difference between the contacting parts, so that damage to the rolling element 4 can be suppressed. In addition, with respect to the rolling element 4, the dimensional stability is improved while the hardness is improved, and the increase in surface pressure and the occurrence of sintering caused by the change in size over time can be suppressed. As a result, the peeling life of the rolling bearing 1 can be improved.

[0041] (2) In the structure of (1) above, the rolling element 4 is a roller.

[0042] (3) In the above-mentioned structure (1) or (2), the rolling element 4 is made of SUJ2 or SUJ3 which is a high carbon chromium bearing steel specified in JIS G4805.

[0043] (4) A method for manufacturing a rolling element 4 according to one embodiment of the present invention is a method for manufacturing a rolling element 4 used in a rolling bearing, comprising: a quenching step, in which, after being processed into a specified shape in a manner to become the rolling element 4, the heated raw material is immersed in oil or water at a temperature of not less than 60°C and not more than 120°C and the raw material is maintained in a state of being immersed in the oil or water, and the temperature of the raw material is maintained at not less than 60°C and not more than 120°C for more than 20 minutes; a first low-temperature holding step, in which, after the quenching step, the raw material is cooled and the raw material is maintained at a temperature of not less than 5°C and not more than 35°C for more than 30 minutes; a vacuum cleaning step, in which, after the first low-temperature holding step, the raw material is vacuum cleaned at a temperature of not less than 100°C and not more than 140°C for more than 40 minutes; and a second low-temperature holding step, in which, after the vacuum cleaning step, the raw material is cooled and the temperature of the raw material is maintained at less than 35°C.

[0044] According to the configuration of (4), the rolling element 4 of the configuration of (1) can be stably manufactured. In addition, the heat treatment conditions can be optimized using common equipment, and the life of the rolling bearing can be extended at low cost.

[0045] (5) In the configuration of (4) above, there is further provided a tempering step of holding the raw material at a temperature of 160° C. to 180° C. for 90 minutes to 150 minutes after the second low temperature holding step.

[0046] (6) In the structure of (4) or (5) above, the rolling element 4 is a roller.

[0047] (7) In any one of the above structures (4) to (6), the rolling element 4 is made of SUJ2 or SUJ3, which is a high carbon chromium bearing steel specified in JIS G4805.

[0048] (8) A rolling bearing according to one aspect of the present invention is a rolling bearing including an inner ring, an outer ring, and rolling elements, and is manufactured by the method for manufacturing a rolling bearing having any one of the structures (4) to (7) above.

[0049] Example

[0050] The embodiment implemented by the inventor is described. In this embodiment, a rolling element 4 is manufactured using the rolling element manufacturing method of the above embodiment, and the residual stress, the amount of retained austenite, and the hardness are investigated. Table 1 shows the conditions of the heat treatment of Examples 1 to 6 as the above embodiment, Comparative Example 1 in which the heat treatment conditions are set to conditions different from those of the above embodiment, and the heat treatment conditions in Comparative Example 2, as well as the results of the residual stress, the amount of retained austenite, and the hardness.

[0051] [Table 1]

[0052]

[0053] In this embodiment, first, as a high temperature holding process, the raw material processed into the shape of the rolling element 4 using SUJ2 as the material is heated to 845°C. Then, as a quenching process, the heated raw material is immersed in oil at 60°C or 90°C for quenching. The time for immersing the raw material in the oil is set to 24 minutes. Furthermore, deoiling is performed for 40 minutes, and then the first low temperature holding process is performed. In the first low temperature holding process, the raw material is kept at a temperature of 5°C or above and 35°C or below for 30 minutes by cooling the raw material at room temperature or by fan cooling the raw material using a fan. Then, as a vacuum cleaning process, vacuum cleaning is performed at a temperature of 120°C for 40 minutes. In addition, in Comparative Example 1, vacuum cleaning is replaced by washing with warm water at 80°C for 30 minutes. Furthermore, as a second low temperature holding process, the raw material is cooled and the temperature is kept at 0°C or above and 10°C or below. In addition, in Comparative Examples 1 and 2, cooling is performed by cooling for 15 minutes or 30 minutes. Then, as a tempering process, the raw material is heated and maintained at a temperature of 160°C, 180°C, or 200°C.

[0054] According to this embodiment, it was confirmed that rolling elements 4 having a retained austenite content of 31 vol% or less, a hardness of HRC61.1 or more, and a surface residual compressive stress of 100 MPa or less can be manufactured. HRC61.1 or more corresponds to 740 or more in HMV (SAE J417).

[0055] Description of Reference Numerals

[0056] 1: rolling bearing; 2: inner ring; 3: outer ring; 4: rolling element.

Claims

1. A rolling bearing, comprising an inner ring, an outer ring and rolling elements, wherein: The rolling element has a hardness of HRC61.1 or higher and a retained austenite content of 31 vol% or less. A ratio of the hardness of the rolling element to the hardness of the inner ring and the outer ring is 1 or more.

2. The rolling bearing according to claim 1, wherein: The rolling elements are rollers.

3. The rolling bearing according to claim 1 or 2, wherein: The rolling elements, the inner ring, and the outer ring are made of the same material, SUJ2 or SUJ3, which is high-carbon chromium bearing steel specified in JIS G4805.

4. A method for manufacturing a rolling body, wherein the rolling body is used in a rolling bearing, wherein: The manufacturing method of the rolling element comprises: A quenching step, after processing into a predetermined shape so as to become the rolling element, immersing the heated raw material in oil or water at a temperature of 60° C. to 120° C., keeping the raw material immersed in the oil or water, and keeping the temperature of the raw material at a temperature of 60° C. to 120° C. for 20 minutes or more; A first low temperature holding step of cooling the raw material after the quenching step, and holding the raw material at a temperature of 5° C. to 35° C. for 30 minutes or more; a vacuum cleaning step of performing vacuum cleaning on the raw material at a temperature of 100° C. to 140° C. for more than 40 minutes after the first low temperature holding step; and The second low temperature keeping step is to cool the raw material after the vacuum cleaning step to keep the temperature of the raw material below 35°C.

5. The method for manufacturing a rolling element according to claim 4, wherein: The rolling element manufacturing method further includes a tempering step of maintaining the raw material at a temperature of 160° C. or higher and 180° C. or lower for 90 minutes or higher and 150 minutes or lower after the second low temperature maintaining step.

6. The method for manufacturing a rolling element according to claim 4 or 5, wherein: The rolling body is a roller.

7. The method for manufacturing a rolling element according to claim 4 or 5, wherein: The rolling elements are made of SUJ2 or SUJ3, which is high carbon chromium bearing steel specified in JIS G4805.

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