Rolling bearing raceway and rolling bearing using the same

Abstract

The present invention provides a rolling bearing component (outer ring or inner ring) and a rolling bearing using the same, which can dramatically improve the indentation resistance required for rolling bearings. [Solution] A rolling bearing raceway is made of alloy steel containing, by mass%, C: 0.40~0.95%, Si: 0.70~2.50%, Mn: 0.10~1.00%, Cr: 1.00~4.00%, W+2Mo: 0.40~3.00%, V: 0.05~0.80%, with the remainder being iron and unavoidable impurities. The raceway surface of the rolling bearing raceway has a carburized nitride layer with a thickness of 300 μm or more, and the amount of retained austenite on the raceway surface is in the range of 15 volume% to 30 volume%.

Description

Technical Field

[0001] The present invention relates to parts (inner and outer rings) of rolling bearings incorporated in automobiles, industrial machines, robots, etc., and rolling bearings using the same.

Background Art

[0002] Rolling bearings used in the fields of automobiles and industrial machines are required to have various properties such as heat resistance and wear resistance. In particular, in addition to the dynamic strength of the inner and outer rings and rolling elements, static strength (indentation resistance) is also required.

[0003] In addition, due to the miniaturization, weight reduction, and cost reduction of machines, the operating environment of bearings has become even more severe than before. In rolling bearings used in such severe operating environments, foreign substances such as burrs and wear powder often混入 the lubricating oil, so foreign matter resistance is also required.

[0004] For example, a technique is disclosed in which a high-hardness material such as high-speed tool steel is used for the material of the raceway ring and rolling elements, and a carburized and nitrided layer is formed after precipitating carbides of several μm or less in the structure of a predetermined depth on the raceway surface of the raceway ring (see Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when a high alloy is applied to the alloy steel that is the base material, the carbon content becomes relatively high, so coarse carbides are likely to precipitate in the matrix structure, and the machinability and grindability during machining into the final shape are significantly reduced.

[0007] On the other hand, while applying low-alloy steel suppresses the precipitation of carbides in the matrix structure, it presents the problem of reduced indentation resistance to rolling elements required for the raceway surface of rolling bearings.

[0008] Therefore, the object of the present invention is to provide a rolling bearing component (outer ring or inner ring) and a rolling bearing using the same, which can be expected to dramatically improve the indentation resistance required when using a rolling bearing, while maintaining the processing characteristics (machinability and abrasiveness) required when manufacturing a rolling bearing. [Means for solving the problem]

[0009] The rolling bearing component of the present invention is a rolling bearing raceway made of alloy steel containing, by mass%, C: 0.40~0.95%, Si: 0.70~2.50%, Mn: 0.10~1.00%, Cr: 1.00~4.00%, W+2Mo: 0.40~3.00%, V: 0.05~0.80%, with the remainder being iron and unavoidable impurities. The surface of the rolling bearing raceway is formed with a carburized and nitrided layer with a thickness of 300 μm or more, and the hardness of the raceway surface is 800 HV or more on a Vickers hardness scale, with a retained austenite content of 15 volume% to 30 volume%. [Effects of the Invention]

[0010] The rolling bearing component of the present invention is made of alloy steel containing, by mass%, C: 0.40~0.95%, Si: 0.70~2.50%, Mn: 0.10~1.00%, Cr: 1.00~4.00%, W+2Mo: 0.40~3.00%, V: 0.05~0.80%, with the remainder being iron and unavoidable impurities. A carburized nitride layer is formed on its surface to a thickness of 300 μm or more. By setting the amount of retained austenite on the raceway surface to 15 volume% to 30 volume%, toughness can be maintained while improving the indentation resistance required for rolling bearings.

[0011] Furthermore, the carbonitriding treatment and sufficient Si addition improve tempering softening resistance, suppressing the decrease in indentation resistance due to heat generation during use. [Brief explanation of the drawing]

[0012] [Figure 1] This graph shows the measurement results of cross-sectional hardness in Example 1. [Figure 2] This is a schematic diagram of the indentation measurement test machine 10 in Example 2. [Figure 3] This graph shows the measurement results of the indentation depth in Example 2. [Modes for carrying out the invention]

[0013] The content of the main chemical components of a rolling bearing raceway, which is one embodiment of the present invention, will be described below.

[0014] ≪C (Carbon)≫ The carbon (C) content in the rolling bearing raceway (alloy steel) of the present invention shall be 0.40 to 0.95% by weight. Carbon plays a role in ensuring the hardness of the steel after quenching and tempering, and in ensuring a high fatigue life when used as a rolling bearing raceway. If the C content in the alloy steel is less than 0.40%, the necessary surface and internal hardness cannot be obtained, and if it exceeds 0.95%, the amount of retained austenite (γ content) increases, degrading the fatigue life of the machine part.

[0015] ≪Si (Silicon)≫ The silicon (Si) content should be between 0.70% and 2.50% by weight. Silicon plays a role in increasing the tempering softening resistance in alloy steel. If the Si content in the alloy steel falls below 0.70%, the necessary tempering softening resistance cannot be obtained, and if it exceeds 2.50%, the hot forgeability deteriorates significantly.

[0016] ≪Mn (Manganese)≫ Mn (Manganese) shall be 0.10 - 1.00% by weight. Manganese is effective in enhancing the hardenability in alloy steel and improving the fatigue life when used as a raceway ring for rolling bearings. If the Mn content in the steel is less than 0.10%, the hardenability of the alloy steel deteriorates, and if it exceeds 1.00%, the hot forging property significantly deteriorates.

[0017] ≪Cr (Chromium)≫ Cr (Chromium) shall be 1.00 - 4.00% by weight. Chromium enhances the hardenability in alloy steel and plays a role in thermally stabilizing cementite and suppressing the solid solution of cementite into the matrix in the high-temperature range. Also, if the Cr content in the alloy steel is less than 1.00%, the hardenability of the alloy steel deteriorates, and if it exceeds 4.00%, coarse carbides occur in the alloy steel.

[0018] ≪W (Tungsten)≫ W (Tungsten) can also be contained in the range of 0.40 - 3.00% by weight as W equivalent (W + 2Mo). In this case, tungsten forms carbides in the steel like molybdenum and contributes to ensuring hardness. If the W equivalent in the steel is less than 0.40%, the required tempering hardness and softening resistance cannot be obtained. On the other hand, if the W equivalent exceeds 3.00%, coarse carbides occur.

[0019] ≪V (Vanadium)≫ V (Vanadium) shall be 从0.05 - 0.80% by weight. V plays a role in increasing the tempering softening resistance by combined addition with silicon in alloy steel. Also, if the V content in the alloy steel is less than 0.10%, the required tempering softening resistance cannot be obtained, and if it exceeds 0.80%, coarse carbides occur. Preferably, V is 0.05 - 0.40%.

[0020] ≪Mo (Molybdenum)≫ Molybdenum (Mo) is contained as W equivalent (W + 2Mo). When contained alone as Mo, it shall be 0.20 to 1.50% by weight. Molybdenum forms carbides in alloy steel and contributes to ensuring hardness. If the Mo content in alloy steel is less than 0.20%, the required tempering hardness and softening resistance cannot be obtained. Also, if the Mo content exceeds 1.50%, coarse carbides will occur. Preferably, it is 0.20 to 0.70% Mo.

[0021] ≪Carburized Nitrided Layer≫ Next, the carburized nitrided layer formed on the raceway surface of the rolling bearing raceway ring will be described. The carburized layer is formed for the purpose of further increasing the hardness of the alloy steel itself as the base material. Its thickness (the thickness of the carburized nitrided layer) is at least 0.3 mm or more from the raceway surface. Considering the maximum shear stress depth at the time of indentation generation, its thickness is preferably 0.5 mm or more.

[0022] Regarding the amount of austenite (γ amount) on the raceway surface of the rolling bearing raceway ring, considering machining (grinding) into a predetermined shape after the carburized nitriding treatment, the range is preferably 15 to 25% by volume, within the range of 15 to 30% by volume.

[0023] By setting the amount of retained austenite within this range, spherical carbides with an average particle size of less than 10 μm are evenly dispersed in the matrix structure, so that a stable value (hardness) of the hardness directly under the carburized nitrided layer can be obtained regardless of the depth (thickness) direction. The amount of retained austenite in the structure is a value calculated by conversion in volume ratio based on the X-ray diffraction measurement method.

[0024] Also, regarding the hardness of the carburized nitrided layer, it shall be 800 HV or more in Vickers hardness (equivalent to 64 HRC on the Rockwell C scale). In particular, if the hardness at the maximum shear stress depth at the time of indentation generation is less than 760 HV, the indentation resistance required for the rolling bearing raceway ring will be significantly reduced.

[0025] Therefore, the carburized-nitrided layer with a hardness of 800 HV or higher is 0.3 mm or thicker, and the hardness of the matrix structure directly beneath the carburized-nitrided layer is 760 HV or higher on the Vickers hardness scale. "Directly beneath the carburized-nitrided layer" is defined as a position 0.2 mm further inward from the depth where the hardness reaches 800 HV. [Examples]

[0026] (Example 1) A comparative test of surface hardness and cross-sectional hardness distribution was conducted using two types of test specimens: one with the chemical composition according to the present invention (inventive material) and a commercially available high-carbon chromium bearing steel (SUJ2: comparative material). The test results will be explained with reference to the drawings. The chemical composition of the inventive material was as follows (by mass%): C:0.91%, Si:1.83%, Mn:0.20%, Cr:1.30%, W:0.1%, Mo:0.41%, V:0.15%. Similarly, the chemical composition of the comparative material was as follows (by mass%): C:1.00%, Si:0.25%, Mn:0.38%, Cr:1.35%, Mo:0.03%.

[0027] Furthermore, the inventive material underwent carburizing, nitriding, and tempering, while the comparative material underwent through quenching and tempering. The size of the test specimens for both the inventive and comparative materials was cylindrical, with a diameter of 61 mm and a height of 5.8 mm.

[0028] <Surface hardness measurement> The surface hardness (unit: Rockwell C scale) of each test specimen of the inventive material and the comparative material described above was measured using a Rockwell hardness tester. As a result, the surface hardness of the inventive material was 64.7 HRC on the Rockwell C scale, and the surface hardness of the comparative material was 62.3 HRC. When the hardness of each test specimen was converted to Vickers hardness (HV), the inventive material was equivalent to 820 HV, and the comparative material was equivalent to 760 HV.

[0029] <Measurement of cross-sectional hardness distribution> Next, each test specimen of the inventive material and the comparative material was cut, and the change in hardness of the cut surface was measured. Hardness was measured at a total of 10 or more locations in the region from the outermost layer to a depth of 3 mm at intervals of approximately 0.05 mm to 0.5 mm. Figure 1 shows graphs of the cross-sectional hardness distribution of the inventive material and the comparative material. First, as shown in Figure 1, the surface hardness of the inventive material was found to be in the range of 830 HV to 800 HV from the outermost surface to a depth of 0.8 mm, and the carburized nitride layer was found to be 0.8 mm thick. Furthermore, the hardness at a depth of 1.0 mm was also 780 HV or higher, indicating that the hardness directly below the carburized nitride layer was also sufficient.

[0030] In contrast, the hardness change of the comparative material was 750-760 HV, and the hardness of the inventive material was consistently 20-70 HV higher than that of the comparative material.

[0031] The test results above confirmed that the inventive material consistently exhibited higher surface and cross-sectional hardness compared to the comparative material, with a particularly significant difference in hardness observed in the surface layer. This suggests that the inventive material was hardened to its deepest layers through carburizing and nitriding treatment, resulting in excellent wear resistance and fatigue durability. Therefore, the rolling bearing material of the present invention is expected to exhibit superior performance even in harsh operating environments.

[0032] (Example 2) Next, in order to evaluate the indentation characteristics of each material, the inventive material and the comparative material, when applied as bearing components, an indentation test was conducted, and the test results will be explained with reference to the drawings. This test was an indentation test using a thrust plate. A schematic diagram of the testing machine (indentation measurement test machine) used in this test is shown in Figure 2. As shown in Figure 2, this indentation measurement test machine consists of a steel ball 1, a pressing component 2, a raceway ring 3, a retainer 4, and a base material 5.

[0033] In this test, when performing the indentation measurement test shown in Figure 2, first the thrust plate W, which is the test piece, is placed on the base material 5. Then, three rolling elements with a diameter of 3 / 8 inch are placed in the pockets of the retainer 4 at equal intervals, and the raceway 3 is arranged as shown in Figure 2. Next, the pressing component 2 is placed on the raceway 3, and a predetermined load is then applied on top of it via the steel ball 1.

[0034] Furthermore, the test conditions used were those of an Autograph test apparatus manufactured by Shimadzu Corporation. The loading speed was set to 0.1 mm / min, and the load was held for 10 seconds after reaching the predetermined load. The test load varied depending on the set surface pressure value. The indentation depth was measured using a laser microscope equipped with a white light interferometer manufactured by Keyence Corporation, measuring the depth of the indentation on the thrust plate.

[0035] For example, when the surface pressure was 4200 MPa, the load on the rolling element was 666 N, and the total load for the entire test (for 3 balls) was 2000 N. Similarly, at a surface pressure of 4500 MPa, the rolling element load was 819 N and the test load was 2460 N. At a surface pressure of 5000 MPa, the rolling element load was 1123 N and the test load was 3370 N. Furthermore, at a surface pressure of 5500 MPa, the rolling element load was 1492 N and the test load was 4480 N, and at a surface pressure of 6000 MPa, the rolling element load was 1940 N and the test load was 5820 N. Thus, the rolling element load and test load increase with increasing surface pressure. Figure 3 shows graphs of the indentation depths of the inventive material and the comparison material measured at surface pressures from 4200 MPa to 6000 MPa (horizontal axis: surface pressure MPa, vertical axis: indentation depth μm).

[0036] Test results confirmed that the inventive material exhibits superior indentation resistance even under high surface pressure conditions compared to the comparative material. In particular, at a surface pressure of 6000 MPa, the indentation depth of the inventive material was significantly lower than that of the comparative material, indicating that the inventive material has excellent shape retention even under high-load environments. Therefore, the rolling bearing material using the chemical composition of the present invention is considered to be very effective in applications requiring durability under high-load conditions. [Explanation of Symbols]

[0037] 1 steel ball 2 Pressing parts 3 Raceway ring 4 Cage 5. Base material W Test specimen (thrust plate)

Claims

1. A rolling bearing raceway made of alloy steel containing, by mass%, C: 0.40-0.95%, Si: 0.70-2.50%, Mn: 0.10-1.00%, Cr: 1.00-4.00%, W+2Mo: 0.40-3.00%, V: 0.05-0.80%, with the remainder being iron and unavoidable impurities, wherein the raceway surface of the rolling bearing raceway has a carburized and nitrided layer with a thickness of 300 μm or more, and the raceway has been quenched and tempered, with the amount of retained austenite on the raceway surface being 15 volume% to 30 volume%.

2. The rolling bearing raceway according to claim 1, characterized in that the hardness of the carburized-nitrided layer is 800 HV or more on a Vickers hardness scale, and the hardness of the alloy steel directly beneath the carburized-nitrided layer is 760 HV or more on a Vickers hardness scale.

3. A rolling bearing characterized by comprising a raceway ring for a rolling bearing as described in claim 1 or 2.

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