Raceway ring for rolling bearing and rolling bearing using the same

Abstract

To provide a rolling bearing part (an outer ring or an inner ring) that demonstrates a dramatic enhancement in anti-indentation property demanded for rolling bearings, and a rolling bearing employing the same.SOLUTION: A raceway ring for rolling bearing is composed of an alloy steel containing, in 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%, and V: 0.05-0.80%, with the remainder consisting of iron and unavoidable impurities, wherein the raceway ring has, on its raceway surface, a carburized layer of 500 μm or more in thickness, and the retained austenite content in the carburized layer is 15 vol% or more to 30 vol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing component (a raceway for a rolling bearing) to be built into automobiles, industrial machinery, robots, etc., and to a rolling bearing using the same. [Background technology]

[0002] Rolling bearings used in fields such as automobiles and industrial machinery require various properties, including heat resistance and wear resistance, and in particular, static strength (resistance to indentations) is required in addition to dynamic strength of the inner and outer rings and rolling elements. Furthermore, as machines become smaller, lighter, and less expensive, the environments in which bearings are used are becoming even more severe than before, and rolling bearings used in such harsh environments often encounter foreign matter such as burrs and wear debris in the lubricating oil, so they also require resistance to foreign matter.

[0003] For example, a technology has been disclosed in which a high-hardness material such as high-speed tool steel is used as the material for the raceway rings and rolling elements, and carbides of several μm or less are precipitated in the structure at a predetermined depth on the raceway surface of the raceway rings, followed by the formation of a carbonitrided layer (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-9449 [Patent Document 2] Japanese Patent Application Publication No. 8-49057 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a high alloy steel is used as the base material (substrate), the carbon content becomes relatively high, which makes it easy for coarse carbides to precipitate in the matrix, significantly reducing machinability and polishability when processing into the final shape.On the other hand, when a low-alloy steel is used, the precipitation of carbides in the matrix is ​​suppressed, but there is a problem that the indentation resistance against rolling elements required for the raceway surface of a rolling bearing is reduced.

[0006] Therefore, an object of the present invention is to provide a rolling bearing component (outer ring or inner ring) that maintains the processing characteristics (machinability and polishability) required when manufacturing a rolling bearing, while at the same time being expected to achieve a dramatic improvement in the indentation resistance required when the rolling bearing is in use, and a rolling bearing using the same. [Means for solving the problem]

[0007] The present invention provides a rolling bearing raceway made of an alloy steel containing, by mass, 0.40-0.95% C, 0.70-2.50% Si, 0.10-1.00% Mn, 1.00-4.00% Cr, 0.40-3.00% W+2Mo, 0.05-0.80% V, and the remainder being iron and unavoidable impurities. The rolling bearing raceway has a carburized layer with a thickness of 500 μm or more on the surface, and the amount of retained austenite on the raceway surface is 15-30% by volume. Preferably, the carburized layer has a Vickers hardness of 800 HV or more, and the alloy steel directly below the carburized layer has a Vickers hardness of 760 HV or more. [Effects of the Invention]

[0008] The raceway ring for a rolling bearing of the present invention is made of an alloy steel containing, by mass, 0.40-0.95% C, 0.70-2.50% Si, 0.10-1.00% Mn, 1.00-4.00% Cr, 0.40-3.00% W+2Mo, 0.05-0.80% V, with the remainder being iron and unavoidable impurities, and has a carburized layer formed on its surface to a thickness of 500 μm or more. By limiting the amount of retained austenite on the raceway surface to 15-30% by volume, the rolling bearing exhibits the improved indentation resistance required for the rolling bearing. Furthermore, by limiting the hardness of the alloy steel directly below the carburized layer to 760 HV or more in Vickers hardness, the base alloy steel itself can maintain its indentation resistance even if the carburized layer wears away after long-term use. DETAILED DESCRIPTION OF THE INVENTION

[0009] The contents of the main chemical components of a rolling bearing raceway according to one embodiment of the present invention will now be described. First, the C (carbon) content in the rolling bearing raceway (alloy steel) of the present invention is 0.40 to 0.95% by weight. Carbon ensures hardness in the steel after quenching and tempering, and plays a role in ensuring a high level of fatigue life when used as a rolling bearing raceway. If the C content in the alloy steel is less than 0.40%, the required surface and internal hardness cannot be obtained, and if it exceeds 0.95%, the amount of retained austenite (γ amount) increases, deteriorating the fatigue life of mechanical components.

[0010] The Si (silicon) content is 0.70 to 2.50% by weight. Silicon plays a role in increasing the temper softening resistance of alloy steel. If the Si content in alloy steel is less than 0.70%, the required temper softening resistance cannot be obtained, and if it exceeds 2.50%, hot forgeability deteriorates significantly.

[0011] The Mn (manganese) content is 0.10 to 1.00% by weight. Manganese improves the hardenability of alloy steel, and is effective in improving fatigue life when used as a raceway for rolling bearings. If the Mn content in steel is less than 0.10%, the hardenability of the alloy steel deteriorates, and if it exceeds 1.00%, hot forgeability deteriorates significantly.

[0012] The Cr (chromium) content is 1.00 to 4.00% by weight. Chromium increases the hardenability of the alloy steel and also thermally stabilizes cementite, preventing the cementite from dissolving in the matrix at high temperatures. If the Cr content in the alloy steel is less than 1.00%, the hardenability of the alloy steel will deteriorate, and if it exceeds 4.00%, coarse carbides will form in the alloy steel.

[0013] W (tungsten) can be included in the range of 0.40 to 3.00% by weight as the W equivalent (W + 2Mo). In this case, tungsten, like molybdenum, forms carbides in the steel, contributing to ensuring hardness. If the W equivalent in the steel is less than 0.40%, the required temper hardness and softening resistance cannot be obtained. On the other hand, if the W equivalent exceeds 3.00%, coarse carbides will form.

[0014] The V (vanadium) content is 0.05 to 0.80% by weight. V has the role of increasing temper softening resistance when added in combination with silicon in the alloy steel. Furthermore, if the V content in the alloy steel is less than 0.10%, the required temper softening resistance cannot be obtained, and if it exceeds 0.80%, coarse carbides are generated. Preferably, V is 0.05 to 0.40%.

[0015] Mo (molybdenum) is contained as the W equivalent (W + 2Mo), but when Mo is contained alone, the content is set to 0.20 to 1.50% by weight. Molybdenum forms carbides in the alloy steel, contributing to ensuring hardness. If the Mo content in the alloy steel is less than 0.20%, the required temper hardness and softening resistance cannot be obtained. If the Mo content exceeds 1.50%, coarse carbides are generated. Preferably, Mo is 0.20 to 0.70%.

[0016] Next, we will explain the carburized layer formed on the raceway surface of the raceway ring for rolling bearings. The carburized layer is formed for the purpose of further increasing the hardness of the base alloy steel itself, and its thickness (thickness of the carburized layer) is at least 500 μm (0.5 mm) from the raceway surface. Considering that it will be machined (ground) into a specified shape after carburizing, the thickness is preferably 1.0 mm or more.

[0017] The amount of retained austenite (γ amount) in the carburized layer is set to a range of 15% to 30% by volume, and considering that the material will be machined (ground) into a predetermined shape after carburizing, the range is preferably 15% to 25% by volume. By setting the amount of retained austenite within this range, spheroidized carbides with an average particle size of less than 10 μm are evenly dispersed throughout the base structure, resulting in a stable hardness value (hardness) directly below the carburized layer regardless of the depth (thickness) direction. The amount of retained austenite in the structure is a value calculated by converting it into a volume ratio based on X-ray diffraction measurement.

[0018] Furthermore, the hardness of the carburized layer must be at least 800 HV on the Vickers hardness scale (equivalent to 64 HRC on the Rockwell C scale). In particular, if the Vickers hardness of the base structure directly below the carburized layer is less than 760 HV, the indentation resistance required of rolling bearing rings will be significantly reduced. For this reason, the hardness of the base structure directly below the carburized layer must be at least 760 HV on the Vickers hardness scale. Note that "directly below the carburized layer" is defined as a position at a depth of 1 mm (1000 μm) or more from the raceway surface.

Claims

1. A raceway ring for a rolling bearing made of alloy steel containing, in mass %, C: 0.40 to 0.95%, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, W+2Mo: 0.40 to 3.00%, V: 0.05 to 0.80%, and the remainder being iron and unavoidable impurities, wherein the raceway surface of the raceway ring for a rolling bearing has a carburized layer having a thickness of 500 μm or more, and the amount of retained austenite on the raceway surface is 15% by volume or more and 30% by volume or less.

2. 2. A raceway for a rolling bearing according to claim 1, characterized in that the hardness of the carburized layer is 800 HV or more in Vickers hardness, and the hardness of the alloy steel directly below the carburized layer is 760 HV or more in Vickers hardness.

3. A rolling bearing comprising the race for a rolling bearing according to claim 1 or 2.