Alloy steal for rolling bearing part, bearing ring for rolling bearing, and method for producing rolling bearing and bearing ring for rolling bearing

Abstract

To provide an alloy steel for rolling bearing parts capable of maintaining original hardness while having electric corrosion resistance to adjacent metal products, a bearing ring for rolling bearings, and a producing method of the rolling bearing and the bearing ring for the rolling bearings.SOLUTION: In wt.%, C: 1.0-1.5%, Si: 1.0-4.0%, Mn: 0.2-2.0%, Cr: 1.0-9.0%, Mo: 1.5-6.0%, Al: 0.01-5.0%, and the remaining part composed of Fe and unavoidable impurities of the alloy steel for rolling bearing parts. Thereby, it is possible to maintain the original hardness while having an electrolytic corrosion resistance function to adjacent metal products.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an alloy steel for rolling bearing parts containing chromium, molybdenum, etc., a raceway for a rolling bearing, a rolling bearing, and a method for manufacturing the raceway for a rolling bearing. [Background technology]

[0002] Conventionally, when manufacturing parts that require insulation using steel, measures to impart insulation have been taken by replacing part of the part with insulating ceramics such as alumina, or by covering the surface of the part with a resin such as PPS (see Patent Document 1).

[0003] Alternatively, some steel materials manufactured with a specified composition can be heated at high temperatures to form an insulating oxide layer on the surface of the part, thereby giving the part insulating properties (see Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-236259 A [Patent Document 2] JP 2013-199674 A [Patent Document 3] JP 2004-84767 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when some of the parts disclosed in Patent Document 1 were replaced with resin and added, there were problems with the wear resistance and strength being insufficient compared to steel. Also, ceramics lacked toughness compared to steel, and there were problems with workability. In addition, the material costs of all of these materials were higher than steel, which increased the cost of the entire part.

[0006] On the other hand, as disclosed in Patent Document 2, when the surface of a steel material is oxidized to impart insulating properties to the parts, this is advantageous in terms of cost, but the hardness of conventional alloy steel is below 50HRC (HRC: Rockwell hardness C scale), and it is difficult to use such steel for long periods of time as parts in high-load environments that require wear resistance, fatigue strength, and the like.

[0007] This is because the carbon content, which contributes greatly to the hardness of alloy steel, is extremely low. In addition, the temperature required to form the oxide layer is in the high range of about 980 to 1220°C, so even if the material had high hardness before treatment, it may soften.

[0008] Even if high hardness could be achieved by heating to about 1200°C for both quenching and oxidation, the dimensions would vary greatly before and after the treatment. Therefore, in order to manufacture high-precision parts, grinding or other processes would be required after oxidation, and the oxide layer that had been so carefully formed would be ground away.

[0009] Furthermore, the material disclosed in Patent Document 3 describes a method for oxidizing the surface of the steel material to provide insulating properties to the parts, but does not disclose any information on the hardness or strength of the material, nor does it include any special consideration of this. In addition, the oxide layer is formed by immersion in an acid solution, which poses problems such as a decrease in material strength due to hydrogen embrittlement and a burden on the natural environment.

[0010] Therefore, the objective of the present invention is to provide an alloy steel for rolling bearing parts that can maintain high strength (or hardness) while having electrical insulation between adjacent metal products, a raceway for a rolling bearing using the same, and a method for manufacturing a rolling bearing and a raceway for a rolling bearing using the same. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the alloy steel for rolling bearing parts according to the present invention is characterized by containing, by weight percent, 1.0-1.5% C, 1.0-4.0% Si, 0.2-2.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, with the balance being Fe and unavoidable impurities.

[0012] Alternatively, the alloy steel for rolling bearing parts may further contain, by weight percent, V: 0.01 to 1.2% and W: 0.01 to 2.0%.

[0013] Next, the raceway for a rolling bearing according to the present invention is formed by forming an oxide film on the surface of the alloy steel for a rolling bearing part using the alloy steel for a rolling bearing part according to the present invention. In the manufacturing method for the raceway for a rolling bearing using the alloy steel for a rolling bearing part according to the present invention, an oxide film can be formed on the surface of the alloy steel for a rolling bearing part at a temperature range of 500° C. to 600° C. In this case, the oxide film may be formed on the surface of the alloy steel for a rolling bearing part in an atmosphere containing at least either oxygen or water vapor. Effect of the Invention

[0014] The alloy steel for rolling bearing parts of the present invention has a predetermined composition and can form an insulating oxide layer (oxide film) on the surface of the steel material while maintaining a hardness exceeding 55HRC (Rockwell hardness C scale). In addition, the raceway for rolling bearing parts of the present invention can achieve a hardness exceeding 55HRC by subjecting the alloy steel for rolling bearing parts to heat treatment by quenching and tempering, and then, by performing finish processing to ensure the dimensional accuracy of the part and then carrying out oxidation heat treatment, even if an insulating oxide film is formed, the dimensional change of the part due to the oxidation treatment can be kept relatively small. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The content of each element contained in the alloy steel for rolling bearing parts, which is one embodiment of the present invention, is described below. The chemical composition of the alloy steel for rolling bearing parts of the present invention satisfies the following conditions: (1) the composition range allows an insulating oxide layer to be formed on the surface, (2) the composition range does not allow conductive precipitate particles (carbides, etc.) of a size large enough to penetrate the oxide layer to be formed, and (3) the composition range does not allow softening even when oxidation treatment is performed after quenching and tempering, and allows a hardness of over 55HRC to be obtained.

[0016] The range of C (carbon) is set to 1.0 to 1.5% by weight. If the C content exceeds 1.5%, the toughness of the alloy steel may decrease, and the carbides in the matrix structure may become coarse. In addition, the hot workability of the alloy steel may deteriorate. On the other hand, if the C content is less than 1.0%, the hardness becomes 55HRC or less.

[0017] The content of silicon (Si) is in the range of 1.0 to 4.0% by weight. If the amount of silicon exceeds 4.0%, the toughness of the alloy steel may decrease, or the hot workability may deteriorate. On the other hand, if the amount of silicon is less than 1.0%, the insulating property of the oxide layer formed on the surface may decrease, or the machinability may deteriorate.

[0018] The Mn (manganese) content is set to the range of 0.2 to 2.0% by weight. If it exceeds this range, the workability may deteriorate. On the other hand, if it is below this range, the raw materials must be carefully selected, which may result in higher material costs.

[0019] Cr (chromium) should be in the range of 1.0 to 9.0% by weight. If it exceeds 9.0%, the oxide layer of the alloy steel becomes thin and the insulating properties of the oxide layer decrease. If it falls below 1.0%, the insulating properties of the oxide layer of the alloy steel decrease.

[0020] Mo (molybdenum) is in the range of 1.5 to 6.0% by weight. If it exceeds 6.0%, the carbides may become coarse or the toughness of the alloy steel may decrease. On the other hand, if it is less than 1.5%, the hardness after oxidation treatment may become 55HRC or less.

[0021] The content of aluminum (Al) is in the range of 0.01 to 5.0% by weight. If it exceeds 5.0%, the hardness after oxidation treatment may become 55HRC or less, or non-metallic inclusions may increase, causing fatigue strength to decrease. On the other hand, if it is less than 0.01%, the insulating properties of the oxide layer may decrease.

[0022] The content of V (vanadium) is set to the range of 0.01 to 1.2% by weight. If this range is exceeded, there is a risk that the conductive carbides will become coarse or the toughness of the alloy steel will decrease.

[0023] The content of W (tungsten) is set to the range of 0.01 to 2.0% by weight. If the content exceeds 2.0%, there is a risk that the carbides will become coarse or the toughness of the alloy steel will decrease.

[0024] Next, a description will be given of a raceway for a rolling bearing using an alloy steel for a rolling bearing part according to one embodiment of the present invention, and a manufacturing method thereof. In the invention of the raceway for a rolling bearing using the alloy steel for a rolling bearing part of the present invention, an oxide film is formed on the surface of the alloy steel for a rolling bearing part, which is the base material. The oxide film coated on the surface of the alloy steel for a rolling bearing part can be composed of a single layer or multiple layers. In this case, it is sufficient that some of the layers of these oxide films have insulating properties.

[0025] In addition, the size of precipitate particles such as carbides present inside the alloy steel for rolling bearing parts is smaller than the thickness of the oxide film, and is finely divided to a level that does not cause the insulating properties of the rolling bearing raceway surface to be lost even if conductive precipitate particles are present in the oxide film.

[0026] Furthermore, even if the alloy steel for rolling bearing parts that has been previously quenched and tempered is again heat treated in a temperature range of 500°C or higher and 600°C or lower, the alloy steel for rolling bearing parts has sufficient temper softening resistance properties and can fully ensure a hardness of more than 55HRC.

[0027] In addition, in the above-mentioned oxidation heat treatment process, the alloy steel for rolling bearing parts is heat-treated in an atmosphere containing either oxygen or water vapor, or in an atmosphere containing both oxygen and water vapor, thereby forming an oxide film on the surface of the alloy steel for rolling bearing parts.

[0028] In this case, it is desirable to carry out the treatment after the final processing such as molding or cutting of the raceway for the rolling bearing. This is because even if heat treatment is carried out in an oxygen atmosphere after the final processing, the heating temperature is relatively low at 500 to 600°C, and the dimensional change of the raceway for the rolling bearing is very small.

Claims

1. An alloy steel for rolling bearing parts, comprising, by weight, 1.0-1.5% C, 1.0-4.0% Si, 0.2-2.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, with the balance being Fe and unavoidable impurities.

2. 2. The alloy steel for rolling bearing parts according to claim 1, further comprising, by weight percent, 0.01 to 1.2% V.

3. The alloy steel for rolling bearing parts according to claim 2, further comprising, by weight percent, W: 0.01 to 2.0%.

4. A raceway for a rolling bearing using an alloy steel for rolling bearing parts according to any one of claims 1 to 3, characterized in that the alloy steel for rolling bearing parts is coated with an oxide film.

5. The raceway for a rolling bearing according to claim 4 is a rolling bearing part, which is either an inner ring for a rolling bearing or an outer ring for a rolling bearing, characterized in that the rolling bearing has the rolling bearing part, which is either the inner ring for a rolling bearing or the outer ring for a rolling bearing.

6. 5. A method for manufacturing a raceway for a rolling bearing according to claim 4, characterized in that the oxide film is formed on the surface of the alloy steel for rolling bearing parts at a temperature in the range of 500°C to 600°C.

7. 7. The method for producing a race for a rolling bearing according to claim 6, wherein the oxide film is formed on the surface of the alloy steel for rolling bearing parts in an atmosphere containing at least either oxygen or water vapor.