JP2004278781A - Rolling bearing, and manufacturing method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing capable of suppressing hydrogen embrittlement separation occurring under hydrogen environment, and a manufacturing method for the same. <P>SOLUTION: At least one component of a rolling element 2, an inner ring 4 and an outer ring 3 of the rolling bearing as a bearing 1 for an alternator has a nitrogen enriched layer, and the area ratio of spheroidal carbide of a face layer part is ≥ 10%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rolling bearing and a method for manufacturing the same, and more specifically to a rolling bearing and a method for manufacturing the same that are less likely to cause hydrogen embrittlement with a white layer in an environment where hydrogen is generated.

  Rolling bearings used in alternator bearings, reduction gears for construction machinery, hydraulic pumps, hydraulic motors, and the like often have a peculiar peeling portion with a white layer at the damage starting point. This white layer is characterized by having no directionality in the rolling direction, unlike a white etching constituent (WEC) generated by rolling fatigue or a butterfly generated around nonmetallic inclusions. In a bearing having a damage including a white layer at the starting point, the hydrogen content in the steel is clearly increased, and the cracks existing in the white layer extend very long along the grain boundaries to the inside. For this reason, it is said that hydrogen is involved in the generation of the damage. Hereinafter, the peculiar peeling with the white layer is referred to as hydrogen embrittlement peeling.

  It is considered that the hydrogen embrittlement peeling is caused by the decomposition of the lubricant by the catalytic action of the chemically active new metal surface generated during rolling and the generated hydrogen penetrating into the steel. Therefore, as measures against hydrogen embrittlement peeling, it has been effective to (a1) change to a lubricant which is hardly decomposed chemically, and (a2) blackening treatment which makes it difficult for a new metal surface to appear.

  Regarding the above (a1), the following bearings have been proposed. 5 to 40% by weight of an aromatic diurea compound or an aromatic urea / urethane compound as a thickener is added to a base oil in which an alkyl diphenyl ether oil and a poly-α-olefin oil are mixed in a weight ratio of 20:80 to 80:20. A grease-enclosed bearing for an alternator in which a grease composition further containing a passivating oxidizing agent and an organic sulfonate is enclosed in a rolling bearing (Patent Document 1).

  With respect to the above (a2), the following bearings have been proposed. A grease-sealed bearing in which grease is sealed in a bearing, wherein a 0.1 to 2.5 μm-thick oxide film is formed on a rolling surface of a bearing ring (Patent Document 2).

Bearings based on the above proposals have actually been confirmed to have a life extension effect in this industry.
JP-A-5-263091 JP-A-2-190615

  However, in recent years, the use environment of rolling bearings has become increasingly severe, and the above measures alone have been insufficient. For this reason, there is a demand for measures to further extend the life of hydrogen embrittlement peeling.

  An object of the present invention is to provide a rolling bearing capable of suppressing the hydrogen embrittlement peeling generated in a hydrogen environment and a method for manufacturing the rolling bearing.

  In the rolling bearing of the present invention, at least one of the rolling element, the inner ring and the outer ring has a nitrogen-enriched layer, and the area ratio of the spheroidized carbide in the surface layer portion of the member having the nitrogen-enriched layer is 10%. That is all.

  The nitrogen-enriched layer can delay the rolling fatigue phenomenon, and can suppress hydrogen embrittlement exfoliation by setting the area ratio of the spheroidized carbide in the surface layer portion to 10% or more. Note that the nitrogen-enriched layer is formed by carbonitriding as described later, but the nitrogen-enriched layer may or may not be enriched with carbon. .

  As an example of a usage mode in which the above-described hydrogen embrittlement is likely to occur, the member is sealed, hydrogen is generated in the sealed portion, and a hydrogen partial pressure is generated, and hydrogen invades steel material forming a general rolling bearing. Use in an environment where the temperature is higher than the threshold value can be mentioned.

  Under the above-described hydrogen environment, hydrogen invades normal steel. The penetrated hydrogen collects at a site where dislocations generated by the rolling load accumulate at a high density or at a site such as a nonmetallic inclusion. It is considered that the collected hydrogen forms an abnormal high-pressure part in a minute part to become a gas molecule, forms a white layer, and becomes a starting point of hydrogen embrittlement separation. In the above-described member of the rolling bearing according to the present invention, hydrogen intrusion can be suppressed, and aggregation of hydrogen can be prevented. For this reason, formation of a white layer does not easily occur, and hydrogen embrittlement separation can be suppressed.

  The area ratio of the spheroidized carbide can be easily obtained from a normal test method, for example, a microstructure such as a commercially available optical microscope or scanning electron microscope using a commercially available area ratio measuring device. It is desirable that the area ratio is obtained and averaged in several visual fields.

  Further, the member having the nitrogen-enriched layer and having the spheroidized carbide having an area ratio of 10% or more may have a grain size number of an austenite crystal grain boundary exceeding number 10. By reducing the austenite particle size in this way, the effect of dramatically suppressing hydrogen embrittlement exfoliation is improved by combination with the nitrogen-enriched layer. Note that the threshold value of the average grain size of the austenite grain boundaries described above may be satisfied in the nitrogen-enriched layer. However, in the normal case, the above criteria for refining austenite crystal grains are satisfied even in the steel material body inside the nitrogen-enriched layer. In the case of austenite grains, traces are left on the ferrite phase such as martensite or bainite after quenching. "Old" may be added to emphasize austenite grain boundaries before quenching. That is, the austenite grains and the former austenite grains express the same thing. The austenite crystal grains are grain boundaries that can be observed by performing a process such as etching on a gold phase sample of a target member to reveal the grain boundaries. As described above, it may be referred to as old austenite grains in the sense of a grain boundary at the time of heating immediately before low-temperature quenching. The measurement may be performed by converting the average value of the particle size numbers of the JIS standard into the average particle size, or the length of the interval between the lines in the random direction superimposed on the metal phase structure by the intercept method or the like and meeting the grain boundary. May be averaged.

  A method for manufacturing a rolling bearing of the present invention is a method for manufacturing a rolling bearing including a rolling element, an inner ring, and an outer ring, wherein a steel material forming at least one member of the rolling element, the inner ring, and the outer ring is subjected to A1 points or more. After heating to a temperature and carbonitriding at a CP (Carbon Potential) value of 1.3 to 1.6, the mixture is oil-cooled to a temperature lower than the A1 point.

  Another method for manufacturing a rolling bearing of the present invention is a method for manufacturing a rolling bearing including a rolling element, an inner ring, and an outer ring, wherein a steel material forming at least one member of the rolling element, the inner ring, and the outer ring is A1 point. After heating to the above temperature and performing the carbonitriding treatment, it is cooled to a temperature lower than the A1 point, and then reheated to a quenching temperature range not lower than the temperature of the A1 point and less than the temperature of the carbonitriding treatment, and quenched.

  By being manufactured in this manner, as described above, a member having a nitrogen-enriched layer that satisfies a predetermined area ratio standard of spheroidized carbide in the surface layer portion and a member that satisfies the standard for miniaturization of austenite crystal grains is used. Obtainable.

  FIG. 1 is a diagram showing an alternator bearing according to an embodiment of the present invention. In the alternator 10, the shaft 11 is inserted into the alternator bearing 1, and the pulley 5 is attached to the protruding end. The pulley 5 is provided with an engagement groove 6 on which a transmission belt is hung. The alternator bearing 1 includes an inner ring 4 and an outer ring 3 which are in contact with steel balls 2 as rolling elements on a rolling surface, and the steel balls are held by a retainer 7 between the inner ring and the outer ring.

  The shaft 11 is rotated at a high speed by the transmission belt, and the rolling elements 2 and the bearing rings 3 and 4 make high-speed contact with each other at a high surface pressure, reflecting the recent trend of high speed and miniaturization. Grease is sealed in the alternator bearing, and this grease is decomposed at the high-pressure, high-speed contact portion to generate hydrogen. Hydrogen is a small element, and easily penetrates into steel when the conditions of the hydrogen partial pressure and the surface layer are met. For this reason, damage is caused at a predetermined location in the steel material to which the load is applied, resulting in formation of a unique crack appearing as a white layer on the fracture surface.

In the alternator bearing according to the embodiment of the present invention, at least one of the rolling elements 2, the outer ring 3 and the inner ring 4 has one of the following two requirements.
(A1): It has a nitrogen-enriched layer, and the area ratio of the spheroidized carbide in the surface layer portion is 10% or more.
(A2): In addition to (A1), the austenite crystal grains have a grain size number of 10 or more specified by JIS.

  A member satisfying any of the above two requirements is less likely to cause hydrogen embrittlement separation, and can have a long life.

  Next, an example in which the above is actually verified will be described.

(Example)
As a steel material of the example of the present invention that hardly causes the above-mentioned hydrogen embrittlement separation, SUJ2 subjected to two kinds of treatments shown in FIGS. 2A and 2B was prepared.

In the process of Example 1 of the present invention shown in FIG. 2A, after performing carbonitriding at a high CP (Carbon Potential) value of 1.3 to 1.6, quenching is performed by oil cooling from that temperature. By performing carbonitriding in an atmosphere having such a high CP value, the area ratio of the spheroidized carbide in the surface layer portion can be reliably increased to 10% or more.
Thereafter, it is tempered at 180 ° C.

  In the treatment of Example 2 of the present invention shown in FIG. 2B, after the carbonitriding treatment and the quenching treatment in Comparative Example 1 (see FIG. 2C), the first quenching of A ° C. (845 ° C.)-Α ° C. was performed. The oil is quenched by heating to a temperature lower than α ° C. The temperature (A-α) ° C. is a temperature not lower than the A1 point and lower than the preceding carbonitriding and quenching temperatures. As shown in the figure, quenching is performed from the temperature of the carbonitriding process, so that the quenching temperature and the carbonitriding temperature are the same. In the present description, the process of heating and quenching at (A-α) ° C. is referred to as low-temperature quenching. After this low-temperature quenching, it is tempered at 180 ° C.

  In any of the above heat treatments, a carbon-nitriding treatment therein forms a nitrogen-enriched layer that is a “carbonitriding treatment layer”. Since the carbon used as the material in the carbonitriding process has a high carbon concentration, carbon may not easily enter the surface of the steel from the atmosphere of the normal carbonitriding process. For example, in the case of steel having a high carbon concentration (steel of about 1 wt%), a carburized layer having a higher carbon concentration may be generated, and a carburized layer having a higher carbon concentration may be hardly generated. However, although the nitrogen concentration depends on the Cr concentration, etc., it is as low as 0.025 wt% or less at maximum in ordinary steel, so that a nitrogen-enriched layer is clearly formed regardless of the carbon concentration of the material steel. . It goes without saying that the nitrogen-enriched layer may be enriched with carbon.

  Further, as steel materials of the comparative example, four steel materials of SUJ2, a normally quenched material of SUJ2, a SUJ2 blackened material, and a 13% Cr steel subjected to the treatment shown in FIG. An evaluation was performed. Table 1 shows a list of the steel materials evaluated.

  FIG. 3 shows a tester used to evaluate the life of hydrogen embrittlement delamination. The bearing of the test body used in this evaluation test is a radial needle bearing having an outer diameter of 32 mm, an inner diameter of 24 mm, and a length of 19.8 mm. Table 2 shows the test conditions in the above test.

  Under the test conditions shown in Table 2, hydrogen embrittlement peeling can be generated with good reproducibility by performing rapid acceleration and deceleration. Table 3 shows the test results under the test conditions.

  FIGS. 4A and 4B show cross sections including hydrogen embrittlement peeling generated in Comparative Example 1. FIG. FIG. 4A is a photograph of the fracture surface, and FIG. 4B is a schematic view thereof. It can be seen that hydrogen embrittlement separation was induced under the above test conditions.

  According to the test results in Table 3, it can be seen that all of the examples of the present invention exhibit longer life than the comparative examples of the conventional products. In particular, in Example 2 of the present invention, the life becomes longer than both the blackening material of Comparative Example 2 and the 13% Cr steel blackening material of Comparative Example 3 in which the resistance to hydrogen embrittlement is improved. I understand.

  In order to investigate the cause of the particularly long life of Invention Example 3, the area ratio of the spheroidized carbide in the surface layer portion of the steel materials of Invention Examples 1-2 and Comparative Examples 1-2 of the conventional product, and austenite The grain size number of the crystal grain boundary according to JIS standard was measured. Table 4 shows the results.

  The area ratio of the spheroidized carbide of Inventive Example 1 is larger than that of Comparative Example 1, and the JIS grain size is not significantly different from that of Comparative Example. Further, in Example 2 of the present invention, the area ratio of the spheroidized carbide was larger than that of the comparative example, and the JIS grain size was finer than that of the comparative example.

Compared with Comparative Example 1, Comparative Example 2 has a longer life, and Example 1 of the present invention has a longer life than Comparative Example 2, and Example 2 of the present invention has a longer life than Example 1 of the present invention. It can be seen that these three factors are effective in suppressing the hydrogen embrittlement resistance peeling.
(1) Having a nitrogen-enriched layer.
(2) The area ratio of the spheroidized carbide is 10% or more.
(3) The austenite crystal grain boundary exceeds JIS standard grain size number 10.

  The present invention example 2 has a very long life because it has all the above three factors. Although the effect of hydrogen embrittlement resistance peeling is recognized only with the above item (1), the effect of extending the life of the hydrogen embrittlement is small, and therefore at least the two requirements (1) and (2) are satisfied as in Example 1 of the present invention. This makes it possible to form a rolling bearing in which hydrogen embrittlement cracking is unlikely to occur in a hydrogen environment.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is shown by the description of the claims, and further includes all modifications within the meaning and scope equivalent to the description of the claims.

  By using the rolling bearing and the manufacturing method of the present invention, hydrogen is generated, and even when used in a usage mode in which hydrogen embrittlement is likely to occur, a rolling bearing capable of suppressing hydrogen embrittlement can be provided. It is expected to be used widely.

It is a figure showing a bearing for alternators in an embodiment of the invention. It is a figure showing processing of each example of the present invention in an example of the present invention, (a) processing of example 1 of the present invention, (b) processing of example 2 of the present invention, (c) processing of comparative example 1, FIG. It is a figure showing a test device which reproduces hydrogen embrittlement exfoliation. It is a figure which shows hydrogen embrittlement peeling, (a) is a photograph of a cross section, (b) is the schematic diagram.

Explanation of reference numerals

  1 Alternator bearing, 2 rolling element (steel ball), 3 outer ring (track ring), 4 inner ring (track ring), 5 pulley, 6 groove for power transmission belt, 7 cage, 10 alternator, 11 shaft, 15 broken surface, 16 rolling surface, 17 white layer.

Claims (6)

  At least one member of the rolling element, the inner ring, and the outer ring of the rolling bearing has a nitrogen-enriched layer, and an area ratio of spheroidized carbide in a surface layer portion of the member having the nitrogen-enriched layer is 10% or more. , Rolling bearings.   2. The rolling bearing according to claim 1, wherein the member having the nitrogen-enriched layer has an austenite crystal grain having a grain size number of more than 10.   The rolling according to claim 1, wherein the member having the nitrogen-enriched layer is subjected to carbonitriding at a CP (Carbon Potential) value of 1.3 to 1.6, and then oil-cooled from the temperature. bearing.   The member having the nitrogen-enriched layer is subjected to carbonitriding at a point A1 or higher of the steel main body, and then cooled to a temperature lower than the point A1. The rolling bearing according to claim 1, wherein the rolling bearing is reheated and quenched to a quenching temperature range lower than the temperature. A method of manufacturing a rolling bearing including a rolling element, an inner ring and an outer ring,
The rolling element, a steel material forming at least one member of the inner ring and the outer ring, after heating to a temperature of the A1 point or more and carbonitriding at a CP (Carbon Potential) value of 1.3 to 1.6, A method for manufacturing a rolling bearing, wherein oil is cooled to a temperature lower than the point A1. A method of manufacturing a rolling bearing including a rolling element, an inner ring and an outer ring,
The steel material forming at least one member of the rolling element, the inner race and the outer race is subjected to carbonitriding by heating to a temperature of A1 point or higher, then cooled to a temperature lower than A1 point, and then cooled to a temperature of A1 point or higher. A method for producing a rolling bearing, comprising reheating and quenching to a quenching temperature range lower than the temperature of the carbonitriding treatment.

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