JP2014088893A - Rolling bearing and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress texture change type peeling due to immersion of hydrogen and surface origin type peeling based on existence of an impression, and to improve durability of a rolling bearing used under a severe environment while suppressing costs.SOLUTION: Surfaces of raceway surfaces of an outer ring raceway 5, inner ring raceways 6, 6 and the like are hardened by high-frequency hardening processing. A residual austenite amount of a surface layer part of each raceway 5, 6 is 12-40 vol.%, and hydrogen concentration in steel is 0.5 ppm or less. Surface origin type peeling is suppressed by securing the residual austenite amount, and texture change type peeling is suppressed by suppressing the hydrogen concentration in steel.

Description

The present invention relates to a rolling bearing that is operated under a high load, such as a rolling bearing incorporated in a rotation support part of a wind power generator, a main shaft, a construction machine, an industrial robot, or the like, and a method for manufacturing the same. Regarding improvement.
Specifically, it suppresses peeling due to structural changes (white structural changes) and minute indentations existing on the raceway surface or rolling surface, thereby improving the durability of rolling bearings used in harsh environments. It is intended to be suppressed.
Note that the rolling bearings that are the subject of the present invention include various radial rolling bearings such as ball bearings, cylindrical roller bearings, tapered roller bearings, and self-aligning roller bearings, as well as various thrust rolling bearings.

  For example, a cylindrical roller bearing is used for a rotation support part of a mechanical device that is operated under a large radial load, such as a rotation support part of a wind power generator, and a tapered roller is used for an application in which a thrust load is applied in addition to a large radial load. Bearings have been widely used in the past. Furthermore, under the condition that it is operated under a large radial load and it is difficult to keep the center axis of the outer ring and the center axis of the inner ring in exact alignment, the self-aligning roller as shown in FIG. A bearing 1 is used.

  The self-aligning roller bearing 1 includes an outer ring 2 and an inner ring 3 that are each formed in an annular shape and arranged concentrically with each other, and an inner peripheral surface of the outer ring 2 and an outer peripheral surface of the inner ring 3. Are provided with a plurality of spherical rollers 4, 4 each of which is a rolling element. These bearing components 2, 3, and 4 are generally made of a hard metal such as an iron-based alloy such as bearing steel, but the rolling elements such as the spherical rollers 4 and 4 are made of ceramics. There is also. The inner peripheral surface of the outer ring 2 is a partially spherical outer ring raceway 5 having a point on the central axis of the outer ring 2 as the center of curvature. Further, double-row inner ring raceways 6 and 6 are provided on the outer peripheral surface of the inner ring 3. The generatrix shape of these inner ring raceways 6 and 6 is symmetrical with the generatrix shape of the outer ring raceway 5 with respect to the central axis of each of the spherical rollers 4 and 4. Further, the spherical rollers 4 and 4 are rotatably provided between the outer ring raceway 5 and the inner ring raceways 6 and 6 while being held by cages 7 and 7, respectively.

  For example, in order to rotatably support the main shaft of the wind power generator in the housing by the self-aligning roller bearing 1 as described above, the outer ring 2 is fitted and fixed to the housing, and the inner ring 3 is externally attached to the main shaft. Fit and fix. In this state, the main shaft is rotatable based on the rolling of the spherical rollers 4, 4 between the outer ring raceway 5 and the inner ring raceways 6, 6. When the central axis of the outer ring 2 and the central axis of the inner ring 3 are shifted (inclined with each other) due to bending of the main shaft, the spherical rollers 4 and 4 are displaced in the width direction of the outer ring raceway 5. This shift is absorbed. During the operation of the automatic center roller bearing 1, the rolling surfaces of the spherical rollers 4 and 4 and the raceway surfaces of the outer ring raceway 5 and the inner ring raceways 6 and 6 are subjected to a large load in a small area. Rolling contact with sliding while supporting. In the following description, these rolling contact surfaces are collectively referred to as “rolling contact surfaces”.

  As can be seen from the above description, a high contact pressure acts repeatedly on the rolling contact surface existing in the rolling bearing such as the self-aligning roller bearing 1 or the like, and the portion directly below the rolling contact surface when the high contact pressure is applied. Shear stress acts on Such a state is a very severe use condition for each of the bearing components 2, 3, and 4 and is rolling even under a normal operation that is operated under a sufficiently lubricated condition and without causing a skew or the like. Metal fatigue tends to occur in the portion directly below the contact surface. In particular, the metal fatigue in the portion immediately below each track surface, which has a smaller curvature than the rolling surface and is easily affected by the high surface pressure, tends to be remarkable.

  Specifically, when sufficient lubrication is performed, the shear stress based on the high surface pressure is present in the portion directly below the rolling contact surface inside the metal material constituting each bearing component. The metal fatigue concentrates around the metal inclusions and locally accumulates metal fatigue in the portion. When metal fatigue accumulates in the portion immediately below the rolling contact surface in this way, a crack is generated in the portion, and the crack further develops and reaches the surface, leading to a damage called internal origin type peeling. If the rolling contact surface is partially lost due to such an internal origin type separation, normal operation of the rolling bearing including the bearing component cannot be continued (the rolling bearing reaches the end of its life). Such internal origin type separation is likely to occur on the raceway surface portions of the outer ring raceway 5 and the inner ring raceways 6 and 6 for the reasons described above, but the rolling surfaces of the rolling elements such as the spherical rollers 4 and 4 and the like. But it can happen. In any case, the time until the breakage is caused by the mechanism as described above is called the life of the rolling bearing due to the internal origin type peeling.

  On the other hand, when the lubrication is insufficient due to the influence of the viscosity of the lubricating oil (including the base oil in the grease) and the surface roughness, the surface portions of the respective rolling contact surfaces are subjected to fatigue. In particular, when a hard foreign object is caught between these rolling contact surfaces, a high stress concentration is generated around the indentation generated on the surface portion of each rolling contact surface, and metal fatigue accumulates in that portion. The In this way, even when stress concentration occurs on the surface portion of each rolling contact surface, as in the case where the above-described internal origin type peeling occurs, the generation and development of cracks are caused from the accumulation of metal fatigue, and rolling occurs. It leads to peeling of the contact surface. Damage caused by such a mechanism is called surface-origin separation.

  Even if it is the above-mentioned internal origin type peeling or the above-mentioned surface origin type peeling, the rolling contact surface is peeled off, and the damage due to such peeling is delayed (extended peeling life, ie, rolling fatigue life is extended). For this purpose, it is effective to improve the fatigue strength itself of the metal material constituting the bearing component having the rolling contact surface. And conventionally, in order to improve the fatigue strength of this metal material, the bearing component is made of an alloy steel with a large amount of carbon, or an alloy steel whose surface carbon concentration is increased by carburizing or carbonitriding, Further, the hardness of the rolling contact surface portion is increased by performing a quenching process.

  In this way, by increasing the hardness of the rolling contact surface portion, by suppressing the metal fatigue of the surface portion of the rolling contact surface and the portion immediately below, it is difficult for the raceway surface and the rolling surface to peel off. In addition, the life of the rolling bearing composed of rolling elements can be extended. As long as the application of the rolling bearing is general, sufficient durability can be ensured. However, some rolling bearings for industrial machinery are often used in places that support large loads, and the labor and cost required to replace damaged rolling bearings increase, resulting in a peeling life (rolling fatigue life). Improvement has become a major issue. In addition, such rolling bearings for industrial machines are often used under severe lubrication conditions in terms of temperature, rotational speed (rotational speed), foreign matter contamination such as dust. For this reason, the bearing components of the rolling bearings for industrial machines are often used in an environment where fatigue is likely to accumulate on the surface (the raceway surface, the rolling surface).

  In response to such circumstances, conventionally, in order to improve the durability of rolling bearings for industrial machines, the main purpose has been to further improve the durability of bearing components against surface fatigue. For example, Patent Document 1 focuses on the state of the separation starting point and regulates the retained austenite and surface hardness to alleviate the stress concentration around the indentation caused by the biting of the foreign material, and fatigue the rolling contact surface portion. Techniques for reducing are described. With such a technique, the durability of the rolling bearing for industrial machinery can be ensured if the operating conditions are somewhat severe.

  On the other hand, for example, in a large-sized rolling bearing that is incorporated in a rotation support portion of a wind power generator that has begun to spread in recent years and is operated under severe conditions, it is based on a structural change that occurs inside the bearing component. It has been known that peeling (early peeling) may occur on the rolling contact surface in a relatively short time. As for the cause of the structural change inside the bearing components that leads to such early peeling, the lubricating oil intervening in the rolling contact part inside the rolling bearing is decomposed by the high contact surface pressure and slippage of this rolling contact part. It is thought that this is caused by the generation of hydrogen and the penetration of this hydrogen into the steel. That is, when hydrogen enters the steel constituting the rolling bearing part, it is considered that the structural change in the steel is promoted due to hydrogen embrittlement, and that the early peeling is caused by fatigue failure. In addition, it is considered that such a change in structure based on hydrogen embrittlement is accelerated by factors such as the use of special lubricants that are likely to generate hydrogen, the presence of static electricity, and the mixing of water.

Therefore, in order to delay the occurrence of the structure change type peeling generated by the mechanism as described above and improve the rolling fatigue life of the rolling bearing, the composition of the lubricant and the composition of the alloy steel constituting the bearing component are changed. It has been proposed to devise. For example, Patent Document 2 discloses that a passivating oxide film is formed on the rolling contact surface by adding a passivating oxidant to the grease, thereby suppressing the decomposition of the base oil in the grease and the hydrogen in the steel. A technique for preventing intrusion and extending the rolling fatigue life of a rolling bearing is described.
Further, in Patent Document 3, by mixing conductive carbon black particles in the grease, the potential difference between the pair of race rings is eliminated, so that the base oil in the grease is decomposed, and the hydrogen A technique is described that suppresses the occurrence and extends the rolling fatigue life of the rolling bearing.
Further, in Patent Document 4, rolling of a rolling bearing incorporating the bearing component is made by using a steel containing a large amount of Cr that delays the structural change to a white structure as an alloy steel constituting the bearing component. A technique for extending the fatigue life is described.
However, as described in Patent Documents 2 and 3, the technique of devising the grease composition cannot be applied when the rolling bearing is lubricated by an oil bath or circulating oil supply. In addition, the technique of adding a large amount of Cr into the alloy steel inevitably increases costs due to the heavy use of Cr, which is an expensive metal.

  The above explanation has been made on the deterioration of the rolling fatigue life due to hydrogen generated by the decomposition of the lubricating oil during operation of the rolling bearing. On the other hand, hydrogen intrusion into the alloy steel constituting the bearing component can occur before the rolling bearing is in operation, and hydrogen that has infiltrated into the steel before operation can also be affected by the rolling bearing. It has been reported that rolling fatigue life is shortened. Specifically, even when hydrogen is infiltrated into the alloy steel by using a chemical reaction such as thiocyanic acid prior to performing a rolling life test to know the durability of the rolling bearing, It has been reported that exfoliation starting from a change in white structure occurs, similar to the case where hydrogen generated with the operation of a bearing enters the alloy steel.

From such a report, it can be seen that when hydrogen enters the steel constituting the bearing component, the durability of the bearing component is impaired regardless of the entry time. By the way, hydrogen may enter into the steel material constituting the bearing component even in the heat treatment step performed to harden the steel bearing component. That is, quenching, which is a heat treatment for hardening bearing steel and carburized steel, which is a steel material constituting the bearing component, is often obtained by reacting hydrocarbons with air in an RX gas atmosphere. Done in This RX gas contains 18 to 25% by volume of CO and 28 to 40% by volume of H ₂ , and the rest is N ₂ , CO _2, etc., and has strong carburizing characteristics due to CO. For this reason, by performing the said heat treatment process in RX gas atmosphere, the fall of the surface carbon amount of the steel materials which comprise the said bearing structural member can be suppressed during high temperature holding | maintenance.

  However, the RX gas contains a considerable amount of hydrogen as described above. There is a possibility that a part of the steel penetrates into the steel material constituting the bearing component. The hydrogen that has penetrated into the steel material is divided into diffusible hydrogen that moves easily and non-diffusible hydrogen that does not move while trapped at the interface, etc. It is known to cause (has an adverse effect). Most of the hydrogen that penetrates into the steel during the heat treatment process is non-diffusible hydrogen, but it does not mean that diffusible hydrogen is not contained at all.

  Considering the above, in order to prevent the deterioration of the durability of the bearing components due to the presence of hydrogen, in the stage of heat treatment of the bearing components, as the heat treatment, in the steel material constituting the bearing components It is desirable to select a method that does not allow hydrogen to enter. Specifically, it is conceivable to employ vacuum quenching or air quenching that excludes hydrogen from the heat treatment atmosphere. However, vacuum quenching among them is not industrially preferable because it requires time and equipment to adjust the atmosphere and costs increase. In addition, air quenching is disadvantageous from the viewpoint of ensuring the surface hardness of the bearing component because the carbon content on the surface of the bearing component is reduced, and is not preferable from the viewpoint of ensuring quality.

Japanese Patent Laid-Open No. 5-25609 Japanese Patent No. 2878749 JP 2002-327758 A JP 2005-147352 A

  In view of the circumstances as described above, the present invention is a rolling bearing used in a harsh environment by suppressing separation based on white structure change due to hydrogen intrusion and surface-origin separation based on the presence of indentations. The invention has been invented to realize a rolling bearing and a method for manufacturing the same that can improve durability while reducing costs.

The rolling bearings that are the subject of the present invention are a pair of race rings, each of which is annular and concentrically arranged and provided with raceway surfaces facing each other, and can freely roll between these raceway surfaces. And a plurality of rolling elements arranged in the.
In particular, in the rolling bearing according to the present invention, at least one type of bearing component (e.g., an inner ring of a radial rolling bearing) out of the three types of bearing components of the raceway and the rolling elements. The parts whose conditions are most severe in terms of ensuring the fatigue life, preferably a pair of race rings, and more preferably all bearing components) are brought into rolling contact with the mating member. From the rolling contact surface to a depth of 100 μm The amount of retained austenite (residual γ) in the surface layer portion that is the range is set to 12 to 40% by volume, and the hydrogen concentration in the steel of the bearing portion is set to 0.5 ppm or less. The amount of retained austenite is preferably 15 to 40% by volume, more preferably 20 to 40% by volume. The hydrogen concentration in the steel is preferably 0.3 ppm or less.

When implementing such a rolling bearing of the present invention, preferably, the amount of retained austenite of the surface layer portion is set to 12 to 40% by volume, and the hydrogen concentration in the steel is set as in the invention described in claim 2. A bearing component of 0.5 ppm or less is used as at least one of the two bearing rings. And the surface of the raceway surface provided in this raceway ring is hardened by the quenching process by high frequency heating.
Further, in order to manufacture the rolling bearing according to claim 2, the soft nitriding treatment is performed before the surface of the raceway surface is hardened by high-frequency heat quenching treatment as in the invention of the manufacturing method according to claim 3. Can also be applied.
Alternatively, as in the invention of the manufacturing method according to claim 4, before the surface of the raceway surface is hardened by induction heating and quenching, carbonitriding is performed at 800 to 1000 ° C., and then a temperature of 750 to 850 ° C. In the nitrogen atmosphere, it can be kept for a predetermined time (about 30 minutes to 3 hours), and then the induction hardening process can be performed. If the holding time is less than 30 minutes, the effect of the treatment is insufficient, and if it exceeds 3 hours, disadvantages such as decarburization are likely to occur.

According to the rolling bearing and the manufacturing method thereof of the present invention configured as described above, it is possible to suppress the peeling based on the change in white structure due to the penetration of hydrogen and the surface-origin type peeling based on the presence of the indentation, thereby causing a severe environment. It is possible to improve the durability of the rolling bearing used below while suppressing costs.
In other words, in the case of the rolling bearing according to the present invention, the hydrogen concentration in the steel of the bearing component, which is strict in terms of ensuring durability, is kept to a very low level of 0.5 ppm or less, so there is hydrogen in the steel The white tissue change caused by For this reason, peeling of the rolling contact surface starting from the change in white structure can be suppressed by the mechanism as described above. If the hydrogen concentration in the steel of the bearing component is suppressed to 0.3 ppm or less, peeling of the rolling contact surface starting from the white structure change can be more sufficiently suppressed.

  Further, since the amount of retained austenite in the surface layer portion of the bearing component is 12 to 40% by volume, it is possible to suppress the stress concentration generated around the indentation caused by foreign matter biting on the rolling contact surface. , Surface-origin type peeling caused by the mechanism as described above can be suppressed. In other words, austenite affects the shape of the indentation and relieves stress concentration on the indentation edge. For this reason, accumulation of metal fatigue in a portion around the indentation can be suppressed, and generation of cracks starting from the portion can be suppressed to suppress the surface starting type peeling. Such an effect cannot be sufficiently obtained when the amount of retained austenite is less than 12% by volume. On the contrary, if it exceeds 40% by volume, not only the effect of suppressing the surface-origin type peeling is saturated, but also the hardness of the rolling contact surface becomes too low, and for another reason, the rolling fatigue life of the rolling contact surface is reduced. It will decline. In the present invention, the amount of retained austenite in the surface layer portion is 12 to 40% by volume, preferably 15 to 40% by volume, more preferably 20 to 40% by volume, so that the rolling contact surface can be obtained from any surface. The rolling fatigue life can be secured.

  In particular, as in the invention described in claim 2, if the surface of the raceway surface of the raceway is quenched by high frequency heating, the amount of carbon decrease in the surface layer portion related to this raceway surface is suppressed, and the hardness of this raceway surface is reduced. While ensuring the thickness, hydrogen intrusion into the surface layer can be suppressed. Moreover, the amount of retained austenite in the surface layer portion can be secured. The reason for this is as follows.

  The quenching treatment by high-frequency heating is a heat treatment method in which the surface portion of the raceway is raised by an induced current in a short time to the temperature required for the quenching treatment using the self-heating of the raceway, To do. Such high-frequency heating directly heats not only the surface but also the inside of the surface layer by self-heating, so that the heating time is short and the holding time is not particularly required. Therefore, even if it is performed in the atmosphere, the carbon content on the surface of the steel material is minimally reduced and stops at the extreme surface portion. Since this pole surface portion is removed by polishing performed after the heat treatment, there is no particular problem with respect to ensuring the quality of the raceway even if the quenching treatment by high-frequency heating is performed in the atmosphere. That is, even if quality assurance is taken into consideration, it is not necessary to carry out in an RX gas atmosphere as in the case of heat treatment heated from the outside. For this reason, hydrogen does not enter the surface layer portion of the raceway surface in accordance with the heat treatment for hardening the raceway surface, and the occurrence of the structure change type peeling as described above can be suppressed. The conditions for high-frequency heating (output of the high-frequency heating coil, energization time, etc.) are appropriately set according to the specifications of the raceway to be quenched by high-frequency heating.

  In addition, when quenching is performed on the raceway surface of the race ring by high-frequency heat induction heating, a high-frequency induction coil is disposed on a portion facing the raceway surface or the fitting surface that requires a hardened layer. A surface, a fitting surface, and its surface layer part can be heated from the surface side. In addition, the surface layer portion of the raceway surface may be selectively heated to a high temperature by arranging the high-frequency induction coil only in a portion facing the raceway surface, or adjusting the electromagnetic field distribution by using a core or the like. it can. Therefore, by heating to a higher temperature, a larger amount of retained austenite can be present on the raceway surface and the surface layer portion than when heating to a temperature higher than the A1 transformation point necessary for curing. And the said surface origin type | mold peeling can be suppressed by making the amount of retained austenites of this track surface and its surface layer part high. Incidentally, the retained austenite decomposes little by little with the operation of the rolling bearing, but the volume slightly increases with the decomposition. Therefore, if the total amount of retained austenite in the bearing ring is excessively increased, it is difficult to ensure the dimensional stability of the bearing ring when long-term use is considered. On the other hand, the dimensional stability of the bearing ring can be ensured by increasing only the amount of retained austenite in the necessary portion by high-frequency heating.

Further, as in the inventions described in claims 3 and 4, soft nitriding treatment may be performed before the induction heating and quenching treatment, or carbonitriding and holding in a nitrogen atmosphere before the induction heating and quenching treatment. As a result, the amount of retained austenite can be more reliably set to a desired amount (sufficiently) while the hydrogen concentration in the steel in the surface layer portion of the raceway surface of the raceway is kept low. And surface origin type peeling can be suppressed more fully, suppressing generation | occurrence | production of structure | tissue change type peeling.
First, in the case of the invention described in claim 3, the soft nitriding treatment temperature is as low as about 550 to 600 ° C. and the treatment time is short, so that the amount of hydrogen permeation can be kept small, and the lifetime related to the structure change type peeling. Can be long. Further, since the amount of retained austenite can be increased along with reheating and quenching after soft nitriding, the life relating to surface-origin separation can be sufficiently extended.
Further, in the case of the invention described in claim 4, since the hydrogen that has penetrated into the steel due to the carbonitriding process is desorbed into the atmosphere by the subsequent treatment in a nitrogen atmosphere, the amount of remaining hydrogen Can be reduced, and the life of the tissue change type peeling can be extended. Further, since the amount of retained austenite can be increased by the effect of nitriding, the life relating to surface-origin separation can also be increased. The reason why the carbonitriding process is set to 1000 ° C. or lower is that when the temperature exceeds 1000 ° C., the decomposition of ammonia, which is a supply source of N, progresses, and the processing time becomes longer. The reason why the temperature is 800 ° C. or higher is that when the temperature is lower than 800 ° C., the diffusion rate of C becomes slow and sufficient carburization is not performed.

The partial cut perspective view which shows an example of the rolling bearing used as the object of this invention. The schematic diagram which shows six examples of the heat processing at the time of sample preparation of the experiment conducted in order to confirm the effect of this invention. The graph which shows the relationship between the hydrogen concentration in the steel in the surface layer of a raceway surface, and structure | tissue peeling type | mold lifetime. Similarly, the graph which shows the relationship between the amount of retained austenite and surface peeling type | mold lifetime.

  The feature of the present invention is that, by appropriately regulating the hydrogen concentration in the steel of the bearing component and the amount of retained austenite in the surface layer portion of this bearing component, the structure peeling type life and surface peeling type of the rolling bearing even under severe use conditions This is to ensure a sufficient life. The structure of the rolling bearing appearing in the drawings is the same as that of various conventionally known rolling bearings including the structure shown in FIG.

  An experiment conducted for confirming the effect of the present invention will be described. In this experiment, a self-aligning roller bearing 1 as shown in FIG. 1 was used as a sample. Of the outer ring 2, the inner ring 3 and the spherical rollers 4, 4 constituting the self-aligning roller bearing 1, the hydrogen concentration in the steel of the outer ring 2 and the inner ring 3, the surfaces of the outer ring raceway 5 and the inner ring raceways 6, 6. Seven types of samples with different amounts of retained austenite in the layer portion were prepared. Regarding each of the spherical rollers 4 and 4, any sample was made of SUJ2, and the whole was heated and soaked in quenching oil after so-called quenching. In order to vary the hydrogen concentration in the steel and the amount of retained austenite, high-carbon chromium bearing steel (SUJ2, JIS G 4805) and chromium steel (SCr420, JIS G 4104) are used as alloy steels constituting the outer ring 2 and the inner ring 3. And the six types of methods shown in FIGS. 2A to 2F were employed as the heat treatment methods for the outer ring raceway 5 and the inner ring raceways 6 and 6. In FIG. 2, the horizontal axis represents elapsed time and the vertical axis represents temperature. Also, the numerical values described in FIG. 2 indicate the processing temperature, and other characters indicate the processing atmosphere or the type of processing.

  Of these six types of heat treatment methods, three types (A) to (C) are out of the technical scope of the present invention. Of these, (A) is a so-called submerged baking in which heating is performed at a temperature equal to or higher than the A1 transformation point in an RX gas atmosphere, followed by rapid cooling, followed by tempering in the atmosphere (at 160 to 200 ° C. for 1 to 3 hours). It is processing. Further, (B) is a general carburizing treatment, and (C) is a general carbonitriding treatment, and the carbon potential value Cp is regulated to about 1.0 to 1.4.

Also, three types (D) to (F) in FIG. 2 belong to the technical scope of the present invention. Of these, (D) represents the outer ring raceway 5 and the inner ring raceway 6 in the atmosphere by high-frequency heating. After 6 portions were rapidly heated, they were quenched with water and then tempered in the air. The tempering conditions (180 ° C., 2 hours) were the same for the six types of heat treatment.
Further, (E) corresponds to the invention described in claim 3, and before the outer ring raceway 5 and the inner ring raceways 6 and 6 are hardened by high-frequency heating quenching, softening at 570 ° C. for 30 minutes. Nitriding treatment was performed.
Further, (F) corresponds to the invention described in claim 4, and carburizing at 880 ° C. for 10 hours before the outer ring raceway 5 and the inner ring raceways 6, 6 are hardened by high-frequency heat quenching treatment. After the nitriding treatment, it was kept in a nitrogen atmosphere at a temperature of 800 ° C. for 1 hour, and then the induction hardening treatment was performed.

With respect to the seven types of samples prepared under the conditions as described above, the rolling fatigue life related to the structure change type peeling and the rolling fatigue life related to the surface origin type peeling were obtained. In these tests, artificial indentations were formed on the raceway surface in the rolling fatigue life test related to surface-origin type peeling. The artificial indentation was formed by pressing Rockwell B scale steel ball indenters at 9.8 kN at four circumferentially equidistant positions in the center in the width direction of the inner ring raceways 6 and 6.
The experimental conditions common to each sample are as follows.
Spherical roller bearing 1 part number: 22211
Outer diameter: 100mm
Inner diameter: 55mm
Width: 25mm
Basic dynamic load rating Cr: 119000N
Applied load: 35700N
Lubrication condition: Forced circulation of VG68 lubricant

The results of the experiment conducted under the above conditions are shown in the following Table 1 together with the hydrogen concentration and the amount of retained austenite on the surface layer portion of the raceway surface of each sample, and are also shown in FIGS. The life ratios described in Table 1 and FIGS. 3 and 4 are ratios with respect to the structure change type peeling and the surface origin type peeling when the life of Comparative Example 1 is 1. A to F described in the column of heat treatment in Table 1 correspond to (A) to (F) in FIG.
In order to measure the hydrogen concentration, extra bearing rings (outer ring 2 and inner ring 3) constituting the self-aligning roller bearing 1 used for the rolling fatigue life test are made under the same conditions, and the corresponding bearing ring (mainly the inner ring 3). ) Was measured with a small piece obtained by cutting. That is, since hydrogen penetrates from the surface of the orbit by heat treatment, it is necessary to cut out and measure the portion including the surface. Further, since it is hydrogen existing in the stress load region of the raceway that affects the peeling life, it is necessary to measure a portion including the raceway. Accordingly, the hydrogen concentration was measured by temperature programmed desorption analysis (TDS) on a small piece obtained by cutting a part of the extra ring raceway including the raceway surface.

As can be seen from the test results shown in Table 1 and FIGS. 3 and 4, according to the present invention, it is possible to suppress both the structure change type peeling and the surface origin type peeling, and use under severe conditions. A sufficient rolling fatigue life can be secured with respect to the rolling bearing. Hereinafter, each sample will be considered.
First, in the case of Comparative Example 1, since the hydrogen concentration was high and the amount of retained austenite was small, the lifetime was short for both the structure change type peeling and the surface origin type peeling.
Next, Comparative Examples 2 and 3 have a longer life with respect to surface-origin type peeling than Comparative Example 1 due to a large amount of retained austenite, but due to the high hydrogen concentration, the life with respect to structure change-type peeling was short. .

On the other hand, in the case of Example 1, since the high carbon material is directly heat-hardened and hardened at high frequency, it is not exposed to RX gas during heat treatment, and the hydrogen concentration can be kept low. The lifespan of change-type peeling can be extended. Further, since the surface layer portion can be heated to a higher temperature than the core portion at a high frequency, the amount of retained austenite in the surface layer portion can be increased, and the life relating to the surface-origin type peeling can be extended.
Next, in the case of Example 2, since the high carbon material is soft-nitrided and then heat-quenched at a high frequency, hydrogen permeation occurs during soft nitriding. The processing time is short compared to the heating time for the quenching treatment in Comparative Examples 1 to 3. Therefore, the amount of hydrogen permeation can be reduced as compared with the cases of Comparative Examples 1 to 3, and the life regarding the structure change type separation can be extended. In addition, since solid solution of nitrogen in the surface matrix occurs during reheating and quenching after soft nitriding, the amount of retained austenite can be increased, and the life for surface-origin separation can be sufficiently prolonged.
Furthermore, in the case of Examples 3 and 4, since the carbonitriding process is performed on the material, hydrogen enters the steel, but the hydrogen that has entered through the subsequent treatment in the nitrogen atmosphere is desorbed into the atmosphere. Therefore, the amount of remaining hydrogen can be reduced. For this reason, the lifetime regarding a structure change type | mold peeling can be lengthened compared with the said Comparative Examples 1-3. Further, since the amount of retained austenite can be increased by the effect of nitriding, the life relating to surface-origin separation can also be increased.

The present invention can be implemented not only by a self-aligning roller bearing as shown, but also by various radial rolling bearings such as ball bearings, cylindrical roller bearings, tapered roller bearings, and various thrust rolling bearings.
In addition, the bearing component that regulates the amount of retained austenite and the hydrogen concentration in the steel is effective from the standpoint of extending the life of the rolling bearing, although it can be a rolling element. Of course, if the amount of retained austenite and the hydrogen concentration in the steel are regulated for all of the races and rolling elements, the life extension effect of the rolling bearing becomes the most excellent.
In addition, the lubrication method can be applied in the case of using an oil bath or circulating oil supply to obtain an effect, but can also be implemented in combination with grease. In this case, when combined with a special grease for suppressing the generation of hydrogen as described in Patent Documents 2 and 3, the life related to the structure change type peeling can be further improved.

1: Spherical roller bearing 2: Outer ring 3: Inner ring 4: Spherical roller 5: Outer ring raceway 6: Inner ring raceway 7: Cage

Claims (4)

  A pair of race rings, each of which is annular and concentrically arranged, and provided with raceway surfaces on opposite surfaces, and a plurality of rolling elements arranged so as to be freely rollable between the raceway surfaces; The amount of retained austenite in the surface layer portion in rolling contact with the mating member of at least one of the three types of bearing components of the bearing rings and the rolling elements. Rolling bearing characterized in that the hydrogen concentration in the steel of the bearing component is 0.5 ppm or less.   The bearing component in which the amount of retained austenite in the surface layer portion is 12 to 40% by volume and the hydrogen concentration in the steel is 0.5 ppm or less is at least one of the two bearing rings. The rolling bearing according to claim 1, wherein a surface of a raceway surface provided on the raceway is hardened by a quenching process by high frequency heating.   3. The method of manufacturing a rolling bearing according to claim 2, wherein a soft nitriding treatment is performed before the surface of the raceway surface is hardened by a high-frequency heat quenching treatment.   The rolling bearing manufacturing method according to claim 2, wherein the surface of the raceway surface is carbonitrided at 800 to 1000 ° C before being hardened by induction heating and quenching, and then at a temperature of 750 to 850 ° C. A method of manufacturing a rolling bearing, wherein the induction hardening process is performed after holding in a nitrogen atmosphere for a predetermined time.

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