JP5211453B2 - Rolling bearing - Google Patents

Description

  The present invention relates to a rolling bearing, and more particularly to a rolling bearing used for transmissions, engines, etc. of automobiles, agricultural machines, construction machines, steel machines and the like.

Foreign materials such as metal chips, shavings, burrs, and abrasion powder mixed in the bearing lubricant can damage the bearing rings and rolling elements of the rolling bearing, resulting in a significant decrease in the life of the rolling bearing. well known. Therefore, in the following Patent Document 1, even when a rolling bearing is used in a lubrication environment in which foreign matter is mixed, the content of C in the rolling surface layer of the bearing, the amount of retained austenite, and the content of carbonitride are appropriate. It is disclosed that, by setting the value, stress concentration at the indentation edge caused by the foreign matter is alleviated, crack generation is suppressed, and the life of the rolling bearing is improved. According to this, it is possible to improve the life in a lubricating environment containing foreign matters by an appropriate amount of retained austenite.
Japanese Patent Laid-Open No. 64-55423

  As described in Patent Document 1, the early separation that occurs in a foreign matter-mixed lubrication environment is caused by an indentation formed by biting foreign matter between the rolling elements and the raceway, and the indentation is It has been said so far that the stress concentration caused by the formation is the cause. However, the present inventors have clarified that the indentation origin type separation is not only caused by the stress concentration at the indentation edge but also by the tangential force acting between the rolling elements and the raceway. Factors affecting the tangential force include surface roughness and surface shape in addition to sliding speed and surface pressure. The smaller the surface roughness and the better the surface shape, the smaller the tangential force acting on the rolling elements and the bearing ring, and the longer the bearing life in a foreign matter-mixed lubrication environment.

  On the other hand, when the amount of retained austenite on the rolling surface is increased as described in Patent Document 1, not only the surface hardness is lowered and the wear resistance is lowered, but also the pressure scar resistance is lowered. Therefore, when the amount of retained austenite on the rolling surface is large, indentations are easily formed on the rolling surface due to the influence of foreign matter. The rolling surface on which the indentation is formed causes shape collapse and an increase in surface roughness. As the size of the indentation is larger and the number is larger, the shape collapse and the increase in surface roughness are more remarkable. That is, in a foreign matter mixed lubrication environment, as the amount of retained austenite on the surface of the rolling surface increases, an indentation is formed and the tangential force acting between the rolling element and the raceway increases.

  When there is a lot of retained austenite on the rolling surface in a foreign matter-contaminated lubrication environment, even if the tangential force increases, the residual austenite is caused by the stress concentration relaxation effect due to the effect of retained austenite as described in Patent Document 1. The life of many members themselves does not decrease. However, since the tangential force of the same magnitude acts on the two objects in contact with each other, the life of the mating member of the member having a large amount of retained austenite on the surface is reduced. For example, when the retained austenite on the surface of the raceway is increased, the life of the raceway is extended due to the stress concentration relaxation effect, but the life of the rolling element as the counterpart member is reduced due to an increase in tangential force.

  Even if the rolling element is peeled off or the raceway ring is peeled off, the life of the bearing is reached. Therefore, in order to extend the life of the entire bearing, it is necessary to extend the life of both the rolling element and the raceway. That is, it is not possible to obtain a sufficient life extension effect by simply increasing the retained austenite on the rolling surface. Further, depending on the use conditions of the bearing, there may be a case where a technique for increasing the retained austenite to extend the life cannot be adopted. For example, when used at a high temperature, the retained austenite deteriorates the dimensional stability, so that the amount of retained austenite is preferably small.

  On the other hand, the present inventors have conducted intensive research to ensure a sufficient indentation-initiated peeling life of themselves (for example, rolling elements), improve their own indentation resistance and wear resistance, and improve surface roughness. Investigate whether there is a material factor that suppresses the deterioration of the surface shape, suppresses the tangential force acting between the two objects (between the rolling element and the race), and extends the life of the mating member (eg, the race). went. As a result, as a material factor for improving the pressure scar resistance and wear resistance, in addition to the surface hardness, the above-mentioned residual austenite, surface nitrogen concentration, nitride containing Si and Mn deposited on the surface (hereinafter referred to as Si・ It was revealed that the area ratio of (Mn nitride) is related.

  In addition, the inventors have reduced the surface roughness of the rolling elements and the raceway rings when the surface roughness of the rolling elements is reduced compared to the case where the surface roughness of the raceway rings is reduced (surface roughness). Now, it was clarified that surface-origin-type peeling can be effectively suppressed when the deterioration of the surface shape is suppressed. That is, the life of the entire bearing can be effectively extended by suppressing the deterioration of the surface roughness and surface system of the rolling elements rather than the race.

  Therefore, although specific numerical limitations will be described later, at least one of the inner and outer rings and rolling elements, preferably the surface hardness of the rolling elements, the amount of surface retained austenite and the surface nitrogen concentration, the area ratio of the Si / Mn nitride By improving the pressure resistance and wear resistance, not only the increase in the tangential force between the rolling element and the raceway surface that occurs during the use of the bearing is suppressed, but also the anti-peeling property is improved and foreign matter contamination lubrication is achieved. It is possible to provide a rolling bearing with a long life against indentation-initiated delamination that occurs in the environment.

  On the other hand, when considering applying such a high nitrogen carburizing treatment to a large-sized rolling bearing, since Si and Mn added for improving hardenability are extracted from the base as nitrides, long life In the vicinity of the surface where the Si / Mn-based nitride that brings about the action is deposited, the hardenability is locally reduced, and an incompletely hardened layer such as pearlite and bainite is formed, which may cause a decrease in life. Yes.

Accordingly, the present inventors have developed and developed a steel type that ensures hardenability with other elements excluding Si and Mn that form nitrides so that they can be applied to large-sized rolling bearings. In the present invention, as will be described later, Si and Mn correspond to the presence of alloy elements in the bearing, for example, to form nitrides and other alloy elements such as Mo and Ni to ensure hardenability. This makes it possible to produce a long life effect even for large bearings.
The present invention has been made paying attention to the above-mentioned problems. By optimizing the composition of the steel, the surface nitrogen concentration, and the Si / Mn-based nitride, the life is longer and the pressure scar resistance is improved. An object of the present invention is to provide a rolling bearing having excellent wear resistance.

In order to solve the above problems, a rolling bearing according to claim 1 of the present invention includes an outer member having a rolling surface on an inner peripheral surface, an inner member having a rolling surface on an outer peripheral surface, and an outer side. In a rolling bearing comprising a plurality of rolling elements that are freely rollable between a rolling surface of the member and a rolling surface of the inner member, at least the outer member, the inner member, and the rolling element. One component member is C: 0.95-1.1 mass%, Si: 0.3-0.7 mass%, Mn: 0.2-1.15 mass%, Cr: 0.9-1 . Carbon steel containing 80 % by mass, Mo: 2% by mass or less, Ni: 2 % by mass or less, containing one or more alloy elements, the balance being Fe and inevitable impurities is subjected to carbonitriding The nitriding concentration of the surface layer of the constituent member is 0.2 to 2.0% by mass, and the Si / Mn nitride of the surface layer of the constituent member It is characterized in that the area ratio was 20% or less than 1%.

The front Kigaikata member rolling surface and the inner member of the rolling surface of the amount of residual austenite gamma _rAB, the amount of retained austenite of the surface of the rolling element in case of a _{γ rC, γ rAB -15 ≦ γ} rC ≦ γ _rAB +15, γ _rAB ≦ 50, γ _rC ≦ 50.

[Nitrogen concentration on rolling element surface is 0.2 to 2.0 mass%, and area ratio of Si / Mn nitride is 1% to 20%]
In the present invention, carbonitriding is performed in order to enrich the predetermined surface nitrogen of the raceway (outer member and inner member) or the surface layer of the rolling element. Nitrogen, like carbon, not only works to strengthen the solid solution strengthening of martensite and ensure the stability of retained austenite, but also forms nitrides or carbonitrides to improve the pressure scar resistance and wear resistance. is there. FIG. 1 shows a state of a pressure scar test, and FIG. 2 shows a state of a two-cylinder wear test. The pressure dent test was performed by pressing a steel ball having a diameter of 2 mm against a sample at 5 GPa and then measuring the depth of the dent. In the two-cylindrical wear test, a high-speed (driving side) cylindrical test piece 11 that is directly driven by the motor 12 is rotated at a peripheral speed of 10 min ⁻¹ , A slippage is forcibly applied by rotating at a peripheral speed of 7 min ⁻¹ through a reduction gear 14, and the torque on both test pieces is detected by a torque meter 15, while the drive side and driven 20 hours after the start of the test. The average amount of wear of the side cylindrical specimen was measured.

  FIG. 3a shows the relationship between the surface nitrogen concentration and the indentation depth of the pressure dent test result, and FIG. 3b shows the relationship between the surface nitrogen concentration and the wear amount of the two-cylinder wear test result. The surface nitrogen amount was measured using an electron beam microanalyzer (EPMA). Moreover, in order to investigate only the effect of the nitrogen concentration, the hardness other than the surface nitrogen concentration and the amount of retained austenite were made constant. As can be seen from FIG. 3, the higher the surface nitrogen concentration, the better the pressure scar resistance and wear resistance, and the effect appears remarkably when the surface nitrogen concentration exceeds 0.2% by mass, but more preferably 0. .45% by mass or more.

  On the other hand, if the nitrogen concentration is too high, there is a drawback that toughness and static strength are lowered. Since the toughness and static strength are necessary performances for rolling elements of a rolling bearing, it is not preferable that the nitrogen concentration is too high. FIG. 4 shows the result of the Charpy impact test. It can be seen that when the nitrogen concentration exceeds 2.0 mass%, the toughness of the voids decreases. Therefore, the upper limit of the surface nitrogen concentration of the present invention is set to 2.0% by mass.

  As described above, it has been clarified that the higher the nitrogen concentration on the surface, the higher the pressure scar resistance and wear resistance of the material. However, the present inventors have further found that even when the nitrogen concentration is the same, the pressure scar resistance and wear resistance change depending on the presence of nitrogen inside the material. Nitrogen may be present as a solid solution inside the material, or may be precipitated as a nitride. Although detailed numerical values will be described later, when a carbon-nitriding material containing a large amount of Si and Mn is subjected to carbonitriding treatment, the surface of the Si / Mn-based nitridation is formed on the surface from the amount of nitrogen present in solid solution in the material even at the same nitrogen concentration. The amount of nitrogen present as a result of the precipitation of substances increases. FIG. 5a shows the relationship between the area ratio of the Si / Mn nitride and the indentation depth of the pressure dent test result, and FIG. 5b shows the area ratio of the Si / Mn nitride and the wear amount of the two-cylinder wear test result. The relationship is shown. The area ratio of Si / Mn nitride is measured using a field emission scanning electron microscope (FE-SEM) by observing the rolling surface at an acceleration voltage of 10 kV, and at least 3 fields of view at a magnification of 5000 times. After the image was taken, the area ratio was calculated using an image analyzer after binarizing the photograph. In order to investigate only the effect of the Si / Mn nitride, the hardness other than the area ratio of the Si / Mn nitride, the amount of retained austenite, and the nitrogen concentration are kept constant. As is clear from FIG. 5, the higher the area ratio of the Si · Mn nitride, the better the pressure scar resistance and wear resistance. When the area ratio of the Si · Mn nitride exceeds 1%, it is remarkable. Although an effect appears, it is preferably 2% or more. In addition, the observation photograph of Si * Mn type nitride is shown in FIG. The lower part of FIG. 6 shows the elemental analysis results of the nitride analyzed by the energy dispersive X-ray dispersive analyzer. From the analysis results, peaks of Si, Mn, and N appear, and it can be seen that the nitride on the surface is Si · Mn nitride.

In addition, in order to investigate the influence of the area ratio of the Si / Mn nitride on the indentation origin type peeling life, a test was performed in a lubrication environment mixed with foreign matters by a thrust type life test. The components of the materials used in the test are shown in Table 1 below. In the table, steel type 1 is a material corresponding to JIS SUJ3 and steel type 2 is a material corresponding to JIS SUJ2. The materials shown in Table 1 were turned into a disk having a diameter of 65 mm and a thickness of 6 mm. After carbonitriding in a mixed gas atmosphere of RX gas, propane gas and ammonia gas at 820 to 900 ° C. for 2 to 10 hours, oil quenching was performed. After that, tempering treatment was performed at 160 to 270 ° C. for 2 hours. Test pieces having various nitrogen concentrations were prepared by changing the treatment temperature, treatment time, and ammonia gas flow rate. After the heat treatment, the surface was mirror finished by polishing and lapping.
The test conditions are as follows.
Test load: 5880N
Rotational speed: 1000min ^-1
Lubricating oil: VG68
Hardness of foreign matter: Hv870
Foreign material size: 74 to 147 μm
Foreign matter contamination: 200ppm

  Table 2 below shows the relationship between the nitrogen concentration, the area ratio of the Si / Mn nitride and the lifetime of contamination. FIG. 7 shows the relationship between the nitrogen concentration of steel types 1 and 2 and the area ratio of the Si / Mn nitride, and FIG. 8 shows the relationship between the area ratio of the Si / Mn nitride and the indentation origin peeling life. Indicates. In addition, the life test result was shown by the ratio when the L10 life of Comparative Example 1 is 1.

  From these, it can be seen that the precipitation amount of nitride increases in proportion to the nitrogen concentration. As will be described in detail later, it can be seen that the steel with a larger amount of Si and Mn added has a larger amount of Si · Mn nitride precipitation and a longer life when compared with the same amount of nitrogen. Similarly to the scratch resistance and wear resistance, when the area ratio of the Si · Mn nitride is 1% or more and the nitrogen concentration is 0.2% by mass or more, the life is remarkably improved.

  On the other hand, as with the nitrogen concentration, there is a drawback that the toughness and the static strength are lowered when the amount of Si / Mn nitride deposited becomes too large. Since the toughness and static strength are necessary performances for rolling elements of a rolling bearing, it is not preferable that the amount of Si / Mn nitride precipitates is excessive. FIG. 9 shows the result of the Charpy impact test. As is clear from the figure, it can be seen that when the area ratio of the Si · Mn nitride exceeds 20%, the toughness rapidly decreases. Therefore, the upper limit of the area ratio of the Si / Mn nitride of the present invention is set to 20%, more preferably 10%.

[The number of Si · Mn nitrides of 0.05 μm or more and 1 μm or less in the surface of the rolling element surface of 375 μm ² is 100 or more]
In the theory of precipitation strengthening, the smaller the distance between the precipitate particles, the better the strengthening ability. Therefore, even if the area ratio of the nitride is the same, the Si · Mn system having an area of 375 μm ² and 0.05 μm or more and 1 μm or less By increasing the number of nitrides to 100 or more, it is preferable to increase the number of precipitates and reduce the distance between the precipitate particles for strengthening. Further, it is possible to further strengthen by setting the number ratio of 0.05 μm to 0.50 μm Si / Mn nitride out of Si / Mn nitride of 0.05 μm or more to 20% or more. .

[C: 0.3 to 1.2% by mass or less]
C is an important element for obtaining the strength and life required for steel. When C is too small, not only a sufficient strength cannot be obtained, but also a heat treatment time for obtaining a hardened layer depth necessary for carbonitriding described later becomes long, leading to an increase in heat treatment cost. Therefore, the C content is 0.3% by mass or more, preferably 0.5% by mass or more. In addition, if the C content is too large, giant carbides are produced during steelmaking, which adversely affects the subsequent quenching characteristics and rolling fatigue life, and the header properties may decrease, leading to an increase in cost. The content was 1.2% by mass. More preferably, the content is 0.95 to 1.10% by mass.

[Si: 0.3-2.2% by mass, Mn: 0.2-2.0% by mass]
As described above, in order to sufficiently precipitate the Si · Mn nitride, it is necessary to use a steel containing a large amount of Si and Mn (SUJ2 (Si content 0.25 mass%, Mn content 0. 4 mass%), even if nitrogen is added excessively by carbonitriding or the like, the amount of Si · Mn nitride is small). For this reason, content of Si and Mn makes the following values critical values.
[Si: 0.3 to 2.2% by mass]
It is an element necessary for the precipitation of the nitride according to the present invention, and due to the presence of Mn, it effectively reacts with nitrogen and precipitates significantly when added in an amount of 0.3% by mass or more. Moreover, in order to suppress the fall of toughness and the spreading | diffusion of nitrogen to a deep part, 2.2 mass% or less is preferable, More preferably, you may be 0.70 mass% or less.

[Mn: 0.2 to 2.0% by mass]
It is an element necessary for precipitation of nitride according to the present invention, and has the effect of promoting the precipitation of Si / Mn nitride by addition of 0.2% by mass or more by coexistence with Si. Further, since Mn has a function of stabilizing austenite, it is 2.0% by mass or less, more preferably 1.15% by mass or less in order to prevent a problem that residual austenite increases more than necessary after the heat treatment for curing. .
[Mo: 2.0% by mass or less]
Mo is an element that increases the hardenability, and does not remarkably concentrate in the above-described Si · Mn nitride or cementite, so it is effective for ensuring the hardenability even after carbonitriding. In order to further obtain this effect, the Mo content is preferably 0.05% by mass or more.
On the other hand, excessive addition of Mo causes problems such as an increase in residual austenite more than necessary and an increase in steel material cost.

[Ni: 2.0% by mass or less]
Ni is an element that increases the hardenability and does not remarkably concentrate in the above-described Si · Mn nitride or cementite, so it is effective for ensuring the hardenability even after carbonitriding. In order to further obtain this effect, Ni is preferably 0.2% by mass or more. On the other hand, excessive addition of Ni causes problems such as an increase in residual austenite more than necessary and an increase in steel material cost.
Further, Cr improves hardenability, prevents crystal coarsening, and improves the spheroidization of the compound. In order to obtain this effect, 0.9% by mass or more is preferable, and workability and cost are reduced. Therefore, 1.8 mass% or less is preferable and 1.6 mass% or less is more preferable.

[The amount of retained austenite of the inner and outer raceway surfaces gamma _rAB, the amount of retained austenite of the rolling element surface when the _{γ rC, γ rAB -15 ≦ γ} rC ≦ γ rAB + 15, γ rAB ≦ 50, γ rC ≦ 50]
As described above, when the amount of retained austenite decreases, the pressure resistance and wear resistance are improved. On the other hand, the larger the amount of retained austenite on the surface, the longer the peeling life. In other words, considering the rolling element as a center, the smaller the amount of austenite on the surface of the rolling element, the better the pressure resistance and wear resistance of the rolling element, and the life of the raceway is extended, but the life of the rolling element itself decreases. . Therefore, there is an optimum amount of retained austenite of the rolling elements for the longest bearing life, but the optimum range varies depending on the amount of retained austenite of the race. When the amount of retained austenite in the raceway is large, the life of the raceway is prolonged, the pressure resistance of the raceway is reduced, and the tangential force between the raceway and the rolling element is increased. It is necessary to extend the life of the rolling element rather than to increase the wear resistance. Therefore, when the amount of retained austenite of the race is large, the amount of retained austenite of the rolling elements must also be increased. That is, since the range of the retained austenite amount (γ _rC ) of the rolling element that achieves the longest bearing life varies depending on the retained austenite amount (γ _rAB ) of the _raceway , γ _rAB −15 ≦ γ _rC ≦ γ _rAB +15, γ _It takes the form of _rAB ≦ 50 (where γ _rAB ≦ 50, γ _rC ≦ 50) (the reason for numerical limitation will be described later). Further, when the amount of retained austenite is too large, not only the hardness is lowered and the pressure resistance and wear resistance are lowered, but also the dimensional stability when used at a high temperature is deteriorated, so the upper limit value was made 50%.

  In the present invention, preferably, the hardness of the rolling element surface is set to Hv750 or more. Surface hardness is first conceived as a material factor for improving the pressure scar resistance and wear resistance. In order to investigate the influence of the surface hardness on the pressure scar resistance and wear resistance, the pressure scar resistance test and the two-cylinder wear test were performed in the same manner as described above. FIG. 10a shows the relationship between the surface hardness and the indentation depth of the indentation test result, and FIG. 10b shows the relationship between the surface hardness and the wear amount of the two-cylinder abrasion test result. As is apparent from the figure, it can be seen that the greater the surface hardness, the better the pressure scar resistance and wear resistance. In particular, when the hardness of the surface is Hv 750 or more for both the scratch resistance and the wear resistance, the effect of the surface hardness is remarkably obtained. In addition, it is known that the higher the hardness, the higher the fatigue strength. By increasing the surface hardness of the rolling surface, not only the indentation resistance and wear resistance, but also the indentation origin peel strength is improved. Is possible.

Thus, according to the rolling bearing according to claim 1 of the present invention, the outer member having the rolling surface on the inner peripheral surface, the inner member having the rolling surface on the outer peripheral surface, and the outer member In a rolling bearing provided with a plurality of rolling elements that are freely rollable between the rolling surface and the rolling surface of the inner member, at least one of the outer member, the inner member, and the rolling element member, C: .95 to 1.1 wt%, Si: 0.3 to 0.7 mass%, Mn: 0.2 to 1.15 mass%, Cr: 0.9 to 1.80 wt% And Mo: 2% by mass or less, Ni: 2 % by mass or less containing any one or more alloy elements, the balance being Fe and unavoidable impurities subjected to carbonitriding, The nitridation concentration of the surface layer of the constituent member is 0.2 to 2.0% by mass, and the area ratio of the Si / Mn nitride of the surface layer of the constituent member is 1% or less. Since it was 20% or less, with longer lifetime, indentation resistance, excellent wear resistance.

Further, the amount of retained austenite of the rolling surface of the rolling surface and the inner member the outer member gamma _rAB, the amount of retained austenite of the rolling element surface when the _{γ rC, γ rAB -15 ≦ γ} rC ≦ γ rAB Since +15, γ _rAB ≦ 50, and γ _rC ≦ 50, a long life of the entire bearing is possible.

Next, an embodiment of the rolling bearing of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of the rolling bearing of this embodiment. This rolling bearing is a tapered roller bearing having a nominal number L44649 / 610, which includes an inner ring 1 that is an inner member, an outer ring 2 that is an outer member, a rolling element 3, and a cage 4.
Using this tapered roller bearing, a life test was conducted in a lubricating environment containing foreign matter. The test conditions are as follows.
Test load: radial load Fr = 12 kN, axial load Fa = 3.5 kN
Rotational speed: 3000 min ^-1
Lubricating oil: VG68
Hardness of foreign matter: Hv870
Foreign material size: 74-134 μm
Foreign matter contamination: 0.1g

  The embodiment of the life test uses the present invention for the rolling element. The inner and outer rings are made of steel carbon chromium bearing steel (SUJ2). After carbonitriding for 1 to 3 hours in RX gas + propane gas + ammonia gas atmosphere at 830 to 850 ° C, tempering at 180 to 240 ° C is performed. As a result, three types of race rings were produced in which the amount of retained austenite on the inner and outer race surface was about 10, 20, and 30%.

  Table 3 below shows the components of the rolling element material used in the experiment and the quality of the completed rolling element. First, the rolling elements were prepared by header processing and rough grinding processing of wire materials having the components shown in Table 3, carbonitriding and quenching (830 ° C. × 5 to 20 hr, RX gas + enrich gas + ammonia gas atmosphere), and tempering at 180 to 270 ° C. The heat treatment and post-process were performed. For the measurement of the surface nitrogen amount of the rolling element, an electron beam microanalyzer (EPMA) was used for quantitative analysis. The amount of retained austenite in the surface layer was measured by an X-ray analysis method. In all cases, the rolling element surface was directly analyzed and measured. Furthermore, the area ratio of the Si / Mn nitride is measured by observing the rolling surface at an acceleration voltage of 10 kV using a field emission scanning electron microscope (FE-SEM), and at least 3 fields of view at a magnification of 5000 times. After taking a photograph as described above, the area ratio was calculated using an image analyzer after binarizing the photograph. In addition, the life test was performed for each sample n = 12, the life time until peeling occurred was measured, a Weibull plot was created, and the L10 life was obtained from the result of the Weibull distribution to obtain a life value. The lifetime was the shortest, and the ratio was expressed as a ratio with Comparative Example 11 as 1.

FIG. 12 shows the relationship between the area ratio of Si / Mn nitride and the life ratio. As is apparent from FIG. 12, steel having a component within the scope of the present invention is used, and the surface nitrogen concentration is 0.2% by mass or more and 2.0% by mass or less, and the Si / Mn nitride area ratio is 1% or more and 20% or less The embodiment of the invention has a greater life extension effect than the comparative example.
FIG. 13 shows the relationship between the retained austenite of the rolling element rolling surface and the life ratio when the amount of retained austenite on the raceway surface is 10, 20, and 30%. The larger the amount of retained austenite on the raceway surface, the longer the tendency of life, but the life depends on the amount of retained austenite on the rolling element rolling surface, and the amount of retained austenite of the rolling element is defined in the scope of the present invention. As a result, the long life of the entire bearing is achieved. In addition, when the amount of retained austenite of the rolling element is less than the range of the present invention, the rolling element is all damaged, and when it is more than the range of the present invention, all the raceways are damaged. It can be seen that the life of the moving body and the race is extended in a well-balanced manner, and a long life is achieved for the entire bearing.

  For example, as described in Japanese Patent Application Laid-Open No. 5-25609, a result of extending the life in a foreign matter-containing lubrication environment when the amount of retained austenite increases is also obtained in this test result. However, that alone is not sufficient, and by defining the amount of retained austenite of the counterpart material, it is possible to extend the life as shown in the examples. In addition, the present invention proposes a method for effectively extending the service life by specifying a range to extend the service life effectively even when the amount of retained austenite cannot be increased by increasing the amount of retained austenite due to problems of cost and usage conditions. It is a creative invention.

In addition, although the said Example is an example which applied this invention to the rolling element, the same effect is acquired even if it applies to any of an inner / outer ring or all of an inner / outer ring and a rolling element.
On the other hand, rolling bodies of various sizes were produced for steel types 1 to 9 shown in Table 3 above, and bearings were produced by applying carbonitriding conditions in which good life characteristics were obtained in the examples so far. Table 4 below shows the life ratio of each heat treatment quality and life test result. In addition, the life ratio represents the life of Comparative Example 23 as 1. This Comparative Example 23 is the same as Comparative Example 1 in Table 2 above.

  First, heat treatment quality will be described. As shown in FIG. 7 described above, the area ratio of the Si · Mn nitride depends on the Si and Mn contents and the nitrogen concentration. In steel types 1 and 3 to 9, since the contents of Si and Mn are almost the same, the precipitation amount of nitride depends on the nitrogen concentration, and the conditions of carbonitriding are the same. It is almost constant at 2-3%. As a result of investigating the incompletely hardened structure on the rolling surface after grinding, it was confirmed that the incompletely hardened structure might be generated when the diameter was 20 mm or more, although it was not observed in the rolling element having a diameter of 10 mm. With the generation of incompletely quenched structure, it can be seen that the long-life effect due to carbonitride is reduced in steel type 1, but in steel types 3 to 9 (Examples 21 to 41), it is incomplete in any rolling element size. It was revealed that a hardened structure was not generated and good life characteristics could be secured.

In this way, the role of alloy elements, such as the ability to generate carbonitrides and ensure hardenability, to understand the characteristics of each alloy element, and by providing a role suitable for each alloy element, long life by carbonitride It can be said that one of the original points of the present invention is that the deterioration of the life due to the incomplete hardening structure is reduced.
In this embodiment, the rolling elements are mainly described. However, the present invention can be similarly applied to large-sized races.

It is explanatory drawing of a pressure | voltage resistant test. It is explanatory drawing of a 2 cylinder abrasion test. (A) is explanatory drawing which shows the relationship between surface nitrogen concentration and indentation depth, (b) is explanatory drawing which shows the relationship between surface nitrogen concentration and wear amount. It is explanatory drawing which shows the relationship between surface nitrogen concentration and absorbed energy. (A) is explanatory drawing which shows the relationship between the area ratio of Si * Mn type nitride, and indentation depth, (b) is explanatory drawing which shows the relationship between the area ratio of Si * Mn type nitride, and the amount of wear. It is an observation photograph of Si.Mn nitride. It is explanatory drawing which shows the relationship between nitrogen concentration and the area ratio of Si * Mn type nitride. It is explanatory drawing which shows the relationship between the area ratio and lifetime ratio of Si * Mn type nitride. It is explanatory drawing which shows the relationship between the area ratio of Si * Mn type nitride, and absorbed energy. (A) is explanatory drawing which shows the relationship between surface hardness and indentation depth, (b) is explanatory drawing which shows the relationship between surface hardness and wear amount. It is a longitudinal cross-sectional view which shows one Embodiment of the rolling bearing of this invention. It is explanatory drawing which shows the relationship between the area ratio and lifetime ratio of Si * Mn type nitride. It is explanatory drawing which shows the relationship between the amount of retained austenite of a rolling element when the amount of retained austenite of a bearing ring changes, and a life ratio.

Explanation of symbols

1 is the inner ring (inner member)
2 is the outer ring (outer member)
3 is a rolling element 4 is a cage

Claims (1)

An outer member having a rolling surface on the inner peripheral surface, an inner member having a rolling surface on the outer peripheral surface, and freely rollable between the rolling surface of the outer member and the rolling surface of the inner member. In a rolling bearing including a plurality of arranged rolling elements, at least one of the outer member, the inner member, and the rolling element is C: 0.95 to 1.1% by mass, Si: 0. 3 to 0.7% by mass, Mn: 0.2 to 1.15% by mass, Cr: 0.9 to 1.80 % by mass, Mo: 2% by mass or less, Ni: 2 % by mass or less Any one or more kinds of alloy elements is contained, and the balance is made of carbon and nitriding treatment on steel composed of Fe and inevitable impurities, and the nitriding concentration of the surface layer of the constituent member is 0.2 to 2.0 mass%. The area ratio of the Si / Mn nitride on the surface layer of the constituent member is 1% to 20%, and the rolling surface and the inner member of the outer member The amount of retained austenite of the rolling surface gamma _rAB, the amount of retained austenite of the surface of the rolling element in case of a _{γ rC, γ rAB -15 ≦ γ} rC ≦ γ rAB + 15, γ rAB ≦ 50, are gamma _rC ≦ 50 A rolling bearing characterized by that.

Images