JP2006322017A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive rolling bearing which has the long rolling-fatigue life even when used in an environment in which the surface tends to be damaged. <P>SOLUTION: A steel material of a roller 3 comprises, by mass ratio, 0.30-1.20% C, 0.50-2.00% Cr, 0.50% or more Mn, 0.85% or more Mn and Si in total, 12 ppm or less O, and the balance Fe with unavoidable impurities. The production method comprises the steps of: working the material into a predetermined shape; and subjecting the workpiece to carbonitriding treatment, quenching treatment, sub-zero treatment and tempering treatment in that order. The roller 3 has a surface part of a rolling contact surface 3a controlled so as to have a N content of 0.20 mass% to 2.00 mass% and contain retained austenite in an amount of 5 vol.% to 24 vol.%, and has the rolling contact surface 3a controlled so as to have lower surface roughness than raceway surfaces 1a and 2a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling bearing.

  Since a rolling bearing is used under repeated shear stress under high surface pressure, it is necessary to withstand this shear stress and ensure a rolling fatigue life. For this reason, as the bearing rings (inner and outer rings) and rolling elements of the rolling bearing, high-carbon chromium bearing steel type 2 (SUJ2) is subjected to quenching and tempering treatment, or case-hardened steel (SCR420, SCM420, SAE4320H, etc.). Carburizing or carbonitriding treatment, quenching and tempering treatment are used to make the surface hardness Hv650-800.

In recent years, rolling bearings used in these mechanisms to achieve high efficiency and miniaturization of power transmission mechanisms and support mechanisms for automobiles, machine tools, general industrial machines, steel equipment, etc. It is increasingly used in harsh environments such as conditions and high temperature conditions.
In particular, in rolling bearings used under high load conditions, it is difficult to form an oil film on the raceway surface, and metal contact occurs between the raceway and the rolling element, and the rolling surface (the raceway surface or the rolling surface) is formed. Since a large tangential force is generated, surface damage is likely to occur. Also, in rolling bearings used under high load conditions, slip due to skew is likely to occur between the bearing ring and the rolling element, and repeated shear stress and large tangential force are generated between the bearing ring and the rolling element. Surface damage is likely to occur.

The life reduction due to surface damage is caused by the above-described lubrication condition in which foreign matter is mixed in addition to the case where a large tangential force is generated on the rolling surface due to insufficient lubrication or slip as described above (hereinafter referred to as “under foreign matter-mixed lubrication”). This also occurs when an indentation is generated on the rolling surface due to the biting of foreign matter, and stress concentration occurs on the edge of the indentation.
As a technique for preventing a decrease in life due to such surface damage, techniques described in Patent Document 1 and Patent Document 2 have been proposed.

  In Patent Document 1, at least the race is in mass ratio, the C content is 0.8% to 1.2%, the Si content is 0.4% to 1.0%, and the Cr content is 0.00. After processing a material made of steel of 2% or more and 1.2% or less and a Mn content of 0.8% or more and 1.5% or less into a predetermined shape, carbonitriding and quenching at 830 to 870 ° C. And a tempering treatment at 160 to 190 ° C., and the amount of retained austenite in the surface layer portion is proposed to be 25% by volume or more and 50% by volume or less. Further, in Patent Document 1, it is preferable to secure a specific surface hardness by setting the amount of retained austenite in the surface layer part to 25 vol% or more and 30 vol% or less in order to obtain an excellent rolling fatigue life in the presence of foreign matter. It is described.

In Patent Document 2, at least the rollers are in a mass ratio, the C content is 0.8% to 1.5%, the Si content is 0.4% to 1.2%, and the Mn content is 0.8. % After processing a material made of steel with a Cr content of 0.8% or more and 1.8% or less to a predetermined shape, followed by carbonitriding, quenching and tempering. It has been proposed that the amount of retained austenite in the surface layer portion is 20% to 40% by volume and the surface hardness is Hv 750 or more.
Japanese Patent Laid-Open No. 7-190072 JP 2000-234147 A

However, in the bearings described in Patent Documents 1 and 2, the rolling fatigue life is improved by increasing both the amount of retained austenite and the hardness of the surface layer portion, so that the manufacturing cost is reduced. There is room for further improvement.
Further, in the bearings described in Patent Documents 1 and 2, only the life of the rolling member in which the life reduction due to surface damage is a problem is considered, and the life of other rolling members is not considered. For this reason, even if only the life of the rolling member in which the life reduction is a problem is lengthened, the life of the other rolling members may be insufficient and the life of the entire bearing may not be lengthened.
Accordingly, the present invention has been made to solve these problems, and it is an object to provide a rolling bearing having a long rolling fatigue life at a low cost even when used in an environment in which surface damage is likely to occur. Yes.

In order to solve such a problem, the present invention provides a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are movably disposed between the inner ring and the outer ring. The rolling element has a C content of 0.30% by mass or more and 1.20% by mass or less, a Cr content of 0.50% by mass or more and 2.00% by mass or less, an Mn content of 0.50% by mass or more, Mn And Si, the total content of 0.85% by mass or more, the O content of 12ppm or less, the balance is processed into a predetermined shape of steel and steel, which is Fe and inevitable impurities, carbonitriding, quenching, The sub-zero treatment and the tempering treatment are performed in this order, and the surface layer portion forming the rolling surface has an N content of 0.20% by mass or more and 2.00% by mass or less and a residual austenite amount of 5 volumes. % To 24% by volume and its rolling surface Surface roughness, provides a rolling bearing, characterized in that is smaller than the surface roughness of the raceway surface of the inner ring and the outer ring.
In the present invention, the surface layer portion refers to a range from the surface to a predetermined depth (for example, 1 μm).

Hereinafter, the critical significance of the numerical limitation of the present invention will be described in detail.
[C content (mass ratio): 0.30 to 1.20%]
C (carbon) has the effect of increasing the strength by converting the base into martensite. In the present invention, carbonitriding is performed after processing a raw material made of steel into a predetermined shape, and C and N (nitrogen) are added to the surface layer portion of the rolling element. Therefore, the C content constituting the material is 0.30% or more in order to ensure the necessary strength for the core of the rolling element. In addition, it is preferable that the hardness of the core part of a rolling element is Hv650 or more, and it is preferable that the C content rate which makes a raw material shall be 0.80% or more.
On the other hand, when there is too much C content which makes a raw material, a coarse carbide | carbonized_material will produce | generate at the time of steelmaking, and rolling fatigue life may be reduced. Therefore, the C content of the material is 1.20% or less.

[Cr content (mass ratio): 0.50 to 2.00%]
Cr (chromium) has the effect of improving hardenability and temper softening resistance and strengthening the base to improve the rolling fatigue life. Moreover, it has the effect | action which produces | generates the fine and high hardness carbide | carbonized_material and carbonitride, and improves abrasion resistance. Furthermore, it has the effect | action which raises C content rate of a carbonitriding layer and improves a carbonitriding characteristic. In order to obtain these effects, the Cr content is 0.50% or more.
On the other hand, if the Cr content is too high, not only the effect is saturated, but also a passive film is formed on the surface layer portion and may impair carbonitriding characteristics, so the Cr content is 2.00% or less. To do.

[Mn content (mass ratio): 0.50% or more, total content of Mn and Si (mass ratio): 0.85% or more]
The present inventor makes the N (nitrogen) content of the surface layer portion forming the rolling surface of the rolling element to be 0.20 mass% or more and reduces the amount of retained austenite in the surface layer portion, thereby reducing the rolling ring and the rolling ring. Focusing on the fact that friction with the moving body can be reduced, it has been found that surface damage to both the rolling element and the race can be suppressed by changing only the rolling element. Further, in order to stably secure the N content of the surface layer portion that forms the rolling surface of the rolling element, the present inventor has a content of Mn (manganese) in the steel constituting the rolling element and Si (silicon). It was also found that the content rate should be specified.

Mn and Si both act as deoxidizers during steelmaking and have the effect of improving the N content of the surface layer during carbonitriding. Further, Mn also has an effect of improving the hardenability of the steel, and Si also has an effect of improving the temper softening resistance of the steel.
In order to obtain these effects, the Mn content is 0.50% by mass or more, preferably 0.70% by mass or more.

Further, by adding Si together with Mn, the effect of improving the N content of the surface layer portion by Mn can be effectively obtained, so even if the rolling element has a large grinding allowance, its rolling surface is The N content in the range of the present invention can be stably secured in the surface layer portion to be formed. For this reason, it is preferable that the total content rate of Mn and Si shall be 0.85 mass% or more, and Si content rate shall be 0.50 mass% or more.
On the other hand, if the Mn content and the Si content are too high, the N content of the surface layer portion that forms the rolling surface of the rolling element becomes extremely large. Machinability such as forgeability and machinability is reduced. Therefore, the Mn content and the Si content are each preferably 2.00% by mass or less.

[O content (mass ratio): 12 ppm or less]
O (oxygen) generates oxide-based non-metallic inclusions that adversely affect the rolling fatigue life, so the content must be reduced as much as possible. For this reason, the O content is 12 ppm or less, preferably 9 ppm or less.

[About inevitable impurities]
In addition to the elements described above, the steel used in the present invention includes, for example, P (phosphorus), S (sulfur), Ni (nickel), Cu (copper), Mo (molybdenum), V (vanadium), and Al (aluminum). , Ti (titanium), Nb (niobium) and the like may be included. Among these, carbide-forming elements such as Mo and V are effective in improving wear resistance because they produce fine and high-hardness carbonitrides by carbonitriding. Therefore, these elements may be added as long as the cost permits, but the amount added is preferably 2.0% by mass or less in total.

[Configuration of rolling element after heat treatment and heat treatment]
After the above-mentioned steel material is processed into the shape of a rolling element by forging or cutting, carburization is performed by heating and holding for a predetermined time in a furnace in which a mixed gas (for example, RX gas + enrich gas + ammonia gas) is introduced. Nitriding treatment is performed.
This carbonitriding process is performed under the condition that the N content of the surface layer portion forming the rolling surface of the rolling element is 0.20 mass% or more and 2.00 mass% or less.

  At this time, if the N content of the surface layer portion forming the rolling surface of the rolling element is less than 0.20% by mass, the effect of suppressing the surface damage of the raceway in contact with the rolling element cannot be sufficiently obtained. On the other hand, the higher the N content of the surface layer portion, the higher the effect of suppressing the surface damage of the bearing ring, but when the N content of the surface layer portion exceeds 2.00% by mass, the carbonitrided layer becomes brittle, The rolling fatigue life required as a rolling member cannot be obtained. From the viewpoint described above, it is preferable that the N content of the surface layer portion forming the rolling surface of the rolling element is 0.50 mass% or more and 1.50 mass% or less.

  Further, the carbon content added in the same manner as N by carbonitriding is to obtain the surface hardness Hv650 required as a bearing member in the surface layer portion forming the rolling surface of the rolling element. It is preferable to adjust the C content so that the total content is 0.80% by mass or more. On the other hand, if the C content of the surface layer portion that forms the rolling surface of the rolling element is too large, coarse carbides precipitate, and the rolling fatigue life of the rolling element itself cannot be sufficiently obtained. Is preferably 2.50% by mass or less, and more preferably 2.00% by mass or less.

  Next, a quenching process is performed at 820 ° C. or more and 920 ° C. or less. At this time, if the quenching temperature is less than 820 ° C., the N content of the surface layer portion forming the rolling surface of the rolling element cannot be within the range of the present invention, and the hardness required for the rolling member cannot be obtained. On the other hand, when the quenching temperature is higher than 920 ° C., the carbide is decomposed during holding at a high temperature, the N content of the base is remarkably increased, and the steel constituting the material is extremely brittle.

Next, sub-zero treatment is performed at -190 to 10 ° C. As a result, the amount of retained austenite in the surface layer portion that forms the rolling surface is reduced and the hardness is remarkably improved, so that the pressure scar resistance and wear resistance of the rolling surface are improved. The friction between them can be effectively reduced. Further, by performing sub-zero treatment after increasing the N content in the surface layer portion forming the rolling surface by carbonitriding, the strain density of martensite is further increased, so that the fatigue resistance of the rolling element itself is improved. .
At this time, if the temperature at the time of sub-zero is lower than −190 ° C., it is necessary to use a coolant in order to maintain the temperature, which causes an increase in cost. On the other hand, if the temperature at the time of sub-zero is higher than 10 ° C., the retained austenite generated at the time of quenching is not transformed into martensite, so that sufficient hardness cannot be obtained.

Next, a tempering process is performed. This tempering treatment is performed under the condition that the amount of retained austenite in the surface layer portion forming the rolling surface of the rolling element is 5% by volume or more and 24% by volume or less.
At this time, if the amount of retained austenite is less than 5% by volume, surface damage is likely to occur under the contamination with foreign matter. On the other hand, when the amount of retained austenite is larger than 24% by volume, the hardness is lowered and the rolling fatigue life of the rolling element itself is shortened. The amount of retained austenite in the surface layer portion forming the rolling surface of the rolling element is preferably 7% by volume or more and 18% by volume or less.
Next, by performing a grinding finishing process, the surface roughness on the rolling surface of the rolling element is made smaller than the surface roughness on the raceway surface of the raceway. Thereby, even if a large tangential force is generated on the rolling surface due to insufficient lubrication or slippage, surface damage is unlikely to occur.

  In the rolling bearing of the present invention, the inner ring and the outer ring each have a C content of 0.30% by mass to 1.20% by mass, a Cr content of 0.50% by mass to 2.00% by mass, and Mn content. The carbonitriding treatment is performed after processing a material made of steel having a rate of 0.35 mass% or more, an Si content of 0.25 mass% or more, an O content of 12 ppm or less, and the balance being Fe and inevitable impurities into a predetermined shape. Then, the quenching treatment and the tempering treatment are performed in this order, and the surface layer portion forming the raceway surface has an N content of 0.10% by mass or more and 2.00% by mass or less and a residual austenite amount. By setting the volume to 15% by volume or more and 40% by volume or less, the rolling fatigue life of the inner ring and the outer ring itself can be increased, so that the rolling fatigue life of the rolling bearing can be further extended.

  Here, the steel that forms the material of the inner ring and the outer ring differs from the steel that forms the material of the rolling element described above only in the numerical limited ranges of the Mn content and the Si content. In order to effectively obtain the effect of improving the N content of the surface layer part forming the raceway surface during carbonitriding and the effect of improving the hardenability and temper softening resistance of steel, The Mn content is 0.35% by mass or more, and the Si content is 0.25% by mass or more.

Further, in order to increase the rolling fatigue life of the inner ring and the outer ring itself, the N content of the surface layer portion forming the raceway surface is set to 0.10 mass% or more and 2.00 mass% or less.
Furthermore, in order to reduce the stress concentration at the indentation edge formed on the raceway surface and to increase the rolling fatigue life of the inner ring and the outer ring itself, the amount of retained austenite in the surface layer portion forming the raceway surface is 15 volume% or more and 40 volumes. % Or less.
Furthermore, in order to increase the rolling fatigue life of the inner ring and the outer ring itself, it is preferable that the hardness of the surface layer portion forming the raceway surface of the inner ring and the outer ring be Hv 743 or more.

According to the rolling bearing of the present invention, it is possible to suppress the surface damage of the rolling element itself and to make contact with the rolling element only by specifying the N content of the surface layer portion and the amount of retained austenite forming the rolling surface of the rolling element. Ring surface damage can also be suppressed. Therefore, even when used in an environment where surface damage is likely to occur, a rolling bearing having a long rolling fatigue life can be provided at low cost.
Further, according to the rolling bearing of the present invention, it is possible to further increase the rolling fatigue life by specifying the configurations of the inner ring and the outer ring combined with the rolling elements.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First embodiment>
In the present embodiment, a tapered roller bearing (outer diameter: 50.292 mm, inner diameter: 26.988 mm, width: 14.224 mm) having the identification number L44649 / 610 shown in FIG. 1 was produced by the following method. As shown in FIG. 1, the tapered roller bearing includes a plurality of conical rollers 3 that are arranged to roll freely between an inner ring 1, an outer ring 2, and raceway surfaces 1 a and 2 a of the inner ring 1 and the outer ring 2. And the cage 4. Further, the large diameter side end surface 3 b of the roller 3 is held by a flange portion 10 formed at the large diameter side end portion of the inner ring 1.

The roller 3 was produced by the following procedure.
First, after the raw material which consists of steel of each structure shown in Table 1 was processed into the predetermined shape by forging, the heat processing of each method shown in Table 1 was given.
Here, the heat treatment shown in Table 1 as “carbonitriding → quenching → subzero → tempering” was performed under the following conditions. First, carbonitriding was performed by holding at 830 to 860 ° C. for 7 to 10 hours in an atmosphere of Rx gas + propane gas + ammonia gas, and then oil quenching was performed. Next, sub-zero treatment was performed by holding at −100 to −60 ° C. for 40 minutes. Next, tempering was performed by holding at a predetermined temperature in the range of 130 to 180 ° C. for 2 hours.

Further, the heat treatment shown in Table 1 as “carbonitriding → quenching → tempering” was performed under the following conditions. First, carbonitriding was performed by holding at 830 to 860 ° C. for 7 to 10 hours in an atmosphere of Rx gas + propane gas + ammonia gas, and then oil quenching was performed. Next, tempering was performed by holding at a predetermined temperature in the range of 130 to 240 ° C. for 2 hours.
Furthermore, the heat treatment shown in Table 1 as “quenching → tempering” was performed under the following conditions. First, in an Rx gas atmosphere, after holding at 830 to 860 ° C. for 0.5 to 1 hour, oil quenching was performed. Next, tempering was performed by holding at 180 ° C. for 2 hours.

Next, finishing such as grinding was performed, and the surface roughness (Ra) of the rolling surface 3a was adjusted to be 0.06 μm or more and 0.10 μm or less. Further, the polishing allowance on the axial end surface of the roller 3 was set to 150 μm for each of the large-diameter side end surface 3b and the small-diameter side end surface 3c.
And using the sample for a destructive inspection among the obtained rollers 3, N content rate and C content rate (mass ratio) of the surface layer part (part from the surface to the depth of 1 micrometer) which make rolling surface 3a, The amount of retained austenite γ _R (volume ratio) of the surface layer portion and the hardness (Vickers hardness) of the surface layer portion were measured by the methods shown below. These results are also shown in Table 1.
The N content and C content of the surface layer were measured using an electron beam microanalyzer (EPMA). The amount of retained austenite in the surface layer was measured using an X-ray diffractometer. Furthermore, the hardness of the surface layer portion was measured using a Vickers hardness test method defined in JIS Z 2244.

The inner ring 1 and the outer ring 2 were produced by the following procedure.
First, after processing a material composed of two types of high carbon chrome bearing steel (SUJ2) into a predetermined shape, oil quenching for 0.5 to 1 hour at 830 to 860 ° C. followed by quenching and holding at 180 ° C. for 2 hours The surface layer part (part from the surface to a depth of 1 μm) forming the raceway surfaces 1a and 2a was set to Hv680 or more, and the residual austenite amount of the surface layer part was set to 9% by volume.

Next, finish processing such as grinding is performed on these so that the surface roughness (Ra) of each raceway surface 1a, 2a is larger than the surface roughness (Ra) of the rolling surface 3a of the roller 3. The surface roughness (Ra) of the raceway surfaces 1a and 2a was adjusted to a range of 0.10 μm to 0.30 μm.
A tapered roller bearing was assembled using the inner ring 1 and the outer ring 2 and the roller 3 obtained in this manner. A life test of the tapered roller bearing was performed by operating the tapered roller bearing under the following conditions assuming that the tapered roller bearing is used under the contamination with foreign matters that are likely to cause surface damage.

This life test was performed by rotating the inner ring 1 until peeling (flaking) occurred on the rolling surface 3a of the roller 3, and the rotation time from the start of the life test until peeling occurred was defined as the life. In addition, this life test was performed 10 times for each sample. This result is obtained by calculating the L ₁₀ life for each sample based on the Weibull distribution function. 15 of L ₁₀ life as a ratio when a 1, also shown in Table 1.
[Life test conditions]
Load ratio (P / Cr): 0.43
Rotational speed: 4000 min ^-1
Lubricating oil: ♯68 turbine oil foreign matter :( composition) Fe ₃ C
(Hardness) HV870
(Particle size) 74-147 μm
(Mixed amount) Mixed in the lubricating oil to 300ppm

As shown in Table 1, the composition of the present invention (the content of C, Cr, Mn, Si in the steel, the heat treatment method, the N content of the surface layer portion forming the rolling surface 3a, the amount of retained austenite) . In the tapered roller bearing using the rollers 3 of 1 to 11, No. 1 outside the configuration of the present invention. Compared with the case of using 12 to 15 rollers 3, the life was longer.
On the other hand, no. 12, no. In the tapered roller bearing using 15 rollers 3, since the Mn content in the steel constituting the material is small and the N content of the surface layer portion forming the rolling surface 3a could not be within the scope of the present invention, The effect of reducing friction between the inner ring 1 and the outer ring 2 was not sufficiently obtained.
No. In the tapered roller bearing using the No. 13 roller 3, the tempering temperature was too high, so that a sufficient amount of retained austenite in the surface layer portion forming the rolling surface 3 a of the roller 3 could not be obtained and formed on the rolling surface 3 a of the roller 3. The effect of reducing the stress at the indentation edge was not sufficiently obtained.

Furthermore, no. In the tapered roller bearing using the 14 rollers 3, the tempering temperature was too low, so that a large amount of retained austenite is present in the surface layer portion that forms the rolling surface 3 a of the roller 3, and between the rollers 3 and the inner ring 1 and the outer ring 2. In this case, the friction reducing effect was not sufficiently obtained.
From the above results, the steel constituting the roller 3 and the N content and the amount of retained austenite of the surface layer part forming the rolling surface 3a of the roller 3 are configured as the present invention, so that foreign matters are likely to be damaged. It was found that the life of tapered roller bearings can be extended even when used under lubrication.

<Second embodiment>
The inner ring 1 and the outer ring 2 of the tapered roller bearing described above were produced by the following procedure.
First, after processing the material which consists of steel of each structure shown in Table 2 into each shape of the inner ring | wheel 1 and the outer ring | wheel 2, it heat-processed by each method shown in Table 2. FIG.
The heat treatment shown in Table 2 as “carbonitriding → quenching → tempering” was performed under the following conditions. First, carbonitriding was performed by holding at 830 to 860 ° C. for 7 to 10 hours in an atmosphere of Rx gas + propane gas + ammonia gas, and then oil quenching was performed. Next, tempering was performed by holding at 180 ° C. for 2 hours.

Further, the heat treatment shown in Table 2 as “carburization → quenching → tempering” was performed under the following conditions. First, in a Rx gas + propane gas atmosphere, carburization was performed by holding at 830 to 860 ° C. for 7 to 10 hours, and then oil quenching was performed. Next, tempering was performed by holding at 180 ° C. for 2 hours.
Next, these were subjected to finishing such as grinding, and the surface roughness (Ra) of each of the raceway surfaces 1a and 2a was adjusted to a range of 0.10 μm to 0.30 μm.

Then, using the sample for destructive inspection among the obtained inner ring 1 and outer ring 2, the N content of the surface layer part (the part from the surface to a depth of 1 μm) forming the raceway surfaces 1a and 2a by the same method as described above. And C content, retained austenite amount (γ _R ) of the surface layer portion, and hardness of the surface layer portion were measured. The results are also shown in Table 2.
The inner ring 1 and the outer ring 2 thus obtained, and the No. 1 shown in Table 1 above. Roll No. 1 (Mn content in steel constituting material: 1.00% by mass, Mn + Si content in steel: 2.00% by mass, N content in surface layer: 0.79% by mass, A tapered roller bearing was assembled using a residual austenite amount: 9% by volume and a surface roughness (Ra): 0.10 μm.
And the life test of the tapered roller bearing was done by operating this tapered roller bearing on the conditions similar to the above-mentioned. The results are shown in Table 1. 15 of L ₁₀ life as a ratio when a 1, shown in Table 2.

As shown in Table 2, Table 1 is a constitution of the present invention (C, Cr, Mn, Si content in steel, N content of surface layer portion forming rolling surface 3a, amount of retained austenite, surface roughness). No. shown in FIG. No. 1 and No. 3 in accordance with the configuration of the present invention (N content of surface layer portion forming raceway surfaces 1a and 2a, amount of retained austenite). The tapered roller bearings using the inner ring 1 and the outer ring 2 of Nos. 21 to 30 are Nos. Shown in Table 1. 1 and the tapered roller bearing (4.3 times the life of No. 15) using the inner ring 1 and the outer ring 2 outside the configuration of the present invention shown in the first embodiment, both are long. It was a lifetime.
Among these, the N content and the amount of retained austenite of the surface layer portions forming the raceway surfaces 1a and 2a of the inner ring 1 and the outer ring 2 are within the scope of the present invention, and the hardness of the surface layer portion is preferably within a range (Hv 743 or more). No. No. No. 1 subjected to the heat treatment of the present invention. 21-No. 23, no. 25-No. 28 and No. 30 had a longer life.

  From the above results, in addition to the steel constituting the roller 3, the N content of the surface layer portion forming the rolling surface 3a of the roller 2 and the amount of retained austenite, the steel constituting the inner ring 1 and the outer ring 2, the inner ring 1 and By making the N content and the amount of retained austenite of the surface layer portion forming the raceway surfaces 1a and 2a of the outer ring 2 into the configuration of the present invention, and further setting the hardness of the surface layer portion forming the track surfaces 1a and 2a within the preferred range of the present invention. It has been found that the life of the tapered roller bearing can be further extended even if it is used under the contamination with foreign matters that are liable to cause surface damage.

<Third embodiment>
No. shown in Table 1 above. 1 was prepared, and rollers 3 were prepared in which the surface roughness (Ra) of the rolling surface 3a was adjusted between 0.03 and 0.10 μm.
And around this time 3 and No. shown in Table 2 mentioned above. A tapered roller bearing was assembled using 25 inner rings 1 and outer rings 2 (the surface roughness of the raceway surfaces 1a and 2a was 0.20 μm). The tapered roller bearing was operated under the same conditions as described above, and a life test of the tapered roller bearing was performed. Using this result, the graph of FIG. 2 showing the relationship between the surface roughness (Ra) of the rolling surface 3a of the roller 3 and the life was created.

As shown in FIG. 2, the smaller the surface roughness (Ra) of the roller 3, the longer the life of the tapered roller bearing. When the surface roughness (Ra) of the roller 3 is 0.03 μm, No. 1 shown in Table 1. A life of 7 times longer than 15 was obtained.
From the above results, it was found that the life of the tapered roller bearing can be further increased by reducing the surface roughness (Ra) of the rolling surface 3a of the roller 3 as much as possible.

It is sectional drawing which shows a tapered roller bearing as an example of the rolling bearing of this invention. It is a graph which shows the relationship between the surface roughness of the rolling surface of a roller, and a lifetime.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring 1a Inner ring raceway surface 2 Outer ring 2a Outer ring raceway surface 3 Roller (rolling element)
3a Rolling surface
3b Large-diameter side end face 3c Small-diameter side end face 10 collar

Claims (2)

In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to roll between the inner ring and the outer ring,
The rolling element has a C content of 0.30% by mass or more and 1.20% by mass or less, a Cr content of 0.50% by mass or more and 2.00% by mass or less, a Mn content of 0.50% by mass or more, After processing a material made of steel with a total content of Mn and Si of 0.85 mass% or more, an O content of 12 ppm or less, and the balance being Fe and inevitable impurities, carbonitriding and quenching, Sub-zero treatment and tempering treatment are performed in this order,
The surface layer portion forming the rolling surface has an N content of 0.20% by mass or more and 2.00% by mass or less and a residual austenite amount of 5% by volume or more and 24% by volume or less,
A rolling bearing characterized in that the surface roughness of the rolling surface is smaller than the surface roughness of the raceway surfaces of the inner ring and the outer ring. The inner ring and the outer ring have a C content of 0.30% by mass to 1.20% by mass, a Cr content of 0.50% by mass to 2.00% by mass, and a Mn content of 0.35% by mass. As mentioned above, after processing the raw material which consists of steel which Si content rate is 0.25 mass% or more, O content rate is 12 ppm or less, and the remainder is Fe and an inevitable impurity, carbonitriding, quenching, and tempering Processing is performed in this order,
The surface layer portion forming the raceway surface has an N content of 0.10% by mass to 2.00% by mass and a residual austenite amount of 15% by volume to 40% by volume. The rolling bearing according to 1.

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