JP2005337361A - Roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roller bearing having a long life even in use under the lubrication where foreign matter gets mixed at a low cost. <P>SOLUTION: A cylindrical roller 3 of this roller bearing is manufactured by machining raw material made of steel to a predetermined form, and performing carbonitriding, quenching and tempering at a temperature from 200°C to 300°C in this order for the formed material. The steel is composed of C having a percentage content of 0.30 mass% to 1.20 mass% both inclusive, Si having a percentage content of 0.50 mass % to 2.00 mass% both inclusive, Mn having a percentage content of 0.20 mass% to 2.00 mass% both inclusive, Cr having a percentage content of 0.50 mass% to 2.00 mass% both inclusive, O having a percentage content of 12ppm or less, and the rest, which is Fe and obligatory impurity. The N percentage content of a surface layer part forming a rolling surface is set to 0.2 mass% to 2.0 mass% both inclusive, the C percentage content of the surface layer part is set to 0.6 mass% to 2.5 mass% both inclusive, the hardness of the surface layer part is set to Hv650 or higher, and the residual austenite quantity of the surface layer part ranges above 0 volume% under 20 volume%. The surface roughness of the rolling surface is set smaller than the surface roughness of the raceway surfaces 1A, 2A of an inner ring 1 and an outer ring 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a roller bearing.

  Rolling bearings such as roller bearings are used under repeated shear stress under high surface pressure, and therefore it is necessary to withstand this shear stress and ensure a rolling fatigue life. For this reason, as the bearing rings (inner ring, outer ring) and rolling elements of the rolling bearing, the high carbon chromium bearing steel type 2 (SUJ2) is subjected to quenching and tempering treatment, or the case hardening 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, roller bearings are often used under high load conditions compared to ball bearings, so that an oil film is not easily formed on the raceway surface, and a metal is formed between the roller rolling surface and the raceway raceway surface. Surface damage due to contact is likely to occur. In addition, the roller bearing is liable to slip due to a skew between the races, repeatedly applies shear stress to the races and generates a tangential force on the raceway surface, and thus easily causes surface damage. For this reason, a roller bearing cannot be used suitably under the foreign material mixing lubrication which is easy to produce surface damage especially.

The life reduction due to surface damage occurs when an indentation is generated on the raceway surface due to the biting of foreign matter and stress concentration occurs on the edge of the indentation, or when a large tangential force is generated on the raceway surface due to insufficient lubrication or slippage.
In order to prevent such a decrease in life due to surface damage, in Patent Document 1, at least the rollers have a mass ratio of C content of 0.8% to 1.5% and Si content of 0.4%. More than 1.2%, Mn content of 0.8% to 1.5%, Cr content of 0.8% to 1.8% steel material is processed into a predetermined shape, then carburized 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 by performing nitriding treatment, quenching treatment and tempering treatment. In this patent document 1, at least in the surface layer portion of the roller, the amount of retained austenite and the hardness which are highly effective in reducing stress concentration are increased, thereby suppressing surface damage under foreign matter lubrication and improving the rolling fatigue life. I am trying.
JP 2000-234147 A

However, in the roller bearing described in Patent Document 1 described above, since the amount of retained austenite and the hardness of the surface layer portion are increased to improve the rolling fatigue life, there is room for further improvement in terms of manufacturing cost. .
Further, in the roller bearing described in Patent Document 1, the life of the roller, in which a decrease in the life due to surface damage is a problem, is considered, but the life of the race that contacts the roller is not considered. For this reason, for example, even if only the life of the roller is increased, the life of the bearing ring may be insufficient and the life of the entire roller bearing may not be extended.
Therefore, the present invention has been made to solve these problems, and it is an object of the present invention to provide a roller bearing having a long service life even at a low cost even when used under a foreign matter mixed lubrication.

In order to solve such a problem, the present invention provides a roller bearing including an inner ring, an outer ring, and a plurality of rollers that are rotatably disposed between the inner ring and the outer ring. The C content is 0.30% by mass to 1.20% by mass, the Si content is 0.50% by mass to 2.00% by mass, and the Mn content is 0.20% by mass to 2.00% by mass. Hereinafter, after processing a material made of steel having a Cr content of 0.50% by mass or more and 2.00% by mass or less, an O content of 12ppm or less, and the balance being Fe and inevitable impurities, carbonitriding The quenching treatment and the tempering treatment at 200 ° C. or more and 300 ° C. or less are performed in this order, and the N content of the surface layer portion forming the rolling surface is 0.2 mass% or more and 2.0 mass% or less. The C content of the surface layer is 0.6% by mass or more and 2.5% by mass. In the following, the hardness of the surface layer portion is Hv650 or more, the amount of retained austenite of the surface layer portion is more than 0% by volume and less than 20% by volume, and the surface roughness of the rolling surface of the roller is the inner ring and the outer ring There is provided a roller bearing characterized by being smaller than the surface roughness of the raceway surface.
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) is an element necessary for increasing the strength by converting the base into martensite. In the present invention, carbonitriding is performed after processing a steel material into a predetermined shape, and C and N (nitrogen) are added to the surface layer of the roller. Therefore, the C content of the material is set to 0.30% or more in order to secure the necessary strength for the roller core. In addition, it is preferable that the core part hardness of a roller is Hv650 or more, and it is preferable to make C content rate into 0.80% or more for that purpose.
On the other hand, if the C content is too high, coarse carbides may be generated during steel making, which may reduce the rolling fatigue life. For this reason, C content rate shall be 1.20% or less.

[Si content (mass ratio): 0.50 to 2.00%]
Si (silicon) is an element necessary for improving the resistance to temper softening while acting as a deoxidizer during steelmaking. In addition, when carbonitriding is performed, there is also an effect of increasing the N content of the surface layer portion of the roller.
As a result of experiments conducted by the present inventors, using a steel having a Si content of 0.50% or more as a material constituting the rollers, carbonitriding, quenching, and at a high temperature of 200 ° C. to 300 ° C. It has been found that the effect of suppressing the surface damage of the bearing ring can be obtained by performing the tempering treatment. Thereby, the Si content is set to 0.50% or more, preferably 0.80% or more.
On the other hand, if the Si content is too high, the machinability of the material may be reduced, leading to an increase in cost. Therefore, the Si content is set to 2.00% or less, preferably 1.50% or less.

[Mn content (mass ratio): 0.20 to 2.00%]
Mn (manganese) is an element necessary for improving hardenability while acting as a deoxidizer and desulfurizer during steelmaking. In order to obtain this effect, the Mn content is 0.20% or more, preferably 0.25% or more. On the other hand, if the Mn content is too high, the amount of non-metallic inclusions increases and the rolling fatigue life decreases, and the machinability such as the forgeability and machinability of the material decreases. 2.00% or less.

[Cr content (mass ratio): 0.50 to 2.00%]
Cr (chromium) is an element necessary for improving hardenability and temper softening resistance and strengthening the base to improve rolling fatigue life. It also has the effect of improving wear resistance by forming fine and hard carbides and carbonitrides. Furthermore, it has the effect | action which raises C content rate of a carbonitriding layer, and is effective also in the improvement of a carbonitriding characteristic. In order to obtain these effects, the Cr content is set to 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 the carbonitriding characteristics, so the Cr content is 2.00% or less. To do.

[O content (mass ratio): 12 ppm or less]
O (oxygen) forms oxide-based non-metallic inclusions that adversely affect the rolling fatigue life, so its content must be reduced as much as possible, but the O content is 12 ppm or less, preferably 9 ppm or less. Acceptable if any.
[About inevitable impurities]
In addition to the above elements, inevitable impurities (for example, P, S, Ni, Cu, Mo, V, Al, Ti, Nb, etc.) may be included.
Of these, carbide-forming elements such as Mo and V are effective in improving wear resistance because they form fine and high-hardness carbonitrides by carbonitriding. Therefore, these elements may be added as long as the cost permits, but the total amount added is preferably 2.00% by mass or less.

[About heat treatment]
First, the above-described steel material is processed into a roller shape by forging or cutting, and then heated and held for several hours in a furnace in which RX gas + enrich gas + ammonia gas is introduced at an ambient temperature of 800 to 860 ° C. Then, carbonitriding is performed.
This carbonitriding process is performed under conditions such that the N content of the surface layer of the roller is 0.2% by mass or more and 2.0% by mass or less.
At this time, if the N content of the surface layer portion of the roller is less than 0.2% by mass, the effect of suppressing the surface damage of the bearing ring in contact with the roller 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 2.0 mass%, the carbonitrided layer becomes brittle, A rolling fatigue life sufficient as a roller bearing cannot be obtained. From the viewpoint described above, a preferable range of the N content in the surface layer portion of the roller is 0.5% by mass or more and 2.0% by mass or less.

  Further, the carbon content added in the same manner as N by carbonitriding is the sum of the N content and the C content so that the surface hardness Hv650 required as a bearing member can be obtained in the surface layer portion of the roller. It is preferable to adjust the C content so that is 0.8 mass% or more, and the C content is 0.6 mass% or more. On the other hand, if the C content of the surface layer portion of the roller is too large, coarse carbides precipitate and the rolling fatigue life of the roller itself cannot be sufficiently obtained, so the C content is 2.5% by mass or less, preferably 2.0 mass% or less.

  Next, after performing a quenching process at 800-860 degreeC, a tempering process is performed at 200 degreeC or more and 300 degrees C or less. At this time, if the tempering temperature is less than 200 ° C., the amount of retained austenite in the surface layer portion of the roller exceeds 20% by volume, so that the effect of suppressing the surface damage of the bearing ring in contact with the roller cannot be sufficiently obtained. . On the other hand, when the tempering temperature exceeds 300 ° C., the amount of retained austenite in the surface layer portion of the roller becomes 0% by volume, so that the rolling fatigue life of the roller itself cannot be sufficiently obtained.

Here, the amount of retained austenite in the surface layer portion forming the rolling surface of the roller exceeds 0% by volume in order to improve the rolling fatigue life of the roller itself and to suppress the surface damage of the bearing ring in contact with the roller. To do. On the other hand, if the amount of retained austenite in the surface layer portion that forms the rolling surface of the roller is too large, the effect of extending the life of the roller and the bearing ring is saturated and the manufacturing cost is increased. A preferred range for the amount of retained austenite in the surface layer portion forming the rolling surface of the roller is 7% by volume or more and 17% by volume or less.
In the roller bearing of the present invention, the surface roughness of the rolling surface of the roller is preferably 0.08 μm or less in terms of arithmetic average roughness (Ra).

According to the roller bearing of the present invention, the N content, C content, hardness, and retained austenite amount of the surface layer portion that forms the rolling surface of the roller are specified, and the surface roughness of the rolling surface of the roller is determined between the inner ring and the outer ring. By making it smaller than the surface roughness of the raceway surface, the surface damage of the roller itself can be suppressed, and the surface damage of the raceway ring in contact with the roller can also be suppressed. Therefore, since the rolling fatigue life of the roller bearing can be extended, the roller bearing can be suitably used even under foreign matter mixed lubrication.
Further, according to the roller bearing of the present invention, the amount of retained austenite and the hardness of the surface layer portion forming the rolling surface of the roller are minimized, so that a roller bearing having a long rolling fatigue life can be provided at a low cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In this embodiment, a roller bearing (with an inner diameter of 55 mm, an outer diameter of 100 mm, and a width of 25 mm) having the configuration shown in FIG. 1 was produced by the following method. As shown in FIG. 1, the roller bearing includes an inner ring 1, an outer ring 2, a plurality of cylindrical rollers 3, and a cage 4.
The cylindrical roller 3 was produced by the following procedure. First, after forging the raw material which consists of steel of each composition shown in Table 1 and processing it into the predetermined shape, the heat processing of each method shown in Table 1 was given. Next, finishing processing such as grinding was performed to adjust the surface roughness (Ra) of the rolling surface (circumferential surface) to 0.04 to 0.06 μm.

Here, the heat treatment shown in Table 1 as “carbonitriding → quenching → tempering” was performed under the following conditions. First, carbonitriding was performed by holding at 800 to 860 ° C. for 2 to 6 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 180 to 350 ° C. for 2 hours.
Further, 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 800 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.

In the cylindrical roller 3 obtained in this way, the N content and C content (mass ratio) of the surface layer portion (the portion from the surface to a depth of 1 μm) forming the rolling surface were measured by an electron beam microanalyzer (EPMA). It was measured. The results are also shown in Table 1.
Further, the amount of retained austenite γ _R (volume ratio) of the surface layer portion was measured with an X-ray diffractometer. The results are also shown in Table 1.
Furthermore, the hardness (Vickers hardness) of the surface layer portion was measured by the Vickers hardness test method defined in JIS Z 2244. The results are also shown in Table 1.

  Moreover, the inner ring | wheel 1 and the outer ring | wheel 2 were produced in the procedure shown below. First, a material composed of two types of high-carbon chromium bearing steel (SUJ2) is processed into a predetermined shape, and then subjected to quenching and tempering treatment, so that the surface layer portion (the depth of 1 μm from the surface) forms the raceway surface of the inner ring 1 and the outer ring 2. The hardness of the above portion) was set to Hv680 or more, and the amount of retained austenite in the surface layer portion was set to 7% by volume or less. Next, a finishing process such as grinding is applied to these so that the surface roughness (Ra) of the inner ring raceway surface 1A and the outer ring raceway surface 2A is greater than the surface roughness (Ra) of the rolling surface of the cylindrical roller 3 by 0. It adjusted so that it might become 1-0.3 micrometer.

A roller bearing was assembled using the inner ring 1, the outer ring 2, the plurality of cylindrical rollers 3, and the nylon cage 4 thus obtained. A life test was performed under the following conditions assuming that the roller bearing is used under the contamination with foreign matter. This life test was performed by rotating the inner ring 1 until peeling occurred on the rolling surface of the cylindrical roller 3, and the rotation time from the start of the life test until peeling occurred was defined as the life. This result is shown in No. 16 of L ₁₀ life as a ratio when a 1, shown in Table 1.
[Life test conditions]
Load ratio (P / Cr): 0.45 (Fr: Fa = 4: 1)
Rotational speed: 2500min ^-1
Lubricating oil: # 68 Turbine oil Foreign matter: (Composition) Fe ₃ C
(Hardness) HRC52
(Particle size) 74-147 μm
(Mixed amount) Mixed in the lubricating oil to 300ppm

Next, a friction coefficient measurement test was performed as follows.
First, a cylindrical test body (inner diameter 30 mm, outer diameter 45 mm, axial length 6 mm) S is prepared so as to have the same configuration (material, heat treatment method, surface layer portion) as the inner ring 1 and outer ring 2 described above. did.
Specifically, first, a material made of SUJ2 is processed into a cylindrical shape, and then subjected to quenching and tempering, thereby forming a surface layer portion (a portion from the surface to a depth of 1 μm) that forms the outer peripheral surface of the cylindrical test body S. ) Was set to Hv 680 or more, and the amount of retained austenite in the surface layer portion was set to 7% by volume or less. Next, these were subjected to finishing such as grinding, and the surface roughness (Ra) of the outer peripheral surface was adjusted to be 0.1 to 0.3 μm.

And as shown in FIG. The cylindrical roller 3 having each configuration of 1 to 17 was fixed by aligning both axes, and the specimen S was rotated under the following conditions in a state where a radial load (Fr) was applied from above the cylindrical roller 3. And the torque of the test body S at this time was measured, and the friction coefficient was computed from the measured torque. This result is shown in No. Table 1 also shows the ratio when the friction coefficient of 16 is 1.
[Friction coefficient measurement test conditions]
Rotation speed of test specimen: 200 min ^-1
Surface pressure: 1764 N / mm ²
Lubricating oil: # 68 turbine oil

  As shown in Table 1, the configuration of the cylindrical roller 3 was set to No. 1 according to the configuration of the present invention (steel composition, heat treatment method, tempering temperature, surface layer portion forming a rolling surface). Nos. 1 to 13 are Nos. Compared with Nos. 14 and 15, the service life is longer. A life of 2.0 to 3.6 times that of 16 was obtained. Among these, "Si content constituting steel: 0.95 mass% or more and 2.00 mass% or less" and "N content of surface layer portion: 0.6 mass% or more and 0.8 mass% or less" are satisfied. No. Nos. 1, 5, 6, 8, 9, 11, and 13 have a particularly long life. A life of 3.1 times longer than 16 was obtained. Moreover, when the total amount of Si content rate which comprises steel, and N content rate of a surface layer part increased, the tendency for the friction coefficient ratio between the cylindrical roller 3, the inner ring | wheel 1, and the outer ring | wheel 2 to reduce was seen. From these results, it can be seen that the total amount of the Si content constituting the steel and the N content of the surface layer part affects the rolling fatigue life.

On the other hand, no. In No. 14, since the tempering temperature was too high, the amount of retained austenite in the surface layer portion forming the rolling surface of the cylindrical roller 3 was 0% by volume. Therefore, the effect of reducing stress concentration at the indentation edge formed on the cylindrical roller 3 was not sufficiently obtained, and flaking occurred frequently on the cylindrical roller 3, resulting in a short life.
No. In No. 15, since the tempering temperature was too low, the amount of retained austenite in the surface layer portion forming the rolling surface of the cylindrical roller 3 could not be within the range of the present invention (over 0 vol% and less than 20 vol%). Therefore, the life extension effect due to the reduction of the friction coefficient between the cylindrical roller 3 and the inner ring 1 and the outer ring 2 was not sufficiently obtained, and thus the life was short.
From the above results, the composition of the steel constituting the cylindrical roller 3, the N content, the C content, the residual austenite amount, the hardness, and the surface roughness of the rolling surface of the surface layer portion forming the rolling surface of the cylindrical roller 3 are described. It has been found that the lifetime of the roller bearing can be extended by using the configuration of the invention even when used under the contamination with foreign matter.

Subsequently, the relationship between the surface roughness of the rolling surface of the cylindrical roller 3 and the rolling fatigue life was verified.
First, No. 1 shown in Table 1 above. The cylindrical roller 3 having a configuration of 1 (steel composition, heat treatment method, tempering temperature, surface layer portion forming a rolling surface) and having a surface roughness (Ra) of the rolling surface within a range of 0.03 to 0.20 μm. Several were prepared.

Next, a roller bearing is assembled using a plurality of cylindrical rollers 3 having the same surface roughness (Ra) and the above-described inner ring 1, outer ring 2, and cage 4, and a life test is performed under the same conditions as described above. went.
And the graph of FIG. 3 which shows the relationship between the surface roughness (Ra) of the rolling surface of the cylindrical roller 3 and the rolling fatigue life of a roller bearing was created using the result of this life test. In FIG. 3, the rolling fatigue life of the roller bearing is shown in No. 1 shown in Table 1 above. 16 of L ₁₀ life was indicated by the ratio of when the 1.
As shown in FIG. 3, a roller bearing having a rolling roller surface roughness (Ra) of 0.08 μm or less is longer in life than a roller bearing having a surface roughness (Ra) exceeding 0.08 μm. Thus, a life of about 1.7 times or more that of a roller bearing having a surface roughness (Ra) of 0.20 μm was obtained.

It is sectional drawing which shows an example of the roller bearing of this invention. It is a schematic diagram which shows a friction coefficient measurement test method. It is a graph which shows the relationship between the surface roughness of a cylindrical roller, and the rolling fatigue life of a roller bearing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring 1A Inner ring raceway surface 2 Outer ring 2A Outer ring raceway surface 3 Cylindrical roller (roller)
4 Cage

Claims (1)

In a roller bearing comprising an inner ring, an outer ring, and a plurality of rollers arranged to roll between the inner ring and the outer ring,
The roller has a C content of 0.30% by mass or more and 1.20% by mass or less, an Si content of 0.50% by mass or more and 2.00% by mass or less, and a Mn content of 0.20% by mass or more. 00% by mass or less, Cr content of 0.50% by mass or more and 2.00% by mass or less, O content of 12ppm or less, and a material made of steel with the balance being Fe and inevitable impurities, and then carburizing A nitriding treatment, a quenching treatment, and a tempering treatment at 200 ° C. or more and 300 ° C. or less are performed in this order.
The N content of the surface layer part forming the rolling surface is 0.2% by mass or more and 2.0% by mass or less, and the C content of the surface layer part is 0.6% by mass or more and 2.5% by mass or less. The hardness of the part is Hv 650 or more, the amount of retained austenite of the surface layer part is more than 0% by volume and less than 20% by volume, and the surface roughness of the rolling surface of the roller is the surface of the raceway surface of the inner ring and the outer ring A roller bearing characterized by being smaller than roughness.

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