JP3013452B2 - Rolling bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing, and more particularly to an improvement in the life of a rolling bearing used for transmissions, engines, etc. of automobiles, agricultural machines, construction machines and steel machines.

[0002]

2. Description of the Related Art Conventionally, rolling bearings are subjected to severe shearing under repeated high stresses under a high surface pressure. In order to withstand the shearing stress and secure a rolling fatigue life, a high carbon chromium steel bearing is used. This was subjected to quenching and tempering to make the Rockwell hardness HRC 58 to 64.

[0003] However, at the present time when it is desired to further extend the life of the bearing, one of the other factors which causes a reduction in the life of the rolling bearing is foreign matter in the bearing lubricating oil. Generally, metal chips, shavings,
In the use environment of a rolling bearing in which burrs and abrasion powder are mixed and the foreign matter is mixed, the foreign matter damages the bearing ring and / or the rolling element of the rolling bearing and shortens the life of the rolling bearing. I was letting it.

[0004] Therefore, as disclosed in JP-B-62-24499 and JP-A-2-34766, spheroidized carbide is precipitated on the surface of low-medium-carbon low-alloy steel by heat treatment such as carburization, so that the surface of the steel is reduced. There is a conventional example that improves the hardness and improves the pitting resistance.
From the viewpoint of occurrence of flaking and the like, there is a limit in improving the life of the rolling bearing.

Therefore, as disclosed in JP-A-64-55423, even when a rolling bearing is used under lubrication in which foreign matter is mixed, the content of C (carbon) in the rolling surface layer of the bearing is reduced. The conventional example of reducing the concentration of stress at the edge of the indentation caused by foreign matter by suppressing the amount of retained austenite and the content of carbonitride to appropriate values, suppressing the occurrence of cracks, and improving the life of rolling bearings Exists.

[0006]

However, in the conventional example disclosed in Japanese Patent Application Laid-Open No. Sho 64-55423,
Although an appropriate amount of retained austenite can improve the life under lubrication with contaminants, on the other hand, there is a problem that the retained austenite lowers surface hardness and lowers fatigue resistance. That is, there is still room for improvement in the appropriate relationship between the amount of retained austenite and the surface hardness.

Another problem is that, in the conventional bearing material, there is no consideration as to what particle size of the carbide and carbonitride should be used to improve the bearing life. That is, when a large carbide is repeatedly subjected to stress, the large carbide tends to be a starting point of fatigue and cracks and flaking tend to occur. Therefore, as a result of diligent studies based on these problems, an optimum relationship between the amount of retained austenite in the rolling surface layer and the surface hardness was found. Further, an optimum value was found for the average particle size of carbides and carbonitrides present in the rolling surface layer. As a result,
Although it has been possible to improve the fatigue resistance of rolling bearings and prevent the occurrence of flaking, it has become possible to improve the life under lubrication with foreign matter, but peeling under severe lubrication such as boundary lubrication. There was still room for improvement to withstand damage and wear.

An object of the present invention is to solve such a problem. The present invention focuses on fine carbides in the surface layer of a bearing. An object of the present invention is to provide a long-life rolling bearing that can withstand peeling damage and abrasion.

[0009]

Means for Solving the Problems In order to achieve this object, the invention according to claim 1 includes a race and a rolling wheel, and at least one of the race and the rolling element has a C: 0.1 to
0.7% by weight, Cr: 1.5 to 15% by weight, O: 9pp
m or less of alloy steel with a small number of said races and rolling elements.
Table layer portion one subjected to carburizing or carbonitriding treatment even without the
And the amount of retained austenite in the surface layer portion is 15 to
In a rolling bearing having a volume hardness of 35 vol% and a surface hardness of HRC 63 to 69, the average particle size of the fine carbide in at least one surface layer of the race and the rolling element is 3
μm or more and less than 12 μm, and the abundance thereof is 10% or more and 50% or less in area ratio and 5000 pieces / mm ²
It is intended to provide a rolling bearing characterized in that the number is 27000 pieces / mm ² or less . Further, according to claim 2
In the first aspect, the surface portion is formed by an oxidation treatment.
Carburizing or carbonitriding after forming the oxide layer
I am trying to

[0010]

According to the first aspect of the present invention, when foreign matter is mixed
Also, the presence of fine carbides creates irregularities on the transfer surface,
Cracks due to stress concentration
To prevent wear and improve wear and peeling wear characteristics
Can be Also, the surface hardness should be as described above.
And to improve the rolling wear resistance and extend the service life
Can be. According to the invention of claim 2, carburizing or carburizing is performed.
The processing time for forming the carbonitrided layer is reduced.

Next, the action of the fine carbide according to the present invention and the critical significance of the characteristic value will be described in detail. [Average particle size of fine carbide in surface layer: 3 μm or more and 1
In 2μm below the present invention, at least one surface layer of the bearing ring and rolling elements, micro fine carbides Ri by the carburization or carbonitriding processing occurs. This fine carbide is hard and excellent in wear resistance, and its size is fine, so that the life of the bearing is improved without causing stress concentration due to the applied load. And
Due to the presence of the fine carbides, irregularities are generated on the rolling surface, and oil (lubricating oil or the like) accumulates in the concave portions (oil pools).
Even under severe lubrication such as boundary lubrication, sufficient oil lubrication can be provided by this oil sump effect, so that the raceway and rolling elements move smoothly, improving the rolling fatigue life and reducing wear. ， Prevents peeling wear and damage and prolongs bearing life.

[0012] The average particle size of the fine carbides sufficiently exhibiting these characteristics is 3 µm or more and less than 12 µm. If the average particle size of the fine carbide is less than 3 μm, the concave portion of the bearing rolling surface exhibiting an oil pool effect becomes small, and it becomes impossible to provide a sufficient oil lubrication state (oil film formation). As a result, the rolling fatigue life is shortened , wear, peeling wear and damage occur.

On the other hand, when the average particle diameter of the fine carbide exceeds 12 μm, the fine carbide becomes a stress concentration source and the rolling life of the bearing is reduced. In addition, the oil pooling effect of the bearing rolling surface for preventing the boundary lubrication state can be obtained even if the average particle diameter of the fine carbide is set to 12 μm or more and the concave portion of the bearing rolling surface is enlarged. The prevention effect is already saturated.

Further, the finer the carbide, the larger the bearing rolling.
Greater degree convex at run surface, tend to be buried smaller ones in a matrix (base). As a result, the average particle size of the fine carbide was set to 3 μm or more and less than 12 μm. [Abundance of fine carbides in surface layer: 10% in area ratio]
50% or less ] As a condition of the fine carbides for improving the life of the bearing, the amount of the fine carbides may also be mentioned.

If the content of the fine carbides is less than 10% in terms of area ratio, the number of recesses on the bearing rolling surface exhibiting an oil reservoir effect is reduced, and a sufficient oil lubrication state (oil film formation) cannot be provided. In addition, it becomes difficult to obtain the surface hardness (HRC 63 to 69) obtained due to the presence of the fine carbides, and a decrease in surface hardness is guaranteed against an increase in the amount of retained austenite accompanying an increase in the amount of carbon dissolved in the matrix. You will not be able to do it. For this reason, the mechanical strength and rolling fatigue life of the bearing are reduced, and wear, peeling wear, and damage occur.

On the other hand, if the amount of fine carbides is 50
%, The fine carbides bond with each other and become coarse, and the large carbides thus formed become a source of stress concentration, and cracks and the like are generated therefrom. The life is shortened. In addition, the amount of carbon dissolved in the matrix decreases, and it becomes difficult to secure a necessary amount of retained austenite. Therefore, the effect of reducing stress concentration and the effect of reducing rolling load cannot be sufficiently exhibited. As a result, the effect of extending the life especially when foreign matter is mixed is reduced.

[0017] The result was a 10% to 50% in abundance the area ratio of fine carbide. [Abundance of fine carbides in the surface layer: 50 in number present]
00 pieces / mm ² or more and 27000 pieces / mm ² or less ] As one of the conditions of the fine carbides for improving the life of the bearing, there is an abundance (pieces / mm ² ).

The amount of fine carbides is 5000
If it is less than pcs / mm ^{2, the} number of recesses on the bearing rolling surface that exhibits an oil pool effect is reduced, and it becomes impossible to provide a sufficient oil lubrication state (oil film formation). As a result, the rolling fatigue life is shortened,
Specific wear, peeling wear and damage will occur. In addition, the amount of carbon dissolved in the matrix increases, and the amount of retained austenite increases more than necessary.As a result, the required surface hardness cannot be secured, and the mechanical strength and rolling fatigue life of the bearing are reduced, and the bearing is not practical. Disappears.

On the other hand, the amount of fine carbides is 2
If it exceeds 7000 particles / mm ² , the fine carbides are bonded to each other and become coarse, and the large-sized carbide thus formed becomes a source of stress concentration, and the amount of carbon dissolved in the matrix decreases. Therefore, it becomes difficult to secure a necessary amount of retained austenite. For this reason, the effect of extending the life especially when foreign matters are mixed is reduced.

As a result, the abundance of the fine carbides was determined to be 5,000 / mm ² or more and 27000 / mm ² or less . In the present invention, the “surface portion” refers to a range from the surface to a certain desired depth, for example, to a depth corresponding to 2% of the rolling element average particle size at which the shear stress is maximized.

In the present invention, the term "carbide" means, for example,
If Cr₇C_Three, Cr_ThreeC₆, Mo _TwoC, VC, V_FourC
_ThreeAnd Fe_ThreeC or a double carbide thereof. So
Then, as carbide forming elements, Cr, Mo, V, W
Although there are various known elements such as Cr, Cr is particularly desirable.
Contains desired one or more of these carbide forming elements
By doing so, various carbides are generated.

The alloy steel specified in at least one of the race and the rolling element includes C: 0.1 to 0.7% by weight, Cr: 1.5 to 15% by weight, and O: 9 ppm or less. Carburizing or carbo-nitriding the alloy steel, the amount of retained austenite in the surface layer is 15-35 vol%, and the surface hardness is HRC 63-69, thereby improving fatigue resistance and generating flaking. Can be prevented, and the life of the bearing can be improved under foreign matter contamination.

That is, C is an element necessary for improving the hardness after quenching and tempering. By specifying C as 0.1 to 0.7% by weight, C is specified for carburizing and carbonitriding. It is possible to prevent the time from becoming long (less than 0.1% by weight), improve the heat treatment productivity, and reduce the toughness and the fracture strength at the core of the bearing material (exceeding 0.7% by weight). Case) can be prevented.

Cr is a necessary element as a carbide forming element, and Cr combines with C to form fine carbides. Cr: 1.5 to 15% by weight,
The amount of fine carbide for obtaining the surface hardness required for the bearing can be secured (Cr: 1.5% by weight or more), and the generation of giant carbide serving as a stress concentration source can be prevented. Also, O
It is an element that generates oxide-based nonmetallic inclusions, and its content must be reduced as much as possible to reduce the rolling life. Therefore, the upper limit was set to 9 ppm.

In addition, fine carbides are generated by carburizing or carbonitriding alloy steel. The retained austenite is usually soft and sticky. By setting the amount of retained austenite in the surface layer portion to 15 to 35 vol%, it is possible to prevent the adhesion of indentations due to foreign substances and the like, to reduce rolling fatigue, to prevent the occurrence of cracks, etc., and to improve the mechanical strength and bearing strength of the bearing material. The rolling fatigue life can be improved.

Further, the surface hardness is HRC 63-69.
By doing so, it is possible to secure hardness enough to withstand rolling fatigue even if a large surface pressure is repeatedly applied locally to the rolling surface. And while using steel of these conditions,
Presence of fine carbides formed on the surface layer (average particle size,
By specifying the existence area ratio and the number of existing parts as described above, the lubrication between the bearing ring and the rolling elements can be improved not only in improving the service life of the bearing under the contamination of foreign matters but also under severe lubrication such as a boundary lubrication state. However, it is possible to prevent the rolling fatigue life from being shortened, the amount of specific wear, the occurrence of peeling wear and damage, and to improve the life of the bearing.

[0027]

Next, an embodiment according to the present invention will be described in detail. For the test pieces 1 to 15 made of alloy steel having the composition shown in Table 1 by casting, the following heat treatments were performed under the conditions shown in Table 2, and thereafter, the test pieces 1 to 1 were made.
5, the average particle size (μm), the area ratio (%), the number present (pieces / mm ² ), the surface hardness, the residual austenite amount (μm) of the fine carbide in the surface layer portion (depth from the surface: 0.1 mm) v
ol%) was measured. Table 3 shows the results. The average particle size and area ratio of the fine carbide were measured by a microscope, and the amount of retained austenite was measured by an X-ray analysis.

[0028]

[Table 1]

[0029]

[Table 2] (Heat treatment) (1) Oxidation treatment After subjecting each of the test pieces 1 to 15 to oxidation treatment at the temperature and time shown in Table 2, oil cooling or air cooling is performed. By performing this oxidation treatment, an oxide layer (porous) with Cr is formed on the surface of the alloy steel, so that the time for carburizing or carbonitriding can be shortened. That is, when the alloy steel containing a large amount of Cr is subjected to carburizing or carbonitriding, a compound (a dense film) with C to be carburized or carbonitrided is formed on the surface of the alloy steel, and C becomes a matrix. There is a problem that the carbonization is difficult and the carburizing or carbonitriding time is prolonged. However, this problem can be prevented by forming an oxide layer with Cr on the surface of the alloy steel by the oxidation treatment. (2) Carburizing treatment After completion of the oxidation treatment, the temperature and time shown in Table 2 and the _Rx gas +
After carburizing each of the test pieces 1 to 15 in an enriched gas atmosphere, the test pieces are oil-cooled or air-cooled. Table 2 shows the surface carbon concentration of each test piece during carburization. (3) Annealing After the carburizing treatment, each test piece 1 to 15 was annealed under the annealing conditions shown in Table 2 (see FIG. 3), and then air-cooled. The size of the carbide becomes finer as the annealing is performed for a longer time, and the size of the carbide becomes finer as the cooling rate near the A ₁ transformation point (723 ° C.) becomes slower and the number of repetitions of ascending and descending increases. (4) Secondary quenching After annealing, each test piece 1 to 15 was subjected to secondary quenching at the temperature and time shown in Table 2 and then oil-cooled. (5) Tempering After the secondary quenching, each test piece 1 was subjected to the temperature and time shown in Table 2.
After tempering to 15, air cooling is performed.

[0030]

[Table 3] Next, using each of the test pieces 1 to 15 shown in Table 3, the fatigue resistance,
The peelability and wear resistance were measured by the following methods. Table 4 shows the results. (Fatigue resistance) A plurality of disk-shaped test specimens were prepared for the test specimens shown in Table 3, and they were prepared in "Special Steel Handbook" (1st edition, edited by Electric Steel Research Institute, Rigaku Corporation 1969).
A thrust life test was performed using a thrust bearing steel tester described on page 10 to 21). The test conditions are as follows.

[0031] _{N = 1000rpm P max = 500kgf /} mm 2 lubricant 8 turbine oil Incidentally, in this test, each test piece for lifetime when the flaking that is visible under a microscope or the naked eye occurs in the 10% (L ₁₀ life ), And the cumulative number of revolutions up to this point was used as a quantitative expression of the life. (Peeling property)
The test pieces shown in Table 3 have an outer diameter of 20 mm and an inner diameter of 13 m
m, 8 mm thick ring-shaped test piece per test piece 4
Each piece was prepared and, using the peeling tester shown in FIG.
The presence or absence of occurrence of each peeling was confirmed. FIG. 1 shows a partial configuration diagram of this peeling tester.

As shown in FIG. 1, the outer diameter surface of the test piece 100 is placed in contact with the upper surface of the mating ring 200 (assuming a cam), and a radial load is applied from above the test piece 100. 300 was rotated so that the test piece 100 (outer ring) rotated (rotated) at 5100 rpm, and the appearance of the test piece 100 was observed every certain time.
The test conditions are as follows.

Rotational speed of outer ring 5100 rpm Radial load 178 kgf / piece Lubricating oil 110 ° C. engine oil, splashing Mating ring Surface hardness HRC 60-61 Surface roughness (Ra) 0.38-0.45 (before test) In the evaluation method of this test, the test specimen in which peeling did not occur in all four specimens was evaluated as ○, the test specimen in which peeling occurred in one to three specimens was evaluated as Δ, and the test specimen in which four peeling occurred was evaluated as ×.
Went as. (Abrasion Resistance) Flat test pieces of 40 mm × 10 mm × 5 mm thickness were prepared for the test pieces shown in Table 3, and the wear resistance of the test pieces was measured using a constant-pressure Savan-type rapid wear tester manufactured by Riken. FIG. 2 (A is a side view and B is a front view) shows a partial configuration diagram of this Riken constant-pressure savan-type rapid wear tester.

As shown in FIG. 2, the test piece 100 is placed in contact with the mating ring 200, and the mating ring 200 is rotated at a speed V to cause sliding wear between the mating ring 200 and the test piece 100. Sliding wear progresses, contact width b
As the load increases, a load P is applied from above the test piece 100, and the pressure applied to the contact surface between the test piece 100 and the mating ring 200 is designed to be always constant.
The test conditions are as follows.

Load P = 3 kgf / mm ² Sliding speed V = 0.15 m / sec Sliding distance 400 m Mating ring material SUJ2 Surface hardness HRC 62 to 64 Surface condition Grinding finish h _{max to} 1.5 μm No lubrication (dry; test specimen, In the present test, the specific wear amount was represented by the contact area (mm ² / Kgf) after the test was completed.

[0036]

[Table 4] According to Table 4, the average particle size of the fine carbide in the surface layer portion (depth from the surface: 0.1 mm) is 3 μm or more and less than 12 μm, the area ratio is 10% or more and less than 50%, and the number of existing particles is 5000 /
mm ² or more and less than 27000 pieces / mm ² , surface hardness is HR
C63-69, the amount of retained austenite in the surface layer is 15-
Specimens 1 to 9 satisfying the condition of 35 vol% proved to be excellent in fatigue resistance, peeling property and wear resistance. As a result, the test pieces 1 to 9 are different from the other test pieces 10 to 1
It can be seen that the life is improved as compared with No. 5.

In this example, the average grain size, the area ratio, the existing number, the surface hardness, and the retained austenite amount of the refined carbide were measured at a depth of 0.1 mm from the surface of the test piece. However, the present invention is not limited to this. A steel having an average particle size, an area ratio, an existing number, a surface hardness and a retained austenite amount of the refined carbide from the surface to a depth corresponding to 2% of the average diameter of the rolling elements satisfying the above values is used. Even when used, the same effect can be obtained.

In this embodiment, gas carburizing is performed as the carburizing treatment. However, the present invention is not limited to this, and the same effect as described above can be obtained by performing ion carburizing as shown in Table 5 below. . In addition, it goes without saying that carbonitriding may be performed instead of carburizing or quenching.

[0039]

[Table 5] In this example, a test piece made of an alloy steel having a composition shown in Table 1 was used, but this component is merely an example, and the present invention is not limited to this, and an alloy steel having another component composition may be used.

[0040]

As described above, according to the first aspect of the present invention,
According to this, unevenness occurs on the rolling surface, and this concave portion becomes an oil reservoir.
Therefore, even if a severe under lubrication, such as the boundary lubrication state,
The oil reservoir effect can sufficiently oil lubrication and to Rukoto, the bearing ring and the rolling elements move smoothly, and improve the rolling fatigue life, wear, prevent the occurrence of peeling wear and damage, the life of the bearing improves.

Further, it is possible to provide the surface hardness and the retained austenite amount necessary for improving the life of the bearing. As a result, it is possible to provide a long-life rolling bearing that can withstand peeling wear and damage under severe lubrication such as boundary lubrication, as well as under lubrication mixed with foreign matter. Further, according to the invention of claim 2, carburizing or carburizing
It also has the effect of shortening the processing time for forming the nitride layer.
You.

[Brief description of the drawings]

FIG. 1 is a partial configuration diagram of a peeling tester according to an embodiment of the present invention.

FIG. 2 is a partial configuration diagram of a constant-pressure savan-type rapid wear tester manufactured by Riken according to an embodiment of the present invention.

FIG. 3 is a diagram showing annealing conditions according to an example of the present invention.

[Explanation of symbols]

 100 Test piece 200 Mating ring 300 Shaft

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification code FI F16C 33/32 F16C 33/32 33/62 33/62 (58) Investigated field (Int.Cl. ⁷ , DB name) C23C 8 / 22,8 / 32,8 / 38

Claims (2)

(57) [Claims] The present invention comprises a bearing ring and a rolling wheel, and at least one of the bearing ring and the rolling element comprises C: 0.1 to 0.7% by weight, Cr: 1.5 to 15% by weight, and O: 9 ppm or less,
Alloy steel of at least the race and the rolling element
One has a table layer portion subjected to carburizing or carbonitriding treatment, the
The amount of retained austenite in the surface layer is 15 to 35 vo
1%, and in a rolling bearing having a surface hardness of HRC 63 to 69, the fine carbide in at least one surface layer of the race and the rolling element has an average particle size of 3 μm or more and less than 12 μm, and its abundance is , 10% or more and 50% or less in area ratio, 5000 pieces / mm ² or more in 27 pieces
A rolling bearing having a number of 000 pieces / mm ² or less . 2. The surface portion includes an oxide layer formed by an oxidation treatment.
It is characterized by being carburized or carbonitrided after forming
The rolling bearing according to claim 1.