JPH04254572A - Roller bearing - Google Patents

Abstract

PURPOSE:To develop a roller bearing excellent in resistance to damage and wear by producing the bearing from a Cr steel having a specified composition and carburizing or carbonitriding the surface. CONSTITUTION:A roller bearing consisting of a bearing ring and a rolling element is produced from an alloy steel contg. 0.1-0.7wt.% C, 1.5-15wt.% Cr and <9ppm O. This bearing member is carburized or carbonitrided to control the austenite remaining in the surface layer of the bearing ring or rolling element to 15-35vol.%, the area ratio of the hard and fine Cr carbide having 3-12mum average particle diameter to 10-50%, the number of the carbides to 5,000-27,000/mm<2> and the surface hardness (HRC) to 63-69. Consequently, a roller bearing resistant to peeling and wear even when used in a lubricating oil mixed with the turnings and shavings of metal and having a long service life is produced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to rolling bearings, and more particularly to improving the life of rolling bearings used in transmissions, engines, etc. of automobiles, agricultural machinery, construction machinery, steel machinery, etc.

0002

[Prior Art] Conventionally, rolling bearings have been used harshly, subjecting them to repeated shear stress under high surface pressure.In order to withstand the shear stress and ensure rolling fatigue life, high carbon chromium steel bearings have been used. This was then quenched and tempered to have a Rockwell hardness of HRC58-64.

[0003] However, as it is desired to further extend the life of bearings, one of the other factors that causes a reduction in the life of rolling bearings is the contamination of foreign matter in bearing lubricating oil. Usually, bearing lubricating oil contains metal chips, shavings,
If a rolling bearing is used in an environment where burrs, wear particles, etc. are mixed in, this foreign material will damage the bearing ring and/or rolling element, reducing the life of the rolling bearing. I was letting it happen.

Therefore, as disclosed in Japanese Patent Publication No. 62-24499 and Japanese Patent Application Laid-Open No. 2-34766, spheroidal carbides are precipitated on the surface of low-medium carbon low-alloy steel by heat treatment such as carburizing, thereby improving the surface of the steel. There are conventional examples of improving hardness and pitting resistance, but cracks occur and
There is a limit to improving the life of rolling bearings due to the occurrence of flaking, etc.

Therefore, as disclosed in JP-A No. 64-55423, even when a rolling bearing is used under lubrication containing foreign matter, the C (carbon) content of the rolling surface layer of the bearing is , a conventional example in which the retained austenite content and carbonitride content are adjusted to appropriate values to alleviate the concentration of stress at the edge of the indentation caused by foreign objects, suppress the occurrence of cracks, and improve the life of rolling bearings. exists.

[0006]

[Problems to be Solved by the Invention] However, in the conventional example disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 64-55423,
Although an appropriate amount of retained austenite can improve the life under lubrication with foreign matter, on the other hand, there is a problem in that retained austenite reduces surface hardness and fatigue resistance. That is, there is still room for improvement regarding the appropriate relationship between the amount of retained austenite and the surface hardness.

Another problem with conventional bearing materials is that there is no consideration given to what value the grain size of carbides and carbonitrides should be in order to improve bearing life. That is, when a large carbide is repeatedly subjected to stress, the large carbide tends to become a starting point of fatigue and cause cracking and flaking. As a result of extensive research in light of these issues, we have discovered the optimal relationship between the amount of retained austenite in the rolling surface layer and surface hardness. Furthermore, we found an optimal value for the average particle size of carbides and carbonitrides present in the rolling surface layer. As a result, it has become possible to improve the fatigue resistance of rolling bearings, prevent the occurrence of flaking, and extend the life of bearings under lubrication contaminated with foreign matter. There was still room for improvement in terms of being able to withstand peeling damage and abrasion underneath.

The present invention aims to solve these problems, and focuses on the fine carbides in the surface layer of bearings, and is suitable for use not only under lubrication with foreign matter, but also under severe lubrication conditions such as boundary lubrication. The purpose of the present invention is to provide a long-life rolling bearing that can withstand peeling damage and wear.

[0009]

[Means for Solving the Problems] In order to achieve this object, the present invention includes a bearing ring and a rolling element, and at least one of the bearing ring and the rolling element has a C: 0.1 to 0.7. % by weight, Cr: 1.5 to 15% by weight, O: 9 ppm or less, and the alloy steel is carburized or carbonitrided so that the amount of retained austenite in the surface layer of the alloy steel is 15 to 35 vol. %, and the surface hardness is HRC63 ~
In the rolling bearing according to No. 69, the fine carbide in the surface layer of at least one of the raceway ring and the rolling element has an average particle size of 3 μm or more and less than 12 μm, and the amount present is:
The present invention provides a rolling bearing characterized in that the area ratio is 10% or more and less than 50%, and the number of existing pieces is 5000 or more and less than 27000 pieces/mm2.

0010

[Operation] According to the present invention, the average grain size of fine carbides in at least one surface layer of the raceway ring and the rolling element is reduced to 3 μm.
or more than 12 μm, and the amount present is 10% in terms of area ratio.
50% or more, less than 50%, and the number of particles present is 5,000 or more and less than 27,000 pieces/mm2. By setting the number of particles to 5,000 or more and less than 27,000 pieces/mm2, the length is long enough to withstand peeling wear and damage not only under lubrication with foreign substances but also under severe lubrication such as boundary lubrication. The aim is to provide rolling bearings with a long service life.

Next, the critical significance of the functions and characteristic values of fine carbides according to the present invention will be explained in detail. [Average particle size of fine carbides in surface layer portion: 3 μm or more and less than 12 μm] In the present invention, fine carbides are generated in the surface layer portion of at least one of the raceway ring and the rolling element by carburizing or carbonitriding treatment. This fine carbide is hard and has excellent wear resistance, and is also fine in size, so it does not cause stress concentration due to applied loads, thereby improving the life of the bearing. and,
Due to the presence of fine carbides, unevenness occurs on the raceway surface, and oil (lubricating oil, etc.) accumulates in these depressions (oil pools).
Even under severe lubrication conditions such as boundary lubrication, this oil pool effect provides sufficient oil lubrication, allowing the raceways and rolling elements to move smoothly, improving rolling fatigue life and reducing wear. ,Prevents peeling wear and damage and improves bearing life.

[0012] The average particle size of the fine carbide that fully exhibits this characteristic 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 portions of the bearing raceway surface that exhibit an oil pool effect will become small, making it impossible to provide a sufficient oil lubrication state (oil film formation). As a result, rolling fatigue life is reduced, and wear, peeling wear, and damage occur.

On the other hand, if the average particle size of the fine carbide exceeds 12 μm, the fine carbide becomes a stress concentration source, reducing the rolling life of the bearing. Furthermore, even if the average grain size of the fine carbide is set to 12 μm or more and the concave portion of the bearing raceway is enlarged, the oil stagnation effect on the bearing raceway to prevent the boundary lubrication state will be reduced. The preventive effect has already been saturated.

[0014]Furthermore, the larger the fine carbide, the more convex it is on the bearing rolling surface, and the smaller the carbide, the more it tends to be buried in the matrix (base). As a result, the average particle size of the fine carbides was set to 3 μm or more and less than 12 μm. [Amount of fine carbides in the surface layer: 10% in area ratio
50% or more] The amount of fine carbide present is also mentioned as a condition for improving the life of the bearing.

[0015] If the amount of fine carbides present is less than 10% in terms of area ratio, the number of concave portions on the bearing raceway surface that exhibits an oil sump effect will decrease, making it impossible to provide a sufficient oil lubrication state (oil film formation). In addition, the presence of fine carbides makes it difficult to obtain the desired surface hardness (HRC 63 to 69), and it is guaranteed that the surface hardness will decrease as the amount of retained austenite increases due to the increase in the amount of carbon dissolved in the matrix. You won't be able to do anything. As a result, the mechanical strength and rolling fatigue life of the bearing are reduced, and wear, peeling wear, and damage occur.

On the other hand, the amount of fine carbides present is 50% in terms of area ratio.
%, fine carbides combine with each other and become coarse, and the large carbides formed in this way become a source of stress concentration, which causes cracks and other problems, especially when the bearing is contaminated with foreign matter. Lifespan decreases. In addition, the amount of carbon dissolved in the matrix decreases, making it difficult to secure the necessary amount of retained austenite, making it impossible to fully exert the effect of alleviating stress concentration and rolling load. As a result, the life extension effect is reduced, especially when foreign matter is mixed in.

As a result, the amount of fine carbides present was set to be 10% or more and less than 50% in terms of area ratio. [Amount of fine carbides present in the surface layer: 5000 pieces/mm2 or more2
Less than 7000 pieces/mm2] One of the conditions for fine carbides to improve the life of a bearing is the number of fine carbides present (pieces/mm2).

[0018] The amount of fine carbides present is 5000 in number.
If it is less than 1/mm2, there will be fewer recesses on the bearing raceway surface that exhibit an oil sump effect, making it impossible to provide sufficient oil lubrication (formation of an oil film), resulting in reduced rolling fatigue life, specific wear, and peeling. Wear and damage will begin to occur. In addition, the amount of carbon dissolved in the matrix increases and the amount of retained austenite increases more than necessary, making it impossible to secure the necessary surface hardness, reducing the mechanical strength and rolling fatigue life of the bearing, and making it unsuitable for practical use. It disappears.

On the other hand, the amount of fine carbides present is 2
When it exceeds 7,000 pieces/mm2, fine carbides combine with each other and become coarse, and the large carbides thus formed become a stress concentration source, and the amount of carbon dissolved in the matrix decreases. It becomes difficult to secure the necessary amount of retained austenite. For this reason, the effect of extending the lifespan is particularly reduced when foreign matter is mixed in.

[0020] As a result, the amount of fine carbides present was determined to be at least 5,000 pieces/mm2 and less than 27,000 pieces/mm2. In the present invention, the term "surface layer" refers to the range from the surface to a certain desired depth, for example, to a depth corresponding to 2% of the average diameter of the rolling elements at which the shear stress is maximum.

In the present invention, carbides include, for example, Cr7 C3, Cr3 C6, Mo2 C, V
C, V4 C3 and Fe3 C or double carbides thereof. And, as a carbide forming element, Cr
, Mo, V, W, etc., but in particular, C
r is desirable. By containing one or more desired types of these carbide-forming elements, various carbides are generated.

[0022] At least one of the raceway ring and the rolling element is made of alloy steel specified in the following ranges: C: 0.1 to 0.7% by weight, Cr: 1.5 to 15% by weight, and O: 9 ppm or less. By carburizing or carbonitriding the alloy steel, the amount of retained austenite in the surface layer is 15 to 35 vol%, and the surface hardness is HRC 63 to 69, thereby improving fatigue resistance.
It becomes possible to prevent the occurrence of flaking, and it becomes possible to improve the life of the bearing even in the presence of foreign matter.

That is, C is an element necessary to improve the hardness after quenching and tempering, and by specifying C: 0.1 to 0.7% by weight, it is possible to improve the hardness of carburizing and carbonitriding treatments. It prevents the time from increasing (when the weight is less than 0.1%) and improves heat treatment productivity. ) can be prevented.

Further, Cr is a necessary element for forming carbides, and Cr combines with C to form fine carbides. By specifying Cr: 1.5 to 15% by weight,
It is possible to secure the amount of fine carbides (Cr: 1.5% by weight or more) to obtain the surface hardness necessary for the bearing, and also to prevent the generation of giant carbides that become a source of stress concentration. Also, O is
It is an element that generates oxide-based nonmetallic inclusions, and its content must be reduced as much as possible to reduce rolling life. Therefore, the upper limit was set at 9 ppm.

Furthermore, fine carbides are generated when alloy steel is carburized or carbonitrided. In addition, retained austenite is usually soft and sticky. By setting the amount of retained austenite in the surface layer to 15 to 35 vol%, it is possible to prevent the adhesion of indentations caused by foreign objects, alleviate rolling fatigue, prevent the occurrence of cracks, etc., and improve the mechanical strength of the bearing material. Rolling fatigue life can be improved.

[0026] Also, the surface hardness is HRC63 to 69.
By doing so, it is possible to ensure hardness that can withstand rolling fatigue even if a large local surface pressure is repeatedly applied to the raceway surface. Then, while using steel under these conditions,
Existence state of fine carbides formed in the surface layer (average particle size,
By specifying the existing area ratio and number of pieces as described above, in the lubrication between the raceway ring and the rolling elements, it is possible to not only improve the life of the bearing under the presence of foreign matter, but also under severe lubrication conditions such as boundary lubrication. However, it is possible to prevent a reduction in rolling fatigue life, specific wear, peeling wear, and damage, and improve the life of the bearing.

[0027]

[Embodiment] Next, one embodiment of the present invention will be explained in detail. Test specimens 1 to 15 made of alloy steel with the composition shown in Table 1 were subjected to the heat treatment shown below under the conditions shown in Table 2 by casting, and then each test specimen 1 to 1
Average grain size (μm), existing area ratio (%), and number of fine carbides in the surface layer (depth 0.1 mm from the surface) of No. 5 (
pieces/mm2), surface hardness, amount of retained austenite (v
ol%) was measured. The results are shown in Table 3. The average particle size and area ratio of fine carbides were measured by microscopy, and the amount of retained austenite was measured by X-ray analysis.

[0028]

[Table 1]

[0029]

[Table 2] (Heat treatment) (1) Oxidation treatment Each test piece 1 to 15 was subjected to oxidation treatment at the temperature and time shown in Table 2, and then cooled in oil or air. By performing this oxidation treatment, it is possible to form an oxide layer (porous) with Cr on the surface of the alloy steel, thereby shortening the carburizing or carbonitriding treatment time. That is, when an alloy steel containing a large amount of Cr is carburized or carbonitrided, a compound (dense film) with the carburized or carbonitrided carbon is formed on the surface of the alloy steel, and C forms a matrix. However, the problem arises that it becomes difficult to penetrate and the carburizing or carbonitriding time becomes longer.
This problem can be prevented by forming an oxide layer with Cr on the surface of the alloy steel through oxidation treatment. (2) Carburizing Treatment After the oxidation treatment, each test piece 1 to 15 was carburized at the temperature and time shown in Table 2 in an atmosphere of RX gas + enriched gas, and then cooled with oil or air. 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 cooled in air. It should be noted that the longer the annealing is carried out, the finer the carbide size becomes.
The slower the cooling rate near the transformation point (723° C.), and the greater the number of repetitions of lifting and lowering, the finer the carbide size becomes. (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 cooled in oil. (5) After tempering and secondary quenching, each test piece 1~
After tempering in step 15, it is air cooled.

[0030]

[Table 3] Next, using each test piece 1 to 15 shown in Table 3, fatigue resistance,
Peelability and abrasion resistance were measured using the following methods. The results are shown in Table 4. (Fatigue resistance) A plurality of disk-shaped test pieces were prepared using the test pieces shown in Table 3, and "Special Steel Handbook" (1st edition, edited by Electric Steel Research Institute, Rikogakusha 196)
A thrust life test was conducted using the thrust type bearing steel testing machine described on pages 10 to 21 (May 25, 1999). The test conditions are as follows.

[0031] N = 1000 rpm Pmax = 500 kgf/mm2 Lubricating oil 8 Turbine oil In addition, during this test, the life span (L10 life) is determined as the point in time when 10% of each test piece shows flaking that can be seen with a microscope or with the naked eye. However, the cumulative number of rotations up to this point was used as a quantitative expression of the lifespan. (Peelability) For the test pieces shown in Table 3, the outer diameter was 20 mm and the inner diameter was 13 m.
m, 4 ring-shaped test pieces with a thickness of 8 mm per test piece.
Each piece was prepared one by one, and using the peeling tester shown in Figure 1,
The presence or absence of peeling was confirmed in each case. A partial configuration diagram of this peeling tester is shown in Figure 1.

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 (assumed to be a cam), a radial load is applied from the top of the test piece 100, and in this state the shaft is 300, test piece 100 (outer ring)
The test piece 100 was rotated at 5100 rpm, and the appearance of the test piece 100 was observed at certain intervals. The test conditions are as follows.

Outer ring rotation speed: 5100 rpm Radial load: 178 kgf/piece Lubricating oil: 110°C engine oil, splashing mating ring
Surface hardness HRC60-61 Surface roughness (Ra) 0.
38-0.45 (before the test) The evaluation method for this test is 4
A test piece in which no peeling occurred in any of the test pieces was marked as ◯, a test piece in which 1 to 3 peelings occurred was marked as △, and a test piece in which all 4 peelings occurred was marked as ×. (wear resistance)
For the test pieces shown in Table 3: 40 mm x 10 mm x thickness 5
A flat test piece of mm in diameter was prepared, and the abrasion resistance of the test piece was measured using a constant pressure Saban type rapid abrasion tester manufactured by Riken. Figure 2 shows a partial configuration diagram of this RIKEN constant pressure Saban type rapid wear tester.
(A is a side view, B is a front view).

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 generate sliding wear between the mating ring 200 and the test specimen 100. As sliding wear progresses, the contact width b
As the pressure increases, a load P is applied from the upper part of 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.

[0035] Load P=3kgf/mm2
Sliding speed V = 0.15m/sec Sliding distance 400m Mating ring Material SUJ2 Surface hardness HRC62~64 Surface condition Grinding finish hmax ~1.5μm Lubrication None (dry; both test piece and mating ring), boundary lubrication condition. During the test, the specific wear amount was expressed as the contact area (mm2/Kgf) after the test.

[0036]

[Table 4] From Table 4, the average particle size of fine carbides in the surface layer (depth 0.1 mm from the surface) is 3 μm or more and less than 12 μm, the existing area ratio is 10% or more and less than 50%, and the number of particles is 5000. /
mm2 or more and less than 27,000 pieces/mm2, surface hardness is HRC63-69, and the amount of retained austenite in the surface layer is 1
Test pieces 1 to 9 that satisfied the conditions of 5 to 35 vol% were proven to have excellent fatigue resistance, peeling property, and abrasion resistance. As a result, test pieces 1 to 9 are different from other test pieces 10 to 9.
It can be seen that the lifespan is improved compared to No. 15.

In this example, the average grain size, existing area ratio, number of existing fine carbides, surface hardness, and amount of retained austenite were measured at a depth of 0.1 mm from the surface of the test piece. , but not limited to this, the average grain size of fine carbides from the surface to a depth corresponding to 2% of the average diameter of the rolling element, the existing area ratio, the number of existing particles, the surface hardness, and the amount of retained austenite satisfy the above values. Similar effects can be obtained by using

Further, in this example, gas carburizing was performed as the carburizing treatment, but the same effect as described above can be obtained by performing ion carburizing as shown in Table 5 below. . Moreover, it goes without saying that carbonitriding treatment may be performed in place of carburizing or quenching.

[0039]

[Table 5] In this example, a test piece made of alloy steel with the composition shown in Table 1 was used, but this composition is only an example, and alloy steel with other compositions could be used. Also good.

[0040]

As explained above, according to the present invention, the average grain size of fine carbides in the surface layer of at least one of the raceway ring and the rolling element is set to 3 μm or more and less than 12 μm, and the amount of fine carbide present is increased to 10 μm in terms of area ratio. % or more and less than 50%, and the number of particles present is 5000 pieces/mm2 or more and less than 27000 pieces/mm2, unevenness will occur on the raceway surface and oil will accumulate in these recesses (oil sump), causing severe conditions such as boundary lubrication. Even under lubrication, this oil pool effect provides sufficient oil lubrication, allowing the raceways and rolling elements to move smoothly.
Improves rolling fatigue life, prevents wear, peeling wear and damage, and extends bearing life.

[0041] Furthermore, it becomes possible to provide the surface hardness and the amount of retained austenite 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 not only under foreign matter mixed lubrication conditions but also under severe lubrication conditions such as boundary lubrication conditions.

[Brief explanation of the drawing]

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 RIKEN constant pressure Saban type rapid wear tester 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 Opponent ring 300 Shaft

Claims (1)

[Claims] 1. A bearing ring and a rolling element, wherein at least one of the bearing ring and the rolling element has a C: 0.1 to 0.7.
% by weight, Cr: 1.5 to 15% by weight, O: 9 ppm or less, and the alloy steel is carburized or carbonitrided so that the amount of retained austenite in the surface layer of the alloy steel is 15 to 35 vol. %, and the surface hardness is HRC6
3 to 69, the fine carbide in the surface layer of at least one of the bearing ring and the rolling element is
The average particle size is 3 μm or more and less than 12 μm, the amount of the particles is 10% or more and less than 50% in area ratio, and 500 in number.
A rolling bearing characterized in that the number of pieces/mm2 is 0 or more and less than 27,000 pieces/mm2.