JP2002257144A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing which is costless and durable even when used in a high vibration, heavy load, and high temperature environment. SOLUTION: The fixed ring of the rolling bearing provided with the fixed ring, the rotation ring, and the rolling body is made of a steel composed of 0.8-1.1% of C, 0.1-1.2% of Si, 0.2-1.2% of Mn, 0.8-1.8% of Cr, and the rest of iron and inevitable impurities and the truck face has 10-30% of carbide in the areal ratio and 50% or more carbide by areal ratio have 0.5 μm or smaller particle size and further, the solid solution carbon ranges 0.5-0.65%.

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 is particularly suitably used for engine accessories (alternator, electromagnetic clutch, intermediate pulley, compressor, etc.) on which high vibration, high load and high temperature act. It relates to a rolling bearing.

[0002]

2. Description of the Related Art Generally, a high Hertzian stress is applied to a rolling bearing during use. Therefore, in order to improve the rolling life, a raceway or the like is subjected to a quenching and tempering treatment to reduce the bearing surface hardness to HRC58 or less. It is raised to about 65. For example, in the case of SUJ2, which is generally used for rolling bearings, a material composed of spheroidized carbide (cementite) and ferrite is heated to 820 to 850 ° C., subjected to oil quenching to transform to martensite, and then to 150 to 850 ° C. Tempering is performed at 180 ° C. By such a treatment, the surface hardness becomes HRC62.
And a structure in which three types of martensite, about 10% of retained austenite, and several% of cementite are mixed.

[0003] On the other hand, in a general rolling bearing, separation occurs due to non-metallic inclusions or the like existing in the material due to the action of shear stress generated on the raceway surface and the rolling surface. In particular, rolling bearings used in automobile engine accessories are subject to high vibration and high load. Move to ferrite) and fine cracks, which may lead to cutting in a short time.

[0004] In addition, with the recent miniaturization and weight reduction of automobiles, engine accessories are also required to be reduced in size and weight, and are also required to have higher performance and higher output. Therefore, during the operation of the engine, for example, high vibration and high load (about 4 to 20 G) due to high-speed rotation act on the rolling bearing for the alternator via the belt, and at the high temperature state (about 90 to 130 ° C.). Will be used.

[0005] Then, carbon (C) dissolved in the matrix is diffused and agglomerated by fatigue at the position of maximum shear stress in the load zone of the outer ring, which is a fixed ring, to change into a white structure, which is a void. A micro-crack containing becomes a starting point of peeling. As a result, the service life of the bearing is reached at an earlier time of about 1/5 to 1/20 of the calculated service life of the bearing (The 137th Spring Meeting of the Iron and Steel Institute of Japan, C
AMP-ISIJ Vol. 12 (1999), p35
1-354).

As a method for solving the above problem, Japanese Patent No. 2852513 discloses a method for reducing the amount of retained austenite to 6% or less. Since the retained austenite is structurally unstable and lowers the yield strength under the above-described environment, the bearing steel (SUJ2) is subjected to a quenching treatment at a normal quenching temperature (845 ° C.) and then to a high temperature tempering (350). C), the retained austenite is reduced and the life is extended.

Further, Japanese Patent Application Laid-Open No. 4-28845 discloses that
C content lower than SUJ2 etc. (0.65-0.
90%), and the Cr content is increased to 2 to 5%.
A technique for improving matrix strength by adding at least one element of Ni, Mo, and V is described. In addition, the present inventors have found that the content of C was
0.80 to 1.10%, which is almost the same as Cr, Mo,
The present inventors have found a method of suppressing or preventing the diffusion of carbon that causes a white structure by depositing different kinds of carbides by using two or more kinds of carbide forming elements such as V, Ti, and Cu in combination.

Further, as a countermeasure for preventing early peeling of the fixed wheel, "SAE Technical Paper: SAE950"
944 (Date 1995.2.27-3.2) "
Paragraphs 14 to 14 disclose the elucidation of the fatigue mechanism of the alternator bearing and change of the filled grease from E grease to M grease. It is described that since this M grease has a high damper effect, when it is used for a bearing used under high vibration and high load, the vibration and load can be sufficiently absorbed to prevent early peeling of the fixed wheel. .

[0009]

However, in the method of Japanese Patent No. 2852513 described above, since high-temperature tempering is performed for the purpose of reducing retained austenite, there is a problem that the hardness is greatly reduced. Was. Furthermore, since the quenching temperature condition is a normal condition, there is a problem that carbon in the matrix is precipitated as carbide by high-temperature tempering, and the strength of the matrix is reduced. For this reason, the demand for higher speed and higher performance for engine accessories, which has been increasing more and more in recent years, sometimes cannot be sufficiently satisfied by the method.

[0010] Further, as in the method described in Japanese Patent Application Laid-Open No. Hei 4-28845, simply using a steel having a low carbon content will slow down the diffusion rate of carbon in the matrix so as not to produce a white structure. The effect is not enough.
Further, the above-described method found by the present inventors can be expected to have an effect of reducing the diffusion rate of carbon in the matrix so as not to generate a white structure, but the cost is increased due to the addition of expensive elements. There is room for improvement in cost reduction.

Therefore, the present invention solves such problems of the conventional rolling bearing, and has a long life even when used in an environment where high vibration, high load and high temperature are applied.
Another object is to provide a low-cost rolling bearing.

[0012]

In order to solve the above problems, the present invention has the following arrangement. That is, the rolling bearing according to the present invention is a rolling bearing including a fixed wheel, a rotating wheel, and a plurality of rolling elements rotatably disposed between the fixed wheel and the rotating wheel. At least the fixed wheel among the wheel, the rotating wheel, and the rolling element,
0.8-1.1% carbon, 0.1-1.2% silicon,
Manganese 0.2-1.2%, chromium 0.8-1.8
%, The balance being iron and steel, which is an unavoidable impurity. The raceway surface has 10 to 30% of carbide in area ratio, and the carbide having an area ratio of 50% or more has a grain size. Is 0.5 μm or less, and the amount of carbon dissolved in the steel is 0.5 to 0.65%.

With such a configuration, even when used in an environment where high vibration, high load and high temperature are applied, the life is long and the cost is low because expensive elements are not used. Hereinafter, the reason why the rolling bearing of the present invention has a long life under the above-described environment will be described.

When the steel having the above composition is quenched at a temperature higher than a normal quenching temperature, a sufficiently large amount of carbon is dissolved in the matrix. When tempering is performed at a temperature higher than the normal tempering temperature, a large amount of carbon solid-dissolved in the matrix precipitates as fine carbides. Since the fine carbides perform the pinning effect, the diffusion and aggregation of carbon dissolved in the matrix are suppressed and a white structure is less likely to occur, so that the rolling bearing has a longer life.

The amount of carbide present on the raceway surface is 1 in area ratio.
If it is less than 0%, diffusion and aggregation of carbon cannot be sufficiently suppressed, and a white structure is likely to be generated.
Since the amount of carbon dissolved in the matrix is reduced, the hardness is reduced, and the strength of the matrix is reduced, so that a white structure is easily generated. In addition, the pinning effect is mainly exhibited by fine carbide having a particle diameter of 50 μm or less, and is hardly exhibited by carbide having a particle diameter of more than 50 μm. Further, among the carbides present on the raceway surface, the particle size is 50
If the proportion of the fine carbide of μm or less is less than 50% in area ratio, the pinning effect becomes insufficient.

The above-mentioned carbide is hardened at normal temperature,
Compared with carbide generated when tempering is performed, its size is fine and its amount is large. In addition, since a sufficiently large amount of carbon is dissolved in the matrix by quenching at a high temperature, even after tempering at a high temperature, compared to the case of quenching at a normal temperature and tempering at a high temperature. ,
The amount of carbon dissolved in the matrix is large
It is 0.65%. From these facts, the fatigue resistance at the maximum shear stress position in the load zone of the fixed wheel is excellent. When the amount of carbon dissolved in the matrix is 0.5
%, The strength of the matrix decreases and sufficient hardness cannot be obtained. If it exceeds 0.65%, a carbide effective for suppressing the white structure cannot be obtained.

The method of defining and measuring the amount of carbon dissolved in the matrix is not particularly limited, but it is preferable to employ the amount of solid solution carbon defined by the following formula. . [C] _M = (100 × C−Cθ × <C>) / (100−
Cθ) where [C] _M is the amount (%) of carbon dissolved in the steel,
Is the total carbide amount (%) in the steel, <C> is the carbon amount (%) in the carbide, and C is the total carbon amount (%) in the steel.

In the present invention, the quenching temperature of the steel is 8
The temperature is preferably set to 50 to 880C. If quenching is performed at a temperature higher than the normal quenching temperature, a sufficiently large amount of carbon can be dissolved in the matrix. If the quenching temperature of the steel is less than 850 ° C, the amount of carbon dissolved in the matrix becomes insufficient, and if it exceeds 880 ° C,
Carbon is excessively dissolved in the matrix, and a required amount of carbide is not precipitated by a predetermined tempering.

In the present invention, the tempering temperature of the steel is preferably 230 to 270 ° C. When tempering is performed at a temperature higher than the normal tempering temperature, a large amount of carbon dissolved in the matrix is precipitated as fine carbides. That is, 50% or more of the carbides on the raceway surface are fine carbides having a particle size of 0.5 μm or less.
When the tempering temperature of the steel is lower than 230 ° C., the amount of precipitated fine carbides becomes insufficient, and when it exceeds 270 ° C.,
The hardness decreases and the rolling bearing has a short life. If a sufficient amount of carbon is not dissolved in the matrix by quenching, the steel cannot have a sufficient hardness (HRC 59 or more) when a predetermined tempering is performed.

Next, each element added to the steel in the present invention will be described. (1) Carbon (C) The content of C needs to be 0.80 to 1.10%. C is an element added in order to obtain the hardness and carbide required for the bearing. The hardness is sufficient and sufficient to give the bearing an excellent life, and changes to a white structure after the precipitation of fine carbide. 0.80% or more is required to obtain an effective matrix strength to prevent the occurrence of the problem.

On the other hand, when the content of C exceeds 1.10%, giant carbides are generated during steel making and segregation becomes strong. For this reason, in the soaking process (diffusion process) for reducing segregation usually performed in bearing steels such as SUJ2, the generation and segregation of giant carbide may not be sufficiently adjusted, and as a result, the fatigue life is reduced. There is a possibility that.

(2) Silicon (Si) The content of Si must be 0.10 to 1.20%. Si is used as a deoxidizing agent during steelmaking of the material and improves the hardenability and strengthens the martensite in the matrix, so that it is effective for improving the life of the bearing. Further, Si is also an effective element for obtaining temper softening resistance, and in order to satisfy the recent demand for high temperature for engine accessories, it is effective to add an appropriate amount thereof.

In order to improve the hardenability and obtain the effect of strengthening the matrix, Si must be 0.10% or more. On the other hand, if the content of Si is too large, the workability such as machinability and forgeability deteriorates, so the upper limit needs to be 1.20%. (3) Manganese (Mn) The content of Mn needs to be 0.20 to 1.20%.

Mn is an element for improving the hardenability, but in order to obtain the effect, it is necessary to add 0.20% or more. On the other hand, when the content of Mn exceeds 1.20%, the processability decreases. Since the presence of S generates MnS, which is a nonmetallic inclusion that may cause a reduction in the life, it is preferable to reduce the amount of MnS to be generated by setting the S content to 0.02% or less.

(4) Chromium (Cr) The Cr content needs to be 0.80 to 1.80%. Cr is an important element for obtaining the hardness and carbide necessary for the bearing, and is an element for strengthening the base martensite, such as improvement in hardenability and temper softening resistance. When quenching at a high temperature and then performing oil tempering at a high temperature, the lower limit of the Cr content is 0 in order to obtain a sufficient amount (area ratio) of carbide and hardness necessary for achieving a long life effect. .80%
It is necessary to

On the other hand, if the Cr content exceeds 1.80%, giant carbides are generated during steelmaking, and segregation becomes strong. For this reason, in the soaking process usually performed on bearing steel such as SUJ2, the generation and segregation of giant carbide may not be sufficiently adjusted, and the machinability may be deteriorated when the content of Cr is increased. Therefore, in order to avoid these problems, the upper limit of the Cr content needs to be 1.80%.

(5) Molybdenum (Mo), Vanadium (V), Nickel (Ni) The steel according to the present invention further comprises M
Preferably, o is contained in a range of 2.0% or less, V is contained in a range of 2.0% or less, and Ni is contained in a range of 2.0% or less. Mo is an element that imparts temper softening resistance to steel, and is also an element that forms carbide. When the tempering softening resistance is improved, high surface hardness can be maintained even when tempering is performed at a high temperature, and strength at a high temperature can be improved. Further, when fine carbide containing Mo is precipitated, it is effective in suppressing a structural change due to a pinning effect.

However, even if Mo is added in excess of 2.0%, these effects are saturated, and furthermore, the workability is lowered and the cost is increased. It is preferable to set the following. V is also a carbide forming element that mainly precipitates at the crystal grain boundaries to suppress the coarsening of the crystal grains and combines with carbon in the steel to form fine carbides. Therefore, when V is added, after tempering at a high temperature, V
Is precipitated as fine carbides, which is effective in suppressing a structural change due to the pinning effect, and further, the hardness of the surface layer portion is increased and the wear resistance is improved.

However, even if V is added in excess of 2.0%, these effects are saturated, and furthermore, the workability is reduced and the cost is increased. It is preferable to set the following. Ni is an element that strengthens the matrix and improves toughness. Therefore, by the addition of Ni, it is expected that the life can be improved by further strengthening the matrix.

However, if the content exceeds 2.0%, the retained austenite increases and the quenching hardness decreases, so that the rolling fatigue life decreases. Further, since Ni is an expensive element, adding a large amount thereof increases the cost, so that the Ni content is preferably 2.0% or less.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a rolling bearing according to the present invention will be described in detail with reference to the drawings and tables. Deep groove ball bearings made of steels of various compositions (No. 630
3) was prepared (Examples 1 to 9 and Comparative Examples 1 to 5), and a life test was performed.

Table 1 shows the composition of the steel constituting the outer ring of each ball bearing (which becomes a fixed ring in the life test described later) and the heat treatment conditions (quenching and tempering).

[0033]

[Table 1]

In any of the ball bearings, the surface hardness of the outer ring is HRC 56 to 64, the retained austenite is 0 to 20%,
The surface roughness Ra of the raceway surface is 0.01 to 0.05 μm. The inner ring and the rolling elements are made of SUJ2, and are quenched and tempered at normal temperatures. The surface hardness of the inner ring and the rolling element is HRC 62 to 64, the surface roughness Ra of the raceway surface of the inner ring is 0.01 to 0.05 μm, and the surface roughness Ra of the rolling element is 0.003 to 0.010 μm. .

The inner race and the rolling elements may be made of the same steel as the outer race and may be subjected to the same heat treatment. For the outer rings of these ball bearings,
The amount Cθ of carbide (cementite) in the finished product after quenching and tempering treatment was determined using an X-ray diffractometer, and was substituted into the above equation together with the separately measured carbon content <C> and total carbon content C in carbide. The amount [C] _M of carbon dissolved in the matrix was determined.

The carbon content <C> in the carbide (cementite) is 6.67%. In the steel constituting the outer ring this time, the carbon content in the ferrite was 0.006%.
Therefore, it was assumed to be 0%. An X-ray diffractometer manufactured by Rigaku Denki Co., Ltd. was used. The X-ray was Co Kα ray, the tube voltage was 40 KV, the tube current was 200 mA, and the irradiation area was 12 mm.
0 mm ² . The amount Cθ of the carbide can be similarly measured not only by the X-ray diffraction method but also by an area quantitative method using an electron microscope or a chemical quantitative method using electrolytic separation.

Further, with respect to the outer ring of the ball bearing, the amount (area ratio) of carbide present on the raceway surface in the finished product after the quenching and tempering treatment was measured. The measurement method is as follows. First, the structure of the raceway surface is photographed with an electron microscope, and then the carbide is picked up from an image photographed using an image analyzer, and the shape, dimensions, area, number, etc. are measured. To calculate the area ratio of carbide.

In this case, the amount (area ratio) of the carbide present on the raceway surface, the ratio (area ratio) of the carbide having a particle size of 0.5 μm or less to the carbide (the carbide existing on the raceway surface), Was measured. The electron microscope used was JSM-T220A manufactured by JEOL Ltd., and the image analysis apparatus used was IBAS2000 manufactured by Carl Zeiss. Of these measurement results, Cθ, [C] _M , and particle size were 0.5 μm
Table 2 summarizes the following carbide ratios.

[0039]

[Table 2]

Next, a life test performed on such a ball bearing will be described. In the life test, the outer ring is fixed,
The inner ring was used as a rotating wheel. The life tester includes a bench rapid acceleration / deceleration tester of a type in which the number of revolutions is switched at predetermined time intervals (every 9 seconds) (the above-mentioned SAE technical paper: SAE
950944). The rotation speeds are 9000 rpm and 18000 rpm.

The load condition of the ball bearings (Examples and Comparative Examples) was P (load load) / C (dynamic rated load) = 0.10, and E grease was used as the grease. Since the calculated life of this ball bearing was 1350 hours, the life test was terminated when the life did not reach even after 1500 hours. Then, the presence or absence of flaking on the raceway surface of the outer ring was confirmed. A life test is performed on 10 types of ball bearings, one by one,
It is shown in Table 2 to calculate the life L _10. In addition, the numerical value in the column of “stripping” in Table 2 is the number of bearings in which the flaking occurred among the ten test bearings.

FIG. 1 is a graph of the results of Table 2. The horizontal axis of this graph indicates the ratio (area ratio) of the carbide having a particle size of 0.5 μm or less among the carbides present on the raceway surface, and the vertical axis indicates the ratio (L ₁₀ / L) between the life L ₁₀ and the calculated life.
L _cal ). As can be seen from Table 2 and the graph of FIG. 1, the ball bearings of Examples 2 to 5 and 7 to 9 did not cause any boring on the raceway surface of the outer ring even when all of the ten test bearings exceeded 1500 hours. .

[0043] In addition, the ball bearings of Examples 1 and 6, but two of the 10 test bearing occurs chestnuts on the raceway surface of the outer ring, the life L ₁₀ is longer than the 1350 hours of the calculated life And had a very long life as compared with the comparative example.
After quenching at a high temperature of 850 ° C. or higher and then tempering at a temperature of 230 ° C. or higher, the raceway of the outer race made of steel having the above composition has a surface area of 10 to 30% carbide. And having an area ratio of 50
% Or more has a particle size of 0.5 μm or less.
The amount of carbon dissolved in the steel as defined by the above equation [C]
_M was 0.5 to 0.65%, and it was confirmed that the bearing had a long life.

The present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, in the present embodiment, a deep groove ball bearing has been described as an example of the rolling bearing, but the present invention is naturally applicable to other types of rolling bearings. For example, radial rolling bearings such as angular ball bearings, cylindrical roller bearings, needle roller bearings, tapered roller bearings, and self-aligning roller bearings, and thrust rolling bearings such as thrust ball bearings and thrust roller bearings. .

The rolling bearing of the present invention has a long life in an environment where high vibration, high load, and high temperature are applied, such as engine accessories, but is excellent even when used in other environments. Of course, it has a long life.

[0046]

As described above, the rolling bearing of the present invention has the following features.
It has a long life and low cost even when used in an environment where high vibration, high load, and high temperature act.

[Brief description of the drawings]

Shown [1] the ratio particle size of less carbide 0.5μm among the carbides present in the raceway surface of the outer ring (area ratio), the ratio of the correlation between the life L ₁₀ of the bearing and the calculated life L _cal It is a graph.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinji Fujita 1-5-150 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 AA13 AA14 AA16 AA24 AA25 AA42 AA52 AA53 AA54 AA62 BA70 CA32 DA03 EA03 FA06 FA31 FA51 FA53 GA01 GA24 GA29 GA60

Claims (1)

[Claims] A fixed wheel, a rotating wheel, and a plurality of rolling elements rotatably disposed between the fixed wheel and the rotating wheel;
In the rolling bearing comprising: at least the fixed ring of the fixed ring, the rotating ring, and the rolling element contains 0.8 to 1.1% of carbon, 0.1 to 1.2% of silicon, and manganese. It contains 0.2-1.2%, chromium 0.8-1.8%, and the balance consists of iron and steel which is an unavoidable impurity, and its raceway surface contains 10-30% carbide in area ratio. Among them, those having an area ratio of 50% or more among the carbides have a particle size of 0.5 μm or less, and the amount of carbon dissolved in the steel is 0.5 to 0.6.
A rolling bearing characterized by 5%.