JP2002206540A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing having excellent resistance against seizure and high strength and resistance against corrosion and fatigue and usable satisfactorily even under bad lubrication environment in which water enters the inside and is mixed with lubricant. SOLUTION: In a tapered roller bearing 1 provided with an inner ring 2, an outer ring 3, and a plurality of rollers 4 arranged between the inner ring 2 and the outer ring 3 so as to roll freely, the outer ring 3 which is a fixed ring is formed by steel having N concentration of 100 ppm or less, O concentration of 15 ppm or less, S concentration of 0.020% or less, Ti concentration of 50 ppm or less, Ni concentration of 1 to 5 %, P concentration of 0.020% or less, and Mo concentration of 0.1 to 5%, C concentration of a raceway surface provided in the outer ring 3 is 0.6 to 1.2%, and a remaining compression stress of the raceway surface is 100 to 500 MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing, such as a rolling bearing for a work roll of a rolling mill, which is suitably used in an environment where water enters and mixes with a lubricant.

[0002]

2. Description of the Related Art As a material of a rolling bearing used in a corrosive environment, martensitic stainless steel is often used. This is because it is known that increasing the corrosion resistance of steel is effective for increasing the corrosion fatigue strength of steel. On the other hand, in a roller bearing, slip due to skew is inherent, and in a ball bearing, differential slip is inherent between a ball and a raceway, so that it is necessary to increase the seizure resistance of the material. However, martensitic stainless steel is not suitable for use in roller bearings because of its low thermal conductivity. Particularly in a poor lubrication environment where water enters the interior of the bearing and water enters the lubricant, the oil film of the lubricant is hardly formed and seizure easily occurs on the sliding surface. The use of stainless steel was difficult.

Further, as a bearing used in an environment where there is a possibility of contact with a fluid such as water, for example, a roll neck bearing of a rolling mill for steel facilities, Japanese Patent Publication No. 60-14933 and Japanese Patent Publication No. 61-12130 are disclosed. A sealed rolling bearing provided with a sealing device as proposed in a gazette or the like is used. FIG. 25 shows a four-row tapered roller bearing provided with a sealing seal as an example of a sealed rolling bearing. FIG. 3 shows the upper half of a longitudinal section not including the axis.

The sealed roller bearing shown in FIG.
A plurality of rollers 104, 104,... Rotatably supported by four rows of retainers 105, 105,. Inner ring 103 for 101, 101, 102,
103 can be rotated. Further, the outer ring 101,
Seal holders 107, 107 are provided at both ends in the axial direction of 101 to hold the seals 108, 108.
The elastic lips 108a, 108a of 08, 108 are in contact with the outer peripheral surfaces at both axial ends of the inner rings 103, 103. Thus, the lubricant in the bearing space S is retained, and a fluid such as water is prevented from entering the bearing space S from outside.

FIG. 26 is a view for explaining the shape of the intermediate seal 109 held on the inner surface of the portion where the inner rings 103 are in contact with each other. The intermediate seal 109 is mainly for preventing moisture or the like from entering the bearing space S when the roll is attached or detached. FIG. 27 shows another example of a conventionally used intermediate seal. This intermediate seal 10
9 ′ is a concave bottom surface 10 of the opposed surface portion of the inner rings 103, 103.
Lip portions 109a, 109 that are in line contact with 3a, 103b
The contact surface pressure is increased by this line contact to seal the inside and outside of the bearing.

[0006] However, the above-mentioned conventional rolling bearing of the related art has a problem that it is not sufficient to prevent water or the like from entering under an environment where temperature changes are severe. For example, FIG.
When the sealed rolling bearing shown in FIG. 5 is used as a roll neck bearing for a rolling mill of steel equipment, the number of rotations of a roll supported by the sealed rolling bearing frequently changes. That is, high-speed rotation, low idle rotation, and stop of the roll are repeated, and the temperature inside the sealed rolling bearing changes according to each condition. For this reason, the expansion and contraction of the air and the like in the bearing space S are repeated, and the air that has expanded when the temperature rises escapes from the elastic seals 108 on the end faces, and then when the temperature drops, the inside of the sealed rolling bearing is reduced. Becomes negative pressure.

The negative pressure value decreases as the temperature in the bearing space S, which has been high, decreases (the temperature difference increases), and therefore, as the number of rotations of the high-rotating roll decreases (the rotation difference decreases). Larger), larger and last longer. This is shown in FIGS. 28 (a), (b) and (c). These figures show the rotation speed of the roll, the bearing temperature (the temperature in the bearing space S), and the pressure inside the bearing (the pressure in the bearing space S) with respect to time (horizontal axis) in this order.

[0008] In a state where some water is present inside,
When the internal temperature exceeds 100 ° C., the water expands as water vapor, and generates a large negative pressure when the temperature decreases. This negative pressure promotes abrasion of the elastic seal lips of the seals 108, 108, deteriorating the function of the seals 108, 108 and causing water to enter from the seals 108, 108.

As described above, when a large negative pressure is generated in the bearing space S, the larger the negative pressure, the more easily the fluid such as water outside enters through the lip portion 108a of the elastic seal. Has been confirmed. That is, as is apparent from FIG. 29, as the negative pressure becomes larger with respect to the atmospheric pressure (0 kPa) (toward the left side of the horizontal axis in FIG. 29), it becomes easier to draw moisture into the sealed bearing, The amount of mixed water increases. Further, the fact that water is easily drawn in also means that the sealing property is reduced. Then, due to the inflow of water and the deterioration of the sealing property, the deterioration of the lubricant in the bearing space S is promoted, the bearing performance is reduced, and problems such as early damage and early peeling occur.

As a rolling bearing which solves such a problem, the following sealed rolling bearing is disclosed in Japanese Patent Application Laid-Open No. 2000-2000.
No. 104747 discloses this. That is, a rolling element is arranged in a bearing space formed between an outer ring and an inner ring to relatively rotate the outer ring and the inner ring, and a rotary seal member is arranged at both axial ends of the bearing space, In a sealed rolling bearing in which the bearing space is sealed by disposing a stationary seal member on the inner ring side, when the fluid state in the bearing space and the external fluid state have a predetermined relationship, the bearing space in the bearing space is reduced. A sealed rolling bearing having a vent means on the inner ring side for bringing the fluid pressure closer to the external fluid pressure.

FIG. 12 is a longitudinal sectional view of a four-row tapered roller bearing 10 provided with a sealing seal, which is an example of such a sealed rolling bearing. The figure shows the upper half of the longitudinal section not including the axis. A four-row tapered roller bearing 10 (hereinafter referred to as a “sealed rolling bearing”) provided with a sealing seal shown in FIG. 1 includes outer rings 11, 12, 11 and inner rings 13, 12.
, A plurality of rollers 14, 14,... Disposed between the outer rings 11, 11, 12 and the inner ring 13, 13, and retainers 15, 15,. ,
Outer ring spacers 16, 16 disposed between the outer ring 12 and the outer rings 11, 11, seal holders 17, 17 disposed at the ends of the outer rings 11, 11, and supported by the seal holders 17, 17 End seals 18, 18 and a pair of inner rings 1
A concave portion 9 formed on the inner diameter surface of the portion where
And an intermediate seal 19 held by the

The entire outer race is composed of a single row of outer races 11, 11 arranged at both ends in the axial direction, and a double row of outer races 12 arranged between them and having two single row outer races connected to each other. It is configured. On the inner peripheral side of the outer rings 11, 11, and 12,
Each has a tapered surface 11a, 11a, 12a. The entire inner ring is composed of two double-row inner rings 13 arranged in the axial direction.
13. The outer peripheral sides of the inner rings 13 and 13 correspond to the tapered surfaces 11a and 12a of the outer rings 11 and 12, respectively, and form a bearing space S between the tapered surfaces 11a and 12a.

The roll shaft 8 is loosely fitted to the inner races 13, 13. That is, the inner peripheral sides of the inner rings 13 and 13 are fitted to the outer peripheral surface of the roll shaft 8 with a small gap. The left and right ends of the inner rings 13, 13 in the axial direction extend longer than those of the outer rings 11, 11, respectively, and the extended portions have elastic lips 18 of end face seals 18, 18, respectively.
The lip sliding surfaces 13a, 13a with which a, 18a contact are formed.

Rollers 14, 14, 1 of four rows as rolling elements
4 and 14 are disposed in the above-mentioned bearing space S, and include tapered surfaces 11 a and 12 a of the outer rings 11 and 12 and inner rings 13 and 1.
3 contacts the outer peripheral surface. Each roller 14 rotates in a predetermined direction when the inner races 13, 13 rotate with the rotation of the roll shaft 8, whereby the inner races 1, 12 are rotated with respect to the outer races 11, 12.
3, 13 rotate smoothly.

Are arranged in the above-mentioned bearing space S, and four cages 15 are formed in an annular shape.
For each cage 15, a large number of rollers 14, 14,
Are rotatably supported. Outer ring spacers 16, 16
It is a member formed in an annular shape, between the double row outer ring 12 and the single row outer ring 11 on the tip (left) side, and the double row outer ring 12
And a single row of outer races 11 on the base end (right) side.

The seal holders 17 are provided with two outer rings 1.
The distal end of the outer race 11 on the distal end of the outer races 11 (left side in FIG. 12) and the base end of the outer race 11 on the proximal end (rightward in FIG. 12).
, And respectively hold end face seals 18 on the inner peripheral side. The end face seals 18, 18, which are rotary seal members, are provided with the seal holder 1 described above.
The elastic lips 18a, 18a are held on the inner circumferential sides of the inner rings 7, 17, respectively, and contact the lip sliding surfaces 13a, 13a of the inner rings 13, 13, respectively. This allows
The bearing space S of the sealed rolling bearing 10 is sealed.

The intermediate seal 19, which is a stationary seal member,
A concave portion 9 formed on an inner diameter surface side of a contact surface with which the pair of inner rings 13 and 13 are opposed to contact with each other;
Get stuck here and be held here. This intermediate seal 19
Is formed with a vent portion (not shown in FIG. 12) which vents under appropriate pressure. FIG.
FIG. 13 is a partially enlarged cross-sectional view illustrating part A of FIG.
FIG. 3 is a diagram illustrating a structure of an intermediate seal 19. FIG. 13A is an enlarged sectional view of the intermediate seal 19, and FIG.
(B) is an enlarged view of the vent portion of the intermediate seal 19 viewed from the direction of arrow C.

The intermediate seal 19 comprises a mandrel 29 for maintaining the shape, and an elastic body 39 such as rubber, which is in close contact with the recess 9. A flexible lip 59 extends from the main body portion 49 of the elastic body 39. The main body portion 49 contacts the bottom wall and the side wall of the concave portion of the one inner ring 13, and the lip 59 abuts the side wall of the concave portion of the other inner ring 13. As a result, the space between the contact surfaces 13c, 13c of the pair of inner rings 13, 13 is sealed, and the airtightness of the bearing space S is maintained.

On the base side of the lip 59, a vent hole 69 as a vent means is formed. This vent hole 69
Can be formed at appropriate intervals over the entire circumference of the intermediate seal 19. In the middle of the vent hole 69, a partition wall 69
a is formed integrally. The partition 69a is made of a thin elastic material and has a slit 6 extending to both ends through the center.
9b is formed.

The slit 69b serves as a valve mechanism, and is closed when no pressure difference is generated between the inside of the bearing (the bearing space S in FIG. 12) and the outside of the bearing. (For example, when the inside of the sealed rolling bearing 10 becomes a negative pressure), a slight gap is formed. As a result, a vent mechanism is formed, and even when a volume change occurs in the air inside the bearing due to a temperature change inside the bearing during the operation of the sealed rolling bearing 10, the slit 69b allows air to be sucked into the inside of the bearing from the outside of the bearing. Alternatively, air can be discharged from the inside of the bearing to the outside of the bearing, and the pressure difference between the inside and outside can be automatically balanced.

The slit 69b is normally closed unless a considerable pressure is applied, and also has a role of preventing water, contaminants and the like from entering the bearing from the vent hole 69. Here, the slit 69b is located at a position that is less likely to be exposed to a liquid such as water, as compared with a case where a vent hole is provided in the seal holder 17 or the end face seal 18.
Prevention of intrusion of water and the like from the vent hole is ensured.

The slit 69b as described above is formed in the intermediate seal 19 that seals the gap between the inner rings 13, 13. For example, when used in a rolling mill, the housing itself such as a chock is machined. As compared with the case where the pressure is added, the pressure inside the bearing can be made closer to the external pressure by a simpler method, and water or the like can be prevented from entering the inside of the bearing from the vent hole 69.

[0023]

As described above, the advance of the hermetic seal technology has made it possible to prevent the inflow of a fluid such as water and to extend the bearing life to some extent.
However, in the sealed rolling bearing 10 as described above, invasion of gaseous water cannot be prevented, and the effect of extending the life is insufficient.

Rolling water mainly composed of water is injected into the steel rolling mill, and the temperature is high, so that the humidity around the rolling mill is extremely high. Therefore, there still remains a problem that gaseous moisture that has entered the inside of the bearing due to a change in the pressure inside the bearing reduces the life of the bearing. Therefore, the present invention solves such problems of the conventional rolling bearing, has excellent seizure resistance and high corrosion fatigue resistance, and water enters into the inside and mixes with the lubricant. It is an object of the present invention to provide a rolling bearing that can be suitably used even in such a poor lubricating environment.

It is another object of the present invention to provide a sealed rolling bearing having a long service life even when gaseous moisture invades.

[0026]

In order to solve the above problems, the present invention has the following arrangement. That is, the rolling bearing of claim 1 according to the present invention is a rolling bearing including an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring. At least the non-rotating raceway ring of the inner ring and the outer ring has an N concentration of 100 ppm or less, an O concentration of 15 ppm or less, an S concentration of 0.020% or less, a Ti concentration of 50 ppm or less, and a Ni concentration of 50 ppm or less.
It is composed of steel having a concentration of 1 to 5%, a P concentration of 0.020% or less, and a Mo concentration of 0.1 to 5%, and has a C concentration of 0.6 to 1. 2%, and the residual compressive stress of the raceway surface is set to 100 to 500 MPa.

Since the rolling bearing having such a configuration has excellent seizure resistance and high corrosion fatigue resistance, poor lubrication such that water enters the inside and mixes with the lubricant. It can be suitably used even in an environment. In a poor lubrication environment where moisture is mixed in the lubricant,
Since rolling fatigue is likely to occur starting from the former austenite grain boundary of the rolling surface (the raceway surface of the raceway or the rolling surface of the rolling element), the fatigue life of the rolling bearing is greatly reduced. this is,
If water is present between the rolling element and the bearing ring, an oil film is less likely to be formed, so that the rolling element and the bearing ring are likely to make metal contact with each other. This is because the rolling surface starts peeling from carbides or nonmetallic inclusions in the boundary.

The non-rotating bearing ring, in which the product of the contact surface pressure and the stress repetition rate is the largest in the rolling bearing, is the most stress-loaded zone of the non-rotating raceway, and is most susceptible to corrosion fatigue. . Accordingly, the stress load zone of the non-rotating raceway, that is, the raceway surface of the non-rotating raceway, that is, the raceway surface and its vicinity (depth range up to 2% (2% Da) of the rolling element diameter) It is effective to increase the corrosion fatigue strength of (1) to extend the life of the rolling bearing.

In order to increase the corrosion fatigue strength without impairing the galling resistance of the rolling bearing, it is not always necessary to increase the corrosion resistance of the bearing material. It is indispensable to strengthen the grain boundaries) and to apply a residual compressive stress to the raceway surface. In order to strengthen the grain boundary, it is effective to reduce the grain size of the prior austenite crystal and to refine the carbide, nitride, nonmetallic inclusion, and phosphorus compound in the grain boundary.

First, the miniaturization of carbide will be described.
When water enters the inside of the rolling bearing, hydrogen is generated from the water. Then, the hydrogen causes hydrogen embrittlement at the grain boundaries on the raceway surface, and the grain boundaries are easily peeled off. In order to suppress such separation of the grain boundaries, the carbide is refined to form a large number of interfaces of the carbide crystal through which hydrogen atoms pass, and the hydrogen is dispersed in inclusions that are often present at the interface of the carbide crystal. It is effective. Then, since hydrogen is dispersed and embrittlement hardly occurs, the effect of retarding hydrogen embrittlement flaking is imparted.

In order to refine the carbides at the grain boundaries, the carbon concentration of the raceway surface of the (finished product) ring after carburizing (carbonitriding) treatment and quenching / tempering is set to 0.6 to 0.6%.
It must be 1.2% by mass. If it is less than 0.6% by mass, it is difficult to set the hardness to HRC 58 or more, and the corrosion fatigue resistance may decrease. In addition, 1.2 mass%
If it exceeds 300, the carbides at the grain boundaries tend to become coarse.

Further, since Ni is an element having an effect of refining old austenite crystal grains, the Ni concentration in steel is preferably set to 1.0% by mass or more. However,
If it exceeds 5.0% by mass, austenite is stabilized,
If the hardness decreases, or if annealing is performed after carburizing, annealing may be difficult. Further, Mo is an element having an effect of refining carbides at grain boundaries, so that the Mo concentration in steel is preferably set to 0.1% by mass or more. However,
If it exceeds 5.0% by mass, Mo is solid-dissolved in the matrix during quenching, so that the quenching temperature needs to be significantly increased, which is uneconomical.

Next, the nitride will be described. Since the compound of iron and nitrogen (N) is hard and brittle, and significantly reduces the strength of the grain boundary, it is necessary to reduce the nitrogen concentration in the steel to 100 ppm or less. The lower the nitrogen concentration, the better, but the cost of steelmaking tends to increase. The steel satisfying this condition (N concentration) includes VAR steel (remelted steel), and the steel constituting the rolling bearing of the present invention includes:
Preferably, VAR steel is used.

Next, non-metallic inclusions will be described. Oxygen (O), sulfur (S), and Ti are elements that form non-metallic inclusions at grain boundaries, and reduce the rolling fatigue life. Therefore, in order to improve the corrosion fatigue resistance, a smaller amount is preferable, and the oxygen concentration in the steel is 15 ppm or less,
Sulfur concentration of 0.020 mass% or less, Ti concentration of 50 pp
m or less. However, in order to improve the corrosion fatigue resistance, a smaller amount is preferable, but the cost of steelmaking tends to increase.

The same applies to phosphorus compounds.
In order to improve the corrosion fatigue resistance, it is more preferable that the P content be less than 0.020% by mass. Next, the residual compressive stress will be described. Giving a residual compressive stress of 100 MPa or more to the raceway surface is effective in improving corrosion fatigue resistance. However, 5
If it exceeds 00 MPa, tensile stress acting on the raceway surface due to slip (tangential force acting on the raceway surface when metal contact occurs)
And conversely reduce the corrosion fatigue resistance. The method for applying the residual compressive stress to the raceway is not particularly limited, but a method by carburizing and quenching is economical and preferable.

According to a second aspect of the present invention, there is provided a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring. In at least one of the inner ring and the outer ring, the non-rotating raceway has an N concentration of 100 ppm or less, a C concentration of 0.05 to 0.45%, and a numerical value of the Ni concentration as Cr concentration and Mo concentration. , Mn concentration is 1.0 to 3.2.

With such a configuration, the above-described claim 1 is provided.
As with rolling bearings, it has excellent seizure resistance and high corrosion fatigue resistance, so it is suitable for use in poor lubricating environments where water can penetrate and mix into lubricants. It is possible. The three elements Cr, Mo, and Mn are effective for improving hardenability and are carbide forming elements, and thus have the effect of improving the hardness and wear resistance of steel.
On the other hand, it tends to decrease the strength and ductility of steel,
In particular, if the amounts of these three elements are too large, harmful carbides are likely to precipitate at grain boundaries in a corrosive fatigue environment. On the other hand, N
i does not form carbides and has the effect of improving toughness and ductility.

As a result of intensive studies on such points,
The present inventors have found that by controlling the quantitative ratio between the three elements and Ni in steel, the corrosion fatigue resistance can be increased. That is, the numerical value of the Ni concentration is C
The value divided by the sum of the respective values of the r concentration, the Mo concentration, and the Mn concentration needs to be 1.0 to 3.2. This can be expressed by the following equation.

1.0 ≦ Ni% / (Cr% + Mo% + Mn%) ≦ 3.2 where Ni%, Cr%, Mo%, and Mn% are the respective concentrations of Ni, Cr, Mo, and Mn in the steel. (%). In order to make the corrosion fatigue resistance excellent, in addition to these conditions, it is necessary to simultaneously satisfy the two conditions of N concentration of steel of 100 ppm or less and C concentration of 0.05 to 0.45%. .

However, since each of these elements has characteristics other than those described above, it is preferable that the concentration of each element simultaneously satisfies the following conditions. First, the C concentration will be described. The bearing ring made of the steel is usually subjected to a surface treatment, and a surface hardened layer is provided to form a finished bearing ring. Since the core of the raceway of the finished product is made of the above-mentioned steel, the C concentration is set to 0.1 in order to impart compressive residual stress.
It must be 45% or less. However, if sufficient core hardness is not obtained, there is a risk of causing premature peeling, so the C concentration needs to be 0.05% or more.

Next, the C concentration on the surface of the completed bearing ring will be described. As described above, when water enters the inside of the rolling bearing, hydrogen is generated from the water, so that the grain boundary on the raceway surface becomes hydrogen-brittle and the grain boundary is easily separated.
Therefore, in order to suppress such separation of the grain boundaries, it is preferable to refine the carbide. As described above, in order to make the carbides at the grain boundaries fine, the C of the raceway surface of the finished race ring after carburizing (carbonitriding) treatment and quenching / tempering is set to 0.6 to 1.0. Must be 2%.
If it is less than 0.6%, it is difficult to increase the hardness to 58 or more, and the corrosion fatigue strength may be reduced. On the other hand, if it exceeds 1.2%, the carbides at the grain boundaries tend to become coarse.

Next, the N concentration will be described. Since N forms carbonitride at the grain boundary, the N concentration is 100 pp.
m or less. However, when the N concentration is 50 ppm
If it is less than 1, the crystal grains become coarse, so that it is preferably at least 50 ppm. Next, the Ni concentration will be described. For the same reason as in the case of the above-mentioned rolling bearing of claim 1, the Ni concentration in the steel is preferably set to 1.0 to 5.0%.

Next, the Cr concentration will be described. Since Cr is an element that improves hardenability and promotes spheroidization of carbide, the Cr concentration is preferably set to 0.35% or more. However, if it exceeds 1.6%, carbides become coarse and the average crystal grains become large, and the machinability may be deteriorated. Therefore, the upper limit is preferably made 1.6%.

Next, the Mo concentration will be described. The Mo concentration is preferably set to 0.1 to 5.0% for the same reason as in the case of the rolling bearing of claim 1 described above. Next, the Mn concentration will be described. Mn is an element necessary as a deoxidizing agent and a desulfurizing agent at the time of steel making, and is an element effective for improving hardenability. Therefore, 0.1% or more is necessary. , Not only lowers the machinability but also lowers the corrosion resistance by coexisting with impurities such as S and P, so that the Mn concentration is preferably 1.5% or less.

Further, it is preferable that the elements other than those described above also satisfy the following conditions. First, the Si concentration will be described. Si is used as a deoxidizing agent in steelmaking at 0.1
% Or more, and has the effect of increasing the tempering softening resistance. However, if added in a large amount, the toughness is reduced and the penetration depth is rapidly reduced during carbonitriding. It is preferably set to 0.5%.

Next, oxygen (O), sulfur (S), Ti
Will be described. As described above, these elements are elements that form nonmetallic inclusions at the grain boundaries, and thus may reduce the rolling fatigue life. Therefore, for the same reason as in the rolling bearing of claim 1, the oxygen concentration in the steel is 15 ppm or less and the sulfur concentration is 0.025%.
Hereinafter, the Ti concentration needs to be 50 ppm or less. However, in order to improve the corrosion fatigue resistance, a smaller amount is preferable, but the cost of steelmaking tends to increase.

The same applies to phosphorus compounds.
In order to improve the corrosion fatigue resistance, it is more preferable that the P concentration be less than 0.025%. The rolling bearings according to the first and second aspects of the present invention are used in a poor lubricating environment in which water enters and mixes with a lubricant, such as a rolling bearing for a work roll of a rolling mill. Although it is particularly suitable as a rolling bearing to be used, it is a matter of course that the rolling bearing has an excellent life even when used in other environments.

Further, a sealed rolling bearing according to a third aspect of the present invention, wherein the plurality of rolling elements are provided so as to freely roll in a bearing space formed between the inner ring, the outer ring, and the inner ring and the outer ring. A moving body, a rotating seal member disposed at both axial ends of the bearing space, and a stationary seal member disposed on the inner race; and the bearing space is formed by the rotational seal member and the stationary seal member. In a sealed rolling bearing, with a vent means for bringing the fluid pressure in the bearing space closer to the external fluid pressure, at least the non-rotating raceway ring of the inner ring and the outer ring, the N concentration is 100 ppm or less, The race is made of steel having an O concentration of 15 ppm or less, an S concentration of 0.020% or less, a Ti concentration of 50 ppm or less, a Ni concentration of 1 to 5%, and a P concentration of 0.020% or less. 0.6 The C concentration of the raceway surface comprising
1.2%, and the residual compressive stress of the raceway surface is 100 to 5
It is characterized by being set to 00 MPa.

Further, a sealed rolling bearing according to a fourth aspect of the present invention is provided with a plurality of rollingly disposed rolling bearings formed in an inner ring, an outer ring, and a bearing space formed between the inner ring and the outer ring. A rolling element, a rotary seal member disposed at both axial ends of the bearing space, and a stationary seal member disposed on the inner race, and the bearing is formed by the rotary seal member and the stationary seal member. In a rolling bearing having a sealed space, a vent means for bringing the fluid pressure in the bearing space closer to the external fluid pressure is provided, and at least the non-rotating raceway ring of the inner ring and the outer ring has an N concentration of 100 ppm or less. , O concentration 15 ppm or less, S concentration 0.020% or less, Ti concentration 50 ppm or less, Ni
It is composed of steel having a concentration of 2 to 5%, a P concentration of 0.020% or less, a Mn concentration of 1.0% or less, a Mo concentration of 0.05 to 5%, and a Cr concentration of 1.5% or less, The C content of the raceway surface of the raceway is set to 0.6 to 1.2%, and the residual compressive stress of the raceway surface is set to 100 to 500 MPa. preferable.

Rolling parts of high hardness such as the outer ring, inner ring and rolling elements of a rolling bearing may have high humidity when the air in contact therewith is high.
Rolling fatigue strength tends to decrease significantly. Rust does not always occur on the rolling surface, but the rolling fatigue strength is reduced by microscopic corrosion fatigue starting from the grain boundary of the rolling surface. And the damage form is peeling or peeling.

The non-rotating raceway, in which the product of the contact surface pressure and the number of stress repetitions is the largest in the bearing, is the most stress-loaded zone of the non-rotating raceway, and is thus easily peeled off. Increasing the fatigue strength is effective in extending the life of the rolling bearing. In order to increase the corrosion fatigue strength of a rolling bearing without impairing its seizure resistance, it is not necessary to increase the corrosion resistance of the bearing material. It is essential to apply stress. That is, in order to increase the corrosion fatigue strength of the rolling bearing, it is necessary to increase the corrosion fatigue strength of the rolling surface of the non-rotating side race.

In order to strengthen the grain boundaries, it is effective to reduce the amount of nitride present at the grain boundaries. This is because the compound of iron and nitrogen significantly lowers the grain boundary strength. It is also effective to reduce the size of carbides, nonmetallic inclusions, and phosphorus compounds present at the grain boundaries. In order to apply a residual compressive stress to the rolling surface, it is economical to perform carburizing and quenching.

In order to reduce the amount of nitride present at the grain boundaries on the rolling surface, it is necessary to reduce the nitrogen concentration of the material to 100 ppm or less. In addition, since the rate of nitrogen entering the rolling surface due to carbonitriding, which is one of the surface hardening methods, is low in the grain boundaries, the carbonitriding process can be used as the surface hardening method, but the nitrogen concentration on the rolling surface is low. 0.3
% Must be capped.

In order to refine the carbide present at the grain boundaries,
It is necessary to reduce the total amount by lowering the carbon concentration of the rolling surface to 1.2% or less, and to add 1% or more, preferably 2% or more of Ni. Further, setting the Mo concentration to 0.05% or more and the Cr concentration to 1.5% or less is more effective for miniaturizing carbides. Further, when the carbon concentration on the surface is less than 0.6%, the fatigue strength is reduced. Further, if Ni is added in excess of 5%, annealing after carburizing becomes difficult, so it is necessary to make it 5% or less. Further, if Mo is added in excess of 5%, the quenching temperature becomes extremely high, so that it is not economical.
% Or less.

To refine the nonmetallic inclusions at the grain boundaries, it is necessary to reduce the oxygen concentration to 15 ppm or less, the sulfur concentration to 0.020% or less, and the Ti concentration to 50 ppm or less.
When the Mn concentration is set to 1.0% or less, MnS becomes small, so that miniaturization of nonmetallic inclusions at grain boundaries is promoted. When the residual compressive stress on the rolling surface is 100 MPa or more, it is effective for improving the corrosion fatigue strength. However, if it exceeds 500 MPa, the tensile stress in the direction perpendicular to the raceway surface cannot be ignored, and conversely, the corrosion fatigue strength decreases, which is not preferable.

[0056]

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. (First Embodiment) FIG. 1 is a sectional view showing the structure of a tapered roller bearing 1 which is a first embodiment of a rolling bearing according to the present invention, together with the structure of a life tester.

The tapered roller bearing 1 includes an inner ring 2 and an outer ring 3.
And a plurality of rollers 4 rotatably arranged between the inner ring 2 and the outer ring 3, and a retainer 5 for holding the rollers 4. The tapered roller bearing 1 has an inner diameter of 85 mm, an outer diameter of 130 mm, an assembly width of 29 mm, and a basic dynamic load rating C = 1.
43 kN, basic static load rating C ₀ = 231 kN, diameter of roller 4 (average diameter) 10.6 mm.
It is composed of steel having the composition shown in FIGS. Then, after adjusting the surface of the outer ring 3 to various carbon concentrations by carburizing treatment, the outer ring 3 was completed by grinding.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

[0062]

[Table 5]

[0063]

[Table 6]

The tapered roller bearing 1 was mounted on a life tester as shown in FIG. 1 and a life test was conducted. That is, the outer ring 3 (fixed wheel) was incorporated in the housing 7, the inner ring 2 (rotating wheel) was fitted to the rotating shaft 6, and a life test was performed while rotating the rotating shaft 6. In that case,
A radial load Fr and an axial load Fa were applied to the tapered roller bearing 1, and water was intermittently injected into the tapered roller bearing 1. The inner ring 2 and the rollers 4 were made of case hardened steel SAE5120. In addition, the rolling surface (inner ring 2
And the raceway surface of the outer ring 3 and the rolling surface of the roller 4) have a surface roughness of about 0.1 μmRa.

The test conditions were as follows: radial load Fr = 71.5
kN, the axial load Fa = 15.6 kN, and the rotation speed of the inner ring 2 is 2500 rpm. The lubricant is L
i A grease composed of a soap (thickening agent) and a base oil having a viscosity of VG64, and 60 g was used. Further, for water injection, 20 ml of water was injected once every three hours. At this time, in order to prevent water leakage, a rubber seal (O-ring) is mounted between the rotating shaft 6 and the housing 7 of the life tester. The test temperature is about 60 ° C and the rated fatigue life (10
% Calculated lifetime) is 67 hours.

The inner ring 2, outer ring 3, and rollers 4 of the tapered roller bearing 1 have an effective hardening depth (surface layer thickness of Vickers hardness Hv550 or more) of 1.5 mm by quenching and tempering after carburization. . The carbon concentration on the surface is adjusted by the dew point at the time of carburization, and is set to various levels within a range of 0.40 to 1.50% by mass. However, inner ring 2
The carbon concentration on the surfaces of the rollers 4 and 0.9 is 0.9% by mass.
The surface hardness of the raceway surface and the rolling surface of the roller 4 is HRC62. The surface hardness of the raceway surface of the outer race 3 is HRC 55 to 62 as shown in Tables 2, 4, and 6.

[0067] By the time half of the tested bearings to cause peeling (L ₅₀ life) were evaluated life. The results of the life test are shown in the rightmost columns of Tables 2, 4, and 6. All of the exfoliated portions were in the stress load zone of the outer ring 3. Incidentally, the residual stress σ _{R on} the raceway surface is obtained by removing the surface layer by 50 μm by electropolishing,
The surface stress was measured by the X-ray method. A negative value of the residual stress σ _R in Tables 2, 4, and 6 indicates that the stress is a compressive stress. The outer ring 3 having the residual stress σ _R of −500 and −600 MPa is subjected to shot peening.

FIGS. 2 to 10 show graphs of the results of Examples and Comparative Examples in Tables 1 to 6. Graph in Figure 2-10, N concentration of the L ₅₀ life and the outer ring 3, O concentrations, S concentration, T
The relationship among the i concentration, the Ni concentration, the P concentration, the Mo concentration, the C concentration on the raceway surface, and the residual stress σ _R on the raceway surface is shown. The points enclosed by the ellipses in the graphs indicate that the variables on the horizontal axis satisfy the conditions of the present invention, but other variables do not satisfy the conditions of the present invention.

From these figures, it can be seen that in a lubricating environment where water is mixed in the lubricant, the steel constituting the outer ring 3 (non-rotating side raceway) has an N concentration of 100 ppm or less and an O concentration of 1%.
5 ppm or less, S concentration of 0.020 mass% or less, Ti concentration of 50 ppm or less, Ni concentration of 1 to 5 mass%, P concentration of 0.020 mass% or less, and Mo concentration of 0.1 to 5 mass%. It can be seen that the tapered roller bearing 1 has a long life.

Similarly, when the C concentration on the raceway surface of the outer race 3 is 0.6 to 1.2 mass% and the residual compressive stress on the raceway surface of the outer race 3 is 100 to 500 MPa, the tapered roller bearing 1 has a longer length. It can be seen that the life is reached. Second Embodiment Next, a life test similar to that of the first embodiment was performed on a tapered roller bearing having exactly the same configuration as the tapered roller bearing 1 of the first embodiment except for the following points (tapered roller bearing). The description of the configuration and test conditions will be omitted.) The difference from the tapered roller bearing 1 of the first embodiment is that the outer ring is made of steel having the composition shown in Tables 7 to 9, and the carbon concentration on the inner ring, outer ring, and roller surfaces is 0.9%. The three points are that they are unified, and the residual stress and hardness of the raceway surface of the outer ring are not measured.

[0071]

[Table 7]

[0072]

[Table 8]

[0073]

[Table 9]

[0074] Then, the results of measuring the lifetime (L ₁₀ life) of each bearing, numerical concentration of Cr Ni concentration in the steel, M
The results are shown in Tables 10 to 12 together with the values obtained by dividing the respective values of the o concentration and the Mn concentration by the sum of the numerical values, and FIG. 11 shows a graph thereof.

[0075]

[Table 10]

[0076]

[Table 11]

[0077]

[Table 12]

In Examples 17 to 25, the C concentration was 0.05 to
0.45%, the N concentration is 100 ppm or less, and the value obtained by dividing the numerical value of the Ni concentration by the sum of the numerical values of the Cr concentration, Mo concentration, and Mn concentration satisfies all three conditions of 1.0 to 3.2. . Therefore, the tapered roller bearing has a long life even in a poor lubrication environment in which water enters and mixes with the lubricant.

On the other hand, Comparative Examples 22 to 39 do not satisfy at least one of the above three conditions, and thus have a short life. (Third Embodiment) FIGS. 12 and 13 show a four-row tapered roller bearing 10 according to a third embodiment of the rolling bearing according to the present invention.
It is sectional drawing which shows the structure of (sealed rolling bearing). In addition,
Its structure is the same as that of the conventional 4 described in the section of the prior art.
The description is omitted because it is the same as the row tapered roller bearing.

However, the outer rings 11, 11, 1 which are fixed wheels
2 has an N concentration of 100 ppm or less and an O concentration of 15 ppm
Hereinafter, the S concentration is 0.020% or less, and the Ti concentration is 50 pp.
m, Ni concentration 1-5%, P concentration 0.020% or less, Mn concentration 1.0% or less, Mo concentration 0.05-5.
%, And a steel having a Cr concentration of 1.5% or less.
The concentration is 0.6 to 1.2%, and the residual compressive stress on the raceway surface is 100 to 500 MPa.

Next, a description will be given of the results of evaluating the life of such a sealed rolling bearing under conditions in which liquid water is prevented from entering the bearing, but gaseous water is allowed to enter. . In this life test, instead of testing the sealed rolling bearing 10 under the above conditions, a bearing similar to the tapered roller bearing 1 of the first embodiment is mounted on a life testing machine as shown in FIG. This was performed while supplying air (humid air) at 120 ° C. saturated with water to the inside of the tapered roller bearing 1 (the supplied air is led out of the inside of the bearing by a pipe (not shown)). ).

The configuration and test conditions of the tapered roller bearing used in the life test are the same as those in the first embodiment, and therefore, description thereof will be omitted. However, the composition of the steel constituting the outer ring 3 and the properties of the raceway surface of the outer ring 3 are as shown in Tables 13 to 20. And the test temperature is 120 ° C.

[0083]

[Table 13]

[0084]

[Table 14]

[0085]

[Table 15]

[0086]

[Table 16]

[0087]

[Table 17]

[0088]

[Table 18]

[0089]

[Table 19]

[0090]

[Table 20]

[0091] By the time half of the tested bearings to cause peeling (L ₅₀ life) were evaluated life. The results of the life test are shown in the rightmost columns of Tables 14, 16, 18, and 20.
All of the exfoliated portions were in the stress load zone of the outer ring 3. The residual stress σ _{R on} the raceway surface was 50 μm for the surface layer by electropolishing.
After the removal, the surface stress was measured by the X-ray method. Table 1
Negative values of the residual stress σ _{R in} 4, 16, 18, and 20 indicate compressive stress. The outer ring 3 having the residual stress σ _R of −500 and −600 MPa is subjected to shot peening.

Graphs of the results of Examples and Comparative Examples in Tables 13 to 20 are shown in FIGS. Figures 14-2
4 graphs, N concentration of L ₅₀ life and the outer ring 3, O concentrations, S
Concentration, Ti concentration, Ni concentration, P concentration, C concentration of track surface,
The relationship between the residual stress σ _{R on} the raceway surface, the Mo concentration, the Mn concentration, and the Cr concentration is shown, respectively. From these figures, in an environment where moist air enters the bearing,
The steel constituting the outer ring 3 (non-rotating raceway) has an N concentration of 100 ppm or less, an O concentration of 15 ppm or less, an S concentration of 0.020 mass% or less, a Ti concentration of 50 ppm or less, and a Ni concentration of 50 ppm or less.
The concentration is 1 to 5% by mass, the P concentration is 0.020% by mass or less,
When the Mo concentration is 0.05 to 5% by mass, the Mn concentration is 1.0% or less, and the Cr concentration is 1.5% or less, the tapered roller bearing 1
It can be seen that has a long life.

Similarly, when the C concentration on the raceway surface of the outer race 3 is 0.6 to 1.2 mass% and the residual compressive stress on the raceway surface of the outer race 3 is 100 to 500 MPa, the tapered roller bearing 1 has a longer length. It can be seen that the life is reached. Note that 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 tapered roller bearing has been described as an example of a rolling bearing. However, the rolling bearing of the present invention can, of course, be applied to other types of rolling bearings. For example, there are radial rolling bearings such as deep groove ball bearings, angular ball bearings, cylindrical roller bearings, and needle roller bearings, and thrust rolling bearings such as thrust ball bearings and thrust roller bearings.

The type of grease is not limited to that used in the present embodiment, and ordinary grease commonly used for rolling bearings can be used.

[0096]

As described above, the rolling bearing of the present invention has excellent seizure resistance and high corrosion fatigue strength.
It can be suitably used even in a poor lubrication environment in which water enters and mixes with the lubricant. In addition, the sealed rolling bearing of the present invention has a long service life even if gaseous moisture enters, without causing problems such as early damage and early peeling.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing the structure of a tapered roller bearing, which is a first embodiment of a rolling bearing according to the present invention, together with the structure of a life tester.

2 is a graph showing the relationship between the N concentration and L ₅₀ life in the first embodiment.

3 is a graph showing the relationship between the O 2 concentration and the L ₅₀ life in the first embodiment.

4 is a graph showing the relationship between S concentration and the L ₅₀ life in the first embodiment.

5 is a graph showing the relationship between the Ti concentration and the L ₅₀ life in the first embodiment.

6 is a graph showing the relationship between the Ni concentration and the L ₅₀ life in the first embodiment.

7 is a graph showing the relationship between the P concentration and the L ₅₀ life in the first embodiment.

8 is a graph showing the relationship between the Mo content and the L ₅₀ life in the first embodiment.

9 is a graph showing the relationship between C concentration of the raceway surface and the L ₅₀ life in the first embodiment.

FIG. 10 shows the residual stress σ _{R on the} raceway surface in the first embodiment.
4 is a graph showing the relationship between the L50 and _L50 life.

FIG. 11 is a graph showing the relationship between the Ni concentration and the C value in the second embodiment;
r concentration is a graph showing the relationship between the Mo content and the value obtained by dividing the sum of the numerical values of Mn concentration and L ₁₀ life.

FIG. 12 is a longitudinal sectional view showing a structure of a four-row tapered roller bearing which is a third embodiment of the rolling bearing according to the present invention.

13 is an enlarged sectional view showing a structure of a peripheral portion of the intermediate seal of the bearing shown in FIG. 12, and a diagram for explaining a main part of the intermediate seal.

14 is a graph showing the relationship between the N concentration and L ₅₀ life in the third embodiment.

15 is a graph showing the relationship between the O 2 concentration and the L ₅₀ life in the third embodiment.

16 is a graph showing the relationship between S concentration and the L ₅₀ life in the third embodiment.

17 is a graph showing the relationship between the Ti concentration and the L ₅₀ life in the third embodiment.

18 is a graph showing the relationship between the Ni concentration and the L ₅₀ life in the third embodiment.

19 is a graph showing the relationship between the P concentration and the L ₅₀ life in the third embodiment.

FIG. 20 shows the C concentration and L _{50 on the} raceway surface in the third embodiment.
It is a graph which shows the relationship with a service life.

FIG. 21 shows residual stress σ _{R on the} raceway surface in the third embodiment.
4 is a graph showing the relationship between the L50 and _L50 life.

22 is a graph showing the relationship between the Mo content and the L ₅₀ life in the third embodiment.

23 is a graph showing the relationship between the Mn concentration and the L ₅₀ life in the third embodiment.

FIG. 24 is a graph showing the relationship between the Cr concentration and the L ₅₀ life in the third embodiment.

FIG. 25 is a longitudinal sectional view showing the structure of a conventional sealed rolling bearing.

26 is an enlarged view illustrating a main part of an intermediate seal of the sealed rolling bearing in FIG. 25.

FIG. 27 is an enlarged cross-sectional view showing a structure of a peripheral portion of a different kind of intermediate seal from FIG. 26;

28A and 28B show the relationship between (a) rotation speed, (b) bearing internal temperature,
(C) It is a graph which shows a bearing internal pressure.

FIG. 29 is a graph showing the relationship between the pressure inside the bearing and the amount of water mixed into the inside of the bearing in the conventional sealed rolling bearing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tapered roller bearing 2 Inner ring 3 Outer ring 4 Roller 9 Intermediate seal 10 Four row tapered roller bearing 11, 12 Outer ring 13 Inner ring 14 Roller 18 End face seal 69 Vent hole S Bearing space

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J016 AA04 BA03 BB03 3J101 AA16 AA25 AA32 AA42 AA44 AA54 AA62 BA70 DA02 DA11 EA04 FA08 GA36

Claims (4)

[Claims] 1. A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring, wherein at least one of the inner ring and the outer ring does not rotate. In the side race, the N concentration is 100 ppm or less and the O concentration is 15 ppm
Hereinafter, the S concentration is 0.020% or less, and the Ti concentration is 50 pp.
m, a Ni concentration of 1 to 5%, a P concentration of 0.020% or less, and a Mo concentration of 0.1 to 5%. 6-1.2%
A rolling bearing, wherein the residual compressive stress on the raceway surface is set to 100 to 500 MPa. 2. A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring, wherein at least one of the inner ring and the outer ring does not rotate. When the N-concentration is 100 ppm or less and the C-concentration is 0.05-
0.45%, and the numerical value of the Ni concentration is the Cr concentration,
The value divided by the sum of the respective values of the Mo concentration and the Mn concentration is 1.0.
A rolling bearing characterized in that the rolling bearing is made of steel having a size of about 3.2. 3. An inner ring, an outer ring, a plurality of rolling elements rotatably disposed in a bearing space formed between the inner ring and the outer ring, and disposed at both axial ends of the bearing space. A rolling bearing, comprising a provided rotary seal member and a stationary seal member disposed on the inner race, and wherein the bearing space is sealed by the rotary seal member and the stationary seal member. A vent means for bringing the fluid pressure closer to the external fluid pressure is provided. At least the non-rotating raceway of the inner ring and the outer ring has an N concentration of 100 ppm or less and an O concentration of 15 ppm.
Hereinafter, the S concentration is 0.020% or less, and the Ti concentration is 50 pp.
m, a Ni concentration of 1 to 5%, and a P concentration of 0.020% or less. The C concentration of the raceway surface of the race is 0.6 to 1.2%.
And the residual compressive stress of the raceway surface is 100 to 500MP.
a sealed rolling bearing characterized in that: a. 4. An inner ring, an outer ring, a plurality of rolling elements rotatably disposed in a bearing space formed between the inner ring and the outer ring, and disposed at both axial ends of the bearing space. A rolling bearing, comprising a provided rotary seal member and a stationary seal member disposed on the inner race, and wherein the bearing space is sealed by the rotary seal member and the stationary seal member. A vent means for bringing the fluid pressure closer to the external fluid pressure is provided. At least the non-rotating raceway of the inner ring and the outer ring has an N concentration of 100 ppm or less and an O concentration of 15 ppm.
Hereinafter, the S concentration is 0.020% or less, and the Ti concentration is 50 pp.
m, Ni concentration 2-5%, P concentration 0.020% or less, Mn concentration 1.0% or less, Mo concentration 0.05-5.
%, And a steel having a Cr concentration of 1.5% or less, wherein the C concentration of the raceway surface of the race is 0.6 to 1.2%.
And the residual compressive stress of the raceway surface is 100 to 500MP.
a sealed rolling bearing characterized in that: a.