JP2003268497A - Roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roller bearing which has a long life at high temperatures and an improved resistance to cracks caused by fitting to the main shaft. <P>SOLUTION: This roller bearing has an inner ring, an outer ring, and a bearing ring having rolling elements and is formed from steel comprising 0.1-0.4 mass% C, 0.3-3.0 mass% Si, 0.2-2.0 mass% Mn, 0.03 mass% or lower P, 0.03 mass% or lower S, 0.3 mass% or higher but lower than 2.5 mass% Cr, 0.1 mass% or higher but lower than 2.0 mass% Ni, 0.05 mass% or lower Al, 0.003 mass% or lower Ti, 0.0015 mass% or lower O, 0.0025 mass% or lower N, and the balance being Fe and unavoidable impurities. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a rolling bearing, and more particularly to a rolling bearing which is used in a high temperature environment while the bearing is fitted in a negative gap with a main shaft.

[0002]

2. Description of the Related Art FIG. 1 is a sectional view of a conventional rolling bearing.

The rolling bearing supports the load acting on the rotating shaft 2. The rolling bearing 1 has an inner ring 3 which is a rotating wheel.
And an outer ring 4 which is a stationary wheel, and a rolling element 5 formed of steel balls or rollers.

The material most frequently used for rolling bearings is high carbon chromium bearing steel (hereinafter referred to as bearing steel). When it is hardened by quenching,
When the retained austenite is present in the microstructure, the retained austenite is decomposed by being kept at high temperature during use, and a dimensional change occurs with the phase transformation. Therefore, a bearing used in a high temperature atmosphere is usually subjected to a tempering treatment at a high temperature after quenching, and a heat treatment for preliminarily decomposing residual austenite which is unstable to heat.

In this case, although the dimensional stability can be secured,
Inevitably, the life is shortened as the hardness decreases.

Further, in order to improve the steel property of the bearing, the bearing has a negative gap with the main shaft (when the inner ring 3 and the shaft 2 are in a free state, the difference between the outer diameter of the shaft 2 and the inner diameter of the inner ring 3). ) Is used by fitting together. In this case, a tensile stress is generated on the raceway surface of the inner ring due to the fitting between the inner ring and the main shaft, and an axial crack is generated in the inner ring due to repeated compressive stress during rolling and tensile stress due to the fitting. May occur. As a countermeasure, it is possible to use carburized steel in which compressive residual stress is formed in the surface layer.

[0007]

Depending on the application, bearings are fitted to the main shaft with a negative clearance, such as bearings for machine tools, supporting bearings for dryer rolls of papermaking machines, bearings for traction motors, etc. There are bearings used under severe conditions that they are used in a high temperature environment. Fully hardened steel such as bearing steel has low cracking strength and impact strength. Even if the rolling bearing is damaged, cracking of the bearing ring may damage the main shaft and housing. As mentioned above, carburized steel may be used for the purpose of avoiding crack defects.

[0008] However, heretofore, there has not been found a technique for stably supplying a rolling bearing which is a carburized steel having heat resistance and which has a long life and high dimensional stability under high temperature conditions.

[0009] For rolling bearings for aircraft jet engines, there is M50 carburized steel sheet M50NiL, but the material cost is high, the heat treatment process is complicated, the cost is high for manufacturing the bearing, and the application is very small. Limited.

Therefore, it is an object of the present invention to provide an improved rolling bearing capable of maintaining a long life and high dimensional stability under high temperature conditions.

[0011]

A rolling bearing according to a first aspect of the present invention is a rolling bearing that supports a main shaft that makes a rotary motion, and includes a bearing ring including an inner ring and an outer ring. The inner ring contains at least 0.1% of C in mass% as an alloy element component.
Or more and 0.4% or less, Si 0.3% or more and 3.0% or less,
Mn 0.2% or more and 2.0% or less, P 0.03% or less, S 0.03% or less, Cr 0.3% or more, 2.5
%, Ni 0.1% or more, less than 2.0%, Al 0.05% or less, Ti 0.003% or less, O 0.0.
It is formed from a steel material containing 015% or less, N of 0.025% or less, and the balance Fe and unavoidable impurities.

Next, the reasons for limiting the content of the chemical component of the present invention will be explained. First, the C content (0.1% or more and 0.4% or less) will be described. C affects the hardness of the core after carburizing or carbonitriding. In order to secure the hardness of the core required to obtain the strength required for the rolling bearing, the content of 0.1% or more is required. However, when the content of C exceeds 0.4%, the toughness, hot workability and machinability deteriorate, so the upper limit of the content must be 0.4%.

Next, the content of Si (0.3% to 3.0%
The following) will be described. Si has the effect of suppressing softening of the member in the high temperature region and improving the heat resistance of the rolling bearing component. However, if the content is less than 0.3%, the effect cannot be obtained, and it is necessary to set the lower limit of the content to 0.3%. Moreover, although the heat resistance improves as the content increases, even if the content exceeds 3.0%, the effect is saturated and the hot workability and machinability are deteriorated. It is necessary to set the upper limit of to 3.0%.

Next, the content of Mn (0.2% to 2.0%
The following) will be described. Mn is an element that improves the hardenability of steel materials. To get that effect, 0.2%
It is necessary to add above. However, if added over 2.0%, the machinability is significantly reduced, so the upper limit of the Mn content needs to be 2.0%.

Next, the P content (0.03% or less) will be described. Since P segregates at the austenite grain boundary of steel and causes toughness and rolling fatigue life to decrease, it is necessary to set the upper limit of the P content to 0.03%. In order to improve the crack fatigue strength of the bearing, the upper limit of the P content must be 0.03%.

Next, the content of S (0.03% or less) will be described. S impairs the hot workability of steel and forms non-metallic inclusions in the steel to reduce toughness and rolling contact fatigue life, so the upper limit of the S content must be 0.03%. . In order to improve the crack fatigue strength of the bearing, it is necessary to set the upper limit of the S content to 0.03%. On the other hand, it also has the effect of improving the machinability. Therefore, although it is desirable to reduce the amount, it may be added within the range of 0.03% or less.

Next, the Cr content (0.3% or more and 2.5
%)). Cr has the effects of improving hardenability, improving temper softening resistance, and improving life. To obtain these effects, 0.3% or more is necessary.
However, even if added in an amount of 2.5% or more, large carbides are formed and the rolling fatigue life is reduced.

Next, the content of Al (0.050% or less)
Will be described. When Al is contained in an amount of more than 0.05%, hard oxide-based inclusions are formed and the rolling fatigue life is significantly reduced. Although Al has the problems as described above, it also has the effect of forming AlN and refining the crystal grains, so that it does not increase the manufacturing cost of steel.
You may contain 005% or more.

Next, the N content (0.025% or less) will be described. N has the effect of combining with Al to form AlN and refining the crystal grains. However, if it is contained in a large amount, the strength of the steel is rather deteriorated.
It is necessary to set the upper limit of the content to 0.025%.

Next, the content of Ti (0.003% or less)
Will be described. Since Ti forms a nitride and becomes a non-metallic inclusion and may become a starting point of rolling fatigue fracture or cracking due to fatigue, the upper limit of the Ti content is set to 0.
It needs to be 003%.

Next, the content of O (0.0015% or less)
Will be described. O forms an oxide in steel and may be a starting point of rolling fatigue fracture and cracking due to fatigue as a non-metallic inclusion, resulting in a decrease in life and strength. The upper limit of the O content needs to be 0.0015%.

Next, the content of Ni (0.1% or more and 2.0
%)). Ni suppresses the change of the structure in the rolling fatigue process when used in a high temperature environment,
It also has the effect of suppressing the decrease in hardness in the high temperature range and improving the rolling fatigue life. In addition, Ni has the effects of improving the toughness, improving the life in the environment in which foreign matter is mixed, and improving the corrosion resistance. To obtain these effects, it is necessary to add 0.1% or more. However, if the content is 2.0% or more, a large amount of retained austenite is generated during carburizing and quenching, a predetermined hardness cannot be obtained, and the cost of the steel material increases.

Even if a large temperature rise locally occurs due to the action of these alloy components, the softening of the surface is prevented, the resistance to surface damage is improved, and the rolling bearing material is excellent in rolling life. However, the characteristics can be further improved by adding the following amounts of V and Mo. Preferably, the steel material is, by mass%, 0.05% or more and 2.5% or less Mo (molybdenum), and 0.05% or more and 1.0% or less.
It is desirable that at least one of the following V (vanadium) is further included. Hereinafter, the reasons for limiting the above chemical components will be described.

First, the content of Mo (0.05% or more 2.
5% or less) will be described. Mo has the effects of improving the hardenability of steel and improving the resistance to temper softening by forming a solid solution in carbides. In particular, Mo
Was added because it was found to have an effect of improving rolling fatigue life in the high temperature range. However, if a large amount is added in excess of 2.5%, the cost of steel increases, the hardness does not decrease during softening treatment to facilitate cutting, and machinability deteriorates significantly. The upper limit of the content is preferably 2.5%. Further, if the content is less than 0.05%, there is no effect on carbide formation, so the lower limit of the content is 0.
It is preferably set to 05%.

Next, the content of V (0.05% or more and 1.0
% Or less) will be described. V has the effect of combining with C to precipitate fine carbides, promoting the refinement of crystal grains, and improving the strength and toughness. In addition, the inclusion of V also improves the heat resistance of the steel material, suppresses softening after high temperature tempering, improves rolling contact fatigue life, and reduces variations in life. Since the content with which this effect is obtained is 0.05% or more, the lower limit of the content is made 0.05%. But,
When V is contained in a large amount exceeding 1.0%, machinability and hot workability are deteriorated. Therefore, the upper limit of the V content is preferably 1.0%.

When the nitrogen content of the surface layer is increased by carbonitriding, Ms (martensite transformation start temperature) of the surface layer
However, when this is quenched, a large amount of untransformed austenite remains in the surface layer. Retained austenite is
It has high toughness and work hardening properties, and acts to suppress the generation and propagation of cracks, but as described above, a large amount thereof causes dimensional change over time.

However, the retained austenite produced by N infiltration by carbonitriding is thermally stable as compared with the one in which N is not infiltrated. That is, infiltration of nitrogen by carbonitriding is advantageous in terms of imparting heat resistance, and not only carburizing treatment but also carbonitriding treatment can be applied.

[0028]

Embodiments of the present invention will be described below.

Rolling life test pieces (Examples 1 to 1 in Table 1) were carburized, carbonitrided, quenched and tempered using the steels having 23 kinds of chemical components shown in Table 1 as raw materials.
1) was prepared.

[0030]

[Table 1]

As the heat treatment of the test piece which has completed the rough processing,
For the carburizing and tempering process, a gas atmosphere furnace was used, RX gas (methane, ethane, propane, etc. was mixed with air, decomposed using a Ni catalyst, and the produced H ₂ O was removed to remove about 20% CO. , H _{2 of} about 40% and N _{2 of} about 40%) in an atmosphere of carbon potential (the carburizing ability of the gas is represented by the C concentration in Fe that is in equilibrium with this, which is called the carbon potential) 1 After holding at 950 ° C. for 300 minutes, the temperature was lowered to 900 ° C. and the product was quenched in oil. Then, a tempering process for 120 minutes was performed. The tempering temperatures are shown in Tables 2 and 3.

[0032]

[Table 2]

[0033]

[Table 3]

In the carbonitriding treatment, after carrying out the above carburizing treatment, a carbon atmosphere is used in an RX gas atmosphere, the carbon potential is 1.0% to 1.2%, and the addition amount of NH ₃ is 5% to 5%.
It was made 10%, held at 850 ° C. for 120 minutes, and then quenched in oil. After this, tempering treatment for 120 minutes was performed. The tempering temperatures are also shown in Tables 2 and 3.

In the case where quenching and tempering treatment is not performed after carburizing or carbonitriding treatment and sufficient surface hardness cannot be obtained, intermediate annealing is performed after quenching treatment.
After holding at 0 ° C. for 60 minutes, it was gradually cooled in the furnace. After that, as secondary quenching, it was held in an atmosphere furnace at 850 ° C. for 30 minutes and then quenched in oil. However, for some, the intermediate annealing can be omitted, and only the secondary quenching was performed under the same conditions. Then, a tempering process for 120 minutes was performed. The tempering temperatures are also shown in Tables 2 and 3.

After the heat treatment was completed, the surface of the test piece was polished to a mirror-finished state. The machining allowance during polishing was 0.1 mm.

Next, a comparative example will be described. Among the steels having 23 kinds of chemical components shown in Table 1, the comparative example is N
O. 12 to 23.

Comparative Example 12 is SCr420, Comparative Examples 13 to 21 are steels out of the chemical composition range of the present application, and Comparative Examples 22 and 23 are examples conducted to examine the effect of tempering temperature. In the comparative example, a test piece was prepared and performed in the same procedure as that of the example.

A rolling life test was conducted on the test piece samples of the above-mentioned examples and comparative examples.

The outline and results of each test are as follows. First, the rolling fatigue test at room temperature will be described. The object is a rolling member, and a long rolling fatigue life under a sufficient lubrication condition is an important characteristic basically required for the member. In the rolling fatigue test, the samples were accelerated and evaluated under the conditions of high surface pressure and high load speed. The test was conducted under the following test conditions. In this test, the number of samples N was set to 10, and the obtained experimental data was set to a Weibull distribution to calculate and evaluate L10 (the number of loads that 90% of the samples can be used without being damaged).

Test piece dimensions: outer diameter 12 mm, length 22 mm Mating steel ball dimensions: diameter 19.05 mm Contact surface pressure Pmax: 5.88 GPa Load speed: 46240 times / min Test results are shown in Tables 2 and 3. Comparative Example No. 12
Is a general-purpose JIS standard steel SCr420, and the life value of each material is described by the ratio when the life is 1.0.

The results of the surface hardness and rolling fatigue life after tempering are shown in Table 2 for this example and Table 3 for the comparative example.

From the results shown in Tables 2 and 3, it was found that in the examples having the composition range of the present invention, the surface hardness was HRC58 or more even after the tempering treatment at 170 ° C. or more and 300 ° C. or less. . It was found that the rolling fatigue life of the present example is longer than that of the comparative example even when the carburizing treatment is simply performed. It was also found that excellent rolling contact fatigue life can be obtained even when carbonitriding treatment is applied instead of carburizing treatment. It was also found that when the tempering temperature was 120 ° C, the rolling fatigue life was slightly reduced, and when the tempering treatment was performed at 400 ° C, the surface hardness was lowered and the rolling fatigue life was shortened.

Next, a rolling fatigue test at high temperature will be described. The problem to be solved is to extend the life under high temperature conditions, and the characteristics of the example products were evaluated under high temperature conditions. The test conditions are described below. The number of samples N was set to 10, and the obtained experimental data was set to a Weibull distribution to calculate and evaluate L10 (the number of loads that 90% of the samples can be used without being damaged).

The test piece used for the life evaluation had a diameter of 50 m.
A round rod raw material of m was machined to form a ring-shaped thrust type rolling contact fatigue life test piece having an outer diameter of 47 mm, an inner diameter of 29 mm and a thickness of 7 mm, which was roughly processed. The heat treatment of the roughened test piece is the same as that of the cylindrical test piece described above. After completing the heat treatment, polish both sides of the test piece,
Finished to a mirror state. The machining allowance during polishing was 0.1 mm on both sides. The surface hardness was obtained by measuring the surface hardness of the test piece using a Rockwell hardness meter and determining the average value of 7 points as the surface hardness.

The rolling fatigue life test was carried out using a thrust type rolling fatigue life tester. The conditions of the test are shown below. The test was carried out while a band heater was attached around the specimen and the housing containing the lubricating oil, and the temperature was kept constant at 200 ° C.

Test piece dimensions: outer diameter φ47 mm, inner diameter φ29 mm, plate thickness 7
mm, flat mate ball dimension: diameter 6.35 mm ceramic ball contact surface pressure Pmax: 5.5 GPa load speed: 3000 times / minute Oil temperature: 200 ° C. 12 is a general-purpose SCr420, and the life value of each material is described by the ratio when the life is 1.0.

From the results shown in Tables 2 and 3, it was found that in the examples having the composition ranges of the present invention, the rolling fatigue life was longer as compared with the comparative example, similarly to the rolling fatigue life at room temperature. did. It was also found that excellent rolling contact fatigue life can be obtained even when carbonitriding treatment is applied instead of carburizing treatment.

It was also found that when the tempering temperature is 120 ° C., the rolling fatigue life is slightly reduced, and when tempering at 400 ° C., the surface hardness is reduced and the rolling fatigue life is shortened.

Next, a rolling fatigue test under high temperature fitting conditions will be described. The remaining problem to be solved is that cracking of the inner ring does not occur when used in high temperature conditions and in a negative clearance where the fitting with the main shaft is large. An invention product having excellent room temperature life and high temperature life was subjected to a life test under high temperature (200 ° C.) fitting conditions. The test is a ball bearing 62
The inner ring for 06 is made of the invention material, assembled with other parts,
The bearing 6206 was constructed and used as a test bearing. The comparative example is 6206 made of bearing steel, which has been subjected to dimensional stabilization treatment by high temperature tempering so that it can be used at 200 ° C.

For the evaluation, a bearing life tester was used, the fit between the load condition and the spindle was kept constant by dimensional control, and rolling fatigue was evaluated by the presence or absence of cracks. The number of samples N was 3.

Test bearing: Ball bearing 6206 Load: Radial load Fr = 6.9 kN Rotation speed: 2000 rpm Lubricating oil: VG100 Ether oil Fitting margin: 0.085 mm Rated life: 191 h (use conditions are not corrected) 191 h × 5 = 955 h Test temperature: 200 ° C. As a result of the test, the inner ring crack was damaged at 81 h, 191 h, and 289 h in the comparative example, but all the example products reached the cutoff time and were not broken. The reason is that it is a carburized material, and has excellent dimensional stability at high temperatures and rolling life.

It should be considered that the embodiments disclosed this time are illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0054]

As explained above, according to the present invention, bearings for machine tools, supporting bearings for dryer rolls of papermaking machines, bearings for traction motors, etc., are fitted in a high-temperature environment while bearings are fitted in a negative gap with the main shaft. As for the bearings used in, there is an effect that a long-lasting bearing without crack damage can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a rolling bearing.

[Explanation of symbols]

1 rolling bearing, 2 shafts, 3 inner ring, 4 outer ring, 5 rolling elements.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F16C 35/063 F16C 35/063 F term (reference) 3J017 AA02 AA06 DA10 DB07 3J101 AA01 AA32 AA41 AA52 AA62 BA53 BA70 DA02 EA02 FA06 FA15 FA31 GA24 GA31 GA60 4K042 AA22 BA04 BA10 CA06 CA08 CA10 CA12 CA13 DA02 DC02

Claims (3)

[Claims] 1. A rolling bearing for supporting a rotating main shaft, comprising an inner ring, an outer ring, and a bearing ring having rolling elements, at least the inner ring containing at least an alloying element as a mass% and a C content of 0. 1
% To 0.4%, Si to 0.3% to 3.0%, Mn to 0.2% to 2.0%, P to 0.03%
Below, S is 0.03% or less, Cr is 0.3% or more 2.5
%, Ni 0.1% or more and less than 2.0%, Al 0.
05% or less, Ti 0.003% or less, O 0.001
5% or less, N 0.025% or less, and the balance F
A rolling bearing formed of a steel material containing e and unavoidable impurities. 2. The V content is 0.05% by mass in the steel material.
The rolling bearing according to claim 1, wherein Mo is added in an amount of 1.0% or less and Mo is added in an amount of 0.05% or more and 2.5% or less. 3. The tempering treatment is performed at 170 ° C. or higher for 30
The surface hardness (HR) of the member obtained by carrying out at 0 ° C or lower.
The rolling bearing according to claim 1, wherein C) is 58 or more.