JP2010180468A - Rolling bearing - Google Patents

Abstract

An object of the present invention is to improve the service life of a rolling bearing used in an environment exposed to a leakage current under the contamination with foreign matter.
SOLUTION: Carbon content 0.10 to 1.2 mass%, silicon content 0.10 to 1.0 mass%, manganese content 0.40 to 1.4 mass%, chromium content 0.5 to Using an alloy steel having 2.0% by mass, molybdenum content of 0.50-2.0% by mass and vanadium content of 2.0% by mass or less, nitriding or carbonitriding treatment, quenching treatment, and tempering treatment are carried out to form an inner ring. And get the outer ring. The carbon content of the surface layer part is 0.80 to 1.2% by mass, the nitrogen content of the surface layer part is 0.01 to 1.00% by mass, and the amount of retained austenite of the surface layer part is 20 to 45% by volume. A surface other than the raceway surface on the outer peripheral surface of the inner ring is covered with a ceramic film.
[Selection] Figure 1

Description

  The present invention relates to a rolling bearing.

  Patent Document 1 listed below describes an environment (foreign matter) in which metal chips, shavings, wear powder, etc. are mixed in the lubricating oil, such as transmissions and engines of automobiles, agricultural machines, construction machines, steel machines, etc. In order to improve the life of rolling bearings used under mixed lubrication environments), the carbon content, chromium content, and molybdenum content of the alloy steel forming the bearing rings and rolling elements, and the carburized or carbonitrided surface layer The amount of retained austenite in the part and the relationship between the amount of retained austenite and surface hardness are described.

  Specifically, it is described that by making the amount of molybdenum added relative to the amount of chromium added to an appropriate amount, the particles of precipitated carbide are refined, and the generation of giant carbide that tends to be the starting point of cracks is suppressed. Further, it is described that when the amount of retained austenite in the surface layer portion is 20 to 45% by volume, the stress concentration at the edge portion of the indentation caused by the foreign matter is alleviated and the generation of cracks is suppressed.

  On the other hand, for example, rolling bearings used on the rotating shafts of electric motors and generators and CT scanners for railway vehicles are in an environment where they are exposed to leakage current, and if the races and rolling elements are made of metal, the leakage current May flow between the rolling elements and the raceway, and there is a risk of electrolytic corrosion (electrochemical corrosion) occurring on the raceway surface of the raceway and the rolling surface of the rolling element. When this electrolytic corrosion occurs, the accuracy of the raceway surface of the raceway and the rolling surface of the rolling element is lowered, the vibration is increased, and the life of the bearing is shortened. Specifically, the electric corrosion causes unevenness on the raceway surface of the raceway and the rolling surface of the rolling element, and the unevenness becomes a stress concentration portion and fatigue peeling occurs.

  In order to prevent this electrolytic corrosion, the following Patent Document 2 describes that a surface other than the raceway surface of the bearing ring of the rolling bearing is coated with a ceramic insulating film having a high alumina content. Specific examples of the insulating coating include a ceramic sprayed layer containing 99 wt% or more of alumina and 0.01 to 0.20 wt% of titanium oxide, 97 wt% or more of alumina, and 0.5 to 2.5. A ceramic sprayed layer containing% by weight of zirconia is described.

Japanese Patent Laid-Open No. 5-25609 International Publication No. WO07 / 049727

However, the rolling bearing described in Patent Document 1 has room for improvement with respect to the life under the contamination with foreign matter.
An object of the present invention is to improve the life of a rolling bearing used in an environment exposed to a leakage current under the contamination with foreign matters.

  In order to solve the above problems, in the present invention, at least one of the inner ring and the outer ring has a carbon (C) content of 0.10% by mass to 1.2% by mass and a silicon (Si) content of 0.00. 10 mass% or more and 1.0 mass% or less, manganese (Mn) content is 0.40 mass% or more and 1.4 mass% or less, and chromium (Cr) content is 0.5 mass% or more and 2.0 mass% or less. A material made of alloy steel having a molybdenum (Mo) content of 0.50% by mass or more and 2.0% by mass or less, a vanadium (V) content of 2.0% by mass or less, and the balance being iron and inevitable impurities. Is obtained by nitriding or carbonitriding treatment, quenching treatment, and tempering treatment, and the carbon content of the surface layer portion is 0.80 mass% or more and 1.2 mass% or less, and the nitrogen of the surface layer portion is obtained. The content is 0.01% by mass or more and 1.00% by mass or less, Table Providing a rolling bearing, wherein the amount of retained austenite parts is not more than 45 vol% to 20 vol%.

  According to the rolling bearing of the present invention, the surface of the surface layer portion (range from the surface to a depth of 50 μm) is specified as described above by using the alloy steel having the specific composition, so that the raceway surface can be obtained under lubrication mixed with foreign matter. In addition, large indentations due to foreign matter are less likely to occur, and stress is less likely to concentrate on the edge of the indentation, so that surface-origin separation that is the main cause of life reduction is less likely to occur. As a result, the life of the rolling bearing under the contamination with foreign matters is improved.

In the rolling bearing according to the present invention, the content of alumina (Al ₂ O ₃ ) is 99.80% by mass or less and 99.99% by mass or less and the content of titanium oxide is 0 on the outer peripheral surface of the inner ring. If it is coated with a ceramic film of 0.01 mass% or more and 0.20 mass% or less, the leakage current will not flow between the rolling element and the raceway when used in an environment where the leakage current is exposed. , Electric corrosion is prevented.

Below, the effect | action of each component contained in the alloy steel used by this invention and the range of content rate are demonstrated.
[Carbon (C) content is 0.10% by mass or more and 1.2% by mass or less]
Carbon (C) dissolves in the matrix (matrix) to improve the strength after quenching and tempering, and also forms carbides by combining with carbide-forming elements such as iron, chromium, molybdenum, vanadium, and wear resistance. It is an element that has the effect of increasing the. If the carbon content in the alloy steel constituting the material is less than 0.10% by mass, the strength required for the bearing cannot be obtained.

In addition, when carbon is introduced into the surface by carbonitriding so that the carbon content of the surface layer portion is 0.80% by mass or more and 1.2% by mass or less, the carbon content in the alloy steel forming the material is included. If the rate is too small, the time required for this treatment becomes long, and the heat treatment cost increases.
From these points, the carbon content in the alloy steel constituting the material is set to 0.10% by mass or more, preferably 0.60% by mass or more.

  On the other hand, when there is too much carbon content, it will become easy to produce | generate a huge carbide | carbonized_material at the time of steelmaking, and it may have a bad influence on subsequent quenching characteristics and rolling fatigue life. Therefore, when carbonitriding is performed and carbon (or carbon and nitrogen) is introduced to the surface, the carbon content is set to 1.4% by mass or less. Further, when nitriding is performed instead of carbonitriding, the carbon content of the alloy steel becomes the carbon content of the surface layer as it is, so the carbon content of the alloy steel is 0.80 mass% or more and 1.2 mass% or less. To.

[Silicon (Si) content is 0.10% by mass or more and 1.0% by mass or less]
Silicon (Si) acts as a deoxidizer during steelmaking and also has the effect of increasing the resistance to temper softening, promoting the martensitic transformation of matrix (matrix) and stabilization of retained austenite, and improving the bearing life. It is an effective element. Moreover, it is an essential component in order to make the nitrogen content of the surface layer part after carbonitriding and the amount of retained austenite within the scope of the present invention. Therefore, it is necessary to add 0.10% by mass or more. Preferably 0.20 mass% or more is added.

  However, if added in a large amount, forgeability, cold workability, machinability, and carburization property may be deteriorated. In addition, a sufficient hardened layer depth and nitrogen diffusion depth may not be ensured by nitriding or carbonitriding. Therefore, it is 1.0 mass% or less.

[Manganese (Mn) content is 0.40 mass% or more and 1.4 mass% or less]
Manganese (Mn), like silicon, is an element that acts as a deoxidizer during steelmaking and has an effect of improving hardenability, and needs to be contained in an amount of 0.40% by mass or more.
However, if the manganese content is too high, not only the cold workability and machinability will decrease, but the Ms point (martensitic transformation start temperature) will decrease too much, and heat treatment (nitriding or carbonitriding, quenching, In addition, a large amount of retained austenite remains after tempering), and sufficient hardness may not be obtained, resulting in a decrease in wear resistance.

[Chromium (Cr) content is 0.5 mass% or more and 2.0 mass% or less]
Chromium (Cr) is an element that has the effect of being dissolved in the matrix and improving the hardenability, temper softening resistance, and the like. Further, the formation of fine carbides and carbonitrides with high hardness has the effect of imparting hardness and preventing coarsening of crystal grains, enhancing wear resistance, and extending the life.

  If the chromium content is less than 0.5% by mass, the above-mentioned action is insufficient, and if it exceeds 2.0% by mass, giant carbides are produced in the steel making process, and the subsequent quenching characteristics are adversely affected. There is a risk that machinability may be reduced. A preferable range of the chromium content is 1.3% by mass or more and 1.6% by mass or less.

[Molybdenum (Mo) content is 0.50 mass% or more and 2.0 mass% or less]
Molybdenum (Mo) is a carbide formation accelerating element. Molybdenum carbide formed by bonding with carbon has a function of enhancing wear resistance because it is fine and has high hardness. When the molybdenum content is less than 0.50% by mass, the above-described effects are insufficient. Preferably it is 0.8 mass% or more.

Molybdenum carbide (including nitrogen carbide) is an alloy-based carbide having a composition of M ₂₃ C ₆ , and the hardness of the alloy-based carbide is Hv 1300 to 1800. On the other hand, the cementite carbide having a composition of M ₃ C has a hardness of Hv 1000 to 1500, and the alloy carbide having a composition of M ₂₃ C ₆ is harder. The wear resistance is improved by the presence of the fine and hard molybdenum carbide.
However, if there is too much molybdenum, undissolved giant carbides such as MoC may appear when steelmaking is melted, and wear resistance may be reduced. Therefore, the molybdenum content is set to 2.0% by mass or less.

[Vanadium (V) content is 2.0 mass% or less]
Although vanadium (V) is not an essential component, it is a carbide formation accelerating element, and since the same action as chromium is obtained, it may be added at a content of 2.0% by mass or less. If the content of vanadium exceeds 2.0 mass%, the material becomes expensive and the workability also decreases, so the production cost increases. Examples of carbide formation promoting elements that are not essential components other than vanadium include tungsten (W), titanium (Ti), and niobium (Nb). These are also added at a content of 2.0% by mass or less for the same reason. You may do it.

[The carbon content of the surface layer portion is 0.80% by mass or more and 1.2% by mass or less]
When the carbon content of the surface layer is less than 0.80% by mass, the material strength necessary for hardness and rolling fatigue life cannot be obtained. If the carbon content of the surface layer exceeds 1.2% by mass, a huge carbide structure is formed after heat treatment, resulting in a state where the material strength is locally insufficient, and the strength required for the bearing is obtained. It becomes impossible.

[Nitrogen content in the surface layer is 0.01% by mass or more and 1.00% by mass or less]
Nitrogen, like carbon, has the effect of strengthening the solid solution of martensite and ensuring the stability of retained austenite. In addition, nitride and carbonitride are formed and present in the surface layer portion, and there is also an effect of increasing wear resistance. In order to obtain these effects, the nitrogen content of the surface layer portion needs to be 0.01% by mass or more. Preferably it is 0.20 mass% or more.

  However, if there are too many nitrides and carbonitrides present in the surface layer part, it will not be possible to secure the necessary retained austenite amount or the hardenability will be reduced, resulting in insufficient hardness. Content rate was made into 1.00 mass% or less.

[The amount of retained austenite in the surface layer is 20% by volume or more and 45% by volume or less]
Austenite is a soft and sticky structure, but has a function of hardening by martensitic transformation by energy applied to the raceway surface subjected to repeated stress by being left in the surface layer portion of the raceway surface after quenching and tempering. When the amount of retained austenite in the surface layer is 20% by mass or more, this effect is exerted, and large indentation due to foreign matter is less likely to occur on the raceway surface under foreign matter mixed lubrication, and stress is less likely to concentrate on the indentation edge. , Surface-origin peeling, which is the main cause of life reduction, is difficult to occur.

  When the amount of retained austenite in the surface layer exceeds 45% by volume, not only the above-described action is saturated, but also the hardness necessary for a rolling bearing cannot be obtained.

  The rolling bearing of claim 1 has a long life under lubrication mixed with foreign matter. Further, according to the rolling bearing of claim 2, even when used in an environment exposed to leakage current, electrolytic corrosion is prevented, and the life under lubrication mixed with foreign matter is prolonged.

It is a figure which shows the rolling bearing corresponded to one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a view showing a rolling bearing corresponding to an embodiment of the present invention.
This rolling bearing is a single row deep groove ball bearing having a nominal number 6316 (inner diameter 80 mm, outer diameter 170 mm, width 39 mm), inner ring 1, outer ring 2, ball (rolling element) 3 and a corrugated cage made of SPCC. 4.

A track groove (track surface) 1a is formed on the outer peripheral surface of the inner ring 1, and a track groove (track surface) 2a is formed on the inner peripheral surface of the outer ring. These raceway grooves 1a and 2a are arranged to face each other, and a ball 3 is arranged so as to be able to roll through a cage 4 therebetween.
As materials for producing the inner ring 1 and the outer ring 2, steel bars made of 12 types of steel shown in Table 1 were prepared. The steel of No. 6 is SUJ2 (high carbon chromium bearing steel type 2).

  About the inner ring | wheel 1, first, after these steel bars were made into the predetermined shape by cutting, it heat-processed on either of the conditions (heat processing AC) shown below. Next, a sealing process was performed after forming a ceramic film on a portion other than the raceway groove 1a on the outer peripheral surface by the method described below. Next, it grind | polished so that it might become a predetermined dimension and precision. In this way, ten inner rings 1 of No. 1 to 12 were produced.

About the outer ring | wheel 2, after making these bar | burrs into a predetermined shape by cutting first, it heat-processed on either of the conditions (heat processing AC) shown below. Next, it grind | polished so that it might become a predetermined dimension and precision. In this way, ten outer rings 2 of No. 1 to 12 were produced.
The balls 3 were subjected to cold quenching and tempering under the following conditions (heat treatment C) after forming a wire made of SUJ2 into a predetermined shape by cold forging. Next, it grind | polished so that it might become a predetermined dimension and precision.

<Heat treatment A: nitriding treatment, quenching treatment, and tempering treatment>
After holding at 820 to 920 ° C. for 1.0 to 24.0 hours in an “R _X gas + ammonia gas” atmosphere, the mixture is allowed to cool, and then at 820 to 850 ° C. in an R _X gas atmosphere to 0.5 to 1.0. After holding for a time, oil quenching at 60-80 ° C. Continuously, this was kept at 160-280 ° C. for 2.0 hours and then allowed to cool.

<Heat treatment B: carbonitriding, quenching, and tempering>
After holding at 820 to 920 ° C. for 1.0 to 24.0 hours in an “R _X gas + enrich gas + ammonia gas” atmosphere, the mixture was allowed to cool, and then at 820 to 850 ° C. in an R _X gas atmosphere, 0.5 to After holding for 1.0 hour, oil quenching at 60-80 ° C. Continuously, this was kept at 160-280 ° C. for 2.0 hours and then allowed to cool.

<Heat treatment C: Subsequent quenching and tempering>
After holding at 820 to 850 ° C. for 0.5 to 1.0 hour in an R _X gas atmosphere, oil quenching at 60 to 80 ° C. Continuously, this was kept at 160-280 ° C. for 2.0 hours and then allowed to cool.

<Ceramic film>
A mixed powder material consisting of 99.80% by mass of alumina (Al ₂ O ₃ ) and 0.20% by mass of titanium oxide is melted by plasma heating to form liquid fine particles, and a raceway groove on the outer peripheral surface of the inner ring 1 together with the plasma jet. It was made to collide and adhere to parts other than 1a at high speed. As a result, a ceramic sprayed layer having an alumina (Al ₂ O ₃ ) content of 99.80% by mass and a titanium oxide content of 0.20% by mass is formed on the outer circumferential surface of the inner ring 1 other than the raceway groove 1a. Formed.

<Sealing treatment>
An epoxy resin-based sealing material was applied to the portion of the inner ring 1 on which the ceramic film was formed, and was then placed in a thermostatic bath maintained at 150 ° C. and cured. Thereby, the hole of the ceramic coating (sprayed layer) was sealed.

  Using the inner ring 1 and outer ring 2 of No. 1-12 obtained in this way, the ball 3 and the cage 4 are the same for all samples, and 10 rolling bearings of No. 1-12 are used. Assembled one by one. Then, 50 g of lithium soap-based grease containing 0.1 mg of 70 to 150 μm cementite-based iron powder is enclosed in the internal space of each rolling bearing, and after the electrolytic corrosion test is performed by the following method, the mixture is lubricated with foreign matter. A life test was conducted.

<Electrical corrosion test>
A steel shaft was attached to the inner ring 1 of the rolling bearing, a steel shaft box was attached to the outer ring 2, a leakage current was assumed, and a DC voltage (1000 V) was applied between the shaft and the shaft box for 1 minute. After that, the shaft and the housing are removed, the rolling bearing is disassembled, the appearance of the inner ring 1, the outer ring 2, and the ball 3 is observed to examine the occurrence of electrolytic corrosion and the occurrence of cracks in the ceramic film. Evaluated.

<Life test under contaminated lubrication>
A rolling bearing is attached to the rotation test device, and the rotation test device is rotated under the conditions of load (P / C): 0.40 and rotation speed: 2000 min ⁻¹ until the vibration value becomes twice the initial value. Rolling bearings were removed from the surface, and the surface of the raceway was observed with a metal microscope to determine whether there was any damage such as wear or delamination. If no damage has occurred, it is attached again to the rotation test device and rotated under the same conditions until the vibration value becomes twice the initial value. This was repeated until damage occurred, and the cumulative rotation time was measured as the lifetime.

Create a Weibull plot from a measurement result of the life of each sample 10 body, it was determined L ₁₀ life. Then, by dividing each sample of the L ₁₀ life L ₁₀ life of No. 6, it was No. 6 L ₁₀ 1 and the relative values of the lifetime of seeking "life ratio".
The results are also shown in Table 1 below. The configuration deviating from the scope of the present invention is underlined.

  As can be seen from the results, the rolling bearings of No. 1 to 5 corresponding to the examples of the present invention have a life of 1.8 to 3.2 times that of No. 6. On the other hand, among Nos. 6 to 12 corresponding to the comparative examples, the life ratio of Nos. 6 to 11 was 0.1 to 1.2.

In sample No. 6, the manganese and molybdenum contents of the alloy steel used, heat treatment, the nitrogen content of the surface layer and the amount of retained austenite were out of the scope of the present invention, and the inner ring raceway surface was peeled off early. did.
In sample No. 7, since the tempering temperature was 280 ° C. and the amount of retained austenite was out of the range of the present invention, the inner ring raceway surface was peeled off early.

In sample No. 8, the carbon content of the alloy steel used was small, and nitriding was performed instead of carbonitriding, so that the carbon content of the surface layer and the amount of retained austenite were out of the scope of the present invention. As a result, the rolling bearing was deformed due to insufficient rigidity, and seizure occurred early.
In sample No. 9, the alloy steel used had a low chromium content, and the surface layer was hardly formed of fine carbides and carbonitrides with high hardness. Occurred.

In sample No. 10, the molybdenum content of the alloy steel used was small, and high hardness fine nitride was hardly formed in the surface layer portion, and peeling occurred early.
In sample No. 11, since the heat treatment was “subsequent quenching → tempering”, very little fine nitride with high hardness was formed on the surface portion, relatively large indentations were formed on the raceway surface, and peeling occurred early. .

  In Sample No. 12, since a ceramic film was not formed on the inner ring, corrosion occurred in the electrolytic corrosion test, and thus a life test could not be performed.

1 Inner ring 1a Track groove (track surface)
2 Outer ring 2a Track groove (track surface)
3 balls (rolling elements)
4 cage

Claims (2)

At least one of the inner ring and the outer ring is
The carbon (C) content is 0.10% by mass to 1.2% by mass, the silicon (Si) content is 0.10% by mass to 1.0% by mass, and the manganese (Mn) content is 0.40. Mass% to 1.4 mass%, chromium (Cr) content of 0.5 mass% to 2.0 mass%, molybdenum (Mo) content of 0.50 mass% to 2.0 mass%, Vanadium (V) content is 2.0 mass% or less, after processing the material consisting of alloy steel of which the balance is iron and inevitable impurities into a predetermined shape,
It is obtained by nitriding or carbonitriding treatment, quenching treatment, and tempering treatment, and the carbon content of the surface layer part is 0.80 mass% or more and 1.2 mass% or less, and the nitrogen content of the surface layer part is 0.01 mass%. A rolling bearing characterized in that it is 1.00% by mass or less and the amount of retained austenite in the surface layer part is 20% by volume or more and 45% by volume or less. Surfaces other than the raceway surface on the outer peripheral surface of the inner ring have an alumina (Al ₂ O ₃ ) content of 99.80% by mass to 99.99% by mass and a titanium oxide content of 0.01% by mass to 0.00%. The rolling bearing according to claim 1, wherein the rolling bearing is coated with a ceramic film of 20% by mass or less.

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