JP4534537B2 - Rolling bearing - Google Patents

Description

  The present invention relates to a rolling bearing.

If foreign matter such as metal chips, shavings, burrs, or wear powder enters the lubricant inside the rolling bearing, the bearing ring or rolling element may be damaged, and the life of the rolling bearing may be significantly reduced. Well known.
Accordingly, various types of rolling bearings have been proposed that have a long life even when used in a harsh environment where foreign matter is mixed in the lubricant inside the rolling bearing as described above (hereinafter referred to as foreign matter mixed lubrication). ing.

  For example, Patent Documents 1 and 2 alleviate the stress concentration at the edge portion of the indentation caused by foreign matter by defining the carbon amount of the surface layer of the bearing ring and rolling element, the amount of retained austenite, the amount of carbonitride, etc. Techniques have been proposed for suppressing the occurrence of cracks and improving the life of rolling bearings. Patent Document 3 discloses a bearing component having an excellent rolling fatigue life, in which the composition, internal hardness, and surface hardness of the steel are defined.

On the other hand, Patent Document 4 discloses a rolling bearing in which the amount of retained austenite, the composition of alloy steel, and the surface hardness are defined for races and rolling elements. This rolling bearing is excellent in dimensional stability and has a long life under lubrication with a clean lubricant in which no foreign matter is mixed.
Japanese Patent No. 2138103 Japanese Patent No. 2128328 Japanese Patent No. 3051944 Japanese Patent No. 2541160

However, since rolling bearings are expected to have higher temperatures and higher speeds in the future, considering the fact that they are used at high temperatures and under contaminated lubrication, the above-described conventional rolling bearings need to have higher performance.
That is, the rolling bearings described in Patent Documents 1 and 2 show excellent characteristics under foreign matter lubrication, but have a low chrome content in the alloy steel, so that dimensional stability is sufficient under high temperature and high speed environments. I could not say. Similarly, the rolling bearing described in Patent Document 4 cannot be said to have sufficient dimensional stability under high temperature and high speed environments.

Furthermore, the bearing component described in Patent Document 3 has good dimensional stability because the chromium content in the alloy steel is sufficient, but the hardness decreases at high temperatures, resulting in poor life. There was a problem of becoming enough. In addition, since the amount of retained austenite on the surface is not defined, there is a risk that the life under lubrication mixed with foreign matter may be insufficient depending on the content of the heat treatment.
SUMMARY OF THE INVENTION Accordingly, the present invention solves the problems of the prior art as described above, and an object thereof is to provide a rolling bearing that has excellent dimensional stability and a long life even when used under high temperature and foreign matter mixed lubrication. .

  In order to solve the above-described problems, the present invention has the following configuration. That is, the rolling bearing of the present invention is a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to freely roll between the inner ring and the outer ring, the inner ring, the outer ring, and the At least one of the rolling elements satisfies the following four conditions.

Condition A: carbon is 0.35 mass% to 0.6 mass%, chromium is 2.5 mass% to 7 mass%, manganese is 0.5 mass% to 2 mass%, and silicon is 0.1 mass % To 1.5% by mass and molybdenum containing 0.5% to 3% by mass.
Condition B: having a surface layer hardened by carburizing or carbonitriding.
Condition C: The amount of retained austenite on the surface is 15% by volume or more and 45% by volume or less.
Condition D: The average retained austenite amount (unit: volume%), which is the average value of the retained austenite amount of the entire member, is the chromium content (unit: mass%) and molybdenum content (unit: mass) in the alloy steel. %) And 2.5 times or less.

As described above, at least one of the inner ring, the outer ring, and the rolling element is made of an alloy steel sufficiently containing chromium and molybdenum, so that the dimensional change associated with the decomposition of the retained austenite hardly occurs at a high temperature and the hardness is high. It is also difficult for the decrease to occur. In addition, since the amount of retained austenite and the amount of average retained austenite on the surface are regulated to appropriate values, the life is long even when used under the contamination with foreign matter.
In the present invention, the “average residual austenite amount” means an average value of the residual austenite amount in the entire member of the inner ring, outer ring, or rolling element, for example, distribution of the residual austenite amount from the surface to the core. Can be obtained by measuring the average value.

Below, the critical significance of each of the above-mentioned numerical values (contents of alloy elements in alloy steel, residual austenite amount, etc.) in the conditions A to D in the rolling bearing of the present invention will be described.
[Carbon content]
Carbon (C) is solid-solved in the base and hardened, improves the hardness after tempering and improves strength, and combines with carbide-forming elements such as iron, chromium, molybdenum, vanadium to form carbides, It is an element that has the effect of enhancing wear resistance.
If the C content in the alloy steel is low, the time required for carburizing or carbonitriding to obtain a sufficient hardened layer depth will increase, leading to an increase in cost and, in some cases, δ ferrite will be generated, resulting in toughness. Decreases. On the other hand, if the C content is large, coarse eutectic carbides are likely to be produced during steelmaking, and the fatigue life and strength may be reduced. In addition, forgeability, cold workability, and machinability may be reduced, leading to an increase in processing cost. For these reasons, the C content in the alloy steel must be 0.2% by mass or more and 0.6% by mass or less, and more preferably 0.3% by mass or more and 0.5% by mass or less. preferable.

[Chromium content]
Chromium (Cr) is an element having a function of improving the hardenability, temper softening resistance, corrosion resistance, and fatigue life by dissolving in a matrix. In addition, the interstitial solid solution elements such as C and nitrogen (N) are substantially made hard to move, so that the base structure is stabilized, and the life reduction at the time of hydrogen intrusion is greatly suppressed. Furthermore, since the carbide finely distributed in the alloy steel is composed of carbides such as (Fe, Cr) ₃ C and (Fe, Cr) ₇ C _{3 having} higher hardness, it has an effect of improving wear resistance. ing.

  If the content of Cr in the alloy steel is small, there is a possibility that the above-described effects cannot be obtained sufficiently. On the other hand, if the content of Cr is large, cold workability, machinability and carburization processability are lowered, which may lead to an increase in cost, and coarse eutectic carbide is likely to be generated during steelmaking. In addition, fatigue life and strength may be reduced. For these reasons, the Cr content in the alloy steel needs to be 2.5 mass% or more and 7 mass% or less. The Cr content is more preferably 2.5% by mass or more and 6% by mass or less, and further preferably 2.5% by mass or more and 5% by mass or less.

[About manganese content]
Manganese (Mn) acts as a deoxidizer during steelmaking, so 0.5% by mass or more needs to be added. Further, like Cr, it has a function of solid solution in the base and lowering the Ms point to secure a large amount of retained austenite and to improve hardenability.
However, if added in a large amount, not only the cold workability and machinability are lowered, but also the martensite transformation start temperature is lowered, and a large amount of retained austenite remains after carburizing treatment, and sufficient hardness is obtained. It may disappear. For these reasons, the Mn content in the alloy steel needs to be 0.5% by mass or more and 2% by mass or less. And it is more preferable to set it as 0.8 mass% or more and 1.5 mass% or less, and it is further more preferable to set it as 0.8 mass% or more and 1.2 mass% or less.

[About silicon content]
Silicon (Si), like Mn, acts as a deoxidizer during steelmaking. Moreover, it is an element effective for improving the bearing life by improving the hardenability as well as Cr and Mn, and strengthening the base martensite. Furthermore, it has the effect | action which raises temper softening resistance. However, if added in a large amount, forgeability, cold workability, machinability, and carburization property may be reduced. For these reasons, the Si content in the alloy steel needs to be 0.1% by mass or more and 1.5% by mass or less. And it is more preferable to set it as 0.1 to 0.7 mass%, and it is still more preferable to set it as 0.3 to 0.5 mass%.

[Molybdenum content]
Molybdenum (Mo) is an element having the effect of increasing the hardenability, temper softening resistance, corrosion resistance, and fatigue life by solid solution in the base like Cr. Further, like Cr, interstitial solid solution elements such as C and N are made substantially hard to move, so that the base structure is stabilized, and the life reduction at the time of hydrogen intrusion is greatly suppressed. Further, by forming a fine carbide such as Mo ₂ C, also it has the effect of increasing the wear resistance.
If the Mo content in the alloy steel is low, the above-described effects may not be obtained sufficiently. On the other hand, if the content of Mo is large, cold workability and machinability may be reduced, resulting in an increase in processing cost or generation of coarse eutectic carbides, which may reduce fatigue life and strength. . For these reasons, the Mo content in the alloy steel needs to be 0.5% by mass or more and 3% by mass or less, and more preferably 0.5% by mass or more and 1.5% by mass or less.

[About the amount of retained austenite on the surface]
Residual austenite has the effect of reducing surface fatigue, so it needs to be 15% by volume or more, and more preferably 20% by volume or more. On the other hand, if the amount of retained austenite on the surface is large, the surface hardness is reduced, or deformation is likely to occur during assembly of the bearing and the assemblability may be deteriorated. % Or less is more preferable.

[Average amount of retained austenite]
Although the action of Cr and Mo can suppress the decomposition of residual austenite at high temperatures, if the amount of residual austenite is large, the decomposition of residual austenite occurs when exposed to high temperatures for a long period of time. And since a clearance reduces by a dimensional change, there exists a possibility that seizing may arise. Therefore, the average retained austenite amount (unit: volume%) is 2.5 times or less of the sum of the Cr content (unit: mass%) and the Mo content (unit: mass%) in the alloy steel. There is a need.

  The rolling bearing of the present invention has excellent dimensional stability and a long life even when used at high temperatures and under contaminated lubrication.

Embodiments of a rolling bearing according to the present invention will be described in detail with reference to the drawings.
The deep groove ball bearing in FIG. 1 includes an inner ring 1, an outer ring 2, and a plurality of balls (rolling elements) 3 that are arranged between the inner ring 1 and the outer ring 2 so as to be able to roll. At least one of the inner ring 1, the outer ring 2, and the ball 3 has a carbon content of 0.2% by mass to 0.6% by mass, a chromium content of 2.5% by mass to 7% by mass, and a manganese content of 0.5% by mass. It is made of an alloy steel containing 2% by mass or less, 0.1% by mass to 1.5% by mass of silicon, and 0.5% by mass or more and 3% by mass or less of molybdenum. Then, carburizing treatment or carbonitriding treatment is performed, and a surface layer cured by this heat treatment is formed on the raceway surfaces of the inner ring 1 and the outer ring 2 and the rolling surfaces of the balls 3. Further, the amount of retained austenite on the surface is 15% by volume or more and 45% by volume or less, and the average retained austenite amount (unit: volume%) is the chromium content (unit: mass%) and molybdenum content in the alloy steel. It is 2.5 times or less of the sum of (unit is mass%). Such deep groove ball bearings are excellent in dimensional stability and have a long life even when used under high temperature and with foreign matter contamination.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. Prepare the inner ring and outer ring made of various alloy steels having the composition shown in Table 1 and rolling elements made of JIS steel type SUJ2, manufacture a deep groove ball bearing with the nominal number 6206, durability test Went. In addition, components other than C, Si, Mn, Cr, and Mo in the alloy steel are iron and inevitable impurities. Moreover, the steel type H of Table 1 is JIS steel type SUJ2. Furthermore, the underline attached to the numerical values in Table 1 means that the numerical values are out of the recommended range of the present invention.

  The inner ring and the outer ring were manufactured by turning alloy steel to a predetermined size, performing carburizing treatment or carbonitriding treatment as described later, further quenching and tempering at a predetermined temperature, and then performing finish grinding. The carburizing conditions are: the atmosphere is a mixture of RX gas and enriched gas, the processing time is about 3 to 5 hours, and the processing temperature is 900 to 960 ° C. And after air-cooling to normal temperature, oil quenching was performed at 840 degreeC for 1 hour, and also tempering was performed at 180 degreeC for 2 hours. The carbonitriding conditions are as follows: the atmosphere is a mixture of RX gas, enriched gas, and ammonia gas (5%), the processing time is about 3 to 5 hours, and the processing temperature is 900 to 960 ° C. And after oil cooling, quenching and tempering were performed under the same conditions as in the case of carburizing treatment.

Properties of the obtained inner and outer rings (surface retained austenite amount (γ _R ) and average retained austenite amount (γ _{R mean} )) are summarized in Table 2. Also, the sum of the chromium content Cr% and the molybdenum content Mo% in the alloy steel (hereinafter referred to as “Cr% + Mo%”), and the average retained austenite content (γ _{R mean} ) and Cr% + Mo % (Γ _{R mean} / [Cr% + Mo%]) is shown in Table 2. The amount of retained austenite (γ _R ) was measured by the X-ray diffraction method. Moreover, the underline attached | subjected to the numerical value in Table 2 means that the numerical value has remove | deviated from the recommended range of this invention.

Next, the endurance test method will be described. The deep groove ball bearing obtained by assembling the inner ring, the outer ring, and the rolling element described above was rotated under oil bath lubrication conditions with an axial load of 3.5 GPa and a rotation speed of 3000 min ⁻¹ . Then, the inner ring, the time when flaking and seizing occurred in at least one of the outer ring and the life was measured 90% residual life (L ₁₀ life). If you did not occur with flaking or grilled be rotated 1500 hours, L ₁₀ life was 1500 hours. In addition, as a lubricating oil, the lubricating oil whose ISO viscosity grade is ISO VG150 was used, and the temperature of the lubricating oil was 160 ° C. Further, 300 ppm of steel powder having a diameter of 74 to 147 μm (hardness Hv600) was added to the lubricating oil as a foreign matter.

The results of the durability test are shown in Table 2. As can be seen from Table 2, Examples 1 to 6 have a much longer life than Comparative Examples 1 to 11. In particular, in Examples 1 to 5 , all of the content of Cr in the alloy steel, the amount of retained austenite on the surface, and the amount of average retained austenite (value of γ _{R mean} / [Cr% + Mo%]) are suitable values. Therefore, flaking and seizure did not occur at all even under high temperature and foreign matter mixed lubrication. Further, in Example 6, although the Cr content was within a suitable range, it was slightly higher, so that amorphous carbide was generated and the life was slightly shorter than in Examples 3-5 .

On the other hand, Comparative Examples 1 to 9 had a shorter life than Examples 1 to 6 because the composition of the alloy steel was out of the scope of the present invention. Comparative Examples 1 and 2 are made of SUJ2, and in case of Comparative Example 1, they are all hardened, and in case of Comparative Example 2, carbonitriding is performed. Since Comparative Example 2 was subjected to carbonitriding, it had a longer life than Comparative Example 1, but was significantly shorter than each Example.

In Comparative Examples 3 and 4, the surface retained austenite amount and the average retained austenite amount (γ _{R mean} / [Cr% + Mo%] value) are within a preferable range, but the Cr content is preferably within a range. Because it is out of the range, it has a short life. Furthermore, Comparative Examples 5 to 9 had a short life because the content of any of C, Si, Mn, and Mo was outside the preferred range. Furthermore, in the case of Comparative Examples 10 and 11, the composition of the alloy steel is suitable, but in Comparative Example 10, the average retained austenite amount (value of γ _{R mean} / [Cr% + Mo%]) is not a suitable value. In Comparative Example 11, the amount of retained austenite on the surface was not a suitable value, so seizure occurred and the life was short.

Here, a graph showing the correlation between the Cr content in the alloy steel and the L10 life of the bearing is shown in FIG. This graph plots the test results of Examples 1 to 6, Reference Example, and Comparative Examples 3 and 4. As can be seen from this graph, when the Cr content is 2.5% by mass or more and 7% by mass or less, the bearing has a long life, and when it is 2.5% by mass or more and 6% by mass or less, the bearing has a longer life. It was.

  The rolling bearing of the present invention can be suitably used even under high temperature and foreign matter mixed lubrication. In particular, it can be suitably used for engines, transmissions and the like of automobiles, agricultural machines, construction machines, and steel machines.

It is a fragmentary longitudinal cross-section which shows the structure of the deep groove ball bearing which is one Embodiment of the rolling bearing which concerns on this invention. Is a graph showing the correlation between L ₁₀ life of the content and the bearing of Cr in the alloy steel.

Explanation of symbols

1 Inner ring 2 Outer ring 3 Ball (rolling element)

Claims (1)

In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are freely rollable between the inner ring and the outer ring, at least one of the inner ring, the outer ring, and the rolling element is: A rolling bearing characterized by satisfying four conditions.
Condition A: carbon is 0.35 mass% to 0.6 mass%, chromium is 2.5 mass% to 7 mass%, manganese is 0.5 mass% to 2 mass%, and silicon is 0.1 mass % To 1.5% by mass and molybdenum containing 0.5% to 3% by mass.
Condition B: having a surface layer hardened by carburizing or carbonitriding.
Condition C: The amount of retained austenite on the surface is 15% by volume or more and 45% by volume or less.
Condition D: The average retained austenite amount (unit: volume%), which is the average value of the retained austenite amount of the entire member, is the chromium content (unit: mass%) and molybdenum content (unit: mass) in the alloy steel. %) And 2.5 times or less.

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