JP2541160B2 - Rolling bearing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing, and more particularly to improving the life of rolling bearings used for transmissions, engines, etc. of automobiles, agricultural machines, construction machines and steel machines.

[0002]

2. Description of the Related Art Foreign matter such as metal chips, shavings, burrs and abrasion powder mixed in bearing lubricating oil damages the races and rolling elements of rolling bearings, resulting in a long life of rolling bearings. It is well known to bring about a decline. Therefore, the applicant of the present invention filed Japanese Patent Application Laid-Open No. 64-55423,
Even when a rolling bearing is used under lubrication containing foreign matter, it is caused by foreign matter by adjusting the content of C in the rolling surface layer of the bearing, the amount of retained austenite, and the content of carbonitride to appropriate values. We proposed to reduce the concentration of stress at the edge of the indentation, suppress the occurrence of cracks, and improve the life of rolling bearings. According to this, a proper amount of retained austenite can improve the life under foreign matter-containing lubrication, but on the other hand, there is a problem that retained austenite reduces surface hardness and fatigue resistance. It was Regarding the influence of the grain size of carbides and carbonitrides in improving the bearing life, in particular, when large carbides are repeatedly subjected to stress, the large carbides become the starting point of fatigue and cracks and flaking occur. Was not considered.

Therefore, as a result of continuous research, the applicant of the present invention found an optimum relationship between the amount of retained austenite in the rolling surface layer and the surface hardness, and furthermore, the average grain size of carbides and carbonitrides present in the rolling surface layer. By optimizing the diameter, it has become possible to provide a rolling bearing that has a longer life than conventional products not only under lubrication containing foreign matter but also under clean lubrication (Japanese Patent Application No. 2-127930).

This is because at least one of the bearing ring and rolling element of the rolling bearing contains a carbide-forming element, and the residual austenite amount (γ _R vol%) of the rolling surface layer is 20 to 20.
The Vickers hardness (H _V ) of the rolling surface was -4.7% with respect to the amount of retained austenite by 45 vol% and dispersion strengthening of fine carbide or carbonitride having an average particle size of 0.5 to 1.5 μm. X (γ _R vol%) + 920 ≦ Hv ≦ −4.7 × (γ _R vol%) + 1020.

[0005]

However, it is difficult to reliably obtain fine carbides or carbonitrides having an average particle size of 0.5 to 1.5 μm in the above-mentioned conventional rolling bearings, and often in carburizing or carbonitriding treatments. In some cases, large pro-eutectoid carbides were locally generated in the surface layer, which caused a slightly insufficient life extension.

Therefore, the present invention has an object to solve such conventional problems, and it is possible to stably obtain fine carbides and carbonitrides in actual production and to obtain the target residual austenite. Achieves quantity and hardness,
The object is to provide a rolling bearing having a longer life.

According to the present invention, in a rolling bearing having a bearing ring and a rolling element, at least one surface layer of the bearing ring and the rolling element has a residual austenite content (γ _R vol
%) Is 20 to 45 vol%, and C is 0.1 to 1.2 weight.
%, Cr; 1 to 3% by weight, and further contains 2.0 Mo.
The surface layer containing less than 1% by weight and not less than 1/3 of the Cr content and carburized or carbonitrided.
With respect to the surface hardness of the (Hv) is the amount of retained _{austenite, -4.7 × (γ R vol%} ) + 920 ≦ Hv ≦ -
It is characterized by being made of an alloy steel in the range of 4.7 × (γ _R vol%) + 1020.

[0008]

The present invention is applicable to carburizing and carburizing steel containing 1 to 3% Cr.
Grain size and amount of carbide and carbonitride during carbonitriding and hardness
The effect of Mo addition on the amount of retained austenite
It was made paying attention. That is, the present inventors
Reduces the surface hardness due to the presence of retained austenite.
The result of repeated research on the refinement of the precipitated carbides to compensate
As a result, Mo was appropriately controlled with respect to the amount of Cr added.
If only an amount is added, the size of the precipitated carbide particles becomes finer.
It was found that (carbide refining effect of Mo). Cr
The carbide composition of the steel to which Mo and Mo are added at the same time
However, the amount of Mo with respect to Cr increases.
The carbide composition is M₃C cementite type
Carbide to M _{twenty three}C₆Changed to alloy carbide
I think that the. Precipitated particles of cementite are carburized or carburized.
Easier to grow faster than other alloy carbides in the γ phase during aging
It is known that
Since the material changed to other carbides, the precipitation carbides became smaller.
It is accelerated, that is, the carbide miniaturization effect of the above Mo.
It is thought to bring fruit. Such a small amount of carbide
The maximum grain size is suppressed by miniaturization, and it becomes the starting point of cracks.
The fact that the appearance of huge carbides that are likely to occur was suppressed
It is estimated that the reason why the bearing life was remarkably extended
You.

It has been experimentally recognized that carbonitriding has a greater tendency for the above carbides to become finer than for carburizing. It is considered that this is because carbonitride (Fe ₃ (CN ₃ )) is more easily refined than carbide, and the carbonitriding temperature is lower than the carburizing temperature. From this,
Carbonitriding is more desirable to achieve stable production.

Cementite has a hardness of Hv 1000 to 1500, whereas M ₂₃ C ₆ alloy carbide has a hardness of Hv.
It is said to be 1300 to 1800, and it is considered that the hardness effect of the carbide itself and the above-described miniaturization effect are combined to prolong the life of the rolling bearing. The Mo content in the present invention is 2.0% by weight or less and does not include Cr.
The amount should be 1/3 or more.

In order to promote the refinement of carbides (including carbonitrides, the same applies hereinafter) by adding Mo, the amount of Mo should be 1/3 of the amount of Cr, assuming a Cr content of 1 to 3%.
3 or more is required. When the amount is less than this amount, the amount of Mo with respect to the content of Cr becomes too small, the precipitation carbide is not refined sufficiently, and the effect of extending the bearing life is low. Hand M o content of 2%
If it exceeds, undissolved giant carbides such as MoC may appear during melting, and the quenching temperature needs to be high at 900 ° C or higher, which is not preferable from the viewpoint of production.

The critical significance of other characteristic values of the alloy steel of the rolling bearing according to the present invention will be described below. Amount of retained austenite in the rolling surface layer (γ _R vol%); 20〜
45 vol%: An indentation is generated on the rolling surface layer due to a foreign substance mixed in the lubricating oil or the like. The cracks that tend to occur at the edge of the indentation are closely related to the retained austenite. Retained austenite is somewhat soft and viscous, although it varies somewhat depending on the C content of the material. Therefore, when the retained austenite is present in the rolling surface layer at a desired ratio, the stress concentration at the edge of the indentation can be reduced, and the occurrence of cracks can be suppressed. Further, the retained austenite in the rolling surface layer undergoes martensite transformation due to the deformation energy applied to the surface when the number of relative passes of the member (for example, the race ring with respect to the rolling element) that passes through the indentation during rolling exceeds a predetermined number. Due to the effect of hardening, it is possible to improve the life of the rolling bearing under lubrication containing foreign matter. The amount of retained austenite in the rolling surface layer that maximizes these effects is 20
It is about 45 vol%.

If the amount of retained austenite is less than 20 vol%, the stress concentration effect at the time of dust indentation cannot be sufficiently exerted. In addition, the amount of retained austenite is 45
When it exceeds vol%, the effect of relaxing stress concentration is saturated,
On the contrary, the surface hardness is lowered, so that the fatigue resistance is lowered. For the above reasons, the amount of retained austenite in the rolling surface layer is 20 to 45 vol%, preferably 2
It was set to 5 to 40 vol%.

Fine carbides present in the rolling surface layer and /
Or average particle size of carbonitride: 0.5 to 1.5 μm: The amount of retained austenite (γ _R vol%) in the rolling surface layer increases, so that the surface hardness (H _V ) decreases. Therefore, in the present invention, the surface hardness with respect to the amount of retained austenite can be improved by strengthening the precipitation of fine carbides and carbonitrides.

Here, the average particle size of carbides and carbonitrides is
It is 0.5 to 1.5 μm. If the average particle size is less than 0.5 μm, the life is insufficiently improved and the wear resistance is reduced.
Further, if the average particle size exceeds 1.5 μm, the carbides and carbonitrides serve as a concentrated source of stress, cracks are likely to occur, and the life of the rolling bearing is shortened. By the way, the content of the fine carbides and carbonitrides contained in the rolling surface layer is preferably 10 to 30% in area ratio. When the amount of carbides and carbonitrides is small, it is not possible to compensate for the decrease in surface hardness with respect to the increase in the amount of retained austenite. On the other hand, if the amount of these is too large, the carbides are coarsened, and the amount of carbon solid-dissolved in the matrix is reduced, so that the required amount of retained austenite cannot be secured. The amounts of carbides and carbonitrides can be controlled by adjusting the amount of carbide forming elements, adjusting the tempering temperature, and the like.

The carbide forming elements include Cr, Mo,
There are various known elements such as V and W (W also forms a nitride). Carbonitride refers to the above carbides and nitrides such as Fe ₃ (CN ) when carbonitriding is performed instead of carburizing. Cr and Mo are preferable as the carbide forming element. Cr is a carbide-forming element necessary for improving the hardenability and tempering resistance of the steel and at the same time precipitating fine carbides to improve the hardness of the alloy steel. The Cr content suitable for refining the carbide precipitated in the rolling surface layer is
It is 1 to 3% by weight. Although it is possible to increase the C concentration and increase only the surface hardness of steel having a Cr content of less than 1% by weight by a treatment such as carburizing, this causes less nucleation of carbides and facilitates the growth of carbides. Occurs.
If the Cr content exceeds 3% by weight, giant carbides will crystallize at the stage of the raw material, and stress concentration will shorten the life. In addition to being disadvantageous in terms of cost, heat treatment productivity, high temperature quenching, and the like for solid-dissolving the carbide in the matrix and reprecipitating it are required to reduce the size of the giant carbide.

As a method for producing a material, there are known powder sintering and the like in addition to casting. In this powder sintering, giant carbides and carbonitrides are crystallized at the stage of the material during sintering. This is a preferable method because it does not occur. Mo is as described above. Regarding other carbide-forming elements, for example, V: 7% by weight or less, particularly 3% by weight or less,
W; 15 .0 and wt% or less, it may be contained in as necessary one or two or of them. Note that spheroidizing annealing may be performed when precipitating fine carbides.

The hardness (H _V ) of the rolling surface layer is −4.7 × (γ _R vol%) + 920 ≦ Hv ≦ −4.7 × with respect to the residual austenite amount (γ _R vol%) of the rolling surface layer. (Γ _R vol%) + 1020: In the present invention, the hardness range corresponding to each retained austenite amount is set within the range shown by the above formula.

In the relationship of the above equation, if the hardness is less than the lower limit value, the fatigue resistance is lowered, and the life is shortened even under the contamination with foreign matter and the lubrication of clean. On the other hand, it is difficult to make the hardness higher than the upper limit value. As the alloy steel used in the present invention, case hardening steel, high carbon chromium bearing steel and high speed bearing high speed steel can be used, and the carbon content thereof is in the range of 0.1 to 1.0% by weight. Carbon content 0.1
The reason why the content is set to be at least wt% is that it is difficult to reduce the amount in terms of steelmaking.

On the other hand, if the carbon content exceeds 1.2% by weight, huge carbides are likely to be generated at the stage of the raw material, and the toughness and the fracture strength are lowered. Therefore, the upper limit is set to 1.2% by weight. did.

[0021]

Next, embodiments of the present invention will be described. Carburizing heat treatment was performed on the test pieces made of steel having the composition shown in Table 1 as follows.

[0022]

[Table 1]

That is, the direct quenching of the carburizing heat treatment of each test piece is performed at 920 for about 3 to 5 hours in an atmosphere of R _X gas + enriched gas as shown in the graph of FIG.
Heat treatment at ~ 960 ° C, air cool to room temperature, then 8
Oil quenching was performed at 40 ° C. for 1 hour, and further tempering was performed at 180 ° C. for 2 hours. As for the carbonitriding heat treatment, as shown in the graph of FIG. 2, with R _X gas + enriched gas + ammonia gas 5% atmosphere of about 3-5 hours,
Carbonitriding heat treatment was performed at 880 ° C., oil cooling was performed, and then the same treatment as in the case of the above carburizing treatment was performed.

Then, the amount of retained austenite, the surface hardness, the average particle size of the carbide and the maximum particle size of each test piece after the above carburizing heat treatment were measured. The amount of retained austenite was measured by X-ray analysis, and the grain size of carbide was measured by microscopy. Further, a disk-shaped test piece applicable to both the inner ring and the outer ring of the rolling bearing was prepared by using each of the test pieces after the carburizing heat treatment as described in "Special Steel Handbook" (No. 1).
Edition, Electric Steel Research Institute, Riko Engineering, May 25, 1969
Sun) A thrust life test was performed using a thrust bearing steel tester described on pages 10 to 21. The test conditions are as follows.

N = 1000 rpm P _max = 500 Kgf / mm ² Lubricating oil # 68 Turbine oil Steel dust (hardness H _V = 870, diameter 74-1)
47 μm of Fe ₃ C) was mixed in the lubricating oil at 300 ppm.

10% of the life of each test piece was judged.
The life (L ₁₀ life) was defined as the time when cracks and flaking were observed with a microscope or the naked eye, and the life was quantitatively expressed by the cumulative number of revolutions up to this time. The test results shows in Table 1., and the amount of retained austenite
Fig. 3 shows the relationship between the surface hardness and the Cr content and the Mo content.
Shows the relationship in Figure 4. In Table 1, test pieces 1 to 5 correspond to the examples of the present invention, and their Cr and Mo contents are included.
Yes amount is in the range of claim 1.

The test pieces 6 and the following are comparative examples of the present invention. Among them, test pieces 6 to 10 were previously applied (Japanese Patent Application No. 2-127).
930), but the amount of Mo added is less than 1/3 of the amount of Cr added, which is below the range of the present invention. The test pieces 11 to 15 have a Mo addition amount of C.
It is less than 1/3 of the added amount of r and the surface hardness is out of the range of the present invention.

In the test pieces 16 to 19, the Mo addition amount, the retained austenite amount, and the surface hardness are all outside the scope of the present invention. As is clear from Table 1, in all of the test pieces 1 to 5 of the present invention, the maximum particle size among all the carbide particle sizes was remarkably smaller than that of the comparative example, and the effect of extending the life was remarkably recognized. To be

On the other hand, in the test pieces 6 to 10 of the comparative examples, the maximum particle size is much larger than that of the present invention even though the average particle size of the carbides is similar to that of the present invention. The life is only 1/2 to 1/3 or less as compared with that of the present invention. It is recognized that the test pieces 11 to 15 of the comparative examples have large variations in the average particle size of the carbides and the maximum particle size is larger, while the lifespan is shorter than that of the test pieces 6 to 10. .

The test pieces 16 to 19 of the comparative examples have a tendency that the maximum particle size of carbides is smaller than that of the test pieces 11 to 15, but the average particle size of the carbides is considerably larger. , The life is the shortest.
In addition, in this example, the test pieces 1 to 5 made of steel having the composition shown in Table 1 were used, but this component is an example, and steel having other component compositions may be used.

In this embodiment, gas carburizing is used as the carburizing method, but the present invention is not limited to this, and ion carburizing may be performed.

[0032]

As described above, according to the present invention, C
By controlling the amount of addition of Mo with respect to the amount of addition of r within a predetermined range, it is possible to promote the miniaturization of the carbide grain size and provide a rolling bearing having a long life even under the contamination with foreign matter. can get.

[Brief description of drawings]

FIG. 1 is a process chart illustrating carburizing heat treatment conditions for manufacturing a rolling bearing according to the present invention.

FIG. 2 is a process chart illustrating carbonitriding heat treatment conditions for manufacturing a rolling bearing according to the present invention.

FIG. 3 Of the amount of retained austenite and the surface hardness of the present invention
It is a characteristic view which shows a relationship.

FIG. 4 The relationship between the Cr content and the Mo content of the present invention is shown.
FIG.

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Claims (2)

(57) [Claims] 1. A rolling bearing provided with a bearing ring and a rolling element, wherein at least one table of the bearing ring and the rolling element is provided.
The surface layer has a residual austenite amount (γ _R vol%) of 20.
~ 45 vol%, C; 0.1-1.2 wt%, Cr;
1 to 3% by weight, and 2.0% by weight or less of Mo
And the surface hardness (Hv) of the surface layer that is 1/3 or more of the Cr content and is carburized or carbonitrided with respect to the residual austenite amount.
7 × (γ _R vol%) + 920 ≦ Hv ≦ −4.7 × (γ
A rolling bearing characterized by being made of an alloy steel in the range of ( _R vol%) + 1020. 2. The rolling bearing according to claim 1, wherein the maximum grain size of the fine carbide or carbonitride is 2.3 μm or less.