JP2616934B2 - Manufacturing method of bearing race - Google Patents

Description

The present invention relates to a method for manufacturing a bearing race.

[Prior Art] Rolling bearings are precision machine parts that are required to rotate with high accuracy while supporting a large load, and require extremely high dimensional accuracy. With the downsizing, higher performance, and higher efficiency of machines, the use conditions of rolling bearings have also diversified, and the conditions have become increasingly severe in each direction, one of which is the high operating conditions. . That is, there has been a strong demand for a bearing that basically has a long life without causing a dimensional change even when used at a high temperature and without shortening the life.

Normally, in order to use rolling bearings at high temperatures, it is important to suppress dimensional changes at high temperatures, and this dimensional change decomposes unstable residual austenite caused during the quenching process into stable martensite Therefore, a method of reducing the retained austenite by performing sub-zero treatment or tempering at a high temperature (approximately 60 to 100 ° C. higher than the use temperature) has been adopted. Currently, tempering sections as shown in the table are provided according to the operating conditions of the bearing.For example, tempering up to 350 ° C is required for use at 200 to 250 ° C, and the hardness of the bearing is H _R It falls to C53-57, so the rolling fatigue life is reduced to less than 1/10.

On the other hand, like bearings for aircraft jet engines,
Materials that do not decrease in hardness due to high-temperature tempering are used as bearing materials used at high temperatures up to about 300 ° C. Currently, such materials for heat-resistant bearings are T1, M50, and SKH9.
There is high speed steel, such as, these materials, as shown in FIG. 1, although the hardness at tempering 300 to 400 ° C. falls below H _R C60, the secondary hardening phenomena cured again at 500-550 ° C. Yes,
Since it is tempered at 500 to 550 ° C, it is considered that there is no reduction in life up to about 400 ° C and that it can be used without dimensional change. However, since these materials contain a large amount of elements such as M ₀ , V, and W, they are expensive (for example, about 10 times as large as bearing steel), have poor forgeability, and have a quenching temperature of about 1100 ° C. However, it is more expensive than general bearing materials.

The applicant of the present invention disclosed in Japanese Patent Application No.
Unlike standard shaft bearing steel (for example, SUJ2), the life of the bearing steel increases with decreasing hardness until tempering to about 260 ° C or less. It was stated that a long-life bearing which does not cause a problem can be manufactured. However, when tempering at 350 ° C or higher, the hardness becomes H _R C60 or less, and the life decreases as the hardness decreases.
It is necessary to also hold the H _R C60 or a high hardness by 0 ℃ more tempered. Conventionally, there is a nitriding treatment as a surface treatment method to increase hardness, but the treatment method is usually 500
Since carried out in a temperature range of to 600 ° C., tried such a nitriding treatment after quenching to Si-containing bearing steel, H _R C60
The above hardness could not be obtained.

[Problems to be solved by the invention]

As described above, the conventional technique has a problem that it is not possible to obtain an inexpensive bearing raceway that has a long life at a high operating temperature of about 200 to 300 ° C.

[Means for solving the problem]

In order to solve the above-mentioned problems, the present invention relates to a method wherein 0.95 to 1.10% by weight of carbon and 1% by weight of silicon or aluminum are used.
~ 2%, manganese 1.15% or less, chromium 0.90 ~ 1.60%, remaining iron and impurities, steel with oxygen content of 13ppm or less, the product made of the material is quenched and heated to the atmosphere gas nitrogen is entering the material surface by the addition of, and tempering at a high temperature of quenching after 350 to 400 ° C., the residual austenite less than 5% is obtained by employing a means to the hardness H _R C60 or more bearing ring . The details are described below.

First, the composition of the material in the present invention, when the product is thick, molybdenum 0.25 to improve hardenability
%, Preferably 0.10 to 0.25% by weight.

Further, the oxygen content was set to 13 ppm or less for the following reason.

Generally, the method of measuring nonmetallic inclusions in steel includes JI
The S method or the ASTM method is used, but these existing measurement methods cannot be meaningful measurement methods for recent clean steel. Because these measurements are
It measures one cross section in steel and has the disadvantage that the probability of measuring the largest inclusion in steel is extremely low.

Therefore, a test for non-metallic inclusions was conducted using the measuring device shown in FIG. This measuring machine is 60φ × 40φ ×
15 is sandwiched between a pair of rotating bodies 2 and 3, and pressure is applied in the direction of the center of the specimen 1 to apply a pair of rotating bodies 2 and 3.
Of these, one of the rotating bodies 2 is rotated to perform a rotational crack fatigue test of the specimen 1, and the outer diameter of the specimen 1 is tempered in advance by high frequency heating at a high temperature to generate a tensile residual stress in the outer diameter portion. Keep it. In this measuring device, the specimen 1 is fatigue-ruptured from the outer diameter, and the fracture surface does not rub in a short time until the measuring device stops. Can be measured.

Using the above-mentioned measuring machine, a ring specimen was formed from SUJ2 bearing steel specified by the above JIS, and a fatigue test was performed when the oxygen content was changed. FIG. 3 shows the results.

As is clear from FIG. 3, there is a correlation between the oxygen content and the size of the inclusions appearing on the fracture surface, and when the oxygen content falls below 13 ppm, large non-metallic inclusions appear on the fracture surface. Almost no objects are observed. That is, when the oxygen content becomes 13 ppm or less, the effect of the retained austenite on the rolling life is considered to disappear.

In the present invention, the content of Si or Al is 1 to 2% by weight.
The reason for this is that if 1% by weight or less of Si is added, the hardness during high-temperature tempering becomes small, and if 2% by weight or more, the toughness is not preferable, and problems arise in workability of forging, turning and grinding. The same can be said for the addition amount of Al as in the case of Si.

Further, the reason why the retained austenite is set to 5% or less in the present invention is that the bearing race of the present invention has a high temperature (200 to 300).
° C) to minimize process changes when using
This is because it is necessary to reduce the amount of austenite, which causes dimensional change, and usually tempering is performed at 350 to 400 ° C.
In this case, the amount of retained austenite can be reduced to the desired 5% or less.

Next, a method of introducing ammonia gas into the atmosphere at the time of quenching to cause nitrogen to penetrate into the surface layer of the material is called so-called marstressing. This is a method in which the point (start temperature of martensitic transformation) is lowered from the inner layer portion, and compressive residual stress is generated in the outer layer portion. Specific conditions that are usually used include heating to a quenching temperature in an RX gas atmosphere to which ammonia has been added, followed by oil cooling. The surface layer undergoes martensitic transformation later than the internal martensitic transformation during quenching and cooling, so that compressive residual stress is generated in the surface layer after quenching, and it is known that the hardness increases slightly due to solid solution hardening of nitrogen. However, the increase in hardness is H _R C for the same tempering temperature.
The number is only around 1 at most. However, although the reason is not clear, in the steel of the present invention containing silicon or aluminum, when the above-mentioned martressing treatment is performed, the hardness of H _R C60 is maintained even with tempering at 400 ° C., and the same. than it increases the 10 or more hardness H _R C than the hardness (H _R C47) standard bearing steel in which the tempering temperature.

〔Example〕

Hereinafter, examples according to the present invention will be described. In addition, as for the steel containing aluminum, since it is the same as the case of the steel using silicon as described above, only the example using the steel using silicon is shown.

A cylindrical specimen of 12 mm in diameter and 22 mm in length of a silicon-containing steel (composed of carbon 1.0%, silicon 1.5%, manganese 0.4%, chromium 1.4%, balance iron and impurities) with an oxygen content of 13ppm or less was treated with ammonia gas. Heated to 830 ° C in an atmosphere, kept at this temperature for 4 hours, and cooled the oil,
Tempering treatment (temperature 180 ° C, 260 ° C, 400 ° C and 450 ° C, holding time 2 hours) was performed. Then, a hardness measurement and a rolling life test were performed on each test piece.

The hardness measurement results were for a tempering temperature of 180 ° C with H _R C64.5, 26
62.5 at 0 ° C and 60.0 at 400 ° C, but 45
In the case of 0 ° C, it was 58.0.

On the other hand, the rolling life test was performed on a 3/4 "SUJ2 hard ball of a mating ball, lubricating turbine ^# 56 splash lubrication, contact stress Pmax = 5880MPa (600kg
F / mm ² ), and the load speed was 46240 cpm. The results obtained are summarized in FIG. 4. It can be seen that the steel subjected to tempering at 400 ° C. has a long life.

Comparative Example: In the same manner as in the above example, a cylindrical test piece having a diameter of 12 mm and a length of 22 mm of silicon-containing steel consisting of 1.0% carbon, 1.5% silicon, 0.4% manganese, 1.4% chromium, the balance iron and impurities was used. Hardened. The quenching conditions were the same as in Example except that the ammonia added to the RX gas was not added.
C., 230.degree. C. and 260.degree. C., holding time 2 hours). Then, a hardness test and a rolling life test were performed on each test piece.

Hardness (H _R C) measurement results were for a tempering temperature of 180 ° C. 63.
Gradually decreases with 61.0 and the temperature rise in those 62.0,260 ° C. at 0,230 ° C. was dropped and sudden H _R C58.0 intended for 350 ° C..

On the other hand, the rolling life test was performed under the same conditions as in the example, but as shown in FIG.
Up to 350 ° C, the service life increases with decreasing hardness
If the quenching and tempering are performed under the conditions of the comparative example, when used in the range from room temperature to around 200 ° C, a long-life bearing will be manufactured without shortening the life. It has been found that such bearings cannot be manufactured at tempering temperatures above 350 ° C., although they can.

〔effect〕

Above As mentioned, after the circle strike Lessing treatment to a silicon-containing steel, it is possible to maintain a higher hardness H _R C60 when subjected to high temperature tempering up to 400 ° C., for use temperature of 200 to 300 [° C., It is now possible to manufacture inexpensive and long-lasting bearings in place of expensive M50 steel and T1 steel currently used, so it can be said that the significance of the present invention is extremely large. .

[Brief description of the drawings]

Figure 1 is a diagram showing the relationship between tempering temperature and hardness H _R C of the high speed steel of the heat-resistant bearing timber currently being used (M50),
Fig. 2 is a diagram for explaining the principle of a non-metallic inclusion measuring machine (fatigue tester), and Fig. 3 is to measure the size of inclusions by changing the oxygen content of the bearing steel specified in JIS. Figure showing the results,
Figure 4 is a diagram showing the relationship between the tempering temperature and 10% life in an embodiment of the present invention (× 10 ⁴ cycles), Fig. 5 tempering temperature and 10% life (× 10 ⁴ cycles in the comparative example of the invention FIG. 1 ... specimen, 2, 3 ... rotating body.

Claims (1)

(57) [Claims] 1. A weight ratio of 0.95 to 1.10% of carbon, 1-2% of silicon or aluminum, 1.15% or less of manganese, 0.90 to 1.60% of chromium, and the balance of iron.
m or less as a material, and ammonia gas is added to the atmosphere at the time of quenching and heating of the product formed by the material to inject nitrogen into the surface layer of the material, and after quenching, tempered at a high temperature of 350 to 400 ° C. Retained austenite 5% or less, hardness
Method of manufacturing a bearing ring, characterized in that the H _R C60 or higher.