JP2000017392A - Bearing steel - Google Patents

Abstract

(57) [Problem] To provide a bearing steel having improved rolling life characteristics. Not only the rolling life is improved, but also the life variation is reduced, and a highly reliable bearing product can be manufactured. SOLUTION: In weight%, C: 0.6 to 1.5%, S
i: 0.3 to 3.0%, Mn: 0.3 to 1.5%, N
i: 0.1 to 3.0%, Cr: 0.3 to 5.0% and Al: 0.005 to 0.050%;
003%, P: 0.0. %, S: 0.03% or less,
O: 0.0015% or less, N: 0.015% or less, the balance being substantially Fe, having an alloy composition of substantially Fe, and having a length of 0.5 mm or more of alumina clusters of 10 ^−. Bearing steel of ³ pieces / mm ³ or less. In addition to the above alloy components, Mo: 0.03-1.5% and V: 0.05-
One or two types of 1.0% may be added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in bearing steel. The steel of the present invention provides a bearing having excellent wear resistance, surface fatigue strength and rolling life, and a small variation in life.

[0002]

2. Description of the Related Art A bearing steel represented by JIS SUJ2 has been used as a material of a bearing which is one of mechanical structural parts. Prolonging the life of a bearing is an eternal problem, and a number of bearing steels with improved rolling fatigue characteristics have been proposed as a solution to this problem. Generally, in order to increase the rolling contact fatigue strength of steel, it is effective to reduce the amount of O in the steel, and it is considered that the addition of alloy elements such as Si and Cr is also effective. In addition, effects of addition of alloy components such as Ni and Mo have been reported.

It is known that regulation of impurities also has a good effect on rolling contact fatigue characteristics. For example, a high-life bearing steel that focuses on Mg-based oxides has been proposed (Japanese Patent Laid-Open No. 8-3682). ).

[0004] Although the fatigue strength is improved by the addition or increase of the amount of the alloy element as described above, there has been a tendency that a product having extremely low strength sometimes occurs and the variation in the life is increased. If some of them have a short life, the life will not be very long even on average. From the viewpoint of the reliability of bearing products, there has been a demand for bearing steel having a small variation in life.

[0005] Research aimed at responding to this request,
The present applicant has developed and has disclosed a bearing steel in which the rolling life is improved and the life variation is reduced by using a specific amount of Si and V in combination.
No. 16508).

[0006] The inventors of the present invention who have further studied have now realized that by using a specific amount of Si and Ni together and controlling impurities, it is possible to improve the rolling life and reduce the variation in life. I found it.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to utilize the above-mentioned new knowledge of the present inventors to improve the rolling life characteristics and improve the rolling life of bearing steel. The object of the present invention is to provide a bearing steel in which the variation of the bearing is significantly reduced, and to enable production of a highly reliable bearing product.

[0008]

The bearing steel of the present invention meeting the above-mentioned object basically has a C: 0.6 to 0.6% by weight.
1.5%, Si: 0.3 to 3.0%, Mn: 0.3 to
1.5%, Ni: 0.1 to 3.0%, Cr: 0.3 to
5.0% and Al: 0.005 to 0.050%, Ti: 0.003%, P: 0.03% or less, S:
0.03% or less, O: 0.0015% or less, and N:
0.015% or less, the balance having an alloy composition substantially consisting of Fe, and the amount of alumina clusters having a length of 0.5 mm or more is 10 ⁻³ / mm ³ or less. And

This bearing steel has a Mo content of 0.03 to 1.5% by weight in addition to the above-mentioned alloy components and impurity regulations.
% And V: 0.05 to 1.0% of one or two kinds, with the balance being substantially Fe. Also in this case, it is necessary that the amount of alumina clusters having a length of 0.5 mm or more is 10 ⁻³ / mm ³ or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The function of the alloy components constituting the bearing steel of the present invention and the reasons for limiting the composition range will be described below.

C: 0.6 to 1.5% C is an essential element for securing the strength of steel, and contains 0.6% or more to obtain a predetermined hardness after quenching and tempering. Need to be done. When the content is large, a network-like carbide precipitates during the spheroidizing annealing treatment, and the toughness and machinability are reduced. In addition, large-sized carbides are likely to be formed after casting of the molten metal, which causes cracks during the subsequent rolling. From these points, 1.5% is set as the upper limit.

Si: 0.3-3.0% Si is an important component for the present invention, and acts as a deoxidizing agent and gives temper softening resistance to steel. In order to sufficiently exhibit this effect, the lower limit of 0.3% or more is required. Even if it is added in a large amount, not only does the effect become saturated, but also the transformation point of the steel rises and it becomes necessary to raise the heat treatment temperature, and the forgeability and machinability are impaired. Therefore, the upper limit is set to 3.0%, and the amount of addition up to this limit is selected.

Mn: 0.3-1.5% Mn has the effect of enhancing the hot workability of steel and ensuring the hardenability, and for this purpose, 0.3% or more is added. If the amount of addition is excessive, soft annealing of the material becomes difficult and the machinability deteriorates. Therefore, the addition is limited to 1.5%.

Ni: 0.1-3.0% Ni improves the hardenability. In addition, the effect of suppressing the formation of a white structure and a carbide structure in the rolling fatigue process can be expected to have an effect of extending the life of the bearing product.
In that sense, Ni is an important component together with Si for the steel of the present invention. If the amount is less than 0.1%, such an effect cannot be expected. On the other hand, if a large amount exceeding 3.0% is added, the effect is saturated and the cost is disadvantageous.

Cr: 0.3-5.0% Cr also improves quenchability and increases temper softening resistance.
The effect becomes clear when the lower limit of 0.3% or more is added, but gradually becomes saturated as the amount becomes large. Exceeding the upper limit of 5.0% only increases costs.

Al: 0.005 to 0.050% Al is an element that performs strong deoxidation and is added for the purpose of refining the crystal grains. 0.0
If it is at least 0.05%, it will be recognized, and if it exceeds 0.050%, it will be saturated, and the toughness will be reduced, which is rather disadvantageous.

Ti: 0.003% or less Ti forms a nitride TiN together with N and is a harmful impurity because it forms a starting point of rolling fatigue fracture as a hard precipitate. In order not to impair the rolling life, Ti
Must be kept below 0.003%.

P: 0.03% or less P segregates at austenite crystal grain boundaries and lowers toughness. In order to prevent this, the P content must not exceed 0.03%.

S: 0.03% or less S impairs hot workability of steel. In addition, non-metallic inclusions are formed, which are stretched by rolling to reduce toughness in a direction perpendicular to the stretching direction. To prevent this effect, use S
The amount must be kept within 0.03%.

O: 0.0015% or less O forms oxides, mainly Al ₂ O ₃ , in steel, which deteriorates the rolling fatigue strength. Although it is desired to reduce as much as possible, the limit of 0.0015% is determined in consideration of the effect of reducing the amount of O and the limit that can be achieved by ordinary refining.

N: 0.015% or less N forms a nitride with Al as described above. AlN
Although there is a view that a very small amount is useful for refining austenite crystal grains, it cannot be contested that it becomes a base of rolling fatigue failure as a hard precipitate. As an acceptable limit from this perspective,
A value of 0.015% was determined.

The reason why the amount of alumina clusters having a length of 0.5 mm or more was limited to 10 ^-3 / mm ³ or less is that large clusters have a significant effect on rolling contact fatigue strength. In order to reduce the variation in the rolling fatigue life and the rolling life as intended in the present invention, such an extremely clean steel must be realized.

The action of the component in which one or two types are arbitrarily added in addition to the basic alloy components and the reason for limiting the composition range are as follows. Mo: 0.03 to 1.5% Mo is an element for improving the hardenability of steel, and is added as necessary. Less than 0.03% has little effect,
If it exceeds 1.5%, the effect is saturated.

V: 0.05 to 1.0% V forms carbides and enhances the wear resistance of the bearing. It is effective when the lower limit is 0.05% or more. Since addition of a large amount leads to formation of a large carbide, an addition amount within 1.0% is selected.

The production of the bearing steel of the present invention can be carried out without any particular problems by those skilled in the art by appropriately incorporating advanced deoxidation and degassing techniques known in ordinary steel refining technology. .

[0026]

EXAMPLE A bearing steel having an alloy composition shown in Table 1 was melted and a hot-rolled material was used as a test material. 100mm × from this material
A test piece of 80 mm x 10 mm is cut out and the frequency is 50 MHz.
Submerged immersion flaw detection using ultrasonic waves at a depth of 0.4 mm
The particle size distribution of the alumina cluster in the region up to was measured. Separately, a radial rolling contact fatigue test specimen having a test part diameter of 12 mm was cut out from the same material.

[0027] Table 1 No. C Si M n Ni Cr Mo / V P S Al Ti O N Example 1 0.83 1.01 0.51 1.01 1.49 - 180 210 210 24 10 90 2 0.83 1.52 0.35 0.71 1.48 - 200 190 200 23 9 100 3 1.01 0.51 0.50 0.95 1.50-190 180 220 23 9 80 4 1.03 1.02 0.44 1.02 1.51-190 180 210 25 11 120 5 1.00 1.03 0.45 2.01 1.49-180 200 210 24 10 90 6 1.01 1.51 0.40 1.00 1.51-200 190 210 23 9 100 7 1.22 1.01 0.46 0.75 1.50-200 200 220 22 11 110 8 1.20 1.00 0.45 1.03 1.48 Mo 0.24 180 210 200 23 9 100 9 1.21 1.02 0.40 2.00 1.49 V 0.75 190 190 200 24 10 90 10 1.47 1.01 0.37 1.02 1.51- 180 170 210 23 11 11
0 Comparative Example 1 0.82 0.24 0.77 0.03 1.51-200 190 200 23 10 90 2 1.00 0.21 0.76 0.02 1.50-160 200 210 23 9 100 3 1.01 1.00 0.35 0.02 1.49-170 190 210 24 9 100 4 1.22 0.23 0.76 0.03 1.48-200 190 200 25 10 100 units are C to Mo / V in% and P to N in ppm.

This is subjected to a quenching and tempering treatment under the following conditions: quenching: 850 ° C. × 30 minutes—oil cooling Tempering: 160 to 250 ° C. × 60 minutes—air cooling (The tempering temperature is HRC hardness after tempering. About 62
Was adjusted within the above range so that ) After polishing the surface by machining, the surface pressure is 5.9 GPa
Under the following conditions. The results are shown in Table 2 together with the amount of the alumina cluster.

Table 2 No. Alumina Rolling life 1 × 10 ⁷ times 5 × 10 ⁷ times Cluster (× 10 ⁷ times) Life rate less than or equal Life rate less than (× 10 ⁻³ pieces / mm ³ ) L ₁₀ L ₅₀ (%) (%) Example 1 0.5 19.3 39.2 0 7.6 20.7 36.2 47.2 0 5.5 3 0.6 21.2 41.1 0 5.0 4 0.5 43.1 49.1 0 4.1 5 0.4>50> 500 00.5 0.5 34.1 46.1 0 4.3 7 0.6 39.3> 500 0 8 0.7>50> 50 0 0 9 0.5>50> 50 0 0 10 0.4>50> 50 0 0 Comparative example 1 0.6 3.4 24.1 3.3 30.3 2 0. 7 2.3 18.5 4.0 34.2 3 0.8 4.1 37.0 2.7 26.5 4 1.2 1. 0 11.2 10.0 44.1 In Table 2, “L ₁₀ ” represents the life when the Weibull cumulative probability is 10%, and L ₅₀ represents the life when the Weibull cumulative probability is 50%.

[0030] From 2 data table, bearing steel of the present invention, as compared with the comparative steel, the rolling life L ₁₀ also L ₅₀ it can be seen that is also significantly improved. The probability of breaking at 1 × 10 ⁷ times or less is practically zero, and the probability of breaking at 5 × 10 ⁷ times or less is one digit lower than that of the comparative steel.
Comparative Example 4 having many alumina clusters has a short life.

[0031]

The bearing steel of the present invention exhibits excellent rolling fatigue characteristics, has a high rolling life and has a small variation. Therefore, when a bearing product is manufactured from this steel, a product having a long life and high reliability can be obtained.

Claims (2)

[Claims] C. 0.6 to 1.5% by weight, S:
i: 0.3 to 3.0%, Mn: 0.3 to 1.5%, N
i: 0.1 to 3.0%, Cr: 0.3 to 5.0% and Al: 0.005 to 0.050%;
003% or less, P: 0.03% or less, S: 0.03% or less, O: 0.0015% or less, and N: 0.015% or less, with the balance being substantially Fe. A bearing steel having an alumina cluster having a length of 0.5 mm or more and a length of 10 ^-3 / mm ³ or less. 2. In addition to the alloy components and impurity regulations specified in claim 1, one or two of Mo: 0.03 to 1.5% and V: 0.05 to 1.0% by weight. Alumina clusters having an alloy composition containing seeds, the balance being substantially Fe, and having a length of 0.5 mm or more.
^-3 pieces / mm ³ or less, a bearing steel.