JPH06287688A - Bearing steel excellent in heat treating productivity and delaying property in change of microstructure caused by repeated stress load - Google Patents

Abstract

PURPOSE:To produce bearing steel high in heat treating productivity and small in the change of the microstructure casued by repeated stress loads under severe using conditions. CONSTITUTION:The bearing steel contg., by weight, 0.001 to 0.015% Sb for improving heat treating productivity and contg., particularly, >1.0 to 3.0% Ni and one or two kinds selected from >0.5 to 2.5% Si, 0.02 to 0.5% Zr, 0.02 to 0.5% Ta, 0.02 to 0.5% Hf, 0.05 to 1.5% Co and >0.012 to 0.050% N as B50 high load rolling fatigue life improving components for promoting the delay in the change of the microstructure caused by repeated stress loads is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing steel used as an element member of a rolling bearing such as a roller bearing or a ball bearing, and particularly with the effect of suppressing the formation of a decarburized layer during heat treatment and the severer environment of bearing use. This is a proposal for a bearing steel that is excellent in the characteristic deterioration that occurs as a result, that is, the delay characteristics for the microstructural change (deterioration) that occurs under the rolling contact surface due to repeated stress loading.

[0002]

2. Description of the Related Art Conventionally, high-carbon chromium bearing steel (JI
S: SUJ 2) is most often used. In general, bearing steel is one of the important properties that long rolling fatigue life is important, but it is considered that the influence of non-metallic inclusions in steel is the most significant factor affecting rolling fatigue life. Was there.
Therefore, the mainstream of recent research has been to take measures to improve the bearing life by controlling the amount and size of non-metallic inclusions by reducing the amount of oxygen in steel. For example, as those developed with the aim of further improving the rolling contact fatigue life of bearings, there are Japanese Patent Laid-Open Nos. 1-306542 and 3-1268.
There are proposals such as Japanese Patent No. 39, which are technologies for controlling the composition, shape, or distribution state of oxide-based nonmetallic inclusions in steel. However, in order to manufacture a bearing steel with a small amount of non-metallic inclusions, it is necessary to install expensive melting equipment or drastically improve conventional equipment, and there is a problem that the economical burden is large.

Another move to improve the characteristics of the above-mentioned high carbon bearing steel (JIS-SUJ 2) is a study on workability, especially suppressing formation of a decarburized layer during heat treatment. In general, the bearing steel specified in JIS-SUJ 2 above is 0.95 to 1.
Since it contains 10 wt% of C, it is very hard. Therefore, rolling bearings can be obtained by performing spheroidizing annealing to improve workability, then forming, and then quenching and tempering. Had the necessary strength and toughness. However, it is known that when the heat treatment for improving the characteristics is repeated many times, a "low C concentration region" called a decarburized layer is generated on the surface of the material due to the reaction between C and the atmosphere gas. There is. This decarburized layer not only lowers the hardness of the rolling bearing but also causes the deterioration of rolling contact fatigue life, and therefore it is usually removed by cutting or grinding. For this reason, the material yield and the productivity have been unavoidably reduced. On the other hand, heretofore, as a means for preventing the formation of the decarburized layer, a method of controlling the carbon potential in the atmosphere gas in the furnace during the heat treatment and the spheroidizing method disclosed in JP-A-2-54717 have been disclosed. A method of carburizing at the initial stage of annealing has been proposed. However, since each of the above methods is performed by cleaning the atmosphere during the heat treatment or the pretreatment thereof, not only the heat treatment cost increases but also the setting of an appropriate gas composition according to the composition of the material, the heat treatment time, etc. There was a problem in that a complicated operation was required.

[0004]

DISCLOSURE OF THE INVENTION The inventors have recently conducted various studies on the above-mentioned conventional technique. as a result,
Unexpectedly, the factors that determine the rolling life are the above-mentioned phenomena that have been generally discussed in the past; namely, the presence of the above-mentioned "non-metallic inclusions" and the "decarburization layer" (low C concentration region) that occurs during heat treatment. ). This is because even if the non-metallic inclusions and decarburized layer are simply reduced under the conventional technology, it is possible to improve the rolling contact fatigue life of the bearing, especially the improvement of the bearing life under severe conditions such as high load or high temperature. Because I experienced many cases where I could not get a big effect. From this,
He was convinced that there were other factors that govern bearing life.

Therefore, the present inventors have investigated the bearing life in consideration of the recent bearing usage environment, in particular, the cause of separation of rolling bearings. As a result, due to the shearing stress generated at the time of contact rolling between the inner and outer races of the bearing, the rolling elements, and the rolling elements due to the intensifying environment in which the bearings are used, the lower layer portion (surface layer portion) of the rolling contact surface has As shown in the photograph of (a), it was found that a microstructure change layer composed of a white strip-shaped product and a rod-shaped precipitate was generated. This microstructure-changed layer gradually grows as the number of rolling increases, and finally, as shown in Fig. 1 (b), fatigue delamination occurs from this microstructure-changed part, which may lead to bearing life. all right. In addition, the harsh bearing operating environment, that is, higher surface pressure (miniaturization) and higher operating temperature, will shorten the time until these microstructural changes occur, resulting in a marked reduction in bearing life. I found out. That is, the life of the bearing due to the severer usage environment is not enough to control the decarburized layer and the non-metallic inclusions as in the prior art. For example, simply reducing the amount of non-metallic inclusions cannot delay the time until the above-described microstructure change occurring under the rolling contact surface occurs. As a result, they have found that the bearing life cannot be further improved.

Therefore, an object of the present invention is to delay the microstructural change that is expected to occur during the use of the bearing under harsh service conditions and to significantly improve the bearing life.
It is an object of the present invention to provide a bearing steel that can suppress the formation of a decarburized layer during heat treatment and improve heat treatment productivity (the effect of reducing the amount of work removed).

[0007]

Based on the above-mentioned findings, the inventors of the present invention pay attention to a new "microstructure change delay characteristic" as the bearing life, and to improve this, of course, It is necessary to design a new alloy (compositional composition), and it is not possible to further improve the life of the bearing without realizing this. Furthermore, various achievements are also made to suppress the formation of decarburized layer. Experiments and examinations were performed. As a result, surprisingly, if Ni and Sb are added in appropriate amounts in combination, the above-mentioned microstructural change generated under the rolling contact surface due to repeated stress loading can be significantly delayed, and at the same time the decarburization layer during heat treatment is suppressed The inventors have found that it is also possible to develop the bearing steel of the present invention.

That is, the bearing steel of the present invention has the following essential constitution. (1) C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0 wt%, Sb:
A bearing steel containing 0.001 to 0.015 wt% and O: 0.0020 wt% or less, the balance being Fe and inevitable impurities, and excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load (first invention). (2) C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0 wt%, S
b: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0 wt
%, Cr: 0.05 to 2.5 wt%, Mo: 0.05 to 0.5 wt%, Cu: 0.
05-1.0 wt%, B: 0.0005-0.01 wt% Al: 0.005-0.07 wt% and N: 0.0005-0.012 wt%, including any one or more selected from the group consisting of:
A bearing steel comprising the balance of Fe and unavoidable impurities, which is excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load (second invention). (3) C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0 wt%, S
b: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: more than 0.5 to 2.5 wt%, Zr: 0.02 to 0.5 wt%
%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt%, Co: 0.
05 to 1.5 wt% and N: more than 0.012 to 0.050 wt%, containing one or more selected from the rest, with the balance being Fe
A bearing steel comprising unavoidable impurities and excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load (third invention). (4) C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0 wt%, S
b: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0 wt
%, Cr: 0.05 to 2.5 wt%, Mo: 0.05 to 0.5 wt%, Cu: 0.
05-1.0 wt%, B: 0.0005-0.01 wt% Al: 0.005-0.07 wt% and N: 0.0005-0.012 wt%, including any one or more selected from the group consisting of:
Furthermore, Si: more than 0.5 to 2.5 wt%, Zr: 0.02 to 0.5 wt%
%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt%, Co: 0.
05 to 1.5 wt% and N: more than 0.012 to 0.050 wt%, containing one or more selected from the rest, with the balance being Fe
A bearing steel which is excellent in heat treatment productivity and delay characteristics of microstructural change due to repeated stress load (4th invention).

[0009]

The background to the idea of the bearing steel of the present invention having the above alloy design will be described below based on the results of experiments conducted by the present inventors. First, in the experiment, SUJ 2 (C: 1.02 wt%, Si: 0.25 wt%, Mn: 0.45 wt
%, Cr: 1.35wt%, Ni: 0.0040wt%, O: 0.0012wt%)
And two materials containing Ni and Sb (C: 1.00 wt%, Si: 0.23 wt%, Mn: 0.40 wt%,
Cr: 1.33wt%, Ni: 1.2wt%, O: 0.0009wt%, Sb: 0.0
032wt%, N: 0.0042wt%) (C: 1.00wt%, Si: 0.20wt%, Mn: 0.38wt%,
Cr: 1.30wt%, Ni: 2.5wt%, O: 0.0008wt%, Sb: 0.0
078 wt%, N: 0.0032 wt%) was prepared. Then, after normalizing these test materials, spheroidizing normalizing, after performing each treatment of quenching and tempering, a cylindrical test piece of 15 mm φ × 22 mm and 12 mm φ × 22 mm of each test material A test piece for rolling fatigue test was prepared.

The rolling fatigue life test was carried out by using a radial type rolling fatigue life tester for the rolling fatigue test piece, and Hertz maximum contact stress: 660 kgf / mm ² , cyclic stress number.
Tested under a load condition of 46500 cpm. The results of the test are plotted on the Weibull distribution establishment paper, which is considered to be a numerical value showing the improvement of the rolling fatigue life due to the increase of the material strength, B ₁₀ (10% cumulative failure probability) and the cyclic stress load during high load rolling. B ₅₀ (50) which is considered to be a numerical value showing the improvement of rolling fatigue life by delaying the occurrence of microstructure change.
% Cumulative damage probability) was calculated. Further, for the test of the decarburized layer, after cutting the above cylindrical test piece vertically in the height direction at a position of 10 mm, it is corroded by Nital and the maximum value of the total decarburized layer on the circumference due to the microstructure change ( Hereinafter, it was evaluated by "the maximum decarburized layer".

The results are shown in Table 1. As can be seen from the results shown in Table 1, for the high Ni and Sb composite additive,
Although the improvement in the B ₁₀ value is not so great,
_{The 50} value is extremely high, and the average bearing life is
It was confirmed that the B ₁₀ value was 3.5 times that of SUJ 2 and that the B ₅₀ value was about 22.6 times that of SUJ 2. In particular, a large amount of composite addition of Ni and Sb has a remarkable effect on the delaying property of the microstructure change generated during high load rolling, and it can be expected that the damage (life) is delayed by that amount. Regarding the maximum decarburized layer, SUJ 2 was 0.10 mm, but Sb: 0.0032 wt
% Containing 0.02mm, Sb: 0.0078wt% containing 0.
It was also found that an appropriate Sb content of 01 mm is effective in suppressing the generation of the decarburized layer.

[0012]

[Table 1]

FIG. 2 is a summary of the results of the above-mentioned bearing rolling fatigue life, showing the relationship between the bearing life due to non-metallic inclusions and the life change due to microstructural changes. It is a schematic diagram. As is clear from this figure, the bearing life indicated by the B ₁₀ value with a cumulative failure probability of 10% (hereinafter referred to as “B ₁₀ rolling contact fatigue life”) is not improved by simply adding a large amount of Ni. However, in terms of B ₅₀ value, this
The effect of adding a large amount of Ni is extremely remarkable. Therefore, based on these findings, the inventors have accumulated cumulative damage probability.
Bearing life indicated by a B ₅₀ value of 50% (hereinafter referred to as “B ₅₀
In order to improve the "high load rolling contact fatigue life") and to suppress the growth of the decarburized layer during heat treatment, the composition of the components described below is effective from the viewpoint of what alloy design is effective. The range has been determined.

C: 0.5 to 1.5 wt% C is an element which forms a solid solution in the matrix and effectively acts on the strengthening of martensite, and in order to secure the strength after quenching and tempering and thereby improve the rolling fatigue life. Contained in. If the content is less than 0.5 wt%, such effects cannot be obtained. On the other hand, if it exceeds 1.5 wt%, the machinability and the forgeability will deteriorate, so the range was limited to 0.5 to 1.5 wt%.

Si: 0.05 to 0.5 wt%, more than 0.5 to 2.5 wt% or less Si is used as a deoxidizer during the melting of steel, and is also solid-dissolved in the matrix to increase the resistance to tempering and quenching, It is effective as an element that increases the strength after tempering and improves the rolling fatigue life. The content of Si added for this purpose is in the range of 0.05 to 0.5 wt%. Furthermore, this Si
Has the effect of delaying the microstructural change under cyclic stress loading and improving the rolling fatigue life by adding more than 0.5% by weight. However, its content is 2.5 wt%
If it exceeds 0.1%, the effect is saturated while the workability and toughness are lowered. Therefore, in order to further improve the microstructure change retardation property, it is effective to add more than 0.5 to 2.5 wt%.

Al: 0.005 to 0.07 wt% Al is used as a deoxidizer during the melting of steel, and at the same time,
Combines with N in the steel to refine the crystal grains and contribute to the improvement of the toughness of the steel. Further, it effectively acts to improve the rolling contact fatigue life by increasing the strength after quenching and tempering. These effects cannot be obtained below 0.005 wt%. On the other hand, 0.07wt
Addition in excess of 5% saturates the above-mentioned effects. Therefore, 0.005 to 0.07 wt% of Al is added.

O: 0.0020 wt% or less O forms a hard non-metallic inclusion, so even if a delay in microstructure change due to repeated stress loading is obtained by controlling other components, rolling fatigue life Therefore, it is desirable to be as low as possible. However, a content of 0.0020 wt% or less is acceptable.

Mn: 0.05 to 2.0 wt% Mn is an element which acts as a deoxidizer during the melting of steel and is effective in reducing oxygen in steel. Also, by improving the hardenability of steel, it improves the toughness and hardness of the base martensite and effectively acts to improve the rolling contact fatigue life. These effects require the addition of at least 0.05 wt%, while 2.0
The effect is saturated when added in excess of wt%, so Mn is 0.05 to 2.
Add in the range of 0nwt%.

Cr: 0.05 to 2.5 wt% Cr improves the hardenability and forms stable carbides.
It is a component that improves strength and wear resistance, and thereby effectively acts to improve rolling fatigue life.
To obtain these effects, addition of 0.05 wt% is required,
On the other hand, addition of more than 2.5 wt% saturates the effect.
Is added in the range of 0.05 to 2.5 wt%.

Mo: 0.05 to 0.5 wt% Mo is an element that improves wear resistance by stabilizing residual carbides. In particular, the addition of 0.05 to 0.5 wt% increases the hardenability and contributes to the improvement of the strength after quenching and tempering, and the precipitation of stable carbide improves the wear resistance and rolling fatigue life.

Ni: more than 1.0 to 3.0 wt% This Ni is an element that plays an important role in the present invention, and when it is added in an amount of more than 1.0 wt%, it delays the above-mentioned microstructural change, Improves rolling contact fatigue life. However, even in this case, if it is added in excess of 3 wt%, a large amount of residual γ will be precipitated, resulting in reduced strength and impaired dimensional stability, as well as cost increase. , Over 1.0 ~ 3.0 wt
It is necessary to add it within the range of%.

Cu: 0.05 to 1.0 wt% Cu is added in order to enhance the strength after quenching and tempering due to the increase in quenching and to improve the rolling contact fatigue life. When added for this purpose, a range of 0.05-1.0 wt% is sufficient.

B: 0.0005 to 0.01 wt% B is added in an amount of 0.0005 wt% or more because it increases the hardenability and thereby enhances the strength after quenching and tempering and improves the rolling contact fatigue life. However, if added in excess of 0.01 wt%, the workability deteriorates, so the range is limited to 0.0005 to 0.01 wt%.

Sb: 0.001 to 0.015 wt% This Sb is an element that plays an important role together with Ni in the present invention. In particular, this Sb contributes to the improvement of the heat treatment productivity by suppressing the reaction between C in the surface layer portion of the steel material and the atmospheric gas during the heat treatment to prevent the generation of the decarburized layer. Moreover, the composite addition with Ni has an effect on the delay of the microstructure change in addition to the suppression of the decarburized layer, so that it is positively added. These two effects become remarkable when the Sb content is 0.001 wt% or more, but even if the Sb content exceeds 0.015 wt%, the effect saturates, and conversely, hot workability and It causes deterioration of toughness. Therefore, Sb was included in the range of 0.001 to 0.015 wt%.

N: 0.0005 to 0.012 wt%, more than 0.012 to 0.05
wt% N combines with the nitride-forming element to refine the crystal grains and to form a solid solution in the matrix to enhance the strength after quenching and tempering.
Improves rolling fatigue life. 0.0005 for this purpose
Add within 0.012 wt%. Also, this N is 0.
When added in excess of 012 wt%, rolling fatigue life is improved by delaying microstructural change due to repeated stress. However, if the amount exceeds 0.05 wt%, the workability decreases, so for this purpose it exceeds 0.012 to 0.
Add 05wt%.

P ≦ 0.025 wt% P is desired to be as low as possible because it lowers the toughness and rolling contact fatigue life of the steel, and the upper limit of its allowable limit is
It is 0.025 wt%.

S ≦ 0.025 wt% S combines with Mn to form MnS and improves the machinability. However, if it is contained in a large amount, the rolling contact fatigue life will be reduced, so 0.025 wt% must be the upper limit.

As described above, a component for improving rolling contact fatigue life by delaying microstructure change due to repeated stress loading, a component for improving rolling contact fatigue life by increasing strength, and a bearing for suppressing generation of a decarburized layer The reason for limiting the components for improving the processability and productivity of was explained. By the way, in the present invention, further, Zr, Ta, Hf and Co
One or two or more selected from the above may be added to further improve the bearing life. Table 2 shows the preferable addition range of each of the above elements, the purpose of addition, and the reasons for limiting the upper limit value and the lower limit value.

[0029]

[Table 2]

In the present invention, in order to improve machinability, S, Se, Te, REM, Pb, Bi, Ca, Ti, Mg, P,
The addition of Sn, As, etc. does not hinder the retardation property due to the change in microstructure due to the repeated stress load, which is the object of the present invention, and the machinability can be easily improved. You may add according to it.

[0031]

[Examples] Steels having the chemical compositions shown in Tables 3 and 4 were melted in a converter and then continuously cast.
After diffusion annealing of h, it was rolled into a steel bar of 65 mmφ. Then
A cylindrical test piece of 15 mmφ × 20 mm and a test piece for rolling fatigue were sampled from the D / 4 part of the steel bar by cutting. afterwards,
These test pieces were tested in the order of normalizing, spheroidizing annealing, quenching, and tempering without controlling the atmosphere (in the air atmosphere). Furthermore, the test piece for rolling fatigue is
For the purpose of completely removing the decarburized layer, polishing and lapping of 1 mm or more were performed, and the size of the test piece was 12 mmφ × 22 mm. The depth of the decarburized layer after heat treatment is the maximum of the total decarburized layer on the circumference measured by microstructure observation after cutting a 15 mmφ × 20 mm cylindrical test piece at a position of 10 mm perpendicular to the height direction and corroding with Nital. The value (hereinafter referred to as "maximum decarburized layer") was evaluated. The rolling fatigue life test was performed by a radial type rolling fatigue life tester under the conditions of Hertz maximum contact stress: 600 kgf / mm ² and cyclic stress number: about 46500 cpm. The test results are summarized on the probability paper assuming that they follow the Weibull distribution, and the average life of steel material No. 1 (cumulative failure probability: 50%
Was evaluated as 1. The evaluation results are also shown in Tables 3 and 4.

[0032]

[Table 3]

[0033]

[Table 4]

As is clear from the results shown in Tables 3 and 4,
Steel No. 3 in which the amount of C in the steel is outside the range of the present invention, Steel No. 4 in which the amount of Ni in the steel is outside the range of the present invention, and Steel No. 5 in which the amount of O in the steel is outside the range of the present invention The maximum decarburized layer is 0.01 to 0.
Although 10 mm is improved compared to 0.12 mm of No. 1 conventional steel, the average life is lower than that of conventional steel (steel material No. 1). On the other hand, the steel material No. 2 whose Sb content in the steel is out of the steel range of the present invention
Although the B ₅₀ average life of the steel is 4 times better than that of the conventional steel (steel material No. 1), the maximum decarburized layer is 0.11 mm, which is not so much improved as compared with the conventional example (SUJ 2). In addition, the average life indicated by the B ₅₀ value of the steel material No. 6 of the present invention is
It is about 4 times better than No. 1), and it can be seen that the addition of Ni significantly delayed the microstructural change, and as a result, effectively acted to improve the rolling fatigue life. Moreover, the maximum decarburized layer depth is 0.01 mm, which is much smaller than that of the conventional steel No. 1, and the improvement effect is about 1/10 compared with the steel No. 2 in which Sb is outside the proper range of the present invention. It is remarkable.

Steel No. No. 1 containing at least one of Si, Mn, Mo, Cr, Cu, Al, B and N is added.
It was found that Nos. 7 to 17 not only improved the B ₅₀ rolling contact fatigue life characteristics that determine the average life, but also significantly improved the maximum decarburized layer depth to 0.02 mm or less.

Further, in the case of steel Nos. 18 to 24 in which Si, Zr, Ta, Hf, Co and N are positively added in a predetermined amount or more,
It was confirmed that the above average life (B ₅₀ rolling contact fatigue life) is further improved in accordance with the improvement in heat treatment productivity. This is the same in the case of steel No. 25 ~ 36 obtained by selectively adding all of the above-mentioned improvement components recommended in the present invention, effective in improving both the bearing steel life and heat treatment productivity. I knew it was.

[0037]

As described above, according to the present invention,
Basically, the processing load during heat treatment can be reduced by adding Sb and high Ni composite bearing steel with more than 1.0 wt% (Sb
(Addition effect), and also causes a delay in microstructural change due to repeated stress loading during high-load rolling fatigue life (high
It is possible to achieve the so-called B ₅₀ high load rolling contact fatigue life improvement and to provide a steel for bearings having a long life and high heat treatment productivity with high productivity. Therefore, it is necessary to further reduce the oxygen content in steel or control the composition, shape, and distribution state of oxide-based nonmetallic inclusions present in steel, which was indispensable under the conventional technology. It is not necessary to improve or construct steelmaking equipment. Further, the development of the bearing steel according to the present invention enables downsizing of the rolling bearing and further increase of the bearing operating temperature.

[Brief description of drawings]

1 (a) and 1 (b) are micrographs of a metal structure showing a microstructure change occurring under repeated stress loading.

FIG. 2 is an explanatory diagram showing the effect of Ni addition on the bearing life due to non-metallic inclusions and the bearing life due to microstructural changes.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akihiro Matsuzaki, 1st Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Shinichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba Address: Kawasaki Steel Corporation Technical Research Division

Claims (4)

[Claims] 1. C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0
wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, the balance consisting of Fe and unavoidable impurities and excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load . 2. C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0
wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0
wt%, Cr: 0.05 to 2.5 wt%, Mo: 0.05 to 0.5 wt%, Cu:
0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt% Al: 0.005 to
0.07 wt% and N: 0.0005 to 0.012 wt%, containing one or more selected from the group consisting of Fe and unavoidable impurities, and the balance of heat treatment productivity and microstructural change due to repeated stress loading. Bearing steel with excellent delay characteristics. 3. C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0
wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: more than 0.5 to 2.5 wt%, Zr: 0.02 to 0.5
wt%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt%, Co:
0.05 to 1.5 wt% and N: more than 0.012 to 0.050 wt% Any one or two or more selected from the rest, the balance
Bearing steel consisting of Fe and unavoidable impurities, which has excellent heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading. 4. C: 0.5 to 1.5 wt%, Ni: over 1.0 to 3.0
wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0
wt%, Cr: 0.05 to 2.5 wt%, Mo: 0.05 to 0.5 wt%, Cu:
0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt% Al: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt%, including one or more selected from the group consisting of:
Furthermore, Si: more than 0.5 to 2.5 wt%, Zr: 0.02 to 0.5 wt%
%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt%, Co: 0.
05 to 1.5 wt% and N: more than 0.012 to 0.050 wt%, containing one or more selected from the rest, with the balance being Fe
A bearing steel consisting of unavoidable impurities and excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading.