JP3379785B2 - Bearing steel with excellent heat treatment productivity and delayed microstructure change due to repeated stress loading - Google Patents

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 to rolling due to a characteristic deterioration caused by the harsh working environment of the bearing, that is, a repeated stress load. We propose a bearing steel that has excellent retardation properties against microstructural changes (deterioration) that occur under the dynamic contact surface, and that has the effect of suppressing the formation of a decarburized layer that occurs during heat treatment.

[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 contact stress between the inner and outer races of the bearing and the rolling elements due to the intensifying environment in which the bearing is used, the shear stress generated at the time of rolling causes the lower layer portion (surface layer portion) of the rolling contact surface to It was found that a microstructure change layer composed of a white product in the form of a strip and a precipitate in the form of a rod was generated as shown in FIG. 1 (a). It was found that the microstructure-change layer gradually grows as the number of rolling increases, and finally the microstructure-change portion causes fatigue separation as shown in FIG. 1 (b), which leads to the bearing life. It was Furthermore, the harsh bearing operating environment, that is, higher surface pressure (miniaturization) and higher operating temperature, will shorten the number of rolling cycles until these microstructural changes occur, leading to a marked reduction in bearing life. I found out. In other words, the bearing life due to the harsh environment of use is not sufficient to control the decarburized layer and non-metallic inclusions as in the conventional technique.For example, simply reducing the non-metallic inclusions is not enough. However, it is not possible to delay the time until the above-mentioned microstructure change occurring under the rolling contact surface occurs. As a result, they have found that the bearing life cannot be further improved.

[0006] Therefore, an object of the present invention is to delay the microstructural change expected to occur during the use of the bearing under harsh operating conditions, and thereby to significantly improve the life of the bearing, and at the time of heat treatment. (EN) A bearing steel capable of suppressing the formation of a decarburized layer and improving heat treatment productivity (reducing work removal).

[0007]

The inventors of the present invention focused on a new "microstructure change delay characteristic" as the bearing life based on the above-mentioned knowledge, and of course, it is necessary to improve it. 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, by adding an appropriate amount of Mn and Sb in combination, it is possible to significantly delay the above-mentioned microstructural change generated under the rolling contact surface due to repeated stress loading, and further suppress the occurrence of a decarburized layer during heat treatment. The inventors have found that it is also possible to develop the bearing steel of the invention.

That is, the bearing steel of the present invention has the following essential constitution. (1) C: over 0.55 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, Sb:
Bearing steel containing 0.001 to 0.015 wt% and O: 0.0020 wt% or less, the balance being Fe and unavoidable impurities and having excellent heat treatment productivity and delay characteristics of microstructure change due to repeated stress load (first invention) . (2) C: over 0.55 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, Sb:
0.001 to 0.015 wt%, O: 0.0020 wt% or less , Si: 0.05 to 0.5 wt%, Cr: 0.05 to 2.5 wt%, Ni: 0.05
~ 1.0wt%, Mo: 0.05 ~ 0.5wt%, Cu: 0.05 ~ 1.0wt%,
B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt% and N:
Bearing steel containing one or more selected from 0.0005 to 0.012 wt% and the balance being Fe and unavoidable impurities and having excellent heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading. (Second invention). (3) C: more than 0.55 to 1.5 wt%, Mn: more than 2.0 to 5.0 wt%, Sb:
It contains 0.001 to 0.015 wt% and O: 0.0020 wt% or less. Furthermore , Si: more than 0.5 to 2.5 wt%, Cr: more than 2.5 to 8.0 wt%, Ni: 1.
Over 0 ~ 3.0wt%, Mo: over 0.5 ~ 2.0wt%, Cu: over 1.0 ~ 2.5wt
%, N: more than 0.012 to 0.050 wt%, V: 0.05 to 1.0 wt%, N
b: 0.05-1.0wt%, W: 0.05-1.0wt%, Zr: 0.02-0.5
wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02 to 0.5 wt% and Co:
Bearing steel that contains one or more selected from 0.05 to 1.5 wt% and the balance is Fe and unavoidable impurities, and is excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load. (Third invention). (4) C: over 0.55 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, Sb:
0.001 to 0.015 wt%, O: 0.0020 wt% or less, further containing any one or more selected from the following group I components, and further containing the following group II Ingredient (just
However, the microstructure change due to heat treatment productivity and repeated stress loading, containing one or more selected from the group (excluding elements selected from Group I) , and the balance consisting of Fe and unavoidable impurities. Bearing steel excellent in retardation property (4th invention). Serial group I: Si: 0.05~0.5wt%, Cr: 0.05~2.5wt%, Ni: 0.
05 ~ 1.0wt%, Mo: 0.05 ~ 0.5wt%, Cu: 0.05 ~ 1.0wt
%, B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt% Group II: Si: more than 0.5 to 2.5 wt%, Cr: more than 2.5 to 8.0 wt%, Ni:
Over 1.0 ~ 3.0wt%, Mo: over 0.5 ~ 2.0wt%, Cu: over 1.0 ~ 2.5
wt%, N: more than 0.012 to 0.050 wt%, V: 0.05 to 1.0 wt%, N
b: 0.05-1.0wt%, W: 0.05-1.0wt%, Zr: 0.02-0.5
wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02 to 0.5 wt% and Co:
0.05-1.5wt%

[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 Mn and Sb (C: 1.01 wt%, Si: 0.21 wt%, Mn: 2.04 wt%, C
r: 1.33wt%, O: 0.0010wt%, Sb: 0.0040wt%, N:
0.0040wt%) (C: 0.98wt%, Si: 0.25wt%, Mn: 4.28wt%, C
r: 1.32wt%, O: 0.0009wt%, Sb: 0.0078wt%, N:
0.0038wt%) of the sample steel 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.

In the rolling fatigue life test, the above-mentioned rolling fatigue test piece was used with a radial type rolling fatigue life tester, and Hertz maximum contact stress: 600 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, with respect to the high Mn-added material, the improvement in the B ₁₀ value is not so large, but the B ₅₀ value shows a remarkably high value, and the average bearing life is longer than that of SUJ 2. It was observed that the B ₁₀ value showed an improvement of about 4 times and the B ₅₀ value showed an improvement of 21 times. In particular, the addition of a large amount of Mn has a remarkable effect on the delay characteristic 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 the one containing Sb: 0.0040 wt% was 0.02 mm, Sb: 0.
It was also found that when the content of Sb is 0.01 mm, the content of Sb is appropriate for 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 experiments, showing the relationship between the bearing life due to non-metallic inclusions and the change in life 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 Mn. However, B with a cumulative damage probability of 50%
Looking at the bearing life indicated by ₅₀ values (hereinafter referred to as “B ₅₀ high load rolling contact fatigue life”), the effect of adding a large amount of Mn is extremely remarkable. So the inventors
Based on these findings, in order to improve the B ₅₀ high load rolling contact fatigue life and to suppress the growth of the decarburized layer during heat treatment,
From the viewpoint of what kind of alloy design is effective, the range of component composition as described below was determined.

C: more than 0.55 to 1.5 wt% C is an element that is solid-dissolved in the matrix and effectively acts to strengthen martensite. It improves the strength after the hardening and tempering and the rolling fatigue life. Is included for If the content is 0.55 wt% or less , such an effect cannot be obtained. On the other hand, if it exceeds 1.5 wt%, the machinability and forgeability deteriorate, so it is limited to the range of more than 0.55 to 1.5 wt%.

Si: 0.05 to 0.5 wt%, more than 0.5 to 2.5wt% Si is used as a deoxidizer during the melting of steel and also as a base material.
Quenching and tempering due to an increase in softening resistance
As an element that increases the strength after rolling and improves rolling contact fatigue life
Is effective. Containing Si added for these purposes
The amount is in the range of 0.05 to 0.5 wt%. Also, this Si is
If more than 0.5 wt% is added, the stress will increase under repeated stress loading.
Improves rolling contact fatigue life by delaying the change in microstructure
Has the effect of However, its content exceeds 2.5 wt%
Then, while the effect is saturated, the workability and toughness decrease.
As a result, it is possible to further improve the microstructure change delay characteristics.
For this reason, it is effective to add more than 0.5 to 2.5 wt%.
It

Mn: more than 2.0 to 5.0 wt% Mn is an element that plays an important role together with Sb in the present invention. Particularly, by adding a large amount exceeding 2.0 wt%, Mn can be Under cyclic stress loading,
It accelerates the delay of the microstructure change described above, and significantly improves the B ₅₀ rolling contact fatigue life. However, if the amount added exceeds 5.0 wt%, a large amount of residual γ is generated and the strength and dimensional stability are reduced. Add in range.

Cr: 0.05 to 2.5 wt%, more than 2.5 to 8.0 wt% Cr improves the hardenability and forms stable carbides.
It is a component that improves strength and wear resistance, and eventually improves rolling contact fatigue life. To obtain this effect, addition of 0.05 to 2.5 wt% is sufficient. Furthermore, when Cr is added in a large amount exceeding 2.5 wt%, it is effective in delaying the microstructure change due to repeated stress loading and improving the rolling fatigue life in this aspect. The effect of Cr addition for this purpose is not only saturated when it exceeds 8.0 wt%, but rather causes a decrease in the amount of solid solution C during quenching, resulting in a decrease in strength. Therefore, when it is added for this purpose, it must be more than 2.5 to 8.0 wt%.

Ni: 0.05 to 1.0 wt%, more than 1.0 to 3.0 wt% Ni increases the hardenability to increase the strength after quenching and tempering, improve toughness, and improve rolling contact fatigue life. Is added in the range of 0.05 to 1.0 wt%. Further, this Ni, when added in excess of 1.0 wt%, delays the microstructure change during rolling, thereby improving rolling fatigue life. However, even in this case, if it is added in excess of 3 wt%, a large amount of residual γ will be deposited, resulting in a decrease in strength and a loss of dimensional stability.
If this effect is expected, it is necessary to add it in the range of more than 1.0 to 3.0 wt% because it increases the cost.

Mo: 0.05-0.5 wt%, more than 0.5-2.0 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. Furthermore, when Mo is added in a large amount of more than 0.5 wt%, the effect of delaying the microstructure change during rolling becomes remarkable, and the rolling fatigue life in this aspect is improved. However, if the amount exceeds 2.0 wt%, machinability,
Forgeability is deteriorated and it causes a cost increase. Therefore, for this purpose, it is necessary to add it in the range of more than 0.5 to 2.0 wt%.

Cu: 0.05 to 1.0 wt%, more than 1.0 to 2.5 wt% Cu is added to enhance the strength after quenching and tempering by increasing quenching and to improve the rolling fatigue life. When added for this purpose, a range of 0.05-1.0 wt% is sufficient. On the other hand, this Cu is also different from the above purpose.
When it is added in a large amount exceeding 1.0%, the microstructural change due to repeated stress loading is delayed to significantly improve the rolling and rolling contact fatigue life. However,
If the amount exceeds 2.5 wt%, this addition effect saturates, and rather the forgeability decreases, so for this purpose it is necessary to add in the range of more than 1.0 to 2.5 wt%. is there.

Sb: 0.001 to 0.015 wt% This Sb is an element that plays an important role together with Al 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, since the combined addition with Al has an effect on the retardation of the microstructure change as well as the suppression of the decarburized layer, 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%.

B: 0.0005 to 0.01 wt% B is added in an amount of 0.0005 wt% or more because it increases the hardenability to increase the strength after quenching and tempering and improves the rolling 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%.

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 also effectively acts to improve rolling fatigue by increasing the strength after quenching and tempering. Due to this effect, it is effective to add 0.005 to 0.07 wt% of Al.

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 desirable because it lowers the toughness and rolling fatigue life of the steel, so it is desirable to be as low as possible.
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.

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.

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, V, Nb, W, Zr, T
The bearing life may be further improved by adding one or more selected from a, Hf and Co. 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]

[Example] Steels having the chemical compositions shown in Tables 3, 4, and 5 were melted in a converter and continuously cast, and the obtained steels were heated to 1240 ° C.
After diffusion annealing for 30 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 collected from the D / 4 part of the steel bar by cutting. Thereafter, these test pieces were tested in the order of normalizing, spheroidizing annealing, quenching, and tempering without controlling the atmosphere (in the air atmosphere). Further, the rolling fatigue test piece was ground and lapped to a size of 1 mm or more for the purpose of completely removing the decarburized layer, 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, 4 and 5.

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

As is clear from the results shown in Tables 3, 4, and 5, steel material No. 3 having a C content in the steel outside the range of the present invention, and steel material No. having a Mn content in the steel outside the range of the present invention steel. 4 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
~ 0.11mm, which is a slight improvement over the conventional steel (steel material No. 1) 0.12mm, but the average bearing life (B ₅₀ life ratio)
In each case, the result was lower than that of the 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 superior to the conventional steel (steel material No. 1) by about 4 times, the maximum decarburized layer is 0.11 mm, which is not so much improved as compared with the conventional example (SUJ 2). On the other hand, the bearing life of the steel material No. 6 of the present invention, which is represented by B ₅₀ rolling contact fatigue life, is about 5 times better than that of the conventional steel (steel material No. 1), and the addition of Mn is It can be seen that the microstructure change was significantly delayed, and as a result, it effectively acted to improve the rolling fatigue life (B ₅₀ ). Moreover, the maximum decarburized layer depth is 0.01 mm, which is much smaller than that of conventional steel No. 1, and the improvement effect is about 1/10 compared to steel No. 3 in which Sb is outside the proper range of the present invention. It is remarkable.

In addition to Mn and Sb, Si, Cr, Mo, Ni,
Steel N made by adding at least one of Cu, Al, B and N
It was found that the average life of 8 to 18 is not only the improvement of the B ₅₀ rolling contact fatigue life characteristic that determines the bearing life, but also the maximum decarburized layer depth is 0.02 mm or less.

Further, in addition to Mn and Sb, Si, Cr, Mo, W,
Any one of V, Nb, Zr, Ta, Hf, Ni, Cu, Co, and N
In the case of Steel Nos. 19 to 32 in which a certain amount of abnormal rolling fatigue life improving component is positively added, the above average life (B ₅₀ rolling fatigue life) is adjusted in accordance with the improvement of heat treatment productivity. It has been confirmed that it will be further improved. This is the same in the case of Steel No. 33 to 45 which is obtained by selectively adding all of the above-mentioned improving components recommended in the present invention, and is effective in both improving the bearing steel life and the heat treatment productivity. I knew it was.

[0038]

As described above, according to the present invention,
Basically, the processing load during heat treatment can be reduced by adding Sb and using Mn of more than 2.0% as a composite additive bearing steel.
(Additional effect of Sb) In addition, it causes a delay in microstructure change due to repeated stress loading during high load rolling fatigue life.
(High Mn content effect) The so-called B ₅₀ high load rolling contact fatigue life can be improved to provide a bearing steel with a long life and high productivity in heat treatment. 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. Also,
The development of the bearing steel according to the present invention makes it possible to reduce the size of the rolling bearing and further increase 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 effects of addition of Mn and Sb on the bearing life due to non-metallic inclusions and the bearing life due to microstructural changes.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works Ltd. Technical Research Division (56) Reference JP-A-4-337048 (JP, A) Special Features Kaihei 4-235251 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. C: over 0.55 to 1.5 wt%, Mn: over 2.0 to 5.0 wt.
%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, the balance being Fe and unavoidable impurities, and is excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load. 2. C: more than 0.55 to 1.5 wt%, Mn: more than 2.0 to 5.0 wt%
%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less , Si: 0.05 to 0.5 wt%, Cr: 0.05 to 2.5 wt%,
Ni: 0.05 to 1.0 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%, and any one or more selected from the rest, and the balance from Fe and inevitable impurities. A bearing steel with excellent heat treatment productivity and excellent delay characteristics for microstructural changes due to repeated stress loading. 3. C: more than 0.55 to 1.5 wt%, Mn: more than 2.0 to 5.0 wt.
%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less , Si: more than 0.5 to 2.5 wt%, Cr: more than 2.5 to 8.0 wt
%, Ni: over 1.0 to 3.0 wt%, Mo: over 0.5 to 2.0 wt%, Cu: 1.
0 to 2.5 wt%, N: 0.012 to 0.050 wt%, V: 0.05 to 1.
0wt%, Nb: 0.05-1.0wt%, W: 0.05-1.0wt%, Zr:
0.02-0.5wt%, Ta: 0.02-0.5wt%, Hf: 0.02-0.5wt
% And Co: 0.05 to 1.5 wt% selected from the group consisting of one or more selected from the group consisting of Fe and unavoidable impurities, and the balance of Fe and unavoidable impurities. Excellent bearing steel. 4. C: more than 0.55 to 1.5 wt%, Mn: more than 2.0 to 5.0 wt.
%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, further containing any one or more selected from the following group I components, and further the following group II components
(However, excluding the elements selected in Group I) , any one or more selected from the group
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. Serial group I: Si: 0.05~0.5wt%, Cr: 0.05~2.5wt%, Ni: 0.
05 ~ 1.0wt%, Mo: 0.05 ~ 0.5wt%, Cu: 0.05 ~ 1.0wt
%, B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt% Group II: Si: more than 0.5 to 2.5 wt%, Cr: more than 2.5 to 8.0 wt%, Ni:
Over 1.0 ~ 3.0wt%, Mo: over 0.5 ~ 2.0wt%, Cu: over 1.0 ~ 2.5
wt%, N: more than 0.012 to 0.050 wt%, V: 0.05 to 1.0 wt%, N
b: 0.05-1.0wt%, W: 0.05-1.0wt%, Zr: 0.02-0.5
wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02 to 0.5 wt% and Co:
0.05-1.5wt%