JPH06287695A - Bearing steel excellent in delaying property in change of microstructure caused by repeated stress load and heat treating productivity - Google Patents

Abstract

PURPOSE:To produce bearing steel small in the change of the microstructure caused by repeated stress loads under severe using conditions and high in heat treating productivity. CONSTITUTION:The bearing steel contg., by weight, 0.001 to 0.015% Sb for improving heat treating productivity and contg., particularly, >2.0 to 5.0% Mn and one or >=two kinds selected from >0.5 to 2.5% Si, >2.5 to 8.0% Cr, >1.0 to 3.0% Ni, >0.5 to 2.0% Mo, >0.012 to 0.050% N, 0.05 to 1.0% V, 0.05 to 1.0% Nb, 0.05 to 1.0% W, 0.02 to 0.5% Zr, 0.02 to 0.5% Ta, 0.02 to 0.5% Hf and 0.05 to 1.5% Co as B50 high load rolling fatigue life improving components for prmoting the delay in the change of the microstructure caused by repeated stress loads and in which the maximum grain size of oxide non-metallic inclusions is regulated to <=8mum 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 bearing steel with few non-metallic inclusions, it is essential to reduce the amount of oxygen in the steel, but this has already reached the limit, and expensive melting equipment or a large amount of conventional equipment has to be installed. There was a problem that improvement was necessary and the financial burden was large.

Another move to improve the characteristics of the above-mentioned high carbon bearing steel (JIS-SUJ 2) is a study to suppress the formation of a decarburized layer during heat treatment. Generally, the above JI
Since the bearing steel specified in S-SUJ 2 contains 0.95 to 1.10 wt% of C, it is very hard. Therefore, the spheroidizing annealing is performed to improve the workability and then the forming process. Then, by quenching and tempering treatment thereafter, the strength and toughness required for the rolling bearing were obtained. 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, in each of the above methods, since the atmosphere cleaning at the time of heat treatment or its pretreatment,
There is a problem in that not only the heat treatment cost increases, but also a complicated operation such as setting an appropriate gas composition according to the composition of the material and the heat treatment time is 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 of bearings 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) that occurs during heat treatment. We have found that there are other factors besides the generation of (region). 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,
The inventors of the present invention have three factors that influence the bearing life: the presence of non-metallic inclusions, the formation of a decarburized layer, and the microstructural change that occurs under the rolling contact surface during high load rolling. I found out that.

Therefore, the present inventors have further 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. The microstructure change layer gradually grows as the number of rolling increases, and finally the microstructure change part causes fatigue delamination as shown in the photograph of Fig. 1 (b), which leads to the bearing life. Was understood. 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, in order to improve the bearing life due to the harsh operating environment, it is not enough to simply control the non-metallic inclusions or suppress the decarburization layer, and further, the microstructure generated under the rolling contact surface described above. We have found that it is necessary to delay the time until changes occur.

Therefore, the object of the present invention is to improve the overall rolling contact fatigue life by controlling the particle size of non-metallic inclusions, and in addition, the occurrence of the problem occurs during the use of the bearing under particularly severe operating conditions. By delaying the expected microstructural changes, the bearing life on this side is improved, and the formation of a decarburized layer during heat treatment is also suppressed to improve heat treatment productivity (the effect of reducing the amount of machining removal). The aim is to obtain long-life bearing steel.

[0007]

Based on the above-mentioned findings, the present inventors have also noticed a new "microstructure change delay characteristic" as the bearing life. In order to improve these characteristics, it is of course necessary to design an alloy (component composition) for that purpose, and it is recognized that the life of the bearing cannot be further improved without realizing this. Various experiments and investigations were performed to achieve the suppression of the formation of the. As a result, surprisingly, Mn and
By adding an appropriate amount of 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 at the same time suppress the generation of a decarburized layer during heat treatment. It was found that the desired bearing steel can be obtained by controlling the maximum grain size of the above, and the present invention was conceived.

That is, the bearing steel of the present invention has the following essential constitution. (1) C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, S
b: 0.001 to 0.015 wt%, the balance consisting of Fe and unavoidable impurities, and the maximum grain size of oxide-based nonmetallic inclusions is 8 μm or less. Bearing steel with excellent productivity (first invention steel). (2) C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, S
b: 0.001 to 0.015 wt%, 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: 0.000
5 to 0.01wt%, Al: 0.005 to 0.07wt%, and N: 0.0005 to
0.012 wt% selected from the group consisting of one or more kinds, the balance being Fe and inevitable impurities,
The maximum particle size of oxide-based non-metallic inclusions is 8 μm or less,
A bearing steel (second invention steel) which is excellent in delay characteristics of microstructure change due to repeated stress loading and heat treatment productivity. (3) C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, S
b: 0.001 to 0.015 wt%, Si: more than 0.5 to 2.5 wt
%, Cr: over 2.5 ~ 8.0 wt%, Ni: over 1.0 ~ 3.0 wt%,
Mo: over 0.5 to 2.0 wt%, N: over 0.012 to 0.050 wt%,
V: 0.05 to 1.0 wt%, Nb: 0.05 to 1.0 wt%, W: 0.0
5 to 1.0 wt%, Zr: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5
wt%, Hf: 0.02 to 0.5 wt%, Co: 0.05 to 1.5 wt%, and any one or more selected from
The balance is Fe and unavoidable impurities, and the maximum grain size of oxide-based non-metallic inclusions is 8 μm or less, which is excellent in retardation property of microstructure change due to repeated stress load and heat treatment productivity (3rd Invention steel). (4) C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0 wt%, S
b: 0.001 to 0.015 wt%, 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: 0.000
5 to 0.01wt%, Al: 0.005 to 0.07wt%, and N: 0.0005 to
It contains one or more selected from 0.012 wt%, and further, Si: more than 0.5 to 2.5 wt%, Cr:
2.5 to 8.0 wt%, Ni: 1.0 to 3.0 wt%, Mo: 0.5 to 2.0 wt%, N: 0.012 to 0.050 wt%, V: 0.05 to 1.0
wt%, Nb: 0.05 to 1.0 wt%, W: 0.05 to 1.0 wt%, Z
r: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02
~ 0.5 wt% and Co: 0.05-1.5 wt%, and one or more selected from the rest, Fe and unavoidable impurities as the balance, and the maximum particle size of the oxide-based non-metallic inclusions. A bearing steel (4th invention steel) having a delay property of microstructure change due to repeated stress loading of 8 μm or less and excellent heat treatment productivity.

[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: 1.35 wt%, N: 0.0040 wt%, O: 0.0012 wt%)
And SUJ 2 (C: 1.01wt%, Si: 0.24wt%, Mn: 0.46wt
%, Cr: 1.32wt%, N: 0.0042wt%, O: 0.0015wt%)
And two materials containing Mn and Sb (C: 1.01 wt%, Si: 0.21 wt%, Mn: 2.04 wt%, C
r: 1.32wt%, Sb: 0.0040wt%, N: 0.0040wt%) (C: 1.02wt%, Si: 0.23wt%, Mn: 2.05wt%, C
r: 1.33wt%, Sb: 0.0038wt%, N: 0.0042wt%) (C: 0.98wt%, Si: 0.25wt%, Mn: 4.28wt%, C
r: 1.32wt%, Sb: 0.0078wt%, N: 0.0038wt%, O:
0.0009wt%) (C: 1.00wt%, Si: 0.24wt%, Mn: 4.29wt%, C
r: 1.33wt%, Sb: 0.0080wt%, N: 0.0041wt%, O:
0.0012wt%) of the sample steel was prepared. Then, normalizing these test materials, spheroidizing normalizing, after performing each treatment of quenching and tempering, from each test material 15 mm φ × 22 mm cylindrical test piece, 12 mm φ × 22 mm 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 4
It was tested under a load condition of 6500 cpm. The results of the test are plotted on Weibull distribution establishment paper and are considered to be the numerical values showing the improvement of rolling fatigue life due to the increase of material strength affected by the control of non-metallic inclusions, and B ₁₀ (10% cumulative failure probability) and B ₅₀ (50% cumulative failure probability), which is considered to be a numerical value showing the improvement of rolling fatigue life by delaying the occurrence of microstructure change due to repeated stress loading during high load rolling
And asked. 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, in the case of simply adding a large amount of Mn and Sb without controlling inclusions, the improvement in the B ₁₀ value was small, while the B _{50 was 50.} It can be seen that the value is considerably high and is improved. For example, the bearing life is about 4 at B ₁₀ value compared to SUJ 2.
And the B ₅₀ value showed an improvement of about 21 times. On the other hand, in the case of adding a large amount of Mn and Sb in combination, and controlling the maximum grain size of non-metallic inclusions, it is remarkable for the delay property of microstructure change generated during high load rolling. It was expected that the damage (life) would be delayed by that amount, and that the improvement effect was also observed for the peeling caused by non-metallic inclusions. Regarding the maximum decarburized layer, SUJ 2
0.10 mm, but 0.02 with Sb: 0.004 wt%
mm, Sb: 0.01 mm when containing about 0.008 wt%, suitable Sb
It has also been found that the inclusion of 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 much improved by simply adding a large amount of Mn. However, when the non-metallic inclusion control is also performed, a remarkable effect is shown. On the other hand, looking at the bearing life indicated by the B ₅₀ value with a cumulative failure probability of 50% (hereinafter referred to as “B ₅₀ high load rolling contact fatigue life”), the effect of adding a large amount of Mn is that non-metallic inclusion control Is irrelevant and has become extremely prominent. Therefore, based on these findings, the present inventors improve the bearing life indicated by the B ₁₀ value and the B ₅₀ value of the cumulative damage probability of 10% and 50%, and suppress the growth of the decarburized layer during heat treatment. In view of what kind of alloy design is effective, the range of component composition as described below was 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 forgeability 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%.

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 1.5 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% Cu is an element that enhances the strength after quenching and tempering by increasing quenching, and from this aspect improves rolling fatigue life.
This effect appears at 0.05 or more and becomes saturated at 1.0 wt%.

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 such an 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.

As described above, the component for improving the rolling fatigue life by delaying the microstructural change due to the repeated stress load, the component for improving the rolling fatigue life by increasing the strength, and the decarburized layer formation are suppressed. 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.

[0028]

[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.

[0030]

[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 as if they follow the Weibull distribution, and the average life of steel No. 1 (cumulative damage probability: 10%
The total number of loads before peeling occurred at 50% and 50%) was evaluated as 1. The evaluation results are shown in Table 3, 4,
Shown in accordance with 5.

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

As is clear from the results shown in Tables 3, 4 and 5, steel No. 5 having a C content in the steel outside the range of the present invention and steel No. having a Mn content in the steel outside the range of the steel of the present invention. In No. 6, both the B ₁₀ and B ₅₀ values of the average bearing life are the same as or slightly worse than those of the conventional steel (steel material No. 1). On the other hand, the B ₅₀ rolling contact fatigue life of steel material No. 4 whose Sb content in the steel is outside the range of the steel of the present invention is
The maximum decarburization layer is 0.11m although it is about 4 times better than
m is not so much improved compared to the conventional example (SUJ2). In addition, the steel material No. 2 which does not contain Sb at all shows a bad result because the maximum decarburized layer is large. Steel No. 2 having a large maximum grain size of inclusions has a low B ₁₀ and B ₅₀ life ratio. On the other hand, steel material No. 7, 8 which is the first invention steel
The average bearing life shown by the B ₅₀ value is about 3 to 4 times better than that of the conventional steel (steel No. 1), and the addition of Mn significantly delays the microstructural change, resulting in rolling fatigue. It can be seen that it effectively acted to improve the life. Moreover, the maximum decarburized layer depth is 0.01 to 0.02 mm, which is far less than the conventional steel No. 1 and improved to about 1/10 compared to steel No. 4 in which Sb is outside the proper range of the present invention. The effect is remarkable.

In addition to Mn and Sb, Si, Cr, Mo,
Steel Nos. 9 to 18 (second invention steel) formed by adding at least one of Ni, Cu, Al, B and N are effective in improving the B ₅₀ rolling contact fatigue life characteristics that determine the bearing life. Other than that,
It was also found that the maximum decarburized layer depth was significantly improved to less than 0.02 mm.

Further, in addition to Mn and Sb, Si, Cr, Mo, V,
In the case of Steel Nos. 19 to 32 in which Nb, W, Zr, Ta, Hf, Co and N are positively added in a predetermined amount or more, the above-mentioned bearing life (B ₅₀ rolling It was confirmed that the fatigue life) was also improved. This is a steel N made by selectively adding all of the above improving components recommended in the present invention.
The same applies to the cases of o. 33 to 45, and it was found that there is an effect of simultaneously improving both the rolling life and heat treatment productivity of all the bearings.

[0037]

As described above, according to the present invention,
Basically, the processing load during heat treatment can be reduced by adding Sb and high Mn of more than 2.0 to 5.0 wt% in combination.
(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. Further, by increasing the material strength by controlling non-metallic inclusions, it is possible to improve the rolling fatigue life in this aspect. Furthermore, it is necessary to further reduce the oxygen content in steel and 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.
The development of the bearing steel according to the present invention makes it possible to downsize 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 view showing the effect of Mn addition on the bearing life due to non-metallic inclusions and the bearing life due to microstructural changes.

FIG. 3 is a graph showing the relationship between the maximum grain size of non-metallic inclusions and B ₁₀ rolling contact fatigue life depending on the steel type.

 ─────────────────────────────────────────────────── ─── 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: 0.5-1.5 wt%, Mn: over 2.0-5.0
wt%, Sb: 0.001 to 0.015 wt%, the balance consisting of Fe and unavoidable impurities, the maximum grain size of oxide-based non-metallic inclusions is 8 μm or less, delay of microstructure change due to repeated stress loading Bearing steel with excellent properties and heat treatment productivity. 2. C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0
wt%, Sb: 0.001 to 0.015 wt%, Si: 0.0
5 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%,
Any one selected from B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt%, and N: 0.0005 to 0.012 wt%
Or 2 or more, the balance consisting of Fe and unavoidable impurities, and the maximum particle size of oxide-based non-metallic inclusions is 8 μm
The following bearing steels have excellent microstructure change delay characteristics due to repeated stress loading and heat treatment productivity. 3. C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0
wt%, Sb: 0.001 to 0.015 wt%, Si: more than 0.5
2.5 wt%, Cr: over 2.5 ~ 8.0 wt%, Ni: over 1.0 ~ 3.0 w
t%, Mo: over 0.5 to 2.0 wt%, N: over 0.012 to 0.050 wt
%, V: 0.05 to 1.0 wt%, Nb: 0.05 to 1.0 wt%,
W: 0.05 to 1.0 wt%, Zr: 0.02 to 0.5 wt%, Ta: 0.0
2 to 0.5 wt%, Hf: 0.02 to 0.5 wt% and Co: 0.05 to 1.5
A microstructure by repeated stress loading, containing one or more selected from wt%, the balance consisting of Fe and unavoidable impurities, and the maximum particle size of oxide-based nonmetallic inclusions being 8 μm or less. Bearing steel with excellent structure change retardation properties and heat treatment productivity. 4. C: 0.5 to 1.5 wt%, Mn: over 2.0 to 5.0
wt%, Sb: 0.001 to 0.015 wt%, Si: 0.0
5 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%,
Any one selected from B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt%, and N: 0.0005 to 0.012 wt%
Or more than two kinds, and further, Si: more than 0.5 to 2.
5 wt%, Cr: over 2.5 ~ 8.0 wt%, Ni: over 1.0 ~ 3.0 wt%,
Mo: over 0.5 to 2.0 wt%, N: over 0.012 to 0.050 wt%,
V: 0.05 to 1.0 wt%, Nb: 0.05 to 1.0 wt%, W: 0.0
5 to 1.0 wt%, Zr: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5
wt%, Hf: 0.02 to 0.5 wt%, Co: 0.05 to 1.5 wt%, and any one or more selected from
A bearing steel having the balance of Fe and unavoidable impurities, and having a maximum grain size of oxide-based non-metallic inclusions of 8 μm or less, which is excellent in delay characteristics of microstructural change due to repeated stress loading and heat treatment productivity.