JPH06287703A - Bearing steel excellent in heat treatment productivity as well as in property of retarding microstructural change due to repeated stress load - Google Patents

Abstract

PURPOSE:To improve rolling fatigue life and heat treatment productivity by specifying respective contents of C, Mo, Al, Sb, Si, Mn, Cr, etc., and controlling the grain size of oxide non-metallic inclusions. CONSTITUTION:The bearing steel has a composition consisting of, by weight, 0.5-1.5% C, 0.5-2% Mo, 0.005-0.07% Al, 0.001-0.05% Sb, and the balance Fe or further containing, besides the above, one or more kinds selected from 0.05-0.5% Si, 0.05-2% Mn, 0.05-2.5% Cr, 0.05-1% Ni, 0.05-1% Cu, 0.0005-0.01% B, and 0.0005-0.012% N. Moreover, the maximum grain size of oxide non-metallic inclusions is regulated to <=8mum. By this method, working load at the time of heat treatment can be reduced and microstructural change due to repeated stress load at the time of heavy load rolling can be retarded, and heavy load rolling fatigue life can be improved.

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 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 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, by adding an appropriate amount of Mo, Al and Sb in combination, it is possible to remarkably delay the above-mentioned microstructural change generated under the rolling contact surface due to repeated stress loading, and at the same time, to remove the decarburized layer during heat treatment. It was found that the desired bearing steel can be obtained by controlling the generation of the non-metallic inclusions and controlling the maximum grain size of the non-metallic inclusions.

That is, the bearing steel of the present invention has the following essential constitution. (1) C: 0.5 to 1.5 wt%, Mo: over 0.5 to 2.0 wt%, A
l: 0.005 to 0.07wt%, Sb: 0.001 to less than 0.05wt%, the balance Fe and unavoidable impurities, the maximum particle size of oxide non-metallic inclusions is 8μm or less, repeated stress load Bearing steel excellent in retardation property of microstructure change due to and heat treatment productivity (first invention). (2) C: 0.5 to 1.5 wt%, Mo: over 0.5 to 2.0 wt%, A
l: 0.005-0.07wt%, Sb: 0.001-0.05wt%, Si: 0.05-0.5wt%, Mn: 0.05-2.0
wt%, Cr: 0.05 to 2.5 wt%, Ni: 0.05 to 1.0 wt%, Cu:
0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, and N: 0.0
005 to 0.012 wt% selected from the group consisting of one or more selected from the group consisting of Fe and unavoidable impurities, the maximum particle size of oxide-based non-metallic inclusions being 8 μm or less, repetitive stress Bearing steel excellent in delay characteristics of microstructure change due to load and heat treatment productivity (second invention). (3) C: 0.5 to 1.5 wt%, Mo: over 0.5 to 2.0 wt%, A
l: 0.005 to 0.07 wt%, Sb: 0.001 to less than 0.05 wt%, 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%, 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
~ 1.0 wt%, Zr: 0.02-0.5 wt%, Ta: 0.02-0.5 wt%
%, Hf: 0.02 to 0.5 wt% and Co: 0.05 to 1.5 wt%, including one or more selected from the group,
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). (4) C: 0.5 to 1.5 wt%, Mo: over 0.5 to 2.0 wt%, A
l: 0.005-0.07wt%, Sb: 0.001-0.05wt%, Si: 0.05-0.5wt%, Mn: 0.05-2.0wt%
%, Cr: 0.05 to 2.5 wt%, Ni: 0.05 to 1.0 wt%, Cu: 0.
05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, and N: 0.000
5 to 0.012 wt% selected from the group of 1 or 2 or more, and Si: more than 0.5 to 2.5 wt%,
Cr: over 2.5 ~ 8.0 wt%, Ni: over 1.0 ~ 3.0 wt%, N: 0.0
More than 12 ~ 0.050 wt%, V: 0.05 ~ 1.0 wt%, Nb: 0.05 ~
1.0 wt%, W: 0.05 to 1.0 wt%, Zr: 0.02 to 0.5 wt%,
Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt% and Co:
Repetitive stress, containing one or more selected from 0.05 to 1.5 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 excellent in retardation property of microstructure change due to load and heat treatment productivity (fourth 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: 1.35 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 Mo and Sb (C: 1.00 wt%, Si: 0.23 wt%, Cr: 1.35 wt%, M
n: 0.46wt%, Mo: 0.75wt%, Sb: 0.0015wt%, N: 0.0
042wt%, Al: 0.18wt%, O: 0.0009wt%) (C: 1.02wt%, Si: 0.21wt%, Cr: 1.34wt%, M
n: 0.45wt%, Mo: 0.77wt%, Sb: 0.0018wt%, N: 0.0
042wt%, Al: 0.020wt%, O: 0.0034wt%) (C: 1.00wt%, Si: 0.20wt%, Cr: 1.30wt%, M
n: 0.43wt%, Mo: 1.28wt%, Sb: 0.0040wt%, N: 0.0
032wt%, Al: 0.047wt%, O: 0.0008wt%) (C: 1.01wt%, Si: 0.21wt%, Cr: 1.31wt%, M
n: 0.42wt%, Mo: 1.29wt%, Sb: 0.0042wt%, N: 0.0
031 wt%, Al: 0.048 wt%, O: 0.0016 wt%) was prepared. Then, after normalizing these test materials, spheroidizing annealing, after performing each treatment of quenching and tempering, a cylindrical test piece of 15 mm φ × 22 mm from each test material, 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 Mo and Sb without controlling inclusions, the improvement in the B ₁₀ value is small, while the B ₅₀ value is small. It can be seen that the value is considerably high and is improved. For example, bearing life is about 2 at B ₁₀ value compared to SUJ 2.
And the B ₅₀ value improved about 23 times. On the other hand, in the case of adding a large amount of Mo and Sb in combination, and controlling the maximum particle size of the non-metallic inclusions, it is remarkable for the delay property of the 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 0.03 wt% Sb: 0.002 wt%
mm, Sb: 0.01 mm when containing about 0.004 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 Mo. 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 Mo 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%, machinability and forgeability will deteriorate, so it is limited to the range of 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%. Also, this Si is
Addition of more than 0.5 wt% has the effect of delaying the microstructural change under cyclic stress loading and improving rolling fatigue life. However, if the content exceeds 2.5 wt%, the effect saturates, but the workability and toughness decrease, so in order to further improve the microstructural change retardation property, it exceeds 0.5 to 2.5 wt%. It is effective to add%.

Mn: 0.05 to 2.0 wt% Mn acts as a deoxidizing agent during the melting of steel, and is an element effective in reducing the oxygen content of 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 fatigue life. For this
Mn is added within the range of 0.05 to 2.0 wt%.

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: more than 0.5 to 2.0 wt% Mo is an element that basically improves wear resistance by stabilizing residual carbides, and especially contributes to an increase in hardenability and an increase in strength after quenching and tempering. In addition, precipitation of stable carbide improves wear resistance and rolling contact fatigue life. However, in the present invention, this Mo plays a more important role, and particularly when a large amount of Mo is added, which exceeds 0.5 wt%, the effect of delaying the above-mentioned microstructural change due to the loading of cyclic stress becomes remarkable. , Improve rolling fatigue life in this aspect. But the amount
If it exceeds 1.5 wt%, the machinability and forgeability will be reduced, and it will cause cost increase, so 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 0.005 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 when 0.005 wt% or more is added, hot workability and toughness deteriorate. Therefore, Sb is 0.001 ~
It was decided to contain it in the range of less than 0.005 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: 0.05-0.07 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. For such an action, it is effective to add Al in an amount of 0.05 to 0.07 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 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]

[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 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 Tables 3, 4 and
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 scope of the present invention and steel No. having a Mo content in the steel outside the scope 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). Further, the steel material No. 2 containing no Sb also shows a bad result in the maximum decarburized layer. Steel No. 3 having a large maximum particle size of inclusions has a low B ₁₀ life ratio. On the other hand, the bearing average life indicated by the B ₅₀ value of the steel material No. 7 which is the first invention steel is about 4 times better than that of the conventional steel (steel material No. 1), and the addition of Mo changes the microstructure. It can be seen that this significantly delayed the rolling contact, and as a result, effectively acted to improve the rolling contact fatigue life. Moreover, the maximum decarburized layer depth is 0.01 mm,
It is much smaller than that of o.1 and is about 1/10 of the improvement effect of steel No. 4 in which Sb is outside the proper range of the present invention, which is a remarkable improvement effect.

In addition to Mo, Al and Sb, Si, Mn,
Steel Nos. 8 to 17 (second invention steels) made by adding at least one of Cr, Ni, Cu, Al, B and N have improved B ₅₀ rolling contact fatigue life characteristics that determine bearing life. It was also found that the maximum decarburized layer depth was significantly improved to less than 0.02 mm.

Further, in addition to Mo, Al and Sb, Si and C are further added.
In the case of steel Nos. 18 to 29 in which r, V, 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 fatigue life)
It was confirmed that it was also improved. This is the same in the case of Steel No. 30 to 44 which is obtained by selectively adding all of the above-mentioned improving components recommended in the present invention, and all the bearing rolling life and heat treatment productivity are simultaneously improved. It was found to be effective in improving.

[0037]

As described above, according to the present invention,
Basically, the processing load during heat treatment can be reduced by adding Sb and high Mo of more than 0.5 to 2.0 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 a so-called B ₅₀ high load rolling contact fatigue life improvement and to provide a bearing steel with a long life and high heat treatment productivity. 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. In addition,
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 effect of Mo 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.

Front page continuation (72) Inventor Akihiro Matsuzaki 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture, Kawasaki Steel Corporation Technical Research Division (72) Inventor Shinichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Iron & Steel Co., Ltd.

Claims (4)

[Claims] 1. C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0
wt%, Al: 0.005 to 0.07 wt%, Sb: 0.001 to less than 0.05 wt%, the balance consisting of Fe and unavoidable impurities,
The maximum particle size of oxide-based non-metallic inclusions is 8 μm or less,
Bearing steel with excellent microstructure change delay characteristics due to repeated stress loading and heat treatment productivity. 2. C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0
wt%, Al: 0.005-0.07wt%, Sb: 0.001-0.50wt%, Si: 0.05-0.5wt%, Mn: 0.05-
2.0 wt%, Cr: 0.05 to 2.5 wt%, Ni: 0.05 to 1.0 wt%,
Any one selected from Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 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: 0.5-1.5 wt%, Mo: over 0.5-2.0
wt%, Al: 0.005-0.07 wt%, Sb: 0.001-0.05 wt%, Si: over 0.5-2.5 wt%, Cr: over 2.5-8.
0 wt%, Ni: over 1.0 to 3.0 wt%, N: over 0.012 to 0.050 w
t%, 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: 0.02 to 0.5
wt%, Hf: 0.02-0.5 wt% and Co: 0.05-1.5 wt
%, A microstructure containing recurring stress load, containing at least one selected from the group consisting of Fe and unavoidable impurities and the maximum grain size of oxide-based nonmetallic inclusions being 8 μm or less. Bearing steel with excellent change delay properties and heat treatment productivity. 4. C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0
wt%, Al: 0.005-0.07 wt%, Sb: 0.001-0.05 wt%, Si: 0.05-0.5 wt%, Mn: 0.05-
2.0 wt%, Cr: 0.05 to 2.5 wt%, Ni: 0.05 to 1.0 wt%,
Any one selected from Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 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%,
N: over 0.012 ~ 0.050 wt%, V: 0.05 ~ 1.0 wt%, N
b: 0.05-1.0 wt%, W: 0.05-1.0 wt%, Zr: 0.02-
0.5 wt%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt%
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 maximum particle size of oxide-based non-metallic inclusions is 8 μm.
Bearing steel with m or less, which is excellent in retardation property of microstructure change due to repeated stress loading and heat treatment productivity.