JP3411388B2 - Bearing member with excellent heat treatment productivity and delay characteristics of microstructure change due to repeated stress load - 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 member used as an element member of a rolling bearing such as a roller bearing or a ball bearing, and in particular, a microstructure change generated under a rolling contact surface due to repeated stress load in a severe operating environment. A bearing member that has excellent delay characteristics against (deterioration) regardless of the cleanliness of the lubricating oil even if the lubricating oil is in a poor state and that has an excellent effect of suppressing the formation of a decarburized layer during heat treatment. To suggest.

[0002]

2. Description of the Related Art Conventionally, high-carbon chromium bearing steel (JIS: JIS:
SUJ 2) has been used most often. It is generally important for bearing steels to have a long rolling contact fatigue life, but it was thought that the influence of hard non-metallic inclusions in the steel was significant as a factor affecting this rolling contact fatigue life. Therefore, the mainstream of recent research has been 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 one developed for the purpose of further improving the rolling contact fatigue life of a bearing, Japanese Patent Laid-Open No. 1-306542 has been proposed.
There are proposals such as Japanese Patent Laid-Open Publication No. 3-126839 and Japanese Patent Laid-Open Publication No. 3-126839, which are techniques 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.

On the other hand, the life of the bearing is greatly affected by the characteristics of the lubricating oil. Generally, in lubricating oil, polishing powder and burrs during polishing, or abrasion powder generated during rotation (hereinafter,
It has been pointed out that these are mixed with "dust", and that the mixing of dust causes a reduction in rolling life of the bearing member. Conventionally, in order to improve the life of the bearing in an environment containing dust, a method of mainly improving the cleanliness of the lubricating oil has been adopted, but JP-A-5-78782 and JP-A-5-78814 are used. According to the disclosure, by carbonitriding the surface layer of the bearing member, by controlling the carbide area ratio of the surface layer, the surface carbon concentration, the amount of surface retained austenite, by improving the characteristics in the surface layer portion, It is proposed to control the shape of the indentation caused by dust, thus leading to the reduction of stress concentration and prolonging the service life. However, this conventional technique does not essentially improve the steel structure, and the so-called carbonitriding / hardening heat treatment
Since it is a method of externally modifying only the surface layer of the bearing member, it does not lead to the improvement of the microstructure change portion observed at the lower side of the surface layer portion as described later, and further the treatment cost is high. Was left.

Another move to improve the characteristics of the above-mentioned high carbon bearing steel (JIS-SUJ 2) is research on workability, especially a technique for suppressing the formation of a decarburized layer during heat treatment. In general, the bearing steel specified in JIS-SUJ2 above is 0.
Since it contains 95-1.10 wt% C, it is very hard,
Therefore, the strength and toughness required for rolling bearings were obtained by performing spheroidizing annealing to improve workability, then forming, then quenching and tempering. 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. That left a problem where complicated operations were required.

[0006]

By the way, according to the recent research results conducted by the inventors, as a factor that determines the rolling life, a phenomenon which has been generally discussed in the past; -78782, 5-78814, etc., "decarburization layer" (low C concentration region) on the surface of a bearing member caused by heat treatment, which is a problem, and JP-A-1-306542.
It was found that there are other factors besides the existence of "non-metallic inclusions" which is a problem in each of the publications, No. 3-126839. This is because the rolling contact fatigue life of the bearing, especially the severe load such as high load or high temperature, is reduced by simply heat-treating the bearing member surface layer under the conventional technique even if the decarburized layer and non-metallic inclusions are simply reduced. This is because we have often experienced that a great effect cannot be obtained for improving the bearing life under the conditions.
From this, the inventors were convinced of the existence of other factors that govern the life of the bearing.

[0007] Therefore, the present inventors have continued to earnestly study bearing life, in particular, the cause of separation of rolling bearings in consideration of the recent bearing usage environment. As a result, as the bearing operating environment became more severe, the repeated shear stress generated during the rolling contact between the inner and outer rings of the bearing and the rolling elements caused
In the lower part of the rolling contact surface (surface layer portion), a microstructure change layer consisting of a white strip-shaped product and a rod-shaped precipitate is generated, which gradually grows as the number of rolling increases,
At the end, it was found that fatigue delamination occurred as shown in Fig. (B) from the microstructure-changed part, and the bearing member surface layer part was damaged to extend the bearing life. 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 also found out.

As described above, the bearing life is not sufficient to control the decarburization layer and the non-metallic inclusions in the surface layer portion of the bearing member as in the prior art.
For example, by simply reducing the amount of decarburized layer in the surface layer and the amount of non-metallic inclusions by various heat treatments such as carburizing / nitriding and spheroidizing annealing, the microstructural changes that occur under the rolling contact surface (surface layer portion) described above. It is not possible to delay the time until the occurrence of. As a result, they have found that the bearing life cannot be further improved.

A main object of the present invention is to propose a means effective for improving rolling fatigue life characteristics under severe use conditions. Another object of the present invention is to improve the characteristics of not only the surface layer but also the steel as a whole by devising the composition of the bearing steel itself and the amount of retained austenite in the steel, especially during use of the bearing under high load and high temperature environment. Another object of the present invention is to provide a bearing member capable of delaying the microstructural change observed under the surface layer portion, which is expected to be generated, and thereby significantly improving the bearing life. Another object of the present invention is to adjust the composition of the steel, especially the Cr content and control the amount of retained austenite in the steel, so that even under a dust-containing environment, the stress concentration around the indentation due to the dust causes In addition to suppressing the occurrence of microstructural changes, it is intended to further improve the rolling contact fatigue life of the surface layer and the characteristics of the material itself, thereby further improving the bearing life. Still another object of the present invention is to improve the heat treatment productivity (eliminating the work of removing the decarburized layer) by suppressing the growth of the thickness of the decarburized layer during the heat treatment.

[0010]

Means for Solving the Problems Based on the above-mentioned findings, the present inventors have paid attention to a new "microstructure change delay characteristic" as a bearing life. Then, it was decided to improve the life of the bearing in this respect by improving this characteristic. To that end, of course, a new alloy design (composition composition) and identification of the steel structure are required, and we will not be able to further improve the life of the bearing without realizing this, and we will carry out further experiments. I examined it. As a result, surprisingly, by adding a proper amount of Cr and Sb in combination and controlling the amount of retained austenite in steel (hereinafter simply referred to as “residual γ amount”), rolling contact due to repeated stress loading is possible. It was found that the above-mentioned microstructural change generated under the surface can be significantly delayed, and the present invention bearing member and its manufacturing method were developed.

That is, the bearing member according to the present invention has the following essential configurations. (1) C: 0.5 to 1.5 wt%, Cr: over 2.5 to 8.0 wt%, Sb:
0.001 to 0.015 wt%, O: 0.0020 wt% or less, with the balance being Fe and inevitable impurities.
In addition, the amount of retained austenite in steel is 10 to 35 in volume ratio.
%, A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load.

(2) C: 0.5 to 1.5 wt%, Cr: more than 2.5 to 8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05
~ 2.0 wt%, Mo: 0.05 ~ 0.5 wt%, Ni: 0.05 ~ 1.0 w
t%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, A
l: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt%, including one or more selected from the group consisting of
The balance has a composition that consists of Fe and unavoidable impurities, and the amount of retained austenite in steel is 10% by volume.
A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load, which has a steel structure of up to 35%.

(3) However, the above basic components (C, Cr, Sb,
O), the optional additives (Si, Mn, Mo, Ni, Cu, B, Al, N) that are selectively added are as described above.
Within the composition range of (2), it is recommended to add in the following combinations. 0.05 to 0.5 wt% Si- (one or more of Mn, Mo, Ni, Cu, B, Al and N) 0.05 to 2.0 wt% Mn- (any of Mo, Ni, Cu, B, Al and N) 1 or more) 0.05 to 0.5 wt% Mo- (any one or more of Ni, Cu, B, Al and N) 0.05 to 1.0 wt% Ni- (any one or more of Cu, B, Al and N) 0.05-1.0 wt% Cu- (Any of B, Al and N 1
0.0005 to 0.01 wt% B- (one or two of Al and N) 0.005 to 0.07 wt% Al-N

(4) C: 0.5 to 1.5 wt%, Cr: more than 2.5 to 8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: more than 0.5 to 2.5 wt%, Ni: 1.0
Super ~ 3.0 wt%, N: 0.012 Super ~ 0.050 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 inevitable impurities, and the residual austenite amount in the steel being the volume ratio. A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading, which has a steel structure of 10 to 35%.

(5) However, the above basic components (C, Cr, Sb,
O), the optional additive components (Si, Ni, N) that are selectively added in large amounts and the other optional additive components (Zr, Ta, Hf and Co) that are added in small amounts are described in (4) above. Within the composition range described, it is recommended to add the following combinations. Over 0.5-2.5 wt% Si- (any one or more of Ni and N)-(any one or more of Zr, Ta, Hf and Co) 1.0-3.0 wt% Ni- (N) − (Zr, Ta, Hf and
More than 0.012 ~ 0.050 wt% N- (any one or more of Zr, Ta, Hf and Co)

(6) C: 0.5 to 1.5 wt%, Cr: over 2.5 to 8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05
~ 2.0 wt%, Mo: 0.05 ~ 0.5 wt%, Ni: 0.05 ~ 1.0 w
t%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, A
l: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt%, any one or more selected from the group is included as a component for improving rolling fatigue under normal environment. When any one or more of the improving components is selected, the following components excluding the element, that is, Si:
Over 0.5 ~ 2.5 wt%, Ni: over 1.0 ~ 3.0 wt%, N: 0.012
Super ~ 0.050 wt%, Zr: 0.02 ~ 0.5 wt%, Ta: 0.02 ~ 0.5
wt%, Hf: 0.02-0.5 wt% and Co: 0.05-1.5 wt%
One or two or more selected from the above are contained as components for improving rolling fatigue life in a harsh environment, and the balance has a component composition of Fe and inevitable impurities, and Volume of retained austenite in
A bearing member having a steel structure of 10 to 35%, which is excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading.

(7) However, in the above item (6), the following combinations are recommended for the rolling fatigue life improving components in a normal environment. 0.05 to 0.5 wt% Si- (one or more of Mn, Mo, Ni, Cu, B, Al and N) 0.05 to 2.0 wt% Mn- (any of Mo, Ni, Cu, B, Al and N) 1 or more) 0.05 to 0.5 wt% Mo- (any one or more of Ni, Cu, B, Al and N) 0.05 to 1.0 wt% Ni- (any one or more of Cu, B, Al and N) 0.05-1.0 wt% Cu- (Any of B, Al and N 1
0.0005 to 0.01 wt% B- (1 or 2 types of Al, N) 0.005 to 0.07 wt% Al-N Also, the combination of rolling fatigue life improving components in the above severe operating environment is as follows. Are recommended. '0.5-2.5 wt% Si- (any one or more of Ni and N)-(any one or more of Zr, Ta, Hf and Co)' 1.0-3.0 wt% Ni- ( N)-(Zr, Ta, Hf and
Any one or more of Co) '> 0.012 to 0.050 wt% N- (Any one or more of Zr, Ta, Hf and Co)

For each of the above-mentioned bearing members, steel having a predetermined composition is rolled into a steel bar by a conventional process after smelting, then normalized and annealed, and then 880 to 10
It can be produced by quenching from 00 ° C (desirably 900 to 950 ° C).

[0019]

First, the background of the development of the bearing member of the present invention relating to the above-mentioned alloy design and microstructure control will be described based on the results of experiments conducted by the inventors. First, in this 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 two materials with Cr and Sb added (C: 1.03 wt%, Si: 0.28 wt%, Mn: 0.47 wt%, C
r: 3.08 wt%, Sb: 0.0038 wt%, N: 0.0051 wt%, O:
0.0008wt%) (C: 1.03wt%, Si: 0.29wt%, Mn: 0.48wt%, C
r: 7.05wt%, Sb: 0.0079wt%, N: 0.0048wt%, O:
Steel having a chemical composition of 0.0009wt%) is melted and cast, then at 1240 ℃
After subjecting it to diffusion annealing for 30 hours, it was rolled into a steel bar with a diameter of 65 mm to obtain a test material. Next, this test material was subjected to normalizing, spheroidizing annealing, and further heat treatment in the order of quenching-tempering, and then lapping finishing was performed to obtain a cylindrical test piece of 12 mmφ × 22 mm.

Next, the above test pieces were subjected to a Hertz maximum contact stress: 600 kgf using a radial type rolling fatigue life tester.
/ mm ² , Cyclic stress: 46500 cpm, Lubrication: # 68 Turbine rolling contact fatigue life test by adjusting the quenching temperature and changing the amount of residual γ in steel under the load condition of turbine splash oil environment. went. The test results are plotted on probability paper as subject to the Weibull distribution, and are the numerical values showing the normal rolling fatigue life that has been studied conventionally, mainly due to the suppression of nonmetallic inclusions in the surface layer and the increase in material strength. B ₁₀ value (10% cumulative failure probability) and rolling caused by delaying the occurrence of so-called microstructure change under the surface layer, which is seen in a severe operating environment, due to cyclic stress loading at high temperature and high load rolling The B ₅₀ value (50% cumulative failure probability), which is considered to be the numerical value indicating the fatigue life, was determined. Regarding the decarburization layer test, 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 total decarburization layer depth (thickness on the circumference due to microstructural change ) It evaluated by the maximum value (henceforth "the maximum decarburization layer").

As a result, as shown in Table 1, for the high Cr-added material, when the residual γ amount is 7%, the B ₁₀ value is not so much improved, but the B ₅₀ value is remarkably improved. High values were shown, and the average bearing life was about 10 times better with Cr: 3.08 wt% than with SUJ 2 material. In particular, when Cr is added in a large amount of 7.05 wt%, the B ₅₀ value reaches about 20 times, and it has a remarkable effect on the delay property of microstructure change generated during high load rolling. It was found that the damage (lifetime) can be greatly delayed. However, even with the same composition, when the residual γ amount increases to 17 to 18%, the improvement of the B ₅₀ value becomes more remarkable, and in addition, the B ₁₀ value also exceeds that of the SUJ 2 material. It was found that the improvement was about 5 times at 3.08 wt% and about 9 times at Cr: 7.05 wt%. In addition, the maximum decarburized layer after heat treatment is
b: 0.002 wt% with 0.038 wt%, Sb: 0.0079 wt
%, The actual thickness is 0.01mm,
It can be seen that the addition of Sb is extremely effective in suppressing the heat-treated decarburized layer.

[0022]

[Table 1]

FIG. 2 is a summary of the above experimental results. The bearing life due to non-metallic inclusions in the surface layer, the microstructure change under cyclic stress loading under the surface layer, and the amount of residual γ FIG. 3 is a schematic diagram showing the effect of the on the rolling contact fatigue life of the bearing. As is clear from this figure, the cumulative damage probability 10 as an index of the amount and form of non-metallic inclusions on the surface layer of the bearing member, C concentration, carbide area ratio, etc. % Bearing ₁₀ life (hereinafter referred to as "B ₁₀ life")
According to the above, the effect cannot be obtained as expected by simply adding a large amount of Cr, but it is understood that when the residual γ amount is increased, it is considerably improved. On the other hand, bearing life as a B ₅₀ value with a cumulative failure probability of 50% as an index showing the microstructure change characteristics found in the zone below the surface layer of the member
(Hereinafter, this is referred to as "B ₅₀ life")
The effect of Cr addition is extremely remarkable, and this tendency is greater than the effect of the residual γ amount.As long as one is aware of the bearing life, which indicates the degree of microstructural change that occurs in harsh environments, high Cr and high residual It can be seen that the control of the γ amount is extremely effective. This is in good agreement with the results in Table 1 above.

As described above, in order to improve both the B ₁₀ life and the B ₅₀ life, it is more appropriate to conduct the normalizing and spheroidizing annealing of the steel containing a proper amount of Cr. It is effective to control the amount of residual γ in the steel within a predetermined range by performing various quenching treatments and, if necessary, tempering treatments. Although the reason why the characteristics are improved by such a treatment has not always been clarified, the inventors have found that this residual γ is a delay in the microstructural change due to repeated stress loading and a hard texture existing in the stress action region. It is believed that the notch action of non-metallic inclusions is mitigated, which improves both B ₁₀ and B ₅₀ life.

The above-mentioned residual γ amount is 10 in terms of volume ratio.
I think ~ 35% is an appropriate amount. This is because if the amount of this residual γ is small, the effect of improving rolling fatigue life, especially B ₁₀ life cannot be obtained, and therefore, 10% or more is necessary. On the other hand, if the residual γ amount exceeds 35%, the bearing strength is insufficient and the dimensional stability is lacking.
%, Preferably in the range of 15-30%, and more preferably in the range of 15-25%.

In the present invention, the range of the composition of components as described below is determined mainly from the viewpoint of improving the microstructure change retarding property due to repeated stress loading.

C: 0.5 to 1.5 wt% C is an element that 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 to improve the rolling fatigue life by it. 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%. Preferably, 0.
The range of 65 to 1.10 wt% is preferable.

Cr: over 2.5 to 8.0 wt% Cr is the most important element in the present invention, and delays the microstructural change due to cyclic stress loading,
In order to improve the rolling fatigue life (B ₅₀ life) in this respect, it is necessary to add a large amount exceeding 2.5 wt%. When the amount of Cr added to improve the B ₅₀ life exceeds 8.0 wt%, not only is it saturated, but rather the amount of solid solution C during quenching is reduced and strength is reduced. Therefore, when added for this purpose, it should be over 2.5 to 8.0.
Must be wt%. Preferably over 2.5 to 5.0 wt
The range of% is good.

Sb: 0.001 to 0.015 wt% This Sb is an element that plays an important role together with Cr 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. In addition, it is effective in retarding the microstructural change as well as suppressing the decarburized layer. 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 is saturated, and conversely, hot workability and It causes deterioration of toughness. Therefore, Sb is included in the range of 0.001 to 0.015 wt%. The content is preferably 0.0020 to 0.0100 wt%, more preferably 0.0025 to 0.0080 wt%.

O: 0.0020 wt% or less O forms hard non-metallic inclusions, so even if other
Microstructure by repeated stress loading by controlling the composition
Even if a delay in change is obtained, B_TenLife span, B ₅₀Of life
It is desirable to be as low as possible because it may cause a decrease
Good However, it is acceptable if the content is 0.0020 wt% or less.
Wear. It is preferably 0.0012 wt% or less.

Si: 0.05 to 0.5 wt%, more than 0.5 to 2.5 wt% Si is used as a deoxidizing agent during the melting of steel, and is also solid-dissolved in the matrix to increase quenching and quenching due to an increase in temper softening resistance. It is effective as an element that enhances the strength after returning and improves the rolling contact fatigue life (B ₁₀ life) that appears in the B ₁₀ value. The content of Si added for these purposes is 0.05 to 0.5 wt.
%, Preferably 0.15 to 0.50 wt%. Furthermore, this Si
Addition of more than 0.5 wt% causes a delay in microstructural change under high temperature, high load, and cyclic stress loading,
It has the effect of improving the rolling fatigue life (B ₅₀ life) that appears as the B ₅₀ value. However, if the content exceeds 2.5 wt%, the effect saturates, but the workability and toughness decrease, so in order to further improve the microstructure change retardation property, 0.5 to 2.5 wt% is exceeded. It is effective to add. More preferably, it is more than 0.5 to 2.0 wt%.

Mn: 0.05 to 2.0 wt% Mn is an element that acts as a deoxidizer during the melting of steel and is effective in reducing the oxygen content of steel. Further, by improving the hardenability of steel, the toughness and hardness of the base martensite are improved, which effectively contributes to the improvement of the general rolling contact fatigue life (B ₁₀ life) in the surface layer of the member. For these purposes, the addition of 0.05 to 2.0 wt% is sufficient, preferably 0.25 to 2.0 wt%.

Mo: 0.05 to 0.5 wt% Mo is an element that improves wear resistance by stabilizing residual carbides. In particular, the addition of 0.05 to 0.5 wt% increases the hardenability and contributes to the improvement of the strength after quenching and tempering, and the precipitation of stable carbide improves the wear resistance and B ₁₀ life.

Ni: 0.05 to 1.0 wt%, more than 1.0 to 3.0 wt% Ni enhances the hardenability and strength after quenching and tempering to improve the toughness as well as the B ₁₀ life. In order to achieve this, the addition is made within the range of 0.05 to 1.0 wt%, preferably 0.15 to 1.0 wt%.
Furthermore, as described above, this Ni delays the microstructure change during rolling when added in excess of 1.0 wt%,
This improves the B ₅₀ life. However, even in this case, a large amount (> 35%) of residual γ is added if added in excess of 3 wt%
In addition to degrading the strength and impairing the dimensional stability, it also increases the cost.If this effect is expected, it is necessary to add it in the range of more than 1.0 to 3.0 wt%. Yes, more than 1.0 to 2.5 wt% is preferable.

Cu: 0.05 to 1.0 wt% Cu is added in order to enhance the strength after quenching and tempering by increasing quenching and to improve the B ₁₀ life. When added for this purpose, a range of 0.05 to 1.0 wt% is sufficient, preferably 0.15 to 1.0 wt%.

B: 0.0005 to 0.01 wt% B increases the hardenability and thereby enhances the strength after quenching and tempering and improves the B ₁₀ life, so 0.0005 wt% or more is added. However, if added in excess of 0.01 wt%, the workability deteriorates, so the range is limited to 0.0005 to 0.01 wt%. 0.0015 to 0.0050 wt% is preferable.

Al: 0.005 to 0.07 wt% Al is used as a deoxidizing agent during the melting of steel, and at the same time,
Combines with N in the steel to refine the crystal grains and contribute to the improvement of the toughness of the steel. Further, it effectively acts to improve the rolling contact fatigue life by increasing the strength after quenching and tempering. For such an effect, it is effective to add 0.005 to 0.07 wt% of Al. It is preferably 0.010 to 0.07 wt%.

N: 0.0005 to 0.012 wt%, more than 0.012 to 0.05
0 wt% N combines with carbonitride forming elements to refine the crystal grains,
It forms a solid solution in the matrix to increase the strength after quenching and tempering and improve the B ₁₀ life. 0.0005-0 for this purpose.
It is added within the range of 012 wt%, but preferably 0.0020 to 0.
012 wt% is good. Also, this N is 0.012 on the one hand.
When it is added in excess of wt%, as described above, the microstructure change due to repeated stress is delayed to increase the B content.
₅₀ life can be improved. However, this amount is 0.
If it exceeds 050 wt%, workability and toughness decrease, so for this purpose, more than 0.012 to 0.050 wt% is added.
More than 0.012 to 0.035 wt% is preferable.

As described above, the rolling fatigue life (B ₅₀ life) is improved by delaying the microstructure change due to the repeated stress load on the surface layer of the member, and the rolling fatigue life (B ₁₀ ) at the surface layer of the member is increased by increasing the strength. Main components (C, Cr, Sb, O and Si, Mn, M for improving life)
o, Ni, Cu, B, Al, N), the respective reasons for limitation have been described. However, in the present invention, one or more selected from Zr, Ta, Hf and Co should be added. Therefore, the rolling fatigue life, that is, the B ₅₀ life in a harsh use environment (with dust, high load, high temperature) may be improved.

The preferred range of addition of each element and the purpose of addition,
The reasons for limiting the upper limit and the lower limit are summarized in Table 2.

[Table 2]

In the present invention, in order to improve machinability, S, Se, Te, REM, Pb, Bi, Ca, Ti, Mg, P, Sn, As
Even if added, etc., it does not inhibit the retardation property due to the microstructural change due to the repeated stress load, which is the object of the present invention, and the machinability can be easily improved, so it is added as necessary. You may.

It is desirable that P is as low as possible because it lowers the toughness and rolling fatigue life of steel, and is kept to 0.025 wt% or less, preferably 0.015 wt% or less. Further, S is an element that combines with Mn to form MnS and improves machinability. However, if it is contained in a large amount, the rolling contact fatigue life is shortened, so it is preferable to keep it to 0.025 wt% or less, preferably 0.015 wt% or less.

[0043]

EXAMPLE Steels having the compositions shown in Tables 3, 4, and 5 were melted and cast, and the obtained steel materials were subjected to diffusion annealing at 1200 ° C. for 30 hours and then rolled into steel bars having a diameter of 65 mm. Next, after normalizing and spheroidizing annealing, steel materials No. 1 and No. 2 are 820 ° C.
Then, the others were tempered at 900 ° C to 950 ° C and tempered at 180 ° C. Furthermore, 12 mmφ × 22 mm and 60 mmφ × 5 mm cylindrical test pieces were prepared by lapping finishing. The surface roughness of each of the test pieces at this time was Ra: 0.1 mm. Then, with respect to each of the above-mentioned test pieces, a measurement test for B ₁₀ life and B ₅₀ life under a clean environment was conducted. The B ₁₀ life and B ₅₀ life tests under this clean environment were carried out using a radial type rolling contact fatigue life tester as shown in Fig. 3, with a maximum Hertzian contact stress of 600 kgf / mm ² , and a repeated stress number of about 46500 cpm and lubricating oil: # 68 Turbine splash oil was used. In addition, the results of the test are summarized on the probability paper as if they follow Weibull distribution,
The average life of steel material No. 1 (SUJ2 which is a conventional steel) (cumulative failure probability: total load frequency before peeling at 10% and 50%) was set to 1 and evaluated in comparison with other steel types.

On the other hand, a ring containing dust for each of the above test pieces
Rolling life under severe conditions (B _TenLife span, B₅₀lifespan)
Is a thrust-type rolling contact fatigue tester manufactured by making disc-shaped test pieces.
, Hertz maximum contact stress: 536 kgf / mm² , Repeat
Stress number: Hardness in # 68 turbine oil under the condition of 1800cpm:
Hv850, average particle size: about 150 ppm of iron powder with about 100 μm
 It mixed and went. The testing machine is improved as shown in Fig. 3.
The iron powder is constantly supplied to the contact area between the steel ball and the test piece.
I did it.

The test results are plotted on probability paper as if they follow Weibull distribution, and the B ₁₀ life (cumulative failure probability: 10
% Of total load until peeling occurs) and B ₅₀ life (
(50%) and steel materials No. 1 were evaluated as 1 for each. Further, the retained austenite amount is measured by using an X-ray analysis device on a test piece after lapping. The above evaluation results are summarized in Tables 3, 4 and 5.

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

Steel Nos. 2 to 6 are shown as comparative examples. Steel No. 5 having a C content in the steel outside the scope of the present invention, Steel No. 6 having a Cr content in the steel outside the scope of the present invention, In the case of Steel No. 3 in which the amount of O in the steel is outside the range of the present invention and Steel No. 2 in which the amount of retained austenite in the steel is outside the range of the present invention, the conventional steel containing no Cr (steel N
O.1), or at least one of B ₁₀ life and B ₅₀ life is low, and it is clear that there is no effect in improving bearing life. Further, No. 4 has Sb in the range outside the scope of the present invention, but B ₁₀ life and B ₅₀ life are better than those of the conventional steel (No. 1), but the maximum decarburized layer depth is It is as large as 0.11 mm, which is not improved at all compared to the conventional steel (No.1).
A treatment for removing this decarburized layer was required. On the other hand, the steel materials No. 7 to 41, which are bearing members of the present invention, have a B ₁₀ life of conventional steel (steel material No. 1) in a normal test under a clean environment.
Compared with the above, the average is improved by about 3 to 21 times, and the B ₅₀ life is also excellent by 5 to 50 times. Furthermore, this tendency shows that even in a test in a dust-containing environment, the B ₁₀ life is about 2 to 9 times better than the conventional one, and the B ₅₀ life is about 4 to 16 times better than the conventional one. It can be seen that it has been improved as well. In addition, the maximum decarburized layer depth is also large.
It can be seen that it is as small as 0.04 mm and has excellent heat treatment productivity. That is, as a bearing member, a large amount of Cr and
The composite addition of Sb significantly delays the rolling life in the environment containing dust, especially the microstructural change indicated by the B ₅₀ life, while controlling the residual γ amount to 10 to 35% significantly improves the B ₁₀ life. Therefore, since the depth of the decarburized layer is also reduced, it is extremely effective in improving the rolling contact fatigue life of the bearing as a whole and contributes to the improvement in productivity.

[0050]

As described above, according to the present invention,
Structure with residual γ content in steel of 10 to 35% and Cr: over 2.5
8.0 wt% and Sb: 0.001 to 0.015 wt% By using a composite-added bearing steel material, even under harsh conditions such as high load and high temperature use not only in a clean environment but also in a dust-filled environment, It causes a delay in microstructural change due to cyclic stress loading, which improves the B ₁₀ and B ₅₀ rolling contact fatigue life (high Cr content effect) and also reduces the processing load during heat treatment (Sb addition). It is possible to increase the productivity. Therefore, the oxygen content in the steel is further reduced in the surface layer of the member, which is indispensable under the conventional technology, or the composition, shape, and distribution state of oxide-based nonmetallic inclusions present in the steel are controlled. The improvement or construction of the steelmaking equipment required to do so is unnecessary in the present invention. Further, the development of the bearing member according to the present invention can be expected 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 under cyclic stress loading,
The micrograph of the metal structure which shows the appearance of the microstructure change which arises in the zone under the surface layer part of a member.

FIG. 2 is an explanatory view showing influences of Cr and Sb contents and residual γ amount on bearing life caused by non-metallic inclusions and bearing life caused by microstructure change.

FIG. 3 is a schematic diagram showing a schematic configuration of a thrust type rolling contact fatigue testing machine.

─────────────────────────────────────────────────── ─── 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-6-287691 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. C: 0.5-1.5 wt%, Cr: over 2.5-8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, with the balance being Fe and inevitable impurities, and the residual austenite amount in the steel being 10% by volume. A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load, which has a steel structure of up to 35%. 2. C: 0.5-1.5 wt%, Cr: over 2.5-8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05
~ 2.0 wt%, Mo: 0.05 ~ 0.5 wt%, Ni: 0.05 ~ 1.0 w
t%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, A
l: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt%, including one or more selected from the group consisting of
The balance has a composition that consists of Fe and unavoidable impurities, and the amount of retained austenite in steel is 10% by volume.
A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load, which has a steel structure of up to 35%. 3. C: 0.5-1.5 wt%, Cr: over 2.5-8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: more than 0.5 to 2.5 wt%, Ni: 1.0
Super ~ 3.0 wt%, N: 0.012 Super ~ 0.050 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 inevitable impurities, and the residual austenite amount in the steel being the volume ratio. A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading, which has a steel structure of 10 to 35%. 4. C: 0.5-1.5 wt%, Cr: over 2.5-8.
0 wt%, Sb: 0.001 to 0.015 wt%, O: 0.0020 wt% or less, Si: 0.05 to 0.5 wt%, Mn: 0.05
~ 2.0 wt%, Mo: 0.05 ~ 0.5 wt%, Ni: 0.05 ~ 1.0 w
t%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, A
l: 0.005 to 0.07 wt% and N: 0.0005 to 0.012 wt%, and any one or more selected from the group is included as a component that improves rolling fatigue under normal environment. When any one or more of the improving components is selected, the following components excluding the element are included: Si: more than 0.5 to 2.5 wt%, Ni: more than 1.0 to 3.0 wt%,
N: more than 0.012 to 0.050 wt%, Zr: 0.02 to 0.5 wt%, Ta:
0.02-0.5 wt%, Hf: 0.02-0.5 wt% and Co: 0.05
Includes one or more selected from ~ 1.5 wt% as a component that improves rolling fatigue life in harsh environments, with the balance being Fe and inevitable impurities. A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load, which has a steel structure in which the amount of retained austenite in the steel is 10 to 35% in volume ratio.