JP3243366B2 - Bearings with excellent microstructure change delay characteristics due to repeated stress loading - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing member used as an element member of a rolling bearing such as a roller bearing or a ball bearing, and more particularly to a microstructural change generated under a rolling contact surface due to a repeated stress load in a severe use environment. delay characteristics for (degradation), regardless of cleanliness of the lubricating oil, it is proposed with the bearing member showing characteristics still excellent a poor condition.

[0002]

2. Description of the Related Art Conventionally, high-carbon chromium bearing steel (JIS:
SUJ 2) has been used most often. In general, it is important for bearing steel to have a long rolling fatigue life, but it has been considered that a hard nonmetallic inclusion in steel has a large effect on the rolling fatigue life. Therefore, the mainstream of recent research has been to increase the life of bearings by controlling the amount and size of nonmetallic inclusions by reducing the amount of oxygen in steel.

For example, Japanese Unexamined Patent Publication (Kokai) No. 1-306542 has been developed with the aim of further improving the rolling fatigue life of a bearing.
And Japanese Patent Application Laid-Open No. 3-126839, which are techniques for controlling the composition, shape or distribution of oxide-based nonmetallic inclusions in steel. However, in order to produce bearing steel with a small amount of nonmetallic inclusions, it is necessary to install expensive smelting equipment or to significantly improve conventional equipment, resulting in a large economic burden.

On the other hand, the life of a bearing is greatly affected by the characteristics of lubricating oil. Generally, lubricating oil contains abrasive powder or burrs during polishing, or wear powder generated during rotation (hereinafter, referred to as
It has been pointed out that mixing of the dust causes a reduction in the rolling life of the bearing member. Conventionally, in order to improve the bearing life in a dust-containing environment, a method of mainly improving the cleanliness of lubricating oil has been adopted, but Japanese Patent Application Laid-Open Nos. 5-78782 and 5-78814 disclose such methods. According to the disclosure of the present invention, by performing carbonitriding of the surface layer of the bearing member, the carbide area ratio of the surface layer, the surface carbon concentration, the amount of surface residual austenite is controlled, and the characteristics in the surface layer portion are improved. It has been proposed to control the shape of the indentation due to dust and thereby reduce the stress concentration to extend the life. However, this conventional technique does not essentially improve the steel structure, but by so-called carbonitriding and hardening heat treatment,
The method involves externally modifying only the surface layer of the bearing member, which not only does not lead to the improvement of the microstructure change observed at the lower side of the surface layer as described later, but also has the problem that the processing cost is higher. Was left.

[0005]

According to the results of recent research conducted by the inventors, the factors that determine the rolling life are phenomena generally discussed in the past; Japanese Patent Application Laid-Open No. 1-306542 describes a "decarburized layer" (low C concentration region) on the surface of a bearing member which occurs during heat treatment, which is a problem in JP-A-78782 and JP-A-5-78814.
It has been found that there are other factors besides the existence of "non-metallic inclusions", which is a problem in each of the above publications. This is because, under the prior art, the rolling contact fatigue life of the bearing, especially by reducing the decarburized layer and nonmetallic inclusions, mainly by heat-treating the bearing member surface layer, especially under high loads or high temperatures This is because they have often experienced that a great effect cannot be obtained for the improvement of the bearing life under the conditions.
From this, the inventors were convinced of the existence of other factors that determine the bearing life.

Accordingly, the present inventors have conducted intensive studies on the cause of the occurrence of peeling of the rolling bearing. As a result, a band-like white product and a rod-like precipitate are formed below the rolling contact surface (surface layer) as shown in FIG. 1 due to the repetitive shear stress generated when the inner and outer rings of the bearing and the rolling element come into rotational contact. A microstructure-changed layer consisting of a material is generated, which gradually grows as the number of rolling increases, and eventually, the microstructure-changed part causes fatigue delamination, losing the surface layer of the bearing member, and the bearing life may be extended. all right. Furthermore, the severer operating environment of the bearing, that is, higher surface pressure (smaller size) and higher operating temperature, shorten the number of rollings before these microstructure changes occur, leading to a significant reduction in bearing life. I also found it. As described above, the bearing life is not sufficient simply by controlling the decarburized layer and non-metallic inclusions in the surface layer portion of the bearing member as in the prior art, for example, carburizing / nitriding or spheroidizing. By simply reducing the decarburized layer on the surface layer and the amount of nonmetallic inclusions by various heat treatments such as annealing,
It is not possible to delay the time until the microstructure change occurring under the rolling contact surface (surface layer) described above. As a result, they found that the bearing life could not be further improved.

A main object of the present invention is to propose an effective means for improving the rolling fatigue life characteristics under severe use conditions. The specific object of the present invention is to devise the composition of the bearing steel itself and the amount of retained austenite in the steel, so that not only the surface layer but also the properties of the steel as a whole, especially the use of bearings under high load and high temperature environments It is an object of the present invention to provide a bearing member capable of delaying a microstructural change observed under a surface layer which is expected to be formed therein, and consequently significantly improving a bearing life. Another specific object of the present invention is to control the composition of the steel and the amount of retained austenite in the steel so that, even in a dusty environment, the microstructure change due to the stress concentration around the indentation due to the dust. Another object of the present invention is to improve the rolling contact fatigue life of the surface layer and the characteristics of the material itself, thereby further improving the bearing life.

[0008]

Means for Solving the Problems Based on the above findings, the present inventors have newly focused on a "microstructure change delay characteristic" as a bearing life, and by improving this characteristic, the bearing life on this surface has been improved. To achieve the improvement, it is naturally necessary to design a new alloy (composition composition) for that purpose, identify the steel structure, and develop appropriate heat treatment conditions.
With the recognition that the bearing life could not be further improved without realizing this, various experiments and studies were further performed. As a result, surprisingly, by adding an appropriate amount of Cr together with Si and controlling the amount of retained austenite in the steel (hereinafter simply referred to as “residual γ amount”),
It has been found that the above-mentioned microstructure change generated below the rolling contact surface due to repeated stress loading can be significantly delayed,
We developed the present invention bearing member.

That is, the bearing member according to the present invention has the following gist configuration. (1) C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, with the balance being Fe and unavoidable impurities. A bearing member excellent in delay characteristics of microstructure change due to repeated stress load, characterized by having a steel structure in which the amount of retained austenite in steel is 10 to 35% by volume.

(2) C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, and Mn: 0.05 to 2.0 wt%, Ni: 0.05 to 1.0 wt%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt%, and N: 0.0005 to 0.012 wt% Including two or more, the balance has a component composition consisting of Fe and unavoidable impurities, and the amount of retained austenite in the steel is expressed as a volume ratio.
A bearing member having a steel structure of 10 to 35% and having excellent characteristics of delaying microstructure change due to repeated stress loading. (3) However, optional components (Mn, Ni, Cu, and Mn) selectively added to the basic components (C, Si, Cr, O).
(B, Al, N), it is recommended to add them in the following combinations within the composition range of the above (2). 0.05-2.0 wt% Mn- (any one or more of Ni, Cu, B, Al and N) 0.05-1.0 wt% Ni- (any one of Cu, B, Al and N)
0.05-1.0 wt% Cu- (one or more of B, Al and N) 0.0005-0.01 wt% B- (one or more of Al and N) 0.005-0.07 wt% Al-N

(4) C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, and Ni: more than 1.0 to 3.0 wt% , Zr: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02 to 0.5 wt%, and Co: 0.05 to 1.5 wt%. It has a component composition consisting of Fe and unavoidable impurities, and the amount of retained austenite in steel is
A bearing member having a steel structure of 10 to 35% and having excellent characteristics of delaying microstructure change due to repeated stress loading. 5) However, the optional components (Ni) added selectively and in large amounts to the above basic components (C, Si, Cr, O) and other optional components (Zr, Ta, Hf and C
As for o), it is recommended to add the following combinations within the composition range described in (4) above. More than 1.0 to 3.0 wt% Ni- (one or more of Zr, Ta, Hf and Co) (one or more of Zr, Ta, Hf and Co)

(6) C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, Mn: 0.05 to 2.0 wt%, Ni: 0.05 to 1.0 wt%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt%, and N: 0.0005 to 0.012 wt% Including two or more as a component for improving rolling fatigue under a normal environment, and when any one or more of the above-mentioned improving components is selected, the following components excluding the element, namely, Furthermore, when any one or more of the above-mentioned improving components is selected, the following components excluding that element are selected: Ni: more than 1.0 to 3.0 wt%, Zr: 0.02 to 0.5 wt%, Ta: 0.02 -0.5 wt%, Hf: 0.02-0.5 wt% and Co: 0.05-1.5 wt% to improve the rolling fatigue life under severe environment. And the balance has a component composition consisting of Fe and unavoidable impurities, and the amount of retained austenite in the steel is expressed as a volume ratio.
A bearing member having a steel structure of 10 to 35% and having excellent characteristics of delaying microstructure change due to repeated stress loading. (7) However, the following combinations are recommended for the rolling fatigue life improvement component in the normal environment. 0.05-2.0 wt% Mn- (any one or more of Ni, Cu, B, Al and N) 0.05-1.0 wt% Ni- (any one of Cu, B, Al and N)
0.05-1.0 wt% Cu- (one or more of B, Al and N) 0.0005-0.01 wt% B- (one or more of Al and N) 0.005-0.07 wt% Al-N The following combinations are recommended for the rolling fatigue life improving component in the above-mentioned severe use environment. More than 1.0 to 3.0 wt% Ni- (any one or more of Zr, Ta, Hf and Co) (any one or more of Zr, Ta, Hf and Co)

[0013] Each of the above bearing members is prepared by rolling steel having a predetermined component composition into a steel bar by a process according to a conventional method after smelting, and then normalizing and annealing the steel.
It can be produced by quenching from 00 ° C (preferably 900 to 950 ° C).

[0014]

First, the development of the bearing member of the present invention relating to the above alloy design and structure 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: 1.35wt%, N: 0.0040wt%, O: 0.0012wt%)
And two types of materials to which Si and a large amount of Cr are added (C: 1.00 wt%, Si: 1.28 wt%, Mn: 0.46 wt%, C
r: 3.56 wt%, N: 0.0046 wt%, O: 0.0009 wt%) (C: 1.00 wt%, Si: 1.32 wt%, Mn: 0.48 wt%, C
r: 7.23 wt%, N: 0.0052 wt%, O: 0.0008 wt%).
And then rolled into a 65 mmφ steel bar to obtain a test material. Then, the test material was normalized, spheroidized, heat-treated in the order of quenching and tempering, and thereafter, a cylindrical test piece of 12 mmφ × 22 mm was prepared by lapping.

Next, the above test piece was subjected to a rolling contact fatigue life tester of a radial type using a Hertz maximum contact stress: 600 kgf.
/ mm ² , Number of cyclic stress: 46500 cpm, Lubrication: # 68 Adjust the quenching temperature under the load condition under the use environment of turbine splash oil.
The rolling fatigue life test was performed by changing the amount of residual γ in the steel (7%, 18%). The test results are plotted on established paper as following the Weibull distribution, and are numerical values showing the conventional rolling fatigue life that has been conventionally studied, mainly due to suppression of nonmetallic inclusions in the surface layer and increase in material strength. B ₁₀ (10% cumulative failure probability), rolling fatigue due to due to repeated stress loads at a high temperature and high-load rolling, viewed under severe use environments, to delay the occurrence of microstructural changes in the so-called surface subordinates It was determined and B ₅₀ that appear to numerical value indicating the lifetime (50% cumulative failure probability).

As a result, as shown in Table 1, when the amount of residual γ is small (<10%), the improvement in the B ₁₀ value is not so large, but the B ₅₀ value is small. Shows a remarkably high value, and the average bearing life is SUJ
Compared with the two materials, Cr: 3.56 wt% showed an improvement of about 21 times. In particular, Cr: and 7.23Wt%, when more heavily added, B ₅₀ value reaches to about 30 times, a remarkable effect on the delay characteristics of the microstructural changes produced during high-load rolling It was found that breakage (lifetime) can be greatly delayed. However, even with the same component composition, when the amount of residual γ increases (≧ 10%), the degree of improvement in the B ₅₀ value becomes even more remarkable, and further, the B ₁₀ value also differs from that of the SUJ2 material in that Cr: It was found that the improvement was about 10 times in the case of 3.56 wt% and about 13 times in the case of 7.23 wt% of Cr.

[0017]

[Table 1]

FIG. 2 summarizes the results of the above experiments. The bearing life attributable to non-metallic inclusions in the surface layer, the state of microstructure change under repeated stress loading under the surface layer, and the amount of residual γ FIG. 4 is a schematic diagram showing the effect of the bearing on rolling fatigue life of a bearing. As can be seen from this figure, the cumulative failure probability 10 as an index of the amount of non-metallic inclusions in the bearing member surface layer, its form, C concentration, carbide area ratio, etc. % of bearing life represented by B ₁₀ value (hereinafter referred to as "B ₁₀ life")
According to the results, the effect cannot be obtained as expected by simply adding Si and Cr, but it can be understood that the effect is considerably improved when the amount of residual γ is increased. On the other hand, as an indicator showing the microstructural variation characteristics found in the band member surface subordinates, cumulative failure probability of 50% B ₅₀ values shown are bearing life (
In the following, this is referred to as “B ₅₀ life”), the effect of adding Si—Cr is extremely remarkable, and this tendency is greater than the effect of the residual γ content, and at least the microstructural change that occurs in a severe environment It can be seen that the addition of an appropriate amount of Si-Cr and the control to a high residual γ content are extremely effective as long as the bearing life indicating the degree of formation of γ is considered.

[0019] As described above, B ₁₀ life, to improve both B ₅₀ life, the steel containing an appropriate amount of Si-Cr, from after the processing of the normalizing and spheroidizing annealing Further, it is effective to control the amount of residual γ in the steel to a predetermined range by performing appropriate quenching and tempering. Although the reason for this has not been clearly elucidated, the inventors found that this residual γ delays microstructure change due to repeated stress loading and the notch effect of hard nonmetallic inclusions existing in the stress action region. relieve, are believed to improve both the B ₁₀ life and B ₅₀ life by this.

The amount of residual γ is 10 to 10% by volume.
We consider 35% to be an appropriate amount. It small amount the rolling fatigue life of the residual gamma, and since no especially to obtain the effect of the B ₁₀ life improvement, it is necessary therefore 10% or more. 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 12-30%, and more preferably in the range of 15-25%.

In the present invention, the range of the component composition as described below is determined mainly from the viewpoint of improving the microstructure change delay characteristic due to repeated stress load.

C: 0.5-1.5 wt% C is an element which forms a solid solution in the matrix and effectively acts to strengthen martensite. To secure strength after quenching and tempering and to improve the rolling fatigue life due to it. To be contained. If the content is less than 0.5 wt%, such effects cannot be obtained. On the other hand, if the content exceeds 1.5 wt%, the machinability and forgeability deteriorate, so the range was limited to the range of 0.5 to 1.5 wt%. Preferably, 0.
The range of 65 to 1.10 wt% is good.

Si: 1.0 to 2.5 wt% Si is used as a deoxidizing agent at the time of smelting steel, and is also dissolved in a matrix to increase the softening resistance, thereby increasing the strength after quenching and tempering. This has the effect of improving the rolling fatigue life. However, in the present invention, in addition to the above-mentioned effects, Si, particularly when added in an amount of 1.0 wt% or more, promotes the delay of the above-described microstructure change under severe repeated stress loading. the rolling contact fatigue life (B ₅₀ life)
Improve. However, if the content exceeds 2.5%, the effect is saturated, but the workability and toughness are reduced.
It must be added in the range of wt%. Preferably 0.5 to
2.5wt% is good.

Cr: 3.0 to 5.0 wt% Cr generally improves strength and abrasion resistance through improvement of hardenability and formation of stable carbides.
Further, it is a component that improves the rolling fatigue life. However, in the present invention, Cr is an element that plays a particularly important role, and when added in excess of 2.5 wt%, due to the combined effect with Si, the above-mentioned Cr under the severe repetitive stress load, especially. to encourage the delay of microstructural changes, improve rolling fatigue life in this area (B ₅₀ life). However, even if the amount exceeds 5.0 wt%, not only the effect is saturated, but also the strength of the solid solution C is lowered due to a decrease in solid solution C during quenching. Therefore, Cr is 3.0
It must be added in the range of ~ 5.0 wt% .

O: 0.0020 wt% or less O forms hard non-metallic inclusions.
Microstructure due to repeated stress loading by controlling components
Even if a delay in change is obtained, B_TenLifespan, B ₅₀Lifetime
It is desirable to be as low as possible, as it may cause a decline
New However, a content of 0.0020 wt% or less is acceptable.
Wear. Preferably it is 0.0012 wt% or less.

Mn: 0.05 to 2.0 wt% Mn acts as a deoxidizing agent during melting of steel and is an effective element for reducing oxygen in steel. Further, the toughness of the base martensite by improving the hardenability of the steel, to improve hardness, effectively contributes to the improvement of the general rolling contact fatigue life (B ₁₀ life) in member surface portion. For this purpose, the addition of 0.05 to 2.0 wt% is sufficient, preferably 0.25 to 2.0 wt%.

[0027] Ni: 0.05~1.0 wt%, 1.0 ultra to 3.0 wt% Ni, as well as improving the toughness enhancing the strength after tempering Quenched by increasing hardenability, so improving the B ₁₀ life, this end For this purpose, it is added in the range of 0.05 to 1.0 wt%, preferably 0.15 to 1.0 wt%.
Further, as described above, when Ni is added in excess of 1.0 wt%, the microstructure change during rolling is delayed,
Thereby improving the B ₅₀ life. However, even in this case, if more than 3 wt% is added, a large amount (> 35%) of residual γ
Precipitation causes a decrease in strength and impairs dimensional stability, and also increases the cost. Therefore, if this effect is expected, it is necessary to add it in the range of more than 1.0 to 3.0 wt%. Yes, preferably more than 1.0 to 2.5 wt%.

[0028] Cu: 0.05~1.0 wt% Cu increases the strength after tempering Quenched by increasing hardening, is added in order to improve the B ₁₀ life. For this purpose, a range of 0.05 to 1.0 wt% is sufficient, and preferably 0.15 to 1.0 wt%.

[0029] B: 0.0005~0.01wt% B increases the strength after tempering Quenched by increasing hardenability, so improving the B ₁₀ life, adding more than 0.0005wt%. However, if added in excess of 0.01 wt%, the workability is degraded, so the range is limited to 0.0005 to 0.01 wt%. Preferably, the content is 0.0015 to 0.0050 wt%.

Al: 0.005 to 0.07 wt% Al is an element that also acts as a deoxidizing agent during melting of steel, combines with N to refine crystal grains, and also contributes to improving the toughness of steel. . Further, it increases the strength after quenching and tempering, and effectively acts to improve the rolling fatigue life. For such an effect, Al is 0.005 to 0.07 wt%, preferably 0.015 to
It must be added in the range of 0.07 wt%.

N: 0.0005 to 0.012 wt% N combines with a carbonitride forming element to refine crystal grains,
Enhance the strength after tempering Quenched and dissolved in the matrix and improving the B ₁₀ life. For this purpose 0.0005-0.
It is added within the range of 012 wt%, but preferably 0.0020 to 0.
012 wt% is good.

The above, as well as improve the rolling fatigue life (B ₅₀ life) by delaying the microstructure change caused by repeated stress loading at the member surface portion, the rolling fatigue life of member surface part through increased strength (B ₁₀ The main components (C, Si, Cr, O and Mn, Ni, Cu,
(B, Al, N) has been described. However, in the present invention, by adding one or more selected from Zr, Ta, Hf and Co, a severe use environment ( dust-containing, high-load, it may be made to improve the rolling contact fatigue life, i.e. B ₅₀ life at high temperatures).

The preferred addition range and purpose of each of the above elements,
Table 2 summarizes the reasons for limiting the upper and lower limits.

[Table 2]

Further, in the present invention, in order to improve machinability, P, S, Se, Te, REM, Pb, Bi, Ca, Ti, Mg,
Even if Sn, As, etc. are added, the above-mentioned object of the present invention does not hinder the retardation characteristics due to the change in microstructure due to the repeated stress load, and the machinability can be easily improved. You may add according to it. Note that P
Is preferably 0.025 wt% or less, and more preferably 0.015 wt% or less, since it reduces the toughness and rolling fatigue life of steel. Further, S combines with Mn to form MnS, and improves machinability. However, if contained in a large amount, the rolling fatigue life is reduced, so it is preferable to keep the content to 0.025 wt% or less, preferably 0.015 wt% or less.

[0035]

EXAMPLES Steel having the composition shown in Tables 3 and 4 was melted and cast, and the obtained steel was subjected to diffusion annealing at 1200 ° C. for 30 hours and then rolled into a 65 mmφ steel bar. Then, normalizing-
After spheroidizing annealing, steel materials No.1 and No.2 are at 820 ° C and others are
Quenched at 900 to 950 ° C and tempered at 180 ° C. 12mmφ × 22mm and 60mm by wrapping
A φ5 mm cylindrical test piece was prepared. At this time, the surface roughness of each test piece was Ra: 0.1 mm. Then, for each test piece, B ₁₀ life under clean environment,
It was measured test for B ₅₀ life. The B ₁₀ life,
B test ₅₀ life, using a rolling fatigue life tester of the radial type as shown in FIG. 3, Hertzian maximum contact stress: 60
0kgf / mm ² , repetitive stress number about 46500 cpm and lubricating oil: # 68 Turbine splash oil was used. The test results were compiled on probability paper assuming that they follow the Weibull distribution, and the steel material No. 1 (conventional steel SUJ
The average life of 2) (cumulative failure probability: the total number of loads until the occurrence of peeling at 10% and 50%) was set to 1, and the evaluation was made by comparing the other steel types.

On the other hand, the rolling life (B ₁₀ life, B ₅₀ life) in dust-containing environment for each specimen, using a thrust-type rolling fatigue tester to prepare a disk-shaped test piece, hertz Maximum contact stress: 536 kgf / mm ² , number of repeated stress: 1800
Under the condition of cpm, hardness in # 68 turbine oil: about Hv850,
Average particle size: about 100 μm was mixed with about 150 ppm of iron powder. The test machine was improved as shown in FIG. 3 so that iron powder was always supplied to the contact portion between the steel ball and the test piece.

The test results are plotted on a probability paper as conforming to the Weibull distribution, B ₁₀ life (cumulative failure probability: 10
% And total life of B ₅₀
(50%), and the steel material No. 1 was evaluated as 1 for each. The amount of retained austenite was measured on the test piece after lapping using an X-ray analyzer. The above evaluation results are summarized in Tables 3 and 4.

[0038]

[Table 3]

[0039]

[Table 4]

Steel Nos. 2 to 5 are shown as comparative examples. Steel No. 5 in which the C content in steel is out of the range of the present invention, Steel No. 6 in which the Cr content in steel is out of the range of the present invention, Steel No. 4 in which the amount of Si in steel is outside the range of the present invention, Steel No. 3 in which the amount of O in steel is outside the range of the present invention, and Steel N in which the amount of retained austenite in the steel is outside the range of the present invention
o.2 of B ₁₀ life, B ₅₀ life is not much different both in comparison with the conventional steel (steel No.1). In contrast, steel No.7, 9 to 35 of the B ₁₀ life is the invention bearing member, an average of about 10 to 26 times compared to the conventional steel in normal test in clean environment (steel No.1), B ₅₀ life has issued a 28-62 times superior results. Moreover, the trend is a high load of dust containing environments, even at test at a high temperature, about 4-12 times in the B ₁₀ life,
About 7-22 times in the B ₅₀ life is also a excellent results. That is, the bearing member, the rolling life in addition dust containing environment of a large amount of Si-Cr, especially B ₅₀
By significantly delaying the microstructural change indicated by the life, while controlling the amount of residual γ to 10-35%, B ₁₀
This results in a remarkable improvement in the service life, and as a result, it can be seen that it is extremely effective in improving the overall rolling contact fatigue life of the bearing.

[0041]

As described above, according to the present invention,
Microstructure with 10-35% residual γ content in steel and large amount of Si-Cr
As a result, the microstructure change due to the repeated stress load under the surface layer of the bearing member is delayed not only in a clean environment but also under a high load with dust and high temperature use, which results in rolling. dynamic fatigue life (B ₁₀ life, B ₅₀ life) to achieve improved, it is possible to provide a bearing member for a long life. Therefore, it is necessary to control the composition, shape, and distribution of oxide-based non-metallic inclusions in steel, which are essential for conventional technology, to further reduce the oxygen content in steel at the surface layer of the member or to control the presence of oxide-based nonmetallic inclusions in steel. The present invention does not require the improvement or construction of the steelmaking equipment required for the production. 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 operating temperature of the bearing.

[Brief description of the drawings]

1 (a) and 1 (b) are views under a repeated stress load.
7 is a micrograph of a metal structure showing a change in microstructure occurring in a zone below a member surface layer.

FIG. 2 shows the effect of Si-Cr and residual γ on bearing life caused by non-metallic inclusions and bearing life caused by microstructure change.
Explanatory drawing which shows the influence of quantity.

FIG. 3 is a schematic diagram illustrating a schematic configuration of a thrust rolling contact fatigue tester.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (56) References JP-A-3-122255 (JP, A) JP-A-49-47212 (JP, A) JP-A-3-56640 (JP, A) JP-A-4-26752 (JP, A) JP-A-2-30733 (JP, A) JP-A-6-271977 (JP JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. A composition comprising C: 0.5-1.5 wt%, Si: 1.0-2.5 wt%, Cr: 3.0-5.0 wt%, O: 0.0020 wt% or less, with the balance being Fe and unavoidable impurities. And a steel structure having a steel structure in which the amount of retained austenite in the steel is 10 to 35% by volume, wherein the bearing member has excellent microstructure change delay characteristics due to repeated stress loading. 2. C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, and Mn: 0.05 to 2.0 wt%, Ni : 0.05 to 1.0 wt%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt%, and N: 0.0005 to 0.012 wt%. Including the species or more, the balance has a component composition consisting of Fe and unavoidable impurities, and the amount of residual austenite in the steel in volume ratio
A bearing member having a steel structure of 10 to 35% and having excellent characteristics of delaying microstructure change due to repeated stress loading. C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, and Ni: more than 1.0 to 3.0 wt%. Zr: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02 to 0.5 wt%, and Co: 0.05 to 1.5 wt%. And the component composition of unavoidable impurities, and the amount of retained austenite in the steel is
A bearing member having a steel structure of 10 to 35% and having excellent characteristics of delaying microstructure change due to repeated stress loading. 4. C: 0.5 to 1.5 wt%, Si: 1.0 to 2.5 wt%, Cr: 3.0 to 5.0 wt%, O: 0.0020 wt% or less, Mn: 0.05 to 2.0 wt%, Ni : 0.05 to 1.0 wt%, Cu: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, Al: 0.005 to 0.07 wt%, and N: 0.0005 to 0.012 wt%. Or more as a component that improves rolling fatigue in a normal environment, and when one or more of the above-mentioned improving components is selected, the following components excluding that element, namely, Ni : At least 1.0 to 3.0 wt%, Zr: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.02 to 0.5 wt%, and Co: 0.05 to 1.5 wt%, any one or two selected from the group Species or more are included as components that improve the rolling fatigue life under severe environments, the balance has a component composition consisting of Fe and unavoidable impurities, and the amount of retained austenite in steel is volume In comparison
A bearing member having a steel structure of 10 to 35% and having excellent characteristics of delaying microstructure change due to repeated stress loading.