JPH0892689A - Bearing steel with excellent delay characteristics for microstructural changes due to repeated stress loading - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a bearing member that has a small microstructure change due to repetitive stress load and a long bearing life not only in a clean environment but also under severe operating conditions containing dust. [Structure] C: 0.5-1.5 wt%, Cu: over 1.0-2.5 wt
%, O: 0.0020 wt% or less, and Mo: over 0.5 to 2.0 w
t% and Ni: contains more than 1.0 to 3.0 wt% and contains one or two kinds, and if necessary, Si: more than 0.5 to
2.5 wt%, Mn: over 2.0 ~ 5.0 wt%, Cr: over 2.5 ~ 8.0 w
t%, N: over 0.012 ~ 0.050 wt%, V: 0.05 ~ 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.
The chemical composition contains 02 to 0.5 wt% and Co: 0.05 to 1.5 wt%, and one or more selected from the rest, with the balance being Fe and inevitable impurities.

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 a rolling bearing such as a roller bearing or a ball bearing, and particularly a microstructural change (deterioration) under the rolling contact surface caused by repeated stress load in a severe operating environment. )
We propose a bearing steel that exhibits excellent retardation properties regardless of the cleanliness of the lubricating oil even when the lubricating oil is in a poor state.

[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 steel. 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 steel, by controlling the carbide area ratio, surface carbon concentration, and surface retained austenite amount of the surface layer, the characteristics of the surface layer can be improved. It is proposed to control the shape of the indentation caused by dust, thereby reducing 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 this is a method of externally modifying only the surface layer of the bearing steel, it does not lead to the improvement of the microstructure change part observed at the lower side of the surface layer part as described later, and further the treatment cost is high. The problem remained.

[0005]

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 under severe conditions such as high load or high temperature, is reduced by simply heat-treating the bearing steel 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 life of the bearing under various conditions.
From this, the inventors were convinced of the existence of other factors that govern the life of the bearing.

[0006] Therefore, the present inventors have continued to earnestly study the cause of the separation of the rolling bearing. As a result, due to the repeated shearing stress generated during the rolling contact between the inner and outer races of the bearing and the rolling element, a strip-shaped white product and rod-shaped deposits were formed under the rolling contact surface (surface layer portion) as shown in FIG. A microstructure-changed layer consisting of a substance is generated, which gradually grows as the number of times of rolling increases.Finally, fatigue separation occurs from this microstructure-changed part, and the bearing steel surface layer part is lost and the bearing life is extended. I understand. Furthermore, the severer bearing usage environment, that is, higher surface pressure (smaller size) and higher operating temperature, shortens the number of rolling cycles until these microstructure changes occur.
We also found that it would lead to a significant reduction in bearing life. As explained above, bearing life is not sufficient to control the decarburization layer and non-metallic inclusions in the surface layer of the bearing steel, as in the prior art. Just by reducing the amount of decarburized surface layer and non-metallic inclusions by various heat treatments such as chemical annealing,
It is not possible to delay the time until the microstructure change occurring under the rolling contact surface (surface layer portion) described above occurs. 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. The specific object of the present invention is to improve the characteristics of not only the surface layer portion but also the characteristics of the steel as a whole by devising the component composition of the bearing steel, especially the surface layer that is expected to be generated during bearing use under high load and high temperature environment. It is an object of the present invention to provide a bearing steel capable of delaying the microstructural change observed in subordinates, and thus significantly improving the bearing life. Another specific object of the present invention is to control the composition of the steel so as to prevent the microstructure change from occurring due to the stress concentration around the indentation due to the dust even in an environment containing dust. In addition to this, the rolling fatigue life of the surface layer and the characteristics of the material itself are improved to further improve the bearing life.

[0008]

Now, based on the above-mentioned findings, the present inventors have paid attention to a new "microstructure change delay characteristic" as a bearing life, and by improving this characteristic, the bearing life in this aspect can be improved. In order to improve, naturally, a new alloy design (component composition) is necessary for that purpose, and further recognition of the fact that without realizing this, the life of bearings cannot be further improved, various experiments and studies will be conducted. And went. As a result, surprisingly, in addition to the appropriate amount of Cu, Mo and /
It was found that the above-mentioned microstructural change generated under the rolling contact surface due to repeated stress loading can be significantly delayed by controlling Ni, and the present invention steel for bearings was developed.

That is, the bearing steel according to the present invention has the following essential constitution. (1) C: 0.5-1.5 wt%, Cu: over 1.0-2.5 wt%,
O: 0.0020 wt% or less is included, and Mo: more than 0.5 to 2.0 wt%
And Ni: containing more than 1.0 to 3.0 wt% selected from the group consisting of one or two, the balance being Fe and unavoidable impurities, for delaying microstructural change due to repeated stress loading. Excellent bearing steel.

(2) C: 0.5 to 1.5 wt%, Cu: more than 1.0 to 2.5 wt%, O: 0.0020 wt% or less, and Mo: 0.5 wt%
Contains one or two selected from ultra-2.0 wt% and Ni: 1.0-3.0 wt%, and Si: 0.5
Over ~ 2.5 wt%, Mn: over 2.0 ~ 5.0 wt%, Cr: over 2.5 ~
8.0 wt%, N: over 0.012 ~ 0.050 wt%, V: 0.05 ~ 1.0
wt%, Nb: 0.05 to 1.0 wt%, W: 0.05 to 1.0 wt%,
Zr: 0.02-0.5 wt%, Ta: 0.02-0.5 wt%, H
f: 0.02 to 0.5 wt% and Co: 0.05 to 1.5 wt%, and any one or more selected from the rest, and the balance
Bearing steel with excellent delay characteristics for microstructural changes due to repeated stress loading, which is characterized by comprising Fe and unavoidable impurities.

(3) However, the above basic components (C, Cu, O,
In addition to Mo and / or Ni), optional additives (Si, Mn, Cr, N) added selectively in large amounts and other optional additives (V, Nb, W, Zr, Ta, Hf and Co)
When adding and combining, it is recommended to add the following combinations within the composition range described in (2) above. Over 0.5-2.5 wt% Si- (any one or more of Mn, Cr and N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) 2.0- 5.0 wt% Mn- (any one or two of Cr and N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) over 2.5 ~ 8.0 wt% Cr- N- (V, Nb, W, Zr, Ta, Hf
And any one or more of Co) N- (any one or more of V, Nb, W, Zr, Ta, Hf and Co)

(4) C: 0.5 to 1.5 wt%, Cu: more than 1.0 to 2.5 wt%, O: 0.0020 wt% or less, and Mo: 0.5
Super-2.0 wt% and Ni: more than 1.0-3.0 wt%, containing one or two selected from the above M.
When any one or more of o and Ni is selected, the following components excluding the element, that is, Si: 0.05 to 0.5 wt
%, Mn: 0.05 to 2.0 wt%, Cr: 0.05 to 2.5 wt%,
Mo: 0.05-0.5 wt%, Ni: 0.05-1.0 wt%, B:
0.0005 to 0.01wt%, Al: 0.005 to 0.07wt%, N: 0.000
5 to 0.012 wt% and Sb: 0.0001 to 0.015 wt% Any one kind or two kinds or more selected from the balance is contained.
Bearing steel with excellent delay characteristics for microstructural changes due to repeated stress loading, which is characterized by comprising Fe and unavoidable impurities.

(5) However, the above basic components (C, Cu, O,
In addition to Mo and / or Ni), a combination of optional additive components (Si, Mn, Cr, N, Mo, Ni) selectively added in small amounts and other optional additive components (B, Al, Sb) When added as a combination, it is recommended to add the following combinations within the composition range described in (4) above. 0.05 to 0.5 wt% Si- (one or more of Mn, Cr, Mo, Ni, B, Al, N and Sb) 0.05 to 2.0 wt% Mn- (Cr, Mo, Ni, B, Al, N and
Sb one or more) 0.05 to 2.5 wt% Cr- (Mo, Ni, B, Al, N and one or more Sb) 0.05 to 0.5 wt% Mo- (Ni, B, Al, N and Any one or more of Sb) 0.05 to 1.0 wt% Ni- (any one or more of B, Al, N and Sb) 0.0005 to 0.01 wt% B- (Any one of Al, N and Sb
0.005 to 0.07 wt% Al- (any one or two of N and Sb) 0.0005 to 0.012 wt% N-Sb

(6) C: 0.5 to 1.5 wt%, Cu: more than 1.0 to 2.5 wt%, O: 0.0020 wt% or less, and Mo: 0.5
Contains one or two selected from ultra-2.0 wt% and Ni: 1.0-3.0 wt%, and Si: 0.5
Over ~ 2.5 wt%, Mn: over 2.0 ~ 5.0 wt%, Cr: over 2.5 ~
8.0 wt%, N: over 0.012 ~ 0.050 wt%, V: 0.05 ~ 1.0
wt%, Nb: 0.05 to 1.0 wt%, W: 0.05 to 1.0 wt%,
Zr: 0.02-0.5 wt%, Ta: 0.02-0.5 wt%, H
f: 0.02 to 0.5 wt% and Co: 0.05 to 1.5 wt%, and any one or more selected from the components as a component that improves rolling contact fatigue life in a harsh environment. Any one of the above Mo, Ni and the above improving components
When more than one kind is selected, the following components excluding the element, namely Si: 0.05 to 0.5 wt%, Mn: 0.05 to
2.0 wt%, Cr: 0.05 to 2.5 wt%, Mo: 0.05 to 0.5 wt
%, Ni: 0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, A
l: 0.005 to 0.07 wt%, N: 0.0005 to 0.012 wt% and S
b: Any one selected from 0.0001 to 0.015 wt%
Bearing having excellent delay characteristics of microstructure change due to repeated stress load, characterized by containing one or more kinds as components for improving rolling fatigue under normal environment, and the balance consisting of Fe and unavoidable impurities For steel.

(7) However, the following combinations of the components for improving rolling contact fatigue life in the above-mentioned severe use environment are recommended. Over 0.5-2.5 wt% Si- (any one or more of Mn, Cr and N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) 2.0- 5.0 wt% Mn- (any one or two of Cr and N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) over 2.5 ~ 8.0 wt% Cr- N- (V, Nb, W, Zr, Ta, Hf
And any one or more of Co) N- (any one or more of V, Nb, W, Zr, Ta, Hf and Co) Further, regarding the rolling fatigue life improving component in the above normal environment, , The following combinations are recommended. '0.05 to 0.5 wt% Si- (Mn, Cr, Mo, Ni, B, Al, N
And any one or more of Sb) '0.05 to 2.0 wt% Mn- (any one or more of Cr, Mo, Ni, B, Al, N and Sb)' 0.05 to 2.5 wt% Cr- (Mo, Ni , B, Al, N and Sb
Any one or more) '0.05-0.5 wt% Mo- (any one or more of Ni, B, Al, N and Sb)' 0.05-1.0 wt% Ni- (Any of B, Al, N and Sb Or more) '0.0005 to 0.01 wt% B- (any one or more of Al, N and Sb)' 0.005 to 0.07 wt% Al- (any one or two of N and Sb) '0.0005 to 0.012 wt% N-Sb

[0016]

First, the history of the development of the bearing steel of the present invention relating to the above alloy design and microstructure control will be described based on the results of experiments conducted by the inventors. First, in this experiment, A: SUJ 2 (C: 1.02wt%, Si: 0.25wt%, Mn: 0.45wt%
%, Cr: 1.35 wt%, N: 0.0040 wt%, O: 0.0012 wt%)
And two materials with Al added: B: (C: 1.00wt%, Si: 0.24wt%, Mn: 0.46wt%, C
u: 1.18wt%, Ni: 1.24wt%, Mo: 0.81wt%, N: 0.004
2wt%, O: 0.0009wt%) C: (C: 1.00wt%, Si: 0.24wt%, Mn: 0.40wt%, C
u: 1.78wt%, Ni: 2.20wt%, Mo: 1.43wt%, N: 0.003
2wt%, O: 0.0008wt%) Steel having a chemical composition is melted and cast, and at 1240 ℃ for 30 hours.
After diffusion annealing, was rolled into a steel bar having a diameter of 65 mm to obtain a test material. Then, this test material was subjected to normalizing, spheroidizing annealing, and further heat treatment in the order of quenching-tempering, and thereafter, a cylindrical test piece of 12 mmφ × 22 mm was prepared by lapping finish.

Next, the above test piece was subjected to a Hertz maximum contact stress: 600 kgf using a radial type rolling fatigue life tester.
/ mm ² , Repetitive stress number: 46500 cpm, Lubrication: # 68 Turbine Fatigue life test was conducted under load condition under turbine oil spray environment. The results of the test are plotted on the 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, which is influenced by the control of non-metallic inclusions.
Bearing life with a cumulative failure probability of 10% (hereinafter referred to as "B ₁₀ rolling contact fatigue life") and rolling due to delaying the occurrence of microstructural changes under cyclic stress loading at high temperature and high load rolling Bearing life at a cumulative damage probability of 50% (hereinafter referred to as "B ₅₀ rolling contact fatigue life"), which is considered to be a numerical value showing improvement in dynamic fatigue life, was obtained, and each steel A was evaluated as 1.

As a result, as shown in Table 1, in the steels containing Cu, Ni and Mo, the B ₁₀ rolling fatigue life is not so much improved, but the B ₅₀ rolling fatigue life is remarkably high. Numerical values are shown. Steel B has an improvement of about 12 times that of SUJ2 and Steel C has an improvement of about 30 times that of SUJ2.

[Table 1]

FIG. 2 is a summary of the above experimental results, showing the bearing life due to non-metallic inclusions in the surface layer and the bearing life due to microstructural change under repeated stress loading under the surface layer. It is a schematic diagram which shows a relationship. As is clear from this figure, the B ₁₀ rolling as an index of the amount of non-metallic inclusions in the surface layer of the bearing steel, its morphology, C concentration, carbide area ratio, etc., which has been discussed generally in the past. According to the fatigue life, the effect cannot be obtained as expected by simply adding Cu, Ni and Mo, but the B ₅₀ rolling as an index showing the microstructure change characteristics observed in the zone below the surface layer portion. In terms of fatigue life, it can be seen that the effect of the combined addition of Cu, Ni and Mo is extremely remarkable. Based on these findings, the inventors have determined the composition of components for improving the rolling fatigue life, in particular, the B ₅₀ rolling fatigue life, from the viewpoint of mainly improving the microstructure change delay property due to repeated stress loading. The range was determined as described below.

C: 0.5 to 1.5 wt% C is an element which forms a solid solution in the matrix and effectively acts to strengthen 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.

Cu: more than 1.0 to 2.5 wt% Cu, when added in a large amount exceeding 1.0%, significantly delays the B ₅₀ rolling contact fatigue life by delaying the microstructural change due to repeated stress loading. become.
However, if the amount exceeds 2.5 wt%, this addition effect will be saturated and, conversely, the forgeability will be reduced. Therefore, for this purpose (improvement of B ₅₀ rolling contact fatigue life),
It is necessary to add in the range of more than 1.0 to 2.5 wt%,
More than 1.0 to 2.0 wt% is preferable.

O: 0.0020 wt% or less O forms a hard non-metallic inclusion. Therefore, even if the delay of microstructure change due to repeated stress loading is obtained by controlling other components, B ₁₀ rolling Fatigue life, B
_{50 Since} rolling fatigue life may be shortened, it is desirable to be as low as possible. However, a content of 0.0020 wt% or less is acceptable. It is preferably 0.0012 wt% or less.

Mo: 0.05 to 0.5 wt%, more than 0.5 to 2.0 wt% Mo is an element which improves wear resistance by stabilizing residual carbides. Particularly, when 0.05 to 0.5 wt% is added, the hardenability is increased to contribute to the improvement of the strength after quenching and tempering, and the precipitation of stable carbide improves the wear resistance and the B ₁₀ rolling contact fatigue life. Furthermore, when Mo is added in a large amount of more than 0.5 wt%, as described above, the effect of delaying the microstructure change during rolling becomes remarkable, and the rolling fatigue life in this aspect, that is, B ₅₀ rolling fatigue Improve life. However, if the amount exceeds 2.0 wt%, the machinability and forgeability are deteriorated, which causes a cost increase. Therefore, in order to improve the B ₅₀ rolling contact fatigue life, the range of more than 0.5 to 2.0 wt% is required. It is necessary to add it within the range of 0.75 to 1.2 wt.
The range of% is good.

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 due to the increase in hardenability, and improves the B ₁₀ rolling contact fatigue life. For this purpose, it is added in the range of 0.05 to 1.0 wt%, preferably 0.15 to 1.0 wt%. Furthermore, this Ni is 1.0 wt% as described above.
If it is added in excess of ₅₀ %, the microstructure change during rolling is delayed, thereby improving the B ₅₀ rolling fatigue life. However, even in this case, if it is added in excess of 3 wt%, a large amount (> 35%) of residual γ will be deposited, resulting in a decrease in strength and impaired dimensional stability, and an increase in cost.
When this effect is expected, it is necessary to add in the range of more than 1.0 to 3.0 wt%, preferably more than 1.0 to 2.5 wt%.

Si: 0.05 to 0.5 wt%, more than 0.5 to 2.5 wt% or less Si is used as a deoxidizing agent 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 B ₁₀ rolling contact fatigue life. The content of Si added for these purposes is 0.05 to 0.5 wt%, preferably 0.15 to 0.50 wt%
Is good. Furthermore, if Si is added in excess of 0.5 wt%,
It has the effect of delaying the microstructural change under high temperature, high load and cyclic stress loading, and improving the B ₅₀ rolling contact 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 microstructure change retardation property, 0.5 to 2.5 wt% is exceeded. It is effective to add. More than 0.50 to 2.0 wt% is preferable.

Mn: 0.05 to 2.0 wt%, more than 2.0 to 5.0 wt% Mn is an element effective as a deoxidizer during the melting of steel and effective in reducing the oxygen content of the steel. Further, by improving the hardenability of the steel, it improves the toughness and hardness of the base martensite and effectively contributes to the improvement of the general rolling contact fatigue life (B ₁₀ rolling contact fatigue life) in the surface layer of the steel. For these purposes, the addition of 0.05 to 2.0 wt% is sufficient, preferably 0.25 to 2.0 wt%. However, in order to improve the B ₅₀ rolling contact fatigue life, which significantly delays the microstructural change due to the loading of cyclic stress, similar to Al, it is necessary to add more than 2.0 wt%. . However, if the added amount exceeds 5.0 wt%, a large amount (> 35
%), Resulting in a decrease in strength and dimensional stability. For the purpose of improving the B ₅₀ rolling contact fatigue life, it is preferable to add it in the range of more than 2.0 to 5.0 wt%. Is more than 2.0 to 4.0 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 in turn, improves rolling fatigue life in a general sense. To obtain such effects, addition of 0.05 to 2.5 wt% is sufficient. The preferable addition amount is 0.15 to 2.5 wt%. Further, Cr is added in a large amount exceeding 2.5 wt% in order to delay the microstructure change due to cyclic stress loading and improve the rolling fatigue life (B ₅₀ rolling fatigue life) in this aspect. There is a need. When the amount of Cr added to improve the B ₅₀ rolling contact fatigue life exceeds 8.0 wt%, not only is it saturated, but rather the amount of solid solution C during quenching decreases and the strength decreases. To do. Therefore, when it is added for this purpose, it must be more than 2.5 to 8.0 wt%. The range of more than 2.5 to 5.0 wt% is preferable.

N: 0.0005 to 0.012 wt%, more than 0.012 to 0.05
0 wt% N combines with the nitride-forming element to refine the crystal grains and form a solid solution in the matrix to enhance the strength after quenching and tempering, and B
₁₀ Improve the rolling fatigue life. 0.00 for this purpose
It is added within the range of 05 to 0.012 wt%, preferably 0.00
20-0.012 wt% is good. Also, this N is
When added in excess of 0.012 wt%, as described above, the B ₅₀ rolling contact fatigue life can be improved by delaying the microstructural change due to repeated stress. However, if this amount exceeds 0.05 wt%, workability and toughness decrease, so for this purpose, more than 0.012 to 0.050 wt%
Is added, but preferably more than 0.012 to 0.035 wt%.

B: 0.0005 to 0.01 wt% B is 0.0005 wt% because it increases the hardenability to increase the strength after quenching and tempering and improves the B ₁₀ rolling contact fatigue life.
Add the above. 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 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 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%.

Sb: 0.001 to 0.015 wt% Sb contributes to the improvement in heat treatment productivity by suppressing the reaction between C in the surface layer of the steel material and the atmospheric gas during heat treatment to prevent the generation of a decarburized layer. Moreover, it forms a solid solution in the matrix and increases the strength after quenching and tempering and improves the rolling fatigue life. The content of these two effects is 0.001 wt%
Notably, the effect becomes saturated even if it is added in excess of 0.015 wt%, but rather it causes deterioration of hot workability and toughness. Therefore, Sb is 0.00
It was decided to contain in the range of 1 to 0.015 wt%. Preferably 0.0020-0.0100 wt%, more preferably 0.0025-0.
It is contained in the range of 0080 wt%.

As described above, the rolling fatigue life (B ₅₀ rolling fatigue life) is improved by delaying the microstructure change due to the repeated stress load in the steel surface layer portion, and the rolling fatigue in the surface layer portion of the steel for use is improved by increasing the strength. The main components (Cu, Mo, Ni) for improving the life (B ₁₀ rolling contact fatigue life)
Although the reasons for limiting Si, Mn, Cr, B, Al, N, Sb) and C, O have been described, the present invention further includes V, Nb, W,
By adding one or more selected from Zr, Ta, Hf and Co, the rolling fatigue life in severe operating environment (including dust, high load, high temperature), that is, B
₅₀ Rolling fatigue life may be improved. 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.

[0033]

[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. Where P is
It is desirable that it is as low as possible in order to reduce the toughness and rolling fatigue life of steel, and it is desirable to keep it to 0.025 wt% or less, preferably 0.015 wt% or less. Also,
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 will be shortened, so 0.025 wt% or less, preferably
It is better to keep it to 0.015 wt% or less.

[0035]

EXAMPLES 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 a steel bar having a diameter of 65 mm. Then, after normalizing, spheroidizing and annealing, heat treatments such as quenching (830 ℃) and tempering (180 ℃) are performed, and further 12 mmφ × 22 mm cylindrical test pieces and 60
A disc-shaped test piece of mmφ × 5 mm was prepared. The surface roughness of each of the test pieces at this time was Ra: 0.1 μm or less. Then, a rolling fatigue life test in a clean environment was performed on the cylindrical test piece. The test was performed using a radial type rolling contact fatigue life tester with a Hertz maximum contact stress of 600.
kgf / mm ² , cyclic stress number about 46500 cpm and lubricating oil:
# 68 Turbine It was done under the condition that splash oil was used. The results of the test are summarized on the probability paper as being in accordance with the Weibull distribution and evaluated by comparing other steel types with B ₅₀ rolling fatigue life of steel No. 1 (conventional steel SUJ2) as 1. .

On the other hand, the rolling fatigue life test of each of the above test pieces under a dust-containing environment was carried out using a thrust type rolling fatigue tester with a disk-shaped test piece, and the maximum Hertzian contact stress was 536.
Under the condition of kgf / mm ² , cyclic stress: 1800cpm, hardness in # 68 turbine oil: Hv850, average particle size: 100μ
m iron powder was mixed at about 150 ppm. The testing machine was improved as shown in FIG. 3 so that the iron powder was constantly supplied to the contact portion between the steel ball and the test piece.

The test results were plotted on probability paper as if they were in accordance with the Weibull distribution, and the B ₅₀ rolling contact fatigue life (cumulative failure probability: the total number of loads until peeling occurred at 50%) was calculated. No. 1 is set to 1 for comparative evaluation. The evaluation results are shown in Tables 3, 4 and 5.

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

Steel Nos. 2 to 4 are shown as comparative examples, and steel No. 2 and Cu, Ni, in steel having a C content outside the range of the present invention are shown.
The B ₅₀ rolling contact fatigue life of steel No. 3 in which Mo is outside the scope of the present invention and steel No. 4 in which the amount of O in the steel is outside the scope of the present invention is the same as that of the conventional steel (steel No.
None have improved compared to 1). In contrast,
The B50 rolling fatigue life of the steel materials No. _{5 to 5,} which are the bearing steels of the present invention, is about 5.5 to 47.7 times better than the conventional steel (steel material No. 1) in a normal test in a clean environment. I understand. This tendency is also seen in tests under high load and high temperature in a dusty environment, and the B ₅₀ rolling contact fatigue life is about 3.2 to 7.
The result is twice as good.

[0042]

As described above, according to the present invention,
By adjusting the composition of components such as Cu, Ni and / or Mo in the steel, not only in a clean environment but also under a high load of dust and under high temperature use, repeated stress load under the surface layer of the bearing steel It causes a delay in the microstructure change associated with the above, and by doing so, an improvement in rolling contact fatigue life (in particular, B ₅₀ rolling contact fatigue life) can be achieved, and a bearing steel having a long life can be provided. Therefore, the oxygen content in the steel is further reduced in the steel surface layer, 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. To improve or construct steelmaking equipment required to
It is unnecessary in the present invention. Further, the development of the bearing steel 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 showing the appearance of the microstructure change which occurs in the zone under the steel surface layer part.

FIG. 2 is an explanatory diagram showing the influence of the steel composition on the bearing life due to non-metallic inclusions and the bearing life due to microstructural changes.

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

Front page continuation (72) Inventor Akihiro Matsuzaki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Steel Research and Development Division Steel Research Laboratory (72) Inventor Shinichi Amano Kawasaki, Chuo-ku, Chiba-shi, Chiba No. 1 Town Kawasaki Steel Co., Ltd.

Claims (4)

[Claims] 1. C: 0.5 to 1.5 wt%, Cu: more than 1.0 to 2.
5 wt%, O: 0.0020 wt% or less, and Mo: over 0.5 ~
2.0 wt% and Ni: more than 1.0 to 3.0 wt%, containing one or two selected from the rest, Fe and unavoidable impurities in the balance, characterized by microstructural changes due to repeated stress loading Bearing steel with excellent delay characteristics. 2. C: 0.5 to 1.5 wt%, Cu: more than 1.0 to 2.
5 wt%, O: 0.0020 wt% or less, and Mo: over 0.5 ~
2.0 wt% and Ni: more than 1.0 to 3.0 wt%, containing any one or two kinds, and further Si: more than 0.5 to
2.5 wt%, Mn: over 2.0 ~ 5.0 wt%, Cr: over 2.5 ~ 8.0 w
t%, N: over 0.012 ~ 0.050 wt%, V: 0.05 ~ 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% Any one kind or two kinds or more are selected, and the balance is composed of Fe and inevitable impurities. Bearing steel with excellent change delay characteristics. 3. C: 0.5-1.5 wt%, Cu: more than 1.0-2.
5 wt%, O: 0.0020 wt% or less, and Mo: over 0.5 ~
2.0 wt% and Ni: more than 1.0 to 3.0 wt%, containing one or two selected from the above.
When any one or more of the above are selected, the following components excluding the element, that is, Si: 0.05 to 0.5 wt%,
Mn: 0.05 to 2.0 wt%, Cr: 0.05 to 2.5 wt%, Mo:
0.05 to 0.5 wt%, Ni: 0.05 to 1.0 wt%, B: 0.0005
~ 0.01wt%, Al: 0.005 ~ 0.07wt%, N: 0.0005 ~ 0.0
12 wt% and Sb: 0.0001 to 0.015 wt% selected from the group consisting of one or more, and the balance being Fe and unavoidable impurities Bearing steel with excellent delay characteristics. 4. C: 0.5-1.5 wt%, Cu: over 1.0-2.
5 wt%, O: 0.0020 wt% or less, and Mo: over 0.5 ~
2.0 wt% and Ni: more than 1.0 to 3.0 wt%, containing any one or two kinds, and further Si: more than 0.5 to
2.5 wt%, Mn: over 2.0 ~ 5.0 wt%, Cr: over 2.5 ~ 8.0 w
t%, N: over 0.012 ~ 0.050 wt%, V: 0.05 ~ 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% selected from the group consisting of one or more selected from the group consisting of components that improve the rolling fatigue life in harsh environments. , Ni and any one or more of the above-mentioned improving components are selected, the following components excluding that element,
That is, Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0 wt
%, Cr: 0.05 to 2.5 wt%, Mo: 0.05 to 0.5 wt%, Ni:
0.05 to 1.0 wt%, B: 0.0005 to 0.01 wt%, Al: 0.005
~ 0.07wt%, N: 0.0005 ~ 0.012wt% and Sb: 0.000
1 to 0.015 wt% selected from the group consisting of 1 or 2 or more selected from the group consisting of Fe and inevitable impurities, with the balance being Fe and inevitable impurities. Bearing steel with excellent delay characteristics for microstructural changes due to stress loading.