JP3243372B2 - 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 more particularly to a microstructural change generated under a rolling contact surface due to a repeated stress load in a severe use environment. A bearing member that has excellent delay characteristics against deterioration (deterioration) regardless of the cleanliness of the lubricating oil, even when the lubricating oil is in a poor condition, and has an excellent effect of suppressing the formation of a decarburized layer that occurs during heat treatment. We suggest about.

[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.

Another move to improve the characteristics of the high-carbon bearing steel (JIS-SUJ2) is a study on workability, particularly on technology for suppressing the formation of a decarburized layer during heat treatment. Generally, the bearing steel specified in the above JIS-SUJ2 is 0.
It is very hard because it contains 95-1.10wt% C,
For this reason, the spheroidizing annealing was performed to improve the workability, followed by forming, followed by quenching and tempering to obtain the strength and toughness required for the rolling bearing. However, when such heat treatment for improving the properties is repeated many times, it is known that a "low C concentration region" called a decarburized layer is generated on the material surface due to a reaction between C and the atmospheric gas. I have. This decarburized layer is not only reduced in hardness of the rolling bearing but also causes deterioration in rolling contact fatigue life. Therefore, the decarburized layer is usually removed by cutting or grinding. As a result, the material yield and the productivity had to be reduced. On the other hand, conventionally, as 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 a method disclosed in JP-A-2-54717, A method of performing a carburizing treatment at an early stage of annealing has been proposed. However, since each of the above methods is based on cleaning the atmosphere during heat treatment or pre-treatment, not only does the heat treatment cost increase, but also setting of an appropriate gas composition according to the material composition, heat treatment time, and the like. The problem remains where complicated operations are required.

[0006]

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.

Therefore, the present inventors have continued a keen study on the bearing life, especially the cause of the occurrence of peeling of the rolling bearing in consideration of the recent bearing operating environment. As a result, due to the repetitive shear stress generated when the inner and outer races of the bearing and the rolling elements are brought into rotational contact with the intensified use environment of the bearings, FIG. 1 (a)
In the lower part of the rolling contact surface (surface layer part), a microstructure change layer composed of a band-like white product and a rod-like precipitate is generated, which gradually grows as the number of rolling increases,
Finally, it was found from the microstructure-changed portion that fatigue peeling occurred as shown in Fig. (B) and the surface layer of the bearing member was lost, resulting in a longer bearing life. 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. Also found out.

As described above, the bearing life is not sufficient only by controlling the decarburized layer and nonmetallic inclusions in the surface layer of the bearing member as in the prior art.
For example, simply reducing the amount of decarburized layer on the surface layer and the amount of non-metallic inclusions by various heat treatments such as carburizing / nitriding and spheroidizing annealing will result in microstructural changes occurring under the above-mentioned rolling contact surface (surface layer). It is not possible to delay the time until the occurrence. 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 rolling fatigue life characteristics under severe use conditions. Another 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 during use of the bearing under high load and high temperature environments Another object of the present invention is to provide a bearing member capable of delaying a change in microstructure observed under the surface layer, which is expected to be generated, and consequently significantly improving the bearing life. Another object of the present invention is to adjust the composition of steel, particularly the Si content, and to control the amount of retained austenite in the steel. In addition to suppressing the occurrence of microstructure change, it is another object of the present invention to further improve the rolling contact fatigue life of the surface layer and the characteristics of the raw material itself, thereby further improving the bearing life. Still another object of the present invention is to improve the heat treatment productivity (saving the work of processing and removing the decarburized layer) by suppressing the growth of the decarburized layer thickness during the heat treatment.

[0010]

Means for Solving the Problems The inventors of the present invention have newly focused on "microstructure change delay characteristic" as a bearing life based on the above-mentioned findings. Then, the improvement of this characteristic is intended to improve the bearing life on this surface. To this end, a new alloy design (composition composition) and a steel structure must be specified, and the bearing life cannot be further improved without realizing this. Considered and done. As a result, surprisingly, if appropriate amounts of Si and Sb are combined and the amount of retained austenite in the steel (hereinafter simply referred to as “residual γ amount”) is controlled, rolling contact due to repeated stress load can be achieved. The present inventors have found that the above-described microstructure change generated below the surface can be significantly delayed, and developed the bearing member of the present invention and a method of manufacturing the same.

That is, the bearing member according to the present invention has the gist configuration as listed below. (1) C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb:
0.001 to 0.015 wt%, Al: 0.005 to 0.07 wt%, O: 0.00
Characterized by having a steel structure containing not more than 20 wt%, the balance having a component composition consisting of Fe and unavoidable impurities, and having a retained austenite content in the steel of 10 to 35% by volume. Bearings with excellent heat treatment productivity and excellent microstructure change delay characteristics due to repeated stress loading.

(2) C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less. , Mn: 0.05~2.0wt%, N i : 0.05~1.0wt%, Mo: 0.05~0.5wt%, Cu: 0.05~1.0wt%, B: 0.0005~0.01wt% and N: the 0.0005～0.012Wt% Including one or more selected from among them, 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 heat treatment productivity and excellent delay characteristics of microstructure change due to repeated stress load.

(3) However, the above basic components (C, Si, S
b, Al, O), and the optional components (Mn , Ni, Mo, Cu, B, N) added selectively as described in (2) above.
It is recommended to add the following combinations within the composition range of 0.05-2.0wt% Mn- (any one or more of Ni, Mo, Cu, B and N) 0.05-1.0wt% Ni- (any one or more of Mo, Cu, B and N) 0.05-0.5wt % Mo- (one or more of Cu, B and N) 0.05 to 1.0 wt% Cu- (one or more of B and N) 0.0005 to 0.01 wt% B- (one or two of N) N

(4) C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less. , N: over 0.012 to 0.050 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% Or containing 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 heat treatment productivity and excellent delay characteristics of microstructure change due to repeated stress load.

(5) However, the above basic components (C, Si, Sb,
Al, O), an optional component (N) added selectively in a large amount and other optional components added in a small amount (
Zr, Ta, Hf and Co) are recommended to be added in the following combinations within the composition range described in (4) above. More than 0.012 to 0.050 wt% N- (one or more of Zr, Ta, Hf and Co)

C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less, and Mn: 0.05~2.0wt%, N i: 0.05~1.0wt% , Mo: 0.05~0.5wt%, Cu: 0.05~1.0wt%, B: 0.0005~0.01wt% and N: selected from among 0.0005～0.012Wt% One or more of the above-mentioned components as components for improving rolling fatigue under a normal environment, and when one or more of the above-mentioned components for improvement are selected, the element is excluded. The following components are selected from the following: N: over 0.012 to 0.050 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%. One or two or more of these as components for improving the rolling fatigue life in a severe environment, the balance having a component composition consisting of Fe and unavoidable impurities, and the amount of retained austenite in the steel. To volume ratio do it
A bearing member having a steel structure of 10 to 35% and having excellent heat treatment productivity and excellent delay characteristics of microstructure change due to repeated stress load.

(7) However, in the above (6), the following combinations are recommended for the rolling fatigue life improvement component in a normal environment. 0.05-2.0wt% Mn- (any one or more of Ni, Mo, Cu, B and N) 0.05-1.0wt% Ni- (any one or more of Mo, Cu, B and N) 0.05-0.5wt % Mo- (one or more of Cu, B and N) 0.05 to 1.0 wt% Cu- (one or more of B and N) 0.005 to 0.01 wt% B- (one or two of N) N

Each of the above-mentioned bearing members is prepared by rolling a steel having a predetermined component composition into a steel bar by a conventional method after melting and then normalizing and annealing the steel.
It can be produced by quenching from 50 ° C (preferably 880 to 920 ° C).

[0019]

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 materials to which Si and Sb are added (C: 1.00 wt%, Si: 0.75 wt%, Mn: 0.40 wt%, C
r: 1.33 wt%, Al: 0.042 wt%, Sb: 0.0018 wt%, N: 0.
0042 wt%, O: 0.0009 wt%) (C: 1.00 wt%, Si: 1.58 wt%, Mn: 0.38 wt%, C
r: 1.30 wt%, Al: 0.048 wt%, Sb: 0.0040 wt%, N: 0.
0032wt%, O: 0.0008wt%).
After 30 hours of diffusion annealing, it was rolled into a 65 mmφ steel bar to obtain a test material. Next, the test material was normalized, spheroidized, heat-treated in the order of quenching and tempering, and then lapping finished to form a cylindrical test piece of 12 mmφ × 22 mm.

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 , Cyclic stress number: 46500 cpm, Lubrication: # 68 Under load conditions under the use environment of turbine splash oil, the quenching temperature is adjusted and the rolling fatigue life test is performed by changing the amount of residual γ in the steel. went. The test results are plotted on probability paper assuming that they follow the Weibull distribution, and are numerical values that show the usual 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 value (10% cumulative failure probability), by repeated stress loads at a high temperature and high-load rolling, viewed under severe use environments, rolling by delaying the occurrence of microstructural changes in the so-called surface subordinates fatigue life numerical and found B ₅₀ value showing the calculated (50% cumulative failure probability) and. In addition, for the test of the decarburized layer, the above cylindrical test piece was cut perpendicularly in the height direction at a position of 10 mm, then corroded with nital, and the total decarburized layer depth (thickness) on the circumference due to microstructure change ) The maximum value (hereinafter referred to as “maximum decarburized layer”) was evaluated.

[0021] As a result, as shown in Table 1, for the high Si additive, when the amount of residual γ is 7-8% and is not insubstantial, improvement for the B ₁₀ value for B ₅₀ value Shows extremely high values, and the average bearing life is SUJ
Compared to the two materials, the improvement was about 14 times at 0.75 wt% Si. In particular, the Ni and 1.58Wt%, when more heavily added, B ₅₀ value reaches to about 23 times, remarkable effect on the delay characteristics of the microstructural changes produced during high-load rolling And it was found that breakage (lifetime) can be greatly delayed. However, even with the same component composition, residual γ
When the amount is large as 18 to 22%, in addition to degree of improvement of the B ₅₀ value is even more pronounced, when further compared with ₁₀ values also SUJ 2 material B, Si: about 7 times in the case of 0.75 wt% In the case of 1.58 wt% of Si, it was found to be improved about 11 times. In addition, the maximum decarburized layer after heat treatment was compared to SUJ2 0.10mm.
Sb: 0.0018 wt% and 0.0040 wt%, the content is actually 0.
The thickness becomes 01 mm, and it can be seen that the addition of an appropriate amount of Sb is extremely effective in suppressing the heat-treated decarburized layer.

[0022]

[Table 1]

FIG. 2 summarizes the above experimental results. The bearing life attributable to non-metallic inclusions in the surface layer, the state of microstructural 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 is clear from this figure, the cumulative failure probability 10 as an index of the amount and form of nonmetallic inclusions in the surface layer of bearing members, C concentration, carbide area ratio, etc. % of bearing life represented by B ₁₀ value (hereinafter referred to as "B ₁₀ life")
According to this, it is found that the effect cannot be obtained as expected by simply adding a large amount of Si, but it can be considerably improved when the amount of residual γ is increased. On the other hand, bearing life indicated by members as an index indicating the microstructural variation characteristics found in the band of the surface layer subordinates, cumulative failure probability of 50% B ₅₀ value
(Hereinafter referred to as " _B50 life")
The effect of the addition of Si is extremely remarkable, and this tendency is greater than the effect of the amount of residual γ, as long as the bearing life, which indicates at least the degree of microstructural change that occurs under harsh environments, is considered high Si and high residual It can be seen that control of the amount of γ is extremely effective. This is in good agreement with the results in Table 1 above.

[0024] As described above, B ₁₀ life, to improve both B ₅₀ life, the steel containing Si proper amount, and for proper from through the processing of normalizing and spheroidizing annealing It is effective to control the amount of residual γ in the steel to a predetermined range by performing a quenching treatment and, if necessary, a tempering treatment. Although the reason why the properties are improved by such treatment is not always clearly understood, the present inventors have found that this residual γ is a delay in microstructural change due to repeated stress loading and the presence of hard relieve notch effect of the non-metallic inclusions, are believed to improve both the B ₁₀ life and B ₅₀ life by this.

The amount of residual γ is 10% by volume.
~ 35% is considered appropriate. 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 15-30%, 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 that forms a solid solution in the matrix and effectively acts to strengthen martensite. To ensure 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: more than 0.5 to 2.5 wt% Si is an element that plays a particularly important role in the present invention. When more than 0.5 wt% is added, the microstructure under high temperature, high load, and repeated stress load is reduced. resulting in delay of tissue changes, rolling contact fatigue life appearing as B ₅₀ value (B ₅₀ life)
Has the effect of improving. However, its content is 2.5wt
%, The effect is saturated and the workability and toughness are reduced, so that in order to further improve the microstructure change delay characteristics, it is effective to add more than 0.5 to 2.5 wt%. More preferably, it is more than 0.5 to 2.0 wt%.

Sb: 0.001 to 0.015 wt% This Sb is an element that plays an important role together with Si in the present invention. In particular, Sb contributes to an improvement in heat treatment productivity by suppressing the reaction between C in the surface layer of the steel material and the atmosphere gas to prevent the formation of a decarburized layer during the heat treatment. In addition, since it also has an effect on the delay of microstructure change in accordance with the suppression of the decarburized layer, it is added positively. These two effects become remarkable when the Sb content is 0.001% by weight or more, but the effect is saturated even when added in an amount exceeding 0.015% by weight. The toughness is deteriorated. Therefore, Sb is contained in the range of 0.001 to 0.015 wt%. Preferably, it is contained in the range of 0.0020 to 0.0100 wt%, more preferably 0.0025 to 0.0080 wt%.

Al: 0.010 to 0.07 wt% Al is used as a deoxidizing agent when melting steel,
Combined with N in steel, it refines crystal grains and contributes to improvement in toughness of steel. In addition, it effectively acts to improve the rolling fatigue life by increasing the strength after quenching and tempering. For such an effect, it is effective to add 0.010 to 0.07 wt% of Al .

O: 0.0020 wt% or less O forms hard non-metallic inclusions, so even if other O
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 is an element that acts as a deoxidizing agent during melting of steel and is effective in 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%.

[0033]

[0034] Ni: 0.05~1.0 wt% Ni, as well as improving the toughness enhancing the strength after tempering Quenched by increasing hardenability, so improving the B ₁₀ life, added in the range of 0.05 to 1.0 wt% Preferably, 0.15 to 1.0 wt% is added.

Mo: 0.05-0.5 wt% Mo is an element which improves wear resistance by stabilizing residual carbides. With particular the addition of 0.05 to 0.5 wt%, increases the hardenability with contributing to the strength improvement after tempering Quenched by precipitation of stable carbides, improving the wear resistance and B ₁₀ life.

[0036] 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. When added for this purpose, a range of 0.05 to 1.0 wt% is sufficient, and preferably 0.15 to 1.0 wt%.

[0037] 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%.

N: 0.0005 to 0.012 wt%, more than 0.012 to 0.05
0 wt% N combines with the carbonitride forming element to refine the 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. This N is 0.012 on the other hand.
When added in excess of wt%, as described above, the microstructure change due to the repetitive stress is delayed to increase the B content.
₅₀ life can be improved. However, this amount is 0.
If the content exceeds 050 wt%, the workability and toughness decrease. For this purpose, more than 0.012 to 0.050 wt% is added.
Preferably, it is more than 0.012 to 0.035 wt%.

As described above, the rolling fatigue life (B ₁₀ life) at the surface layer of the member is improved by delaying the microstructural change due to the repeated stress load on the surface layer of the member (B ₅₀ life) and increasing the strength. (C, Si, Sb, Al, O and Mn, C)
(r, Ni, Mo, Cu, B, N) have been described, respectively. However, in the present invention, one or more selected from Zr, Ta, Hf and Co may be further added. Accordingly, harsh environment (dust containing, high load, high temperature) may be caused to improve the rolling contact fatigue life, i.e. B ₅₀ life in.

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

[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., the above-mentioned object of the present invention does not inhibit the retardation characteristics due to the change in microstructure due to the repeated stress load, and the machinability can be easily improved. May be.

P is desirably as low as possible from the viewpoint of reducing the toughness and rolling fatigue life of steel, and is suppressed to 0.025 wt% or less, preferably 0.015 wt% or less. S is an element that 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.

[0043]

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
The steel was quenched at 880 ° C to 920 ° C and tempered at 180 ° C. In addition, 12mmφ × 22mm and 60mm
A cylindrical test piece of mmφ × 5 mm 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, the measurement test for B ₅₀ life was conducted. B ₁₀ life of the under clean environment, test B ₅₀ life, using a rolling fatigue life tester of the radial type as shown in FIG. 3, Hertzian maximum contact stress: 600 kgf / mm ^2, about the number of repeated stress 46
500 cpm and lubricating oil: Performed on condition that # 68 turbine splash oil is used. The test results were compiled on a probability paper assuming that they follow the Weibull distribution.
Average life of (conventional steel SUJ2) (Cumulative failure probability: 10
% And 50%, the total number of loadings before the occurrence of peeling) was set to 1, and evaluations were made in comparison with those of other steel types.

On the other hand, the dust-containing ring for each of the above test pieces
Rolling life under severe conditions (B _TenLifespan, B₅₀lifespan)
Manufactures a disk-shaped test piece and uses a thrust-type rolling fatigue tester
Hertz maximum contact stress: 536 kgf / mm^Two , Repeat
Hardness in # 68 turbine oil under the condition of stress number: 1800cpm:
Approx. Hv850, average particle diameter: about 100 ppm, iron powder about 150 ppm
 It was mixed. The testing machine has been improved as shown in Fig. 3.
And 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 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 is obtained by measuring the test piece after lapping using an X-ray analyzer. The above evaluation results are summarized in Tables 3 and 4.

[0046]

[Table 3]

[0047]

[Table 4]

Steel Nos. 2 to 6 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 Si content in steel is out of the range of the present invention, In the case of steel No. 3 in which the amount of O in the steel is out of the range of the present invention and steel No. 2 in which the amount of retained austenite in the steel is out of the range of the present invention, the same level as the conventional steel containing no Si (steel No. 1) or, B ₁₀ life, B ₅₀ or lifetime at least one of low, it can be seen that no effect in improving bearing life. Further, No.4 is Sb are of the present invention outside the range, B ₁₀ life, B ₅₀ life, conventional steel is better than the (steel No.1), the maximum decarburized layer depth Is as large as 0.11 mm
Since there is no improvement compared to o.1), a treatment to remove this decarburized layer was required. On the other hand, steel materials No. 7 to 10, 12 to 14, 17 to 22, 3
2, in a normal test under clean environment, B ₁₀ life is improved an average of about three to five times as compared with the conventional steels (steel No.1), also, B ₅₀ life excellent 5-11 times The results are out. In addition, this tendency has been observed in tests in garbage environments,
About 2-3 times that of the conventional and the B ₁₀ life, B ₅₀ shows the approximately 5-6 times superior results in the lifetime, it can be seen that are improved as well as under clean environment. Furthermore, the depth of the maximum decarburized layer is large, about 0.03 mm, which is small, indicating that the heat treatment productivity is excellent. That is, the bearing member, the rolling life which was added combined with a large amount of Si and Sb are under dust-containing environment, especially B significantly delay the microstructure changes represented by ₅₀ life, whereas the residual γ amount 10% to 35% to result in significant improvement in the B ₁₀ life by controlling and since also reduces the depth of the decarburized layer, but also contribute to the highly effective at improving the productivity improvement of the overall rolling fatigue life of the bearing It can be seen that

[0049]

As described above, according to the present invention,
Microstructure with 10-35% residual γ content in steel and Si: more than 0.5
2.5 wt% and Sb: 0.001 to 0.015 wt% By using a composite-added bearing steel material, it can be used not only in a clean environment but also in a dusty environment, under severe conditions such as high load and high temperature use, under the surface layer of the bearing member. introduces a delay of microstructural changes due to repeated stress loads, while achieving the improvement of B _10, B ₅₀ rolling fatigue life by this (high Si-containing effect), further reducing the processing load during the heat treatment (Sb added Effect) to increase productivity. 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 is an explanatory diagram showing the influence of Si, Sb content and residual γ content on bearing life caused by nonmetallic inclusions and bearing life caused by microstructure change.

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-63-57749 (JP, A) -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, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less, with the balance being less It has a composition of Fe and unavoidable impurities, and the amount of retained austenite in the steel is 10% by volume.
A bearing member having a steel structure of up to 35% and having excellent heat treatment productivity and excellent microstructure change delay characteristics due to repeated stress loading. 2. C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less. Mn: 0.05~2.0wt%, N i: 0.05~1.0wt%, Mo: 0.05~0.5wt%, Cu: 0.05~1.0wt%, B: 0.0005~0.01wt% and N: of 0.0005～0.012Wt% Containing at least one selected from the group consisting of a balance of Fe and unavoidable impurities, and an amount of retained austenite in the steel in a volume ratio.
A bearing member having a steel structure of 10 to 35% and having excellent heat treatment productivity and excellent delay characteristics of microstructure change due to repeated stress load. C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less. N: over 0.012 to 0.050 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% 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 heat treatment productivity and excellent delay characteristics of microstructure change due to repeated stress load. 4. C: 0.5 to 1.5 wt%, Si: more than 0.5 to 2.5 wt%, Sb: 0.001 to 0.015 wt%, Al: 0.010 to 0.07 wt%, O: 0.0020 wt% or less. Mn: 0.05~2.0wt%, N i: 0.05~1.0wt%, Mo: 0.05~0.5wt%, Cu: 0.05~1.0wt%, B: 0.0005~0.01wt% and N: of 0.0005～0.012Wt% One or more selected from the group consisting of a component that improves rolling fatigue in a normal environment; and, when one or more of the above-described components is selected, the element Of the following components excluding: N: over 0.012 to 0.050 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% One or more selected from the group consisting of a component that improves the rolling fatigue life in a severe environment, the balance having a component composition consisting of Fe and unavoidable impurities, and a residue in steel. Austenite amount is volume ratio To 10
A bearing member having a steel structure of up to 35% and having excellent heat treatment productivity and excellent microstructure change delay characteristics due to repeated stress loading.