JP3420331B2 - Bearing steel and bearing members excellent in heat treatment productivity and delay characteristics of microstructure change 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 steel and a bearing member used as an element member of a rolling bearing such as a roller bearing or a ball bearing, and is particularly generated under a rolling contact surface due to repeated stress load in a severe operating environment. The delay property against microstructure change (deterioration) is excellent regardless of the cleanliness of the lubricating oil even if it is in a poor state, and the effect of suppressing the formation of the decarburized layer during heat treatment is excellent. Bearing steel and bearing members.

[0002]

2. Description of the Related Art Conventionally, high-carbon chromium bearing steel (JI
S: 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 take measures to improve the bearing life by controlling the amount and size of non-metallic inclusions by reducing the amount of oxygen in steel.

For example, as 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.
Japanese Patent Laid-Open No. 3-126839 and Japanese Patent Laid-Open Publication No. 3-126839 propose techniques for controlling the composition, shape, or distribution of oxide-based nonmetallic inclusions in steel. However, in order to manufacture a bearing steel with a small amount of non-metallic inclusions, it is necessary to install expensive melting equipment or drastically improve conventional equipment, and there is a problem that the economical burden is large.

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

Another move to improve the characteristics of the above-mentioned high carbon bearing steel (JIS-SUJ 2) is a study on a workability, especially a technique for suppressing the formation of a decarburized layer during heat treatment. Generally, the bearing steel specified in JIS-SUJ2 above is 0.9
Since it contains 5 to 1.10 mass% C, it is very hard. Therefore, it is spheroidized and annealed to improve the workability, and then molded and then hardened and tempered. , Had obtained the strength and toughness required for rolling bearings. However, it is known that when the heat treatment for improving the characteristics is repeated many times, a "low C concentration region" called a decarburized layer is generated on the surface of the material due to the reaction between C and the atmosphere gas. There is. This decarburized layer not only lowers the hardness of the rolling bearing but also causes the deterioration of rolling contact fatigue life, and therefore it is usually removed by cutting or grinding. For this reason, the material yield and the productivity have been unavoidably reduced. On the other hand, conventionally, as a means for preventing the formation of the decarburized layer, a method of controlling the carbon potential in the atmosphere gas in the furnace during the heat treatment, or the spheroidizing method disclosed in JP-A-2-54717. A method of carburizing at the initial stage of annealing has been proposed. However, since each of the above methods is performed by cleaning the atmosphere during the heat treatment or the pretreatment thereof, not only the heat treatment cost increases but also the setting of an appropriate gas composition according to the composition of the material, the heat treatment time, etc. That left a problem where complicated operations were required.

[0006]

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

[0007] Therefore, the present inventors have continued to earnestly study the bearing life in consideration of the recent bearing usage environment, especially the cause of the separation of the rolling bearing. As a result, as the bearing operating environment became more severe, the repeated shear stress generated during the rolling contact between the inner and outer rings of the bearing and the rolling elements caused
In the lower part of the rolling contact surface (surface layer portion), a microstructure change layer consisting of a white strip-shaped product and a rod-shaped precipitate is generated, which gradually grows as the number of rolling increases,
At the end, it was found that fatigue delamination occurred as shown in FIG. 1 (b) from this microstructure-changed portion, and the bearing member surface layer portion was damaged to extend the bearing life. Furthermore, the harsh bearing operating environment, that is, higher surface pressure (smaller size) and higher operating temperature,
It was also found that the number of rolling cycles until the microstructure change occurs can be shortened, leading to a significant reduction in bearing life.

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

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

[0010]

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

That is, the bearing steel and the bearing member according to the present invention have the essential configurations as listed below. (1) C: 0.5 to 1.5 mass%, Mo: over 1.0 to 2.0 mass%, Sb:
0.005 to 0.015 mass%, O: contains 0.0020 mass% or less,
Bearing steel with balance of Fe and unavoidable impurities and excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading.

(2) C: 0.5 to 1.5 mass%, Mo: over 1.0 to 2.0
mass%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05
~ 2.0mass%, Cr: 0.05 ~ 2.5mass%, Ni: 0.05 ~ 1.0mass
s%, Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%,
B: 0.0005 to 0.01 mass% and N: 0.0005 to 0.012 mass%
A bearing steel containing one or more selected from the group consisting of Fe and unavoidable impurities with the balance being excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load.

(3) However, the basic components (C, Mo, Sb,
O), optionally added components (S
For i, Mn, Cr, Ni, Cu, Al, B, N), see (2) above.
Within the range of the composition, it is recommended to add the following combinations. 0.05 to 0.5 mass% Si- (any one or more of Mn, Cr, Ni, Cu, Al, B and N) 0.05 to 2.0 mass% Mn- (Cr, Ni, Cu, Al, B and N
0.05 to 2.5 mass% Cr- (any one or more of Ni, Cu, Al, B and N) 0.05 to 1.0 mass% Ni- (any of Cu, Al, B and N 1) Species or more) 0.05-1.0mass% Cu- (any of Al, B and N 1
0.005 to 0.07 mass% Al- (any one or more of B and N) 0.0005 to 0.01 mass% B- (N)

(4) C: 0.5 to 1.5 mass%, Mo: over 1.0 to 2.0
mass%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: more than 0.5 to 2.5 mass%, Cr: 2.5
Super ~ 8.0mass%, Ni: over 1.0 ~ 3.0mass%, N: over 0.012 ~
0.050mass%, V: 0.05 to 1.0mass%, Nb: 0.05 to 1.0mass
s%, W: 0.05 to 1.0 mass%, Zr: 0.02 to 0.5 mass%, T
a: 0.02-0.5mass%, Hf: 0.02-0.5mass% and Co: 0.0
Any one or two selected from 5 to 1.5 mass%
A bearing steel that contains more than one type of material, with the balance consisting of Fe and unavoidable impurities, and that has excellent heat treatment productivity and delay characteristics for microstructural changes due to repeated stress loading.

(5) However, the basic components (C, Mo, Sb,
O), optionally added components (Si, Cr, Ni, N) added selectively in large amounts and other added components (V, Nb, W, Zr, Ta, Hf and Co) added in small amounts. With respect to, it is recommended to add the following combinations within the composition range described in (4) above. Over 0.5 to 2.5 mass% Si- (any one or more of Cr, Ni and N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) over 2.5- 8.0mass% Cr- (any one or more of Ni or N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) over 1.0 to 3.0mass% Ni- (N )-(V, Nb, W, Zr, T
Any one or more of a, Hf and Co) over 0.012 to 0.050 mass% N- (V, Nb, W, Zr, Ta, Hf
And any one of Co and Co)

(6) C: 0.5 to 1.5 mass%, Mo: over 1.0 to 2.0
mass%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05
~ 2.0mass%, Cr: 0.05 ~ 2.5mass%, Ni: 0.05 ~ 1.0mass
s%, Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%,
B: 0.0005 to 0.01 mass% and N: 0.0005 to 0.012 mass%
When any one or more selected from the above is contained as a component that improves rolling fatigue in a normal environment, and when any one or more of the above-mentioned improving components is selected, The following components excluding that element, namely S
i: over 0.5 to 2.5 mass%, Cr: over 2.5 to 8.0 mass%, Ni: 1.0
Super ~ 3.0mass%, N: 0.012 Super ~ 0.050mass%, V: 0.05
~ 1.0mass%, Nb: 0.05 ~ 1.0mass%, W: 0.05 ~ 1.0mass
s%, Zr: 0.02-0.5mass%, Ta: 0.02-0.5mass%, H
f: 0.02-0.5mass% and Co: 0.05-1.5mass%, any one kind or two kinds or more selected as a component for improving rolling fatigue life in a harsh environment, and the balance
Bearing steel consisting of Fe and unavoidable impurities, which has excellent heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading.

(7) However, in the above item (6), the following combinations are recommended for the rolling fatigue life improving components in a normal environment. 0.05 to 0.5 mass% Si- (any one or more of Mn, Cr, Ni, Cu, Al, B and N) 0.05 to 2.0 mass% Mn- (Cr, Ni, Cu, Al, B and N
0.05 to 2.5 mass% Cr- (any one or more of Ni, Cu, Al, B and N) 0.05 to 1.0 mass% Ni- (any of Cu, Al, B and N 1) Species or more) 0.05-1.0mass% Cu- (any of Al, B and N 1
0.005 to 0.07mass% Al- (any one or more of B and N) 0.0005 to 0.01mass% B- (N) In addition, a combination of components for improving rolling contact fatigue life in the above severe operating environment The following are recommended. More than 0.5 to 2.5 mass% Si- (any one or more of Cr, Ni and N)-(V, Nb, W, Zr, Ta, Hf and Co
More than 2.5 to 8.0 mass% Cr- (any one or more of Ni or N)-(V, Nb, W, Zr, Ta, Hf and Co 1 More than 1.0) ~ 1.0 to 3.0 mass% Ni- (N)-(V, Nb, W, Zr, T
Any one or more of a, Hf and Co) '> 0.012 to 0.050 mass% N- (V, Nb, W, Zr, Ta, H
Any one or more of f and Co)

(8) C: 0.5 to 1.5 mass%, Mo: over 1.0 to 2.0
mass%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, and the balance Fe and unavoidable impurities,
In addition, the amount of retained austenite in steel is 10 to 35 in volume ratio.
%, A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load.

(9) C: 0.5 to 1.5 mass%, Mo: over 1.0 to 2.0
mass%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05
~ 2.0mass%, Cr: 0.05 ~ 2.5mass%, Ni: 0.05 ~ 1.0mass
s%, Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%,
B: 0.0005 to 0.01 mass% and N: 0.0005 to 0.012 mass%
A steel structure containing at least one selected from the above, the balance being Fe and unavoidable impurities, and having a residual austenite amount in the steel of 10 to 35% by volume. A bearing member with excellent heat treatment productivity and delay characteristics of microstructure change due to repeated stress load.

(10) However, the basic components (C, Mo, Sb,
O), optionally added components (S
i, Mn, Cr, Ni, Cu, Al, B, N), see (9) above.
Within the range of the composition, it is recommended to add the following combinations. 0.05 to 0.5 mass% Si- (any one or more of Mn, Cr, Ni, Cu, Al, B and N) 0.05 to 2.0 mass% Mn- (Cr, Ni, Cu, Al, B and N
0.05 to 2.5 mass% Cr- (any one or more of Ni, Cu, Al, B and N) 0.05 to 1.0 mass% Ni- (any of Cu, Al, B and N 1) Species or more) 0.05-1.0mass% Cu- (any of Al, B and N 1
0.005 to 0.07 mass% Al- (any one or more of B and N) 0.0005 to 0.01 mass% B- (N)

(11) C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.
0mass%, Sb: 0.005 to 0.015mass%, O: 0.0020mass%
Contains the following: Si: more than 0.5 to 2.5 mass%, Cr: 2.
5 to 8.0 mass%, Ni: 1.0 to 3.0 mass%, N: 0.012 to 0.050 mass%, V: 0.05 to 1.0 mass%, Nb: 0.05 to 1.0 m
ass%, W: 0.05 to 1.0 mass%, Zr: 0.02 to 0.5 mass%, T
a: 0.02-0.5mass%, Hf: 0.02-0.5mass% and Co: 0.0
Any one or two selected from 5 to 1.5 mass%
Containing at least one species, the balance consisting of Fe and unavoidable impurities, and the amount of retained austenite in the steel being 10% by volume.
A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load, which has a steel structure of up to 35%.

(12) However, the basic components (C, Mo, Sb,
O), optionally added components (Si, Cr, Ni, N) added selectively in large amounts and other added components added in small amounts (V, Nb, W, Zr, Ta, Hf and Co). about,
Within the composition range described in (11) above, it is recommended to add the following combinations. Over 0.5 to 2.5 mass% Si- (any one or more of Cr, Ni and N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) over 2.5- 8.0mass% Cr- (any one or more of Ni or N)-(any one or more of V, Nb, W, Zr, Ta, Hf and Co) over 1.0 to 3.0mass% Ni- (N )-(V, Nb, W, Zr, T
Any one or more of a, Hf and Co) over 0.012 to 0.050 mass% N- (V, Nb, W, Zr, Ta, Hf
And any one of Co and Co)

(13) C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.
0mass%, Sb: 0.005 to 0.015mass%, O: 0.0020mass%
Contains the following, and further Si: 0.05 to 0.5 mass%, Mn: 0.0
5 to 2.0mass%, Cr: 0.05 to 2.5mass%, Ni: 0.05 to 1.0ma
ss%, Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%,
B: 0.0005 to 0.01 mass% and N: 0.0005 to 0.012 mass%
When any one or more selected from the above is contained as a component that improves rolling fatigue in a normal environment, and when any one or more of the above-mentioned improving components is selected, The following components excluding that element, namely S
i: over 0.5 to 2.5 mass%, Cr: over 2.5 to 8.0 mass%, Ni: 1.0
Super ~ 3.0mass%, N: 0.012 Super ~ 0.050mass%, V: 0.05
~ 1.0mass%, Nb: 0.05 ~ 1.0mass%, W: 0.05 ~ 1.0mass
s%, Zr: 0.02-0.5mass%, Ta: 0.02-0.5mass%, H
f: 0.02-0.5mass% and Co: 0.05-1.5mass%, any one kind or two kinds or more selected as a component for improving rolling fatigue life in a harsh environment, and the balance
Featuring a steel structure consisting of Fe and unavoidable impurities and having a residual austenite content in the steel of 10 to 35% by volume, heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading Excellent bearing material.

(14) However, in the above (13), the following combinations are recommended for the rolling fatigue life improving components in the normal environment. 0.05 to 0.5 mass% Si- (any one or more of Mn, Cr, Ni, Cu, Al, B and N) 0.05 to 2.0 mass% Mn- (Cr, Ni, Cu, Al, B and N
0.05 to 2.5 mass% Cr- (any one or more of Ni, Cu, Al, B and N) 0.05 to 1.0 mass% Ni- (any of Cu, Al, B and N 1) Species or more) 0.05-1.0mass% Cu- (any of Al, B and N 1
0.005 to 0.07mass% Al- (any one or more of B and N) 0.0005 to 0.01mass% B- (N) In addition, a combination of components for improving rolling contact fatigue life in the above severe operating environment The following are recommended. More than 0.5 to 2.5 mass% Si- (any one or more of Cr, Ni and N)-(V, Nb, W, Zr, Ta, Hf and Co
More than 2.5 to 8.0 mass% Cr- (any one or more of Ni or N)-(V, Nb, W, Zr, Ta, Hf and Co 1 More than 1.0) ~ 1.0 to 3.0 mass% Ni- (N)-(V, Nb, W, Zr, T
Any one or more of a, Hf and Co) '> 0.012 to 0.050 mass% N- (V, Nb, W, Zr, Ta, H
Any one or more of f and Co)

In each of the above-mentioned bearing members, steel having a predetermined composition is rolled into a steel bar by a process according to a conventional method after smelting, followed by normalizing and annealing, and then 880 to 980.
It can be produced by quenching at a temperature of preferably from 900C (desirably 900 to 950C).

[0026]

First, the history of the development of the bearing steel and bearing member of the present invention relating to the above alloy design and structure control will be described.
A description will be given based on the results of experiments conducted by the inventors. First,
In this experiment, SUJ 2 (C: 1.02 mass%, Si: 0.25 mass%, Mn: 0.45
mass%, Cr: 1.35 mass%, N: 0.0040 mass%, O: 0.00
12mass%) and two kinds of materials added with Mo and Sb (C: 1.00mass% , Si: 0.21mass%, Mn: 0.43mass)
%, Cr: 1.33mass%, Mo: 1.14mass%, Sb: 0.0061mass
%, N: 0.0035mass%, O: 0.0008mass%) (C: 0.98mass% , Si: 0.20mass%, Mn: 0.41mass
%, Cr: 1.31mass%, Mo: 1.81mass%, Sb: 0.0094mass
%, N: 0.0033mass%, O: 0.0009mass%) was melted and cast, then subjected to diffusion annealing at 1240 ° C for 30 hours and then rolled into a steel bar of 65mmφ. And Then, normalize this test material, spheroidize,
Further, heat treatment was performed in the order of quenching-tempering, and then lapping finishing was performed to obtain a cylindrical test piece of 12 mmφ × 22 mm.

Then, 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: 46500cpm, Lubrication: # 68 Turbine splash oil Adjust the quenching temperature under load conditions under the environment
A rolling fatigue life test was performed by changing the amount of residual γ in the steel. The test results are plotted on probability paper as subject to the Weibull distribution, and are numerical values showing the normal rolling fatigue life that has been conventionally studied, mainly due to the suppression of nonmetallic inclusions in the surface layer and the increase in material strength. B
Rolling fatigue by delaying the occurrence of so-called microstructure change under the surface layer, which is seen in a harsh service environment due to ₁₀ values (10% cumulative failure probability) and repeated stress load during high temperature / high load rolling B _{50, which is} considered to be the value indicating the life
The value (50% cumulative damage probability) was calculated. Also, for the decarburization layer test, after cutting the above cylindrical test piece vertically in the height direction at a position of 10 mm, it is corroded by Nital and the total decarburization layer depth (thickness on the circumference due to microstructure change ) Maximum value (hereafter
"Maximum decarburized layer").

As a result, as shown in Table 1, for the high Mo additive material, when the residual γ amount was as small as 6 to 7%, the B
The improvement in ₁₀ values is not so big,
The B ₅₀ value was remarkably high, and the average life of the bearings was improved by about 18 times in the case of Mo: 1.14 mass% as compared with the SUJ 2 material. In particular, in the case of a high Mo additive material in which a large amount of Mo is added at 1.81 mass%, the B ₅₀ value is about 26.
It has been found that the damage (life) can be greatly delayed by showing a remarkable effect on the delay property of microstructure change generated during high load rolling. However, even with the same composition, if the residual γ amount increases to 17-18%, B
_In addition to the more remarkable improvement in the ₅₀ value, the B ₁₀ value is about 9 times higher when the Mo: 1.14mass% and about 12 times when the Mo: 1.81mass% is compared to the SUJ 2 material. It turned out to be doubled. In addition, regarding the maximum decarburized layer after heat treatment, the thickness of SJ: 0.040 mm relative to 0.10 mm of SUJ 2 is 0.02 mm, and the content of Sb: about 0.0082 mass% is actually 0.01 mm thick, It can be seen that the addition of an appropriate amount of Sb is extremely effective in suppressing the heat-treated decarburized layer.

[0029]

[Table 1]

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

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

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

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

C: 0.5 to 1.5 mass% 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 due to it. Contained in. If the content is less than 0.5 mass%, such effects cannot be obtained. On the other hand, if it exceeds 1.5 mass%, the machinability and the forgeability are deteriorated, so the range is limited to 0.5 to 1.5 mass%. Preferably,
The range of 0.65 to 1.10 mass% is good.

Mo: more than 1.0 to 2.0 mass% Mo is an element that plays the most important role in the present invention, and promotes the delay of the above-mentioned microstructure change particularly under severe cyclic stress loading. In this respect, the rolling fatigue life (B ₅₀ life) is improved. To obtain that effect, more than 1.0 mass% is required, but the amount is 2.0 mass%
If it exceeds 1.0, the machinability and forgeability will be reduced, and this will cause a cost increase. Therefore, in order to improve the B ₅₀ life, 1.0
It is necessary to add within the range of more than 2.0 mass%, but preferably more than 1.0 to 1.8 mass%, more preferably 1.0
Super ~ 1.5mass% is good.

Sb: 0.005 to 0.015 mass% This Sb is an element that plays an important role together with Al in the present invention. In particular, this Sb contributes to the improvement of the heat treatment productivity by suppressing the reaction between C in the surface layer portion of the steel material and the atmospheric gas during the heat treatment to prevent the generation of the decarburized layer. Moreover, since the combined addition with Al has an effect on the retardation of the microstructure change as well as the suppression of the decarburized layer, it is positively added. These two effects become remarkable when the Sb content is 0.005 mass% or more, but even if the Sb content exceeds 0.015 mass%, the effect is saturated, and conversely, hot workability and It causes deterioration of toughness. Therefore, Sb is 0.005-0.015mass
It was decided to contain in the range of%. Preferably 0.005
It is contained in the range of 0.010 mass%.

O: 0.0020 mass% or less O forms a hard non-metallic inclusion, so even if the control of other components can delay the microstructure change due to repeated stress loading, the B ₁₀ life, Since it may lead to a decrease in B ₅₀ life, it is desirable that the content be as low as possible. However, a content of 0.0020 mass% or less is acceptable. It is preferably 0.0012 mass% or less.

Si: 0.05 to 0.5 mass%, more than 0.5 to 2.5 mass% Si is used as a deoxidizing agent during the melting of steel, and is also solid-dissolved in the matrix to increase quenching and quenching due to an increase in temper softening resistance. Rolling fatigue life that appears in B ₁₀ value by increasing the strength after returning
It is effective as an element for improving (B ₁₀ life). The content of Si added for these purposes is 0.05 to 0.5 mass.
%, Preferably 0.15 to 0.50 mass%. Furthermore, this
When Si is added in an amount of more than 0.5 mass%, it causes a delay in microstructure change under high temperature, high load, and repeated stress load, and improves rolling fatigue life (B ₅₀ life) that appears as a B ₅₀ value. There is. However, its content is 2.5 mass
%, The effect is saturated while the workability and toughness are reduced. Therefore, in order to further improve the microstructure change retardation property, it is effective to add more than 0.5 to 2.5 mass%. More preferably, it is more than 0.5 to 2.0 mass%.

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

Cr: 0.05 to 2.5 mass%, more than 2.5 to 8.0 mass% 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 mass% is sufficient. The preferable addition amount is 0.15 to 2.5 mass%. Furthermore, this Cr delays the microstructural change due to cyclic stress loading, and the rolling fatigue life (B ₅₀
In order to improve the (life), it is necessary to add a large amount exceeding 2.5 mass%. When the amount of Cr added to improve the B ₅₀ life exceeds 8.0 mass%, not only the amount of Cr is saturated, but also the amount of solid solution C during quenching is rather decreased and the strength is reduced. Therefore, when it is added for this purpose, it should be more than 2.5 to 8.0 mass%.
The range of more than 2.5 to 5.0 mass% is preferable.

Ni: 0.05 to 1.0 mass%, more than 1.0 to 3.0 mass% Ni enhances the hardenability and enhances the strength after quenching and tempering to improve the toughness and the B ₁₀ life. In order to achieve this, the addition is made within the range of 0.05 to 1.0 mass%, preferably 0.15 to 1.0 mass%. Further, as described above, this Ni, when added in an amount of more than 1.0 mass%, delays the microstructure change during rolling, thereby improving the B ₅₀ life. However, even in this case, if it is added in excess of 3 mass%, a large amount (> 35%)
In addition to precipitating the residual γ of the product, it will reduce the strength and impair the dimensional stability, and also increase the cost. Therefore, when expecting this effect, add it in the range of more than 1.0 to 3.0 mass%. Is required, preferably more than 1.0 to 2.5 mass%
Is good.

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

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

B: 0.0005 to 0.01 mass% B enhances the hardenability to increase the strength after quenching and tempering and improves the B ₁₀ life, so 0.0005 mass% or more is added. However, if added in excess of 0.01 mass%, the workability deteriorates, so the content is limited to 0.0005 to 0.01 mass%. It is preferably 0.0015 to 0.0050 mass%.

N: 0.0005 to 0.012 mass%, more than 0.012 to 0.05
0mass% N combines with carbonitride forming elements to refine the crystal grains,
It forms a solid solution in the matrix to increase the strength after quenching and tempering and improve the B ₁₀ life. 0.0005-0 for this purpose.
It is added within the range of 012mass%, but preferably 0.0020-
0.012 mass% is good. Also, this N is 0.0
When added in excess of 12 mass%, as described above,
By delaying the microstructural change due to repeated stress, the B ₅₀ life can be improved. However, if this amount exceeds 0.050 mass%, the workability and toughness deteriorate, so for this purpose, more than 0.012 to 0.050 mass% is added, but more than 0.012 to 0.035 mass% is preferable.

As described above, the rolling fatigue life (B ₅₀ life) is improved by delaying the microstructural change due to the repeated stress load in the surface layer of the member, and the rolling fatigue life (B ₁₀ The main components (C, Mo, Sb, O and Si, Cr, Mn,
Ni, Cu, Al, B, N) has been explained, but in the present invention, any one or more selected from V, Nb, W, Zr, Ta, Hf and Co is further used. May be added to improve the rolling fatigue life, that is, the B ₅₀ life in a harsh environment of use (including dust, high load, high temperature).

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

[Table 2]

In the present invention, in order to improve machinability, S, Se, Te, REM, Pb, Bi, Ca, Ti, Mg, P, Sn, A
Even if s or the like is added, it does not impair the retardation property due to the microstructure change due to the repeated stress load which is the object of the present invention, and the machinability can be easily improved, so that it is possible as necessary. You may add.

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

[0050]

EXAMPLE Steels having the chemical compositions shown in Tables 3 and 4 were melted and cast, and the obtained steel material was subjected to diffusion annealing at 1200 ° C. for 30 hours and then rolled into a steel bar having a diameter of 65 mm. Then normalize-
After spheroidizing annealing, the steel No.1, No.2 at 820 ° C., others were subjected to tempering quenching, at 180 ° C. at 900 ° C. to 950 ° C..
Furthermore, 12mmφ × 22mm and
A cylindrical test piece of 60 mmφ × 5 mm was prepared. The surface roughness of each of the test pieces at this time was Ra: 0.1 mm. And
Each of the above test pieces was subjected to a measurement test for B ₁₀ life and 4B ₅₀ life under a clean environment. The B ₁₀ life and B ₅₀ life tests under this clean environment were carried out using a radial type rolling contact fatigue life tester as shown in FIG.
Hertz maximum contact stress: 600kgf / mm ² , cyclic stress number about 46
500 cpm and lubricating oil: # 68 Turbine spray oil was used under the condition. The results of the test are summarized on the probability paper as being in accordance with the Weibull distribution.
Average life of SUJ 2 (conventional steel) (cumulative damage probability: 10%
And the total load frequency until peeling at 50%) is 1
Was evaluated in comparison with those of other steel types.

On the other hand, the rolling life (B ₁₀ life, B ₅₀ life) of each of the above test pieces under harsh conditions in an environment containing dust.
Made a disk-shaped test piece and used a thrust-type rolling contact fatigue tester. Hertz maximum contact stress: 536 kgf / mm ² , cyclic stress: 1800 cpm, hardness in # 68 turbine oil: Hv8
About 50 and an average particle diameter: about 100 μm of iron powder was mixed at about 150 ppm. The testing machine was improved as shown in Fig. 3,
Iron powder was constantly supplied to the contact portion between the steel ball and the test piece.

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

[0053]

[Table 3]

[0054]

[Table 4]

[0055]

[Table 5]

Steel Nos. 2 to 6 are shown as comparative examples. Steel No. 5 has a C content in the steel outside the scope of the present invention, and Steel No. 6 has a Mo content in the steel outside the scope of the present invention. Steel No. 4 in which the amount of O in the steel is outside the range of the present invention and Steel No. 2 in which the amount of retained austenite in the steel is outside the range of the present invention are the same as the conventional steel containing no Mo (Steel No. 1). At least one of B ₁₀ life and B ₅₀ life is low, and it is understood that there is no effect in improving the bearing life. Further, No. 3 has Sb in the range outside the present invention, but B ₁₀ life and B ₅₀ life are better than the conventional steel (No. 1), but the maximum decarburized layer depth is Since it was as large as 0.09 mm, which was not improved compared to the conventional steel (No. 1), it was necessary to perform treatment to remove this decarburized layer. On the other hand, the steel materials No. 7 to 45, which are the bearing members in which the residual steel amount of the bearing steel of the present invention is adjusted within the predetermined range, have a B ₁₀ life of the conventional steel (in the normal test in a clean environment). Steel material No.
Compared to 1), it is improved about 3 to 25 times on average, and B
_{The 50-year} life is also 4 to 61 times superior. further,
This tendency shows that even in a test in a dust-containing environment, the B ₁₀ life is about 2 to 11 times better than the conventional one, and the B ₅₀ life is about 4 to 18 times better. You can see that it has been improved. Furthermore, it is clear that the maximum decarburized layer has a large depth of about 0.02 mm, which is excellent in heat treatment productivity. That is, as the bearing member, the one in which a large amount of Mo and Sb are added in combination significantly delays the rolling life in the environment containing dust, especially the microstructural change indicated by the B ₅₀ life, while the residual γ amount is 10 to 35%. By controlling the temperature to B _{10, the} B ₁₀ life is significantly improved, and the depth of the decarburized layer is also reduced, so it is extremely effective in improving the overall rolling contact fatigue life of the bearing and also contributes to the improvement of productivity. It can be seen that

[0057]

As described above, according to the present invention,
The residual γ content in the steel was reduced to 10 by quenching the bearing steel with a composite addition of Mo: more than 1.0 to 2.0 mass% and Sb: 0.005 to 0.015 mass%.
By setting up to 35% structure, delay of microstructure change due to repeated stress load under the surface layer of bearing member even under severe conditions such as high load and high temperature use not only in clean environment but also in environment containing dust Which improves the B ₁₀ and B ₅₀ rolling contact fatigue life (high Mo content effect), and also reduces the processing load during heat treatment (Sb addition effect) to improve productivity. it can. Therefore, it is indispensable under the conventional technology to further reduce the oxygen content in the steel in the surface layer of the member or control the composition, shape, and distribution state of oxide-based nonmetallic inclusions present in the steel. The improvement or construction of the steelmaking equipment required to do so is unnecessary in the present invention.
Further, the development of the bearing member according to the present invention can be expected to reduce the size of the rolling bearing and further increase the bearing operating temperature.

[Brief description of drawings]

1A and 1B are micrographs of a metal structure showing a microstructure change occurring in a zone below a surface layer of a member under repeated stress loading.

FIG. 2 is an explanatory diagram showing the effects of the Mo and Sb contents and the residual γ amount on the bearing life caused by non-metallic inclusions and the bearing life caused by microstructural changes.

FIG. 3 is a schematic diagram showing a schematic configuration of a thrust type rolling fatigue tester.

Continued Front Page (72) Inventor Shinichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works, Ltd. Technical Research Division (56) Reference JP-A-5-78814 (JP, A) JP-A-5 -306432 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00

Claims (8)

(57) [Claims] 1. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, the balance consisting of Fe and unavoidable impurities, and excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress load. 2. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05 to 2.0
mass%, Cr: 0.05 to 2.5 mass%, Ni: 0.05 to 1.0 mass%,
Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%, B: 0.
0005 ~ 0.01mass% and N: 0.0005 ~ 0.012mass% any one kind or two or more kinds selected, the balance consisting of Fe and unavoidable impurities, the heat treatment productivity and microstructure change due to repeated stress load Bearing steel with excellent delay characteristics. 3. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, and Si: more than 0.5 to 2.5 mass%, Cr: more than 2.5
8.0mass%, Ni: more than 1.0 to 3.0mass%, N: more than 0.012 to 0.05
0mass%, V: 0.05-1.0mass%, Nb: 0.05-1.0mass
%, W: 0.05 to 1.0 mass%, Zr: 0.02 to 0.5 mass%, Ta:
0.02-0.5mass%, Hf: 0.02-0.5mass% and Co: 0.05-
Containing one or more selected from 1.5 mass%, the balance being Fe and inevitable impurities,
Bearing steel with excellent heat treatment productivity and delay characteristics for microstructural changes due to repeated stress loading. 4. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05 to 2.0
mass%, Cr: 0.05 to 2.5 mass%, Ni: 0.05 to 1.0 mass%,
Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%, B: 0.
0005 ~ 0.01mass% and N: 0.0005 ~ 0.012mass% any one kind or two or more kinds selected from the above is included as a component for improving rolling fatigue in a normal environment, and When any one or more of them are selected, the following components excluding the element, that is, Si: 0.
Over 5 ~ 2.5mass%, Cr: over 2.5 ~ 8.0mass%, Ni: over 1.0 ~
3.0mass%, N: more than 0.012 to 0.050mass%, V: 0.05 to 1.0
mass%, Nb: 0.05 to 1.0 mass%, W: 0.05 to 1.0 mass%,
Zr: 0.02-0.5mass%, Ta: 0.02-0.5mass%, Hf: 0.02
~ 0.5mass% and Co: 0.05-1.5mass% selected from the group consisting of one or more selected as a component to improve rolling fatigue life under harsh environments, with the balance being Fe and inevitable Bearing steel that is made of impurities and has excellent heat treatment productivity and delay characteristics for microstructural changes due to repeated stress loading. 5. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, with the balance being a component composition consisting of Fe and inevitable impurities, and the amount of retained austenite in the steel being 10 to 35 by volume ratio. % Of steel structure,
Bearing members with excellent heat treatment productivity and delay characteristics for microstructural changes due to repeated stress loading. 6. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05 to 2.0
mass%, Cr: 0.05 to 2.5 mass%, Ni: 0.05 to 1.0 mass%,
Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%, B: 0.
[0005] 0.01-mass% and N: 0.0005-0.012mass% any one kind or two or more kinds selected from, and the balance has a component composition consisting of Fe and unavoidable impurities, and retained austenite in steel 10% to 35% in volume ratio
A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading, which is characterized by having a steel structure of 7. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, and Si: more than 0.5 to 2.5 mass%, Cr: more than 2.5
8.0mass%, Ni: more than 1.0 to 3.0mass%, N: more than 0.012 to 0.05
0mass%, V: 0.05-1.0mass%, Nb: 0.05-1.0mass
%, W: 0.05 to 1.0 mass%, Zr: 0.02 to 0.5 mass%, Ta:
0.02-0.5mass%, Hf: 0.02-0.5mass% and Co: 0.05-
It contains one or two or more selected from 1.5 mass%, the balance has a composition composition of Fe and unavoidable impurities, and the amount of retained austenite in steel is 10 to 35% in volume ratio. A bearing member excellent in heat treatment productivity and delay characteristics of microstructure change due to repeated stress loading, which is characterized by having a steel structure of 8. C: 0.5 to 1.5 mass%, Mo: more than 1.0 to 2.0 mass
%, Sb: 0.005 to 0.015 mass%, O: 0.0020 mass% or less, Si: 0.05 to 0.5 mass%, Mn: 0.05 to 2.0
mass%, Cr: 0.05 to 2.5 mass%, Ni: 0.05 to 1.0 mass%,
Cu: 0.05 to 1.0 mass%, Al: 0.005 to 0.07 mass%, B: 0.
0005 ~ 0.01mass% and N: 0.0005 ~ 0.012mass% any one kind or two or more kinds selected from the above is included as a component for improving rolling fatigue in a normal environment, and When any one or more of them are selected, the following components excluding the element, that is, Si: 0.
Over 5 ~ 2.5mass%, Cr: over 2.5 ~ 8.0mass%, Ni: over 1.0 ~
3.0mass%, N: more than 0.012 to 0.050mass%, V: 0.05 to 1.0
mass%, Nb: 0.05 to 1.0 mass%, W: 0.05 to 1.0 mass%,
Zr: 0.02-0.5mass%, Ta: 0.02-0.5mass%, Hf: 0.02
~ 0.5mass% and Co: 0.05-1.5mass% selected from the group consisting of one or more selected as a component to improve rolling fatigue life under harsh environments, with the balance being Fe and inevitable Delay of microstructure change due to heat treatment productivity and cyclic stress loading, characterized by having a steel structure having a composition of impurities and having a residual austenite content in the steel of 10 to 35% by volume Bearing member with excellent characteristics.