JPH083691A - Bearing steel and bearing member - Google Patents

Abstract

PURPOSE:To produce a bearing steel, superior to SUJ2 in workability and rolling fatigue life characteristic, and a bearing member without causing the increase of costs and the reduction of productivity. CONSTITUTION:The structure of a steel, consisting of, by weight, 0.45 to 0.85% C, <0.50% Si, 1.5 to 3.0% Mn, <=0.07% Al, 0.001 to 0.015% Sb, <=0.0030% O, 0.0015 to 0.020% N, and the balance Fe with inevitable impurities, is formed into an acicular martensitic structure containing, by volume ratio, <=5% residual carbide and 10 to 30% retained austenite by heat treatment.

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 bearing steel which is a raw material of the bearing member.
In particular, we propose a technique for improving workability and rolling fatigue life characteristics.

[0002]

2. Description of the Related Art High-carbon chrome bearing steel (representative steel type JIS: SUJ 2) has been most often used as rolling bearing steel used in automobiles and industrial machines. This S
UJ 2 has the advantage that it is possible to manufacture a bearing member of stable quality, because it is possible to obtain the strength required for a rolling bearing by immersion quenching without using carburizing quenching or induction quenching. However, since SUJ 2 contains 1.30 wt% or more of Cr, which is an expensive alloying element in steel, it causes an increase in cost and is contained in this Cr and steel.
With 0.95 wt% or more of C, huge Fe, Cr-based eutectic carbides are formed during casting. Then, when the steel material in this state is directly processed into a bearing member and subjected to quenching / tempering treatment, this carbide remains in the bearing member,
This will deteriorate the rolling contact fatigue life characteristics. Therefore, it is necessary to perform diffusion annealing heat treatment for extinction in the conventional steel composed of such components. However, since this diffusion annealing requires high temperature and long-time treatment, there are problems that the material manufacturing cost increases and the productivity decreases. In addition to that, since the obtained material is very hard, in order to process it into a rolling bearing member, spheroidizing annealing is indispensable, and therefore, as in the above-mentioned annealing, an increase in manufacturing cost, There was a problem of causing a decrease in productivity. Moreover, even if such a heat treatment is taken, the rolling fatigue life characteristics are still insufficient and there is room for improvement.

Therefore, an attempt to solve the above-mentioned drawbacks of SUJ2 has been proposed in Japanese Patent Laid-Open No. 2-54739. That is, the technique disclosed in Japanese Patent Application Laid-Open No. 2-54739 makes it possible to omit diffusion annealing by reducing C to 0.45 to 0.70 wt%, and further improves spheroidizing annealing to improve workability. It is also possible to omit. However, although this conventional technology can certainly improve the workability and suppress the increase of the manufacturing cost and the decrease of the productivity, the rolling fatigue life characteristic is
It remained at the same level as UJ2, and there was a problem that the rolling fatigue life characteristics needed to be further improved. Further, this technique has a problem that it is necessary to add Cr, which is an expensive alloying element, in order to maintain hardenability or rolling fatigue life.

[0004]

SUMMARY OF THE INVENTION A main object of the present invention is to provide a bearing steel and a bearing member which are superior in workability (such as cold forgeability) and rolling fatigue life characteristics to SUJ2. Another object of the present invention is to propose a technique for achieving these characteristic improvements without increasing costs and decreasing productivity.

[0005]

In order to solve the above-mentioned problems, the inventors of the present invention have the workability required for processing a bearing steel into a bearing member having a desired shape, and quenching the processed member, The following facts were found as a result of detailed research on the effects of alloying elements, precipitates, and metallographic structure on the rolling contact fatigue life characteristics required for the bearing member after the tempering treatment. 1) Since carbides remaining after quenching and tempering adversely affect the rolling contact fatigue life characteristics, the amount should be as small as possible. For that purpose, it is preferable to reduce the content of the carbide stabilizing element typified by Cr, and desirably not add it. 2) The decrease in hardenability due to the treatment for reducing the amount of C and Cr taken for improving the workability can be compensated by Mn. Further, reduction of Si is also effective in improving workability. 3) Austenite remaining after quenching and tempering treatment, so-called retained austenite (hereinafter simply referred to as “retained γ”), suppresses the occurrence of delamination at the position of a hard non-metallic inclusion, so that the rolling fatigue life is reduced. Improve.
Further, the residual γ is used to suppress the reduction in rolling contact fatigue life caused by abrasive powder, burrs, or wear powder (hereinafter collectively referred to simply as "dust") mixed in the lubricating oil of the bearing. Also works effectively. 4) As long as the residual γ after quenching and tempering does not become excessive, the strength required for rolling bearings (specifically, HRC 58
It is possible to obtain the above), and further, there is no dimensional change that causes a practical problem during use. Such a small dimensional change is due to the stable residual γ formed when a large amount of Mn is added.

Based on the above findings, the inventors have
The invention was conceived. That is, this invention is
It has a summary structure as listed below. (1) C: 0.45 to 0.85 wt%, Si: less than 0.50 wt%, Mn:
1.5 ~ 3.0wt%, Al: 0.07wt% or less, Sb: 0.001 ~
0.015wt%, O: 0.0030wt% or less, N: 0.0015〜0.020wt
%, The balance being Fe and unavoidable impurities, and a bearing steel.

(2) C: 0.45 to 0.85 wt%, Si: 0.50 wt
%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, S
b: 0.001 to 0.015wt%, O: 0.0030wt% or less, N: 0.00
15 to 0.020wt%, Ni: 1.5wt% or less, M
o: 1.2 wt% or less, Cu: 1.0 wt% or less, B: 0.012 wt%
A bearing steel comprising one or more selected from the following, with the balance being Fe and inevitable impurities.

(3) However, the above basic components (C, Si, Mn,
For the optional additive components (Ni, Mo, Cu, B) that are selectively added to Al, Sb, O, N), within the composition range of (2) above, the following combinations It is recommended to add in. 1.5 wt% or less Ni- (one or more of Mo, Cu, B) 1.2 wt% or less Mo- (one or more of Cu, B) 1.0 wt% or less Cu-B 0.012 wt% or less B

(4) C: 0.45 to 0.85 wt%, Si: 0.50 wt
%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, S
b: 0.001 to 0.015wt%, O: 0.0030wt% or less, N: 0.00
Needle-like martensite containing 15 to 0.020 wt%, the balance being Fe and unavoidable impurities, and containing 5% or less by volume of residual carbides and 10 to 30% of residual γ. A bearing member having a texture.

(5) C: 0.45 to 0.85 wt%, Si: 0.50 wt
%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, S
b: 0.001 to 0.015wt%, O: 0.0030wt% or less, N: 0.00
15 to 0.020wt%, Ni: 1.5wt% or less, M
o: 1.2 wt% or less, Cu: 1.0 wt% or less, B: 0.012 wt%
And a residual carbide containing at least one selected from the following, having the composition of the balance being Fe and inevitable impurities, and having a volume ratio of 5% or less.
A bearing member having a needle-like martensite structure containing residual γ of 10 to 30%.

(6) However, the above basic components (C, Si, Mn,
For the optional additive components (Ni, Mo, Cu, B) that are selectively added to Al, Sb, O, N), within the composition range of (2) above, the following combinations It is recommended to add in. 1.5 wt% or less Ni- (one or more of Mo, Cu, B) 1.2 wt% or less Mo- (one or more of Cu, B) 1.0 wt% or less Cu-B 0.012 wt% or less B

[0012]

The reason why the chemical composition, the amount of residual carbides and the amount of residual γ of the present invention are limited to the above ranges will be described below.

C: 0.45 to 0.85 wt%; C is an element that forms a solid solution in the matrix and effectively acts to strengthen martensite, and secures strength after quenching and tempering and improves rolling contact fatigue life. It is included in order to allow it. Its content is 0.
If it is less than 45 wt%, such an effect cannot be obtained. On the other hand, 0.85
If it exceeds wt%, huge carbides will be generated during casting to reduce the rolling fatigue life, and in order to dissipate the carbides, diffusion annealing for a long time is required, resulting in an increase in cost and a decrease in productivity. Therefore, the C content is 0.45 to 0.85 wt.
%, Preferably 0.55-0.80 wt%.

Si: less than 0.50 wt%; Si is used as a deoxidizing agent during the melting of steel, and it also forms a solid solution in the matrix to enhance the hardness after quenching and tempering and improve the rolling fatigue life. It is effective as an element. However, if added excessively, the workability is deteriorated. Therefore, Si is less than 0.50 wt%, preferably
It is added in an amount of 0.35 wt% or less, more preferably 0.20 wt% or less.

Mn: 1.5-3.0 wt%; Mn acts as a deoxidizing material during the melting of steel, and also improves the hardenability to increase the hardness of the base martensite and improve the rolling contact fatigue life. Contribute effectively. It also contributes to the stabilization of austenite. However, if added excessively, the machinability is deteriorated. Therefore, the amount of Mn added is 1.5 to 3.0 wt.
%, Preferably 1.5 wt% to 2.0 wt%.

Al: 0.07 wt% or less; Al is used as a deoxidizing agent when steel is melted, and at the same time, it combines with N in the steel to refine the crystal grains and contribute to the improvement of the toughness of the steel. However, if the addition amount is too large, it bonds with O to form hard non-metallic inclusions and deteriorates the rolling fatigue life. Therefore, Al is
It is added in an amount of 0.07 wt% or less, preferably 0.005 wt% to 0.05 wt%.

Sb: 0.001 to 0.015 wt%; Sb is added in order to suppress the reaction between C in the surface layer of the steel material and the atmospheric gas during the heat treatment to suppress the generation of the decarburized layer. But,
If the added amount is too large, hot workability and toughness will be deteriorated. Therefore, Sb is included in the range of 0.001 to 0.015 wt%. Preferably 0.001 to 0.010 wt
%, More preferably 0.002 to 0.008 wt%.

O: 0.0030 wt% or less; O forms hard non-metallic inclusions and causes a reduction in rolling contact fatigue life, so it is desirable to be as low as possible. But 0.0030wt
% Or less, preferably 0.0020 wt% or less is acceptable.

N: 0.0015 to 0.020 wt%; N combines with carbonitride forming elements to refine the crystal grains and improve toughness. However, if the addition amount is too large, machinability and forgeability deteriorate. Therefore, N is added in the range of 0.0015 to 0.020 wt%, preferably 0.0020 to 0.010 wt%.

As described above, the basic components (C, Si, Mn, Al, Sb,
Each of the reasons for limiting O and N) has been described above. However, in the present invention, any one or more selected from Ni, Mo, Cu and B described below can be selectively added. .

Ni: 1.5 wt% or less; Ni has the effect of increasing hardness after quenching and tempering by increasing hardenability and improving rolling fatigue life. However, if the amount of addition is too large, the amount of residual γ produced becomes too large, which reduces the hardness of the steel material and rather reduces the rolling fatigue life. Therefore, the addition amount of Ni is 1.5 wt% or less, preferably 0.1 to 1.
The range is 0 wt%.

Mo: 1.2 wt% or less; Mo has the effect of increasing the hardness after quenching and tempering by increasing the hardenability and improving the rolling contact fatigue life. However, if the addition amount is too large, the precipitation of stable carbide improves wear resistance, but it lowers the hardness of steel and reduces the rolling fatigue life. Therefore, the addition amount of Mo is 1.2 wt% or less,
The preferred range is 0.05 to 0.5 wt%.

Cu: 1.0 wt% or less; Cu has the effect of increasing the hardness after quenching and tempering by increasing the hardenability and improving the rolling contact fatigue life. However, if the addition amount is too large, the forgeability of steel is deteriorated. Therefore, the amount of Cu added is
The amount is 1.0 wt% or less, preferably 0.05 to 0.5 wt%.

B: 0.012 wt% or less; B has the effect of improving the rolling fatigue life by increasing the hardness after quenching and tempering by increasing the hardenability. However, if the addition amount is too large, cracking may occur during casting, which may lead to a decrease in productivity. Therefore, the amount of B added is 0.012 wt%
Below, it is preferably in the range of 0.001 to 0.008 wt%.

Further, in the present invention, even if S, Pb, Ca, Bi, REM, etc. are added in order to improve the machinability, the above-mentioned object of the present invention is the workability and rolling fatigue life. Since machinability can be easily improved without impeding the characteristics, it may be added if necessary.

It is desirable that P is as low as possible because it lowers the toughness and rolling fatigue life of the steel, and is preferably 0.025 wt% or less, more preferably 0.015 wt% or less.
It is better to set it to wt% or less. In addition, S is bound to Mn to form Mn
It is an element that forms S and improves machinability. But,
If contained in a large amount, the rolling contact fatigue life will be reduced, so it is preferably 0.025 wt% or less, more preferably 0.015 wt% or less.
It is better to keep it below wt%. Further, Ti is desirable to be small because it combines with N to form hard non-metallic inclusions and deteriorates rolling fatigue life. Therefore, it is preferably 0.005 wt% or less, and more preferably 0.003 wt% or less.

In the present invention, the rolling contact fatigue life characteristics of the bearing member obtained by subjecting the bearing steel having the above-mentioned chemical composition to heat treatment such as quenching and tempering after working, in contrast to the rolling fatigue life characteristics, is important. First, the hardness required for the bearing member to maintain rolling fatigue life is HRC 58 or higher, preferably HRC 60. In order to achieve this hardness, it is necessary to make the matrix structure an acicular martensite structure. In addition, it is necessary to control the residual carbide amount and the residual γ amount within the above range. The reasons for the limitation will be described below.

Residual carbide content: 5% or less (volume ratio); If the amount of residual carbonization in the steel after quenching and tempering increases, the rolling fatigue life characteristics deteriorate, so it is desirable that it is as small as possible. In particular, if the amount exceeds 5% in terms of volume ratio, the degree of adverse effect on rolling contact fatigue life increases. Therefore, the residual carbide amount needs to be 5% or less, preferably 2% or less in terms of volume ratio.

Residual γ amount: 10 to 30% (volume ratio); Residual γ
Improves rolling contact fatigue life characteristics in clean and dust environments. On the other hand, if the amount is too large, the hardness will be sufficient
HRC 58 or higher) will not be obtained, and the rolling fatigue life will be shortened, and the dimensional change when used as a bearing will be large. Therefore, the amount of residual γ is 10-
It should be 30%, preferably 15-25%.

In order to manufacture a bearing member satisfying the amount of residual carbides and the amount of residual γ from the steel having the chemical composition as described above, an appropriate quenching temperature may be selected during the heat treatment for quenching and tempering. . Quenching temperature is usually 830-
It may be carried out in the temperature range of 860 ° C, but by adding a large amount of elements such as Cr and Mo that have a strong tendency to form carbides, it is feared that the hardness and the residual γ amount may decrease due to the decrease of C in the matrix. Temperature range from 850 to 980 ° C,
Further, when there is a possibility that the residual γ amount becomes excessive by adding Mn and Ni in combination, it is desirable to carry out in the temperature range of 800 to 850.

[0031]

EXAMPLES Steels having the chemical compositions shown in Table 1 were melted and cast. Here, Steel No. 1 is a component corresponding to SUJ 2, and Steel No. 2 is a component corresponding to the steel disclosed in JP-A-2-54739.
Of these steels, Steel No. 1 was subjected to diffusion annealing at 1240 ° C for 30h, and other steels were heated to 1100 ° C for 1h and then heated to 65mm.
It was rolled into φ steel bar. From the D / 4 part of this steel bar, 12 mmφ ×
22 mm cylindrical test pieces (for hardness measurement and microstructure investigation), forged test pieces and rolling fatigue life test pieces were sampled by cutting. In addition, as for a part of Steel No. 8, each test piece was sampled after spheroidizing the steel bar. Forgeability is 50% to 80% under conditions of complete restraint and room temperature, using a 10 mmφ × 15 mm forged test piece.
Incidence of forging cracks when a compression ratio of
The deformation resistance of the test piece in which no cracking occurred at a compressibility of 0.1% was evaluated by comparing the value of SUJ 2 (steel No. 1), which is a conventional material, with 1. The rolling fatigue life characteristics are as shown in Table 2 after oil quenching (some steel No. 7 is induction hardened at 15kHz).
, 180 ° C for 1h, and then lapping polishing to make a 12mmφ x 22mm test piece. Using this test piece, the Hertz maximum contact stress: 600kgf / mm ² , repeated stress by a radial type rolling fatigue tester. Number: 46,500 cpm, Lubricating oil: # 68 Turbine splash oil Tested in an environment where oil is used. The test results were obtained by plotting them on probability paper assuming that they follow the Weibull distribution, and SUJ 2 (Steel No.
The B ₁₀ value of 1) (10% cumulative failure probability) was evaluated as a comparison of 1. 12mmφ x 22mm for hardness measurement and structure survey
After subjecting the cylindrical test piece of No. 1 to heat treatment and processing in the same manner as the rolling fatigue test piece, the surface hardness and the residual γ were measured by X-ray diffraction. Further, the sample was cut at a height of 11 mm perpendicularly to the height direction, its cross section was corroded by Picral, and the area ratio of residual carbide immediately below the surface was measured by image analysis to obtain the volume ratio. The above evaluation results are summarized in Table 2. The structure of the invention material was mainly acicular martensite structure in addition to residual γ and residual carbide.

[0032]

[Table 1]

[0033]

[Table 2]

In Table 2, Test No. 4 in which the amount of C is lower than the range of the present invention has a deformation resistance of 0.7 (0.7 times SUJ),
Furthermore, forging cracks do not occur up to 70%, and the forgeability is excellent. However, the hardness after quenching and tempering is as low as HRC 55, and the residual γ is as low as 4%, so the rolling fatigue life is inferior at 0.4 (0.4 times that of SUJ). Test No. 5 in which the C content is higher than the range of the present invention and Test No. 6 in which the Si and N contents are high,
Excellent rolling fatigue life of 5.0 or 6.1. However, the deformation resistance was slightly higher at 1.2 or 1.4, and the compressibility at which forging cracking occurred was 60% for test material No. 5, which was not improved compared to the conventional material, and therefore the forgeability was improved. Is hard to say. In Test No. 3 with high Mn or Test No. 7 with high Al and O, the deformation resistance was as low as 0.8. Here, test material No. 3, which has a low residual γ of 7%, has a rolling fatigue life of 1.2, and test No. 7 has an inferior value of o.8, so rolling fatigue life has not been improved. On the other hand, the material of the present invention (Test No. 8 to 2
In 1), the deformation resistance is as low as 0.6 to 0.9, and in particular, it is improved to 0.6 in the test material No. 11 which was spheroidized and annealed before the forging test. In addition, the compressibility at which forging cracks occur is improved to 70% for most of the invention materials,
Although it is 60%, which is the same as the conventional material, its incidence is lower than that of test No.1 or No.2. Furthermore, the rolling fatigue life is 3.
It is excellent at 9 to 8.8, and in particular, when induction hardening is performed, the B10 life is long compared to normal immersion hardening. In addition, the addition of one or more selected from Mo, Ni, Cu and B adjusts the heat treatment conditions as necessary, and controls the residual carbides and residual γ content appropriately to achieve rolling fatigue. It is understood from the improvement of life that it is possible to freely combine them depending on the purpose of use. That is, as is clear in Test No. 20 and No. 21, in the case of quenching at the same temperature as in Test No. 1,
The rolling fatigue life is 1.2, but it can be seen that the rolling fatigue life is dramatically improved to 8.8 by increasing the quenching temperature.

[0035]

EFFECTS OF THE INVENTION According to the present invention, a bearing steel and a bearing member are obtained which are superior in workability such as cold forgeability and rolling fatigue life to SUJ2. Further, according to the present invention,
Since spheroidizing annealing is not necessary, it greatly contributes to productivity improvement and cost reduction. Also, reduce C,
Since Cr is not added, diffusion annealing is not necessary, and since the cost of Cr is not necessary, the material cost is significantly reduced. As a result, it is possible to apply to rolling element parts that undergo complicated and heavy working, in which the compressibility of each part is different at the working stage. In addition, Ni, Mo, Cu and B
Since it is possible to increase the hardenability by adding, increase the hardness after quenching and tempering, and improve the rolling contact fatigue life, it is effective for increasing the strength and extending the life of automobile parts such as hubs. It can also be applied to large bearings such as industrial machinery.

Front page continuation (72) Inventor Akihiro Matsuzaki 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture, Kawasaki Steel Corporation Technical Research Division (72) Inventor Shinichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Iron & Steel Co., Ltd.

Claims (4)

[Claims] 1. C: 0.45 to 0.85 wt%, Si: less than 0.50 wt%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, Sb: 0.
001 ~ 0.015wt%, O: 0.0030wt% or less, N: 0.0015〜
A bearing steel containing 0.020 wt% and the balance Fe and unavoidable impurities. 2. C: 0.45 to 0.85 wt%, Si: less than 0.50 wt%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, Sb: 0.
001 ~ 0.015wt%, O: 0.0030wt% or less, N: 0.0015〜
Contains 0.020 wt%, Ni: 1.5 wt% or less, Mo: 1.2
wt% or less, Cu: 1.0 wt% or less, B: 0.012 wt% or less, for one or more selected, and the balance being Fe and inevitable impurities. steel. 3. C: 0.45 to 0.85 wt%, Si: less than 0.50 wt%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, Sb: 0.
001 ~ 0.015wt%, O: 0.0030wt% or less, N: 0.0015〜
A needle-like martensite structure containing 0.020 wt% and the balance being Fe and inevitable impurities, and containing 5% or less of residual carbides and 10 to 30% of residual austenite in volume ratio. A bearing member having. 4. C: 0.45 to 0.85 wt%, Si: less than 0.50 wt%, Mn: 1.5 to 3.0 wt%, Al: 0.07 wt% or less, Sb: 0.
001 ~ 0.015wt%, O: 0.0030wt% or less, N: 0.0015〜
Contains 0.020 wt%, Ni: 1.5 wt% or less, Mo: 1.2
wt% or less, Cu: 1.0 wt% or less, B: 0.012 wt% or less, and has a composition that the balance is Fe and inevitable impurities, and , 10% by volume of residual carbide and less than 5%
A bearing member having a needle-like martensite structure containing 30% of retained austenite.