JP6639839B2 - Bearing steel with excellent whitening resistance and exfoliation life - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a bearing steel having excellent white structure change resistance and rolling life in an environment in which hydrogen enters a steel material to cause a white structure change caused by hydrogen.

  In electrical bearings for automobiles, there is a problem of early breakage accompanied by a change in white structure due to hydrogen. In addition, there is a concern about similar early breakage in bearings, such as marine wind turbines and rolling mills for steel, in which moisture is likely to enter the lubricating oil. The early peeling of these structural change types requires more and more measures to be taken in the use of bearings in recent years in which materials have been reduced in size, the load has increased, and the viscosity of lubricating oil has been reduced.

  To cope with these changes in white structure caused by hydrogen, measures such as the use of additives, design for preventing temperature rise, and prevention of hydrogen generation and intrusion on the lubricating oil side have been adopted. However, such measures are often inadequate or difficult to apply, and therefore, countermeasures are also required on the steel side for early peeling due to changes in white structure.

  Under these circumstances, as a countermeasure on the steel side, the formation of carbides such as V, Ti, and Nb is performed as a countermeasure on the steel side against hydrogen generation due to lubricating oil decomposition in a rolling environment such as a bearing and white structure change due to hydrogen intrusion. There is a technique for extending the life of a steel material by trapping hydrogen in a carbide by adding an element (for example, see Patent Document 1). However, the addition of these elements results in a significant increase in material costs. Further, the carbide itself is likely to be a source of stress concentration, and localization of hydrogen around the carbide may lead to early breakage accompanied by white structure change.

  Further, as a conventional technique, it is assumed that suppression of hydrogen concentration at the martensite block interface is effective against white structure change due to hydrogen entering steel, and heat treatment and formation of carbides and carbonitrides such as Cr, Mo, and V are performed. A technique for reducing solid solution C and N by adding an element has been proposed (for example, see Patent Document 2). However, a reduction in the amounts of C and N during carburizing and carbonitriding leads to a reduction in material hardness and a reduction in strength. Therefore, a method that can be used without reducing C and N is required.

JP 2008-280583 A JP 2012-036475 A

  The problem to be solved by the present invention is that the white structure change caused by hydrogen can be reduced without relying on the technology that may reduce the rolling fatigue life characteristics such as carbide precipitation and reduction of the amount of solid solution C and N. It is an object of the present invention to provide a bearing steel which is excellent in a white structure change resistance peeling life and a rolling fatigue life in an environment where it occurs.

  The present inventors reviewed the component design for the phenomenon that hydrogen invaded and caused early breakage accompanied by white structure change caused by hydrogen, and found that Si, Mn, Cr, and Ni dissolved in the matrix phase component. , Mo and the like and the residual γ amount are not less than a certain amount, it is possible to suppress the white structure change even in an environment where hydrogen enters and a white structure change caused by hydrogen occurs. It has been found that it is possible to produce molten steel bearing having excellent dynamic fatigue life.

Means of the present invention for solving the above-mentioned problem is that, in the means of claim 1, C: 0.13 to 0.35%, Si: 0.20 to 0.65%, Mn: 0% by mass. .50 to 1.80%, P: 0.030% or less, S: 0.030% or less, Cr: 2.30 to 3.50%, and Ni: 0.10 to 0.50% , Mo: steel containing one or two selected from 0.03 to 0.50%, the balance being Fe and unavoidable impurities, in a state of being carburized and quenched and tempered or in a state of being carbonitrided and quenched and tempered. The total amount of Si, Mn, Cr, Ni, and Mo dissolved in the matrix component of 100 to 300 μm from the outermost surface is 3.0% or more, and the residual γ amount is 27 to 50% by volume. And the rest is martensitic, characterized by a change in white structure resistance. A bearing steel which is excellent in life.

According to the means of claim 2, in addition to the chemical components described in claim 1, V: 0.01 to 0.20%, Nb: 0.01 to 0.20%, Ti: 0 by mass%. A steel containing one or more selected from .01 to 0.20%, the balance being Fe and unavoidable impurities, in a carburized and quenched and tempered state or in a carbonitrided and quenched and tempered state; The total of Si, Mn, Cr, Ni, and Mo dissolved in the matrix component of 100 to 300 μm from the outermost surface is 3.0% or more, and the residual γ amount is 27 to 50% by volume. The remainder is a bearing steel having a martensitic structure and excellent in whitening change resistance and exfoliation life.

According to the means of claim 3, C: 0.13 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.50 to 1.80%, P: 0.030% by mass%. Hereinafter, S: 0.030% or less, Cr: 2.30 to 3.50%, Ni: 0.10 to 0.50%, Mo: 0.03 to 0.50% A matrix containing 100% to 300 μm from the outermost surface of a steel containing one or two kinds, the balance being Fe and inevitable impurities, in a state of being carburized and quenched and tempered or in a state of being carbonitrided and quenched and tempered. The total of Si, Mn, Cr, Ni, and Mo dissolved therein is 3.0% or more, the residual γ content is 27 to 50 vol%, and the remainder of the residual γ content is a martensite structure. It is a bearing part with excellent whitening resistance and whitening characteristic characterized by being made of steel. .

In the means of claim 4, C: 0.13 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.50 to 1.80%, P: 0.030% by mass%. Hereinafter, S: 0.030% or less, Cr: 2.30 to 3.50%, Ni: 0.10 to 0.50%, Mo: 0.03 to 0.50% One or two kinds, and one or two selected from V: 0.01 to 0.20%, Nb: 0.01 to 0.20%, Ti: 0.01 to 0.20% Steel containing at least one species and the balance consisting of Fe and inevitable impurities is in a state of being carburized and quenched and tempered or in a state of being carbonitrided and quenched and tempered , and is solidified in a matrix component of 100 to 300 μm from its outermost surface. dissolved the Si, Mn, Cr, Ni, total Mo is 3.0% or more, further residual γ amount 27 ～50Vo A%, the remainder of the residual γ amount is bearing parts excellent in 耐白 color tissue changes flaking life, characterized in that it consists of steel is martensite structure.

  By adopting the above means, the steel for bearing of the present invention and the bearing component made of this steel can be subjected to carburizing, quenching and tempering in an environment where a white structure change caused by hydrogen is caused by infiltration of hydrogen into steel. The total amount of Si, Mn, Cr, Ni, and Mo dissolved in a matrix component of 100 to 300 μm from the outermost surface of the steel after or after carbonitriding, quenching, and quenching and tempering is set to 3.0% or more, and further, the amount of residual γ Is 20 to 50 vol% or more, the rolling fatigue life and the whitening change resistance peeling life of twice or more of SUJ2 are excellent.

It is a shape figure of a thrust test piece, (a) is a top view and (b) is a side view. It is a figure showing a carburizing quenching pattern. 5 is a graph showing the relationship between the amount of residual γ and the change in white structure resistance and the peeling life.

  Prior to describing the modes for carrying out the invention, the reasons for limiting the chemical composition of the steel for bearing and the various reasons for limiting the steel according to the claims of the present application will be described in order. In addition,% of the chemical component is% by mass, and% of the amount of residual γ is vol%.

C: 0.13 to 0.35%
C is an element that affects the hardenability, forgeability, and machinability of the core. If C is less than 0.13%, sufficient core hardness cannot be obtained, and the strength is reduced. Therefore, it is necessary to add 0.13% or more. On the other hand, if C is more than 0.35%, the hardness of the steel material increases, and the workability such as machinability and forgeability is impaired. Therefore, C is set to 0.13 to 0.35%, preferably 0.15 to 0.30%.

Si: 0.20 to 0.65%
Si is an element necessary for deoxidation, and is an element that further increases the strength of a steel material in a high-temperature environment, suppresses structural change, and improves the rolling fatigue life. In order to obtain these effects sufficiently, it is necessary to add 0.20% or more of Si. On the other hand, if Si is more than 0.65%, the hardness of the steel material increases, impairing machinability and workability such as forgeability, and also impairs carburization, which is sufficient even if carburizing or carbonitriding. High material strength cannot be obtained. Therefore, Si is set to 0.20 to 0.65%, preferably 0.25 to 0.50%.

Mn: 0.50 to 1.80%
Mn is an element necessary for ensuring hardenability, and when carburizing or carbonitriding a steel material, increasing the amount of residual γ is an element that leads to suppression of white structure change caused by hydrogen. . To obtain these effects sufficiently, Mn needs to be added at 0.50 or more. On the other hand, when Mn is more than 1.80%, the hardness of the steel material increases, impairs the machinability such as machinability and forgeability, and combines with S to form MnS, thereby reducing hydrogen. This is the starting point of the white structure change caused. Therefore, Mn is set to 0.50 to 1.80%, preferably 0.65 to 1.60%.

P: 0.030% or less When P is contained in an amount of more than 0.030%, it is an element that embrittles the steel material and lowers the fatigue strength. Therefore, P is set to 0.030% or less.

S: 0.030% or less When S is contained in an amount of more than 0.030%, it is an element that impairs the cold workability of the steel material and deteriorates the fatigue strength. Therefore, S is set to 0.030% or less.

Cr: 2.30 to 3.50%
Cr is an element necessary for ensuring hardenability, and is an element that increases the amount of residual γ when carburizing or carbonitriding a steel material, thereby leading to suppression of a change in white structure caused by hydrogen. Further, Cr is effective in forming fine and uniform residual γ, and enhances the effect of suppressing a change in white structure caused by hydrogen. To obtain these sufficient effects, Cr must be added in an amount of 2.30% or more. On the other hand, when Cr is excessive, it is an element that forms an oxide on the outermost surface of the steel material during carburizing or carbonitriding, thereby inhibiting carburization and leading to deterioration in strength. Further, Cr forms coarse carbides during carburization and becomes a starting point of white structure change caused by hydrogen around the coarse carbides, so that Cr needs to be 3.50% or less. Therefore, Cr is set to 2.30 to 3.50%, preferably 2.50 to 3.20%.

Ni: 0.10 to 0.50%
Ni enhances the hardenability of the steel material by addition, and increases the amount of residual γ when the steel material is carburized or carbonitrided. In order to obtain these effects sufficiently, it is necessary to add Ni in an amount of 0.10% or more. On the other hand, if Ni is added excessively, the material cost increases significantly. In addition, Ni is liable to form massive residual γ during carburizing or carbonitriding, and loses the effect of suppressing white structure change caused by hydrogen due to residual γ. Therefore, Ni is added up to 0.50% as an upper limit. Is good. Therefore, Ni is set to 0.10 to 0.50%.

Mo: 0.03 to 0.50%
Mo is effective in increasing the hardenability of the steel material by adding Mo, increasing the amount of residual γ when the steel material is carburized or carbonitrided, homogenizing the structure, and uniformly distributing the residual γ. In order to obtain these effects sufficiently, Mo needs to be 0.03% or more. On the other hand, if Mo is added excessively, the material cost increases greatly, and the effect of suppressing the structural change for homogenizing the structure saturates at 0.50%. Therefore, Mo is added at 0.50% or less. Therefore, Mo is set to 0.03 to 0.50%, preferably 0.03 to 0.40%.

V: 0.01 to 0.20%
V suppresses white structure change caused by hydrogen by refining crystal grains and reducing hydrogen concentration at grain boundaries, and forms carbides and carbonitrides of submicron order during carburizing or carbonitriding. Thus, the pixel functions as a hydrogen trap and effectively acts to suppress the change in white structure. To obtain a sufficient effect, the addition of 0.01% or more is necessary. On the other hand, the effect of refining the crystal grains by adding V and suppressing the change in the white structure due to the precipitation of carbides and carbonitrides is saturated with the addition of V up to 0.20%. V is set to 0.20% or less because carbon nitride is precipitated and adversely affects the carbon nitride. Therefore, V is set to 0.01 to 0.20%.

Nb: 0.01 to 0.20%
Nb suppresses a change in the white structure caused by hydrogen by making the crystal grains fine and reducing the hydrogen concentration at the grain boundaries. Also, Nb functions as a hydrogen trap by forming carbides and carbonitrides on the order of submicrons during carburizing or carbonitriding, and is effective in suppressing white structure change. To obtain these sufficient effects, Nb must be added at 0.01% or more. On the other hand, the effect of refining the crystal grains by adding Nb and suppressing the change of the white structure due to the precipitation of carbides and carbonitrides is saturated when Nb is added up to 0.20%. Nb is added at 0.20% or less because carbonitrides are precipitated, which has an adverse effect. Therefore, Nb is set to 0.01 to 0.20%.

Ti: 0.01 to 0.20%
Ti suppresses a white structure change caused by hydrogen by making crystal grains fine and reducing the hydrogen concentration at the grain boundaries. Further, Ti forms a submicron-order carbide or carbonitride during carburizing or carbonitriding, thereby functioning as a hydrogen trap, and is effective in suppressing a change in white structure. In order to obtain these effects sufficiently, Nb needs to be added at 0.01% or more. On the other hand, the effect of adding Nb to refine the crystal grains and suppress the change in white structure due to precipitation of carbides and carbonitrides is that Nb is saturated up to 0.20% and coarse carbides / carbonitrides when added excessively. Precipitation causes adverse effects. Therefore, the addition of Ti is set to 0.20% or less. Therefore, Ti is set to 0.01 to 0.20%.

100 to 300 μm from the outermost surface of the steel after carburizing and quenching and tempering of the steel or after carbonitriding and quenching and tempering
Since the structural change due to hydrogen occurs repeatedly at 100 to 300 μm from the outermost surface of the steel that is repeatedly subjected to high shear stress and leads to breakage, it is important to suppress the structural change at this position. Therefore, the thickness is defined as 100 to 300 μm from the outermost surface of the steel after carburizing and quenching and tempering or after carbonitriding and quenching and tempering of the steel.

The total of Si, Mn, Cr, Ni, and Mo dissolved in the matrix component is 3.0% or more. When carburized or carbonitrided, the amount of alloying elements in the matrix is actually increased due to the formation of carbides and carbonitrides. Is lower than the added amount. Therefore, in order to obtain a sufficient amount of residual γ, it is necessary to increase the amount of alloying elements dissolved in the matrix. In addition, the structural change is suppressed by reducing the diffusion rate of hydrogen. In order to obtain these effects sufficiently, the total amount of Si, Mn, Cr, Ni, and Mo in the matrix needs to be 3.0% or more. Therefore, the total of Si, Mn, Cr, Ni, and Mo dissolved in the matrix component is specified to be 3.0% or more.

The residual γ amount is 20 to 50 vol%
The amount of residual γ functions as a non-diffusible hydrogen trap site, suppressing the concentration of hydrogen during use, and also has the effect of slowing the diffusion rate of hydrogen diffusing in steel, resulting from hydrogen. It is very effective in suppressing organizational changes. In order to obtain these effects sufficiently, the residual γ amount needs to be 20 vol% or more. On the other hand, if the residual γ content is more than 50 vol%, the hardness of the steel is reduced, leading to a deterioration in strength, a reduction in dimensional stability and the generation of massive γ. Therefore, the amount of residual γ is set to 50 vol% or less. Therefore, the amount of residual γ is set to 20 to 50 vol%.

The remainder is a martensite structure. If a low-strength structure such as ferrite or pearlite is present, it becomes a starting point of a white structure change caused by hydrogen. Therefore, the remainder is a martensite structure.

  Next, embodiments of the invention will be described. Sample No. of the example steel satisfying the components of the present invention having the chemical composition shown in Table 1. Samples No. A to O and comparative example steels not partially satisfying the components of the present invention. Each of P to T was melted in a 100 kg vacuum melting furnace to obtain steel. In addition, the sample No. of the comparative example steel. Q is SUJ2 which is a high carbon chromium bearing steel material specified by JIS. R is SCM420 which is a chromium molybdenum steel according to JIS. Next, these steels were forged to a diameter of 65 mm at 1250 ° C., held at 900 ° C. for 1 hour, and air-cooled for normalization. In addition, the sample No. of the comparative example steel. SUJ2 of Q was further subjected to spheroidizing annealing at 800 ° C. Then, the sample No. of the comparative example steel was used. All the steels except for SUJ2 of Q were rough-worked into thrust-type rolling fatigue test pieces shown in FIG. 1 having an outer diameter of 60 mm, an inner diameter of 20 mm, and a thickness of 8.3 mm. Sample No. of Comparative Example Steel As for SUJ2 of Q, a thrust type rolling fatigue test piece having an outer diameter of φ60 mm, an inner diameter of φ20 mm, and a thickness of 6.0 mm shown in FIG. 1 was roughly processed.

  Sample No. of Comparative Example Steel Except for SUJ2 of Q, the thrust type rolling fatigue test specimens of all steel types were subjected to gas carburizing and quenching under the conditions of carburizing and quenching pattern shown in FIG. 2 (carburizing temperature: 930 ° C., target Cp = 0.80%). After that, a tempering treatment was performed by holding at 180 ° C. for 90 minutes and air cooling. In addition, the sample No. of the comparative example steel. SUJ2 of Q was kept at 840 ° C. for 30 minutes to perform oil cooling, quenched, and then tempered by being kept at 180 ° C. for 90 minutes and air-cooled.

  In addition, the sample No. of the example steel was used. Under the conditions of the carburizing and quenching pattern shown in FIG. 2, the steels shown in B and K are subjected to gas carburizing and quenching and tempering with the target Cp = 1.2% at the time of carburizing, whereby the residual γ amount is intentionally excessively increased. And the machining No. of the comparative steel. 21 and 22. In addition, the No. of the example steels. After the steel shown in E was subjected to gas carburizing and quenching and tempering in the same process, annealing was performed by holding at 600 ° C. for 5 hours in Ar gas and rapidly cooling for the purpose of the residual γ amount phenomenon. After that, holding at 830 ° C. for 30 minutes to perform oil cooling and quenching, holding at 180 ° C. for 90 minutes to air-cool, performing a tempering treatment, and performing processing No. 23. Further, the sample No. of the example steel was used. After the steel shown in L was subjected to the same process up to the rough processing of the test piece, gas carburizing and quenching were performed under the same carburizing and quenching pattern conditions (carburizing temperature: 930 ° C., target Cp = 0.80%) as in FIG. After the implementation, a sub-zero treatment with liquid nitrogen was carried out for the purpose of reducing the residual γ content, and thereafter, it was kept at 180 ° C. for 90 minutes and air-cooled to perform a tempering treatment. 24.

  After performing the above heat treatment, the processing No. With respect to all the test pieces except SUJ2 of No. 17, the test surface was polished by 0.15 mm and the other side was polished to finish the height to 8.0 mm. Processing No. of Comparative Example Steel For SUJ2 No. 17, the test surface was polished by 0.20 mm, and the opposite side was further polished to a height of 5.6 mm. These test surfaces were mirror-finished by buffing.

  Using the thrust-type rolling fatigue test specimen prepared above, in order to measure the white structure resistance peeling life, after hydrogenation to the test specimen by the cathode charge method under the conditions of carburizing and quenching pattern shown in Table 2. Using a thrust-type rolling fatigue tester at a maximum contact surface pressure of 5.3 GPa, the rolling fatigue life until peeling was measured. In addition, a thin film sample was cut out from a position that was 100 to 300 μm from the outermost surface using a thrust-type rolling fatigue test piece manufactured in the same manner, and observed with a TEM (transmission electron microscope). In TEM observation, the position was adjusted so as to avoid carbides, and EDS analysis was performed to measure the amounts of Si, Mn, Cr, Ni, and Mo dissolved in the mother phase itself, and the total amount was calculated. . Similarly, after performing electropolishing using a thrust-type rolling fatigue test piece to a depth of 100 to 300 μm from the outermost surface, the residual γ amount was measured using X-ray diffraction. Similarly, using a thrust-type rolling fatigue test piece, the structure of the cross section of the sample was observed by SEM (scanning electron microscope) at a position of 100 to 300 μm from the outermost surface. It was confirmed that the organization consisted of martensite.

  As described above, the measurement results of the total amount of Si, Mn, Cr, Ni, and Mo dissolved in the matrix phase itself, the amount of residual γ, and the L50 life in a thrust rolling fatigue test at a position of 100 to 300 μm from the outermost surface And No. of the comparative steel. Table 3 shows the results of calculating the L50 life ratio of the No. 17 with SUJ2.

  As shown in Table 3, machining No. No. 1 to No. 15 show the rolling fatigue characteristics in a hydrogen environment, and machining Nos. 17 has twice or more the L50 life as compared to SUJ2 of 17 and is excellent in the peeling life due to the change in white structure resistance. On the other hand, No. In No. 19, the residual γ amount at a position of 100 to 300 μm from the outermost surface was excessively large at 68%, and sufficient material strength could not be secured. In addition, machining No. of the comparative example steel to which a large amount of Ni was added was used. No. 20 was damaged relatively early, which indicates that a sufficient amount of Ni was added to form a coarse bulky residual γ, whereby a sufficient change in white structure resistance and a peeling life could not be exhibited. Further, the sample No. of the example steel was used. B and K were used to increase the C concentration during carburization to increase the residual γ content. In Nos. 21 and 22, the peeling life of the change in the white structure was clearly shortened. This is because sufficient material strength could not be secured. On the other hand, the machining No. No. 12 and No. 5 were subjected to the annealing treatment and the sub-zero treatment, respectively. In Nos. 21 and 22, the peeling life of the change in white structure resistance was clearly shortened, and it can be seen that it is important to secure a certain amount of residual γ in a high shear stress region.

  FIG. 3 is a graph showing the relationship between the residual γ content and the whitening resistance change peeling life of the example steel and the comparative example steel. As described above, the working steel No. of the comparative example steel having a short life due to insufficient strength due to an excessive amount of residual γ and generation of massive γ due to a large amount of Ni addition. Nos. 19, 21 and 22, and Comparative Example Steel Nos. Excluding 20, the residual γ content and the whitening resistance change peeling life show a good correlation.

  1 Thrust type rolling fatigue test piece

Claims (4)

In mass%, C: 0.13 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.50 to 1.80%, P: 0.030% or less, S: 0.030 % Or less, Cr: 2.30 to 3.50%, Ni: 0.10 to 0.50%, Mo: 0.03 to 0.50% The balance of the steel consisting of Fe and unavoidable impurities is in a state of being carburized and quenched and tempered or in a state of being carbonitrided and quenched and tempered, and Si dissolved in a matrix component of 100 to 300 μm from its outermost surface, A total of Mn, Cr, Ni, and Mo being 3.0% or more, a residual γ content of 27 to 50% by volume, and the remaining balance being a martensite structure; Excellent bearing steel. In addition to the chemical components according to claim 1, V: 0.01 to 0.20%, Nb: 0.01 to 0.20%, Ti: 0.01 to 0.20% by mass%. A steel containing one or two or more of the above and the balance consisting of Fe and inevitable impurities is in a state of being carburized and quenched and tempered or in a state of being carburized and quenched and quenched and tempered, and is 100 to 300 μm from the outermost surface thereof. The total amount of Si, Mn, Cr, Ni, and Mo dissolved in the phase component is 3.0% or more, the residual γ amount is 27 to 50% by volume, and the remaining balance is a martensite structure. A bearing steel that has a distinctive white structure change resistance and excellent flaking life. In mass%, C: 0.13 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.50 to 1.80%, P: 0.030% or less, S: 0.030 % Or less, Cr: 2.30 to 3.50%, Ni: 0.10 to 0.50%, Mo: 0.03 to 0.50% Si in a state in which the balance is steel and a carburized and quenched and tempered state of Fe and unavoidable impurities or in a state of carbonitrided and quenched and tempered, and a solid solution in a matrix component of 100 to 300 μm from its outermost surface, The total of Mn, Cr, Ni, and Mo is 3.0% or more, the residual γ content is 27 to 50% by volume, and the remainder of the residual γ content is made of a steel material having a martensitic structure. Bearing parts with excellent whitening resistance and exfoliation life. In mass%, C: 0.13 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.50 to 1.80%, P: 0.030% or less, S: 0.030 % Or less, Cr: 2.30 to 3.50%, Ni: 0.10 to 0.50%, Mo: 0.03 to 0.50% And further contains one or more selected from V: 0.01 to 0.20%, Nb: 0.01 to 0.20%, Ti: 0.01 to 0.20%, and the balance Is Si, Mn, Cr in a state in which a steel consisting of Fe and unavoidable impurities has been carburized and quenched and tempered or carbonitrided and quenched and tempered, and has a solid solution in a matrix component of 100 to 300 μm from its outermost surface. , Ni, total Mo is 3.0% or more, a further residual γ amount 27 ~50vol%, the residual γ The balance of the amount is a steel material having a martensitic structure, characterized in that it is a bearing component having an excellent whitening resistant change in flaking life.

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