JPWO2019142947A1 - Carburized bearing steel parts and steel bars for carburized bearing steel parts - Google Patents

Abstract

It has a predetermined chemical composition, has a circle equivalent diameter of 5 μm or more, contains CaO, Al2O3 and SiO2, and has an Al2O3 content of 50 mass with respect to the total mass of CaO, Al2O3 and SiO2 in an arbitrary component cross section. The number density of oxides of% or more is 3.0 pieces / cm2 or less, the Vickers hardness at a depth of 50 μm from the rolling surface is 750 or more, and the compressive residual stress of the rolling surface is 900 MPa or more, carburizing. Bearing steel parts and steel bars for carburized bearing steel parts suitable for obtaining the carburized bearing steel parts.

Description

The present disclosure relates to carburized bearing steel parts and steel bars for carburized bearing steel parts.

Bearing steel parts used in automobiles and the like have become increasingly harsh in recent years due to miniaturization of parts and low viscosity of lubricating oil in order to improve fuel efficiency. In particular, peeling may occur starting from the raised portion of the indentation peripheral edge formed by the biting of foreign matter such as abrasion powder, and the function as a bearing may be impaired. In order to prevent such a phenomenon, a bearing steel part having an improved rolling fatigue life (hereinafter referred to as a pressure resistance mark life) in the presence of indentations is desired.

Conventionally, Patent Document 1 discloses a technique of suppressing a raised portion at the periphery of an indentation by increasing the amount of retained austenite on the rolling surface in order to improve the life of the indentation. Further, Patent Document 1 states that the amount of retained austenite is in the range of 20% to 45%.

Patent Document 2 discloses that the shot peening process on a bearing steel part is softened, that is, the compression residual stress is reduced to suppress the generation of minute cracks generated during shot peening. Further, Patent Document 2 discloses that the pressure-resistant mark life is improved by suppressing the occurrence of minute cracks.

In addition, Patent Documents 3 to 5 also disclose techniques related to bearing steel parts. Specifically, it is as follows.

In Patent Document 3, the amount of AlN precipitated is limited to 0.01% or less, the equivalent circle diameter is more than 20 μm, the aspect ratio is more than 3, the sulfide density d (pieces / mm ² ), and the S content [ A skin-baked steel in which S] (mass%) satisfies d ≦ 1700 [S] +20 is disclosed. In Patent Document 3, by controlling the contents of AlN, sulfide, and S, it is possible to prevent the generation of coarse grains of hardened steel, and it is excellent in cold workability, machinability, and fatigue characteristics after carburizing and quenching. Is disclosed.

Further, in Patent Document 4, CaO-SiO ₂ system flux which does not substantially contain a fluorine source is used, and Ca is added to the molten steel after stirring the molten steel deoxidized by Al and the flux in the atmosphere. After that, a method for producing bearing steel in which molten steel is refined under reduced pressure is disclosed. Then, in Patent Document 4, a flux containing no fluorine source such as CaF ₂ is used to miniaturize inclusions in steel and at the same time reduce the number of inclusions, which is highly clean and has excellent rolling fatigue life characteristics. It is disclosed that bearing steel can be manufactured.

Further, Patent Document 5 discloses a bearing steel in which all oxide-based inclusions contained in the steel have a particle diameter of 15 μm or less and particles of 10 μm or more account for less than 2% of the total particles. Further, Patent Document 5 discloses that high strength, long life and high heat resistance are realized by controlling the particle size of oxide-based inclusions.

Patent Document 1: Japanese Patent Application Laid-Open No. 64-55423 Patent Document 2: Japanese Patent Application Laid-Open No. 2006-329319 Patent Document 3: International Publication No. WO2010-116555 Patent Document 4: Japanese Patent Application Laid-Open No. 2010-196114 Japanese Patent Application Laid-Open No. 5-140696, Japanese Patent Application Laid-Open No. 5-140696

However, in the bearing steel parts of Patent Document 1, since the increase in retained austenite reduces the surface hardness, the rolling fatigue life other than the pressure resistance mark life (that is, the internal fatigue fracture at the inclusion origin in a clean environment or seizure). (Strength against breakage) decreases. Further, the surface hardness cannot be maintained above the level of general bearing steel parts (Vickers hardness of 750 or more) generally used for automobiles.
Further, in order to further improve the pressure resistance mark life, it is necessary to apply a sufficient compressive residual stress instead of lowering the compressive residual stress as in the bearing steel parts of Patent Document 2.

The techniques relating to bearing steel parts disclosed in Patent Documents 3 to 5 are techniques relating to suppression of internal fatigue fracture starting from non-metal inclusions (that is, improvement of rolling fatigue life other than pressure resistance mark life). Therefore, no consideration is given to the pressure resistance mark life. Therefore, in the techniques related to bearing steel parts disclosed in Patent Documents 3 to 5, there is room for improvement in improving the pressure resistance mark life.

Therefore, an object of the present disclosure is a carburized bearing steel part having an excellent pressure-resistant mark life while maintaining the surface hardness equal to that of a general bearing steel part, and a carburized bearing steel part suitable for obtaining the carburized bearing steel part. To provide steel bars for use.

The above-mentioned problems include the following means.
<1>
From the surface of carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
C: 0.15-0.25%,
Si: 0.70 to 1.50%,
Mn: 0.40-1.50%,
Cr: 0.15 to 1.50%,
Mo: 0.001 to 0.150%,
S: 0.001 to 0.030%,
N: 0.004 to 0.020%,
Ca: 0.0002 to 0.0100%
Al: 0.001 to 0.010%,
O: 0 to 0.005%,
P: 0 to 0.030%,
Ni: 0 to 3.00%,
Cu: 0-1.00%,
Co: 0 to 3.00%,
W: 0 to 1.00%,
V: 0 to 0.30%,
Ti: 0 to 0.300%,
Nb: 0 to 0.300%,
B: 0 to 0.0050%
Pb: 0 to 0.50%,
Bi: 0-0.50%,
Mg: 0-0.0100%,
Zr: 0-0.0500%,
Te: 0 to 0.1000%,
Rare earth elements: 0-0.0050%,
Sn: 0-2.0%,
In: 0 to 0.50%, and the balance: Fe and impurities.
In any of the parts cross section, a circle equivalent diameter of 5μm or more, CaO, comprise _Al 2 _{O 3} and SiO _2, and the CaO, of the _Al 2 _{O 3} to the total mass of the _Al 2 _{O 3} and the SiO ₂ The number density of oxides with a content of 50% by mass or more is 3.0 pieces / cm ² or less.
The Vickers hardness at a depth of 50 μm from the rolling surface is 750 or more.
The compressive residual stress of the rolling surface is 900 MPa or more.
Carburized bearing steel parts.
<2>
From the surface of carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Ni: 0.01 to 3.00%,
Cu: 0.01-1.00%,
Co: 0.01 to 3.00%,
W: 0.01 to 1.00%,
V: 0.01 to 0.30%,
Ti: 0.001 to 0.300%,
Nb: 0.001 to 0.300%, and B: 0.0001 to 0.0050%
The carburized bearing steel component according to <1>, which contains one or more of the above.
<3>
From the surface of carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Pb: 0.01 to 0.50%,
Bi: 0.01-0.50%,
Mg: 0.0001 to 0.0100%,
Zr: 0.0001 to 0.0500%,
Te: 0.0001 to 0.1000%,
Rare earth elements: 0.0001 to 0.0050%
The carburized bearing steel component according to <1> or <2>, which contains one or more of the above.
<4>
The carburized bearing steel component according to any one of <1> to <3>, wherein the C content of the carburized layer on the rolling surface is 0.60 to 1.10% by mass.
<5>
From the surface of steel bars for carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
C: 0.15-0.25%,
Si: 0.70 to 1.50%,
Mn: 0.40-1.50%,
Cr: 0.15 to 1.50%,
Mo: 0.001 to 0.150%,
S: 0.001 to 0.030%,
N: 0.004 to 0.020%,
Ca: 0.0002 to 0.0100%
Al: 0.001 to 0.010%,
O: 0 to 0.005%,
P: 0 to 0.030%,
Ni: 0 to 3.00%,
Cu: 0-1.00%,
Co: 0 to 3.00%,
W: 0 to 1.00%,
V: 0 to 0.30%,
Ti: 0 to 0.300%,
Nb: 0 to 0.300%,
B: 0 to 0.0050%
Pb: 0 to 0.50%,
Bi: 0-0.50%,
Mg: 0-0.0100%,
Zr: 0-0.0500%,
Te: 0 to 0.1000%,
Rare earth elements: 0-0.0050%,
Sn: 0-2.0%,
In: 0 to 0.50%, and the balance: Fe and impurities.
In any steel bar cross section, a circle equivalent diameter of 5μm or more, CaO, comprise _Al 2 _{O 3} and SiO _2, and the CaO, of the _Al 2 _{O 3} to the total mass of the _Al 2 _{O 3} and the SiO ₂ The number density of oxides with a content of 50% by mass or more is 3.0 pieces / cm ² or less.
Steel bars for carburized bearing steel parts.
<6>
From the surface of steel bars for carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Ni: 0.01 to 3.00%,
Cu: 0.01-1.00%,
Co: 0.01 to 3.00%,
W: 0.01 to 1.00%,
V: 0.01 to 0.30%,
Ti: 0.001 to 0.300%,
Nb: 0.001 to 0.300%, and B: 0.0001 to 0.0050%
The steel bar for carburized bearing steel parts according to <5>, which contains one or more of the above.
<7>
From the surface of steel bars for carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Pb: 0.01 to 0.50%,
Bi: 0.01-0.50%,
Mg: 0.0001 to 0.0100%,
Zr: 0.0001 to 0.0500%,
Te: 0.0001 to 0.1000%,
Rare earth elements: 0.0001 to 0.0050%
The steel bar for carburized bearing steel parts according to <5> or <6>, which contains one or more of the above.

According to the present disclosure, a carburized bearing steel part having an excellent pressure-resistant mark life while maintaining the surface hardness equivalent to that of a general bearing steel part, and a steel bar for a carburized bearing steel part suitable for obtaining the carburized bearing steel part. Can be provided.

FIG. 1 is a schematic surface view showing a columnar rolling fatigue test piece having an external dimension of φ12 mm × 22 mm.

Hereinafter, embodiments that are an example of the present disclosure will be described.
In the present specification, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.
In addition, the numerical range when "greater than" or "less than" is added to the numerical values before and after "~" means a range in which these numerical values are not included as the lower limit value or the upper limit value.
Further, regarding the content of elements in the chemical composition, "%" means "mass%".

(Carburized bearing steel parts)
The carbonized bearing steel component according to the present embodiment (hereinafter, also simply referred to as “bearing steel component”) has a predetermined chemical component, has a circular equivalent diameter of 5 μm or more in an arbitrary component cross section, and CaO, Al ₂ O. includes ₃ and SiO _2, and CaO, with _Al 2 _{O 3} and the content of _Al 2 _{O 3} to the total mass of SiO ₂ is 50 percent by mass or more oxides (hereinafter, "equivalent circle diameter of 5μm or more and The number density of (also referred to as "oxide having an Al ₂ O ₃ content of 50% by mass or more") is 3.0 pieces / cm ² or less, and the Vickers hardness at a depth of 50 μm from the rolling surface is 750 or more. Yes, the compressive residual stress of the rolling surface is 900 MPa or more.

According to the above configuration, the bearing steel component according to the present embodiment is a bearing steel component having an excellent pressure-resistant mark life while maintaining the surface hardness at the same level as that of a general bearing steel component. The bearing steel parts according to this embodiment were found based on the following findings.

First, the present inventors carried out the following evaluation in order to realize a bearing steel component having an excellent pressure-resistant mark life while maintaining the surface hardness equal to or higher than that of a general bearing steel component. Specifically, a pressure-resistant mark life was evaluated when bearing steel materials having systematically changed chemical compositions were made into bearing steel parts by combining various processing processes. As a result, the following findings (1) and (2) were obtained.

(1) The decrease in the life of the pressure-resistant mark is caused by a crack generated from the raised surface around the indentation.
(2) Select a steel material with a circle-equivalent diameter of 5 μm or more and a small number of oxides with an Al ₂ O ₃ content of 50% by mass or more, and further apply compressive residual stress to the rolling surface of the part by shot peening. By imparting it, cracks can be suppressed and the pressure-resistant mark life can be improved.

Here, by reducing the number of oxides having a circle-equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more, the properties of minute inclusions present in the steel (for example, the base material). Adhesion with) is considered to change. As a result, it is considered that the occurrence of minute cracks generated during shot peening and cracks in the raised portion is suppressed.

In Patent Document 2, the generation of microcracks is suppressed by softening the shot peening process, that is, reducing the compressive residual stress. However, by applying normal shot peening that is not soft, bearing steel parts that do not generate minute cracks while giving sufficient compressive residual stress are realized.

Further, in order to improve the pressure-resistant mark life, a mechanism that does not use retained austenite, that is, a mechanism that utilizes the effect of compressive residual stress and the effect of suppressing minute cracks, and does not require a large amount of retained austenite, thus reducing the surface hardness. There is also the advantage of not letting it.

From the above findings, it has been found that the bearing steel component according to the present embodiment is a bearing steel component having an excellent pressure-resistant mark life while maintaining the surface hardness at the same level as that of a general bearing steel component.
Since the bearing steel parts according to the present embodiment have an excellent pressure-resistant mark life, they can be used even in an environment where foreign matter is mixed.

Hereinafter, the bearing steel parts according to the present embodiment will be described in detail.

(Chemical composition)
First, the reason for limiting the chemical composition of the steel according to the present embodiment will be described. The chemical composition of the steel described below indicates the chemical composition inside the carburized bearing steel component from a depth of 2.00 mm.

C: 0.15-0.25%
The C content affects the hardness of the non-carburized region of the bearing steel component. In order to secure the required hardness, the lower limit of the C content is set to 0.15%. On the other hand, if the C content is too large, the workability during machining is reduced, so the upper limit of the C content is set to 0.25%. The lower limit of the C content is preferably 0.17%, more preferably 0.18%. The preferred upper limit of the C content is 0.24%, more preferably 0.23%.

Si: 0.70 to 1.50%
Si is an element that is effective in deoxidizing steel and affects the composition of oxides, and is also an element that is effective in imparting strength in a high temperature environment required for bearing steel parts. If the Si content is less than 0.70%, the effect is insufficient. Further, when the Si content exceeds 1.50%, an oxide containing Si appears, which causes cracks during shot peening. For the above reasons, the Si content needs to be within the range of 0.70 to 1.50%. The lower limit of the Si content is preferably 0.75%, more preferably 0.80%. Further, the lower limit of the Si content may exceed 0.90% or 1.0%. The preferred upper limit of the Si content is 1.40%, more preferably 1.20%.

Mn: 0.40-1.50%
Mn is an element effective for imparting the required strength and hardenability to steel. If the Mn content is less than 0.40%, this effect is insufficient. If the Mn content exceeds 1.50%, the amount of retained austenite increases after carburizing and quenching, and the hardness decreases. For the above reasons, the Mn content needs to be in the range of 0.40 to 1.50%. The preferred lower limit of the Mn content is 0.45%, more preferably 0.5%. The preferred upper limit of the Mn content is 1.40%, more preferably 1.30%.

Cr: 0.15 to 1.50%
Cr is an effective element for imparting the required strength and hardenability to steel. If the Cr content is less than 0.15%, the effect is insufficient. When the Cr content exceeds 1.50%, the effect is saturated. For the above reasons, the Cr content needs to be in the range of 0.15 to 1.50%. The lower limit of the Cr content is preferably 0.18%, more preferably 0.20%. The preferred upper limit of the Cr content is 1.45%, more preferably 1.40%.

Mo: 0.001 to 0.150%
Mo is an element effective for improving the fatigue strength of steel because it suppresses segregation of P at grain boundaries in addition to imparting the necessary hardenability. If the Mo content is less than 0.001%, this effect is insufficient. When the Mo content exceeds 0.150%, the effect is saturated. For the above reasons, the Mo content needs to be in the range of 0.001 to 0.150%. The lower limit of the Mo content is preferably 0.010%, more preferably 0.020%. The preferred upper limit of the Mo content is 0.140%, more preferably 0.130%.

S: 0.001 to 0.030%
S forms MnS in the steel, thereby improving the machinability of the steel. In order to obtain a level of machinability that allows cutting of parts, an S content equivalent to that of general machine structural steel is required. For the above reasons, the S content needs to be in the range of 0.001 to 0.030%. The lower limit of the S content is preferably 0.002%, more preferably 0.003%. The preferred upper limit of the S content is 0.025%, more preferably 0.020%.

N: 0.004 to 0.020%
N is an element that is inevitably mixed, but it has a grain refinement effect by forming a compound with Al, Ti, V, Cr and the like. Therefore, it is necessary to add 0.004% or more of N. However, if the N content exceeds 0.020%, the compound becomes coarse and the crystal grain refinement effect cannot be obtained. For the above reasons, the N content needs to be in the range of 0.004 to 0.020%. The preferred lower limit of the N content is 0.0045%, more preferably 0.005%. The preferred upper limit of the N content is 0.015%, more preferably 0.012%.

Ca: 0.0002 to 0.0100%
Ca is an element that is effective in deoxidizing steel and lowers the content of Al ₂ O ₃ in the oxide. If the Ca content is less than 0.0002%, this effect is insufficient. When the Ca content exceeds 0.0100%, a large amount of coarse oxide containing Ca appears, which causes a decrease in rolling fatigue life. For the above reasons, the Ca content needs to be in the range of 0.0002 to 0.0100%. The preferred lower limit of the Ca content is 0.0003%, more preferably 0.0005%. The preferred upper limit of the Ca content is 0.0080%, more preferably 0.0060%.

Al: 0.001 to 0.010%
Al crystallizes in steel as Al ₂ O ₃ , and affects the generation of cracks generated during shot peening and cracks at the indentation peripheral ridge. Therefore, the Al content needs to be limited to 0.010% or less. The preferred upper limit of the Al content is 0.009%, more preferably 0.007%. Since the Al content is preferably low, the Al content is preferably 0%. However, the lower limit of the Al content is 0.001% because it is always mixed as an impurity in the auxiliary raw material used during production.

O: 0 to 0.005%
O is an element that affects the generation of cracks and cracks in the raised portion during shot peening because it forms an oxide in steel. The O content needs to be limited to 0.005% or less. The preferable upper limit of the O content is 0.003% or less, and more preferably 0.002%. Since it is preferable that the O content is low, the lower limit of the O content is 0%. That is, O does not have to be contained.

P: 0 to 0.030%
P segregates at the austenite grain boundaries during heating before carburizing and quenching, thereby reducing fatigue strength. Therefore, it is necessary to limit the P content to 0.030% or less. The preferred upper limit of the P content is 0.025% or less, more preferably 0.023%. Since it is preferable that the P content is low, the lower limit of the P content is 0%. That is, P does not have to be contained. However, if P is removed more than necessary, the manufacturing cost increases. Therefore, the practical lower limit of the P content is preferably 0.004%.

The bearing steel parts according to the present embodiment are made of Ni, Cu, Co, W, V, Ti, Nb, and B instead of a part of Fe in order to enhance the hardenability or the grain refinement effect. It may contain one or more selected from the group. That is, the lower limit of the content of these elements is 0%. When these elements are contained, the upper limit of the element content is the upper limit of the range described later. The content of each element is preferably more than 0% and not more than the upper limit of the range described later, and more preferably the range described later.

Ni: 0.01 to 3.00%
Ni is an effective element for imparting the required hardenability to steel. If the Ni content is less than 0.01%, this effect may be insufficient. Therefore, the Ni content is preferably 0.01% or more. If the Ni content exceeds 3.00%, the amount of retained austenite may increase after carburizing and quenching, and the hardness may decrease. For the above reasons, the upper limit of the Ni content is set to 3.00%. The upper limit of the Ni content is preferably 2.00%, more preferably 1.80%. The lower limit of the preferable Ni content is 0.10%, more preferably 0.30%.

Cu: 0.01-1.00%
Cu is an element effective for improving the hardenability of steel. If the Cu content is less than 0.01%, this effect may be insufficient. Therefore, the Cu content is preferably 0.01% or more. If the Cu content exceeds 1.00%, the hot ductility may decrease. Therefore, the upper limit of the Cu content is set to 1.00%. The upper limit of the Cu content may be 0.50%, 0.30%, or 0.20%. When Cu is contained to obtain the above-mentioned effect, the lower limit of the Cu content is preferably 0.05%, more preferably 0.10%.

Co: 0.01 to 3.00%
Co is an element effective for improving the hardenability of steel. If the Co content is less than 0.01%, this effect may be insufficient. Therefore, the Co content is preferably 0.01% or more. If the Co content exceeds 3.00%, the effect may be saturated. Therefore, the upper limit of the Co content is set to 3.00%. The upper limit of the Co content may be 1.00%, 0.50%, or 0.20%. When Co is contained to obtain the above-mentioned effect, the lower limit of the Co content is preferably 0.05%, more preferably 0.10%.

W: 0.01 to 1.00%
W is an element effective for improving the hardenability of steel. If the W content is less than 0.01%, this effect may be insufficient. Therefore, the W content is preferably 0.01% or more. If the W content exceeds 1.00%, the effect may be saturated. Therefore, the upper limit of the W content is set to 1.00%. The upper limit of the W content may be 0.50%, 0.30%, or 0.20%. When W is contained to obtain the above-mentioned effect, the lower limit of the W content is preferably 0.05%, more preferably 0.10%.

V: 0.01 to 0.30%
V is an element that forms a compound with C and N and brings about a grain refinement effect. If the V content is less than 0.01%, this effect may be insufficient. Therefore, the V content is preferably 0.01% or more. If the V content exceeds 0.30%, the compound becomes coarse and the crystal grain refinement effect may not be obtained. Therefore, the upper limit of the V content is set to 0.30%. The upper limit of the V content may be 0.20%. When V is contained to obtain the above-mentioned effect, the preferable lower limit of the V content is 0.10%, and more preferably 0.15%.

Ti: 0.001 to 0.300%
Ti is an element that produces fine TiC, (Ti, Nb) C, TiCS and other Ti-based precipitates in steel and brings about a refinement effect of crystal grains. If the Ti content is less than 0.001%, this effect may be insufficient. Therefore, the Ti content is preferably 0.001% or more. If the Ti content exceeds 0.300%, the effect may be saturated. For the above reasons, the Ti content is set to 0.300% or less. The preferred upper limit of the Ti content is 0.250%, more preferably 0.200%.

Nb: 0.001 to 0.300%
Nb is an element that produces (Ti, Nb) C in steel and brings about a grain refinement effect. If the Nb content is less than 0.001%, this effect may be insufficient. Therefore, the Nb content is preferably 0.001% or more. If the Nb content exceeds 0.300%, the effect may be saturated. For the above reasons, the Nb content is set to 0.300% or less. The preferred upper limit of the Nb content is 0.250%, more preferably 0.200%.

B: 0.0001 to 0.0050%
B has a function of suppressing the grain boundary segregation of P. In addition, B also has an effect of improving grain boundary strength and intragranular strength, and an effect of improving hardenability, and these effects improve the fatigue strength of steel. If the B content is less than 0.0001%, this effect may be insufficient. Therefore, the B content is preferably 0.0001% or more. If the B content exceeds 0.0050%, the effect may be saturated. For the above reasons, the content of B is set to 0.0050% or less. The preferred upper limit of the B content is 0.0045%, more preferably 0.0040%.

The chemical composition of the bearing steel component according to the present embodiment is further one or more selected from the group consisting of Pb, Bi, Mg, Zr, Te and rare earth element (REM) instead of a part of Fe. May be contained. That is, the lower limit of the content of these elements is 0%. When these elements are contained, the upper limit of the element content is the upper limit of the range described later. The content of each element is preferably more than 0% and not more than the upper limit of the range described later, and more preferably the range described later.

Pb: 0.01 to 0.50%
Pb is an element that improves machinability by melting and embrittlement during cutting. If the Pb content is less than 0.01%, this effect may be inadequate. Therefore, the Pb content is preferably 0.01% or more. On the other hand, if it is added excessively, the manufacturability may decrease. Therefore, the upper limit of the Pb content is 0.50%. The upper limit of the Pb content may be 0.30%, 0.20%, or 0.10%. When Pb is contained to obtain the above-mentioned effect, the preferable lower limit of the Pb content is 0.02%, more preferably 0.05%.

Bi: 0.01-0.50%
Bi is an element that improves machinability by finely dispersing sulfide. If the Bi content is less than 0.01%, this effect may be insufficient. Therefore, the Bi content is preferably 0.01% or more. On the other hand, if it is added excessively, the hot workability of the steel deteriorates, which may make hot rolling difficult. Therefore, the upper limit of the Bi content is set to 0.50%. The upper limit of the Bi content may be 0.20%, 0.10%, or 0.05%. When Bi is contained to obtain the above-mentioned effect, the preferable lower limit is 0.02%, and more preferably 0.05%.

Mg: 0.0001 to 0.0100%
Mg is a deoxidizing element and forms oxides in steel. Further, the Mg-based oxide formed by Mg tends to become a nucleus for crystallization and / or precipitation of MnS. Further, the sulfide of Mg becomes a composite sulfide of Mn and Mg, so that MnS is spheroidized. As described above, Mg is an effective element for controlling the dispersion of MnS and improving the machinability. If the Mg content is less than 0.0001%, this effect may be insufficient. Therefore, the Mg content is preferably 0.0001% or more. However, if the Mg content exceeds 0.0100%, a large amount of MgS may be produced and the machinability of the steel may decrease. Therefore, when Mg is contained to obtain the above-mentioned effect, the upper limit of the Mg content is set to 0.0100%. The preferred upper limit of the Mg content is 0.0080%, more preferably 0.0050%. The preferred lower limit of the Mg content is 0.0005%, more preferably 0.0010%.

Zr: 0.0001 to 0.0500%
Zr is a deoxidizing element and produces oxides. Furthermore, the Zr-based oxide formed by Zr tends to be the nucleus of MnS crystallization and / or precipitation. As described above, Zr is an element effective for controlling the dispersion of MnS and improving the machinability. If the Zr content is less than 0.0001%, this effect may be inadequate. Therefore, the Zr content is preferably 0.0001% or more. However, if the amount of Zr exceeds 0.0500%, the effect may be saturated. Therefore, when Zr is contained to obtain the above-mentioned effect, the upper limit of the Zr content is set to 0.0500%. The preferred upper limit of the Zr content is 0.0400%, more preferably 0.0100%. The preferred lower limit of the Zr content is 0.0005%, more preferably 0.0010%.

Te: 0.0001 to 0.1000%
Te promotes the spheroidization of MnS and thus improves the machinability of steel. If the Te content is less than 0.01%, this effect may be insufficient. Therefore, the Te content is preferably 0.01% or more. If the Te content exceeds 0.1000%, the effect may be saturated. Therefore, when Te is contained to obtain the above-mentioned effect, the upper limit of the Te content is set to 0.1000%. The preferred upper limit of the Te content is 0.0800%, more preferably 0.0600%. The upper limit of the Te content may be 0.0100%, 0.0070%, or 0.0050%. The preferred lower limit of the Te content is 0.0005%, more preferably 0.0010%.

Rare earth elements: 0.0001 to 0.0050%
Rare earth elements are elements that promote the formation of MnS by forming sulfides in steel and the sulfides becoming precipitation nuclei of MnS, and improve the machinability of steel. If the total content of rare earth elements is less than 0.0001%, this effect may be insufficient. Therefore, the total content of rare earth elements is preferably 0.0001% or more. However, if the total content of rare earth elements exceeds 0.0050%, the sulfide becomes coarse and the fatigue strength of the steel may be lowered. Therefore, when the above-mentioned effect is obtained by containing a rare earth element, the upper limit of the total content of the rare earth element is set to 0.0050%. The preferred upper limit of the total content of rare earth elements is 0.0040%, more preferably 0.0030%. The preferable lower limit of the total content of rare earth elements is 0.0005%, more preferably 0.0010%.

The rare earth elements referred to in the present specification are 15 elements from atomic number 57 lanthanum (La) to atomic number 71 lutetium (Lu) in the periodic table, plus yttrium (Y) and scandium (Sc)17. It is a general term for elements. The content of rare earth elements means the total content of one or more of these elements.

The chemical composition of the bearing steel component according to the present embodiment may further contain one or two selected from the group consisting of Sn and In instead of a part of Fe. That is, the lower limit of the content of these elements is 0%. When these elements are contained, the upper limit of the element content is the upper limit of the range described later. The content of each element is preferably more than 0% and not more than the upper limit of the range described later, and more preferably the range described later.

Sn: 0.01% to 2.0%
Sn has the effect of embrittlement of ferrite to prolong the tool life and improve the surface roughness after cutting. In order to obtain the effect stably, the Sn content is preferably 0.01% or more. Further, even if Sn is contained in excess of 2.0%, the effect is saturated. Therefore, when Sn is contained, the Sn content is set to 2.0% or less.

In: 0.01% to 0.50%
In is an element that improves machinability by melting and embrittlement during cutting. If the In content is less than 0.01%, this effect may be insufficient. Therefore, the In content is preferably 0.01% or more. On the other hand, if it is added excessively, the manufacturability may decrease. Therefore, the upper limit of the In content is 0.50%. The upper limit of the In content may be 0.30%, 0.20%, or 0.10%. When In is contained to obtain the above effect, the lower limit of the In content is more preferably 0.02% and further preferably 0.05%.

The bearing steel component according to the present embodiment contains the above-mentioned alloy component, and the balance contains Fe and impurities. When elements other than the above alloy components (for example, elements such as Sb, Ta, As, H, Hf, and Zn) are mixed into steel as impurities from raw materials and manufacturing equipment, the amount of mixing is a characteristic of steel. It is acceptable as long as it does not affect.

Here, the bearing steel component according to the present embodiment is a carburized steel bearing steel component that has been carburized. From the viewpoint of satisfying the conditions of the metallographic structure described later, the C content of the carburized layer on the rolling surface of the steel bearing steel part is preferably 0.60 to 1.10%, preferably 0.65 to 1.05%. More preferred.
Here, the C content of the carburized layer is the average C content at a position from the surface to a depth of 50 μm on the rolling surface of the steel bearing steel part.

(Metal structure)
Next, the metal structure of the bearing steel parts according to the present embodiment will be described.

The number density of oxides having a circle-equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more will be described.
In order to suppress cracks during shot peening and crack generation and propagation from the raised part of the indentation periphery, the inventors used steel materials with different types and amounts of oxides, and the relationship between oxides and pressure resistance mark life. investigated.

First, the effects of the types and amounts of oxide species that make up the oxide were examined. As a result, among the various oxide species present in the steel, the proportions of Al ₂ O ₃ , CaO, and SiO ₂ affect the pressure resistance mark life, and Al with respect to the total mass of the three oxide species. It was found that the content of ₂ O ₃ strongly correlates with the pressure resistance mark life. That is, in the _oxide, Al ₂ O 3, CaO, and also contain oxides other than SiO _2, Al ₂ O 3, CaO, and the content of _Al 2 _{O 3} to the total mass of SiO ₂ is It was found that it strongly correlates with the pressure-resistant mark life.

Next, the shape and number of oxides affecting the pressure resistance mark life were examined. As a result, it was found that the number density of oxides having a circle equivalent diameter of 5 μm or more correlates with the pressure resistance mark life. Therefore, as a result of plotting the content of Al ₂ O ₃ and the number density of oxides having a circle-equivalent diameter of 5 μm or more, which have a large effect on the pressure-resistant mark life, on the vertical and horizontal axes, the circle-equivalent diameter is obtained. A good pressure-resistant mark life is obtained in a region where the number density of oxides having an Al ₂ O ₃ content of 50% by mass or more is 3.0 pieces / cm ² or less, which is 5 μm or more, and the pressure resistance increases as it deviates from that region. It was found that the scar life was reduced.

This is due to the control of oxides having an equivalent circle diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more, and “shot peening” due to minute inclusions at a level that cannot be discriminated by an optical microscope. It is presumed that this is because "small cracks that sometimes occur" and "cracks in the raised part" can be rendered harmless.
No cracks were observed in the bearing steel parts having a circle equivalent diameter of 5 μm or more and an oxide number density of 3.0 mass% or more and an Al ₂ O ₃ content of 50 mass% or more and 3.0 pieces / cm2 or less. A good pressure-resistant mark life was obtained. Therefore, the upper limit of the number density of oxides is set to 3.0 pieces / cm ² . The preferred upper limit of the number density of oxides having an Al ₂ O ₃ content of 50% by mass or more is 2.0 pieces / cm ² , and more preferably 1.5 pieces / cm ² . Since it is preferable that no oxide is present, the lower limit is 0 pieces / cm ² .
The number density of oxides is a value measured by the method described in [Example] except for the selection of the observation field of view. As for the observation field of view, it is sufficient that the total area of the observation portion of the cut surface can be secured at 4 cm ² .

Next, the Vickers hardness at a depth of 50 μm from the rolling surface will be described.
When the surface hardness is lowered, the raised portion around the indentation is crushed, so that the pressure-resistant mark life can be improved, but the rolling fatigue life other than the pressure-resistant mark life is reduced. Therefore, in order to maintain the rolling fatigue life other than the pressure resistance mark life, the hardness of the bearing steel component level generally used for automobiles, that is, the Vickers hardness of about 750 is required. From this, the hardness of the surface, that is, the Vickers hardness at a depth of 50 μm from the rolling surface needs to be 750 or more. However, if the Vickers hardness becomes too high, it becomes brittle, so it is necessary to set the upper limit at 1050. The preferred upper limit of Vickers hardness is 1000, more preferably 950.
The Vickers hardness is a value measured by the method described in [Example] except for the cutting position. The cutting position differs depending on the shape of the part, but it may be a cross section cut perpendicular to the surface of the transfer portion.

Next, the compressive residual stress of the rolling surface will be described.
The compressive residual stress on the rolling surface has the effect of suppressing the generation of cracks from the raised portion of the indentation peripheral edge and improving the pressure resistance scar life. In order to obtain the effect, the compressive residual stress of the rolling surface needs to be 900 MPa or more. The higher the compressive residual stress of the rolling surface, the more preferable it is. However, in order to make the compressive residual stress excessively high, intense processing such as increasing the projection pressure during shot peening is required, and the shape of the part changes and the function cannot be performed. Therefore, the upper limit of the compressive residual stress of the rolling surface is 2000 MPa.
The compressive residual stress is a value measured by the method described in [Example].

Next, the metal structure of the bearing steel parts will be described.
The bearing steel parts according to the present embodiment can be obtained by, for example, carburizing, quenching and tempering.
Therefore, the metal structure of the bearing steel part is composed of, for example, a surface layer portion (that is, a carburized layer) that is carburized and has a gradient of C concentration, and a core portion that has the same C concentration as the base material before carburizing.
The metal structure of the surface layer portion (that is, the carburized layer) is exemplified by a metal structure composed of tempered martensite, retained austenite, and the balance (bainite, ferrite, cementite, etc.).
On the other hand, as the metal structure of the core portion, a metal structure composed of tempered martensite and the rest (bainite, ferrite, pearlite, etc.) can be exemplified.
The metal structure of the core portion is a metal structure inside from a depth of 2.00 mm from the surface of the steel bar for bearing steel parts.

(Steel bars for bearing steel parts)
The steel bars for carburized bearing steel parts (hereinafter, also referred to as “steel for bearing steel parts”) according to the present embodiment suitable for obtaining the bearing steel parts according to the present embodiment are as follows.
The steel bar for bearing steel parts according to the present embodiment has the same chemical composition as the bearing steel parts according to the present embodiment, has a circle equivalent diameter of 5 μm or more in an arbitrary steel bar cross section, and CaO, Al ₂ O ₃ and SiO. It comprises _2, and CaO, the number density of the _Al 2 _{O 3} and the content of _Al 2 _{O 3} to the total mass of SiO ₂ oxides of 50 mass% or more is 3.0 / cm ² or less.
The method for measuring the number density of oxides is the same as the method for measuring the number density of oxides in the bearing steel parts according to the present embodiment.

The metal structure of the steel bar for bearing steel parts according to the present embodiment mainly contains ferrite (for example, with an area ratio of 60% or more), and a metal structure consisting of pearlite, bainite, and the balance can be exemplified.
The metal structure of the steel bar for bearing steel parts is a metal structure inside from a depth of 2.00 mm from the surface of the steel bar for bearing steel parts.

(Manufacturing method of bearing steel parts)
Next, a method of manufacturing the bearing steel parts according to the present embodiment will be described.
As an example, the bearing steel part having the above metal structure may be manufactured as follows.
First, primary refining is performed in a converter using iron ore or scrap-based raw materials. Si is added to the molten steel discharged from the converter, and then Al is added to carry out the deoxidation treatment. After the deoxidization treatment, the molten steel component having the above chemical composition is adjusted by secondary refining by a ladle refining method or a refining method using a vacuum treatment device. It is preferable to continuously cast molten steel whose composition has been adjusted to form an ingot. By controlling this refining method, the number density of the oxides can be controlled. When only Al deoxidation is carried out, for example, even if Si is contained as a chemical component or SiO ₂ is contained in the flux to be added, the SiO ₂ component is not mixed in the oxide as an inclusion. This is because a reducing action acts on Si or SiO ₂ .
Here, at the time of casting, the molten steel temperature in the tundish is super-heated at 5 to 200 ° C., and electromagnetic stirring is performed in the mold.
Next, ingot rolling is performed on the ingot, the ingot is processed into a predetermined cross-sectional shape by hot rolling, and then cooled to obtain a steel bar for bearing steel parts. The cooling rate after hot rolling is preferably controlled in the range of 0.1 to 5 ° C./sec, which is the average cooling rate when the surface temperature of the steel material is between 800 ° C. and 300 ° C.
Next, the obtained steel bar for bearing steel parts is subjected to carburizing, quenching and tempering by hot forging, cold forging, machining, etc. to form a part shape in which the amount removed by polishing is added. In order to improve the efficiency of forging and machining, heat treatment such as normalizing or spheroidizing annealing may be performed during this period. Further, the carburizing and quenching may be performed by carburizing and nitriding regardless of the carburizing method such as gas carburizing and vacuum carburizing. Tempering may be carried out under reduced pressure or in a non-oxidizing atmosphere. Machining may be performed after carburizing, quenching and tempering.
Then, a shot peening process is performed on the processed product after the process. After that, polishing is performed to ensure dimensional accuracy. If the predetermined dimensional accuracy can be ensured after the shot peening process, the polishing step may be omitted. By manufacturing the bearing steel parts in this way, the above metal structure can be obtained.

Next, an example of the present disclosure will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present disclosure, and the present disclosure is based on this one condition example. It is not limited. The present disclosure may adopt various conditions as long as the gist of the present disclosure is not deviated and the object of the present disclosure is achieved.

Various ingots having the chemical components shown in Table 1 were hot-rolled to obtain steel bars. Then, the steel bar was hot forged to a diameter of 28 mm. The heating temperature before forging was 1250 ° C. Steel number 25 is JIS-defined SUJ2 for general-purpose bearing steel, and only steel number 25 has different heat treatment conditions. With respect to steel numbers other than 25, the forged product was subjected to normalizing treatment under the condition that after forging, the forged product was held at 950 ° C. for 1 hour to be completely austenitized and then allowed to cool. Steel No. 25 was heated at 960 ° C. and subjected to normalizing treatment. Next, after holding at 795 ° C. for 1.5 hours, the normalized product was spheroidized and annealed under the conditions of cooling to 650 ° C. at 12 ° C./hour and allowing it to cool.
Next, it was processed into a cylinder having a diameter of 12.2 mm × 150 mm. Then, the columnar product was held at 930 ° C. for 5 hours with an atmosphere of carbon potential of 0.8, and was subjected to gas carburizing treatment under the condition of oil quenching at 130 ° C., and then 150 ° C. It was tempered under the condition that it was held for 2 hours. Steel No. 25 was held at 830 ° C. in an argon atmosphere for 0.5 hours, quenched under the condition of oil cooling at 60 ° C., and then tempered under the condition of holding at 180 ° C. for 2 hours.

Then, according to Table 2, the obtained tempered columnar products of steel numbers 1 to 24, 26 to 33, 35 to 36 were shot peened. In addition, No. Shot peening A was assigned to Nos. 1 to 24 and 26 to 33. Shot peening B for No. 35 Shot peening C was applied to 36. No. Shot peening was not applied to 25 and 34.
In this way, a sample of the bearing steel part was obtained.

<Shot peening A>
-Shot grain: Steel round cut wire φ1.0, HV800
・ Projection pressure: 0.5 MPa
・ Coverage: 400%

<Shot peening B>
-Shot grain: Steel round cut wire φ1.0, HV800
・ Projection pressure: 0.3 MPa
・ Coverage: 200%

<Shot peening C>
-Shot grain: Steel round cut wire φ1.0, HV600
・ Projection pressure: 0.2 MPa
・ Coverage: 200%

Then, a sample of the bearing steel part was processed by polishing and finished by buffing to obtain a columnar rolling fatigue test piece having an external dimension of φ12 mm × 22 mm as shown in FIG. Then, the pressure resistance mark life was evaluated. An NTN cylindrical rolling fatigue tester was used to evaluate the pressure resistance mark life. Specifically, it is as follows.
First, hold, including the acceleration time under 46240rpm load 530kgf / mm ² 10 seconds to give prospect the position to hit the indentation in the specimen. Indentation was applied four every 90 degrees prospect with the Rockwell hardness tester position. After that, under a load of 600 kgf / mm ^2, the occurrence of peeling was detected by a vibrometer at 46240 rpm using FBK turbine ISO viscosity grade 56 manufactured by JX Nikko Nisseki Energy as the lubricating oil, and peeling was performed up to 107 times. The life was measured. The peeling life obtained at N = 10 was plotted on a Weibull diagram, and the life of 10% breakage was defined as the pressure resistance mark life. Further, as the rolling fatigue life of the non-voltage trace life, the flaking life of 10 ⁸ times in a state without imparting indentations upper limit determined by N = 2, and the average value and rolling fatigue life.

The Vickers hardness at a depth of 50 μm from the rolling surface was measured as follows. A micro Vickers hardness tester was used in accordance with JIS Z 2244: 2009 for a cross section obtained by cutting vertically in the longitudinal direction at a position approximately 7 mm from the end face, which is a position equivalent to the test execution of the columnar rolling fatigue test piece. Was measured. Specifically, under the conditions of a load of 200 g and a holding time of 10 seconds, the hardness at a depth of 50 μm from the rolling surface is measured at five points 150 μm apart from the center of the depression, and arithmetically averaged. Vickers hardness was calculated.

The compressive residual stress on the rolling surface was measured as follows. Masking was performed so that a range of 2 mm × 2 mm could be measured around a position of about 7 mm from the end face of the columnar rolling fatigue test piece. Then, for a range of 2 mm × 2 mm, the rolling surface is compressed by the 2θ · sin ² ψ method and the parallel tilt method (Iso-Inclination Method) with the collimator φ1 mm using Automate (using Cr tube) manufactured by Rigaku Denki. Residual stress was measured.

The number density of oxides having a circle-equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more was measured as follows. The columnar rolling fatigue test piece was cut perpendicularly in the longitudinal direction at positions 3, 7, 15, and 19 mm from the end face. The cut surface of each test piece was mirror-polished using diamond paste. After that, on the cut surface of each test piece, a 1 cm × 1 cm region set so that the center of the circle and the center of the square coincide with each other is observed with an optical microscope, and the positions of inclusions having a circle equivalent diameter of 5 μm or more are recorded. did. Then, the spectrum obtained from the analysis of the entire inclusion region is analyzed using an energy dispersive X-ray analyzer (EDS) mounted on a scanning electron microscope (JSM-6500F manufactured by JEOL Ltd.), and oxides and sulfurizations are analyzed. The thing and the carbonitride were judged. In the analysis, the acceleration voltage was set to 20 keV, and the measurement was performed in each region for 10 seconds. The software Analysis Station manufactured by JEOL Ltd. was used for the analysis and quantification of the spectrum.
For inclusions determined to be oxides, the mass ratio of three elements other than oxygen, Ca, Al, and Si, was determined, and the oxides produced by each of the three elements (that is, CaO, Al ₂ O ₃ and SiO _{2) were obtained.} ) To calculate the Al ₂ O ₃ content with respect to the total mass of CaO, Al ₂ O ₃ and SiO ₂ , and the oxidation in which the Al ₂ O ₃ content is 50% by mass or more. The number density was calculated by dividing the number of objects by the observation area of 4 cm ² (1 cm × 1 cm observation × total observation area of 4 visual fields).
By the same method, the "number density of oxides having an equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more" of the obtained unforged steel bar was measured.

A method for measuring the C content of the carburized layer on the rolling surface will be described. An EPMA, JXA-8200 manufactured by Nippon Denshi Co., Ltd. was used to obtain a cross section obtained by cutting the columnar rolling fatigue test piece vertically at a position approximately 7 mm from the end face in the longitudinal direction, which is a position equivalent to the test. The concentration distribution of C in the depth direction is measured at a pitch of 5 μm, and the arithmetic mean of the concentration of 50 μm from the surface on the rolling surface is taken as the measurement start point (that is, the position 5 μm from the surface is the measurement start point, and the pitch from the surface to 50 μm is 5 μm. The arithmetic mean of the concentrations measured in (1) was taken as the C content of the carburized layer. The size of the measurement point (electron beam diameter of EPMA) was φ5 μm.

Table 2 shows the number densities of oxides having a circle-equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more in the steel type of each sample (denoted as “oxide number density” in the table). The Vickers hardness (denoted as "surface hardness" in the table) at a depth of 50 μm from the rolling surface, the compressive residual stress of the rolling surface, the pressure resistance mark life, and the rolling fatigue life are shown. The C content of the carburized layer is also shown.
In the table, the notation "10 ^ X" means "10 ^X ". For example, "10 ^ 6" means "10 ⁶ ".
The underlined values in Tables 1 and 2 indicate values outside the scope of the present disclosure. The blanks in the column of chemical composition in Table 1 indicate that the element corresponding to the blanks was not intentionally added.

Disclosure example No. 1 to 24 have good pressure resistance mark life and rolling fatigue life while maintaining Vickers hardness at a depth of 50 μm from the rolling surface equal to that of general bearing steel parts (Vickers hardness 750 or more).
Comparative example No. Reference numeral 25 denotes SUJ2, which is widely used, and has a chemical component content, a number density of oxides having a circle equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more, and compression of the rolling surface. Since the residual stress was outside the specified range of the present disclosure and the carburizing treatment was not performed, both the pressure resistance mark life and the rolling fatigue life were reduced.
Comparative example No. In 26, 27, 30 to 32, the number densities of oxides having a chemical component content and a circle equivalent diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more are outside the specified range of the present disclosure. Therefore, it had only a low pressure resistance mark life.
Comparative example No. 28 and 29 have a low rolling fatigue life because the content of chemical components is outside the specified range of the present disclosure and the Vickers hardness at a depth of 50 μm from the rolling surface is low even if appropriate shot peening treatment is performed. Had only.
Comparative example No. No. 33 had only a low pressure resistance mark life because the content of the chemical component was out of the specified range of the present disclosure.
Comparative example No. Since the shot peening process was not performed in No. 34, the Vickers hardness at a depth of 50 μm from the rolling surface and the compressive residual stress of the rolling surface were out of the specified ranges of the present disclosure. Both of the lifespans have decreased.
Comparative example No. No. 35 had a low pressure-resistant mark life because the projection pressure and coverage in the shot peening process were low and the compressive residual stress of the rolling surface was out of the specified range of the present disclosure.
Comparative example No. In No. 36, the hardness, projection pressure, and coverage of shot grains in the shot peening process were low, and the Vickers hardness at a depth of 50 μm from the rolling surface and the compressive residual stress of the rolling surface were outside the specified ranges of the present disclosure. Both the scar life and the rolling fatigue life were reduced.

If the steel bars having the chemical components shown in steel numbers 1 to 24 are subjected to appropriate shot peening treatment, bearing steel parts having excellent pressure-resistant mark life while maintaining the surface hardness at the same level as general bearing steel parts can be obtained. Since it is obtained, it can be seen that the steel bar is suitable for obtaining the bearing steel part.

The entire disclosure of Japanese Patent Application No. 2018-008181 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

Claims (7)

From the surface of carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
C: 0.15-0.25%,
Si: 0.70 to 1.50%,
Mn: 0.40-1.50%,
Cr: 0.15 to 1.50%,
Mo: 0.001 to 0.150%,
S: 0.001 to 0.030%,
N: 0.004 to 0.020%,
Ca: 0.0002 to 0.0100%
Al: 0.001 to 0.010%,
O: 0 to 0.005%,
P: 0 to 0.030%,
Ni: 0 to 3.00%,
Cu: 0-1.00%,
Co: 0 to 3.00%,
W: 0 to 1.00%,
V: 0 to 0.30%,
Ti: 0 to 0.300%,
Nb: 0 to 0.300%,
B: 0 to 0.0050%
Pb: 0 to 0.50%,
Bi: 0-0.50%,
Mg: 0-0.0100%,
Zr: 0-0.0500%,
Te: 0 to 0.1000%,
Rare earth elements: 0-0.0050%,
Sn: 0-2.0%,
In: 0 to 0.50%, and the balance: Fe and impurities.
In any of the parts cross section, a circle equivalent diameter of 5μm or more, CaO, comprise _Al 2 _{O 3} and SiO _2, and the CaO, of the _Al 2 _{O 3} to the total mass of the _Al 2 _{O 3} and the SiO ₂ The number density of oxides with a content of 50% by mass or more is 3.0 pieces / cm ² or less.
The Vickers hardness at a depth of 50 μm from the rolling surface is 750 or more.
The compressive residual stress of the rolling surface is 900 MPa or more.
Carburized bearing steel parts. From the surface of carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Ni: 0.01 to 3.00%,
Cu: 0.01-1.00%,
Co: 0.01 to 3.00%,
W: 0.01 to 1.00%,
V: 0.01 to 0.30%,
Ti: 0.001 to 0.300%,
Nb: 0.001 to 0.300%, and B: 0.0001 to 0.0050%
The carburized bearing steel component according to claim 1, which contains one or more of the above. From the surface of carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Pb: 0.01 to 0.50%,
Bi: 0.01-0.50%,
Mg: 0.0001 to 0.0100%,
Zr: 0.0001 to 0.0500%,
Te: 0.0001 to 0.1000%,
Rare earth elements: 0.0001 to 0.0050%
The carburized bearing steel component according to claim 1 or 2, which contains one or more of the above. The carburized bearing steel component according to any one of claims 1 to 3, wherein the C content of the carburized layer on the rolling surface is 0.60 to 1.10% by mass. From the surface of steel bars for carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
C: 0.15-0.25%,
Si: 0.70 to 1.50%,
Mn: 0.40-1.50%,
Cr: 0.15 to 1.50%,
Mo: 0.001 to 0.150%,
S: 0.001 to 0.030%,
N: 0.004 to 0.020%,
Ca: 0.0002 to 0.0100%
Al: 0.001 to 0.010%,
O: 0 to 0.005%,
P: 0 to 0.030%,
Ni: 0 to 3.00%,
Cu: 0-1.00%,
Co: 0 to 3.00%,
W: 0 to 1.00%,
V: 0 to 0.30%,
Ti: 0 to 0.300%,
Nb: 0 to 0.300%,
B: 0 to 0.0050%
Pb: 0 to 0.50%,
Bi: 0-0.50%,
Mg: 0-0.0100%,
Zr: 0-0.0500%,
Te: 0 to 0.1000%,
Rare earth elements: 0-0.0050%,
Sn: 0-2.0%,
In: 0 to 0.50%, and the balance: Fe and impurities.
In any steel bar cross section, a circle equivalent diameter of 5μm or more, CaO, comprise _Al 2 _{O 3} and SiO _2, and the CaO, of the _Al 2 _{O 3} to the total mass of the _Al 2 _{O 3} and the SiO ₂ The number density of oxides with a content of 50% by mass or more is 3.0 pieces / cm ² or less.
Steel bars for carburized bearing steel parts. From the surface of steel bars for carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Ni: 0.01 to 3.00%,
Cu: 0.01-1.00%,
Co: 0.01 to 3.00%,
W: 0.01 to 1.00%,
V: 0.01 to 0.30%,
Ti: 0.001 to 0.300%,
Nb: 0.001 to 0.300%, and B: 0.0001 to 0.0050%
The steel bar for carburized bearing steel parts according to claim 5, which contains one or more of the above. From the surface of steel bars for carburized bearing steel parts to a depth of 2.00 mm, the internal chemical components
By mass%
Pb: 0.01 to 0.50%,
Bi: 0.01-0.50%,
Mg: 0.0001 to 0.0100%,
Zr: 0.0001 to 0.0500%,
Te: 0.0001 to 0.1000%,
Rare earth elements: 0.0001 to 0.0050%
The steel bar for carburized bearing steel parts according to claim 5 or 6, which contains one or more of the above.