KR20200102488A - Carburized bearing steel parts and rods for carburized bearing steel parts - Google Patents

Abstract

The total mass of CaO, Al ₂ O ₃ and SiO ₂ containing CaO, Al ₂ O ₃ and SiO ₂ and also containing CaO, Al ₂ O ₃ and SiO ₂ with a predetermined chemical composition and a circle equivalent diameter of 5 μm or more in an arbitrary cross section of a part Carburized bearing, wherein the number density of oxides with a content of Al ₂ O ₃ of 50% by mass or more is 3.0/cm2 or less, Vickers hardness at a depth of 50 μm from the raceway is 750 or more, and the compressive residual stress of the raceway is 900 MPa or more Steel parts and bars for carburized bearing steel parts suitable for obtaining the carburized bearing steel parts.

Description

Carburized bearing steel parts and rods for carburized bearing steel parts

The present disclosure relates to a carburized bearing steel component and a bar for a carburized bearing steel component.

For bearing steel parts used in automobiles, etc., in recent years, the harshness of the use environment has been increasing due to miniaturization of parts and low viscosity of lubricating oil in order to improve fuel efficiency. In particular, peeling occurs starting from the raised portion of the periphery of the indentation formed by the curling of foreign matter such as abrasion powder, and the function as a bearing may be impaired. In order to prevent such a phenomenon, there is a demand for a bearing steel component having an improved rolling fatigue life in the presence of an indentation (hereinafter, referred to as an internal indentation life).

Conventionally, in order to improve the indentation resistance life, patent document 1 discloses a technique for suppressing the bulging portion of the periphery of the indentation by increasing the amount of retained austenite in the raceway. In addition, in Patent Document 1, the amount of retained austenite is described in the range of 20% to 45%.

In Patent Document 2, it is disclosed to soften the shot peening process for bearing steel parts, that is, to reduce the compressive residual stress, thereby suppressing the occurrence of minute cracks occurring during shot peening. In addition, Patent Document 2 discloses that the indentation resistance life is improved by suppressing the occurrence of minute cracks.

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

In Patent Document 3, the precipitation amount of AlN is limited to 0.01% or less, and the equivalent circle diameter is more than 20 µm and the aspect ratio is more than 3, the density d (pieces/mm 2) of the sulfide and the content of S [S] (mass% ) Has been disclosed that satisfies d≤1700[S]+20. In addition, Patent Document 3 discloses that by controlling the content of AlN, sulfide, and S, the generation of coarse grains of Kiso steel is prevented, and that the cold workability, machinability, and fatigue properties after carburization quenching are excellent.

In addition, in Patent Document 4, a CaO-SiO ₂ based flux which does not contain a fluorine source substantially is used, and after stirring the molten steel and the flux deoxidized by Al in the atmosphere, Ca is added to the molten steel, Thereafter, a method for producing a bearing steel in which molten steel is refined under reduced pressure is disclosed. In addition, in Patent Document 4, by using a flux that does not contain a fluorine source such as CaF ₂ , the number of inclusions in the steel is reduced, while the number of inclusions is reduced, and a bearing steel having excellent rolling fatigue life characteristics is manufactured. What can be done is disclosed.

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

Japanese Patent Application Publication No. 64-55423 Japanese Patent Publication No. 2006-329319 International Publication No. WO2010-116555 Japanese Patent Publication No. 2010-196114 Japanese Patent Laid-Open No. Hei 5-140696

However, in the bearing steel component of Patent Document 1, since an increase in retained austenite lowers the surface hardness, rolling fatigue life other than the indentation resistance life (that is, internal fatigue failure at the origin of inclusions in a clean environment, or Strength against fracture) is lowered. In addition, the surface hardness cannot be maintained above the level (Vickers hardness 750 or more) of general bearing steel parts generally used for automobiles.

Further, in order to further improve the indentation resistance life, it is necessary not to lower the compressive residual stress as in the bearing steel component of Patent Document 2, but to provide sufficient compressive residual stress.

In addition, the technology related to bearing steel parts disclosed in Patent Documents 3 to 5 is a technology related to suppression of internal fatigue failure based on non-metallic inclusions (i.e., improvement of rolling fatigue life other than indentation life). The indentation life is not considered at all. Therefore, in the technology related to the bearing steel component disclosed in Patent Documents 3 to 5, there is room for improvement with respect to the improvement of the indentation resistance life.

Accordingly, an object of the present disclosure is to provide a carburized bearing steel component having excellent indentation resistance life while maintaining the surface hardness equal to that of a general bearing steel component, and a bar for a carburized bearing steel component suitable for obtaining the carburized bearing steel component.

The said subject includes the following means.

<1>

The internal chemical composition at a depth of 2.00 mm from the surface of the carburized bearing steel part,

In mass%,

C: 0.15 to 0.25%,

Si: 0.70 to 1.50%,

Mn: 0.40 to 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 to 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 to 0.50%,

Mg: 0 to 0.0100%,

Zr: 0 to 0.0500%,

Te: 0 to 0.1000%,

Rare earth elements: 0 to 0.0050%,

Sn: 0 to 2.0%,

In: 0 to 0.50%, and

Balance: consisting of Fe and impurities,

In an arbitrary part cross section, the equivalent circle diameter is 5 μm or more, and contains CaO, Al ₂ O ₃ and SiO ₂ , and the Al to the mass of the sum of the CaO, Al ₂ O ₃ and SiO ₂ The number density of oxides having a content of ₂ O ₃ of 50% by mass or more is 3.0 pieces/cm 2 or less,

Vickers hardness at a depth of 50㎛ from the raceway is 750 or more,

The compressive residual stress of the raceway is 900 MPa or more,

Carburized bearing steel parts.

<2>

The internal chemical composition at a depth of 2.00 mm from the surface of the carburized bearing steel part,

In mass%,

Ni: 0.01 to 3.00%,

Cu: 0.01 to 1.00%,

Co: 0.01-3.00%,

W: 0.01 to 1.00%,

V: 0.01 to 0.30%,

Ti: 0.001 to 0.300%,

Nb: 0.001-0.300% and

B: 0.0001 to 0.0050%

The carburized bearing steel component as described in <1> containing 1 type or 2 or more types of.

<3>

The internal chemical composition at a depth of 2.00 mm from the surface of the carburized bearing steel part,

In mass%,

Pb: 0.01 to 0.50%,

Bi: 0.01 to 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> containing one or two or more of.

<4>

The carburized bearing steel component according to any one of <1> to <3>, wherein the C content of the carburized layer in the raceway is 0.60 to 1.10% by mass.

<5>

The internal chemical composition at a depth of 2.00mm from the surface of the bar for carburized bearing steel parts,

In mass%,

C: 0.15 to 0.25%,

Si: 0.70 to 1.50%,

Mn: 0.40 to 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 to 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 to 0.50%,

Mg: 0 to 0.0100%,

Zr: 0 to 0.0500%,

Te: 0 to 0.1000%,

Rare earth elements: 0 to 0.0050%,

Sn: 0 to 2.0%,

In: 0 to 0.50%, and

Balance: consisting of Fe and impurities,

In any of the bars cross, the circle equivalent diameter of more than 5㎛, CaO, Al ₂ O ₃ and include SiO _2, and also the Al ₂ to the CaO, Al ₂ O ₃ and the total weight of said SiO ₂ The number density of oxides having a content of O ₃ of 50% by mass or more is 3.0 pieces/cm 2 or less,

Bar for carburizing bearing steel parts.

<6>

The internal chemical composition at a depth of 2.00mm from the surface of the bar for carburized bearing steel parts,

In mass%,

Ni: 0.01 to 3.00%,

Cu: 0.01 to 1.00%,

Co: 0.01-3.00%,

W: 0.01 to 1.00%,

V: 0.01 to 0.30%,

Ti: 0.001 to 0.300%,

Nb: 0.001-0.300% and

B: 0.0001 to 0.0050%

The steel bar for carburized bearing steel parts according to <5> containing one or two or more of.

<7>

The internal chemical composition at a depth of 2.00mm from the surface of the bar for carburized bearing steel parts,

In mass%,

Pb: 0.01 to 0.50%,

Bi: 0.01 to 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 bar for carburized bearing steel parts according to <5> or <6>, containing one or more of the following.

According to the present disclosure, it is possible to provide a carburized bearing steel component having excellent indentation resistance life while maintaining the surface hardness equal to that of a general bearing steel component level, and a bar for a carburized bearing steel component suitable for obtaining the carburized bearing steel component.

1 is a schematic surface view showing a cylindrical rolling fatigue test piece having an external dimension of φ 12 mm×22 mm.

Hereinafter, an embodiment that is an example of the present disclosure will be described.

In addition, in this specification, the numerical range displayed using "-" means a range including the numerical value described before and after "-" as a lower limit value and an upper limit value.

In addition, the numerical range in the case where "greater than" or "less than" is attached to the numerical values described before and after "to" means a range not including these numerical values as a lower limit value or an upper limit value.

In addition, about the content of an element of a chemical composition, "%" means "mass%".

(Carburized bearing steel parts)

The carburized bearing steel component (hereinafter, also simply referred to as “bearing steel component”) according to the present embodiment has a predetermined chemical composition, has a circle equivalent diameter of 5 μm or more in an arbitrary cross section of the component, and CaO, Al ₂ include O ₃ and SiO _2, and is also CaO, Al ₂ O ₃ and the content of Al ₂ O ₃ oxide is 50% or more by weight based on the total weight (hereinafter referred to as "equivalent circle diameter of SiO ₂ is 5㎛ or more, and Also referred to as an oxide having an Al ₂ O ₃ content of 50% by mass or more"), the number density is 3.0 pieces/cm 2 or less, the Vickers hardness at a depth of 50 μm from the raceway is 750 or more, and the compressive residual stress of the raceway is 900 MPa or more. .

The bearing steel component according to the present embodiment is a bearing steel component having excellent indentation resistance life while maintaining the surface hardness equal to the level of a general bearing steel component by the above configuration. The bearing steel component according to this embodiment was discovered by the following knowledge.

First, the present inventors performed the following evaluation in order to realize a bearing steel component having excellent indentation resistance life while maintaining the surface hardness equal to or higher than that of a general bearing steel component level. Specifically, for bearing steel materials whose chemical composition was systematically changed, various processing processes were combined to evaluate the indentation resistance life at a time as bearing steel parts. As a result, knowledge of the following (1) to (2) was obtained.

(1) The decrease in the life of the indentation is caused by a crack occurring from the raised surface of the periphery of the indentation.

(2) By selecting a steel material with a small number of oxides having a circle equivalent diameter of 5 μm or more and a content of Al ₂ O ₃ of 50% by mass or more, and applying a compressive residual stress to the raceway of the part by shot peening, Cracking is suppressed, and indentation resistance life can be improved.

Here, by reducing the number of oxides with an equivalent circle diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more, the properties of microscopic inclusions present in the steel (for example, adhesion to the base material) change. I think it works. As a result, it is thought that the occurrence of minute cracks and cracks in the protrusions occurring during shot peening are suppressed.

In Patent Document 2, the occurrence of microcracks is suppressed by softening the shot peening process, that is, reducing the compressive residual stress. However, by performing ordinary shot peening rather than soft, bearing steel parts that do not generate minute cracks while providing sufficient compressive residual stress are realized.

In addition, in order to improve the indentation resistance life, it is a mechanism that does not use retained austenite, that is, a mechanism that uses the effect of compressive residual stress and the effect of suppressing microcracks, and because a large amount of retained austenite is not required, the surface hardness is reduced. There is also the advantage of not letting them.

From the above findings, it has been found that the bearing steel component according to the present embodiment has an excellent bearing steel component in the indentation resistance life while maintaining the surface hardness equal to that of the general bearing steel component level.

In addition, since the bearing steel component according to the present embodiment has an excellent pressure mark life, it can also be used in an environment in which foreign matters are mixed.

Hereinafter, a bearing steel component 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. In addition, the chemical composition of the steel described below represents the internal chemical composition at a depth of 2.00 mm from the surface of the carburized bearing steel component.

C: 0.15 to 0.25%

The C content affects the hardness of the region where the bearing steel parts are not carburized. In order to ensure 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 at the time of machining decreases, so the upper limit of the C content is set to 0.25%. The preferable lower limit of the C content is 0.17%, more preferably 0.18%. The upper limit of the C content is preferably 0.24%, and more preferably 0.23%.

Si: 0.70 to 1.50%

Si is an element that is effective for deoxidation of steel and affects the composition of oxides, and is an element effective for imparting strength under a high-temperature environment required as a bearing steel component. If the Si content is less than 0.70%, the effect is insufficient. In addition, when the Si content exceeds 1.50%, an oxide containing Si appears, which causes cracking during shot peening. For the above reasons, it is necessary to make the Si content within the range of 0.70 to 1.50%. The preferred lower limit of the Si content is 0.75%, more preferably 0.80%. In addition, the lower limit of the Si content may be more than 0.90% or 1.0%. The upper limit of the Si content is preferably 1.40%, and more preferably 1.20%.

Mn: 0.40 to 1.50%

Mn is an element that is effective in imparting required strength and quenching properties to steel. If the Mn content is less than 0.40%, this effect is insufficient. Moreover, when the Mn content exceeds 1.50%, the residual austenite becomes large after carburizing and quenching, and the hardness decreases. For the above reasons, it is necessary to make the Mn content within the range of 0.40 to 1.50%. The preferred lower limit of the Mn content is 0.45%, more preferably 0.5%. A preferable upper limit of the Mn content is 1.40%, more preferably 1.30%.

Cr: 0.15 to 1.50%

Cr is an element that is effective in imparting required strength and toughness 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, it is necessary to make the Cr content within the range of 0.15 to 1.50%. The preferable lower limit of the Cr content is 0.18%, more preferably 0.20%. The upper limit of the Cr content is preferably 1.45%, and more preferably 1.40%.

Mo: 0.001 to 0.150%

Mo is an element that is effective for improving the fatigue strength of steel, since it suppresses segregation of P at grain boundaries in addition to imparting necessary quenching properties. 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, it is necessary to make the Mo content within the range of 0.001 to 0.150%. The preferred lower limit of the Mo content is 0.010%, more preferably 0.020%. The upper limit of the Mo content is preferably 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 capable of cutting parts, an S content equivalent to that of general mechanical structural steel is required. From the above reason, it is necessary to make the content of S within the range of 0.001 to 0.030%. The preferable lower limit of the S content is 0.002%, more preferably 0.003%. The upper limit of the S content is preferably 0.025%, more preferably 0.020%.

N: 0.004 to 0.020%

Although N is an element that is inevitably incorporated, it has an effect of refining grains by forming a compound such as Al, Ti, V, Cr, and the like. Therefore, it is necessary to add 0.004% or more of N. However, when the N content exceeds 0.020%, the compound becomes coarse, and the effect of refining crystal grains cannot be obtained. For the above reasons, it is necessary to make the N content within the range of 0.004 to 0.020%. The preferable lower limit of the N content is 0.0045%, more preferably 0.005%. The upper limit of the N content is preferably 0.015%, more preferably 0.012%.

Ca: 0.0002 to 0.0100%

Ca is an element that is effective for deoxidation of steel and reduces the content rate 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%, coarse oxides containing Ca appear in large quantities, resulting in a decrease in rolling fatigue life. For the above reasons, it is necessary to make the Ca content within the range of 0.0002 to 0.0100%. The preferable lower limit of the Ca content is 0.0003%, more preferably 0.0005%. The upper limit of the Ca content is preferably 0.0080%, and more preferably 0.0060%.

Al: 0.001 to 0.010%

Al is crystallized in the steel as Al ₂ O ₃ , and has an influence on cracks occurring during shot peening and cracks in the ridges around the indentations. Therefore, the Al content needs to be limited to 0.010% or less. The upper limit of the Al content is preferably 0.009%, and more preferably 0.007%. Since it is preferable that the Al content is small, the Al content is preferably 0%. However, since it is necessarily mixed as an impurity such as an auxiliary raw material used in production, the lower limit of the Al content is 0.001%.

O: 0 to 0.005%

O is an element that affects the occurrence of cracks and cracks in the raised portions during shot peening to form oxides in steel. The O content needs to be limited to 0.005% or less. The upper limit of the O content is preferably 0.003% or less, and more preferably 0.002%. Since the smaller O content is preferable, the lower limit of the O content is 0%. That is, O does not need to be contained.

P: 0 to 0.030%

P segregates at the austenite grain boundary during heating before carburization and quenching, thereby reducing the fatigue strength. Therefore, it is necessary to limit the P content to 0.030% or less. The upper limit of the P content is preferably 0.025% or less, and more preferably 0.023%. Since it is preferable that the P content is small, the lower limit of the P content is 0%. That is, it is not necessary to contain P. However, when P is removed more than necessary, manufacturing cost increases. Therefore, the practical lower limit of the P content is preferably 0.004%.

The bearing steel component according to the present embodiment is one selected from the group consisting of Ni, Cu, Co, W, V, Ti, Nb, and B, instead of a part of Fe, in order to increase the effect of quenching or refining grains. Or you may further contain 2 or more types. That is, the lower limit of the content of these elements is 0%. In the case of containing these elements, the upper limit of the content of the element is set as the upper limit of the range described later. The content of each element exceeds 0% and is preferably equal to or less than the upper limit of the range described later, and more preferably the range described later.

Ni: 0.01-3.00%

Ni is an element that is effective in imparting necessary hardening properties to steel. When the Ni content is less than 0.01%, this effect may become insufficient. Therefore, the Ni content is preferably 0.01% or more. When the Ni content exceeds 3.00%, residual austenite becomes large 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 preferred Ni content is 0.10%, more preferably 0.30%.

Cu: 0.01 to 1.00%

Cu is an element that is effective in improving the hardness of steel. When the Cu content is less than 0.01%, this effect may become insufficient. Therefore, the Cu content is preferably 0.01% or more. When the Cu content exceeds 1.00%, hot ductility may decrease. Therefore, the upper limit of the Cu content is 1.00%. The upper limit of the Cu content may be 0.50%, 0.30%, or 0.20%. When Cu is contained and the above-described effect is obtained, the preferable lower limit of the Cu content is 0.05%, more preferably 0.10%.

Co: 0.01-3.00%

Co is an element that is effective in improving the hardness of steel. If the Co content is less than 0.01%, this effect may become insufficient. Therefore, the Co content is preferably 0.01% or more. When 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 and the above-described effect is obtained, the preferred lower limit of the Co content is 0.05%, more preferably 0.10%.

W: 0.01 to 1.00%

W is an element that is effective in improving the elasticity of steel. If the W content is less than 0.01%, this effect may become insufficient. Therefore, the W content is preferably 0.01% or more. When the W content exceeds 1.00%, the effect may be saturated. Therefore, the upper limit of the W content is 1.00%. The upper limit of the W content may be 0.50%, 0.30%, or 0.20%. When W is contained and the above-described effect is obtained, 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 refining effect. If the V content is less than 0.01%, this effect may become insufficient. Therefore, the V content is preferably 0.01% or more. When the V content exceeds 0.30%, the compound becomes coarse, and the effect of refining crystal grains may not be obtained in some cases. Therefore, the upper limit of the V content is set to 0.30%. As the upper limit of the V content, it may be 0.20%. When V is contained and the above-described effect is obtained, the preferred lower limit of the V content is 0.10%, more preferably 0.15%.

Ti: 0.001 to 0.300%

Ti is an element that generates fine Ti-based precipitates such as TiC, (Ti, Nb)C, and TiCS in steel, and has an effect of refining crystal grains. If the Ti content is less than 0.001%, this effect may become insufficient. Therefore, the Ti content is preferably 0.001% or more. When the Ti content exceeds 0.300%, the effect may be saturated. From the above reasons, the content of Ti is made 0.300% or less. The upper limit of the Ti content is preferably 0.250%, and more preferably 0.200%.

Nb: 0.001 to 0.300%

Nb is an element that generates (Ti, Nb)C in steel and has a grain refining effect. If the Nb content is less than 0.001%, this effect may become insufficient. Therefore, the Nb content is preferably 0.001% or more. When the Nb content exceeds 0.300%, the effect may be saturated. From the above reasons, the content of Nb is made 0.300% or less. A preferable upper limit of the Nb content is 0.250%, more preferably 0.200%.

B: 0.0001 to 0.0050%

B has an action of suppressing the grain boundary segregation of P. In addition, B also has an effect of improving grain boundary strength and intra-particle strength, and an effect of improving quenching property, and these effects improve the fatigue strength of the steel. If the B content is less than 0.0001%, this effect may become insufficient. Therefore, 0.0001% or more of B content is preferable. When the B content exceeds 0.0050%, the effect may be saturated. From the above reasons, the content of B is made 0.0050% or less. The upper limit of the B content is preferably 0.0045%, and more preferably 0.0040%.

The chemical composition of the bearing steel part according to the present embodiment further contains one or two or more selected from the group consisting of Pb, Bi, Mg, Zr, Te, and rare earth elements (REM) instead of part of Fe. You can do it. That is, the lower limit of the content of these elements is 0%. In the case of containing these elements, the upper limit of the content of the element is set as the upper limit of the range described later. The content of each element exceeds 0% and is preferably equal to or less 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 become insufficient. Therefore, the Pb content is preferably 0.01% or more. On the other hand, when it is added excessively, the manufacturability may decrease. Therefore, the upper limit of the Pb content is set to 0.50%. The upper limit of the Pb content may be 0.30%, 0.20%, or 0.10%. When Pb is contained and the above-described effect is obtained, the preferable lower limit of the Pb content is 0.02%, more preferably 0.05%.

Bi: 0.01 to 0.50%

Bi is an element that improves machinability by fine dispersion of sulfides. If the Bi content is less than 0.01%, this effect may become insufficient. Therefore, the Bi content is preferably 0.01% or more. On the other hand, when excessively added, the hot workability of steel is deteriorated, and hot rolling may become difficult. Therefore, the upper limit of the Bi content is set to 0.50%. As the upper limit of the Bi content, it may be 0.20%, 0.10%, or 0.05%. When Bi is contained and the above-described effect is obtained, the preferable lower limit is 0.02%, 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 complex sulfide of Mn and Mg, thereby spheroidizing MnS. As described above, Mg is an effective element for controlling the dispersion of MnS and improving machinability. When the Mg content is less than 0.0001%, this effect may become insufficient. Therefore, the Mg content is preferably 0.0001% or more. However, when the Mg content exceeds 0.0100%, a large amount of MgS is produced, and the machinability of the steel may decrease. Therefore, when Mg is contained and the above-described effect is obtained, the upper limit of the Mg content is set to 0.0100%. The upper limit of the Mg content is preferably 0.0080%, and more preferably 0.0050%. The preferable lower limit of the Mg content is 0.0005%, more preferably 0.0010%.

Zr: 0.0001 to 0.0500%

Zr is a deoxidation element and produces an oxide. Further, the Zr-based oxide formed by Zr tends to become a nucleus for crystallization and/or precipitation of MnS. In this way, Zr is an effective element for controlling the dispersion of MnS and improving machinability. If the Zr content is less than 0.0001%, this effect may become insufficient. Therefore, the Zr content is preferably 0.0001% or more. However, when the Zr amount exceeds 0.0500%, the effect may be saturated. Therefore, when Zr is contained and the above-described effect is obtained, the upper limit of the Zr content is set to 0.0500%. The upper limit of the Zr content is preferably 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%

Since Te promotes the spheroidization of MnS, the machinability of steel is improved. If the Te content is less than 0.01%, this effect may become insufficient. Therefore, the Te content is preferably 0.01% or more. When the Te content exceeds 0.1000%, the effect may be saturated. Therefore, when Te is contained and the above-described effect is obtained, the upper limit of the Te content is set to 0.1000%. The upper limit of the Te content is preferably 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%

The rare earth element is an element that promotes the formation of MnS by generating sulfides in steel, and the sulfides become precipitation nuclei of MnS, and improves the machinability of steel. If the total content of the rare earth elements is less than 0.0001%, this effect may be insufficient. Therefore, the total content of the rare earth elements is preferably 0.0001% or more. However, when the total content of the rare earth elements exceeds 0.0050%, the sulfide becomes coarse and the fatigue strength of the steel may be lowered. Therefore, when the above-described effect is obtained by containing a rare earth element, the upper limit of the total content of the rare earth elements is made 0.0050%. A preferable 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 element referred to in the present specification is a generic term for 17 elements obtained by adding yttrium (Y) and scandium (Sc) to 15 elements from lanthanum (La) of atomic number 57 to lutetium (Lu) of atomic number 71 in the periodic table. The content of rare earth elements means the total content of one or two 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%. In the case of containing these elements, the upper limit of the content of the element is set as the upper limit of the range described later. The content of each element exceeds 0% and is preferably equal to or less than the upper limit of the range described later, and more preferably the range described later.

Sn: 0.01% to 2.0%

Sn embrittles ferrite, prolongs tool life, and has an effect of improving the surface roughness after cutting. In order to stably obtain the effect, the Sn content is preferably 0.01% or more. Moreover, even if it contains Sn in excess of 2.0%, the effect is saturated. Therefore, when it contains Sn, the Sn content is made 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 become insufficient. Therefore, 0.01% or more of In content is preferable. On the other hand, when it is added excessively, the manufacturability may decrease. Therefore, the upper limit of the In content is set to 0.50%. As the upper limit of the In content, it 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 still more preferably 0.05%.

The bearing steel component according to the present embodiment contains the above-described alloy component, and the balance contains Fe and impurities. When elements other than the above-described alloy components (e.g., elements such as Sb, Ta, As, H, Hf, Zn, etc.) are incorporated as impurities into the steel from raw materials and manufacturing equipment, the amount of the mixture affects the properties of the steel. It is allowed as long as it does not cause any problems.

Here, the bearing steel component according to the present embodiment is a carburized steel bearing steel component subjected to a carburization treatment. And, from the viewpoint of satisfying the conditions of the metal structure described later, the C content of the carburized layer in the raceway of the steel bearing steel component is preferably 0.60 to 1.10%, and more preferably 0.65 to 1.05%.

Here, the C content in the carburized layer is an average C content at a position from the surface to a depth of 50 µm in the raceway of the steel bearing steel component.

(Metal structure)

Next, the metal structure of the bearing steel component according to the present embodiment will be described.

The number density of oxides having a circle equivalent diameter of 5 µm or more and a content of Al ₂ O ₃ of 50 mass% or more will be described.

In order to suppress the occurrence and propagation of cracks and cracks from the ridges around the indentation during shot peening, the inventors investigated the relationship between the oxide and the indentation resistance using steel materials of different types and amounts of oxides.

First, the influence of the type and amount of the oxide species constituting the oxide was examined. As a result, while various oxide species are present in the steel, the ratio of Al ₂ O ₃ , CaO and SiO ₂ affects the indentation resistance life, and the content of Al ₂ O ₃ to the total mass of the three oxides It was found that there was a strong correlation with this indentation life. That is, even if oxides other than Al ₂ O ₃ , CaO and SiO ₂ are included in the oxide, the content rate of Al ₂ O ₃ with respect to the total mass of Al ₂ O ₃ , CaO and SiO ₂ strongly correlates with the indentation resistance life. I could see that.

Next, the shape and number of oxides exerted on the indentation life were examined. As a result, it was found that the number density of oxides having an equivalent circle diameter of 5 μm or more correlates with the indentation life. Therefore, the content rate of Al ₂ O ₃ and the number density of oxides having a circle equivalent diameter of 5 μm or more, which have a great influence on the indentation life, were plotted on the vertical and horizontal axes, respectively, and as a result, the equivalent circle diameter was 5 μm or more. In addition, it was found that a good indentation life was obtained in a region where the number density of oxides having an Al ₂ O ₃ content of 50% by mass or more was 3.0 pieces/cm 2 or less, and the indentation life was lowered as it deviated from the region.

This is accompanied by controlling an oxide having an equivalent circle diameter of 5 μm or more and an Al ₂ O ₃ content of 50% by mass or more, and “at the time of shot peening” due to minute inclusions at a level that cannot be discriminated with an optical microscope. It is presumed that this is because it is possible to detoxify the "minor cracks" and "the occurrence of cracks in the ridges".

In addition, bearing steel parts having an equivalent circle diameter of 5 µm or more and a number density of oxides of 50 mass% or more and an Al ₂ O ₃ content of 3.0 pieces/cm 2 or less do not show cracks and have good indentation resistance. Was obtained. Therefore, the upper limit of the number density of oxides was set to 3.0 pieces/cm 2. The preferable 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, more preferably 1.5 pieces/cm 2. Since it is preferable that no oxide is present, the lower limit is 0 pieces/cm 2.

In addition, the number density of oxides is a value measured by the method described in [Example] except for selection of the observation field. The observation field only needs to be able to secure a total area of 4 cm 2 of the observation portion of the cut surface.

Next, Vickers hardness at a depth of 50 µm from the raceway will be described.

If the surface hardness is lowered, the ridges around the indentations collapse, so that the indentation resistance life can be improved, but the rolling fatigue life other than the indentation resistance life is lowered. Therefore, in order to maintain rolling fatigue life other than the indentation resistance life, a hardness of about 750 in terms of the hardness of the bearing steel component generally used for automobiles, that is, the Vickers hardness is required. From this, the hardness of the surface, that is, the Vickers hardness at a depth of 50 µm from the raceway needs to be 750 or more. However, if the Vickers hardness becomes too high, it becomes brittle, so it is necessary to set 1050 as the upper limit. The upper limit of the Vickers hardness is preferably 1000, more preferably 950.

In addition, Vickers hardness is a value measured by the method described in [Example] except for the cutting position. The cutting position varies depending on the shape of the part, but a cross section cut perpendicular to the surface of the transmission unit is sufficient.

Next, the compressive residual stress of the raceway will be described.

The compressive residual stress of the raceway has an effect of suppressing the occurrence of cracks from the ridges around the indentation and improving the indentation resistance life. In order to obtain the effect, it is necessary that the compressive residual stress of the raceway is 900 MPa or more. The higher the compressive residual stress of the raceway is, the more preferable, but in order to excessively increase the compressive residual stress, severe processing such as increasing the projection pressure during shot peening is required, and the shape of the part is changed and the function cannot be achieved. Therefore, the upper limit of the compressive residual stress of the raceway is 2000 MPa.

In addition, the compressive residual stress is a value measured by the method described in [Example].

Next, the metal structure of the bearing steel component will be described.

The bearing steel component according to the present embodiment is obtained, for example, by performing carburizing quenching and tempering.

Therefore, the metal structure of the bearing steel part is composed of, for example, a surface layer portion (ie, a carburized layer) having a gradient of C concentration by carburizing, and a core portion having the same C concentration as the base material before carburization.

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 remainder (bainite, ferrite, cementite, etc.).

On the other hand, as the metal structure of the core part, a metal structure made of tempering martensite and the remainder (bainite, ferrite, pearlite, etc.) can be exemplified.

In addition, the metal structure of the core portion is a metal structure inside at a depth of 2.00 mm from the surface of the bar for bearing steel parts.

(Bar for bearing steel parts)

The bar for carburized bearing steel parts (hereinafter also referred to as "bar for bearing steel parts") according to the present embodiment suitable for obtaining the bearing steel part according to the present embodiment is as follows.

The bar for bearing steel parts according to the present embodiment has the same chemical composition as the bearing steel component according to the present embodiment, has a circle equivalent diameter of 5 μm or more in an arbitrary bar cross section, and CaO, Al ₂ O ₃ and SiO ₂ , and the number density of oxides in which the content ratio of Al ₂ O ₃ to the total mass of CaO, Al ₂ O ₃ and SiO ₂ is 50% by mass or more is 3.0 pieces/cm 2 or less.

In addition, the measuring method of the number density of oxides is the same as the measuring method of the number density of oxides in the bearing steel component according to the present embodiment.

The metal structure of the bar for bearing steel parts according to the present embodiment includes ferrite as a main body (for example, at an area ratio of 60% or more), and a metal structure comprising pearlite, bainite, and the remainder can be exemplified.

The metal structure of the bar for bearing steel parts is an internal metal structure at a depth of 2.00 mm from the surface of the bar for bearing steel parts.

(Method of manufacturing bearing steel parts)

Next, a method of manufacturing the bearing steel component according to the present embodiment will be described.

As an example, the bearing steel component having the metal structure is preferably 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 perform deoxidation treatment. After the deoxidation treatment, it is adjusted to a molten steel component having the above chemical composition by secondary refining by a ladle refining method and a refining method using a vacuum treatment device. It is recommended to continuously cast molten steel with adjusted components to form a steel ingot. By controlling this refining method, the number density of the oxides can be controlled. In addition, when only Al deoxidation is performed, for example, even if Si is included as a chemical component or SiO ₂ is included 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, during casting, the molten steel temperature in the tundish is superheated at 5 to 200°C, and electromagnetic stirring is performed in the mold.

Subsequently, the steel ingot is subjected to pulverization rolling, processed into a predetermined cross-sectional shape by hot rolling, and then cooled to obtain a bar for bearing steel parts. The cooling rate after hot rolling is preferably controlled in the range of 0.1 to 5°C/sec with the average cooling rate at the surface temperature of the steel material between 800°C and 300°C.

Next, the obtained bar for bearing steel parts is subjected to hot forging, cold forging, machining, or the like, into a part shape to which the abrasive removal powder is added, and carburizing and tempering is performed. In order to increase the efficiency of forging or machining, heat treatment such as sintering or spheroidizing annealing may be performed in between. In addition, carburizing and quenching may perform carburizing and nitriding regardless of a carburizing method such as gas carburization and vacuum carburization. Tempering may be performed under reduced pressure or in a non-oxidizing atmosphere. After carburizing, quenching, tempering, machining may be performed.

Then, a shot peening treatment is performed on the processed product. After that, polishing is performed to ensure dimensional accuracy. If a predetermined dimensional accuracy can be ensured after the shot peening treatment, the polishing step may be omitted. By manufacturing the bearing steel component in this way, the metal structure is obtained.

Example

Next, an embodiment of the present disclosure will be described, but the conditions in the embodiment are an example of a condition adopted to confirm the feasibility and effect of the present disclosure, and the present disclosure is not limited to this example. . The present disclosure can adopt various conditions as long as the object of the present disclosure is achieved without deviating from the gist of the present disclosure.

Various steel 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 No. 25 is SUJ2 of the JIS standard for general-purpose bearing steel, and steel No. 250,000 differs in heat treatment conditions. Regarding other than steel number 25, after forging, it was kept at 950°C for 1 hour to completely austenite, and then annealed treatment was performed on the forged product under conditions of standing to cool. The steel number 25 heated at 960°C and subjected to a sintering treatment. Subsequently, after holding at 795°C for 1.5 hours, cooling to 650°C under the condition of 12°C/hour and standing to cool, spheroidizing annealing was performed on the pre-prepared product.

Subsequently, it was processed into a cylinder of φ 12.2 mm × 150 mm. And, with respect to the columnar article, except for steel number 22, the gas carburization treatment was carried out at 930°C for 5 hours in an atmosphere of carbon potential 0.8 and oil quenching at 130°C, followed by 2 hours at 150°C. Tempering was performed under the condition of maintaining. Steel number 25 was kept at 830°C for 0.5 hours in an argon atmosphere, quenched under oil cooling at 60°C, and then tempered under conditions of holding at 180°C for 2 hours.

Thereafter, according to Table 2, shot peening was performed on the obtained tempered cylindrical articles of steel numbers 1 to 24, 26 to 33, and 35 to 36. In addition, shot peening A was performed for Nos. 1 to 24 and 26 to 33, short peening B was performed for No. 35, and shot peening C was performed for No. 36. For Nos. 25 and 34, shot peening was not performed.

In this way, a sample of the bearing steel component was obtained.

<Short Peening A>

·Short grain: Steel round cut wire φ1.0, HV800

·Throwing pressure: 0.5 MPa

·Coverage: 400%

<Short Peening B>

·Short grain: Steel round cut wire φ1.0, HV800

·Throwing pressure: 0.3 MPa

Coverage: 200%

<Short Peening C>

·Short grain: Steel round cut wire φ1.0, HV600

·Throwing pressure: 0.2 MPa

Coverage: 200%

Thereafter, a sample of the bearing steel component was processed by polishing, and then finished by buffing, and a cylindrical rolling fatigue test piece having an external dimension of φ12 mm×22 mm as shown in FIG. 1 was obtained. And the indentation resistance life evaluation was performed. For evaluation of the indentation resistance life, an NTN cylindrical rolling fatigue tester was used. Specifically, it is as follows.

First, under a load of 530 kgf/mm 2, the target was set at 46 240 rpm for 10 seconds including the acceleration time, and the position where the indentation on the test piece was taken was set as a target. Four indentations were applied every 90 degrees by a Rockwell hardness tester at the target set position. Thereafter, under a load of 600 kgf/mm 2, using an FBK turbine ISO viscosity grade 56 manufactured by JX Nikko Nisseki Energy as a lubricating oil, at 46 240 rpm, the occurrence of peeling was detected by a vibration meter, and the peeling life was measured with 107 times as the upper limit. I did. The peeling life obtained at N=10 was plotted on a Weibull diagram, and the life at which 10% breakage was made was referred to as the indentation life. In addition, as the rolling fatigue life other than the indentation life, the peeling life was measured at N=2 with 10 ⁸ times as the upper limit in the state where no indentation was applied, and this average value was referred to as the rolling fatigue life.

The Vickers hardness at a depth of 50 µm from the raceway was measured as follows. Test execution of a cylindrical rolling fatigue test piece A cross section obtained by cutting vertically in the longitudinal direction at a position approximately 7 mm from the end surface was measured using a Micro Vickers hardness tester according to JIS Z 2244:2009. Specifically, under conditions of a load of 200 g and a holding time of 10 seconds, a hardness of 50 µm from the raceway was measured for five points separated by 150 µm from the center-to-center distance of the concave portion, and the Vickers hardness was obtained by an additive average.

The compressive residual stress of the raceway was measured as follows. Masking was performed to measure a range of 2 mm x 2 mm centered at a position of about 7 mm from the end surface of the cylindrical rolling fatigue test piece. And, for the range of 2mm×2mm, using an Automate manufactured by Rigaku Denki (using Cr tube), using a collimator φ1mm and using the 2θ·sin ² ψ method and the Iso-Inclination Method, the compressive residual stress of the raceway Was measured.

The number density of oxides having a circle equivalent diameter of 5 µm or more and a content of Al ₂ O ₃ of 50 mass% or more was measured as follows. It was cut vertically in the longitudinal direction at positions 3, 7, 15, and 19 mm from the end face of the cylindrical rolling fatigue test piece. The cut surface of each test piece was mirror-polished using diamond paste. Then, in the cut surface of each test piece, an area of 1 cm x 1 cm set so that the center of the circle and the center of the square coincide with each other was observed with an optical microscope, and the positions of inclusions having a circle equivalent diameter of 5 µm or more were recorded. Then, using an energy dispersive X-ray analyzer (EDS) mounted on a scanning electron microscope (JSM-6500F manufactured by Nippon Denshi), the spectrum obtained from the analysis of the entire inclusion region was analyzed, and oxides, sulfides, and carbonitrides were Judgment was made. At the time of analysis, the acceleration voltage was set to 20 keV, and measured for 10 seconds in each region. For the analysis and quantification of the spectrum, Nippon Denshi Corporation software Analysis Station was used.

For inclusions determined to be oxides, the mass ratio of the three elements Ca, Al, and Si other than oxygen is calculated, and the mass ratio of the oxides (i.e., CaO, Al ₂ O ₃ and SiO ₂ ) generated by each of the three elements By converting to, the Al ₂ O ₃ content rate with respect to the total mass of CaO, Al ₂ O ₃ and SiO ₂ was calculated, and the number of oxides in which the content rate of Al ₂ O ₃ was 50% by mass or more was determined by an observation area of 4 cm 2 ( The number density was calculated by dividing by 1 cm x 1 cm observation x total observation area of 4 fields of view).

In addition, the "number density of oxides having an equivalent diameter of 5 µm or more and a content of Al ₂ O ₃ of 50 mass% or more" of the obtained steel bar before forging was measured by the same method.

A method of measuring the C content in the carburized layer of the raceway will be described. Conducting the test of the cylindrical rolling fatigue test piece For the cross section obtained by cutting vertically in the longitudinal direction at a position approximately 7 mm from the end surface, using EPMA, JXA-8200 manufactured by Nihon Denshi Co., Ltd. The concentration distribution of C was measured at a pitch of 5 µm, and the additive average of the concentration of 50 µm from the surface of the raceway (i.e., the position of 5 µm from the surface is the measurement starting point, and from the surface to 50 µm is 5 µm) The additive average of the concentration measured by pitch) was taken as the C content of the carburized layer. The size of the measuring point (EPMA electron beam diameter) was set to φ5 μm.

Table 2 shows the number density of oxides with a circle equivalent diameter of 5 μm or more and a content of Al ₂ O ₃ of 50% by mass or more (indicated as “number density of oxides” in the table), raceway Vickers hardness at a depth of 50 µm (indicated as "surface hardness" in the table), compressive residual stress of the raceway, indentation resistance life, and rolling fatigue life are shown. In addition, the C content of the carburized layer is also shown.

In addition, in the table, the notation of "10 ^X " means "10 ^X ". For example, "10^6" means "10 ⁶ ".

In addition, the underlined values in Tables 1 and 2 indicate values outside the range of the present disclosure. The blank portion of the column of the chemical composition of Table 1 indicates that the element corresponding to the blank portion is not intentionally added.

Nos. 1 to 24 of the disclosure examples have good indentation resistance and rolling fatigue life while maintaining the Vickers hardness at a depth of 50 µm from the raceway equal to the level of general bearing steel parts (Vickers hardness 750 or more).

No. 25 of the comparative example is SUJ2, which is generally used, and the number density of oxides having a chemical component content, a circle equivalent diameter of 5 μm or more, and a content of Al ₂ O ₃ of 50% by mass or more, and the compressive residual stress of the raceway are observed. Since it was outside the specified range of the disclosure and was not subjected to a carburization treatment, both the indentation resistance life and the rolling fatigue life were reduced.

Nos. 26, 27, and 30 to 32 of the comparative example had the number density 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 were outside the specified range of the present disclosure. Therefore, it had only a low indentation resistance life.

Nos. 28 and 29 of Comparative Examples had only a low rolling fatigue life because the content of the chemical component was outside the specified range of the present disclosure, and the Vickers hardness at a depth of 50 µm from the raceway was low even when an appropriate shot peening treatment was performed.

No. 33 of the comparative example had only a low indentation resistance because the content of the chemical component was outside the specified range of the present disclosure.

Since No. 34 of the comparative example was subjected to the shot peening treatment, the Vickers hardness at a depth of 50 µm from the raceway and the compressive residual stress of the raceway became out of the specified ranges of the present disclosure, and as a result, both the indentation resistance and the rolling fatigue life were reduced. .

No. 35 of the comparative example had low projection pressure and coverage in the shot peening treatment, and because the compressive residual stress of the raceway was outside the specified range of the present disclosure, it had only a low indentation resistance life.

In Comparative Example No. 36, the hardness, projection pressure, and coverage of the shot particles in the shot peening treatment were low, and the Vickers hardness at a depth of 50 µm from the raceway and the compressive residual stress of the raceway were outside the specified ranges of the present disclosure. Both indentation life and rolling fatigue life were reduced.

In addition, for steel bars having the chemical components shown in steel numbers 1 to 24, if appropriate shot peening treatment is performed, bearing steel parts having excellent indentation resistance life while maintaining the surface hardness equal to the level of general bearing steel parts can be obtained. It can be seen that it is a bar suitable for obtaining bearing steel parts.

In addition, as for the indication of Japanese Patent Application No. 2018-008181, the whole is incorporated into this specification by reference.

All documents, patent applications, and technical specifications described in this specification are specifically incorporated by reference, and are incorporated by reference in this specification to the same extent as when individually described, that individual documents, patent applications, and technical specifications are incorporated by reference.

Claims (7)

The internal chemical composition at a depth of 2.00 mm from the surface of the carburized bearing steel part,
In mass%,
C: 0.15 to 0.25%,
Si: 0.70 to 1.50%,
Mn: 0.40 to 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 to 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 to 0.50%,
Mg: 0 to 0.0100%,
Zr: 0 to 0.0500%,
Te: 0 to 0.1000%,
Rare earth elements: 0 to 0.0050%,
Sn: 0 to 2.0%,
In: 0 to 0.50%, and
Balance: consisting of Fe and impurities,
In an arbitrary part cross section, the equivalent circle diameter is 5 μm or more, contains CaO, Al ₂ O ₃ and SiO ₂ , and the Al to the mass of the sum of the CaO, Al ₂ O ₃ and SiO ₂ The number density of oxides having a content of ₂ O ₃ of 50% by mass or more is 3.0 pieces/cm 2 or less,
Vickers hardness at a depth of 50㎛ from the raceway is 750 or more,
The compressive residual stress of the raceway is 900 MPa or more,
Carburized bearing steel parts. The chemical composition of claim 1, wherein at a depth of 2.00 mm from the surface of the carburized bearing steel part,
In mass%,
Ni: 0.01 to 3.00%,
Cu: 0.01 to 1.00%,
Co: 0.01-3.00%,
W: 0.01 to 1.00%,
V: 0.01 to 0.30%,
Ti: 0.001 to 0.300%,
Nb: 0.001-0.300% and
B: 0.0001 to 0.0050%
Carburized bearing steel parts containing one or two or more of The chemical composition of claim 1 or 2, wherein at a depth of 2.00 mm from the surface of the carburized bearing steel part,
In mass%,
Pb: 0.01 to 0.50%,
Bi: 0.01 to 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%
Carburized bearing steel parts containing one or two or more of The carburized bearing steel component according to any one of claims 1 to 3, wherein the C content of the carburized layer in the raceway is 0.60 to 1.10% by mass. The internal chemical composition at a depth of 2.00mm from the surface of the bar for carburized bearing steel parts,
In mass%,
C: 0.15 to 0.25%,
Si: 0.70 to 1.50%,
Mn: 0.40 to 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 to 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 to 0.50%,
Mg: 0 to 0.0100%,
Zr: 0 to 0.0500%,
Te: 0 to 0.1000%,
Rare earth elements: 0 to 0.0050%,
Sn: 0 to 2.0%,
In: 0 to 0.50%, and
Balance: consisting of Fe and impurities,
In any of the bars cross, the circle equivalent diameter of more than 5㎛, CaO, Al ₂ O ₃ and include SiO _2, and also the Al ₂ to the CaO, Al ₂ O ₃ and the total weight of said SiO ₂ The number density of oxides having a content of O ₃ of 50% by mass or more is 3.0 pieces/cm 2 or less,
Bar for carburizing bearing steel parts. The chemical composition of claim 5, wherein at a depth of 2.00 mm from the surface of the bar for carburizing bearing steel parts,
In mass%,
Ni: 0.01 to 3.00%,
Cu: 0.01 to 1.00%,
Co: 0.01-3.00%,
W: 0.01 to 1.00%,
V: 0.01 to 0.30%,
Ti: 0.001 to 0.300%,
Nb: 0.001-0.300% and
B: 0.0001 to 0.0050%
Bar for carburized bearing steel parts containing one or two or more of The chemical composition of claim 5 or 6, wherein the internal chemical composition at a depth of 2.00 mm from the surface of the bar for carburizing bearing steel parts,
In mass%,
Pb: 0.01 to 0.50%,
Bi: 0.01 to 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%
Bar for carburized bearing steel parts containing one or two or more of

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