JP2008266683A - Method for producing rolling bearing constituting member, and rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the service life of a rolling bearing by restraining the breakage of the inner starting point. <P>SOLUTION: An inner ring 1 and an outer ring 2 are produced by using steel satisfying equation (2) in the relation of DI value indicated with equation (1) and the thickness t(mm). (1) DI=(0.2[C]+0.128)(1+0.7[Si])(1+3.45[Mn])(1+0.07[Ni]+0.27[Ni][Ni])(1+2[Cr])(1+2.5[Mo])(1+0.35[Cu]). (2) DI/t≥0.45. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a rolling bearing component.

  As a conventional technique for extending the life of a rolling bearing, a method that focuses on the hardness of the raceway surface and inclusions is mainly used. As steel used for the bearing, there are high carbon steel that can be quenched as it is to obtain sufficient surface strength, and low carbon steel (hardened steel) that is hardened by carburizing or carbonitriding. In applications where high toughness and impact strength are required, a method of hardening the surface using low carbon steel is often employed.

In Patent Document 1 below, when it is necessary to form a carbonitriding layer deeply on the raceway surface, such as a large bearing such as a steel roller support bearing, carburizing in the presence of rare earth elements, It is described that the carburizing time is shortened.
Patent Document 2 below specifies the size of the oxide inclusions in the inner ring and the number per unit area of the rolling bearing for the backup roll of the multi-high rolling mill, thereby suppressing damage to the inner ring and extending the bearing life. It is described to do.
JP 2002-256411 A JP 2004-84869 A

  A large rolling bearing with an outer diameter of 200 mm or more is formed to have a large thickness, so that the depth of the completely hardened layer due to quenching becomes insufficient, resulting in a decrease in fatigue limit and life due to incomplete quenching. Concerned. In particular, when carburized or carbonitrided, there is a residual tensile stress at the boundary (cut) between the hardened layer and the core, and therefore there is an incompletely quenched structure (bainite) that is the source of stress concentration in this part. Then, there is a possibility that destruction will occur starting from that part.

  An object of the present invention is to manufacture the inner ring, outer ring, and rolling element of a rolling bearing manufactured by processing a raw material made of steel into a predetermined shape, followed by carburizing or carbonitriding, followed by quenching and tempering. It is to extend the life of the rolling bearing by suppressing the destruction of the internal starting point.

In order to solve the above problems, the present invention provides an inner ring, an outer ring, and a rolling element of a rolling bearing by processing a raw material made of steel into a predetermined shape, followed by carburizing or carbonitriding, followed by quenching and tempering. A method for manufacturing a rolling bearing component is provided, wherein a steel satisfying the following configurations (a) and (b) is used.
Moreover, it is preferable that the average value M and the standard deviation σ of the core hardness (Vickers hardness: Hv) satisfy the following expression (3).
M-4σ ≧ 400 (3)

[Configuration (a)]
Carbon content [C] is 0.10 mass% or more and 0.20 mass% or less, Silicon content [Si] is 0.10 mass% or more and 0.50 mass% or less, and manganese content [Mn] is 0.20. Mass% or more and 0.60 mass% or less, nickel content [Ni] is 3.00 mass% or more and 5.00 mass% or less, chromium content [Cr] is 0.50 mass% or more and 1.50 mass% or less, Molybdenum content [Mo] is 0.10 mass% or more and 0.50 mass% or less, copper content [Cu] is 0.30 mass% or less, oxygen content [O] is 0.01 mass% or less, and the balance Consists of iron (Fe) and inevitable impurities.

[Configuration (b)]
The relationship between the DI value represented by the following formula (1) and the thickness t (mm) of the constituent member satisfies the following formula (2).
DI = (0.2 [C] +0.128) (1 + 0.7 [Si]) (1 + 3.45 [Mn]) (1 + 0.07 [Ni] +0.27 [Ni] [Ni]) (1 + 2 [Cr ] (1 + 2.5 [Mo]) (1 + 0.35 [Cu]) (1)
DI / t ≧ 0.45 (2)

[Configuration (a)]
The reason for limiting [C] to 0.10% by mass to 0.20% by mass is as follows.
Carbon is an element that strengthens steel by converting the structure to martensite. In the method of the present invention, the surface is hardened by carburizing or carbonitriding, but the carbon content is set to 0.10% by mass or more in order to give the core the necessary strength. However, if the carbon content exceeds 0.20 mass%, toughness and machinability become insufficient.

The reason for limiting [Si] to 0.10 mass% or more and 0.50 mass% or less is as follows.
Silicon is an element that has a function of densifying the structure after quenching and improving toughness, fatigue resistance, and hardenability. If the silicon content is less than 0.10% by mass, the action cannot be substantially obtained. However, if the silicon content exceeds 0.50% by mass, the workability (forgeability, hot workability, etc.) and machinability become insufficient.

The reason for limiting [Mn] to 0.20 mass% or more and 0.60 mass% or less is as follows.
Manganese is an element that acts as a deoxidizing agent and a desulfurizing agent during steelmaking and improves the hardenability by dissolving in a matrix. When the manganese content is less than 0.20% by mass, these effects are not substantially obtained. However, if the manganese content exceeds 0.60% by mass, the workability and machinability become insufficient.

The reason why Ni is 3.00 mass% or more and 5.00 mass% or less is as follows.
Nickel is an element having an effect of improving the hardenability of steel and the toughness after tempering. If the nickel content is less than 3.00% by mass, the effect is not substantially obtained. However, if the nickel content exceeds 5.00% by mass, workability and machinability become insufficient.

The reason for limiting [Cr] to 0.50 mass% or more and 1.50 mass% or less is as follows.
Chromium is an element that improves the hardenability and temper softening resistance by solid solution in the matrix and also has the effect of improving the rolling fatigue life. Moreover, it has the effect | action which forms fine carbide | carbonized_material and carbonitride and improves toughness. When the chromium content is less than 0.50% by mass, these effects are not substantially obtained. However, if the chromium content exceeds 1.50% by mass, a passive film is formed on the surface, which may inhibit carburization.

The reason for limiting [Mo] to 0.10 mass% or more and 0.50 mass% or less is as follows.
Molybdenum is an element that has the effect of improving the hardenability of steel and the strength and toughness after tempering. When the molybdenum content is less than 0.10% by mass, these effects cannot be substantially obtained. However, when the molybdenum content exceeds 0.50% by mass, the hardenability and machinability become insufficient.

The reason for limiting [Cu] to 0.30% by mass or less is as follows.
Copper is an element having an effect of improving hardenability and weather resistance. However, when the content exceeds 0.30 mass%, workability and toughness become insufficient. Moreover, since it is expensive, cost also becomes high.
The reason for limiting [O] to 0.01% by mass or less is as follows.
When the oxygen content exceeds 0.01% by mass, large inclusions such as SiO ₂ and Al ₂ O ₃ increase, and the rolling fatigue strength becomes insufficient.

[Configuration (b)]
By producing a rolling bearing constituent member using steel satisfying “DI / t ≧ 0.45” between the DI value represented by the formula (1) and the thickness t (mm) of the constituent member. In addition, an incompletely quenched structure (bainite) that becomes a stress concentration source hardly occurs at the boundary between the hardened layer and the core. Therefore, the internal fracture starting from the boundary is less likely to occur in the rolling bearing assembled by using the rolling bearing component produced by this method.

The present invention also manufactures a constituent member composed of an inner ring, an outer ring, and a rolling element of a rolling bearing by processing a material made of steel into a predetermined shape, followed by carburizing or carbonitriding, followed by quenching and tempering. A rolling method characterized by using a steel satisfying the above-mentioned constitutions (a) and (b), and making the local strain of the core obtained from the Hall-Williamson plot by X-ray diffraction be 0.70 or more. A method for manufacturing a bearing component is provided.
The present invention also provides a rolling bearing component obtained by the method of the present invention, wherein the local strain of the core portion determined from the Hall-Williamson plot by X-ray diffraction is 0.70 or more.

The DI value is a value indicating the hardenability of the steel. By using steel with good hardenability (steel with a large DI value), when the same size member is heat-treated under the same conditions, the local strain of the core increases and the fatigue limit becomes higher, which causes rolling. The rolling fatigue life of the bearing is improved.
Further, the local strain and “DI / t” are in a linear relationship, and the local strain of the core can be made 0.70 or more by using steel satisfying “DI / t ≧ 0.45”. When the local strain of the core part of the rolling bearing component is 0.70 or more, the rolling fatigue life of the rolling bearing is remarkably increased as compared with the case of less than 0.70.

The local strain of the core can be obtained by the following procedure. First, the half-value width β _m of the Kα ₁ intensity curve of the sample obtained by X-ray diffraction and the half-value width β _r of the Kα ₁ intensity curve of the standard sample (undistorted raw iron powder) are measured. Then, to calculate the true half width beta _s by substituting the measured values of these half-value width in relation ^{_{β s 2 = β m 2 +}} β r 2 of the true half width beta _s. Next, the local strain ε _hkl is calculated by substituting the true half-value width β _s into the Hall-Williamson plot equation shown by the following equation (4).
β _s cos θ / λ = (2ε _hkl ) sin θ / λ + (K / D _hkl ) (4)
θ is the diffraction angle, λ is the X-ray wavelength used, K is Scherrer's constant, and D _hkl is the crystal lattice size.

  According to the method for manufacturing a rolling bearing constituent member of the present invention, it is possible to extend the life of the rolling bearing by suppressing breakage of the internal starting point of the obtained members (the inner ring, outer ring, and rolling element of the rolling bearing). .

Hereinafter, embodiments of the present invention will be described.
Prepare materials made of steel having the composition shown in Table 1 below, and each material is an inner ring of a cylindrical roller bearing (inner diameter: 140 mm, outer diameter: 250 mm, width: 42 mm) having the identification number “NU228” shown in FIG. 1, each of the outer ring 2 and the cylindrical roller (rolling element) 3 was processed by an ordinary method.

Next, heat treatment was performed according to the following procedure.
First, as a carburizing treatment, after holding in an RX gas atmosphere at a temperature of 850 to 1050 ° C. for 10 to 120 hours, cooling is performed at a cooling rate of 5 to 300 ° C./min. By this carburizing treatment, the carbon content of the surface layer portion was 0.90 to 1.05% by mass, and the carburized depth was 5 to 7 mm. Next, as an annealing treatment, it is allowed to cool after being held at 600 to 700 ° C. for 1 to 5 hours. Next, as a quenching treatment, oil cooling is performed after holding at 780 to 900 ° C. for 1 to 3 hours. Next, as a tempering treatment, it is allowed to cool after being held at 150 to 240 ° C. for 2 hours.

  In the quenching, the temperature of the refrigerant and the stirring conditions are changed so that the cooling rate is the same as the cooling rate when quenching a ring having a thickness of 14.5 mm, 29.0 mm, and 45.0 mm. went. Therefore, heat treatment was previously performed on rings having a thickness of 14.5 mm, 29.0 mm, and 45.0 mm under the same conditions as described above, and the cooling rate of the core during quenching was measured. As a result, the inner ring 1, the outer ring 2, and the cylindrical roller 3 obtained at each cooling rate have the same core state as the rings having the respective thicknesses. “T” in Table 1 indicates the thickness.

A cylindrical roller bearing is assembled using the obtained inner ring, outer ring, and cylindrical roller, and a rotation test is performed under the conditions of radial load: P / C = 0.6, rotation speed: 1000 min ⁻¹ , lubricant: Ro68, The time until the inner ring 1, the outer ring 2 or the cylindrical roller 3 was broken, such as peeling, was defined as the bearing life. The life test results are as follows: Sample No. 1-7 has sample No. 1 as “1”, No. 8-14 as sample No. 8 as “1”, and No. 15-20 as sample Relative values were calculated, assuming that the life of No. 15 was “1”. The results are also shown in Table 1.

  Moreover, the raw material which consists of steel of the same composition as sample No. 1-20 is made into the test piece of thickness 14.5mm, 29.0mm, 45.0mm by 50 mm x 100 mm, and it is a carbon-proof beforehand with respect to each test piece. After preventing plating from being carburized by applying plating, each sample was heat-treated by the same method as described above. Thereby, the surface of the obtained test piece was made into the same state as a core part. And the test piece for smooth rotation bending tests with a diameter of 8 mm was cut out from the center part of each obtained test piece. Using this specimen, a rotating bending test was performed to measure the fatigue limit. The results are also shown in Table 1 below.

In addition, the Vickers hardness of the core portion was measured at a test load of 4900 N at 30 points or more in the region within 4 mm from the center of each obtained test piece (test piece before cutting for the rotational bending test), and the average value thereof (M) and standard deviation (σ) were determined. And M-4σ was calculated from these results. The results are also shown in Table 1 below.
Also, a graph summarizing these results in the relationship between “M-4σ” and the fatigue limit is shown in FIG. 2, and a graph summarizing the relationship between the fatigue limit and life for each thickness (t) is shown in FIGS. FIGS. 6 to 8 are graphs summarizing the relationship between DI / t and life for each thickness (t).

As can be seen from this result, when the thickness is 14.5 mm, Nos. 3 to 7 with DI / t of 0.45 or more and M-4σ of 385 or more have a lifetime that is more than twice that of No. 1. Obtained. When the thickness was 29.0 mm, Nos. 11 to 14 having a DI / t of 0.48 or more and an M-4σ of 424 or more had a life twice as long as that of No. 8. When the thickness was 45.0 mm, Nos. 18 to 20 having DI / t of 0.53 or more and M-4σ of 414 or more had a life more than twice that of No. 15.
Further, it can be seen from the graph of FIG. 2 that the fatigue limit increases as “M-4σ” increases. From the viewpoint of securing toughness, it is preferable to set “M-4σ” to 500 or less.

Next, a material made of steel having the composition shown in Table 2 below is prepared, and each material is a cylindrical roller bearing having an identification number “NU228” shown in FIG. 1 (inner diameter: 140 mm, outer diameter: 250 mm, width: 42 mm). ) Of the inner ring 1, outer ring 2, and cylindrical roller (rolling element) 3.
Next, heat treatment was performed by the same method as described above, and a bearing life test was performed by the same method, and a test piece was prepared and tested by the same method. Further, local strain was measured by an X-ray diffraction method using Co—Kα rays. The results are also shown in Table 2 below. The results of the life test show that the life of sample No. 21 is “1” for sample Nos. 21 to 25 and the life of sample No. 27 is “1” for Nos. 26 to 32 for each thickness (t). As for No. 33 to 38, the life of Sample No. 33 was set to “1”, and the relative values were calculated.

  Also, FIG. 9 is a graph summarizing these results for each thickness (t) in the relationship between the local strain and the DI value, and FIG. 10 is a graph summarizing the relationship between the local strain and “DI / t” in FIG. FIG. 11 shows a graph summarizing the relationship between local strain and fatigue limit, and FIG. 12 shows a graph summarizing the relationship between local strain and life.

  As can be seen from this result, when the thickness is 14.5 mm, No. 23 to 25 having DI / t of 0.53 or more and local strain of 0.70 or more are more than twice as long as No. 21. was gotten. When the thickness was 29.0 mm, Nos. 29 to 32 having a DI / t of 0.48 or more and a local strain of 0.71 or more had a life twice as long as that of No. 27. In the case where the thickness was 45.0 mm, Nos. 36 to 38 having a DI / t of 0.53 or more and a local strain of 0.72 or more had a life twice as long as that of No. 33.

  From the graph of FIG. 9, it can be seen that the greater the DI value, the greater the local distortion. It can be seen from the graph of FIG. 10 that the local distortion and “DI / t” have a linear relationship. From the graph of FIG. 11, it can be seen that the greater the local strain, the higher the fatigue limit. From the graph of FIG. 12, it can be seen that there is a large difference in the L10 life when the local strain is 0.70 or more and less than 0.70.

It is sectional drawing which shows the rolling bearing produced in embodiment. It is the graph which put together the result of the test done in the embodiment in the relation between “M-4σ” and the fatigue limit. It is the graph which put together the result (in the case of t = 14.5mm) of the test done in the embodiment in the relation between a fatigue limit and a life. It is the graph which put together the result (in the case of t = 29.0mm) of the test done in the embodiment in the relation between a fatigue limit and a life. It is the graph which put together the result (in the case of t = 45.0mm) of the test done in the embodiment in the relation between a fatigue limit and life. It is the graph which put together the result (in the case of t = 14.5mm) of the test done in the embodiment in the relation between DI / t and life. It is the graph which put together the result (in the case of t = 29.0mm) of the test done in the embodiment in the relationship between DI / t and life. It is the graph which put together the result (in the case of t = 45.0 mm) of the test done in the embodiment in the relation between DI / t and life. It is the graph which put together the result of the test done in the embodiment in the relation between local strain and DI value for every thickness (t). It is the graph which put together the result of the test done in the embodiment in the relation between local distortion and "DI / t". It is the graph which put together the result of the test done in the embodiment in the relation between local strain and fatigue limit. It is the graph which put together the result of the test done in the embodiment in the relation between local strain and life.

Explanation of symbols

1 inner ring 1a raceway surface 2 outer ring 2a raceway surface 3 cylindrical roller (rolling element)
4 Cage

Claims (5)

In a method of manufacturing a constituent member composed of an inner ring, an outer ring, and a rolling element of a rolling bearing by performing a carburizing or carbonitriding process after processing a material made of steel into a predetermined shape, followed by quenching and tempering,
Carbon content [C] is 0.10 mass% or more and 0.20 mass% or less, Silicon content [Si] is 0.10 mass% or more and 0.50 mass% or less, and manganese content [Mn] is 0.20. Mass% or more and 0.60 mass% or less, nickel content [Ni] is 3.00 mass% or more and 5.00 mass% or less, chromium content [Cr] is 0.50 mass% or more and 1.50 mass% or less, Molybdenum content [Mo] is 0.10 mass% or more and 0.50 mass% or less, copper content [Cu] is 0.30 mass% or less, oxygen content [O] is 0.01 mass% or less, and the balance Consists of iron (Fe) and inevitable impurities,
A rolling bearing constituent member characterized by using a steel having a relationship between a DI value represented by the following formula (1) and a thickness t (mm) of the constituent member satisfying the following formula (2): Production method.
DI = (0.2 [C] +0.128) (1 + 0.7 [Si]) (1 + 3.45 [Mn]) (1 + 0.07 [Ni] +0.27 [Ni] [Ni]) (1 + 2 [Cr ] (1 + 2.5 [Mo]) (1 + 0.35 [Cu]) (1)
DI / t ≧ 0.45 (2) The method for manufacturing a rolling bearing component according to claim 1, wherein the average value M and the standard deviation σ of the hardness of the core (Vickers hardness: Hv) satisfy the following expression (3).
M-4σ ≧ 400 (3) In a method of manufacturing a constituent member composed of an inner ring, an outer ring, and a rolling element of a rolling bearing by performing a carburizing or carbonitriding process after processing a material made of steel into a predetermined shape, followed by quenching and tempering,
Carbon content [C] is 0.10 mass% or more and 0.20 mass% or less, Silicon content [Si] is 0.10 mass% or more and 0.50 mass% or less, and manganese content [Mn] is 0.20. Mass% or more and 0.60 mass% or less, nickel content [Ni] is 3.00 mass% or more and 5.00 mass% or less, chromium content [Cr] is 0.50 mass% or more and 1.50 mass% or less, Molybdenum content [Mo] is 0.10 mass% or more and 0.50 mass% or less, copper content [Cu] is 0.30 mass% or less, oxygen content [O] is 0.01 mass% or less, and the balance Consists of iron (Fe) and inevitable impurities,
Using steel satisfying the following formula (2) with the relationship between the DI value represented by the following formula (1) and the thickness t (mm) of the component member, from the Hall-Williamson plot by X-ray diffraction A method for manufacturing a rolling bearing constituent member, wherein the required local strain of the core is 0.70 or more.
DI = (0.2 [C] +0.128) (1 + 0.7 [Si]) (1 + 3.45 [Mn]) (1 + 0.07 [Ni] +0.27 [Ni] [Ni]) (1 + 2 [Cr ] (1 + 2.5 [Mo]) (1 + 0.35 [Cu]) (1)
DI / t ≧ 0.45 (2)   A structural member comprising an inner ring, an outer ring, and a rolling element of a rolling bearing obtained by processing a material made of steel into a predetermined shape, followed by carburizing or carbonitriding, followed by quenching and tempering. A rolling bearing structural member obtained by the method 1 and having a core local strain of 0.70 or more determined from a Hall-Williamson plot by X-ray diffraction.   The rolling bearing provided with the inner ring | wheel, the outer ring | wheel, or rolling element obtained by the method of any one of Claims 1-3.