JP2007024260A - Rolling member and roller bearing using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling member having well-balanced workability and strength while maintaining preferable forgeability, and a roller bearing using the rolling member. <P>SOLUTION: The rolling member is formed of steel containing alloy elements of 0.5% to 0.7% C by mass, more than 0% and not less than 1.2% Si by mass, 0.2% to 1.2% Mn by mass, more than 0% and not less than 0.3% Cu by mass, more than 0% and not less than 0.20% Ni by mass, and the balance Fe with inevitable impurities. The contents of Cu and Ni fulfill the following expression (1): (1) [Cu]/[Ni]≤2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling component and a rolling bearing using the rolling component, and more particularly to a rolling component formed of carbon steel and a flanged rolling bearing using the rolling component.

  Rolling parts used for automobile undercarriage, etc., especially hub parts of hub bearings with flanges for connecting bolts, rolling parts constituting flanged rolling bearings such as constant velocity joint races, etc. Its shape is complicated. For this reason, in consideration of forgeability and workability, a medium carbon steel such as S53C is used for the rolling parts constituting the flanged rolling bearing, and the rolling contact part where high surface pressure acts on the rolling parts. Has been induction hardened. In S53C, the content of each of C, Si, Mn, P, and S is C: 0.50 to 0.56%, Si: 0.15 to 0.35%, Mn 0.60 to 0.90% , P: 0.030% or less, and S: 0.035% or less. In order to cope with resource saving, energy saving, compactness, etc. as future technological trends, especially the rolling parts as described above are required to be compact and thin, and accordingly the usage conditions of the rolling parts Is getting harsh.

Conventionally, as a countermeasure against such demands, high strength has been achieved by adding expensive alloy elements such as Cr and Mo to steel. In JP 2004-315890 A (Patent Document 1), as a rolling bearing material, C: 0.7 to 1.1 mass%, Si: 0.2 to 2.0 mass%, Mn: 0.4 -2.5% by mass, Cr: 1.6-4.0% by mass, Mo: 0.1-0.5% by mass, Al: 0.010-0.050% by mass, balance Fe and inevitable A technique using a steel material made of mechanical impurities is disclosed.
JP 2004-315890 A

  However, the addition of the above alloy elements to steel not only causes an increase in cost but also causes deterioration in forgeability and workability. Furthermore, from the viewpoint of resource saving, it is not suitable for the times and disadvantageous in terms of procurement.

  Conventionally, impurities contained in steel have caused deterioration of forgeability. Examples of impurities that deteriorate the forgeability include S, P, and Cu. Among these, S and P can be reduced to a level at which the forgeability can be made sufficiently harmless by recent progress in steelmaking technology. On the other hand, about 0.1% by mass of Cu remains unavoidably even in the case of electric furnace steel. This is because the electric furnace steel is a steel manufactured by utilizing recycled iron scrap as a resource, and therefore, the ratio of non-ferrous materials contained in the steel is higher than that of the blast furnace steel. If the scrap recycling rate is improved in the future, the residual amount of Cu is expected to increase further. Cu has a low solubility in steel, and therefore precipitates at grain boundaries and lowers the grain boundary strength. This is considered to be a factor that causes cracking during forging when dealing with forging with more complicated shapes in the future.

  As described above, the conventional rolling parts have a problem that it is difficult to balance good workability and strength while maintaining good forgeability. This problem is not limited to the rolling parts constituting the flanged rolling bearing, but is a problem common to all rolling parts.

  Accordingly, an object of the present invention is to provide a rolling component capable of maintaining a balance between good workability and strength while maintaining good forgeability, and a rolling bearing using the rolling component.

  In the rolling component of the present invention, C: 0.5% by mass or more and 0.7% by mass or less as an alloy element, Si: greater than 0 and 1.2% by mass or less, Mn: 0.2% by mass or more and 1.2% by mass % Or less, Cu: greater than 0 and 0.3 mass% or less, Ni: greater than 0 and 0.20 mass% or less, and each content of Cu and Ni satisfies the formula (1), and the balance is It is made of steel made of Fe and inevitable impurities.

[Cu] / [Ni] ≦ 2 (1)
When the present inventors add Ni to steel such that each content of Cu and Ni satisfies the formula (1), an intermetallic compound is formed by Cu, Ni, and Fe, and Cu enters the steel. It has been found that the solubility is improved. As a result, Cu is rendered harmless and no grain boundary precipitation occurs, and good forgeability can be maintained in a non-tempered state (a state in which quenching and tempering is not performed).

  In addition, the inventors of the present application use a steel in which the amounts of C, Si, and Mn are appropriately adjusted as a rolling part material, thereby maintaining good workability while maintaining good forgeability in a non-tempered state. And found that it is possible to balance strength.

  By making the content ratio of C in steel 0.5% by mass or more, when high-frequency quenching is performed on a rolling contact portion that is a portion where a high surface pressure acts on a rolling part, a high level stabilized by induction quenching is achieved. Hardness can be obtained. By making the C content in steel 0.7% by mass or less, the material hardness is unlikely to increase, so that a significant decrease in workability can be prevented. In addition, when the C content in the steel is 0.7% by mass or less, a high-temperature diffusion heat treatment for preventing component segregation and a special heat treatment such as carbide spheroidization are not required, thereby reducing manufacturing costs. be able to.

  By making the content rate of Si in steel larger than 0 and 1.2 mass% or less, it is possible to prevent a decrease in cold workability and hot workability.

  By setting the content ratio of Mn in the steel to 0.2% by mass or more, S contained in a small amount as an impurity can be combined with Mn and precipitated as MnS. Thereby, it can prevent that S segregates to a crystal grain boundary. By making the content rate of Mn in steel 1.2 mass% or less, the fall of workability and machinability can be prevented. This is because Mn is an effective element for improving the hardenability of steel, while it has the effect of increasing the hardness of the material by substituting with Fe atoms in cementite to increase the material hardness. This is because the workability and machinability deteriorate.

  Since Cu has the effect of making the generated rust amorphous and suppressing the formation of corrosion pits, the resistance of the rolling parts to stress corrosion cracking is improved when the steel contains Cu. By setting the content ratio of Cu in the steel to 0.3% by mass or less, Cu can be prevented from precipitating at grain boundaries.

  By setting the Ni content in the steel to 0.2% by mass or less, Ni is not added excessively, so that the hardness does not increase, and a decrease in machinability can be suppressed. Moreover, the hardenability in steel can be improved effectively. Furthermore, an increase in cost due to the addition of a large amount of Ni can be suppressed while ensuring good machinability and hardenability.

  Note that the strength of the steel can be increased also by normalizing and tempering, but this leads to an increase in cost due to an increase in the number of manufacturing steps. According to the present invention, it is possible to increase the strength while maintaining good forgeability in a non-tempered state, so that the cost is not increased.

  In the rolling component of the present invention, preferably, H obtained by the formula (2) from the contents of C, Si, and Mn is formed of steel satisfying the formula (3).

H = 244.8 [C] +29.1 [Si] +58.7 [Mn] +55.7 (2)
230 ≦ H ≦ 260 (3)
By setting the value of H to 230 or more, the rotational bending fatigue limit of the rolling component can be 350 MPa or more. Further, by setting the value of H to 260 or less, the hardness in the non-tempered state is not too high, and good workability can be ensured.

  The rolling bearing of the present invention includes an outer member having a rolling surface on the inner periphery, an inner member having a rolling surface facing each of the rolling surfaces, and the outer member and the inner member. A plurality of intervening rolling elements, and at least one of the outer member, the inner member, and the rolling element is constituted by the above-described rolling component.

  Thereby, it can be set as the rolling bearing with the balance of favorable workability and intensity | strength, maintaining favorable forgeability.

  In the rolling bearing according to the present invention, preferably, either the outer member or the inner member has a flange portion to be attached to the wheel.

  Since the rolling component having the flange portion has a more complicated shape than the rolling component not having the flange portion, higher forgeability and workability are required. For this reason, the rolling component of this invention is suitable.

  According to the rolling component of the present invention and the rolling bearing using the rolling component, it is possible to balance good workability and strength while maintaining good forgeability.

Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a schematic cross-sectional view showing a wheel bearing device according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of FIG.

  Referring to FIGS. 1 and 2, wheel bearing device 10 as a rolling bearing in the present embodiment rotates a rotating side member such as wheel 28 and tire 29 with respect to a fixed side member such as outer member 4. It is possible to support. The wheel bearing device 10 is a rolling bearing with a flange, and includes an outer member 4, an inner member 1, and a plurality of tapered rollers 5a and 5b as rolling elements. The outer member 4 is disposed around the inner member 1. The tapered rollers 5 a and 5 b are interposed between the inner member 1 and the outer member 4. In the present embodiment, the outer member 4, the inner member 1, and the tapered rollers 5a and 5b correspond to rolling members.

  The outer member 4 has double-row rolling surfaces 4a and 4b on the inner peripheral surface. In the present embodiment, the double-row rolling surfaces 4 a and 4 b are directly formed on the inner peripheral surface of the outer member 4.

  The inner member 1 includes a hub ring 2 and inner rings 3a and 3b. An inner ring 3 a is fitted and fixed to the hub wheel 2 at the center of the outer peripheral surface of the hub wheel 2. An inner ring 3 b is externally fitted and fixed to the hub ring 2 on the inner end side (right side in FIG. 2) of the outer peripheral surface of the hub ring 2. Thereby, the hub ring 2 and the inner rings 3a and 3b are integrated to form the inner member 1. The inner member 1 has double-row rolling surfaces 7a and 7b that face each of the double-row rolling surfaces 4a and 4b. The rolling surface formed by the rolling surfaces 4a and 4b and the rolling surfaces 7a and 7b is tapered. In the present embodiment, the double-row rolling surfaces 7a and 7b are formed on the outer peripheral surfaces of the inner rings 3a and 3b.

  The tapered rollers 5a in the first row (center portion in FIG. 2) are rotatably held by a first cage 17a and are fixed between the outer member 4 and the inner ring 3a. The tapered rollers 5b in the second row (right side in FIG. 2) are rotatably held by the second cage 17b and are fixed between the outer member 4 and the inner ring 3b. With this configuration, the inner member 1 is held rotatably with respect to the outer member 4.

  A spline hole 15 is provided at the center of the hub wheel 2, and a stem shaft 27 of a constant velocity joint can be engaged with the spline hole 15. A wheel mounting flange 8 as a flange portion is provided on the outer side in the axial direction of the hub wheel 2 (left side in FIG. 2). The wheel 28 and the tire 29 are rotatably supported on the hub wheel 2 by the hub bolt 20 fitted to the wheel mounting flange 8. The outer member 4 has a vehicle body mounting flange 9 at the axially central portion of the outer peripheral surface. The outer member 4 is fixed to a suspension device (not shown) such as a knuckle by a vehicle body mounting flange 9.

  Seal rings 19 a and 19 b are installed between both end portions of the inner peripheral surface of the outer member 4 and the central portion and inner end portion of the outer peripheral surface of the hub wheel 2. Thereby, the space in which the tapered rollers 5a and 5b are held is blocked from the outside.

  In the rolling part of the present embodiment, C: 0.5% by mass or more and 0.7% by mass or less as an alloy element, Si: greater than 0 and 1.2% by mass or less, Mn: 0.2% by mass or more. 2 mass% or less, Cu: greater than 0 and 0.3 mass% or less, Ni: greater than 0 and 0.20 mass% or less, and each content of Cu and Ni satisfies the above formula (1), And the balance is formed of steel composed of Fe and inevitable impurities, and preferably, the steel satisfying the above formula (3) where H obtained by the above formula (2) from the respective contents of C, Si, and Mn. Is formed.

  According to the rolling part of the present embodiment, Cu is rendered harmless and no grain boundary precipitation occurs, and by appropriately adjusting the amount of addition of C, Si, and Mn, good forgeability in a non-tempered state It is possible to balance good workability and strength while maintaining the above.

  Further, the wheel bearing device 10 of the present embodiment includes an outer member 4 having rolling surfaces 4a and 4b on the inner periphery, and rolling surfaces 7a and 7b facing the rolling surfaces 4a and 4b, respectively. An inner member 1 and a plurality of tapered rollers 5 a and 5 b interposed between the outer member 4 and the inner member 1 are provided. The outer member 4, the inner member 1, and the tapered rollers 5a and 5b are constituted by the above rolling parts. Thereby, it is possible to balance the good workability and strength of the rolling bearing while maintaining good forgeability.

  Furthermore, since the inward member 1 has the vehicle body attachment flange 9 for attaching to a wheel, a shape is complicated. For this reason, higher forgeability and workability are required. Therefore, the rolling component is suitable.

  In the present embodiment, the case of the wheel bearing device 10 in which the inner member 1 is provided with the wheel mounting flange 8 has been described. However, the present invention can be applied to the outer member 4 as shown in FIG. The present invention can also be applied to a wheel bearing device 10 provided with a flange 8. In FIG. 3, hard balls 5c and 5d are used as rolling elements instead of tapered rollers. For the other structures shown in FIG. 3, the same reference numerals are assigned to the same members, and the description thereof is omitted.

  Further, in the present embodiment, the wheel bearing device 10 is formed by the rolling bearing constituted by each of the first row tapered rollers 5a and the rolling bearing constituted by each of the second row tapered rollers 5b. Shown for the case. However, the rolling bearing of the present invention is not limited to such a case, and may be at least one row of rolling bearings.

  In the present embodiment, the case where the rolling bearing is a flanged rolling bearing has been described. However, the present invention is not limited to the flanged rolling bearing, and can be applied to all rolling bearings.

  Moreover, in this Embodiment, although the case where the said rolling component was used for all the outer members 4, the inner members 1, and the tapered rollers 5a and 5b was shown, the rolling bearing of this invention is such It is not limited to a case, The said rolling components should just be used for at least any one member among an outer member, an inner member, and a rolling element.

  In this example, the forgeability of the rolling component of the present invention was examined. First, based on S53C, steels to be samples A1 to A10 and samples B1 to B10 were manufactured by changing the ratio of the Cu content and the Ni content, respectively. In any steel, the contents of C, Si, and Mn are respectively C: 0.5 mass% to 0.7 mass%, larger than Si: 0 to 1.2 mass%, Mn: 0 .2% by mass or more and 1.2% by mass or less. Using these steels, cylindrical test pieces each having a diameter of 20 mm and a length of 30 mm were formed. Thereafter, in order to simulate the hardness of the non-tempered state, each of the test pieces was subjected to a heat treatment at 1200 ° C. for 1 hour and then air-cooled, and each of the samples A1 to A10, which is the product of the present invention, was a comparative product and Samples B1 to B10 were obtained.

Next, upset deformation was applied to each of Samples A1 to A10 and Samples B1 to B10 at an upsetting rate of 50% with the end faces restrained. Then, the amount of defects introduced by upsetting deformation was investigated using hydrogen as a tracer. Specifically, a cube sample having a side of 4 mm is cut out from a predetermined sampling position of the test piece before and after upsetting deformation, and a current density of 10 mA / cm ² is applied to this cube sample. Cathodic field hydrogen charge was applied for 20 hours. A 3% saline solution added with 3 g / L of ammonium thiocyanate was used as the electrolyte solution for hydrogen charging. Ten minutes after the completion of hydrogen charging, the amount of hydrogen released until the temperature was increased to 300 ° C. at 3 ° C./min was measured by a gas chromatograph. The results are shown in Table 1 and FIG. In Table 1, ΔH _d is a value obtained by subtracting the amount of hydrogen released from the test piece before upsetting deformation from the amount of hydrogen released from the test piece after upsetting deformation. As ΔH _d is larger, defects are more easily introduced by deformation.

With reference to Table 1 and FIG. 4, in samples A1 to A10 in which the value of [Cu] / [Ni] is 2.00 or less, ΔH _d is a low value of 0.00 to 0.01 wt-ppm. Yes. On the other hand, in samples B1 to B10 in which the value of [Cu] / [Ni] exceeds 2.00, ΔH _d is a high value of 0.01 to 0.12 wt-ppm. From this result, it can be seen that the rolling component of the present invention has good forgeability.

If the hardness in the non-tempered state that is air-cooled after forging is too low, sufficient fatigue strength cannot be obtained. In the future, when the rolling parts use conditions become severe and a large load repeatedly acts on the non-quenched hardened part, the rolling bending fatigue limit (10 ⁷ times fatigue strength) of the rolling parts is 350 MPa or more. It is desirable to be. Here, it is conventionally known that a relational expression of σ _wb = 1.54 × H holds between the rotational bending fatigue limit σ _wb (MPa) and the hardness H (HV). According to this relational expression, the hardness in the non-tempered state is required to be 230 HV or more. On the other hand, if the hardness in the non-tempered state is too high, good workability cannot be obtained when performing complicated cutting or drilling thereafter. Specifically, it is desirable that it is 260 HV or less.

  Therefore, in this example, the conditions to be satisfied by the steel having the hardness H of 230HV ≦ H ≦ 260HV were examined. First, steels to be samples C1 to C9 and samples D1 to D7 were manufactured by changing the contents of C, Si, and Mn, respectively. In any steel, the contents of Cu and Ni were 0.09 mass% or more and 0.11 mass% or less, respectively, so that [Cu] / [Ni] ≦ 2 was satisfied. Each of these cylindrical steel test pieces having a diameter of 30 mm and a length of 30 mm was formed using these steels. Thereafter, in order to simulate the hardness of the non-tempered state, each of the test pieces was heat-treated at 1200 ° C. for 1 hour and then air-cooled to obtain each of Samples C1 to C9 and Samples D1 to D7 which are the products of the present invention. It was.

  Next, for each of Samples C1 to C9 and Samples D1 to D7, hardness H (measured hardness) near the center of the sample was measured. The results are shown in Table 2.

  With reference to Table 2, hardness H changed with the difference in each content of C, Si, and Mn. The hardness H of each of the samples C1 to C9 was 230 HV or more and 260 HV or less, while the hardness H of each of the samples D1 to D7 was out of this range.

Subsequently, a multiple regression analysis was performed with hardness H as a target variable and contents of C, Si, and Mn as dependent variables. As a result, the above equation (2) was obtained. Table 2 shows the hardness H _est (predicted hardness) obtained by substituting the contents of C, Si, and Mn for each of Samples C1 to C9 and Samples D1 to D7 into the above equation (2). Further, FIG. 5 shows the relationship between the hardness H (measured hardness) and the hardness H _est (predicted hardness). Referring to Table 2 and FIG. 5, there is a linear correlation between hardness H (measured hardness) and hardness H _est (predicted hardness), which are almost the same value. For this reason, the hardness after forging can be accurately predicted based on the contents of C, Si, and Mn using the above formula (2). Therefore, not only the contents of C, Si, and Mn in this example, but also C, Si, and Mn such that the hardness H _est (predicted hardness) calculated by the above equation (2) is 230 HV or more and 260 HV or less. It can be said that any steel with a content of

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is suitable for rolling parts formed of carbon steel and flanged rolling bearings using the rolling parts.

It is a schematic sectional drawing which shows the wheel bearing apparatus in one embodiment of this invention. It is a principal part enlarged view of FIG. It is a schematic sectional drawing which shows the modification of the wheel bearing apparatus in one embodiment of this invention. It is a diagram showing the relationship between the [Cu] / [Ni] and [Delta] H _d in the first embodiment of the present invention. It is a figure which shows the relationship between hardness H (measured hardness) and hardness _Hest (predicted hardness).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Inner member, 2 Hub wheel, 3a, 3b Inner ring, 4 Outer member, 4a, 4b, 7a, 7b Rolling surface, 5a, 5b Tapered roller, 5c, 5d Steel ball, 8 Wheel mounting flange, 9 Body mounting Flange, 10 wheel bearing device, 15 spline hole, 17a, 17b cage, 19a, 19b seal ring, 20 hub bolt, 27 stem shaft, 28 wheel, 29 tire.

Claims (4)

As alloy elements, C: 0.5% by mass or more and 0.7% by mass or less, Si: larger than 0 and 1.2% by mass or less, Mn: 0.2% by mass or more and 1.2% by mass or less, Cu: larger than 0 Steel containing 0.3% by mass or less, Ni: greater than 0 and 0.20% by mass or less, each of Cu and Ni satisfying the formula (1), and the balance being Fe and inevitable impurities Rolling parts characterized by being formed by
[Cu] / [Ni] ≦ 2 (1) The rolling part according to claim 1, wherein H obtained from the content of each of C, Si, and Mn by formula (2) is formed of steel that satisfies formula (3).
H = 244.8 [C] +29.1 [Si] +58.7 [Mn] +55.7 (2)
230 ≦ H ≦ 260 (3) An outer member having a rolling surface on the inner periphery;
An inner member having a rolling surface facing each of the rolling surfaces;
A plurality of rolling elements interposed between the outer member and the inner member;
A rolling bearing in which at least one of the outer member, the inner member, and the rolling element is constituted by the rolling component according to claim 1.   4. The rolling bearing according to claim 3, wherein either the outer member or the inner member has a flange portion to be attached to a wheel.

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