JP2007197773A - Rolling bearing, hub unit bearing, and manufacturing method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily manufacture an inner member and an outer member of a hub unit bearing, and an outer race and an inner race with a flange integrated therewith in a cold working manner while ensuring the strength of the flange and the performance as a rolling bearing. <P>SOLUTION: A rolling bearing and a hub unit bearing is formed of a material after annealing a steel material having the composition consisting of, by mass, ≥0.20% and ≤0.45% carbon (C), ≥0.10% and ≤1.20% chromium (Cr), ≤0.50% silicon (Si), ≤1.50% manganese (Mn), and the balance iron (Fe) with inevitable impurities. This material is cold-worked in a substantially final shape, and nitrided so that the total content of carbon and nitrogen of a surface layer part is ≥0.50%, and the hardness of the surface layer part is ≥Hv260. Then, a raceway surface is hardened, and subjected to the finishing process such as grinding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling bearing in which a flange is integrally formed with an outer ring or an inner ring, and a hub unit bearing (an inner ring raceway is formed on an outer peripheral surface of a hub for fitting an axle, and a flange for fixing a wheel side member is formed on the hub. The present invention relates to an integrated inner member, an outer member in which a flange for fixing a vehicle body side member is formed integrally with an outer ring, and a bearing provided with rolling elements.

In recent years, in order to improve the fuel efficiency of automobiles, unitization of wheel support bearings for the purpose of weight reduction has been advanced. FIG. 1 is a cross-sectional view showing an example of a unitized wheel support bearing (hub unit bearing). This unit includes an inner member 1, an inner ring 10, an outer member 2, a ball (rolling element) 3, and a cage 4, and has two rows of tracks on which the balls 3 roll.
The inner member 1 is formed by integrating an inner ring 11 having a track 11a, a hub 12 into which an axle is fitted, and a flange 13 for fixing the wheel side member 8. The inner ring 10 has a raceway 10a and is externally fitted into a recess 14 provided at the end of the inner member 1 opposite to the flange 13. These tracks 11a and 11b form two rows of inner ring tracks.

The outer member 2 is formed integrally with an outer ring 21 having two rows of raceways 21a and 21b and a flange 22 in which a bolt hole 22a for fixing a vehicle suspension device (vehicle body side member) is formed.
An inner member (an inner ring with a flange and a hub) 1 and an outer member (an outer ring with a flange) 2 having such a complicated shape are conventionally made of medium carbon steel (such as S35C) containing about 0.5% by mass of carbon. After the material is processed into a predetermined shape by hot forging, the surface layer portion of the raceway surface is hardened by induction hardening, and then turning, drilling, grinding, and the like are performed.

In recent years, for the purpose of reducing the manufacturing cost, it has been proposed that these members have a substantially final shape by cold working using a steel pipe or a steel plate (see Patent Documents 1 to 4 below).
JP 2003-25803 A Japanese Patent No. 3352226 JP-A-9-151950 JP 7-317777 A

  When manufacturing the inner member and outer member of the hub unit bearing, it is processed with a material made of medium carbon steel having a carbon content of 0.50 to 0.55 mass% in order to obtain a substantially final shape by cold working. The nature is bad. On the other hand, when a material made of low carbon steel having a carbon content of 0.20 to 0.45 mass% is used, the cold workability is improved, but the strength of the flange and the performance as a rolling bearing are lowered. .

  The present invention facilitates cold working of the inner and outer members of such a hub unit bearing and the outer ring and inner ring integrated with the flange while ensuring the strength of the flange and the performance as a rolling bearing. An object is to enable manufacture.

  In order to solve the above-described problems, in the present invention, an inner member of a hub unit bearing (an inner ring raceway is formed on an outer peripheral surface of a hub for fitting an axle, and a flange for fixing a wheel side member is integrated with the hub. Member), an outer member of the hub unit bearing (a member in which a flange for fixing a vehicle body side member is formed integrally with the outer ring), an outer ring with a flange in which the flange is formed integrally with the outer ring, and a flange is formed integrally with the inner ring. A flanged inner ring is produced by the following method.

  First, the carbon (C) content is 0.20% by mass or more and 0.45% by mass or less, the chromium (Cr) content is 0.10% by mass or more and 1.20% by mass or less, and silicon (Si) is contained. The rate is 0.50% by mass or less, the content of manganese (Mn) is 1.50% by mass or less, and the balance is made of a steel material that is iron (Fe) and inevitable impurity elements, and after the annealing treatment is performed Use material. This material is made into a substantially final shape by cold working and then subjected to nitriding treatment so that the total content of carbon and nitrogen in the surface layer portion is 0.50% by mass or more, and the hardness of the surface layer portion is Hv 260 or more. And Next, after the raceway surface is quenched and hardened, a finishing process such as grinding is performed.

  According to this method, the inner and outer members of the hub unit bearing, the outer ring and the inner ring in which the flange is integrated are easily manufactured by cold working while ensuring the strength of the flange and the performance as a rolling bearing. be able to. Therefore, the hub unit bearing having the inner member and / or the outer member obtained by this method and the rolling bearing having the outer ring and / or inner ring in which the flange is integrated can be obtained at low cost, and the flange The durability is excellent and the performance as a rolling bearing is excellent.

Below, the reason for each numerical limitation will be described.
[Carbon content of steel material constituting the material: 0.20 mass% to 0.45 mass%]
When the carbon content exceeds 0.45% by mass, the cold workability of the material is lowered. Further, cracks are likely to occur in the flange. Preferably it is 0.40 mass% or less. This is described in detail in [Embodiments of the Invention] below.
On the other hand, when the carbon content is less than 0.20% by mass, the time required for the nitriding treatment to make the total content of carbon and nitrogen in the surface layer part 0.50% by mass or more becomes longer, and the production cost is increased. Get higher.

[Chromium content of steel material: 0.10 mass% or more and 1.20 mass% or less]
Chromium (Cr) is a carbide forming element and improves the hardness of steel. It also has the effect of improving hardenability. If the chromium content is less than 0.10% by mass, these effects cannot be substantially obtained.
On the other hand, chromium has an effect of strengthening ferrite, and when the chromium content exceeds 1.20% by mass, cold workability is lowered.

[Silicon content of steel material: 0.50% by mass or less]
If the content of silicon (Si) exceeds 0.50% by mass, the solid solution dissolves in ferrite and the deformation resistance increases, and the cold workability decreases. Preferably it is 0.40 mass% or less, More preferably, it is 0.35 mass% or less.
In addition, since the improvement effect of a rolling fatigue life is acquired by presence of silicon, it is preferable to contain 0.1 mass% or more.

[Manganese content of steel material: 1.50% by mass or less]
When the content of manganese (Mn) exceeds 1.50% by mass, the solid solution dissolves in ferrite and deformation resistance increases, and cold workability decreases. Preferably it is 0.90 mass% or less.
In addition, since manganese is added as a deoxidizer during steelmaking and has an effect of improving hardenability, it is preferable to contain 0.30% by mass or more.
Molybdenum (Mo) also has the effect of improving the hardenability, but if added excessively, the cold workability is lowered, so it is preferable to contain molybdenum in the range of 0.20% by mass or less. .

[Total content of carbon and nitrogen in the surface layer portion [C + N]: 0.50% by mass or more]
This is described in detail in [Embodiments of the Invention] below. Further, in order to suppress the generation of ferrite as an initial precipitate and reduce the time required for the nitriding treatment, the [C + N] of the surface layer portion is preferably 1.20% by mass or less, and 0.80% by mass. More preferably, it is more preferably 0.60% by mass or less.

[Hardness of surface layer portion not quenched: Hv 260 or more]
By setting the hardness of the surface layer portion to Hv 260 or more, the flange strength is sufficient. However, in the case of the inner member of the hub unit bearing (inner ring with flange and hub), the inner ring (reference numeral 10 in FIG. 1) of another member is fixed to the tip of the hub (reference numeral 12 in FIG. 1) by “caulking”, so that it is good. In order to obtain excellent “caulking” performance, Hv is preferably 500 or less.

  In addition, in the method of the present invention, after forming a substantially final shape by cold working, nitriding treatment, quenching hardening of the raceway surface, and finishing work are performed, like a hot forged product using the conventional product S53C, There is no need to drill bolt holes after nitriding. Therefore, the surface layer portion that is not quenched can be made harder than Hv260.

  According to the method of the present invention, the inner member and the outer member of the hub unit bearing, the outer ring and the inner ring in which the flange is integrated can be easily processed by cold working while ensuring the strength of the flange and the performance as a rolling bearing. Since it can be manufactured, a hub unit bearing and a rolling bearing excellent in durability and performance as a rolling bearing can be obtained at low cost.

Hereinafter, embodiments of the present invention will be described.
Spheroidizing annealing was performed on a plate material (steel plate having a thickness of 9 mm) made of steel No. A to R shown in Table 1 below. Moreover, the steel plate after annealing was cut out into the shape of the test piece, and hardness (HRB: Rockwell B hardness) was measured. Moreover, the steel plate after annealing is cut out into a disk shape having a diameter of 150 mm, and after the steps (a) to (e) shown in FIG. Individual pieces were produced, and the number of cracks in the flange 13 was examined. In addition, the deformation resistance was measured at the time of press forming to obtain the state shown in FIG.

  These test results are also shown in Table 1. Moreover, the graph which put together these results is shown in FIG. FIG. 3 is a graph showing the relationship between the carbon content of steel and the deformation resistance. FIG. 4 is a graph showing the relationship between the carbon content of steel and the crack occurrence rate of the flange.

[Method for producing molded product 50]
The code | symbol 5 of Fig.2 (a) shows the disk-shaped raw material obtained by cutting out the steel plate after annealing. By deep-drawing the material 5, as shown in FIG. 2 (b), an intermediate molded product 51 having a cylindrical shape with a round bottom and having a flange at the opening is obtained.

Next, as shown in FIG. 2 (c), the bottom of the intermediate molded product 51 is punched out round by piercing to open a hole 52. Reference numeral 53 denotes a portion removed by the piercing process.
Next, press molding is performed using a male mold and a female mold to obtain a substantially final shape. As a result, as shown in FIG. 2 (d), a recess 14 is formed on the outer peripheral surface to fit the flange 13, the inner ring raceway 11 a, and the inner ring of another member, and the inner peripheral surface is formed into the inner shape 12 a of the hub 12.

  Next, as shown in FIG. 2E, a piercing process and a trimming process are performed to form bolt holes 13a and thin portions 13b in the flange 13. Reference numeral 54 denotes a portion removed in the piercing process, and reference numeral 55 denotes a portion removed in the trimming process. Thereby, the molded product 50 having the substantially final shape of the inner member 1 is obtained.

  As can be seen from the graph of FIG. 3, the higher the carbon content of the steel used, the higher the deformation resistance, so the cold workability is excellent. In particular, when the carbon content is 0.40 mass% or less, the deformation resistance can be 750 MPa or less. On the other hand, as can be seen from the graph of FIG. 4, when the carbon content exceeds 0.45 mass%, the flange is cracked.

  Next, it is the molded product 50 shown in FIG. 2 (e) obtained by the above-described method, and is a sample (No. 1-9 shown in Table 2 below) formed of a material made of steels A to G, L. ) Was prepared. And about the sample of No. 1-6, after performing the nitriding process by the following method, induction hardening with respect to the track surface was performed by the following method. The samples No. 7 to 9 were subjected to induction hardening on the raceway surface without performing nitriding treatment.

  Next, finishing such as grinding was performed to finish the inner member 1 in FIG. The inner member 1 of No. 1 to 9 thus obtained, the outer member 2 and the inner ring 10 made by the same method using the same steel as the inner member 1 of No. 1, and a normal heat treatment made of SUJ2. The hub unit bearing shown in FIG. 1 was assembled using the balls 3 and the cage 4 made of synthetic resin, and a rolling life test and a flange strength test were performed by the following methods. Moreover, before these tests, the hardness (Hv) of the flange of the inner member 1 and the total content [C + N] of carbon and nitrogen in the surface layer portion were measured.

  These results are also shown in Table 2 below. Moreover, the graph which put together these results is shown in FIG. FIG. 5 is a graph showing the relationship between the total content of carbon and nitrogen [C + N] and rolling life (relative value) in the surface layer portion. FIG. 6 is a graph showing the relationship between the carbon content of the steel constituting the material and the flange strength (relative value).

〔Nitriding treatment〕
After being held at 570 ° C. for 3 to 10 hours in a gas containing ammonia gas as a main component, it is cooled at a cooling rate of 50 ° C./min or more.
[Rolling life test]
The hub unit bearings of No. 1 to 9 are attached to the rotation testing machine, and a radial load of 7000 N and an axial load of 5000 N are applied to the flange 13 of the inner member 1 and fitted to the hub 12 of the inner member 1 at a rotational speed of 300 min ^−1. The shaft was rotated. The vibration generated in the inner member 1 and the outer member 2 during the rotation was measured, and the occurrence of flaking was detected from the vibration measurement value. Then, the number of rotations until the occurrence of flaking was detected was examined, and this was regarded as the rolling life, and the relative value was calculated with the value of No. 7 being “1”.

[Flange strength test]
50 hub unit bearings No. 1 to 9 were prepared. Each hub unit bearing is attached to a rotation testing machine, an axial load of 6000 N and a predetermined radial load are applied to the flange 13 of the inner member 1, and a shaft fitted to the hub 12 of the inner member 1 is rotated at a rotational speed of 400 min ^−1. Rotated for hours. Thereafter, it was examined whether or not a crack occurred at the base portion of the flange 13 with respect to the hub 12.
This test was carried out by changing the radial load from 5000 N to 9600 N for the hub unit bearings prepared for each sample number. And the minimum value of the radial load which a crack generate | occur | produces for every sample No. was investigated, this was made into flange strength, and the relative value which set the value of No. 7 to "1" was computed.

  As can be seen from the graph of FIG. 5, the higher the surface layer portion [C + N], the longer the rolling life, and the surface layer portion [C + N] includes No. 1 to 6 inner members 1 of 0.50 mass% or more. In addition, the life of the hub unit bearing is equal to or longer than that of the hub unit bearing having the inner member 1 of No. 7 which is a conventional product. Moreover, as can be seen from the graph of FIG. 6, the inner members 1 of Nos. 1 to 6 in which the carbon content of the steel constituting the material is 0.20% by mass or more and 0.45% by mass or less are conventional Nos. The flange strength is higher than that of the inner member 1 in FIG.

  In this embodiment, the hub unit bearing shown in FIG. 1 is described. However, since the inner member 1 of this hub unit bearing is included in the flanged inner ring and the outer member 2 is a flanged outer ring, this embodiment is This corresponds to all embodiments of the present invention according to claims 1 to 4.

It is sectional drawing which shows an example of the shape of a hub unit bearing. It is a figure explaining the manufacturing method of the inner member of the hub unit bearing employ | adopted by embodiment. It is a graph which shows the relationship between the carbon content rate and deformation resistance of steel. It is a graph which shows the relationship between the carbon content rate of steel, and the crack generation rate of a flange. It is a graph which shows the relationship between the total content rate [C + N] of carbon and nitrogen of a surface layer part, and a rolling lifetime (relative value). It is a graph which shows the relationship between the carbon content rate of the steel which makes a raw material, and flange strength (relative value).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner member 10 Inner ring 10a Inner ring track 11a Inner ring track 11 Inner ring 12 Hub 12a Inner shape of hub 13 Flange 13a Flange bolt hole 13b Thin wall portion of flange 14 Recessed portion for fitting inner ring 2 Outer member 21 Outer ring 21a Track groove 21b Track groove 22a Suspension groove Bolt hole for fixing the device (vehicle body side member) 22 Flange 3 Ball (rolling element)
4 Cage 5 Material 50 Molded product having substantially final shape of inner member 51 Intermediate molded product 52 Hole 8 Wheel side member

Claims (4)

A method of manufacturing a rolling bearing comprising a flanged outer ring in which a flange is integrally formed with an outer ring, or a flanged inner ring in which a flange is integrally formed with an inner ring,
The flanged outer ring or flanged inner ring,
The carbon (C) content is 0.20 mass% to 0.45 mass%, the chromium (Cr) content is 0.10 mass% to 1.20 mass%, and the silicon (Si) content is 0.50% by mass or less, manganese (Mn) content is 1.50% by mass or less, the balance is made of iron (Fe) and an inevitable impurity element steel material, and the material after annealing is applied. Then, after forming a substantially final shape by cold working, nitriding is performed to make the total content of carbon and nitrogen in the surface layer portion 0.50% by mass or more, and the hardness of the surface layer portion is Hv (Vickers hardness) ) 260 or more, and then, after hardening and hardening the raceway surface, it is obtained by performing a finishing process such as grinding. An inner ring raceway is formed on the outer peripheral surface of the hub that internally fits the axle, and a flange that fixes the wheel side member is integrated with the hub; and
A hub unit bearing manufacturing method comprising: an outer member in which a flange for fixing a vehicle body side member is formed integrally with an outer ring; and a rolling element,
At least one of the inner member and the outer member,
The carbon (C) content is 0.20 mass% to 0.45 mass%, the chromium (Cr) content is 0.10 mass% to 1.20 mass%, and the silicon (Si) content is 0.50% by mass or less, manganese (Mn) content is 1.50% by mass or less, the balance is made of iron (Fe) and an inevitable impurity element steel material, and the material after annealing is applied. Then, after making the substantially final shape by cold working, nitriding treatment is performed, the total content of carbon and nitrogen in the surface layer portion is 0.50 mass% or more, the hardness of the surface layer portion is Hv260 or more, A hub unit bearing manufacturing method obtained by performing a finishing process such as grinding after quenching and hardening a raceway surface. A rolling bearing having a flanged outer ring in which a flange is formed integrally with an outer ring, or a flanged inner ring in which a flange is formed integrally with an inner ring,
The flanged outer ring or flanged inner ring is
The carbon (C) content is 0.20 mass% to 0.45 mass%, the chromium (Cr) content is 0.10 mass% to 1.20 mass%, and the silicon (Si) content is 0.50% by mass or less, manganese (Mn) content is 1.50% by mass or less, the balance is made of iron (Fe) and an inevitable impurity element steel material, and the material after annealing is applied. Then, after making the substantially final shape by cold working, nitriding treatment is performed, the total content of carbon and nitrogen in the surface layer portion is 0.50 mass% or more, the hardness of the surface layer portion is Hv260 or more, A rolling bearing obtained by quenching and hardening a raceway surface and then performing a finishing process such as grinding. An inner ring raceway is formed on the outer peripheral surface of the hub that internally fits the axle, and a flange that fixes the wheel side member is integrated with the hub; and
A hub unit bearing comprising an outer member in which a flange for fixing a vehicle body side member is formed integrally with an outer ring, and a rolling element,
At least one of the inner member and the outer member is
The carbon (C) content is 0.20 mass% to 0.45 mass%, the chromium (Cr) content is 0.10 mass% to 1.20 mass%, and the silicon (Si) content is 0.50% by mass or less, manganese (Mn) content is 1.50% by mass or less, the balance is made of iron (Fe) and an inevitable impurity element steel material, and the material after annealing is applied. Then, after making the substantially final shape by cold working, nitriding treatment is performed, the total content of carbon and nitrogen in the surface layer portion is 0.50 mass% or more, the hardness of the surface layer portion is Hv260 or more, A hub unit bearing obtained by quenching and hardening the raceway surface and then performing a finishing process such as grinding.

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