JPH09242763A - Manufacture of rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an inexpensive rolling bearing by which even a complicated shape can be easily and accurately worked and machining work thereafter can also be eliminated by performing rolling work at quenching time. SOLUTION: After being turned into austenite by heating a ring-shaped raw material which contains C: 7 to 1.2%, Si: 0.15 to 0.7%, Mn: 0.2 to 1.5% and Cr: 0.5 to 2% in weight % and on which a residual part is formed of steel composed of Fe and unavoidable impurity, it is rapidly quenched to a temperature of 200 to 350 deg.C, and prescribed rolling work is performed on the ring-shaped raw material still in an austenite condition, and afterwards, it is cooled up to a temperature not more than a Ms point, and a martensite transformation is caused, and hardness is set not less than HRC 57.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rolling bearing, and more particularly to a method for rolling a bearing ring which can greatly reduce turning.

[0002]

2. Description of the Related Art Conventionally, when a bearing ring of a rolling bearing is manufactured by rolling using a low alloy steel (for example, SUJ2), a ring-shaped material (hereinafter referred to as a blank) is hot-rolled or cold-rolled. It is carried out by rolling.

[0003] In the case of hot rolling, a forging ring or a blank obtained by cutting a tube material is used for rolling, followed by turning, followed by heat treatment and grinding. If cold rolling is used, rolling is performed using a blank created by turning from a forged ring or tube material, and then heat treatment and grinding are performed after turning if necessary. .

[0004]

Since the hot rolling is performed in the austenite state in which the blank is heated to a high temperature of 1000 ° C. or higher, there is an advantage that the material has a large deformability and the rolling process is easy. Since oxide scale and decarburization occur on the surface of the steel, there is a problem that the surface must be turned after hot rolling to remove them.

On the other hand, in cold rolling, since rolling is carried out at room temperature, oxide scale and decarburization do not occur on the surface of the product,
Since the deformability of the material is smaller than that in hot rolling, cracks may occur during rolling as described in JP-A-2-209452. Further, since the deformability is small, there is a problem that it is difficult to process a complicated shape such as a seal groove of a ball bearing. Further, in cold rolling, a large residual stress is generated in the bearing ring after processing, which causes a problem that large heat treatment deformation occurs in heat treatment.

Therefore, the present invention has been made by paying attention to such a problem that has not been solved in the related art. By performing a rolling process at the time of quenching, a complicated shape can be easily and accurately processed, and The present invention provides a method for manufacturing a low-cost rolling bearing, which can reduce the turning work.

[0007]

The rolling bearing manufacturing method according to the present invention is, by weight%, C: 0.7 to 1.2%, Si:
0.15-0.7%: Mn: 0.2-1.5%, Cr:
The material on the ring formed of steel containing 0.5 to 2% and the balance being Fe and unavoidable impurities is heated to a predetermined temperature to be austenitized, and then rapidly cooled to a temperature of 200 to 350 ° C. The ring-shaped material is subjected to a predetermined rolling process in the austenite state, then cooled to a temperature below the Ms point to cause martensite transformation, and the hardness is HR.
It is characterized in that it is C57 or more.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. According to the present invention, a blank is rapidly cooled from a predetermined austenitizing temperature to a temperature of 200 to 350 ° C. without causing martensitic transformation, so that the blank can be subjected to a rolling process in an austenitic state having a large deformability. As compared with the conventional cold rolling, a complicated shape such as a seal groove can be easily processed and no crack is generated.

Further, since the rolling process is performed at a temperature of 200 to 350 ° C., an oxide scale and a decarburized layer are not formed on the surface of the product unlike the hot rolling. Furthermore, since the blank structure is rolled in a state where the deformability of the austenite phase is large, the pressing force required during the rolling process is small and the life of the mandrel is greatly extended. Since the residual stress generated in the heat treatment is reduced, the deformation after the heat treatment can be reduced.

The material flow of the bearing ring made by the method of the present invention is as shown in FIGS. 1 (b) and 2 (b).
It flows along the surface including the seal groove, which is also preferable for rolling life.

According to the method of manufacturing a rolling bearing of the present invention, the temperature of the surface of a blank quenched at a temperature of 200 to 350 ° C. becomes almost the same as that of the inside, and then this blank is set in a rolling machine. Complete the rolling process. For that purpose, 2 of the isothermal transformation curve (TTT curve, S curve)
At a temperature of 00 to 350 ° C., the time Ta from austenite to the start of bainite transformation or ferrite / cementite transformation is 10 seconds or more, preferably 20.
It is necessary to use steel that has more than a second. Figures 3-6 show the T.V. T. T. The curve is shown. In particular, FIG. T. T. The relationship between a curve and the rolling conditions of the present invention is shown.

In the rolling process, the temperature of the blank is 20
If the temperature is lower than 0 ° C, martensitic transformation occurs in most steels, resulting in increased deformation resistance, which makes rolling difficult. On the other hand, when the temperature of the blank is higher than 350 ° C., as shown in FIG. 6, for example, the time Ta from the austenite to the start of bainite transformation or ferrite / cementite transformation becomes short, so that the rolling process becomes difficult. Therefore, in the present invention, the range of the temperature at which the rolling process is performed is defined as 200 to 350 ° C.

By performing air-cooling or water-cooling at a temperature below the Ms point after the rolling process, martensitic transformation progresses and a hardness of HRC 57 or higher required for a rolling bearing is obtained. Since this cooling is performed from 200 to 350 ° C., the temperature difference between the inside and outside of the bearing ring and the temperature unevenness on the circumference are smaller than in normal quenching, so the deformation of the bearing ring after cooling can be reduced. it can.

Further, the hardness of HRC57 or higher required for the rolling bearing is obtained by holding the material at a predetermined temperature of 200 to 350 ° C. for a predetermined time and forming a bainite structure without cooling immediately after the rolling process. At the same time, it is possible to obtain a uniform compressive residual stress in the surface layer, and at the same time, in order to prevent martensitic transformation from occurring, it is possible to further reduce the deformation of the bearing ring compared to the case where air cooling or water cooling is performed after the rolling process. it can.

As described above, according to the present invention, in the quenching step, the bearing ring of the bearing having the complicated sectional shape having the seal groove can be formed from the blank by the rolling process without generating the surface crack. Further, since the heat treatment deformation is small, a product with high accuracy can be obtained. Therefore, it is possible to omit the turning process that was conventionally performed before the heat treatment and to omit the turning process such as the seal groove that was performed after the rolling process, so that the manufacturing cost of the bearing ring can be significantly reduced. .

In the present invention, the reason why each element is contained in the bearing material steel and the reason for limiting the content thereof are as follows. [C] C is 0.7 to obtain hardness of HRC57 or more.
It is necessary to be more than weight%. On the other hand, if it exceeds 1.2% by weight, coarse carbides are likely to be formed.

[Si] Si is required to be 0.15% by weight or more as a deoxidizing agent during steelmaking and to improve hardenability, but if it exceeds 0.7% by weight, the toughness tends to decrease. In order to make it visible, the upper limit was set to 0.7% by weight.

[Mn] Mn is required as a deoxidizing element in the same manner as Si and 0.2% by weight or more for improving the hardenability, but if it is too much, the upper limit is 1.
It was set to 5% by weight.

[Cr] Cr is 0.5 to improve hardenability.
The upper limit was set to 2% by weight, because if it is added in an amount of not less than 2% by weight, if it is contained in an amount exceeding 2% by weight, the steel becomes hard and brittle.

[Mo] Mo is added in an amount of 0.1% by weight or more in order to improve hardenability as in the case of Cr, but 0.8% by weight is added.
Even if the content exceeds 5, the effect does not differ, so the upper limit is set to 0.
It was 8% by weight.

(Embodiment) Next, with respect to the bearing outer ring, an experimental example will be described in which test specimens of an embodiment of the manufacturing method of the present invention and a comparative example of the conventional method were experimentally manufactured.

(1) Manufacture of blank First, bearing steel SUJ2 (1 wt% C, 1.4 wt% C
Using r), a blank as shown in FIG. 1 (a) was manufactured from a hot-rolled tube by a cut-off process.

In order to see the influence of the flow of material,
A blank as shown in FIG. 2 (a) was manufactured from a forged ring of bearing steel. (2) Test method (a) Fabrication of specimen of comparative example: In case of comparative example A: Fig. 1
Using the blank of (a), the outer ring of 608ZZ as shown in FIG. 1 (b) was processed by the conventional cold rolling process. Reference numeral 1 is a raceway surface, 2 is an inner diameter surface, and 3 is a seal groove. Then, the presence or absence of cracks on the inner diameter surface 2, the shape of the seal groove 3 and the occurrence of cracks were checked. After that, the outer ring of 608ZZ is heated to 860 ° C, and then 80 ° C.
After quenching in the above oil, tempering was performed at 180 ° C.

Comparative Example B: The outer ring of 608ZZ produced by ordinary turning was heated to 860 ° C. to austenite, then quenched in oil at 80 ° C. and then 180 ° C.
It was tempered in.

Comparative Example C: The bearing steel blank used in Comparative Example A was austenitized at 860 ° C., and then 30
Hardened in 0 ° C salt and held for about 180 seconds, and then the rolling part (mandrel, pressure roll, guide roll) was heated to 260 ° C. The outer ring of 608ZZ was processed.

In the case of Comparative Example D: 8 blanks of S58C
After austenitizing at 20 ° C, quenching is performed in 350 ° C salt for about 20 seconds, and then the rolled part is
The outer ring of 608ZZ was processed by a rolling machine heated to 80 ° C.

(B) Fabrication of specimen of Example: In the case of Example E: The blank of the bearing steel used in Comparative Example A was austenitized at 860 ° C. and then quenched in a salt at 280 ° C. for about 30 minutes. After holding for 2 seconds, the rolling portion was rolled into a 608 ZZ outer ring as shown in FIG. 1B without being particularly heated, and then air-cooled to room temperature.

In the case of Example F: The bearing steel blank used in Comparative Example B was austenitized at 860 ° C.
After quenching in 0 ° C salt and holding for about 30 seconds, the rolling part was heated to 250 ° C.
The outer ring of 608ZZ as shown in (b) was rolled and then held in a constant temperature bath at 250 ° C. for 3 hours to complete bainite transformation and then air-cooled.

In the case of Example G: The bearing steel blank shown in FIG. 2 (a) was austenitized at 860 ° C., quenched in a salt at 350 ° C. and held for about 30 seconds, and then the rolled portion was particularly heated. 6 as shown in FIG.
The outer ring of 08ZZ was rolled.

In the case of Example C: A blank of bearing steel SUJ3 was used. This was austenitized to 840 ° C., then quenched in a salt at 210 ° C., held for about 80 seconds, and then the rolled part was heated to 210 ° C. with a rolling machine as shown in FIG. 1 (b). The outer ring of 608ZZ was processed.

In the case of the example, a blank of 1070M steel was used. After austenitizing this to 840 ° C.,
Hardened in 300 ° C salt and held for about 20 seconds, and then the rolling part was heated to 280 ° C.
The outer ring of 608ZZ as shown in (b) was processed.

(C) Rolling method: FIGS. 7 (a) and 7 (b)
The outline of the rolling process method is shown in. (3) Test contents For each test piece with different heat treatment conditions and rolling forming conditions as described above, the presence or absence of cracks after processing, mandrel life, heat treatment deformation amount, and hardness were measured. Compared.

(4) Test results: Table 1 shows heat treatment conditions and molding condition data, and Table 2 shows comparison results. Table 3 shows the chemical composition of the steel used.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

In Comparative Example A, as shown in FIGS. 8 and 9,
Cracks 5 were generated on the inner diameter surface 2 of the outer ring 10 and the seal surface 4 of the seal groove portion 3, but no cracks were found on the inner diameter surface 2 and the seal groove portion 3 in the example. As for the forming load, the example was able to be formed with a lower load as compared with Comparative Example A.

In Comparative Examples C and D, since the bainite transformation had already started during the rolling process, the deformability deteriorated, and it was not possible to perform accurate machining within the safe forming load range due to the strength of the mandrel.

Regarding the heat treatment deformation, in Comparative Example B, the residual stress due to the rolling process is large, so that the heat treatment deformation amount is large, but in the embodiment, the deformation amount is smaller than that of the outer ring by the conventional turning process (Comparative Example B). there were.

Further, regarding Comparative Example A and Example E,
When the mandrel lifespans were compared by carrying out mass production experiments, it was found that the lifespan of the example F was twice as long as that of the comparative example A.

In Table 4, the evaluation results for each item of the comparative example and the example are shown by ◯ ×.

[0042]

[Table 4]

As is clear from the above results, according to the method of manufacturing a rolling bearing of the present invention, rolling is performed in an austenite state having a large deformability at 200 to 350 ° C., so that oxide scale is generated. There is no decarburization phenomenon and it can be molded with a small molding load.

Also, there is no crack in the seal groove,
The shape and size of the seal groove can be accurately formed, and the life of the mandrel can be greatly extended. Further, the residual stress at the time of molding is small and the martensitic transformation is caused by cooling from a relatively low temperature, so that the heat treatment deformation can be reduced.

Although the outer ring of the ball bearing has been described in the above embodiment, the present invention can be similarly applied to other rolling bearing members such as the inner ring of the ball bearing.

[0046]

As described above, according to the method of manufacturing a rolling bearing of the present invention, the shape of a bearing component, especially a bearing ring, can be improved even if a complicated shape such as a seal groove is included. Since it is possible to manufacture products with excellent dimensional accuracy by rolling, it is possible to significantly reduce turning including the previously required turning of sealing grooves, and as a result, it is possible to provide rolling bearings at low cost. Play.

[Brief description of drawings]

1A is a half sectional view of a blank of a bearing outer ring cut out from a tube material or the like, and FIG. 1B is a half sectional view showing a material flow of a molded product thereof.

FIG. 2A is a half cross-sectional view of a blank of a bearing outer ring cut out from a forged ring, and FIG. 2B is a half cross-sectional view showing a material flow of the molded product.

FIG. 3 shows the T.E. of SAE 1050C steel. T. T. It is a figure showing a curve.

FIG. 4 shows the T.E. of SAE 1062C steel. T. T. It is a figure showing a curve.

FIG. 5: T. of Mo steel T. T. It is a figure which shows a curve.

FIG. 6 shows the T.E. of SYJ2 steel. T. T. It is a figure showing a curve.

7A and 7B show an outline of a rolling method for a bearing race, in which FIG. 7A is a plan view and FIG. 7B is a side view.

FIG. 8 is an enlarged perspective view showing a part of a molded sample of Comparative Example A.

9A and 9B are enlarged views of cracks observed in parts A and B of FIG. 8, where FIG. 9A is an enlarged view of part A, FIG. 9B is an enlarged view of part A crack, and FIG. (D) It is a B part crack enlarged view.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C22C 38/00 301 C22C 38/00 301Z 38/18 38/18

Claims (1)

[Claims] 1. By weight%, C: 0.7-1.2%, S
i: 0.15 to 0.7%: Mn: 0.2 to 1.5%, C
r: 0.5 to 2%, with the balance being Fe and inevitable impurities, a material on a ring formed of steel is heated to a predetermined temperature to be austenitized, and then 200 to 350 ° C.
To a temperature of Ms point or lower to cause martensitic transformation, and the hardness is set to HRC57 or higher. A method of manufacturing a rolling bearing, comprising: