JP2003193138A - Method for manufacturing steel part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing steel parts in which carburizing and quenching treatment is applied to ball rolling grooves axially extending to end faces and the shape accuracy (dimensional accuracy) of the ball rolling grooves after the carburizing and quenching, is improved. <P>SOLUTION: This method is applicable to the manufacture of an inner race 10 for a constant velocity joint. In a step of applying carburizing and quenching treatment to inner grooves 16, cooling is performed while disposing cooling- controlling members 30 and 40 on the upper end face 12 and the lower end face 14 of the inner race 10. Hereby cooling velocities at the end faces 12 and 16 can be controlled in the course of cooling in the carburizing and quenching treatment, and cooling velocities in the respective positions of the inner grooves 16 can be kept practically equal. Because the degree of quenching in the respective positions of the inner grooves 16 and the degree of shape change attendant on the carburizing and quenching can be axially uniformized, the forming of the inner race 10 before the carburizing and quenching can be carried out taking the shape change into account. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a steel part having a ball rolling groove extending in the axial direction and reaching an end surface, and an inner race for a constant velocity joint.

[0002]

2. Description of the Related Art In manufacturing a steel part having a ball rolling groove such as an inner race which is a component of a constant velocity joint, the durability (rolling fatigue life) of the ball rolling groove is improved. For the purpose of, the surface of the ball rolling groove may be carburized and quenched. In such carburizing and quenching treatment, the surface of the steel component changes its structure, so that the shape of the steel component changes as compared with that before the treatment. On the other hand, the ball rolling groove is required to have high shape accuracy (diameter of rolling groove, contact angle between rolling groove surface and ball, etc.). Therefore, in the conventional general method of manufacturing a steel part having such a ball rolling groove, in order to secure the dimensional accuracy of the ball rolling groove, carburizing and quenching treatment is performed on the ball rolling groove. After that, a step of processing (for example, grinding) the shape of the ball rolling groove was performed. As a result, the strain caused by the carburizing and quenching process was removed. However, if the step of performing the shape processing after the carburizing treatment can be omitted or simplified, the manufacturing cost of the steel part can be reduced, which is desirable.

In Japanese Patent Laid-Open No. 02-298249, in a shaft provided with a key groove, a carburizing agent is applied to the key groove processed portion in order to suppress the shape change of the key groove due to carburizing and quenching (key. Techniques for carburizing and quenching (preventing the penetration of carbon into the grooves) are disclosed. However, when this technique is applied, a carburizing agent is applied to the ball rolling groove, and therefore, the ball rolling groove cannot be carburized and quenched.
That is, this technique does not improve the dimensional accuracy of the portion (eg, ball rolling groove) to be carburized and quenched after the carburizing and quenching process. Japanese Patent Laid-Open No. 11-229110
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a technique for preventing deterioration of machinability by carburizing and quenching machine parts by applying a carburizing agent to a portion that requires machining later. It does not improve the dimensional accuracy after the carburizing and quenching treatment of the portion to be quenched.

Further, in Japanese Patent Laid-Open No. 63-111119, the axial end walls of the annular part are airtightly covered to prevent carbon from penetrating into this part, while the inner or outer peripheral wall of the annular part is sealed. A technique for maintaining the shape accuracy of a carburized and hardened portion (for example, a cam surface in an outer race of a one-way clutch) by carburizing and quenching a wall is disclosed. However, there is a demand for further improving the shape accuracy after carburizing and quenching in a portion such as a ball rolling groove where dimensional accuracy is severe. JP-A-6-2102 discloses a technique of controlling the depth of a carburized layer by covering a predetermined portion of a carburized material with a plating film having a pinhole and then performing a gas carburizing treatment. However, this technology is not intended to improve the shape accuracy after carburizing and quenching.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a steel part in which the ball rolling groove is subjected to carburizing and quenching treatment and the ball rolling groove after the carburizing and quenching has high shape accuracy. The purpose is to provide. Another object of the present invention is to
Ball rolling groove shape accuracy (dimensional accuracy) after carburizing and quenching
The object of the present invention is to provide a method of manufacturing a steel part that does not require processing for securing Another object of the present invention is to provide an inner race for a constant velocity joint, which is not subjected to processing for removing the surface of the ball rolling groove after the carburizing and quenching treatment.

[0006]

MEANS FOR SOLVING PROBLEMS, ACTIONS AND EFFECTS The present inventor can solve the above problems by making the cooling rate of the ball rolling groove surface uniform in the axial direction in the cooling process of the carburizing and quenching treatment. I found it.

The manufacturing method of the present invention includes a step of carburizing and quenching the surface of the ball rolling groove extending in the axial direction and reaching the end surface. The cooling process of the carburizing and quenching treatment is characterized in that the cooling rate of the rolling groove surface in the vicinity of the end face of the steel part and the cooling rate of the rolling groove surface in the intermediate portion between both end faces are maintained substantially equal. To do. According to this manufacturing method, the degree of change in the shape of the ball rolling groove due to the carburizing and quenching treatment (hereinafter, also referred to as “heat treatment change amount”) is made uniform in the axial direction of the steel part. This makes it possible to improve the shape accuracy (dimensional accuracy) of the ball rolling groove after the carburizing and quenching process.

Here, the phrase "the cooling rates of the rolling groove surfaces are" approximately equal "" means that the difference between the cooling rates is 1/2 or less. That is, when the cooling rate of the rolling groove surface at the intermediate portion between both end surfaces (for example, represented by "° C./min") is 1, the cooling rate of the rolling groove surface near the end surface is 1/2 to 3/2
It should be in the range of. As the position representative of the "intermediate portion between both end surfaces", for example, the central position in the axial direction of the steel part can be used. Although not particularly limited, the cooling rate of the rolling groove surface near the end face of the steel part is suppressed (hardened to cool) so that the cooling rate of the rolling groove surface near the end face is set to an intermediate portion between both end faces. Can be maintained approximately equal. As a method for suppressing the cooling of the rolling groove surface near the end surface, a method of arranging a cooling suppressing member having an appropriate heat capacity near the end surface to keep the temperature warm, and heating near the end surface appropriately (heat retention) by a heater or the like The method etc. can be used.

The manner in which the shape accuracy of the ball rolling groove after the carburizing and quenching treatment is improved by adjusting the cooling rate will be described. In the cooling process of the carburizing and quenching process, the portion having a relatively high cooling rate is hardened (firmly) more strongly than the portion having a relatively low cooling rate. Generally, the hardened part is weaker (harder)
The amount of heat treatment change is larger than that of the part. In the conventional manufacturing method, since there is no intention of adjusting the relative cooling rate of each part of the component in this cooling process, the steel component is cooled faster in the vicinity of the end faces than in the intermediate portion (for example, the central position) between both end faces ( Easy to cool). That is, the cooling rate of the rolling groove surface in the vicinity of the end surface of the steel part is higher than the cooling rate of the rolling groove surface in the intermediate portion between both end surfaces. Therefore, before and after carburizing and quenching, the portion of the rolling groove located near the end surface of the steel part is
The heat treatment change amount is larger than that in the portion located in the middle portion of the steel part.

In the manufacturing method of the present invention, since the relative cooling rate of each part of the rolling groove is maintained within a predetermined range (being almost equal) in the cooling process of the carburizing and quenching process, the rolling groove is maintained. The heat treatment change amount is made uniform in each part of. As a result, it is possible to manufacture steel parts before carburizing and quenching in consideration of the amount of heat treatment change due to subsequent carburizing and quenching (that is, so that the ball rolling groove has a predetermined shape after carburizing and quenching). It will be easy. If the steel part is deformed in the axial direction unevenly before and after quenching, it is difficult to machine the rolling surface shape in anticipation of the uneven deformation, but if the amount of deformation is almost uniform in the axial direction. This is because it is possible to machine the rolling surface shape in anticipation of its uniform deformation. For example, it is possible to design a forging mold for steel parts in consideration of this heat treatment change amount. This improves the accuracy of the shape of the ball rolling groove after the carburizing and quenching process.

Further, according to the present invention, there is provided another method of manufacturing a steel part having a ball rolling groove extending in the axial direction and reaching the end surface. This manufacturing method includes a step of performing carburizing and quenching treatment on the surface of the ball rolling groove. Then, in the cooling process of the carburizing and quenching treatment, a cooling suppressing member is arranged on the end surface of the steel component for cooling. According to such a manufacturing method, heat is stored in the cooling suppressing member arranged on the end face, and cooling near the end face of the steel component is suppressed (it becomes difficult to cool). Therefore, as compared with the case where this cooling suppression member is not used, the cooling rate of the rolling groove surface near the end surface and the cooling rate of the rolling groove surface at the intermediate portion between both end surfaces are made closer (preferably, maintained substantially equal). can do. As a result, the amount of heat treatment change in each part of the rolling groove is made more uniform, so that it is possible to improve the shape accuracy (dimensional accuracy) of the ball rolling groove after the carburizing and quenching process.

This cooling suppressing member is arranged on at least the end surface (preferably both end surfaces) of the steel part on the side where the ball rolling groove reaches. The cooling suppressing member and the end surface of the steel component do not necessarily have to be in direct contact with each other, and in this case, the cooling suppressing effect can be obtained. When the cooling suppression member is in direct contact with the steel parts (including the case where they are in contact via the carburizing prevention film described later), the effect of arranging the cooling suppression member (the effect of making the heat treatment change amount uniform) Is preferable because it is well exhibited.

The shape of the cooling suppressing member is not particularly limited.
It is preferable that the steel member has a shape capable of covering at least a portion of the end surface of the steel component where the ball rolling groove reaches, and is arranged so as to cover that portion. Further, it is preferable to have a shape that is rotationally symmetrical with respect to the axis of the steel part. This eliminates the need for circumferential alignment when disposing the cooling suppressing member, thus improving workability. As a constituent material of the cooling suppressing member, a metal material or a ceramic material having heat resistance can be used. Of these, it is preferable to use a metal material because it has excellent thermal shock resistance. For example, a cooling suppression member made of cast iron, stainless steel or the like is preferably used. These members have a heat capacity equal to or higher than that of steel and exert a cooling suppressing effect.

Such a cooling suppressing member may be arranged at least on the end face of the steel part in the cooling process of the carburizing and quenching process, but the cooling suppressing member is continuously operated from the carburizing process of the carburizing and quenching process to the cooling process. It is preferable to arrange them from the viewpoint of workability and the like. In particular, when the cooling suppressing member covers the end surface of the steel component and is in direct contact with the steel component, the carburizing process is performed in the state where the cooling suppressing member is arranged, whereby the carburization of the end surface of the steel component can be suppressed. By suppressing the carburization of the end face of the steel part, the heat treatment change amount of the ball rolling groove located near the end face is reduced. Therefore, the effect of suppressing the cooling rate of the rolling groove surface near the end surface and the effect of suppressing the carburization of the end surface are combined, and the heat treatment change amount of each part of the ball rolling groove is further equalized. It

In a preferred embodiment of the present invention, the carburizing step of the carburizing and quenching treatment is carried out by covering the end faces of the steel parts with a carburizing preventive film. If carburization of the end face (at least the end face where the ball rolling groove reaches) is prevented or suppressed by the carburization prevention film,
Since the change amount of heat treatment on the end face is small, the change amount of heat treatment of the ball rolling groove located near the end face is also small. Adjusting the cooling rate of each part of the ball rolling groove (for example, by arranging a cooling suppressing member) and covering the end surface of the steel part with a carburizing prevention film to suppress carburizing of the end surface, thereby changing the amount of heat treatment of each part of the rolling groove. Are further homogenized. Therefore, it is possible to further improve the shape accuracy of the ball rolling groove after the carburizing and quenching.

As such a carburizing prevention film, a carburizing agent coating formed by applying a conventionally known carburizing agent to the end surface of a steel part, or metal plating (for example, copper plating) on the end surface of a steel part is applied. A plated film or the like can be used. This carburizing prevention film is preferably formed uniformly on the end surface of the steel part. As the carburizing method in the carburizing process, any method such as solid carburizing, liquid carburizing, gas carburizing, vacuum carburizing and vacuum ion carburizing may be used.

According to the method for manufacturing a steel part of the present invention, the step of processing the shape of the ball rolling groove (for example, processing of grinding the rolling groove surface) after the carburizing and quenching treatment can be omitted. By applying the present invention, the shape accuracy of the ball rolling groove after carburizing and quenching is improved, so that the dimensional accuracy of the ball rolling groove can be sufficiently secured even if the processing step after carburizing and quenching treatment is omitted. Because. The fact that the ball rolling groove has not been processed after the carburizing and quenching treatment can be confirmed by, for example, observing the surface state of the ball rolling groove (the surface is blackened).

The manufacturing method of the present invention can be applied to steel parts of various shapes having a shaft. For example, the present invention is applied to steel parts having a rough shape such as a tubular shape (annular shape), a bottomed tubular shape, and a columnar shape. The shape of the steel part (eg cross-sectional shape) is
It may be uniform in the axial direction, or may be different in each part in the axial direction. When the steel part has a shape having an outer circumference and an inner circumference (for example, a cylindrical shape), the ball rolling groove may be formed on either the outer circumference or the inner circumference, or may be formed on both.

The ball rolling groove extends in the axial direction of the steel part and reaches the end surface of the steel part. Here, "extending in the axial direction" means that the range where the ball rolling groove is formed has a certain spread in the axial direction of the steel part,
It is meant to include both the case where the rolling groove extends substantially parallel to the axial direction (along the axial direction) and the case where the rolling groove extends non-parallel to the axial direction (for example, in a spiral shape). The shape (eg, cross-sectional shape) of the ball rolling groove may be uniform in the axial direction of the steel part, and the shape (eg, depth of the rolling groove) may be different in each axial part of the steel part. May be different. Suitable examples of steel parts manufactured by applying the present invention include inner races and outer races for constant velocity joints.

Further, according to the present invention, there is provided an inner race for a constant velocity joint in which the surface of the ball rolling groove is covered with a black skin. In such an inner race for a constant velocity joint, the surface of the ball rolling groove is carburized and quenched, and the surface of the ball rolling groove is not processed after the carburizing and quenching treatment. Therefore, the manufacturing process can be simplified.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is also characterized by being embodied in the following modes.

(Mode 1) The steel part manufactured by the method of the present invention has a tubular shape. In such a steel part, the difference in the cooling rate on the surface of the ball rolling groove tends to be large at each axial portion, as compared with the solid shape (for example, columnar) steel part. Therefore, according to the conventional manufacturing method, the shape accuracy (dimensional accuracy) of the ball rolling groove after the carburizing and quenching treatment is likely to be deteriorated. Therefore, the effect of applying the present invention is well exhibited. In the case where the ball rolling groove is provided on the outer circumference of such a tubular steel part, the difference in the cooling speed is likely to be larger than that when the rolling groove is provided on the inner circumference. The significance of using the manufacturing method is more significant. A typical example of such a steel part is an inner race for a constant velocity joint.

(Mode 2) The difference between the contact angle change amount of the rolling groove in the vicinity of the end face of the steel part and the contact angle change amount of the rolling groove at the intermediate portion between both end faces is within 3 ° (more preferably 2 °). Within).
Here, the "contact angle change amount (°)" is an index of the heat treatment change amount, and is an index of the contact angle of the ball rolling groove (angle between the groove surface and the ball) before the carburizing and quenching treatment. The difference from the contact angle of the ball rolling groove after charcoal quenching. If the difference (variation) in the amount of change in the contact angle of each part of the rolling groove is less than or equal to the above value, the dimensional accuracy of this rolling groove can be improved without performing the step of machining the shape of the ball rolling groove after carburizing and quenching treatment. Can be secured.

[0024]

EXAMPLES Example 1 Production Example Using Carburizing Prevention Film and Spacer> An example of producing an inner race for a constant velocity joint by applying the production method (carburizing method) of the present invention will be described with reference to the drawings. explain. As shown in FIG. 1, an inner race for a constant velocity joint (hereinafter, also referred to as a "workpiece") 10, which is an object of carburizing and quenching treatment, has a roughly cylindrical shape. This work 10 is typically
It is produced by a method including a forging step and a step of cutting the forged product obtained by this forging step. A plurality of (for example, six) inner grooves 16 extending from the upper end surface 12 to the lower end surface 14 along the axial direction of the work 10 are formed on the outer periphery of the work 10. These inner grooves 16 are
The workpieces 10 are arranged at equal intervals (at a constant angle) in the circumferential direction. Further, the inner circumference of the work 10 is formed with a shaft hole 18 for receiving a shaft (not shown).
The completed inner race 10 is used by rolling balls (not shown) in each of the inner grooves 16 so as to be rollable.

These inner grooves (ball rolling grooves) 16
Carburizing and quenching treatment is applied to the surface of the work 10 including the surface of the above as follows. That is, first, a carburizing agent is applied to the entire upper surface 12 and lower surface 14 of the work 10 to form a carburizing prevention film (not shown). The thickness of this carburizing preventive film is preferably in the range of 0.01 mm to 2 mm. Also,
The thickness of the carburizing preventive film is preferably substantially uniform in each part of the coating range. In this example, a carburizing prevention film having a film thickness of about 1 mm and a substantially uniform thickness was formed.

On the other hand, as shown in FIG. 2, a vertical bar 54 as a carburizing and quenching jig is attached to a holder 52 of a carburizing and quenching furnace (not shown).
Set. The upright bar 54 is provided between the handle 54a and the penetrating portion 54b, and a cylindrical handle 54a provided at the lower end, a cylindrical penetrating portion 54b extending continuously above the handle 54a. And a disc-shaped collar portion 54c. Holder 5
The shank 54a is inserted into the hole provided in 2 until the collar 54c contacts the upper surface of the holder 52. In this way, the upright bar 54 is held by the holder 52. The diameters of the handle 54a and the penetrating portion 54b are slightly smaller than the minimum inner diameter of the shaft hole 18 of the work 10.

As shown in FIG. 2, the lower spacer 40 has a ring shape and is made of cast iron. The outer diameter of the lower spacer 40 is slightly smaller than the maximum outer diameter of the work 10, but larger than the outer diameter of the end surface of the work 10. Therefore, the lower spacer 40 can cover the end surface of the work 10. The inner diameter of the lower spacer 40 is approximately the same as the inner diameter (minimum inner diameter) of the work 10. Further, the thickness (axial length) of the lower spacer 40 is 1/3 of the axial length of the work 10.
It is about 1/2. The hole 42 of the lower spacer 40
The lower spacer 40 is placed on the flange portion 54c of the upright bar 54 by penetrating the penetrating portion 54b of the upright bar 54.

Next, the work 1 on which the carburizing prevention film is formed.
Insert the penetrating portion 54b of the upright bar 54 into the shaft hole 18 of 0,
The work 10 is placed on the lower spacer 40. As a result, the lower end surface 14 of the work 10 and the lower spacer 40 are interposed via the carburizing prevention film formed on the lower end surface 14 of the work 10.
Contact the upper surface 44 of the. Further, the ring-shaped upper spacer 30 is provided on the work 10, and the vertical bar 54 is provided in the hole 32.
The penetrating portion 54b is inserted and placed. Upper spacer 3
The shape and material composition of 0 are similar to those of the lower spacer 40. As a result, the upper end surface 12 of the work 10 and the lower surface 36 of the upper spacer 30 come into contact with each other through the carburizing prevention film formed on the upper end surface 12 of the work 10.

With the upper spacer 30, the work 10 and the lower spacer 40 set as shown in FIG. 2, carburizing and quenching treatment is carried out according to a conventional method. According to this manufacturing method, the dimensional accuracy of the inner groove 16 can be secured without processing the shape of the inner groove 16 after the carburizing and quenching process. Therefore, it is possible to obtain the inner race 10 (completed product) for a constant velocity joint in which the surface of the inner groove 16 is blackened.

It should be noted that in the above embodiment, the anti-carburizing agent is used as the upper end surface 12
And was applied to the entire bottom surface 14 with a thickness of about 1 mm,
The coating range and coating thickness can be appropriately changed. Further, in the above embodiment, the upper spacer 30 and the lower spacer 40 have the same shape and material composition, but the shape and / or material composition of these spacers 30, 40 may be different from each other. Furthermore, these spacers 3
The shapes of 0 and 40 (inner diameter, outer diameter, thickness, etc.) and material composition can be appropriately changed. The coating conditions (coating range, coating thickness, etc.) of the carburizing agent and the types (shape, material composition, etc.) of the spacers 30, 40 are such that the heat treatment change amount of the inner groove 16 is between the end face of the work 10 and between both end faces. (For example, the central position in the axial direction) can be determined so as to be substantially the same.

<Example 2; Manufacturing Example Using Spacers> The same work as in Example 1 was carried out in the same manner as in Example 1 except that the carbonizing agent was not applied (the upper spacer and the lower spacer were arranged). Then, an inner race for constant velocity joints was manufactured by carrying out carburizing and quenching treatment.

<Evaluation of Manufactured Inner Race> The inner race manufactured according to Example 1 was examined for the change in hardness depending on the distance (depth in the axial direction) from the surface of the lower end surface. The hardness was evaluated by measuring Vickers hardness (HV). Further, as a comparative example, the same applies to the inner race for a constant velocity joint manufactured in the same manner as in Example 1 except that the carburizing agent is not applied to the work and neither the upper spacer nor the lower spacer is used. Vickers hardness was measured. The result is shown in FIG. Figure 3
As can be seen from the above, the inner race of Example 1 has a lower surface hardness than the inner race of the Comparative Example, and its case hardening depth is shallow (for example, 0.5 to 0.5 based on HV550).
It was about 0.6 mm). It should be noted that the above "hardening depth"
Indicates that the inner race has a predetermined Vickers hardness (for example, H
It can be evaluated by the depth indicating V550).

Further, in the manufacturing methods of Examples 1, 2 and Comparative Example, the heat treatment change amount of the inner groove before and after the carburizing and quenching treatment was measured. As an index of heat treatment change amount,
The difference (contact angle change amount) between the contact angle (°) between the surface of the inner groove and the ball placed in the inner groove during actual use before and after the carburizing and quenching treatment was used. Measure the contact angle between the inner groove surface and the ball before and after carburizing and quenching at three points: near the upper end face of the inner race, near the lower end face, and in the axial center position. The value of the amount of change was used. The measurement results are shown in FIG. As you can see from Figure 4,
In the manufacturing methods of Example 1 and Example 2, the difference (variation) in the contact angle change amount at three points (near the upper end surface, near the lower end surface, and the central position) was small, and was about 3 ° (about 1 ° in Example 1).
Was within the range. On the other hand, in the manufacturing method of the comparative example, the contact angle change amount at the center position was about the same as that of the example, but the contact angle change amount near the upper end face and the lower end face was large (the variation of three points was 6). It is clear that the shape of the inner groove is considerably distorted due to the carburizing and quenching treatment at these parts.

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. Further, the technical elements described in the present specification or the drawings are
The technical usefulness is exhibited alone or in various combinations, and is not limited to the combinations described in the claims at the time of filing. In addition, the technique illustrated in the present specification or the drawings achieves a plurality of purposes at the same time, and achieving the one purpose among them has technical utility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an inner race for a constant velocity joint according to an embodiment.

FIG. 2 is a cross-sectional view showing a state in which an inner race for a constant velocity joint according to an embodiment is set in a carburizing and quenching furnace.

FIG. 3 is a characteristic diagram showing a change in hardness of a carburized and quenched inner race depending on the distance from the lower end surface.

FIG. 4 is a characteristic diagram showing a contact angle change amount before and after carburizing and quenching treatment for each portion of the inner groove.

[Explanation of symbols]

10: Inner race for constant velocity joint, work (steel part) 12: Upper end surface 14: Lower end surface 16: Inner groove (ball rolling groove) 30: Upper spacer (cooling suppressing member) 40: Lower spacer (cooling suppressing member) 52: Holder 54: Vertical bar

Claims (5)

[Claims] 1. A method of manufacturing a steel part having a ball rolling groove extending in the axial direction and reaching an end surface, the method including a step of subjecting the surface of the rolling groove to a carburizing and quenching treatment, the carburizing and quenching treatment being carried out. In the cooling process of, the steel part is characterized in that the cooling rate of the rolling groove surface near the end face of the steel part and the cooling rate of the rolling groove surface in the middle part between both end faces are maintained substantially equal. Method. 2. A method for manufacturing a steel part having a ball rolling groove extending in the axial direction and reaching an end surface, the method including the step of subjecting the surface of the rolling groove to a carburizing and quenching treatment, the carburizing and quenching treatment comprising: In the cooling process, the steel component manufacturing method is characterized in that a cooling suppressing member is arranged on the end face of the steel component to cool it. 3. The method of manufacturing a steel component according to claim 1, wherein in the carburizing process of the carburizing and quenching treatment, an end face of the steel component is covered with a carburizing prevention film. 4. The shape of the rolling groove is not processed after the carburizing and quenching treatment.
The method for manufacturing a steel part according to. 5. An inner race for a constant velocity joint, wherein the surface of the ball rolling groove is covered with a black skin.