JP2020105560A - Joint member and manufacturing method of joint member - Google Patents

Abstract

To improve toughness of a cup portion to suppress a decrease in strength while hardening an inner surface side of the cup portion of a joint member.SOLUTION: A manufacturing method of the joint member includes: a forging step to form a first intermediate product W1 with the cup portion having a tubular portion and a bottom portion, and a shaft portion extending axially from the bottom portion, by hot forging a material W0 made of carbon steel having a carbon content of 0.30 wt.% or more and 0.70 wt.% or less; and a quenching step to cool the first intermediate product W1, of which temperature has been kept following the hot forging, into a second intermediate product. In the quenching step, a cooling start temperature on an outer surface side of the cup portion is lower than a cooling start temperature on the inner surface side of the cup portion, and therefore the inner surface side is cooled from a single-phase region of austenite, and the outer surface side is cooled from two-phase region of ferrite and austenite.SELECTED DRAWING: Figure 3

Description

The present invention relates to a joint member and a method for manufacturing the joint member.

In automobiles and various industrial machines, a constant velocity joint is used as part of a power transmission device. In the case of an automobile, a constant velocity joint of a drive shaft is connected to a hub unit that supports wheels. The constant velocity joint includes an outer joint member connected to the hub unit, an inner joint member on the vehicle center side, a plurality of balls provided between the outer joint member and the inner joint member, and a cage for holding the plurality of balls. (For example, see Patent Document 1).

JP, 2017-149253, A

FIG. 7 is a cross-sectional view of the outer joint member (hereinafter referred to as the joint member 90). The joint member 90 includes a bottomed tubular (bowl-shaped) cup portion 91 having a tubular portion 99 and a bottom portion 98, and a shaft portion 92 extending axially from the bottom portion 98. Since the balls make rolling contact with a part of the inner surface 97 of the cup portion 91, the inner surface 97 is required to have a predetermined hardness. A spline 95 is formed on the outer peripheral surface of the shaft portion 92, and the shaft portion 92 is spline-coupled with the inner shaft of the hub unit. Therefore, the outer peripheral surface (spline 95) of the shaft portion 92 also needs to have a predetermined hardness.

Therefore, conventionally, partial hardening by high frequency heating is performed on the joint member 90 formed into a predetermined shape. That is, the inner surface 97 of the cup portion 91 and the outer peripheral surface of the shaft portion 92 are subjected to high frequency heating, and then a cooling liquid is injected to perform rapid cooling.

In the joint member 90 as described above, it is desired to shorten the manufacturing process and reduce the cost. Therefore, the inventor of the present invention is conducting research on a method of manufacturing the joint member 90 by forging and quenching. In the manufacturing method by forging and quenching, a material made of carbon steel is heated, and by hot forging, a forging step of forming a first intermediate product having a cup portion 91 and a shaft portion 92, and a temperature following the hot forging. The quenching step of cooling the first intermediate product, which has been maintained, from the outside and from the inner surface 97 side of the cup portion 91 to obtain the second intermediate product is performed.

In the case of forging and quenching as described above, in the quenching step, the entire cup portion is hardened. Then, the inventor of the present invention has found that the strength may decrease due to insufficient toughness.

Therefore, the present invention is a method for manufacturing a joint member in which the inner surface side of the cup portion is hard, and moreover, it is possible to improve the toughness of the cup portion and suppress a decrease in strength, and a method for manufacturing the joint member. The object is to provide a joint member.

The method for manufacturing a joint member according to the present invention is a method in which a material made of carbon steel having a carbon content of 0.30% by weight or more and 0.70% by weight or less is hot-forged to form a cup portion having a tubular portion and a bottom portion. A forging step of forming a first intermediate product having a shaft portion extending in the axial direction from the bottom portion, and cooling the first intermediate product whose temperature is maintained following the hot forging to obtain a second intermediate product. And a quenching step, wherein in the quenching step, the cooling start temperature on the outer surface side of the cup portion is lower than the cooling start temperature on the inner surface side of the cup portion, and the inner surface side is a single-phase region of austenite. From the two-phase region of ferrite and austenite.

According to this manufacturing method, the inner surface side of the cup portion is harder and the outer surface side thereof is softer than the inner surface side, so that the toughness of the cup portion can be improved and the decrease in strength can be suppressed. It is possible to manufacture the joint member by forging quenching, instead of the conventional manufacturing method of obtaining a forged product by forging, lowering the temperature, and then partially heating and quenching the forged product as in the past. Therefore, the number of manufacturing steps can be reduced.

Further, the joint member of the present invention includes a cup portion having a tubular portion and a bottom portion, and a shaft portion extending in the axial direction from the bottom portion, and the tubular portion is made of a quench-hardened layer and is a first hard material. Inner surface side layer having a thickness, an outer surface side layer having a second hardness lower than the first hardness, and from the first hardness to the second hardness from the inner surface side layer toward the outer surface side layer And an intermediate layer whose hardness value is gradually reduced within the range of.

In the joint member, the inner surface side of the cup portion is hard and the outer surface side is softer than the inner surface side, so that the toughness of the cup portion is improved and the decrease in strength is suppressed. The joint member is not a conventional manufacturing method in which a forged product is obtained by forging, the temperature is lowered, and then the forged product is partially heated and quenched, but a method including forging and quenching as described above. Manufactured by. Therefore, the number of manufacturing steps can be reduced.

As described above, as the joint member in which the inner surface side of the cup portion is hard and the toughness of the cup portion is improved, preferably, the first hardness is 650 HV or more and the second hardness is 500 HV or less. .. Thus, there is a difference in hardness between the inner surface side and the outer surface side of the cup portion.

According to the method for manufacturing a joint member of the present invention, the inner surface side of the cup portion becomes harder and the outer surface side becomes softer than the inner surface side, so that the toughness of the cup portion can be improved and the strength reduction can be suppressed.
According to the joint member of the present invention, the inner surface side of the cup portion is hard and the outer surface side is softer than the inner surface side, so that the toughness of the cup portion is improved and the strength reduction is suppressed.

It is sectional drawing of a joint member. It is a flowchart of a manufacturing method. It is a schematic plan view of manufacturing equipment. It is the schematic block diagram which looked at a part of hardening machine from the side. It is a phase diagram of carbon steel. It is a figure explaining the hardness of a cylinder part. It is sectional drawing of a joint member.

[About joint members]
FIG. 1 is a sectional view of a joint member. The joint member 10 is a part (outer joint member) of a constant velocity joint used in an automobile. In addition to the joint member 10 shown in FIG. 1, the constant velocity joint holds an inner joint member, a plurality of balls arranged between the joint member 10 and the inner joint member, and a plurality of balls (not shown). It is equipped with a cage.

The joint member 10 includes a cup-shaped (cup-shaped) cup portion 12 and a shaft portion 18. The cup portion 12 has a bottomed tubular shape having a tubular portion 14 and a bottom portion 16. The shaft portion 18 extends in the axial direction from the bottom portion 16 of the cup portion 12. The joint member 10 further includes a screw portion 20. The threaded portion 20 is provided at the tip of the shaft portion 18, which is opposite to the cup portion 12 in the axial direction. Since the balls make rolling contact with a part of the inner surface 22 of the cup portion 12, the inner surface 22 is required to have a predetermined hardness. Further, a spline 19 is formed on the outer peripheral surface of the shaft portion 18, and the shaft portion 18 is spline-coupled with the inner shaft of the hub unit. Therefore, the outer peripheral surface (spline 19) of the shaft portion 18 is required to have a predetermined hardness.

Therefore, as will be described later, the joint member 10 is subjected to a quenching process as a heat treatment. The quenching treatment of the present disclosure is a forging quenching treatment. That is, in order to manufacture the joint member 10, hot forging is performed on the steel material, and the heat given to the steel material for the hot forging is used to continuously perform quenching.

The joint member 10 is made of carbon steel (medium carbon steel or high carbon steel), and the joint member 10 of the present disclosure is carbon steel for machine structure (S55C).

[About manufacturing method]
A method of manufacturing the joint member 10 having the above configuration will be described. FIG. 2 is a flow chart of the manufacturing method. In order to manufacture the joint member 10, the forging step S1 is performed, and then the quenching step S2 is performed. After the quenching step S2, the tempering step S3 and the machining step S4 are performed. FIG. 3 is a schematic plan view of manufacturing equipment for implementing the manufacturing method. The manufacturing equipment includes a heater device 31 for the forging step S1 and a forging device 32 including a press machine, a quenching machine 33 for the quenching step S2, a tempering machine 34 for the tempering step S3, and a machine. A machining device 35 for the machining step S4 is included. A transfer machine (transfer robot) 36 that transfers the material W0 or the intermediate products W1, W2, and W3 to the next facility (the next step) is provided between the apparatuses.

In the forging step S1, the material W0 made of carbon steel is first entirely heated by the heater device 31. The material W0 is heated to a temperature (around 1000° C.) that becomes an austenite structure. The temperature of the material W0 after heating is, for example, 930° C. or higher and 1050° C. or lower. Almost all of the material W0 has a uniform temperature.

The heated material W0 is forged by the forging device 32. The material W0 is forged in the austenitic state. In the forging step S1, the material W0 is hot-forged so that the cup portion 12 having the tubular portion 14 and the bottom portion 16 (see FIG. 1), the shaft portion 18 axially extending from the bottom portion 16, and the screw And a first intermediate product W1 including the part 20. The process until the material W0 is molded into the first intermediate product W1 includes a plurality of press molding processes, and the material W0 gradually includes the cup portion 12, the shaft portion 18, and the screw portion 20. Molded to W1. The temperature gradually decreases until the first intermediate product W1 is obtained from the heated material W0.

In the quenching step S2, the first intermediate product W1 forged in the state of the austenite structure as described above is quenched by the quenching machine 33 as it is, and the second intermediate product W2 is obtained. FIG. 4 is a schematic configuration diagram of a part of the quenching machine 33 viewed from the side. The quenching machine 33 has a cooling jacket 37 and a nozzle portion 38. The cooling jacket 37 injects the cooling liquid toward the outer peripheral surface of the shaft portion 18 of the first intermediate product W1 and the outer surface of the bottom portion 16 of the cup portion 12. The nozzle portion 38 sprays the cooling liquid onto the inner surface 22 of the cup portion 12 of the first intermediate product W1. As shown in FIG. 4, the first intermediate product W1 is cooled with the cup portion 12 facing downward.

The quenching machine 33 has a cover 40 that covers the screw portion 20 of the first intermediate product W1. The threaded portion 20 is threaded in a later machining step S4. Therefore, in the first intermediate product W1, it is preferable that the screw portion 20 is not quenched. The cover 40 prevents the cooling liquid from the cooling jacket 37 from being sprayed on the screw portion 20 and prevents it from being quenched.

After the forging step S1, until the cooling of the first intermediate product W1 is started in the quenching step S2, following the hot forging of the forging step S1, the temperature of the cup portion 12 of the first intermediate product W1 is As a whole, it does not fall below the critical temperature (A1 transformation point) at which quenching is possible and is maintained above this critical temperature. The maintenance of this temperature may be performed by a heat source such as another heater, but in the present disclosure, it is not performed by a heat source such as another heater but by heat storage of the first intermediate product W1. The details of the temperature of the cup portion 12 will be described later. Similarly to the cup portion 12, the temperature of the shaft portion 18 of the first intermediate product W1 is maintained at the critical temperature at which quenching is possible or higher. The first intermediate product W1 whose temperature is maintained in this way is cooled (quenched) by the quenching machine 33 to become the second intermediate product W2.

The temperature at the start of cooling the cup portion 12 in the quenching step S2 will be described. In the quenching step S2, the cooling start temperature on the outer surface 23 side of the cup portion 12 is lower than the cooling start temperature on the inner surface 22 side of the cup portion 12. The cooling start temperature is a quenching start temperature and is also called a quenching temperature. More specifically, the inner surface 22 side is cooled from the austenite single-phase region (single hatch region in FIG. 5), and the outer surface 23 side is cooled from the two-phase region of ferrite and austenite (cross hatch region in FIG. 5). Cooling. FIG. 5 is a state diagram of carbon steel. That is, the cooling start temperature on the inner surface 22 side is a temperature in which the inner surface 22 side is in the austenite single phase region, and the cooling start temperature on the outer surface 23 side is a temperature in which the outer surface 23 side is in the two-phase region of ferrite and austenite.

The reason why the temperature can be made different between the inner surface 22 side and the outer surface 23 side of the cup portion 12 at the start of the quenching step S2 (start of cooling) is as follows.
The temperature difference between the inner surface 22 side and the outer surface 23 side is due to the difference (difference) in heat radiation amount between the inner surface 22 side and the outer surface 23 side in the forging step S1 before the quenching step S2. That is, heat transfer is delayed on the inner surface 22 side as compared with the outer surface 23 side because the circulation of the surrounding air is poor. Further, since the inner surface 22 side is located inside the cup portion 12, the temperature is less likely to drop than the outer surface 23 side due to the effect of radiant heat. Further, the outer surface 23 side is in contact with the die for forging longer than the inner surface 22 side, and heat escapes to the die, and the temperature is likely to decrease.

The forging step S1 includes a time period in which the molded product, which is the first intermediate product W1, is left as it is. This time becomes the cooling time, and by adjusting this cooling time, the inner surface 22 side and the outer surface 23 side can be brought to desired temperatures.
As described above, in the quenching step S2, the cooling start temperature on the outer surface 23 side can be made lower than the cooling start temperature on the inner surface 22 side. In the quenching step S2, the start time of cooling (jetting of the cooling liquid) may be the same or different on the inner surface 22 side and the outer surface 23 side.

When forging is advanced in the forging step S1, the temperature of each part of the material W0 (first intermediate product W1) is gradually lowered. Therefore, in the quenching step S2, in order to obtain the temperature of each part (the inner surface 22 side and the outer surface 23 side) of the cup portion 12 as described above, the heating temperature of the material W0 by the heater device 31 in the forging step S1 is set to (the conventional 920). Set higher than (°C).

By quenching the inner surface 22 side of the cup portion 12 from a single phase of austenite, the inner surface 22 side becomes hard. For example, the hardness (Vickers hardness) of the inner surface 22 is 650 HV or more, and further 700 HV or more. On the other hand, by quenching the outer surface 23 side of the cup portion 12 from two phases of ferrite and austenite, ferrite is precipitated and the outer surface 23 side becomes softer than the inner surface 22 side. For example, the hardness (Vickers hardness) of the outer surface 23 is 500 HV or less. The Vickers hardness is based on JISZ2244 (2009).

In the present disclosure, the material W0 is carbon steel for machine structural use (S55C), and the carbon content is 0.52% by weight or more and 0.58% by weight or less. The manufacturing method of the present disclosure can be applied to other materials W0 having different carbon components. As an example of the applicable material W0 (carbon steel), the carbon content is 0.30% by weight or more and 0.70% by weight or less. Further, as another example of the material W0 (carbon steel), the carbon content is 0.30% by weight or more and 0.58% by weight or less. As still another example of the material W0 (carbon steel), the carbon content is 0.42% by weight or more and 0.58% by weight or less.

In the case of the present disclosure in which the carbon content is 0.52 wt% or more and 0.58 wt% or less, the cooling start temperature on the inner surface 22 side is 780° C. or more as an example of the temperature in the single-phase region of austenite. The temperature is 1450° C. or lower, and the cooling start temperature on the outer surface 23 side is 730° C. or higher and lower than 780° C. as an example of the temperature in the two-phase region of austenite and ferrite.

The temperatures at which the single-phase region of austenite and the two-phase region of austenite and ferrite respectively change are slightly changed depending on the carbon content in the material W0. Therefore, the cooling start temperature on the inner surface 22 side and the outer surface 23 side may be changed depending on the content of the carbon component.

For example, when the carbon content is low (for example, less than 0.52% by weight), the cooling start temperature on the inner surface 22 side is 780° C. or higher and 1500° C. as an example of the temperature in the single-phase region of austenite. Below, the cooling start temperature on the outer surface 23 side is 730° C. or higher and lower than 820° C. as an example of the temperature in the two-phase region of austenite and ferrite.

As another example, when the carbon content is high (for example, greater than 0.58% by weight), the cooling start temperature on the inner surface 22 side is 780° C. or higher as an example of the temperature in the single-phase region of austenite. Is 1450° C. or lower, and the cooling start temperature on the outer surface 23 side is 730° C. or higher and lower than 780° C. as an example of the temperature in the two-phase region of austenite and ferrite.

After the quenching step S2, the tempering process S3 is performed by the tempering machine 34 (see FIG. 2). In the tempering step S3, the second intermediate product W2 is reheated and tempered within a range not exceeding the critical temperature (A1 transformation point). The tempering process is based on a conventionally known method. A third intermediate product W3 is obtained by tempering.

In the machining process S4, the machining device 35 performs predetermined machining on the third intermediate product W3. Specifically, the inner surface 22 of the cup portion 12 is machined. The machining is grinding, and a groove or the like with which the balls make rolling contact is formed on the inner surface 22. Further, the spline 19 is finished on the shaft portion 18. Further, the threaded portion 20 is threaded.
The joint member 10 is manufactured as described above.

[Regarding the joint member 10 of the present disclosure and the manufacturing method thereof]
The joint member 10 (see FIG. 1) manufactured by the manufacturing method is as follows. That is, the joint member 10 includes a bottomed tubular cup portion 12 having a tubular portion 14 and a bottom portion 16, and a shaft portion 18 extending from the bottom portion 16 in the axial direction. The tubular portion 14 has an inner surface side layer 41 including the inner surface 22 thereof, an outer surface side layer 42 including the outer surface 23 thereof, and an intermediate layer 43 existing between the inner surface side layer 41 and the outer surface side layer 42. The inner surface side layer 41 is constituted by a quench hardening layer and has a first hardness. The outer surface side layer 42 has a second hardness lower than the first hardness. The outer surface side layer 42 of the present disclosure is configured by a quench hardening layer.

FIG. 6 is a diagram illustrating the hardness of the tubular portion 14 (representative portion having a thickness of 5 mm). In FIG. 6, “◯” is the value of the joint member 10 of the present disclosure, and “Δ” is the value of the conventional joint member. A conventional joint member is formed into a predetermined shape by forging, and then reheated from a cooled state to partially quench the inner surface side of the cup portion. 6, the horizontal axis is the distance in the direction from the inner surface 22 to the outer surface 23, the left side of the horizontal axis is the inner surface 22 side, and the right side is the outer surface 23 side. The inner surface layer 41 extends from the inner surface 22 outward to the first position of 1.0 mm (P1 in FIG. 6), and the outer surface side extends from the outer surface 23 to the second position of 1.0 mm inward (P4 in FIG. 6). When defined as the layer 42, the intermediate layer 43 is an area between the first position (P1 in FIG. 6) and the second position (P4 in FIG. 6).

The first hardness is 650 HV or higher (preferably 700 HV or higher), and the second hardness is 500 HV or lower. The value of the first hardness is the hardness of the inner surface 22, and the value of the second hardness is the hardness of the outer surface 23. To further explain the first hardness and the second hardness, the upper limit (reference) of the first hardness is 850 HV and the lower limit (reference) of the second hardness is 190 HV.

As shown in FIG. 6, the intermediate layer 43 of the joint member 10 of the present disclosure gradually hardens in the range from the first hardness to the second hardness as it goes from the inner surface side layer 41 to the outer surface side layer 42. Value is small. The “gradually decreasing hardness value” means that the hardness value decreases continuously, and as a guide, the direction (thickness) from the inner surface 22 side to the outer surface 23 side over the entire area of the intermediate layer 43. This is the case where the amount of change in hardness per millimeter along the depth direction) is less than 200 HV (preferably less than 150 HV).

In the case of the joint member 10 of the present disclosure (“◯” in FIG. 6 ), the hardness value of the intermediate layer 42 gradually decreases from the inner surface side layer 41 toward the outer surface side layer 42, and the intermediate layer 43. Then, in the entire area, the amount of change in hardness per millimeter in the direction from the inner surface 22 side to the outer surface 23 side is less than 200 HV (less than 150 HV).
In the case of the conventional joint member (“Δ” in FIG. 6), in the intermediate layer, the first position P1 in FIG. 6 and a position 1.0 mm outward from the first position P1 (P2 in FIG. 6) are provided. The hardness change amount per millimeter exceeds 400 HV. That is, the conventional hardness value of the intermediate layer does not change continuously but changes discontinuously. Further, in the case of the conventional joint member, the hardness value increases from the position P2 toward the outside.

And the manufacturing method of the joint member 10 of this indication contains the forge process S1 and the hardening process S2, as shown in FIG. 2 and FIG. In the forging step S1, a material W0 made of carbon steel having a carbon content of 0.30% by weight or more and 0.70% by weight or less is hot forged to form a cup portion 12 having a tubular portion 14 and a bottom portion 16 and a bottom portion. A first intermediate product W1 having a shaft portion 18 extending from 16 in the axial direction. In the quenching step S2, the first intermediate product W1 that has been kept at a temperature following the hot forging is cooled to be a second intermediate product W2. In the quenching step S2, the cooling start temperature on the outer surface 23 side of the cup portion 12 is lower than the cooling start temperature on the inner surface 22 side of the cup portion 12, the inner surface 22 side is cooled from the austenite single-phase region, and the outer surface 23 side is cooled. Cool from the two-phase region of ferrite and austenite.

According to this manufacturing method, cooling starts on the inner surface 22 side of the cup portion 12 from a temperature in the single-phase region of austenite, and the inner surface 22 side becomes hard. The outer surface 23 side becomes softer than the inner surface 22 side by starting cooling from the temperature in the two-phase region of ferrite and austenite. Therefore, the toughness of the cup part 12 can be improved, and the strength reduction of the cup part 12 due to, for example, a crack can be suppressed. The reduction in strength of the joint member 10 is suppressed, which enables downsizing and contributes to weight reduction.

According to the manufacturing method of the present disclosure, the joint member 10 is manufactured by forging and quenching. For this reason, reheating for partial quenching after forging, which is necessary in the conventional manufacturing method, is unnecessary, and the manufacturing process can be reduced. That is, the heat treatment in each step from the material W0 to the production of the finished joint member 10 is only the heat treatment by the heater device 31 performed at the beginning of the forging step S1.

The embodiments disclosed this time are illustrative in all points and not restrictive. The scope of rights of the present invention is not limited to the above-described embodiments, and includes all modifications within the scope equivalent to the configurations described in the scope of claims.
The quenching machine 33 (cooling jacket 37 and nozzle portion 38) may have a configuration other than that shown in FIG. 4 (FIG. 4).
In the present disclosure, among the constant velocity joints, the joint member 10 on the hub unit side of the automobile has been described, but the joint member on the vehicle center side has the same configuration and is manufactured by the same manufacturing method.

10: Joint member 12: Cup part 14: Cylindrical part 16: Bottom part 18: Shaft part 41: Inner surface side layer 42: Outer surface side layer 43: Intermediate layer W0: Material W1: First intermediate product W2: Second intermediate product

Claims (3)

A material made of carbon steel having a carbon content of 0.30% by weight or more and 0.70% by weight or less is formed by hot forging, and a cup portion having a tubular portion and a bottom portion and a shaft portion extending axially from the bottom portion. A forging step of forming into a first intermediate product having
A quenching step of cooling the first intermediate product whose temperature is maintained following the hot forging to a second intermediate product,
Including
In the quenching step, the cooling start temperature on the outer surface side of the cup portion is lower than the cooling start temperature on the inner surface side of the cup portion, the inner surface side is cooled from a single-phase region of austenite, and the outer surface side is ferrite and A method for manufacturing a joint member, comprising cooling from a two-phase region of austenite. A cup portion having a tubular portion and a bottom portion; and a shaft portion extending in the axial direction from the bottom portion,
The tubular portion is composed of a quench-hardened layer and has an inner surface side layer having a first hardness, an outer surface side layer having a second hardness lower than the first hardness, and the inner surface side layer to the outer surface side layer. The intermediate member having a hardness value gradually decreasing within the range from the first hardness to the second hardness. The joint member according to claim 2, wherein the first hardness is 650 HV or more and the second hardness is 500 HV or less.

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