JPS6164817A - Manufacture of hollow stabilizer using electric welded pipe - Google Patents

Abstract

PURPOSE:To manufacture hollow stabilizers in large quantities by hardening and tempering each straight electric welded pipe of low carbon steel and carrying out forming. CONSTITUTION:Each straight electric welded pipe of low carbon steel contg. 0.1-0.35% carbon is hardened by rapid heating at >=30 deg.C/sec heating rate by direct electrification heating and by water quenching. It is then tempered by heating at >=30 deg.C/sec heating rate in the temp. range of 120-250 deg.C or 375-500 deg.C by direct electrification heating. The heat treated pipe is bent to the desired shape of a stabilizer by cold working, and it is subjected to stress relief annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a hollow stabilizer using an electric vi tube for use in vehicles such as automobiles.

[Technical background of the invention and its problems]

As is well known, in automobiles, stabilizers are used in the suspension structure as a means of assisting roll rigidity. Conventionally, a solid round bar was generally used for bending. However, recently, from the viewpoint of reducing the weight of vehicles and saving resources, it has been desired to use lightweight pipe materials instead of solid materials.

By the way, the conventional manufacturing process for solid stabilizers is generally as shown in Fig. 5, in which a solid round bar is perforated at the end, then hot bent and formed, then oil quenched and then tempered. We are trying to correct the shape.

On the other hand, in the case of a hollow stabilizer, since it is made of pipe material, the bent portion of the pipe tends to become flat during bending by hot pressing. Furthermore, oil may enter the pipe during oil quenching, creating a risk of fire during the subsequent tempering process.

Therefore, a method of manufacturing hollow stabilizers, which is currently in some practical use, is carried out by the steps shown in FIG. 6. That is, cold bending is performed using a rotary bender instead of hot press bending, and water quenching is used instead of oil quenching. This method also has problems, such as uneven heating and cooling during quenching, and unevenness in product shape due to quenching distortion, making a straightening step indispensable. For this reason, at present, a method for mass-producing hollow stabilizers has not yet been fully established.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its purpose is to enable mass production of hollow stabilizers of stable quality using electric resistance welded tubes through a process that is simpler than conventional methods.

[Summary of the invention]

The gist of the present invention is to rapidly heat a straight low carbon wA electric resistance welded tube with a carbon content of 0.10 to 0.35% by a direct current heating method, water quench it, and then heat it at 120°C to 250°C or It is tempered in a temperature range of 375° C. to 500° C., then bent and formed into a desired stabilizer shape by cold working, and further subjected to strain relief annealing after forming.

In the present invention, since the pipe is water quenched in a straight pipe state, cooling performance during quenching can be effectively obtained. Therefore, it is not necessary to use special steel types such as 5UP9, which had conventionally been necessary to improve hardenability, and it is also possible to prevent uneven heating and cooling during hardening. Also,
As mentioned above, water-quenched low carbon steel has relatively high toughness, and since it is tempered and then cold bent, its bending workability is stable, and it can be annealed for strain relief after forming the stabilizer. By implementing this, stable performance quality can be obtained. Moreover, it is quenched in the straight pipe state.
Since tempering is performed and then bending is performed, the straightening step, which is essential in conventional methods, can be omitted, and mass productivity is improved.

(Example of the invention) (Example 1) C: 0.23%, Si: 0.21
%, Mn: 0.58%, a straight low carbon steel electric resistance welded tube is used to manufacture a hollow stabilizer through the steps shown in FIG. First, the low carbon steel electric resistance welded tube is water quenched.

The quenching heating uses a direct current heating method in which a current is passed through both ends of the tube 1, as shown in FIG. Heating rate is 30℃/
Rapid heating is performed for more than seconds to a temperature of 950°C to 1100°C. Then, the heated tube 1 is passed through the water cooling jacket 2 to be quenched. Quenching hardness is C:
In the case of 0.23%, the HRC is 45 to 47. In Fig. 2, 3 is a transformer, 4 is a feed roller, and 5 is a transformer.
indicates a restraining roller.

After the above straight pipe quenching, low-temperature tempering is performed in a furnace at 150° C. for 30 minutes. Next, using a rotary bender, the stabilizer is cold bent into a desired stabilizer shape, and the end is marked.

Next, in order to remove the strain caused by the cold bending process,
Annealing is performed at 00°C for 50 minutes. Hardness is HRC37 to 39. Next, shot peening and painting are performed in the same manner as before to create a product.

(Example 2) Using the low carbon steel N gutter pipe described in Example 1, water quenching was performed in the same manner as in Example 1, and then rapid heating was performed at 30°C/second or more by direct current heating method,
Rapid tempering is carried out at a temperature of 470°C. The cold bending and end marking processing are the same as in Example 1. After forming, strain relief annealing is performed at 450° C. for 50 minutes. Hardness is HR631-34.

(Example 3) Using the above low carbon steel ERW pipe, Example 1
After water quenching in the same manner as
Tempering is performed for 30 minutes. The cold bending and end marking processing are the same as in Example 1. Further, strain relief annealing after molding is performed at 300° C. for 50 minutes. Hardness is HRo32
The number is between 34 and 34.

Table 1 below compares the durability test results of the hollow stabilizers obtained in Examples 1 to 3 above and the hollow stabilizers obtained by the conventional method. Here, the conventional method refers to a method in which the green material is bent and formed, then subjected to end processing, and further tempered at 400'C x 50 minutes after being quenched by heating with electric current.

Table 1 As shown above, each of the examples showed durability that was 1.5 to 2 times as good as that of the conventional method.

By the way, as described in the above example, 0,
It is known that martensite of 10 to 0.35% low carbon steel is relatively tough and can withstand cold working to some extent. According to experiments and considerations conducted by the inventors, as shown in FIG. 3, even a pipe material (corresponding to S23C) with only quenching shows an elongation of about 12%. Therefore, although it is possible to perform cold forming (stabilizer bending) with only quenching,
According to experiments conducted by the present inventors, the mechanical properties of the material are unstable immediately after quenching because martensitic transformation is in progress, and as a result, the bending properties are also extremely unstable. understood.

Table 2 below shows the results of an experiment that investigated the relationship between the tempering temperature and the defective rate during bending in 823C-equivalent electric resistance welded tubes.

From this experiment, it was found that bending workability becomes very stable by performing tempering at a low temperature of 120°C to 250°C or at a temperature of 375°C or higher. However, if the tempering temperature exceeds 500°C, the material becomes too soft and sufficient durability cannot be obtained. In Table 2, the weld bead position A means the case where the welding dot 10 is located on the outside with respect to the bending center C, as shown in FIG. 4(A), and the weld bead position B This means that the weld bead 10 is located inside the bending center C as shown in FIG. 4(B). The reason why the experiment was conducted with the bead section set at the above position was to improve the durability of the stabilizer, and as disclosed in Japanese Patent Publication No. 57-59451, the applicant of the present application had already filed an application and the radius of curvature of the curved section was determined. This is because the angle must be within a predetermined angle range centered on position A or position @B due to the relationship.

Table 2 As shown above, by limiting the tempering temperature between 120°C and 250°C or between 375°C and 500°C,
It was found that the bending workability of the low carbon electric resistance welded tube after water quenching and tempering is very stable.

In addition, the quenching heating rate by direct current heating method was increased to 30℃/
By setting the time to 2 seconds or more, coarsening of crystal grains and occurrence of decarburization can be prevented, and the production speed is high, making it suitable for production.

Further, as described in Example 2, if the tempering heating is performed by the direct current heating method and the heating rate is rapid heating of 30° C./sec or more, the productivity can be further improved.

According to research conducted by the present inventors, if the strain relief annealing temperature is less than 300°C, residual stress (strain) during bending cannot be sufficiently removed, and if it exceeds 450°C, the material becomes too soft. Therefore, sufficient durability cannot be obtained. Therefore, it is desirable that the strain relief annealing temperature be between 300°C and 450°C. Furthermore, if the carbon content of the material is lower than 0.10%, it will not be sufficiently hardened, and if the carbon content exceeds 0.35%, cracking will become noticeable during cold working. Therefore, in the present invention, a low carbon steel 1iti4 tube having a carbon content between 0.10 and 0.35% is used. In addition, the quenching hardness is, for example, HRc50 to 52.0 at 0.30C.
．． 23C HRc45~47.0.13G HRc
It is 38-40.

〔Effect of the invention〕

As mentioned above, according to the present invention, a hollow stabilizer of stable quality can be obtained using a low carbon 14uA tube without using any special steel type, and it is also possible to obtain a hollow stabilizer of stable quality by quenching and tempering the straight tube and then forming it. Therefore, there is no need for the straightening process that was required in the past, and there is no need for quenching oil, making this method of manufacturing hollow stabilizers excellent in mass production.

[Brief explanation of the drawing]

Fig. 1 is a process explanatory diagram showing one embodiment of the method of the present invention;
The figure is a schematic diagram showing an example of a quenching device, and Figure 3 is a 523C
Diagram showing the relationship between the tempering temperature and material properties of the corresponding material, No. 4
Figures (A) and (B) are end views showing the positional relationship between the bending center and the bead portion, respectively. FIG. 5 is a diagram showing the manufacturing process of a conventional solid stabilizer, and FIG. 6 is a diagram showing the manufacturing process of a conventional hollow stabilizer. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (4)

[Claims] (1) A straight low carbon steel ERW tube with a carbon content of 0.10 to 0.35% is rapidly heated by direct current heating method and water quenched, then heated from 120℃ to 250℃ or from 375℃ to 500℃. A method for manufacturing a hollow stabilizer using an electric resistance welded tube, characterized by tempering in a temperature range, then bending and forming into a desired stabilizer shape by cold working, and further performing strain relief annealing after forming. (2) The quenching heating rate by the above direct current heating method is 3
A method for manufacturing a hollow stabilizer using an electric resistance welded tube according to claim 1, characterized in that the temperature is 0° C./second or more. (3) A hollow tube using an electric resistance welded pipe according to claim 1, characterized in that the tempering heating is performed by a direct current heating method, and the heating rate is rapid heating of 30° C./second or more. Stabilizer manufacturing method. (4) The temperature of the above strain relief annealing was changed from 300℃ to 450℃.
A method for manufacturing a hollow stabilizer using an electric resistance welded tube according to claim 1, wherein the temperature is between .degree.