JPH0641631A - Method for reinforcing spring - Google Patents

Abstract

PURPOSE:To simply and economically reinforce the spring by executing the cold spring formation of the stock for spring where OT treatment is executed after wire drawing, executing stress relieving and annealing, and then starting the shot peening in the specified temperature range in the subsequent cooling process. CONSTITUTION:A spring stock with a high tensile strength is obtained by executing the OT treatment after executing the wire drawing of the spring steel with a high strength. The cold spring formation of this stock is executed, and the heating at the temperature of 380-400 deg.C, the stress relieving and the annealing are executed. In the cooling process after this annealing, the shot peening is started in the temperature range where the temperature of the spring reaches 150 deg.C, preferably in the temperature range of 150-350 deg.C. This constitution allows the residual compressive stress into the surface layer to be correctly given without causing decarburization, and the fatigue strength of the spring is improved and reinforced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for strengthening a spring, and more particularly, to strengthening a coil spring manufactured by cold spring forming using a spring material which has undergone OT treatment (quenching and tempering treatment) after drawing. It is about the method.

[0002]

2. Description of the Related Art Generally, a coil spring is manufactured by drawing a hot-rolled wire rod into a spring material, which is used as a polishing rod, and then hot-springing the material after heating, quenching and tempering it, and then cold-working it. Hot-forming of a so-called coil spring that is manufactured by performing shot peening (hereinafter referred to as SP processing) in the state or in a warm state (400 ° C or less) in the tempering process and then performing setting and painting. A spring material obtained by drawing a hot-rolled wire rod and then subjecting it to OT treatment is subjected to cold spring forming, then strain relief annealing (heating to about 380 to 400 ° C.), and then SP processing in a cold state. A so-called cold forming of a coil spring which is manufactured by setting and painting is known.

The former hot forming is mainly applied to the one having a large wire diameter, which is difficult to be easily spring formed by a cold spring forming machine. SP processing is performed in a warm or warm state.
On the other hand, the latter cold forming has a relatively small wire diameter (about 15
mm or less), and SP processing is performed in a cold state as a spring strengthening method.

On the other hand, in recent years, as part of measures for reducing the weight of automobiles, weight reduction of suspension coil springs of automobiles has been promoted. The weight of the suspension coil spring can be reduced by making the wire diameter of the spring material thinner, but the strength of the material is increased by that amount, and sufficient compressive residual stress is applied to the surface layer after spring molding. It is necessary to keep it.

[0005]

However, in the above-mentioned spring forming, residual compressive stress is applied to the surface layer by SP processing to improve fatigue strength, but in the former hot spring forming, after heating In addition to the possibility of decarburization occurring during the spring forming process from spring to spring forming, when SP processing is performed in the cold state after tempering treatment, the effect of SP processing increases as the spring material becomes stronger. May not be fully expected, and if SP is processed in a warm state by reheating after performing a tempering process, SP
Although the effect of processing can be obtained, it is uneconomical to reheat, and when SP processing is performed in the warm state in the tempering process without further reheating, S
There is a problem that temperature control is required because it is said that the effect cannot be expected if P processing is performed.

Further, in the latter cold spring forming, residual compressive stress is applied to the surface layer by SP processing without worrying about various problems during the hot spring forming, but in the cold state. Since SP processing is performed, its effect cannot be expected sufficiently. Further, if SP processing is performed in a warm state by reheating, the effect of SP processing can be expected, but it is uneconomical because reheating is performed.

The present invention has been made based on the above circumstances, and its object is the cold spring forming described above, and it is economical without reheating and without extra trouble. The present invention provides a method for strengthening a spring, which can accurately apply residual compressive stress to the surface layer.

[0008]

In order to achieve the above-mentioned object, a method for strengthening a spring according to the present invention is a method in which a spring material subjected to OT treatment after wire drawing is subjected to cold spring forming, followed by strain relief annealing. The SP processing is started in the temperature range until the temperature of the spring material reaches 150 ° C in the cooling process after the annealing.

Then, SP in the above-mentioned spring strengthening method
After the processing, the SP processing may be further performed.

[0010]

In the present invention, after forming the cold spring, it is usually 380 to 4
Since the SP processing is started in the temperature range until the temperature of the spring material reaches 150 ° C in the cooling process of the strain relief annealing performed by heating to about 00 ° C, the heating temperature is low and there is no fear of decarburization.
In addition, it is economical because there is no need to newly reheat. In addition, since SP processing is started when the temperature of the spring material is in the warm range until it reaches 150 ° C, residual compressive stress can be accurately applied to the surface layer, greatly improving the fatigue strength of the spring material. Can be expected. In order to obtain such an effect more effectively, it is desirable to start the SP processing when the temperature of the spring material in the cooling process is in the range of 150 to 350 ° C, and outside this range, the expected effect becomes small.

[0011]

[Examples] The high-strength spring steel materials shown in Table 1 were drawn to a wire diameter of 11.6 mm, and the tensile strength was adjusted to 210 kgf / mm ² by OT treatment. The test material thus obtained was treated under the treatment conditions corresponding to strain relief annealing at 390 ° C for 20 minutes and the cooling process
At 00 ℃ and 250 ℃, after further cooling to room temperature for comparison, SP processing was performed under the following SP processing conditions.
The residual compressive stress of the surface layer after P processing was investigated by the X-ray diffraction method. The results of this investigation are shown in FIG. The warm shot in FIG. 1 is at room temperature. Also,
In the warm shot of FIG.
This is the case where after applying at 50 ° C or 300 ° C, the temperature is lowered to room temperature and then SP processing conditions are applied. In addition, FIG.
FIG. 6 is a graph chart in the case where the area up to a depth of 0.3 mm of the curve obtained in (1) is 100 at room temperature. In addition, FIG.
It is a figure showing the cooling characteristic by natural cooling (cooling in the air) of the wire rod surface after processing equivalent to stress relief annealing, a solid line is a case where the wire diameter is 11.6 mm, and a broken line is a case where the wire diameter is 4.0 mm.

[0012]

[Table 1]

SP processing conditions: Steel balls having a grain size of 0.8 mm at a speed of 95 m / sec 1
Project 30kg. : Steel ball with a grain size of 0.3 mm at a speed of 50 m / sec 1
Project 30kg. (However, it is performed at room temperature.): The above projection is performed after the above projection.

As is clear from FIG. 1 of the above-mentioned survey results,
In contrast to the results after cooling performed for comparison, those subjected to SP processing at the temperatures of 300 ° C. and 250 ° C., which are the methods of the present invention, have a high residual compressive stress value of the surface layer and the residual compressive stress reaches The depth is deep. Further, in the case of SP processing in which SP processing is performed in addition to SP processing, the residual compressive stress value of the surface layer becomes higher. Moreover, FIG. 2 shows that the method of the present invention causes a large residual compressive stress as compared with room temperature. From this, it can be seen that the method of the present invention strengthens the spring.

As is clear from FIG. 3, when the wire diameter is small, the rate of temperature decrease is high, and therefore S at the time when the surface temperature is high.
It is necessary to start P processing. In addition, if SP processing is applied, the rate of temperature decrease will be even faster.
It is necessary to determine the temperature at which processing starts.

[0016]

As described above, according to the method for strengthening a spring according to the present invention, a large residual amount can be economically retained on the surface layer without reheating by cold spring forming and without extra work. Compressive stress can be applied, which greatly improves fatigue strength and life, and the strength can be improved to reduce the wire diameter of the spring, which can be useful for reducing the weight of automobiles or aircraft. .

[Brief description of drawings]

FIG. 1 is a residual compressive stress distribution diagram of a surface layer of a spring.

FIG. 2 is a graph showing a case where the area up to a depth of 0.3 mm of the curve obtained in FIG. 1 is 100 at room temperature.

FIG. 3 is a diagram showing a cooling characteristic by natural cooling of a surface of a wire after a treatment corresponding to strain relief annealing.

[Explanation of symbols]: Steel balls with a grain size of 0.8 mm at a speed of 95 m / sec 1
Residual compressive stress curve when projecting 30 kg: Steel ball with a grain size of 0.3 mm at a speed of 50 m / sec 1
Residual compressive stress curve when projecting 30 kg: Residual compressive stress curve when projecting above after projecting above

Claims (2)

[Claims] 1. A spring material, which has been subjected to OT treatment after wire drawing, is subjected to cold spring forming, then strain relief annealing is performed, and a temperature range until the temperature of the spring material reaches 150 ° C. in the cooling process after the annealing. A method for strengthening a spring, characterized by starting shot peening in. 2. A method for strengthening a spring, wherein after the shot peening according to claim 1, shot peening is further performed.