JPS6030736B2 - Manufacturing method for cold-formed coil springs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a coil spring formed between sleeves, which contains 2.2% or less of silicon, 1.0% or less of manganese, 1.1% or less of chromium, and has a carbon content of 0.35~0
．． 5% low alloy steel is quenched and tempered by induction heat treatment to give it a strength of 150k9/m or more, and then cold-formed. It is.

The currently used manufacturing methods for coil springs are broadly divided into cold forming methods and hot forming methods.

The cold forming method is mainly used for wires with a small diameter, and the hot forming method is mainly used for wires with a large recess of, for example, 8 sails J or more. As the diameter of the material increases, the higher the strength, the more difficult it becomes to cold form the material. With the collar forming method, the material strength is 150 with a large diameter.
It is said that it is difficult to manufacture coil springs with a diameter of k9' or more. According to the hot forming method, it is easy to form even large-diameter springs, and high-strength coil springs can be manufactured by heat treatment after forming, but in practice, the heat treatment tends to be uneven and the surface Due to additional factors such as problems such as rough skin and poor shape, the quality is usually lower with cold molding. The present invention aims to provide a method for forming a coil spring between the sleeves, which eliminates the difficulties inherent in the conventional manufacturing methods as described above. The present invention has the following configuration.

1 Contains 2.2% or less silicon, 1.0% or less manganese, 1.1% or less chromium, and has a carbon content of 0.3
A woven material made of low alloy steel with a content of 5 to 0.5% is given a strength of 150k9/iso or higher by rapid heating and cooling treatment such as high frequency heat treatment.

The most required mechanical property for springs is high fatigue strength.

It is well known that fatigue strength is correlated with tensile strength or hardness. As the tensile strength increases, the fatigue strength also increases, but on the other hand, the brittleness that gradually decreases in toughness due to elongation, drawing, etc. increases, so industrially, the strength of spring materials is 150 kg/fence to 160 kg in tensile strength. / The limit is about the size of a square. Currently, oil-tempered wire such as hard steel wire, piano wire, or spring steel is used as spring material for cold forming, but all of them have a relatively high carbon content of about 0.5 to 0.9%. After drawing the material, it is usually manufactured by subjecting it to a deep tempering treatment to give it a predetermined strength, and after forming the material, removing residual stress and performing shot peening.

In contrast, in the present invention, the carbon content of the spring material is limited to a range of 0.35 to 0.50%.

According to the experiments of the present inventor, rapid heating and rapid cooling heat treatment such as high-frequency induction heating can produce a very fine martensitic structure, which has high strength and high plowability, when compared with normal heat treatment. It has been found that it has favorable mechanical properties as a spring material, and because the heating time is short, there is almost no risk of surface damage during the heat treatment process, and combined with the fine structure, higher fatigue strength can be obtained. There is. Figure 1 shows part of the test results for already known carbon steel. The relationship between carbon content and rotating bending fatigue strength is shown, with 1 showing the case of induction hardening and 2 showing the case of electric furnace hardening.

From FIG. 1, it is known that a rapid heating method such as high-frequency heat treatment can provide higher fatigue strength than a normal heat treatment method. Therefore, the lower the carbon content of the material, the greater the difference in fatigue strength between the materials obtained by each of the two methods, and the difference becomes smaller when the carbon content is 0.5% or more. On the other hand, when a steel material containing a high carbon content, such as the oil-tempered wire mentioned above, is subjected to a rapid cooling treatment such as water injection, the strain stress on the surface of the steel material increases, and the adjacent transformation stress increases. This is compounded and there is a risk of localized quenching cracking.

Therefore, in order to provide the spring material with the effect of rapid heating and cooling most safely and effectively, it is preferable to use a steel material with a carbon content within the above-mentioned range as the material. In the present invention, the carbon content of the spring material is 0.35 to 0.5.
The reason for limiting the range to % is due to the reasons mentioned above, including those described below. In the present invention, in addition to the above-mentioned carbon content, the chemical composition of the spring material has a silicon content of 2.2% or less, and a manganese content of 1.0%.
Hereinafter, the chromium content is limited to 1.1% or less.

According to the inventor's experiments, the carbon content is 0.35 to 0.5
% Si, Cr steel has a tensile strength of 150 by rapid heating and cooling treatment.
It was found that mechanical properties of k9/iso to 180 kg/iso, elongation, and about 12 to 15% could be obtained.

The present inventor has shown in Table 1 that the Si, Cr steel wire rod according to the present invention whose chemical composition is shown and the conventional Sup6 were subjected to induction quenching and tempering treatment and oil tempering treatment, respectively. The mechanical properties are shown in the table.

From Table 2, it can be seen that according to the present invention, high-frequency heat treated Si,
It turns out that Cr steel has higher tensile strength and higher rutting resistance than oil tempered Sup6. Table 2 The inventor further found that C: 0.35-0.5%, Si<2
．． 2%, Mn<1.0%, Cr<1.1%, several types of alloy steels were subjected to ordinary induction heat treatment similar to that described above, and all test specimens had a tensile strength of 1.
It was found that mechanical properties of 50k9/base to 180k9/base and elongation of 12 to 15% could be obtained.

In this case, as the amount of Si added increased, the effect of suppressing crystal grain growth and the effect of reducing low-temperature tempering brittleness increased, but when the amount added exceeds 2.2%, these effects became constant. However, no improvement in effectiveness was observed. This is the reason why the Si content is limited to 2.2% or less in this application. In addition, increasing the amount of Mn added improves the hardenability, but in the case of this application, Si
, Mn is 1.0% due to the coexistence of Cr.
Exceeding this will result in the development of akifang arm. To prevent this,
In this application, the Mn content is set to 1.0% or less. Furthermore, the addition of Cr is used to refine crystal grains, inhibit grain growth,
It is effective in improving hardenability, but if it exceeds 1.1%,
It was found that the impact properties deteriorated significantly. Therefore, in this application, the Cr content is limited to 1.1% or less.
In addition, for example, for steel materials for large diameters of 8 ribs ◇ or more, adding Mn in the range of 0.5 to 1.0% and boron in the range of 5/1000% or less will give even better competition. It's also possible to get help. Of course. 2. Manufacture a coil spring using the material in 1 by cold forming.

Therefore, it has been found that by using the above-described steel material according to the present invention, it is actually possible to easily form a large meridian wire rod, for example, about 16 side J, by cold working.

Table 3 shows some of the experimental conditions and experimental results of experiments conducted by the inventor in this regard. It is clear from the experimental results shown in Table 3 that a product can be produced that fully satisfies the mechanical properties required for, for example, below-the-knee springs for automobiles.

On the other hand, cold-formed coil springs undergo cold plastic processing and residual strain stress remains, which causes a decrease in strength, so it is common to heat the spring to 400° to 500° after forming to remove stress. In this case, the residual stress decreases as the temperature rises and almost disappears at about 500 pm.

Coil spring material according to the present invention (C: 0.47%, Si: 1
．． 70%, Mn: 0.73%, Cr: 0.46%), the relationship between the tempering temperature and tensile strength is shown in Figure 2. As the competitive tempering temperature increases, the tensile strength gradually decreases. However, the spring material according to the present invention containing 0.35% or more of carbon has a higher resistance than carbon steel, and has a resistance of 400 to 400%.
Even at a competition temperature of 500 qo, the intensity level is still 15
Since 0k9/fence to 180k9/fence can be secured, there is almost no fear that the strength before heating will decrease even if heating is performed to remove stress after molding. Furthermore, it is well known that shot peening after stress relief improves the mechanical properties of coil springs. clearly shows.

In Figure 3, 3 is the fatigue strength when the material Sup6 shown in Table 1 is heat treated and heated to remove stress;
' is the fatigue strength after shot peening the above material 3, 4 is the fatigue strength when the Si, Cr steel shown in Table 1 is subjected to high frequency heat treatment and heated to remove stress, 4
' is a diagram showing the fatigue strength after subjecting the material 4 to shot peening treatment. As is clear from the above,
According to the present invention, Si is 2.2% or less, Mml. 0% or less, Crl. 1% or less, carbon content 0.35-0.
By quenching and tempering the 5% steel material using high-frequency heat treatment, it has no fear of dawn cracking and has high fatigue strength.
Moreover, it is possible to provide a coil spring that is easy to form between the lines even in a large area, and even when the coil spring is heated for stress relief after forming between the lines, there is almost no effect on the mechanical properties before the heating. As a result,
It is possible to provide a particularly large-diameter, high-strength, and inexpensive coil spring that has been difficult to manufacture in the past.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the carbon content of the heated material and the rotating bending fatigue strength in rapid heating and cooling treatments such as induction quenching and tempering, and heat treatment in a normal electric furnace. FIG. 3 is a diagram showing the relationship between the temperature at dawn and the tensile strength of the material in the present invention, and FIG. FIG. Tsutomu'zu Iso 2 Kojichin 3

Claims (1)

[Claims] 1 Contains 2.2% or less silicon, 1.0% or less manganese, 1.1% or less chromium, and has a carbon content of 0.35
A cold-formed coil characterized in that a wire made of low-alloy steel of ~0.5% is quenched and tempered by induction heat treatment to impart a strength of 150 kg/mm^2 or more, and then cold-formed. Spring manufacturing method.