JP3045795B2 - High-strength spring and oil-tempered wire for spring used in its manufacture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength spring having excellent fatigue strength suitable for a valve spring or a suspension spring of an engine of an automobile or a motorcycle, and an oil temper for a spring suitable for manufacturing the high-strength spring. About the line.

[0002]

2. Description of the Related Art At present, a part of a valve spring or a suspension spring of an engine of an automobile or a motorcycle is formed by cold-forming an oil-tempered wire into a spring.

In recent years, valve springs and suspension springs having high strength and high fatigue strength have been strongly demanded in order to increase the output of an engine and reduce the weight of a vehicle body. Increasing the strength of the spring material is one effective means for improving the fatigue strength of the spring. Therefore, a spring material with an increased amount of alloying elements has been proposed as a spring material. However, when the strength of the spring material is increased, ductility and toughness are reduced, and the notch sensitivity is increased, so that it is difficult to perform spring working by cold forming.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an oil-tempered wire for a spring having excellent spring workability by cold forming and high strength, and a high-strength spring using the same.

[0005]

The present inventors have conducted various experiments to solve this problem, and as a result, intentionally decarburized the outermost layer of the steel wire at the time of oil tempering. It has been found that the spring workability by cold forming is remarkably improved. In addition, when the outermost layer of the steel wire is decarburized, the hardness of the surface layer of the steel wire is reduced and the fatigue strength is reduced. The present invention was found to be improved by performing the treatment and the shot peening treatment, and it was found that a high-strength spring having high fatigue strength was obtained.

In the present application, (1) by weight%, C: 0.50 to 0.80, Si: 1.00 to 2.50 Mn: 0.40 to 1.00, Cr: 0.40 to 2.00 V: 0.05 to 0.60, Mo: 0.10 to 1.00, and the balance being Hv using a low alloy steel wire substantially composed of Fe and decarburizing during oil tempering. Is a high-strength spring characterized in that the hardness of the surface layer is increased to 900 or more in Hv by cold forming into a spring and thereafter nitriding or carbonitriding and shot peening. (2) In weight%, C: 0.50 to 0.80, Si: 1.00 to 2.50 Mn: 0.40 to 1.00, Cr: 0.40 to 2.00 V: 0. 0.5 to 0.60, Mo: 0.10 to 1.00, and the balance is a low alloy steel wire substantially composed of Fe.
A spring oil-tempered wire used for manufacturing a high-strength spring according to (1), wherein the hardness of the surface layer is reduced to 400 or less in Hv by decarburization during oil tempering.

C: C is an element effective for increasing the strength of steel. If the content is less than 0.50%, the required strength cannot be obtained. Since there is no advantage in strength, the range is 0.50 to 0.80%.

Si: Si is an element effective for increasing the strength of steel and improving sag resistance by forming a solid solution in ferrite. When the Si content is less than 1.00%, sufficient sag resistance is secured. Therefore, if the content exceeds 2.50%, no further effect can be obtained, so that the content is set in the range of 1.0 to 2.50%.

Mn: Mn is an element effective for improving the deoxidation of steel and the hardenability of steel. If its content is less than 0.40%, its effect is insufficient. Since no further effect can be obtained, the range is set to 0.40 to 1.00%.

[0010] Cr: Cr is an element effective for improving the hardenability of steel together with Mn. If its content is less than 0.40%, its effect is insufficient. 0.40 to 2.00 in order to suppress and lead to deterioration of strength.
%.

Mo: Mo is an element necessary for imparting strength and toughness to a spring by increasing temper softening resistance and precipitating fine carbides. Mo is effective at less than 0.10%. However, if the content exceeds 1.00%, the effect is saturated. Therefore, the content is set in the range of 0.10 to 1.00%.

V: V is an element effective for refining steel crystal grains, improving strength by precipitation hardening, and improving sag resistance. If V is less than 0.05%, the effect is not recognized. The effect is saturated even if it exceeds 0.60%, so the range is 0.05 to 0.60%.

In the present invention, the surface is decarburized at the time of oil tempering so as to prevent the oil tempered wire from being broken at the time of spring working, and the surface hardness is set to 400 or less in Hv. If the strength of the oil-tempered wire is increased without specially devising it, the sensitivity of the steel wire to flaws is increased, and extremely fine surface defects, which have been regarded as harmless in the past, serve as starting points, and are easily broken during spring processing. As will be described later with reference to FIG. 2, when the surface is decarburized at the time of oil tempering and the surface hardness is set to 400 or less in Hv, breakage during spring working can be effectively prevented. The decarburization and the adjustment of the surface hardness can be achieved by adjusting the atmosphere of the heating furnace during oil tempering. In the process before the oil tempering, a decarburization treatment may be performed in advance.

A second aspect of the present invention is a high-strength spring using the oil-tempered wire. A decrease in surface hardness causes a decrease in the fatigue strength of the spring. Therefore, in the present invention, nitriding or carbonitriding and shot peening are performed after the spring processing to adjust the surface hardness of the spring to 900 or more in Hv. The oil-tempered wire of the present invention has a low surface hardness before spring processing, but by performing spring processing and performing carbonitriding and shot peening, the surface hardness of the spring is sufficiently increased as described later with reference to FIG. Hv can be 900 or more.

[0015]

EXAMPLES Using a steel wire having the chemical composition shown in Table 1, an oil-tempered wire having a diameter of 3.2 mm and a tensile strength of 2160 N / mm ² was produced. At the time of the oil tempering treatment, the surface of the heating furnace was decarburized by adjusting the amount of atmospheric oxygen in an electric furnace as described below. A: 2-3% by volume, B: 5-7% by volume, C: 10-15% by volume, D: 2
The hardness distribution of the surface layer of the oil-tempered wire manufactured in the atmosphere of A to D with 0% or more by volume is shown by A to D in FIG. The comparative material in the figure is an example of an oil-tempered wire having the same chemical composition as the product of the present invention and having no surface decarburization by the conventional method.

The comparative material and each of the oil-tempered wires A to D were formed into the spring specifications shown in Table 2, and the breakage rate during the spring processing was examined. The results are shown in FIG. As shown in the comparative material of FIG. 2 and the oil-tempered wires having high surface hardness as shown in A and B, breakage occurred by spring processing, but C and D in FIG.
As can be seen, when the surface hardness was 400 or less in Hv, there was no breakage by spring processing. Therefore, in the present invention, the surface hardness is set to 400 or less in Hv.

[0017]

[Table 1]

FIG. 3 shows the results obtained by subjecting a spring manufactured using the D material of the present invention and the comparative material to carbonitriding and shot peening and examining the surface hardness of the spring. The conditions of carbonitriding and shot peening applied to the D material and the comparative material are the same. In the oil-tempered wire, the D material has a lower surface hardness than the comparative material, but when subjected to spring processing and further carbonitriding and shot peening, the surface hardness of the spring becomes 900 or more in Hv, which is equivalent to the comparative material. It becomes the surface hardness.

[0019]

[Table 2]

FIG. 4 shows the results of a spring fatigue test of the D material of the present invention, which was subjected to spring working, and further subjected to carbonitriding and shot peening, and a comparative material. The spring fatigue test was performed using a star coil spring fatigue tester (manufactured by Tokai Testing Machine Co., Ltd.). As shown in FIG. 4, the spring fatigue strength of the D material of the present invention was equivalent to that of the comparative material.

[0021]

Example 2 An oil-tempered wire having a diameter of 3.2 mm and a tensile strength of 2210 N / mm ² and a surface hardness of 400 or less in Hv was produced using a steel wire having a chemical composition shown in Table 3 and a tensile strength of 2210 N / mm ^2. did. FIG. 5 shows an example of the surface hardness. The oil-tempered wire was spring-processed according to the spring specifications shown in Table 2, but no breakage occurred during the spring processing. The spring was further subjected to carbonitriding and shot peening to conduct a spring fatigue test. The surface of the spring after carbonitriding and shot peening is sufficiently hard as seen in FIG.
As a result, a high fatigue strength of 590 ± 530 N / mm ² was obtained in 5 × 10 ⁷ times.

[0022]

[Table 3]

[0023]

When the oil-tempered wire of the present invention is used,
Breakage during spring processing can be effectively prevented. Therefore, even if an oil-tempered wire having higher strength than the conventional one is used, breakage during spring processing can be prevented. As a result, it becomes possible to manufacture a spring having higher strength and higher fatigue strength than before.

[Brief description of the drawings]

FIG. 1 is a diagram showing the surface hardness of an oil-tempered wire in Example 1.

FIG. 2 is a diagram showing an example of the relationship between the surface hardness of an oil-tempered wire and breakage in spring processing.

FIG. 3 is a diagram showing an example of the surface hardness of a spring after carbonitriding and shot peening;

FIG. 4 is a view showing an example of a result of a spring fatigue test;

FIG. 5 is a diagram showing another example of the surface hardness of an oil-tempered wire;

FIG. 6 is a diagram of another example of the surface hardness of a spring after carbonitriding and shot peening.

Continued on the front page (72) Inventor Mitsuyoshi Onoda 7-5-1 Higashi Narashino, Narashino City, Chiba Prefecture Inside Suzuki Metal Industry Co., Ltd. (72) Inventor Hiroaki Hayashi 7-5-1 Higashi Narashino City, Narashino City, Chiba Prefecture Suzuki Metal Industry Co., Ltd. In-house (72) Inventor Osamu Nakano 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. Inventor Naoshi Uchida 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (56) References JP-A-2-301541 (JP, A) JP-A-63-176430 (JP, A JP-A-62-177152 (JP, A) JP-A-63-303036 (JP, A) JP-A-3-162550 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 301 C21D 7/06 C22C 38/24 C22C 8/32

Claims (2)

(57) [Claims] C: 0.50 to 0.80, Si: 1.00 to 2.50 Mn: 0.40 to 1.00, Cr: 0.40 to 2.00 V: 0% by weight 0.05 to 0.60, Mo: 0.10 to 1.00, the balance being a low alloy steel wire substantially composed of Fe, and the hardness of the surface layer is 400 or less in Hv by decarburization during oil tempering. A high-strength spring characterized by having a surface hardness of 900 or more in Hv by cold forming into a spring and thereafter nitriding or carbonitriding and shot peening. 2. In% by weight, C: 0.50 to 0.80, Si: 1.00 to 2.50 Mn: 0.40 to 1.00, Cr: 0.40 to 2.00 V: 0 0.05 to 0.60, Mo: 0.10 to 1.00, and the balance is a low alloy steel wire substantially composed of Fe.
The oil tempered wire for a spring used for manufacturing a high-strength spring according to claim 1, wherein the hardness of the surface layer is reduced to 400 or less in Hv by decarburization during oil tempering.