JPH09122807A - Manufacture of coil spring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To omit an oxide film removing process and to reduce hours required for nitriding by applying low temp. annealing and nitriding after spring forming using an oil tempered wire specified the thickness of surface oxide films in the case of manufacturing coil springs. SOLUTION: Spring forming, low temp. annealing and nitriding are successively applied to manufacture coil springs based on the oil tempered wire wherein the thickness of surface oxide films is <1.5-3.0μm. Further, if necessary, shot peening is applied. The upper limit of the thickness of oxide films is preferably specified to be <=2.0μm. The control of the thickness of oxide films is performed by heating and quenching wire stocks under an inert gas atmosphere such as gaseous nitrogen, etc., or under a low oxygen partial pressure atmosphere, and by further tempering them under an inert gas atmosphere. By this way, coil springs are manufactured without applying the oxide film removing process before nitriding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a coil spring which does not undergo an oxide film removing step before nitriding.

[0002]

2. Description of the Related Art Conventionally, the spring working of a steel wire (oil temper wire = OT wire) that has been subjected to quenching and tempering treatments is performed in the following steps. OT wire → spring working → low temperature annealing → shot blast → (low temperature annealing) → nitriding treatment ... Here, the low temperature annealing before shot blasting is for removing the residual stress generated by the spring working. Residual stress causes cracks and other defects. Shot blasting is a step for removing the oxide film of the OT line and effectively performing the subsequent nitriding treatment. Normal OT wire has a thickness of 3-5
It has a μm oxide film. If the oxide film remains, the surface of the wire cannot be hardened sufficiently even if nitriding is performed. Further, if necessary, in order to remove the residual stress due to shot blasting, low temperature annealing may be performed immediately before the nitriding treatment.

[0003]

By the way, in the spring subjected to shot blasting, the hardness after the nitriding treatment and the depth of the hardened layer vary due to the variation of the residual stress due to the shot blasting and the dislocation introduced by the variation. It is expected that. Therefore, if possible, omitting this step is more effective in terms of performance and cost. Further, by omitting the shot blasting, the adverse effect on the nitriding treatment due to the shot blasting is eliminated, so that the nitriding treatment time may be shortened. Furthermore, it is more preferable if the low temperature annealing can be omitted.

[0004]

In view of the above circumstances, the present inventors have conducted studies so that the shot blasting and low temperature annealing steps can be omitted, and the present invention has been completed.
The features of the present invention are as follows. A method for manufacturing a coil spring in which spring working, low temperature annealing and nitriding treatment are sequentially performed using an oil tempered wire having a surface oxide film thickness of 1.5 μm or more and less than 3.0 μm as a base material. A method for manufacturing a coil spring, in which spring working, low temperature annealing, nitriding treatment and shot peening are sequentially performed using an oil tempered wire having a surface oxide film thickness of 1.5 μm or more and less than 3.0 μm as a base material. The oil-tempered wire whose surface oxide film has a thickness of 1.5 μm or more and less than 3.0 μm is used as a base material for spring processing,
A method for manufacturing a coil spring, which is followed by nitriding. The oil-tempered wire whose surface oxide film has a thickness of 1.5 μm or more and less than 3.0 μm is used as a base material for spring processing,
A method of manufacturing a coil spring in which nitriding treatment and shot peening are sequentially performed subsequently to this.

The reason why the structure is limited as described above will be described below. <Oxidation film thickness: 1.5 μm or more and less than 3.0 μm> When a wire having an oxide film of 3.0 μm or more is subjected to nitriding treatment without the oxide film removing step, sufficient hardness and hardened layer depth cannot be obtained. More preferably, the upper limit is 2.0 μm or less. On the other hand, if the thickness is less than 1.5 μm, an oxide film removing step is usually required, which is troublesome. Examples of the oxide film removing step include chemical means such as pickling, electrical means such as electrolytic polishing, and mechanical means such as shot blasting. If this step is performed, the nitriding treatment can be effectively performed, but the cost is increased.

As a method for obtaining a wire having an oxide film thickness within the above range without performing an oxide film removing step, there is a technique described in Japanese Patent Application Laid-Open No. 7-88894. That is, the wire is heated and quenched in an inert gas atmosphere such as nitrogen gas or in an atmosphere with a low oxygen partial pressure, and further tempered in an inert gas atmosphere to control the thickness of the oxide film. Prior to quenching, it is preferable to wash and remove the pretreatment agent and the wire drawing lubricant remaining on the surface of the wire after drawing. In addition, by performing quenching heating in a short time, a wire having an oxide film thickness within the above range can be obtained. By these means, a wire having an oxide film thickness of 1.5 μm or more and less than 3.0 μm can be obtained from the beginning. Since it can be obtained, the oxide film removing step can be omitted and the nitriding characteristics are not deteriorated.

<Manufacturing Method: Spring Working-Low Temperature Annealing-Nitriding Treatment> By using a wire having an oxide film thickness within the above range, the effect of nitriding treatment is achieved without performing an oxide film removing process such as shot blasting. You get enough. Therefore, the oxide film removing step such as shot blasting after the low temperature annealing can be omitted. Particularly, in the past, in order to remove the residual stress associated with shot blasting, low temperature annealing was sometimes performed immediately before the nitriding treatment, but by omitting shot blasting, this low temperature annealing step can also be omitted.

<Manufacturing method: Spring processing-nitriding treatment> Further, low-temperature annealing can be omitted if the nitriding treatment is carried out promptly so that no cracking occurs after the spring processing. Further, by omitting this, it is possible to prevent the formation of an oxide film during low temperature annealing, and it is possible to further improve the nitriding treatment efficiency.

<Manufacturing Method: Nitriding Treatment-Shot Peening> Even when shot peening is performed after the nitriding treatment in each of the above manufacturing methods, the oxide film removing step and the low temperature annealing step before the nitriding treatment can be omitted. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific examples. (Example 1) An oil-tempered wire (line A) having an oxide film thickness of 2.2 μm and an oil-tempered wire (line B) having the same thickness of 4.5 μm were used to nitrid a spring which has undergone the following steps. . Process I: A line → Spring machining → Low temperature annealing →→→→→→→→→→→ Nitriding treatment Process II: A line → Spring machining →→→→→→→→→→→→→→→ Nitriding treatment Step III: B wire → spring processing → low temperature annealing → shot blast → low temperature annealing → nitriding step IV: B wire → spring processing → low temperature annealing →→→→→→→→→→→ nitriding processing The surface hardness (hardness at a depth of 50 μm from the surface of the line) was measured to evaluate the nitriding characteristics. Table 1 shows the evaluation results. The hardness of the central portion of the wire after the nitriding treatment was about 470 (Hmv).

[0011]

[Table 1]

As is clear from Table 1, the examples (steps I and II) show surface hardness equivalent to that of the step (step III) which has been conventionally performed, and the oxide film removing step such as shot blasting or the low temperature step. It can be seen that the annealing process can be omitted. In addition, it can be seen that, in the case of a wire rod having a surface oxide film thickness of 4.5 μm (step IV), if shot blasting is omitted, it is hardly cured even if nitriding is performed.

Example 2 Shot peening was performed on the spring after the nitriding treatment in each step in Example 1 to measure the surface hardness (hardness at a depth of 50 μm from the line surface). Table 2 shows the results.

[0014]

[Table 2]

As shown in Table 2, even after shot peening, the embodiment (steps I and II) has a surface hardness equivalent to that of the step (step III) which has been conventionally performed, and oxidation such as shot blasting occurs. It can be seen that the film removing step and the low temperature annealing step can be omitted. Also, it can be seen that the wire material having a surface oxidation film thickness of 4.5 μm (step IV) is insufficiently hardened by the nitriding treatment, and thus is shot peened to have a low surface hardness.

[0016]

As described above, the oxide film removing step and the low temperature annealing step which have been conventionally performed can be omitted by using the wire having the oxide film having a thickness of 1.5 μm or more and less than 3.0 μm. In addition, the nitriding property does not deteriorate due to this omission. Therefore, it is possible to obtain at low cost a spring having the same properties as those of the conventional spring after the nitriding treatment or the shot peening.

Claims (4)

[Claims] 1. An oil tempered wire having a surface oxide film thickness of 1.5 μm or more and less than 3.0 μm as a base material,
A method for manufacturing a coil spring, which comprises sequentially performing spring processing, low temperature annealing and nitriding. 2. An oil tempered wire having a surface oxide film thickness of 1.5 μm or more and less than 3.0 μm as a base material,
A method for manufacturing a coil spring, which comprises sequentially performing spring working, low-temperature annealing, nitriding, and shot peening. 3. A coil spring comprising: an oil-tempered wire having a surface oxide film having a thickness of 1.5 μm or more and less than 3.0 μm as a base material, which is subjected to spring processing, and subsequently subjected to nitriding treatment. Production method. 4. A spring processing is performed using an oil tempered wire having a surface oxide film having a thickness of 1.5 μm or more and less than 3.0 μm as a base material, and subsequently, nitriding treatment and shot peening are sequentially performed. For manufacturing a coil spring.