JP2510230B2 - Method for manufacturing suspension spring for automobile having excellent high temperature sag - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spring manufacturing method which is used as a suspension spring for an automobile and which is excellent in high temperature sag.

(Prior Art) In order to improve the running performance and fuel efficiency of bicycles, the weight of automobile bodies is being reduced, and springs, which are one of the components of automobiles, are also required to be lightweight and highly stressed. There is. Particularly, in order to increase the stress of suspension springs for automobiles, it is necessary to improve the sag resistance.

Furthermore, recently, the front wheel drive system of automobiles has become the mainstream, and the operating temperature conditions of suspension springs have become severe.
Emphasis is given to the sag in the high temperature region, and the emergence of springs with excellent sag is desired.

The term "settling" is a phenomenon in which the coil spring undergoes permanent deformation during use and its free height changes. If a spring with excellent sag resistance is developed, the design stress of the spring will be reduced. It is possible to further raise the spring, and as a result, it is possible to reduce the weight of the spring.

By the way, conventional suspension springs for automobiles are JIS SUP6 ~
7 represented by Si-Mn system and SAE9254 represented by Si-C
r-type steel types or these recently developed steel types have Nb,
Hot or cold springs using spring steel to which alloy elements such as V have been added are used (Japanese Patent Publication Nos. 59-41502 and 62-37108).

Hot springs are formed by quenching the above spring steel into hot springs
It is manufactured through tempering, room temperature setting, shots, and painting processes. A cold spring is made by quenching and tempering a spring steel wire (so-called OT wire) that is cold formed into a spring and then subjected to strain relief annealing at low temperature, shot, setting, and painting.

In any of the springs manufactured by any of the processes, the conventional springs manufactured by the method of setting at room temperature cannot satisfy the strict requirement for fatigue.

(Problems to be Solved by the Invention) The present invention relates to a method for manufacturing a spring which has improved the sag property at high temperatures, which has recently become a problem as described above.

(Means for Solving the Problems) The present inventors have conducted research to solve the above problems and achieved the invention.

That is, in wt% C: 0.40 to 0.85 Si: 0.10 to 1.50 Mn: 0.30 to 1.50 Cr: 0.10 to 1.00 Al: less than 0.015 N: 0.0060 to 0.0200 is contained in the steel, and the rest is essentially Fe. Then, after hot forming, quenching and tempering, and in the case of a cold spring, after quenching and tempering the steel wire is cold formed, it is heated to 80 to 400 ° C, and in that temperature range, the spring has a shear strain of 0.005 to A method for manufacturing a suspension spring for an automobile, which is excellent in high temperature sag characteristics, characterized by giving a setting strain of 0.030.

Fig. 1 shows a wire rod with the chemical composition shown in Table 1 that has a hardness adjusted by heating and quenching a wire rod with a diameter of 11 mm to 900 ° C and then tempering it at various temperatures with shear strain γ at temperatures of 25, 100 and 150 ° C.
After applying a twisting strain of 0.019, a kneading creep test was performed at 80 ° C. to measure the residual shear strain amount after 96 hours passed.
As can be seen from the figure, when the steel is strained at 150 ° C, the residual shear strain is smaller and the settling property is better than that of SUP7 steel, which is the current standard spring, set at room temperature (25 ° C). It is understood that there is.

The present inventors have completed the present invention on the basis of such new findings for improvement in fatigue at high temperatures.

(Operation) The reasons for limiting the action of each of the constituent factors of the invention specified in the present invention will be described below.

C is an element that influences the hardenability and strength of the material, and if it is 0.40% or less, the hardness required as a spring cannot be obtained. If it exceeds 0.85%, the toughness of the spring will be reduced and it will become brittle, so it must be avoided.

Si is necessary as a deoxidizing agent, to secure hardenability and to improve sagability. The upper limit was set to 1.50% because the improvement effect saturates even if it exceeds 1.50%.

Mn is necessary as a deoxidizer and for ensuring hardenability and for obtaining a spring having a predetermined hardness. If it is less than 0.30%, the effect as a deoxidizer cannot be sufficiently obtained. Even if added over 1.50%, no further effect can be obtained, so it was excluded from the claims.

Cr is necessary to prevent the precipitation of graphite, which tends to appear when Si is high, and to improve the hardenability and obtain a predetermined hardness, like Si and Mn. Therefore, 0.10% or more is required, and 1.
Even if added in excess of 00%, no further effect can be obtained, so it was excluded from the scope of the claims.

N is necessary to effectively set the setting strain at 80 to 400 ° C. to improve the fatigue of the spring, and if 0.0060% or less, the effect is insufficient, and if 0.0200% or more, more effect can be obtained. Absent.

Al combines with N to become AlN and contributes to grain refinement. However, if the Al content is excessively large, the solid content N necessary for improving the sag property decreases due to the AlN bond, so the upper limit of the Al content is set. It was less than 0.015%.

Another point of the present invention is to apply a predetermined strain in the temperature range of 80 to 400 ° C. after forming the steel in which the chemical composition is controlled as described above into a spring.

The temperature range that gives strain is 80 to 400 ° C. Where 8
Even if strain is applied in a temperature range lower than 0 ° C, a sufficient sag-improving effect cannot be obtained. Further, even if it is heated to a temperature over 400 ° C. and strained, no further effect can be obtained, and problems such as bending of the spring will occur, so it must be avoided.

The amount of setting strain to be applied is shear strain in the range of 0.005 to 0.030. If the amount of strain applied is less than 0.005, the effect of improving fatigue is not sufficient. In addition, even if strain exceeds 0.030, no further effect can be obtained, and depending on the shape of the spring it will stick, so it must be avoided.

Two types of springs are known, the so-called hot springs and cold springs. There are two known methods for manufacturing springs. However, when the strain is applied, the hot springs are hot-molded and then quenched and tempered. Later, in the case of cold springs, steel wires (so-called OT wires) that have been quenched and tempered are cold formed into springs, which are applied after low-temperature annealing.

(Examples) The present invention will be further described below with reference to Examples.

Steel having the chemical composition shown in Table 2 was melted and rolled into a wire rod having a diameter of 12.8 mm by a usual method. From this wire, wire diameter
A suspension spring for automobiles with a diameter of 12.5 mm, an average coil diameter of 140 mm, and a height of 370 mm was hot-molded and the hardness was adjusted to H _R C52.5 by quenching and tempering.

This spring was set to 0.019 by shear strain under the conditions shown in Table 3. After that, shot projection, painting and baking were performed to make a suspension spring.

In order to evaluate the sag resistance, a tightening test was performed at 100 ° C. for a test stress of 115 kg / mm ² for 96 hours, and the sag amount (residual shear strain) at that time was compared. The results are shown in Table 3.

As is clear from the results shown in Table 3, the spring according to the method of the present invention has a sag characteristic equal to or higher than that of the existing spring.

(Effects of the Invention) By carrying out the present invention, a spring for automobile suspension having an excellent sag property can be provided by an inexpensive method instead of being manufactured using expensive expensive spring alloy steel. It can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing the residual shear strain amount at each setting temperature.

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Claims (1)

(57) [Claims] 1. A steel containing C: 0.40 to 0.85 Si: 0.10 to 1.50 Mn: 0.30 to 1.50 Cr: 0.10 to 1.00 Al: less than 0.015 N: 0.0060 to 0.0200 with the balance Fe and unavoidable impurities. In the case of a hot spring, after hot forming and quenching and tempering, and in the case of a cold spring, the quenched and tempered steel wire is cold formed and then heated to 80 to 400 ° C. A method for manufacturing a suspension spring for an automobile having excellent high temperature sag characteristics, characterized by imparting a setting strain of 0.005 to 0.030 by shear strain