JPS59229416A - Production of spring steel wire having excellent resistance to permanent set in fatigue - Google Patents

Abstract

PURPOSE:To produce inexpensively a spring steel wire having excellent resistance to permanent set in fatigue without increasing strength by subjecting a spring steel wire rod contg. a specific compsn. amt. of carbon to a hardening treatment then to a tempering treatment under the tensile strain applied thereon. CONSTITUTION:A spring steel wire rod 2 contg. 0.5-0.7wt% C is fed from a supply 1 by pinch rolls 3 and is heated to a prescribed hardening temp. by a heater 4. The heated wire rod is cooled in a cooling tanks to complete the hardening treatment. The wire rod 2, which is kept applied with tensile strain by strain applying devices 6, 7, is heated to a tempering temp. by a heater 8 so as to attain prescribed strength and affter the heated wire rod is cooled in a cooling tank 9, the wire rod is taken up on a coiler 10. A spring steel wire 11 having remarkably improved resistance to permanent set in fatigue is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a method for manufacturing a spring steel wire with excellent fatigue resistance used in vehicle suspension springs and the like.

(b) Background of the Technology 1 - There are problems with steel wires for suspension springs for vehicles, such as fatigue resistance and relaxation value. Here, "settling" is a phenomenon in which a coil spring undergoes permanent deformation during use and its free height changes. Conventionally, such spring steel wires were manufactured by JISSU.
Although steel wires of steel grades such as P 6-7 and 5AE9254 are used, there is a need to reduce the weight of vehicles to save energy, and one of these demands is a steel wire for springs with excellent fatigue resistance. There is. That is, if a spring steel wire with excellent resistance to fatigue could be developed, it would be possible to further reduce the design stress, and as a result, the weight of the coil spring could be reduced. In order to improve this resistance to fatigue, attempts have been made to increase the strength of the columns by heat treatment, but if the strength is increased unnecessarily, the increased strength will result in a lack of toughness such as elongation and drawing. There is a problem with doing so.

In addition, increasing the strength of the steel wire increases its sensitivity to minute eaves and internal defects on the surface of the steel wire, resulting in practical problems such as a lack of reliability such as easy breakage during spring processing or use. The inventors of the present invention have conducted various studies to obtain a spring steel wire with excellent fatigue resistance without reducing strength, and have succeeded in achieving the objective. It is.

(C) Disclosure of the Invention A feature of the present invention is a method for producing a spring steel wire with excellent resistance to set, which comprises performing a tempering treatment while applying tensile strain after quenching.

The spring steel wire of the present invention is manufactured as follows.

FIG. 1 is a schematic diagram showing the process. The wire rod 2 supplied from the supply 1 is sent in the direction of the arrow by the feeding pinch roller 5 and sent to the heating device 4 . Here, the wire rod is heated to a quenching temperature determined by the steel type of the steel product, and is cooled in a cooling tank 5 to complete the quenching process. Thereafter, the steel wire is subjected to tensile strain by devices 6 and 7, and heated to a tempering temperature by heating device 8 so as to have a predetermined strength. After that, the winder 1 is cooled by a cooling tank 9.
It is wound up to 0. It was found that the steel wire 11 manufactured in this manner is a spring steel wire with significantly improved resistance to set. Although the cooling tank 9 is located in front of the strain applying device 7 in FIG. 1, it may be located after this. Next, an example will be explained.

B) Best Mode for Carrying Out the Invention Embodiment 1 Two sets of two caterpillars rotating in the same direction while being in pressure contact with each other are arranged in the tensile strain imparting devices 6 and 7 at an interval, and one set is on the exit side. The caterpillars are configured to be driven at a faster circumferential speed than the set of caterpillars on the entrance side. Second
The figure shows an example of this device, with A on the entrance side,
A steel wire 2 is sandwiched between a pair of caterpillars made up of two B strips, and fed in while being held by caterpillars A and B so that it does not slip even when tension is applied to the steel wire 2 as shown by the arrow. The steel wire rotates the caterpillar CD faster than the caterpillar AB so that a tensile strain is applied between the tracks AB and CD.

During this time, it is heated to the tempering temperature by the heating device 8 and cooled to room temperature in the cooling tank 9.

SAE 9254 (
0.56wt%C, 1.37wt%Si, 0.70
Tempering treatment was performed while applying tensile strain using wt% Mn, [ ], and 559 wt% Cr. During this time, the quenching temperature was 970°C, the tempering temperature was 465°C, and the tensile strain was 1.2% and 2.5%.

It gave 3.2%. The tensile strength of the steel wire after heat treatment is approximately 2
It was 00 hair. The steel wire produced in this manner was processed into a coil spring and subjected to a static test to test its resistance to fatigue. For comparison, coil springs with the same specifications were made using SAE 9254 and 5UP7 steel wires that had been subjected to normal quenching and tempering treatments to have a tensile strength of 200 hairs.
The specifications of the coil spring are as follows.

Wire diameter: 9.5. m Coil average diameter: 60y Free height: 260. m Effective number of turns: 4.25 Total number of turns + 6.25 After setting with a stress of 125" and Q using this, a constant load of 1 is applied so that the test stress is 120 kg/Il.
Table 1 shows the results of a settling test at room temperature under continuous loading for 00 hours.

5-41 As shown in Table 1, the spring steel wire according to the present invention was found to have extremely superior fatigue resistance compared to conventional products.

Embodiment 2 Two capstans are used as the tensile strain imparting devices 6 and 7, and the capstan on the exit side is configured to be driven at a faster circumferential speed than the capstan on the inlet side. Figure 6 shows an example of this device, in which the steel wire is connected to the capstan F so that tensile strain is applied between the capstans E and F.
Rotate faster than capstan E. During this time, the material is heated to the tempering temperature by the heating device 8 and cooled to room temperature in the cooling tank 9. Using the above-mentioned equipment, 6 pieces of real fruit were used as test materials.
- Tempering treatment was performed using SAE 9254, the same as in Case 1, while applying tensile strain. At this time, the quenching temperature is 970°C9
The tempering temperature was 465°C and the tensile strain was 1.2%.

2.5% and 6.2% were given. The tensile strength of the steel wire after heat treatment was approximately 185'Q/d. A coil spring with the same specifications as in Example 1 was prepared using this steel wire and tested for resistance to settling at room temperature. As expected, 5AE9254 is a comparison product.
, 5UP7 steel wire was prepared with a tensile strength of 185"/d by normal quenching and tempering treatment, and a coil of the same shape was prepared. After setting these with a stress of 125 ki//, II, the test was carried out. Table 2 shows the results of a resistance test at room temperature in which a constant load was applied continuously for 100 hours so that the stress was 120''/d.

Table 2 As shown in Table 2, the products of the present invention have significantly better resistance to settling than the comparative products. As is clear from the following two examples, the steel wire of the present invention has excellent fatigue resistance without increasing the strength or using expensive special metals as in the conventional manufacturing method of oil tempered wire. Steel wire for springs can be manufactured. It has also been found that the steel wire of the present invention is useful for weight reduction when used in cold-worked vehicle suspension springs.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 6 are process schematic diagrams for carrying out the manufacturing method of the present invention. 1: Supply, 2: Wire rod, 3 = Pinch roll for feeding, 4
, 8: heating device, 5, 9: cooling tank, 6, 7: strain imparting device, 10: winding machine, 11: steel wire of the present invention. A, B, C, D: Caterpillar, E, F: Capstan. 8-

Claims (1)

[Claims] (1) In the manufacture of spring steel wire that contains 0.5 to 0.7 wt% carbon and is manufactured by quenching and tempering, after the quenching treatment, the steel wire is subjected to tensile strain while being A method for producing a spring steel wire with excellent resistance to setting, characterized in that the steel wire is tempered to provide resistance to setting. (2. In the manufacturing method described in claim (1), the method of imparting tensile strain is cold-open molding, and the spring has excellent fatigue resistance, characterized in that it is used in a vehicle suspension. Method of manufacturing steel wire.