JPH05195175A - Production of high fatigue strength beta-titanium alloy spring - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for manufacturing a β-titanium alloy spring having excellent fatigue characteristics. [Structure] Based on titanium, Al is 2.0 to 4.0% by weight, V is 7.0 to 9.0% by weight, and Cr is 5.0 to 7.0.
% By weight, Mo by 3.0 to 5.0% by weight, Zr by 3.0 to
Area reduction of 70 for β-titanium alloy wire containing 5.0% by weight
% After cold working to make coil spring, then 5
Aging treatment is performed at a temperature of 25 ° C. or higher and 600 ° C. or lower, and further shot peening treatment is performed.

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 titanium alloy spring that requires high fatigue strength, such as for a valve spring of an engine.

[0002]

2. Description of the Related Art Titanium alloy has a specific gravity of 4.8 g / cm ³ , which is about 40% lighter than steel and has a lateral elastic modulus of 4000 kgf.
/ Mm ² and half of steel. From such characteristics, if a spring having the same performance as steel, that is, the same spring constant is made of a titanium alloy, the weight of the spring is reduced by about 60%. Further, the height of the spring is reduced, the natural frequency is also increased, and when a high-speed amplitude is applied, resonance, so-called surging phenomenon is suppressed. Therefore, when it is used as a valve spring for an engine, the effect of improving the engine efficiency by reducing the frictional resistance of the valve train can be expected.

Titanium alloy springs exhibiting such excellent effects are disclosed in, for example, Ti-3Al-8V as shown in Preprints p15 to 20 of "Communications on Ti alloys" published by Spring Technology Research Society. A β-titanium alloy wire rod such as −6Cr-4Mo-4Zr or Ti-13V-11Cr-3Al is used, and is manufactured through the manufacturing process shown in FIG. 6.

In the above manufacturing process, the aging treatment is carried out after the coiling work. The temperature range of the aging treatment which has been conventionally carried out is JP-A-2-133578 and JP-A-2-2213.
As disclosed in Japanese Patent Publication No. 77, no.
It was ℃.

[0005]

This is because the highest tensile strength and hardness can be obtained by performing the aging treatment in this temperature range. In other words, the fatigue strength of steel wire rods, which are conventional spring wire rods, is proportional to the tensile strength and hardness of the wire rods.
The temperature condition was selected so that the hardness could be obtained.

In FIG. 5, 80% cold worked Ti-3Al
The relationship between the aging temperature and the tensile property of -8V-6Cr-4Mo-4Zr is shown. As shown in the figure, 400 ~ 500 ℃
Tensile strength of 160-180kgf / mm ²
And a value comparable to the carbon steel oil tempered wire for valve spring (SWO-V) can be obtained. However, in the spring manufacturing process, even if the aging temperature is set in the same temperature range, the SWO-V
The average spring fatigue strength was not obtained. Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a β-titanium alloy spring having excellent fatigue characteristics.

[0007]

In order to achieve the above-mentioned object, the manufacturing method of the present invention is based on titanium and contains Al of 2.
0-4.0 wt%, V 7.0-9.0 wt%, Cr 5.0-7.0 wt%, Mo 3.0-5.0 wt%,
A β-titanium alloy wire rod containing 3.0 to 5.0% by weight of Zr is cold-worked with a surface reduction rate of 70% or more to form a coil spring, and then 525 ° C to 600 ° C, preferably 5
The aging treatment is performed at a temperature of 50 ° C. or more and 600 ° C. or less, and the shot peening treatment is further performed.

[0008]

The β-titanium alloy spring manufactured by the conventional manufacturing method cannot obtain a high fatigue strength because it is treated at an aging temperature of 400 to 500 ° C., so that the tensile strength becomes high, but
This is because the elongation and the reduction of drawing are extremely reduced and the toughness becomes poor. In this respect, in the present invention, since the aging temperature is 525 ° C. or higher, preferably 550 ° C. or higher, the tensile strength is slightly decreased, but the elongation and the drawing are increased and the toughness is improved. Here, the upper limit of the aging temperature is set to 600 ° C. or less because the tensile strength is extremely lowered above this temperature, and the fatigue phenomenon becomes remarkable when high stress is used.

Further, in the spring which has been treated under the above-mentioned aging conditions,
By performing the shot peening treatment, the fatigue strength can be further improved. The shot peening treatment has a function of applying a compressive stress to the surface of the spring to reduce the tensile stress which is a cause of the fracture, but this treatment causes unevenness on the surface, and conversely, this unevenness causes the damage. It will be the starting point. At the aging temperature in the conventional manufacturing process of β-titanium alloy springs, as described above, the toughness was low and the sensitivity to surface irregularities was high, and the effect of improving the fatigue strength by shot peening was low. When treated in the aging temperature range of the present invention, the toughness is improved, the sensitivity to surface irregularities is reduced, and the effect of improving the fatigue strength by the shot peening treatment can be further exerted.

[0010]

【Example】

(Example 1) The spring of the present invention was actually manufactured and a fatigue test was conducted on the spring. The wire used to manufacture the spring is 8 mm
φ β titanium alloy rolled wire "Ti-3Al-8V-6C
r-4Mo-4Zr (wt%) ". First, this was cold drawn to 3.2 mmφ, and then coiled with the spring specifications shown in Table 1. Next, under the conditions shown in Table 2, an aging treatment was performed in an argon inert gas, and a shot peening treatment was further performed to produce 20 coil springs for each aging condition.

[0011]

[Table 1]

[0012]

[Table 2]

Further, as a comparative material, Ti-15V-3Al
Similarly, a spring was manufactured using a wire material of -3Cr-3Sn, Ti-6Al-4V. Incidentally, Ti-15V-3Al-3Cr
For -3Sn, a sample was obtained without any particular problem, but with Ti-6Al-4V, wire breakage occurred during cold wire drawing with a surface reduction rate of 30%, so 750 was used for wire drawing with a surface reduction rate of 25% or less. Annealing at 0 ° C. was repeated to obtain a coil spring of 3.2 mmφ. Furthermore, 20 coil springs made of SWO-V were manufactured as conventional materials according to the spring specifications shown in Table 3. For spring sample obtained above, stress τm = 60kgf / mm ² tightening average spring fatigue test, the amplitude stress .tau.a = 35 kgf / mm ^2, number of repetitions = 10 ⁷
The test was performed once, and the sag (residual shear strain) after the test was measured. The results are shown in Table 4.

[0014]

[Table 3]

[0015]

[Table 4]

As shown in Table 4, comparative materials (alloy type A, aging conditions-and all alloy types B and C)
Generally has a large number of breakages after the test and a high value of residual shear strain. On the other hand, the springs (alloy type A, aging condition ~) obtained in the examples of the present invention all have a small number of breakages,
The value of the strain was also comparatively small, and a value similar to that of a coil spring made of SWO-V was obtained, and it was confirmed that the fatigue characteristics were excellent.

Example 2 Next, a coil spring was manufactured using the same wire material as in Example 1, and a fatigue test was conducted. 1
0mmφ β titanium alloy rolled wire "Ti-3Al-8V"
-6Cr-4Mo-4Zr (wt%) "3.0mmφ
The wire was cold drawn up to and then coiled with the spring specifications shown in Table 5. Next, under the conditions shown in Table 6, an aging treatment was performed in an argon inert gas, and a shot peening treatment was further performed to make the coil spring 3 times for each aging condition.
0 pieces were produced. As a conventional material, 30 pieces of SWO-V coil springs were manufactured according to the spring specifications shown in Table 7.

[0018]

[Table 5]

[0019]

[Table 6]

[0020]

[Table 7]

With respect to such a coil spring, a spring fatigue test was conducted to find an average tightening stress τm = 60 kgf / mm ² ,
Amplitude stress τa = 30, 32.5, 35, 37.5, 40
It was carried out at kgf / mm ² , and the fatigue limit was determined when the number of repetitions was 10 ⁷ . Further, the sag (residual shear strain) after the test was measured. The results are shown in Table 8, the aging conditions,
SN diagrams of the springs obtained in 1. and SWO-V springs are shown in FIGS. 1 to 4, respectively.

[0022]

[Table 8]

As shown in Table 8 and FIGS. 1 and 3, the comparative materials (aging conditions ~ and and) have low fatigue limits,
The value of residual shear strain is also high. On the other hand, the springs (aging conditions ~) obtained in the examples of the present invention have a relatively high fatigue limit (see FIG. 2) and a small value of the same strain, and it is confirmed that they have excellent fatigue characteristics. It was These results are comparable to the test results for the SWO-V springs shown in Table 8 and FIG.

[0024]

As described above, according to the manufacturing method of the present invention, a titanium alloy spring having excellent fatigue characteristics can be obtained. Therefore, it can be expected to be effectively used in fields requiring high reliability such as automobile engines. In particular, when it is used as a valve spring, it is possible to reduce the frictional resistance of the engine valve operating system, and contribute to the improvement of engine efficiency and high rotation speed.

[Brief description of drawings]

FIG. 1 is an SN diagram showing a fatigue test result of a sample under an aging condition in Example 2.

FIG. 2 is an SN diagram showing a fatigue test result of a sample under an aging condition in Example 2.

FIG. 3 is an SN diagram showing a fatigue test result of a sample under an aging condition in Example 2.

FIG. 4 is an S- showing the fatigue test results of a SWO-V spring.
N diagram.

FIG. 5 is a graph showing the tensile properties of β-titanium alloy springs.

FIG. 6 is a manufacturing process drawing of a β titanium alloy spring.

Claims (1)

[Claims] 1. A titanium-based aluminum alloy having an Al content of 2.0 to 4.0.
% By weight, V is 7.0 to 9.0% by weight, Cr is 5.0 to
A β titanium alloy wire rod containing 7.0% by weight, 3.0 to 5.0% by weight of Mo, and 3.0 to 5.0% by weight of Zr was subjected to cold working with a surface reduction rate of 70% or more. The rear coil spring,
After that, 525 ℃ to 600 ℃, preferably 550 ℃
A method for producing a high fatigue strength β-titanium alloy spring, which comprises performing an aging treatment at a temperature of 600 ° C or lower and further performing a shot peening treatment.