JPH03115550A - Method for working beta-type titanium alloy - Google Patents

Abstract

PURPOSE:To give superplasticity in the titanium alloy and to easily execute its working with good workability at a low cost by subjecting a beta-type Ti alloy having a specified compsn. contg. V, Cr, Sn, Al and Ti to preworking at a specified high working ratio and thereafter executing isothermal working. CONSTITUTION:A beta-type Ti alloy contg., by weight, 10 to 20% V, 1 to 5% Cr, 1 to 5% Sn, 1 to 5% Al and the balance Ti is subjected to preworking at >=70% working ratio. The preworking is preferably executed in the temp. range of a room temp. to 750 deg.C. After that, the alloy is subjected to isothermal working. The isothermal working is preferably executed in the temp. range of 650 to 775 deg.C. Furthermore, the above isothermal working is preferably executed in the range of 1X10<-4>S<-1> to 3X10<-2>S<-1> strain rate. In this way, at the time of executing the isothermal working to the alloy, crystalline grains are refined in the stage of holding under heating to give superplasticity, by which the reduction of the manufacturing cost, the improvement of the transferability, the diversification of the design by diffusion joining or the like are permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a processing method for improving the isothermal workability of β-type titanium alloy.

- [Summary of the invention] Vanadium 10-20%, chromium 1-5%, tin 1-5
%, aluminum 1-5%, balance titanium, in the temperature range from room temperature to 750°C.
By performing pre-processing at a processing rate of 0% or more, subsequent constant-temperature processing, i.e. processing temperature range from 650°C to 775°C, strain rate range from I × 10-'S-' to 3 × 10-''
Under the conditions of S-', the isothermal workability (elongation, elongation,
deformation stress, etc.).

[Conventional technology]

Since β-type titanium alloys generally have good cold workability, they are made into thin sheets by cold rolling, then subjected to solution treatment to remove processing strain from the thin sheets, and then subjected to sheet forming processing. There is. Since the solution treatment heats to the β single-phase temperature range, grain growth is likely to occur, and the Mi texture before forming is a coarse grain structure with a grain size of about 100 μm or more. Forming is generally performed at room temperature, taking advantage of the good cold workability of β-type titanium alloys. Thick plates are also die forged at room temperature. In addition to cold-open forming, hot die forging and hot sheet forming are also carried out at temperatures above the solution treatment temperature.

[Problem to be solved by the invention]

Although β-type titanium alloy has excellent cold workability,
With conventional cold working, large deformations can be made without edge cracking, but the forming process requires intermediate annealing in order to harden the material, resulting in a very large number of steps. To solve this problem, hot working is performed at a high temperature higher than the solution treatment temperature to reduce the deformation resistance. However, in conventional hot processing, the temperature is higher than the solution treatment temperature, which tends to cause grain growth, and the molded product is prone to rough skin.
It is also believed that coarse grains have a negative effect on mechanical properties after processing. Furthermore, in conventional hot working, Near/N
et-3 hape molding was not possible.

Therefore, in order to solve these conventional drawbacks, the present invention provides pre-processing before constant-temperature processing of β-type titanium alloy, increases the temperature to the constant-temperature processing temperature, and refines the crystal grains during holding at the constant-temperature processing temperature. It is possible to develop superplasticity that allows large deformations under low stress, and to utilize this superplasticity not only to reduce manufacturing costs but also to diversify designs through good transferability and grain number bondability. The purpose of this is to improve the constant temperature processability that can be achieved.

[Means to solve the problem]

In order to solve the above problems, the present invention provides vanadium 1
0-20%, chromium 1-5%, tin 1-5%.

A β-type titanium alloy consisting of 1 to 5% aluminum and the balance titanium was heated at a temperature range of 750°C from room temperature to 750°C before isothermal processing.
% or more, the subsequent isothermal processing, i.e. processing temperature from 650°C to 775°C, strain rate l ×
The alloy was made to exhibit superplasticity under conditions ranging from 10-' to 3 x 10-''S-'.

[Effect]

Vanadium 1 to 20 to 5%. β-type titanium alloy, which is made up of 1 to 5% aluminum and the balance titanium, can be made into a uniformly fine, equiaxed grade Mi collar by applying heavy working and then heat treatment to complete recrystallization under appropriate conditions. Can be done. In addition, even if the recrystallization is not completed, the alloy recovers quickly, and the α phase precipitates in uniform and fine grains when subjected to strong working.
Just below the recrystallization temperature, it becomes a uniform, fine sub-grain structure.

By refining the crystal grains or subgrains, the alloy exhibits a superplastic phenomenon during constant temperature processing.

〔Example〕

The present invention will be explained in detail below with reference to Examples.

Example-1 Table 1 shows the chemical components of the test materials used in the present invention. The test material was hot rolled to a strength of 15 wW.

It is a board material. Next 3F from this sample material! A sample of 1i was prepared. One is a 90% cold-rolled material (Spe.

The second method is to cold-roll this sample material to a thickness of 51), then solution treatment, and then cold-roll it at a reduction rate of 70% to obtain a 70% cold-rolled thickness of 1.5 mm. Rolled material (Spe.
The third one, which is B), is a solution-treated material (Spe.

C), tensile test pieces were taken from these 1.5 fi thick samples so that the rolling direction and the tensile axis were parallel. Note that the cold rolling temperature here is room temperature, and in the present invention, 2
It was 0°C.

In the high temperature tensile test (constant temperature processing), the tensile test piece was placed in a vacuum at a temperature range of 0°C to 825°C, 1 x 10-4S-1.
The test was conducted using an Instron type tensile tester under the strain rate range of I x 10-'S-'.

The total elongation and flow stress of each test piece were then measured. Table 2 shows the test temperature at 750℃ and the strain rate at l×10-'
The test results in the case of S-' are shown.

Table 2 Total elongation and flow stress of each cold rolled test piece at a test temperature of 750° C. and a strain rate of 1×10 −4 S - Example 2 The same test materials as in Example 1 were used. The following four types of samples were prepared from this sample material. First, this test material was
90% warm rolling was performed at 750°C and 750°C, respectively. Then, the 90% warm rolled material at 400°C was Spe,
D, 90% warm rolled material at 750℃ Spe, E
Next, the sample material was cold rolled to a thickness of 51, then solution-treated, and further rolled to a thickness of 70% at 400°C and 750°C.
Warm rolling was performed. The 70% warm-rolled material at 400°C at this time was designated as Spe and P, and the 70% warm-rolled material at 750°C was designated as Spe and G. The thickness of all samples thus obtained is approximately 1.5 fi. Next, these l.

A tensile test piece was taken from a sample with a thickness of 5 mm so that the rolling direction and the tensile axis were parallel. Here, when rolling at 750° C. or higher, recovery and recrystallization proceeded rapidly after the rolling was completed, making it difficult to obtain fine crystal grains during the high-temperature tensile test. The recrystallization temperature of the alloy is 740°C.

A high-temperature tensile test (constant temperature processing) was performed on the test piece in vacuum using an Instron type tensile tester under the same temperature range and strain rate range as in Example-1. Table 3 shows the test temperature at 750℃ and the strain rate at I × 10-'S.
-' test results are shown.

Table 3. Total elongation and flow stress of each warm-rolled specimen at a test temperature of 750°C and a strain rate of I × 10-'S-'. It has been found that by performing pre-processing of 70% or more in the temperature range from 100 to about the recrystallization temperature, a large total elongation can be obtained during constant temperature processing and flow stress can be reduced.

From this result, the pre-processing temperature is near the recrystallization temperature (750℃)
or less, and as long as the processing rate is 70% or more, it goes without saying that cold working and warm working may be combined in the preprocessing, or a processing method other than rolling such as extrusion may be used.

Figure 1 shows a 90% as-cold-rolled specimen (Spe,
After 90% cold rolling with A), a test piece (Spe, H) with a grain size of 16 μm by solution treatment and a grain size of 75 μm were obtained.
Figure 2 shows changes in total elongation and flow stress with tensile test temperature for a test piece (Spe, C) with m.

In the temperature range from 650°C to 775°C, Spe, ^ is S
It can be seen that the total elongation is improved and the flow stress is lower than that of pa, C and Spe, H. Spa above 775℃
.

It is thought that A also undergoes grain growth and the crystal grains become coarser, so that the total elongation does not differ much from that of Spe, C and Spe, H. Therefore, the constant temperature processing temperature range was set from 650°C to 775°C.

Figure 2 shows the change in total elongation with the initial strain rate at various test temperatures for Spe, A and Spe, II.
It can be seen that 100% or more can be obtained in the range of -1 to 3 x 10-''S-'. Therefore, the isothermal processing strain rate range was set from to-'s-' to 3 x 10-''S-'.

Furthermore, from Fig. 1 and Fig. 2, 90% cold rolled material (
Spe, ^), the processing temperature was 700°C to 750°C, and the strain rate was I × 10-' S-1 to I × 10-' S.
It can be seen that the optimum machining conditions are around -'.

〔Effect of the invention〕

As explained above, in this invention, superplasticity is developed during constant temperature processing by subjecting β-type titanium alloy to extremely simple pre-processing, and the total elongation is significantly improved compared to conventional hot working and constant temperature working. At the same time, flow stress can also be significantly reduced. As a result, it is possible not only to significantly reduce manufacturing costs, but also to diversify designs that take advantage of transferability and diffusion bonding properties.

In addition, since it is possible to roll to a high reduction rate, it is possible to make thin strips, and by processing these thin strips by sandwiching them between similar or dissimilar materials, metal-to-metal bonding that takes advantage of high deformation and diffusion bonding is possible. It also has the effect of making it possible to join metals, ceramics, etc.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram for evaluating the method of the present invention, showing a test piece (Spe, A) that was 90% cold rolled and a test piece that was 90% cold rolled and then subjected to solution treatment to obtain a grain size of 16 μm. A test piece (Spe, H) and a test piece with a particle size of 75 μm (Sp
Initial strain rate I ×10-' S-
Figure 2 shows the change in total elongation and flow stress with test temperature at 1 and I x 10-''S-'.
pe. It is a characteristic diagram showing changes in total elongation with initial strain rate at various test temperatures in A, Spe, and H. that's all

Claims (4)

[Claims] (1) Vanadium 10-20%, chromium 1-5% by weight
%, tin 1 to 5%, aluminum 1 to 5%, and the balance titanium, β type titanium alloy is characterized by performing constant temperature processing after pre-processing at a processing rate of 70% or more.
Processing method of type titanium alloy. (2) The method for processing a β-type titanium alloy according to claim 1, characterized in that the pre-processing is performed in a temperature range from room temperature to 750°C. (3) The method for processing a β-type titanium alloy according to claim 1, wherein the constant temperature processing is performed in a temperature range of 650°C to 775°C. (4) Constant temperature processing from 1x10^-^4S^-^1 to 3x
A method for processing a β-type titanium alloy according to claim 1, characterized in that the processing is carried out in a strain rate range of 10^-^2S^-^1.