JPS61217563A - Manufacture of titanium alloy - Google Patents

Abstract

PURPOSE:To minimize the amount of working in an alpha+beta region and to improve productivity by carrying out working successively in alpha+beta and beta regions at each prescribed reduction in area and then by carrying out ageing after water quenching in subjecting an alpha+beta type titanium alloy to strengthening heat treatment. CONSTITUTION:The alpha+beta type titanium alloy e.g. Ti-6Al-4V is worked at >=20% reduction in area at the temp. slightly lower than its beta-transus (usually 980-1,000 deg.C), at 800-950 deg.C in a high temp. region of the alpha+beta region. After that the alloy is hot-worked again at >=10% reduction in area, with or without cooling to the room temp., at 1,000-1,050 deg.C in a low temp. region of the beta-region, above the beta-transus; as to the above heating, it is desirable that the alloy is held with heating e.g. for <=30min in order to inhibit the growth of beta-recrystallized grains. After the hot working in the beta-region, the alloy is subjected to water quenching without delay and then to ageing treatment as usual.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for producing a titanium alloy, in particular, a method for manufacturing a titanium alloy, in which the amount of processing in the α+β region is minimized, and ductility is ensured.
This invention relates to a method for producing a high-strength, high-ductility titanium alloy.

(Prior art) α+β type titanium alloy is hardened by high temperature quenching to form a martensitic structure, and then aged at 500 to 600°C to decompose the martensite into fine α+β, thereby strengthening it, i.e. by temporary solution treatment. Strengthening is possible. When such temporary solution treatment is performed, the pre-structure is a fine equiaxed α obtained by sufficient processing in the α+β region.
It is necessary to have a +β structure. Therefore, conventionally,
The annealing heat treatment method for titanium alloys that ensures strength without impairing ductility is to apply hot working at a sufficient working rate in the α + β region to generate an equiaxed α + β structure and to refine it, and then to For the obtained fine equiaxed α+β phase,
It had been subjected to solution treatment and aging.

By the way, Ti-6AQ-4, which is a typical example of titanium alloy,
V alloy is said to be an α+β type alloy, and consists of two phases of α+β at temperatures below about 1000°C, and becomes a single β phase at temperatures above that temperature. Since deformation resistance is lower when processing is carried out at high temperatures, it can be said that it is preferable to process α+β type titanium alloys in the β-phase single phase range of about 1000°C or higher from the viewpoint of hot workability. Because the phase region is too high, over 1000℃, the β crystal grains become coarse during heating, and these coarse grains are carried over to the final product that has been subjected to temporary solution treatment, which is a strengthening heat treatment. resulting in deterioration of ductility.

Therefore, as mentioned above, the strengthening heat treatment of α+β type titanium alloys has traditionally been carried out with sufficient α to obtain the necessary ductility.
It has been thought that it is necessary to perform this on materials having an equiaxed α+β structure obtained by +β processing. It has also been reported that in order to obtain such an equiaxed α+β structure, processing with a cross-sectional reduction rate of 50% or more in the α+β region is required.

FIG. 1 is a diagram showing a conventional strengthening heat treatment method,
The processing degree (section reduction rate) in the α+β range from 0 to 950℃ is 5
0% or more, which requires a considerable amount of processing,
Considering that the α+β region is a difficult-to-process region, the resulting drop in productivity is significant.

After processing in the α+β region, the next process of solution treatment is performed after air cooling, but this also requires heating and holding time at 955° C. for 1 to 2 hours, which also increases costs.

(Problem to be solved by the invention) However, as already mentioned, it is generally difficult to process α+β type titanium alloys in the α+β region, and reducing the amount of processing in the α+β region requires a large or medium cost.・It is thought that it will lead to down.

Therefore, an object of the present invention is to provide a method for improving productivity by minimizing the amount of processing in the α+β region.

Another object of the present invention is to provide an efficient method that combines hot working and aging treatment.

A further object of the present invention is to develop a method in which fine β crystal grains are obtained during the subsequent strengthening heat treatment, improving not only strength but also ductility, even though the amount of processing in the α+β region is reduced. It is to provide.

(Means for solving the problem) As already mentioned, according to the research conducted by the present inventors, when using a material that has been hot-worked in the β region, aging during solution treatment is sufficient. The reason why such ductility cannot be obtained is that β crystal grains easily grow during processing in the β region, and the grain size of the β phase, which is the parent phase, increases. It turns out that this is because the crystal grains at the site also become larger.

For example, the Ti 6A12 4V mentioned above is 980-10
At temperatures above 00°C (7) β-transus
Although it becomes a single phase, the β region is at a high temperature, so even if β processing is performed, the β crystal grains cannot be easily refined.

However, Ti-6! As a result of our research on -4V, we found that after processing with a cross-section reduction ratio of 20% or more in the α+β region, we held it in the low temperature region of the β region (below 1050°C) for a short time and then water-quenched it. As a result, it was found that β crystal grain refinement was achieved even though the machining in the α+β region was only 20% or more. It was found that unexpectedly finer β-crystal grains could be obtained by water quenching immediately after a slight (10% or more) processing after holding, and the present invention was completed.

In this way, the present invention is a method that secures the necessary ductility and achieves strengthening through temporary solution treatment, even though the amount of processing in the α+β region, which is said to be difficult to process, is minimized. The gist of this is that when hot working α+β type titanium alloys, the area reduction rate is 20 in the temperature range of 800 to 950°C, which is the high temperature range of α+β range.
% or more, and furthermore, the low temperature range of β region is 100%.
After being heated to a temperature range of 0 to 1050℃, it is processed to a cross-section reduction rate of 10% or more, then immediately water quenched, and then subjected to aging treatment.It has excellent strength and ductility. This is a method for manufacturing titanium alloy.

Here, as is already clear from the above description, the titanium alloy in the present invention is not particularly limited as long as it is α+β type.
Q 6V 25nSTi-6A12 2 Sn
-4Zr-2MO% Ti-6Kl 2Sn-4Zr
It is clear that it can be similarly applied to α+β type titanium alloys such as -6Mo.

(Function) Hereinafter, the present invention will be explained using Ti, which is a typical α+β type titanium alloy.
-6A12-4V will be taken as an example to explain its configuration, but as already stated, it goes without saying that the present invention is not limited thereto.

FIG. 2 is a diagram showing each step of the method according to the present invention.
(generally 980-1000℃) slightly lower than 800℃
After heating to a temperature range of ~950°C, hot working with a cross-sectional reduction rate of 20% or more is performed in the state of α + β structure, then cooling to room temperature or again without cooling to β-transus.
It is heated to a temperature range of 1000 to 1050°C, which is the higher β range, and hot worked with a cross-section reduction rate of 10% or more in the β structure state. In order to suppress the growth of β-recrystallized grains, the heating at this time is preferably maintained for 30 minutes or less, for example. Immediately after hot working in the β region, water quenching is performed and aging treatment is performed as in the conventional method. This aging treatment has already been carried out as part of the strengthening heat treatment method in the past, and is not particularly limited as far as it goes, but it is preferably carried out by heating at 540 to 620° C. for 4 to 8 hours, followed by air cooling.

As described above, according to the present invention, the processing temperature range in the α+β region is limited to 800 to 950°C;
At temperatures exceeding ℃, the ratio of α phase becomes extremely small (e.g., 50%
(below) The purpose of imparting distortion to the α phase will no longer be achieved.

Therefore, in the present invention, as mentioned above, 800 to 9
Limit to 50°C. Preferably it is 850-950°C.

The degree of working (area reduction rate) in the above temperature range should be 20% or more, but generally 20 to 30% is sufficient, considering that the conventional technology required 50% or more as mentioned above. ,The effect can be said to be remarkable.
D. Figure 3 shows the Ti-6Ai24V alloy at 95θ℃.
The processing amount in the α+β region when forging is performed in the +β region, then heated at 1050°C for 30 minutes, and water quenched with or without processing with a 10% area reduction rate in the β region. (area reduction rate) and grain size of β grains after water quenching (
It is a graph which shows the relationship with am). In all cases, the crystal grains are finer when processing is performed in the β region. In addition, the finer effect is greater when the processing degree in the α+β region is 20% or more, and moreover, the refinement effect is greater than the processing degree of 30%.
%, processing at a processing degree higher than that is unnecessary from the viewpoint of achieving miniaturization.

Next, after the processing in the α+β region is completed, the temperature is heated to 1000 to 1050°C after cooling to room temperature or without cooling.
As mentioned above, this is to further refine the β crystal grains, and if the heating temperature exceeds 1050°C, the β crystal grains will be processed by 10% or more. The temperature range is set to 1000 to 1050°C because grains tend to become coarser and β single phase does not occur at temperatures below 1000°C.

The processing amount in the β region is limited to 10% or more, but from the viewpoint of refining the β crystal grains, 10 to 20% is generally sufficient. However, it goes without saying that further processing may be added to give the desired shape, and the processing itself is considered to be relatively easy since it is processing in the β region. After completion of processing, water quenching is immediately performed to form a martensitic structure as before.

The microstructure at room temperature obtained in this way is
Fine martensite is generated by quenching in the β matrix, which has become fine crystal grains.Next, this is subjected to an aging treatment, for example 540~b.A conventional solution of a material with an equiaxed α+β structure. It has the same strength and ductility as those obtained by chemical treatment and aging.

Next, the present invention will be further explained by examples.

EXAMPLE A Ti-6AQ-4V alloy whose alloy composition is shown in Table 1 was processed and heat treated according to the process diagram shown in FIG. Each processing condition at this time is summarized in Table 2. Processing was performed by forging.

The mechanical properties of the obtained sample gold were determined. Similarly, the results are summarized in Table 2. As is clear from the results shown in the same table, according to the method according to the present invention shown in FIG. It has become possible to reduce the processing rate in the α+β region, secure the necessary ductility, and strengthen the steel.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the steps of the conventional method; Fig. 2 is a diagram showing the steps of the method according to the present invention; and Fig. 3 shows that the processing amount in the α+β region in the present invention is FIG. 2 is a graph showing the influence of Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Akira Hirose - Figure 1 Figure 2

Claims (1)

[Claims] When performing hot working, α + β type titanium alloy has a reduction in area of 2 in the temperature range of 800 to 950 °C, which is the high temperature range of α + β region.
0% or more processing, and furthermore, the low temperature range of β region is 10
After heating to a temperature range of 00 to 1050 degrees Celsius, processing with a cross-section reduction rate of 10% or more is performed, followed by immediately water quenching and then aging treatment.It has excellent strength and ductility. Method of manufacturing titanium alloy.