JPH0196360A - Manufacture of titanium alloy material for cold working - Google Patents

Abstract

PURPOSE:To drastically improve the cold moldability of the title material as a fine beta crystal grain structure by subjecting a beta type Ti alloy to a heat treatment, aging treatment, cold working and heat treatment under specific conditions. CONSTITUTION:A Ti-15V-3Al-3Sn-3Cr alloy as a beta type Ti alloy is subjected to a solution heat treatment in such a manner that it is heated to the temp. or above of the beta transformation point of said alloy, is retained for 3min-2hr and is thereafter cooled at >=0.5 deg.C/sec cooling rate. The alloy is successively retained for 10hr in the temp. range of 550-650 deg.C, is subjected to an aging treatment and is thereafter cold rolled at >=15% sectional reduction ratio. The alloy is then subjected to a secondary solution heat treatment in such a manner that it is heated for 3min-2hr, is retained and is thereafter cooled at >=0.5 deg.C/sec cooling rate to deposit the recrystallization alpha phase having fine grain size, by which the beta type Ti alloy material for cold working having excellent cold moldability is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention provides a Ti- 15V -3Affi -3Sn-
The present invention relates to a method for stably manufacturing 3Cr alloy material.

Background technology> Ti-15V-3Af, known as β-type titanium alloy
The fi-3Sn-3Cr alloy is a material that was developed primarily as a titanium alloy for cold working, but the typical processing method used for this type of β-type titanium alloy does not easily refine the β crystal grains. First, it was difficult to obtain a fine grain structure with an average grain size of 40 mm or less.

111chi, Ti-15V 3Aj subjected to cold working
! Conventionally, 3Sn-3Cr alloy has been treated as a β single phase with a temperature of 780 to 850
A solution treatment was carried out in which the material was heated and held at a temperature of 3 to 60 minutes, and then cooled to room temperature at a cooling rate faster than air cooling.

However, such solution-treated materials do not have sufficient ductility due to coarse β-crystal grains, and there is a problem in that good-quality processed surfaces cannot be obtained during press working.

In other words, a major problem with the Ti-15V 3Al-3Sn-3Cr alloy is that the β grain size cannot be easily refined, and only a low elongation value could be obtained with coarse grain β.

Therefore, T with fine crystal grains, which is preferable for press working, etc.
For the purpose of obtaining a material for cold forming of i-15V-381-3Sn-3Cr alloy, "solution treatment was carried out in a higher temperature range (over 830 °C to 1150 °C) than before". , β which undergoes cold working with a higher degree of working (50% or more)
A method for adjusting crystal grains was proposed (Japanese Patent Laid-Open No. 62-151)
No. 551).

However, even with the above method, the β grain size obtained is only about 20 mm at the minimum, and cannot be said to exhibit sufficiently satisfactory cold workability.

<Means for Solving the Problems> From the above-mentioned viewpoint, the present inventors have developed Ti-15V, which has a finer β-grain structure and exhibits superior ductility.
-3M -3Sn -3Cr We conducted research to find a stable and reliable manufacturing method for cold working materials, but in the process, we discovered rTi-15V -3AJ! -3Sn -3
It is well known that when a Cr alloy is solution treated at a temperature above the β transformation point and then aged at 300 to 600°C, the α phase precipitates and hardens, and this technology is used as a means of strengthening materials. However, it has been found that if the aging treatment is carried out at high temperatures and for a long period of time (at 550° C. or higher and for 10 hours or more), the precipitated α phase grows and becomes “overaged.” Based on this fact, they thought that when the above-mentioned alloy becomes "overaged," the material softens, making further cold working possible.

For these reasons, the inventors of the present invention aimed to achieve the desired goal (after examining the above-mentioned Ti-15V-3AR-3Sn-3Cr alloy over-aged material from various viewpoints, (a) Ti-15V -3Af-3Sn-3Cr alloy can be further cold-worked to achieve a reduction in area of 15% or more in an over-aged state.

fb) For this reason, it is possible to apply sufficient processing strain to the α phase grown by overaging. When the oxidation treatment is performed, a β phase with extremely fine crystal grains, which could not be obtained by conventional methods, is formed by recrystallization.

This led us to the following knowledge.

This invention was made based on the above knowledge, and the rTi-15V-3Al-3Sn-3Cr alloy was heated and held at a temperature equal to or higher than the β transformation point for 3 minutes to 2 hours, and then the cooling rate was 0.5. Solution treatment with cooling for more than ℃ seconds),
Next, after aging treatment for 10 hours or more in a temperature range of 550 to 650°C, cold working is performed so that the cross-section reduction rate is 15% or more, and further heated to a temperature above the β transformation point for 3 minutes to 2 hours. Cooling rate: 0.5℃ After cooling for 7 seconds or more (solution treatment), it is possible to stably produce a titanium alloy material for cold working with excellent ductility and fine β crystal grains. It is characterized by the fact that it is made as follows.

Here, the Ti-15V-381-3Sn-3Cr alloy is, as is well known, 7214 to 16% (hereinafter, % representing the component ratio is % by weight).
).

AJ: 2.5-3.5%, Sn: 2.5
~3.5%.

It goes without saying that this refers to a titanium alloy (beta transformation point near 30 to 750°C) containing 2.5 to 3.5% Cr, with the remainder being Ti and inevitable impurities.

In the method of the present invention, the manufacturing conditions for the cold working material are limited as described above for the following reasons.

a) First solution treatment conditions Ti-15V-3AN-3Sn-3Cr Now,
The reason why solution treatment is first performed at a temperature above the β transformation point is to precipitate an overaged α phase that can be cold-worked by 15% or more in the subsequent overaging treatment, but the heating temperature at this time is If the temperature is lower than the β transformation point, recrystallization of the matrix β phase does not occur, so cold working of 15% or more cannot be achieved. In this case, if the holding time is less than 3 minutes, recrystallization of the β phase will not be completed, whereas if the holding time exceeds 2 hours, the recrystallized β will grow, so in any case, the above 15% or more Cold working becomes impossible. Also, the cooling rate at temperatures above the β transformation point is 0.
If it is slower than 5° C./sec, the α phase will precipitate during cooling, and cold working of 15% or more cannot be achieved.

Therefore, the conditions for the first solution treatment are heating and holding at a temperature equal to or higher than the β transformation point for 3 minutes to 2 hours, and then cooling at a rate of 0.
It was determined that the cooling rate should be 5°C/second or more.

b) Aging treatment conditions The method of the present invention has a major feature in that coarse grains α in an overaged state are precipitated by aging treatment.
If the temperature is less than 50°C, the precipitated α phase becomes fine and increases the strength, making cold working of 15% or more impossible. As a result, you will not be able to achieve your desired goal. Further, if the aging time is less than 10 hours, the precipitated α phase will not grow, so cold working of 15% or more cannot be achieved.

Therefore, the aging treatment was determined to be maintained at 550 to 650°C for 10 hours or more.

C) Cold working conditions The area reduction rate (processing rate) of cold working performed after aging is 1
If it is less than 5%, the desired recrystallization β of fine crystal grains cannot be obtained even if the solution treatment is performed again thereafter. Therefore, it was decided that the above-mentioned cold working should be carried out under the condition that the area reduction rate is 15% or more.

d) Conditions for second solution treatment In the method of the present invention, after cold working which imparts processing strain to the α phase grown by overaging, solution treatment is performed again at a temperature equal to or higher than the β transformation point. Recrystallization β with a fine grain size is obtained, but if the heating temperature at this time is lower than the β transformation temperature, recrystallization will not occur, and even if the heating and holding time is less than 3 minutes, the β phase will not be recrystallized. Unable to complete the crystal. on the other hand,
If the heating/holding time exceeds 2 hours, the recrystallized β grains will grow, making it impossible to obtain the desired fine β grains. Furthermore, if the cooling rate from the β transformation point or higher after heating and holding is slower than 0.5° C./sec, the desired fine β grains cannot be obtained.

Therefore, the conditions for the solution treatment performed after cold working were determined to be heating and holding at a temperature equal to or higher than the β transformation point for 3 minutes to 2 hours, and then cooling at a cooling rate of 0.5° C./sec or higher.

Next, the present invention will be specifically explained using examples and comparing with comparative examples.

<Example> First, Ti having a chemical composition as shown in Table 1 was prepared.
-15V -3Aj! A cold-rolled material of -3Sn-3Cr alloy was used, and before the final cold rolling, it was subjected to solution treatment (first solution treatment) and aging treatment under the conditions shown in Table 2.

Next, the cold rolled material after the aging treatment was subjected to a final cold rolling, and then a second solution treatment was performed. Note that the cold rolling reduction rate (area reduction rate) and solution treatment conditions were as shown in Table 2.

Next, Ti-15V-3Aj manufactured in this way
! -3Sn-3Cr plywood was investigated for its average β grain size and measured for mechanical properties at room temperature. These results are also shown in Table 2.

As is clear from the results shown in Table 2, Ti-15V-3AIl manufactured according to the conditions specified in the present invention
-3Sn -3Cr plywood has a very fine β-grain structure, has a high elongation value, and has excellent cold formability, but the manufacturing conditions are not specified by the present invention. It can be seen that the comparative examples and conventional examples that deviate from the conditions cannot achieve a fine β-grain structure and have insufficient elongation values.

<Summary of Effects> As explained above, according to the present invention, Ti − has an extremely fine β grain structure and exhibits excellent cold-open formability.
15V 38J! It is possible to stably manufacture 3Sn-3Cr alloy materials, and even when manufacturing aircraft parts that require complex shapes, it is possible to handle them with high dimensional accuracy using high-yield processing methods. This brings about extremely useful effects industrially.

Claims (1)

[Claims] The Ti-15V-3Al-3Sn-3Cr alloy is heated and held at a temperature above the β transformation point for 3 minutes to 2 hours, then cooled at a cooling rate of 0.5°C/sec or more, and then 550 to 650°C.
After aging treatment for 10 hours or more in the temperature range of A method for producing a Ti-15V-3Al-3Sn-3Cr alloy material for cold working, characterized by cooling at a rate of 0.5° C./sec.