JPS62109956A - Manufacture of titanium alloy - Google Patents

Abstract

PURPOSE:To manufacture a Ti-alloy cold-rolled material having superior yield strength and free from anisotropy in yield strength by subjecting a Ti-Al-V alloy to hot working, to cold working in the above state or after going through the stage of annealing treatment, and further to ageing treatment under specific conditions. CONSTITUTION:The hot-rolled stock of (alpha+beta)-type Ti alloy having a composition consisting of, by weight, 2.5-3.5% Al, 2.0-3.0% V, and the balance Ti is cold-worked at <=85% cold draft in the above state or after annealing treatment. Succeedingly, the above material is subjected to strain ageing treatment at 140-300 deg.C in the range represented by an inequality 4R+T>=480 [where R is cold draft (%) and T is ageing temp. ( deg.C)] for >=1hr. In this way, the Ti-alloy cold-rolled material free from anisotropy in yield strength and having >=85kgf/mm<2> yield strength is manufactured.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing a titanium alloy, particularly in a rolling direction (hereinafter referred to as "L direction") and a direction perpendicular thereto (hereinafter referred to as "L direction").
The present invention relates to a method for manufacturing a cold-rolled Ti-3Al-2,5V alloy sheet that has approximately the same mechanical properties after annealing in the T direction.

(Prior technology) Among α+β type titanium alloys that are generally difficult to cold work, T
i-3Al 2. The SV series alloy can be cold rolled by 75 to 85%, and is the only α+β type practical titanium alloy that can be manufactured into seamless pipes and thin plates by cold rolling.

However, a drawback of this Ti-3M-2,5V alloy is that it has the lowest strength among the α+β type practical alloys, and therefore improvements in yield strength, etc. have been desired.

On the other hand, it was also known that when a titanium alloy is cold rolled in the same direction as the hot rolling direction, the yield strength after heat treatment is higher in the T direction than in the L direction.

As a method for reducing the anisotropy of mechanical properties, especially the anisotropy of proof stress, there is a cross rolling method, that is, a rolling method in which the rolling direction is usually changed by 90 degrees before the next rolling.
This method cannot be applied to long objects such as coils due to their nature.

In addition, if a hot rolled annealed sheet of Ti-3Al-2,5V alloy is cold rolled in the same direction as the hot rolling direction at a cold rolling reduction of 67% or more, and then annealed at a temperature of 650 to 900°C, ,
Yield strength in T force direction (σo, z(L) 3 Yield strength in direction [
σ. , 2(T) ), that is, σ. , z(T)/σ.

, 2(L) of 1.1 or less and a low anisotropy can be obtained. However, in this case, the yield strength obtained is mostly recrystallized, so at 66 kgf/m
m2, 62 kgf/mm2 in the L direction, so high yield strength could not be expected.

On the other hand, as a manufacturing method for temporary Q, -2,5V alloy cold-rolled to Ti-3 with high yield strength, as shown below, Ti-3M
A method of cold rolling a -2,5V alloy by 75 to 85% (hereinafter referred to as "as-cold-rolled method" for convenience), 700-lower (
1/2 in the temperature range from 370℃ to below 1200℃ (650℃)
A heat treatment method of holding for ~3 hours and cooling in air (standardized in the old L-H-81200, also called "stress relief annealing method"),
and below 1600 (870℃) to below 1700 (930℃)
A heat treatment method (also known as "S
There is a TA method (standardized in the old L-111] BK-697A).

The yield strength obtained by these manufacturing methods is 118 ksi (83 kgf/mmz) for the as-cold rolled method, 110 ksi (77 kgf/mmz) for the stress relief annealing method, and 113 ksi (79 kgf/mm") for the STA method.
It is. On the other hand, in these cases, the anisotropy of the yield strength in the inward direction and the yield strength in the 'r force direction is σ. , 2(T)/g. , 2(L) gives the following value.

1.00 for the as-cold rolled method, 1.09 for the stress relief annealing method, and 1.25 for the STA method (where σ., z(T) = 128
ks i, σ0.2(L) = 102ksi).

Therefore, a thin sheet of Ti-3Al-2,5V alloy with high yield strength and low anisotropy of yield strength in the downward direction in the L direction is an as-cold rolled alloy sheet, and the higher the cold rolling rate, the more processed it is. It is thought that hardening increases yield strength.

However, Ti 3Al 2.5 with good cold workability
Even for V-based alloys, a cold rolling rate of about 85% is the limit due to the material quality, and it was impossible to increase the yield strength by cold rolling further.

(Problems to be Solved by the Invention) Thus, the object of the present invention is to provide a titanium alloy material that not only has a high yield strength even in (α+β) type titanium alloys, but also has a low yield strength and anisotropy of yield strength, especially titanium alloy materials. An object of the present invention is to provide a method for manufacturing cold rolled material.

Here, if Ti alloys are classified based on their crystal structure, they are α type, α
It is divided into three types: + β type and β type, and these have different properties.The 6Ti-3Al 2.5V system is α +
It is a β-type titanium alloy and tends to exhibit anisotropy.
It is well known that large cold working rates can be achieved. However, other α+β type titanium alloys are difficult to cold work. In addition, other types of alloys that cannot be subjected to cold stress include β-type alloys, but the LTT stress anisotropy does not pose much of a problem.

Therefore, a more specific object of the present invention is to use Ti-3M-2,5V which is relatively easy to process and exhibits anisotropy.
It is an object of the present invention to provide a method for producing a titanium alloy material, particularly a cold-rolled material, which has as little proof stress anisotropy as possible in a series alloy.

(Means for solving the problem) Therefore, the present inventors focused on the fact that strain aging occurs even in titanium alloys, and developed Ti 3Al-2,5V
While investigating the relationship between the cold rolling rate, aging conditions, and tensile properties of the alloy, we found that a cold alloy that maintains the same isotropy of yield strength as 85% cold-rolled and has a higher yield strength than that of the 85% cold rolled alloy. He discovered that there are elongation and aging conditions, and completed the present invention.

That is, the graph in FIG. 1 shows the tensile test results of a series of Ti-3Al-2,5V alloy plates manufactured by the present inventors by the conventional method for preliminary experiments.

The graph in Figure 1 also shows an example of the present invention in which after 70% cold rolling, the material was heated to 300°C for 1 hour and then air cooled. This is a titanium alloy plate. From the results shown in this figure, except for the case of the present invention, ■
It can be seen that the 85% as-cold-rolled material has the smallest anisotropy in yield strength and the highest yield strength. The yield strength (higher IT) of this 85% cold-rolled material is 85 Jf/mm', and L
The ratio of the force in the direction and the T force direction is 0.97, or 0.9
7≦σ. , 2(T)/σ0°2(L)≦1.03. Thus, according to the present invention, it is possible to obtain a material having properties equivalent to those of the as-cold rolled material, which was conventionally considered to be the best.

In addition, even in the past, cold-rolled materials were annealed for the purpose of stress relief, but the heating temperature in that case was 380° C. or higher.

Here, the gist of the present invention is 8Q in weight%.
:2.5-3.5%, V:2. Q~3.0%, balance Ti
and a titanium alloy consisting of ordinary impurities, after hot working, as it is, or after sintering, cold working at a cold rolling rate of 85% or less, and then at 140 to 300°C in the range shown by the following formula. A method for producing a titanium alloy having no anisotropy in yield strength and having a yield strength of 85 kgf/mm'' or more, which is characterized by strain aging treatment for 1 hour or more.

4R+ T ≧ 480 However, R: Cold rolling ratio (%) T: Aging temperature (°C) Here, the titanium alloy targeted by the present invention is
~3.5%, V:2. ASTM Grade 9 Ti consisting of Q~3.0%, balance Ti and normal impurities
It is a 3Al 2°5v alloy.

Thus, according to the method of the present invention, Q-2°5 to Ti-3
A hot-rolled annealed plate of a V-based alloy is cold-rolled in the same direction as the hot-rolling direction,
In the case of aging, the following cold rolling ratio (R・%), aging degree (T: %), aging time (t: hr), i.e. 4R+
T≧480, R≦85, T≦300, and 1≦t≦
By performing the test within the range shown by 8, 0,97≦σ, which is the isotropy of the yield strength of the 85% as-cold-rolled material. , 2(T)
/σ. , 2(L) ≦1.03, and has isotropy of yield strength, and 85 kg, which is the yield strength of 85% as-cold-rolled material.
It is possible to manufacture titanium alloy plates with higher yield strength than f/2.

(Function) FIG. 2 shows a graph of the relationship between cold rolling reduction (%) and aging temperature (° C.) in the present invention. The rolling rate is indicated by the reduction rate of plate thickness. In the figure, the shaded area is within the scope of the present invention.

By the way, the effect of increasing the yield strength according to the present invention is obtained through the effects of work hardening due to cold rolling and strain aging. Therefore, when the cold rolling rate is low, the increase in yield strength due to work hardening is small, and when the aging temperature is low or the aging time is short, the effect of strain aging is small, so the increase in yield strength is small.

Therefore, 135 kgf, which is the financial strength of 85% cold rolled
/mm2 cannot be exceeded. According to the invention, 8
As a result of experiments, the lower limit of the cold rolling rate and aging temperature to obtain financial strength higher than 5 kgf/mm2 was 4R'
It turns out that 480 conditions must be met.

The reason why the aging IFA degree is set to 140° C. or higher is that at less than 140° C., there is almost no increase in yield strength due to strain aging. Also, to exceed the proof stress of 85 kgf/mm2, t
An aging time of ≧1 is required.

As the aging temperature increases, the yield strength in the L direction and the T direction aggregates due to the upper limit of the aging temperature.) The yield strength in the L direction decreases, resulting in anisotropy in the yield strength. occurs. The present inventors investigated the relationship between aging temperature and yield strength anisotropy, and as shown in FIG. 2, when aging is performed at a temperature higher than 300°C, σ. , 2(T)/σ. , 2(
L)>1.03, and it was found that the yield strength of the 85% as-cold-rolled material is isotropic. Therefore, in the present invention, it is limited to T≦300.

In addition, the Q-2,5V alloy to Ti-3 is 85% in terms of material.
% is the limit, and if cold rolling is attempted beyond that, δ warping will occur. Therefore, R≦85.

In addition, in the case where the aging time is 8 hours, although there is an effect of increasing the yield strength, the effect is small and is considered to be rather inferior to productivity.

In the titanium alloy that is the object of the present invention, eight Q and
is added to increase the strength (σ8, σ., 2), and Ti-3Al-2,5V alloy is, for example, A
STM Grade 9 as 2,5≦Q≦3.5
wt%, 2゜0≦V≦3. It is defined as Q wt%. Q is less than 2.5 wt% or V is 2.0 w
If it is less than t%, the strength of both will be low, and conversely, if Al is 3.5
When iVt% or ■ exceeds 30 wt%, the cold workability becomes 8.

In this way, secondly, the present invention is able to reduce the distortion of the wire, which was conventionally thought to be the most distorted, by performing cold rolling and aging treatment after hot rolling, and by limiting the processing conditions at that time. This makes it possible to produce a titanium alloy with yield strength and anisotropy comparable to that of cold-rolled as-built materials.

Next, the present invention will be explained in more detail with reference to Examples.

Example A Ti-3Al-2,5V alloy having the composition shown in Table 1 was cold rolled using a hot rolling annealing machine in the same direction as the hot rolling direction at a cold rolling rate of 30 to 85%. Te100-35
Aging treatment was performed at a temperature of 0° C. for a time of 0.5 to 8 hr. Each of the obtained materials was then subjected to a tensile test to determine the L and downward 0.2% yield strength and their ratio.

Table 2 summarizes each processing condition and mechanical properties.

Table 1, table 2? J, Tests 1kl to 14 are all examples of the present invention, and are alloys that have been cold-rolled and aged according to the present invention, and the proof stress in the L direction [σo, z(L)) is also lower than that in the downward direction. Yield strength [σ. .
r)/σ. , z(L)≦1.03.

On the other hand, 4R+T shown in test numbers 16 to 19.22.23
For the alloy manufactured by the method of <480, the yield strength in both the L direction and the downward direction could not exceed 85 kgf/mm2.

In addition, test magnet 20.21.24.25 has an aging temperature of 3
It is a titanium alloy plate manufactured by a method that does not satisfy 50°C, that is, T≧300, and σ. , 2(T)/σ. , 2(
L)>1.03, and the anisotropy of proof stress increases.

Plus, exams! ! 1126-32 has an aging time of 0.5
hr, that is, 1≦t≦8, and the aging treatment time is short, so 1. Either or both of the direction and downward strength is 85 kgf/force 2
not exceed.

In addition, Test Roll 15 is the conventional cold rolling (as is).

FIG. 2 shows the results of this example by plotting the test patients. Test results 1 to 14 all fall within the shaded area of the present invention, and all other cases fall outside of that area.

Figure 3 summarizes the relationship between cold rolling reduction and yield strength with respect to aging treatment time based on the data in Table 2, and the numbers in the figure indicate the test results in Table 2. (indicates 85 kgf/mm in the case of the present invention example)
It can be seen that the value is 2 or more.

(Effects of the Invention) As detailed above, even when a hot-rolled annealed sheet of Ti 3Al-2,5V alloy is cold-rolled in the same direction as the hot-rolling direction, the conventional method is improved by aging. 85 kg, which is almost the same as the yield strength anisotropy of the as-cold-rolled titanium alloy plate, and the yield strength in both the L direction and the T direction is the yield strength of the conventional material.
It is possible to manufacture alloy plates with a diameter exceeding "f/mm".

[Brief explanation of drawings]

Figure 1 is a graph showing the ah& characteristics of various treated materials: FIG. 2 is a graph showing the processing conditions of the present invention, -8 and FIG. 3 is a graph showing the results of an example of the present invention.

Claims (1)

[Claims] In weight percent, Al: 2.5-3.5%, V: 2.0-3.
A titanium alloy consisting of 0% titanium, the balance Ti and normal impurities is hot worked and then heated as is or after sintering.
% or less, and then cold worked at a cold rolling rate of 140 to 30
It is characterized by strain aging treatment at 0℃ for 1 hour or more in the range shown by the following formula, has no anisotropy in yield strength, and is 85 kgf.
A method for producing a titanium alloy having a yield strength of /mm^2 or more. 4R+T≧480 where R: Cold rolling reduction (%) T: Aging temperature (°C)