U.S. patent application number 13/179754 was filed with the patent office on 2011-12-29 for titanium alloys and method for manufacturing titanium alloy materials.
This patent application is currently assigned to SUMITOMO METAL INDUSTRIES, LTD.. Invention is credited to Atsuhiko KURODA.
Application Number | 20110318220 13/179754 |
Document ID | / |
Family ID | 45352750 |
Filed Date | 2011-12-29 |
United States Patent
Application |
20110318220 |
Kind Code |
A1 |
KURODA; Atsuhiko |
December 29, 2011 |
TITANIUM ALLOYS AND METHOD FOR MANUFACTURING TITANIUM ALLOY
MATERIALS
Abstract
A cold rolled titanium alloy plate with a sufficient cold
workability and excellent superplasticity characteristics is
provided. The cold rolled titanium alloy plate consists of, by mass
%, Al of 2.0 to 4.0% and V of 4.0 to 9.0%, one element selected
from Zr of not more than 2.0% and Sn of not more than 3.0% and the
balance being Ti and impurities, a ratio of .alpha./.beta. is not
less than 0.3 and not more than 0.6; where ".alpha." is an area of
a phase in the plate and ".beta." is an area of .beta. phase in the
plate, and the plate has an elongation at break in a tensile test
conducted at 800.degree. C. exceeds 200%.
Inventors: |
KURODA; Atsuhiko;
(Joetsu-shi, JP) |
Assignee: |
SUMITOMO METAL INDUSTRIES,
LTD.
Osaka
JP
|
Family ID: |
45352750 |
Appl. No.: |
13/179754 |
Filed: |
July 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11604840 |
Nov 28, 2006 |
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13179754 |
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PCT/JP2004/007614 |
Jun 2, 2004 |
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11604840 |
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Current U.S.
Class: |
420/419 ;
420/420; 72/199 |
Current CPC
Class: |
C22F 1/183 20130101;
C22C 14/00 20130101 |
Class at
Publication: |
420/419 ;
420/420; 72/199 |
International
Class: |
C22C 14/00 20060101
C22C014/00; B21B 3/00 20060101 B21B003/00 |
Claims
1. A cold rolled titanium alloy plate consisting of, by mass %, Al
of 2.0 to 4.0% and V of 4.0 to 9.0%, one element selected from Zr
of not more than 2.0% and Sn of not more than 3.0% and the balance
being Ti and impurities, wherein a ratio of .alpha./.beta. is not
less than 0.3 and not more than 0.6; where ".alpha." is an area of
a phase in the plate and ".beta." is an area of .beta. phase in the
plate, and wherein the plate has an elongation at break in a
tensile test conducted at 800.degree. C. exceeds 200%.
2. A cold rolled titanium alloy plate consisting of, by mass %, Al
of 2.0 to 4.0% and V of 4.0 to 9.0%, one element selected from Zr
of not more than 2.0% and Sn of not more than 3.0%, further one or
more elements selected from Fe of not less than 0.20% and not more
than 0.95%, Cr of not less than 0.01% and not more than 0.95%, Cu
of 0.01 to 1.0% and Ni of 0.01 to 1.0%, and the balance being Ti
and impurities, wherein a ratio of .alpha./.beta. is not less than
0.3 and not more than 0.6; where ".alpha." is an area of a phase in
the plate and ".beta." is an area of 13 phase in the plate, wherein
the plate has an elongation at break in a tensile test conducted at
800.degree. C. exceeds 200%, and wherein Veq obtained by the
following equation (1) is in a range of 4.0 to 9.5:
Veq=V+1.9Cr+3.75Fe (1) where a symbol of element on a right side of
the equation (1) means a content of the element by mass %.
3. A method for manufacturing the titanium alloy material
consisting of, by mass %, Al of 2.0 to 4.0%, V of 4.0 to 9.0%, Zr
of 0 to 2.0%, Sn of 0 to 3.0%, further one or more elements
selected from Fe of 0.20 to 1.0%, Cr of 0.01 to 1.0%, Cu of 0.01 to
1.0% and Ni of 0.01 to 1.0%, and the balance being Ti and
impurities, wherein the titanium alloy with the Veq obtained by the
following equation (1) being in the range of 4.0 to 9.5 is
subjected to the cold working at the cross-section reduction rate
of 40% or more: Veq=V+1.9Cr+3.75Fe (1) where a symbol of element on
the right side of the equation (1) means a content of the element
by mass %.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to titanium alloys in use in
chemical industry members such as machine structure members and
heat exchanger members and consumer goods members such as golf
clubs, and a method for manufacturing titanium alloy materials. The
present invention particularly relates to titanium alloys with an
excellent cold workability and superplasticity characteristics, and
a method for manufacturing the titanium alloy materials.
BACKGROUND ART
[0002] Heat exchangers are instruments capable of transmitting
thermal energy between different fluids. The heat exchangers are
used in, for example, air conditioners, refrigerators, air
preheating equipment of burners, radiators in automobiles, parts
for the chemical industry, parts for seawater and the like. In
particular, heat exchangers made of titanium are used in fields
requiring excellent corrosion resistance such as in the chemical
industry or in salt water. In order to reduce the size of heat
exchangers, it is necessary to increase the strength of the parts
being used and that is why titanium alloy which are light and
strong are used as a material for such heat exchangers.
[0003] A Ti-6Al-4V alloy has been widely used as the heat exchanger
material due to its excellent superplasticity characteristics as
described in, for example, Non-patent document 1. However, this
alloy has poor cold workability. For example, when thin plates are
manufactured by cold rolling the Ti-6Al-4V alloy plate which is
wrapped around a coil, there is a drawback that the number of
intermediate annealing needs to be increased.
[0004] Non-patent document 2 shows that a Ti-9V-2Mo-3Al alloy is a
titanium alloy which has an excellent cold workability and also an
excellent superplasticity workability. However, this alloy contains
Mo as an essential element, which results in a high cost of raw
materials. Also, because of a high melting point of Mo, there is a
higher incidence of unmelted portions or solidification segregation
in melting.
[0005] Patent document 1 describes a titanium alloy with excellent
superplasticity workability containing, by mass %, Al of 5.5 to
6.5%, V of 3.5 to 4.5%, O of 0.2% or less, Fe of 0.15 to 3.0%, Cr
of 0.15 to 3.0% and Mo of 0.85 to 3.15%, in which Fe, Cr and Mo are
within a range represented by a specific equation and an average
grain diameter of an a crystal is 6 .mu.m or less. This alloy can
be said to be superior to the Ti-6Al-4V alloy in the
superplasticity workability, but the cold workability is not
considered. Namely, this alloy has a high content of Al which is
5.5% or more, which results in high distortion resistance in the
cold rolling and a high possibility of edge cracks occurring in the
edges of a plate if this alloy is subjected to cold rolling at a
cross-section reduction rate of 50%.
[0006] Patent document 2 describes a titanium alloy with excellent
workability which contains, by mass %, Al of 3.0 to 5.0%, V of 2.1
to 3.7%, Mo of 0.85 to 3.15%, 0 of 0.15% or less, and further one
or more elements of Fe, Cr, Ni and Co, in which the content of
these elements is in a range represented by a specific equation.
There is also described a manufacturing method of a titanium alloy
material in a specific hot rolling condition, and a superplastic
processing method of the titanium alloy material in the specific
heat treatment condition. However, since this alloy contains Mo,
there will be the same problem with the alloy described in
Non-patent document 2. [0007] Patent document 1: Japanese Examined
Patent Publication No. 1996-195026 [0008] Patent document 2:
Japanese Examined Patent Publication No. 1996-23053B [0009]
Non-patent document 1: N. Furushiro and three other persons,
Titanium' 80, 1980, pp. 993-998, published by Metallurgical Society
of AIME [0010] Non-patent document 2: T. Oka and 2 other persons,
"What is being studied about titanium materials in Japan?", pp.
58-60, edited on Dec. 1, 1989 by The Iron and Steel Institute of
Japan
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0011] An object of the present invention is to provide titanium
alloys with the excellent cold workability and the superplasticity
characteristics and a method for manufacturing the titanium alloy
materials.
Means Adapted to Solve the Problem
[0012] The present invention was accomplished as a result of
repeated research made by the present inventors based on a
Ti-3Al-2.5V alloy which is said to have the excellent cold
workability.
[0013] The present invention is characterized by titanium alloys as
shown in (1) and (2) below, and a method for manufacturing a
titanium alloy materials as shown in (3) below.
[0014] (1) A cold rolled titanium alloy plate consisting of, by
mass %, Al of 2.0 to 4.0% and V of 4.0 to 9.0%, one element
selected from Zr of not more than 2.0% and Sn of not more than 3.0%
and the balance being Ti and impurities, wherein a ratio of
.alpha./.beta. is not less than 0.3 and not more than 0.6; where
"a" is an area of a phase in the plate and ".beta." is an area of
.beta. phase in the plate, and wherein the plate has an elongation
at break in a tensile test conducted at 800.degree. C. exceeds
200%.
[0015] (2) A cold rolled titanium alloy plate consisting of, by
mass %, Al of 2.0 to 4.0% and V of 4.0 to 9.0%, one element
selected from Zr of not more than 2.0% and Sn of not more than
3.0%, further one or more elements selected from Fe of not less
than 0.20% and not more than 0.95%, Cr of not less than 0.01% and
not more than 0.95%, Cu of 0.01 to 1.0% and Ni of 0.01 to 1.0%, and
the balance being Ti and impurities, wherein a ratio of
.alpha./.beta. is not less than 0.3 and not more than 0.6; where
".alpha." is an area of a phase in the plate and ".beta." is an
area of .beta. phase in the plate, wherein the plate has an
elongation at break in a tensile test conducted at 800.degree. C.
exceeds 200%, and wherein Veq obtained by the following equation
(1) is in a range of 4.0 to 9.5:
Veq=V+1.9Cr+3.75Fe (1)
[0016] where a symbol of element on a right side of the equation
(1) means a content of the element by mass %.
[0017] (3) A method for manufacturing titanium alloy materials is
characterized in that the titanium alloy described in the above (1)
or (2) is subjected to the cold working at a cross-section
reduction rate of 40% or more.
Effect of the Invention
[0018] A titanium alloy of the present invention has a sufficient
cold workability as well as the excellent superplasticity
characteristics. Therefore, it is possible to easily produce a coil
by the cold rolling, and a material for superplastic molding with a
uniform distribution of a plate thickness can be manufactured.
Therefore, it is possible to easily produce thin plates made of
titanium alloy at a low cost, allowing for the expansion of an
application field for the titanium alloy thin plates.
BEST MODE FOR CARRYING OUT THE INVENTION
[0019] First, chemical compositions in the titanium alloy of the
present invention and the reasons for the limitation will be
described. "%" in each component means "mass %" in the following
explanation.
Al: 2.0 to 4.0%
[0020] Al is an element that plays a very important role in
increasing the strength of the titanium alloy. Al is also an
effective element for stabilizing the .alpha. phase of the titanium
alloy. The superplasticity characteristics are exhibited in a
temperature range in which the ratio of the .alpha. phase and the
.beta. phase is approximately 50/50. If the content of Al is low,
this temperature range is narrowed, which results in difficulties
obtaining stable superplasticity characteristics. The content of Al
needs to be 2.0% or more so as to obtain the superplasticity
characteristics in a wider temperature range. However, the cold
workability reduces as the content of Al increases. In particular,
if a titanium alloy in which the content of Al exceeds 4.0% is
subjected to the cold working at a cross-section reduction rate of
about 50%, the edge cracks occur in the edges of the plate.
Therefore, the content of Al is limited to 2.0 to 4.0%.
V: 4.0 to 9.0%
[0021] V is an effective element for stabilizing the .beta. phase
of titanium alloys, and has an effect of increasing the ratio of
the .beta. phase in a temperature range of about 800 to 850.degree.
C. In particular, if the content of V is 4.0% or more, the
temperature range in which the ratio of the a phase and the 13
phase is approximately 50/50 can be increased. However, if the
content of V exceeds 9.0%, oxidation resistance characteristics of
the titanium alloy material are lowered. This is because an oxide
of V has a sublimation property, so that a scale generated on the
surface of the alloy is not dense but has a high permeability of
oxygen if the titanium alloy in which the content of V exceeds 9.0%
is exposed to a high temperature. Therefore, cracks occur more
easily on the surface of the alloy, and a high temperature
ductility is decreased. Accordingly, the content of V is limited to
4.0 to 9.0%.
Zr: 0 to 2.0%
[0022] Zr is an element that may not be necessarily added. If Zr is
added, it contributes to strengthen the titanium alloy due to a
solid solution strengthening effect thereof. If a titanium alloy
containing Zr is exposed to the high temperature, a strong Zr oxide
is formed on the surface thereof to suppress oxidation inside the
alloy, so that a generation of the cracks can be prevented in a
deformation of the titanium alloy at the high temperature.
Therefore, elongation of the titanium alloy is increased at the
high temperature, and the superplasticity characteristics are
improved. These effects are largely exhibited in 0.5% or more.
However, Zr is an expensive element, and the oxidation suppression
effect described above is saturated if the content of Zr exceeds
2.0%, leading to a cost increase. Therefore, if Zr is contained,
the content is preferably limited to 2.0% or less.
Sn: 0 to 3.0%
[0023] Sn is also an element that may not be necessarily added.
Although Sn does not contributes to stabilize the a phase or the 13
phase, it is an element that contributes to strengthen the titanium
alloy. To obtain such effect of Sn, the content is preferably 0.2%
or more. However, if the content of Sn exceeds 3.0%, a low melting
point region is formed in a coagulation process, and the cracks
occur from this region as a starting point. Therefore, if Sn is
contained, the content is preferably 3.0% or less.
[0024] The titanium alloy of the present invention has the chemical
compositions described above, and the balance being Ti and
impurities. The alloy may contain one or more elements selected
from Fe of 0.20 to 1.0%, Cr of 0.01 to 1.0%, Cu of 0.01 to 1.0% and
Ni of 0.01 to 1.0% as substitute for a part of Ti. This is based on
the following reasons.
[0025] Fe and Cr are elements contained, as impurities, in a
titanium sponge which is a titanium raw material, or in an
aluminum-vanadium alloy which is an additional material. Therefore,
Fe of less than 0.20% and Cr of less than 0.01% are contained in
the titanium alloy even if these elements are not positively added.
These elements are a .beta.-phase stabilizing element having the
same effect as V, but they are cheaper than V. Accordingly, cost
reduction can be realized by positively adding these elements, so
that it is desirable to contain Fe of 0.20% or more and Cr of 0.01%
or more. However, Fe and Cr are a eutectoid type element forming an
intermetallic compound in the titanium alloy. If Fe and Cr of
exceeding 1.0% are respectively contained, there will be
embrittlement caused by excessive precipitations of the
intermetallic compound.
[0026] Cu and Ni are a .beta. stabilizing element in the same
manner with V, and an effective element to increase the ratio of
the .beta. phase in a temperature range of 800 to 850.degree. C.
These elements are cheaper than V, and can be added as an
alternative element of V. It is desirable to contain Cu of 0.01% or
more and Ni of 0.01% or more in order to obtain this effect.
However, the intermetallic compound is formed and the cold
workability is lowered if Cu and Ni of exceeding 1.0% are
respectively added, because Cu and Ni are the eutectoid type
element for titanium.
[0027] Accordingly, if one or more elements of these are contained
in the titanium alloy of the present invention, the content is
limited to Fe of 0.20 to 1.0%, Cr of 0.01 to 1.0%, Cu of 0.01 to
1.0% and Ni of 0.01 to 1.0%.
Veq(=V+1.9Cr+3.75Fe):4.0 to 9.5
[0028] As an index to exhibit the stability of the 13 phase in the
titanium alloy, there is a Veq represented by the following
equation (1):
Veq=V+1.9Cr+3.75Fe (1)
[0029] where a symbol on the right side of the equation (1) means a
content of each element.
[0030] If the Veq is less than 4.0, the ratio of the .beta. phase
is lowered in a temperature range of 800 to 850.degree. C., and the
superplasticity characteristics are hardly exhibited in this
temperature range. However, if the Veq exceeds 9.5, the ratio of
the a phase is lowed, the superplasticity characteristics
deteriorate in a temperature range of 800 to 850.degree. C. and the
specific gravity of the alloy itself increases. Accordingly, if Fe
and/or Cr are contained to the titanium alloy of the present
invention, it is necessary to limit Veq in a range of 4.0 to
9.5.
[0031] O (oxygen), C (carbon), N (nitrogen) and H (hydrogen) are
major impurities contained in the titanium alloy of the present
invention. O is an impurity contained in the titanium sponge and a
raw material of V, while C and N are impurities contained in the
titanium sponge. Also, H is an impurity which is absorbed from an
atmosphere in heating or absorbed in an acid washing process.
Impurities are preferably as low as possible in a range where O is
0.2% or less, C is 0.01% or less, N is 0.01% or less, and H is
0.01% or less.
[0032] A ratio of .alpha./.beta.: not less than 0.3 and not more
than 0.6
[0033] ".alpha." is an area of .alpha. phase in the plate and
".beta." is an area of .beta. phase in the plate. Crystal grain
becomes coarse when an alloy is subjected to a deformation at high
temperature; thereby the elongation property of the alloy
deteriorates. But it is possible to prevent grain coarsening if
.beta. phase exists sufficiently in the alloy. Therefore, the ratio
of .alpha./.beta. must set 0.6 or less. In contrast, excessive
existence of .beta. phase causes damages to the alloy surface.
Because .beta. phase absorbs gases at high temperature and
encourages oxidizing of the alloy surface. A fracture progresses
from the damage, and the elongation property of the alloy also
deteriorates in this case. Therefore, the ratio of .alpha./.beta.
must set 0.3 or more.
[0034] Next, a method for manufacturing titanium alloy materials of
the present invention will be explained referring to a case of
manufacturing a thin plate. An ingot is prepared by an ordinary
melting method such as VAR and is subjected to hot blooming forging
or hot rolling so as to form a slab, after which hot rolling is
conducted to prepare a hot coil, followed by the cold rolling to a
target plate thickness and annealing to provide the titanium alloy
material. The cold rolling is a step that largely influences
product characteristics, and a titanium alloy material with the
excellent superplasticity characteristics at the high temperature
can be obtained particularly by the cold working (cold rolling) at
the cross-section reduction rate of 40% or more. This is based on
the following reasons.
[0035] When the cross-section reduction rate is increased in the
cold rolling, a crystal grain diameter in the titanium alloy,
particularly a grain diameter of a pro-eutectoid a phase is
decreased. Then, if the crystal grain diameter in the titanium
alloy is decreased, elongation is increased upon superplastic
deformation at the high temperature, thereby the titanium alloy
material with the excellent superplasticity characteristics at the
high temperature is exhibited. As described above, when the
cross-section reduction rate is increased in the cold rolling, the
elongation upon superplastic deformation at the high temperature is
sharply increased up to the cross-section reduction rate of about
40%, and less change is observed in a region of 40% or more.
[0036] Therefore, in the method for manufacturing the titanium
alloy materials of the preset invention, the cold working is
performed at the cross-section reduction rate of 40% or more.
Although there is no particular upper limit in the cross-section
reduction rate, when the cold rolling is performed at a
cross-section reduction rate of exceeding 80%, the edge cracks
occur in the edges of the plate. Accordingly, it is desirable in
the cold working to limit the cross-section reduction rate in 80%
or less. However, if the intermediate annealing is conducted for
the purpose of recovering the ductility of materials, the cold
working may be performed in a condition that the cross-section
reduction rate exceeds 80%.
[0037] The cross-section reduction rate is obtained by the
following equation (a).
Cross-section reduction rate (%)={(cross-section area before
working-cross-section area after working)/cross-section area before
working}.times.100 (a)
Embodiment 1
[0038] Using an arc melting furnace of plasma, a button ingot with
a width of 50 mm, a thickness of 15 mm and a longitude of 80 mm was
prepared. After the button ingot was heated at 850.degree. C., it
was subjected to hot rolling to prepare a hot-rolled plate with a
thickness of 5 mm. After this hot-rolled plate was annealed at
750.degree. C. for ten minutes, an oxide scale was removed by shot
blast and acid washing, and the surface was further cut to a
thickness of 4 mm by machine working so as to prepare a material
for the cold rolling. This material was subjected to the cold
rolling to prepare a cold-rolled plate with a thickness of 2 mm. At
this time, as an evaluation of cold-rolling property, presence of
cracks in the edges on the surface of the cold-rolled plate was
performed a visual observation.
[0039] A plate with no cracks in the cold rolling was subjected to
a heat treatment in an argon atmosphere at 700.degree. C. for 30
minutes, followed by cold rolling to a thickness of 1.5 mm, and
again subjected to the heat treatment in the argon atmosphere at
700.degree. C. for 30 minutes to provide a test specimen. From this
test specimen, a platy test piece with a thickness of 1.5 mm and a
width of 12.5 mm in a parallel part was obtained so that the
longitudinal direction of the test piece was in parallel with the
rolling direction. The distance between gauge marks of this tensile
test piece was set to be 20 mm, and a tensile test was conducted at
a test temperature of 800.degree. C. and a tensile speed of 9
mm/min., so as to measure elongation at break.
[0040] Table 1 shows chemical compositions of the cold-rolled
plate, evaluations of cold rolling property and elongation at
break.
TABLE-US-00001 TABLE 1 Cold Elongation Chemical composition rolling
at break (mass %, the balance being Ti and impurities) property
Ratio of Elongation No. Al V Zr Sn Fe Cr Cu Ni Veq evaluation
.alpha./.beta. (%) Evaluation Remarks 1 1.58* 5.08 -- -- 0.11 -- --
-- 5.5 .smallcircle. 0.61* 180 x Comparative example 2 2.05 4.96 --
-- 0.12 -- -- -- 5.4 .smallcircle. 0.48 320 .smallcircle. Example
of the present invention 3 3.00 4.98 -- -- 0.16 -- -- -- 5.6
.smallcircle. 0.40 440 .smallcircle. Example of the present
invention 4 3.96 4.90 -- -- 0.15 -- -- -- 5.5 .smallcircle. 0.31
470 .smallcircle. Example of the present invention 5 4.20* 4.94 --
-- 0.24 -- -- -- 5.8 x -- -- -- Comparative example 6 3.01 3.50* --
-- 0.15 -- -- -- 4.1 .smallcircle. 0.25* 160 x Comparative example
7 3.05 4.12 -- -- 0.17 -- -- -- 4.8 .smallcircle. 0.39 295
.smallcircle. Example of the present invention 8 3.00 7.02 -- --
0.17 -- -- -- 7.7 .smallcircle. 0.48 400 .smallcircle. Example of
the present invention 9 2.98 8.88 -- -- 0.15 -- -- -- 9.4
.smallcircle. 0.53 320 .smallcircle. Example of the present
invention 10 3.01 5.05 -- -- 0.50 -- -- -- 6.9 .smallcircle. 0.48
355 .smallcircle. Example of the present invention 11 3.03 4.98 --
-- 0.98 -- -- -- 8.7 .smallcircle. 0.55 275 .smallcircle. Example
of the present invention 12 3.02 5.11 -- -- 1.20* -- -- -- 9.6*
.smallcircle. 0.65* 150 x Comparative example 13 2.99 4.97 -- --
0.12 0.49 -- -- 6.3 .smallcircle. 0.45 335 .smallcircle. Example of
the present invention 14 2.97 4.96 -- -- 0.11 0.95 -- -- 7.2
.smallcircle. 0.50 300 .smallcircle. Example of the present
invention 15 2.99 5.00 -- -- 0.11 2.21* -- -- 9.6* x -- -- --
Comparative example 16 3.02 5.01 -- -- 0.50 1.15* -- -- 9.1 x -- --
-- Comparative example 17 3.04 4.90 -- -- 0.88 1.01* -- -- 10.2*
.smallcircle. 0.65* 125 x Comparative example 18 3.03 4.98 0.51 --
0.13 -- -- -- 5.5 .smallcircle. 0.41 310 .smallcircle. Example of
the present invention 19 3.00 5.03 0.95 -- 0.14 -- -- -- 5.6
.smallcircle. 0.45 335 .smallcircle. Example of the present
invention 20 3.05 4.98 1.88 -- 0.12 -- -- -- 5.4 .smallcircle. 0.43
340 .smallcircle. Example of the present invention 21 3.00 5.01 --
-- 0.98 -- -- -- 8.7 .smallcircle. 0.55 275 .smallcircle. Example
of the present invention 22 3.03 5.05 -- -- 0.14 -- 0.05 -- 5.6
.smallcircle. 0.43 420 .smallcircle. Example of the present
invention 23 3.01 5.02 -- -- 0.15 -- 0.98 -- 5.6 .smallcircle. 0.42
435 .smallcircle. Example of the present invention 24 3.02 4.98 --
-- 0.16 -- 1.13* -- 5.6 x -- -- -- Comparative example 25 2.99 5.01
-- -- 0.18 -- -- 0.08 5.7 .smallcircle. 0.44 410 .smallcircle.
Example of the present invention 26 3.00 5.03 -- -- 0.17 -- -- 0.75
5.7 .smallcircle. 0.41 405 .smallcircle. Example of the present
invention 27 2.99 5.05 -- -- 0.15 -- -- 1.28* 5.6 x -- -- --
Comparative example 28 3.02 4.97 -- 0.15 0.16 -- -- -- 5.6
.smallcircle. 0.42 425 .smallcircle. Example of the present
invention 29 3.03 5.02 -- 0.88 0.17 -- -- -- 5.7 .smallcircle. 0.42
430 .smallcircle. Example of the present invention 30 3.00 5.04 --
1.55 0.17 -- -- -- 5.7 .smallcircle. 0.41 440 .smallcircle. Example
of the present invention 31 2.99 4.99 -- 2.85 0.17 -- -- -- 5.6
.smallcircle. 0.42 400 .smallcircle. Example of the present
invention 32 3.02 5.01 -- 3.10* 0.17 -- -- -- 5.6 x -- -- --
Comparative example 33 3.01 6.51 -- -- 0.90 -- -- -- 9.9*
.smallcircle. 0.67* 170 x Comparative example 34 3.21 7.02 -- --
0.51 0.45 -- -- 9.8* .smallcircle. 0.70* 165 x Comparative example
35 3.11 7.55 -- -- 0.16 0.95 -- -- 10.0* .smallcircle. 0.82* 135 x
Comparative example (1) [*] means outside of the range specified in
the present invention (2) [--] in the chemical composition means an
impurity level, in which Fe is less than 0.20% and other than Fe is
less than 0.01%. (3) Examples with [x] in the cold rolling property
had no tensile test conducted.
[0041] In the cold rolling property evaluation, a plate with no
cracks is indicated as [.smallcircle.] and a plate with cracks is
indicated as [x] when a cold-rolled plate with a thickness of 2 mm
was prepared. Also, in the elongation at break, a plate of
exceeding 200% in elongation at break is indicated as
[.smallcircle.], and a plate of 200% or less in elongation at break
is indicated as [x] when a tensile test was conducted at
800.degree. C.
[0042] As shown in Table 1, alloys satisfying the chemical
compositions specified in the present invention are capable of
being cold rolled to obtain an excellent superplastic
elongation.
Embodiment 2
[0043] A material for cold rolling containing Al of 3.0%, V of 5.0%
and the balance being Ti and impurities was prepared with a
thickness of 4 mm in the same manner with Example 1.
[0044] The material for cold rolling was subjected to a cold
rolling in different cross-section reduction rates to prepare
cold-rolled plates with thicknesses of 3.5 mm, 3.0 mm, 2.5 mm, 2.0
mm and 1.5 mm. After these cold-rolled plates were subjected to the
heat treatment in the argon atmosphere at 700.degree. C. for 30
minutes, a platy test piece with a thickness of 1.0 mm and a width
of 12.5 mm in a parallel part was obtained so that the longitudinal
direction of the test piece was in parallel with the rolling
direction. The distance between the gauge marks in this tensile
test piece was set to 20 mm, and the tensile test was conducted at
the test temperature of 800.degree. C. and a tensile speed of 9
mm/min., so as to measure the elongation at break.
[0045] Further, in order to examine the influence of a
cross-section reduction rate to the superplasticity characteristics
in the cold rolling after the intermediate annealing, the
cold-rolled plate with a thickness of 2.0 mm was subjected to the
heat treatment in the argon atmosphere at 700.degree. C. for 30
minutes, followed by the cold rolling to a thickness of 1.5 mm or
1.0 mm, and again subjected to the hot treatment in the argon
atmosphere at 700.degree. C. for 30 minutes so as to prepare a test
specimen. From this test specimen, the platy test piece with the
thickness of 1.0 mm and the width of 12.5 mm in the parallel part
was obtained, and the same tensile test as described above was
conducted to measure the elongation at break. Table 2 shows the
cross-section reduction rate and the elongations at break.
TABLE-US-00002 TABLE 2 Before intermediate After intermediate
annealing annealing Plate Cross- Plate Cross- thickness section
thickness section Elongation after cold reduction after cold
reduction rate rolling rate rolling rate at break No. (mm) (%) (mm)
(%) (%) 36 3.50 12.5 -- -- 210 37 3.02 24.5 -- -- 240 38 2.47 38.3
-- -- 360 39 1.99 50.3 -- -- 470 40 1.51 62.3 -- -- 485 41 2.02
49.5 1.52 24.8 440 42 2.03 49.3 1.05 48.3 425
[0046] As shown in Table 2, since all the examples are within a
range of the chemical compositions specified in the present
invention, the elongation at break exceeds 200% and the excellent
superplasticity characteristics have been obtained. In particular,
the elongation at break is increased in accordance with the
increase of the cross-section reduction rate, and there is almost
no change in the elongation at break under a condition that the
cross-section reduction rate is 40% or more. Also, from the results
of No. 39 and No. 40, it is understood that an excellent elongation
at break is observed if the cross-section reduction rate before the
intermediate annealing is 40% or more, even though the cold rolling
rate after the intermediate annealing is low.
[0047] Although only some exemplary embodiments of this invention
have been described in detail above, those skilled in the art will
readily appreciated that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention.
INDUSTRIAL APPLICABILITY
[0048] The titanium alloy of the present invention has the
sufficient cold workability as well as the excellent
superplasticity characteristics. Accordingly, it is possible to
easily prepare the coil by the cold rolling, and also to
manufacture a material for a superplasticity molding having a
uniform distribution in a plate thickness. Therefore, the titanium
alloy thin plates can be easily manufactured at a low cost,
allowing the expansion of the application field for the titanium
alloy thin plates.
* * * * *