U.S. patent application number 11/665499 was filed with the patent office on 2008-04-24 for beta-type titanium alloy.
Invention is credited to Satoshi Matsumoto.
Application Number | 20080092997 11/665499 |
Document ID | / |
Family ID | 36148452 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080092997 |
Kind Code |
A1 |
Matsumoto; Satoshi |
April 24, 2008 |
Beta-Type Titanium Alloy
Abstract
Disclosed is a .beta.-titanium alloy consisting of, in weight
percent, 5-15% of V, 0.5-2.5% of Fe, 0.5-6% of Mo, 0.5-5% of Cr,
1.5-5% of Al, and the balance of Ti and impurities. When the weight
% of V content is expressed as X.sub.V, the weight % of Fe content
is expressed as X.sub.Fe, the weight % of Mo content is expressed
as X.sub.Mo, and the weight % of Cr content is expressed as
X.sub.Cr; the value of X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65
X.sub.Cr is 15-23%. Such a .beta.-titanium alloy has excellent cold
workability, while having higher strength than Ti-20V-4Al-1Sn
.beta.-titanium alloy.
Inventors: |
Matsumoto; Satoshi; (Osaka,
JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW
SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
36148452 |
Appl. No.: |
11/665499 |
Filed: |
October 14, 2005 |
PCT Filed: |
October 14, 2005 |
PCT NO: |
PCT/JP05/18979 |
371 Date: |
April 16, 2007 |
Current U.S.
Class: |
148/669 ;
148/421 |
Current CPC
Class: |
C22C 14/00 20130101 |
Class at
Publication: |
148/669 ;
148/421 |
International
Class: |
C22F 1/18 20060101
C22F001/18; C22C 14/00 20060101 C22C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2004 |
JP |
2004-301186 |
Claims
1. A .beta.-type titanium alloy comprising, by mass %, V: 5 to 15%,
Fe: 0.5 to 2.5%, Mo: 0.5 to 6% and Cr: 0.5 to 5%, wherein the value
of X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr is from 15 to 23%,
wherein X.sub.V represents the mass % of the V, X.sub.Fe represents
the mass % of the Fe, X.sub.Mo represents the mass % of the Mo and
X.sub.Cr represents the mass % of the Cr, and further comprising,
by mass %, Al: 1.5 to 5%, wherein Ti and impurities constitute the
residue.
2. A .beta.-type titanium alloy comprising, by mass %, V: 5 to 15%,
Fe: 0.5 to 2.5%, Mo: 0.5 to 6% and Cr: 0.5 to 5%, wherein the value
of X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr is from 15 to 23%,
wherein X.sub.V represents the mass % of the V, X.sub.Fe represents
the mass % of the Fe, X.sub.Mo represents the mass % of the Mo and
X.sub.Cr represents the mass % of the Cr, and further comprising,
by mass %, Al: 1.5% to less than 5% and at least one of the group
consisting of Sn: not more than 5% and Zr: not more than 5%,
wherein the value of X.sub.Al+(X.sub.Sn/3)+(X.sub.Zr/6) is from 1.5
to 5, wherein X.sub.Al represents the mass % of the Al, X.sub.Sn
represents the mass % of the Sn and X.sub.Zr represents the mass %
of the Zr, wherein Ti and impurities constitute the residue.
3. A .beta.-type titanium alloy comprising, by mass %, V: 5 to 15%,
Fe: 0.5 to 2.5%, Mo: 0.5 to 6%, Cr: 0.5 to 5% and at least one
selected from the group consisting of Nb: 0.5 to 2%, Ta: 0.5 to 2%,
Ni: 0.25 to 1%, Mn: 0.25 to 1% and Co: 0.25 to 1%, wherein the
value of
X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr+0.4X.sub.Nb+0.3X.sub.Ta+1.6-
X.sub.Ni+2.3X.sub.Mn+2.1X.sub.Co is from 15 to 23%, wherein X.sub.V
represents the mass % of the V, X.sub.Fe represents the mass % of
the Fe, X.sub.Mo represents the mass % of the Mo, X.sub.Cr
represents the mass % of the Cr, X.sub.Nb represents the mass % of
the Nb, X.sub.Ta represents the mass % of the Ta, X.sub.Ni
represents the mass % of the Ni, X.sub.Mn represents the mass % of
the Mn and X.sub.Co represents the mass % of the Co, and further
comprising, by mass %, Al: 1.5 to 5%, wherein Ti and impurities
constitute the residue.
4. A .beta.-type titanium alloy comprising, by mass %, V: 5 to 15%,
Fe: 0.5 to 2.5%, Mo: 0.5 to 6%, Cr: 0.5 to 5% and at least one
selected from the group consisting of Nb: 0.5 to 2%, Ta: 0.5 to 2%,
Ni: 0.25 to 1%, Mn: 0.25 to 1% and Co: 0.25 to 1%, wherein the
value of
X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr+0.4X.sub.Nb+0.3X.sub.Ta+1.6-
X.sub.Ni+2.3X.sub.Mn+2.1X.sub.Co is from 15 to 23%, wherein X.sub.V
represents the mass % of the V, X.sub.Fe represents the mass % of
the Fe, X.sub.Mo represents the mass % of the Mo, X.sub.Cr
represents the mass % of the Cr, X.sub.Nb represents the mass % of
the Nb, X.sub.Ta represents the mass % of the Ta, X.sub.Ni
represents the mass % of the Ni, X.sub.Mn represents the mass % of
the Mn and X.sub.Co represents the mass % of the Co, and further
comprising, by mass %, Al: 1.5% to less than 5% and at least one
selected from the group consisting of Sn: not more than 5% and Zr:
not more than 5%, wherein the value of
X.sub.Al+(X.sub.Sn/3)+(X.sub.Zr/6) is from 1.5 to 5, wherein
X.sub.Al represents the mass % of the Al, X.sub.Sn represents the
mass % of the Sn and X.sub.Zr represents the mass % of the Zr, and
wherein Ti and impurities constitute the residue.
5. A method for heat treatment of the .beta.-type titanium alloy of
claim 1, comprising heating a .beta.-type titanium alloy to a
temperature equal to or above the .beta. transformation
temperature, and then cooling the same at an average cooling rate
of 1 to 100.degree. C./sec to at least 500.degree. C. or below.
6. A method for heat treatment of the .beta.-type titanium alloy of
claim 2, comprising heating a .beta.-type titanium alloy to a
temperature equal to or above the .beta. transformation
temperature, and then cooling the same at an average cooling rate
of 1 to 100.degree. C./sec to at least 500.degree. C. or below.
9. A method for heat treatment of the .beta.-type titanium alloy of
claim 3, comprising heating a .beta.-type titanium alloy to a
temperature equal to or above the .beta. transformation
temperature, and then cooling the same at an average cooling rate
of 1 to 100.degree. C./sec to at least 500.degree. C. or below.
10. A method for heat treatment of the .beta.-type titanium alloy
of claim 4, comprising heating a .beta.-type titanium alloy to a
temperature equal to or above the .beta. transformation
temperature, and then cooling the same at an average cooling rate
of 1 to 100.degree. C./sec to at least 500.degree. C. or below.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a .beta.-type titanium
alloy and a method for heat treatment thereof.
BACKGROUND OF THE INVENTION
[0002] Titanium alloys are light in weight and high in strength,
and of them, there exist titanium alloys called as .beta.-type
titanium alloys that comprise only the .beta.-phase, many of which
are excellent in cold workability compared with titanium alloys
that comprise mainly the .alpha.-phase, and many being able to be
increased in strength by an aging treatment.
[0003] Examples of the known .beta.-type titanium alloys include
Ti-20V-4Al-1Sn (Patent Reference 1), Ti-15V-3Cr-3Al-3Sn, Ti-22V-4Al
(Patent Reference 2), Ti-15V-6Cr-4Al (Patent Reference 3),
Ti-13V-9Cr-3Al, Ti-15Mo-5Zr-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr,
Ti-13V-11Cr-3Al, and Ti-4.5Fe-6.8Mo-1.5Al.
[0004] Of them, Ti-15V-6Cr-4Al, Ti-13V-9Cr-3Al, Ti-15Mo-5Zr-3Al,
Ti-3Al-8V-6Cr-4Mo-4Zr and Ti-13V-11Cr-3Al are high in strength, but
have a high deformation resistance in cold working and hot working,
deteriorating the workability thereof, and thus are limited in
application to special fields. On the other hand, Ti-20V-4Al-1Sn,
Ti-15V-3Cr-3Al-3Sn and Ti-22V-4Al are slightly lower in strength
but are excellent in cold workability and thus are broadly and
generally used. Of them, Ti-20V-4Al-1Sn is used in sports products,
such as golf clubs and bicycles, as well as various other products,
because of its excellent cold workability and relatively high
strength.
[0005] In recent years, .beta.-type titanium alloys are required to
be increased in strength for further application in various fields,
further weight reduction and cost reduction, and specifically
required to have a higher strength while having excellent
workability as the Ti-20V-4Al-1Sn does. However, no .beta.-type
titanium alloys that have excellent cold workability and a higher
strength than Ti-20V-4Al-1Sn have been found through the studies
made up to the present, and therefore the above demands have not
yet been satisfied.
[0006] Patent Reference 1: Japanese Patent No. 2640415
[0007] Patent Reference 2: Japanese Examined Patent Application
Publication No. Hei-6-99765
[0008] Patent Reference 3: Japanese Unexamined Patent Application
Publication No. 2000-144286
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] In consideration of the above problems, it is an object of
the present invention to provide a titanium alloy that has
excellent cold workability, and higher strength than Ti-20V-4Al-1Sn
.beta.-type titanium alloy.
Means to Solve the Problems
[0010] The present inventors made intensive studies in order to
solve the above problems, and found that there can be provided an
indicator for precisely indicating the degree of stabilization of
the .beta.-phase, by determining the content of each of
.beta.-phase stabilizing elements, namely V, Fe, Mo and Cr, not on
the basis of a general method using the ratio of the minimum amount
to be added for .beta.-phase stabilization when they are added
independently of each other to titanium, but by the use of a novel
coefficient conceived in consideration of the interaction between
the respective elements.
[0011] More specifically, the respective elements contained in a
.beta.-type titanium alloy are given indices on .beta.-phase
stabilizing effects realized by them, which indices each are
generated by a reciprocal number of the minimum amount enabling a
titanium alloy to comprise only the .beta.-phase by each element,
and as a general knowledge, it is known that a titanium alloy can
comprise only the .beta.-phase by containing, by mass %, V: 15%,
Fe: 3.6%, Mo: 10% and Cr: 6.3%, and therefore when designating V as
a reference, the numerical value determined by multiplying the mass
% of the Fe by 15/3.6 is considered as an equivalence when the said
numerical value of V is contained.
[0012] Accordingly, it is assumed from the conventional way of
thinking that the degree of stabilization of the .beta.-phase can
be determined by the value of
X.sub.V+(15/3.6)X.sub.Fe+(15/10)X.sub.Mo+(15/6.3)X.sub.Cr when V is
designated as a reference, in which X.sub.V represents the mass %
of the V contained, X.sub.Fe represents the mass % of the Fe
contained, X.sub.Mo represents the mass % of the Mo contained, and
X.sub.Cr represents the mass % of the Cr contained. However, from
the studies based on experiments made by the inventors et al., it
was found that the employment of the value of
X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr can provide an index
for precisely indicating the degree of stabilization of the
.beta.-phase.
[0013] That is, according to the present invention, there is
provided a .beta.-type titanium alloy characterized by comprising,
by mass %, V: 5 to 15%, Fe: 0.5 to 2.5%, Mo: 0.5 to 6% and Cr: 0.5
to 5%, wherein the value of
X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr is from 15 to 23%,
wherein X.sub.V represents the mass % of the V, X.sub.Fe represents
the mass % of the Fe, X.sub.Mo represents the mass % of the Mo and
X.sub.Cr represents the mass % of the Cr, and further comprising,
by mass %, Al: 1.5 to 5%, wherein Ti and impurities constitute the
residue.
ADVANTAGES OF THE INVENTION
[0014] According to the present invention, it is possible to
provide a titanium alloy that is more excellent in strength than
the Ti-20V-4Al-1Sn .beta.-type titanium alloy due to the solid
solution hardening action, while having excellent cold workability
as compared with a Ti-20V-4Al-1Sn.beta.-type titanium alloy, by
containing Fe, Mo and Cr in addition to the V, and specifically
containing, by mass %, V: 5 to 15%, Fe: 0.5 to 2.5%, Mo: 0.5 to 6%,
and Cr: 0.5 to 5%, wherein the value of
X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr is from 15 to 23%, in
which X.sub.V represents the mass % of the V, X.sub.Fe represents
the mass % of the Fe, X.sub.Mo represents the mass % of the Mo and
X.sub.Cr represents the mass % of the Cr.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] Now, the description will be made for the reason for
determining the content of each element in a titanium alloy of this
embodiment.
[0016] The titanium alloy of this embodiment contains, by mass %,
V: 5 to 15%, Fe: 0.5 to 2.5%, Cr: 0.5 to 5% and Al: 1.5 to 5%, and
Ti and impurities, in which the Ti and the impurities constitute
the residue.
[0017] It is possible to provide a .beta.-type titanium alloy,
which has excellent cold workability, by melting a titanium alloy
of these elements and rapidly cooling the same.
[0018] Then, the .beta.-type titanium alloy is processed into a
desired shape and then is subjected to a heat treatment which is
called as an aging treatment to have the .alpha.-phase, which has a
higher strength than the .beta.-phase, precipitated in the
.beta.-type titanium alloy and thereby can be increased in
strength.
[0019] V is contained, by mass %, within a range from 5 to 15%
because when the content of V is less than 5%, the cold workability
of a .beta.-type titanium alloy is deteriorated and thus excellent
cold workability is not obtainable; and when the content of V
exceeds 15%, the precipitation of the .alpha.-phase in the aging
treatment is inhibited and hence more excellent strength than
Ti-20V-4Al-1Sn is not obtainable.
[0020] Fe is contained, by mass %, within a range from 0.5 to 2.5%
because when the content of Fe is less than 0.5%, an advantage of
solid solution hardening action is not obtainable and hence more
excellent strength than Ti-20V-4Al-1Sn is not obtainable; and when
the content of Fe exceeds 2.5%, segregation of Fe occurs in a
.beta.-type titanium alloy and hence unevenness in characteristics
occurs.
[0021] Mo is contained, by mass %, within a range from 0.5 to 6%
because when the content of Mo is less than 0.5%, an advantage of
solid solution hardening action is not obtainable and hence more
excellent strength than Ti-20V-4Al-1Sn is not obtainable; and when
the content of Mo exceeds 6%, excellent cold workability is not
obtainable. Furthermore, Mo is an expensive material and therefore
a problem of increasing costs is caused by increasing the content
thereof.
[0022] Cr is contained, by mass %, within a range from 0.5 to 5%
because when the content of Cr is less than 0.5%, an advantage of
solid solution hardening action is not obtainable, and hence more
excellent strength than Ti-20V-4Al-1Sn is not obtainable; and when
the content of Cr exceeds 5%, segregation of Cr occurs in a
.beta.-type titanium alloy and hence unevenness in characteristics
occurs.
[0023] Al acts on the stabilization of the .alpha.-phase while V,
Fe, Mo and Cr are elements for stabilizing the .beta.-phase, and Al
is contained, by mass %, within a range from 1.5 to 5% because when
the content of Al is less than 1.5%, the precipitation of the
.alpha.-phase by an aging treatment cannot be accelerated, and
hence more excellent strength than Ti-20V-4Al-1Sn is not
obtainable. Furthermore, Al has an advantage of inhibiting the
precipitation of the .omega.-phase, and therefore the .omega.-phase
may be precipitated and thereby the alloy may be weakened, when the
content of Al is less than 1.5%.
[0024] When the content of Al exceeds 5%, the cold workability is
deteriorated and hence excellent cold workability is not
obtainable.
[0025] The contents of V, Fe, Mo and Cr are set so that the value
represented by X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr is
from 15 to 23%, in which X.sub.V represents the mass % of the V,
X.sub.Fe represents the mass % of the Fe, X.sub.Mo represents the
mass % of the Mo and X.sub.Cr represents the mass % of the Cr.
Whereby, it is possible to provide a cold workability equivalent to
that of Ti-20V-4Al-1Sn. When the said value is less than 15, a
titanium alloy comprising only the .beta.-phase is difficult to be
obtained even by increasing the cooling rate from the temperature
equal to or above the B transformation temperature, and hence the
workability is deteriorated due to the precipitation of the
martensitic phase, the .alpha.-phase or the like. Contrarily to
this, when the said value exceeds 23, the precipitation of the
.alpha.-phase in the aging treatment is inhibited and more
excellent strength than Ti-20V-4Al-1Sn is not obtainable.
[0026] In order to be able to inhibit the possibility of
deteriorating the cold workability due to the precipitation of the
.alpha.-phase or any phase other than the .beta.-phase, the average
cooling rate from the temperature equal to or above the B
transformation temperature to at least 500.degree. C., at which a
different phase is unlikely to be precipitated, is preferably from
1 to 100.degree. C./sec. Especially, for an intermediate having a
value represented by X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+1.65X.sub.Cr
being not more than 17%, a different phase is easy to be
precipitated due to the low cooling rate, and therefore it is
preferably cooled at a rate within the above range. The cooling
rate is from 1 to 100.degree. C./sec because when it is 1.degree.
C./sec or below, a phase other than the .beta.-phase is easy to be
precipitated, and when it is increased to 100.degree. C./sec or
above, an effect of preventing the precipitation of a different
phase is unlikely to be enhanced.
[0027] It is possible to use Nb, Ta, Ni, Mn and Co solely or in
combination with each other as .beta.-phase stabilizing elements
other than V, Fe, Mo and Cr. In this case, a titanium alloy
contains Nb: 0.5 to 2%, Ta: 0.5 to 2%, Ni: 0.25 to 1%, Mn: 0.25 to
1% and Co: 0.25 to 1%, and the value of
X.sub.V+2.95X.sub.Fe+1.5X.sub.Mo+165X.sub.Cr+0.4X.sub.Nb+0.3X.sub.Ta+1.6X-
.sub.Ni+2.3X.sub.Mn+2.1X.sub.Co is from 15 to 23%, in which X.sub.V
represents the mass % of the V, X.sub.Fe represents the mass % of
the Fe, X.sub.Mo represents the mass % of the Mo, X.sub.Cr
represents the mass % of the Cr, X.sub.Nb represents the mass % of
the Nb, X.sub.Ta represents the mass % of the Ta, X.sub.Ni
represents the mass % of the Ni, X.sub.Mn represents the mass % of
the Mn and X.sub.Co represents the mass % of the Co, so that the
titanium alloy can have more excellent strength than
Ti-20V-4Al-1Sn, while having excellent cold workability. It is
possible to use neutral atoms Sn, Zr as optional components solely
or in combination by substituting a part of Al therewith according
to needs and circumstances. In this case, a titanium alloy contains
Sn: not more than 5%, Zr: not more than 5%, and the value of
X.sub.Al+(X.sub.Sn/3)+(X.sub.Zr/6) is from 1.5 to 5, in which
X.sub.Al represents the mass % of the Al, X.sub.Sn represents the
mass % of the Sn and X.sub.Zr represents the mass % of the Zr, so
that the titanium alloy has more excellent strength than
Ti-20V-4Al-1Sn.
[0028] As impurities, inevitable impurities such as O and H exist,
and in order to have a good ductility, the content of O is
preferably not more than 0.25% by mass, and in order to efficiently
improve the strength by an aging treatment, the content of H is
preferably not more than 0.05% by mass.
EXAMPLES
[0029] Now, the description will be made in more detail for the
present invention by citing Examples, without intention to limit
the present invention to them.
Examples 1 to 11
Comparative Examples 1 to 6
[0030] Each ingot was prepared by button arc melting to have the
respective elements contained in each ratio as shown in Table 1,
then hot rolled to have a 4 mm thickness plate and then subjected
to a solution treatment.
[0031] Each intermediate was cooled to 500.degree. C. at an average
cooling rate of 4.degree. C./sec after the solution treatment, and
then stood to cool at room temperature.
[0032] Then, scales were removed, and thus a thin plate specimen of
a 1 mm thickness .beta.-type titanium alloy was prepared.
[0033] (Evaluation)
[0034] The respective Examples and Comparative Examples were
evaluated in the manners mentioned below.
[0035] <Hot Deformation Resistance>
[0036] Hot deformation resistance was determined by the working
Formaster test using a test piece (a diameter of 8 mm by a length
of 12 mm) cut out from the ingot. Specifically, the test piece was
rapidly heated to 900.degree. C. by infra-red radiation, and
pressed at a rate of 50 mm/sec with 50% deformation and stress at
that time was determined and designated as hot deformation
resistance.
[0037] <Limit of Cold Rolling Reduction Ratio>
[0038] A 4 mm thickness plate prepared by hot rolling of an ingot
was subjected to a solution treatment, then cooled, and each
surface thereof was cut off by 0.5 mm by machine and scales were
removed. Thus, a 3 mm thickness plate was prepared.
[0039] Then, end faces were polished by an abrasive paper (#100)
and then the plate was cold rolled. The end faces were observed
each time a 10% cold rolling is carried out and checked on the
presence or absence of cracks.
[0040] The reduction ratio, at which one or more cracks each having
a 1 mm or more depth from the end faces are caused in every 10 mm,
was designated as the limit of cold rolling reduction ratio.
[0041] For the limit of cold rolling reduction ratio, an evaluation
was made with a value of 70% (a thickness of 0.9 mm) being
designated as a maximum value.
[0042] <Proof Stress and Tensile Strength>
[0043] A 1 mm thickness thin plate specimen was heat treated in
vacuum, and a specimen subjected only to a solution treatment
(800.degree. C. for 15 min), and a specimen subjected to an aging
treatment (500.degree. C. for 8 hrs) following the solution
treatment, were prepared. From these heat treated thin plate
specimens, half-sized specimens having a parallel portion width of
6.25 mm and a gage length of 25 mm were prepared, and a tensile
test was carried out according to JIS Z 2241 at a rate of 0.1
mm/min, and a tensile strength and a 0.2% proof stress were
determined. TABLE-US-00001 TABLE 1 B-PHASE COMPONENTS (%)
STABILIZATION V Fe Cr Mo Al Sn Zr Nb Ta Ni Co Mn Ti INDICES *1 EX.
1 8 1.5 4 0.5 3.5 0 0 0 0 0 0 0 Residue 19.8 EX. 2 8 1 4 2 3.5 0 0
0 0 0 0 0 Residue 20.6 EX. 3 15 1 0.5 0.5 3.5 0 0 0 0 0 0 0 Residue
19.6 EX. 4 8 1.5 4 0.5 3.5 1 0 0 0 0 0 0 Residue 20.5 EX. 5 8 1.5 4
0.5 3.5 0 1 0 0 0 0 0 Residue 20.5 EX. 6 8 1.5 4 2 3.5 0 0 0 0 0 0
0 Residue 22.0 EX. 7 8 1.5 4 0.5 3.5 0 0 0.5 0.5 0 0 0 Residue 20.1
EX. 8 8 1.5 4 0.5 3.5 0 0 0.5 0.5 0.5 0 0 Residue 20.9 EX. 9 8 1.5
4 0.5 3.5 0 0 0.5 0.5 0 0.5 0 Residue 21.3 EX. 10 8 1.5 4 0.5 3.5 0
0 0.5 0.5 0 0 0.5 Residue 21.2 EX. 11 8 1 2 1.5 3.5 0 0 0 0 0 0 0
Residue 16.5 COMP. 8 3 6 0 3.5 0 0 0 0 0 0 0 Residue 26.8 EX. 1
COMP. 8 0.5 0.5 0 3.5 0 0 0 0 0 0 0 Residue 10.5 EX. 2 COMP. 20 0 0
0 3.5 0 0 0 0 0 0 0 Residue 20.0 EX. 3 COMP. 13 0 9 0 3.5 0 0 0 0 0
0 0 Residue 27.9 EX. 4 COMP. 15 0 6 0 4 0 0 0 0 0 0 0 Residue 24.9
EX. 5 COMP. 11 1.5 4 0.5 3.5 0 0 0 0 0 0 0 Residue 23.5 EX. 6 *1:
Values represented by Xv + 2.95X.sub.Fe + 1.5X.sub.Mo +
1.65X.sub.Cr + 0.4X.sub.Nb + 0.3X.sub.Ta + 1.6X.sub.Ni +
2.3X.sub.Mn + 2.1X.sub.Co
[0044] TABLE-US-00002 TABLE 2 LIMIT OF HOT COLD BEFORE AGING AFTER
AGING DEFORMATION ROLLING PROOF TENSILE PROOF TENSILE RESISTANCE
REDUCTION STRESS STRENGTH STRESS STRENGTH (MPa) RATIO (%) (MPa)
(MPa) (MPa) (MPa) EX. 1 205 70 831 882 1360 1446 EX. 2 190 70 814
857 1316 1394 EX. 3 201 70 654 699 1252 1334 EX. 4 208 70 812 844
1337 1042 EX. 5 207 70 815 852 1345 1412 EX. 6 215 70 820 845 1120
1203 EX. 7 205 70 807 840 1342 1405 EX. 8 210 70 815 845 1331 1395
EX. 9 214 70 810 842 1295 1342 EX. 10 213 70 812 850 1296 1350 EX.
11 193 70 450 725 1210 1305 COMP. EX. 1 233 60 782 839 870 950
COMP. EX. 2 175 20 -- -- -- -- COMP. EX. 3 185 70 642 672 1088 1198
COMP. EX. 4 295 70 866 885 940 1009 COMP. EX. 5 270 70 834 856 1034
1146 COMP. EX. 6 225 60 822 860 1050 1190
[0045] As Reference Examples 1 to 7, specimens were prepared in the
same manner as Example 1, except that an average cooling rate to
500.degree. C. after the solution treatment was set as shown in
Table 3, and the result of the observation of the formation of a
different phase is shown in Table 3. In the observation, the
judgment on the formation of a phase other than the .beta.-phase
was made based on a chart by using an X-ray diffraction system.
TABLE-US-00003 TABLE 3 AVERAGE COOLING RATE TO 500.degree. C. AFTER
FORMATION OF A SOLUTION TREATMENT DIFFERENT PHASE REFERENCE EX. 1
50 NOT OBSERVED REFERENCE EX. 2 10 NOT OBSERVED REFERENCE EX. 3 2
NOT OBSERVED REFERENCE EX. 4 80 NOT OBSERVED REFERENCE EX. 5 0.5
.alpha.-PHASE WAS OBSERVED REFERENCE EX. 6 0.1 .alpha.-PHASE WAS
OBSERVED REFERENCE EX. 7 0.01 .alpha.-PHASE WAS OBSERVED
[0046] As shown above, it is seen that, in Examples 1 to 11, the
limit of cold rolling reduction ratio is not lowered as compared
with the result of Comparative Example 3 representative of a
Ti-20V-4Al-1Sn 8-type titanium alloy, and excellent cold
workability equivalent to that of a Ti-20V-4AI-1Sn 8-type titanium
alloy is obtained. Also, the proof stress and the tensile strength
before and after the aging treatment are high as compared with
Comparative Example 3, and thus it is seen that a titanium alloy
having more excellent strength than a Ti-20V-4Al-1Sn .beta.-type
titanium alloy can be obtained.
[0047] Furthermore, it is seen from the results of Reference
Examples 1 to 7 that the possibility of precipitating a different
phase can be reduced by setting an average cooling rate to
500.degree. C. after the solution treatment within a given
range.
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