U.S. patent application number 10/592892 was filed with the patent office on 2007-08-16 for heat resistant titanium alloy sheet excellent in cold workability and a method of production of the same.
This patent application is currently assigned to NIPPON STEEL CORPORATION. Invention is credited to Hideki Fujii, Hiroaki Otsuka, Kazuhiro Takahashi.
Application Number | 20070187008 10/592892 |
Document ID | / |
Family ID | 34993724 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070187008 |
Kind Code |
A1 |
Fujii; Hideki ; et
al. |
August 16, 2007 |
Heat resistant titanium alloy sheet excellent in cold workability
and a method of production of the same
Abstract
The present invention provides a heat resistant titanium alloy
sheet excellent in cold workability having high temperature
strength characteristics better than JIS Type 2 pure titanium and
having a cold workability and high temperature oxidation resistance
equal to or better than that of JIS Class 2 pure titanium and a
method of production of the same, that is, a heat resistant
titanium alloy sheet excellent in cold workability characterized by
comprising, by mass %, 0.3 to 1.8% of Cu, 0.18% or less of oxygen,
0.30% or less of Fe, and, as needed, at least one of Sn, Zr, Mo,
Nb, and Cr in a total of 0.3 to 1.5%, and the balance of Ti and
less than 0.3% of impurity elements and, further, a method of
production of that titanium alloy sheet characterized by performing
the final annealing at 650 to 830.degree. C. in temperature range
or performing the hot-rolled sheet or coil annealing or
intermediate annealing at 650 to 830.degree. C. in temperature
range and perform the final annealing after cold working at 600 to
650.degree. C. in temperature.
Inventors: |
Fujii; Hideki; (Chiba,
JP) ; Otsuka; Hiroaki; (Chiba, JP) ;
Takahashi; Kazuhiro; (Chiba, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Assignee: |
NIPPON STEEL CORPORATION
Tokyo
JP
100-8071
|
Family ID: |
34993724 |
Appl. No.: |
10/592892 |
Filed: |
March 16, 2005 |
PCT Filed: |
March 16, 2005 |
PCT NO: |
PCT/JP05/05292 |
371 Date: |
September 15, 2006 |
Current U.S.
Class: |
148/670 ;
148/421 |
Current CPC
Class: |
C22C 14/00 20130101;
C22F 1/00 20130101; C22F 1/18 20130101; F01N 2530/00 20130101; C22F
1/183 20130101 |
Class at
Publication: |
148/670 ;
148/421 |
International
Class: |
C22C 14/00 20060101
C22C014/00; C22F 1/18 20060101 C22F001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2004 |
JP |
2004-080280 |
Mar 10, 2005 |
JP |
2005-067175 |
Claims
1. A heat resistant titanium alloy sheet excellent in cold
workability characterized by comprising, by mass %, 0.3 to 1.8% of
Cu, 0.18% or less of oxygen, 0.30% or less of Fe, and the balance
of Ti and less than 0.3% of impurity elements.
2. A heat resistant titanium alloy sheet excellent in cold
workability as set forth in claim 1, characterized in that said
titanium alloy sheet further contains at least one or more of Sn,
Zr, Mo, Nb, and Cr in a total of 0.3 mass % to 1.5 mass %.
3. A method of production of heat resistant titanium alloy sheet
excellent in cold workability produced by the steps of remelting,
hot rolling, hot-rolled sheet or coil annealing, cold rolling,
intermediate annealing, final annealing, etc., said method of
production of a titanium alloy sheet characterized by adjusting the
ingredients at said remelting to the composition of ingredients as
set forth in claim 1 and performing said final annealing at 650 to
830.degree. C. in temperature range.
4. A method of production of heat resistant titanium alloy sheet
excellent in cold workability produced by the steps of remelting,
hot rolling, hot-rolled sheet or coil annealing, cold rolling,
intermediate annealing, final annealing, etc., said method of
production of a titanium alloy sheet characterized by adjusting the
ingredients at said remelting to the composition of ingredients as
set forth in claim 1, performing said annealing of the hot-rolled
sheet annealing or said intermediate annealing at 650 to
830.degree. C. in temperature range, and performing said final
annealing at 600 to 650.degree. C. in temperature range.
Description
TECHNICAL FIELD
[0001] The present invention relates to a heat resistant titanium
alloy sheet excellent in cold workability and a method of
production of the same, more particularly relates to a heat
resistant titanium alloy sheet excellent in cold workability suited
for exhaust system parts of two-wheeled and four-wheeled vehicles
and other applications where characteristics in a high temperature
range and cold workability are required and a method of production
of the same.
BACKGROUND ART
[0002] The exhaust system of a two-wheeled or four-wheeled vehicle
(hereinafter referred to as an "automobile") is comprised of an
exhaust manifold, exhaust pipe, muffler, and other parts. To enable
it to withstand high temperature exhaust gas or to cope with
complicated shapes, stainless steel excellent in corrosion
resistance, high temperature strength, workability, etc. is being
made considerable use of.
[0003] However, in recent years, pure titanium, which has a
corrosion resistance superior to stainless steel, is light in
weight, is excellent in workability as well, has a small heat
expansion coefficient, is superior in heat fatigue characteristics,
and is excellent in terms of aesthetic design due to its unique
color and impression, has started to be used in the exhaust systems
of some automobiles, in particular for the mufflers. The amount
used has been rapidly increasing.
[0004] A muffler is the final part in an exhaust system. The
exhaust gas there has been cooled to a certain extent. Further, it
is frequently used for the outside pipe exposed to the outside air
for design purposes. For this reason, pure titanium, which is not
that high in high temperature strength, can also be used for
muffler applications. Rather, the excellent cold workability of
pure titanium is being utilized for working the metal into
complicated shapes.
[0005] Such pure titanium parts, like stainless steel parts, are
mainly made of cold rolled annealed thin-gauge sheet which is bent,
press formed, drawn, and enlarged in holes (bored) or is bent and
welded to form welded pipe or is cold worked in various ways to
form it into the desired shape for use.
[0006] Such pure titanium thin-gauge sheet is generally produced by
the following process. That is, VAR (vacuum arc remelting) or EBR
(electron beam remelting) or another remelting process is used to
form an ingot, this is hot forged or break-down rolled to form a
slab, then this is hot rolled to form a hot rolled strip and
further descaled, then cold rolled to form a cold rolled strip.
Alternatively, this is cut to produce cut sheet products.
[0007] Note that during these processes, the metal may be annealed
as required before the cold rolling (after the hot rolling) or in
the middle of the cold rolling. Further, the final cold rolled
strip is also generally annealed.
[0008] On the other hand, the exhaust pipe or exhaust manifold near
the engine is often exposed to a high temperature. If trying to use
a titanium material for the inside and outside pipes of a muffler
of an automobile with a high exhaust temperature, it would be
necessary to use thick pure titanium to reinforce the strength or
use an alloy excellent in high temperature strength such as
Ti-3Al-2.5V alloy.
[0009] However, using thick pure titanium has the problem of
detracting from the special feature of titanium of its light
weight, Further, an alloy having 3% or so of Al such as a
Ti-3Al-2.5V alloy is poor in cold workability. Therefore, there
were the problems that the cold rollability to thin-gauge sheet of
the material when producing pipe for an exhaust system part was
impaired or the cold formability such as pipe bending dropped.
[0010] To solve the above problems, Japanese Patent Publication (A)
No. 2001-234266 discloses an invention relating to a titanium alloy
for muffler use to which 0.5 to 2.3 mass % of Al has been added,
that is, a titanium alloy for an exhaust system part superior to
even pure titanium in heat resistance and oxidation resistance and
having a cold rollability equal to that of pure titanium.
DISCLOSURE OF THE INVENTION
[0011] However, the invention described in the above Japanese
Patent Publication (A) No. 2001-234266 does indeed have an
excellent cold rollability equal to that of the JIS Class 2 pure
titanium made much use of for mufflers, but as shown in Table 1 and
FIGS. 2 to 4 of that publication, compared with JIS Class 2 pure
titanium, the yield strength is high and the ductility is low, so
when the sheets or the pipes produced using the same are bent,
enlarged, reduced, enlarged in hole size (bored), or otherwise
secondarily worked, a further higher cold workability is
sought.
[0012] Further, in ships etc. as well, there is a strong need for
reducing the weight of the exhaust system parts. A titanium
material excellent in both workability and high temperature
strength has therefore been strongly sought.
[0013] The present invention was made taking note of the above
situation and has as its object the provision of heat resistant
titanium alloy sheet excellent in cold workability having high
temperature strength characteristics better than JIS Class 2 pure
titanium and having cold workability and high temperature oxidation
resistances equal to or better than those of JIS Class 2 pure
titanium and a method of production of the same.
[0014] To solve the above problems, the present invention has the
following means as its framework:
[0015] (1) A heat resistant titanium alloy sheet excellent in cold
workability characterized by comprising, by mass %, 0.3 to 1.8% of
Cu, 0.18% or less of oxygen, 0.30% or less of Fe, and the balance
of Ti and less than 0.3% of impurity elements.
[0016] (2) A heat resistant titanium alloy sheet excellent in cold
workability as set forth in the above (1), characterized in that
said titanium alloy sheet further contains at least one or more of
Sn, Zr, Mo, Nb, and Cr in a total of 0.3 mass % to 1.5 mass %.
[0017] (3) A method of production of heat resistant titanium alloy
sheet excellent in cold workability produced by the steps of
remelting, hot rolling, hot-rolled sheet or coil annealing, cold
rolling, intermediate annealing, final annealing, etc., said method
of production of a titanium alloy sheet characterized by adjusting
the ingredients at said remelting to the composition of ingredients
as set forth in the above (1) or (2) and performing said final
annealing at 650 to 830.degree. C. in temperature range.
[0018] (4) A method of production of heat resistant titanium alloy
sheet excellent in cold workability produced by the steps of
remelting, hot rolling, hot-rolled sheet or coil annealing, cold
rolling, intermediate annealing, final annealing, etc., said method
of production of a titanium alloy sheet characterized by adjusting
the ingredients at said remelting to the composition of ingredients
as set forth in the above (1) or (2), performing said hot-rolled
sheet or coil annealing or said intermediate annealing at 650 to
830.degree. C. in temperature range, and performing said final
annealing at 600 to 650.degree. C. in temperature range.
BEST MODE FOR WORKING THE INVENTION
[0019] The inventors carefully evaluated the effects of ingredient
elements in the high temperature strength, oxidation resistance,
and cold workability of titanium so as to solve the above problems
and as a result discovered that if adding a certain amount of Cu to
the titanium, it is possible, without impairing the cold
workability or oxidation resistance, to remarkably improve the high
temperature strength in the temperature range in which automobile
exhaust system members etc. are used, i.e., about 500 to about
700.degree. C. The present invention was completed based on this
epoch making discovery.
[0020] Now, in the invention described in claim 1 (hereinafter
referred to as "the present invention (1)"), the alloy is comprised
of, by mass %, 0.3 to 1.8% of Cu, 0.18% or less of oxygen, 0.30% or
less of Fe, and the balance of Ti and less than 0.3% of impurity
elements.
[0021] If adding Cu to titanium, it enters into solid solution in
the .alpha.-phase in as much as 1.5%. This solid solution Cu, like
Al, has the effect of increasing the high temperature strength by
solid solution strengthening. On the other hand, in Al-added
titanium and Cu-added titanium, a remarkable difference appears in
the cold workability.
[0022] That is, if cold working Al-added titanium, not only does
the slip deformation responsible for deformation become harder to
occur, but also the occurrence of twinning deformation, the main
reason for the high workability of titanium, is suppressed, the
yield strength becomes higher, and the ductility falls. As a
result, the cold workability falls.
[0023] However, with Cu-added titanium, while the slip deformation
is suppressed by the solution strengthening, the occurrence of
twinning deformation is not impaired at all. The result is like
pure titanium. As a result, a low yield strength and ductility on a
par with Type 2 pure titanium are maintained. Of course, this
effect is an effect expressed when the twinning deformation is the
main deformation mechanism. Like with Al, oxygen, which as an
effect of suppression of the occurrence of twinning, has to be
limited to the upper limit value for active twinning, that is,
0.18% or less.
[0024] Here, the amount of addition of Cu is given an upper limit
of 1.8% because if Cu is added over this, a Ti.sub.2Cu phase will
be formed in a large amount and the cold workability will be
impaired. Further, the amount of addition of Cu is given a lower
limit of 0.3% because to sufficiently bring out a high temperature
strength, the Cu has to be added in an amount of 0.3% or more.
[0025] Note that content of Fe has to be 0.30% or less. Fe is an
element stabilizing the .beta.-phase and causes the formation of
the .beta.-phase from room temperature to the high temperature
range. If the content of Fe is 0.30% or less, the amount of
formation of the .beta.-phase is slight, but if more than this is
added, the amount of the .beta.-phase increases, Cu, an element
which easily concentrates at the .beta.-phase, will concentrate
there heavily, and the amount of solid solution in the
.alpha.-phase required for improving the high temperature strength
will fall. Therefore, to suppress the formation of an excessive
.beta.-phase, Fe has to be made 0.30% or less.
[0026] However, nitrogen, carbon, Ni, Cr, Al, Sn, Si, hydrogen, and
other elements normally contained in a titanium material as
impurity elements and other elements may be contained without
problem if the total does not impair the workability, i.e., is less
than 0.3%.
[0027] Further, the high temperature oxidation resistance, an
important characteristic to be possessed by a heat resistant
material like high temperature strength, is not impaired at all
even if Cu is added.
[0028] In the alloy of the present invention (1), from the
viewpoint of the workability, the content of oxygen is preferably
0.10% or less. This is because, with this range of oxygen amount,
the occurrence of twinning is further promoted and the workability
is further improved. Oxygen has almost no effect on the high
temperature strength, so even if limiting the oxygen to 0.10% or
less, the high temperature characteristics are not impaired at
all.
[0029] This type of effect can be manifested further by limiting
the content of oxygen to 0.06% or less. That is, in the alloy of
the present invention (1), if the content of oxygen is 0.06% or
less, the effect of the present invention is exhibited the
strongest.
[0030] Next, the present invention described in claim 2
(hereinafter referred to as "the present invention (2)") will be
explained. In the present invention (2), there is provided the
alloy of the present invention (1) further containing at least one
or more of Sn, Zr, Mo, Nb, and Cr in a total of 0.3 mass % to 1.5
mass %.
[0031] This is to try to further improve the high temperature
strength of the alloy of the present invention (1) and to try to
further improve the high temperature oxidation resistances. Sn, Zr,
Mo, Nb, and Cr all enter the a-phase to a certain extent in solid
solution and overlap with the Cu to raise the high temperature
strength. Further, simultaneously, the high temperature oxidation
characteristics are also improved.
[0032] However, the amount of addition has to be, in total, 0.3% or
more. This is because if not the above amount of addition, an
improvement in the high temperature strength and an improvement in
the high temperature oxidation resistance cannot be obtained.
Further, the amount of addition has to be, in total, not more than
1.5%. This is because these elements have the effect of promoting
the precipitation of Ti.sub.2Cu. If added in a large amount, the
amount of production of Ti.sub.2Cu increases and therefore the
workability is impaired. However, if the total is 1.5% or less,
this effect is small.
[0033] The present invention described in claim 3 or 4 (hereinafter
referred to as "the present inventions (3) and (4)") relates to a
method of production of thin-gauge sheet used in large amounts in
exhaust systems of automobiles. That is, the present invention (3)
is a method of production of thin-gauge sheet having titanium alloy
ingredients of the present invention (1) or (2) produced by the
steps of remelting, hot rolling, and cold rolling, said method of
production of a titanium alloy sheet of the present invention (1)
or (2) characterized in that the final annealing is performed at
650 to 830.degree. C. in temperature range.
[0034] This condition aims at increasing the amount of solid
solution Cu as much as possible from the viewpoint of the
workability and the high temperature strength. Of course, even if
performing annealing or other heat treatment outside of this
temperature range, if the ingredients are those of the present
invention (1) or (2), the effects of the present invention are
sufficiently exhibited, but if performing the annealing in this
temperature range, the effect of the present invention can be
further enhanced.
[0035] That is, 650 to 830.degree. C. is a temperature range where
the amount of production of Ti.sub.2Cu is small and the amount of
solid solution Cu in the .alpha.-phase becomes larger. By annealing
in this temperature range, the high temperature strength can be
particularly raised.
[0036] Note that if Ti.sub.2Cu is produced during the cooling after
the annealing, it is pointed out that the targeted annealing effect
ends up being impaired, but Ti.sub.2Cu precipitates very slowly.
With the cooling rate of the extent of air cooling or furnace
cooling, not enough Ti.sub.2Cu is produced for the annealing effect
to be impaired.
[0037] Further, if once annealing at 650 to 830.degree. C. in
temperature range, even if later cold working the alloy and again
annealing it at less than 650.degree. C. in temperature, since
Ti.sub.2Cu precipitates slowly, within the actual heat treatment
time, almost no Ti.sub.2Cu will be produced and therefore the large
amount of Cu in solid solution in the .alpha.-phase can be
maintained.
[0038] That is, if performing the annealing before the final cold
rolling (hot-rolled sheet or coil annealing or intermediate
annealing) at 650 to 830.degree. C. in temperature range, even if
performing the final annealing after the cold rolling at less than
650.degree. C. in temperature, the large amount of Cu in solid
solution in the a-phase can be maintained. This method of
production is used by the present invention described in claim 4.
However, at less than 600.degree. C. in temperature, strain becomes
difficult to remove and softening becomes difficult, so sufficient
cold workability cannot be obtained, so this should be avoided.
EXAMPLES
Example 1
[0039] VAR (vacuum arc remelting) was used to remelt the titanium
material of each composition shown in Table 1. This was hot forged
to form a slab which was then heated to 860.degree. C., then hot
rolled by a hot continuous rolling mill to a strip of a thickness
of 3.5 mm.
[0040] This hot rolled strip was continuously annealed with air
cooling at 720.degree. C..times.2 minutes (hot-rolled coil
annealing), then the oxide scale was removed by shot blast and
pickling, then the strip was cold rolled to a strip of a thickness
of 1 mm. After this, the strip was vacuum annealed with furnace
cooling at 680.degree. C..times.4 hours (final annealing). A
tensile test piece was taken in parallel with the rolling direction
and was used for tensile tests at room temperature, 550.degree. C.,
625.degree. C., and 700.degree. C. The strength characteristics
were evaluated by the 0.2% proof stress or yield stress
(hereinafter referred to as "0.2% yield strength"), while the
workability was evaluated by the elongation value at room
temperature. Further, a 30 mm.times.30 mm square test piece was
heat treated at 700.degree. C..times.200 hours in the air and
measured for increase in weight due to oxidation. The results of
these evaluations are shown together in Table 1. TABLE-US-00001
TABLE 1 Room 700.degree. C., 200 h temperature Room 550.degree. C.
625.degree. C. 700.degree. C. oxidation 0.2% yield temperature 0.2%
yield 0.2% yield 0.2% yield weight Test Cu Al Fe O strength
elongation strength strength strength increase no. (mass %) (mass
%) (mass %) (mass %) (MPa) (%) (MPa) (MPa) (MPa) (mg/cm.sup.2)
Remarks 1 -- -- 0.05 0.18 275 39.5 60 21 8 3.02 Conv. mat. 2 -- 1.1
0.05 0.13 310 28.9 105 62 20 2.98 Conv. mat. 3 -- 2.1 0.05 0.08 403
25.2 126 81 37 2.94 Conv. mat. 4 0.2 -- 0.05 0.08 205 40.6 65 28 11
2.97 Comp. ex. 5 0.4 -- 0.05 0.08 203 41.8 101 80 31 3.01 Inv. (1),
(3) 6 0.8 -- 0.05 0.08 207 41.0 116 87 35 2.96 Inv. (1), (3) 7 1.6
-- 0.05 0.08 211 40.3 133 95 41 3.02 Inv. (1), (3) 8 2.0 -- 0.05
0.08 220 31.8 135 97 44 3.00 Comp. ex. 9 0.8 -- 0.15 0.08 202 40.5
118 89 36 3.03 Inv. (1), (3) 10 0.8 -- 0.26 0.08 225 40.1 116 88 40
2.99 Inv. (1), (3) 11 0.8 -- 0.33 0.08 232 37.2 103 75 18 3.05
Comp. ex. 12 1.1 -- 0.06 0.12 251 38.3 118 90 38 2.99 Inv. (1), (3)
13 1.1 -- 0.05 0.16 279 36.2 120 88 37 2.96 Inv. (1), (3) 14 1.1 --
0.05 0.20 301 30.5 120 87 37 2.98 Comp. ex. 15 1.5 -- 0.05 0.16 280
35.8 130 97 41 3.08 Inv. (1), (3) 16 1.0 -- 0.04 0.07 207 42.5 115
88 36 3.01 Inv. (1), (3) 17 1.0 -- 0.04 0.04 195 47.5 114 86 35
2.96 Inv. (1), (3) 18 1.0 -- 0.03 0.02 189 48.3 115 87 34 3.00 Inv.
(1), (3)
[0041] In Table 1, Test No. 1 is an example of JIS Class 2
commercially pure titanium, while Test Nos. 2 and 3 are examples of
alloys to which Al has been added in an extent of 1 to 2%. Test No.
1 has an elongation at room temperature of as much as 39.5% and a
sufficient cold workability, but the 0.2% yield strength at high
temperatures is poor being only 60 MPa at 550.degree. C., 21 MPa at
625.degree. C., and 8 MPa at 700.degree. C., i.e., the high
temperature strength is insufficient.
[0042] As opposed to this, Test Nos. 2 and 3 to which Al are added
have 0.2% yield strengths at 550.degree. C., 625.degree. C., and
700.degree. C. all far above that of the pure titanium of Test No.
1, i.e., high high-temperature strength is achieved, the elongation
at room temperature is 30% or less, and the cold workability is
insufficient.
[0043] In this way, if a small amount of Al is added, the high
temperature strength is improved, but the cold workability falls.
The market demand for a titanium alloy satisfying both requirements
is not been achieved by this.
[0044] As opposed to this, Test Nos. 5, 6, 7, 9, 10, 12, 13, 15,
16, 17, 18 representing examples of the present invention (1)
produced by the method described in the present invention (3) all
have high elongations at room temperature of at least 35% and have
0.2% yield strengths at 550.degree. C., 625.degree. C., and
700.degree. C. of at least 100 MPa, at least 80 MPa, and at least
30 MPa. Both an excellent cold workability and high
high-temperature strength are achieved, i.e, the effect of the
present invention is sufficiently exhibited.
[0045] In particular, in Test Nos. 5, 6, 7, 9, 10, 16, 17, and 18
where the content of oxygen is 0.10% or less, 40% or higher
elongations at room temperature are obtained, that is, the effects
of the present invention (1) are sufficiently exhibited. In
particular, in Test Nos. 17 and 18 where the content of oxygen is
0.06% or less, 45% or higher extremely high elongations at room
temperature are obtained. The effect of the present invention (1)
is most strongly exhibited. Note that the amount of increase in
weight due to oxidation during heat treatment in the air at
700.degree. C. for 200 hours was, in the examples of the present
invention, about the same level as that of the pure titanium of
Test No. 1 and the Al-added titanium alloys of Test Nos. 2 and
3.
[0046] However, in Test No. 4, while a high 40.6% room temperature
elongation was obtained, the 0.2% yield strengths at 550.degree.
C., 625.degree. C., and 700.degree. C. were 100 MPa, 80 MPa, and 30
MPa or less, that is, a sufficient improvement was not achieved in
the high temperature strength. Further, Test No. 11 also exhibited
at a high 37.2% room temperature elongation, but the 0.2% yield
strengths at 625.degree. C. and 700.degree. C. were 80 MPa and 30
MPa or less, i.e., the improvement in the high temperature strength
was not sufficient.
[0047] The reason is that, in Test No. 4, the amount of addition of
Cu is less than the lower limit value of 0.3% of the present
invention, so the amount of Cu in solid solution required for
improving the high temperature strength was insufficient. In Test
No. 11, the content of Fe, the .beta.-phase stabilization element,
is over the upper limit value of 0.30% of the present invention, so
the amount of the .beta.-phase increases, Cu concentrates there
heavily, and the amount in solid solution in the .alpha.-phase
required for improvement of the high temperature strength
falls.
[0048] Further, in Test Nos. 8 and 14, the high temperature
strengths were sufficiently high, but the room temperature
elongations were both not more than 35% or were considerably lower
values compared with JIS Class 2 pure titanium. This is because, in
Test No. 8, Cu is added over the upper limit value of 1.8% of the
present invention, so a large amount of the Ti.sub.2Cu phase is
produced and the cold ductility is impaired. In Test No. 14, the
content of oxygen is over the upper limit value of 0.18% of the
present invention, so the twinning deformation is suppressed and
the cold deformability drops.
[0049] In the above way, the titanium alloy sheet comprised of the
elements defined in the present invention is provided with
excellent cold workability and high temperature strength and,
further, has high temperature oxidation characteristics on a par
with pure titanium, but if deviating from the amounts of alloying
elements defined in the present invention, both the cold
workability and the high temperature strength cannot be
achieved.
Example 2
[0050] VAR (vacuum arc remelting) was used to remelt the titanium
material of each composition shown in Table 2. This was hot forged
to form a slab which was then heated to 860.degree. C., then hot
rolled by a hot continuous rolling mill to a strip of a thickness
of 3.5 mm.
[0051] This hot rolled strip was continuously annealed with air
cooling at 720.degree. C..times.2 minutes (hot-rolled coil
annealing), then the oxide scale was removed by shot blast and
pickling, then the strip was cold rolled to a strip of a thickness
of 1 mm. After this, the strip was vacuum annealed with furnace
cooling at 680.degree. C..times.4 hours (final annealing). A
tensile test piece was taken in parallel with the rolling direction
and was used for tensile tests at room temperature and 700.degree.
C.
[0052] The strength characteristics were evaluated by the 0.2%
yield strength, while the workability was evaluated by the
elongation value at room temperature. Further, a 30 mm.times.30 mm
square test piece was heat treated at 700.degree. C..times.200
hours in the air and measured for increase in weight due to
oxidation. The results of these evaluations are shown together in
Table 2. TABLE-US-00002 TABLE 2 Room 700.degree. C. 700.degree. C.,
200 h temperature Room 0.2% oxidation Cu Sn Zr Mo Nb Cr Fe O 0.2%
yield temperature yield weight Test (mass (mass (mass (mass (mass
(mass (mass (mass strength elongation strength increase no. %) %)
%) %) %) %) %) %) (MPa) (%) (MPa) (mg/cm.sup.2) Remarks 19 0.8 1.3
-- -- -- -- 0.05 0.08 303 38.0 42 2.84 Inv. (2), (3) 20 0.8 1.7 --
-- -- -- 0.05 0.08 310 37.0 45 2.82 Comp. ex. 21 0.8 -- 1.3 -- --
-- 0.05 0.08 302 39.2 48 2.85 Inv. (2), (3) 22 0.8 -- 1.8 -- -- --
0.05 0.08 318 33.0 45 2.79 Comp. ex. 23 0.8 -- -- 1.4 -- -- 0.05
0.08 301 39.3 48 2.84 Inv. (2), (3) 24 0.8 -- -- 1.7 -- -- 0.05
0.08 318 32.8 48 2.80 Comp. ex. 25 0.8 -- -- -- 1.4 -- 0.05 0.08
299 38.7 46 2.81 Inv. (2), (3) 26 0.8 -- -- -- 1.8 -- 0.05 0.08 321
31.5 45 2.74 Comp. ex. 27 0.8 -- -- -- -- 1.2 0.05 0.08 298 36.8 49
2.86 Inv. (2), (3) 28 0.8 -- -- -- -- 1.6 0.05 0.08 320 31.2 50
2.86 Comp. ex. 29 0.8 0.5 0.7 -- -- -- 0.05 0.08 299 38.8 44 2.79
Inv. (2), (3) 30 0.8 0.5 -- 0.7 -- -- 0.05 0.08 297 37.7 46 2.79
Inv. (2), (3) 31 0.8 0.5 -- -- 0.6 -- 0.05 0.08 295 36.6 44 2.74
Inv. (2), (3) 32 0.8 0.5 -- -- -- 0.5 0.05 0.08 290 37.9 45 2.81
Inv. (2), (3) 33 0.8 -- 0.5 0.5 0.3 -- 0.05 0.08 302 36.0 44 2.77
Inv. (2), (3) 34 0.8 -- -- 0.5 0.3 0.5 0.05 0.08 305 37.5 47 2.77
Inv. (2), (3) 35 0.8 -- -- 0.2 1.0 -- 0.05 0.08 310 37.7 42 2.74
Inv. (2), (3) 36 0.8 0.5 -- 0.8 -- 0.5 0.05 0.08 325 29.8 50 2.76
Comp. ex. 37 0.8 0.8 -- -- -- 0.8 0.05 0.08 327 30.5 49 2.80 Comp.
ex. 38 1.1 -- -- -- -- 0.8 0.06 0.12 293 38.2 43 2.87 Inv. (2), (3)
39 1.1 -- -- -- 0.5 -- 0.06 0.12 272 37.8 45 2.84 Inv. (2), (3) 40
1.1 -- -- 1.0 -- -- 0.06 0.12 290 39.3 47 2.81 Inv. (2), (3) 41 1.1
-- 0.9 -- -- -- 0.06 0.12 292 40.1 44 2.80 Inv. (2), (3) 42 1.1 0.9
-- -- -- -- 0.06 0.12 288 37.5 46 2.79 Inv. (2), (3) 43 1.0 -- --
-- -- 0.33 0.04 0.07 285 37.9 44 2.89 Inv. (2), (3) 44 1.0 -- -- --
0.4 -- 0.04 0.07 271 37.5 46 2.88 Inv. (2), (3) 45 1.0 -- -- 0.4 --
-- 0.04 0.07 288 39.5 48 2.87 Inv. (2), (3) 46 1.0 -- 0.4 -- -- --
0.04 0.07 295 40.2 45 2.87 Inv. (2), (3) 47 1.0 0.5 -- -- -- --
0.04 0.07 289 37.3 47 2.89 Inv. (2), (3) 48 1.0 -- -- -- -- 0.2
0.04 0.07 283 37.7 37 2.95 Inv. (1), (3) 49 1.0 -- -- -- 0.2 --
0.04 0.07 270 38.0 38 2.96 Inv. (1), (3) 50 1.0 -- -- 0.2 -- --
0.04 0.07 286 39.3 38 2.94 Inv. (1), (3) 51 1.0 -- 0.2 -- -- --
0.04 0.07 292 41.0 39 2.95 Inv. (1), (3) 52 1.0 0.2 -- -- -- --
0.04 0.07 285 38.1 39 2.94 Inv. (1), (3)
[0053] In Table 2, Test Nos. 19, 21, 23, 25, 27, 29, 30, 31, 32,
33, 34, and 35 representing examples of the present invention
produced by the method described in the present invention (3) all
had high elongations at room temperature of over 35%. Further,
compared with Test No. 6 comprised of the same amounts of Cu, Fe,
and oxygen, the 0.2% yield strengths at 700.degree. C. became at
least 7 MPa higher. The effect of addition of Sn, Zr, Mo, Nb, and
Cr alone or combined was therefore exhibited.
[0054] Further, the increases in weight due to oxidation during
heat treatment in the air at 700.degree. C. for 200 hours were also
smaller than that of Test No. 6--less than 2.90 mg/cm2 in each
case, i.e., an improvement in high temperature oxidation resistance
was also achieved. This was due to the effect of addition of Sn,
Zr, Mo, Nb, or Cr alone or in combination.
[0055] Test Nos. 20, 22, 24, 26, 28, 36, 37 exhibited 0.2% yield
strengths at 700.degree. C. higher than Test No. 6 and increases in
weight due to oxidation during heat treatment in the air at
700.degree. C. for 200 hours smaller than Test No. 6. The high
temperature strengths and the high temperature oxidation
characteristics were improved, but the room temperature elongations
were less than 35% in each case, i.e., the workabilities ended up
being impaired.
[0056] This is because the total of the amounts of addition of the
one or more of Sn, Zr, Mo, Nb, and Cr was over the upper limit
value of 1.5% of the present invention, so the precipitation of
Ti.sub.2Cu was promoted and the workability was impaired.
[0057] Test Nos. 38 to 42 are examples of the present invention (2)
comprised of the alloy of Test No. 12 to which Sn, Zr, Mo, Nb, and
Cr are further added. Since the amounts of addition were suitable,
high room temperature elongations of 35% or more, 0.2% yield
strengths at 700.degree. C. of over that of Test No. 12, and high
temperature oxidation characteristics during heat treatment in the
air at 700.degree. C. for 200 hours were achieved.
[0058] Test Nos. 43 to 52 are examples of the alloy of Test No. 16
to which Sn, Zr, Mo, Nb, and Cr are added. Test Nos. 43 to 47 to
which suitable amounts were added as prescribed in the present
invention (2) achieved high room temperature elongations of 35% or
more, high temperature strengths (0.2% yield strengths at
700.degree. C.) higher than Test No. 16 by more than 5 MPa, and
high high-temperature oxidation characteristics (high temperature
oxidation characteristics during heat treatment in the air at
700.degree. C. for 200 hours) were achieved. On the other hand,
Test Nos. 48, 49, 50, 51, and 52 in which the amounts of addition
of Sn, Zr, Mo, Nb, and Cr were less than the 0.3% prescribed by the
present invention (2) had margins of improvement of the high
temperature strength of at most 3 MPa, and the margin of
improvement of the high temperature oxidation characteristics was
little.
Example 3
[0059] Sheets were taken from the intermediate products when
producing the materials of Test No. 6 of Table 1 and Test Nos. 29,
34 and 44 of Table 2, that is, hot rolled strips of 3.5 mm
thickness. These were hot-rolled sheet annealed under the
conditions shown in Tables 3 to 6, the oxide scales were removed by
shot blast and pickling, then these were cold rolled to 1 mm thick
strips. After this, each strip was cold-rolled sheet annealed under
the conditions described in Tables 3 to 6 (final annealing). A
tensile test piece was taken in parallel to the rolling direction
and was used for tensile tests at room temperature and 700.degree.
C.
[0060] The strength characteristics were evaluated by the 0.2%
yield strength, while the workability was evaluated by the
elongation value at room temperature. Further, a 30 mm.times.30 mm
square test piece was heat treated at 700.degree. C..times.200
hours in the air and measured for increase in weight due to
oxidation. The results of these evaluations are shown together in
Tables 3 to 6. TABLE-US-00003 TABLE 3 Hot-rolled Room temperature
Room 700.degree. C. 700.degree. C., 200 h sheet 0.2% yield
temperature 0.2% yield oxidation Test annealing Cold-rolled sheet
strength elongation strength weight increase no. conditions
annealing conditions (MPa) (%) (MPa) (mg/cm.sup.2) Remarks 53
720.degree. C., 2 min, 580.degree. C., 6 h, furnace cooling 218
40.0 31 2.98 Inv. (1) air cooling 54 720.degree. C., 2 min,
630.degree. C., 4 h, furnace cooling 209 40.3 35 2.98 Inv. (1), (4)
air cooling 55 720.degree. C., 2 min, 680.degree. C., 4 h, furnace
cooling 207 41.0 35 2.96 Inv. (1), (3) air cooling 56 720.degree.
C., 2 min, 780.degree. C., 30 min, furnace cooling 205 42.0 34 2.98
Inv. (1), (3) air cooling 57 720.degree. C., 2 min, 810.degree. C.,
5 min, air cooling 200 42.3 34 2.95 Inv. (1), (3) air cooling 58
720.degree. C., 2 min, 850.degree. C., 3 min, air cooling 198 42.5
31 2.96 Inv. (1) air cooling 59 630.degree. C., 10 min, 630.degree.
C., 4 h, furnace cooling 207 40.8 32 2.99 Inv. (1) air cooling 60
630.degree. C., 10 min, 680.degree. C., 4 h, furnace cooling 209
40.5 35 2.95 Inv. (1), (3) air cooling 61 630.degree. C., 10 min,
780.degree. C., 30 min, furnace cooling 207 41.0 36 3.00 Inv. (1),
(3) air cooling 62 630.degree. C., 10 min, 810.degree. C., 5 min,
air cooling 201 41.0 34 2.99 Inv. (1), (3) air cooling 63
630.degree. C., 10 min, 850.degree. C., 3 min, air cooling 197 42.8
31 3.01 Inv. (1) air cooling 64 850.degree. C., 2 min, 630.degree.
C., 4 h, furnace cooling 207 42.2 31 2.95 Inv. (1) air cooling 65
850.degree. C., 2 min, 680.degree. C., 4 h, furnace cooling 208
40.5 36 2.93 Inv. (1), (3) air cooling 66 850.degree. C., 2 min,
780.degree. C., 30 min, furnace cooling 208 41.2 36 2.98 Inv. (1),
(3) air cooling 67 850.degree. C., 2 min, 810.degree. C., 5 min,
air cooling 201 42.3 35 2.98 Inv. (1), (3) air cooling 68
850.degree. C., 2 min, 850.degree. C., 3 min, air cooling 190 43.3
32 3.00 Inv. (1) air cooling
[0061] TABLE-US-00004 TABLE 4 Hot-rolled Room temperature Room
700.degree. 700.degree. C., 200 h sheet 0.2% yield temperature 0.2%
yield oxidation Test annealing Cold-rolled sheet strength
elongation strength weight increase no. conditions annealing
conditions (MPa) (%) (MPa) (mg/cm.sup.2) Remarks 69 720.degree. C.,
2 min, 630.degree. C., 4 h, furnace cooling 302 37.7 46 2.82 Inv.
(2), (4) air-cooling 70 720.degree. C., 2 min, 680.degree. C., 4 h,
furnace cooling 299 38.8 44 2.80 Inv. (2), (3) air-cooling 71
720.degree. C., 2 min, 780.degree. C., 30 min, furnace cooling 290
38.7 47 2.82 Inv. (2), (3) air-cooling 72 720.degree. C., 2 min,
810.degree. C., 5 min, air-cooling 285 39.5 46 2.80 Inv. (2), (3)
air-cooling 73 720.degree. C., 2 min, 850.degree. C., 3 min,
air-cooling 281 39.6 40 2.79 Inv. (2) air-cooling
[0062] TABLE-US-00005 TABLE 5 700.degree. C., 200 h Room
temperature Room 700.degree. C. oxidation Cold-rolled 0.2% yield
temperature 0.2% yield weight Test Hot-rolled sheet sheet annealing
strength elongation strength increase no. annealing conditions
conditions (MPa) (%) (MPa) (mg/cm.sup.2) Remarks 74 630.degree. C.,
10 min, air-cooling 630.degree. C., 4 h, 311 36.5 40 2.84 Inv. (2)
furnace cooling 75 680.degree. C., 5 min, air-cooling 630.degree.
C., 4 h, 308 37.4 46 2.81 Inv. (2), (4) furnace cooling 76
720.degree. C., 2 min, air-cooling 630.degree. C., 4 h, 305 37.5 47
2.78 Inv. (2), (4) furnace cooling 77 810.degree. C., 2 min,
air-cooling 630.degree. C., 4 h, 298 38.1 46 2.79 Inv. (2), (4)
furnace cooling 78 850.degree. C., 2 min, air-cooling 630.degree.
C., 4 h, 290 38.3 41 2.81 Inv. (2) furnace cooling
[0063] Table 3 shows the results of tests on materials of the same
composition as in Test No. 6. Regardless of the conditions of the
hot-rolled sheet annealing, Test Nos. 55, 56, 57, 60, 61, 62, 65,
66, and 67 involving final annealing, that is, cold-rolled sheet
annealing, at 650 to 830.degree. C. in temperature range all gave
high room temperature elongations of over 40% and high 0.2% yield
strengths at 700.degree. C. of over 34 MPa. The oxidation
resistances were also on the level of pure titanium.
[0064] In this way, by applying the method described in the present
invention 3, it is possible to produce products featuring all of
room temperature workability, high temperature strength, and high
temperature oxidation resistances.
[0065] Further, Test No. 54 had a temperature of the final
annealing, that is, the cold-rolled sheet annealing, of 630.degree.
C. This was outside the range of conditions prescribed in the
present invention (3), but a high room temperature elongation of
over 40%, a high 0.2% yield strength at 700.degree. C. of over 34
MPa, and oxidation resistances on a par with pure titanium were
exhibited. This was because the annealing before the cold rolling,
that is, the hot-rolled sheet annealing, was conducted at 650 to
830.degree. C. in temperature range, so the effects of the present
invention (4) were exhibited.
[0066] Note that Test Nos. 53, 58, 59, 63, 64, 68 all gave high
room temperature elongations of over 40% and high 0.2% yield
strengths a 700.degree. C. of over 30 MPa, but compared with the
invention examples, the high temperature strengths became somewhat
lower. The reason is as follows:
[0067] Test No. 53 involved the annealing before cold rolling, that
is, the hot-rolled sheet annealing, performed at the 650 to
830.degree. C. temperature range prescribed in the present
invention (4), but the final annealing, that is, the cold-rolled
sheet annealing, was conducted at less than the 600.degree. C.
prescribed in the present invention (4), so the margin of
improvement of the high temperature strength ended up becoming
somewhat small. Test No. 58 had a final annealing, that is, a
cold-rolled sheet annealing, outside of the temperature range
prescribed by the present invention (3) or (4), so the margin of
improvement of the high temperature strength ended up becoming
somewhat smaller.
[0068] Test Nos. 59, 63, 64, and 68 had annealing before the cold
rolling, that is, the hot-rolled sheet annealing, performed outside
the 650 to 830.degree. C. temperature range prescribed in the
present invention (4) and had final annealing, that is, cold-rolled
sheet annealing, outside the temperature range prescribed in the
present invention (3), so the margin of improvement of the high
temperature strength became somewhat small.
[0069] Now, Table 4 shows the results of tests on materials of the
same composition as Test No. 29. The cold-rolled and annealed
sheets produced by the method of present invention (3) or (4) (Test
Nos. 69 to 72) all gave high room temperature elongations of over
35%, high 0.2% yield strengths at 700.degree. C. of over 44 MPa,
and excellent high temperature oxidation resistance.
[0070] However, Test No. 73 which involved final annealing, that
is, the cold-rolled sheet annealing, performed outside of the
temperature range prescribed in the present invention (3) or (4)
had a 0.2% yield strength at 700.degree. C. somewhat lower compared
with the examples of Test Nos. 69 to 72.
[0071] Further, Table 5 shows the results of tests on materials of
the same composition as Test No. 34. The cold-rolled and annealed
sheets of Test Nos. 75 to 77 produced by the method described in
the present invention (4) all gave high room temperature
elongations of over 35%, high 0.2% yield strengths at 700.degree.
C. of over 46 MPa, and excellent high temperature oxidation
resistances.
[0072] However, in Test Nos. 74 and 78 involving annealing before
the cold-rolling, that is the hot-rolled sheet annealing, performed
outside of the 650 to 830.degree. C. temperature range prescribed
in the present invention (4) and involving final annealing, that
is, cold-rolled sheet annealing, performed outside of the
temperature range prescribed in the present invention (3), the 0.2%
yield strengths at 700.degree. C. became somewhat lower compared
with the examples of Test Nos. 75 to 77.
[0073] Further, Table 6 shows the results of tests on materials of
the same composition as Test No. 44. Test No. 80 produced by the
method described in the present invention (3) and Test No. 81
produced by the method described in the present invention (4) both
gave high room temperature elongations equal to Test No. 44, high
0.2% yield strengths at 700.degree. C., and excellent high
temperature oxidation resistances. TABLE-US-00006 TABLE 6 Room
700.degree. C., 200 h Hot-rolled temperature Room 700.degree. C.
oxidation sheet 0.2% yield temperature 0.2% yield weight Test
annealing Cold-rolled sheet strength elongation strength increase
no. conditions annealing conditions (MPa) (%) (MPa) (mg/cm.sup.2)
Remarks 80 810.degree. C., 2 min, 700.degree. C., 4 h, furnace 268
39.2 45 2.85 Inv. (2), (3) air-cooling cooling 81 810.degree. C., 2
min, 640.degree. C., 4 h, furnace 275 37.0 48 2.88 Inv. (2), (4)
air-cooling cooling
INDUSTRIAL APPLICABILITY
[0074] The titanium alloy sheet of the present invention can be
particularly utilized for parts of an exhaust system of two-wheeled
and four-wheeled automobiles, that is, the exhaust manifold,
exhaust pipe, muffler, and other parts used for the discharge route
of burned exhaust gas.
* * * * *