U.S. patent application number 14/403437 was filed with the patent office on 2015-06-04 for titanium thin sheet.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is NIPPON STEEL & SUMITOMO METAL CORPORATION. Invention is credited to Takashi Maeda, Yoshihisa Shirai, Hidenori Takebe.
Application Number | 20150152538 14/403437 |
Document ID | / |
Family ID | 50685605 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150152538 |
Kind Code |
A1 |
Takebe; Hidenori ; et
al. |
June 4, 2015 |
TITANIUM THIN SHEET
Abstract
A titanium thin sheet of 0.2 mm or less in thickness,
containing: Fe of 0.1 mass % or less and O (oxygen) of 0.1 mass %
or less in a bulk, wherein a sheet thickness (mm)/a grain size (mm)
.gtoreq.3, and the grain size .gtoreq.2.5 .mu.m are satisfied, and
a hardened layer is included at a surface, and a region of the
hardened layer is a depth of 200 nm or more and 2 .mu.m or less
from the surface. The titanium thin sheet is supplied with
excellent workability and high surface hardness, and is able to be
suitably used for various purposes such as, for example, acoustic
components (a speaker vibration plate and so on).
Inventors: |
Takebe; Hidenori; (Tokyo,
JP) ; Shirai; Yoshihisa; (Tokyo, JP) ; Maeda;
Takashi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMITOMO METAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
|
Family ID: |
50685605 |
Appl. No.: |
14/403437 |
Filed: |
August 13, 2013 |
PCT Filed: |
August 13, 2013 |
PCT NO: |
PCT/JP2013/071869 |
371 Date: |
November 24, 2014 |
Current U.S.
Class: |
148/421 ;
428/687 |
Current CPC
Class: |
C22C 14/00 20130101;
Y10T 428/12993 20150115; C22F 1/183 20130101 |
International
Class: |
C22F 1/18 20060101
C22F001/18; C22C 14/00 20060101 C22C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2012 |
JP |
2012-179861 |
Claims
1. A titanium thin sheet of 0.2 mm or less in thickness,
containing: Fe of 0.1 mass % or less and O (oxygen) of 0.1 mass %
or less in a bulk, wherein a sheet thickness (mm)/a grain size (mm)
.gtoreq.3, and the grain size .gtoreq.2.5 .mu.m are satisfied, and
a hardened layer is included at a surface, and a region of the
hardened layer is a depth of 200 nm or more and 2 .mu.m or less
from the surface.
2. The titanium shin sheet according to claim 1, wherein after a
cold-rolling, a finish annealing is performed at 500.degree. C. or
more and 850.degree. C. or less by a BAF or a continuous annealing.
Description
TECHNICAL FIELD
[0001] The present invention relates to a titanium thin sheet, in
more detail, to a high-strength titanium thin sheet having
excellent workability and high surface hardness, and excellent in
workability capable of suitably being used for a speaker vibration
plate and so on. This application is based upon and claims the
benefit of priority of the prior Japanese Patent Application No.
2012-179861, filed on Aug. 14, 2012, the entire contents of which
are incorporated herein by reference.
BACKGROUND ART
[0002] A titanium material has high specific strength and excellent
corrosion resistance, and is used for various purposes as
industrial raw materials for a chemical plant, for architecture,
and for many others, or as materials of consumer products such as
camera bodies, clocks, sports equipments. A thin sheet such as a
foil of 0.2 mm or less in thickness is used for purposes making use
of characteristics thereof such as acoustic components (a speaker
vibration plate and so on), an anticorrosive film, sheet.
[0003] In general, there is a tendency in which high-strength is
required for metal materials, and in addition, workability is also
required. The titanium material is no exception, and it is often
the case in which the high-strength is also required in addition to
the excellent workability. However, in general, the workability is
lowered when it is highly strengthened, and therefore, in the
titanium material, an attempt to optimize a balance between
strength and workability has been done by controlling an oxygen
amount, an iron amount, a crystal grain size, and so on.
[0004] For example, in Patent Document 1, a titanium sheet in which
strength is improved while suppressing lowering of ductility of the
titanium sheet by increasing an Fe content (Fe: 0.1 mass % to 0.6
mass %) while setting an O (oxygen) content in the titanium
material at a predetermined value, and formability is improved by
setting an average grain size to be 10 .mu.m or less is
disclosed.
[0005] In Patent Document 2, a Ti sheet material having fine
forming workability whose nitrogen amount and hydrogen amount are
limited in addition to an iron amount and an oxygen amount such
that the Fe content is 300 ppm or more and a [Fe+O+N+H] amount is
1500 ppm or less is disclosed.
[0006] Besides, in Patent Document 3, a manufacturing method of a
pure titanium sheet in which an iron amount, an oxygen amount,
further nickel and chromium amounts are specified into a
predetermined range and an average grain size is set to be 20 .mu.m
to 80 .mu.m to keep fine formability even when a cheap raw material
whose purity is low is used is disclosed.
[0007] However, all of the arts described in these Patent Documents
are arts whose target is a general titanium material whose of 0.3
mm to 1 mm in thickness.
[0008] On the other hand, a thin sheet and a foil of 0.2 mm or less
in thickness used for the speaker vibration plate and so on is
thinner than a material for general purposes, and it is inferior in
workability. Accordingly, there is a problem in which working
failure occurs even if the arts described in the above-stated
Patent Documents 1 to 3 are applied.
[0009] As for the workability of the titanium thin sheet of 0.2 mm
or less in thickness, a manufacturing method of a titanium foil
excellent in formability is disclosed in Patent Document 4.
According to this art, a titanium foil of 25 .mu.m in thickness is
rolled under a predetermined rolling condition, and a crystal grain
size is controlled to be ASTM No. 12 to 14, and thereby, the fine
Erichsen value is secured.
[0010] However, in the titanium foil of 0.2 mm in thickness or
less, fine shape retentivity after the forming work is required. In
general, strength of a material is improved, and thereby, the fine
shape retentivity is secured, but at the same time, there is a
problem in which fine workability cannot be obtained. Besides, a
part where a large work is performed improves in strength by work
hardening and the fine shape retentivity can be obtained, but a
part where working ratio is low is inferior in the shape
retentinity.
[0011] For example, in Patent Document 5, an art in which a layer
containing a carbide and/or nitride of titanium is formed as an
inner surface layer by a bright annealing or a vacuum annealing,
and thereafter, an electrolytic acid pickling is performed is
disclosed. This art is one in which a contact between a soft
titanium base material and a die is suppressed, to thereby prevent
an adhesion of the titanium base material to the die, and at the
same time, to form an oxide layer excellent in lubricity at a press
time at a surface of titanium. According to this art, it is
possible to avoid that the carbide and/or nitride of titanium is in
contact with the die, and wear of the die is prevented.
[0012] However, it is a rare case in which a severe work as
disclosed in the Patent Document 5 is performed for the titanium
foil of 0.2 mm or less in thickness. For example, in the work of
the speaker vibration plate and so on, it is often the case in
which an internal pressure is applied to form into a dome state,
and a possibility of the contact with the die during the work is
small compared to a general forming by a thin-sheet press, and a
surface lubricity of the material in itself is not such a problem.
Accordingly, an workability improvement effect owing to a
lubricating effect of the oxide is not exhibited even if the art
described in the Patent Document 5 is applied. Further, in the art,
the electrolytic acid pickling is performed, and therefore,
lowering of yield when the art is applied for the titanium foil
material of 0.2 mm or less in thickness cannot be overlooked. In
addition, there is a case when shipment as a product becomes
impossible caused by unevenness of the sheet thickness.
PRIOR ART DOCUMENT
Patent Document
[0013] Patent Document 1: Japanese Patent Publication No.
4605514
[0014] Patent Document 2: Japanese Laid-open Patent Publication No.
S63-103043
[0015] Patent Document 3: Japanese Patent Publication No.
3228134
[0016] Patent Document 4: Japanese Patent Publication No.
2616181
[0017] Patent Document 5: Japanese Laid-open Patent Publication No.
2009-97060
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0018] The present invention is made in consideration of
circumstances as stated above, and an object thereof is to provide
a titanium thin sheet of 0.2 mm or less in thickness, and excellent
in shape retentivity and workability.
Means for Solving the Problems
[0019] To solve the above-stated problems, the present inventors
focus attention on surface hardness of the titanium foil, and think
that it is possible to enable both the shape retentivity and the
workability if the surface is hard and an inner side is soft
compared to the surface, and study about a method to improve the
workability and the surface hardness of the titanium thin
sheet.
[0020] As an effective method to improve the workability of the
titanium thin sheet, at first, it is conceivable to reduce elements
such as iron and oxygen. These elements are elements inevitably
introduced at manufacturing time, but as described in the Patent
Documents 1 to 3, it is necessary to limit to a predetermined
amount or less.
[0021] Next, it is conceivable to make crystal grains coarse. It is
possible to make a twinning deformation which is important for the
workability of the titanium material easily occur by making the
grain coarse, and the workability is improved. A crystal grain size
is controlled at a finish annealing process at the last, and
therefore, it is easily controlled by changing annealing
conditions.
[0022] A tensile test is performed by using a titanium thin sheet
with a sheet thickness of 0.2 mm or less to investigate elongation.
As a result, the elongation is lowered by refining the crystal
grain as same as a general knowledge also in the sheet thickness of
0.2 mm or less. However, it turns out that there is a case when the
elongation is lowered if the crystal grain becomes too coarse in
the titanium thin sheet of 0.2 mm or less in thickness. Besides,
whether or not this phenomenon occurs is determined by a ratio
between the sheet thickness and the grain size, and it turns out
that this phenomenon occurs when the sheet thickness/the grain size
<3. Note that in case of the thin sheet of approximately 0.3 mm
to 1 mm in thickness, the phenomenon in which the elongation is
lowered by the coarseness of the crystal grain does not occur
because the grain size is approximately within a range of 10 .mu.m
to 60 .mu.m.
[0023] From this investigation result, the crystal grain is made
coarse within a range in which the sheet thickness/the grain size
.gtoreq.3 in accordance with the product sheet thickness, and
thereby, it becomes possible to exploit the workability of the
titanium thin sheet of 0.2 mm or less in thickness to the
maximum.
[0024] In a process further advancing the investigation, there is a
case when cracks frequently occur at a press working time, and a
cause thereof is investigated, then it turns out that a carbon
amount and a nitrogen amount in a vicinity of a material surface
are high at a part where the cracks occur. Normally, when the thin
sheet of 0.2 mm or less in thickness is manufactured, a bright
annealing (BA) to give formability and workability by softening is
performed after a cold-rolling. However, when removal of rolling
oil at a cleaning line before the annealing is insufficient, a lot
of rolling oil remains at the material surface, and an entering
amount of carbon in the vicinity of the material surface becomes
large. Nitrogen is nitrogen gas remained at a gas exchange time of
an annealing furnace, and when the exchange is insufficient, a lot
of nitrogen remains, and an entering amount of nitrogen becomes
large.
[0025] The entered carbon, nitrogen form TiC, TiN, incur
solid-solution strengthening, and therefore, the surface hardness
becomes high, and the shape retentivity becomes good also in an
ultrathin shape titanium thin sheet of 0.2 mm or less in thickness.
However, when they enter too deep, the elongation of the material
is remarkably lowered. It is necessary to set entering depths of
carbon, nitrogen, oxygen to be within a range of 200 nm to 2 .mu.m
from a surface to enable the above-stated both characteristics
(namely, the improvement in the surface hardness and the
suppression of the elongation lowering). Namely, it is necessary
that a region of a hardened layer formed by the entering of carbon,
nitrogen, oxygen is to be within the range of 200 nm to 2 .mu.m
from the surface.
[0026] The present invention is made based on the studied
information, and a content thereof is a high-strength titanium thin
sheet excellent in workability described below.
[0027] Namely, it is a titanium thin sheet of 0.2 mm or less in
thickness, which contains Fe of 0.1 mass % or less and O (oxygen)
of 0.1 mass % or less in a bulk, satisfies a sheet thickness (mm)/a
grain size (mm) .gtoreq.3, and a grain size .gtoreq.2.5 .mu.m,
includes a hardened layer at a surface, and a region of the
hardened layer is at a depth of 200 nm or more and 2 .mu.m or less
from the surface.
[0028] After a cold-rolling, it is desirable if a finish annealing
(bright annealing) is performed for the titanium thin sheet of the
present invention at 500.degree. C. or more and 850.degree. C. or
less by a BAF (batch heat treatment) or a continuous annealing
because stable workability is thereby secured.
[0029] The "titanium thin sheet" described here means industrial
pure titanium defined by JISH4600, and a thin sheet or a foil of
0.2 mm or less in thickness.
[0030] The "grain size" means an average grain size found by a
quadrature defined by JISH0501. There is a case when it is
described as an "average grain size" with an emphasis on the
above.
[0031] Besides, the "hardened layer" is a concentrated layer of
oxygen, nitrogen, carbon formed at an annealing time by carbon,
nitrogen and oxygen comes from rolling oil remaining at a surface,
and nitrogen and oxygen gas contained in a gas atmosphere of an
annealing furnace.
Effect of the Invention
[0032] A titanium thin sheet of the present invention is a titanium
thin sheet of 0.2 mm or less in thickness, where excellent
workability and high surface hardness are given, and is a titanium
thin sheet (foil) capable of suitably being used for various
purposes such as, for example, acoustic components (speaker
vibration plate, and so on).
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a view exemplifying a relationship between a
crystal grain size and elongation in a tensile test of a titanium
thin sheet.
[0034] FIG. 2 is a view exemplifying a relationship between a
stress and a strain in the tensile test of a titanium thin sheet
(foil) with a thickness of 25 .mu.m.
[0035] FIG. 3 is a view exemplifying a relationship between a sheet
thickness/a grain size and elongation in the tensile test of the
titanium thin sheet.
[0036] FIG. 4 is a view illustrating a relationship between a
hardened layer thickness and a surface hardness at the titanium
thin sheet.
[0037] FIG. 5 is a view exemplifying a relationship between a
hardened layer thickness and elongation at the titanium thin sheet
of 100 .mu.m in thickness, and a sheet thickness/a grain size
.gtoreq.3.
MODE FOR CARRYING OUT THE INVENTION
[0038] A titanium thin sheet of the present invention is a titanium
thin sheet of 0.2 mm or less in thickness, which contains Fe of 0.1
mass % or less and O (oxygen) of 0.1 mass % or less in a bulk,
satisfies a sheet thickness (mm)/a grain size (mm) .gtoreq.3, and a
grain size .gtoreq.2.5 .mu.m, includes a hardened layer at a
surface, and a region of the hardened layer is at a depth of 200 nm
or more and 2 .mu.m or less from the surface.
[0039] In the present invention, a reason why the titanium thin
sheet of 0.2 mm or less in thickness is intended for is to provide
a high-strength titanium thin sheet excellent in workability
capable of suitably being used also for, for example, the speaker
vibration plate and so on.
[0040] In the titanium thin sheet of the present invention, a
reason why the bulk Fe is defined to be 0.1 mass % or less is as
described below. Namely, Fe is an element stabilizing .beta.-phase,
and when the .beta.-phase exists, a growth of a crystal grain is
disturbed by the .beta.-phase during an annealing. When a content
exceeds 0.1 mass %, a function thereof becomes remarkable, and
therefore, the content of Fe is set to be 0.1 mass % or less. A
lower limit is not particularly limited, but mixture of Fe is
inevitable when it is industrially manufactured, and 0.01 mass % or
more is contained, and therefore, a desirable lower limit is set to
be 0.01 mass %.
[0041] Besides, a reason why the bulk O (oxygen) is defined to be
0.1 mass % or less is to suppress lowering of workability. O is
added, and thereby, the titanium thin sheet is highly strengthened,
but the workability is lowered, and when a content exceeds 0.1 mass
%, a tendency thereof becomes remarkable, and therefore, the
content of O is set to be 0.1 mass % or less. A lower limit is not
particularly limited, but mixture of O is inevitable when it is
industrially manufactured as same as Fe, and therefore, a desirable
lower limit is set to be 0.01 mass %.
[0042] Note that the bulk means an inside of the titanium thin
sheet except the hardened layer formed at a surface of the titanium
thin sheet. In the present invention, an Fe concentration is 0.1
mass or less, and an O concentration is 0.1 mass % or less in the
bulk.
[0043] In the titanium thin sheet of the present invention, a
reason why the grain size .gtoreq.2.5 .mu.m is to be satisfied is
that when the grain size is less than 2.5 .mu.m, the elongation is
largely lowered, and it is inferior in the workability as
illustrated in FIG. 1.
[0044] FIG. 1 is a view exemplifying a relationship between the
crystal grain size and the elongation in a tensile test of the
titanium thin sheet. As illustrated in the drawing, when the
crystal grain size is less than 2.5 .mu.m, it becomes too
high-strengthened even if a non-recrystallized grain does not
exist, and therefore, the elongation is largely lowered.
[0045] In the titanium thin sheet of the present invention, a
reason why the sheet thickness (mm)/the grain size (mm) .gtoreq.3
(hereinafter, "the sheet thickness (mm)/the grain size (mm)" is
just referred to as "the sheet thickness/the grain size") is to be
satisfied is as described below.
[0046] FIG. 2 is a view exemplifying a relationship between a
stress and a strain in the tensile test of a titanium thin sheet
(foil) of 25 .mu.m in thickness. In the drawing, "the grain size:
5.3 .mu.m" and "the grain size: 12.3 .mu.m" are measurement results
as for test pieces whose average grain sizes are respectively 5.3
.mu.m and 12.3 .mu.m.
[0047] As illustrated in FIG. 2, in any of the test pieces, after
passing through a uniform elongation state, it starts local
deformation, and reaches a fracture. A local deformation amount is
small, and a uniform deformation amount, namely, the uniform
elongation is an index of the workability, and when the uniform
elongation is lowered, it means the lowering of the
workability.
[0048] In a deformation of a polycrystalline material, when one
grain deforms, relaxation of deformation occurs by crystal grains
at a periphery thereof. However, when the number of crystal grains
are small relative to a sheet thickness direction, a contribution
to the deformation of one crystal grain becomes large, the
deformation progresses at a specific crystal grain, and therefore,
the local deformation early starts. FIG. 2 illustrates this
state.
[0049] Accordingly, by the number of crystal grains existing in the
sheet thickness direction, namely, by the ratio of the sheet
thickness/the grain size, an upper limit of a range of an average
crystal grain size capable of improving the workability by
coarsening is determined.
[0050] FIG. 3 is a view exemplifying a relationship between the
sheet thickness/the grain size and the elongation in the tensile
test of the titanium thin sheet. As illustrated in FIG. 3, the
elongation is remarkably lowered at around the sheet thickness/the
grain size=3 in any of the titanium thin sheets of 25 .mu.m to 150
.mu.m in thickness, and it can be seen that it is necessary to
satisfy the sheet thickness (mm)/the grain size (mm) .gtoreq.3.
[0051] Further, in the titanium thin sheet of the present
invention, it is necessary to have the hardened layer at the region
at the depth of 200 nm or more and 2 .mu.m or less from the
surface. In other words, it is necessary to have the hardened layer
of 200 nm to 2 .mu.m in thickness in the vicinity of the
surface.
[0052] The hardened layer is the concentrated layer of oxygen,
nitrogen and carbon formed at the annealing time by carbon,
nitrogen and oxygen comes from the rolling oil remaining at the
surface, nitrogen and oxygen gas contained in the gas atmosphere of
the annealing furnace, and is a region containing oxygen of 0.5
mass % or more, a region containing nitrogen of 0.5 mass % or more,
a region containing carbon of 0.5 mass % or more, or a region
containing oxygen, nitrogen, and carbon of 0.5 mass % or more as a
total. Note that the thickness of the hardened layer is able to be
measured by a GDS (Glow discharge optical emission
spectrometer).
[0053] FIG. 4 is a view illustrating a relationship between the
hardened layer thickness and the surface hardness in the titanium
thin sheet. As illustrated in FIG. 4, the thicker the thickness of
the hardened layer is, the higher the surface hardness becomes.
When the thickness of the hardened layer is thinner than 200 nm, it
is the same degree as a material hardness (illustrated in FIG. 4)
measured at a cross section of the material, and an increase of the
hardness is not recognized. Besides, when the increase of the
surface hardness is insufficient, it is inferior in the shape
retentivity. Accordingly, the thickness of the hardened layer is
set to be 200 nm or more.
[0054] FIG. 5 is a view exemplifying a relationship between the
hardened layer thickness and the elongation in the titanium thin
sheet of 100 .mu.m in thickness, and the sheet thickness/the grain
size .gtoreq.3. As illustrated in FIG. 5, even when the sheet
thickness/the grain size .gtoreq.3, the elongation is lowered if
the hardened layer thickness is too thick to lead to the lowering
of the workability, and therefore, the hardened layer thickness is
set to be 2000 nm (2 .mu.m) or less.
[0055] The titanium thin sheet of the present invention is
desirable if the finish annealing is performed at 500.degree. C. or
more and 850.degree. C. or less by the BAF or the continuous
annealing after the cold-rolling, because stable workability is
secured.
[0056] When an annealing temperature is low, the non-recrystallized
grain remains, and the workability is lowered. A recrystallization
temperature of the titanium thin sheet of the present invention is
500.degree. C., and therefore, the finish annealing is performed at
500.degree. C. or more. Besides, the finish annealing is performed
at 850.degree. C. or less to obtain an equiaxed structure in which
a balance between excellent strength and ductility (elongation) is
easy to obtain. An operation in accordance with an object of an
annealing process is performed also in a normal operation, but the
workability is stably secured by performing the finish annealing
under the above-stated desirable temperature condition.
[0057] The thickness of the hardened layer is able to be set to an
objected thickness by, for example, changing a remaining amount of
the rolling oil at the cleaning process normally performed after
the cold rolling, and changing the remaining nitrogen and the
oxygen amount of the bright annealing furnace.
EXAMPLE
[0058] To verify effects of the present invention, the following
tests are performed.
[0059] At first, cold-rolled sheets of 25 .mu.m to 150 .mu.m in
thickness are manufactured as for one kind of pure titanium
(thickness of 0.5 mm) defined by JISH4600 by passing through the
cold rolling and an intermediate annealing. Subsequently, the
finish annealing is performed while changing conditions in an Ar
atmosphere (dew point.ltoreq.-40.degree. C.) to thereby change
crystal grain sizes variously. Besides, the hardened layer is
formed at a surface of the sheet by concentrating any of oxygen,
nitrogen, carbon by the rolling oil remained at the surface of the
sheet and the gas atmosphere of the annealing furnace. The
thickness (depth) of the hardened layer is adjusted by changing the
remaining amount of the rolling oil and the nitrogen amount and the
oxygen amount in the atmosphere at the bright annealing time.
[0060] Each of these cold-rolled sheets (each test piece) after the
finish annealing is processed into a test piece with a parallel
part of 6.25 mm in width, a parallel part of 50 mm in length, and
thereafter, a tensile test is performed. Besides, a sheet
thickness, a crystal grain size, surface hardness, and a thickness
of the hardened layer are measured as for each test piece. Fe
concentration (bulk mass %), O concentration (bulk mass %) of each
test piece used for the example, and each measurement result are
illustrated together in Table 1.
TABLE-US-00001 TABLE 1 SHEET HARDENED SHEET CRYSTAL THICK- LAYER
SURFACE 0.2% THICK- GRAIN NESS/ THICK- HARD- PROOF TENSILE ELONGA-
Fe O NESS SIZE GRAIN NESS NESS STRESS STRENGTH TION (mass %) (mass
%) (.mu.m) (.mu.m) SIZE (nm) (HV.sub.0.025) (MPa) (MPa) (%)
COMPARATIVE 0.04 0.05 25 NON- -- 202 329 420 5.9 EXAMPLE 1
RECRYSTAL- LIZED GRAIN EXAMPLE 1 0.04 0.05 25 2.6 9.6 320 152 284
406 12.7 EXAMPLE 2 0.04 0.05 25 3.1 8.1 480 151 285 387 13.6
EXAMPLE 3 0.04 0.05 25 3.7 6.8 450 156 248 365 15.5 EXAMPLE 4 0.04
0.05 25 7 3.6 400 157 191 318 13.2 EXAMPLE 5 0.04 0.05 25 8.2 3 300
155 206 336 15 COMPARATIVE 0.04 0.05 25 12.3 2 460 156 142 261 11.4
EXAMPLE 2 COMPARATIVE 0.04 0.05 25 20.1 1.2 320 149 137 258 7.3
EXAMPLE 3 COMPARATIVE 0.04 0.05 50 NON- -- 190 362 459 13.9 EXAMPLE
4 RECRYSTAL- LIZED GRAIN EXAMPLE 6 0.04 0.05 50 2.8 17.9 470 145
281 432 22.4 EXAMPLE 7 0.04 0.05 50 3.4 14.7 490 150 291 406 24.6
EXAMPLE 8 0.04 0.05 50 5.3 9.4 510 154 238 362 25 EXAMPLE 9 0.04
0.05 50 9.3 5.4 500 158 191 329 24.1 EXAMPLE 10 0.04 0.05 50 12.4 4
500 152 168 299 22.6 COMPARATIVE 0.04 0.05 50 19.9 2.5 510 147 151
271 18.4 EXAMPLE 5 COMPARATIVE 0.04 0.05 50 23.3 2.2 520 153 157
264 14.9 EXAMPLE 6 COMPARATIVE 0.03 0.03 100 2.1 47.6 480 151 272
372 25.1 EXAMPLE 7 EXAMPLE 11 0.03 0.03 100 3 33.3 500 156 250 353
30.4 EXAMPLE 12 0.03 0.03 100 3.2 31.3 530 155 223 354 30.2 EXAMPLE
13 0.03 0.03 100 4.7 21.2 450 151 187 341 33.7 EXAMPLE 14 0.03 0.03
100 8.2 12.2 630 158 151 315 33 EXAMPLE 15 0.03 0.03 100 11.6 8.6
1080 198 147 302 34.4 COMPARATIVE 0.03 0.03 100 15.6 6.4 2510 262
216 306 26.3 EXAMPLE 8 EXAMPLE 16 0.03 0.03 100 17.9 5.6 1160 184
145 303 35.2 EXAMPLE 17 0.03 0.03 100 31.3 3.2 1760 199 151 302 33
COMPARATIVE 0.03 0.03 100 30.2 3.3 180 135 90 288 36.1 EXAMPLE 9
COMPARATIVE 0.03 0.03 100 33.1 3 2300 242 182 298 27.7 EXAMPLE 10
COMPARATIVE 0.03 0.03 100 38.7 2.6 1820 227 147 282 29.3 EXAMPLE 11
COMPARATIVE 0.03 0.03 100 56.1 1.8 2430 254 167 278 25.2 EXAMPLE 12
COMPARATIVE 0.03 0.03 150 1.9 78.9 410 171 279 388 30.1 EXAMPLE 13
EXAMPLE 18 0.03 0.03 150 2.6 57.7 500 162 250 372 33.4 EXAMPLE 19
0.03 0.03 150 5.3 28.3 480 159 186 330 36.2 EXAMPLE 20 0.03 0.03
150 8.1 18.4 420 160 158 311 35 EXAMPLE 21 0.03 0.03 150 12.5 12
410 155 148 302 40.6 EXAMPLE 22 0.03 0.03 150 28.8 5.2 1810 246 150
289 39.5 COMPARATIVE 0.03 0.03 150 31.5 4.8 190 138 93 279 41.2
EXAMPLE 14 EXAMPLE 23 0.03 0.03 150 45 3.3 1930 254 141 281 37.6
COMPARATIVE 0.03 0.03 150 44.6 3.4 160 136 85 274 41.5 EXAMPLE 15
COMPARATIVE 0.03 0.03 150 52 2.9 2120 253 145 257 28.7 EXAMPLE 16
COMPARATIVE 0.03 0.03 150 68.3 2.2 600 168 91 252 28.3 EXAMPLE
17
[0061] The tensile test is performed in a direction (L direction)
in parallel to a rolling direction, under conditions of a strain
rate of 0.5%/min up to 0.2% proof stress, and thereafter, 20%/min
up to fracture, under a room temperature.
[0062] The crystal grain size is found by using the quadrature and
square approximation as for a region of 40,000 .mu.m.sup.2 or more
of a sample surface.
[0063] As for the surface hardness, a Vickers hardness meter is
used, a Vickers indenter is pressed onto the sample surface with a
load of 0.245 N (25 gf), and it is evaluated by an average value of
10 points.
[0064] The thickness of the hardened layer is set to be a thickness
in which a depth direction analysis of each of oxygen, nitrogen,
carbon, titanium, and iron is performed by an Ar ion sputtering by
using the GDS, at a region of 4 mm in diameter of the sample
surface, and any of concentrations of oxygen, nitrogen, and carbon,
or a total concentration of these becomes 0.5 mass % or more. As
for quantification, each measurement value is calibrated by using
each of zinc oxide (oxygen: 19.8 mass %) as for oxygen, austenitic
stainless steel (nitrogen content: 0.3 mass %) as for nitrogen,
titanium alloy (carbon content: 0.12 mass %) as for carbon, to be
corresponded to a measurement portion (depth) of pure titanium (JIS
one kind) to thereby perform the depth direction analysis of each
element.
[0065] In Table 1, characteristic values of the titanium material
change depending on the sheet thickness, contents (bulk
concentration) of Fe, O, and therefore, they are each compared
under approximately the same condition. Besides, even when the
sheet thickness, the contents of Fe, O are the same, they are
affected by the grain size, and therefore, the comparison is
performed in consideration of the grain size. Note that it is a
problem in the shape retentivity in which the shape deforms by
deformation of a part where a processing amount is small, and
therefore, the shape retentivity is able to be evaluated at a value
of 0.2% proof stress at each sheet thickness.
[0066] A comparative example 1 and a comparative example 4 are both
cases when non-recrystallized grains remain, and the elongations
are remarkably low.
[0067] Each of comparative examples 2, 3, 5, 6, 11, 12, 16, 17 is a
case when (the sheet thickness/the grain size) <3, and the
elongation is remarkably low. In particular, the elongation of the
comparative example 17 is lower than examples 18 to 23.
[0068] A comparative example 7 and a comparative example 13 are
both cases when the crystal grain sizes are too fine (less than 2.5
.mu.m), and the elongations are low.
[0069] Each of comparative examples 8, 10, 12 is a case when the
thickness of the hardened layer is larger than the thickness (200
nm or more and 2 .mu.m or less) defined in the present invention,
and the elongation is low. In particular, in the comparative
example 12, the sheet thickness/the grain size is less than 3, and
the hardened layer is thick, and therefore, the elongation is lower
than examples 11 to 17. In a comparative example 16, the sheet
thickness/the grain size is less than 3, and the hardened layer is
also thick, and therefore, the elongation is lower than examples 18
to 23.
[0070] In each of comparative examples 9, 14, 15, the thickness of
the hardened layer is thin (less than 200 nm), 0.2% proof stress is
low, and the shape retentivity is not good. In particular, in the
comparative example 14, the proof stress is remarkably low compared
to the example 22 having approximately the same grain size. In the
comparative example 15, the proof stress is remarkably low compared
to the example 23 having approximately the same grain size.
[0071] When they are summarized by the same sheet thickness,
results are as follows.
[0072] "As for 25 .mu.m material"
[0073] The comparative example 1 is a non-recrystallized structure,
and therefore, the elongation is low.
[0074] In each of the comparative examples 2, 3, the sheet
thickness/the grain size is less than 3, and the elongation, the
proof stress, and the tensile strength are low compared to the
examples 1 to 5.
[0075] "As for 50 .mu.m material"
[0076] The comparative example 4 is the non-recrystallized
structure, and therefore, the elongation is low.
[0077] In each of the comparative examples 5, 6, the sheet
thickness/the grain size is less than 3, and the elongation, the
proof stress, and the tensile strength are low compared to the
examples 6 to 10.
[0078] "As for 100 .mu.m material"
[0079] The comparative example 7 is too grain-refined, and
therefore, the elongation is low.
[0080] In the comparative example 8, the sheet thickness/the grain
size .gtoreq.3 is satisfied, but the hardened layer is thick, and
the elongation is low.
[0081] In the comparative example 9, the hardened layer is thin,
and the proof stress is remarkably low compared to the example 17
having approximately the same grain size.
[0082] In the comparative example 10, the hardened layer is thick,
and the elongation is low compared to the examples 11 to 17.
[0083] In the comparative example 11, the sheet thickness/the grain
size is less than 3, and the elongation is low compared to the
examples 11 to 17.
[0084] In the comparative example 12, the sheet thickness/the grain
size is less than 3, the hardened layer is also thick, and
therefore, the elongation is low compared to the examples 11 to
17.
[0085] "As for 150 .mu.m material"
[0086] The comparative example 13 is too grain-refined, and
therefore, the elongation is low.
[0087] In the comparative example 14, the hardened layer is thin,
and the proof stress is remarkably low compared to the example 22
having approximately the same grain size.
[0088] In the comparative example 15, the hardened layer is thin,
and the proof stress is remarkably low compared to the example 23
having approximately the same grain size.
[0089] In the comparative example 16, the sheet thickness/the grain
size is less than 3, the hardened layer is also thick, and
therefore, the elongation is low compared to the examples 18 to
23.
[0090] In the comparative example 17, the sheet thickness/the grain
size is less than 3, and the elongation is low compared to the
examples 18 to 23.
[0091] On the other hand, each of the examples 1 to 23 is a case
when the conditions defined in the present invention are satisfied,
and exhibits high elongation and surface hardness.
INDUSTRIAL APPLICABILITY
[0092] The titanium thin sheet of the present invention includes
excellent workability and high surface hardness, and is able to be
used for wide purposes as materials of consumer products and for
industries such as, for example, a speaker vibration plate.
* * * * *