U.S. patent application number 14/418031 was filed with the patent office on 2015-06-18 for titanium alloy material.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is NIPPON STEEL 7 SUMITOMO METAL CORPORATION. Invention is credited to Masaru Abe, Norio Inoue, Hideya Kaminaka, Hiroshi Kamio, Satoshi Matsumoto, Kouichi Takeuchi.
Application Number | 20150167121 14/418031 |
Document ID | / |
Family ID | 50068272 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150167121 |
Kind Code |
A1 |
Kaminaka; Hideya ; et
al. |
June 18, 2015 |
TITANIUM ALLOY MATERIAL
Abstract
[Object] To provide a titanium alloy material containing a
platinum group metal, the titanium alloy material being able to
sufficiently suppress corrosion accompanying surface roughening.
[Solution] Provided is a titanium alloy material including a
platinum group metal. When an average value of intensity of
background signals in surface mapping analysis using an EPMA
surface analysis apparatus is N and N+3N.sup.1/2 is maximum
intensity of the background signal of an Fe or S characteristic
X-ray, an area ratio at which a signal of an Fe or S characteristic
X-ray exceeding the maximum intensity is obtained is 0.1% or
less.
Inventors: |
Kaminaka; Hideya; (Tokyo,
JP) ; Takeuchi; Kouichi; (Tokyo, JP) ; Kamio;
Hiroshi; (Tokyo, JP) ; Matsumoto; Satoshi;
(Tokyo, JP) ; Inoue; Norio; (Tokyo, JP) ;
Abe; Masaru; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL 7 SUMITOMO METAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
|
Family ID: |
50068272 |
Appl. No.: |
14/418031 |
Filed: |
August 12, 2013 |
PCT Filed: |
August 12, 2013 |
PCT NO: |
PCT/JP2013/071788 |
371 Date: |
January 28, 2015 |
Current U.S.
Class: |
420/421 ;
420/417 |
Current CPC
Class: |
C22F 1/183 20130101;
C22C 14/00 20130101 |
International
Class: |
C22C 14/00 20060101
C22C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2012 |
JP |
2012-179003 |
Claims
1-7. (canceled)
8. A titanium alloy material comprising: a platinum group metal,
wherein, when an average value of intensity of background signals
in surface mapping analysis using an EPMA surface analysis
apparatus is N and N+3N.sup.1/2 is maximum intensity of the
background signal of an Fe characteristic X-ray, an area ratio at
which a signal of an Fe characteristic X-ray exceeding the maximum
intensity is obtained is 0.1% or less.
9. A titanium alloy material comprising: a platinum group metal,
wherein, when an average value of intensity of background signals
in surface mapping analysis using an EPMA surface analysis
apparatus is N and N+3N.sup.1/2 is maximum intensity of the
background signal of a S characteristic X-ray, an area ratio at
which a signal of a S characteristic X-ray exceeding the maximum
intensity is obtained is 0.1% or less.
10. The titanium alloy material according to claim 8, wherein the
area ratio at which the signal of the Fe characteristic X-ray
exceeding the maximum intensity is 0.05% or less and the area ratio
at which the signal of the S characteristic X-ray exceeding the
maximum intensity is 0.05% or less.
11. The titanium alloy material according to claim 9, wherein the
area ratio at which the signal of the Fe characteristic X-ray
exceeding the maximum intensity is 0.05% or less and the area ratio
at which the signal of the S characteristic X-ray exceeding the
maximum intensity is 0.05% or less.
12. The titanium alloy material according to claim 8, wherein a
content of Fe obtained by point analysis of part in which Fe is
present on the surface of the titanium alloy material is 0.5 or
less in atomic ratio of Fe with respect to Ti.
13. The titanium alloy material according to claim 10, wherein a
content of Fe obtained by point analysis of part in which Fe is
present on the surface of the titanium alloy material is 0.5 or
less in atomic ratio of Fe with respect to Ti.
14. The titanium alloy material according to claim 11, wherein a
content of Fe obtained by point analysis of part in which Fe is
present on the surface of the titanium alloy material is 0.5 or
less in atomic ratio of Fe with respect to Ti.
15. The titanium alloy material according to claim 8, wherein the
platinum group metal is contained in 0.01 to 0.25% by mass.
16. The titanium alloy material according to claim 9, wherein the
platinum group metal is contained in 0.01 to 0.25% by mass.
17. The titanium alloy material according to claim 8, wherein at
least one selected from the group consisting of Ni in 0.05 to 1.0%
by mass, Cr in 0.05 to 0.3% by mass, and Mo in 0.05 to 0.5% by mass
is further contained.
18. The titanium alloy material according to claim 9, wherein at
least one selected from the group consisting of Ni in 0.05 to 1.0%
by mass, Cr in 0.05 to 0.3% by mass, and Mo in 0.05 to 0.5% by mass
is further contained.
19. The titanium alloy material according to claim 15, wherein at
least one selected from the group consisting of Ni in 0.05 to 1.0%
by mass, Cr in 0.05 to 0.3% by mass, and Mo in 0.05 to 0.5% by mass
is further contained.
20. The titanium alloy material according to claim 16, wherein at
least one selected from the group consisting of Ni in 0.05 to 1.0%
by mass, Cr in 0.05 to 0.3% by mass, and Mo in 0.05 to 0.5% by mass
is further contained.
21. The titanium alloy material according to claim 8, wherein Pd is
contained in 0.01 to 0.25% by mass as the platinum group metal.
22. The titanium alloy material according to claim 9, wherein Pd is
contained in 0.01 to 0.25% by mass as the platinum group metal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a titanium alloy material,
particularly to a titanium alloy material containing a platinum
group metal.
BACKGROUND ART
[0002] Titanium is being actively used in the aircraft field and
the like, utilizing its feature of lightness and strength. Further,
having high corrosion resistance, titanium is beginning to be used
in wide range of fields as a material for chemical industry
equipment, a material for thermal and nuclear power generation
equipment, and a material for seawater desalination equipment, and
the like.
[0003] However, the environment in which titanium can exhibit its
high corrosion resistance is limited to oxidizing acid (nitric
acid) environment and neutral chloride environment such as
seawater. Titanium does not have sufficient crevice corrosion
resistance in a high-temperature chloride environment, nor
sufficient corrosion resistance in a non-oxidizing acid solution
such as hydrochloric acid (hereinafter, in this section, the
crevice corrosion resistance and the corrosion resistance are
referred to as "corrosion resistance").
[0004] An example of a titanium alloy having improved corrosion
resistance is a Ti-0.15 Pd alloy (Gr. 7 and Gr. 11 according to the
ASTM standard) (hereinafter, "Gr." (Grade) complies with the ASTM
standard). This titanium alloy is produced by using the phenomenon
that Pd in the alloy reduces hydrogen overvoltage to maintain the
natural potential within a passivation range. That is, in this
alloy, Pd eluted from the alloy by corrosion is precipitated again
on the surface of the alloy to be deposited, and thereby hydrogen
overvoltage is reduced and the natural potential is maintained
within the passivation range. Accordingly, this alloy has high
corrosion resistance.
[0005] Gr. 7 having high corrosion resistance, however, contains
Pd, which is a very expensive platinum group metal; accordingly,
the fields using Gr. 7 have been limiting.
[0006] To solve this problem, as disclosed in Patent Document 1
below, a titanium alloy (Gr. 17) and the like having high crevice
corrosion resistance while having a lower content rate of Pd, which
is 0.01 to 0.12% by mass, than Gr. 7, is proposed and put into
practical use. In this manner, a titanium alloy containing a
platinum group metal is gaining widespread use, so that the
titanium alloy is beginning to be used even in a harsh environment
such as a high-temperature chloride environment.
[0007] However, the titanium alloy containing a platinum group
metal and having high corrosion resistance may cause corrosion that
is different from pitting corrosion or so-called crevice corrosion
(accompanying whitening and wastage due to the generation of
TiO.sub.2). The present inventors have closely examined this kind
of corrosion.
[0008] FIG. 1 is a photograph showing the outside appearance of a
Gr. 17 titanium alloy material in which corrosion has occurred. As
shown in FIG. 1, a corroded part often has high surface roughness
(hereinafter, getting high surface roughness is referred to as
"surface roughening"). Further, it is found that black matter has
adhered or the titanium alloy has changed its color into black in
the vicinity of the corroded part. Then, the present inventors have
confirmed the existence of hydride (TiH or TiH.sub.2) in the
corroded part. Therefore, this corrosion is closely related to
hydrogen.
[0009] FIG. 2 is a photograph showing a cross-sectional structure
of the corroded Gr. 17 titanium alloy material. On the surface of
the corroded part of the titanium alloy material, a plurality of
concave portions are formed (in FIG. 2, arrows denote the parts
where concave portions are formed.). From FIG. 2, it is found that
spotted or pointed substances are formed in the range from the
vicinity of the surface to the inside. The present inventors have
confirmed that the substances are hydride. Hydride is considered to
have been generated from hydrogen that entered from the surface of
the material.
[0010] FIG. 3 is a photograph showing a cross-sectional structure
of a non-corroded Gr. 17 titanium alloy material. Surface
roughening of the titanium alloy material has not progressed, and
in such a titanium alloy material, there is not as much hydride as
in the titanium alloy material shown in FIG. 2, at least.
[0011] Patent Document 2 below discloses a material having improved
grain-boundary corrosion resistance by orienting precipitates
(Ti.sub.2Ni) contained in a titanium alloy containing a platinum
group along a rolling direction.
[0012] Patent Document 3 discloses a material in which, in order to
prevent embrittlement caused by hydrogen absorption, a hydride
layer is formed in advance only in the vicinity of the surface and
further hydrogen absorption and hydrogen embrittlement are
prevented in the usage environment of the material.
PRIOR ART DOCUMENT(S)
Patent Document(s)
[0013] [Patent Document 1] JP 3916088B [0014] [Patent Document 2]
JP 2012-12636A [0015] [Patent Document 3] JP 2005-36314A
Non-Patent Document(s)
[0015] [0016] [Non-Patent Document 1] Soejima, Hiroyoshi, Electron
Probe Microanalysis: Scanning Electron Microscope and X-ray
Micro-analyzing Method, Nikkan Kogyo Shimbun, LTD., 1987, Chapter
4: Spatial Resolution by EPMA, 4.2.4.3 Statistical Fluctuation, p.
112.
SUMMARY OF THE INVENTION
Problem(s) to be Solved by the Invention
[0017] Although various measured have been proposed for the
problems of corrosion accompanying surface roughening of a titanium
alloy material, conventional measures cannot suppress this kind of
corrosion sufficiently.
[0018] The present invention has been made in view of the above
circumstance, and aims to provide a titanium alloy material
containing a platinum group metal, the titanium alloy material
being able to sufficiently suppress corrosion accompanying surface
roughening.
Means for Solving the Problem(s)
[0019] The present inventors have closely studied to solve the
above problems of corrosion, and have made the present invention.
The present invention relates to a titanium alloy material as
described in the following (1) to (7). [0020] (1) A titanium alloy
material including:
[0021] a platinum group metal,
[0022] wherein, when an average value of intensity of background
signals in surface mapping analysis using an EPMA surface analysis
apparatus is N and N+3N.sup.1/2 is maximum intensity of the
background signal of an Fe characteristic X-ray, an area ratio at
which a signal of an Fe characteristic X-ray exceeding the maximum
intensity is obtained is 0.1% or less. [0023] (2) A titanium alloy
material including:
[0024] a platinum group metal,
[0025] wherein, when an average value of intensity of background
signals in surface mapping analysis using an EPMA surface analysis
apparatus is N and N+3N.sup.1/2 is maximum intensity of the
background signal of a S characteristic X-ray, an area ratio at
which a signal of a S characteristic X-ray exceeding the maximum
intensity is obtained is 0.1% or less. [0026] (3) The titanium
alloy material according to (1) or (2),
[0027] wherein the area ratio at which the signal of the Fe
characteristic X-ray exceeding the maximum intensity is 0.05% or
less and the area ratio at which the signal of the S characteristic
X-ray exceeding the maximum intensity is 0.05% or less. [0028] (4)
The titanium alloy material according to (1) or (3),
[0029] wherein a content of Fe obtained by point analysis of part
in which Fe is present on the surface of the titanium alloy
material is 0.5 or less in atomic ratio of Fe with respect to Ti.
[0030] (5) The titanium alloy material according to any one of (1)
to (4),
[0031] wherein the platinum group metal is contained in 0.01 to
0.25% by mass. [0032] (6) The titanium alloy material according to
any one of (1) to (5),
[0033] wherein at least one selected from the group consisting of
Ni in 0.05 to 1.0% by mass, Cr in 0.05 to 0.3% by mass, and Mo in
0.05 to 0.5% by mass is further contained. [0034] (7) The titanium
alloy material according to any one of (1) to (6),
[0035] wherein Pd is contained in 0.01 to 0.25% by mass as the
platinum group metal.
Effect(s) of the Invention
[0036] The titanium alloy material according to the present
invention can be used for applications that need high corrosion
resistance (e.g., crevice corrosion resistance and acid
resistance), resistance against corrosion progress, processability,
and economic efficiency. Specifically, the titanium alloy material
according to the present invention can be used in a harsh
environment such as an anode of a brine electrolytic cell and salt
processing equipment.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0037] FIG. 1 is a photograph showing the outside appearance of a
corroded Gr. 17 titanium alloy material.
[0038] FIG. 2 is a photograph showing a cross-sectional structure
of a corroded Gr. 17 titanium alloy material.
[0039] FIG. 3 is a photograph showing a cross-sectional structure
of a non-corroded Gr. 17 titanium alloy material.
[0040] FIG. 4 shows results of surface mapping analysis with an
EPMA surface analysis apparatus for samples according to the
present invention.
[0041] FIG. 5 shows results of surface mapping analysis with an
EPMA surface analysis apparatus for samples not according to the
present invention.
[0042] FIG. 6 is a schematic diagram of a sample used for corrosion
testing and a schematic diagram of a sample for crevice corrosion
testing.
MODE(S) FOR CARRYING OUT THE INVENTION
[0043] The present invention is based on the present inventors'
knowledge as follows.
[0044] In a case in which a titanium alloy is used in a crevice
structure, corrosion may occur accompanying surface roughening,
which is different from so-called crevice corrosion. This kind of
corrosion may rarely accompany expansion. The present inventors
have studied parts where such corrosion has occurred, and have
confirmed that one or both of Fe and S is detected in the corroded
parts in many cases. Further, the present inventors have studied
the relation between the surface state of a titanium alloy material
and the presence and absence of the occurrence of corrosion.
Accordingly, as will be described later, they have found out that
the occurrence of corrosion accompanying surface roughening can be
suppressed by adjusting the ratio of Fe and/or S existing on the
surface to be a certain level or lower.
[0045] As shown above, when a cross section of the part where
corrosion accompanying surface roughening has occurred is observed,
spotted or pointed hydride can be seen only in the vicinity of the
corroded surface, and accordingly, the corrosion is considered to
be related to hydride. It is after a long period of time lapses
after the titanium alloy is placed in a crevice structure in a
normal environment, for example, when such corrosion can be
visually observed as a change in appearance; such a change in
appearance cannot be seen after a short period time lapses.
Accordingly, the present inventors have conducted acceleration
testing in which such corrosion has been caused to analyze the
relation between the surface state before corrosion of the titanium
alloy and corrosion.
1) Identify Surface Contaminating Element
[0046] Gr. 11, Gr. 13, and Gr. 17 materials having different
surface contaminating degrees were commercially obtained and were
subjected to surface analysis with an electron probe micro analyzer
(EPMA) surface analysis apparatus to find out elements that are
present on the surface. For each of the Gr. 11, Gr. 13, and Gr. 17
materials, elements that are present on the surface are as
follows.
[0047] On the surface of the Gr. 11 and Gr. 17 materials, Ti and Pd
were detected as matrix components, and C, O, Fe, Zn, S, Cl, Na,
and F were detected as components other than matrix components.
[0048] On the surface of the Gr. 13 material, Ti, Ni, and Ru were
detected as matrix components, and C, O, Fe, Zn, S, Cl, Na, Ca, and
F were detected as components other than matrix components.
[0049] The factor of detection of the elements other than the
matric components among the above elements was studied.
[0050] C is considered to be from rolling oil used in a
manufacturing process. O is from a passivation film of titanium, so
that O is generally observed on the surface of a titanium
material.
[0051] On the other hand, Fe, Zn, and S are elements that are not
observed in a general titanium alloy material, and are each defined
as "surface contaminating element" in this specification. Note that
Fe is in some cases added to a titanium material in order to
improve strength, and such a titanium alloy material contains Fe in
a base material regardless of contamination by Fe. Such Fe is
normally molten in the titanium material and distributed uniformly,
so that, when the titanium alloy material is analyzed with the EPMA
surface analysis apparatus, signals of Fe are counted as
backgrounds. Fe that the present application focuses on is Fe that
is brought by Fe contamination and is present in a condensed state
on the surface of the titanium material, without being molten
therein.
[0052] The surface analysis detects Ca, Na, and Cl. However, the
detected amounts of such elements are minute, and accordingly such
elements are excluded from the contaminating elements defined in
this specification. Such elements are assumed to have been adhered
on the titanium alloy material mainly from humans who handled the
titanium alloy material commercially.
[0053] The surface contamination by Fe is assumed to be from a
stainless steel product or steel product produced in the same
manufacturing line as the target titanium alloy material, or from a
shot piece remaining on the surface of the titanium alloy material,
the shot piece being used for shot peening at a time of descaling
of a hot rolled sheet (Fe contamination caused by a shot piece will
be described later in detail in the section "6) Method of
manufacturing titanium alloy material according to the present
invention"). In a case in which a titanium alloy material is used
in a crevice structure, a black oxide that is assumed to be
Fe.sub.3O.sub.4 may be generated on the surface thereof in the
crevice structure. A part where such an oxide is generated
undergoes surface roughening by corrosion, as shown in FIG. 1, and
hydride is generated right below the part. Accordingly, Fe that
generates oxide is considered to be related to corrosion of a
titanium alloy material accompanying surface roughening.
[0054] Surface contamination by Zn is assumed to be caused by zinc
phosphate that is used as a seizure prevention agent in a
manufacturing process of the target titanium alloy material, and Zn
remaining on the surface after rolling processing. When metal-like
Zn is present on the surface of the titanium alloy material,
heterologous metals are in contact with each other. In such a
state, hydrogen absorption is promoted, and a part contaminated by
Zn may generate hydride.
[0055] S is a component that is contained in a part of an extreme
pressure additive used for rolling lubricating oil, and
accordingly, surface contamination by S is assumed to be from such
an additive. In a part of a crevice structure, the surface of the
titanium alloy material is contaminated by S and a solution
containing chlorine ions is present on the surface thereof, sulfur
chloride (S.sub.2Cl.sub.2) is produced in a crevice. Sulfur
chloride accelerates corrosion of pure titanium, and accordingly
may also have a function of progressing corrosion of a titanium
alloy.
[0056] Next, various samples using the Gr. 11 material were
fabricated, and on the surface of each sample, ratios of areas
(area ratios) where the presence of Fe and S, among the elements
defined as contaminating elements above, is recognized is studied.
Then, crevice corrosion treatment that will described later in
Examples was performed, and the relation among the distribution of
Fe and S, the amount thereof, and corrosion resistance was studied
(by visual observation and measurement of corrosion weight
loss).
2) Area Ratio of Fe Contamination
[0057] On the surface of each sample, for a 200-nm square region,
surface mapping analysis for Fe was performed with an EPMA surface
analysis apparatus. When the average value of intensity of
background signals is N and N+3N.sup.1/2 is maximum intensity of
the background signal of an Fe characteristic X-ray, the area ratio
at which a signal of the Fe characteristic X-ray exceeding the
maximum intensity (hereinafter referred to as "Fe area ratio") is
obtained was calculated (a detailed method of calculating the area
ratio will be described later).
[0058] Five regions that were arbitrarily selected on the surface
of the sample had Fe area ratios of 0.002% to 2.4% according to the
surface mapping analysis. After crevice corrosion treatment was
performed on the samples, corroded regions having high surface
roughness were formed locally. Among these corroded regions, a
sample for which corrosion weight loss was confirmed had an Fe area
ratio exceeding 0.1%.
[0059] Surface roughening was recognized in some samples of which
the Fe area ratio was 0.1% or less and for which corrosion weight
loss was not confirmed. In a sample of which the Fe area ratio was
0.01% or less, such rough parts were not recognized. From the above
results, in order to secure corrosion resistance, in particular, in
a case of contamination only by Fe (not accompanying contamination
by S), the Fe area ratio on the surface of the titanium alloy
material needs to be 0.1% or less. The Fe area ratio on the surface
of the titanium alloy material in a case of F-only contamination is
preferably 0.01% or less.
3) Area Ratio of S Contamination
[0060] On the surface of each sample, for a 200-nm square region,
surface mapping analysis for S was performed with an EPMA surface
analysis apparatus. When the average value of intensity of
background signals is N and N+3N.sup.1/2 is maximum intensity of
the background signal of a S characteristic X-ray, the area ratio
at which a signal of the S characteristic X-ray exceeding the
maximum intensity (hereinafter referred to as "S area ratio") was
calculated.
[0061] Five regions that were arbitrarily selected on the surface
of the sample had S area ratios of 0.002% to 3.9% according to the
surface mapping analysis. After crevice corrosion treatment was
performed on the samples, corroded regions having high surface
roughness were formed locally. Among the samples in which these
corroded regions were recognized, a sample for which corrosion
weight loss was confirmed had a S area ratio exceeding 0.1%. From
these results, in order to secure corrosion resistance, in
particular, in a case of S-only contamination (not accompanying Fe
contamination), the S area ratio on the surface of a titanium alloy
material needs to be set to 0.1% or less.
4) Fe and S Complex Contamination Area Ratio
[0062] In some cases, the above described commercially available
material is contaminated by both Fe and S.
[0063] Five regions that were arbitrarily selected from the sample
had Fe area ratios of 0.001% to 2.4% and S area ratios of 0.001% to
3.9% according to surface mapping analysis performed for both Fe
and S with an EPMA surface analysis apparatus.
[0064] After crevice corrosion treatment was performed on the
samples, corroded regions having high surface roughness were formed
locally. A sample for which corrosion weight loss was confirmed had
an Fe area ratio exceeding 0.05% and a S area ratio exceeding
0.05%. From these results, in order to secure corrosion resistance
of a titanium alloy material that is contaminated by both Fe and S,
it is preferable to set the Fe area ratio to be 0.05% or less and
the S area ratio to be 0.05% or less on the surface of the titanium
alloy material.
5) Fe Content
[0065] For the samples contaminated by Fe, not only the Fe area
ratio, but also the relation between the content of Fe that is
present in the vicinity of the surface of the sample (according to
point analysis) and temporal change of contained hydrogen amount
was studied.
[0066] When samples having an Fe area ratio of 0.1% or less and a S
area ratio of 0.1% or less and containing a platinum group metal in
0.01 to 0.25% by mass are compared with each other, the sample that
has an Fe content of over 0.5 in an atomic ratio of Fe to Ti, the
contained hydrogen amount has been changed over time more largely
than the sample that has an Fe content of below 0.5 in an atomic
ratio of Fe to Ti, even when the samples have the same Fe area
ratio.
[0067] Further, as described in the above "2) Area ratio of Fe
contamination", although the corrosion weight loss was not
confirmed, some samples generated surface roughening. Since such
samples had high Fe contents, Fe is considered to increase hydrogen
absorption speed and accelerate corrosion related to hydrogen
embrittlement.
[0068] From the above description, it is preferable that the Fe
content obtained by point analysis on the part where Fe is present
on the surface of the titanium alloy material is 0.5 or less in an
atomic ratio of Fe to Ti. On the surface of the titanium alloy
material, the content of C (atomic %) varies by remaining fat or
the like. Accordingly, the content of Fe (atomic %) also varies by
being influenced by the variation of the content of C in the part
there Fe is present. In order to avoid such variations, in the
present invention, the Fe content is regulated by the ratio of the
Fe content (atomic %) to the Ti content (atomic %) which is a
component of a base material.
6) M Method of Manufacturing Titanium Alloy Material According to
the Present Invention
[0069] An example of a method of manufacturing the titanium alloy
material according to the present invention will be described.
[0070] Usually, a process of manufacturing a titanium alloy
material is divided into a hot rolling step and a cold rolling
step. In hot rolling, scale (oxide) is generated on the surface of
the titanium alloy material. For descaling, shot peening is
performed on the surface of the hot rolled sheet obtained by hot
rolling to remove scale, and in addition, a crack is given to the
scale generated in the superficial layer part of the hot rolled
sheet, and then acid cleaning is performed. In acid cleaning, since
acid for cleaning penetrates the crack, the remaining scale is
removed easily. However, a part of a shot piece remains on the
surface of the titanium alloy material and cannot be removed
completely by acid cleaning performed later. In particular, in a
case of using a large shot piece, the descaling property is high
but the remaining shot piece is hardly removed only by Kolene
treatment and acid cleaning treatment, as will be described later.
Accordingly, in some cases, cleaning with an aqueous solution of
ferric chloride (FeCl.sub.3) is necessary.
[0071] The titanium alloy material that has been subjected to the
hot rolling step is then subjected to cold rolling and annealing
plural times until a desired sheet thickness is obtained. Usually,
as the annealing treatment, bright annealing (BA) is performed in
an argon atmosphere. Since descaling is not performed on the
annealed titanium alloy material that has been subjected to bright
annealing, contamination by Fe and S is not likely to be removed by
descaling.
[0072] Through the hot rolling and cold rolling steps, on the
titanium alloy material, Fe contamination due to the above
described remaining shot piece and S contamination due to rolling
lubricating oil for cold rolling are generated. In the annealing
step, S and Fe as the source of contamination diffuse in the entire
surface of the titanium alloy material by thermal diffusion and
penetrate inside thereof.
[0073] To remove S and Fe, the source of contamination, after
annealing, the superficial layer part of the titanium alloy
material is removed by being dissolved by acid cleaning or being
grinded mechanically. Further, it is more preferable to perform,
before the acid cleaning, treatment with an alkali molten salt bath
(salt bath which contains NaOH as a main component and to which
oxidizing agents such as NaNO.sub.3 and KNO.sub.3 are added)
(commonly known as "Kolene treatment"). The removal of the
superficial layer part is preferably performed every time after
annealing is performed; however, the removal after the first and
last annealing can efficiently remove S and Fe contamination. The
removal amount (thickness) at each time is 1 .mu.m or more,
preferably 5 .mu.m or more, for a target plane of the titanium
alloy material.
[0074] As described above, treatment for removal of the
contamination source is not limited to once, but plural times of
treatment may be needed to achieve the surface as defined in the
present invention.
[0075] Further, after descaling of the hot rolled sheet, it is also
effective to perform both cleaning with the aqueous solution of
ferric chloride and brushing of the surface of the hot rolled steel
sheet. This is because the aqueous solution of ferric chloride does
not hardly dissolve titanium but dissolves Fe faster than a mixed
solution of fluonitric acid, so that a shot piece and a titanium
base material on the shot piece side are dissolved, and brushing
treatment performed concurrently can remove the shot piece
efficiently. This step becomes necessary in a case of using a large
shot piece.
[0076] Further, it is effective to perform cleaning before
annealing and to add a step of removing lubricating oil and the
like in order to reduce the contamination amount of S.
7) Alloy Element
[0077] The content of a platinum group metal is preferably 0.01 to
0.25% by mass. Thus, the raw material cost can be suppressed and
the corrosion resistance of the titanium alloy material can be
obtained. The platinum group metal may be Pd, for example.
[0078] The titanium alloy material according to the present
invention may further contain one or more selected from the group
consisting of Ni in 0.05 to 1.0% by mass, Cr in 0.05 to 0.3% by
mass, and Mo in 0.05 to 0.5% by mass.
[0079] Containing Ni, the titanium alloy material has higher
crevice corrosion resistance. Note that, this effect saturates when
Ni in more than 1.0% by mass is contained. Further, processability
is reduced by the addition of Ni. Accordingly, in a case of adding
Ni, it is preferable to set the content thereof to 1.0% by mass or
less. In order to surely obtain the above effect, it is preferable
to set the content of Ni to 0.05% by mass or more, more preferably
0.1% by mass or more.
[0080] Containing Cr, the titanium alloy material has higher
crevice corrosion resistance. Note that, this effect saturates when
Cr in more than 0.3% by mass is contained. Accordingly, in a case
of adding Cr, it is preferable to set the content thereof to 0.3%
by mass or less. In order to surely obtain the above effect, it is
preferable to set the content of Cr to 0.05% by mass or more.
[0081] Containing Mo, the titanium alloy material has higher
crevice corrosion resistance and higher resistance against sulfuric
acid. Note that, this effect saturates when Mo in more than 0.5% by
mass is contained. Further, processability is reduced by the
addition of Mo. Accordingly, in a case of adding Mo, it is
preferable to set the content thereof to 0.5% by mass or less. In
order to surely obtain the above effect, it is preferable to set
the content of Mo to 0.05% by mass or more.
EXAMPLE 1
[0082] To confirm effects of the present invention, samples having
different contamination amounts of Fe and S were fabricated and
corrosion resistance testing was conducted.
1. Method of Fabricating Sample used for Corrosion Resistance
Testing
[0083] Base materials used for the samples each have a sheet
thickness of 3 mm, are Gr. 11, Gr. 13, Gr. 17, Gr. 33 materials
according to the ASTM standard and a laboratory sample material
(fabricated by performing vacuum arc remelting (VAR), hot forging,
and hot rolling in order), and have compositions shown in Table 1.
After defatting and ultrasonic cleaning were performed on these
base materials, the following treatment was performed in order to
reproduce contamination at the time of manufacture using actual
equipment.
TABLE-US-00001 TABLE 1 Base Material C H O N Fe Pd Ru Ni Cr Mo Ti
Gr. 11 0.011 0.0014 0.098 0.0046 0.005 0.17 -- -- -- -- Remain Gr.
13 0.004 0.0008 0.09 0.0058 0.02 -- 0.044 0.52 -- -- Remain Gr. 17
0.004 0.0002 0.0033 0.003 0.025 0.054 -- -- -- -- Remain Gr. 33
0.006 0.001 0.045 0.002 0.016 0.015 0.025 0.42 0.15 -- Remain
Sample 0.005 0.0011 0.068 0.003 0.02 0.051 -- -- -- 0.17 Remain %
by mass
[0084] Table 2 shows conditions for fabrication of samples provided
for the corrosion testing and contamination amounts of Fe and S in
the samples. In order to easily fabricate samples having different
degrees of Fe and S contamination, the mixing rates of iron powder
in a rolling lubricating agent and an extreme-pressure additive to
be applied onto the base materials were adjusted in a manner that
the contamination amounts of Fe and S became different among the
samples (Example 4 to Example 16 and Comparative Example 1 to
Comparative Example 12 in Table 2).
TABLE-US-00002 TABLE 2 Mixing rate of Treatment Rate of palm Mixing
extreme- with aqueous Kolen oil-derived rate of iron pressure
solution of treatment Fluonitric component in powder in additive in
ferric with alkali acid Fe S Base rolling lubri- rolling lubri-
rolling lubri- chloride molten cleaning area area Classifi- Mate-
cating oil cating oil cating oil on hot rolled salt bath time ratio
ratio cation rial (% by mass) (% by mass) (% by mass) sheet
(470.degree. C.) (second) (%) (%) Remarks Example 1 Gr. 11 100 --
-- Yes -- 10 0.004 0.004 -- (clean material) Example 2 Gr. 13 100
-- -- Yes -- 10 0.006 0.007 -- (clean material) Example 3 Gr. 17
100 -- -- Yes -- 10 0.002 0.002 -- (clean material) Example 4 Gr.
11 99.90 0.10 -- -- -- 10 0.09 0.002 Fe contamination Example 5 Gr.
11 99.95 0.05 -- -- -- 10 0.03 0.004 Fe contamination Example 6 Gr.
11 95 -- 5 -- -- 10 0.008 0.03 S contamintaion Example 7 Gr. 11 90
-- 10 -- -- 10 0.009 0.09 S contamintaion Example 8 Gr. 11 97.74
0.08 2.18 -- -- 10 0.05 0.02 Complex contamination Example 9 Gr. 13
99.90 0.10 -- -- -- 10 (per- 0.0094 0.002 Fe contamination formed
twice, before and after annealing) Example 10 Gr. 17 99.90 0.10 --
-- -- 10 0.08 0.003 Fe contamination Example 11 Gr. 17 95 -- 5 --
-- 10 0.003 0.04 S contamintaion Example 12 Gr. 17 97.74 0.08 2.18
-- -- 10 0.06 0.03 Complex contamination Example 13 Gr. 11 92.92
0.08 7.00 -- -- 10 0.06 0.070 Complex contamination Example 14 Gr.
33 99.90 0.10 -- -- -- 10 0.09 0.003 Fe contamination Example 15
Sample 92.92 0.08 7.00 -- -- 10 0.05 0.07 Complex contamination
Example 16 Gr. 17 99.50 0.50 -- -- Yes 10 0.007 0.006 -- (Kolene
treatment) Comparative Gr. 11 99.90 0.10 -- -- -- 5 * 0.13 0.008 Fe
contamination Example 1 Comparative Gr. 11 99.50 0.50 -- -- -- 10 *
2.4 0.007 Fe contamination Example 2 Comparative Gr. 11 80.00 --
20.00 -- -- 10 0.008 * 2.110.sup. S contamintaion Example 3
Comparative Gr. 11 70.00 -- 30.00 -- -- 10 0.009 * 3.900.sup. S
contamintaion Example 4 Comparative Gr. 11 84.85 0.15 15 -- -- 10 *
0.22 * 1.840.sup. Complex Example 5 contamination Comparative Gr.
11 84.50 0.50 15 -- -- 10 * 2.20 * 1.640.sup. Complex Example 6
contamination Comparative Gr. 11 87.85 0.15 12 -- -- 10 * 0.30 *
0.300.sup. Complex Example 7 contamination Comparative Gr. 17 99.5
0.50 -- -- -- 10 * 1.72 0.008 Fe contamination Example 8
Comparative Gr. 17 75.00 -- 25.00 -- -- 10 0.007 * 2.470.sup. S
contamintaion Example 9 Comparative Gr. 17 87.67 0.15 12.18 -- --
10 * 0.940.sup. * 1.020.sup. Complex Example 10 contamination
Comparative Gr. 13 99.5 0.50 -- -- -- 10 * 2.110.sup. 0.006 Fe
contamination Example 11 Comparative Gr. 13 86 -- 14 -- -- 10 0.008
* 1.140.sup. S contamintaion Example 12 * indicates an item beyond
the scope of the present invention.
(i) Fe Contamination
[0085] FEE13PB iron powder (purity: 2 Nup, grain size: 3 to 5
.mu.m) produced by Kojundo Chemical Laboratory Co., Ltd. was mixed
to rolling lubricating oil containing palm oil as a main component
in various amounts (% by mass) as shown in Table 2, this rolling
lubricating oil was applied onto the base materials with a sheet
thickness of 4 mm, and the base materials were rolled so that the
sheet thickness became 3 mm. In this manner, remaining shot pieces
at the time of shot peening were imitated, and samples having
different amounts of Fe contamination (Fe contamination degrees)
were obtained.
(ii) S Contamination
[0086] DAILUBE GS-440L olefin metal working oil (preliminary
sulfurizing agent containing sulfur in 40%) which is an
extreme-pressure additive produced by DIC Corporation was mixed to
rolling lubricating oil in % by mass as shown in Table 2, this
rolling lubricating oil was applied onto the base materials with a
sheet thickness of 4 mm, and the base materials were rolled so that
the sheet thickness became 3 mm. In this manner, samples having
different amounts of S contamination (S contamination degrees) were
obtained.
(iii) Fe and S Complex Contamination
[0087] By combining treatment in (i) and (ii), samples that are
complex-contaminated by Fe and S were obtained.
(iv) Samples without Contamination Treatment
[0088] Samples denoted by "(clean material)" (Example 1 to Example
3) in Table 2 were not subjected to contamination treatment of Fe
and S. That is, these samples were obtained by applying a rolling
lubricating agent, to which neither Fe (iron powder) nor S
(extreme-pressure additive containing sulfur) were added, onto base
materials with a sheet thickness of 4 mm, and by rolling the base
materials so that the sheet thickness became 3 mm.
(v) Treatment After Rolling
[0089] After defatting, the rolled materials obtained through
treatment (i) to (iv) were subjected to annealing treatment in an
Ar atmosphere furnace at 750.degree. C. for 30 minutes, and then to
fluonitric acid cleaning to be provided for corrosion testing. A
sample denoted by "(Kolene treatment) (Example 16) in Table 2 was
obtained by performing Kolene treatment after the above described
treatment of Fe contamination and before fluonitric acid cleaning.
For some samples, in order to obtain the surface as defined in the
present invention, the Kolene treatment or treatment using an
aqueous solution of ferric chloride (including brushing treatment)
was performed. Further, for a sample (Example 9), fluonitric
cleaning was performed twice, which is before and after
annealing.
2. Method of Measuring Surface Contamination Degree
[0090] The samples before corrosion treatment were subjected to
surface analysis with the EPMA surface analysis apparatus.
(2-1) Conditions for EPMA Analysis
[0091] Apparatus: JXA-8530F produced by JEOL Ltd.
[0092] Accelerating voltage: 15 kv
[0093] Irradiation current: 100 nA
[0094] Number of measured points (pixels): 500.times.500
[0095] Shape of beam: spot
[0096] Measured pitch: 0.4 .mu.m
[0097] Measured time: 30 msec (for each point)
[0098] Spectroscopic crystals used: LIFH (for Fe K.alpha.-ray),
PETH (for S K.alpha.-ray), LIF (for Ti K.alpha.-ray), LIFH (for Zn
K.alpha.-ray)
(2-2) Measurement of Background Intensity of Fe, S, and Zn
Analysis
[0099] High-purity Ti of standards (UHV STANDARDS) for electron
spectroscopy for chemical analysis (ESCA), auger electron
spectroscopy (AES), and EPMA was analyzed under the above described
conditions, background count intensity of Fe, S, and Zn was
measured at 500.times.500 points arranged in a lattice, and average
values N(Fe), N(S), and N(Zn) of background counts (intensity) of
the respective elements were calculated.
[0100] According to Non-Patent Document 1 above, when the average
value of a plurality of measured values N is set to N.sub.0, the
ratio of the measured value N being beyond the range of
N.sub.0.+-.3N.sub.0.sup.1/2 is 0.3%. Accordingly, by substituting
the average value of background intensity to N.sub.0 in this
equation, the obtained value can be set as the threshold to
distinct a signal whose intensity is raised by an existing element
from the background signal. The threshold intensity for Fe, S, and
Zn is as follows.
[0101] Fe threshold intensity: N(Fe)+3N(Fe).sup.1/2
[0102] S threshold intensity: N(S)+3N(S).sup.1/2
[0103] Zn threshold intensity: N(Zn)+3N(Zn).sup.1/2
[0104] In the present Example, specific values of the threshold
intensity for Fe, threshold intensity for S, and threshold
intensity for Zn are 25 counts (cnt), 15 cnt, and 50 cnt,
respectively.
[0105] When a count having intensity higher than the above
threshold intensity, 99.85% of the time, there is an element
corresponding to the threshold intensity at the measured point, and
a signal from the element is measured.
[0106] Among the 500.times.500 measured points, the rate of points
at which the intensity higher than the threshold intensity is
counted is defined as contamination area ratio. For example, in a
case in which the intensity higher than the threshold intensity is
counted at 300 points, the contamination area ratio is as
follows.
Contamination area ratio=300/(500.times.500)=0.12%
In Table 2, Table 4, and Table 5, the contamination amounts of Fe
and S in the samples are shown as the contamination area ratios of
Fe and S (Fe area ratio and S area ratio).
[0107] FIG. 4 and FIG. 5 shows results of the surface mapping
analysis with an EPMA surface analysis apparatus for the samples
according to the present invention and the samples not according to
the present invention. As for Fe, S, and Zn, points are binarized
depending on whether or not the value is higher than the threshold
intensity; a point having intensity less than or equal to the
threshold intensity is shown in black, and a point having intensity
over the threshold intensity is shown in white.
[0108] FIG. 4 shows results of analysis of the sample of "Example 3
(clean material)" in Table 2. In this sample, it is found that, for
each of Fe, S, and Zn, there are almost no points having intensity
over the threshold intensity.
[0109] FIG. 5 shows results of analysis of the sample of
"Comparative Example 6" in Table 2. This sample was obtained by
performing contamination treatment of both Fe and S. From the
analysis results in FIG. 5, it is found that, for both Fe and S,
there are points having intensity over the threshold intensity
throughout the analyzed region.
(2-3) Measurement of Quantitative Concentration of Contaminants
[0110] Quantitative concentration of contaminants can be measured
by using general analyzing means such as EPMA or AES. In Examples,
in order to measure surface contamination, a field emission-auger
electron spectroscopy (FE-AES) by which information on the vicinity
of the surface is obtained was employed as the analyzing means. The
analyzing conditions are as follows.
[0111] Apparatus: Model 680 produced by ULVAC-PHI Incorporated.
[0112] Primary beam: Accelerated voltage 10 kV, Sample current 10
nA
[0113] Detection depth: Several nanometers (for Ti and Fe, 3 to 5
nm)
[0114] On the basis of the obtained measurement results, the ratio
of Fe content (atomic %)/Ti content (atomic %) was calculated. The
results are shown in Table 5.
3. Evaluation of Corrosion Resistance
[0115] In order to study the influence of surface contamination on
the corrosion resistance, an environment in which a titanium alloy
containing a platinum group metal is used was imitated, and testing
based on general crevice corrosion resistance testing was
conducted.
[0116] FIG. 6 is a schematic diagram of a sample used for corrosion
testing and a schematic diagram of a sample for crevice corrosion
testing. As shown in FIG. 6(a) and FIG. 6(b), a sample 1 provided
for corrosion testing has a thickness of 3 mm and a plane shape of
a 30-mm square, in which, in a central portion, a hole with a
diameter of 7 mm is formed. Two samples 1 formed under the same
conditions were disposed on opposite sides of a crevice formation
film (crevice formation material) 2 as shown in FIG. 6(c). A bolt
of a CP Ti bolt-nut 4 was made to penetrate the hole of the sample
1, and the CP Ti bolt-nut 4 was tightened between the samples 1 via
a PTFE bush 3. In this manner, a sample for crevice corrosion
testing 5 was obtained.
[0117] The surface skin of the samples 1 was made to maintain the
state at the time when the treatment described in the section "1.
Method of fabricating sample used for corrosion resistance testing"
above was completed. As the crevice formation film 2, a NEOFLON
(trademark) PCTFE film (thickness: 50 .mu.m) produced by DAIKIN
INDUSTRIES, LTD. was used. As the CP Ti bolt-nut 4, a bolt-nut that
was heated by a gas burner, the surface of which was oxidized
sufficiently, was used. The tightening torque of the CP Ti bolt-nut
4 was 40 kgfcm (1 kgf is approximately 9.8 N).
[0118] In order to conduct acceleration testing that reveals the
influence of contamination on the corrosion resistance, the sample
was subjected to treatment using an autoclave (autoclave
treatment). Prior to the autoclave treatment, as a pre-measurement
of testing, the weight of the samples 1 was measured by a precision
balance. The weight of the samples 1 was in a range from 11 to 11.5
g. After that, the sample for crevice corrosion testing 5 was
subjected to treatment using the autoclave. Conditions for the
autoclave treatment are shown in Table 3.
TABLE-US-00003 TABLE 3 Apparatus used hastelloy C276-lined
autoclave Condition for solution pH = 2, 250 g/L-NaCl Condition for
corrosion 150.degree. C. .times. 1000 hours treatment
[0119] After the treatment was completed, the CP Ti bolt-nut 4 was
untightened and the sample for crevice corrosion testing 5 was
decomposed. The samples 1 were subjected to ultrasonic cleaning in
which cleaning water was exchanged three times, and dried
sufficiently, and then the weight thereof was measured by the
precision balance. Further, a corrosion weight loss D was
calculated from the following equation.
Corrosion weight loss D (mg)=Weight after corrosion treatment
(mg)-Weight before corrosion treatment (mg)
[0120] The weight of each of the two samples 1 (on the bolt side
and on the nut side) of the sample for crevice corrosion testing 5
was measured, and the average value of the corrosion weight losses
of these two samples was set as the corrosion weight loss D of the
sample for crevice corrosion testing 5.
[0121] According to results of the corrosion weight loss
measurement, some samples 1 showed a minute amount of increase in
weight, not a loss or 0; however, this increase in weight is
considered to be caused by oxidation, so that the corrosion weight
loss D of such samples 1 is assumed to be 0.
[0122] Further, the increased amount (the absorbed amount) of
hydrogen H was calculated from the following equation.
Increased amount of hydrogen H (ppm)=Hydrogen content rate (ppm) in
the sample 1 (bulk) after corrosion treatment-Hydrogen content rate
(ppm) in the sample 1 (bulk) before corrosion treatment
[0123] Table 4 shows base materials of the samples 1 provided for
the corrosion testing, the Fe area ratios, the S area ratios, and
results of the corrosion testing.
TABLE-US-00004 TABLE 4 Increased Fe area S area Corrosion amount of
Base ratio ratio weight loss Surface hydrogen H in Classification
Material (%) (%) D (mg) roughening bulk (ppm) Remarks Example 1 Gr.
11 0.004 0.004 0.0 No 2 -- (clean material) Example 2 Gr. 13 0.006
0.007 0.0 No 3 -- (clean material) Example 3 Gr. 17 0.002 0.002 0.0
No 1 -- (clean material) Example 4 Gr. 11 0.09 0.002 0.0 Yes
(slightly) 12 Fe contamination Example 5 Gr. 11 0.03 0.004 0.0 Yes
(slightly) 11 Fe contamination Example 6 Gr. 11 0.008 0.03 0.0 No 5
S contamintaion Example 7 Gr. 11 0.009 0.09 0.0 No 4 S
contamintaion Example 8 Gr. 11 0.05 0.02 0.0 Yes (slightly) 13
Complex contamination Example 9 Gr. 13 0.0094 0.002 0.0 No 14 Fe
contamination Example 10 Gr. 17 0.08 0.003 0.0 Yes (slightly) 15 Fe
contamination Example 11 Gr. 17 0.003 0.04 0.0 No 7 S contamintaion
Example 12 Gr. 17 0.06 0.03 0.0 Yes (slightly) 10 Complex
contamination Example 13 Gr. 11 0.06 0.070 0.1 Yes (slightly) 19
Complex contamination Example 14 Gr. 33 0.09 0.003 0.0 Yes
(slightly) 11 Fe contamination Example 15 Sample 0.05 0.07 0.1 Yes
(slightly) 18 Complex contamination Example 16 Gr. 17 0.007 0.006
0.0 No 3 -- (Kolene treatment) Comparative Gr. 11 * 0.13 0.008 3.1
Yes 2 Fe contamination Example 1 Comparative Gr. 11 * 2.4 0.007
16.2 Yes 24 Fe contamination Example 2 Comparative Gr. 11 0.008 *
2.110.sup. 2.1 Yes 42 S contamintaion Example 3 Comparative Gr. 11
0.009 * 3.900.sup. 3.5 Yes 45 S contamintaion Example 4 Comparative
Gr. 11 * 0.22 * 1.840.sup. 4.1 Yes 63 Complex contamination Example
5 Comparative Gr. 11 * 2.20 * 1.640.sup. 18.7 Yes 73 Complex
contamination Example 6 Comparative Gr. 11 * 0.30 * 0.300.sup. 1.5
Yes 39 Complex contamination Example 7 Comparative Gr. 17 * 1.72
0.008 18.4 Yes 03 Fe contamination Example 8 Comparative Gr. 17
0.007 * 2.470.sup. 2.8 Yes 44 S contamintaion Example 9 Comparative
Gr. 17 * 0.940.sup. * 1.020.sup. 14.7 Yes 87 Complex contamination
Example 10 Comparative Gr. 13 * 2.110.sup. 0.006 17.3 Yes 26 Fe
contamination Example 11 Comparative Gr. 13 0.008 * 1.140.sup. 5.4
Yes 72 S contamintaion Example 12 * indicates an item beyond the
scope of the present invention.
[0124] From the testing results shown in FIG. 4, the following 1)
to 3) are found.
[0125] 1) The Fe area ratios of the samples of "Example 1 (clean
material)" to "Example 3 (clean material)", "Example 4" to "Example
7", "Example 9" to "Example 11", and "Example 14" (hereinafter
these samples are each referred to as "non-complex contamination
sample") were each 0.1% or less, and accordingly, the Fe
contamination degree on the surface was low. In the same manner,
the S area ratios of the non-complex contamination samples were
each 0.1% or less, and accordingly, the S contamination degree on
the surface was low.
[0126] Further, as for the non-complex contamination samples,
corrosion weight loss due to corrosion treatment was not
recognized, and it is obvious that the non-complex contamination
samples have high corrosion resistance. Furthermore, the increased
amount of hydrogen H due to corrosion treatment on the non-complex
contamination samples was 20 ppm or less. Among the non-complex
contamination samples, on samples whose Fe area ratio is 0.01% or
less (Examples 1 to 3, 6,7,11, and 16), surface roughening was not
recognized on the plane that became a crevice. Accordingly, the
samples have extremely high corrosion resistance, and the absorbed
amount of hydrogen is less than 10 ppm, which is extremely
small.
[0127] 2) Even when the Fe area ratio was 0.1% or less, corrosion
weight loss was recognized for the sample in which complex
contamination with S was recognized and the Fe area ratio and the S
area ratio each exceeded 0.05% (the sample of "Example 13" in Table
4). Further, the increased amount of hydrogen H of this sample is
larger than 15 ppm. In a case of Fe and S complex contamination, in
order to achieve a material having higher corrosion resistance, it
is preferable that each of the Fe area ratio and the S area ratio
is 0.05% or less.
[0128] 3) As described in the section "(v) Treatment after
rolling", the sample of Example 16 was obtained by performing
Kolene treatment after Fe contamination treatment (in which rolling
lubricating oil mixed with iron powder was applied and rolling was
performed) and before fluonitric acid cleaning. Although the sample
of Example 16 was subjected to Fe contamination treatment, it
showed almost as low Fe contamination area ratio as a clean
material, so that it is found that Kolene treatment is effective to
obtain a titanium alloy material having a clean surface.
[0129] From the above testing results, it is revealed that
corrosion resistance (crevice corrosion resistance: resistance
against corrosion accompanying surface roughening) that is much
higher than before can be secured by suppressing the contamination
amounts of Fe and S that are present on the surface of the titanium
alloy material.
EXAMPLE 2
[0130] Next, the influence of the concentration of Fe as a
contamination element was studied. Table 5 shows conditions for
fabricating samples provided for testing and evaluation
results.
[0131] Samples of Examples 17, 19, and 21 were each obtained by
rolling a base material with a thickness of approximately 4 mm
through two-time passes in a manner that the thickness of each
sample was reduced to 3.5 mm through the first pass and was again
reduced to 3.0 mm through the second pass. Meanwhile, samples of
Examples 18 and 20 were each obtained by rolling a base material
with a thickness of approximately 4 mm through one-time pass in a
manner that the thickness thereof became 3.0 mm. Further, samples
of Comparative Examples 13, 14, and 15 were each obtained by
rolling a base material with a thickness of approximately 4 mm
through one-time pass in a manner that the thickness thereof became
3.0 mm.
[0132] For each of the obtained samples, in arbitrarily selected
five regions, the Fe area ratio and the S area ratio were measured,
quantitative analysis was performed in a part of each region in
which maximum Fe intensity was obtained, and the ratio of the Fe
content (atomic %) to the Ti content (atomic %) was calculated. The
average values of the five regions are shown in Table 5 as Fe/Ti
(atomic ratio) representing each sample.
[0133] The samples of Example 17 to 21 and the samples of
Comparative Examples 13 to 15 were subjected to the autoclave
treatment (corrosion treatment) under the conditions shown in Table
3, and hydrogen content rates before and after the treatment were
analyzed.
TABLE-US-00005 TABLE 5 Mixing rate of Rate of palm Mixing extreme-
Hydrogen Hydrogen oil-derived rate of pressure Fluonitric content
content component in iron powder in additive in acid Corrosion rate
rate rolling lubri- rolling lubri- rolling lubri- cleaning Fe area
S area Fe/Ti weight before after Classi- Base cating oil cating oil
cating oil time ratio ratio (atomic loss treatment treatment
fication Material (% by mass) (% by mass) (% by mass) (second) (%)
(%) ratio) D (mg) (ppm) (ppm) Example 17 Gr. 11 99.90 0.10 4
.fwdarw. 3.5 .fwdarw. 3.0 10 0.08 0.003 0.37 0 42 53 Example 18 Gr.
11 99.90 0.10 4 .fwdarw. 3.0 10 0.09 0.002 0.67 0 42 113 Example 19
Gr. 17 99.90 0.10 4 .fwdarw. 3.5 .fwdarw. 3.0 10 0.07 0.003 0.41 0
38 44 Example 20 Gr. 17 99.90 0.10 4 .fwdarw. 3.0 10 0.08 0.003
0.65 0 38 106 Example 21 Gr. 17 99.88 0.12 4 .fwdarw. 3.5 .fwdarw.
3.0 10 0.09 0.004 0.78 0 38 122 Comparative Gr. 11 99.50 0.50 4
.fwdarw. 3.0 10 * 2.4 0.005 1.4 9.8 42 249 Example 13 Comparative
Gr. 13 99.40 0.60 4 .fwdarw. 3.0 10 * 3.2 0.007 2.1 10.2 35 274
Example 14 Comparative Gr. 17 99.50 0.50 4 .fwdarw. 3.0 10 * 2.2
0.004 1.7 9.6 38 241 Example 15 * indicates an item beyond the
scope of the present invention.
[0134] From Table 5, the following 1) to 5) are found.
[0135] 1) By the autoclave treatment (150.degree. C..times.1000
hours), none of the samples (Examples 17 to 21) according to the
present invention showed corrosion weight loss.
[0136] 2) As for samples whose Fe/Ti (atomic ratio) exceeded 0.5,
an increase in the hydrogen content rate was recognized by the
corrosion treatment. In these samples, it is assumed that the
amount of hydrogen after the corrosion treatment exceeded 100 ppm,
and hydrogen was increased by absorption over time.
[0137] 3) Among Examples 17 to 21, samples whose Fe/Ti (atomic
ratio) exceeded 0.5 (Examples 18, 20, and 21) are also within the
scope of the present invention. However, considering a case of
being used in an environment in which hydrogen embrittlement might
occur (high-temperature environment), it is preferable that Fe/Ti
(atomic ratio) is 0.5 or less.
[0138] 4) Samples that are beyond the scope of the present
invention (samples of "Comparative Example 13" to "Comparative
Example 15" in Table 5) had concave portions on the surface, and
large corrosion weight losses were recognized. Even if a Ti alloy
containing a platinum group metal is used, these samples cannot be
said to be corrosion-resistant against treatment under harsh
conditions (the above autoclave treatment). In these samples, it is
considered that the increased amount of hydrogen H due to treatment
is over 35 ppm and corrosion of these samples are related to
hydrogen absorption. The increased amount of hydrogen H of these
samples exceeded 200 ppm, which might cause hydrogen
embrittlement.
[0139] 5) Among the samples of Comparative Examples 13 to 15,
samples having high Fe area ratio and high Fe/Ti (atomic ratio) had
large corrosion weight losses and the hydrogen content rate after
corrosion treatment exceeded 200 ppm, which might cause hydrogen
embrittlement.
[0140] Heretofore, preferred embodiments of the present invention
have been described in detail with reference to the appended
drawings, but the present invention is not limited thereto. It
should be understood by those skilled in the art that various
changes and alterations may be made without departing from the
spirit and scope of the appended claims.
* * * * *