U.S. patent application number 14/423328 was filed with the patent office on 2015-08-13 for ni-based alloy having excellent hydrogen embrittlement resistance, and method for producing ni-based alloy material.
This patent application is currently assigned to THE JAPAN STEEL WORKS, LTD.. The applicant listed for this patent is THE JAPAN STEEL WORKS, LTD.. Invention is credited to Takashi Hatano, Eiji Maeda, Shinya Sato, Tatsuya Takahashi, Kouichi Takasawa.
Application Number | 20150225827 14/423328 |
Document ID | / |
Family ID | 50150009 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150225827 |
Kind Code |
A1 |
Takasawa; Kouichi ; et
al. |
August 13, 2015 |
NI-BASED ALLOY HAVING EXCELLENT HYDROGEN EMBRITTLEMENT RESISTANCE,
AND METHOD FOR PRODUCING NI-BASED ALLOY MATERIAL
Abstract
An object is to provide a Ni-based alloy having high strength
and excellent hydrogen embrittlement resistance even in a
high-temperature and high-pressure environment and particularly
capable of being used for an ammonothermal pressure vessel and the
like. The present invention relates to a Ni-based alloy including,
in terms of mass ratios, Fe: 30 to 40%, Cr: 14 to 16%, Ti: 1.2 to
1.7%, Al: 1.1 to 1.5%, Nb: 1.9 to 2.7%, and P: 40 to 150 ppm, with
the remainder being Ni and unavoidable impurities.
Inventors: |
Takasawa; Kouichi;
(Hokkaido, JP) ; Maeda; Eiji; (Hokkaido, JP)
; Sato; Shinya; (Hokkaido, JP) ; Hatano;
Takashi; (Hokkaido, JP) ; Takahashi; Tatsuya;
(Muroran-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE JAPAN STEEL WORKS, LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
THE JAPAN STEEL WORKS, LTD.
Tokyo
JP
|
Family ID: |
50150009 |
Appl. No.: |
14/423328 |
Filed: |
August 22, 2013 |
PCT Filed: |
August 22, 2013 |
PCT NO: |
PCT/JP2013/072431 |
371 Date: |
February 23, 2015 |
Current U.S.
Class: |
148/707 ;
420/584.1 |
Current CPC
Class: |
C22C 19/05 20130101;
C22C 19/058 20130101; C22F 1/10 20130101; C22C 30/00 20130101 |
International
Class: |
C22F 1/10 20060101
C22F001/10; C22C 30/00 20060101 C22C030/00; C22C 19/05 20060101
C22C019/05 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2012 |
JP |
2012-184966 |
Claims
1. A Ni-based alloy comprising, in terms of mass ratios, Fe: 30 to
40%, Cr: 14 to 16%, Ti: 1.2 to 1.7%, Al: 1.1 to 1.5%, Nb: 1.9 to
2.7%, and P: 40 to 150 ppm, with the remainder being Ni and
unavoidable impurities.
2. The Ni-based alloy according to claim 1, which further comprises
at least either one of Mg: 0.01% or less and Zr: 0.1% or less in
terms of mass ratios.
3. The Ni-based alloy according to claim 1, wherein a hydrogen
embrittlement index EI defined by EI=(RA.sub.A-RA.sub.H)/RA.sub.A
when a reduction of area of a hydrogen charged material and a
reduction of area of a hydrogen non-charged material at a tensile
test are indicated as RA.sub.H and RA.sub.A, respectively, is 0.1
or less at 625.degree. C.
4. The Ni-based alloy according to claim 1, wherein a creep rupture
time at 700.degree. C. and 333 MPa is 1,500 hours or more.
5. The Ni-based alloy according to claim 1, wherein a minimum creep
rate at 700.degree. C. and 333 MPa is 1.times.10.sup.-8 s.sup.-1 or
less.
6. The Ni-based alloy according to claim 1, which is used as an
ammonothermal pressure vessel material.
7. A method for producing a Ni-based alloy material, said method
comprising subjecting the Ni-based alloy according to claim 1 to a
solution treatment and subsequently to an aging treatment twice at
a temperature of 825 to 855.degree. C. and at a temperature of 710
to 740.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention relates to a Ni-based alloy having
excellent hydrogen embrittlement resistance and a method for
producing a Ni-based alloy material.
BACKGROUND ART
[0002] An ammonothermal method has been known as a kind of single
crystal growing method and the ammonothermal method has been, for
example, applied to single crystal growth of gallium nitride that
is a nitride semiconductor for a blue light emitting diode.
[0003] Gallium nitride has been expected to be utilized as an
optical device such as a high-brightness LED and a semiconductor
laser, and an electronic device for use in a transistor for
electric vehicle, an amplifier for mobile phone base station, or
the like. For the application to these devices, it is necessary to
enlarge the size of the gallium nitride single crystal and a size
of 2 inches or more to 6 inches or more, further a size larger than
that has been desired.
[0004] Hitherto, a vapor-phase growth method has been a main stream
for the growth of the gallium nitride single crystal. However, for
coping with the enlargement and mass production of the crystal as
described above or cost reduction, the method is being replaced by
the ammonothermal method in which a crystal is grown in
high-temperature and high-pressure ammonia. Since a temperature of
600 to 650.degree. C. and a pressure of 200 to 250 MPa are
generally used as synthetic conditions in the ammonothermal method,
application of a Ni--Fe-based alloy is attempted as a pressure
vessel material having high strength under a high-temperature
environment.
[0005] Since operations are conducted under high temperature and
high pressure in the ammonothermal method, ammonia as a raw
material is decomposed to generate a large amount of high-pressure
hydrogen. Therefore, as characteristics required for the pressure
vessel material, excellent hydrogen embrittlement resistance at
high temperature is first mentioned. In addition, since the vessel
is used under a high-temperature environment, creep properties are
also required.
[0006] Hitherto, some techniques relating to a Ni--Fe-based alloy
having high strength and excellent hydrogen embrittlement
resistance have been developed. For example, Patent Document 1
discloses a technique relating to an Fe--Ni-based alloy having high
strength and excellent hydrogen embrittlement resistance, which is
used as a high-pressure hydrogen piping material for hydrogen
station. The document presents a two-layer structure piping
material consisting of an outer layer having high strength imparted
thereto by aging and an inner layer having hydrogen embrittlement
resistance imparted thereto.
[0007] Patent Document 2 discloses a Ni--Fe alloy in which high
strength and hydrogen embrittlement resistance are exhibited by
controlling particle size of the .gamma.' phase and fractions of
individual precipitation phases.
[0008] Moreover, Patent Document 3 discloses a technique dealing
with hydrogen embrittlement resistance and the like at high
temperature.
BACKGROUND ART DOCUMENT
Patent Document
[0009] Patent Document 1: JP-A-2010-174360
[0010] Patent Document 2: JP-A-2009-68031
[0011] Patent Document 3: JP-A-5-255788
SUMMARY OF THE INVENTION
Problems that the Invention is to Solve
[0012] However, the temperature at which the alloys have high
strength and excellent hydrogen embrittlement resistance is room
temperature in Patent Documents 1 and 2 and it is unclear whether
these characteristics may be assured or not under high temperature
and high pressure. Moreover, although Patent Document 3 deals with
a high Ni-based alloy having high strength and excellent hydrogen
embrittlement resistance, which is usable at 200 to 500.degree. C.,
it is considered that characteristics at 600 to 650.degree. C.,
which are problems of the present invention, cannot be secured in
the alloy and also characteristics under high pressure cannot be
assured at all.
[0013] As mentioned above, any of the conventional Ni--Fe-based
alloys having high strength and excellent hydrogen embrittlement
resistance cannot assure those characteristics under the conditions
dealt with in the present invention.
[0014] The present invention has been made based on the above
circumstances and an object thereof is to provide a Ni-based alloy
having high strength and excellent hydrogen embrittlement
resistance even in a high-temperature and high pressure
environment, such as 600 to 650.degree. C. and 200 to 250 MPa, and
a method for producing a Ni-based alloy material.
Means for Solving the Problems
[0015] The present inventors have found that a Ni-based alloy
having high strength and excellent hydrogen embrittlement
resistance even under high temperature and high pressure is
obtained by restricting the composition of the Ni-based alloy to a
specific range and thus they have accomplished the present
invention. Namely, the gist of the invention lies on the following
<1> to <7>.
<1> A Ni-based alloy including, in terms of mass ratios, Fe:
30 to 40%, Cr: 14 to 16%, Ti: 1.2 to 1.7%, Al: 1.1 to 1.5%, Nb: 1.9
to 2.7%, and P: 40 to 150 ppm, with the remainder being Ni and
unavoidable impurities. <2> The Ni-based alloy according to
<1>, which further includes at least either one of Mg: 0.01%
or less and Zr: 0.1% or less in terms of mass ratios. <3> The
Ni-based alloy according to <1> or <2>, in which a
hydrogen embrittlement index EI defined by
EI=(RA.sub.A-RA.sub.H)/RA.sub.A when a reduction of area of a
hydrogen charged material and a reduction of area of a hydrogen
non-charged material at a tensile test are indicated as RA.sub.H
and RA.sub.A, respectively, is 0.1 or less at 625.degree. C.
<4> The Ni-based alloy according to any one of <1> to
<3>, in which a creep rupture time at 700.degree. C. and 333
MPa is 1,500 hours or more. <5> The Ni-based alloy according
to any one of <1> to <4>, in which a minimum creep rate
at 700.degree. C. and 333 MPa is 1.times.10.sup.-8 s.sup.-1 or
less. <6> The Ni-based alloy according to any one of
<1> to <5>, which is used as an ammonothermal pressure
vessel material. <7> A method for producing a Ni-based alloy
material, the method including subjecting the Ni-based alloy
according to <1> or <2> to a solution treatment and
subsequently to an aging treatment twice at a temperature of 825 to
855.degree. C. and at a temperature of 710 to 740.degree. C.
Advantage of the Invention
[0016] According to the present invention, it becomes possible to
provide a Ni-based alloy having good hydrogen embrittlement
resistance at such a high temperature as 600.degree. C. or higher
and excellent creep properties in such a higher-temperature region
as 700.degree. C. Furthermore, as a secondary effect, application
of the Ni-based alloy to a pressure vessel material for an
ammonothermal method enables production of a pressure vessel
capable of coping with a higher-temperature and higher-pressure
environment and thus, for example, it is expected that enlargement,
mass production, and cost reduction of a gallium nitride single
crystal useful as an electronic device may be remarkably
advanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a relationship between hydrogen embrittlement
index and P content of invention materials and comparative
materials.
[0018] FIG. 2 shows a relationship between creep stress and creep
rupture time of the invention materials and the comparative
materials.
[0019] FIG. 3 shows a relationship between creep test time and
creep rate of the invention materials and the comparative
materials.
MODE FOR CARRYING OUT THE INVENTION
[0020] The following will explain embodiments of the present
invention in detail but the invention is not limited to the
following explanations and can be carried out with appropriately
changing it in the range without departing from the gist of the
invention.
[0021] Here, "% by weight", "ratio by weight", and "ppm by weight"
are the same as "% by mass", "ratio by mass", and "ppm by mass",
respectively.
[0022] The Ni-based alloy according to the invention includes, in
terms of mass ratios, Fe: 30 to 40%, Cr: 14 to 16%, Ti: 1.2 to
1.7%, Al: 1.1 to 1.5%, Nb: 1.9 to 2.7%, and P: 40 to 150 ppm, with
the remainder being Ni and unavoidable impurities.
[0023] Moreover, it is more preferable that the Ni-based alloy
further includes at least either one of Mg: 0.01% or less and Zr:
0.1% or less.
[0024] The following will explain reasons for determining the
above-mentioned alloy composition. Hereinafter, the content of each
element other than P is shown in terms of % by mass and the content
of P is shown in terms of ppm by mass.
Fe: 30 to 40%
[0025] Fe is effective for cost reduction of the alloy when the
content thereof increases but a Laves phase forms when Fe is
excessively incorporated together with Nb incorporation and the
formation invites deterioration of material characteristics, such
as an increase in hydrogen embrittlement susceptibility. Therefore,
the content of Fe is controlled to 30 to 40%. For the same reason,
it is preferable to determine the lower limit thereof to 33% and
the upper limit thereof to 38%.
Cr: 14 to 16%
[0026] Cr is an element necessary for enhancing oxidation
resistance, corrosion resistance, and strength. Also, it combines
with C to form a carbide, thereby enhancing high-temperature
strength. However, too large content thereof invites
destabilization of matrix and promotes the formation of harmful TCP
phases such as a .sigma. phase and .alpha.-Cr, resulting in adverse
influences on ductility and toughness. Also, there is a concern
that the .sigma. phase acts as a hydrogen accumulation site in the
alloy to enhance the hydrogen embrittlement susceptibility.
Therefore, the content of Cr is limited to 14 to 16%.
Ti: 1.2 to 1.7%
[0027] Ti mainly forms a MC carbide to suppress crystal grain
coarsening of the alloy and also combines with Ni to precipitate a
.gamma.' phase, thereby contributing to precipitation strengthening
of the alloy. However, when Ti is exceedingly incorporated, the
stability of the .gamma.' phase at high temperature is lowered and
an .eta. phase is formed, thereby impairing strength, ductility,
toughness, and high-temperature long-term structural stability.
Moreover, there is a concern that the .eta. phase also acts as a
hydrogen accumulation site in the alloy to enhance the hydrogen
embrittlement susceptibility. Therefore, the content of Ti is
limited to the range of 1.2 to 1.7%.
Al: 1.1 to 1.5%
[0028] Al combines with Ni to precipitate a .gamma.' phase, thereby
contributing to precipitation strengthening of the alloy. However,
when the content thereof is too large, the .gamma.' phase
aggregates at grain boundaries and is coarsened, thereby
drastically impairing mechanical properties at high temperature and
also lowering hot workability. Therefore, the content of Al is
limited to 1.1 to 1.5%.
Nb: 1.9 to 2.7%
[0029] Nb is an element that stabilizes the .gamma.' phase and
contributes to strength enhancement but when Nb is exceedingly
incorporated, the precipitation of the .eta. phase, the .sigma.
phase, and the Laves phase that are harmful phases is promoted,
thereby remarkably lowering the structural stability and enhancing
the hydrogen embrittlement susceptibility. Therefore, the content
of Nb is limited to 1.9 to 2.7%.
P: 40 to 150 ppm
[0030] P is considered to have an effect of suppressing excessive
accumulation of hydrogen at grain boundaries by increasing
consistency of the grain boundaries and lowering the hydrogen
embrittlement susceptibility, so that P is incorporated. In order
to obtain the above effect, a P content of 40 ppm or more is
necessary. Also, P has effects of lengthening the creep rupture
time and decreasing the minimum creep rate. However, when P is
exceedingly incorporated, there is a possibility that grain
boundary segregation of P becomes excessive to contrarily lower the
consistency of the grain boundaries and the effect of reducing the
hydrogen embrittlement susceptibility is lost. Therefore, the
content of P is limited to 40 to 150 ppm. For the same reason, it
is preferable to determine the lower limit thereof to 45 ppm and
the upper limit thereof to 140 ppm.
Mg: 0.01% or Less
[0031] Mg mainly combines with S to form a sulfide and enhances hot
workability, so that Mg is incorporated as desired. However, when
the content thereof is too large, the grain boundaries are
contrarily embrittled and hot workability decreases, so that the
content of Mg is preferably controlled to 0.01% or less.
Incidentally, for sufficiently exhibiting the above effect, the
lower limit of the Mg content is more preferably controlled to
0.0005% or more.
Zr: 0.1% or Less
[0032] Zr segregates at grain boundaries to contribute to an
improvement in high-temperature characteristics, so that Zr is
incorporated as desired. However, when Zr is exceedingly
incorporated, the hot workability of the alloy is lowered, so that
the content of Zr is preferably controlled to 0.1% or less.
Moreover, in order to obtain the above effect, it is more
preferable to incorporate it in an amount of 0.01% or more.
[0033] It is preferable that at least either one of Mg and Zr is
contained in the above ranges but it is more preferable to contain
both of Mg and Zr in view of securing good hot workability.
[0034] The remainder in the Ni-based alloy according to the
invention is Ni and unavoidable impurities.
[0035] The unavoidable impurities mean elements which are initially
contained in raw materials of the alloy or are unavoidably mixed in
during the smelting of the alloy, and examples thereof include O, N
and S. The content of the unavoidable impurities in the whole
Ni-based alloy is preferably as low as possible and is more
preferably 50 ppm or less in view of high purification of the
alloy.
[0036] The Ni-based alloy of the invention has excellent hydrogen
embrittlement resistance and can be suitably used as a material to
be exposed to a hydrogen atmosphere. Also, it is excellent in high
strength characteristic at high temperature and can be suitably
used as an ammonothermal pressure vessel material.
[0037] The Ni-based alloy of the invention can be smelted by a
usual method and, as the invention, the smelting method is not
particularly limited.
[0038] The Ni-based alloy of the invention can be subjected to
processing such as forging as desired and can be subjected to a
solution treatment or a thermal treatment by aging (aging
treatment).
[0039] The solution treatment can be performed, for example, under
conditions of 1,040 to 1,140.degree. C. for 4 to 10 hours.
Moreover, the aging treatment is preferably a treatment performed
in at least two stages. For example, the aging treatment can be
performed twice at a temperature of 825 to 855.degree. C. and at a
temperature of 710 to 740.degree. C. As the temperature for the
aging treatment, the treatment is preferably performed first at a
temperature of 825 to 855.degree. C. (first stage) and subsequently
at a temperature of 710 to 740.degree. C. (second stage) in this
order. Furthermore, the time for the aging treatment is more
preferably from 4 to 10 hours at the first stage and from 4 to 24
hours at the second stage.
[0040] By adopting the above-mentioned conditions for the solution
treatment and the aging treatment, high tensile strength at room
temperature and high tensile strength at a high temperature of
600.degree. C. or higher can be secured and a Ni-based alloy
material having excellent hydrogen embrittlement resistance can be
obtained. The resulting tensile strength is preferably 1,000 MPa or
more at room temperature and 820 MPa or more at 625.degree. C.
[0041] Incidentally, when the temperature at the first stage of the
aging treatment is lower than 825.degree. C. or higher than
855.degree. C., there is a concern that the .gamma.' phase cannot
be sufficiently grown and the above tensile strength cannot be
secured.
[0042] Moreover, M.sub.23C.sub.6 type carbide precipitates in
excess when the temperature at the second stage of the aging
treatment is lower than 710.degree. C., and MC type carbide is
coarsened when the temperature is higher than 740.degree. C.
Thereby, there is a concern that adverse influences such as a
decrease in high-temperature ductility are caused in both
cases.
[0043] Among the Ni-based alloys obtained in the above, more
preferred is the Ni-based alloy affording such hydrogen
embrittlement resistance that hydrogen embrittlement index EI
defined by EI=(RA.sub.A-RA.sub.H)/RA.sub.A when a reduction of area
of a hydrogen charged material and a reduction of area of a
hydrogen non-charged material at a tensile test are indicated as
RA.sub.H and RA.sub.A, respectively, is 0.1 or less at 625.degree.
C. The hydrogen charge is simulated by intrusion of a hydrogen
quantity of 50 ppm.
[0044] Moreover, among the Ni-based alloys obtained in the above,
more preferred is also the Ni-based alloy affording such a
high-temperature creep property that a creep rupture time at
700.degree. C. and 333 MPa is 1,500 hours or more.
[0045] Furthermore, among the Ni-based alloys obtained in the
above, more preferred is also the Ni-based alloy affording such a
high-temperature creep property that a minimum creep rate at
700.degree. C. and 333 MPa is 1.times.10.sup.-8 s.sup.-1 or
less.
[0046] Incidentally, the Ni-based alloy having the above-mentioned
hydrogen embrittlement index and high-temperature creep properties
can be obtained by satisfying the compositional requirements
mentioned above, and particularly containing P in an amount of 40
ppm or more.
[0047] The material using the Ni-based alloy according to the
invention can be used for any desired uses capable of exhibiting
the hydrogen embrittlement resistance through plastic working or
machining, and particularly can be suitably used as an
ammonothermal pressure vessel material. Thereby, it becomes
possible to realize the enlargement, mass production, and cost
reduction of a gallium nitride single crystal, for example.
EXAMPLES
[0048] The following will explain examples of the present
invention.
[0049] Smelting and forging of a material of 50 kg round steel
ingot were performed by a vacuum induction melting method to form
plates so as to achieve compositions shown in Table 1, in order to
obtain two kinds of invention materials and two kinds of
comparative materials, respectively.
[0050] The obtained forged plates were cut into ones having an
appropriate size, which were then subjected to a solution treatment
of 1,040.degree. C..times.4 hours and to a two-stage aging
treatment of 840.degree. C..times.10 hours and subsequent
730.degree. C..times.24 hours, thereby obtaining test materials
(invention materials P1, P2 and comparative materials 1, 2).
Subsequently, the test materials were machined to form tensile test
pieces for evaluation of hydrogen embrittlement resistance and
creep test pieces.
TABLE-US-00001 TABLE 1 Chemical composition of test material (% by
mass; ppm by mass for P, S, N, and O) P S N O Test material C Si Mn
(ppm) (ppm) Ni Cr Al Ti Nb Fe Mg Zr (ppm) (ppm) Invention 0.011
0.01 0.01 45 2 41.40 15.41 1.26 1.45 2.05 38.26 0.0015 0.030 13 16
material (P1) Invention 0.012 0.01 0.01 130 2 41.37 15.40 1.26 1.44
2.06 38.30 0.0015 0.030 12 15 material (P2) Comparative 0.011 0.01
0.02 33 <1 41.66 15.10 1.11 1.68 2.06 38.20 <0.0005 <0.010
31 7 material 1 Comparative 0.011 0.01 0.01 8 3 41.39 15.40 1.24
1.41 2.08 38.24 0.0012 0.036 7 16 material 2
[0051] Evaluation of the hydrogen embrittlement resistance was
performed by the following procedure.
[0052] First, a test piece having a diameter and a length of the
parallel part of 10 mm and 50 mm, respectively, was hold in an
atmosphere of a temperature of 450.degree. C. and a hydrogen
pressure of 25 MPa for 72 hours to charge hydrogen. The hydrogen
charging conditions are set so as to simulate 50 ppm that is a
hydrogen quantity which is assumed to intrude into the material in
an actual ammonothermal method. Using a hydrogen charged material
after the hydrogen charge, a tensile test was performed at
625.degree. C. and a tensile strength and a reduction of area were
measured.
[0053] Also, for a test piece in a hydrogen uncharged state
(hydrogen non-charged material), a tensile strength and a reduction
of area were similarly measured.
[0054] As for the hydrogen embrittlement resistance, also using the
tensile test results of the hydrogen non-charged material at
625.degree. C., the hydrogen embrittlement index EI defined by the
following equation (1) was calculated to perform evaluation:
hydrogen embrittlement index EI=(RA.sub.A-RA.sub.H)/RA.sub.A
(1)
in which RA.sub.A is a reduction of area of a hydrogen non-charged
material and RA.sub.H is a reduction of area of a hydrogen charged
material.
[0055] A smaller value of the hydrogen embrittlement index
indicates more excellent hydrogen embrittlement resistance.
[0056] The creep properties were evaluated by performing a creep
rupture test and a creep rate test. In both tests, test temperature
was 700.degree. C., and test stress was 333 MPa and 275 MPa in the
rupture test and was 333 MPa in the rate test.
[0057] Table 2 shows the tensile strength, reduction of area, and
hydrogen embrittlement index of each of the hydrogen charged
materials and the hydrogen non-charged materials at 625.degree. C.
Incidentally, the hydrogen embrittlement index of the invention
material P1 became negative but this is indicated as 0.00 for
convenience sake in Table 2.
TABLE-US-00002 TABLE 2 Tensile strength, reduction of area, and
hydrogen embrittlement index of invention material and comparative
material at 625.degree. C. Hydrogen charged Hydrogen non-charged
material material Hydrogen Reduction Reduction embrittle- Tensile
of Tensile of ment strength/ area RA.sub.H strength/ area RA.sub.A
index Test material MPa (%) MPa (%) EI Invention 725 30.1 733 28.7
0.00 material (P1) Invention 729 38.8 794 39.9 0.03 material (P2)
Comparative 721 17.0 711 25.2 0.33 material 1 Comparative 732 15.5
717 35.1 0.56 material 2
[0058] FIG. 1 shows a relationship between the hydrogen
embrittlement index of each of the invention materials P1 and P2
(hereinafter sometimes collectively referred to as "invention
material") and the comparative materials 1 and 2 (hereinafter
sometimes collectively referred to as "comparative material") at
625.degree. C. and the P content in each Ni-based alloy.
[0059] From the figure, the hydrogen embrittlement index of the
invention material is remarkably small as compared with that of the
comparative material and thus it is realized that the invention
material is extremely excellent in the hydrogen embrittlement
resistance at high temperature. As shown at the shaded section in
the figure, when the P content becomes 40 ppm or more, the hydrogen
embrittlement index decreases to 0.1 or less and the hydrogen
embrittlement susceptibility reduces to such a degree that the
influence of hydrogen can be almost ignored. From the results, it
is realized that P has effects of suppressing excessive
accumulation of hydrogen at grain boundaries by increasing the
consistency of the grain boundaries and lowering the hydrogen
embrittlement susceptibility and a P content of 40 ppm or more is
necessary for improving the hydrogen embrittlement resistance by
increasing the P content.
[0060] FIG. 2 and FIG. 3 show results of the creep rupture test and
results of the creep rate test, respectively. From FIG. 2, the
rupture time of the invention material is greatly longer than that
of the comparative material. The rupture time of the invention
material in the case where the test stress is 333 MPa is at least
ten times that of the comparative material 1 and the rupture time
is about 1,500 hours in the case of the invention material P1 and
is about 2,000 hours in the case of the invention material P2.
Furthermore, from FIG. 3, it is realized that the minimum creep
rate of the invention material is at least one fourth or less as
compared with that of the comparative material 2 and the value is
1.times.10.sup.-8 s.sup.-1 (3.6.times.10.sup.-5 h.sup.-1) or
less.
[0061] From the above, it becomes obvious that the invention
material according to the present invention has excellent creep
properties.
[0062] While the invention has been described based on the above
embodiments and examples, it will be apparent to one skilled in the
art that the invention is not limited to the contents of the above
embodiments and examples and various changes and modifications can
be made therein without departing from the spirit and scope of the
invention.
[0063] The present application is based on Japanese Patent
Application No. 2012-184966 filed on Aug. 24, 2012, and the
contents are incorporated herein by reference.
* * * * *