[Document Name] Description
[Title of Invention] Ni-BASED HEAT RESISTANT ALLOY
[Technical Field]
Loo0 11
The present invention relates to a Ni-based heat resistant alloy. More
particularly, the invention relates to a high-strength Ni-based heat resistant
alloy excellent in hot workability and in toughness and ductility after longterm
use, which is used as a pipe material, a thick plate for parts having heat
resistance and pressure resistance, a rod material, a forging, and the like in
power generating boilers, chemical industry plants, and the like.
[Background Art]
[00021
In recent years, a number of ultra super critical boilers which are
operated at an increased temperature and pressure to achieve high efficiency
are newly constructed in the world.
[00031
Specifically, in some projects, the steam temperature, which has so far
been about 600°C, is further increased to 650°C or higher and further to 700°C
or higher. This is based on the fact that energy saving, effective use of
resources, and reduction in CO2 gas emission for environmental preservation
are challenges to solve energy problems, and are included in important
industrial policies. In the case of power generating boilers burning a fossil
fuel and reactors for the chemical industry, a highly efficient ultra super
critical boilers and reactors are advantageous.
[OOO~]
e Such high temperature and pressure of steam also increases the
temperature of a superheater tube of boiler, a reactor tube for the chemical
industry, and a thick plate and a forging used as a part having heat resistance
and pressure resistance to 700°C or higher at the time of actual operation.
Therefore, an alloy used in a harsh environment for a long period of time must
be of excellent in not only high-temperature strength and high-temperature
corrosion resistance but also long-term stability of metal micro-structure, creep
rupture ductility, and creep fatigue resistance.
[00051
Further, during the maintenance work such as repair after long-term
use, a material aged in a long period of time needs to be cut, worked, or welded,
and therefore, not only the characteristics for a new material but also the
soundness of an aged material have been required strongly in recent years.
[0006]
In meeting the severe requirements, an Fe-based alloy such as an
austenitic stainless steel suffers lack of creep rupture strength. Therefore, it
is inevitable to use a Ni-based alloy in which the precipitation of a y' phase or
the like is utilized.
[00071
Accordingly, Patent Documents 1 to 8 disclose Ni-based alloys that
contain Mo andlor W to achieve solid-solution strengthening, and contain A1
and Ti to utilize precipitation strengthening of the y' phase, which is an
intermetallic compound, or specifically utilize precipitation strengthening of
Nis(Al, Ti) for use in the above-described harsh high-temperature environment.
[0008l
In the alloys disclosed in Patent Documents 4 to 6, since 28% or more of
Cr is contained, an a large amount of a-Cr phase having a bcc structure also
precipitates and contributes to strengthening.
[Citation List]
[Patent Document]
[00091
[Patent Document 11 JP51-84726A
[Patent Document 21 JP51-84727A
[Patent Document 31 JP7- 150277A
[Patent Document 41 JP7-216511A
[Patent Document 51 JP8- 127848A
[Patent Document 61 JP8-218140A
[Patent Document 71 JP9- 157779A
[Patent Document 81 JP2002-518599A
[Summary of Invention]
[Technical Problem]
[00101
The Ni-based alloys disclosed in Patent Documents 1 to 8 have ductility
lower than that of the conventional austenitic steel because the y' phase
precipitates or the y' phase and the a-Cr phase precipitate, and may experience
changes over time especially when being used for a long period of time, so that
the ductility and toughness thereof decrease greatly as compared with a new
material.
[00111
In the periodic inspection after the long-term use and the maintenance
work performed on account of an accident or a trouble during the use, a
defective material must be cut out partially and be replaced with a new
material, and in this case, the new material must be welded to the aged
@ material to be used continuously. Also, depending on the situation, partial
bending work must be performed.
[00121
However, Patent Documents 1 to 8 do not disclose countermeasures for
restraining the deterioration in material caused by the long-term use. That is,
in Patent Documents 1 to 8, no studies are conducted on how the long-term
aging is restrained, and how a safe and reliable material is ensured in a
present large plant used in a high-temperature and pressure environment that
the past plant did not have.
COO 131
The present invention has been made in view of the circumstances, and
accordingly an objective thereof is to provide a Ni-based heat resistant alloy in
which the creep rupture strength is improved by the solid-solution
strengthening and the precipitation strengthening of y' phase, the dramatic
improvement in ductility after long-term use at high temperatures is achieved,
and the SR cracks that pose a problem in repair welding and the like can be
avoided.
[Solution to Problem]
[OO14 1
The present inventors examined the improvement in ductility after longterm
use at high temperatures and the prevention of SR cracks of a Ni-based
alloy using the precipitation strengthening of the y' phase (hereinafter,
referred to as a "y' strengthening Ni-based alloy"). As a result, the present
inventors obtained an important finding of the following item (a).
[00151
@ (a) In order to improve the ductility after long-term use at high
temperatures and to prevent the SR cracks of the y' strengthening Ni-based
alloy, it is effective to contain Nd.
As a result of various examinations made further, the present inventors
obtained findings of the following items (b) to (e).
[00161
(b) The average grain size and the degree of strengthening within the
grain are important indexes of the improvement in ductility and the
prevention of SR cracks.
[00171
(c) The degree of strengthening within the grain can be quantified by the
amounts of Al, Ti and Nb which are y' phase stabilizing elements, and form the
y' phase together with Ni.
[OOI~I
(d) According to the average grain size and the degree of strengthening
within the grain, the minimum necessary amount of Nd to be contained for the
improvement in ductility and the prevention of SR cracks varies.
[00191
(e) In order to ensure the Nd amount effective in contributing to the
improvement in ductility and the prevention of SR cracks, the content of
oxygen must be regulated strictly according to the content of Nd.
[00201
The present invention was completed on the basis of the above-described
findings, and the gist thereof is Ni-based heat resistant alloys described in the
following items (1) to (3).
Lo02 11
(1) A Ni-based heat resistant alloy consisting, in mass percent, of C:
0.15% or less, Si: 2% or less, Mn: 3% or less, P: 0.03% or less, S: 0.01% or less,
@ Cr: 15% or more and less than 28%, Mo: 3 to 15%, Co: more than 5% and not
more than 25%, Al: 0.2 to 2%, Ti: 0.2 to 3%, Nd: f l to 0.08%, and 0: 0.4Nd or
less, the balance being Ni and impurities, wherein the f l refers to the following
formula, and in the formula, d denotes an average grain size (pm), and each
symbol of an element denotes the content (mass%) of that element, and
likewise, Nd in 0.4Nd denotes the content (mass%) of Nd.
f l = 1.7 x 10-5d + 0.05{(A1/26.98) + (Til47.88))
[00221
(2) A Ni-based heat resistant alloy consisting, in mass percent, of C:
0.15% or less, Si: 2% or less, Mn: 3% or less, P: 0.03% or less, S: 0.01% or less,
Cr: 15% or more and less than 28%) Mo: 3 to 15%) Co: more than 5% and not
more than 25%, Al: 0.2 to 2%, Ti: 0.2 to 3%) Nd: f2 to 0.08%, and 0: 0.4Nd or
less, further containing at least one kind of Nb: 3.0% or less and W: less than
4% (however, Mo + (Wl2): 15% or less), 'the balance being Ni and impurities,
wherein the f2 refers to the following formula, and in the formula, d denotes
an average grain size @m), and each symbol of an element denotes the content
(mass%) of that element, and likewise, each symbol of an element in 0.4Nd and
Mo + (W12) also denotes the content (mass%) of that element.
f2 = 1.7 x 10-5d + 0.05{(Av26.98) + (Ti147.88) + (Nb192.91))
100231
(3) The Ni-based heat resistant alloy described in the above item (1) or
(2), wherein the alloy contains one or more kinds of elements selected from the
following groups to <4> instead of part of Ni:
B: 0.01% or less, Zr: 0.2% or less, and Hf: 1% or less
<2> Mg: 0.05% or less, Ca: 0.05% or less, Y: 0.5% or less, La: 0.5% or less,
and Ce: 0.5% or less
<3> Ta: 8% or less, and Re: 8% or less
<4> Fe: 15% or less.
@ [0024]
The "impurities" in the "Ni and impurities" of the balance means
impurities mixed from ore and scrap used as a raw material, a manufacturing
environment, and the like when the heat resistant alloy is manufactured on an
industry basis.
[Advantageous Effects of Invention]
[00251
The Ni-based heat resistant alloy of the present invention is an alloy in
which the dramatic improvement in ductility after long-term use at high
temperatures is achieved, and further the SR cracks that pose a problem in
repair welding and the like can be avoided. Therefore, this Ni-based heat
resistant alloy can be used suitably as a pipe material, a thick plate for parts
having heat resistance and pressure resistance, a rod material, a forging, and
the like in power generating boilers, chemical industry plants, and the like.
[Description of Embodiments]
100261
The reason for restricting the chemical composition of the Ni-based heat
resistant alloy in the present invention is as described below. In the following
description, "%" representing the content of each element means "mass%."
Lo0271
C: 0.15% or less
C (carbon) is an element effective in securing tensile strength and creep
strength, by forming carbides, which are necessary when the material is used
in a high-temperature environment, and therefore is contained appropriately
in the present invention. However, if the C content exceeds 0.15%, the
amount of carbides that do not form a solid solution in a solution state
@ increases, so that not only C does not contribute to the improvement in hightemperature
strength but also C deteriorates the mechanical properties such
as toughness and the weldability. Therefore, the C content was set to 0.15%
or less. The C content is preferably 0.1% or less.
[00281
In order to achieve the effect of C, the lower limit of C content is
preferably 0.005%, and further preferably 0.01%. The lower limit of C content
is still further preferably 0.02%.
[00291
Si: 2% or less
Si (silicon) is added as a deoxidizing element. If the Si content exceeds
2%, the weldability and hot workability are decreased. Also, the production of
an intermetallic compound phase such as a o phase and the like is promoted,
so that the toughness and ductility decrease due to deterioration of the
structural stability at high temperatures. Therefore, the Si content was set to
2% or less. The Si content is preferably 1.0% or less, further preferably 0.8%
or less.
[00301
In order to achieve the effect of Si, the lower limit of Si content is
preferably 0.05%, further preferably 0.1%.
Coo311
Mn: 3% or less
Mn (manganese) has a deoxidizing function like Si, and also has an
effect of improving the hot workability by fixing S, which is contained as an
impurity in the alloy, as a sulfide. However, if the Mn content increases, the
formation of a spinel type oxide film is promoted, and the oxidation resistance
at high temperatures is deteriorated. Therefore, the Mn content is 3% or less.
The Mn content is preferably 2.0% or less, further preferably 1.0% or less.
In order to achieve the effect of Mn, the lower limit of the Mn content is
preferably set to 0.05%, and more preferably set to 0.08%. The further
preferable lower limit of the Mn is 0.1%.
Lo0331
P: 0.03% or less
P (phosphorus) is contained in the alloy as an impurity, and remarkably
decreases the weldability and hot workability if being contained in large
amounts. Therefore, the P content was set to 0.03% or less. The P content
should be made as low as possible, and is preferably 0.02% or less, further
preferably 0.015% or less.
100341
S: 0.01% or less
S (sulfur) is, like phosphorus, contained in the alloy as an impurity, and
remarkably decreases the weldability and hot workability if being contained in
large amounts. Therefore, the S content was set to 0.01% or less.
100351
The S content in the case where importance is attached to the hot
workability is preferably 0.005% or less, further preferably 0.003% or less.
100361
Cr: not less than 15% and less than 28%
Cr (chromium) is an important element for achieving an effect excellent
in improving corrosion resistance such as oxidation resistance, steam oxidation
resistance, and high-temperature corrosion resistance. However, if the Cr
content is less than 15%, the desired effect cannot be achieved. On the other
hand, if the Cr content exceeds 28%, the micro-structure is unstabilized on
account of the deterioration in hot workability, the precipitation of o phase,
and the like. Therefore, the Cr content was set to 15% or more and less than
@ 28%. The lower limit of the Cr content is preferably 18%. Also, the upper
limit of the Cr content is preferably 26%, further preferably 25%.
[00371
Mo: 3 to 15%
Mo (molybdenum) dissolves in the parent phase and has effects of
improving the creep rupture strength and decreasing the linear expansion
coefficient. In order to achieve these effects, 3% or more of Mo must be
contained. However, if the Mo content exceeds 15%) the hot workability and
structural stability decrease. Therefore, the Mo content is set to 3 to 15%.
[00381
In addition to Mo of the above-described content range, the laterdescribed
amount of W may be contained. In this case, however, the Mo
content must be such that the sum of the Mo content and a half of the W
content, that is, [Mo + (W/2)] is 15% or less.
[00391
The preferable lower limit of the Mo content is 4%, and the preferable
upper limit thereof is 14%. The further preferable lower limit of the Mo
content is 5%, and the further preferable upper limit thereof is 13%.
[00401
Co: more than 5% and not more than 25%
Co (cobalt) dissolves in the parent phase, and improves the creep
rupture strength. Further, Co also has an effect of further improving the
creep rupture strength by increasing the precipitation amount of y' phase
especially in the temperature range of 750°C or higher. In order to achieve
these effects, an amount more than 5% of Co must be contained. However, if
the Co content exceeds 25%, the hot workability decreases. Therefore, the Co
content is set to more than 5% and not more than 25%.
[00411
In the case where importance is attached to the balance between hot
workability and creep rupture strength, the preferable lower limit of the Co
content is 7%, and the preferable upper limit thereof is 23%. The further
preferable lower limit of the Co content is lo%, and the further preferable
upper limit thereof is 22%.
[00421
In the case where importance is attached to the creep rupture strength
especially in the temperature range of 750°C or higher, 17% or more of Co is
preferably contained, and it is further preferable that more than 20% of cobalt
be contained.
[00431
Al: 0.2 to 2%
Al (aluminum) is an important element in the Ni-based alloy, which
precipitates the y' phase (NisAl), an intermetallic compound, and improves the
creep rupture strength remarkably. In order to achieve this effect, 0.2% or
more of Al must be contained. However, if the Al content exceeds 2%, the hot
workability is decreased, and hot forging and hot pipe-making become difficult
to do. Therefore, the Al content was set to 0.2 to 2% or less. The preferable
lower limit of the Al content is 0.8%, and the preferable upper limit thereof is
1.8%. The more preferable lower limit of the Al content is 0.9%, and the more
preferable upper limit thereof is 1.7%.
Lo0441
Ti: 0.2 to 3%
Ti (titanium) is an important element in the Ni-based alloy, which forms
the y' phase (NidAl, Ti)), which is an intermetallic compound, together with Al,
and improves the creep rupture strength remarkably. To achieve this effect,
0.2% or more of titanium must be contained. However, if the Ti content
exceeds 3%, the hot workability is decreased, and hot forging and hot pipe@
making become difficult to do. Therefore, the Ti content was set to 0.2 to 3%.
The preferable lower limit of the Ti content is 0.3%, and the preferable upper
limit thereof is 2.8%. The more preferable lower limit of the Ti content is
0.4%, and the more preferable upper limit thereof is 2.6%.
[00451
Nd: f l to 0.08% (when Nb is not contained) or f2 to 0.08% (when Nb is
contained)
Nd (neodymium) is an important element characterizing the Ni-based
heat resistant alloy in accordance with the present invention. That is, Nd is
an important element that is very effective in improving the ductility after
long-term use at high temperatures and preventing the SR cracks of the y'
strengthening Ni-based alloy. In order to achieve these effects, Nd of an
amount of f l or larger, f l represented by a formula described below of the
average grain size d (pm) and the contents (mass%) of Al and Ti, must be
contained in the case where the Ni-based heat resistant alloy does not contain
Nb, and also Nd of an amount of f2 or larger, f2 represented by a formula
described below of the average grain size d (pm) and the contents (mass%) of
Al, Ti, and Nb, must be contained in the case where the Ni-based heat
resistant alloy contains Nb.
fl = 1.7 x 10m5+d 0.05{(A1/26.98) + (Til47.88))
f2 = 1.7 x lO+d + 0.05{(A1/26.98) + (Til47.88) + (Nb192.91))
Lo0461
The improvement in ductility and the prevention of SR cracks are also
affected by the average grain size and the degree of strengthening within the
grain. The degree of strengthening within the grain is affected by the
amounts of Al, Ti and Nb which are y' phase stabilizing elements, and form the
y' phase together with Ni. Therefore, the minimum necessary amount of Nd
to be contained for the improvement in ductility and the prevention of SR
• cracks varies according to the average grain size and the degree of
strengthening within the grain.
Lo0471
On the other hand, if the Nd content is excessive and exceeds 0.8%, the
hot workability decreases, and the ductility decreases on account of inclusions.
Therefore, the Nd content was set to f l to 0.08% (when Nb is not contained) or
f2 to 0.08% (when Nb is contained).
Lo0481
Generally, Nd is also contained in a mischmetal. Therefore, Nd of the
above-described amount may be contained by being added in a form of
mischmetal.
[00491
0: 0.4Nd or less
0 (oxygen) is contained in the alloy as an impurity, and decreases the
hot workability and ductility. Moreover, in the case of the present invention
in which Nd is contained, 0 combines easily with Nd to form oxides, and
undesirably reduces the above-described function of improving the ductility
after long-term use at high temperatures and preventing the SR cracks of Nd.
Therefore, an upper limit is placed on the 0 content, and the 0 content was set
to 0.4Nd or less, that is, 0.4 times or less of the Nd content. The 0 content is
preferably made as low as possible.
[00501
One of the Ni-based heat resistant alloys of the present invention
consists of the above-described elements of C through 0, the balance being Ni
and impurities.
[00511
Hereunder, Ni in the balance of the Ni-based heat resistant alloy of the
present invention is explained.
Ni (nickel) is an element for stabilizing the austenitic structure, and is
an element important for securing corrosion resistance as well. In the
present invention, the Ni content need not be defined especially, and is made a
content obtained by removing the content of impurities from the balance.
However, the Ni content in the balance preferably exceeds 50%, and further
preferably exceeds 60%.
[00531
As described already, the "impurities" means impurities mixed from ore
and scrap used as a raw material, a manufacturing environment, and the like
when the heat resistant alloy is manufactured on an industry basis.
[00541
Another of the Ni-based heat resistant alloys of the present invention
further contains one or more kinds of elements selected from Nb, W, B, Zr, Hf,
Mg, Ca, Y, La, Ce, Ta, Re and Fe in addition to the above-described elements.
[00551
Hereunder, the operational advantages of these optional elements and
the reasons for limiting the contents thereof are explained.
[00561
Both Nb and W have a function of improving the creep strength.
Therefore, these elements may be contained.
[00571
Nb: 3.0% or less
Nb (niobium) has a function of improving the creep strength. That is,
Nb forms the y' phase, which is an intermetallic compound, together with A1
and Ti, and has a function of improving the creep strength. Therefore,
niobium may be contained. However, if the Nb content increases and exceeds
3.0%, the hot workability and toughness are decreased. Therefore, the
* content of Nb at the time of being contained was set to 3.0% or less. The
content of Nb at the time of being contained is preferably 2.5% or less.
[00581
On the other hand, in order to achieve the effect of Nb, the Nb content is
preferably 0.05% or more, further preferably 0.1% or more.
[00591
W: less than 4% (however, Mo + (W12): 15% or less)
W (tungsten) has a function of improving the creep strength. That is,
W dissolves in the parent phase, and has a function of improving the creep
strength as a solid-solution strengthening element. Therefore, W may be
contained. However, if the W content increases to 4% or more, the hot
workability decreases. Further, in the present invention, Mo is contained. If
Mo and W are contained compositely in an amount such that the sum of the
Mo content and a half of the W content, that is, [Mo + (W/2)1 is more than 15%,
the hot workability decreases greatly. Therefore, the content of W at the time
of being contained was set to less than 4%, and further was set so that [Mo +
(W/2)] is 15% or less. The content of tungsten at the time of being contained
is preferably 3.5% or less.
[0060]
On the other hand, in order to stably achieve the effect of W, the W
content is preferably 1% or more, further preferably 1.5% or more.
[OO~II
The above-described Nb and W can be contained in only either one kind
or compositely in two kinds. The total amount of these elements contained
compositely is preferably 6% or less.
[00621
Any of B, Zr and Hf belonging to the group of has a function of
improving the creep strength. Therefore, these elements may be contained.
Lo0631
B: 0.01% or less
B (boron) has a function of improving the creep strength. B also has a
function of improving the high temperature strength. That is, B exists at
grain boundaries as a simple substance, and has a function of restraining
grain boundary sliding caused by grain boundary strengthening during the use
at high temperatures. Further, B exists in carbo-nitrides together with C and
N, and has a function of improving the creep strength by accelerating fine
dispersion precipitation of carbo-nitrides, and also has a function of improving
the high temperature strength. Therefore, B may be contained. However, if
the B content increases and exceeds 0.01%, the weldability deteriorates.
Therefore, the content of B at the time of being contained was set to 0.01% or
less. The upper limit of content of B at the time of being contained is
preferably 0.008%, further preferably 0.006%.
Coo641
On the other hand, in order to stably achieve the effect of B, the lower
limit of the B content is preferably 0.0005%, and further preferably 0.001%.
[00651
Zr: 0.2% or less
Zr (zirconium) is a grain boundary strengthening element, and has a
function of improving the creep strength. Zr also has a function of improving
the rupture ductility. Therefore, Zr may be contained. However, if the Zr
content increases and exceeds 0.2%, the hot workability is decreased.
Therefore, the content of Zr at the time of being contained was set to 0.2% or
less. The content of Zr at the time of being contained is preferably 0.1% or
less, further preferably 0.05% or less.
lo0661
@ On the other hand, in order to stably achieve the effects of Zr, the Zr
content is preferably 0.005% or more, and further preferably 0.01% or more.
[00671
Hf: 1% or less
Hf (hafnium) contributes mainly to the grain boundary strengthening,
and has a function of improving the creep strength. Therefore, Hf may be
contained. However, if the Hf content exceeds 1%, the workability and
weldability are impaired. Therefore, the content of Hf at the time of being
contained was set to 1% or less. The content of Hf at the time of being
contained is preferably 0.8% or less, further preferably 0.5% or less.
[OO~BI
On the other hand, in order to stably achieve the effect of Hf, the Hf
content is preferably 0.005% or more, and further preferably 0.01% or more.
The Hf content is still further preferably 0.02% or more.
[00691
The above-described B, Zr and Hf can be contained in only either one
kind or compositely in two or more kinds. The total amount of these elements
contained compositely is preferably 0.8% or less.
[OO~O]
Any of Mg, Ca, Y, La and Ce belonging to the group of <2> immobilizes S
as a sulfide, and has a function of improving the hot workability. Therefore,
these elements may be contained.
[007 11
Mg: 0.05% or less ,
Mg (magnesium) fixes S, which hinders the hot workability, as a sulfide,
and has a function of improving the hot workability. Therefore, Mg may be
contained. However, if the Mg content exceeds 0.05%, the cleanliness is
impaired, and the hot workability and ductility are rather impaired.
Therefore, the content of Mg at the time of being contained was set to 0.05% or
less. The content of Mg at the time of being contained is preferably 0.02% or
less, further preferably 0.01% or less.
[00721
On the other hand, in order to stably achieve the effect of Mg, the Mg
content is preferably 0.0005% or more, and further preferably 0.001% or more.
Coo731
Ca: 0.05% or less
Ca (calcium) fixes S, which hinders the hot workability, as a sulfide, and
has a function of improving the hot workability. Therefore, Ca may be
contained. However, if the Ca content exceeds 0.05%, the cleanliness is
impaired, and the hot workability and ductility are rather impaired.
Therefore, the content of Ca at the time of being contained was set to 0.05% or
less. The content of Ca at the time of being contained is preferably 0.02% or
less, further preferably O.Ol%.or less.
[00741
On the other hand, in order to stably achieve the effect of Ca, the Ca
content is preferably 0.0005% or more, and further preferably 0.001% or more.
[00751
Y: 0.5% or less
Y (yttrium) fixes S as a sulfide, and has a function of improving the hot
workability. Also, Y has a function of improving the adhesion of Cr203
protective film on the surface of alloy, and especially has a function of
improving the oxidation resistance at the time of repeated oxidation. Further,
Y contributes to the grain boundary strengthening, and also has a function of
improving the creep strength and creep rupture ductility. Therefore, Y may
be contained. However, if the Y content increases and exceeds 0.5%,
inclusions such as oxides increase in amount, and therefore the workability
I @ and weldability are impaired. Therefore, the content of Y at the time of being ~ contained was set to 0.5% or less. The content of Y at the time of being
contained is preferably 0.3% or less, further preferably 0.15% or less.
[00761
On the other hand, in order to stably achieve the effects of Y, the Y
content is preferably 0.0005% or more, further preferably 0.001% or more.
The Y content is still further preferably 0.002% or more.
[00771
La: 0.5% or less
La (lanthanum) fixes S as a sulfide, and has a function of improving the
hot workability. Also, La has a function of improving the adhesion of Cr203
protective film on the surface of alloy, and especially has a function of
improving the oxidation resistance at the time of repeated oxidation. Further,
La contributes to the grain boundary strengthening, and also has a function of
improving the creep strength and creep rupture ductility. Therefore, La may
be contained. However, if the La content exceeds 0.5%, inclusions such as
oxides increase in amount, and therefore the workability and weldability are
impaired. Therefore, the content of La at the time of being contained was set
to 0.5% or less. The content of La at the time of being contained is preferably
0.3% or less, further preferably 0.15% or less.
[00781
On the other hand, in order to stably achieve the effects of La, the La
content is preferably 0.0005% or more, further preferably 0.001% or more.
The La content is still further preferably 0.002% or more.
[00791
Ce: 0.5% or less
Ce (cerium) fixes S as a sulfide, and has a function of improving the hot
workability. Also, Ce has a function of improving the adhesion of Cr203
@ protective film on the surface of alloy, and especially has a function of
improving the oxidation resistance at the time of repeated oxidation. Further,
Ce contributes to the grain boundary strengthening, and also has a function of
improving the creep rupture strength and creep rupture ductility. Therefore,
Ce may be contained. However, if the Ce content increases and exceeds 0.5%,
inclusions such as oxides increase in amount, and therefore the workability
and weldability are impaired. Therefore, the content of Ce at the time of
being contained was set to 0.5% or less. The content of Ce at the time of being
contained is preferably 0.3% or less, further preferably 0.15% or less.
[00801
On the other hand, in order to stably achieve the effects of Ce, the Ce
content is preferably 0.0005% or more, further preferably 0.001% or more.
The La content is still further preferably 0.002% or more.
[0081]
The above-described Mg, Ca, Y, La and Ce can be contained in only
either one kind or compositely in two or more kinds. The total amount of
these elements contained compositely is preferably 0.5% or less.
[0082]
Both Ta and Re of a <3> group have a function of improving the hightemperature
strength and creep strength as solid-solution strengthening
elements. Therefore, these elements may be contained.
[00831
Ta: 8% or less
Ta (tantalum) forms carbo-nitrides, and has a function of improving the
high-temperature strength and creep strength as a solid-solution
strengthening element. Therefore, Ta may be contained. However, if the Ta
content exceeds 8%, the workability and mechanical properties are impaired.
Therefore, the content of Ta at the time of being contained was set to 8% or
0 less. The content of Ta at the time of being contained is preferably 7% or less,
further preferably 6% or less.
[00841
On the other hand, in order to stably achieve the effect of Ta, the Ta
content is preferably 0.01% or more, further preferably 0.1% or more. The Ta
content is still further preferably 0.5% or more.
[0085]
Re: 8% or less
Re (rhenium) has a function of improving the high-temperature strength
and creep strength mainly as a solid-solution strengthening element.
Therefore, Re may be contained. However, if the Re content increases and
exceeds 8%, the workability and mechanical properties are impaired.
Therefore, the content of Re at the time of being contained was set to 8% or
less. The content of Re at the time of being contained is preferably 7% or less,
further preferably 6% or less.
[OOB~I
On the other hand, in order to stably achieve the effect of Re, the Re
content is preferably 0.01% or more, further preferably 0.1% or more. The Re
content is still further preferably 0.5% or more.
[00871
The above-described Ta and Re can be contained in only either one kind
or compositely in two kinds. The total amount of these elements contained
compositely is preferably 8% or less.
[00881
Fe: 15% or less
Fe (iron) has a function of improving the hot workability of Ni-based
alloy. Therefore, Fe may be contained. In the actual manufacturing process,
even if Fe is not contained, about 0.5 to 1% of Fe is sometimes contained as an
impurity on account of contamination from a furnace wall caused by the
melting of Fe-based alloy. In the case where Fe is contained, if the Fe content
exceeds 15%, the oxidation resistance and structural stability deteriorate.
Therefore, the Fe content is set to 15% or less. In the case where importance
is attached to the oxidation resistance, the Fe content is preferably 10% or less.
C00891
In order to achieve the effect of Fe, the lower limit of the Fe content is
preferably set to 1.5%, and further preferably set to 2.0%. The still further
preferable lower limit of the Fe content is 2.5%.
[0090l
Hereunder, the present invention is explained more specifically with
reference to examples, however, the present invention is not limited to these
examples.
[Examples]
[009 11
Ni-based alloys 1 to 14 and A to G having chemical compositions shown
in Table 1 were melted by using a high-.frequency vacuum furnace to obtain
30-kg ingots.
Tab l el
[00931
The ingot obtained as described above was heated to 1160°C, and
thereafter was hot forged into a 15 mm-thick plate material so that the
finishing temperature was 1000°C.
[00941
Next, the 15 mm-thick plate material was subjected to softening heat
treatment at llOO°C and was cold-rolled to 10 mm, and further was held at
1180°C for 30 minutes and thereafter was water cooled.
[0095l
By using a part of the 10 mm-thick plate material, which had been held
at 1180°C for 30 minutes and had been water cooled, a test specimen, which
had been cut and embedded in a resin so that the rolling longitudinal direction
was an observation surface, was mirror polished, and thereafter was etched
with mixed acid or a Kalling reagent, and optical microscope observation was
made. In the optical microscope observation, photographing was performed at
xlOO magnification in five visual fields, the average grain intercept length was
measured by the cutting method in a total of four directions of each visual field,
longitudinal (perpendicular to the rolling direction), transverse (parallel to the
rolling direction), and diagonal line, and the average grain size d (pm) was
determined by multiplying the average grain intercept length by a factor of
1.128.
[00961
By using the average grain size d ( ~ md)e termined as described above,
fl = 1.7 x 10-5d + 0.05(611/26.98) + (Ti147.88))
or
f2 = 1.7 x 10m5+d 0.05(611/26.98) + (Ti147.88) + (Nb192.91))
was calculated, and the relationship between the Nd content in each alloy and
the lower limit value of Nd content defined in the present invention was
examined.
100971
For each alloy, Table 2 summarizedly gives the calculation result of f l or
f2 together with the average grain size d (pm). Further, Table 2 additionally
gives the contents of Nd, Al, Ti and Nb given in Table 1.
[00981
[Table 21
I!
Tab l e2
[00991
It was revealed from Table 2 that only the Nd contents of alloy B and
alloy C were lower than the lower limit value of Nd content defined in the
present invention.
[01001
A1 ~ O Y
1
2
3
4
5
6
7
8
9
10
1 1
1 2
13
1 4
A
B
C
D
E
F
G
f2=1.7x 10-5d+0. 05((A1/26.98) + (Ti/47.88) + (Nb/92.91))
* mark denotes deviation from cond i t i on defined in the present invent ion.
Average
grain size
d ( ~ m )
152
224
8 3
198
104
25 1
179
202
142
305
11 6
125
21 0
122
21 5
230
188
21 9
181
21 0
178
f1=1.7x 10-6d+0.
Nd content
(mass%>
0.021
0.025
0.008
0.01 4
0.015
0.048
0.031
0.028
0.016
0.025
0.009
0.010
0.032
0.024
* -
* 0.005
* 0.005
* 0.091
* 0.089
0.023
0.027
f l or f2
0.005
0.007
0.005
0.006
0.004
0.009
0.006
0.006
0.006
0.010
0.005
0.006
0.007
0.005
0.006
0.007
0.007
0.006
0.006
0.006
0.006
Content
A l
1.08
1.23
1.44
1.28
1.17
0.98
0.57
1.14
0.87
1.66
1.26
0.67
1.31
0.56
1.19
1.20
0.58
1.22
0.54
1.25
0.51
05{(A1/26.98)
of e t
(mass%)
Ti
0.50
0.44
1.15
0.51
0.47
1.28
2.14
0.51
1.91
1.93
0.71
2.12
0.50
2.20
0.48
0.46
2.19
0.47
2.07
0.45
2.11
+
ement
Nb
-
-
-
-
-
2.24
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(Ti/47.88)}
Therefore, it was revealed that, of the alloys given in Table 1, a total of
seven alloys, that is, the alloys B and C added to alloys A and D to G were
alloys having the chemical composition deviating from the condition defined in
the present invention.
[o 1011
On the other hand, it was revealed that alloys 1 to 14 were alloys having
the chemical composition within the range defined in the present invention.
[01021
Next, By using a remaining part of the 10 mm-thick plate material,
which had been held at 1180°C for 30 minutes and had been water cooled, from
a central portion in the thickness direction, a round-bar tensile test specimen
having a diameter of 6 mm and a gage length of 30 mm was prepared, by
machining, in parallel to the longitudinal direction, and a creep rupture test
and a high-temperature tensile test at a very low strain rate were conducted
by using this round-bar tensile test specimen.
[01031
The creep rupture test was conducted by applying an initial stress of 300
MPa to the round-bar tensile test specimen having the above-described shape
at 700°C to measure the rupture time and rupture elongation.
[O 1041
Further, by using the round-bar tensile test specimen having the abovedescribed
shape, the tensile test was conducted at 700°C and at a very low
strain rate of 10-61s to measure the reduction of area at rupture.
[01051
The strain rate of 10.61s is a very low strain rate such as to be 11100 to
111000 of the strain rate in the usual high-temperature tensile test.
Therefore, by measuring the reduction of area at rupture at the time when the
I! tensile test is conducted at this very low strain rate, the relative evaluation of
preventing SR crack susceptibility can be performed.
[01061
Specifically, in the case where the reduction of area at rupture at the
time when the tensile test is conducted at the above-described very low strain
rate is high, it can be evaluated that the preventing SR crack susceptibility is
low, and the effect of preventing SR cracks is great.
[01071
Table 3 summarizes the test results.
[OIO~I
[Table 31
Tab l e3
[O 1091
Table 3 reveals that in the case of test Nos. 1 to 14 of example
embodiments of the present invention using alloys 1 to 14 having the chemical
composition within the range defined in the present invention, all of the creep
rupture time, the creep rupture ductility, and the reduction of area at rupture
in the tensile test at very low strain rate (that is, effects of preventing SR
cracks) are good.
[01101
=u
m s
2
V)
rn
X
!3 x CD
m
So
-P. z 3
rt
0
--h
I+
T m
'9,
m
V)
CD
7
Pi- -.
7 <
m
=I
I-i.-
0
3
o 0 u
n3
7 m
!?
c
CD
(D
X P
I3_
(D
Tens i l e test at 100°C and
at very low strain rate
Reduct ion of area at rupture
(96)
37. 2
28. 9
21.3
26. 7
24. 1
20. 5
22.4
32. 5
24. 6
19. 1
21.8
23.2
25. 1
20.4
4.2
5.8
2.4
3.3
3. 1
6.8
3.9
the present invent ion.
,-
Test
No.
1
2
3
4
5
6
7
8
9
1 0
1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
2 0
2 1
* mark
A1 1 oy
1
2
3
4
5
6
7
8
9
1 0
1 1
1 2
13
1 4
* A
*I3
* C
* D
* E
* F
* G
denotes
Creep rupture
at 700°C
Creep rupture time
(h)
1180
1527 '
1819
1733
1637
1725
3135
1638
3352
3409
1612
3268
21 51
3643
648
684
1018
952
1055
720
1082
deviation from
test
and 300 MPa
Creep rupture
elongat ion
(%>
31.4
22. 5
19. 2
21.1
21.4
18.4
la. 2
26. 4
22. 1
17.4
18. 1
18. 8
21.0
18.0
5. 2
7. 0
1.8
4. 1
4. 3
7. 3
3. 1
condition defined in
a In contrast, in the case of test Nos. 15 to 21 of comparative examples
using alloys A to G having the chemical composition deviating from the
condition defined in the present invention, as compared with the case of test
Nos. 1 to 14 of example embodiments of the present invention, all of the creep
rupture time, the creep rupture ductility, and the reduction of area at rupture
in the tensile test at very low strain rate (that is, effects of preventing SR
cracks) are poor.
[01111
That is, in the case of test Nos. 15, 16 and 18, although alloys A, B and D
each have a chemical composition almost equivalent to that of alloy 2 used in
test No. 2 except that Nd is not contained, or the Nd content is out of the range
defined in the present invention, all of the creep rupture time, the creep
rupture ductility, and the reduction of area at rupture in the tensile test at
very low strain rate (that is, effects of preventing SR cracks) are poor.
[01121
In the case of test Nos. 17 and 19, although alloys C and E each have a
chemical composition almost equivalent to that of alloy 7 used in test No. 7
except that the Nd content is out of the range defined in the present invention,
all of the creep rupture time, the creep rupture ductility, and the reduction of
area at rupture in the tensile test at very low strain rate (that is, effects of
preventing SR cracks) are poor.
[01131
In the case of test No. 20, although alloy F has a chemical composition
almost equivalent to that of alloy 2 used in test No. 2 except that the 0 content
is out of the range defined in the present invention, all of the creep rupture
time, the creep rupture ductility, and the reduction of area at rupture in the
tensile test at very low strain rate (that is, effects of preventing SR cracks) are
poor.
In the case of test No. 21, although alloy G has a chemical composition
almost equivalent to that of alloy 7 used in test No. 7 except that the 0 content
is out of the range defined in the present invention, all of the creep rupture
time, the creep rupture ductility, and the reduction of area at rupture in the
tensile test at very low strain rate (that is, effects of preventing SR cracks) are
poor.
[Industrial Applicability]
[01151
The Ni-based heat resistant alloy of the present invention is an alloy in
which the dramatic improvement in ductility after long-term use at high
temperatures can be achieved, and the SR cracks that pose a problem in repair
welding and the like can be avoided. Therefore, this Ni-based heat resistant
alloy can be used suitably as a pipe material, a thick plate for parts having
heat resistance and pressure resistance, a rod material, a forging, and the like
in power generating boilers, chemical industry plants, and the like.

We claim:
ORIGINAL
[Claim 11
2 3 DEC 20%
A Ni-based heat resistant alloy consisting, in mass percent, of C: 0.15%
or less, Si: 2% or less, Mn: 3% or less, P: 0.03% or less, S: 0.01% or less, Cr:
15% or more and less than 28%, Mo: 3 to 15%) Co: more than 5% and not more
than 25%) Al: 0.2 to 2%, Ti: 0.2% to 3%, Nd: f l to 0.08%) and 0: 0.4Nd or less,
the balance being Ni and impurities, wherein the fl refers to the following
formula, and in the formula, d denotes an average grain size (pm), and each
symbol of an element denotes the content (mass%) of that element, and
likewise, Nd in 0.4Nd denotes the content (mass%) of Nd.
f l = 1.7 x 10.5d + 0.05((AU26.98) + (Td47.88))
[Claim 21
A Ni-based heat resistant alloy consisting, in mass percent, of C: 0.15%
or less, Si: 2% or less, Mn: 3% or less, P: 0.03% or less, S: 0.01% or less, Cr:
15% or more and less than 28%, Mo: 3 to 15%) Co: more than 5% and not more
than 25%, Al: 0.2 to 2%, Ti: 0.2% to 3%) Nd: f2 to 0.08%, and 0: 0.4Nd or less,
further containing at least one kind of Nb: 3.0% or less and W: less than 4%
(however, Mo + (W12): 15% or less), the balance being Ni and impurities,
wherein the f2 refers to the following formula, and in the formula, d denotes
an average grain size (pm), and each symbol of an element denotes the content
(mass%) of that element, and likewise, each symbol of an element in 0.4Nd and
Mo + (W12) also denotes the content (mass%) of that element.
f2 = 1.7 x 10-5d + 0.05{@ll26.98) + (Ti147.88) + (M3192.91))
[Claim 31
The Ni-based heat resistant alloy according to claim 1 or 2, wherein the
alloy contains one or more kinds of elements selected from the following groups
<1> to <4> instead of part of Ni:
B: 0.01% or less, Zr: 0.2% or less, and Hf: 1% or less
8 3 DjC 2013 <2> Mg: 0.05% or less, Ca: 0.05% or less, Y: 0.5% or less, La: 0. /o or ess,
and Ce: 0.5% or less
<3> Ta: 8% or less, and Re: 8% or less
<4> Fe: 15% or less.
Dated this 23*day of December, 20 13.
Sumitorno Metal Corporation
Suresh A. Shroff & Co.
Attorneys for the Applicant