The present invention relates to a Ni-based alloy. Specifically, the present
invention relates to a high strengtliNi-based alloy which is high in creep rupture strength
(creep rupture time), creep rupture ductility, and reheat cracking resistance.
10 Priority is claimed on Japanese Patent Application No. 2012-129649, filed on
June 7,2012, and the content of which is incorporated herein by reference.
Background Art
[0002]
15 In recent years, ultra super critical boilers in which steam temperature and
pressure are to increase for high efficiency have been newly built in the world
Specifically, it is planned to increase the steam temperature which is heretofore
approximately 600°C up to 650°C or more, or further up to 700°C or morc, arld to
increase the steam pressure which is heretofore approximately 25 MPa up to
20 approximately 35 MPa. The reason for the above is based on the fact that energy saving,
efficient use of resources, and reduction in COz emission for environmental protection
are one of objects for solving energy problems and are important industrial policies. In
addition, in a case of boilers for power generating plants and reacting funlaces for
chemical industrial plants where fossil fuel is combusted, it is advantageous to use high
25 enicient ultra super critical boilers and high efficient reacting furnaces.
[0003]
2
With increasing the steam temperature and pressure, the temperature of plates,
forgings, or the like which are used as superheater tubes in boilers, chemical industrial
reaction tubes, and heat resisting and pressure resisting materials increases up to 700°C
or more during actual operation. 'Thus, it is required for the alloy used in the above
5 severe environment for a long time to be excellent in not only high temperature strength
and high temperature corrosion resistance but also creep rupture ductility or the like.
[0004]
Furthcrmore, at the time of maintenance such as repairs aftcr usage for a long
time, it is necessary for materials aged by the usage for the long timc to be subject to the
10 treatment such as cutting, working, or welding. Thus, it has been eagerly required to
have not only characteristics as new materials but also soundness as aged materials. In
particular, it has been required to he excellent in reheat cracking resistance in order to
make the welding possible after the usage for the long time.
[OOOS]
With regard to the above severe requirements, in the conventional austenitic
stainless steels or the like, creep rupture strength (creep rupture time) is insufficient.
Thus, it is necessary to use a Ni-based heat resistant alloy in which precipitalic~n
strengthening derived from intermetallic compounds such as y' phase is utilized. Herein,
the creep rupture strength represents an estimated value obtained by Larson-Miller
20 parameter using a creep test temperature and a creep rupture time. Specifically, the
estimated value of creep rupture strength increases with an increase in the creep rupture
time. Thus, in the present invention, the creep rupture time is used as a parameter of
high temperature strength.
[0006]
Patent Documents 1 to 9 disclose Ni-based alloys used in the severe
3
environment suchas high-temperature as descr~beda bove. In the NI-based alloys, solld
solution strengthening is utilized by containing Mo andlor W, and precipitation
strengthening derivcd from intermctallic compounds such as y' phase, specifically Ni3(Al,
Ti), is utilized by containing Al and Ti.
5 [0007]
Among the Patent Documents, the alloys disclosed in the Patent Documents 4 to
6 include 28% or more of Cr, so that a large number of a-Cr phase having a bcc body
centered cubic) stnlcture precipitates, which contributes to the strengthening.
10 Related Art Documents
Patcnt Documents
[0008]
[Patent Document 11 Japanese Unexamined Patent Application, First
Publication No. S5 1-84726
15 [Patent Document 21 Japanese Unexammed Patent Apphcation, Flrst
Publication No. S51-84727
[Patent Document 31 Japanese Unexamined Patent Application, First
Publication No. 1107.150277
[Patent Document 41 Japanese Unexamined Patent Application, First
20 Publication No. H07-2165 11
[Patent Document 51 Japanese Unexamined Patent Application, First
Publication No. H08-127848
[Patent Document 61 Japanese Unexamined Patent Application, First
Publication No. H08-218 140
25 [Patent Document 71 Japanese Unexamiued Patent Application, First
Publication No. 1309-157779
4
&tent Document 81 Published Japanese Translation No.2002-5 18599 of the
PCT Lntcmational Publication
[Patent Document 91 Lnternal~onaPl ublication No. WO 20101038826
5 Summary of Invention
Technical Problem to be Solved
[0009]
In the Ni-based alloys disclosed in the Patent Documents 1 to 8, since y' phase or
a-Cr phase precipitates, the high temperature strength is excellent, however the creep
10 rupture ductility is inferior as compared with that of coiiventional austenitic heat resistant
steels or the like. Ln particular, since the aging deterioration occurs after the usage for
the long timc, the ductility and toughness drastically decrease as comparect with those of
new materials.
[OOlO]
15 At the time of periodical inspection after the usage for the long time and of
maintenance for troubles during the usage, deteriorated materials need to be partly cut
out and to be replaced with new materials. In this case, it is necessary to weld the new
materials to the aged materials to be used. Moreover, it is necessary to partly bend the
materials as required.
20 [OOll]
However, the Patent Documeilts 1 to 8 fail to disclose any solution in order to
suppress the dctcrioration of the matenals after the usage for thc long tlme. Spec~fically,
the Paienl Documents 1 to 8 do not consider how to suppress the aging dete~iorationa fter
the usage for the long time in thc prcscnt large plant under unprecedented conditions
25 such as higher temperature and higher pressure as compared with those of the past plant.
[0012]
5
The Patent Document 9 considers the above problems and discloses the alloy
which shows much higher strength than that of the conventional Ni-based heat resistant
alloy, further improved ductility and toughness after the usage for the long time in the
high-temperature, and improved hot workability. However, the Patent Document 9 does
5 not particularly consider the reheat cracking which may occur at welding.
[0013]
The present invention has been made in consideration of the above cncntioned
situations. An object of the present invention is to provide the Ni-based alloy in which
the creep rupture strength (creep rupture time) is improved by the solid solution
10 strengthening and the precipitation strengthening of y' phase, the ductility (creep rupture
ductility) after the usage for the long time in the high-temperature is drastically improved,
and the reheat cracking or the like which may occur at welding for repair or the like is
suppressed.
[0014]
Specifically, in the Ni-based alloy according to an aspect of the present
invention, y' phase or the like precipitates under usage environment in the plant, and as a
result, the high tempcrztture strength increases. In other words, in the Ni-best:d alloy
according to the aspect of the present invention, since y' phase or the lilce does not
precipitate before being installed in the plant, which is the solid solution state, the plastic
20 deformability is excellent. During the usage in the plant after being installed in the
plant, the high temperature strength (creep rupture time) increases, and also the creep
rupture ductility and the reheat craclcing resistance arc excellent. The object of the
present invention is to provide the above mentioned Ni-based alloy.
25 Solution to Problem
6
[OO15] -
The inventors have investigated how to improve the ductility after the usage for
the long time in the high-temperature and to suppress the reheat cracking with respect to
the Ni-based alloy which utilizes the precipitation strengthening of y' phase (hereinafter,
5 referred to as "y' hardened Ni-based alloy"'). Specifically, the inventors have
investigated the creep rupture time, the creep rupture ductility, and the reheat cracking
resistance with respcct to they' hardened Ni-based alloy. As a result, the inventors have
obtained the following findings (a) to (g).
[00 161
10 (a) In order to improve the ductility after the usage for the long time in the
high-temperature and to suppress the reheat cracking in they' hardened Ni-based alloy, it
is necessary to control carbonitrides which precipitate during thc usage in the plant.
Specifically, it is effcctivc to take account of an area fiaction p which represents the area
fraction of grain boundaries covered by the carbonitrides which precipitate in the grain
~.
I 15 boundaries with respect to the total grain boundarics.
[0017]
@) It is found that the area fraction p is quantified by an average gvai~si~z e and
amounts of B, C, and Cr which affect the precipitation amount of the carbonitrides which
precipitate in the grain boundaries. Thus, since the usage environment such as
20 operating temperature in the plant is predetermined, it is possible to control the
carbonitrides which precipitate during the usage in the plant by controlling the average
grain size after solution treatment and the chemical composition of they' hardened
Ni-based alloy.
[OO18]
(c) In addition to the area fraction p, iirtragranular strengthening is also an ,
7
important factor in order to improve the ductility and to suppress the rehcat cracking.
[00 191
(d) It is possible to quantify the intragranular strengthening by amounts of Al, Ti,
and Nb which are y' stabilizer and are included with Ni in y' phase. Thus, since the
5 usage environment such as operating temperature in the plant is predetermined, it is
possible to control y' phase which precipitate during the usage in the plant by controlling
the chemical coinposition of they' hardened Ni-based alloy.
[0020]
(e) As a result of investigating the relation between the area fraction p, thc
10 average grain size, and the intragranular strengthening in detail, it is found that thc area
fraction p which is minimum-required to improve the ductility and to suppress the reheat
cracking changes dcpending on the average grain size and the intragranular strengthening
Thus, by comprehensively controlling the chemical composition, the average grain size,
and the area fraction p, it is possible to obtain they' hardencd Ni-based alloy which is
15 excellent in the creep mpture time, the creep mpture ductility, and the reheat cracking
resistance.
[002 11
(f) Moreover, in order to segregate B which promotes the grain boundary
precipitation of the carbonitrides to the grain bonndaries in advance of P, P content needs
20 to be fl or less, when fl is cxprcssed by a following Expression Ausing B content
(mass %)
fl =0.01 -0.012/[1 +exp{(B - 0.0015)/0.001}] ---(ExpressionA)
[0022]
(g) Moreover, when precipitates with a major axis of 100 nm or more exist in
25 metallographic structure of the y' hardened Ni-based alloy after the solution treatment,
8
coarse precipitates increase during the usage in the plant, and as a rcsult, the creep
rupture strength decreases. Thus, it is preferable that the precipitates with the major
axis of 100 nix or more are absent in the metallographic structure after the solution
treatment.
5 [0023]
The present invention has been completed based on these findings. An aspect
of the present invention employs the following (1) to (6).
[0024]
(1) ANi-based alloy according to an aspect of the present invention includes,
10 as a chemical coir,position, by mass%,
0.001% to 0.15% of C,
0.01% to 2% of Si,
0.01% to 3% of Mn,
15% to less than 28% of Cr,
3% to 15% of Mo,
more than 5% to 25% of Co,
0.2% to 2% oFA1,
0.2% to 3% of Ti,
0.0005% to 0.01% of B,
0% to 3.0% of Nb,
0% to 15% of W,
0% to 0.2% of Zr,
0% to 1% of Hf,
0% to 0.05% of Mg,
0% to 0.05% of Ca.
0% to 0.5% of Y,
0% to 0.5% of La,
0% to 0.5% of Ce,
0% to 0.5% of Nd,
0% to 8% of Ta,
0% to 8% of Re,
0% to 15% of Fe,
fl expressed by a following Expression 1 or less of P,
0.01% or less of S, and
',
a balance consisting of Ni and impurities,
!
I
1
wherein, when an average grain size d is an average grain size in unit of pm of a
I
y phase included in a metallograpbic stmcture of the Ni-based alloy, the average grain
size d is 10 km to 300 pm,
wherein precipitates with a major axis of 100 nm or more are absent in the
15 metallographic structure, and
wherein, when an area fiaction p is expressed by a following Expression 2 wing
the average grain sizc d and amounts in unit of mass% of each element in thc chemical
composition, the area fraction p is f2 expressed by a following Expression 3 or more.
fl = 0.01 - 0.012 1 [1 + exp{(B - 0.0015) /0.001)] ...( Expression 1)
p = 21 x d0I5 + 40 x (500 x B / 10.81 + 50 x C / 12.01 + Cr / 52.00)'.~
. .(Expression 2)
iZ = 32 x doo7 + 115 x (A1 / 26.98 +Ti / 47.88 + Nb / 92.91)'.~ ...( Expression
3)
[0025]
(2) The Ni-based alloy according to (1) may include, as the chemical
composition, by mass%,
0.05% to 3.0% of Nb.
[0026]
(3) The Ni-based alloy according to (1) or (2) may include, as the chemical
5 composition, by mass%,
1% to 15% ofW.
[0027]
(4) The Ni-based alloy according to any one of (1) to (3) may include, as the
chemical composition, by mass%,
10 0.005% to 0.2% of Zr,
0.005% to 1% of Hf,
0.0005% to 0.05% of Mg,
0.0005% to 0.05% of Ca,
0.0005% to 0.5% of Y,
0.0005% to 0.5% of La,
0.0005% to 0.5% of Ce,
0.0005% to 0.5% of Nd,
0.01% to 8% ofTa,
0.01% to 8% of Re, and
1.5% to 15% of Fe.
[0028]
(5) A Ni-based alloy tube according to an aspect of the present invention
includes a Ni-based alloy according to any one of (1) to (4) for a production thereof.
25 Effects of Invenlion
11
[0029]
The Ni-based alloy according to the above aspects of the present invention is the
alloy in which the ductility (creep rupture ductility) after the usage for the long time in
the high-temperature is drastically improved and the reheat cracking or the like which
5 may occur at welding for repair or the like is suppressed. In other words, in the
Ni-based alloy according to the above aspect of the present invention, since y' phase or
the like does not precipitate before being installed in the plant, which is the solid solution
state, the plastic deformability is excellent. In addition, since y' phase or the like
precipitates during the usage in the plant after being installed in the plant, the high
10 temperature strength (creep rupture time) increases. Also, since the carbonitrides
preferably precipitate, the creep rupture ductility and the reheat cracking resistance are
high. Thus, it is possible to appropriatcly apply the Ni-based alloy to plates, bars,
forgings, or the like which are used as alloy tubes and heat resisting and pressure
resisting materials in boilers for power generating plants, chemical industrial plants, or
15 the hke
Detailcd Description of Preferred Embodiments
[0030]
Hereinafter, a preferable embodiment of the present invention will be described
20 in detail. First, a chemical compositiotl of a Ni-based alloy according to the
embodiment will be described
1. Chemical component (chemical composition) of alloy
Limitation reasons of each element are as follows. Hereinafter, "% of the
25 amount of respective elements as described below expresses "mass%. Moreover, the
limitation range of respective elemcnts as described below includes a lower limit and a11
12
-- ~~ upper limit thereof. I-Iowever, the limitation range inwhich the lower limit is shown as
"more than" does not include the lower limit, and the limitation range in which the upper
limit is shown as "less than" does not include the upper limit.
[0032]
5 The Ni-based alloy according to the embodiment includes, as base elements, C,
Si, Mn, Cr, Mo, Co, Al, Ti, and B.
[0033]
C: 0.001% to 0.15%
Carbon (C) is an important element which characterizes the embodiment with
10 below mentioned P, Cr, and B. Specifically, C is the element which affects an area
fraction p by forming carbonitrides. Moreover, C is the element which is effective in
ensuring creep rupture strength (creep rupture time) and tensile strength that are
necessary to be used in the environment such as high-temperature. However, when
more than 0.15% of C is included, at1 amount of insoluble carbonitrides increases in a
15 solid solution state, and as a result, not only C does not contribute to the improvement in
high temperature strength but also C deterioratcs mechanical properties such as
toughness and weldahility. Thus, C content is to be 0.15% or less. C conti:rrt is
preferably 0.1% or less. In addition, when C content is less than 0.001%, the
precipitation of the carbonitrides which occupy the grain boundaries may be insufficient.
20 Thus, in order to obtain the above effects, C content is to be 0.001% or more. C content
is preferably 0.005% or more, is further preferably 0.01% or more, and is much further
preferably 0.02% or more.
100341
Si: 0.01% to 2%
Si (silicon) is included as a deoxidizing element. However, when more than
13
2% of Si is included, the weldability and hot workab~htyd ecrease Also, the toughness
and ductility decrease because of the deterioration of microstructural stability in the
high-temperature by promoting the formation of intermetallic compounds such as o
phase. Thus, Si content is to be 2% or less. Si content is preferably 1.0% or less and
5 is further preferably 0.8% or less. In addition, in order to obtain the above effects, Si
content is to be 0.01% or more. Si conteiit is preferably 0.05% or more and is further
preferably 0.1 % or more.
[0035]
Mn: 0.01% to 3%
10 Mn (manganese) has a deoxidizing effect in common with Si. Also, Mn has an
I
I
4 effect in improving the hot workability by fixing S which is included as an impurity in
the alloy as sulfides. However, when Mn content is excessive, the formation of spinel
type oxide films is promoted, and as a result, oxidation resistance in the high-temperature
decreases. Thus, Mn content is to be 3% or less. Mn content is preferably 2.0% or
15 less and is further preferably 1.0% or less. In addition, in order to obtain the above
effects, Mn content is to be 0.01% or more. Mn content is preferably 0.05% or more
and is further preferably 0.08% or inore.
[0036]
Cr: 15% to less than 28%
20 Cr (chromium) is an important element which characterizes the embodiment
with the above mentioned C and the below mentioned P and B. Specifically, Cr is the
element which affects the area fraction p. Moreover, Cr is the important element which
is more effective in improving corrosion resistance such as the oxidation resistance,
steam oxidation resistance, and high temperature coi-rosion resistance. However, when
25 Cr content is less than 15%, the above intended effects are not obtained. On the other
14
hand, when Cr content is 28% or more, the hot workability decreases and the
microstmctural stability deteriorates by precipitating o phase. Thus, Cr content 1s to be
15% or more and less than 28%. Cr content is preferably 18% or more, is furthcr
preferably 20% or more, and is most preferably more than 24%. Cr content is
5 preferably 26% or less and is further preferably 25% or less.
100371
Mo: 3% to 15%
Mo (molybdenum) has effects in increasing the creep rupture strength by being
solid-soluted into matrix and in decreasing linear expansion coefficient. In order to
10 obtain the above effects, 3% or more of Mo need to be included. However, when Mo
content is more than 15%, the hot worlcability and the microstructural stability decreasc.
Thus, Mo content is to be 3% to 15%. Mo content is preferably 4% or more and is
further preferably 5% or morc. Mo content is preferably 14% or less and is further
preferably 13% or less
15 [0038]
Co: more than 5% to 25%
Co (cobalt) 1x1s an effect in increasing the creep mpture strength by li,cing
solid-soluted into the matrix. Also, Co has an effect 111 further increasing the creep
rupture strength by increasing the precipitation amount of y' phase in a temperature range
20 of 750°C or more in pa~ticular. In order to obtain the above effects, more than 5% of
Co need to be included. I-lowever, when Co content is morc than 25%, the hot
worlcability decreases. Thus, Co content is to be more than 5% and 25% or less. 111 a
case where the balance between the hot workability and the creep rupture strength is
regarded as important, Co conteut is preferably 7% or more and is further preferably 8%
25 or more. Also, Co content is preferably 20% or less and is further preferably 15% or
less.
[0039]
Al: 0.2% to 2%
A1 (alumiilum) is an important element which precipitates y' phase (Ni,Al) that
5 is the intermetallic compound in the Ni-based a!loy and which considerably increases the
creep rupture strength. In order to obtain the above effects, 0.2% or more ofAl need to
be included. However, when A1 content is more than 2%, the hot workability decreases,
and it is difficult to conduct hot forging and hot tubemaking. in addition, when A1
content is more than 2%, creep rupture ductility and reheat cracking resistance may
10 decrease. Thus, .41 content is to be 0.2% to 2%. A1 content is preferably 0.8% or more
and is further preferably 0.9% or more. A1 content is preferably 1.8% or less and is
further preferably 1.7% or less.
[0040]
Ti: 0.2% to 3%
j
15 Ti (titanium) is an important element which precipitates y' phase (Ni3(AI,Ti))
that is the intermetallic compound with A1 in the Ni-based alloy and which considerably
increases the creep rupture strength. In order to obtain the above effects, 0.2% or more
of Ti need to he included. However, when Ti content is more than 3%, the hot
workability decreases, and it is difficult to conduct the hot forging and the hot
20 tubemaking. In addition, when Ti content is inore than 3%, the crccp rupture ductility
and the reheat cracking resistance may decrease. Thus, Ti content is to be 0.2% to 3%.
Ti content is preferably 0.3% or more and is further preferably 0.4% or more. Ti
content is preferably 2.8% or less and is further preferably 2.6% or less.
[0041]
B: 0.0005% to 0.01%
16
B (boron) is an important element which characterizes the embodimnt with the
above mentioned C and Cr and the below mentioned P. Specifically, B is the element
which is included in the carbonitrides with C and N and which affects the area fraction p.
Moreover, B has an effect in increasing the creep rupture stsength by promoting the fine
5 and dispersive precipitation of the carbonitrides. Fu~thermoreB, has an effect in
drastically increasing the creep rupttire strength, the creep rupture ductility, and the hot
workability in a lower temperature range such as approximately 1000°C or less for the
Ni-based alloy according to the embodiment. In order to obtain the above effects,
0.0005% or more of B need to be included. On the other hand, when B content is
10 excessive, in particular, when B content is more than 0.01%, the hot workability
decreases in addition to a decrease in the weldability. Thus, B content is to he 0.0005%
to 0.01%. B content is preferably 0.001% or more. B content is preferably 0.008% or
less and is further preferably 0.006% or less.
[0042]
15 The Ni-based alloy according to the embodiment includes the above mentioned
elements and the below mentioned optional elements, and the balance consists of Ni and
impurities. Next, NI included as the balance of the Ni-based alloy according io the
embodiment will be described.
[0043]
20 Ni (nickel) is an important element which stabilizes y phase having fcc (face
centered cubic) structure and which ensure the corrosion resistance. In the embodiment,
Ni content does not need to be particularly limited. Ni content may be the content
obtained by removing the impurity content from the balance. Ni content in the balance
is preferably more than 50% and fulthcr preferably more than 60%.
25 100441
17
Next, the impurities included as the balance of the Ni-based alloy according to
the embodiment will bc dcscribed. Herein, "impurities" represent elements which are
contaminated during industrial production of the Ni-based alloy from ores and scarp that
are used as a raw matcrial or from environment of a production process. Among the
5 impurities, it is preferable that P and S are limited to the following in order to sufficiently
obtain the above mentioned effects. Moreover, since it is preferable that the amount of
rcspective impurities is low, a lower limit docs not need to be limited, and the lower limit
of the respcctivc impurities may be 0%.
[0045]
10 P: limited to f 1 or less, f 1 bcing expressed by a following Expression A
P (phosphorus) is a noticcablc clement which characterizes the embodiment with
the abovc mentioned C, Cr, and B. Specifically, P is included as thc impurity in the
alloy, and the weldability and the hot workability drastically decrease when Pis
excessively included. Moreover, P tends to segregate to the grain boundaries in advance
15 of B which let the carbonitrides precipitate finely and dispersedly. Thereby, the
fo~mationo f precipitates is suppressed, and the creep rupture strength, the creep ruphlre
ductility, and the reheat cracking resista~ced ecrease. Thus, P content needs lo be
limited in proportion as B content. Specifically, P content needs to be limited to fl or
less when fl is expressed by a following Expression A. It is preferable to control P
20 content as low as possible, and P content is preferably 0.008% or less.
fl = 0.01 - 0.012 1 [l + exp{(B - 0.0015) / 0.001}] ..-(Expressionh)
[0046]
S: limited to 0.01% or less
S (sulfur) is included as t11e impurity in the alloy in common with P: When S is
25 excessively included, the weldability and the hot workability drastically decrease. Thus,
18
S content is limlted to 0.01% or less In a case where thc hot workability is regarded as
important, S content is preferably 0.005% or less and is further preferably 0.003% or
Icss.
[0047]
5 In addition, N (nitrogen) is included as an impurity in the Ni-based alloy
according to the embodiment. However, even if the Ni-based alloy includes N which is
contaminated as the impurity by ordinary producing condition, the above mentioned
effects of the Ni-based alloy according to the embodiment are not affected. Thus, N
content does not need to be particularly limited. Although N included as the impurity
10 bonds to other elements to form the carbonitrides in thc alloy, the amount of N which is
contaminated as thc impurity does not affect the folmation of the carbonitrides. Thus, it
is not necessary to take account of N content in order to control the carbonitrides. In
order to preferably control the formation of the carbonitrides, N content may be 0.03% or
less.
I
15 [0048]
In substitution for a part of the above mentioned Ni, the Ni-based alloy
according to the embodiment may hrther include at least one optional elemc-r~sle lected
from the group consisting of Nb, W, Zr, Hf, Mg, Ca, Y, La, Ce, Nd, Ta, Re, and Fe whose
contents are mentioned below. The optional elements may be included as necessary.
20 Thus, a lower limit of the respective optional elements does not need to be limited, and
the lower limit may be 0%. Moreover, even if the optional elements may be included as
impurities, the above mentioned effects are not affected.
[0049]
Nb: 0% to 3.0%
Nb (niobium) has an effect in increasing the creep rupture strength. Since Nb
19
has the effect in increasing the creep rupture strength hy forming y' phase that is the
intermetallic compound with A1 and Ti, Nb may be included as necessary. However,
when more than 3.0% of Nb is included, the hot worltability and the toughness decrease
Moreover, Nb content is more thali 3.0%, the creep rupture ductility and the reheat
5 cracking resistance may decrease. Thus, Nb content may be 0% to 3.0% as necessary.
Nb content is preferably 2.5% or less. In order to stably obtain the above effects, Nb
content is preferably 0.05% or more and is further preferably 0.1% or more.
[0050]
W: 0% to 15%
10 W (tungsten) has an effect in increasing the creep rupture strength. Since W
4 has the effect in increasing the creep rupture strength by being solid-soluted into the
::
matrix as a solid solution hardening element, W may be included as necessary.
Although Mo is included as one of the base elements in the embod~menti,t is possible to
obta~nth e preferable properties for zero duct~liiyte mperature and the hot workab~lityin a
15 hgher temperature range such as approx~mately 11 50°C or more by includmg W as
compared with the same Mo equivalent. Thus, in order to ensure the hot worltability in
the higher temperature range, it is preferable that W is included. Moreove~.i,l lthough
Mo and W are solid-soluted into y' phasc which precipitates by including A1 and Ti, W
tends to be sufficiently solid-soluted into y' phase as compared with the same Mo
20 equivalent, and thereby, it is possible to suppress y' phase eoarscning during the usage for
the long time. Thus, in order to stably ensure the high creep rupture strength for the
long time in the high-tenlperature, it is preferable that W is included. Thus, W content
may be 0% to 15% as necessary. 01 order to stably obtain the above effects, W content
is preferably 1% or more and is further preferably 1.5% or more.
[0051]
20
Any one or two of the above-mentioned Nb and W may be included. In a case
where the elements are simultaneously included, total amount is preFerably 6% or less.
[0052]

Zr: 0% to 0.2%
Hf:O%to 1%
Each of Zr and Hf of the group has an effect in increasing the creep rupture
strength. Thus, thc clements may be included as necessary.
[0053]
10 Zr: 0% to 0.2%
Zr (zirconium) is an elcmcnt which strengthens the grain boundaries and has the
effect in increasing the creep rupture strength. Also, Zr has an effect in increasing the
creep rupture ductility. Thus, Zr may be included as necessary. However, when Zr
content is excessive and is more than 0 254, the hot worlcabllity may decrease Thus, Zr
I
15 content may be 0% to 0.2% as necessary. Zr content is preferably 0.1% or less and is
further preferably 0.05% or less. On the other hand, in order to stably obtaln the above
effects, Zr content is preferably 0.005% or more and is further preferably 0 0 1% or more.
[0054]
Elf. 0% to 1%
Hf (hafnium) mainly contributes to the grain boundary strengthening and has the
effect in increasing the creep tupture strength. Thus, Nf may be included as necessary.
However, when ilf content is more than 1%, the workability and the weldability may
decrease. Thus, Hf content may be 0% to 1% as necessary. Hf content is preferably
0.8% or less and is further preferably 0.5% or less. On the other hand, in order to stably
25 obtain the above effccts, I-If content is preferably 0.005% or more, is further preferably
21
0.01% or morc, and is furthepmrmorper eferably 0.02% or more.
[0055]
Any one or two of the above-mentioned Zr and I-If may be included. In a case
where the elements arc simultaneoitsly included, total amount is preferably 0.8% or less.
5 [0056]
<2>
Mg: 0% to 0.05%
Ca: 0% to 0.05%
Y 0% to 0.5%
La: 0% to 0.5%
Ce: 0% to 0.5%
Nd: 0% to 0.5%
Each of Mg, Ca, Y, La, Ce, and Nd of the <2> group has an effect in illcreasing
the hot workability by fixing S as the sulfides. Thus, the elements may be included as
15 necessary.
[0057]
Mg: 0% lo 0.05%
Mg (magnesium) has an effect in improving the hot worlcability by fixing S
which deteriorates the hot workability as sulfides. Thus, Mg may be included as
20 necessary. However, when Mg content is more than 0.05%, material properties may
deteriorate. Specifically, the hot workability and the ductility may decrease. Thus, Mg
content may be 0% to 0.05% as necessary. Mg content is preferably 0.02% or less and
is further preferably 0.01% or less. On the other hand, in order to stably obtain the
above effects, Mg content is preferably 0.0005% or more and is further preferably
25 0.001% or more.
[0058]
Ca: 0% to 0.05%
Ca (calcium) has an effect in improving the hot workability by fixing S which
deteriorates the hot workability as sulfides. Thus, Ca may be included as necessary.
5 However, when Ca content is more than 0.05%, the material properties may deteriorate.
Specifically, the hot workability and the ductility may decrease. Thus, Ca content may
be 0% to 0.05% as necessaxy. Ca content is preferably 0.02% or less and is further
preferably 0.01% or less. On the other hand, in order to stably obtain the above effects
of Ca, Ca content is preferably 0.0005% or more and is further preferably 0.001% or
10 more.
[0059]
Y: 0% to 0.5%
Y (yttrium) has an effect in improving the hot workability by fixing S as sulfides.
Moreover, Y has effects in improving adhesiveness of a Crz03 protective fihn on the
15 alloy surface and in improving the oxidation resistance at cyclic oxidation. Furthermore,
Y contributes to the grain boundary strengthening and has an effect in increasing the
creep supture strength and the creep supture ductility. Thus, Y may be incln
Ta: 0% to 8%
Re: 0% to 8%
Each of Ta and Re of the <3> group act as the solid solution hardening element
and has an effect in increasing the high temperature strength, specifically, the creep
25 rupture strength. Thus, the elements may be included as necessary.
25
100651 ~
Ta: 0% to 8%
Ta (tantalum) forms the carbonitrides and has an effect in increasing the high
temperature strength, specifically, the creep rupture strength as the solid solution
5 hardening element. Thus, Ta may be included as necessary. IIowever, when Ta
content is Inore than 8%, the workability and the mechanical properties may decrease.
Thus, Ta content may be 0% to 8% as necessary Ta content is preferably 7% or less
and is further preferably 6% or less. On the other haud, in order to stably obtain the
above effects, Ta content is preferably 0.01% or more, is further preferably 0.1% or more,
10 and is furthermore preferably 0.5% or more.
I [0066]
I
Re: 0% to 8%
Re (rhenium) has an effect in increasing the high temperature strength,
specifically, the creep rupture strength as mainly the solid solution hardening element.
15 Thus, Re may be included as necessary. However, when Re content is more than 8%,
the worlcability and the mechanical properties may decrease. Thus, Re content may be
0% to 8% as necessary Re content is preferably 7% or less and is further prcrerably 6%
or less. On the other hand, in order to stably obtain the above effects, Re content is
preferably 0.01% or more, is further preferably 0.1% or more, and is furthermore
20 preferably 0.5% or more.
[0067]
Any one or two of the abovc-ment~onedT a and Re may bc included. In a case
where the elements are simultaneously included, total amount is preferably 8% or less.
[0068]
25 <4>

CLAIMS
1. ANi-based alloy cornpnsing, as a chemical composition, by mass%,
0.001% to 0.15% of C,
0.01% to 2% of Si,
0.01% to 3% of Mn,
15% to less than 28% of Cs,
3% to 15% of Mo,
more than 5% to 25% of Co,
0.2% to 2% of Al,
0.2% to 3% of Ti,
0.0005% to 0.01% of B,
0% to 3.0% of Nb,
0% to 15%ofW,
0% to 0.2% of Zr,
0% to 1 % of Hf,
0% to 0.05% of Mg,
0% to 0.05% of Ca,
0% to 0.5% of Y,
0% to 0.5% of La,
0% to 0.5% of Ce,
0% to 0.5% of Nd,
0% to 8% ofTa,
0% to 8% of Re,
0% to 15% of Fe,
45
fl expressed by a following Expression 1 or less of P,
0.01% or less of S, and
a balance consisting ofNi and impurities,
wherein, when an average grain size d is an average grain size in unit of pm of a
I
4 5 y phase included in a metallographic structure of the Ni-based alloy, the average grain
size d is 10 pm to 300 pm,
wherein precipitates with a major axis of 100 nm or inore are absent in the
metallographic structure, a:id
wherein, when an area fraction p is expressed by a following Expression 2 using
10 the average grain size d and amounts in unit of mass% of each element in the chemical
composition, the area haction p is f2 expressed by a following Expression 3 or more,
fl = 0.01 - 0.012 / [l + exp{(B - 0.0015) 10.001)] .-.(Expression I),
(Expression 2),
2. The Ni-based alloy according to claim 1 comprising, as the chemical
composition, by mass%,
20 0.05% to 3.0% ofNb.
3. The Ni-based alloy according to claim 1 or 2 comprising, as the chemical
coinposition, by mass%,
1% to 15% of W.
46
4. The Ni-based alloy according to any one of claims 1 to 3 comprising, as the
chemical composition, by mass%, at least one selected from
0.005% to 0.2% of Zr,
0.005% to 1% of Hf,
5 0.0005% to 0.05% of Mg,
0.0005% to 0.05% of Ca,
!
I
'1 0.0005% to 0.5% ofY,
0.0005% to 0.5% of La,
0.0005% to 0.5% of Ce,
10 0.0005% to 0.5% of Nd,
0.01% to 8% ofTa,
'I ': 0.01% to 8% of Rc, and
I
15 5. ANi-bascd alloy tube compris~nga Ni-based alloy according to any one of
claims 1 to 4 for a production thcreof