1. A high-temperature piping product for flowing a high-temperature fluid, configured from a plurality of primary pipe members and a welding material, 5 wherein the primary pipe members are each made from an Ni-based forged alloy which contains Ni, Al, and at least one of Mo and W, the total content of the Mo and the W being 3 mass - or more and 8 mass& or less, the Ni-based forged alloy having a yl-phase dissolution temperature of from 920 to 970°C, and a 10 y' phase being precipitated in the Ni-based forged alloy in 30 volume% or more in a temperature range of from 700 to 800°C, wherein the welding material is made from an Ni-based cast alloy having a cast structure formed by welding, the Ni-based cast alloy containing Ni, Al, and at least one of Mo and W, the 15 total content of the Mo and the W being 9 mass8 or more and 15 mass% or less, the Ni-based cast alloy having a yl-phase dissolution temperature of from 850 to 900°C, a y1 phase being precipitated in the Ni-based cast alloy in 20 volume> or more in a temperature range of from 700 and 800°C, and 20 wherein the welding material is buttered to the primary pipe members in portions to be welded to each other.

2. The high-temperature piping product according to claim 1, 25 whereintheNi-basedforgedalloycontains:Alof3.5mass?. or more and 4.5 mas's% or l e s s ; C r of 15 mass% or more and 20 mass% o r l e s s ; Co of 25 mass% o r l e s s ; C of 0.01 mass8 or more and 0.15mass% o r l e s s ; a t l e a s t o n e o f M o a n d W i n a t o t a l c o n t e n t of 3 mass% t o 8 mass%; and N i and unavoidable impurities 5 accounting for the reminder, and wherein the Ni-based c a s t a l l o y contains: A1 of 3 massor more and 3.5 mass% or l e s s ; C r of 15 mass% or more and 20 mass% or l e s s ; Co of 25 mass% o r l e s s ; C of 0.01 mass% or more and 0.15mass% or l e s s ; a t l e a s t o n e o f M o a n d W i n a t o t a l c o n t e n t 10 of 9 mass% t o 15 mass%; and N i and unavoidable impurities accounting f o r the reminder.

3. A method f o r producing the high-temperature piping product according t o claim 1 or 2 , the method comprising: 15 a secondarypipememberforming s t e p o f w e l d i n g t h e p r i m a r y pipe members t o each other with the welding m a t e r i a l b u t t e r e d t o welding portions of the primary pipe members and forming secondary pipe members each constructed from the p l u r a l i t y of primary pipe members; and 20 a high-temperaturepiping product forming s t e p of welding the secondary pipe members t o each other with the welding m a t e r i a l b u t t e r e d t o welding portions of the secondary pipe members and forming a high-temperature piping product.

4. The method according t o claim 3, f u r t h e r comprising 26 apre-agingheattreatmentstepof subjectingthe secondarypipe members to a heat treatment at a temperature equal to or greater than the y'-phase dissolution temperature of the Ni-based cast alloy and at a temperature equal to or less than the 7'-phase 5 dissolution temperature of the Ni-based forged alloy to precipitate 5 volume% or more and 15 volume% or less of the y' phase in the primary pipe members, the pre-aging heat treatment step being performed after the secondary pipe member forming step and before the high-temperature piping product forming 10 step. 5 . The method according to claim 4, wherein the high-temperature piping product forming step is not followed by an aging heat treatment in which 30 volume% or more of the 15 y' phase is precipitated in the primary pipe members under e x t e r n a l h e a t a p p l i e d t o t h e w h o l e o f t h e h i g h - t e m p e r a t u r e p i p i n g product.

6. A boiler for power plants, the boiler comprising the 20 high-temperature piping product according to claim 1 or 2.

7. A high-temperature piping product for flowing a high-temperature fluid, substantially as herein described with reference to accompanying drawings and examples. 25

8. A b o i l e r f o r power p l a n t s , s u b s t a n t i a l l y as h e r e i n d e s c r i b e d w i t h r e f e r e n c e t o accompanying drawings andexamples.

TITLE OF THE INVENTION
HIGH-TEMPERATURE PIPING PRODUCT AND METHOD FOR PRODUCING SAME
5 BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to high-temperature piping
products for power plants, particularly to high-temperature
piping products used in coal-fired power plants and gas turbine
10 power plants, and methods for producing such piping products.
2. DESCRIPTION OF RELATED ART
In order to improve the power generating efficiency of
power plants such as coal-fired power plants and gas turbine
power plants, it is effective to increase the main steam
15 temperature of a boiler and the combustion temperature of a gas
turbine. In this connection, piping products with higher
tolerable temperature are needed to further increase the main
steam temperature or the combustion temperature.
For example, coal-firedpowerplantsusinga steamturbine
20 include large scale high-temperature piping products for the
boiler. Such large scale high-temperature piping products are
assembled usually by welding short pipe members. In the power
plants which produce a main steam of a temperature of around
700°C, an Ni-based alloy precipitation-strengthened with y'
25 phase (Ni3Alphase) is usedas amaterial ofthe high-temperature
piping products.
In an Ni-based alloy, it is indispensable that they' phase
is evenly dispersed and precipitated in a matrix phase by heat
treatment to attain high mechanical strength at a
5 high-temperature. On the other hand, precipitation of the y'
phase is detrimental to weldability, and makes the welding
difficult. It is accordingly desirable to perform the heat
treatment after the welding. A problem, however, is that,
because the welded and assembled high-temperature piping
10 product is a large structure, it is very difficult after
assemblingtoconductaheattreatmentprecipitatingthey' phase
(anagingheattreatment, socalled) tothewholepipingproduct.
As a countermeasure, W02009/028671 reports a technique
whereby boiler components are welded and assembled without
15 precipitating the y' phase, and the y' phase is evenly dispersed
and precipitated in the matrix phase of the boiler component
by heat generated through a power plant operation. More
specifically, the publication describes a
low-thermal-expansion Ni-based super-heat-resistant alloy
20 preferred for use as a boiler component material. The alloy
contains, in mass%, C of 0.2% or less, Si of 0.5% or less, Mn
of 0.5% or less, Cr of 10 to 24%, one of or both of Mo and W
in amounts specified by the equation of "Mo + 0.5W = 5 to 17, ",
A1 of 0.5 to 2.0%, Ti of 1.0 to 3.0%, Fe of 10% or less, and
25 one of or both of B (0.02% or less; excluding 0%) and Zr (0.2'
or less; excluding O%), with the reminder being Ni and
unavoidableimpurities. T h e a l l o y h a s a V i c k e r s h a r d n e s s o f 2 4 0
or less.
The assumed operating temperature of the Ni-based alloy
5 (or theboiler component) describedinW02009/028671ranges from
700 to 750°C (700°C class), and the precipitation amount of the
y' phase is about 20%. In response to the recent strong demand
for further improvement of the power generating efficiency of
power plants, there have been studies directed to increasing
10 the main steam temperature or combustion temperature to above
750°C and as high as about 800°C (800°C class). In order to
increase the tolerable temperature of the high-temperature
piping product in the power plant to temperatures of the 800°C
class, there is required a yl-phase precipitation amount of 30%
15 or more in the material Ni-based alloy.
In one known method of attaining a yl-phase precipitation
amount of 30% or more to obtain an effective high-temperature
strength for the Ni-based alloy, for example, a heat treatment
is performed at 900°C or more to precipitate about 108 of the
20 y1 phase, followed by an aging heat treatment at 700 to 800°C.
However, as described above, it is difficult to perform such
a series of heat treatments for the welded and assembled
high-temperature piping product. Furthermore, it is revealed
through studies conducted by the present inventors that it is
25 difficult to ensure the required high-temperature strength
characteristics by the direct application pfthe Ni-based alloy
described in W02009/028671. (This will be described later in
greater detail.)
5 SUMMARY OF THE INVENTION
Inviewofthe foregoing, it is anobjective ofthe present
invention to solve the above-describedproblems, and to provide
high-temperature piping products exhibiting a tolerable
temperature of the 800°C class, and a method for producing such
10 high-temperature piping products. The present invention also
provides a boiler for power plants of the 800°C class equipped
with the high-temperature piping product.
(I) According to an aspect of the present invention, there
is provided a high-temperature piping product for flowing a
15 high-temperature fluid, configured from a plurality of primary
pipe members and a welding material,
wherein the primary pipe members are each made from an
Ni (nickel)-basedforgedalloywhichcontains Ni, A1 (aluminum),
and at least one of Mo (molybdenum) and W (tungsten), the total
20 content of the Mo and the W being 3 mass% or more and 8 mass?
or less, the Ni-based forged alloy having a y' (gamma
prime) -phase dissolution temperature of from 920 to 970°C, and
a y' phase being precipitated in the Ni-based forged alloy in
30 volume% or more in a temperature range of from 700 to 800°C,
25 wherein the weldingmaterial is made froman Ni-based cast
alloy having a cast structure formed by welding, the Ni-based
cast alloy containing Ni, Al, and at least one of Mo and W, the
total content of the Mo and the W being 9 mass% or more and 15
mass% or less, the Ni-based cast alloy having a yl-phase
5 dissolution temperature of from 850 to 900°C, a y ' phase being
precipitated in the Ni-based cast alloy in 20 volume% or more
in a temperature range of from 700 and 800°C, and
wherein the welding material is buttered to the primary
pipe members in portions to be welded to each other.
10 In the present invention, the y1 phase means an Ni:Al
intermetallic compound phase having an L12 structure, and
encompasses compounds in which the A1 site is partially
substituted with other elements. The process leading to the
production of the Ni-based cast alloy is not limited, as long
15 as the final structure is a cast structure.
In the above aspect (I) of the invention, the following
modifications and changes can be made.
(i) The Ni-based forged alloy contains: A1 of 3.5 mass:
or more and 4.5 mass% or less; Cr (chromium) of 15 mass% or more
20 and 20 mass% or less; Co (cobalt) of 25 mass% or less; C (carbon)
of 0.01 mass% or more and 0.15 mass% or less; at least one of
Mo and W in a total content of 3 mass% to 8 mass%; and Ni and
unavoidable impurities accounting for the reminder.
Furthermore, the Ni-based cast alloy contains: A1 of 3 mass.
25 or more and 3.5 mass% or less; Cr of 15 mass% or more and 20
mass% or less; Co of 25 mass8 or less; C of 0.01 mass8 or more
and0.15mass% or less; atleastoneofMoand Winatotalcontent
of 9 mass% to 15 mass%; and Ni and unavoidable impurities
accounting for the reminder.
5 (11) According toanother aspect ofthe present invention,
there is provided a method for producing the above-described
high-temperature piping product, the method including:
asecondarypipememberforming stepofweldingtheprimary
pipe members to each other with the welding material buttered
10 to welding portions of the primary pipe members and forming
secondary pipe members each constructed from the plurality of
primary pipe members; and
a high-temperature piping product forming step of welding
the secondary pipe members to each other with the welding
15 material buttered to welding portions of the secondary pipe
members and forming a high-temperature piping product.
In the above aspect (11) of the invention, the following
modifications and changes can be made.
(ii) The method further includes a pre-aging heat
20 treatment step of subjecting the secondary pipe members to a
heat treatment at a temperature equal to or greater than the
yl-phase dissolution temperature of the Ni-based cast alloy and
at a temperature equal to or less than the yl-phase dissolution
t e m p e r a t u r e o f t h e N i - b a s e d f o r g e d a l l o y t o p r e c i p i t a t e 5 v o l u m e %
25 or more and 15 volume% or less of the y' phase in the primary
pipe members, the pre-aging heat treatment step being performed
after the secondary pipe member forming step and before the
high-temperature piping product forming step.
(iii) The high-temperature piping product forming step
5 is not followed by an aging heat treatment in which 30 volumeo
r m o r e o f t h e y ' p h a s e i s p r e c i p i t a t e d i n t h e p r i m a r y p i p e m e m b e r s
under external heatappliedtothewhole ofthe high-temperature
piping product.
(111) According to still another aspect of the present
10 invention, there is provided a boiler for power plants, the
boiler including the above-described high-temperature piping
product.
(Advantages of the Invention)
According to the present invention, it is possible to
15 provide a high-temperature piping product exhibiting a
tolerabletemperature ofthe 800°C class, and to provide amethod
for producing such high-temperature piping products. The
present invention can also provide a boiler for power plants
of the 800°C class with the use of the high-temperature piping
20 product.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view representing an exemplary
procedure of producing a high-temperature piping product
25 according to an embodiment of the present invention.
FIG. 2 is a schematic view showing microstructures of weld
joints of Samples 1 to 6.
FIG. 3is a schematic view showingmicrostructures of weld
joints of Samples 7 to 9.
5
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will be described
below. However, the present invention is not limited to the
specific embodiments described below, but various combinations
10 andmodificationsarepossiblewithoutdepartingfromthe spirit
and scope of the invention.
(High-Temperature Piping Product)
As described above, the high-temperature piping product
according to an embodiment of the present invention is a
15 structure formed by welding and assembling relatively short
primarypipe members with a welding material. And the Ni-based
forged alloy forming the primary pipe member, and the Ni-based
cast alloy forming the welding material have differentyl-phase
dissolution temperatures ("yl-phase dissolution temperature of
20 the Ni-based forged alloy" > "yl-phase dissolution temperature
of the Ni-based cast alloy"). The welding portions of the
primary pipe members represent a weld joint buttered with the
welding material.
In order to ensure desirable weldability and desirable
25 tolerabletemperature ofthe 800°C class (sufficient mechanical
strength in this temperature range), the primary pipe member
is preferably made from an Ni-based forged alloy that exhibits
a y' phase (Ni3Al phase) dissolution temperature of from 920 to
970°C, and in which 30 volume8 or more and 40 volume% or less
5 (30-40 volume%) of the y' phase is dispersed and precipitated
in a temperature range of from 700 to 800°C. A sufficient
tolerable temperature cannot be obtained when the amount of the
y' phase dispersed and precipitated in the 700 to 800°C
temperature range is less than 30 volume%, and the ductility
10 degrades greatly when the amount of the dispersed and
precipitated y' phase is above 40 volume%.
Furthermore, when they'-phase dissolution temperature of
the Ni-based forged alloy is less than 920°C, it becomes
difficult to obtain the high-temperature piping product
15 exhibiting a tolerable temperature of the 800°C class by means
oftheproducingmethodaccordingto anembodiment ofthe present
invention (details will be described later). With a yl-phase
dissolution temperature in excess of 970°C, the weldability of
theprimarypipememberdegrades, andthehotworkabilitysuffers
20 (the ductility degrades), making it difficult to produce the
pipe member itself.
Preferably, the Ni-based forged alloy has a composition
containing:Alof3.5mass%ormoreand4.5mass%orless (3.5-4.5
mass%); Cr of15mass% ormoreand20mass% or less (15-20massTj);
25 Co of 25 mass% or less; C of 0.01 mass% or more and 0.15 massor
less (0.01-0.15 mass%); at least one of Mo and W in a total
content of 3 mass% to 8 mass%; and Ni and unavoidable impurities
accounting for the reminder.
The Mo component and the W component are constituent
5 elements that have strong effects on the precipitation amount
and the dissolution temperature of the y1 phase, and on the hot
workability of the Ni-based alloy. A sufficient tolerable
temperature cannot be obtained when the total content of the
Mo component and the W component is less than 3 mass;. Above
10 8 mass%, the hot workability suffers (the ductility degrades) ,
making it difficult to produce the pipe member itself.
The A1 component is an essential component for forming
the y' phase. With an A1 component content less than 3.5 mass ,
the y'-phase precipitation amount becomes deficient, and a
15 sufficient tolerable temperature cannot be obtained. Above 4.5
mass%, the hot workability suffers (the ductility degrades),
making it difficult to produce the pipe member itself.
The Cr component dissolves in the matrix, and has the
effect of improving the oxidation resistance of the Ni-based
20 alloy. This effect is hardly obtained when the content of the
Cr component is less than 15 mass%. Above 20 mass%, a harmful
phaseisprone toprecipitate, andtheductilitydegrades, making
it difficult to produce the pipe member itself.
The Co component dissolves in the matrix, and has the
25 effect of improving the high-temperature mechanical strength
by formation of a solid solution. However, the Co component is
added in preferably 25 mass% or less, because it also acts to
stabilize the harmful phase.
I
The C component has the effect of preventing the excess
I ~ 5 coarsening of the Ni-based alloy crystal grains through
I ~ formation of carbides. This effect is hardly obtained when the
I ~ content of the C component is less than 0.01 mass%. Above 0.15
mass%, the hot workability suffers (the ductility degrades),
making it difficult to produce the pipe member itself. For
10 improved weldability, the content of the C component is
preferably 0.01 mass% to 0.05 mass%.
On the other hand, the welding material differs from the
primary pipe member in that it is used in the state of a
solidification structure, and that it is not subjectedtoplastic
15 forming (for example, not processed into a tubular shape).
Preferably, the welding material is made from an Ni-based cast
alloy that exhibits a y' phase (Ni3A1 phase) dissolution
temperature of from 850 to 900°C, and in which 20 volume% or more
and30volume% or less (20-30volume%) ofthey' phase is dispersed
20 and precipitated in a temperature range of from 700 to 800°C.
A sufficient tolerable temperature cannot be obtained when the
amount of the y' phase dispersed and precipitated in the 700 to
800°C temperature range is less than 20 volume%. Above 30
volume%, weld cracking is prone to occur.
25 Furthermore, whenthey1-phase dissolution temperature of
the Ni-based c a s t a l l o y is l e s s than 850°C, it becomes d i f f i c u l t
t o obtain the high-temperature piping product exhibiting a
t o l e r a b l e temperature of the 800°C c l a s s by means of the
producing method according t o an embodiment of the present
5 invention ( d e t a i l s w i l l be described l a t e r ) . With a yl-phase
dissolution temperature i n excess of 900°C, t h e b u t t e r i n g
weldability degrades.
Preferably, t h e N i - b a s e d c a s t a l l o y h a s acomposition t h a t
contains: A1 of 3 mass% or more and 3.5 mass% or l e s s (3-3.5
10 mass%); C r of15massB ormoreand20mass% or l e s s (15-20mass');
Co of 25 mass% or l e s s ; C of 0.01 mass% or more and 0.15 mass'
or l e s s (0.01-0.15 mass%) ; a t l e a s t one of Mo and W i n a t o t a l
content of 9mass%to15mass%a; n d N i a n d u n a v o i d a b l e i m p u r i t i e s
accounting for the reminder.
15 As described above, the Mo component and the W component
are constituent elements t h a t have strong e f f e c t s on the
p r e c i p i t a t i o n amount and t h e d i s s o l u t i o n temperature of the y1
phase, andonthehotworkabilityofthe Ni-basedalloy. However,
because the welding material does not require p l a s t i c forming,
20 the Mo component and the W component can be added in larger
amountsthanintheprimarypipemembertoensurehighmechanical
strength a t high-temperatures. A s u f f i c i e n t high-temperature
mechanical strength cannot be obtained when the t o t a l content
of the Mo component and the W component is l e s s than 9 mass:.
25 Above 15 mass%, the d u c t i l i t y , and t h e p r o c e s s i b i l i t y of a weld
w i r e s u f f e r .
The c o n t e n t of t h e A1 component i n t h e Ni-based c a s t a l l o y
f o r t h e welding m a t e r i a l ranges from 3 t o 3.5 mass%. The
mechanical s t r e n g t h becomes i n s u f f i c i e n t when t h e A1 component
5 c o n t e n t is below 3 mass%. Above 3.5 mass%, t h e wire
p r o c e s s i b i l i t y and w e l d a b i l i t y become i n s u f f i c i e n t . The C r
component, t h e Co component, and t h e C component a r e same a s
i n t h e primary p i p e member.
D e s i r a b l y , t h e N i - b a s e d f o r g e d a l l o y a n d t h e N i - b a s e d c a s t
10 a l l o y u s e d i n t h e p r e s e n t i n v e n t i o n d o n o t c o n t a i n a T i ( t i t a n i u m )
component, a Ta ( t a n t a l u m ) component, and an Nb (niobium)
component. I n o t h e r words, t h e s e components a r e not
i n t e n t i o n a l l y added. When mixed u n i n t e n t i o n a l l y , t h e t o t a l
c o n t e n t o f t h e T i component, t h e Ta component, and t h e Nb
15 component is p r e f e r a b l y 0.5 mass% o r less.
T i , Ta, and Nb have t h e c h a r a c t e r i s t i c s of more s t r o n g l y
s t a b i l i z i n g t h e y' phase a t t e m p e r a t u r e s of l,OOO°C and h i g h e r ,
comparedtoA1. However, t h e e f f e c t of s t a b i l i z i n g t h e y' phase
i s w e a k e r t h a n t h a t o f Alatoperatingtemperatures ( 7 0 0 t o 800°C).
20 It i s difficulttoobtaindesirablehotworkabilityanddesirable
w e l d a b i l i t y of t h e Ni-based a l l o y when t h e y' phase is s t a b l e
a t t e m p e r a t u r e s of l,OOO°C and h i g h e r . It is t h e r e f o r e more
p r e f e r a b l e t o s t a b i l i z e t h e y' phase with A1 a l o n e , without
adding T i , Ta, and Nb, i n o r d e r t o r e a l i z e good hot w o r k a b i l i t y
25 and w e l d a b i l i t y a t t h e same time a s t h e mechanical s t r e n g t h a t
operating temperatures.
(Method for Producing ~ i ~ h - ~ e m ~ e r a tPuirpien g Product)
T h e m e t h o d f o r p r o d u c i n g a h i g h - t e m p e r a t u r e p i p i n g p r o d u c t
according to an embodiment of the present invention will be
5 described below. First, the primarypipe member ofthe Ni-based
forgedalloy, a n d t h e w e l d i n g m a t e r i a l o f t h e N i - b a s e d c a s t a l l o y
are prepared. The primary pipe member is subjected to a heat
treatment (solution heat treatment) at a temperature equal to
or greaterthantheyl-phase dissolution temperature to dissolve
10 the y1 phase in the matrix.
Figure 1 is a schematic view representing an exemplary
procedure of producing the high-temperature piping product
according to the embodiment of the present invention. As shown
in FIG. 1, the primary pipe members are welded to each other
15 with the welding material buttered to the welding portions of
the primary pipe members to form a secondary pipe member
constructed from the plurality of primary pipe members (this
step is referred to as secondary pipe member forming step).
The secondary pipe member is then subjected to a heat
20 treatment at a temperature equal to or greater than the y'-phase
d i s s o l u t i o n t e m p e r a t u r e o f t h e N i - b a s e d c a s t a l l o y o f t h e w e l d i n g
material and a temperature equal to or less than the yl-phase
dissolution temperature of the Ni-based forged alloy of the
primary pipe member (specifically, at a temperature of, for
25 example, above 900°C and below 920°C) to precipitate 5 volume?
or more and 15 volume% or l e s s (for example, 10 volume%) of the
y' phase in the primary pipe members ( t h i s step i s referred t o
as pre-aging heat treatment s t e p ) .
Prior t o the pre-aging heat treatment s t e p , t h e welding
5 materialmaybebuttered totheweldingportion s o f t h e secondary
pipe members (see FIG. 1). P r e c i p i t a t i o n of the y' phase i n the
primary pipe member lowers the weldability of the primary pipe
member i t s e l f . However, because the aging heat treatment
temperature is equal t o or g r e a t e r t h a n t h e y l - p h a s e dissolution
10 temperature of t h e b u t t e r e d welding material, the y' phase does
not p r e c i p i t a t e in the welding material. This provides
d e s i r a b l e w e l d a b i l i t y f o r the next step.
Thereafter, the welding material is buttered t o the
welding portions of the secondary pipe members t o weld the
15 secondarypipememberstoeachother and forma high-temperature
piping product ( t h i s step i s r e f e r r e d t o as high-temperature
piping product forming s t e p ) . As described above, the welding
m a t e r i a l m a y b e b u t t e r e d t o t h e w e l d i n g p o r t i o n s o f t h e secondary
pipe members before or a f t e r the pre-aging heat treatment step.
20 The high-temperature piping product obtained a f t e r the
high-temperature piping product forming step is d i r e c t l y used
for the assembly of t h e a c t u a l product (for example, a b o i l e r
for power plants of the 800°C c l a s s ) . The y' phase evenly
disperses and p r e c i p i t a t e s i n 30 volume% or more in the primary
25 pipe members as a high-temperature f l u i d of the 800°C c l a s s i s
flown during the operation of the power p l a n t , and high
mechanical strength a t high-temperatures can be ensured. I n
otherwords, intheproducingmethodaccordingtotheembodiment
of the present invention, the high-temperature piping product
5 forming step i s not followed by the aging heat treatment
performed t o p r e c i p i t a t e 30 volume% or more of the y' phase in
the primary pipe members under the external heat applied t o the
whole high-temperature piping product.
1 0 [ EXAMPLES ]
The present invention w i l l be described in more d e t a i l
below by way of Examples. It should be noted, however, t h a t the
present invention is not limitedby the s p e c i f i c Examples below.
(Preparation of Primary Pipe Member and Welding Material)
15 Ni-based alloys (Alloys T I t o T5) of the compositions
p r e s e n t e d i n T a b l e l w e r e p r e p a r e d , and specimens o f t h e primary
pipememberswereproducedaccordingtothe followingprocedures.
F i r s t , an Ni-based alloy ingot was produced by vacuum melting
andvacuumarc remelting (doublemeltingprocess). TheNi-based
20 alloy ingot was subjected t o hot forging t o produce a b i l l e t .
Then, hot extrusion and cold working were performed for the
b i l l e t t o produce a primary pipe member (inner diameter of 50
mm; thickness of 8 mm) t h a t simulates a b o i l e r tube for power
p l a n t s . The r e s u l t i n g primary pipe members (Alloys T1 t o T5)
25 were examined with respect t o the y'-phase dissolution
temperature, and the yl-phase precipitation amount in the aging
heat treatment (800°C) . The results are presented in Table 1.
Alloys T1 and T2 are conventional Ni-based alloys, and Alloys
T3 to T5 represent the Ni-based alloys according to the present
5 invention.
Table 1 : Compositions of Ni-based alloys for primary pipe member
Ni-based alloys (Alloys W1 to W5) of the compositions
10 presentedinTable 2 were prepared, and specimens ofthewelding
materials were produced according to the following procedures.
First, an Ni-based alloy ingot was produced by vacuum melting.
The Ni-based alloy ingot was then subjected to hot forging and
cold drawing to produce a welding material (a weld wire with
15 an outer diameter of 1 mrn). The resulting welding materials
(Alloys W1 to W5) were examined with respect to the yl-phase
dissolution temperature, and the yl-phase precipitation amount
Al
C r
Co
C
Mo
W
Ti
Ta
Nb
y'-phase dissolution
temperature
y'-phase precipitation
amount
Alloy TI
1.9
23.2
18.7
0.14
2.1
3.8
1.38
1 .o
9300C
20%
Alloy T2
5.4
8.3
9.2
0.08
0.49
9.4
0.8
3.19
940°C
18%
Alloy T3
4.0
15
24
0.01
6.0
930°C
33%
Alloy T4
4.2
16
15
0.03
4.0
3.0
945°C
35%
Alloy T5
3.7
17
0
0.05
0.1
8.0
91 5°C
30%
i n t h e aging h e a t t r e a t m e n t (800°C). The r e s u l t s a r e p r e s e n t e d
i n Table 2 . Alloys W 1 and W2 a r e c o n v e n t i o n a l Ni-based a l l o y s ,
and Alloys W3 t o W5 r e p r e s e n t t h e Ni-based a l l o y s a c c o r d i n g t o
t h e p r e s e n t i n v e n t i o n .
5
Table 2: Compositions of Ni-based alloys for welding material
( P r o d u c t i o n of Weld J o i n t , and T e s t i n g and E v a l u a t i o n of Weld
J o i n t )
10 The primary p i p e members and t h e welding m a t e r i a l s
p r e p a r e d a s abovewere u s e d i n a T I G ( t u n g s t e n i n e r t g a s ) welding
p e r f o r m e d i n t h e c o m b i n a t i o n s a n d c o n d i t i o n s p r e s e n t e d i n T a b l e s
3 and 4 t o produce weld j o i n t s (Samples 1 t o 9) a s t h e secondary
p i p e members. The weld j o i n t s (Samples 1 t o 9) were then
15 s u b j e c t e d t o m i c r o s t r u c t u r e o b s e r v a t i o n of a sample c r o s s
s e c t i o n ( i n c l u d i n g an e v a l u a t i o n of t h e p r e s e n c e o r absence of
weld c r a c k i n g ) , and a c r e e p t e s t . The m i c r o s t r u c t u r e
observationwas alsoperformedto unwelded samples and t o samples
taken out in the middle of the creep t e s t (creep t e s t suspended
specimens). The creep t e s t was conducted a t a temperature of
800°C under 190 MPa s t r e s s . The r e s u l t of the creep t e s t was
5 used for the evaluation of a creep t o l e r a b l e temperature
according t o t h e Larson-Miller method (Larson-Miller parameter
= 20). The creep t o l e r a b l e temperature is the temperature a t
which the product can withstand a 100-MPa s t r e s s for 100,000
hours. The evaluation r e s u l t s for the presence or absence of
10 weldcracking, andthe creeptolerabletemperature arepresented
in Tables 3 and 4 .
Table 3: Specifications of weld joints of Samples 1 to 6 and testing and evaluation results
Primary pipe
member
Welding material
Buttering material
Solution heat
treatment
Pre-aging heat
treatment
Weld cracking
Creep tolerable
temperature
Sample
1
Alloy T2
Alloy W2
Sample
2
Alloy TI
Alloy Wl
Sample
3
Alloy T2
Alloy W2
1,160°C x2 h
800°C x 16 h
Present
733°C
Present
728°C
1,160°C x2 h
Sample
6
Alloy T5
Alloy W3
Sample
4
Alloy TI
Alloy W2
Absent
742°C
1,160°C x2 h
Sample
5
Alloy T3
Alloy W5
Absent
738°C
Absent
770°C
Absent
772°C
Table 4: Specifications of weld joints of Samples 7 to 9 and testing and evaluation resu
I
Primary pipe member
Welding material
Buttering material
Solution heat treatment
Pre-aaina heat treatment
The results of the microstructure observation are shown
5 in FIGs. 2 and 3. Figure 2 is a schematic view showing
microstructures of weld joints of Samples 1 to 6. Figure 3 is
a schematic view showing microstructures of weld joints of
Samples7to9. Theseresultsareexplainedbelowwithreference
to Tables 3 and 4, and FIGs. 2 and 3.
10 The weld joints of Samples 1 and 2 were obtained from the
conventional Ni-based alloys after the pre-aging heat treatment
(800°C x 16 hours) performed before welding. Buttering was not
performed. The y' phase already precipitated in the unwelded
samples (labeled as "before welding"), and the same structure
15 was observed also in samples examined immediately after the
welding (labeledas "as-welded"), andin the creep test suspended
specimens (labeled as "during creep test"). Weld cracking was
also observed. The creep tolerable temperature was in the
vicinity of 730°C (Sample 1: 733°C; Sample 2: 728"C), unsuited
20 for the high-temperature piping product of the 800°C class.
The weld joints of Samples 3 and 4 were obtained from the
" "
Weld cracking
Creep tolerable temperature
Sample 7
Alloy T3
Alloy W5
Alloy W5
1 ,160°C x 2 h
- - - - . - 900°C x 16- .h .
Sample 8
Alloy T4
Alloy W3
Alloy W3
Absent
805°C
Sample 9
Alloy T5
Alloy W4
Alloy W4
1 ,OOO°C x 2 h
Absent
802°C
Absent
800°C
conventional Ni-based alloys without performing the pre-aging
heat treatment before welding (onlythe solution heat treatment
was performed). Buttering was not performed. The y' phase did
not precipitate in the unwelded samples (before welding) and
5 in samples examined immediately after the welding (as-welded),
whereas yl-phase precipitation was observed in the creep test
suspended specimens (during creep test). There was no weld
cracking. The creep tolerable temperature was in the vicinity
of 740°C (Sample 3: 742OC; Sample 4: 738OC), unsuited for the
10 high-temperature piping product of the 800°C class.
The weld joints of Samples 5 and 6 were obtained from the
Ni-based alloys according to the present invention without
performing the pre-aging heat treatment before welding (only
the solution heat treatment was performed). Buttering was not
15 performed. The y1 phase did not precipitate in the unwelded
samples (before welding) and in samples examined immediately
after the welding (as-welded), whereas coarse y'-phase
precipitation of an abnormal (amoeba-like) shape was observed
in the creep test suspended specimens (during creep test). This
20 i s c o n s i d e r e d t o b e d u e t o t h e c o m p o s i t i o n s o f t h e N i - b a s e d a l l o y s
of the present invention that generate more y'-phase
precipitation than the conventional compositions, causing the
y' phase to precipitate at once at the creep test temperature
(corresponds to the actual operating temperature), and
25 resultinginabnormal graingrowth. Therewas noweldcracking.
The creep tolerable temperature was in the vicinity of 770°C
(Sample 5: 770°C; Sample 6: 772OC), unsuited for the
high-temperature piping product of the 800°C class. This is
probably because of the lack of fine y' phase dispersion and
5 precipitation (the y' phase underwent abnormal grain growth).
The weld joints of Samples 7 to 9 were obtained from the
Ni-based alloys according to the present invention after the
pre-aging heat treatment (900°C x 16 hours) performed before
welding. Buttering was performed. The y' phase did not
10 precipitateintheprimarypipemembers and theweldingmaterial
in samples examined immediately after the buttering (labeled
as "as-buttered"), and about 10-volume% yl-phase precipitation
was observed after the pre-aging heat treatment only in the
primary pipe members (labeled as "as-pre-aging heat treated") .
15 In the creep test suspended specimens (labeled as "during creep
test"), finey' phase dispersion and precipitation was observed
in 30 volume% or more in the primary pipe members, and in 20
volume% or more in the welding material. There was no weld
cracking. The creep tolerable temperature was 800°C or more
20 (Sample 7 : 805OC; Sample 8 : 802OC; Sample 9: 800°C) , confirming
that the products are sufficiently applicable to the
high-temperature piping product of the 800°C class.
As demonstrated above, it was confirmed to provide the
high-temperature piping product exhibiting a tolerable
25 temperatureofthe 800°C class, and themethod forproducing such
high-temperature piping products. With the high-temperature
piping product of the present invention, a boiler for power
plants of the 800°C class can be provided. This greatly
contributes to improving the power generating efficiency of
5 power plants.
The above embodiments of the invention as well as the
appended claims and figures show multiple characterizing
features ofthe invention in specific combinations. The skilled
10 person will easily be able to consider further combinations or
sub-cornbinations of these features in order to adapt the
invention as defined in the claims to his specific needs.

We claim:
1. A high-temperature piping product for flowing a
high-temperature fluid, configured from a plurality of primary
pipe members and a welding material,
5 wherein the primary pipe members are each made from an
Ni-based forged alloy which contains Ni, Al, and at least one
of Mo and W, the total content of the Mo and the W being 3 mass -
or more and 8 mass& or less, the Ni-based forged alloy having
a yl-phase dissolution temperature of from 920 to 970°C, and a
10 y' phase being precipitated in the Ni-based forged alloy in 30
volume% or more in a temperature range of from 700 to 800°C,
wherein the welding material is made from an Ni-based cast
alloy having a cast structure formed by welding, the Ni-based
cast alloy containing Ni, Al, and at least one of Mo and W, the
15 total content of the Mo and the W being 9 mass8 or more and 15
mass% or less, the Ni-based cast alloy having a yl-phase
dissolution temperature of from 850 to 900°C, a y1 phase being
precipitated in the Ni-based cast alloy in 20 volume> or more
in a temperature range of from 700 and 800°C, and
20 wherein the welding material is buttered to the primary
pipe members in portions to be welded to each other.
2. The high-temperature piping product according to
claim 1,
25 whereintheNi-basedforgedalloycontains:Alof3.5mass?.
or more and 4.5 mas's% or l e s s ; C r of 15 mass% or more and 20
mass% o r l e s s ; Co of 25 mass% o r l e s s ; C of 0.01 mass8 or more
and 0.15mass% o r l e s s ; a t l e a s t o n e o f M o a n d W i n a t o t a l c o n t e n t
of 3 mass% t o 8 mass%; and N i and unavoidable impurities
5 accounting for the reminder, and
wherein the Ni-based c a s t a l l o y contains: A1 of 3 massor
more and 3.5 mass% or l e s s ; C r of 15 mass% or more and 20
mass% or l e s s ; Co of 25 mass% o r l e s s ; C of 0.01 mass% or more
and 0.15mass% or l e s s ; a t l e a s t o n e o f M o a n d W i n a t o t a l c o n t e n t
10 of 9 mass% t o 15 mass%; and N i and unavoidable impurities
accounting f o r the reminder.
3. A method f o r producing the high-temperature piping
product according t o claim 1 or 2 , the method comprising:
15 a secondarypipememberforming s t e p o f w e l d i n g t h e p r i m a r y
pipe members t o each other with the welding m a t e r i a l b u t t e r e d
t o welding portions of the primary pipe members and forming
secondary pipe members each constructed from the p l u r a l i t y of
primary pipe members; and
20 a high-temperaturepiping product forming s t e p of welding
the secondary pipe members t o each other with the welding
m a t e r i a l b u t t e r e d t o welding portions of the secondary pipe
members and forming a high-temperature piping product.
4. The method according t o claim 3, f u r t h e r comprising
26
apre-agingheattreatmentstepof subjectingthe secondarypipe
members to a heat treatment at a temperature equal to or greater
than the y'-phase dissolution temperature of the Ni-based cast
alloy and at a temperature equal to or less than the 7'-phase
5 dissolution temperature of the Ni-based forged alloy to
precipitate 5 volume% or more and 15 volume% or less of the y'
phase in the primary pipe members, the pre-aging heat treatment
step being performed after the secondary pipe member forming
step and before the high-temperature piping product forming
10 step.
5 . The method according to claim 4, wherein the
high-temperature piping product forming step is not followed
by an aging heat treatment in which 30 volume% or more of the
15 y' phase is precipitated in the primary pipe members under
e x t e r n a l h e a t a p p l i e d t o t h e w h o l e o f t h e h i g h - t e m p e r a t u r e p i p i n g
product.
6. A boiler for power plants, the boiler comprising the
20 high-temperature piping product according to claim 1 or 2.
7. A high-temperature piping product for flowing a
high-temperature fluid, substantially as herein described with
reference to accompanying drawings and examples.
25
8. A b o i l e r f o r power p l a n t s , s u b s t a n t i a l l y as h e r e i n
d e s c r i b e d w i t h r e f e r e n c e t o accompanying drawings andexamples.