TECHNICAL FIELD
-
This invention relates to steam turbine rotor materials
for use in thermal electric power generation.
BACKGROUND ART
-
High-temperature rotor materials for use in steam
turbine plants for thermal electric power generation include
CrMoV steel and 12Cr steel. Of these, the use of CrMoV steel
is restricted to plants having a steam temperature up to
566°C because of its limited high-temperature strength. On
the other hand, rotor materials based on 12Cr steel have more
excellent high-temperature strength than CrMoV steel and can
hence be used in plants having a steam temperature up to
593°C. However, if the steam temperature exceeds 593°C, such
rotor materials have insufficient high-temperature strength
and cannot be easily used for steam turbine rotors.
DISCLOSURE OF THE INVENTION
-
Accordingly, it is an object of the present invention to
provide 12Cr steel-based steam turbine rotor materials for
high-temperature applications which have excellent high-temperature
strength and can be used at steam temperatures
higher than 593°C.
-
As a result of intensive investigations, the present
inventors have now invented the following excellent steam
turbine rotor materials (1) to (6) for high-temperature
applications.
- (1) A steam turbine rotor material for high-temperature
applications consisting essentially of, on a weight
percentage basis, 0.05 to 0.13% carbon, 0.01 to 0.1% silicon,
0.1 to 1% manganese, 9.5 to 11% chromium, 0.1 to 0.8% nickel,
0.1 to 0.3% vanadium, a total of 0.01 to 0.2% niobium and/or
tantalum, 0.01 to 0.1% nitrogen, 0.01 to 0.5% molybdenum, 0.9
to 3.5% tungsten, 0.1 to 4% cobalt, 0.01 to 0.2% hafnium, and
the balance being iron and incidental impurities [hereinafter
referred to as the inventive material (1)].
- (2) A steam turbine rotor material for high-temperature
applications consisting essentially of, on a weight
percentage basis, 0.05 to 0.13% carbon, 0.01 to 0.1% silicon,
0.01 to 0.1% manganese, 9.5 to 11% chromium, 0.1 to 0.8%
nickel, 0.1 to 0.3% vanadium, a total of 0.01 to 0.2% niobium
and/or tantalum, 0.01 to 0.1% nitrogen, 0.01 to 0.5%
molybdenum, 0.9 to 3.5% tungsten, 0.1 to 4% cobalt, 0.01 to
0.2% hafnium, and the balance being iron and incidental
impurities [hereinafter referred to as the inventive material
(2)].
- (3) A steam turbine rotor material for high-temperature
applications consisting essentially of, on a weight
percentage basis, 0.05 to 0.13% carbon, 0.01 to 0.1% silicon,
0.1 to 1% manganese, 9.5 to 11% chromium, 0.1 to 0.3%
vanadium, a total of 0.01 to 0.2% niobium and/or tantalum,
0.01 to 0.1% nitrogen, 0.01 to 0.5% molybdenum, 0.9 to 3.5%
tungsten, 0.1 to 4% cobalt, 0.01 to 0.2% hafnium, and the
balance being iron and incidental impurities [hereinafter
referred to as the inventive material (3)].
- (4) A steam turbine rotor material for high-temperature
applications consisting essentially of, on a weight
percentage basis, 0.05 to 0.13% carbon, 0.01 to 0.1% silicon,
0.01 to 0.1% manganese, 9.5 to 11% chromium, 0.1 to 0.3%
vanadium, a total of 0.01 to 0.2% niobium and/or tantalum,
0.01 to 0.1% nitrogen, 0.01 to 0.5% molybdenum, 0.9 to 3.5%
tungsten, 0.1 to 4% cobalt, 0.01 to 0.2% hafnium, and the
balance being iron and incidental impurities [hereinafter
referred to as the inventive material (4)].
- (5) A steam turbine rotor material for high-temperature
applications as described in any of (1) to (4) above which
further contains 0.001 to 0.01% by weight or less of boron
[hereinafter referred to as the inventive material (5)].
- (6) A steam turbine rotor material for high-temperature
applications as described in any of (1) to (5) above wherein
part or all of the hafnium and/or part of the iron are
replaced with neodymium that is present in an amount of 0.005
to 0.5% [hereinafter referred to as the inventive material
(6)].
-
BEST MODE FOR CARRYING OUT THE INVENTION
-
The present inventors made intensive investigations in
order to improve high-temperature strength by using 12Cr
steel as a basic material and adding carefully selected
alloying elements thereto, and have now invented new steam
turbine rotor materials for high-temperature applications
which have excellent high-temperature properties.
INVENTIVE MATERIAL (1)
-
The reasons for content restrictions in the inventive
material (1) are described below. In the following
description, all percentages are by weight.
- C: C, together with N, forms carbonitrides and thereby
contributes to the improvement of creep rupture strength.
However, if its content is less than 0.05%, no sufficient
effect will be produced. If its content is greater than
0.13%, the carbonitrides will aggregate during use to form
coarse grains, resulting in a reduction in long-time high-temperature
strength. Accordingly, the content of C should
be in the range of 0.05 to 0.13%.
- Si: Si is effective as a deoxidizer. If its content is
less than 0.01%, no sufficient effect will be produced in
this respect. Moreover, Si causes a reduction in high-temperature
strength and, in particular, creep rupture
strength. Consequently, with concurrent consideration for
the fact that the inventive material (1) may be subjected to
a vacuum carbon deoxidation process, Si is added in a minimum
amount required for steel making. Thus, the content of Si
should be in the range of 0.01 to 0.1%.
- Mn: Mn is an element which is also useful as a
deoxidizer. Moreover, Mn has the effect of inhibiting the
formation of δ-ferrite. On the other hand, the addition of a
large amount of this element will cause a reduction in creep
rupture strength. Consequently, the addition of more than 1%
of Mn is undesirable. Furthermore, Mn also reacts with S
introduced as an impurity to form MnS and thereby serves to
negate the adverse effect of S. However, with consideration
for forging at the stage of steel making, an Mn content of
not less than 0.1% is advantageous from the viewpoint of cost
because this makes scrap control easy. Accordingly, the
content of Mn should be in the range of 0.1 to 1%.
- Cr: Cr form a carbide and thereby contributes to the
improvement of creep rupture strength. Moreover, Cr
dissolves in the matrix to improve oxidation resistance and
also contributes to the improvement of long-time high-temperature
strength by strengthening the matrix itself. If
its content is less than 9.5%, no sufficient effect will be
produced, while if its content is greater than 11%, the
formation of δ-ferrite will tend to occur and cause a
reduction in strength and toughness. Accordingly, the
content of Cr should be in the range of 9.5 to 11%.
- Ni: Ni is an element which is effective in improving
toughness. Moreover, Ni also has the effect of reducing the
Cr equivalent and thereby inhibiting the formation of
δ-ferrite. However, since the addition of this element may
cause a reduction in creep rupture strength, it is desirable
to add Ni in a required minimum amount. In the present
invention, Co is added as an element for exhibiting the
effects of Ni, so that the role of Ni can be performed by Co.
However, since Co is an expensive element, it is necessary
from an economic point of view to reduce the content of Co as
much as possible. Consequently, the formation of δ-ferrite
is inhibited by adding not greater than 0.8% of Ni, though
this may depend on other alloying elements. Its lower limit
is determined to be 0.1% with consideration for the amount of
Ni which is introduced as an incidental impurity.
Accordingly, the content of Ni should be in the range of 0.1
to 0.8%.
- V: V forms a carbonitride and thereby improves creep
rupture strength. If its content is less than 0.1%, no
sufficient effect will be produced. On the other hand, if
its content is greater than 0.3%, the creep rupture strength
will contrarily be reduced. Accordingly, the content of V
should be in the range of 0.1 to 0.3%.
- Nb and/or Ta: Nb and/or Ta form carbonitrides and
thereby contribute to the improvement of high-temperature
strength. Moreover, they cause finer carbides (M23C6) to
precipitate at high temperatures and thereby contribute to
the improvement of long-time creep rupture strength. If
their total content is less than 0.01%, no beneficial effect
will be produced. On the other hand, if their total content
is greater than 0.2%, the carbides of Nb and/or Ta formed
during the manufacture of steel ingots will fail to dissolve
fully in the matrix during heat treatment (solution treatment
at 980-1,150°C) and will coarsen during use to cause a
reduction in long-time creep rupture strength. Accordingly,
the total content of Nb and/or Ta should be in the range of
0.01 to 0.2%.
- N: N, together with C and alloying elements, forms
carbonitrides and thereby contributes to the improvement of
high-temperature strength. If its content is less than
0.01%, no sufficient amount of carbonitrides can be formed
and, therefore, no sufficient creep rupture strength will be
achieved. If its content is greater than 0.1%, the
carbonitrides will aggregate to form coarse grains after the
lapse of a long time and, therefore, no sufficient creep
rupture strength can be achieved. Accordingly, the content
of N should be in the range of 0.01 to 0.1%.
- Mo: Mo, together with W, dissolves in the matrix and
thereby improves creep rupture strength. If Mo is added
alone, it may be used in an amount of about 1.5%. However,
where W is also added as is the case with the present
invention, W is more effective in improving high-temperature
strength. Moreover, if Mo and W are added in unduly large
amounts, δ-ferrite will be formed to cause a reduction in
creep rupture strength. Consequently, with consideration for
a balance with the content of W, the content of Mo should be
not greater than 0.5%. Furthermore, since the addition of W
alone fails to give sufficient high-temperature strength, at
least a slight amount of Mo needs to be added. That is, the
content of Mo should be not less than 0.01%. Accordingly,
the content of Mo should be in the range of 0.01 to 0.5%.
- W: As described above, W, together with Mo, dissolves
in the matrix and thereby improves creep rupture strength. W
is an effective element which exhibits a more powerful solid
solution strengthening effect than Mo. However, if W is
added in an unduly large amount, δ-ferrite and a large
quantity of Laves phase will be formed to cause a reduction
in creep rupture strength. Accordingly, with consideration
for a balance with the content of Mo, the content of W should
be in the range of 0.9 to 3.5%.
- Co: Co dissolves in the matrix to inhibit the formation
of δ-ferrite. However, Co does not reduce high-temperature
strength as contrasted with Ni. Consequently, if Co is
added, strengthening elements (e.g., Cr, W and Mo) may be
added in larger amounts than in the case where no Co is
added. As a result, high creep rupture strength can be
achieved. In addition, Co also has the effect of enhancing
resistance to temper softening and is hence effective in
minimizing the softening of the material during use. These
effects are manifested by adding Co in an amount of not less
than 0.1%, though it may depend on the contents of other
elements. However, the addition of more than 4% of Co tends
to induce the formation of intermetallic compounds such as δ
phase. Once such intermetallic compounds are formed, the
material will become brittle. In addition, this will also
lead to a reduction in long-time creep rupture strength.
Accordingly, the content of Co should be in the range of 0.1
to 4%.
- Hf: Hf is an alloying element which is added to nickel-base
superalloys and the like, and is highly effective in
enhancing grain boundary strength to bring about an
improvement in high-temperature strength and, in particular,
creep rupture strength. This effect of Hf is also useful in
the rotor materials of the present invention which comprise
high-Cr steels. That is, as described above, Hf is highly
effective in improving creep rupture strength. In addition
to the above-described effect, Hf has the effect of improving
the long-time creep rupture strength of high-Cr steels, for
example, by dissolving in the matrix to strengthen the matrix
itself and by retarding the aggregation and coarsening of
carbonitrides. This effect will not function properly at an
Hf content of less than 0.01%. On the other hand, if more
than 0.2% of Hf is added, it will fail to dissolve in the
matrix during preparation, so that no additional effect
cannot be expected. In addition, such a large amount of Hf
will react with the refractories to form inclusions, thus
reducing the purity of the material itself and causing damage
to the melting furnace. Consequently, Hf must be added in a
required minimum amount. For the above-described reasons,
the content of Hf should be in the range of 0.01 to 0.2%.
-
INVENTIVE MATERIAL (2)
-
Now, the reasons for content restrictions in the
inventive material (2) are described below. However, the
same explanations as those given in connection with the
inventive material (1) are omitted. Here, only the reason
why the content of Mn is newly restricted to a narrower range
is explained.
- Mn: As described in connection with the inventive
material (1), Mn is an element which is useful as a
deoxidizer. Moreover, Mn has the effect of inhibiting the
formation of δ-ferrite. However, as described previously,
the addition of this element causes a reduction in creep
rupture strength similarly to Ni. Consequently, it is
necessary to minimize the content of Mn. Especially if the
content of Mn is restricted to 0.1% or less, creep rupture
strength is markedly improved. Furthermore, Mn also reacts
with S introduced as an impurity to form MnS and thereby
serves to negate the adverse effect of S. For this reason,
it is necessary to add Mn in an amount of not less than
0.01%. Accordingly, in the inventive material (2), the
content of Mn is restricted to a range of 0.01 to 0.1%.
-
INVENTIVE MATERIAL (3)
-
The reasons for content restrictions in the inventive
material (3) are described below. However, the same
explanations as those given in connection with the inventive
material (1) are omitted. Here, the reason why no Ni is
added as contrasted with the inventive materials (1) and (2)
is explained.
- Ni: As described in connection with the inventive
material (1), Ni has the effect of dissolving in the matrix
to inhibit the formation of δ-ferrite. In addition, Ni is
effective in improving toughness. However, as described
previously, the addition of Ni will cause a reduction in
creep rupture strength. Consequently, it is necessary to
minimize the content of Ni. In the inventive material (3),
the effects of Ni can be exhibited by adding Co in place of
Ni. Consequently, the addition of Ni exerting an adverse
influence on creep rupture strength can be omitted by adding
properly controlled elements (e.g., Co, C and N) so as to
prevent the formation of δ-ferrite. This omission of Ni
makes it possible to achieve a much higher creep rupture
strength as compared with rotor materials containing Ni.
-
INVENTIVE MATERIAL (4)
-
The reasons for content restrictions in the inventive
material (4) are described below. The inventive material (4)
has the same composition as the inventive material (2),
except that no Ni is added similarly to the aforesaid
inventive material (3). The reasons for content restrictions
on other components have already been described in connection
with the inventive materials (1) and (2) and are hence
omitted here.
INVENTIVE MATERIAL (5)
-
The reasons for content restrictions in the inventive
material (5) are described below. However, the explanations
for the same components as described in connection with the
inventive materials (1) to (4) are omitted. Here, only the
reason why the specified content of B is newly added is
explained.
- B: B has the effect of enhancing grain boundary
strength. Consequently, it contributes to the improvement of
creep rupture strength. However, if B is added in unduly
large amounts, poor hot workability low toughness will
result. If its content is less than 0.001%, no sufficient
effect will be produced. On the other hand, if its content
is greater than 0.01%, a reduction in hot workability and
toughness will result. Accordingly, the content of B should
be in the range of 0.001 to 0.01%.
-
INVENTIVE MATERIAL (6)
-
The reasons for content restrictions in the inventive
material (6) are described below. However, the explanations
for the same components as described in connection with the
inventive materials (1) to (5) are omitted. Here, only the
reason why the specified content of Nd is newly added is
explained.
- Nd: Nd is highly effective not only in enhancing grain
boundary strength, but also in improving high-temperature
strength and, in particular, creep rupture strength by
dissolving in the matrix to strengthen the matrix itself and
by retarding the aggregation and coarsening of carbonitrides.
These effects will not function properly at an Nd content of
less than 0.005%. On the other hand, the addition of an
unduly large amount of Nd will form inclusions, thus reducing
the purity of the steel and causing a reduction in toughness
and creep rupture strength. The upper limit of the Nd
content should be 0.5%.
-
EXAMPLES
-
In order to demonstrate the effects of the present
invention, the steam turbine rotor materials for high-temperature
applications in accordance with the present
invention are more specifically explained with reference to
the following examples.
(Example 1)
-
An example concerned with the inventive material (1) is
described below.
-
The chemical compositions of materials used for testing
purposes are summarized in Table 1. All test materials were
prepared by melting the components in a 50 kg vacuum high-frequency
furnace. These test materials were hot-forged at a
heating temperature of 1,200°C and then subjected to the
following heat treatment. The heat treatment was carried out
by hardening the test materials under conditions which
simulated the central part of an oil-quenched rotor having a
drum diameter of 1,200 mm, and then tempering them at a
temperature which had been determined so as to give a 0.2%
yield strength of about 68-74 kgf/mm2.
-
The mechanical properties and creep rupture strengths of
inventive materials (1) and comparative materials are shown
in Table 2. Although there is little difference in the
results of room-temperature tension tests, the elongation and
reduction in area of comparative material Nos. 10, 14 and 19
are lower than those of the inventive materials (1). With
respect to impact properties, comparative material Nos. 8-11,
14-17, 19 and 20 show lower values, revealing that the
toughness of these comparative materials is lower than that
of the inventive materials (1). Moreover, this table shows
the rupture times obtained in creep rupture tests performed
at a test temperature of 650°C and a stress of 15 kgf/mm
2.
It is evident from these results that the creep rupture
strength of the inventive materials (1) is much more
excellent than that of all comparative materials except No.
10.
(Example 2)
-
An example concerned with the inventive material (2) is
described below.
-
The chemical compositions of materials used for testing
purposes are summarized in Table 3. The compositions of
inventive materials (2) are substantially the same as those
of the inventive materials (1), except that the content of Mn
is reduced as compared with the inventive materials (1).
Similarly to Example 1, all test materials were prepared by
melting the components in a 50 kg vacuum high-frequency
furnace. These test materials were hot-forged at a heating
temperature of 1,200°C and then subjected to the following
heat treatment. The heat treatment was carried out by
hardening the test materials under conditions which simulated
the central part of an oil-quenched rotor having a drum
diameter of 1,200 mm, and then tempering them at a
temperature which had been determined so as to give a 0.2%
yield strength of about 68-74 kgf/mm2.
-
The mechanical properties and creep rupture strengths of
the inventive materials (2) and the inventive materials (1)
used for comparative purposes are shown in Table 4. It is
evident from this table that there is little difference in
the results of room-temperature tension tests. With respect
to impact properties, the inventive materials (2) show
somewhat lower impact values than the corresponding inventive
materials (1), because they have a lower Mn content.
However, such reductions are slight and unworthy of serious
consideration. On the other hand, a comparison of the creep
rupture strengths reveals that the inventive materials (2)
show an increase in rupture time over the respective
inventive materials (1), indicating a distinct improvement in
creep rupture strength.
(Example 3)
-
An example concerned with the inventive material (3) is
described below.
-
The chemical compositions of materials used for testing
purposes are summarized in Table 5. The compositions of
inventive materials (3) are substantially the same as those
of the inventive materials (1), except that Ni is completely
eliminated from the inventive materials (1). Similarly to
Examples 1 and 2, all test materials were prepared by melting
the components in a 50 kg vacuum high-frequency furnace.
These test materials were hot-forged at a heating temperature
of 1,200°C and then subjected to the following heat
treatment. The heat treatment was carried out by hardening
the test materials under conditions which simulated the
central part of an oil-quenched rotor having a drum diameter
of 1,200 mm, and then tempering them at a temperature which
had been determined so as to give a 0.2% yield strength of
about 68-74 kgf/mm2.
-
The mechanical properties and creep rupture strengths of
the inventive materials (3) and the inventive materials (1)
used for comparative purposes are shown in Table 6. It is
evident from this table that there is little difference in
the results of room-temperature tension tests. With respect
to impact properties, the inventive materials (3) show
somewhat lower impact values than the corresponding inventive
materials (1), because they have a lower Ni content.
However, similarly to the inventive materials (2) having a
lower Mn content, such reductions are slight and unworthy of
serious consideration. On the other hand, a comparison of
the creep rupture strengths reveals that, as a result of the
elimination of Ni, the inventive materials (3) show a
distinct improvement in creep rupture strength over the
respective inventive materials (1).
(Example 4)
-
An example concerned with the inventive material (4) is
described below.
-
The chemical compositions of materials used for testing
purposes are summarized in Table 7. The compositions of
inventive materials (4) are substantially the same as those
of the inventive materials (3), except that the content of Mn
is reduced as compared with the inventive materials (3).
Similarly to Examples 1 to 3, all test materials were
prepared by melting the components in a 50 kg vacuum high-frequency
furnace. These test materials were hot-forged at a
heating temperature of 1,200°C and then subjected to the
following heat treatment. The heat treatment was carried out
by hardening the test materials under conditions which
simulated the central part of an oil-quenched rotor having a
drum diameter of 1,200 mm, and then tempering them at a
temperature which had been determined so as to give a 0.2%
yield strength of about 68-74 kgf/mm2.
-
The mechanical properties and creep rupture strengths of
the inventive materials (4) and the inventive materials (3)
used for comparative purposes are shown in Table 8. It is
evident from this table that, also in this case, there is
little difference in the results of room-temperature tension
tests. With respect to impact properties, the inventive
materials (4) show somewhat lower impact values than the
corresponding inventive materials (3), because they have a
lower Mn content. However, such reductions are slight and
unworthy of serious consideration. On the other hand, a
comparison of the creep rupture strengths reveals that, as a
result of the reduction in Mn content, the inventive
materials (4) show a distinct improvement in creep rupture
strength over the respective inventive materials (3).
(Example 5)
-
An example concerned with the inventive material (5) is
described below.
-
The chemical compositions of materials used for testing
purposes are summarized in Table 9. Inventive materials (5)
were derived from some typical inventive materials (1) to (4)
by adding B thereto. Specifically, the compositions of
inventive materials (5) Nos. 51 to 58 are based on the
compositions of inventive material (1) Nos. 3 and 4,
inventive material (2) Nos. 21 and 22, inventive material (3)
Nos. 34 and 35, and inventive material (4) Nos. 41 and 42,
except that B is added to the respective base materials.
Similarly to the inventive materials (1) to (4), all test
materials were prepared by melting the components in a 50 kg
vacuum high-frequency furnace. These test materials were
hot-forged at a heating temperature of 1,200°C and then
subjected to the following heat treatment. The heat
treatment was carried out by hardening the test materials
under conditions which simulated the central part of an oil-quenched
rotor having a drum diameter of 1,200 mm, and then
tempering them at a temperature which had been determined so
as to give a 0.2% yield strength of about 68-74 kgf/mm2.
-
The mechanical properties and creep rupture strengths of
the inventive materials (5) and some inventive materials (1)
to (4) used for comparative purposes are shown in Table 10.
It is evident from these results that, when the inventive
materials (5) are compared with the inventive materials (1)
to (4), there is little difference in mechanical properties.
A comparison of the creep rupture strengths reveals that, as
a result of the addition of B, the inventive materials (5)
show a distinct improvement in creep rupture strength over
the respective base materials.
(Example 6)
-
An example concerned with the inventive material (6) is
described below.
-
The chemical compositions of materials used for testing
purposes are summarized in Table 11. Inventive materials (6)
were derived from some typical inventive materials (1) to (5)
by replacing part or all of Hf and/or part of Fe with Nd.
Specifically, the compositions of inventive materials (6)
Nos. 61 to 68 are based on the compositions of inventive
material (1) No. 3, inventive material (2) No. 21, inventive
material (3) No. 34, inventive material (4) No. 41, and
inventive material (5) Nos. 52, 54, 56 and 58, except that
part or all of Hf and/or part of Fe are replaced with Nd in
the respective base materials. In addition, further
comparative materials (sample Nos. 71 and 72) were provided
by adding Nd to inventive material Nos. 64 and 68 in an
amount exceeding the upper limit of the Nd content in the
present invention. Similarly to the inventive materials (1)
to (5), all test materials were prepared by melting the
components in a 50 kg vacuum high-frequency furnace. These
test materials were hot-forged at a heating temperature of
1,200°C and then subjected to the following heat treatment.
The heat treatment was carried out by hardening the test
materials under conditions which simulated the central part
of an oil-quenched rotor having a drum diameter of 1,200 mm,
and then tempering them at a temperature which had been
determined so as to give a 0.2% yield strength of about 68-74
kgf/mm2.
-
The mechanical properties and creep rupture strengths of
the inventive materials (6), some inventive materials (1) to
(5) used for comparative purposes, and further comparative
materials (sample Nos. 71 and 72) are shown in Table 12. It
is evident from these results that, when the inventive
materials (6) are compared with the inventive materials (1)
to (5), there is little difference in mechanical properties.
A comparison of the creep rupture strengths reveals that, as
a result of the addition of Nd, the inventive materials (6)
show a distinct improvement in creep rupture strength over
the respective base materials. On the other hand, sample
Nos. 71 and 72 to which Nd was added in excess show a marked
reduction in impact value and creep rupture strength as
compared with the base materials [i.e., inventive material
(6) Nos. 64 and 68], indicating that the addition of Nd
beyond its upper limit contrarily reduces material
characteristics.
-
All of the disclosures of Japanese Patent Application
No. 9-1360 which was filed with the Japanese Patent Office on
January 8, 1997, i.e. the contents of the specification
(including claims) and abstract attached to the application,
are incorporated herein by reference in their entirety.
-
All of the disclosures of Japanese Patent Application
No. 9-223243 which was filed with the Japanese Patent Office
on August 20, 1997, i.e. the contents of the specification
(including claims) and abstract attached to the application,
are incorporated herein by reference in their entirety.
EXPLOITABILITY IN INDUSTRY
-
The steam turbine rotor materials for high-temperature
applications in accordance with the present invention have
excellent high-temperature strength and are hence useful as
high-temperature steam turbine rotor materials for use in
hypercritical-pressure electric power plants having a steam
temperature higher than 593°C. Thus, it may be said that the
present invention is useful in further raising the operating
temperature of the current hypercritical-pressure electric
power plants to afford a saving of fossil fuels and,
moreover, to reduce the amount of carbon dioxide evolved.
