Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- ~169782
A HEAT RESISTING STEEL
RELATED APPLICATION
This application is a division of Canadian Patent
Application Serial No. 2,009,120 filed February 1, 1990.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a heat resisting
steel.
DESCRIPTION OF THE PRIOR ART
In general, Cr-Mo-V steel specified in accordance
with ASTM (Designation: A470-84, Class 8) is used as a
material of a high pressure rotor exposed to high
temperature steam (steam temperature: about 538C) and 3.5
Ni-Cr-Mo-V steel specified in accordance with ASTM
(Designation: A470-84, Class 7) is used as a material of a
low pressure (steam temperature: about 100C) rotor. The
former Cr-Mo-V steel is superior in high temperature
strength, but inferior in low temperature toughness. The
latter 3.5 Ni-Cr-Mo-V steel is superior in low temperature
toughness, but inferior in high temperature strength.
A turbine having a large capacity comprises a
high pressure portion, an intermediate pressure portion,
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and a low pressure portion in accordance with the steam
conditions thereof, and high and intermediate pressure
rotors are fabricated from Cr-Mo-V steel and a low
pressure rotor is fabricated from 3.5 Ni-Cr-Mo-V steel.
Turbines having a small capacity less than
100,000 and an intermediate capacity of 100,000 to
300,000 KW have a rotor small in size and thus if a
material having both the advantages of the above
materials used in the high and low pressure rotors is
available, the high and the low pressure portions
thereof can be integrated (fabricated from the same
material). This integration makes the turbine compact
as a whole and the cost thereof is greatly reduced. An
example of a material o~ the rotor integrating high and
low pressure portions is disclosed in Japanese Patent
Publication No. 58-11504 and in Japanese Patent Laid-
Open Publication Nos. 54-40225 and 60-224766.
If the high and low pressure portions are
integrated by using the currently available rotor
materials, i.e., Cr-Mo-V steel or Ni-Cr-Mo-V steel, the
former cannot provide safety against the brittle
fracture of the low pressure portion, because it is
inferior in low temperature toughness, while the latter
cannot provide safety against the creep fracture of the
high pressure portion because it is inferior in high
temperature strength.
The above-mentioned Japanese Patent
Publication No. 58-11504 discloses a rotor integrating
-- 2169702
high and low pressure portions fabricated from a
material consisting, by weight, of 0.15 to 0.3% C, not
more than 0.1% Si, not more than 1.0% Mn, 0.5 to 1.5%
Cr, 0.5 to 1.5% Ni, not more than 1.5~ but more than
0.5% Mo, 0.15 to 0.30~ V, 0.01 to 0.1% Nb, and the
balance Fe, but it does not exhibit sufficient toughness
after heated at a high temperature for a long time and
thus long blades having a length not less than 30 inches
cannot be planted thereon.
Japanese Patent Laid-open Publication No. 60-
22~766 discloses a steam turbine rotor fabricated from a
material consisting, by weight, of 0.10 to 0.35~ C, not
more than 0.10% Si, not more than 1.0% Mn, 1.5 to 2.5~
Ni, 1.5 to 3.0% Cr, 0.3 to 1.5% Mo, 0.05 to 0.25% V, and
the balance Fe, and further discloses that this material
may contain 0.01 to 0.1% Nb, and 0.02 to 0.1% N. This
rotor, however, is inferior in creep rupture strength.
Japanese Patent Laid-open Publication No. 62-
189301 discloses a steam turbine integrating high and
low pressure portions, which, however, uses a rotor
shaft fabricated by mechanically combining a material
superior in high temperature strength but inferior in
tou~hness and a material superior in toughness but
inferior in high temperature strength, and thus it is
not fabricated from a material having the same
component. This mechanical combination requires a large
structure to obtain strength and thus the rotor shaft
_ 2169782
cannot be made small in size and, in addition, the
reliability is impaired.
SUMMARY OF THE INVENTION
The present invention provides a heat resisting
steel of Ni-Cr-Mo-V low alloy steel containing, by weight
0.15 to 0.4% C, not more than 0.1% Si, 0.05 to 0.25% Mn,
1.5 to 2.5% Ni, 0.8 to 2.5% Cr, 0.8 to 2.5% Mo, and 0.15 to
0.35% V, said steel having a ratio (Mn/Ni) not more than
0.12 and/or a ratio (Si+Mn~/Ni not more than 0.18.
The invention also provides a Ni-Cr-Mo-V low
alloy steel, consisting, by weight, of 0.15 to 0.4% C, not
more than 0.1% Si, 0.05 to 0.5% Mn, 1.6 to 2.5% Ni, 0.8 to
2.5% Cr, 0.8 to 2.5% Mo, 0.1 to 0.5% V, and the balance Fe
and incidental impurities, said steel having a ratio
(V+Mo)/(Ni+Cr) of 0.45 to 0.7.
In addition, the invention consists of a method
of producing a steam turbine rotor shaft, comprising the
steps of preparing a steel ingot by electro-remelting a
steel ingot containing by weight 0.15 to 0.4% C, not more
than 0.1~ Si, 0.05 to 0.5% Mn, 1.5 to 2.5% Ni, 0.8 to
2.5% Cr, 0.8 to 2.5% Mo and 0.15 to 0.35% V in which steel
ingot a ratio (Mn/Ni) is not more than 0.12 and/or
(Si+Mn)/Ni is not more than 0.18, hot-forging said steel
ingot, quenching said steel ingot in such a manner that
said steel ingot is heated to an austenitizing temperature
of 900 to 1,000C and cooled at a predetermined cooling
2169782
speed, and annealing said steel ingot at a temperature of
630 to 700C.
BRIEF DESCRIPTION OF THE INVENTION
Figures 1, 8, and 9 are partial cross sectional
views of a steam turbine using a rotor shaft integrating
high and low pressure portions;
Figure 2 is a graph showing a relationship
between a ratio (V + Mo) / (Ni + Cr), and creep rupture
strength and impact value;
Figure 3 is a graph showing a relationship
between creep rupture strength and oxygen;
Figure 4 is a graph showing a relationship
between creep rupture strength and Ni; and
Figure 5 to Figure 7 are graphs showing
relationships between a V-shaped notch impact value,
and Ni, Mn, Si + Mn, a ratio Mn/Ni, and a ratio
(Si + Mn)/Ni.
2169782
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PREFERRED EMBODIMENTS OF THE INVENTION
EXAMPLE 1
A turbine rotor is described below with reference
to examples. Table 1 shows chemical compositions of
typical specimens subjected to toughness and creep rupture
tests. The specimens were obtained in such a manner that
they were melted in a high frequency melting furnace, made
to an ingot, and hot forged to a size of 30 mm square at a
temperature from 850 to 1150C. The specimens Nos. 1, 3
and 7 to 11 are materials according to the present
invention. The specimens Nos. 2, 4 to 6 were prepared
for the comparison with the invented materials. The
specimen No. 5 is a material corresponding to ASTM A470
Class 8 and the specimen No. 6 is a material corre-
sponding to ASTM A470 Class 7. These specimens werequenched in such a manner that they were made to have
austenitic structure by being heated to 950C in
accordance with a simulation of the conditions of the
center of a rotor shaft integrating high and low
pressure portions of a steam turbine, and then cooled at
a speed of 100C/h. Next, they were annealed by being
heated at 665C for 40 hours and cooled in a furnace.
Cr-Mo-V steels according to the present invention
included no ferrite phase and were made to have a
bainite structure as a whole.
An austenitizing temperature of the invented
steels must be 900 to 1000C. When the temperature is
- 2169782
less than 900C, creep rapture strength is lowered,
although superior toughness can be obtained. When the
temperature exceeds 1000C, toughness is lowered,
although superior creep rapture strength can be
obtained. An annealing temperature must be 630 to
700C. If the temperature is less than 630C, superior
toughness cannot be obtained, and when it exceeds 700C,
superior creep strength cannot be obtained.
Table 2 shows the results of a tensile
strength test, impact test, and creep rupture test.
Toughness is shown by Charpy impact absorbing energy of
a V-shaped notch tested at 20C. Creep rupture strength
is determined by Larason Mirror method and shown by a
strength obtained when a specimen was heated at 538C
for 100,000 hours. As apparent from Table 2, the
invented materials have a tensile strength not less than
88 kgf/mm2 at a room temperature, a 0.2~ yield strength
not less than 70 kgf/mm2, an FATT not more than 40C, an
impact absorbing energy not less than 2.5 kgf-m both
before they were heated and after they had been heated,
and a creep rapture strength not less than about 11
kg/mm2, and thus they are very useful for a turbine
rotor integrating high and low pressure portions. In
particular, a material having a strength not less than
15 kg/mm2 is preferable to plant long blades of 33.5
inches.
Table 1
Specimen Composition (wt%) V~Mo . Si+Mn
No. C Si Mn P S Ni Cr Mo V Ni+Cr Mn/Nl Ni
1 0.29 0.08 0.18 0.012 0.012 1.85 1.20 1.21 0.22 - 0.47 0.097 0.141
2 0.24 0.06 0.07 0.007 0.010 1.73 1.38 1.38 0.27 - 0.53 0.040 0.075
3 0.27 0.04 0.15 0.007 0.009 1.52 1.09 1.51 0.26 - 0.68 0.099 0.125
4 0.30 0.06 0.19 0.008 0.011 0.56 1.04 1.31 0.26 - 0.98 0.339 0.446
0.33 0.27 0.77 0.007 0.010 0.34 1.06 1.28 0.27 - 1.11 2.265 3.059
6 0.23 0.05 0.30 0.009 0.012 3.56 1.66 0.40 0.12 - 0.10 0.084 0.098
7 0.31 0.07 0.15 0.007 0.009 2.00 1.15 1.32 0.22 - O.49 o.075 0.110 ~
8 0.26 0.06 0.17 0.007 0.008 1.86 1.09 1.41 0.24 LOa 2COe 0.56 0.091 0.124 4D
9 0.25 0.07 0.17 0.010 0.010 1.72 1.40 1.42 0.24 0 COaO5 0.53 0.099 0.140
0.24 0.05 0.13 0.009 0.007 1.73 1.25 1.39 0.25 0zOr4 0.55 0.075 0.104
11 0.26 0.03 0.09 0.008 0.009 1.71 1.23 1.45 0.23 o~oll 0.57 0.052 0.070
12 0.29 0.09 0.23 0.013 0.009 1.70 1.06 1.32 0.25 - 0.57 0.135 0.188
13 0.29 0.21 0.33 0.012 0.007 1.74 1.04 1.20 0.23 - 0.51 0.190 0.310
14 0.31 0.25 0.90 0.010 0.007 1.86 1.06 1.29 0.22 - 0.52 0.484 0.618
Table 2
Value in parenthesis: after heated at 500C for 3000 h
Tensile 0.02% yieldElonga- Contrac- Impact 50~ FATT 538C Creep
Specimen strength strength tion tion of absorbing (C) rapture
No. (kg/m~2) (kg/mm2) (%) area (%) energy (kg-m) (kgf/mm2)
1 92.4 72.5 21.7 63.7 3.5 (3-3) 30 12.5
2 92.5 72.6 21.3 62.8 3.3 (3.0) 39 15.6
3 90.8 71.4 22.5 64.0 2.8 (2.7) 38 18.4
4 90.8 71.9 20.4 61.5 1.2 119 15.5 c~
88.1 69.2 20.1 60.8 1.3 120 14.6 ~~6 72.4 60.1 25.2 75.2 12.0 -20 5.8
7 89.9 70.3 22.3 64.5 3.6 (3.3) 29 10.8
8 90.8 70.7 21.9 63.9 4.2 21 14.8
9 91.0 71.4 21.7 63.5 3.9 25 15.1
92.0 72.2 20.9 62.2 3.7 34 15.6
11 90.6 71.1 21.5 61.8 3.7 36 15.5
12 - - - - 3.0 (2.4)
13 - - - - 3.4 (2.4)
14 - - _ _ 3.6 (2.3)
-- 2163782
Fig. 2 shows a relationship between a ratio
of a sum of V and Mo acting as carbide creating elements
to a sum of Ni and Cr acting as quenching ability
improving elements, and creep rupture strength and
S impact absorbing energy. The creep rupture strength is
increased as the component ratio (V + Mo)/(Ni ~ Cr) is
increased until it becomes about 0.7. It is found that
the impact absorbing energy is lowered as the component
ratio is increased. It is found that the toughness
(vE20 ~ 2.5 kgf/m) and the creep rupture strength (6R 2
11 kg~/mm2) necessary as the characteristics of a
material orming the turbine rotor integrating high and
low pressure portions are obtained when (V + Mo)/(Ni +
Cr) = 0.45 to 0.7. Further, to examine the brittle
characteristics of the invented material No. 2 and the
comparative material Nos. 5 (corresponding to a material
currently used to a high pressure rotor) and 6
(corresponding to a material currently used to a low
pressure rotor), an impact test was effected to
specimens before subjected to a brittle treatment for
3000 h at 500C and those after sub]ected to the treat-
ment and a 50~ fracture appearance transition tempera-
ture (FATT) was examined. An FATT of the comparative
material No. 5 was increased (made brittle) from 119C
to 135C (~FATT = 16C), an FATT of the material No. 6
was increased from -20C to 18C (~FATT = 38C) by the
brittle treatment, whereas it was also confirmed that an
FATT of the invented material No. 3 remained at 38C
_ 10
2169782
before and after the brittle treatment and thus it was
confirmed that this material was not made brittle.
The specimens Nos. 8 to ll of the invented
materials added with rare earth elements (La - Ce)l Ca,
Zr, and Al, respectively, have toughness improved by
these rare earth elements. In particular, the addition
of the rare earth elements is effective to improve the
toughness. A material added with Y in addition to La -
Ce was also examined and it was confirmed that Y was
very effective to improve the toughness.
Table 3 shows the chemical compositions and
creep rapture strength of the specimens prepared to
examine an influence of oxygen to creep rapture strength
of the invented materials. A method of melting and
forging these specimens were the same as that of the
above-mentioned specimens Nos. 1 to ll.
Table 3
Specimen Composition (wt~)
C Si Mn P S Ni Cr Mo V O
0.26 0.05 0.08 0.008 0.011 1.71 1.24 1.37 0.25 0.0004
16 0.23 0.04 0.10 0.009 0.011 1.60 1.24 1.37 0.25 0.0014
17 0.25 0.05 0.09 0.010 0.012 1.61 1.25 1.36 0.24 0.0019
18 0.24 0.05 0.12 0.008 0.010 1.65 1.20 1.38 0.24 0.0030
19 0.25 0.04 0.11 0.009 0.010 1.69 1.29 1.29 0.23 0.0071 c~
0.23 0.06 0.09 0.010 0.012 1.72 1.30 1.32 0.25 0.0087 _~
1-- ~
-- 2169782
The specimens were quenched in such a manner
that they were austenitized by being heated to 950C and
then by being cooled at a speed of 100C/h. Next, they
were annealed by being heated at 660C for 40 hours.
Table 4 shows 538C creep rapture strength in the same
manner as that shown in Table 2. Figure 3 is a graph
showing a relationship between creep rupture strength
and oxygen. It is found that a superior creep rupture
strength not less than about 12 kgf/mm2 can be obtained
by making 2 to a level not more than 100 ppm, further,
a superior creep rupture strength not less than 15
kgf/mm2 can be obtained by making 2 level thereof be
not more than 80 ppm, and furthermore, a superior creep
rupture strength not less than 18 kgf/mm2 can be
obtained by making 2 level thereof be not more than
40 ppm.
Table 4
No. Mn Si+Mn V+MoCreep rupture
Ni Ni Ni+Cr(kgf/mm2)
0.047 0.076 0.55 19.9
16 0.063 0.088 0.57 21.0
17 0.056 0.087 0.56 20.3
18 0.073 0.103 0.57 18.5
19 0.065 0.089 0.51 15.6
0.052 0.087 0.52 14.3
-- 2169782
Figure 4 is a graph showing a relationship
between 538C, 105 hour creep rupture strength and an
amount of Ni. As shown in Figure 4, the creep rupture
strength is abruptly lowered as an amount of Ni is
increased. In particular, a creep rupture strength not
less than about 11 kgf/mm2 is exhibited when an amount
of Ni is not more than about 2~, and in particular, a
creep rupture strength not less than about 12 kgf/mm2 is
exhibited when an amount of Ni is not more than 1.9%.-
Figure 5 is a graph showing a relationship
between an impact value and an amount of Ni after the
specimens have been heated at 500C for 3,000 hours. As
shown in Figure 5, the specimens of the present
invention in which a ratio (Si + Mn)/Ni is not more than-
0.18 or in which another ratio Mn/Ni is not more than
0.1 can bring about high impact value by the increase in
an amount of Ni, but the comparative specimens Nos. 12
to 14 in which a ratio (Si + Mn)/Ni exceeds 0.18 or in
which another ratio Mn/Ni exceeds 0.12 have a low impact
value not more than 2.4 kgf-m, and thus an increase in
the amount of Ni is little concerned with the impact
value.
Likewise, Figure 6 is a graph showing a
relationship between impact value after being subjected
to heating embrittlement and an amount of Mn or an
amount of Si + Mn of the specimens containin~ 1.6 to
1.9% of Ni. As shown in Figure 6, it is apparent that
Mn or (Si + Mn) greatly influences the impact value at a
_ 14 _
-
- 2169782
particular amount of Ni. That is, the specimens have a
very high impact value when an amount of Mn is not more
than 0.2% or an amount of Si + Mn is not more than
0.25%.
Likewise, Figure 7 is a graph showing a
relationship between an impact value and a ratio Mn/Ni
or a ratio (Si + Mn)/Ni of the specimens containing 1.52
to 2.0% Ni. As shown in Figure 7, a high impact value
not less than 2.5kgf-m is exhibited when a ratio Mn/Ni
is not more than 0.12 or a ratio Si + Mn/Ni is not more
than 0.18.
EXAMPLE 2
Table 5 shows typical chemical compositions
(wt%) of specimens used in an experiment.
The specimens were obtained in such a manner
that they were melted in a high frequency melting
furnace, made to an ingot, and hot forged to a size of
30 mm square at a temperature from 850 to 1250C. The
specimens Nos. 21 and 22 were prepared for the
comparison with the invented materials. The specimens
Nos. 23 to 32 are rotor materials superior in toughness
according to the present invention.
The specimens Nos. 23 to 32 were quenched in
such a manner that they were austenitized being heated
to 950C in accordance with a simulation of the
conditions of the center of a rotor shaft integrating
high and low pressure portions of a steam turbine, and
_ 15- _
2169782
then cooled at a speed of 100C/h. Next, they were
annealed by being heated at 650C for 50 hours and
cooled in a furnace. Cr-Mo-V steel according to the
present invention included no ferrite phase and was made
to have a bainite structure as a whole.
An austenitizing temperature of the invented
steels must be 900 to 1000C. When the temperature was
less than 900C, creep rupture strength was lowered,
although superior toughness can be obtained. When the
temperature exceeded 1000C, toughness was lowered,
although superior creep rapture strength was obtained.
An annealing temperature must be 630 to 700C. If the
temperature is less than 630C superior toughness cannot
be obtained, and when it exceeds 700C, superior creep
strength cannot be obtained.
Table 6 shows the results of a tensile
strength test, impact test, and creep rupture test.
Toughness is shown by Charpy impact absorbing energy of
a V-shaped notch tested at 20C and 50% fracture
transition temperature (FATT).
The creep rupture test by a notch was effected
using specimens each having a notch bottom radius of 66
mm, a notch outside diameter of 9 mm, and a V-shaped
notch configuration of 45 (a radius of a notch bottom
end) "r" is 0.16 mm).
_ 16 _
- 2169782
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_ 17
21697~2
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-- 18
216978Z
Creep rupture strength is determined by a
Larson Mirror method and shown by strength obtained when
a specimen was heated at 538C for 105 hours. As
apparent from Table 6, the invented materials have a
tensile strength not less than 88 kgf/mm2 at a room
temperature, an impact absorbing energy not less than 5
kgf/mm2, a 50% FATT not more than 40C, and a creep
rupture strength of 17 kgf/mm2, and thus they are very
useful for a turbine rotor integrating high and low
pressure portions.
These invented steels have greatly improved
toughness as compared with that of the material
(specimen No. 21) corresponding to a material currently
used to a high pressure rotor (having a high impact
absorbing energy and a low FATT). Further, they have a
538C, 105 hour notch creep rupture strength superior to
that of the material (specimen No. 22) corresponding to
a material currently used to a low pressure rotor.
In the relationship between a ratio of a sum
of V and Mo as carbide creating elements to a sum of Ni
and Cr as quenching ability improving elements, and
creep rapture strength and impact absorbing energy, the
creep rupture strength is increased as the component
ratio (V + Mo)/(Ni ~ Cr) is increased until it becomes
about 0.7. The impact absorbing energy is lowered as
the component ratio is increased. The toughness (vE20 >
2.5 kgf-m) and the creep rupture strength (R > 11
kgf/mm2) necessary as the turbine rotor integrating high
-- 19
- 21fi9782
and low pressure portions are obtained when (V + Mo)/(Ni
+ Cr) is made to be in the range of 0.45 to 0.7.
Further, to examine brittle characteristics of the
invented materials and the comparative material No. 21
(corresponding to a material currently used to a high
pressure rotor) and the comparative material No. 22
(corresponding to a material currently used to a low
pressure rotor), an impact test was effected to
specimens before subjected to a brittle treatment at
500C for 3000 h and those after subjected to the
treatment and a 50% fracture transition temperature
(FATT) was examined. As a result, an FATT of the
comparative material No. 21 was increased (made brittle)
from 119C to 135C (~FATT = 16C), an FATT of the
material, No. 2 was increased from -20C to 18C (~FATT
= 38C) by the brittle treatment, whereas it was also
confirmed that an FATT of the invented materials were
39C both before and after subjected to the brittle
treatment and thus it was confirmed that they were not
made brittle.
The specimens Nos. 27 to 32 of the invented
materials added with rare earth elements (La - Ce), Ca,
Zr, and Al, respectively, have toughness improved
thereby. In particular, an addition of the rare earth
elements is effective to improve the toughness. A
material added with Y in addition to La - Ce was also
examined and it was confirmed that Y was very effective
to improve the toughness.
- 20 -
2169782
As a result of an examination of an influence
of oxygen to creep rupture strength of the invented
materials, it is found that a superior strength not less
than about 12 kgf/mm2 can be obtained by making 2 to be
in a level not more than 100 ppm, further, a superior
strength not less than 15 kgf/mm2 can be obtained at a
level thereof not more than 800 ppm, and, furthermore, a
superior strength not less than 18 kgf/mm2 can be
obtained at a level thereof not more than 400 ppm.
As a result of an examination of the
relationship between 538C, 105 hour creep rupture
strength and an amount of Ni, it is found that the creep
rapture strength is abruptly lowered as an amount of Ni
is increased. In particular, a strength not less than
about 11 kgf/mm2 is exhibited when an amount of Ni is
not more than about 2%, and in particular, a strength
not less than about 12 kgf/mm2 is exhibited when an
amount of Ni is not more than 1.9%.
Further, as a result of an examination of a
relationship between impact value and an amount of Ni
after the specimens have been heated at 500C for 3000
hours, the specimens according to the present invention
in which the ratio (Si + Mn)/Ni is not more than 0.18
bring about high impact values by the increase in an
amount of Ni, but the comparative specimens in which the
ratio (Si + Mn)/Ni exceeds 0.18 have a low impact value
not more than 2.4 kgf/mm2, and thus an increase in the
amount of Ni is little concerned with the impacts value.
- 21 -
2 16978~
As a result of an examination of a relation-
ship between impact value and an amount of Mn or an
amount of Si + Mn of the specimens containing 1.6 to
1.9% of Ni, it is found that Mn or Si ~ Mn greatly
influences the impact value at a particular amount of
Ni, and the specimens have a very high impact value when
an amount of Mn is not more than 0.2~ or an amount of Si
+ Mn is in a range from 0.07 to 0.25%.
As a result of an examination of a relation-
ship between impact value and a ratio Mn/Ni or a ratio
(Si + Mn)/Ni of the specimens containing 1.52 to 2.0% of
Ni, a high impact value not less than 2.5 kgf/mm2 is
exhibited when the ratio Mn/Ni is not more than 0.12
or the ratio (Si + Mn)/Ni is in a range from 0.04 to
0.18.
EXAMPLE 3
Figure 1 shows a partial cross sectional view
of a steam turbine integrating high and low pressure
portions. A conventional steam turbine consumes high
pressure and temperature steam of 80 atg and 480C at the
main steam inlet thereof and low temperature and pressure
steam of 722 mmHg and 33C at the exhaust portion thereof
by a single rotor thereof, whereas the steam turbine
integrating high and low pressure portions of the
invention can increase an output of a single turbine by
increasing a pressure and temperature of steam at the
_ 22 _
.
2169782
main steam inlet thereof to 100 atg and 536C,
respectively. To increase an output of the single
turbine, it is necessary to increase a blade length of
movable blades at a final stage and to increase a flow
rate of steam. For example, when a blade length of the
movable blade at a final stage is increased from 26
inches to 33.5 inches, an rin~-shaped band area is
increased by about 1.7 times. Consequently, a
conventional output of 100 MW is increased to 170 MW,
and further when a blade length is increase to 40
inches, an output per a single turbine can be increased
by 2 times or more.
When a Cr-Mo-V steel containing 0.5% of Ni is
used for a rotor integrating high and low pressure
portions as a material of the rotor shaft having blades
o~ a length not less than 33.5 inches, this rotor
material can sufficiently withstand an increase in a
steam pressure and temperature at the main stream inlet
thereof, because this steel is superior in high
temperature strength and creep characteristics to be
thereby used at a high temperature region. In the case
of a long blade of 26 inches, however, tangential stress
in a low temperature region, in particular, tangential
stress occurring at the center hole of the turbine rotor
at a final stage movable blade portion is about 0.95 in
a stress ratio (operating stress/allowable stress) when
the rotor is rotated at a rated speed, and in the case
of a long blade of 33.5 inches, the tangential stress is
-- 2 169782
about 1.1 in the stress ratio, so that the above steel
is intolerable to this application.
On the other hand, when 3.5% Ni-Cr-Mo-V steel
is used as a rotor material, the above stress ratio
thereof is about 0.96 even when long blades of 33.5
inches are used, because this material has toughness in
the low temperature region, and tensile strength and
yield strength which are 14% higher than those of the
Cr-Mo-V steel. However, long blades of 40 inches are
used, the above stress ratio is 1.07, and thus this
rotor material is intolerable to this application.
Since this material has creep rupture stress in the high
temperature region which is about 0.3 times that of the
CR-Mo-V steel and thus it is intolerable to this
application due to lack of high temperature strength.
To increase an output as described above, it
is necessary to provide a rotor mateial which
simultaneously has both superior characteristics of the
Cr-Mo-V steel in a high temperature region and superior
characteristics of the Ni-Cr-Mo-V steel in a low
temperature region.
When a long blade of a class from 30 to 40
inches is used, a material ahving a tensile strength not
less than 88 kgf/mm2 is necessary, because conventional
Ni-Cr-Mo-V steel (ASTM A470 Class 7) has the stress
ratio of 1.07, as described above.
Further, a material of a steam turbine rotor
integrating high and low pressure portions on, which
_ 24 _
-- 216g782
long blades not less than 30 inches are attached must
have a 538C, 105 h creep rapture strength not less than
15 kgf/mm2 from a view point of securing safety against
high temperature breakdown on a high pressure side, and
an impact absorbing energy not less than 2.5 kgf-m (3
kg-m/cm2) from a view point of securing safety against
breakdown due to brittleness on a low pressure side.
From the above view point, in the invention
there was obtained heat resisting steels which can
satisfy the above requirements and which increase an
output per a single turbine.
The steam turbine includes thirteen stages of
blades 4 planted on a rotor shaft 3 integrating high and
low pressure portions, and steam having a high tempera-
ture and pressure of 538CC and 88 atg, respectively, issupplied from a steam inlet 1 through a steam control valve
5. The steam flows in one direction from the inlet 1 with
the temperature and pressure thereof being decreased to
33C and 722 mmHg, respectively and then discharged from an
outlet 2 through final stage blades 4. Since the rotor
shaft integrating high and low pressure
portions 3 according to the present invention is exposed
to a steam temperature ranging from 538C to 33C,
forged steel composed of Ni-Cr-Mo-V low alloy steel
having the characteristics described inthe example 1 is
used. The portions of the rotor shaft 3 where the
blades 4 are planted are formed to a disk shape by
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2169782
integrally machining the rotor shaft 3. The shorer the
blade is, the longer the disk portion, whereby the
vibration thereof is reduced.
The rotor shaft 3 was manufactured in such a
manner that cast ingot having the alloy compositions of the
specimen No. 16 shown in the example 1 and the specimen No.
24 shown in the example 2, respectively was electro-slug
remelted, forged to a shaft having a diameter of 1.2 m,
heated at 950C for 10 hours, and then the shaft was cooled
at a cooling speed of 100 C/h by spraying water while it is
rotated. Next, the shaft was annealed by being heated at
665 C for 40 hours. A test piece cut from the center of
the rotor shaft was subjected to a creep test, an impact
test of a V-shaped notch (a cross sectional area of the
specimen: 0.8 cm2) before the specimen was heated and after
it had been heated (after it had been heated at 500 C for
300 hours), and a tensile strength test, and values
substantially similar to those of the examples 1 and 2 were
obtained.
Each portion of the present examples are
fabricated from a material having the following
composltion .
(1) Blade
Blades composed of three stages on a high
temperature and pressure side have a length of about 40
mm in an axial direction and are fabricated from forged
martensitic steel consisting, by weight, of 0.20 to
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~1~97g2
0.30% C, 10 - 13% Cr, 0.5 to 1.5% Mo, 0.5 to 1.5% W, 0.1
to 0.3% V, not more than 0.5% Si, not more than 1% Mn,
and the balance Fe and incidental impurities.
Blades at an intermediate portion, of which
length is gradually made longer as they approach a low
pressure side, are fabricated from forged martensitic
steel consisting, by weight, of 0.05 to 0.15% C, not
more than 1% Mn, not more than 0.5% Si, 10 to 13% Cr,
not more than 0.5% Mo, not more than 0.5% Ni, and the
balance Fe and incidental impurities.
Blades having a length of 33.5 inches at a
final stage, ninety pieces of which were planted around
one circumference of a rotor were fabricated from forged
martensitic steel consisting, by weight, of 0.08 to
0.15% C, not more than 1% Mn, not more than 0.5% Si, 10
to 13% Cr, 1.5 to 3.5% Ni, 1 to 2% Mo, 0.2 to 0.5% V,
0.02 to 0.08% N, and the balance Fe and incidental
impurities. An erosion-preventing shield plate
fabricated from a stellite plate was welded to the
leading edge of the final stage at the tèrminal end
thereof. Further, a partial quenching treatment was
effected regarding portions other than the shield plate.
Furthermore, a blade having a length not less than 40
inches may be fabricated from Ti alloy containing 5 to
7% Al and 3 to 5% V.
Each of 4 to 5 pieces of these blades in the
respective stages was fixed to a shroud plate through
tenons provided at the extreme end thereof and caulked
216978~
to the shroud plate made of the same material as the
blades.
The 12% Cr steel shown above was used to
provide a blade which was rotated at 3000 rpm even in a
case of its length of 40 inches. Although Ti alloy was
used when a blade having a length of 40 inches was
rotated at 3600 rpm, the 12% Cr steel was used to
provide a blade having a length up to 33. 5 inches and
being rotated at 3600 rpm.
(2) Stationary blades 7 provided in the first to third
stages at the hiqh pressure side were fabricated from
martensitic steel having the same composition as those
of the corresponding movable blades and stationary
blades other than those of the first to third stages
were fabricated from martensitic steel having the same
composition as those of the movable blades at the
intermediate portion.
(3) A casing 6 was fabricated from Cr-Mo-V cast steel
comprising by weight 0.15 to 0.3% C, not more than 0.5%
Si, not more than 1% Mn, 1 to 2% Cr, 0.5 to 1.5% Mo,
0.05 to 0.2~ V, and not more than 0.1% Ti.
Designated at 8 is a generator capable of
generating an output of 100,000 to 200,000 KW. In the
present examples, a distance between bearings 12 of the
rotor shaft was about 520 cm, an outside diameter of a
final blade was 316 cm, and a ratio of the distance
between bearings to the outside diameter was 1.65. The
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~ 2169782
generator had a generating capacity of 100,000 KW. A
distance between the bearings was 0.52 m per 10,000 KW.
Further, in the present examples, when a blade
of 40 inches was used at a final stage, an outside
diameter thereof was 365 cm, and thus a ratio of a
distance between bearings to this outside diameter was
1.43, whereby an output of 200,000 KW was generated with
a distance between the bearings being 0.26 m per 10,000
KW.
In these cases, a ratio of an outside diameter
of a portion of the rotor shaft where the blades were
planted to a length of the final stage blade is 1.70 for
a blade of 33.5 inches and 1.71 for a blade of 40
inches.
In the present examples, steam having a tem-
perature of 566C was applicable, and pressures thereof
of 121, 169, or 224 atg were also applicable.
EXAMPLE 4
Figure 8 is a partially taken-away sectional
view of an arrangement of a reheating type steam turbine
integrating high and low pressure portions. In this
steam turbine, steam of 538C and 126 atg was supplied
from an inlet 1 and discharged from an outlet 9 through
a high pressure portion of a rotor 3 as steam of 367C
and 38 atg, and further steam having been heated to
538C and to a pressure of 35 atg was supplied from an
inlet 10, flowed to a low pressure portion of the rotor
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2169782
3 through an intermediate pressure portion thereof,
and discharged from an outlet 2 as steam having a
temperature of about 46C and a pressure of 0.1 atg. A
part of the steam discharged from the outlet 9 is used
as a heat source for the other purpose and then again
supplied to the turbine from the inlet 10 as a heat
source therefor. If the rotor for the steam turbine
integrating high and low pressure portions is fabricated
from the material of the specimen No. 5 of the example
1, the vicinity of the steam inlet 1, i.e., a portion a
will have sufficient high temperature strength, however,
since the center of the rotor 3 will have a high
ductility-brittle transition temperature of 80 to 120C,
there will be caused such drawback that, when the
vicinity of the steam outlet 2, i.e., a portion b has a
temperature of 50C, the turbine is not sufficiently
ensured with respect to safety against brittle fracture.
On the other hand, if the rotor 3 is fabricated from the
material of the specimen No. 6, safety against brittle
fracture thereof at the vicinity of the steam outlet 2,
i.e., the portion b will be sufficiently ensured, since
a ductility-brittle transition temperature at the center
of the rotor 3 is lower than a room temperature,
however, since the vicinity of the steam inlet 1, i.e.,
the portion a will have insufficient high temperature
strength and since the alloy constituting the rotor 3
contains a large amount of Ni, there will be such a
drawback that the rotor 3 is apt to become brittle when
- 3~ _
-- 21637 82
it is used (operated) at a high temperature for a long
time. More specifically/ even if any one of the
materials of the specimens Nos. 5 and 6 is used, the
steam turbine rotor integrating high and low pressure
portions made of the material composed of the specimens
No. 5 or 6 has a certain disadvantage, and thus it
cannot be practically used. Note thatl in Figure 8, 4
designates a movable blade, 7 designates a stationary
blade, and 6 designates a casing, respectively. A high
pressure portion was composed of five stages and a low
pressure portion was composed of six stages.
In this example, the rotor shaft 3, the
movable blades 4, the stationary blades 7, and the
casing 6 were formed of the same materials as those of
the above-mentioned example 3. The movable blade at a
final stage had a length not less than 33.5 inches and
was able to generate an output of 120,000 KW. Similar
to the example 3, 12~ Cr steel or Ti alloy steel is used
for this blade having length of not less than 33.5
inches. A distance between bearings 12 was about 454
cm, a final stage blade of 33.5 inches in length had a
diameter of 316 cm and a ratio of the distance between
the bearings to this outside diameter was 1. 72 . When a
final stage blade of 40 inches in length was used/ an
output of 200,000 KW was generated. The blade portion
thereof had a diameter of 365 cm and a ratio of a
distance between bearings to this diameter was 1.49. A
distance between the bearings per a generated output of
_ 31 -
-- 2169782
lO,000 KW in the former of 33.5 inches was 0.45 m and
that in the latter of 40 inches was 0.27 m. The above
mentioned steam temperature and pressures were also
applicable to this example.
EXAMPLE 5
The rotor shaft integrating high and low pressure
portions was also able to be applied to a single flow type
steam turbine in which a part of steam of an intermediate
pressure portion of a rotor shaft was used as a heat source
for a heater and the like. The materials used in the
example 3 were used regarding the rotor shaft, movable
blades, stationary blades and casing of this example.
EXAMPLE 6
The steam turbines described in the examples 3
to 5 were directly connected to a generator, and a gas
turbine was directly connected to the generator. A steam
turbine of this example was applied to a combined
generator system, wherein steam was generated by a
waste-heat recovery boiler using exhaust combustion gas
occurring in the gas turbine and the steam turbine was
rotated by the steam. The gas turbine generated an
output of about 40,000 KW and the steam turbine
generated an output of about 60,000 KW, and thus this
combined generator system generated a total output of
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2 169782
100,000 KW. Since the steam turbine of this example was
made compact, it was manufactured at a cost lower than
that of a conventional large stem turbine supposing that
they have the same generating capacity and it has an
advantage of being economically operated when an output
to be generated fluctuates.
In the gas turbine, air compressed by a
compressor was fed in a burner to produce a combustion
gas having a high temperature not less than 1100C an-d a
disc on which blades were planted was rotated by the
combustion gas. The disc was formed of three stages,
wherein a movable blade was fabricated from Ni base cast
alloy containing by weight 0.04 to 0.1% C, 12 to 16% Cr,
3 to 5% Al, 3 to 5% Ti, 2 to 5% Mo, and 2 to 5% Ni and a
stationary blade was fabricated from Co base cast alloy
containing by weight 0.25 to 0.45 C, 20 to 30% Cr, 2 to
5% at least one selected from the group consisting of Mo
and W, and 0.1 to 0.5% at least one selected from the
group consisting of Ti and Nb. A burner liner was
fabricated from FE-Ni-Cr austenitic alloy containing by
weight 0.05 to 0.15% C, 20 to 30% Cr, 30 to 45% Ni, 0.1
to 0.5% at least one selected from the group consisting
of Ti and Nb, and 2 to 7% at least one selected from the
group consisting of Mo and W. A heat shielding coating
layer made of a Y2O2 stabilizing zirconia sprayed onto
the outer surface of the liner was provided to the flame
side of the liner. Between the ~e-Ni-Cr austenitic
alloy and the zirconia layer was disposed a MCrAlY alloy
2169782
-
layer consisting, by weight, of 2 to 5% Al, 20 to 30%
Cr, 0.1 to 1~ Y, and at least one selected from the
group consisting of Fe, Ni and Co, that is, M is at
least one selected from the group consisting of Fe, Ni
and Co.
An Al-diffused coating layer was provided on
the movable and stationary blades shown above.
A material of the turbine disc was fabricated
from a martensitic forged steel containing by weight
0.15 to 0.25% C, not more than 0.5% Si, not more than
0.5~ Mn, 1 to 2% Ni, 10 to 13% Cr, 0.02 to 0.1~ at least
one selected from the group consisting of Nb and Ta,
0.03 to 0.1~ N, and 1.0 to 2.0% Mo; a turbine spacer,
distant piece and compressor disc at a final stage being
fabricated from the same martensitic steel,
respectively.
EXAMPLE 7
Figure 9 is a partially sectional view of a steam
turbine integrating high and low pressure portions. A
rotor shaft integrating high and low pressure portions 3
used in this example was fabricated from the Ni-Cr-Mo-V
steel having the bainite structure as a whole described in
the example 3. The left side is a high pressure side and
the right side is a low pressure side in Figure 9, and a
final stage blade had a length of 33.5 or 40 inches.
Blades on the left high pressure side were made of the
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~ ~169782
same material as that described in the example 3 and
final stage blades were made of the same material as
that described in the Example 3. Steam of this example
had a temperature of 538C and a pressure of 102 kg/cm2
at an inlet and had an temperature no more than 46C and
a pressure not more than an atmospheric pressure at an
outlet, which steam was supplied to a condenser as shown
by numeral 2. A material of the rotor shaft of this
example had an FATT not more than 40C, a V-shaped notch
impact value at a room temperature not less than 4.8
kgf-mm2 (a cross sectional area: not less than 0.8 cm2),
a tensile strength at a room temperature not less than
81 kgf/mm2, a 0.2 yield strength not less than 63
kgf/mm2, an elongation not less than 16%, a contraction
of area not less than 45 percent, and a 538C, 105 hour
creep rupture strength not less than 11 kgf/mm2. Steam
was supplied from an inlet 14, discharged from an outlet
15 through high pressure side blades, again supplied to
a reheater 13, and supplied to a low pressure side as
high temperature steam of 538C and 35 atg. Designated
at 12 are bearings disposed at the opposite sides of the
rotor shaft 3, and a distance between bearings was about
6 m. The rotor of this example rotated at 3600 rpm and
generated an output of 120,000 KW. Blades 4 were
composed of six stages on the high pressure side and ten
stages on the low pressure side. In this example, a
distance between bearings was 0.5 m per a generated
output of 10,000 KW, and thus the distance was about 40%
- 35 -
~ 21~9782
shorter than a conventional distance of 1.1 m.
Further, in this example, a final stage blade
of 33.5 inches had a diameter of 316 cm and thus a ratio
of a distance between the bearings to this outside
diameter was 2.22. In another case, a final stage blade
of 40 inches having a diameter of 365 cm was used, a
ratio of the distance between the bearings to the
diameter being 1.92, which enables an output of 200,000
KW to be generated. As a result, a distance between-the
bearings per a generated output of 10,000 KW was 0.3 m
in this another case, whereby the steam turbine was able
to be made very compact.
_ 36 -
