U.S. patent application number 12/153552 was filed with the patent office on 2009-03-12 for heat resisting steel, gas turbine using the steel, and components thereof.
This patent application is currently assigned to HITACHI, LTD.. Invention is credited to Masahiko Arai, Hiroyuki Doi, Hirotsugu Kawanaka, Hidetoshi Kuroki, Isao Takehara.
Application Number | 20090068052 12/153552 |
Document ID | / |
Family ID | 32866695 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090068052 |
Kind Code |
A1 |
Arai; Masahiko ; et
al. |
March 12, 2009 |
Heat resisting steel, gas turbine using the steel, and components
thereof
Abstract
The invention is of a heat resisting martensitic steel
comprising, by weight, 0.05 to 0.30% C, not more than 0.50% Si, not
more than 0.60% Mn, 8.0 to 13.0% Cr, 0.5 to 3.0% Ni, 1.0 to 3.0%
Mo, 0.1 to 1.5% W, 0.5 to 4% Co, 0.05 to 0.35% V, 0.02 to 0.30% in
total of one or two elements selected from the group consisting of
Nb and Ta, and 0.02 to 0.10% N, wherein a value of the square of a
difference between the Ni amount and the Co amount, and the Ni
amount are not more than values determined by a straight line drawn
on a point A (1.0, 2.7%) and a point B (2.5, 1.0%) in the
orthogonal coordinates shown in the attached drawing of FIG. 2
which represents a relationship between the above square value and
the Ni amount, and an amount ratio of Mo/(Mo+0.5W) is not less than
0.5. The heat resisting steel is suitably used in various
components of a gas turbine.
Inventors: |
Arai; Masahiko; (Hitachi,
JP) ; Kawanaka; Hirotsugu; (Hitachi, JP) ;
Doi; Hiroyuki; (Tokai, JP) ; Takehara; Isao;
(Hitachi, JP) ; Kuroki; Hidetoshi; (Hitachi,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
HITACHI, LTD.
Tokyo
JP
|
Family ID: |
32866695 |
Appl. No.: |
12/153552 |
Filed: |
May 21, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10757847 |
Jan 16, 2004 |
|
|
|
12153552 |
|
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Current U.S.
Class: |
420/38 ;
420/69 |
Current CPC
Class: |
C22C 38/48 20130101;
C22C 38/54 20130101; C22C 38/52 20130101; C22C 38/02 20130101; C22C
38/04 20130101; C22C 38/46 20130101; C22C 38/001 20130101; C22C
38/002 20130101; C22C 38/44 20130101 |
Class at
Publication: |
420/38 ;
420/69 |
International
Class: |
C22C 38/52 20060101
C22C038/52; C22C 38/44 20060101 C22C038/44 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2003 |
JP |
2003-101401 |
Claims
1. A heat resisting martensitic steel for a gas turbine disc,
comprising, by weight, 0.05 to 0.30% C, not more than 0.50% Si,
0.05 to 0.30% Mn, 8.0 to 13.0% Cr, 0.5 to 3.0% Ni, 1.0 to 3.0% Mo,
0.1 to 1.5% tungsten (W), 0.5 to 4% Co, 0.05 to 0.35% vanadium (V),
0.02 to 0.22% of Nb, and 0.02 to 0.10% nitrogen (N), wherein a
value of the square of a difference between the Ni amount and the
Co amount, and the Ni amount are not more than values determined by
a straight line drawn on a point A (1.0, 2.7%) and a point B (2.5,
1.0%) in the orthogonal coordinates shown in the attached drawing
of FIG. 2 which represents a relationship between the above square
value and the Ni amount, where the square value does not exceed
1.8, and wherein an amount ratio of Mo/(Mo+0.5W) is not less than
0.75.
2. (canceled)
3. A heat resisting martensitic steel according to claim 1, which
further comprises, by weight, not more than 1.5% Re, and 0.001 to
0.015% boron (B).
4-7. (canceled)
8. A heat resisting martensitic steel according to claim 1, which
further comprises, by weight, at least one of not more than 0.5%
Cu, not more than 0.5% Ti, not more than 0.2% Al, not more than
0.1% Zr, not more than 0.1% Hf, not more than 0.01% Ca, not more
than 0.01% Mg, not more than 0.01% yttrium (Y), and not more than
0.01% of a rare earth element.
9-14. (canceled)
15. A gas turbine disc formed of a heat resisting martensitic steel
made by a method as set forth in claim 1.
16. A gas turbine disc formed of a heat resisting martensitic steel
made by a method as set forth in claim 3.
17. A gas turbine disc formed of a heat resisting martensitic steel
made by a method as set forth in claim 8.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a novel heat resisting
steel, a gas turbine using the steel, and various members of the
gas turbine.
[0002] At present, a Cr--Mo--V steel, and 12Cr--Mo--Ni--V--N steel
have been used in a disc for a gas turbine. In recent years, from a
standpoint of energy saving, there has been a demand for
enhancement of a thermal efficiency of the gas turbine. When power
is generated with a high efficiency, a fossil fuel can be saved, an
emission amount of an exhaust gas can be reduced, and this can
contribute to global environment preservation. Most effective means
for enhancing the thermal efficiency is to raise a gas temperature
and pressure. When the gas temperature is raised to an order of
1500.degree. C. from an order of 1300.degree. C., a great
efficiency enhancement can be anticipated. Even when a combustion
temperature does not rise, a part of an amount of compressed air
for use in cooling the members is saved, and accordingly the
efficiency enhancement can be anticipated.
[0003] However, with the increase of the temperature/pressure, the
conventional Cr--Mo--V steel and 12Cr--Mo--Ni--V--N steel have
insufficient strength, and materials having higher strengths are
required. As the strength, a creep rupture strength which
influences high-temperature characteristics most is required.
Moreover, for a gas turbine disc, a high tensile strength and high
toughness are also required as well as the creep strength, and
especially embrittlement has to be inhibited from occurring at the
high temperature during the use.
[0004] As a structural material having a high creep rupture
strength, austenitic steel, Ni-base alloy, Co-base alloy,
martensitic steel, and the like have generally been known. The
Ni-base alloy and Co-base alloy are not preferable from the
standpoint of hot workability, machinability, and vibration damping
property. The austenitic steel does not have a very high strength
at around 400 to 450.degree. C., and is not preferable in a whole
gas turbine system. On the other hand, the martensitic steel has
satisfactory matching with another corresponding component, and
also has a sufficient high-temperature strength.
[0005] In JP-A-2001-49398, a heat resisting steel having high
strength and toughness has been disclosed as a high/low pressure
integral type steam turbine rotor. Further in JP-A-11-209851,
PCT/JP97/04609, and JP-A-10-251809, a heat resisting steel for a
gas turbine disc material has been disclosed.
[0006] However, the heat resisting steels disclosed in the
publications cannot satisfy especially the high creep rupture
strength and embrittlement reduction at the same time among the
characteristics such as the high creep rupture strength, high
tensile strength, high toughness, and embrittlement reduction, and
are not sufficient as the gas turbine disc having a higher
efficiency. Only with the use of the conventional material simply
having the high strength against the high temperature/pressure of
the gas turbine, the gas temperature cannot further rise. When a
high-temperature portion is cooled by a large amount of cooling
air, further rise of the gas temperature can be anticipated, but
thermal efficiency remarkably drops. Therefore, cooling air needs
to be saved in order to prevent the drop of the thermal efficiency,
but the saving is impossible until the above-described high
material characteristics are obtained. Moreover, in general, when
the high-temperature strength is enhanced, the toughness is
lowered, and it is therefore difficult to achieve both the
characteristics at the same time.
BRIEF SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a heat
resisting steel which has high creep rupture strength to be capable
of handling a higher temperature and which has high toughness even
after heating at a high temperature for a long time, a gas turbine
using the heat resisting steel, and various components of the gas
turbine.
[0008] According to one aspect of the present invention, there is
provided a heat resisting martensitic steel comprising, by weight,
0.05 to 0.30% C, not more than 0.50% Si, not more than 0.60% Mn,
8.0 to 13.0% Cr, 0.5 to 3.0% Ni, 1.0 to 3.0% Mo, 0.1 to 1.5%
tungsten (W), 0.5 to 4% Co, 0.05 to 0.35% vanadium (V), 0.02 to
0.30% in total of one or two elements selected from the group
consisting of Nb and Ta, and 0.02 to 0.10% nitrogen (N), wherein a
value of the square of a difference between the Ni amount and the
Co amount, and the Ni amount are not more than values determined by
a straight line drawn on a point A (1.0, 2.7%) and a point B (2.5,
1.0%) in the orthogonal coordinates shown in the attached drawing
of FIG. 2 which represents a relationship between the above square
value and the Ni amount, and wherein an amount ratio of
Mo/(Mo+0.5W) is not less than 0.5. Preferably, the above square
value is not more than 1.8.
[0009] According to one feature of the martensitic steel of the
invention having the above chemical composition, an amount ratio of
W/Mo, and the Mn amount are not more than values determined by a
straight line drawn on a point C (1.3, 0.15%) and a point D (2.5,
0.37%) in the orthogonal coordinates shown in the attached drawing
of FIG. 4 which represents a relationship between the amount ratio
and the Mn amount.
[0010] According to another feature of the martensitic steel of the
invention having the above chemical composition, an amount ratio of
Mo/(Mo+0.5W), and the Mn amount are not less than values determined
by a straight line drawn on a point E (0.25, 0.4%) and a point F
(0.7, 0.15%) in the orthogonal coordinates shown in the attached
drawing of FIG. 6 which represents a relationship between the
amount ratio and the Mn amount.
[0011] The invention steel may comprise, by weight, at least one
element of not more than 1.5% Re and 0.001 to 0.015% boron (B). The
invention steel may comprise, by weight, at least one element
selected from the group consisting of not more than 0.5% Cu, not
more than 0.5% Ti, not more than 0.2% Al, not more than 0.1% Zr,
not more than 0.1% Hf, not more than 0.01% Ca, not more than 0.01%
Mg, not more than 0.01% yttrium (Y), and not more than 0.01% of a
rare earth element.
[0012] Preferably, the invention heat resisting steel is adjusted
to have such a chemical composition that the Cr-equivalent, as
defined by the following equation, is not more than 10, and the
steel does not essentially contain the 6 ferrite phase:
[0013] the
Cr-equivalent=Cr+6Si+4Mo+1.5W+11V+5Nb-40C-30N-30B-2Mn-4Ni-2Co+2-
.5Ta (where each element is of a content, by weight %, of the heat
resisting steel).
[0014] The invention steel preferably has not less than 1180 MPa of
tensile strength at room temperature, more preferably not less than
1200 MPa, not less than 420 Mpa of creep rupture strength at
510.degree. C. for 10.sup.5 hours, more preferably not less than
430 Mpa, and not less than 19.6 J/cm.sup.2 of a V-notch Charpy
impact value at 25.degree. C. after heating at 530.degree. C. for
10.sup.4 hours.
[0015] According to another aspect of the present invention, there
is provided a gas turbine comprising:
[0016] a turbine stub shaft;
[0017] a plurality of turbine discs connected to the turbine stub
shaft by turbine stacking bolts via turbine spacers;
[0018] turbine blades each implanted in the respective disc to
rotate by high-temperature combustion gas generated in a combustion
device;
[0019] a distant piece connected to the turbine discs;
[0020] a plurality of compressor rotors connected to the distant
piece;
[0021] compressor blades which are implanted to compressor discs
constituting the respective compressor rotor, and which compress
air; and
[0022] a compressor stub shaft connected to the compressor rotors,
wherein [0023] at least one of the turbine discs, the distant
piece, the turbine spacers, the compressor disc at a last stage,
and the turbine stacking bolts is made of the above heat resisting
steel.
[0024] According to still another aspect of the present invention,
there is provided a disc for a gas turbine, which is a disc member
comprising a circumferential implanting section for a turbine
blade, and a plurality of bores receiving a plurality of stacking
bolts by which a plurality of the disc members are integrally
fastened to one another, wherein the disc is made of the heat
resisting steel having the above chemical composition and
properties. The disc member may have optionally a central bore.
[0025] The gas turbine disc should have high fatigue strength as
well as high tensile strength in order to bear high centrifugal
stress and vibration stress due to high-speed rotation. If the gas
turbine disc has a metal structure containing the detrimental delta
(.delta.) ferrite, the fatigue strength is excessively
deteriorated. Therefore, the Cr-equivalent is so adjusted to be not
more than 10 that the steel has an entire temper martensite
structure.
[0026] According to still another aspect of the present invention,
there is provided a gas turbine distant piece which is a
cylindrical member comprising protrusions provided at both opposite
ends of the cylindrical member; a plurality of bores in one of the
protrusions, which receive a plurality of stacking bolts by which
the cylindrical member is integrally fastened to turbine discs, and
a plurality of other bores in the other protrusion, which receive a
plurality of other stacking bolts by which the cylindrical member
is integrally fastened to compressor discs, wherein the gas turbine
distant piece is made of the above heat resisting steel having the
same properties as mentioned above.
[0027] According to still another aspect of the present invention,
there are provided gas turbine compressor discs each of which is a
disc member comprising a circumferential implanting section for
compressor blades, and a plurality of bores receiving a plurality
of stacking bolts by which a plurality of the disc members are
integrally fastened to one another, wherein the gas turbine
compressor discs are made of the above heat resisting steel having
the same properties as mentioned above.
[0028] According to still another aspect of the present invention,
there is provided a gas turbine stacking bolt which is a bar member
comprising a screw portion at one end thereof, and a polygonal head
portion at the other end, wherein the gas turbine stacking bolt is
made of the above heat resisting steel having the same properties
as mentioned above.
[0029] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0030] FIG. 1 is a graph showing a relationship between creep
rupture strength and a value of the square of a difference between
the Ni amount and the Co amount;
[0031] FIG. 2 is a graph showing a relationship between the Ni
amount and the square value, in which the line represents a steel
having not less than 420 MPa of creep rupture strength at
510.degree. C. for 10.sup.5 hours on the basis the relationship
shown in FIG. 1;
[0032] FIG. 3 is a graph showing a relationship between a V-notch
Charpy impact value at 25.degree. C. and an amount ratio of W/Mo
after an embrittle treatment;
[0033] FIG. 4 is a graph showing a relationship between the ratio
of W/Mo and the Mn amount, in which the line represents a steel
having not less than 19.6 J/cm.sup.2 of a V-notch Charpy impact
value at 25.degree. C. after the embrittle treatment;
[0034] FIG. 5 is a graph showing a relationship between the V-notch
Charpy impact value at 25.degree. C. and an amount ratio of
Mo/(Mo+0.5W) after the embrittle treatment;
[0035] FIG. 6 is a graph showing a relationship between the amount
ratio of Mo/(Mo+0.5W) and the Mn amount, according to which line
not less than 19.6 J/cm.sup.2 of the V-notch Charpy impact value at
25.degree. C. is obtained after the embrittle treatment;
[0036] FIG. 7 is a sectional view of a rotary section of a gas
turbine according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Reasons for limitations on component range of heat resisting
steel of the present invention will be described.
[0038] A carbon (C) content is set to not less than 0.05% in order
to obtain high tensile strength and yield strength. However, if the
C amount exceeds 0.30%, the metal structure becomes unstable when
exposed to high temperature for a long time, a creep rupture
strength and toughness are deteriorated. Therefore, the content is
set to not more than 0.30%, especially preferably 0.07 to 0.23%,
more preferably 0.10 to 0.20%.
[0039] Si is a deoxidizer, and Mn is a desulfurizing/deoxidizing
agent. These are added at the time of melting of heat resisting
steel, and are effective even in small amounts. Si is a .delta.
ferrite generating element. When a large amount of this element is
added, detrimental .delta. ferrite is generated to lower fatigue
strength and toughness. Therefore, the content is set to 0.50% or
less. It is to be noted that Si does not have to be added in a
carbon vacuum deoxidizing process and electro slag remelting
process, and no Si is preferably added. The content is especially
preferably 0.10% or less, more preferably 0.05% or less.
[0040] When a small amount of Mn is added, the toughness is
enhanced. However, when a large amount is added, the toughness is
lowered. Therefore, the content is set to 0.60% or less.
Especially, since Mn is effective as the desulfurization agent, the
content is preferably 0.30% or less, especially preferably 0.25% or
less, further preferably 0.20% or less from the standpoint of
enhancement of the toughness. The content of 0.05% or more is
preferable from the standpoint of the toughness.
[0041] Cr enhances corrosion resistance and tensile strength, but
with an addition amount exceeding 13%, a .delta. ferrite structure
is generated. When the amount is smaller than 8%, the corrosion
resistance and high-temperature strength are insufficient, and
therefore the content of Cr is set to 8 to 13%. The content is
especially preferably 10.0 to 12.8%, more preferably 10.5 to
12.5%.
[0042] Mo is effective in improving the creep rupture strength by
virtue of solid-solution strengthening and precipitation
strengthening with carbide/nitride. When the Mo content is not more
than 1.0%, Mo has an insufficient effect of enhancing the creep
rupture strength. When the Mo content is not less than 3%, delta
(.delta.) ferrite is generated. Therefore, the Mo content is set to
1.0 to 3.0%, preferably 1.2 to 2.7%, more preferably 1.3 to
2.5%.
[0043] W has an effect similar to that of Mo. For a higher
strength, the content may be equal to that of Mo. With a content of
0.1% or less, W has an insufficient effect of enhancing the creep
rupture strength. With a content exceeding 1.5%, the toughness is
lowered, and therefore the content is set to 0.1 to 1.5%. The
content is preferably 0.2 to 1,4%, more preferably 0.3 to 1.3%.
[0044] Since Co enhances the strength at a higher temperature, the
content is preferably increased with the increase of the
temperature. With a content less than 0.5%, the effect is not
sufficient. With a content exceeding 4.0%, heating embrittlement is
promoted, and therefore an upper limit is set to 4%. The content is
preferably 0.8 to 3.5%.
[0045] V and Nb precipitate carbide, enhance the tensile strength,
and further have an effect of enhancing the toughness. With not
more than 0.05% V, or not more than 0.02% Nb, the effect is
insufficient. From the standpoint of reduction of .delta. ferrite
generation, not more than 0.35% V, and not more than 0.3% Nb are
preferable. Especially, the content of V is preferably 0.15 to
0.30%, more preferably 0.20 to 0.30%. The content of Nb is 0.04 to
0.22%, more preferably 0.10 to 0.20%. Instead of Nb, Ta can be
added in the same manner, and a total amount is similar to the
content even in composite addition.
[0046] Ni enhances low-temperature toughness, and also has an
effect of preventing .delta. ferrite from being generated. This
effect is preferable with not less than 0.5% Ni, and the effect is
saturated with an addition amount exceeding 3.0%. When a large
amount of Ni is added, the creep rupture strength is lowered. The
content is preferably 0.5 to 2.5%, more preferably 0.7 to 2.3%.
[0047] N is effective in enhancing the creep rupture strength and
in preventing .delta. ferrite from being generated. However, the
effect is insufficient with a content less than 0.02%, and the
toughness is lowered with a content exceeding 0.10%. Especially,
superior properties are obtained in a range of 0.04 to 0.080%.
[0048] Re is effective in improving the creep rupture strength by
virtue of solid-solution strengthening. Since an excess addition
promotes the embrittlement, an addition amount of not more than 2%
is preferable. However, since Re is a rare element, a content of
not more than 1.5% is preferable in a practical use, more
preferably not more than 1.2%.
[0049] B has a function of enhancing a grain boundary strength, and
has an effect of enhancing the creep rupture strength. This effect
is insufficient with a content of not more than 0.001%, and the
toughness drops with an addition amount exceeding 0.015%. The
content is especially preferably 0.002 to 0.008%.
[0050] The reduction of P and S has an effect of enhancing the
low-temperature toughness without impairing the creep rupture
strength, and the reduction to the utmost is preferable. From the
standpoint of the enhancement of the low-temperature toughness, not
more than 0.015% phosphor (P), not more than 0.015% sulfur (S) are
preferable. Especially, not more than 0.010% phosphor (P), not more
than 0.010% sulfur (S) are preferable.
[0051] The reduction of Sb, Sn, and As also has the effect of
enhancing the low-temperature toughness, and the reduction to the
utmost is preferable, but from the standpoint of an existing steel
making technique level, the content is limited to not more than
0.0015% Sb, not more than 0.01% Sn, and not more than 0.02% As.
Especially, not more than 0.001% Sb, 0.005% Sn, and not more than
0.01% As are preferable.
[0052] At least one of MC carbide forming elements such as Ti, Al,
Zr, Hf, Ta is preferably contained by not more than 0.5% in total.
The content of Al, which is used as a deoxidizer and a grain
refiner, is set to not less than 0.0005%. If the Al content exceeds
0.2%, nitrogen, which is effective for improving the creep
strength, is fixed to deteriorate the creep rupture strength. Thus,
the Al content is preferably not more than 0.2%.
[0053] The present inventors turned their attention to a content
balance of additive Ni and Co. Accordingly, a value of the square
of a difference between the Ni amount and the Co amount, and the Ni
amount have been set to be not more than values determined by a
straight line drawn on a point A (1.0, 2.7%) and a point B (2.5,
1.0%) in the orthogonal coordinates shown in the attached drawing
of FIG. 2 which represents a relationship between the above square
value and the Ni amount, and an amount ratio of Mo/(Mo+0.5W) is set
to be not less than 0.5, whereby the above properties can be
obtained. Especially, remarkable properties can be obtained when
the tungsten (W) amount is not more than 1.5%. Further, the above
square value is preferably set to be not more than 1.8. If the
tungsten (W) amount exceeds 1.5%, the high creep strength mentioned
above can be obtained, but the toughness is deteriorated after
heating at high temperature for a long time. Thus, more than 1.5%
tungsten (W) is not preferable.
[0054] Ni and Co contribute to improving martensitic steel in
toughness. Ni is effective for improving the toughness, but
deteriorates the creep strength. Co is effective for improving the
creep strength, but promotes embrittlement of the steel during
operation, and deteriorates the toughness. Therefore, since the
toughness and creep strength are kept and the heating embrittlement
is inhibited, it has been found that the difference between the Ni
amount and the Co amount is an effective index indicating a
preferable balance between the additive amounts of Ni and Co in the
present invention.
[0055] Further, in the present invention, an amount ratio of W/Mo,
and the Mn amount are set to be not more than values determined by
a straight line drawn on a point C (1.3, 0.15%) and a point D (2.5,
0.37%) in the orthogonal coordinates shown in the attached drawing
of FIG. 4 which represents a relationship between the amount ratio
and the Mn amount. Accordingly, a high toughness is obtained even
after the heating at high temperature for the long time.
[0056] Further, in the present invention, an amount ratio of
Mo/(Mo+0.5W), and the Mn amount are set to be not less than values
determined by a straight line drawn on a point E (0.25, 0.4%) and a
point F (0.7, 0.15%) in the orthogonal coordinates shown in the
attached drawing of FIG. 6 which represents a relationship between
the amount ratio and the Mn amount.
[0057] Accordingly, the high toughness is obtained especially even
after the heating at high temperature for the long time.
[0058] That is, in the present invention, also for the addition of
Mo and W, it has been found that a specific ratio of both the
addition amounts is an effective index indicating a preferable
balance. As the elements contributing to improvement of
high-temperature strength of martensitic steel, Mo and W function
as a solid-solution strengthening element, respectively, and the
effect is represented by the Mo-equivalent=(Mo(%)+0.5W(%)) or the
amount ratio of W/Mo. However, these elements lower the toughness
after the heating at high temperature for the long time, but a
small amount of Mn performs an important function of enhancing the
toughness after the heating at high temperature for the long time,
and the effect is remarkably obtained by a composite addition with
a specific content from the relation with the Mn amount. Mo and W
are different from each other in the effect, the addition of W is
more effective in enhancing the strength at the high temperature.
However, when a ratio of W is large, the toughness tends to drop as
described above.
[0059] Especially, the addition of W is effective under a use
environment at a temperature exceeding 600.degree. C., but a use
temperature of the gas turbine disc is lower, and the high
toughness is required. Therefore, the Mo addition is more
preferable in the present invention.
[0060] Therefore, when the amount ratio of (Mo/(Mo+0.5W) is set to
0.5 or more, preferably 0.6 to 0.95, more preferably 0.75 to 0.95,
the high toughness is obtained even after the heating at high
temperature for the long time.
[0061] In a preferable thermal treatment of the material of the
present invention, first the material is uniformly heated at a
temperature sufficient for transformation to complete austenite,
1000.degree. C. at minimum, 1150.degree. C. at maximum, quenched
(preferably oil cooling or water spraying), and subsequently
heated/retained and cooled at a temperature of 540 to 600.degree.
C. (primary tempering). Subsequently, the material is
heated/retained and cooled at a temperature of 550 to 650.degree.
C. (secondary tempering) to form an entirely tempered martensitic
steel. The temperature of the secondary tempering is set to be
higher than a primary tempering temperature. When quenching, it is
preferable to stop cooling just above an Mf point in order to
prevent occurrence of cracks. Specifically, the above cooling-stop
temperature is preferably not lower than 150.degree. C. When
conducting a primary tempering, the material is heated from the
above temperature.
EMBODIMENTS
Example 1
[0062] Table 1 indicates a chemical composition (weight %) of heat
resisting 12% Cr steel for a gas turbine disc material, and the
balance is Fe. Each specimen was subjected to vacuum arc melting at
150 kg, heated at 1150.degree. C., and forged to form a raw
material. The raw material was heated at 1050.degree. C. for two
hours and subsequently oil-cooled, heated at 560.degree. C. for
five hours and subsequently air-cooled to be subjected to the
primary tempering, and next heated at 580.degree. C. for five hours
and furnace-cooled to be subjected to the secondary tempering.
After the thermal treatment, a creep rupture specimen, tensile
specimen, and V-notch Charpy impact specimen were sampled from the
raw material, and used in experiments. An impact test was conducted
with respect to the thermally treated material and a
heated/embrittled material at 530.degree. C. for 10,000 hours. The
embrittled material has conditions equal to those of a material
heated at 510.degree. C. for 100 thousand hours on the basis of the
Larson-Miller parameter.
TABLE-US-00001 TABLE 1 C Si Mn Ni Cr Mo W V Nb Co N Fe
(Ni--Co).sup.2 Mo/(Mo + 0.5W) 1 0.12 0.01 0.13 2.7 11.4 1.9 0 0.19
0.06 0 0.036 Bal. 7.18 1.00 2 0.16 0.04 0.11 2.6 11.5 2.1 0 0.24
0.15 2.8 0.076 Bal. 0.04 1.00 3 0.10 0.06 0.60 0.3 10.2 0.2 2.8
0.20 0.07 2.5 0.020 Bal. 5.06 0.13 4 0.15 0.03 0.15 1.2 11.0 1.9
0.6 0.23 0.12 4.2 0.070 Bal. 9.00 0.86 5 0.12 0.03 0.15 3.2 10.2
1.5 0.8 0.23 0.12 1.1 0.068 Bal. 4.41 0.79 6 0.15 0.03 0.15 1.2
10.9 0.7 1.8 0.23 0.12 1.8 0.069 Bal. 0.36 0.44 7 0.10 0.03 0.15
1.0 11.0 1.9 0.3 0.23 0.12 2.2 0.070 Bal. 1.44 0.93 8 0.17 0.25
0.32 0.8 10.5 2.1 0.2 0.20 0.17 0.6 0.075 Bal. 0.04 0.95 9 0.19
0.10 0.10 2.2 11.0 1.3 1.2 0.29 0.08 1.8 0.052 Bal. 0.16 0.68 10
0.15 0.03 0.15 1.2 10.9 1.9 0.3 0.23 0.12 1.0 0.069 Bal. 0.04 0.93
11 0.11 0.03 0.40 1.2 10.9 1.1 1.4 0.23 0.12 1.0 0.064 Bal. 0.04
0.61 12 0.11 0.03 0.40 2.6 10.9 1.1 1.4 0.23 0.12 3.3 0.061 Bal.
0.49 0.61 13 0.14 0.03 0.15 1.2 10.9 1.5 0.8 0.23 0.11 1.0 0.071
Bal. 0.04 0.79
[0063] Table 2 shows mechanical properties of these specimens.
Specimen Nos. 7 to 13 are of the invention steel exhibiting not
less than 1180 MPa of tensile strength at room temperature which is
required for a high-temperature/high-pressure gas turbine disc
material, not less than 420 MPa of creep rupture strength at
510.degree. C. for 10.sup.5 hours, and not less than 19.6
J/cm.sup.2 of the V-notch Charpy impact value at 25.degree. C.
after embrittle treatment. It has been confirmed that the specimens
are sufficiently satisfactory. On the other hand, Specimen Nos. 1
to 6, which are of comparative steel, cannot simultaneously satisfy
mechanical properties required for the high-temperature/pressure
gas turbine disc material. For any one of Specimen Nos. 1, 3, 4,
and 5 which are of comparative steel, the above square value
increases, and this indicates that the addition amount of one of Ni
and Co is large. For Comparative Specimen Nos. 1 and 5 having a
large Ni addition amount, the tensile strength and the V-notch
Charpy impact value at 25.degree. C. before/after the heating
embrittlement are satisfied, but the creep strength cannot be
satisfied. For Comparative Specimen Nos. 3 and 4 having a large Co
addition amount, the creep rupture strength is satisfied, but the
V-notch Charpy impact value at 25.degree. C. after the heating
embrittlement is remarkably deteriorated.
[0064] Specimen Nos. 3 and 6 in which the amount ratio of
Mo/(Mo+0.5W) of an Mo-equivalent is less than 0.5 have a low impact
value. Specimen No. 2 to which Mo alone is added (the W amount=0)
has a low creep rupture strength.
TABLE-US-00002 TABLE 2 Reduction Rupture strength at Impact value
(J/cm.sup.2) Tensile strength 0.2% Yield strength Elongation of
area 510.degree. C. for 10.sup.5 hours Before After (MPa) (MPa) (%)
(%) (Mpa) embrittlement embrittlement 1 1222 1063 19.2 78.1 336
114.2 72.2 2 1315 1144 18.1 75.6 344 98.1 42.2 3 1024 891 17.2 71.3
438 10.2 6.2 4 1243 1081 19.2 74.6 421 42.3 5.3 5 1189 1034 17.5
78.6 338 74.3 31.2 6 1230 1070 16.5 65.1 431 48.1 11.4 7 1210 1053
18.7 73.2 429 45.3 22.1 8 1237 1076 17.5 73.4 442 58.5 35.6 9 1250
1088 19.2 76.2 445 69.1 41.2 10 1223 1064 18.8 74.9 440 49.2 26.4
11 1232 1072 18.8 75.2 433 48.1 28.5 12 1240 1079 17.9 74.6 428
72.4 27.4 13 1245 1021 18.3 73.8 430 45.6 24.5
[0065] Furthermore, the specimens of the chemical compositions
shown in Table 3 were manufactured by the melting and forging, and
subjected to the same thermal treatment for use in the experiments.
The test results are shown in Table 4. As shown in Table 4, for
Specimen Nos. 17 to 19 which are the present invention materials,
it has been confirmed that the properties are obtained so as to
sufficiently satisfy the room temperature tensile strength required
for the high-temperature/pressure gas turbine disc material of not
less than 1180 MPa, the creep rupture strength at 510.degree. C.
for 10.sup.5 hours of not less than 420 MPa, and the V-notch Charpy
impact value at 25.degree. C. after the embrittle treatment of not
less than 19.6 J/cm.sup.2. On the other hand, for Specimen Nos. 14
and 15 of the comparative materials to which B is excessively
added, elongation and impact value of the tensile test are low, and
the mechanical properties required for the
high-temperature/pressure gas turbine disc material cannot
simultaneously be satisfied. Specimen No. 14 of the comparative
material to which Mo is added alone (the W amount=0) has a slightly
low creep strength. The Specimen No. 16 of the comparative material
to which Re is excessively added has a sufficient creep strength,
but a value of drawing is low.
TABLE-US-00003 TABLE 3 C Si Mn Ni Cr Mo W V Nb Co N B Re Fe
(Ni--Co).sup.2 Mo/(Mo + 0.5W) 14 0.16 0.03 0.15 1.1 11.0 1.9 0 0.23
0.13 1.0 0.025 0.018 0.5 Bal. 0.01 1.00 15 0.15 0.03 0.15 1.2 11.0
1.1 0.8 0.23 0.12 1.5 0.045 0.025 0.6 Bal. 0.09 0.73 16 0.15 0.03
0.15 1.2 11.0 1.5 0.8 0.23 0.12 1.5 0.045 0.008 2.1 Bal. 0.09 0.79
17 0.18 0.03 0.10 1.9 11.0 2.1 0.5 0.23 0.12 0.8 0.070 0 0.2 Bal.
1.21 0.89 18 0.12 0.03 0.33 1.2 11.0 1.7 0.5 0.23 0.12 1.2 0.070 0
0.6 Bal. 0 0.87 19 0.15 0.03 0.15 1.2 11.0 1.9 0.3 0.23 0.12 1.0
0.020 0.010 0.8 Bal. 0.04 0.93
TABLE-US-00004 TABLE 4 Reduction Rupture strength at Impact value
(J/cm.sup.2) Tensile strength 0.2% Yield strength Elongation of
area 510.degree. C. for 10.sup.5 hours Before After (MPa) (MPa) (%)
(%) (Mpa) embrittlement embrittlement 14 1198 1018 15.1 62.3 420
10.5 6.2 15 1254 1066 16.2 54.5 434 16.4 7.4 16 1254 1066 18.2 48.2
421 52.1 25.2 17 1241 1055 18.1 72.4 444 67.2 45.1 18 1217 1034
18.8 73.6 458 60.5 36.4 19 1221 1038 19.6 71.6 452 54.2 33.3
[0066] FIG. 1 is a diagram showing a relation between the creep
rupture strength and the square of (difference between Ni amount
and Co amount). As shown in FIG. 1, the creep rupture strength
remarkably drops as the value of the square of a difference between
the Ni amount and the Co amount increases. Especially, the relation
with the Ni amount is large. When the Ni amount is 1.0 to 1.2%, the
creep rupture strength is high as compared with an amount of 2.2 to
3.2%. However, with high Ni, when the square value increases, the
creep rupture strength rapidly drops.
[0067] Especially, when the Co amount is larger than the Ni amount,
the creep strength drops slightly, and an influence by the square
value is small.
[0068] FIG. 2 is a linear diagram showing a relationship between
the square value and the Ni amount having a creep rupture strength
at 510.degree. C. for 10.sup.5 hours of not less than 420 MPa from
the relation of FIG. 1. As described above, for the creep rupture
strength, the above square value has a close relation with the Ni
amount. When the value represented by the relation between the
square value and the Ni amount is set to be not more than the value
determined by a straight line drawn on a point A (1.0, 2.7%) and a
point B (2.5, 1.0%) in the orthogonal coordinates shown in the
attached drawing of FIG. 2 which represents a relationship between
the above square value and the Ni amount, a creep rupture strength
of 420 MPa or more is obtained.
[0069] FIG. 3 is a linear diagram showing a relation between the
V-notch Charpy impact value at 25.degree. C. and an amount ratio of
W/Mo after the embrittle treatment. As shown in FIG. 3, the impact
value rapidly drops with an increase of the ratio of W/Mo. The
impact value is high with a large Mn amount of 0.32 to 0.4% as
compared with an amount of 0.15%, and is further high with a large
C amount. Furthermore, the impact value remarkably drops with any
Mn amount, when the ratio of W/Mo increases.
[0070] FIG. 4 is a linear diagram showing a relationship between
the ratio W/Mo and the Mn amount having a V-notch Charpy impact
value at 25.degree. C. of 19.6 J/cm.sup.2 or more after the
embrittle treatment. As shown in FIG. 4, when the value represented
by the relation between the (W amount/Mo amount) ratio and the Mn
amount is set to be not more than the value determined by a
straight line drawn on a point C (1.3, 0.15%) and a point D (2.5,
0.37%) in the orthogonal coordinates shown in the attached drawing
of FIG. 4 which represents a relationship between the amount ratio
and the Mn amount, a 25.degree. C. V-notch Charpy impact value of
not less than 19.6 J/cm.sup.2 is obtained. It is to be noted that
FIG. 4 is applied with a C amount of not more than 0.17%.
[0071] FIG. 5 is a linear diagram showing a relationship between
the V-notch Charpy impact value at 25.degree. C. and an amount
ratio of Mo/Mo+0.5W) after the embrittle treatment. As shown in
FIG. 5, when the ratio is further increased, the high toughness is
obtained even after the heating at high temperature for the long
time. The impact value is high with a large Mn amount of 0.32 to
0.4% as compared with an amount of 0.15%, and further with a large
C amount, and increases as the ratio of Mo/(Mo+0.5W) increases.
When the Mn amount is 0.15%, a carbon amount is not more than
0.15%. When the Mn amount is 0.32 to 0.4%, the carbon amount is
0.11 to 0.17%.
[0072] FIG. 6 is a linear diagram showing a relationship between
the amount ratio of Mo/(Mo+0.5W) and the Mn amount in which a
V-notch Charpy impact value at 25.degree. C. after the embrittle
treatment of not less than 19.6 J/cm.sup.2 is obtained. When the
value represented by this relation is set to be not less than the
value determined by a straight line drawn on a point E (0.25, 0.4%)
and a point F (0.7, 0.15%) in the orthogonal coordinates shown in
the attached drawing of FIG. 6 which represents a relationship
between the amount ratio and the Mn amount, the above-described
impact value is obtained. It is to be noted that FIG. 6 is applied
with a carbon amount of 0.17% or less.
Example 2
[0073] FIG. 7 is a sectional view of a turbine upper half of an air
compression type three-stage turbine including an air cooling
system. As shown in FIG. 7, a gas turbine of the present example is
constituted of a casing 80, a compressor including a compressor
rotor 2 and a blade array of an outer peripheral portion, a
combustion unit 84, alternately arranged turbine nozzles 81 to 83
and turbine blades 51 to 53, a turbine rotor 1, and the like. The
turbine rotor 1 includes three turbine discs 11, 12, 13 and a
turbine stub shaft 4, and is closely bonded as a high-speed
rotating member. The turbine blades 51 to 53 are disposed on the
outer periphery of each turbine disc, connected to the compressor
rotor 2 and turbine stub shaft via a distant piece 3, and rotatably
supported by a bearing. In this constitution, air compressed by the
compressor is used, and a high-temperature/pressure working gas
generated by the combustion unit 84 expands while flowing.
Accordingly, the turbine rotor 1 is rotated to generate a motive
energy. A combustion gas flowing out of the turbine section is fed
to an exhaust heat recovery boiler (HRSG) to produce steam.
[0074] Although there are also portions not shown, in addition to
the above-described constitution, a main constitution of the gas
turbine in the present embodiment includes the turbine stub shaft
4, turbine stacking bolts 5, turbine spacers 18, the distant piece
3, compressor discs 17 constituting a compressor rotor, compressor
blades, compressor stacking bolts, and a compressor stab shaft. The
compressor discs 17 are of not less than seventeen stages, and the
turbine blades are of three stages. The constitution can similarly
be applied also with respect to four stages.
[0075] In the present embodiment, air compressed by the compressor
is used to cool each component by a flow of air shown by an arrow
in FIG. 7. Air flows in via an outer side wall in the first-stage
turbine nozzle 81 and the second-stage turbine nozzle 82, and is
exhausted from a blade section. The second-stage turbine nozzle 82
is cooled over an inner side wall. In the third-stage turbine
nozzle 83, air flows in via the outer side wall, flows out of the
inner side wall, and is exhausted to the outside via the spacer
section. For the first-stage turbine blade 51, compressed air
passes through the side wall from a central portion of the turbine
disc 11. The air passes through a spacer 18 section and through
cooling bores provided in the blade, and is exhausted via the tip
end of the blade and a trailing portion of a blade section to cool
both the blade and disc. In the blade, the combustion gas is sealed
not to flow inside by a seal fin disposed in a shank portion.
Similarly, in the second-stage turbine blade 52, air passes through
the spacer 18 and the cooling bore provided in the blade from the
turbine disc 12, and is exhausted via the tip end, and cooled. The
third-stage turbine blade 53 does not include any cooling bore, but
air passes through the side wall from the central portion of the
turbine disc 13, passes through the seal fins to cool these fins,
and enters the exhaust heat recovery boiler together with the
combustion gas. In the boiler, steam is formed as a power source of
a steam turbine.
[0076] As the material for use in the turbine discs 11, 12, 13 in
the present embodiment, a large-sized specimen including
composition No. 1 shown in Table 1 of Example 1 was melted, heated
at 1150.degree. C., and forged to form an experiment material. The
material was heated at 1050.degree. C. for eight hours and cooled
with a blast air, and the cooling temperature was stopped at
150.degree. C. The material was heated at 580.degree. C. for 12
hours and air-cooled to perform the secondary tempering. Next, the
material was heated at 605.degree. C. for five hours, and
furnace-cooled to perform the secondary tempering. A creep rupture
specimen, tensile specimen, and V-notch Charpy impact test specimen
were sampled from the material after the thermal treatment, and
used in the experiments. The impact test of the thermally treated
material was conducted with respect to the heated/embrittled
material in the same manner as in Example 1. These properties in
the present embodiment are equivalent to those of Example 1.
[0077] In the present example, any of the entirely tempered
martensitic steel Nos. 7 to 13, Nos. 17 to 19 shown in Example 1 is
usable in the distant piece 3 and turbine stacking bolt 5 in
addition to the turbine discs 11, 12, 13.
[0078] Moreover, these martensitic steels have a ferrite-based
crystalline structure, but the ferrite-based material has a small
thermal expansion coefficient as compared with an austenite-based
material such as Ni-base alloy. When the heat resisting steel of
the present embodiment is used in the turbine disc instead of the
Ni-base alloy, the thermal expansion coefficient of the disc
material is further small. Therefore, thermal stress generated in
the disc is reduced, cracks are inhibited from being generated, and
collapse can be reduced. The compressor blade includes 17 stages,
and an obtained air compression ratio is 18.
[0079] Further in the present example, an Ni-base super alloy is
used in the first-stage turbine nozzle 81 and first-stage turbine
blade 51 of the gas turbine. Depending on a combustion gas
temperature, a polycrystalline cast material is used in
1300.degree. C. class, and a monocrystalline cast material is used
in 1500.degree. C. class. In the monocrystalline cast material, an
Ni-base super alloy is used containing, by weight percentage, 4 to
10% Cr, 0.5 to 1.5% Mo, 4 to 10% W, 1 to 4% Re, 3 to 6% Al, 4 to
10% Ta, 0.5 to 10% Co, and 0.03 to 0.2% Hf. The equivalent alloy
containing 10 to 15% Cr is used in the polycrystalline cast
material.
[0080] The second-stage turbine nozzle and third-stage turbine
nozzle are constituted of the Ni-base super alloy containing, by
weight percentage, 21 to 24% Cr, 18 to 23% Co, 0.05 to 0.20% C, 1
to 8% W, 1 to 2% Al, 2 to 3% Ti, 0.5 to 1.5% Ta, and 0.05 to 0.15%
B. These nozzles include an equiaxed structure obtained by usual
casting.
[0081] The Ni-base super alloy is used in the second-stage turbine
blade 52 and third-stage turbine blade 53. Depending on the
combustion gas temperature, the polycrystalline cast material is
used in the 1300.degree. C. class, and a directionally solidified
prismatic Ni-base super alloy cast material is used in 1500.degree.
C. class. Either material is constituted of the Ni-base super alloy
containing, by weight percentage, 5 to 18% Cr, 0.3 to 6% Mo, 2 to
10% W, 2.5 to 6% Al, 0.5 to 5% Ti, 1 to 4% Ta, 0.1 to 3% Nb, 0 to
10% Co, 0.05 to 0.21% C, 0.005 to 0.025% B, 0.03 to 2% Hf, and 0.1
to 5% Re. The blade of the directionally solidified prismatic
Ni-base super alloy is obtained by entire solidification in one
direction toward a dove-tail direction from the tip end.
[0082] In the present exceeding, the toughness is high even with
strength enhancement and heating embrittlement. Accordingly, since
especially the material temperature of the turbine disc can be set
to be high, the above-described cooling can be reduced.
Furthermore, the thickness or diameter of the above-described
member for use can be reduced, reduction in weight is achieved, and
start properties are enhanced.
[0083] By the above-described constitution, a gas turbine generally
balanced with high reliability is obtained. It is possible to
achieve a gas turbine for power generation, in which a natural gas,
light oil, and the like are used as fuels for use, a gas inlet
temperature into the first-stage turbine nozzle is 1500.degree. C.,
a metal temperature of the first-stage turbine blade is 900.degree.
C., an exhaust gas temperature of the gas turbine is 650.degree.
C., and a power generation efficiency is 37% or more in LHV
indication. This also applies with the gas inlet temperature into
the first-stage turbine nozzle of 1300.degree. C.
[0084] Moreover, in the present embodiment, it is possible to
constitute a multiaxial combined cycle power generation system
including a combination of one gas turbine and one high/medium/low
pressure integral steam turbine having a steam inlet temperature
into the first-stage turbine blade at 566.degree. C. Each turbine
includes a power generator. A higher power generation efficiency
can be obtained.
[0085] According to the present invention, a high-efficiency
high-temperature gas turbine is obtained in which a creep rupture
strength and an impact value after heating embrittlement required
especially for a gas turbine in a gas temperature class at 1300 to
1500.degree. C. are high. Furthermore, the present invention can
also be applied to a turbine stacking bolt, turbine spacer, and
distant piece exposed at a high temperature in a heating
embrittlement range. Therefore, according to the present invention,
since a combustion temperature and member temperature of a gas
turbine power generation plant can be raised, the cooling in a
high-temperature section can be reduced. Further, on the other
hand, a rotation section can be reduced in weight, and therefore
further high efficiency is achieved. Moreover, it is possible to
save a fossil fuel and to reduce a generated amount of exhaust gas
and to contribute to global environment preservation.
[0086] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *