U.S. patent application number 12/395983 was filed with the patent office on 2009-10-15 for ni-base alloy for turbine rotor of steam turbine and turbine rotor of steam turbine.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Masafumi Fukuda, Kiyoshi Imai, Takahiro KUBO, Masayuki Yamada.
Application Number | 20090257865 12/395983 |
Document ID | / |
Family ID | 41060805 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090257865 |
Kind Code |
A1 |
KUBO; Takahiro ; et
al. |
October 15, 2009 |
NI-BASE ALLOY FOR TURBINE ROTOR OF STEAM TURBINE AND TURBINE ROTOR
OF STEAM TURBINE
Abstract
An Ni-base alloy for a turbine rotor of a steam turbine contains
in percent by weight C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22,
Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1 to 0.6, B: 0.001 to
0.006, Re: 0.1 to 2.5, and the balance of Ni and unavoidable
impurities.
Inventors: |
KUBO; Takahiro;
(Yokohama-shi, JP) ; Imai; Kiyoshi; (Taito-ku,
JP) ; Yamada; Masayuki; (Yokohama-shi, JP) ;
Fukuda; Masafumi; (Saitama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
41060805 |
Appl. No.: |
12/395983 |
Filed: |
March 2, 2009 |
Current U.S.
Class: |
415/200 |
Current CPC
Class: |
F05C 2201/0466 20130101;
F01D 5/02 20130101; C22C 19/055 20130101 |
Class at
Publication: |
415/200 |
International
Class: |
F01D 1/02 20060101
F01D001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2008 |
JP |
2008-092782 |
Claims
1. An Ni-base alloy for a turbine rotor of a steam turbine, the
Ni-base alloy contains in percent by weight C: 0.05 to 0.15, Cr: 22
to 28, Co: 10 to 22, Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1
to 0.6, B: 0.001 to 0.006, Re: 0.1 to 2.5, and the balance of Ni
and unavoidable impurities.
2. The Ni-base alloy for a turbine rotor of a steam turbine
according to claim 1, wherein the unavoidable impurities are
suppressed in percent by weight to Si: 1 or below and Mn: 1 or
below.
3. A turbine rotor configured to dispose through a steam turbine
into which high-temperature steam is introduced, wherein at least a
predetermined portion is formed of the Ni-base alloy for a turbine
rotor of a steam turbine according to claim 1.
4. A turbine rotor configured to dispose through a steam turbine
into which high-temperature steam is introduced, wherein at least a
predetermined portion is formed of the Ni-base alloy for a turbine
rotor of a steam turbine according to claim 2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2008-092782
filed on Mar. 31, 2008; the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a material configuring a
turbine rotor of a steam turbine into which high-temperature steam
flows as a working fluid, and more particularly to an Ni-base alloy
for a turbine rotor of a steam turbine excelling in
high-temperature strength and the like, and a turbine rotor of a
steam turbine made of the Ni-base alloy.
[0004] 2. Description of the Related Art
[0005] For a thermal power plant including a steam turbine, a
technology for suppression of the emission of carbon dioxide is
being watched with interest in view of the global environmental
protection, and needs for highly efficient power generation are
increasing.
[0006] To increase the power generation efficiency of the steam
turbine, it is effective to raise the turbine steam temperature to
a high level, and the recent thermal power plant having the steam
turbine has its steam temperature raised to 600.degree. C. or
higher. There is a tendency that the steam temperature will be
increased to 650.degree. C., and further to 700.degree. C. in
future.
[0007] A turbine rotor, in which moving blades rotated by
high-temperature steam are implanted, has a high temperature by
circulation of high-temperature steam and generates a high stress
by rotating. Therefore, the turbine rotor is required to withstand
a high temperature and a high stress, and a material configuring
the turbine rotor is demanded to have excellent strength, ductility
and toughness in a range of room temperature to a high
temperature.
[0008] Particularly, if the steam temperature exceeds 700.degree.
C., a conventional iron-based material is poor in high-temperature
strength, so that the application of the Ni-base alloy is
considered in for example JP-A 7-150277(KOKAI).
[0009] The Ni-base alloy has been applied extensively as a material
mainly for jet engines and gas turbines because it is excellent in
high-temperature strength and corrosion resistance. As its typical
examples, Inconel 617 alloy (manufactured by Special Metals
Corporation) and Inconel 706 alloy (manufactured by Special Metals
Corporation) have been used.
[0010] As a mechanism to enhance the high-temperature strength of
the Ni-base alloy, Al and Ti are added to secure the
high-temperature strength by precipitating a precipitated phase
called as a gamma prime phase (Ni.sub.3(Al, Ti)) or a gamma double
prime phase, or both of them within the mother phase material of
the Ni-base alloy. There is for example Inconel 706 alloy which
secures high-temperature strength by precipitating both the gamma
prime phase and the gamma double prime phase.
[0011] Meanwhile, the high-temperature strength of Inconel 617
alloy is secured by reinforcing (solid-solution strengthening) the
mother phase of Ni group by adding Co and Mo. For example, JP-A
2002-88455(KOKAI) and JP-A 2001-247942(KOKAI) disclose a Ni-base
alloy having high-temperature strength characteristic improved by
adjusting added element components based on the components of
Inconel alloy. The Ni-base alloy of JP-A 2002-88455(KOKAI) is
provided with improved sulfidation corrosion at a high temperature.
JP-A 2001-247942(KOKAI) describes a rotor shaft using a Ni-base
alloy which suppresses a fragile intermetallic compound formed when
used for a long time.
[0012] Since the above-described conventional Ni-base alloys are
poor in productivity, they were used for relatively small
high-temperature parts and the like only.
[0013] Therefore, in a case where the conventional Ni-base alloy is
applied to, for example, jet engine or gas turbine members,
portions where the Ni-base alloy is used are limited to small
blades having a length of less than 1 m, a disk material having a
gross weight of less than 1 ton or the like.
BRIEF SUMMARY OF THE INVENTION
[0014] Accordingly, the present invention provides an Ni-base alloy
for a turbine rotor of a steam turbine that workability such as
forgeability is excellent, and a large-size forged product turbine
rotor can be produced, and a turbine rotor of a steam turbine.
[0015] According to an aspect of the invention, there is provided
an Ni-base alloy for a turbine rotor of a steam turbine, which
contains in percent by weight C: 0.05 to 0.15, Cr: 22 to 28, Co: 10
to 22, Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1 to 0.6, B:
0.001 to 0.006, Re: 0.1 to 2.5, and the balance of Ni and
unavoidable impurities.
[0016] According to an aspect of the invention, there is also
provided a turbine rotor which is disposed through a steam turbine
into which high-temperature steam is introduced, wherein at least a
predetermined portion is formed of the Ni-base alloy for the
turbine rotor of a steam turbine described above.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Embodiments of the invention will be described below.
[0018] An Ni-base alloy for a turbine rotor of a steam turbine in
an embodiment according to the present invention is composed of the
compositional component ranges shown below. In the following
description, percentages indicating the compositional components
are by weight unless otherwise indicated.
[0019] (Ml) Ni-base alloy which contains C: 0.05% to 0.15%, Cr: 22%
to 28%, Co: 10% to 22%, Mo: 8% to 12%, Al: 0.8% to less than 1.5%,
Ti: 0.1% to 0.6%, B: 0.001% to 0.006%, Re: 0.1% to 2.5%, and the
balance of Ni and unavoidable impurities.
[0020] In the unavoidable impurities in the Ni-base alloy of the
above (Ml), it is preferably suppressed that at least Si is 1% or
less, and Mn is 1% or less.
[0021] The Ni-base alloy having the compositional component ranges
described above is suitable as a material configuring a turbine
rotor of a steam turbine which has a temperature in a range of 680
to 750.degree. C. during its operation. All portions of the turbine
rotor of the steam turbine may be made of the Ni-base alloy, and
some portions, which have a particularly high temperature, of the
turbine rotor of the steam turbine may be made of this Ni-base
alloy. As some portions of the turbine rotor of the steam turbine
which have a high temperature, there are specifically all regions
of a high-pressure steam turbine section, or regions ranging from
the high-pressure steam turbine section to some portions of an
intermediate-pressure steam turbine section.
[0022] The Ni-base alloys of the compositional component ranges
described above can improve workability such as forgeability. In
other words, the Ni-base alloy is used to configure the turbine
rotor of the steam turbine, so that the workability such as
forgeability of the turbine rotor can be improved, and the turbine
rotor having high reliability can be produced without generating a
crack or the like when manufacturing.
[0023] The reasons of limiting the individual compositional
component ranges of the Ni-base alloy according to the present
invention described above will be described below.
(1) C (Carbon)
[0024] C is useful as a component element of M.sub.23C.sub.6 type
carbide which is a strengthening phase, and particularly, the creep
strength of the alloy is maintained by precipitating the
M.sub.23C.sub.6 type carbide during the operation of the steam
turbine in a high-temperature environment of 650.degree. C. or
higher. And, it also has an effect of securing the fluidity of a
molten metal at the time of casting. If the C content is less than
0.05%, a sufficient precipitation amount of carbide cannot be
secured, so that mechanical strength is degraded, and the fluidity
of the molten metal at the time of casting lowers considerably.
Meanwhile, if the C content exceeds 0.15%, the tendency of
segregation of components increases at the time of producing a
large ingot, the generation of M.sub.6C type carbide which is an
embrittlement phase is promoted, and mechanical strength is
improved, but forgeability is degraded. Therefore, the C content is
determined to be 0.05% to 0.15%.
(2) Cr (Chromium)
[0025] Cr is an indispensable element to improve oxidation
resistance, corrosion resistance and mechanical strength of the
Ni-base alloy. Besides, it is indispensable as a component element
of the M.sub.23C.sub.6 type carbide, and particularly, the creep
strength of the alloy is maintained by precipitating the
M.sub.23C.sub.6 type carbide during the operation of the steam
turbine in a high-temperature environment of 650.degree. C. or
higher. And, Cr improves the oxidation resistance in a
high-temperature steam environment. If the Cr content is less than
22%, the oxidation resistance decreases. Meanwhile, if the Cr
content exceeds 28%, precipitation of the M.sub.23C.sub.6 type
carbide is accelerated considerably, resulting in increasing the
tendency of coarsening. Therefore, the Cr content is determined to
be 22% to 28%.
(3) Co (Cobalt)
[0026] In the Ni-base alloy, Co improves the mechanical strength of
a mother phase by forming a solid solution in the mother phase.
But, if the Co content exceeds 22%, an intermetallic compound phase
which degrades the mechanical strength is generated, and
forgeability is degraded. Meanwhile, if the Co content is less than
10%, workability is degraded, and the mechanical strength is
lowered. Therefore, the Co content is determined to be 10% to
22%.
(4) Mo (Molybdenum)
[0027] Mo provides an effect of forming a solid solution into an Ni
mother phase to enhance the mechanical strength of the mother
phase, and its partial substitution in M.sub.23C.sub.6 type carbide
enhances the stability of the carbide. If the Mo content is less
than 8%, the above effect is not exerted, and if the Mo content
exceeds 12%, a tendency of segregation of components increases when
a large ingot is produced, and the generation of M.sub.6C type
carbide which is an embrittlement phase is accelerated. Therefore,
the Mo content is determined to be 8% to 12%.
[0028] Mo is common with the above-described Co on a point that
they have an effect to improve the mechanical strength of the
mother phase. And, to exhibit effectively the common characteristic
and their other characteristics, when the Mo content is for example
8 to less than 10%, it is desirable that the Co content is larger
than 15% and not larger than 22%. When the Mo content is for
example 10 to 12%, it is desirable that the Co content is 10% to
15%.
(5) Al (Aluminum)
[0029] Al generates a .gamma.' phase (gamma prime phase:
Ni.sub.3Al) with Ni and improves the mechanical strength of the
Ni-base alloy based on the precipitation. If the Al content is less
than 0.8%, the mechanical strength is not improved in comparison
with a conventional steel, and if the Al content is 1.5% or more,
the mechanical strength is improved, but forgeability is degraded.
Therefore, the Al content is determined to be 0.8% to less than
1.5%.
(6) Ti (Titanium)
[0030] Similar to Al, Ti generates a .gamma.' phase (gamma prime
phase: Ni.sub.3Ti) with Ni and improves the mechanical strength of
the Ni-base alloy. If the Ti content is less than 0.1%, the above
effect is not exerted, and if the Ti content exceeds 0.6%, hot
workability is degraded, and notch sensitivity becomes high.
Therefore, the Ti content is determined to be 0.1% to 0.6%.
(7) B (Boron)
[0031] B segregates in the grain boundary to affect the
high-temperature characteristics. And, B has an effect to improve
the mechanical strength of an Ni mother phase by precipitating in
the mother phase. If the B content is less than 0.001%, the effect
to improve the mechanical strength of the mother phase is not
exerted, and if the B content exceeds 0.006%, there is a
possibility that the grain boundary is embrittled. Therefore, the B
content is determined to be 0.001% to 0.006%.
(8) Re (Rhenium)
[0032] Re has an effect to improve the mechanical strength of an Ni
mother phase by forming a solid solution in the mother phase. If
the Re content is less than 0.1%, an effect to improve the
mechanical strength of the mother phase is not exerted, and if the
Re content exceeds 2.5%, a fragile phase is formed. Therefore, the
Re content is determined to be 0.1% to 2.5%.
[0033] Similar to the Re, Co and Mo have an effect to improve the
mechanical strength of the Ni mother phase by forming a solid
solution in the mother phase. But, when the content is same, the Re
is most excellent in improvement of the mechanical strength and can
improve the mechanical strength without largely varying the
chemical component composition of a base metal.
(9) Si (Silicon), Mn (Manganese), Cu (Copper), Fe (Iron) and S
(Sulfur)
[0034] Si, Mn, Cu, Fe and S are classified to unavoidable
impurities in the Ni-base alloy according to the present invention.
The residual contents of the unavoidable impurities are desired to
be decreased toward 0% as much as possible. It is desirable that at
least Si and Mn in the unavoidable impurities are suppressed to 1%
or below.
[0035] Si is added to the ordinary steel to supplement the
corrosion resistance. But, since the Ni-base alloy has a large Cr
content to secure sufficient corrosion resistance, a residual
content of Si in the Ni-base alloy according to the present
invention is determined to be 1% or less, and it is desired that
the residual content is reduced to 0% as much as possible.
[0036] In the ordinary steel, Mn prevents brittleness, which
results from S (sulfur), in a form of MnS. But, since the S content
in the Ni-base alloy is very small, it is not necessary to add Mn.
Therefore, the residual content of Mn in the Ni-base alloy
according to the present invention is determined to be 1% or below,
and it is desired that the residual content is reduced to 0% as
much as possible.
[0037] The above-described Ni-base alloy according to the present
invention is produced by melting the compositional components
configuring the Ni-base alloy by a vacuum induction melting
furnace, subjecting the obtained ingot to a soaking treatment,
forging it, and conducting a solution treatment.
[0038] It is preferable that the soaking treatment is maintained at
a temperature range of 1050 to 1250.degree. C. for 5 to 72 hours,
and the solution treatment is maintained at a temperature range of
1100 to 1200.degree. C. for 4 to 5 hours. Here, the solution
treatment temperature is determined to form a homogeneous solid
solution of the .gamma.' phase precipitates, and if the temperature
is lower than 1100.degree. C., a solid solution is not formed
adequately. If the temperature exceeds 1200.degree. C., crystal
grains are coarsened and the strength is degraded. And, forging is
performed at a temperature range of 950 to 1150.degree. C.
[0039] In a case where the above-described Ni-base alloy according
to the present invention is used to configure a turbine rotor of a
steam turbine, for example, as one method (double melt), the raw
material is subjected to vacuum induction melting (VIM) and
electro-slag remelting (ESR) and then poured into a prescribed
mold. Subsequently, a forging treatment and a heat treatment are
performed to produce the turbine rotor. As another method (double
melt), the raw material is subjected to vacuum induction melting
(VIM) and vacuum arc remelting (VAR) and then poured into a
prescribed mold. Subsequently, a forging treatment and a heat
treatment are performed to produce the turbine rotor. As still
another method (triple melt), the raw material is subjected to
vacuum induction melting (VIM), electro-slag remelting (ESR) and
vacuum arc remelting (VAR) and then poured into a prescribed mold.
Subsequently, a forging treatment and a heat treatment are
performed to produce the turbine rotor. The turbine rotors produced
by the above methods are inspected by ultrasonic inspection or the
like.
[0040] It is described below that the Ni-base alloy according to
the present invention is excellent in forgeability.
[0041] (Evaluation of Forgeability)
[0042] It is described below that the Ni-base alloy having the
chemical composition ranges of the present invention has excellent
forgeability. Table 1 shows chemical compositions of Sample 1 to
Sample 5 used for evaluation of the forgeability. And, Sample 1 to
Sample 4 are Ni-base alloys with the chemical composition ranges of
the present invention, and Sample 5 is an Ni-base alloy with its
composition not within the chemical composition ranges of the
present invention and used as a comparative example. Sample 5 has a
chemical composition corresponding to a conventional steel Inconel
617. The Ni-base alloy with the chemical composition ranges of the
present invention contains Fe (iron), Cu (copper) and S (sulfur) as
unavoidable impurities in addition to Si and Mn.
TABLE-US-00001 TABLE 1 (Wt %) Ni C Si Mn Cr Fe Al Mo Co Cu Ti B S
Re Example Sample 1 Balance 0.099 0.55 0.57 23 1.56 1.21 8.9 19.6
0.24 0.36 0.0039 0.001 0.12 Sample 2 Balance 0.099 0.55 0.57 27.4
1.56 1.21 8.9 14.5 0.24 0.36 0.0039 0.001 2.48 Sample 3 Balance
0.096 0.53 0.57 25.7 1.55 1.2 10.3 12.2 0.24 0.35 0.0041 0.0009
0.13 Sample 4 Balance 0.096 0.53 0.57 23.2 1.55 1.2 11.9 12.2 0.24
0.35 0.004 0.0009 2.47 Comparative Sample 5 Balance 0.076 0.51 0.55
22.9 1.57 1.21 8.9 12.2 0.25 0.36 0.0038 0.0009 0 Example
[0043] For evaluation of forgeability, Ni-base alloys of Sample 1
to Sample 5 having the chemical compositions shown in Table 1 each
in 10 kg were melted in a vacuum induction melting furnace, and
test specimens made of cylindrical ingots having a diameter of 87
mm and a length of 140 mm were produced. Subsequently, the ingots
were undergone a soaking treatment at 1050.degree. C. for five
hours. Forging treatment was conducted by a 500-kgf hammer forging
machine at a temperature range of 950 to 1100.degree. C. (reheating
at 1100.degree. C.). For the forgeability, the above-described
forging treatment was performed until the test specimens came to
have a diameter of 30 mm. Evaluation was performed based on a
forging ratio of the above treatment and the presence or not of a
forging crack at that time.
[0044] The forging ratio is defined by the division of a length of
the test specimen which is a forged object stretched by the forging
treatment by a length of the test specimen which is the forged
object before the forging treatment. According to the forging
treatment, if the temperature of the test specimen lowers, namely
if the test specimen becomes hardened, the forging treatment is
repeated by reheating up to a reheating temperature of 1100.degree.
C. And, for the presence or not of a forging crack, the test
specimens undergone the forging treatment are visually checked. If
there is no crack, it is indicated as "None", and the forgeability
is evaluated as "0" to indicate that the forgeability is excellent.
Meanwhile, if there is a crack, it is indicated as "Yes", and the
forgeability is evaluated as "X" to indicate that the forgeability
is inferior.
[0045] Table 2 shows results obtained by evaluating the
forgeability of the respective samples.
TABLE-US-00002 TABLE 2 Forging ratio Crack Forgeability Example
Sample 1 6.6 NONE .smallcircle. Sample 2 6.3 NONE .smallcircle.
Sample 3 6.7 NONE .smallcircle. Sample 4 6.4 NONE .smallcircle.
Comparative Sample 5 5.4 YES x Example
[0046] As shown in Table 2, it was found that Sample 1 to Sample 4
have excellent forgeability in comparison with Sample 5.
[0047] Although the invention has been described above by reference
to the embodiments of the invention, the invention is not limited
to the embodiments described above. It is to be understood that
modifications and variations of the embodiments can be made without
departing from the spirit and scope of the invention.
* * * * *