Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Coating – specific composition or characteristic
Reexamination Certificate
2001-03-05
2002-07-16
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Coating, specific composition or characteristic
C415S200000, C148S325000, C420S038000
Reexamination Certificate
active
06419453
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotor shaft for a high-strength steam turbine fit for a new thermal power plant, more particularly fit for a ultra-super critical pressure thermal power plant.
2. Description of the Prior Art
For higher efficiency of power generation, the recent thermal power plants have used higher temperature and higher pressure. For example, recent steam turbines use steam of about 600 degrees C which is the highest steam temperature at present. In the near future, steam of 650 degrees C will be used. To use steam of such a high-temperature, the conventional heat-resisting ferrite steel must be substituted by high heat-resisting materials whose strength is excellent at such a high temperature. Some of austenite heat-resisting alloys are superior at such a high temperature, but their thermal fatigue strengths are inferior because their coefficients of thermal expansion are very big.
Some examples of new heat-resisting ferrite steel whose strength at a high temperature is improved are disclosed by Japanese Non-examined Patent Publications No.04-147948(1992) and No.08-30249(1996).
However, when used for a long time at an extremely high steam temperature of 650 degrees C, these proposed alloys containing much tungsten produce fragile intermetallic compounds which reduce the long-term creep rupture strength. Therefore, these alloys are still not perfect as materials to be used at an extremely high vapor temperature. The world has expected high heat-resisting ferrite steel whose strength is extremely stable for a long time at such a high temperature.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a rotor shaft for a high-temperature steam turbine which is very strong for a long time at a selected temperature of 650 degrees or above.
It is an object of the present invention to provide a steam turbine rotor shaft comprising martensite steel containing 0.05% to 0.20% by weight of carbon, 0.20% or less by weight of silicon, 0.05% to 1.5% by weight of manganese, 0.01% to 1.0% by weight of nickel, 9.0% to 13.0% by weight of chrome, 0.05% to 0.5% by weight of molybdenum, 0.5% to 5.0% by weight of tungsten, 0.05% to 0.30% by weight of vanadium, 0.01% to 0.20% by weight of niobium, 0.5% to 10.0% by weight of cobalt, 0.01% to 0.1% by weight of nitrogen, 0.001% to 0.030% by weight of boron, and 0.0005% to 0.006% by weight of aluminum, wherein the remaining parts of this steel substantially comprise iron.
It is another object of the present invention to provide a steam turbine rotor shaft comprising martensite steel containing 0.09% to 0.15% by weight of carbon, 0.03% to 0.15% by weight of silicon, 0.35% to 0.65% by weight of manganese, 0.02% to 0.5% by weight of nickel, 9.5% to 11.5% by weight of chrome, 0.05% to 0.4% by weight of molybdenum, 1.0% to 3.0% by weight of tungsten, 0.15% to 0.30% by weight of vanadium, 0.04% to 0.13% by weight of niobium, 1.5% to 3.5% by weight of cobalt, 0.01% to 0.04% by weight of nitrogen, 0.005% to 0.025% by weight of boron, and 0.0005% to 0.005% by weight of aluminum; wherein the remaining parts of this steel substantially comprise iron.
It is yet a further object of the invention to provide a steam turbine rotor shaft comprising martensite steel containing 9.0% to 13.0% by weight of chrome, 0.5% to 5.0% by weight of tungsten, 0.05% to 0.30% by weight of vanadium, 0.01% to 0.20% by weight of niobium, 0.5% to 10.0% by weight of cobalt, and 0.001% to 0.030% by weight of boron; wherein the creep rupture strength at 650 degrees C for 100,000 hours is 9 kg/mm
2
or more preferentially 10 kg/mm
2
. More preferentially said rotor shaft comprises a martensite steel having the above composition and the creep rupture strength for 100,000 hours is 20 kg/mm
2
or more at 600 degrees C, 14 kg/mm
2
or more at 625 degrees C, 25 kg/mm
2
or more at 700 degrees C, more preferentially 22 kg/mm
2
or more at 600 degrees C, 16 kg/mm
2
or more at 625 degrees C, 3 kg/mm
2
or more at 700 degrees C.
It is a more particular object of the invention to provide a steam turbine rotor shaft comprising martensite steel containing 0.09% to 0.15% by weight of carbon, 0.15% or less by weight of silicon, 0.3% to 0.7% by weight of manganese, 0.02% to 0.5% by weight of nickel, 9.0% to 13.0% by weight of chrome, 0.05% to 0.5% by weight of molybdenum, 1.0% to 3.0% by weight of tungsten, 0.15% to 0.30% by weight of vanadium, 0.04% to 0.13% by weight of niobium, more than 1.5% to 4.0% or less by weight of cobalt, 0.01% to 0.04% by weight of nitrogen, 0.001% to 0.030% by weight of boron, and 0.0005% to 0.006% by weight of aluminum; wherein the remaining parts of this steel substantially comprise iron.
It is still another object of the invention to provide a steam turbine rotor shaft comprising martensite steel containing 0.05% to 0.20% by weight of carbon, 0.20% or less by weight of silicon, 0.05% to 1.5% by weight of manganese, 0.01% to 1.0% by weight of nickel, 9.0% to 13.0% by weight of chrome, 0.05% to 2.0% by weight of molybdenum, 0.5% to 5.0% by weight of tungsten, 0.05% to 0.30% by weight of vanadium, 0.01% to 0.20% by weight of niobium, more than 1.0% to 10.0% or under by weight of cobalt, 0.01% to 0.1% by weight of nitrogen, 0.001% to 0.030% by weight of boron, and 0.0005% to 0.006% by weight of aluminum; wherein the remaining parts of this steel substantially comprise iron.
Carbon is an indispensable element to assure quenching, to separate carbides of M
23
C
6
in the tempering processes, and thus to increase the high-temperature strength of the steel. The martensite steel of the present invention requires a minimum of 0.05% by weight of carbon.
More than 0.20% by weight of carbon causes excessive separation of M
23
C
6
carbides and reduction of the degree of matrix. This lessens the high-temperature strength of the steel when used for a long time. The martensite steel of the present invention uses 0.05% to 0.20% by weight of carbon, more preferentially 0.09% to 0.13%.
Manganese(Mn) suppresses production of &dgr; ferrite and accelerates separation of carbides of M
23
C
6
. The martensite steel of the present invention requires a minimum of 0.05% by weight of manganese, usually 0.02% to 1.5%, preferentially 0.3% to 0.7%, more preferentially 0.35% to 0.65%. 1.5% by weight or above of manganese in the steel will reduce the resistance to oxidization. Nickel(Ni) suppresses production of &dgr; ferrite and adds toughness to the steel. The martensite steel of the present invention requires a minimum of 0.05% by weight of nickel.
More than 1.0% by weight of nickel reduces the creep rupture strength at 620 degrees C or above. The martensite steel of the present invention uses 0.02% to 1.0% by weight of nickel, more preferentially 0.1% to 0.5%.
Chrome(Cr) is an indispensable element to increase the resistance to oxidization of the steel, to separate M
23
C
6
carbides, and thus to increase the high-temperature strength of the steel. The martensite steel of the present invention requires a minimum of 9% by weight of chrome.
More than 13% by weight of chrome causes production of &dgr; ferrite and reduces strength and toughness at high temperatures. The martensite steel of the present invention uses 9.0% to 13.0% by weight of carbon, preferentially 9.5% to 11.5%, more preferentially 10.0% to 11.0%.
Molybdenum(Mo) accelerates separation of fine particles of M
23
C
6
carbides and prevents them from cohering. Consequentially, molybdenum Mo is effective to give high strength at a high temperature for a long time. The martensite steel of the present invention requires a minimum of 0.05% by weight of molybdenum. 2% or above by weight of molybdenum causes easy production of &dgr; ferrite. The martensite steel of the present invention uses 0.05% to 2.0% by weight of molybdenum, preferentially 0.05% to 0.5%, more preferentially 0.1% to 0.3%.
Tungsten(W) is more effective than molybdenum to suppress cohesion of M
23
C
6
carbide particles, to solidify and strengthen the matrix and to increase the high
Arai Masahiko
Doi Hiroyuki
Fujita Toshio
Fukui Yutaka
Hiraga Ryo
Hitachi , Ltd.
Look Edward K.
Mattingly Stanger & Malur, P.C.
McAleenan James M
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