JP2004169562A - Steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam turbine capable of preventing a thermal stress and thermal strain from occurring even when steam condition is not less than 650°C class. <P>SOLUTION: An austenitic heat resisting alloy typifying Ni base super alloy and iron base super alloy is restricted to use. The austenitic heat resisting alloy is avoided to use especially for a thick wall turbine casing. Temperature rising is suppressed by applying heat shield coating on the thick wall turbine casing to enable the usage of ferritic heat resisting steel in which steam condition is not less than 650°C class, and to obtain high temperature strength using the austenitic heat resisting alloy on the part where the high temperature strength is needed in lieu of the ferritic heat resisting steel. This process provides the steam turbine in which steam condition having high generation efficiency is not less than 650°C class. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steam turbine for thermal power generation driven by high-temperature and high-pressure steam.
[0002]
[Prior art]
High temperature and high pressure of the steam conditions of a thermal power plant are very important and fundamental factors that contribute to the improvement of the efficiency. Since the steam conditions for single-stage reheating at 24.1 MPa and 538/566 ° C were established as the standard for Japanese commercial thermal turbines in the latter half of the 1960s, breakthrough progress has been seen until recently. However, energy conservation has been strongly promoted since the oil crisis, and the rapid increase in interest in global warming has led to higher efficiency of thermal power plants.
[0003]
It is most effective to raise the steam temperature of the steam turbine in order to increase the power generation efficiency. However, since the steam condition of the conventional steam turbine equipment is a steam temperature of 600 ° C. class or less, the rotor shaft of the steam turbine and the turbine Ferrite heat-resistant steel is used for main members such as a rotor blade and a turbine casing. As these ferritic heat-resistant steels, high-strength heat-resistant steels are known (see Patent Document 1). In particular, high-strength heat-resistant steels having higher high-temperature strength are known as these materials (see Patent Document 2). ).
[0004]
[Patent Document 1]
JP-A-2-149649
[Patent Document 2]
JP-A-8-3697
[Problems to be solved by the invention]
However, when the steam conditions of the steam turbine reach a steam temperature of 650 ° C. or higher, the strength of the ferrite heat-resistant steel for the main members such as the rotor shaft, turbine rotor blade, and turbine casing of the steam turbine becomes severe. Therefore, it has been considered that an austenitic heat-resistant alloy such as a Ni-based superalloy or an iron-based superalloy is used.
[0007]
These austenitic heat-resistant alloys are materials whose high-temperature strength is greatly improved as compared with ferritic heat-resistant steel, especially at a high temperature of 650 ° C. or higher, and are preferable materials from the viewpoint of high-temperature strength. The material has a disadvantage that the thermal conductivity is smaller than that of the material. Low thermal conductivity in high temperature machines, such as steam turbines, results in large temperature differences between the inner and outer surfaces of turbine components, especially turbine casings having thicker sections, and as a result, such There is a disadvantage that large thermal stress and thermal strain are generated in various turbine components, and the probability of occurrence of damage such as deformation and cracking becomes extremely large.
[0008]
Further, the heat-resistant austenitic alloy has a larger coefficient of linear expansion than the heat-resistant ferritic steel, which also causes a problem of increasing thermal stress and thermal strain. In addition, heat-resistant austenitic steels are more expensive than heat-resistant ferritic steels, and have limitations in the productivity of large alloy ingots, which makes it difficult to apply them to large integrated parts such as turbine casings. There's a problem.
[0009]
An object of the present invention is to provide a steam turbine that can suppress the occurrence of thermal stress and thermal distortion even when the steam condition is 650 ° C. or higher.
[0010]
[Means for Solving the Problems]
The steam turbine of the present invention restricts the use of an austenitic heat-resistant alloy typified by a Ni-based superalloy or an iron-based superalloy, and avoids using an austenitic heat-resistant alloy in a turbine casing, which is a particularly thick-walled part. . The heat insulation coating is applied to the turbine casing, which is a thick part, to suppress the rise in temperature, enabling the use of heat-resistant ferritic steel even when the steam condition is 650 ° C or higher, and requiring high-temperature strength. Austenitic heat-resistant alloy is used in place of ferritic heat-resistant steel to ensure high-temperature strength. This provides a steam turbine having high power generation efficiency and a steam condition of 650 ° C. class or higher.
[0011]
For example, heat-resistant ferritic steel is used for the turbine casing, Ni-based superalloy is used for the turbine rotor blades in the high-temperature portion of the high-pressure or medium-pressure turbine, and Ni-based superalloy or the like is used for the rotor shaft of the high-pressure or medium-pressure turbine. An austenitic heat-resistant alloy typified by an iron-based superalloy is used, and a thermal barrier coating is applied to a portion of the inner surface of the inner casing that is exposed to high-temperature steam of at least 650 ° C or higher. If necessary, a center hole is formed in the rotor shaft and the diameter thereof is set to 200 mm or more to suppress a temperature rise. Similarly, if necessary, a thermal barrier coating may be applied to a portion of the surface of the rotor shaft that is exposed to high-temperature steam of at least 650 ° C. or a turbine axial portion where the steam temperature of the steam passage is at least 650 ° C. The cooling steam is guided to the surface of the rotor shaft at the portion where the cooling steam is to be cooled.
[0012]
Further, for the rotor shaft of the high-pressure turbine or the medium-pressure turbine, a heat-resistant ferritic steel is used instead of an austenitic heat-resistant alloy. If necessary, a center hole having a diameter of 200 mm or more is provided in the rotor shaft. A thermal barrier coating is applied to a portion of the surface exposed to high-temperature steam of at least 650 ° C. or cooling steam is applied to a surface of the rotor shaft in a portion of the steam passage portion located in a turbine axial direction where a steam temperature is at least 650 ° C. or more. To induce cooling.
[0013]
In addition, heat-resistant ferritic steel is used for a turbine casing and a rotor shaft, and a thermal barrier coating is applied to a surface of a portion of the rotor shaft of the high-pressure turbine or the intermediate-pressure turbine that is exposed to high-temperature steam. Then, if necessary, a thermal barrier coating is applied to the surface of the turbine blade in the stage exposed to the high-temperature steam of the high-pressure turbine or the intermediate-pressure turbine.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. In the embodiment of the present invention, a Ni-based superalloy is a component that contains 35% by weight or more of Ni and has the largest Ni by weight, and has a mechanical strength of 0.2% at room temperature. Austenitic heat-resistant alloy having a proof stress of 500 MPa or more and a creep rupture strength at 650 ° C. for 100,000 hours of 100 MPa or more. Representative examples thereof include Inconel 718 and Inconel 738.
[0015]
The iron-based superalloy is iron (Fe) which is the largest constituent component in weight ratio, has a mechanical strength of 0.2% proof stress at room temperature of 500 MPa or more, and has a creep rupture strength at 100,000 hours at 650 ° C. Refers to an austenitic heat-resistant alloy satisfying 100 MPa or more. A286 is a typical example thereof. Further, the austenitic heat-resistant alloy includes an austenitic stainless steel represented by SUS316 in the embodiment of the present invention.
[0016]
FIG. 1 is a partially cutaway longitudinal sectional view of a steam turbine according to a first embodiment of the present invention, and FIG. 2 is a partially notched longitudinal sectional view of an inner casing of a turbine casing. The steam turbine 1 shown in FIG. 1 is a part of the high-pressure turbine 2 and the medium-pressure turbine 3 of the steam turbine 1 including the high-pressure turbine 2, the medium-pressure turbine 3, and the low-pressure turbine 4 shown in the schematic diagram of the steam turbine 1 in FIG. 1 shows a vertical cross section.
[0017]
In FIG. 1, a high-pressure turbine 2 and a medium-pressure turbine 3 are housed in a turbine casing 7 with a turbine blade 6 attached to a rotor shaft 5. Rotating parts of the steam turbine 1, such as the rotor shaft 5 and the turbine blade 6, are collectively referred to as a turbine rotor. The turbine casing 7 houses a high-pressure casing that houses the high-pressure turbine 2, a medium-pressure casing that houses the medium-pressure turbine 3, a low-pressure casing that houses the low-pressure turbine 4, or integrally houses the high-pressure turbine 2 and the medium-pressure turbine 3. The turbine casing 7 of the steam turbine 1 according to the present invention includes inner casings 8 a and 8 b and an outer casing 9.
[0018]
The internal casing 8a of the high-pressure turbine 2 or the internal casing 8b of the intermediate-pressure turbine 3 is formed of ferritic heat-resistant steel, and a thermal barrier coating 11 is applied to a portion of the inner surface 10 that is exposed to at least 650 ° C. or higher high-temperature steam. Have been. Further, the rotor shaft 5 in which the high-pressure portion and the intermediate-pressure portion are integrally formed is formed of an austenitic heat-resistant alloy, and the turbine blade 6 in the high-temperature portion is formed of a Ni-based superalloy.
[0019]
Generally, high stress acts on each part of the turbine rotor under the influence of a strong centrifugal force due to the rotation of the turbine rotor of the steam turbine 1. In the first embodiment, however, the 700 A Ni-based superalloy having high strength even at a high temperature of 700 ° C is applied, and a Ni-based superalloy or iron having high strength even at a high temperature of 700 ° C is applied to the rotor shaft 5 exposed to high-temperature steam. An austenitic heat-resistant alloy such as a base superalloy is applied to cope with high stress caused by centrifugal force.
[0020]
At the same time, the inner surface 10 of the high-pressure inner casing 8a and the inner surface 10 of the intermediate-pressure inner casing 8b of the steam turbine 1 which is exposed to the highest high-temperature steam and has a thick portion such as a horizontal flange is exposed to high-temperature steam of at least 650 ° C. By applying the thermal barrier coating 11 to the portion to be heated, the temperature of the turbine casing 7 is suppressed from becoming high, and it is possible to use a ferritic heat-resistant steel which is inferior in high-temperature strength to an austenitic heat-resistant alloy.
[0021]
FIG. 4 is an explanatory diagram of the temperature distribution of the thick section of the inner casing 8 of the turbine casing 7. FIG. 4 (a) is a characteristic diagram when the thermal barrier coating is not applied, and FIG. It is a characteristic diagram at the time of constructing 11. The inner surface 10 of the inner casing 8 is exposed to high-temperature steam, while the outer surface 12 of the inner casing 8 is exposed to steam whose temperature has been reduced by the work performed by the turbine blades 6. That is, the inner casing 8 is heated on the inner surface 10 and cooled on the outer surface 12. Therefore, the temperature distribution is such that the temperature decreases from the inner surface 10 to the outer surface 12 as shown in FIGS.
[0022]
When the thermal barrier coating 11 is not applied to the inner casing 8, the temperature distribution becomes sharp from the outside to the inside as shown in FIG. In general, a ferritic heat-resistant steel has a remarkable decrease in high-temperature strength as represented by creep rupture strength at 100,000 hours or more at about 600 ° C. or higher. To a level that makes design difficult.
[0023]
On the other hand, when the inner surface 10 is covered with the thermal barrier coating 11 as in the first embodiment, as shown in FIG. 4B, the temperature distribution becomes gentler than that in FIG. 4A. That is, since the thermal conductivity of the material of the thermal barrier coating 11 is significantly lower than the thermal conductivity of the metal material forming the turbine casing 7, the metal forming the inner casing 8 via the inner surface 10 of the inner casing 8 Since the heat flux to flow into is reduced, the metal surface temperature on the high temperature side of the inner surface 10 of the inner casing 8 is lowered, and accordingly, the temperature of the entire metal portion of the inner casing 8 can be kept low. Therefore, even if the temperature of the steam supplied to the high-pressure turbine or the intermediate-pressure turbine is 650 ° C. or higher, a ferritic heat-resistant steel having a high thermal conductivity can be used without using an austenitic heat-resistant alloy for the turbine casing. .
[0024]
In the first embodiment, since the rotor shaft 5 is formed of an austenitic heat-resistant alloy having a low thermal conductivity, a center hole 13 is formed in the rotor shaft 5 as shown in FIG. The thickness of the rotor shaft 5 is reduced to reduce the temperature difference generated in the radial direction of the rotor shaft 5 to suppress the generation of thermal stress. From the viewpoint of suppressing thermal stress, the diameter of the center hole 13 of the rotor shaft 5 is preferably 200 mm or more. Thereby, the reliability of the steam turbine is improved, and the operability, that is, the start-up time can be shortened.
[0025]
According to the first embodiment, since the heat-resistant ferritic steel is applied to the turbine casing 7 and the heat-resistant coating 11 is applied to the inner surface of the inner casing 8, the heat stress is small, the starting characteristic is excellent, and the cost is low. , 650 ° C. or higher, and a steam turbine with high efficiency.
[0026]
Next, a second embodiment of the present invention will be described. FIG. 6 is a partially cutaway longitudinal sectional view of a steam turbine according to a second embodiment of the present invention. This second embodiment is different from the first embodiment shown in FIG. 1 in that rotor shaft 5A is formed of ferritic heat-resistant steel instead of austenitic heat-resistant alloy, and at least 650 of the surface of rotor shaft 5A is formed. The thermal barrier coating 14 is applied to a portion exposed to high-temperature steam of not less than ° C. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.
[0027]
The internal casings 8a and 8b of the high-pressure turbine 2 and the intermediate-pressure turbine 3 are formed of heat-resistant ferritic steel, and a heat-shielding coating 11 is applied to a portion of the inner surface 10 that is exposed to at least 650 ° C. or higher steam. I have. The rotor shaft 5A in which the high-pressure portion and the intermediate-pressure portion are integrally formed is formed of heat-resistant ferritic steel, and the turbine blade 6 in the high-temperature portion is formed of a Ni-based superalloy. Further, a thermal barrier coating 14 is applied to a portion of the surface of the rotor shaft 5A that is exposed to high-temperature steam of at least 650 ° C. Further, instead of the thermal barrier coating 14, cooling steam is guided to the turbine axial surface of the rotor shaft 5A at a portion where the steam temperature of the steam passage portion 15 becomes at least 650 ° C. to cool the rotor shaft 5A.
[0028]
Further, similarly to the first embodiment, a center hole is formed in the rotor shaft 5A, the thickness of the rotor shaft 5A is reduced, and the temperature difference in the radial direction generated in the rotor shaft 5A is reduced to generate thermal stress. May be suppressed. From the viewpoint of suppressing thermal stress, the diameter of the center hole of the rotor shaft 5A is preferably 200 mm or more. Thereby, the reliability of the steam turbine is improved, and the operability, that is, the start-up time can be shortened.
[0029]
As described above, since the heat-resistant ferritic steel having high thermal conductivity is used for the rotor shaft 5A and the heat-shielding coating 14 is applied to the surface of the rotor shaft 5A exposed to high-temperature steam of at least 650 ° C., the inner casing is formed. Like the thermal barrier coating 11 of 8a, 8b, the temperature of the metal part of the high temperature part of the rotor shaft 5A can be made lower than the steam temperature. Further, since the cooling steam is guided to the surface of the rotor shaft 5A exposed to the high-temperature steam of at least 650 ° C. or more, the temperature of the metal portion of the high-temperature portion of the rotor shaft 5A is set lower than the steam temperature. be able to.
[0030]
In the above description, the case where the thermal barrier coating 14 is applied to the surface of the rotor shaft 5A has been described. However, when the high-temperature strength of the rotor shaft 5A can be secured, the thermal barrier coating 14 may be omitted, and the cooling steam The guidance may be omitted.
[0031]
According to the second embodiment, the ferrite heat-resistant steel is applied to the turbine casing 7 and the rotor shaft 5A in the steam turbine in which the temperature of the steam supplied to the high-pressure turbine or the medium-pressure turbine is 650 ° C. or more. It is possible to provide a high-efficiency steam turbine using steam having a temperature of 650 ° C. or higher with low generation of thermal stress, excellent startup characteristics and low cost.
[0032]
Next, a third embodiment of the present invention will be described. FIG. 7 is a partially cutaway longitudinal sectional view of a steam turbine according to a third embodiment of the present invention. The third embodiment differs from the first embodiment shown in FIG. 1 in that a thermal barrier coating 14 is applied to a portion of the surface of the rotor shaft 5 that is exposed to high-temperature steam of at least 650 ° C. or higher. is there. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.
[0033]
The inner casings 8a and 8b of the high-pressure turbine 2 or the intermediate-pressure turbine 3 are formed of heat-resistant ferritic steel, and a portion of the inner surface 10 that is exposed to high-temperature steam of at least 650 ° C. is provided with a thermal barrier coating 11. I have. Further, the turbine blade 6 in the high temperature section is formed of a Ni-based superalloy.
[0034]
The rotor shaft 5 in which the high-pressure portion and the medium-pressure portion are integrally formed is formed of an austenitic heat-resistant alloy, and a portion of the axial surface of the rotor shaft 5 that is exposed to high-temperature steam of at least 650 ° C. or more has a thermal barrier coating 14. Has been constructed. Further, instead of the thermal barrier coating 14, cooling steam is guided to the turbine axial surface of the rotor shaft 5 at a portion where the steam temperature of the steam passage portion 15 becomes at least 650 ° C. to cool the rotor shaft 5.
[0035]
Further, since the rotor shaft 5 is formed of an austenitic heat-resistant alloy having a low thermal conductivity, a center hole is formed in the rotor shaft 5 to reduce the thickness of the rotor shaft 5 as in the first embodiment. Then, the temperature difference generated in the radial direction of the rotor shaft 5 is reduced to suppress the generation of thermal stress. From the viewpoint of suppressing thermal stress, the diameter of the center hole of the rotor shaft 5 is preferably 200 mm or more. Thereby, the reliability of the steam turbine is improved, and the operability, that is, the start-up time can be shortened.
[0036]
According to the third embodiment, an austenitic heat-resistant alloy having high high-temperature strength is used for the rotor shaft 5, and the heat-insulating coating 14 is applied to the surface of the rotor shaft 5 exposed to high-temperature steam of at least 650 ° C. Alternatively, since the cooling steam is guided to the surface of the rotor shaft 5 to cool the same, the temperature of the metal portion of the high-temperature portion of the rotor shaft 5 is set lower than the steam temperature similarly to the thermal barrier coating 11 of the inner casing 8. can do. As a result, the safety in terms of strength can be enhanced and the startup time can be shortened. Therefore, it is not necessary to increase the turbine startup time by using an austenitic heat-resistant alloy having a low thermal conductivity, and the startup characteristics can be improved.
[0037]
Next, a fourth embodiment of the present invention will be described. FIG. 8 is a partially cutaway longitudinal sectional view of a steam turbine according to a fourth embodiment of the present invention. This fourth embodiment is different from the first embodiment shown in FIG. 1 in that the rotor shaft 5A is formed of ferritic heat-resistant steel instead of the austenitic heat-resistant alloy, and the heat-shielding coating 11 of the inner casing 8 is formed. Instead, a thermal barrier coating 14 is applied to an arbitrary portion of the surface of the rotor shaft 5A in the turbine axial direction. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.
[0038]
The internal casing 8 of the high-pressure turbine 2 is formed of heat-resistant ferritic steel. Further, the rotor shaft 5A in which the high-pressure portion and the intermediate-pressure portion are integrally formed is formed of heat-resistant ferritic steel, and a heat-shielding coating 14 is applied to an arbitrary portion on the surface of the rotor shaft 5A in the turbine axial direction. Metal parts are not exposed to high temperature steam. As described above, since the thermal barrier coating 14 is applied to the surface of the arbitrary part in the turbine axial direction exposed to the high temperature of the rotor shaft, the temperature rise of the rotor shaft 5A is suppressed.
[0039]
Furthermore, a thermal barrier coating is preferably applied to the surface of the turbine blade 6 of any stage that is exposed to high temperatures. As a result, a rise in temperature of the turbine blade 6 is suppressed, a decrease in the strength of the turbine blade 6 is suppressed, and a heat flux flowing into the turbine blade 6 from high-temperature steam is reduced. Accordingly, the heat flux flowing into the rotor shaft 5A from the turbine blade 6 is also reduced, and the temperature rise of the rotor shaft 5A is suppressed.
[0040]
According to the fourth embodiment, since the temperature rise of the rotor shaft 5A is suppressed, the amount of thermal elongation of the rotor shaft 5A is suppressed, and the difference in elongation is further reduced. As a result, the amount of steam leaking from the labyrinth seal applied to the rotating part and the stationary part of the steam turbine is reduced, so that the steam flowing through the steam passage is effectively used to provide a high-efficiency steam turbine. It is possible to do.
[0041]
【The invention's effect】
As described above, according to the present invention, an inexpensive steam turbine that generates little thermal stress in a casing or a rotor shaft and has excellent startup characteristics is used as a high-efficiency steam turbine that uses steam at 650 ° C. or higher. Can be provided. In addition, the amount of thermal expansion of the rotor shaft is suppressed and the difference in expansion from the stationary part such as the casing is small, and therefore, the amount of steam leaking from the labyrinth seal applied to the seal portion of the steam turbine is reduced, so that high efficiency is achieved. It is possible to provide a steam turbine.
[Brief description of the drawings]
FIG. 1 is a partially cutaway longitudinal sectional view of a steam turbine according to a first embodiment of the present invention.
FIG. 2 is a partially cutaway longitudinal sectional view of an inner casing of the turbine casing according to the first embodiment of the present invention.
FIG. 3 is a schematic diagram showing a configuration of the steam turbine according to the first embodiment of the present invention.
FIG. 4 is an explanatory diagram of a temperature distribution of a thick section of the inner casing of the turbine casing according to the first embodiment of the present invention.
FIG. 5 is a sectional view of the rotor shaft according to the first embodiment of the present invention.
FIG. 6 is a partially cutaway longitudinal sectional view of a steam turbine according to a second embodiment of the present invention.
FIG. 7 is a partially cutaway longitudinal sectional view of a steam turbine according to a third embodiment of the present invention.
FIG. 8 is a partially cutaway longitudinal sectional view of a steam turbine according to a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Steam turbine, 2 ... High pressure turbine, 3 ... Medium pressure turbine, 4 ... Low pressure turbine, 5 ... Rotor shaft, 6 ... Turbine rotor blade, 7 ... Turbine casing, 8 ... Inner casing, 9 ... Outer casing, 10 ... Inner surface , 11: thermal barrier coating, 12: outer surface, 13: center hole, 14: thermal barrier coating, 15: steam passage

Claims (12)

In a steam turbine having at least a turbine part of a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine, and having a turbine casing composed of an inner casing and an outer casing, wherein the temperature of steam supplied to the high-pressure turbine or the intermediate-pressure turbine is 650 ° C. or more. A heat-resistant ferritic steel for the turbine casing, a Ni-base superalloy for a turbine rotor blade in a high-temperature portion of the high-pressure turbine or the medium-pressure turbine, and a Ni-based superalloy for the rotor shaft of the high-pressure turbine or the medium-pressure turbine. Using a heat-resistant austenitic alloy typified by a base superalloy or an iron-base superalloy, a heat barrier coating is applied to a portion of the inner surface of the inner casing that is exposed to high-temperature steam of at least 650 ° C. or more. Steam turbine. The steam turbine according to claim 1, wherein a center hole is formed in the rotor shaft. The steam turbine according to claim 2, wherein a diameter of a center hole of the rotor shaft is 200 mm or more. The steam turbine according to claim 1, wherein a thermal barrier coating is applied to a portion of the surface of the rotor shaft that is exposed to high-temperature steam of at least 650 ° C. 2. The steam according to claim 1, wherein cooling steam is guided to a surface of the rotor shaft in a portion located in a turbine axial direction where a steam temperature in a steam passage portion of the turbine portion is at least 650 ° C. or more to cool the steam. Turbine. The steam turbine according to claim 4, wherein a center hole having a diameter of 200 mm or more is provided in the rotor shaft. In a steam turbine having at least a turbine part of a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine, and having a turbine casing composed of an inner casing and an outer casing, wherein the temperature of steam supplied to the high-pressure turbine or the intermediate-pressure turbine is 650 ° C. or more. A ferrite heat-resistant steel is used for the turbine casing, a Ni-base superalloy is used for a turbine rotor blade of a high-temperature portion of the high-pressure turbine or the medium-pressure turbine, and a ferrite is used for a rotor shaft of the high-pressure turbine or the medium-pressure turbine. A steam turbine using a heat-resistant steel and applying a thermal barrier coating to a portion of the inner surface of the inner casing that is exposed to high-temperature steam of at least 650 ° C. The steam turbine according to claim 7, wherein a thermal barrier coating is applied to a portion of the surface of the rotor shaft that is exposed to high-temperature steam of at least 650 ° C. The steam according to claim 7, wherein cooling steam is guided to a surface of a rotor shaft of a portion located at a turbine axial direction portion where a steam temperature of a steam passage portion of the turbine portion is at least 650 ° C. or more to cool the steam. Turbine. The steam turbine according to any one of claims 7 to 9, wherein the rotor shaft has a center hole having a diameter of 200mm or more. In a steam turbine having at least a turbine part of a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine, and having a turbine casing composed of an inner casing and an outer casing, wherein the temperature of steam supplied to the high-pressure turbine or the intermediate-pressure turbine is 650 ° C. or more. A ferrite heat-resistant steel is used for the turbine casing, a Ni-base superalloy is used for a turbine rotor blade of a high-temperature portion of the high-pressure turbine or the medium-pressure turbine, and a ferrite is used for a rotor shaft of the high-pressure turbine or the medium-pressure turbine. A steam turbine using a heat-resistant steel and applying a thermal barrier coating to a surface of a portion of the rotor shaft exposed to high-temperature steam. The steam turbine according to claim 11, wherein a thermal barrier coating is applied to a surface of the turbine blade in a stage exposed to high-temperature steam of the high-pressure turbine or the intermediate-pressure turbine.

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