JPH0321620B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a novel main steam temperature 600-650℃, pressure
The present invention relates to a steam turbine of 4000 to 5000 Psi, and particularly to an ultra-high-temperature, high-pressure steam turbine in which the turbine rotor shaft is made of a material that has excellent high-temperature strength and is resistant to heat embrittlement. In recent years, the demand for energy has been increasing as chemical technology has progressed. On the other hand, in Japan, where the import dependence rate for all energy is as high as 88%, the development of alternative energy sources and the improvement of the efficiency of power generation plants are being promoted as a matter of urgency due to factors such as the decline in global oil resources. Now, consideration is being given to increasing the temperature and pressure of steam power plants. In current power plants that use steam at 538°C, low alloy steel such as Cr-Mo-V steel is used as the material for the casing and turbine rotor shaft. However, the steam temperature is 600℃ and the pressure is
When targeting high-temperature, high-pressure power generation plants exceeding 4000 Psi, these low-alloy steels are difficult to use because their high-temperature strength, including creep strength, decreases significantly. Therefore, in the temperature range of 600°C or higher, austenitic alloys are suitable for controlling strength, but in these alloys, a wide variety of precipitated phases precipitate in a distributed manner at high temperatures, which promotes embrittlement and significantly reduces high-temperature strength. There is a risk of An object of the present invention is to provide a highly reliable ultra-high-temperature, high-pressure steam turbine, particularly at temperatures between 600 and 650 degrees Celsius.
An object of the present invention is to provide an ultra-high-temperature, high-pressure steam turbine comprising a rotor shaft made of austenitic forged steel that has high high-temperature strength under steam conditions, high high-temperature ductility, and little heat embrittlement. The present invention includes a casing, a blade that rotates in response to injection of steam flow within the casing, and a rotor shaft that holds and rotates the blade, and the casing has an interior in which stationary blades that guide the steam flow are held. The rotor shaft is composed of a casing and an outer casing that covers the inner casing and has an approximately spherical outer shape, and the rotor shaft is heated at 650°C.
An ultra-high-temperature, high-pressure steam turbine characterized by having a 1000-hour creep rupture strength of 25 Kg/mm ² or more and being made of austenitic steel having a specific composition. Preferably, the wing portions of the rotor shaft are arranged at equal intervals in the axial direction of the rotor shaft within the casing, and are asymmetrical at a center position with respect to the axial direction. The weight of the rotor shaft is C0.01~0.035
%, Mn2% or less, Si1% or less, Cr10~20%, Ni20
~30%, Mo1~2%, Ti1.5~3%, V0.29~0.32
%, Al0.1~less than 0.5%, B0.003~0.007% and the balance
It is made of austenitic forged steel with Fe and γ′ phase precipitated in the austenite base.
A product with a 1000 hour creep rupture strength at ℃ of 25 kg/mm ² or more can be obtained. The outer casing is made of Cr-Ni austenitic forged steel or Cr-Mo-V exhibiting a bainitic structure.
Those made of cast steel are preferred. The inner casing is preferably made of Cr-Ni austenitic cast steel. C is added in an amount of 0.01% or more to increase high-temperature strength, but in order to reduce heat embrittlement, the amount of carbon is particularly reduced.
The content shall be 0.035% by weight or less. titanium, molybdenum,
For alloys containing more than a certain amount of chromium, MX type,
M ₂₃ C ₆ type and MC ₆ type carbides precipitate due to high temperature and long heating. It is preferable to add these carbides so that they do not preferentially precipitate at grain boundaries in the temperature range of 600 to 650°C and reduce toughness and oxidation resistance. In addition, 12Cr steel, which is the current rotor material,
The absorbed energy value of Cr-Mo-V steel is generally 1.1Kg
-m and 0.69Kg-m or more. It has been clarified that in order to satisfy these values, by keeping the temperature below 0.030%C, there will be no problem even if it is used for a long time. On the other hand, carbides with molybdenum and the like are expected to precipitate within the grains and improve high-temperature strength, but the upper limit is set at 0.035% by weight in view of heat embrittlement. Mn is an important deoxidizing component in manufacturing. Toughness/
2% by weight to prevent negative effects on oxidation resistance.
It is as follows. In particular, 0.7 to 1.5% is preferable. Ni is an austenite-forming element and is 20% or more to improve high-temperature strength. If the amount of nickel is increased, chromium, which improves oxidation resistance, can be increased on balance, but in order to maintain high high-temperature ductility and yield strength at 600 to 650°C, the amount should be 30% by weight or less. In particular, 23 to 29% is preferable. Like Mn, Si is an important deoxidizing component in manufacturing. In order to maintain high toughness, ductility and weldability, the upper limit is set at 1.0% by weight. Mo is added to strengthen the austenite base and form carbides to improve creep strength.
% or more. In order to maintain high high-temperature ductility and workability, the content should be 2% by weight or less. In particular, 1~
1.5% is preferred. Cr is an important component that improves oxidation resistance.
10% by weight or more is required to maintain sufficient oxidation resistance at 600-650°C. The content must be 20% by weight or less to prevent embrittlement due to high temperature use and to create a stable structure. Particularly preferred is 12 to 18%. Along with aluminum, Ti forms a γ′ phase [Ni ₃ (Al,
Ti)] is formed. The γ′ phase is a regular lattice-like compound that is uniformly dispersed in an almost perfect spherical shape in the austenite matrix, and is an important factor in obtaining high high temperature strength at 600 to 650℃ due to precipitation hardening. 1.5% by weight or more is required to obtain this. The amount that prevents a decrease in ductility and prevents notch embrittlement is 3% by weight.
It is as follows. V is necessary to form carbides and increase high-temperature strength, and 0.29% or more is required to obtain sufficient strength, but since no significant effect can be obtained with 0.32% or more, it is set to 0.32% or less. Al forms the γ' phase together with titanium and is an important factor contributing to strengthening. The amount that prevents precipitation of the η phase (Ni ₃ Ti), which does not have age hardenability, is 0.1% by weight or more. Moreover, since excessive Al increases the creep rate, it is set to less than 0.5%. B is effective in significantly strengthening grain boundaries, increasing creep strength particularly over long periods of time, and in particular significantly increasing high temperature fatigue. This effect becomes more noticeable at about 0.003%, but hot workability decreases, so the content is set to 0.007% or less. FIG. 1 is an example of a cross-sectional configuration diagram of the main section of the ultra-high temperature and high pressure steam turbine of the present invention. Steam enters through a main steam pipe 1 and is injected in a predetermined direction by stationary blades 3 attached to an inner casing 2, which causes blades 5 attached to a rotor shaft 4 to rotate. The steam that has done the work is transferred to the outer casing 6.
and the inner casing 2, and is discharged from the cooling steam outlet 7, the exhaust outlet 8, and the auxiliary exhaust outlet 9. This discharged steam is then sent to a steam turbine operating at a lower temperature. 10 is the bearing center of the rotor shaft, 11 is the gland part, 12 is the intermediate gland leak outlet, 1
3 is a nozzle box. Arrows indicate the flow of steam. Below, Cr-Ni austenitic cast steel is used for the internal casing, and Cr-Ni is used for the rotor shaft.
An example in which Ni austenitic forged steel is used will be specifically explained. Table 1 shows the chemical composition of the test materials. Nos. 1 to 10 were subjected to solution treatment by heating at 980°C for 1 hour and cooling in water, and then subjected to aging treatment by heating at 720°C for 16 hours and cooling in air. The structure consists of γ′ phase precipitated on an austenite base. Nos. 3, 5, 8, and 9 are comparative steels, No. 10 is conventional steel, and the others are steels of the present invention. The Cr-Mo-V steel was heated at 970°C for 15 hours, blast cooled, then heated at 670°C for 48 hours, and then furnace cooled. 12Cr steel is heated to 1050℃ x 24h and then cooled with water spray.
It was heated at 570°C for 20 hours and then tempered at 650°C for 20 hours. V-notched Alpi impact tests and creep rupture tests were conducted on these steel types. Figure 2 shows the influence of the amount of C on heat embrittlement caused by heating at 650°C for 1500 hours using an impact test. According to these results, the absorbed energy of the material is almost constant regardless of the C content, whereas in the material heated at 650°C for 1500 hours, it monotonically decreases as the C content increases, and the higher the C content, the more heat embrittlement occurs. is remarkable. 12Cr steel and Cr-Mo-V, which are currently used rotor materials
The absorbed energy value of steel at 20°C is generally specified as 1.1 Kg-m and 0.69 Kg-m or more, respectively. Even after heating, the steel of the present invention has a C content of 0.035%, which is higher than that of 12% Cr steel, and Cr-Mo-V
higher than that of steel. In the material of the present invention with a C content of 0.030% by weight or less, intragranular fracture (white triangle) is maintained, but the C content is
As the content increases to 0.048% by weight, the fracture mode shifts to a grain boundary type (black triangle). This change in the form of destruction is
Analysis revealed that this is because MX type and M ₂₃ C ₆ type carbides precipitate at grain boundaries and deteriorate the grain boundaries. Therefore, to reduce heat embrittlement, the amount of C must be increased.
The present invention material limited to 0.035% or less is effective.

【table】

[Table] Figure 3 shows an operation pattern assuming operation under the most severe conditions at the current steam temperature of 566°C. If this operation pattern is also suitable for the ultra-high temperature and high pressure steam turbine of the present invention, the rotor shaft used therein will undergo severe low-cycle fatigue due to high stress during startup and shutdown, as shown in the figure. Also, during steady operation, it is subject to creep due to centrifugal force. Table 2 shows the results of tensile tests, creep rupture tests and low cycle fatigue tests conducted at 650°C for the steel according to the invention and at 550°C for the conventional steel. As shown in the table, the material of the present invention has tensile strength and 0.2% yield strength equal to or higher than Cr-Mo-V steel, and its elongation rate is 1.5 to 1.57 times higher. Creep rupture strength is 1.1 to 1.20 times higher, and low cycle fatigue is equivalent to or higher than Cr-Mo-V steel. Low cycle fatigue testing is performed without holding, strain rate
It shows the number of repetitions until breakage at 0.1%/sec and strain amounts of 1.0% and 0.65%.

[Table] Figure 4 shows alloys No. 5 to 10 at a temperature of 650°C.
FIG. 2 is a diagram showing the relationship between fatigue life and B amount according to the number of repetitions of rupture in a tension-compression triangular waveform with a strain range of 1.0% and a strain rate (0.1%/sec). As shown in the figure, it can be seen that the fatigue life is significantly affected by the amount of B. In particular, the B amount of the present invention is from 0.003 to
It is clear that the lifespan is significantly longer at 0.007%. As described above, according to the material of the present invention, the special properties required for Cr-Mo-V steel currently used at 550°C can be raised to 650°C, and satisfactory results can be obtained. 650℃ and steam pressure 4000
It has become clear that it can be fully used in ultra-high temperature and high pressure steam turbines at ~5000 Psi.

[Brief explanation of the drawing]

FIG. 1 is an example of a cross-sectional configuration diagram of an ultra-high-temperature, high-pressure steam turbine according to the present invention, FIG. 2 is a diagram showing the relationship between the amount of carbon and absorbed energy of the material according to the present invention, and FIG. 3 is a diagram showing a current steam turbine. FIG. 4 is a graph showing the acting stress generated on the rotor shaft depending on the driving pattern, and FIG. 4 is a diagram showing the relationship between the amount of B and the number of repeated fractures. 1...Main steam pipe, 2...Inner casing, 3...
...Stator blade, 4...Rotor shaft, 5...Wing, 6...
...external casing.

Claims (1)

[Claims] 1. A casing, a rotor shaft that holds and rotates the blades that rotate in response to the injection of steam flow within the casing, and an inner casing that holds stationary blades that guide the steam flow; The rotor shaft is composed of an outer casing that covers an inner casing, and the rotor shaft has a weight of C0.01 to 0.035%, Mn2% or less, and Si1
% or less, Cr10~20%, Ni20~30%, Mo1~2%,
Ti1.5~3%, V0.29~0.32%, Al0.1~0.5%,
An ultra-high-temperature, high-pressure steam turbine characterized by being made of austenitic forged steel consisting of 0.003 to 0.007% B and the balance Fe, with a γ' phase precipitated in an austenite matrix.