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In gas turbines, high temperature alloy steel casting is one of the core technologies for manufacturing turbine blades and combustion chamber components. These components need to withstand extreme working conditions, including high temperature, high pressure, corrosive gases and mechanical stress.
Application of turbine blades
Working environment and performance requirements
Turbine blades are one of the most critical components in gas turbines, directly exposed to high temperature gas flow, and the temperature may be as high as 1000°C or more.
High temperature alloy steel castings must have the following properties:
High temperature resistance: Ability to maintain strength and stability in high temperature environment for a long time.
Creep resistance: Prevent plastic deformation under high temperature and high stress conditions.
Oxidation resistance: Resist high temperature oxidation and avoid the formation of brittle oxide layer on the surface.
Thermal fatigue resistance: Cope with frequent start-stop cycles and temperature fluctuations.
Material selection
Nickel-based high temperature alloy:
The most commonly used material with excellent high temperature strength, oxidation resistance and creep resistance.
Common grades include Inconel 718, Inconel 625, CMSX-4, etc.
Cobalt-based superalloys:
It has higher oxidation resistance and corrosion resistance, and is suitable for use in extremely corrosive environments.
Common grades include Haynes 188, Mar-M 509, etc.
Iron-based superalloys:
It has lower cost, but its temperature resistance is slightly inferior to that of nickel-based and cobalt-based alloys, and is suitable for medium temperature areas.
Casting process
Investment Casting
Investment casting is the main process for manufacturing turbine blades, which can achieve complex shapes and high precision.
Using ceramic molds, defect-free blades are produced through investment casting.
Internal cooling channels (such as hollow blades) can be manufactured to improve heat dissipation efficiency.
Directional Solidification (DS)
By controlling the solidification direction, the grains grow in a specific direction, reducing the number of grain boundaries, and thus improving creep resistance.
Single Crystal Casting (SC)
Single crystal blades have no grain boundaries, have higher high temperature strength and creep resistance, and are the first choice for high-end turbine blades.
Surface treatment
Coating technology:
Thermal barrier coating (TBC): Ceramic materials (such as zirconium oxide) are coated on the surface of the blade to reduce the temperature of the substrate and extend the service life.
Anti-oxidation coating: Such as aluminide coating or MCrAlY (metal chromium aluminum yttrium) coating to enhance the anti-oxidation ability.
Cooling design:
The surface temperature of the blade is reduced through internal cooling channels and external air film cooling technology.
Application of combustion chamber components
Working environment and performance requirements
The combustion chamber components are directly in contact with high-temperature combustion gases and are subjected to high pressure and corrosive media (such as sulfides and nitrogen oxides).
The main performance requirements include:
High temperature resistance: Able to withstand combustion temperatures above 1500°C.
Corrosion resistance: Resist erosion by combustion products.
Structural stability: Maintains geometric shape unchanged under high temperature and high pressure.
Material selection
Nickel-based high-temperature alloy: Widely used in combustion chamber components, with excellent high-temperature strength and anti-oxidation properties.
Common grades include Inconel 617, Hastelloy X, etc.
Cobalt-based high-temperature alloys:
Used in high-temperature areas in combustion chambers, with better corrosion resistance.
Casting process
Precision casting:
Used to manufacture complex combustion chamber liners, flame tubes and other components.
By optimizing the casting process, the wall thickness of the components is ensured to be uniform and the thermal stress concentration is reduced.
Welding and assembly:
For large combustion chamber components, segmented casting and welding are usually adopted.
Surface treatment
Thermal barrier coating (TBC):
Ceramic coating is applied to the inner wall of the combustion chamber to reduce the substrate temperature and improve heat resistance.
Anti-oxidation coating:
Improve the oxidation resistance of combustion chamber components and extend service life.
Cooling design:
Combustion chamber components are usually designed with porous cooling structures to reduce the temperature through film cooling and convection cooling.
Advantages of high-temperature alloy steel casting
Capability of manufacturing complex shapes
High-temperature alloy steel casting can produce complex geometries, such as hollow structures and cooling channels of turbine blades.
This ability is critical to optimizing component performance (such as improving cooling efficiency).
Applicability of high-performance materials
High-temperature alloy steel has excellent high-temperature strength, oxidation resistance and creep resistance, which can meet the needs of extreme working conditions of gas turbines.
Long life and reliability
Through advanced casting processes and surface treatment technologies, high-temperature alloy steel castings can operate stably and for a long time in high temperature, high pressure and corrosive environments.
The application of high-temperature alloy steel casting in gas turbines is mainly reflected in the manufacture of turbine blades and combustion chamber components. These technologies not only meet the needs of extreme working conditions of gas turbines, but also promote technological progress in the fields of aerospace and energy.
