Incoloy 800HT Superalloy
Incoloy 800HT is a nickel-iron-chromium superalloy designed for exceptional high-temperature strength, oxidation resistance, and creep resistance. It is a modified version of Incoloy 800, optimized with higher carbon, aluminum, and titanium content to enhance creep performance at elevated temperatures (up to 1100°C). This makes it a critical material in high-temperature industrial applications such as power generation, petrochemical processing, and heat treatment. Below is a detailed overview of its composition, properties, processing, and applications:
1. Chemical Composition
Incoloy 800HT’s composition is engineered to balance high-temperature strength, oxidation resistance, and structural stability. Key elements and their typical ranges are as follows:
Element Content Range (%) Role in the Alloy
Nickel (Ni) 30.0-35.0 Forms the matrix with iron, provides high-temperature stability, and enhances resistance to thermal fatigue.
Iron (Fe) Base element (~40-45) Reduces alloy cost while contributing to mechanical strength; works with nickel to form a stable austenitic structure.
Chromium (Cr) 19.0-23.0 Primary element for oxidation and carburization resistance, forming a dense chromium oxide (Cr₂O₃) film that protects the alloy at high temperatures.
Carbon (C) 0.06-0.10 Enhances creep strength by forming carbides at grain boundaries, preventing grain boundary sliding under high-temperature stress.
Aluminum (Al) 0.30-0.80 Aids in forming a protective oxide layer, improving oxidation resistance, and contributes to precipitation strengthening.
Titanium (Ti) 0.60-1.20 Forms carbides and intermetallic phases (e.g., TiC, Ni₃Ti) to enhance high-temperature strength and creep resistance.
Manganese (Mn) ≤1.5 Improves hot workability and deoxidation during alloy production.
Silicon (Si) ≤1.0 Assists in forming a protective oxide layer, enhancing oxidation resistance in high-temperature air.
2. Physical Properties
Incoloy 800HT exhibits physical properties tailored for consistent performance in extreme high-temperature environments:
Density: Approximately 7.94 g/cm³, making it suitable for structural components where high-temperature strength is prioritized over weight.
Melting Point: 1350-1400°C, ensuring stability in extreme heat without melting or structural degradation.
Thermal Conductivity: Increases with temperature, ranging from ~10.8 W/(m·℃) at 100°C to ~25.1 W/(m·℃) at 1000°C, facilitating effective heat dissipation in high-heat applications.
Coefficient of Linear Expansion: 13.5×10⁻⁶/℃ (20-100°C) and 18.4×10⁻⁶/℃ (20-1000°C). Compatibility with mating materials is critical to minimize thermal stress during temperature cycles.
Magnetic Property: Non-magnetic in the annealed condition, ideal for applications near sensitive electronics or where magnetic interference must be avoided.
3. Mechanical Properties
Incoloy 800HT’s mechanical performance is characterized by exceptional high-temperature strength, creep resistance, and oxidation stability:
Tensile Strength:
At room temperature: Tensile strength (Rm) ≥ 585 MPa; yield strength (Rp0.2) ≥ 240 MPa.
At 800°C: Tensile strength remains ≥ 345 MPa; yield strength ≥ 165 MPa, ensuring robust load-bearing capacity in high-temperature service.
Ductility: Elongation (A5) ≥ 30% at room temperature and ≥ 15% at 800°C, providing sufficient formability for fabrication.
Creep Resistance: Excellent resistance to creep deformation under long-term high-temperature stress (e.g., creep rupture strength ≥ 100 MPa for 1000 hours at 850°C), critical for extended service life in hot components.
Oxidation Resistance: Maintains structural integrity in oxidizing atmospheres up to 1100°C, with minimal weight loss from oxidation even after prolonged exposure, thanks to the protective chromium-aluminum oxide layer.
Carburization Resistance: Resistant to carburization in hydrocarbon-rich environments, making it suitable for petrochemical and refining applications.
4. Processing Performance
Incoloy 800HT can be processed using standard methods, though its high-temperature properties require careful control of heat treatment and deformation:
Hot Working:
Suitable for hot forging, rolling, and extrusion. Optimal temperature range: 1100-1200°C, where the alloy exhibits high plasticity and low deformation resistance.
Uniform heating and controlled cooling are critical to avoid grain coarsening and ensure consistent mechanical properties.
Cold Working:
Can be cold-rolled, drawn, or stamped with moderate work hardening. Intermediate annealing (at 980-1040°C followed by air cooling) restores ductility for further processing.
Welding:
Weldable using common techniques such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and electron beam welding.
Filler metals matching the alloy’s composition (e.g., ERNiCr-3) are recommended. Post-weld annealing (1000-1050°C followed by air cooling) is advised to restore grain structure and corrosion resistance.
Heat Treatment:
Standard treatment: Solution annealing at 980-1040°C (held for 1-2 hours) followed by air cooling, which optimizes grain structure and 均匀 izes alloying elements for maximum creep resistance.
5. Application Fields
Incoloy 800HT’s superior high-temperature performance makes it indispensable in industries requiring stability under extreme thermal stress:
Power Generation:
Components of gas turbines, such as combustion chambers, transition pieces, and heat shields.
Boiler tubes, superheater tubes, and heat exchangers in fossil fuel and nuclear power plants.
Petrochemical and Refining:
Furnace tubes, reformer tubes, and catalytic reactor components exposed to high temperatures and hydrocarbon-rich environments.
Pyrolysis coils and ethylene crackers in chemical processing.
Heat Treatment and Metallurgy:
High-temperature furnace fixtures, radiant tubes, and conveyor belts for annealing, sintering, and brazing processes.
Crucibles and molten metal handling equipment.
Aerospace and Defense:
Structural components for rocket engines and aircraft auxiliary power units (APUs) requiring high-temperature strength.
In summary, Incoloy 800HT is a high-performance superalloy valued for its exceptional high-temperature strength, creep resistance, and oxidation stability. Its ability to perform reliably in extreme thermal environments makes it a material of choice for critical applications in power generation, petrochemical processing, and high-temperature manufacturing, where durability under prolonged heat stress is essential.