Incoloy 800 Plate Composition, Heat Treatment, Properties, and Applications

Incoloy 800 plates are widely used in power generation, petrochemical processing, chemical industries, and aerospace applications, where they serve as critical structural components, heat exchangers, and high-temperature vessels. This article introduces its chemical composition, heat treatment processes, properties, and applications.

Incoloy 800 Chemical Composition

The following table outlines the standard chemical composition requirements per ASTM B409:

Notes:

Nickel (30–35%): Provides corrosion resistance and stabilizes the austenitic structure.

Chromium (19–23%): Enhances oxidation and scaling resistance at high temperatures.

Titanium and Aluminum: Serve as stabilizing elements to prevent carbide precipitation, improving long-term thermal stability.

This composition allows Incoloy 800 plates to maintain dimensional integrity and mechanical strength during prolonged exposure to temperatures up to 1,100°F.

Incoloy 800 Plate Heat Treatment Processes

Heat treatment is a critical step in the production of Incoloy 800 plates. The primary objective is to achieve a homogeneous microstructure that maximizes corrosion resistance and mechanical properties. The standard heat treatment for Incoloy 800 is solution annealing.

Solution Annealing Procedure:

Incoloy 800 plates are typically solution annealed at temperatures between 1800°F (982°C) and 2000°F (1093°C). Following the heating cycle, the material must be rapidly cooled, usually via water quenching or air cooling, depending on the thickness of the plate. This rapid cooling prevents the precipitation of carbides along the grain boundaries, which could lead to intergranular corrosion.

Grain Size Control:

While standard Incoloy 800 does not have a mandatory grain size requirement, controlling grain structure is vital for high-temperature creep resistance. For applications involving significant thermal stress, a finer grain structure may be preferred to enhance fatigue strength. Conversely, for extreme creep conditions, variants like Incoloy 800H specify a controlled grain size (ASTM No. 5 or coarser). During production, we monitor annealing parameters closely to ensure the microstructure aligns with the intended service environment.

Stress Relieving:

For fabricated plate assemblies, stress relieving may be conducted at 1600°F (870°C) to reduce residual stresses from welding or forming without significantly altering the mechanical properties. Proper heat treatment ensures the plate remains dimensionally stable during subsequent fabrication processes.

Incoloy 800 Plate Properties

Incoloy 800 plates combine high strength, excellent ductility, and superior corrosion resistance, making them suitable for a wide range of demanding industrial applications.

Mechanical Properties

Highlights:

High tensile and yield strength ensure structural integrity at elevated temperatures.

Elongation ≥30% provides excellent ductility, allowing for forming, rolling, and welding.

Moderate hardness balances machinability and resistance to wear.

Physical Properties

These properties highlight Incoloy 800's suitability for high-temperature components that require minimal thermal expansion and reliable structural performance.

Corrosion and Oxidation Resistance

Oxidation: The high chromium content forms a stable oxide layer that protects the material from scaling up to 1800°F (982°C).

Carburization: The alloy resists carbon uptake in carburizing atmospheres, preventing embrittlement.

Chloride Stress Corrosion Cracking (SCC): Unlike standard austenitic stainless steels, Incoloy 800 is highly resistant to chloride SCC, a common failure mode in chemical processing and marine environments.

Acid Resistance: It demonstrates good resistance to nitric and organic acids, though it is less suitable for highly reducing acidic environments without additional protection.

Incoloy 800 Plate Common Industrial Applications

Incoloy 800 plate is used in virtually every sector of heavy industry.

Petrochemical and Chemical Processing

Incoloy 800 is the industry standard for heat exchanger components, particularly those handling acidic or chloride-rich process streams. Its resistance to stress corrosion cracking (SCC) makes it superior to the 300-series stainless steels in environments where cooling water may contain high chloride levels.

Specific Components: Heat exchanger shells, reformer pigtails, and pressure vessel internals.

Power Generation

In both conventional and nuclear power plants, Incoloy 800 plate is used for steam generator tubing and superheater components. The alloy's ability to resist "steam-side" oxidation and "fire-side" corrosion ensures a long service life for critical energy infrastructure.

Thermal Processing and Heat Treating

For the manufacture of industrial furnaces, 800 plate is used to construct muffles, trays, and fixtures. Its high iron content makes it more cost-effective than pure nickel-based alloys (like Inconel 600), while still providing the necessary heat resistance.

Home Appliances

In a surprising crossover to the consumer market, Incoloy 800 is frequently used as the sheathing material for electric heating elements (e.g., in range tops and water heaters) because of its excellent combination of formability and high-temperature corrosion resistance.

Conclusion

Selecting Incoloy 800 plates, careful consideration of the specific service environment, temperature requirements, and fabrication needs will guide optimal material specification.

For applications demanding enhanced creep-rupture strength at the highest temperatures, the 800H or 800HT variants may be more appropriate. However, for the majority of high-temperature and corrosive service conditions, Incoloy 800 delivers dependable performance with cost-effective material selection.