Alloy 800HT UNS N08811 High-Temperature Corrosion-Resistant Material

# Alloy 800HT UNS N08811 High-Temperature Corrosion-Resistant Material

## Introduction to Alloy 800HT

Alloy 800HT (UNS N08811) is a high-temperature, corrosion-resistant material designed for demanding industrial applications. This nickel-iron-chromium alloy offers exceptional resistance to oxidation and carburization at elevated temperatures, making it a preferred choice for various high-temperature environments.

## Chemical Composition

The chemical composition of Alloy 800HT plays a crucial role in its performance characteristics:

– Nickel (Ni): 30-35%
– Chromium (Cr): 19-23%
– Iron (Fe): Balance
– Carbon (C): 0.06-0.10%
– Aluminum (Al): 0.15-0.60%
– Titanium (Ti): 0.15-0.60%

## Key Properties and Advantages

Alloy 800HT offers several distinct advantages that make it suitable for high-temperature applications:

### High-Temperature Strength

The alloy maintains excellent mechanical properties at temperatures up to 1500°F (815°C), with good creep and rupture strength.

### Oxidation Resistance

Alloy 800HT forms a protective chromium oxide layer that resists oxidation at temperatures up to 2100°F (1150°C).

### Carburization Resistance

The material demonstrates superior resistance to carburization in hydrocarbon environments compared to standard stainless steels.

### Thermal Stability

The alloy maintains dimensional stability during thermal cycling, making it suitable for applications with frequent temperature changes.

## Common Applications

Alloy 800HT finds use in numerous industrial sectors:

– Petrochemical processing equipment

– Heat treating fixtures and baskets
– Industrial furnace components
– Power generation systems
– Chemical processing equipment
– Nuclear reactor components

## Comparison with Similar Alloys

While similar to Alloy 800 and 800H, Alloy 800HT offers improved high-temperature properties:

– Higher creep and rupture strength than Alloy 800
– Better carburization resistance than standard 800H
– More stable microstructure at prolonged high temperatures

## Fabrication and Welding Considerations

Working with Alloy 800HT requires specific considerations:

### Forming

The alloy can be formed using standard techniques, though its work hardening characteristics require more force than carbon steels.

### Welding

Alloy 800HT is readily weldable using common techniques such as GTAW, GMAW, and SMAW. Matching filler metals are recommended for optimal performance.

### Heat Treatment

Solution annealing at 1900-2100°F (1038-1149°C) followed by rapid cooling is typically performed to optimize properties.

## Conclusion

Alloy 800HT UNS N08811 stands as a versatile high-performance material for extreme temperature applications. Its combination of oxidation resistance, carburization resistance, and mechanical strength at elevated temperatures makes it an excellent choice for demanding industrial environments where conventional materials would fail.