# Alloy 800HT UNS N08811: Properties and Applications
## Introduction to Alloy 800HT
Alloy 800HT, designated as UNS N08811, is a high-temperature austenitic nickel-iron-chromium alloy known for its excellent resistance to oxidation and carburization. This alloy is a variant of Alloy 800 with enhanced high-temperature strength due to its controlled chemical composition and thermal treatment.
## Chemical Composition
Key Elements in Alloy 800HT
The chemical composition of Alloy 800HT plays a crucial role in its performance. The primary elements include:
- 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%
This specific combination ensures superior performance in high-temperature environments.
## Mechanical Properties
Strength and Durability
Alloy 800HT exhibits remarkable mechanical properties, especially at elevated temperatures:
- Tensile Strength: 550-760 MPa
- Yield Strength: 200-550 MPa
- Elongation: 30-45%
- Hardness: 150-200 HB
These properties make it suitable for demanding applications where both strength and ductility are required.
## Thermal Properties
High-Temperature Performance
Alloy 800HT is designed to withstand extreme temperatures:
- Operating Temperature: Up to 1100°C (2012°F)
- Melting Point: 1350-1400°C (2462-2552°F)
- Thermal Expansion Coefficient: 14.4 μm/m°C (20-1000°C)
Its ability to maintain structural integrity at high temperatures makes it ideal for heat-intensive applications.
## Corrosion Resistance
Protection Against Degradation
Alloy 800HT offers excellent resistance to various forms of corrosion:
- Oxidation resistance up to 1100°C
- Resistance to carburization and nitridation
- Good performance in sulfur-containing environments
- Resistance to chloride stress corrosion cracking
These characteristics make it valuable in aggressive chemical environments.
## Applications of Alloy 800HT
Industrial Uses
Due to its unique properties, Alloy 800HT finds applications in numerous industries:
- Petrochemical processing equipment
- Heat treatment furnaces and components
- Power generation systems
- Nuclear reactor components
- Industrial heating elements
- Chemical processing vessels
Specific Examples
Keyword: Alloy 800HT UNS N08811
Some specific applications include:
- Radiant tubes in heat treatment furnaces
- Catalyst support grids in reforming furnaces