Alloy 800 UNS N08800: Properties and Applications

# Alloy 800 UNS N08800: Properties and Applications

## Introduction to Alloy 800 UNS N08800

Alloy 800, also known as UNS N08800, is a nickel-iron-chromium alloy that offers excellent resistance to oxidation and carburization at high temperatures. This material is widely used in various industries due to its unique combination of mechanical properties and corrosion resistance.

## Chemical Composition

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

– Nickel (Ni): 30-35%
– Chromium (Cr): 19-23%
– Iron (Fe): Balance
– Carbon (C): ≤0.10%
– Manganese (Mn): ≤1.5%

– Silicon (Si): ≤1.0%
– Aluminum (Al): 0.15-0.60%
– Titanium (Ti): 0.15-0.60%

## Mechanical Properties

Alloy 800 exhibits impressive mechanical properties across a wide temperature range:

– Tensile Strength: 500-700 MPa (72-102 ksi)
– Yield Strength: 200-350 MPa (29-51 ksi)
– Elongation: 30-45%
– Hardness: 120-200 HB
– Density: 7.94 g/cm³ (0.287 lb/in³)

## Physical Properties

The physical characteristics of Alloy 800 include:

– Melting Range: 1350-1400°C (2460-2550°F)
– Thermal Conductivity: 11.2 W/m·K (at 100°C)
– Electrical Resistivity: 0.98 μΩ·m (at 20°C)
– Coefficient of Thermal Expansion: 14.4 μm/m·K (20-100°C)

## Corrosion Resistance

Alloy 800 demonstrates excellent resistance to various corrosive environments:

– Oxidation resistance up to 1100°C (2010°F)
– Resistance to carburizing and sulfidizing atmospheres
– Good performance in aqueous corrosion environments
– Resistance to stress corrosion cracking

## Heat Treatment

Proper heat treatment enhances the properties of Alloy 800:

– Solution annealing: 980-1040°C (1800-1900°F) followed by rapid cooling
– Stress relieving: 540-650°C (1000-1200°F)
– Stabilization annealing: 900°C (1650°F) for improved resistance to intergranular corrosion

## Fabrication and Welding

Alloy 800 can be readily fabricated using standard techniques:

– Hot working: 870-1230°C (1600-2250°F)
– Cold working: Requires intermediate annealing
– Welding: Can be welded using GTAW, GMAW, SMAW, and SAW methods
– Post-weld heat treatment is often recommended

## Applications of Alloy 800

Alloy 800 finds extensive use in various industries:

### Chemical Processing

– Heat exchangers
– Reactor vessels
– Piping systems
– Catalyst support grids

### Power Generation

– Steam generator tubing
– Superheater tubes
– Heat recovery systems
– Nuclear reactor components

### Petrochemical Industry

– Furnace components
– Transfer piping
– Cracking tubes
– Reformer tubes

### Other Applications

– Food processing equipment
– Pharmaceutical manufacturing
– Aerospace components
– Heat treating fixtures

## Advantages of Alloy 800

The key benefits of using Alloy 800 include:

– Excellent high-temperature strength
– Good resistance to oxidation and carburization
– Maintains mechanical properties at elevated temperatures
– Good fabricability and weldability
– Cost-effective compared to higher nickel alloys

## Limitations and Considerations

While Alloy 800 offers many advantages, some limitations should be considered: