# Alloy 690 UNS N06690: Properties and Applications in High-Temperature Environments

## Introduction to Alloy 690 UNS N06690

Alloy 690 UNS N06690 is a nickel-chromium-iron alloy known for its exceptional resistance to high-temperature oxidation and corrosion. This material is widely used in industries where components are exposed to extreme environments, such as nuclear power plants, chemical processing, and aerospace applications.

## Chemical Composition

The chemical composition of Alloy 690 plays a crucial role in its performance characteristics:

– Nickel (Ni): 58-63%
– Chromium (Cr): 27-31%
– Iron (Fe): 7-11%
– Carbon (C): ≤0.05%
– Manganese (Mn): ≤0.50%
– Silicon (Si): ≤0.50%
– Copper (Cu): ≤0.50%
– Aluminum (Al): ≤0.50%
– Titanium (Ti): ≤0.50%

## Key Properties of Alloy 690

### High-Temperature Resistance

Alloy 690 maintains excellent mechanical properties at elevated temperatures, making it suitable for applications up to 1100°C (2012°F). Its high chromium content provides outstanding oxidation resistance in both continuous and intermittent service.

### Corrosion Resistance

The alloy demonstrates superior resistance to:

– Stress corrosion cracking
– Pitting corrosion
– Intergranular attack
– Carburization and nitridation

### Mechanical Properties

Typical mechanical properties at room temperature include:

– Tensile Strength: 550-690 MPa
– Yield Strength: 240-310 MPa
– Elongation: 30-45%
– Hardness: 150-220 HB

## Applications in High-Temperature Environments

### Nuclear Industry

Alloy 690 is extensively used in nuclear power plants for:

– Steam generator tubing
– Reactor vessel internals
– Pressurizer heaters
– Control rod drive mechanisms

### Chemical Processing

The alloy finds applications in:

– Furnace components
– Heat exchangers
– Catalyst support grids
– Combustion chambers

### Aerospace and Power Generation

Other notable applications include:

– Gas turbine components
– Combustion liners
– Afterburner parts
– Heat treatment fixtures

## Fabrication and Welding Considerations

Alloy 690 can be fabricated using standard techniques, though some precautions are necessary:

– Hot working should be performed between 925-1205°C (1700-2200°F)
– Cold working requires intermediate annealing
– Welding is typically done using matching filler metals (ERNiCrFe-7 or ERNiCrFe-7A)
– Post-weld heat treatment may be required for certain applications

## Comparison with Similar Alloys

Alloy 690 offers several advantages over similar materials:

– Better high-temperature strength than Alloy 600
– Superior corrosion resistance compared to Alloy 800
– More stable microstructure than Alloy 601 at elevated temperatures

## Conclusion

Alloy 690 UNS N06690 stands out as a premier material for demanding high-temperature applications. Its combination of excellent oxidation resistance, mechanical properties, and corrosion resistance makes it indispensable in critical industries where reliability and performance are paramount. As technology advances and operating conditions become more severe, the importance of this high-performance alloy continues to grow.