# Alloy 738 UNS N06738: Properties and Applications

## Introduction to Alloy 738 UNS N06738

Alloy 738, also known as UNS N06738, is a nickel-based superalloy renowned for its exceptional high-temperature strength and corrosion resistance. This material is widely used in demanding industrial applications where extreme conditions are present.

## Chemical Composition

The composition of Alloy 738 contributes significantly to its remarkable properties:

– Nickel (Ni): 58-63%
– Chromium (Cr): 15-17%
– Cobalt (Co): 8-10%
– Molybdenum (Mo): 1.5-2.5%
– Tungsten (W): 2.4-2.8%
– Aluminum (Al): 3.2-3.7%
– Titanium (Ti): 3.2-3.7%
– Iron (Fe): ≤1.0%
– Carbon (C): ≤0.15%

## Mechanical Properties

Alloy 738 exhibits outstanding mechanical characteristics:

– Tensile Strength: 1100-1300 MPa at room temperature
– Yield Strength: 750-900 MPa
– Elongation: 10-20%
– Hardness: 30-40 HRC
– Creep Resistance: Excellent at temperatures up to 850°C (1562°F)

## Physical Properties

Key physical properties include:

– Density: 8.22 g/cm³
– Melting Range: 1260-1340°C (2300-2444°F)
– Thermal Expansion Coefficient: 13.5 μm/m·°C (20-1000°C)
– Thermal Conductivity: 11.5 W/m·K at 20°C

## Heat Treatment

Proper heat treatment enhances Alloy 738’s properties:

– Solution Annealing: 1080-1120°C (1976-2048°F) followed by rapid cooling
– Aging Treatment: 760-870°C (1400-1600°F) for 16-24 hours

## Corrosion Resistance

Alloy 738 demonstrates excellent resistance to:

– Oxidation at high temperatures
– Sulfidation
– Hot corrosion
– Carburization
– Chloride-induced stress corrosion cracking

## Applications

### Gas Turbine Components

Alloy 738 is extensively used in:

– Turbine blades
– Vanes
– Combustion chambers
– Afterburner parts

### Aerospace Industry

Critical applications include:

– Jet engine components
– Rocket motor parts
– High-temperature fasteners

### Industrial Applications

Other significant uses:

– Chemical processing equipment
– Nuclear reactor components
– Heat treatment fixtures
– Power generation systems

## Fabrication and Machining

Working with Alloy 738 requires special considerations:

– Machining: Requires rigid setups and sharp tools
– Welding: Gas tungsten arc welding (GTAW) is preferred
– Forming: Hot working is recommended above 1000°C (1832°F)

## Advantages Over Other Superalloys

Alloy 738 offers several benefits:

– Superior creep-rupture strength
– Better microstructural stability
– Enhanced oxidation resistance
– Longer service life in extreme environments

## Conclusion

Alloy 738 UNS N06738 represents a pinnacle of nickel-based superalloy technology, offering an exceptional combination of high-temperature strength, corrosion resistance, and mechanical properties. Its versatility makes it indispensable in critical applications across aerospace, power generation, and industrial sectors where performance under extreme conditions is paramount.