# Alloy 738 UNS N06738: Properties and Applications

## Introduction to Alloy 738 UNS N06738

Alloy 738, also known by its UNS designation N06738, is a nickel-based superalloy specifically designed for high-temperature applications. This precipitation-hardened alloy exhibits exceptional strength and corrosion resistance, making it a preferred choice for demanding environments in various industries.

## Chemical Composition

The chemical composition of Alloy 738 plays a crucial role in its performance characteristics:

– Nickel (Ni): Primary base element (approximately 60-65%)
– Chromium (Cr): 15-17% for oxidation resistance
– Cobalt (Co): 8-10% for solid solution strengthening
– Molybdenum (Mo): 1.5-2.5% for creep resistance
– Titanium (Ti) and Aluminum (Al): For precipitation hardening
– Tungsten (W): 2.4-2.8% for strengthening
– Niobium (Nb): 0.6-1.2% for grain boundary stabilization
– Carbon (C): 0.09-0.13% for carbide formation

## Mechanical Properties

Alloy 738 demonstrates impressive mechanical properties across a wide temperature range:

– Tensile Strength: Approximately 1,200 MPa at room temperature
– Yield Strength: Around 850 MPa at room temperature
– Elongation: Typically 15-20% in 50 mm
– Hardness: 35-40 HRC in the aged condition
– Creep Resistance: Excellent performance up to 980°C (1,800°F)

## Physical Properties

The physical characteristics of Alloy 738 include:

– Density: 8.22 g/cm³
– Melting Range: 1,315-1,370°C (2,400-2,500°F)
– Thermal Expansion Coefficient: 13.3 μm/m·°C (20-1,000°C)
– Thermal Conductivity: 11.2 W/m·K at 100°C
– Electrical Resistivity: 1.25 μΩ·m at 20°C

## Heat Treatment

Proper heat treatment is essential for optimizing Alloy 738’s properties:

– Solution Annealing: Typically performed at 1,120-1,170°C (2,050-2,140°F) followed by rapid cooling
– Aging Treatment: Usually conducted at 840-870°C (1,550-1,600°F) for 24 hours, followed by air cooling
– Stress Relief: Recommended after welding or forming operations

## Corrosion Resistance

Alloy 738 offers excellent resistance to various forms of corrosion:

– Oxidation resistance up to 1,100°C (2,012°F)
– Good resistance to sulfidation and carburization
– Moderate resistance to hot corrosion
– Excellent performance in reducing and oxidizing atmospheres

## Fabrication and Machining

Working with Alloy 738 requires special considerations:

– Forming: Can be hot or cold worked, but requires higher forces than conventional alloys
– Welding: Typically performed using matching filler metal or similar nickel-based alloys
– Machining: Requires rigid setups, sharp tools, and appropriate cutting parameters
– Grinding: Recommended for finishing operations

## Applications of Alloy 738 UNS N06738

Alloy 738 finds extensive use in high-temperature applications:

### Gas Turbine Components

– Turbine blades and vanes
– Combustion chambers
– Afterburner components

### Aerospace Industry

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

### Industrial Applications

– Heat treatment fixtures
– Chemical processing equipment
– Nuclear reactor components

## Advantages of Alloy 738

The key benefits of using Alloy 738 include:

– Exceptional high-temperature strength