# Alloy 625 UNS N06625: Properties and Applications

## Introduction to Alloy 625

Alloy 625, also known as UNS N06625, is a nickel-chromium-based superalloy renowned for its exceptional strength, corrosion resistance, and high-temperature performance. This versatile material finds applications across various industries, from aerospace to chemical processing.

## Chemical Composition

The unique properties of Alloy 625 stem from its carefully balanced chemical composition:

– Nickel (Ni): 58% minimum
– Chromium (Cr): 20-23%
– Molybdenum (Mo): 8-10%
– Niobium (Nb): 3.15-4.15%
– Iron (Fe): 5% maximum
– Carbon (C): 0.10% maximum
– Manganese (Mn): 0.50% maximum
– Silicon (Si): 0.50% maximum
– Phosphorus (P): 0.015% maximum
– Sulfur (S): 0.015% maximum
– Aluminum (Al): 0.40% maximum
– Titanium (Ti): 0.40% maximum

## Mechanical Properties

Alloy 625 exhibits impressive mechanical characteristics across a wide temperature range:

– Tensile Strength: 120-160 ksi (827-1103 MPa)
– Yield Strength: 60-120 ksi (414-827 MPa)
– Elongation: 30-45%
– Hardness: 150-250 HB
– Density: 8.44 g/cm³ (0.305 lb/in³)

## Key Properties

### Corrosion Resistance

Alloy 625 demonstrates outstanding resistance to:

– Pitting and crevice corrosion
– Stress corrosion cracking
– Oxidation at high temperatures
– Acidic environments (including nitric and phosphoric acids)
– Seawater and marine atmospheres

### High-Temperature Performance

The alloy maintains its strength and stability at elevated temperatures up to 1800°F (982°C), making it suitable for:

– Gas turbine components
– Heat exchangers
– Combustion chambers
– Exhaust systems

### Fabrication Characteristics

Despite its high strength, Alloy 625 can be:

– Welded using common techniques (TIG, MIG, SMAW)
– Machined with carbide tools
– Formed using standard methods
– Heat treated for specific applications

## Common Applications

### Aerospace Industry

– Jet engine components
– Rocket motor casings
– Aircraft ducting systems
– Spacecraft structural elements

### Chemical Processing

– Reactor vessels
– Heat exchangers
– Piping systems
– Valves and pumps

### Marine Engineering

– Propeller blades
– Submarine components
– Offshore platform equipment
– Desalination plants

### Energy Sector

– Nuclear reactor components
– Gas turbine blades
– Heat recovery systems
– Flue gas desulfurization equipment

## Comparison with Similar Alloys

While Alloy 625 shares some characteristics with other nickel-based alloys, it offers distinct advantages:

– Better oxidation resistance than Alloy 600
– Superior strength at high temperatures compared to Alloy 800
– More cost-effective than cobalt-based superalloys for many applications
– Easier fabrication than some precipitation-hardened alloys

## Conclusion

Alloy 625 UNS N06625 continues to be a material of choice for engineers facing demanding environments that require exceptional corrosion resistance, high strength, and thermal stability. Its versatility across multiple industries ensures its ongoing relevance in advanced engineering applications.

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