# Alloy X-750 (UNS N07750) Properties and Applications

## Introduction to Alloy X-750

Alloy X-750, also known by its UNS designation N07750, is a nickel-chromium alloy that has been widely used in various industries due to its excellent mechanical properties and resistance to high temperatures. This precipitation-hardenable superalloy is known for its combination of strength, corrosion resistance, and good fabricability.

## Chemical Composition

The chemical composition of Alloy X-750 plays a crucial role in its performance characteristics:

– Nickel (Ni): 70% minimum
– Chromium (Cr): 14-17%
– Iron (Fe): 5-9%
– Titanium (Ti): 2.25-2.75%
– Aluminum (Al): 0.4-1.0%
– Niobium (Nb) + Tantalum (Ta): 0.7-1.2%
– Carbon (C): 0.08% maximum
– Manganese (Mn): 1.0% maximum
– Silicon (Si): 0.5% maximum
– Sulfur (S): 0.01% maximum
– Copper (Cu): 0.5% maximum

## Mechanical Properties

Alloy X-750 exhibits impressive mechanical properties, especially when properly heat treated:

### Room Temperature Properties (After Heat Treatment)

– Tensile Strength: 1200-1450 MPa (175-210 ksi)
– Yield Strength: 800-1000 MPa (115-145 ksi)
– Elongation: 15-25%
– Hardness: 35-45 HRC

### Elevated Temperature Properties

Alloy X-750 maintains good strength at elevated temperatures up to about 700°C (1300°F), making it suitable for high-temperature applications.

## Physical Properties

The physical characteristics of Alloy X-750 include:

– Density: 8.28 g/cm³ (0.299 lb/in³)
– Melting Range: 1390-1425°C (2535-2600°F)
– Electrical Resistivity: 1.22 μΩ·m
– Thermal Conductivity: 11.4 W/m·K (at 100°C)
– Coefficient of Thermal Expansion: 13.3 μm/m·K (20-100°C)

## Heat Treatment

Proper heat treatment is essential to achieve the desired properties in Alloy X-750. The standard heat treatment process includes:

1. Solution Annealing: 1150-1200°C (2100-2200°F) followed by rapid cooling
2. Aging Treatment: Typically performed at 705-760°C (1300-1400°F) for 16-20 hours

## Corrosion Resistance

Alloy X-750 offers excellent corrosion resistance in various environments:

– Good resistance to oxidation up to 870°C (1600°F)
– Excellent resistance to chloride ion stress corrosion cracking
– Good performance in fresh and saltwater environments
– Resistance to many organic and inorganic chemicals

## Fabrication and Machining

While Alloy X-750 can be fabricated using standard techniques, some considerations should be noted:

### Forming

– Can be formed using conventional methods when in the annealed condition
– More difficult to form after aging due to increased strength

### Machining

– Machining should be performed in the annealed condition
– Requires rigid setups and positive feeds
– Carbide tools are recommended for best results

### Welding

– Can be welded using common techniques (TIG, MIG, resistance)
– Post-weld heat treatment is recommended for optimum properties
– Filler metals should match base metal composition

## Applications of Alloy X-750

Alloy X-750 finds applications in numerous industries due to its unique combination of properties