# Alloy 925 UNS N09925: Properties and Applications

## Introduction to Alloy 925

Alloy 925, also known as UNS N09925, is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium. This superalloy is designed to offer excellent corrosion resistance, high strength, and good fabricability, making it suitable for demanding applications in various industries.

## Chemical Composition

The chemical composition of Alloy 925 plays a crucial role in its performance characteristics:

– Nickel (Ni): 42-46%
– Iron (Fe): Balance
– Chromium (Cr): 19.5-22.5%
– Molybdenum (Mo): 2.5-3.5%
– Copper (Cu): 1.5-3.0%
– Titanium (Ti): 1.9-2.4%
– Carbon (C): ≤0.03%

– Manganese (Mn): ≤1.0%
– Silicon (Si): ≤0.5%
– Sulfur (S): ≤0.03%
– Aluminum (Al): ≤0.2%

## Mechanical Properties

Alloy 925 exhibits impressive mechanical properties across various conditions:

### Room Temperature Properties

– Tensile Strength: 100-120 ksi (690-830 MPa)
– Yield Strength: 50-80 ksi (345-550 MPa)
– Elongation: 30-50%
– Hardness: 200-250 HB

### Elevated Temperature Properties

The alloy maintains good strength at elevated temperatures up to 600°C (1112°F), with excellent creep resistance and stress rupture properties.

## Physical Properties

Key physical properties of Alloy 925 include:

– Density: 8.14 g/cm³ (0.294 lb/in³)
– Melting Range: 1350-1400°C (2460-2550°F)
– Thermal Expansion Coefficient: 13.9 μm/m·°C (20-100°C)
– Thermal Conductivity: 11.4 W/m·K (at 100°C)
– Electrical Resistivity: 1.12 μΩ·m

## Corrosion Resistance

Alloy 925 offers outstanding corrosion resistance in various environments:

– Excellent resistance to general corrosion, pitting, and crevice corrosion
– Good resistance to stress corrosion cracking
– Performs well in sour gas environments containing H2S and CO2
– Resistant to seawater and chloride-containing solutions
– Maintains corrosion resistance in acidic environments

## Fabrication and Heat Treatment

### Forming

Alloy 925 can be formed using standard techniques, though it requires more force than austenitic stainless steels due to its higher strength.

### Welding

The alloy is readily weldable using common techniques such as:

– Gas tungsten arc welding (GTAW)
– Gas metal arc welding (GMAW)
– Shielded metal arc welding (SMAW)

Post-weld heat treatment is recommended for optimal corrosion resistance.

### Heat Treatment

The standard heat treatment for Alloy 925 involves:

– Solution annealing at 980-1010°C (1800-1850°F)
– Rapid cooling (water quenching)
– Aging at 620-650°C (1150-1200°F) for 4 hours

## Applications of Alloy 925

Alloy 925 finds applications in numerous demanding industries:

### Oil and Gas Industry

– Downhole components
– Wellhead equipment
– Valves and pumps
– Fasteners and connectors
– Tubing and casing for sour gas wells

### Chemical Processing

– Reactors and vessels
– Heat exchangers
– Piping systems
– Mixing equipment

### Marine Applications

– Seawater handling systems
– Offshore platform components
– Propeller shafts
– Pump impellers

### Other

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