# Alloy 825 UNS N08825: Properties and Applications

## Introduction to Alloy 825

Alloy 825, also known as UNS N08825, is a nickel-iron-chromium alloy with additions of molybdenum and copper. This material is designed for excellent resistance to both reducing and oxidizing acids, making it particularly useful in highly corrosive environments.

## Chemical Composition

The chemical composition of Alloy 825 plays a crucial role in its performance:

– Nickel (Ni): 38-46%
– Chromium (Cr): 19.5-23.5%
– Iron (Fe): 22% min
– Molybdenum (Mo): 2.5-3.5%
– Copper (Cu): 1.5-3.0%
– Titanium (Ti): 0.6-1.2%

## Mechanical Properties

Alloy 825 exhibits impressive mechanical properties:

– Tensile Strength: 586 MPa (85 ksi) min
– Yield Strength: 241 MPa (35 ksi) min
– Elongation: 30% min
– Hardness: Rb 90 max

## Corrosion Resistance

One of the most significant advantages of Alloy 825 is its exceptional corrosion resistance:

– Excellent resistance to sulfuric and phosphoric acids
– Good resistance to chloride stress corrosion cracking
– Performs well in both oxidizing and reducing environments
– Resistant to pitting and crevice corrosion in chloride-containing solutions

## Heat Treatment

Alloy 825 is typically supplied in the annealed condition. The recommended annealing temperature range is 927-1038°C (1700-1900°F), followed by rapid cooling to maintain optimal corrosion resistance.

## Applications of Alloy 825

Due to its unique combination of properties, Alloy 825 finds applications in various industries:

### Chemical Processing

– Acid production equipment
– Pickling tanks and heating coils
– Reactor vessels for sulfuric and phosphoric acid

### Oil and Gas Industry

– Downhole equipment
– Wellhead components
– Offshore platform components

### Power Generation

– Flue gas desulfurization systems
– Nuclear fuel reprocessing
– Heat exchangers in power plants

### Other Applications

– Marine components
– Pollution control equipment
– Fasteners and springs in corrosive environments

## Fabrication and Welding

Alloy 825 can be readily fabricated using standard techniques:

– Hot working should be performed between 1149-1260°C (2100-2300°F)
– Cold working requires intermediate annealing
– Welding can be performed using matching filler metal (ERNiCrMo-3)
– Post-weld heat treatment is generally not required

## Conclusion

Alloy 825 UNS N08825 offers an excellent combination of corrosion resistance, mechanical properties, and fabricability. Its versatility makes it a preferred material for demanding applications across multiple industries where resistance to aggressive environments is required.

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