# Alloy 825 UNS N08825: Properties and Applications
## Introduction to Alloy 825 UNS N08825
Alloy 825, also known as UNS N08825, is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium. This material is designed for excellent corrosion resistance in various environments, including sulfuric and phosphoric acids. Its balanced composition makes it suitable for a wide range of industrial applications where both strength and corrosion resistance are required.
## Chemical Composition
The chemical composition of Alloy 825 plays a crucial role in its performance characteristics:
– 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%
– Carbon (C): 0.05% max
– Manganese (Mn): 1.0% max
– Silicon (Si): 0.5% max
– Sulfur (S): 0.03% max
– Aluminum (Al): 0.2% max
## Mechanical Properties
Alloy 825 exhibits excellent mechanical properties across a wide temperature range:
Property | Value
Tensile Strength | 586 MPa (85 ksi) min
Yield Strength (0.2% offset) | 241 MPa (35 ksi) min
Elongation | 30% min
Hardness (Rockwell B) | 95 max
## Physical Properties
The physical characteristics of Alloy 825 include:
– Density: 8.14 g/cm³ (0.294 lb/in³)
– Melting Range: 1370-1400°C (2500-2550°F)
– Electrical Resistivity: 1.02 μΩ·m
– Thermal Conductivity: 11.1 W/m·K (77 BTU·in/hr·ft²·°F)
– Coefficient of Thermal Expansion: 14.4 μm/m·°C (8.0 μin/in·°F) at 20-100°C
## Corrosion Resistance
Alloy 825 offers outstanding corrosion resistance in various environments:
– Excellent resistance to reducing and oxidizing acids
– Good resistance to stress corrosion cracking
– Performs well in sulfuric and phosphoric acid environments
– Resistant to chloride ion stress corrosion cracking
– Maintains corrosion resistance in both alkaline and acidic solutions
## Heat Treatment
Proper heat treatment enhances the performance of Alloy 825:
– Solution annealing is typically performed at 927-1038°C (1700-1900°F)
– Rapid cooling (water quenching) is recommended after annealing
– Stress relieving can be done at 593-649°C (1100-1200°F) for 1 hour per inch of thickness
## Fabrication and Welding
Alloy 825 can be fabricated using standard techniques:
– Hot working should be performed at 1038-1232°C (1900-2250°F)
– Cold working requires intermediate annealing
– Welding can be performed using GTAW, GMAW, SMAW, and SAW methods
– Matching filler metals (ERNiCrMo-3 or ENiCrMo-3) are recommended
## Applications of Alloy 825
Alloy 825 finds applications in numerous industries:
### Chemical Processing
– Acid production equipment
– Reactor vessels
– Heat exchangers
– Piping systems
### Oil and Gas Industry
– Downhole components
– Wellhead equipment
– Subsea applications
– Gas processing equipment
### Power Generation
– Flue gas desulfurization systems
Keyword: Alloy 825 UNS N08825
– Nuclear fuel reprocessing
