Hastelloy C-276: High-Performance Nickel-Chromium-Molybdenum Alloy (UNS N10276)

# Hastelloy C-276: High-Performance Nickel-Chromium-Molybdenum Alloy (UNS N10276)

## Introduction to Hastelloy C-276

Hastelloy C-276, also known as UNS N10276, is a nickel-chromium-molybdenum alloy renowned for its exceptional corrosion resistance and high-temperature performance. This superalloy belongs to the Hastelloy family of materials developed by Haynes International and has become a benchmark for corrosion-resistant alloys in demanding industrial applications.

## Chemical Composition and Properties

The outstanding performance of Hastelloy C-276 stems from its carefully balanced chemical composition:

– Nickel (Ni): 57% (min) – forms the matrix of the alloy
– Chromium (Cr): 14.5-16.5% – provides resistance to oxidizing environments
– Molybdenum (Mo): 15-17% – enhances resistance to reducing conditions
– Iron (Fe): 4-7% – contributes to overall stability
– Tungsten (W): 3-4.5% – improves high-temperature strength
– Cobalt (Co): ≤2.5% – enhances thermal stability

This unique combination of elements gives Hastelloy C-276 its remarkable properties:

– Excellent resistance to pitting, crevice corrosion, and stress corrosion cracking
– Outstanding performance in both oxidizing and reducing environments
– Good mechanical properties at elevated temperatures
– Superior resistance to a wide range of corrosive media

## Key Applications

Hastelloy C-276 finds extensive use in industries where conventional materials fail due to extreme corrosion or high temperatures:

### Chemical Processing Industry

– Reactors, heat exchangers, and piping systems handling aggressive chemicals
– Equipment for sulfuric, hydrochloric, and phosphoric acid production
– Components exposed to chlorides and other halides

### Pollution Control Systems

– Flue gas desulfurization (FGD) systems
– Waste incineration and scrubbing equipment
– Chemical waste treatment facilities

### Oil and Gas Industry

– Downhole components in sour gas environments
– Offshore platform equipment exposed to seawater
– Refinery components handling corrosive crude oils

### Pharmaceutical and Food Processing

– Equipment requiring high purity and corrosion resistance
– Components exposed to sterilization processes

– Processing vessels for aggressive pharmaceutical compounds

## Fabrication and Welding Considerations

Working with Hastelloy C-276 requires special attention to maintain its corrosion resistance:

### Forming

The alloy can be formed using standard techniques, but requires more force than austenitic stainless steels. Annealing may be necessary between forming operations to relieve work hardening.

### Welding

Hastelloy C-276 is readily weldable using:

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

Proper filler metals (such as ERNiCrMo-4) and shielding gases must be used to maintain corrosion resistance in the weld zone.

### Heat Treatment

Solution annealing at 2050-2150°F (1121-1177°C) followed by rapid cooling is recommended to optimize corrosion resistance and mechanical properties.

## Comparison with Other Hastelloy Alloys

While Hastelloy C-276 offers outstanding performance, other alloys in the family may be better suited for specific applications:

– Hastelloy C-22 (UNS N06022): Improved resistance to oxidizing environments
– Hastelloy C-2000 (UNS N06200): Enhanced resistance to sulfuric acid
– Hastelloy B-3 (UNS N10675): Superior resistance to reducing acids like hydrochloric

## Conclusion

Hastelloy C-276 (UNS N10276) remains one of the most versatile and widely used nickel-based alloys for severe corrosive environments. Its balanced composition provides reliable performance across a broad spectrum of industrial applications, making it a preferred choice for engineers