Differences between Hastelloy C22 and Hastelloy C276

Hastelloy C-22 and C-276 are both nickel-chromium-molybdenum (Ni-Cr-Mo) "superalloys"designed for extreme corrosion resistance, but they have key differences in composition, performance, and applications:

 1. Composition (Key Differences)

    Hastelloy C-276 (UNS N10276):

    Ni (~57%), Cr (~15.5%), Mo (~16%), W (~3.5%), Fe (~5%), Co (~2.5%), C (~0.01%).  

    Contains tungsten (W) for enhanced strength in reducing environments.

    Hastelloy C-22 (UNS N06022):

    Ni (~56%), Cr (~22%), Mo (~13%), W (~3%), Fe (~3%), Co (~2.5%), C (~0.005%).  

    Higher chromium (Cr) and lower molybdenum (Mo) than C-276.  

    Lower iron (Fe) and carbon (C).

2. Corrosion Resistance

   Oxidizing Environments (e.g., HNO₃, FeCl₃, bleach):

   C-22 excels due to its higher chromium content (22% vs. 15.5%). Chromium forms a protective oxide layer.  

   Example: Better resistance to nitric acid, hypochlorite, and oxidizing salts.

   Reducing Environments (e.g., HCl, H₂SO₄):

   C-276 has a slight edge in pure reducing acids due to higher Mo + W content (19.5% vs. 16% in C-22).  

   Example: Slightly better in hot, concentrated hydrochloric acid.

   Localized Corrosion (Pitting/Crevice):

  Both are excellent, but C-22 generally performs better in chloride-rich environments due to optimized Cr/Mo/W balance.  

  Example: Higher critical pitting temperature (CPT) in seawater-like conditions.

  Mixed Acids & Complex Media:

  C-22 is superior in environments with both oxidizing and reducing agents (e.g., waste treatment, FGD systems) due to balanced composition.

3. Thermal Stability

C-22 is more resistant to precipitation of harmful intermetallic phases (e.g., μ-phase, σ-phase) during welding or high-temp exposure.  

C-276 is more prone to carbide precipitation in heat-affected zones (HAZ), requiring post-weld heat treatment in severe services.

4. Fabrication & Welding

Both are weldable via common methods (TIG, MIG).  

C-22 is easier to weld due to better thermal stability (less HAZ sensitization).  

C-276 may need solution annealing after welding for critical applications.

5. Applications

      C-276 Preferred For:

    - Chemical processing (reactors, pipes in HCl/H₂SO₄).  

    - Pollution control (scrubbers).  

    - Pulp/paper industry (bleach plants).  

    - Use where reducing conditions dominate.

      C-22 Preferred For:

    - Waste treatment (harsh, mixed-chemistry environments).  

    - Flue gas desulfurization (FGD).  

    - Pharmaceutical industry (aggressive solvents).  

    - Seawater applications (superior pitting resistance).  

    - Use where oxidizing conditions or mixed acids exist.

6. Cost

    C-22 is typically more expensive due to higher nickel/chromium content and superior performance in complex media.

Quick Comparison Table

 Key Takeaway:

Choose C-276 for applications dominated by  reducing acids (HCl, H₂SO₄) . Choose  C-22  for harsher, mixed-acid or oxidizing environments  (e.g., waste treatment, FGD) where superior pitting resistance and versatility are critical. Always validate with corrosion testing for your specific conditions!