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Stainless Steel Type 321 & 321H are stabilized austenitic stainless steels, very similar to 304 but with titanium added for better resistance to intergranular corrosion at elevated temperatures. The main difference between 321 and 321H is the carbon content.
Chemical Composition
Element
Type 321 Stainless Steel (wt%)
Type 321H Stainless Steel (wt%)
Carbon (C)
≤ 0.08%
0.04 – 0.10%
Manganese (Mn)
≤ 2.00%
≤ 2.00%
Phosphorus (P)
≤ 0.045%
≤ 0.045%
Sulfur (S)
≤ 0.030%
≤ 0.030%
Silicon (Si)
≤ 0.75%
≤ 0.75%
Chromium (Cr)
17.0 – 19.0%
17.0 – 19.0%
Nickel (Ni)
9.0 – 12.0%
9.0 – 13.0%
Titanium (Ti)
≥ 5 * C content and typically ≤ 0.70%
≥ 5 * C content and typically ≤ 0.70%
Nitrogen (N)
≤ 0.10%
≤ 0.10%
Iron (Fe)
Balance (remainder)
Balance
Key Differences & Characteristics
Stabilization with Titanium
Titanium is added to tie up carbon as titanium carbides, preventing chromium carbide precipitation at grain boundaries. This gives both 321 and 321H good resistance to intergranular corrosion in the 425–870°C (800–1600°F) range, where 304-type steels can become sensitized.
321 vs 321H Comparison
Type 321: Lower carbon content (≤ 0.08%), providing better weldability and slightly better resistance to sensitization.
Type 321H: Higher carbon content (0.04–0.10%), giving higher creep and stress‑rupture strength at elevated temperatures (typically above ~500–600°C), making it preferred for high‑temperature service.
Applications
Type 321: Exhaust manifolds, aircraft exhaust systems, thermal oxidizers, and general high‑temperature piping
Type 321H: Furnace components, high‑temperature heat exchangers, boiler tubes, and petrochemical/refinery service where long-term high‑temperature strength is needed
For design or certification purposes, always check the exact standard (ASTM/EN/JIS) and product form (plate, pipe, forging), as allowable ranges can vary slightly between specifications and manufacturers.
