321 vs 321H stainless steel

Q1: What is the primary difference in chemical composition between 321 and 321H stainless steel?

A: The key difference is carbon content.

321 has a standard carbon range of 0.04–0.08%, stabilized with titanium (Ti = 5×C – 0.70%).

321H is a high-carbon variant, with a carbon range of 0.04–0.10%, also titanium-stabilized to prevent sensitization.

Q2: How do their high-temperature strength properties compare?

A: 321H outperforms 321 in high-temperature applications.

321H's higher carbon content enhances creep and rupture strength at temperatures above 500°C, making it suitable for long-term service under heat and load.

321 has good oxidation resistance but lower high-temperature structural stability than 321H.

Q3: Do 321 and 321H differ in intergranular corrosion resistance?

A: Both grades have excellent intergranular corrosion resistance, via the same mechanism.

Titanium in both grades binds with carbon to form titanium carbides, preventing chromium carbide precipitation at grain boundaries during welding or heating.

No significant difference in this performance; both avoid sensitization without post-weld heat treatment.

Q4: Which grade is more suitable for pressure vessel and boiler applications?

A: 321H is the preferred choice for these applications.

Its enhanced high-temperature creep strength meets the requirements of ASME and other pressure vessel standards for elevated-temperature service.

321 is better suited for general corrosion-resistant applications at moderate temperatures (below 500°C).

Q5: How to select between 321 and 321H for specific industrial uses?

A: Select based on operating temperature and load conditions:

Choose 321 for chemical processing equipment, exhaust systems, and cryogenic components (prioritizing corrosion resistance at moderate temperatures).

Choose 321H for steam turbines, heat exchanger tubes, and high-temperature pressure vessels (prioritizing long-term strength under heat and pressure).