Type 321 is a stabilized austenitic stainless steel similar to Type 304 but with a titanium addition of at least five times the carbon content. This titanium addition reduces or prevents carbide precipitation during welding and in 800 - 1500°F (427 - 816°C) service. It also improves the elevated temperature properties of the alloy.

Type 321 provides excellent resistance to oxidation and corrosion and possesses good creep strength. It is used primarily in applications involving continuous and intermittent service temperatures within the carbide precipitation range of 800 - 1500°F (427 - 816°C).

Applications include annealing covers, high-temperature tempering equipment, diesel and heavy duty automotive exhaust systems, firewalls, stack liners, boiler casings, welded pressure vessels, jet aircraft components, radiant superheaters, bellows and oil refinery equipment.