Type 321 contains a titanium addition of at least five times the carbon content to overcome the sensitizing tendency during welding. Its corrosion resistance is similar to Type 304 but 321 performs better in the 800°-1650°F sensitization range. In Type 321, the oxide or carbonitride of titanium may develop minute black or dark gray inclusions. When the metal is ground or buffed these inclusions may appear and destroy surface appearance, although it will not damage the utility or workability of the metal. Resistance to abrasion is favorable.
Uses include aircraft engine components, chemical kilns, exhaust systems and stack liners, flash boilers and welded equipment.