Types 309 and 309S are austenitic chromium-nickel stainless steels that provide excellent corrosion resistance and heat resistance plus good strength at room and elevated temperatures. Type 309S is identical to Type 309 except for a lower carbon content that minimizes carbide precipitation and improves weldability. They are essentially nonmagnetic as annealed and become slightly magnetic when cold worked.

Typical uses include furnace parts, heating elements, aircraft and jet engine parts, heat exchangers, carburizingannealing boxes, sulfite liquor handling equipment, kiln liners, boiler baffles, refinery and chemical processing equipment, and auto exhaust parts.