309 is an austenitic heat resistant alloy with useful oxidation resistance to 2000°F under constant temperature conditions. When frequent heating and cooling is involved the alloy is resistant to about 1850°F. 309 is particularly suited for oxidizing environments involving constant temperature or mild cycling with slow rates of heating and cooling. Because of its relatively high rate of thermal expansion the alloy is not suggested for applications involving severe thermal cycling, such as liquid quenching.