2009 R&D 100 Winner
AFA: Alumina-Forming Austenitic Stainless Steels, developed by materials researchers at Oak Ridge National Laboratory, Oak Ridge, Tenn., represent a new class of high-temperature alloys that feature an increased upper-temperature oxidation (corrosion) limit that is greater or equal than 50°C to 200°C higher than that of conventional stainless steels. This level of performance approaches that of more expensive nickel-base alloys without abandoning the lower cost, formability, and weldability of conventional stainless steels. The corrosion resistance results from the formation of a protective aluminum oxide surface layer that protects the metal under operation temperatures ranging from 600°C to 900°C. All of the available AFA compositions exhibit a transition from protective alumina layer formation to internal oxidation of aluminum if the oxidation temperature is raised too high. Three distinct grade ranges of AFA alloys have been developed, each representing different balance points of alloy cost, creep strength, and upper-temperature limit for oxidation resistance.
Oak Ridge National Laboratory