The effect of water vapor on Cr depletion in advanced recuperator alloys

Durable alloy foils are needed for gas turbine recuperators operating at 650°-700°C. It has been established that water vapor in the exhaust gas causes more rapid consumption of Cr in austenitic stainless steels leading to a reduction in operating lifetime of these thin-walled components. Laboratory testing at 650°-800°C of commercial and model alloys is being used to develop a better understanding of the long-term rate of Cr consumption in these environments. Results are presented for commercial alloys 709, 120 and 625. After 10,000h exposures at 650° and 700°C in humid air, grain boundary Cr depletion was observed near the surface of all these materials. In the Fe-base alloys, 709 and 120. this depletion led to localized Fe-rich nodule formation. This information then can be used to develop low-cost alternatives to currently available candidate materials.