Factors Affecting Corrosion Resistance of Recuperator Alloys

Abstract

As microturbine recuperators are needed to operate at higher temperatures in order to achieve higher engine operating efficiencies, a recurring problem encountered is a severe degradation in environmental resistance of type 347 stainless steel. Above 600°C, stainless steels can experience accelerated attack caused by water vapor, which is often present as a combustion product. Nickel-base alloys are less susceptible to this accelerated attack but their cost is prohibitive. In order to provide a clear, fundamental understanding of alloy composition effects on corrosion resistance of stainless steel components used in recuperators, the oxidation behavior of model alloys is being studied. A composition range of Cr and Ni contents has been identified with better corrosion resistance than type 347 stainless steel. Finer-grained alloys showed improved corrosion resistance compared to coarse-grained alloys with the same composition. It also has been demonstrated that minor alloy additions of Mn and Si are beneficial to corrosion resistance in these environments. This type of information will aid in the development of a corrosion-resistant and cost-effective recuperator material for operation at 650°–700°C.