Microstructural investigation of the KCl-induced corrosion of the austenitic alloy Sanicro 28 (35Fe27Cr31Ni) at 600°C

AbstractHigh-temperature corrosion of stainless steel is important, particularly in bio-fuelled boiler applications. The flue gas is rich in water vapour and alkali salts, which accelerate the corrosion of the boiler material. The focus of this paper is on the breakdown of the protective oxide scale formed on Sanicro 28, which is a highly alloyed austenitic stainless steel (35Fe27Cr31Ni), in the presence of KCl(s). Laboratory exposures were carried out at 600°C in 5% O2+40% H2O for 1, 24 and 168 hours. The samples were coated with 0.10 mg/cm2 KCl prior to exposure and uncoated samples were exposed for reference. The aim was to link the observed mass gains and microstructure to oxidation mechanisms. The oxidized samples were analyzed by XRD, SEM/EDX, FIB and TEM/EDX. The exposures results in a very complex corrosion chemistry, including, e.g. the formation of potassium chromate and the rapid transport of iron species on the surface resulting in accumulation of oxide on the former KCl particles. However, th...