Microstructural investigation of the KCI-induced corrosion of the austenitic alloy Sanicro 28 (35Fe27Cr31IMi) at 600 deg C

• Published in: Materials at high temperatures 2009-02, Vol.26 (2), p.113-125
• Main Authors: Proff, C, Jonsson, T, Pettersson, C, Svensson, J-E, Johansson, L-G, Halvarsson, M
• Format: Article
• Language: English
• ISSN: 0960-3409
• DOI: 10.3184/096034009X464339

High-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 deg 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, the consumption of chromium and the presence of chloride on the surface does not result in the breakdown of the protective oxide. The ability of the alloy to withstand this harsh environment is tentatively attributed to the high Cr/Fe ratio.