Abstract
Metal dusting corrosion is a catastrophic degradation phenomenon that initiates on metallic surfaces of chemical process equipment at elevated temperature and under carburizing atmospheres. It proceeds by a gradual breakdown of the metallic matrix into fine particles. The work is performed to correlate the surface and bulk composition and structure of application relevant alloys to the initial carbon formation and the progress towards metal dusting. UNS N08800 alloy coupons were prepared, polished and oxidized in diluted steam at 540 °C. Formation of carbon on the surface of the pre-oxidized samples was investigated by exposure to reducing, highly carburizing atmosphere (CO in Ar) at 20 bar and varying temperature (550- 750 °C). The resulting surfaces were examined by scanning electron microscopy (SEM), Raman spectroscopy, depth profile analysis by Auger electron spectroscopy (AES) under ion-sputtering. Given that very high carbon activity ac >> 1, the conditions represent an accelerated regime relative to the industrial environment, and hence significant amounts of carbon are formed. The amount and the type of carbon are found to vary strongly with the exposure temperature and the interaction with the metallic matrix. At the highest temperature, also the alloy undergoes considerable change in the elemental distribution as a function of depth.
