Study of metal dusting of Fe-Cr and Fe-Ni-Cr alloys under cyclic conditions

摘要

Model Fe-Cr and Fe-Ni-Cr alloys were studied to examine the effect of M{sub}3C formation on metal dusting. The alloys were exposed to a 68%CO-26%H{sub}2-6%H{sub}2O gas mixture at 680°C (a{sub}c =2.9) under thermal cycling conditions. Equilibrium calculations predicted the formation of M{sub}3C at the surface of Fe-25Cr, but not Fe-60Cr. Fe-25Cr with 2.5, 5, 10, and 25% nickel additions were reacted to study the role of nickel in destabilizing M{sub}3C. Metal dusting was observed on all alloys except Fe-60Cr. For Fe-25Cr, Fe-2SCr-2.5Ni, and Fe-25Cr-5Ni, the carburisation and dusting process was localized, and its incidence decreased in Fe-25Cr-2.5Ni, consistent with destabilization of M{sub}3C precipitation. However, Fe-25Cr-10Ni and Fe-25Cr-25Ni both underwent extensive dusting in the absence of protective Cr{sub}2O{sub}3 formation. Carbon deposited as filaments, which contained particles at their tips. These were exclusively Fe{sub}3C on the low nickel alloys, but a mixture of austenite and (Fe,Ni){sub}3C on Fe-25Cr-10Ni and Fe-25Cr-25Ni.