| Abstract: | Metal dusting of Fe-Ni-Cr alloys has been observed in industrial processes in strongly carburizing atmospheres at temperatures from 450°C to 800°C. At temperatures below 650°C the alloys are generally not able to form dense, well adherent oxide layers in spite of relatively high Cr-contents, therefore, metal dusting can take place. Already a lot of experimental work has been done to elucidate the mechanism and to compare the resistance against metal dusting for high alloy steels 1]. The intention of this study was to obtain additional information concerning the role of alloying elements and the effects of carbide precipitates in austenitic high alloy steels such as Alloy 800. The susceptibility to metal dusting was determined by measuring the metal loss under metal dusting conditions of Fe-20%Cr-32%Ni alloys modified with additions of different carbide formers (W, Mo, Nb) or oxide formers (Si, Al). The samples were exposed at 600°C in a CO-H2-H2O-gas mixture for repeated periods up to 500 – 1500 h. The attack by the oxidizing and carburizing atmosphere leads to the precipitation of internal carbides and metal dusting and more or less to formation of an oxide layer. In comparison to the undoped material, the addition of carbide formers retards the initiation of metal dusting attack. The additions of Si and Al seem to prevent metal dusting under the given laboratory conditions. When carbides are present at the metal surface, they affect the initial oxide growth and have a negative effect on the protectivity of scales. Very striking is the effect of Ce, this rare earth element is generally known to favour Cr-oxide formation and to improve the adherence of the oxide layer 2], but in the case of metal dusting it clearly enhances metal dusting and metal wastage. |
