OCCURRENCE AND PREVENTION OF METAL DUSTING ON STAINLESS STEELS

摘要

Metal dusting is a disintegration of metals and alloys into a dust of graphite and metal particles, occurring after carbon ingress and oversaturation. This corrosion process can be prevented by a dense Cr-rich oxide layer which inhibits the carbon ingress. To obtain such protective scale on Cr-steels at the relatively low temperatures 400 - 600 deg C, critical concerning occurrence of metal dusting, fast diffusion paths must be provided for rapid supply of Cr to the surface upon exposure to the carburizing and oxidizing atmosphere. This is achieved by a fine grain microstructure and/or surface working of the steels: the grain boundaries, sub-boundaries and dislocations act as fast diffusion paths. Studies on the metal dusting behaviour of austenitic stainless steels in a strongly carburizing H_2-CO-H_2O atmosphere at 600 deg C have demonstrated that fine grain size and surface deformation clearly improve the metal dusting resistance of the steels.