Abstract
In strongly carburizing atmospheres metals and alloys are endangered by 'metal dusting', a disintegration into a dust of graphite and metal particles. Protection against metal dusting is possible by formation of a dense Cr-rich scale, which should be formed rapidly to avoid ingress of carbon from the process gas. At intermediate temperatures the oxide formation can be favoured by a fine grain microstructure and surface working, also alloying additions of Mn, Al and Si should help in the formation of a protective scale. These ways and means for improved protection were tried for stainless steels. Tests on modified austenitic 18Cr-10Ni-steels were conducted at 600 °C in flowing H 2 -24%CO-2%H 2 O mixtures. Metal dusting starts locally and gradually spreads over the steel surface, accordingly the metal wastage increase. This increase is retarded by a fine grain microstructure and surface working (grinding), both―measures which introduce fast-diffusion paths for supply of chromium to the surface. Also enhanced concentrations of Si (> 1.7 % ) and Al (> 2 %) are helpful in the protection by rapid formation of a protective oxide scale.
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