Resistance of 9-20%Cr-steels against metal dusting

The metal dusting resistance of various 21/4Cr to 20%Cr steels has been tested in flowing CO-H-2-H2O atmospheres at 525, 560, 600 and 650 degrees C. For the 21/4Cr-steel immediately a constant rate of metal wastage is reached, for the high alloy steels the approach to this rate where all surface area is attacked, is more or less retarded by an oxide layer. The formation of a protective Cr-rich oxide layer is favoured by a high Cr-content of the steels, by the ferritic structure, by a fine-grained microstructure, by surface working and by high temperatures - these factors hinder or suppress metal dusting, whereas low Cr-concentration, austenitic structure, coarse-grained microstructure, removal of surface deformation by etching and a critical temperature of less than or equal to 600 degrees C accelerate and enhance metal dusting.