The role of Cr, Al and Mn in the resistance of refractory steels to hot salt corrosion from combustion deposits

Abstract

Molten salts from combustion residues assume differentiated compositions depending on the type of fuel and the environmental variables The choice of resistant materials should be made on the basis of more specific criteria with respect to those adopted in hot air oxidation Three different kinds of steel (a) Fe-Cr-AI-Y, (b) Fe-Mn-Al, (c) Fe-Cr-Ni-Mn were tested in a basic mixture of molten salts (KCl-K₂SO₄-Fe₂O₃) occurring in the furnace of ferrous mineral agglomeration and in an acid one (Na₂SO₄-V₂O₅) typical of combustion systems using liquid hydrocarbons. This proved how chlorides are dangerous, particularly towards chromium-rich scales or matrices. Vanadium pentoxide is dangerous if it is associated with ferrous oxide. Manganese in the alloy helps with protection, particularly in sulphur-bearing atmospheres, also in the presence of chlorides, provided that there is no V₂O₅. Alloying with manganese is preferable in aluminium steels rather than in chromium steels, because of the high diffusivity of the element in Cr₂O₃ scales.