Production of aluminium coated ferritic stainless steel by co-rolling and annealing

Ferritic stainless steel enriched with aluminium (>7%) represents the best material for the productionof substrates in catalytic converters because of its good corrosion resistance at high temperature(700-1000 °C). Enriching steel surface with aluminium avoids brittleness problems relatedto the traditional metallurgical process and, due to the high superficial aluminium concentration,enhances the Al2O3 scale formation in the early stages of the oxidation process. Among severaltechniques, the co-rolling process appears to be a promising technology for enriching ferritic stainlesssteel surface with aluminium. That versatile technology produces, at room temperature,a very adherent aluminium coating without affecting the structural and mechanical propertiesof the substrate. In this work annealed AISI 430 ferritic stainless steel has been cold rolled together withaluminium foil to form an Al-steel-Al sandwich. The aim of the work was to enhance the oxidationresistance through a controlled oxidation of a thin aluminium layer. The diffusion bonding obtained via anannealing treatment was evaluated studying the concentration profiles as a function of processtemperature. Intermetallics and /or solid solutions formed were characterized by X-Ray Diffraction (XRD)

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

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

High temperature scaling behaviour of ferritic stainless steels alloyed with yttrium

The thermal oxidation resistance of a 25 Cr-1.5 Al steel has been tested after the addition of various quantities of yttrium. The oxides formed at high temperature have been examined with the ESCA technique, particularly in the first stages of formation. The authors suggest that yttrium operates in various ways, depending on the composition of the basic alloy, the quantity of yttrium added, the surface and bulk pre-treatments and the work temperature