Effect of active elements on the oxidation behavior of a FeCrAl alloy produced by co-rolling and annealing

The choice of a metal alloy for supporting catalytic converter bodies depends on the mechanical, thermal and chemical resistance of the alloy under operative conditions. The demand for providing a more efficient conversion instigated the development of improved substrate technologies. In this paper, a thin foil of FeCrAl alloy was produced by diffusion alloying of aluminum clad ferritic stainless steel containing very small amounts of active elements (Hf, Y, Zr). The effect of the active elements on the oxidation behavior of such an alloy has been evaluated. Isothermal tests carried out In air at 900°C, 1000°C and 1100°C showed kinetics representing a very protective behavior. The oxide scale always appeared very flat and adherent to the substrate. The beneficial effect of active elements on scale protectiveness was apparent also during cyclic oxidation tests carried out in air over the 800-1000°C temperature range. Breakaway oxidation was never observed. Active elements are believed to limit diffusion processes through the scale, and this leads to the formation of a flat and adherent alumina scale that can withstand additional stress due to the thermal expansion mismatch between the oxide and the metal. Copyright © 2008 by ASTM International.