On elevated temperature stability of high carbon Fe-Al alloys

Ingots of Fe-Al alloys containing 1.1 wt.% C each and 8.5, 16 and 20 wt% Al, respectively were prepared by a combination of air induction melting and electroslag remelting. These ESR ingot samples were placed in a hearth furnace at 1273 K for 24 h and then furnace cooled to room temperature. The ESR ingots exhibited a significant amount of precipitation of Fe3AlC0.5 phase. Fe-16 wt% Al-1.1wt% C and Fe-20 wt% Al-1.1 wt% C ESR ingots exhibited coarse columnar grains along the ingot axis. No significant change in microstructure was observed in these ingots after heat treatment. Dendritic solidification was observed in ESR ingots of the Fe-8.5 wt% Al-1.1 wt% C alloy with copious precipitation of fine Fe3AlC0.5 phase in the interdendritic region. After heat treatment some coarsening of the interdendritic precipitates and precipitation within the dendrites was observed leading to a more homogeneous microstructure. Fe-8.5 wt% Al-1.1 wt% C alloy samples were badly oxidized after the heat treatment. This was accompanied by significant decarburization in regions near the sample surfaces leading to a localised loss in hardness. It would appear from the present work that high carbon Fe-Al alloys containing 16 wt% Al or more are resistant to oxidation and decarburization. (C) 1999 Elsevier Science S.A. All rights reserved.