Effect of carbon addition on structure and mechanical properties of electroslag remelted Fe-20 wt% Al alloy

A high carbon Fe-20 wt.% Al-1.1 wt.% C alloy based on Fe,AI was melted under a flux cover by air induction melting (AIM). The AIM ingots were sound and free from gas porosity. Electroslag remelting of AIM ingots leads to alloys with good machinability and an attractive combination of mechanical properties. This is in contrast to the poor machinability and inferior strength reported for alloys with low ( < 0.01 wt.%) carbon contents. The presence of a large (1.1 wt.%) amount of carbon resulted in significant strengthening due to extensive precipitation of Fe3AlC0.5 phase and to the formation of a duplex Fe3Al-Fe3AlC0.5 structure. The role of carbon in Fe-Al alloys with different Al-contents will be discussed. For Fe-Al alloys with low ( < 14 wt.%) aluminium content, carbon addition results in an increase in strength which, however, is also accompanied by a loss in ductility. Alloys with aluminium contents > 14 wt.% are susceptible to environmental embrittlement. The addition of carbon to these alloys may improve resistance to this embrittlement. It also leads to a significant increase in strength. Carbon addition has been shown to be beneficial for Fe-Al alloys containing up to 20 wt.% aluminium. It is argued that carbon is not an attractive alloying addition to alloys containing > 22 wt.% (36.5 at.%) Al as it is likely to precipitate out as a soft graphite phase. (C) 1998 Elsevier Science S.A. All rights reserved.