PHASE-TRANSFORMATIONS IN AN FE-7.8AL-29.5MN-1.5SI-1.05C ALLOY

Phase transformations in an Fe-7.8Al-29.5Mn-1.5Si-1.05C alloy have been investigated by means of optical microscopy and transmission electron microscopy. In the as-quenched condition, a high density of fine (Fe,Mn)3AlC carbides could be observed within the austenite matrix. When the as-quenched alloy was aged at temperatures ranging from 550-degrees-C to 825-degrees-C, a gamma --> coarse (Fe,Mn)3AlC carbide + DO3 reaction occurred by a cellular precipitation on the gamma/gamma grain boundaries and twin boundaries. Both of the observations are quite different from those observed by other workers in Fe-Al-Mn-C alloys. In their studies, it was found that the as-quenched microstructure was austenite phase (gamma), and (Fe,Mn)3AlC carbides could only be observed within the austenite matrix in the aged alloys. In addition, a gamma --> alpha (ferrite) + coarse (Fe,Mn)3AlC carbide reaction or a gamma --> alpha + coarse (Fe,Mn)3AlC carbide + beta-Mn reaction was found to occur on the gamma/gamma grain boundary in the aged Fe-Al-Mn-C alloys.