PHASE-TRANSFORMATION IN AN FE-10.1AL-28.6MN-O.46C ALLOY

The microstructure of an (alpha + gamma) duplex Fe-10.1A1-28.6Mn-0.46C alloy has been investigated by means of optical microscopy and transmission electron microscopy (TEM). In the as-quenched condition, extremely fine D0(3) particles could be observed within the ferrite phase. During the early stage of isothermal aging at 550-degrees-C, the D0(3) particles grew rapidly, especially the D0(3) particles in the vicinity of the alpha/gamma grain boundary. After prolonged aging at 550-degrees-C, coarse K-phase (Fe, Mn)3AlC precipitates began to appear at the regions contiguous to the D0(3) particles, and beta-Mn precipitates occurred on the alpha/gamma and alpha/alpha grain boundaries. Subsequently, the grain boundary beta-Mn precipitates grew into the adjacent austenite grains accompanied by a gamma --> alpha + beta-Mn transition. When the alloy was aged at 650-degrees-C for short times, coarse K-phase precipitates were formed on the alpha/gamma grain boundary. With increasing the aging time, the alpha/gamma grain boundary migrated into the adjacent austenite grain, owing to the heterogeneous precipitation of the Mn-enriched K phase on the grain boundary. However, the alpha/gamma grain boundary migrated into the adjacent ferrite grain, even though coarse K-phase precipitates were also formed on the alpha/gamma grain boundary in the specimen aged at 750-degrees-C.