Observing the massive transformation in an Fe–Mn–Al alloy

Abstract

Slabs with a composition of Fe–27.6 wt.% Mn–5.3 wt.% Al–0.11 wt.% C were studied in several heat treatments. They were heated at 1573 K for 30 min in air, and then quenched into cold brine or room temperature water. The austenite phase was observed as it spread through the external area, surrounding the ferrite phase within the internal part of the specimen. According to the measurement in EPMA, there are no differences in the overall concentrations of Fe, Mn and Al between the exterior austenite and the interior ferrite phase. In the glow discharge measurement, there is almost no carbon left in either the austenite or ferrite phase due to significant decarburization during the high temperature heat treatment. After the slabs were heated at high temperatures and then furnace-cooled, almost all the ferrite transformed into austenite, a result viewed by both X-ray and light microscope studies. Judging from the phases existing in the specimens with high-temperature quenching versus those with furnace cooling, we concluded that the stable high-temperature phase at 1573 K is ferrite and the stable phase at low temperature is austenite. These results are quite consistent with the phase diagrams showing the Fe–Mn–Al ternary systems. The fact that there were no changes in the overall Fe–Mn–Al concentrations between the exterior austenite phase and the interior ferrite phase is characteristic of massive transformation. Therefore, the phase transformation for changing ferrite to austenite during high-temperature quenching is massive transformation.