Effect of aging treatment on microstructure and intrinsic mechanical behavior of Fe-31.4Mn-11.4Al-0.89C lightweight steel

Abstract

The microstructure and the intrinsic mechanical behavior of an austenite-based lightweight steel containing 11.4 wt.% Al under aging heat treatment were investigated with respect to β-Mn precipitation. The solution-treated lightweight steel samples were aged at 550 °C for various periods of time. The β-Mn phase nucleated at both ferrite/austenite phase boundaries and austenite/austenite grain boundaries after aging for 300 min, and grew extensively into the austenite matrix with lath-type morphology by further aging treatment. Lattice expansion of austenite and κ-carbide after β-Mn precipitation was observed by X-ray diffractometry (XRD) peak shift. This result suggested that the β-Mn phase expelled carbon to the austenite matrix during formation of β-Mn, which increased the lattice parameter of the austenite and κ-carbide. The Vickers hardness increased dramatically after an aging time of 1000 min. The singular aging behavior also proceeded from precipitation of the β-Mn phase. The intrinsic mechanical property of austenite phase, which was obtained by nanoindentation, was correlated with the increase and inhomogeneous distribution of carbon in the austenite matrix.