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 beta-Mn precipitation. The solution-treated lightweight steel samples were aged at 550 degrees C for various periods of time. The beta-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 K-carbide after beta-Mn precipitation was observed by X-ray diffractometry (XRD) peak shift. This result suggested that the beta-Mn phase expelled carbon to the austenite matrix during formation of beta-Mn, which increased the lattice parameter of the austenite and K-carbide. The Vickers hardness increased dramatically after an aging time of 1000 min. The singular aging behavior also proceeded from precipitation of the beta-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. (C) 2015 Elsevier B.V. All rights reserved.