Tensile deformation behavior and work hardening mechanism of Fe-28Mn-9Al-0.4C and Fe-28Mn-9Al-1C alloys

Tensile properties and deformation microstructures of duplex Fe-28Mn-9Al-0.4C and austenitic Fe-28Mn-9Al-1C alloys have been investigated under various temperatures and strain rates. In a temperature range of 573-873 K, both alloys exhibit serrated flow, negative strain rate sensitivity and high work hardening, which are typical manifestations of the dynamic strain aging. The characteristics of the serrations as well as the dependence of the critical strain for the onset serrated flow on strain rate and temperature are examined. Five different types of serrations (A, B, C, D, E) are identified in the flow curves. In addition, anomalous temperature and strain rate dependence of the critical strain is observed and is attributed to the precipitation of the κ-phase. The deformation mode shifts from extensive strain-induced twinning at room temperature to massive slipping at 873 K and to grain boundary sliding at 1073 K. Based on the above results and other studies reported in literature, a schematic diagram showing possible work hardening mechanisms for the Fe-Mn-Al-C alloys is proposed.