Nano-precipitation behavior and mechanical properties of Ti-containing Fe–12Mn–9Al–3Cr-1.4C medium-Mn lightweight steel

Abstract

The role of Ti in lightweight steel has been widely concerned due to its influence on the precipitation of nano-particle and its inherent low density. In this work, the nano-precipitation behavior and mechanical properties of Ti-containing Fe–12Mn–9Al–3Cr-1.4C-xTi (wt.%, x = 0.02/0.04) medium-Mn lightweight steels were systematically investigated. It was found that the increase of 0.02 wt% Ti content had little influence on the two-phase structure of ferrite and austenite. TEM characterization revealed that Ti could suppress the precipitation and growth of κ-carbide in austenite while promoting the precipitation of TiC particle. Based on thermodynamics and first-principles calculations, the suppression of κ-carbide precipitation by the Ti element resulted from the increased formation energy of κ-carbide and the decreased diffusion coefficient of C in austenite. The reduction of κ-carbide decreased the precipitation strengthening in lightweight steels. However, the precipitation of TiC particle not only resulted in additional strength, but also refined the austenite grain and introduced a large number of dislocations, improving the grain boundary strengthening and dislocation strengthening. For the aged lightweight steels at 450–550 °C for 3 h, the increase of 0.02 wt% Ti content mainly affected the precipitation strengthening of κ-carbide and dislocation strengthening. Especially, when the ageing temperature exceeded 500 °C, the precipitation strengthening of κ-carbides became the primary factor contributing to the reinforcement of lightweight steels.