Effect of Cu and solid solution temperature on microstructure and mechanical properties of Fe-Mn-Al-C low-density steels

Abstract

Relatively low yield strength (YS) level restricts austenitic low-density steels to some applications requiring small or no deformation than impact energy absorption. Therefore, to enhance the YS of this type of steel, this research investigates variations of microstructure and mechanical properties of two austenitic low-density steels (Fe-25Mn-10Al-1.1C-(0,0.25) Cu) with solid solution temperatures (TS, 850 °C–1050 °C). The results show that TS and Cu have significant impacts on the microstructure characteristics and mechanical properties of the two tested steels. At low TS of 850 °C, an increase of 170 MPa in YS compared with that of Cu-free steel was obtained in Cu-containing steel, which is mainly attributed to much finer grain size, more fine twins, and high dislocation density of the latter. An increase in TS caused the κ-carbides in the two steels to dissolve completely, but the austenite content in Cu-containing steel remained largely stable for the addition of Cu. As a result, the strength of the two tested steels decreased while the ductility increased, and both the strength and yield-to-tensile strength ratio of Cu-containing steel are remarkably higher than those of Cu-free steel. It is concluded that the Cu-containing steel exhibits a superior combination of YS and ductility together with a ∼17% reduction in density compared to pure iron. This study provides a promising way to further enhance the YS of austenitic low-density steels through the addition of a small amount of Cu and tailoring TS.