Effect of alloying content on microstructure and mechanical properties of Fe–Mn–Al–C low-density steels

Abstract

A series of low-density steels with alloying contents of C from 0.6 to 1.5%, Mn from 20 to 35%, and Al from 6.0 to 12.0% were fabricated in the laboratory. The microstructure, density and mechanical properties of the resulting steels were examined to explore the effects of varying alloy content. The results reveal a significant influence of alloy content on the microstructure of the low-density steels after solution processing in terms of ferrite phase fraction, grain size, and κ-carbide size. It was found that the dependence of alloy density on the C, Mn, and Al content can be formulated ρ = 8.1–0.102C-0.10Al-0.01Mn g/cm3 (with the alloy content given as mass%). Both the yield strength and the work hardening rate varied significantly with alloying content, where the yield strength decreased with increasing Mn content, and increased with increasing Al and C content. The impact toughness of the low-density steels was found also to be strongly affected by the alloying content, showing Charpy impact toughness lower than 10 J for C content above 1.2%, for Mn content below 25%, and for Al content above 10%. The effects of alloy content on the mechanical properties are attributed to differences in the precipitation and coarsening of κ-carbides during the solution treatment process.