Microstructure and mechanical properties of a Fe–28Mn–9Al-1.2C-(0, 3, 6, 9)Cr austenitic low-density steel

Abstract

In this work, the effects of Cr addition on microstructure, carbide formation and mechanical properties of Fe–28Mn–9Al-1.2C-xCr (x = 0, 3, 6, 9) strips fabricated under a near-rapid solidification condition are investigated. It is found that Cr addition makes as-cast strips present a nonlinear evolution on yield strength, i.e. firstly reduces and then increases beyond that of Cr-free strip, and the total elongation of as-cast strips clearly decreases. The evolution is related to precipitation reduction of κ-carbides, increased dislocation density, and formation of Cr23C6 instead of κ-carbides in 9Cr strip with Cr addition. Annealing at 550 °C for 5 h enhances yield strengths of all strips due to more carbide precipitations. An observed unusual phenomenon is that after annealing, Cr-free strip shows lower total elongation than the as-cast strip, while all Cr-containing strips show higher total elongation due to reduction of dislocations. Formation of Cr23C6 carbides at austenite grain boundaries is a reason for the lowest ductility of as-cast and annealed strips containing 9 wt% Cr. Analysis in 0Cr and 6Cr strips indicates that both slip bands and dislocations contribute to ductility of this austenitic low-density steel.