## 4 Discussion
These oscillations were not seen at 5 s\({}^{-1}\); rather, a steady-state-flow stress was dominant. These trends suggest the occurrence of DRX and dynamic recovery during deformation of the alloys at these respective strain rates. Previous studies [31; 32] on low-density steels have shown that DRX and dynamic recovery are some of the common softening mechanisms in hot-worked low-density steels, and their occurrence depends on certain combinations of strain rate and temperatures. To identify the deformation conditions that favor DRX and dynamic recovery during hot working of the two alloys, the microstructural features in the as-cast and deformed samples were compared. The as-cast microstructure of the duplex Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C low-density stainless steel contained predominantly dendritic ferrite and austenite, while the austenitic-based low-density steel had carbides with dendritic configuration. The dendritic ferrite and austenite evolved to elongated and globular austenite in the duplex low-density steel at temperatures below 1000 \({}^{\circ}\)C regardless of the strain rates. The globular and elongated ferrite phase appeared as islands within the austenitic matrix. However, at 1000 \({}^{\circ}\)C, the strain rate influenced the dendritic microstructure. For the duplex low-density steel, hot working at 1000 \({}^{\circ}\)C and 5 s\({}^{-1}\) resulted in elongated and globular ferrite such as those deformed at lower temperatures. The globular ferrite confirmed that one of the softening mechanisms of the alloy is dynamic globularization. However, when higher-magnification SEM images were taken in the austenitic region (Figure 12), the presence of equiaxed austenite grains confirmed the occurrence of DRX as an additional softening mechanism. In contrast, hot-worked duplex low-density steel showed no ferrite phase, and there was no evidence of dynamically recrystallized grains at 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\). It can be concluded that both DRX of the austenitic phase and dynamic globularization of the ferrite phase contributed to the softening of the duplex low-density stainless steel when hot-worked at 800 \({}^{\circ}\)C at 0.1 s\({}^{-1}\), 800\({}^{\circ}\)C at 5 s\({}^{-1}\), 900 \({}^{\circ}\)C at 0.1 s\({}^{-1}\), 900 \({}^{\circ}\)C at 5 s\({}^{-1}\), and 1000 \({}^{\circ}\)C at 5 s\({}^{-1}\), while the dominant softening mechanism at 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\) was dynamic recovery. Higher deformation temperatures and low strain rates allow for thermal softening with enough time for atom diffusion and grain boundary migration, favoring dynamic recovery [26]. For the austenitic Fe-21.3 Mn-7.6 Al-4.3 Cr-1C low-density stainless steel, the dendritic carbide in the as-cast condition was redistributed within and around the austenite grains at deformation temperatures below 1000 \({}^{\circ}\)C and strain rates of 0.1 and 5 s\({}^{-1}\). More elongated austenite grains were serrated and a few austenite globules were visible. This confirms dynamic recovery as the dominant softening mechanism despite some occurrence of dynamic globularization. The hot-worked austenitic low-density steel showed a different response at 1000 \({}^{\circ}\)C and different strain rates. The dendritic structure remained at 1000 \({}^{\circ}\)C at 5 s\({}^{-1}\), while at 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\), the carbides were redistributed within and around the austenite grain as observed when deforming at lower deformation temperatures. It can be concluded that hot-working low-density steel at 1000 \({}^{\circ}\)C at 5 s\({}^{-1}\) was ineffective in breaking down as-cast dendritic carbides in the alloy. Due to macro- and micro-segregation arising from significant alloying elements, different carbides may form in low-density steels [4]; however, XRD only confirmed the M\({}_{7}\)C\({}_{3}\) carbide type. Even M\({}_{23}\)C\({}_{6}\) predicted by Thermo-Calc was not confirmed experimentally.