## 3 Results
### Microstructural Evolution
#### 3.3.2 Scanning Electron Microscope Images  
SEM images of deformed Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C and Fe-21.3 Mn-7.6 Al-4.3 Cr-1C low-density steels are presented in Figures 10 and 11, respectively. The SEM images were taken in either back-scattered electron or secondary electron imaging mode at 500\(\times\) magnification. The elongated and globular ferrite phase that was mentioned in Section 3.3.1 can be observed in the Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C austenitic-based duplex low-density steel under all deformation conditions (Figure 10), except at 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\) (Figure 10e) where the ferrite phase dissolved into the austenite and carbides seen at the austenite boundaries. Dendritic configurations that were dominant in the as-cast condition were not seen in Figure 11. However, for the austenitic Fe-21.3 Mn-7.6 Al-4.3 Cr-1C low-density steel (Figure 11), dendritic features were seen in samples deformed at 1000 \({}^{\circ}\)C at 5 s\({}^{-1}\) (Figure 11e). At 800 \({}^{\circ}\)C at 0.1 s\({}^{-1}\), 800 \({}^{\circ}\)C at 5 s\({}^{-1}\), 900 \({}^{\circ}\)C at 5 s\({}^{-1}\), and 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\) (Figure 11a,b,d,e), the carbides were distributed within the matrix and around the austenite boundaries. Only at 900 \({}^{\circ}\)C at 0.1 s\({}^{-1}\) (Figure 11c) did the carbides form a rounded or petal-like feature within the matrix. These features were evenly distributed within the austenite matrix.  
Figure 12 shows selected SEM images of deformed Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C and Fe-21.3 Mn-7.6 Al-4.3 Cr-1C low-density stainless steels taken at higher magnification. Apart from the elongated and globular ferrite phase, equiaxed grains were visible in the austenitic region of the duplex low-density Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C stainless steel (Figure 12a,b). These equiaxed grains are signatures of DRX [25; 26]. Furthermore, carbide particles were seen within the equiaxed grains. This suggests that the duplex low-density steel consisted of ferrite and austenite + carbide phases. However, this was not the case at 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\), where the phase constituent was predominantly an austenite matrix with embedded carbides around the austenite grains (Figure 12c). For the austenitic Fe-21.3 Mn-7.6 Al-4.3 Cr-1C low-density steel (Figure 12d,e), the carbides were seen within and around the austenite boundaries. At 1000 \({}^{\circ}\)C at 5 s\({}^{-1}\) (Figure 12f), most of the carbides maintained the dendritic configuration, but at 900 \({}^{\circ}\)C at 0.1 s\({}^{-1}\) (Figure 12e), the carbides had a rounded morphology, suggesting that there was some degree of dynamic globalization. Unlike in  
the duplex low-density steel, there was no evidence of an equiaxed austenite grain in this alloy and, as such, dynamic recovery was the dominant softening mechanism under the deformation conditions.  
Figure 11: Scanning electron microscope images of deformed Fe-21.3 Mn-7.6 Al-4.3 Cr-1C under different deformation conditions: **(a)** 800 \({}^{\circ}\)C at 0.1 s\({}^{-1}\); **(b)** 800 \({}^{\circ}\)C at 5 s\({}^{-1}\); **(c)** 900 \({}^{\circ}\)C at 0.1 s\({}^{-1}\); **(d)** 900 \({}^{\circ}\)C at 5 s\({}^{-1}\); **(e)** 1000 \({}^{\circ}\)C at 0.1 s\({}^{-1}\); **(f)** 1000 \({}^{\circ}\)C at 5 s\({}^{-1}\).