## 3 Results
### Mechanical Properties  
The structure after ECAP significantly increased the strength characteristics of the Fe-Mn-5 Si alloy samples (Figure 3a, Table 2). In this case, the tensile strength doubles to 1419 MPa compared with the state after annealing (696 MPa), and the yield strength up to 1352 MPa, 4 times higher than the yield strength of the samples after annealing (329 MPa).  
The increase in strength after ECAP is accompanied by a decrease in ductility. The relative elongation after deformation decreases by a factor of three from 33% to 10.7%, remaining at an acceptable ECAP level (Figure 3a, Table 2).  
Dynamic indentation tests based on the analysis of the dependence of the load on the indenter on the depth of its indentation into the surface of the samples after ECAP (Figure 3a, Table 2) revealed a decrease in Young's modulus by more than 2.6 times and an increase in elastic recovery by 2.5 times compared with the measured values in the state after annealing (Figure 3b, Table 3). Measurement of Vickers microhardness of ECAP-treated alloy samples showed an increase by more than 2 times compared to the annealed sample (Table 3).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Precision** & **Space Group** & **Phase** & **a, Å** & **Content, wt.\%** & **Strain, \%** & **Dislocation Density \(\rho\), cm\({}^{-2}\)** \\ \hline Annealing at 1100 \({}^{\circ}\)C (12 h) & 225: Fm-3m & \(\gamma\) & 3.604(1) & 100 & 0.04(1) & \(6\times 10^{9}\) \\ \hline ECAP at 400 \({}^{\circ}\)C, 4 passes & 225: Fm-3m & \(\gamma\) & 3.604(1) & 100 & 0.40(1) & \(6\times 10^{11}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of the X-ray line profile analysis of the Fe-Mn-5 Si alloy after various processing methods.  
Figure 3: Stress–strain curve of Fe-Mn-Si alloys after annealing and ECAP (**a**); the loading–unloading indentation curves for the samples (dynamic indentation tests) (**b**) at room temperature.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**\(\lambda\)** & **Alloy and Condition** & **\(\sigma_{\text{{ITS }}^{1}}\), MPa** & **\(\sigma_{\text{{lys }}^{2}}\), MPa** & **\(\varepsilon\)****3, \%** \\ \hline
1. & Fe (for comparison) & 395.00 \(\pm\) 4 & 320.5 \(\pm\) 6.5 & 40.6 \(\pm\) 1.5 \\
2. & Fe-Mn-Si, annealing & 696 \(\pm\) 24 & 329 \(\pm\) 17 & 33 \(\pm\) 0.45 \\
3. & Fe-Mn-Si, ECAP at 400 \({}^{\circ}\)C & 1419 \(\pm\) 14 & 1352 \(\pm\) 6 & 10.7 \(\pm\) 0.3 \\ \hline \hline \end{tabular} \({}^{\dagger}\) ultimate tensile strength; \({}^{2}\) yield strength; \({}^{3}\) total elongation.  
\end{table}
Table 2: Mechanical properties of the Fe-Mn-Si alloys after annealing and ECAP.  
Transmission Electron Microscopy (TEM) Studies of the Fe-Mn Alloys after Equal-Channel Angular Pressing  
The results of mechanical property measurements testify to significant structural changes during ECAP. In samples of the Fe-Mn-5 Si alloy after ECAP, the formation of an ultrafine-grained structure was revealed by transmission electron microscopy (Figure 4).  
In shear bands in the range of 150-650 nm, with an average thickness of 301 \(\pm\) 31 nm, twins of different sizes are formed. A typical image of the twins' microstructure is confirmed by an electron diffraction pattern from a fine structure area with a diameter of 125 nm (Figure 4c,d). Figure 4d shows a dark-field image of thin twins with a thickness of 11 \(\pm\) 1 nm. Inside these twins, nanograins are formed as a result of their interaction with dislocation walls. Thicker twins with increased dislocation density are also observed (Figure 4e,f). The formation of a grain-subgrain structure also occurs when shear bands are  
Figure 4: TEM micrographs of the microstructure of Fe-Mn-5 Si alloy after ECAP: BF images (**a**–**c**,**e**) and DF images with SAED pattern indicating the diffraction spots corresponding to twins (**d**,**f**).  
crossed by thick dislocation bridges and nanotwins (Figure 4b). The dislocation density inside the grains/subgrains according to TEM data exceeds 4 \(\times\) 10\({}^{11}\) cm\({}^{-2}\).