## 3 Results and Discussion
### SI Characteristics
#### 3.2.3 Microhardness and Phase Analysis Results  
The surface microhardness values obtained from different DB processes are shown in Figure 7a. All the DB processes significantly increase the surface microhardness, with the maximum nominal value achieved under flood lubrication (specimen F). The lowest nominal surface microhardness value was obtained for sample N (dry DB with nitrogen cooling). Notably, all four nominal values fall within a narrow range from 440 (specimen N) to 459 HV (specimen F).  
The microhardness distributions versus depth from the surface obtained in different DB configurations are plotted in Figure 7b. The measurements were performed on polished cross-sections. The highest microhardness at depth was obtained when DB was performed either under flood lubrication (specimen F) or under dry conditions without  
Figure 6: Effects of different processes on roughness parameter Ra.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Specimen** & \(\mathbf{R_{a}}\) & \(\mathbf{R_{q}}\) & \(\mathbf{R_{p}}\) & \(\mathbf{R_{v}}\) & \(\mathbf{R_{ku}}\) & \(\mathbf{R_{k}}\) & \(\mathbf{R_{pk}}\) & \(\mathbf{R_{vk}}\) \\  & \(\mathbf{\mu m}\) & \(\mathbf{\mu m}\) & \(\mathbf{\mu m}\) & \(\mathbf{\mu m}\) & \(\mathbf{\mu m}\) & \(\mathbf{\mu m}\) & \(\mathbf{\mu m}\) \\ \hline F & 0.041 & 0.054 & 0.15 & 0.255 & \(-\)0.329 & 6.527 & 0.134 & 0.058 & 0.066 \\ A & 0.047 & 0.064 & 0.197 & 0.293 & \(-\)0.559 & 7.542 & 0.146 & 0.064 & 0.117 \\ N & 0.049 & 0.062 & 0.172 & 0.241 & \(-\)0.255 & 4.946 & 0.156 & 0.069 & 0.081 \\ D & 0.048 & 0.066 & 0.164 & 0.406 & \(-\)1.29 & 11.032 & 0.149 & 0.065 & 0.115 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of 2D roughness parameters obtained via DB under different conditions.  
Figure 7: Microhardness obtained via turning and different DB processes: (**a**) surface microhardness; (**b**) microhardness distribution along the depth from the surface.  
cooling (specimen D). Under these two conditions, the highest surface microhardness values were also obtained (see Figure 7a). Due to the absence of lubrication and cooling the highest temperature in the diamond-burnished surface contact zone can assumed to occur in sample D, followed sequentially by samples F, A, and N, as the LCL temperature is significantly higher than that of the air (\(-19\)\({}^{\circ}\)C) and nitrogen (\(-31\)\({}^{\circ}\)C) used for cooling in this process. Given the selected burnishing device with elastic normal contact used in this experiment and also the temperature in the contact area, the same sequence can also be assumed for the depth of penetration, i.e., greatest in sample D, followed by samples F, A, and N, due to the so-called softening effect. Therefore, the greater equivalent plastic deformation, which is a direct consequence of increasing temperature and penetration depth, explains the greater microhardness values recorded in samples D and F.  
Figure 8 shows the phase analysis outcomes. The presence of strain-induced \(\alpha^{\prime}\)-martensite was not observed in any of the samples. From the X-ray \(\gamma\)-Fe (220) line profile, the greatest broadening is observed in sample A, followed by samples D, N, and F.