## 3 Results
### Structural Characterization of the Atomized Powders  
It is well known that nitrogen has limited solubility in iron-based alloys, and the saturation limit depends on the temperature of the melt, as well as the partial pressure of nitrogen above the melt. According to Sievert's law, the amount of nitrogen dissolved in the melt is directly proportional to the square root of pressure [PERSON] et al. (2018). It is important to remember that the ejection pressure is the pressure at which the melt is held for 5 min in the crucible before the effective atomization. Figure 6 shows the Rietveld refined XRD diffractograms of Fe-N powders of the atomized powders prepared at an ejection temperature of 1588 \({}^{\circ}\)C, an atomization pressure of 20 bar, an ejection nozzle diameter of 100 \(\upmu\)m, and different ejection pressures (between 1 and 3 bar). The reliability factors of the Rietveld refinement and the percentage concentration of the phases resulting from the XRD analysis are listed in Table 1.  
Figure 5: SEM images of gas-atomized powders at different atomization pressures. P\({}_{\text{at}}\) = 10 bar (**a**), P\({}_{\text{at}}\) = 15 bar (**b**), and P\({}_{\text{at}}\) = 20 bar (**c**). It can be observed that the reliability factors of the Rietveld refinement, such as the goodness of fit (\(\chi^{2}\)) and the residual factor of the weighted profile (Rwp), have values <2 and <15%, respectively, indicating a good agreement of refinement. The structures of the powders consist of a mixture of \(\alpha\)-Fe, \(\gamma\)-F\({}_{4}\)N, \(\alpha^{\prime}\)-Fe\({}_{8}\)N, and \(\alpha^{\prime\prime}\)-Fe\({}_{16}\)N\({}_{2}\) crystalline phases. In order to explain the formation of these phases, we will refer to the Fe-N phase diagram [43]. According to the phase diagram, the formation of the austenite \(\gamma\)-phase optimally occurs with the combination of nitrogen potential and temperatures above 592 \({}^{\circ}\)C. The austenite \(\gamma\)-phase is a face-centered cubic (fcc) arrangement of Fe atoms, with N randomly occupying up to one in ten of the octahedral interstices [44]. When the \(\gamma\)-phase is quenched (what happens to the melt droplets immediately after formation), a martensitic transformation takes place: the Fe atom arrangement changes from a fcc arrangement to a body-centered cubic (bcc) arrangement [44,45]. Due to the rapid cooling of the \(\gamma\)-phase, part of the nitrogen atoms that do not have enough energy cannot diffuse to the desired position, remaining stuck in the previous positions, so a transformation without diffusion takes place, and the \(\alpha^{\prime}\)-Fe\({}_{8}\)N phase is formed. The \(\alpha^{\prime\prime}\)-Fe\({}_{16}\)N\({}_{2}\) has a structure that is very similar to that of \(\alpha^{\prime}\)-Fe\({}_{8}\)N, except for the arrangement of nitrogen atoms: in the \(\alpha^{\prime}\)-Fe\({}_{8}\)N phase, the N \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**P\({}_{\text{ej}}\) (Bar)**} & \multirow{2}{*}{\(\chi^{2}\)} & \multirow{2}{*}{**Rwp (\%)**} & \multicolumn{4}{c}{**Phase Volume Fraction (\%)**} \\ \cline{5-8}  & & & \(\alpha\)**-Fe** & \(\gamma\)**-F\({}_{4}\)N** & \(\alpha^{\prime}\)**-Fe\({}_{8}\)N** & \(\alpha^{\prime\prime}\)**-Fe\({}_{16}\)N\({}_{2}\)** \\ \hline
1 & 1.45 & 12.53 & 74.5 & - & 11.2 & 14.3 \\ \hline
2 & 1.67 & 13.24 & 55 & 4.3 & 18.6 & 22.1 \\ \hline
3 & 1.32 & 11.81 & 40.5 & 12.4 & 20.3 & 26.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The reliability factors of the Rietveld refinement and the evolution of the phase composition vs. ejection pressure of the atomized Fe-N powders. Figure 6: The Rietveld refinement results of the Fe-N powders atomized at different ejection pressures—P\({}_{\text{ej}}\) = 1 bar (**a**), P\({}_{\text{ej}}\) = 2 bar (**b**), and P\({}_{\text{ej}}\) = 3 bar (**c**). The experimentally observed profile (black color), calculated profile (red color), the difference between the calculated and experimental data (blue color), and the contribution of specific phases are shown.