# Metallurgical Alchemy: Synthesizing Steel Microstructure Images Using DCGANs
## 2 Materials and Methods  
### Steel Samples and Dataset  
To conduct the experiments, optical images of steel samples subjected to annealing and quenching heat treatments were used to obtain the microstructures of pearlite, ferrite, and martensite, independently. The steels used for obtaining micrographs were C25E and C45E for the annealing treatment and C45E, 37 Cr4, and 34 CrNiMo6 for the quenched steels. The detailed chemical composition of each is provided in Table 1.  
Following the heat treatments, the samples were prepared using the polishing procedure and chemical etching with Nital. The images were then obtained using an optical microscope at 400\(\times\) and 1000\(\times\) magnifications to distinguish different areas formed by steel microconstituents. The initial image dataset consists of 29 images for typical annealed samples and 40 for typical quenched samples, together a Widmanstatten structure, with a resolution of 2080 \(\times\) 1542 pixels. Figures 1 and 2 shows some samples where the areas of microconstituents generated in each heat treatment can be identified. In Figure 1, the lamellar area corresponds to pearlite and the white area to ferrite. The microstructures are very similar, although some heterogeneity has been included based on the carbon content of the steels (Table 1), as well as the cooling velocity during the treatment. Thus, Figure 1c presents a finer lamellar structure of the perlite due to the higher cooling velocity compared to Figure 1b. If the annealing treatment is carried out starting at a very high temperature, at which the austenite grains are large, the ferrite cannot nucleate at grain boundaries and the structure ferrite-perlite becomes atypical, receiving the name \"Widmanstatten structure\" (Figure 2a). Ferrite and perlite acquire acicular shapes in some way, which could create confusion for novice observers familiar with quenching structures. In any case, despite \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Steel** & **C** & **Si** & **Mn** & **P** & **S** & **Cr** & **Mo** & **Ni** & **Cu** \\ \hline C25E & 0.22–0.29 & 0.10–0.40 & 0.40–0.70 & 0.025 & 0.035 & 0.40 & 0.10 & 0.40 & 0.30 \\ C45E & 0.42–0.50 & 0.10–0.40 & 0.50–0.80 & 0.025 & 0.035 & 0.40 & 0.10 & 0.40 & 0.30 \\
37 Cr4 & 0.34–0.41 & 0.10–0.40 & 0.60–0.90 & 0.025 & 0.035 & 0.90–1.20 & - & - & 0.40 \\
34 CrNiM06 & 0.30–0.38 & 0.10–0.40 & 0.50–0.80 & 0.025 & 0.035 & 1.30–1.70 & 0.15–0.30 & 1.30–1.70 & 0.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition (weight %) of low-carbon steel samples. Figure 1: Images of annealed steel samples showing microstructures with ferrite and pearlite (\(\times\)1000). (a) C25E; (b) C45E steel; (c) C45E steel. Figure 2: Images (\(\times\)400) of a Widmanstatten sample of a C25E steel (**a**), a complete martensite structure of a quenched 37 Cr4 steel (**b**), and a martensite and lower bainite structure corresponding to a 34 CrNiM06 steel after an incomplete quenching treatment (**c**). the acidicular morphology of the microconstituents, the included heterogeneity remains relevant. Additionally, Figure 2c corresponds to a typical incomplete quenching treatment, where, besides the typical martensite appearing, some lower bainite can be observed. The appearance of the lower bainite is similar to the martensite but is more colored due to metallographic etching caused by existing inner Fe3C precipitates. The typical martensite coming from a complete quenching treatment can be observed in Figure 2b. Moreover, sometimes the three structures represented in Figure 2 can be obtained with high cooling velocities that sometimes are identified as quenching conditions; however, in reality, the results may be very different, as indicated above. The treatments referred to in Figure 2 have all been considered together in order to subject them to the methodology applied herein, as well as to evaluate the strength of the methodology under adverse conditions.