2.1.2. Microstructural Characterization

After mechanical polishing to a mirror-surface finish (0.03 μm colloidal silica suspension), the AISI 316 and UNS S46500 samples were etched with aqua regia solution and Kalling I reagent, respectively. Microstructural characterization was performed using optical microscopy (Epiphot 200, Nikon, Tokyo, Japan) (Figure 1). The AISI 316 microstructure consisted of austenitic grains, some of which exhibited twinning, whereas the UNS S46500 stainless steel showed mainly a martensitic matrix.

(**a**) AISI 316 Microstructure (**b**) UNS S46500 Microstructure
