*2.1. Sample Preparation and Surface Treatments*

Prior to machining, the 304L cylindrical specimens were fully annealed at 900 ◦C for 40 min resulting in an average grain size of approximately 40 μm. The fatigue behavior was studied under rotating–bending (RB) and tension–compression (TC) tests. For RB, 6-mm-diameter samples with a gauge length of 25 mm were machined and ground in order to remove the grooves generated by the machining procedure. For TC, 9-mm-diameter samples with a gauge length of 12.5 mm were machined and then polished to a mirror finish. The SMAT was carried out using a machine developed by SONATS company (Carquefou, France) [29]. The samples were treated using a vibrating amplitude of 60 μm with ø2 mm 100Cr6 steel shots. For rotating–bending, the SMAT was carried out for 20 min at two temperatures: (i) at room temperature (RT), or (ii) under cryogenic conditions (CT) at about −100 ◦C. For tension–compression samples, SMAT was done for 60 min at room temperature.
