*3.1. Friction*

In order to evaluate the microstructural response to the tribo-contact during the burnishing process, the COF was computed for each of the studied stainless steels. Figure 4 summarizes the COFs generated by the interactions of austenitic and martensitic milled textured surfaces as a function of the contact pressure. The friction on the already characterized AISI 1038 ferritic steel textured surface [11] was established for comparison purposes.

Under the same ball-burnishing configuration, the steels' microstructure responses were not coincident. The COF on austenitic steel (0.17) exceeded the COF on ferritic steel (0.15) by 15%. The gap between the austenitic (0.17) and martensitic (0.13) stainless steels' COFs amounted to a 30 % difference. This means that the frictional shear stress and, therefore, the surface finish and compressive layer induced by the process will be substantially different. After load increment on the martensitic surface, the friction coefficient increased. Henceforth, it is convenient to take into account the tribological performance of the process (which includes the COF, initial roughness, and initial stress state of the target material [21]) in order to achieve a particular surface integrity depending on the machined microstructure.
