**5. Conclusions**

In the quest to enhance the surface finish and mechanical properties of stainless steels using a ball-burnishing process, the tribological performance of the process must be considered first. The interaction capability between the ball and the machined surface, quantified by the friction coefficient, defines the surface integrity improvements of the burnished components. Neither the friction value nor its effects are trivial during the ball-burnishing setup. Therefore, to obtain a balance between roughness reduction, design tolerance, and directional and residual anisotropy, or to prioritize one of them, a pertinent COF must be defined. Hence, the present work provides the starting point for a new methodology to parameterize the process based on its interaction (tribological characteristics) at the time when the friction coefficient is delivered as a factual variable in the current numerical methodologies. In addition, this study provides the friction effect on two previously textured microstructures (austenitic and martensitic surfaces) in order to contribute to the guidelines for future ball-burnishing crystalline plasticity numerical conceptualization while demonstrating the process's capability of enhancing the surface integrity of martensitic stainless steel UNS S46500. The microstructural deformation mechanisms at the local level due to the different tribo-contacts (dislocations, crystallographic orientations, recrystallization, hardness modification, self-hardening), as well as their effect on the thickness of the compressive layer, should be addressed in further research.

**Author Contributions:** Conceptualization, A.T., N.C., J.A.T.-R., J.L. and M.V.; methodology, A.T., N.C., J.A.T.-R. and J.L.; software, A.T., N.C., J.A.T.-R. and J.L.; validation, N.C., J.A.T.-R., J.L. and M.V.; formal analysis, A.T., N.C., J.A.T.-R., J.L. and M.V.; investigation, A.T., N.C.; J.A.T.-R. and J.L.; resources, N.C., J.A.T.-R., J.L. and M.V.; data curation, N.C.; writing—original draft preparation, A.T. and N.C.; writing—review and editing, A.T., N.C., J.A.T.-R., J.L. and M.V.; visualization, A.T. and N.C.; supervision, N.C., J.A.T.-R., J.L. and M.V.; project administration, M.V.; funding acquisition, J.A.T.-R., J.L. and M.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Eurecat's "Vicente López" PhD grant program and by the Ministry of Science and Innovation of Spain, through grant PDC2022-133596-I00, which is greatly appreciated.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The raw/processed data required to reproduce these findings cannot be shared at this time as they also form part of an ongoing study.

**Conflicts of Interest:** The authors declare no conflict of interest.
