Effects of surface mechanical attrition treatment (SMAT) on a rough surface of AISI 316L stainless steel

► A roughness decreasing phenomenon during the SMAT is observed. ► Stages in surface smoothening by the SMAT: (1) rapid reduction, (2) saturation roughness. ► Indentation and material removal by the impact of milling balls are the two principal mechanisms. ► A smoother surface and larger mass reduction are yielded by the SMAT with bigger milling balls. ► The initial surface roughness does not influence the work hardening by the SMAT.