(**a**) Residual stress component in the parallel direction to the burnishing path

(**b**) Residual stress component in the perpendicular direction to the burnishing path AISI 316 UNS S46500

The residual tensor component introduced by milling on the austenitic surface was 61% higher in the parallel direction (σx) than in the perpendicular direction (σz) to the burnishing path. The opposite occurred on martensitic and ferritic surfaces [21], where the perpendicular component exceeded the parallel component by 45%. In this manner, although the feed of the milling cutter on the austenitic surface increased the tensor component in its perpendicular direction, on the martensitic surfaces, it increased the tensor parallel to the milling route. However, after burnishing, on the austenitic surface there was a substantial increase in the lower compressive state component (σz) (4 times greater), whereas in the other direction (x-axis), a tensile state was induced. This extended the hypothesis of an anisotropic state independent of the initial tensor on ferritic surfaces [21] to austenitic surfaces. When burnishing was performed on the martensitic surface, the initial anisotropy was reduced by 9% at a 270 N load, whereas with increasing load, the anisotropy increased by 30%. Therefore, the residual isotropy was qualitatively in agreement with the directional isotropy (Str) for both materials after the burnishing process (Section 3.2.1). Regarding the skewness (Ssk), there was no evidence of a directly proportional relationship with the surface tensor, as mentioned in another study [19]. Depending on the microstructure, the surface integrity varied considerably under the same burnishing conditions.
