Inhomogeneity of plastic deformation in austenitic stainless steel after surface mechanical attrition treatment

Inhomogeneity of microstructure evolution in cold-rolled austenitic stainless steel after surface mechanical attrition treatment (SMAT) was investigated. A characteristic deformation pattern was obtained for all studied specimens. Selected areas were examined through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Estimation of the α′-martensite volume fraction below the treated surfaces showed, that some of the studied areas are characterised by significant different amount of this phase (from 10 to 22% - BB, from 19 to 31% - GIXD). The performed finite element (FE) numerical analysis showed, that the reason for this may be the presence of an air gap between the impacted material and fixation and also relatively short high stress time duration due to surface inclination during the surface treatment. Annealing at 550 and 650 °C greatly increased the volume fraction of α′-martensite (up to 47% - BB) and formed Fe2O3 as well as Fe3O4, whereas annealing at 700 °C resulted in both disappearance of α′-martensite and in reduction of oxides.