Severe Shot Peening is a promising surface treatment technique to substantially enhance mechanical and also biomedical properties by intensively modifying material’s microstructure. By introducing high grades of plastic deformation and the accompanied defects grain refinement can be introduced that leads to a great variety of property changes. In this study, austenitic steel AISI 316L that is frequently used for biomedical implants was severely shot peened and analyzed by means of stresses, strains, hardness, wetting angles, surface topography and phase transformation. The results show an extraordinary hardness increase and a substantial surface nanocrystallization in combination with a gradient of refined grains, also compared to conventional shot peening. EBSD analysis reveals a textured and layered transformed martensite structure which is formed inside nanograins close to the surface that gives insights into the deformation mechanism. Within this structure non transformed areas are also influenced.