The results of theoretical and experimental studies of the surface of the sample of steel 45 after surface plastic deformation (SPD) with multi-radius roller (MR-roller) is shown. The goal of this study is to expand the technological capabilities of the method of SPD through the use of a new design of the deforming tool developed at the Department of Engineering Technology of KuzSTU. The advantage of the MR-roller (Patent RU № 2557377) over the traditional tool for SPD (single-radius roller) is the possibility of creating a large hydrostatic pressure in the deformation zone, without destroying the surface layer of the processed material. The research technique included finite element modeling (FEM), microhardness measurement, metallographic studies of the sample structure. As a result of the study, some regularities of the process of hardening by a multi-radius tool with high hydrostatic pressure and a large number of quasi-monotonic deformation sites were revealed. The results indicate a significant hardening without metal destruction and the formation of nanoscale grains, which allows to improve the properties of rolled products in the application of high operating loads.