## 5 Conclusions  
The paper presents the results of numerical and experimental studies of the nanostructuring burnishing hardened bearing steel AISI 52100 with an innovative tool having a flat cylindrical indenter made of CBN010 from SECO, inclined at an angle to the surface being machined. Finite element simulations and experimental studies were performed under dry processing conditions with a burnishing speed of 25 m/min, while the indenter tilt angle changed from 0.5\({}^{\circ}\) to 2.5\({}^{\circ}\). The main findings of the study are as follows:  
* FEM analysis indicates that the maximum values of contact pressure and plastic strain occur when the tilt angle is 2\({}^{\circ}\). At a burnishing force of 250 N, the pressure reaches 3.5 GPa, the plastic strain is more than 1.2, and the temperature is 405 \({}^{\circ}\)C, which fully corresponds to the conditions of steel nanostructuring;
* Burnishing the planes of the split disk with a tool installed in a Kistler 9257 BA dye-namometer made it possible to establish that the friction coefficient decreases linearly from 0.33 to 0.26 as the tilt angle varies from 0.5\({}^{\circ}\) to 2.0\({}^{\circ}\);
* 3D profilometry of the mating surfaces of the split disk enabled the determination of shear strains. True strains increase from 1.05 to 2.4 within the same range of tilt angle;
* The studies at an optimal burnishing force of 250 N and a feed rate of 0.04 mm/rev reveal that the minimum value of microhardness 1,152.6 HV\({}_{0.05}\) corresponds to an angle of 0.5\({}^{\circ}\), while the maximum value of 1508.2 HV\({}_{0.05}\) occurs at a tilt angle of 2\({}^{\circ}\);
* Transmission microscopy fully explains the achieved level of microhardness since the minimum size of nanocrystallites in the range of 15-30 nm occurs at indenter tilt angles of 2-2.5\({}^{\circ}\);
* The surface roughness changes in the opposite direction to hardness, ranging from 120.3 to 161.8 nm at small tilt angles to 360.16 nm at an angle of 2.5\({}^{\circ}\). Directions for further studies of the developed tool will be related to nanostructuring burnishing under the conditions of the cooling lubricant, which will allow the establishment of a new balance in achieving microhardness and roughness of the formed surface layer. In addition, process studies are needed for other tools and workpiece materials. It is planned to develop a 3D finite element model of the process as well. Conceptualization, V.K. ; methodology, V.K. ; software, I.S. and A.A.; validation, A.S.; formal analysis, I.S. and A.S.; investigation, V.K. and A.S.; resources, V.K. and I.S. ; data curation, I.S. and A.S.; writing--original draft preparation, I.S. and A.S.; writing--review and editing, V.K. ; visualization, I.S., A.S. and A.A.; supervision, V.K. ; project administration, V.K. ; funding acquisition, V.K. All authors have read and agreed to the published version of the manuscript. The research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program) is gratefully acknowledged. The numerical model was developed according to the Government research assignment for ISPMS SB RAS, project FWRW-2022-0003. Not applicable. The data presented in this study are available on request from the corresponding author. The authors declare no conflict of interest. [PERSON] [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON] A review of numerical simulation of ball burnishing process. _Finite Elem. Anal. Des._**2023**, _218_, 103926. [CrossRef]
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