Abstract
This study investigates the effect of Ultrasonic Nanocrystal Surface Modification (UNSM) treatment on the microstructure, hardness, roughness, and tribological characteristics of 45 steel. The treatment was carried out under static loads of 20, 40, and 60 N. Microstructural analysis was performed using scanning electron microscopy. Mechanical properties were evaluated by instrumental indentation and Vickers hardness methods. It was established that UNSM treatment promotes the formation of a hardened surface layer and grain refinement due to severe plasticdeformation. The maximum instrumental hardness value, HIT, reached 5722.4 N/mm² at a load of 40 N. At the same time, a decrease in surface roughness and friction coefficient was observed. The obtained results demonstrate the high efficiency of UNSM treatment for improving the performance properties of 45 steel.