Ultrasonic nanocrystal surface modification of A516 ferritic-pearlitic steel: Effect on subsurface morphology and properties

In this study, ultrasonic nanocrystal surface modification (UNSM) was employed to improve the performance of the top surface layer of a ferritic-pearlitic steel sheet, which is most susceptible to degradation during service. The microstructural changes induced by UNSM treatment and their underlying mechanisms were examined. Significant grain refinement within a surface layer with a maximum depth of 80 μm, and surface compressive residual stress were found for all treatment conditions. The combination of a refined microstructure and accumulated plastic deformation led to a 25–68% increase in hardness. Based on the evaluation of surface hardness, compressive residual stresses and surface roughness, the optimal processing parameters were found to be a single pass with 80 N of static load and 50 μm of vibration amplitude. The present study demonstrates the potential of UNSM as a sustainable, room-temperature surface modification technique for enhancing the durability and performance of the surface layer of pipeline steel and provides guidance for the future selection of processing parameters.