Ultrasonic impact treatment (UIT) combined with high energy electropulsing (EP) was applied to low carbon steel to introduce severe plastic deformation on the surface. The investigation indicated that a strengthened layer with a maximum hardness of approximately 330 HV on cross section was obtained, in comparison with the hardness value of 260 HV resulted from UIT solely. Alongside with high hardness, the enhanced structure layer was extended to a distinguishing depth of 2 mm. Microstructure in the cross section revealed a crack-free superficial layer by EP-UIT and pearlite colonies here experienced morphology variations by redistribution and spheroidization of cementite. A 3 μm oxide layer consisting of amorphous oxide and nitride as well as MnFe2O4 and hematite crystalline was formed on the treated surface. Thermal and athermal effect of EP was the key factor in these phenomena and it is assumed that acoustic softening, electro plasticity, and thermal softening were engaged simultaneously.
