On the influence of vibration assisted low-frequency burnishing on near-surface properties of a quenched and tempered 42CrMo4 steel

Mechanical surface treatments are widely used to improve fatigue and wear performance by introducing compressive residual stresses through near-surface plastic deformation. In addition to conventional processes such as shot peening, deep rolling or burnishing, ultrasonic vibration-assisted processes have demonstrated efficient subsurface modification, yet their industrial applicability is limited by complex hardware integration. The present study therefore investigates a vibration-assisted burnishing approach operating at low excitation frequencies in order to decouple dynamic loading effects from ultrasonic excitation mechanisms. A newly developed process of low-frequency burnishing was applied to quenched and tempered 42CrMo4 steel. Here, the vibration amplitude and the number of vibration periods per revolution were systematically varied. Surface topography, roughness, residual stress depth profiles and hardness distributions were analyzed to identify the governing deformation characteristics. The results show that the superimposed oscillatory loading does not primarily increase peak compressive residual stresses compared to conventional burnishing. Instead, it increases the penetration depth of the compressive residual stress field and leads to a direct transfer of vibration kinematics to the surface morphology. While residual stresses exhibit a robust depth effect, hardness responds locally and non-monotonically due to spatially heterogeneous plastic deformation. These findings indicate that low-frequency burnishing modifies the temporal characteristics of plastic deformation during continuous rolling contact rather than introducing impact-dominated deformation. Low-frequency burnishing therefore represents a distinct process variant positioned between conventional burnishing and high-frequency vibration-assisted treatments, enabling controllable subsurface modification governed by the temporal characteristics of loading rather than ultrasonic-specific mechanisms or impact-dominated deformation.