Influence of Ultrasonic‐Assisted Milling on Surface Integrity and Fatigue Strength of a Low Alloy Steel

ABSTRACT The milling process significantly influences the surface integrity of metallic components through machining induced near‐surface residual stresses. Modern hybrid machining processes, such as ultrasonic‐assisted milling (USAM), offer the potential to induce beneficial near‐surface compressive residual stresses compared to the near‐surface tensile residual stresses typically resulting from conventional milling (CM). This study investigates the effects of USAM compared to CM on the near‐surface residual stress state and fatigue performance of a S355J2C low‐alloy steel. Milling experiments and subsequent rotating bending tests revealed that USAM significantly reduces cutting force by approximately 45% and induces near‐surface compressive residual stresses as low as −733 MPa. This leads to a significant improvement in fatigue strength estimated in approximately 34% compared to polished specimens and 11% compared to the CM. These findings highlight the potential of USAM to enhance the fatigue performance of components made of steel.