Enhancing the Rotational Bending Fatigue Performance of 20CrMoH via Carburizing and Surface Ultrasonic Nanotechnology

To alleviate the risk of rotational bending fatigue (RBF) failure in 20CrMoH alloy steel, a hybrid surface modification strategy combining carburizing and surface ultrasonic nanotechnology (SUNT) is developed in the present work. The synergistic effects of the combined treatment on surface integrity, residual stress distribution, microstructural evolution, and RBF performance were systematically examined in this work. The surface microhardness of combined‐treated specimens reaches 939 HV 0.2 , representing increases of 193% and 21% relative to the untreated and carburized specimens, respectively. The maximum residual compressive stress (RCS) of combined‐treated specimens reaches −945 MPa, corresponding to a 350% enhancement compared with the carburized specimen. Microstructural analysis reveals that SUNT‐induced severe plastic deformation refine the average grain size from 1.39 to 0.51 μm. Consequently, at a bending stress of 1.25 GPa, the RBF life is extended by approximately 435% compared to carburized specimen. The improved RBF resistance is predominantly ascribed to grain refinement, elevated surface hardness, and the generation of high‐level RCS.