Microstructural Evolution and Crack Initiation Behavior During HCF in a New Weathering Bridge Composite Plate: 316L/Q420qENH With Smooth and Notched Specimens

ABSTRACT The 316L/Q420qENH composite bridge steel, designed for the challenging Qinghai‐Tibet Plateau environment, exhibits excellent mechanical properties and superior weathering resistance. However, its fatigue performance in structural engineering remains poorly understood. This work comparatively investigates the fatigue behaviors and life of a novel 316L/Q420qENH composite under high‐cycle fatigue (HCF) conditions at a load ratio of R = −1. The findings indicate that the HCF failure of the composite is predominantly due to non‐inclusion‐induced crack initiation (NIICI) on the softer Q420qENH side. At the microstructural level, slip in the ferritic {110} < 111 > system results in a dense network of low‐angle grain boundaries (LAGBs), increasing the kernel average misorientation (KAM) and promoting intergranular fatigue crack initiation. Fatigue limits for smooth and notched specimens are 426 and 291 MPa, respectively, with notches significantly reducing fatigue resistance. The experimental data support a proposed crack initiation mechanism for the 316L/Q420qENH composite under HCF loading.