Mechanism of Enhanced Bending Fatigue Performance of GCr15 Steel via Multiscale Microstructural Synergistic Regulation by Double‐Quenching Process

To improve the service reliability of high‐carbon bearing steels under complex alternating stresses, a novel heat treatment route combining double quenching and low‐temperature tempering was proposed in this study. The effects of this process on the microstructural evolution and four‐point bending fatigue behavior of GCr15 steel were systematically investigated. Multiscale characterization techniques, including SEM, EBSD, and TEM, were employed to elucidate the evolution of prior austenite grain structure, martensitic transformation behavior, and nanoscale carbide precipitation mechanisms. The results demonstrated that, compared with the conventional single‐quenching process, the double‐quenching treatment significantly refined the microstructure. The prior austenite grain size was reduced from 18.61 to 5.23 μm, and the martensite lath width decreased from 4.8 to 2.8 μm. EBSD analysis further revealed that the fraction of high‐angle grain boundaries increased from 26.55% to 35.83% after secondary quenching, thereby constructing an effective grain‐boundary barrier network. Four‐point bending fatigue tests indicated that the optimized microstructure fundamentally improved the fatigue performance. The crack propagation path exhibited frequent deflection, branching, and blunting due to the synergistic effects of grain boundaries, refined martensite laths, and dispersed carbides.