Abstract: This study focuses on analyzing the failure mechanism of the nitriding layer of austenitic stainless steel under sliding contact conditions through systematic experimental analysis methods. By combining metallographic microscopy observation with scanning electron microscopy characterization, the macroscopic/microscopic structural characteristics of the nitrided layer are clarified; Based on Vickers hardness gradient testing and energy spectrum analysis, quantitatively evaluate the synergistic effect of sudden hardness changes and Cr element segregation on the interface mechanical mismatch between the nitriding layer and the substrate interface; Through three-point bending experiments, the influence of hardness gradient and composition segregation on the crack propagation resistance of the nitriding layer was verified, revealing the layered peeling failure mode dominated by interface brittleness. The results showed that the overall Cr content of the nitriding layer decreased by 18.7% compared to the matrix, leading to a decrease in oxidation resistance; At the same time, the precipitation of Cr rich nitrides at grain boundaries significantly increases grain boundary brittleness. The severe hardness gradient between the nitriding layer and the substrate leads to a mismatch in the mechanical properties of the interface, which induces cracks to propagate along brittle grain boundaries during the sliding process of the copper ring, ultimately causing the nitriding layer to peel off. The study established for the first time a quantitative relationship between "hardness gradient composition segregation bending performance" under medium temperature nitriding conditions, providing experimental evidence for evaluating the stability of the nitriding layer interface.