Fatigue Behavior and Fracture Mechanism of 310S Austenitic Stainless Steel Processed by Surface Mechanical Rolling Treatment at 650°C

This study investigates the microstructure, residual stress stability, fatigue property, and fracture mechanism of a gradient structure specimen fabricated on 310S austenitic stainless steel via surface mechanical rolling treatment at 650°C. The gradient structure enhances yield strength and ultimate tensile strength by 100% and 12.4%, respectively. Fatigue strength improves across a wide strain amplitude range due to the gradient microstructure and multiaxial stress state. Fatigue ductility increases when Δε/2 < 0.45% but decreases at higher strains. Compressive residual stress has minimal impact on fatigue properties due to rapid relaxation at 650°C. Fractography analysis reveals grain coarsening and sigma brittle phase precipitation after high-temperature fatigue. All fatigue cracks initiate in the oxide layer, driven by high stress concentrations at grain boundaries, leading to brittle intergranular and interfacial cracking. These findings highlight the role of the gradient structure in improving mechanical performance under elevated temperatures.