Thickness-dependent deformation and fracture characteristics of AL6XN super-austenitic stainless steel subjected to tensile and fatigue loads

The thickness-dependent tensile and fatigue behavior of AL6XN super-austenitic stainless steel was investigated over 0.1–––2.0 mm. With the increase in specimen thickness, the ultimate tensile strength increases from 585 MPa to 728 MPa, the tensile fracture strain rises from 22% to 52%, and the fatigue life under the cyclic stress amplitude of 275 MPa extends from approximately 5.7 × 10 3 cycles to 1.1 × 10 5 cycles. The fracture surface roughness, quantified by the fractal dimension D f increases, reflecting progressively more tortuous crack paths in thicker specimens. The improved mechanical performance under both monotonic and cyclic loading is attributed to the increased grain boundary area, which provides more sites for dislocation storage and twin nucleation, promoting a progressive transition from planar slip to deformation twinning as thickness increases. Furthermore, the elevated stress triaxiality in thicker specimens suppresses localized necking and retards crack propagation. In fatigue, the increased twin density induces crack deflection and creates more tortuous crack paths, which further enhances crack propagation resistance. These findings establish a mechanistic link between specimen thickness and deformation mode transition in austenitic stainless steels, and provide a critical reference for the design of thin-walled components in nuclear, chemical, and marine engineering applications.