Mechanical Behavior and Fracture Characteristics of AISI 304 Stainless Steel at Sub-Zero Temperatures

AISI~304 austenitic stainless steel (ASS) is widely used in structural and harsh-environment applications due to its excellent ductility, corrosion resistance, and strength. However, its mechanical response under sub-zero temperatures and varying strain rates remains insufficiently understood. This study investigates the tensile behaviour of AISI~304 ASS using cylindrical specimens with a gauge length of 50~mm and a diameter of 8~mm. Mechanical testing was conducted at room temperature and at sub-zero temperatures of $-30^{\circ}\mathrm{C}$ (243~K), $-60^{\circ}\mathrm{C}$ (213~K), and $-80^{\circ}\mathrm{C}$ (193~K) under strain rates of $1.0\times10^{-4}$, $1.0\times10^{-3}$, and $1.0\times10^{-2}~\mathrm{s^{-1}}$. Post-tensile fractographic analysis was performed using scanning electron microscopy (SEM). Two-way ANOVA was employed to evaluate the significance of temperature and strain rate on the mechanical properties.The results show that yield strength increases with decreasing temperature and increasing strain rate. Ultimate tensile strength also increases with decreasing temperature, although its dependence on strain rate differs from that of yield strength. The yield-to-UTS ratio increases with strain rate, reflecting enhanced strain-hardening capacity. At sub-zero temperatures, strain-induced martensitic transformation contributes to a transition in the stress--strain curve from a parabolic to an inverted S-shape. SEM fractographs consistently revealed ductile fracture features across all conditions. Statistical analysis confirmed that temperature and strain rate significantly influence both yield and ultimate tensile strengths, with their interaction being significant only for ultimate strength. Overall, the findings demonstrate that AISI~304 ASS maintains high strength and good ductility at sub-zero temperatures, underscoring its suitability for very low-temperature applications.