Strain Hardening Behavior of Cryogenic Tensile Prestrained CHN01 Austenitic Stainless Steel at Various Temperatures

Nitrogen‐strengthened CHN01 (Fe‐21%Cr‐14%Ni‐5%Mn) austenitic stainless steel (ASS) has been expected to be applied for structural components in next‐generation magnetic confinement fusion and aerospace industries due to its excellent mechanical performance at cryogenic temperatures. This study investigated the combined influence of cryogenic tensile prestrain and test temperature on tensile properties and hardening behavior of the CHN01 ASS. When the CHN01 ASS is 5%–25% tensile prestrained at 77 K and then tensile tested at 77 and 4.2 K, a unique cryogenic prestrain activated twinning (CPAT) effect is observed, which weakens hardening capacity through elevating the yield‐to‐tensile strength ratio to 0.8–1.0. The CPAT effect is characterized by a V‐shaped trough in the strain hardening rate curves and is considered to result from interactions between preexisting dislocations during cryogenic tensile prestrain and newly‐generated defects during subsequent cryogenic deformation. Hardening capacity of the CHN01 ASS collapses when cryogenic tensile prestrain reach es 35%, as evidenced by reduced elongation at fracture of 4.2% at 77 K and 1.8% at 4.2 K. These findings provide a cryogenic tensile prestrain‐threshold framework for optimizing cryogenic forming processes of the CHN01 ASS, which target tailor of strength‐ductility trade‐offs in aerospace cryogenic pressure vessels.