Role of ferrite and austenite phases on the deformation behavior and mechanical properties in heterogeneous nanostructured duplex stainless steel aged at different temperatures

The effects of aging on the mechanical properties of a heavily cold-rolled ferrite–austenite duplex stainless steel were systematically investigated. The heterogeneous-nano (HN) structure, composed of “eye-shaped” twin domains, shear bands, and low-angle lamellae, was developed in the austenite ( γ ) phase after heavy cold rolling. In contrast, no distinct substructure was formed in the ferrite ( α ) phase. The yield stress and ultimate tensile strength (UTS) of the specimen peak-aged at 723 K increased significantly, whereas only the UTS increased in the specimen peak-aged at 773 K. Nanoindentation hardness measurements revealed that both the α and γ phases were significantly hardened by aging at 723 K, but peak-aging at 773 K only increased the hardness of the γ phase. In situ x-ray diffraction measurements during tensile tests in a synchrotron radiation facility revealed that the yielding of the α phase corresponded to the macroscopic yielding of the specimens, and that the phase stress of γ increased significantly after macroscopic yielding. Consequently, the age hardening of the α phase at 723 K contributed significantly to the increase in both yield stress and UTS. Among the tested conditions, aging at 773 K resulted in the highest phase stress of γ , which contributed to the increase in UTS compared to the as-rolled specimen. Stress partitioning from the α phase to the γ phase was identified as the main factor in the notable strengthening of HN structured duplex stainless steels.