Synergistic enhancement of strength and ductility in TRIP lean duplex stainless steel through cyclic pre-deformation

In this study, a transformation-induced plasticity (TRIP) lean duplex stainless steel (LDSS) was strengthened by cyclic plastic deformation with small strain amplitudes ( ). This methodology effectively enhances both the strength and elongation of the TRIP LDSS. After the cyclic pre-deformation, spatial dislocation structures are observed within the ferrite, causing ferrite softening and modulating the strain partitioning between ferrite and austenite during subsequent tensile deformation. Initially, strain is predominantly localized within the ferrite. As deformation progresses, strain partitioning gradually shifts to the austenite. This shift prevents excessive early transformation and depletion of the austenite. It ensures the accumulation of adequate plastic strain in the austenite in later deformation stages, which facilitates phase transformation and thus promoting the TRIP effect. Concurrently, the austenite exhibits extensive formation of slip bands, stacking faults, and -martensite, providing numerous nucleation sites for martensitic transformation. Such changes alter the characteristics of the rapid phase transformation after sufficient nucleation during uniaxial tensile deformation of the TRIP LDSS. This enables the TRIP LDSS to undergo substantial phase transformation in the early stages of deformation while maintaining stable phase transformation capability in the later stages, ensuring uniform and stable martensitic transformation throughout the entire tensile deformation process. Consequently, this enhances phase transformation saturation, thereby fully harnessing the TRIP effect. After cyclic pre-deformation, the strength and elongation of the TRIP LDSS significantly increase.