Realizing strength–ductility synergy in a lean duplex stainless steel through enhanced TRIP effect via pulsed electric current treatment

Abstract

Optimization of the strength–ductility compromise in lean duplex stainless steels (LDSSs) often involves controlling the stability of austenite by chemically adjusting it to be metastable and enabling phase transformation through a transformation-induced plasticity (TRIP) effect during plastic deformation. This study investigated the effects of pulsed electric current (PEC) treatment on the spatial distribution of alloying elements within the microstructure and enhancement of the mechanical properties of a new type of LDSS material, NSSC2120. The results showed that PEC treatment had a significant positive impact on the mechanical properties of NSSC2120. Specifically, after applying 20 pulses of PEC treatment at a current density of 700 A/mm2 for 8 ms, the material exhibited a 27% increase in ductility and 8% increase in strength. The microstructural evolution induced by the PEC treatments was investigated using quasi-in-situ electron backscatter diffraction and energy-dispersive X-ray spectroscopy. The PEC treatment facilitated the diffusion of alloying elements, which played a crucial role in triggering the TRIP effect during plastic deformation owing to the decreased stability of austenite with a lower content of austenite-stabilizing elements, thereby resulting in simultaneous improvement in both strength and ductility. Significantly, the rapid thermal process employed in the PEC treatment did not give rise to detrimental precipitates within the microstructure of the material, rendering PEC treatment a promising alternative to conventional heat treatment. The simplicity, speed, and low energy consumption associated with the PEC treatment make it an appealing choice for processing similar materials and achieving both microstructural modification and optimization of mechanical properties.