Effect of Mo addition on aging behavior of TRIP-aided duplex stainless steel

Abstract

The effects of Mo addition and an aging heat treatment on microstructural evolution and transformation-induced plasticity (TRIP) in cold-rolled lean duplex stainless steel (DSS) samples were investigated. 21Cr lean DSS with 0–2% Mo was cold-rolled into 1-mm-thick plates and solution-treated at 1050 °C for 5 min. With increasing Mo content, a smaller thermal α′ phase formed after solutionization. During the subsequent aging treatment, redistribution of alloying elements, such as chromium (Cr), nickel (Ni) and Nitrogen (N), occurred in the α and γ phases, which resulted in local segregation and precipitation of Cr2N in the α/γ phase boundary. In turn, this led to a decrease in the stability of the γ phase, allowing deformation-induced martensite transformation (DIMT) to occur more easily. Due to the instability of the γ phase, the fraction of the thermal α′ phase increased with aging. Steels with a higher Mo content exhibited a more stable γ phase, which suppressed the formation of deformation-induced martensite (DIM). The effect of DIM (caused by TRIP) on the strength and elongation of the steels according to the fraction of the thermal α′ phase was evaluated.