Influence of phase morphology on hydrogen embrittlement of type 2205 duplex stainless steel

Abstract

Hydrogen embrittlement (HE) is a significant challenge in duplex stainless steels (DSSs). This study explores the effect of phase morphology on HE in type 2205 DSS subjected to combined heavy cold-rolling and annealing treatments. Fracture analysis and finite element (FE) simulations of hydrogen diffusion were performed to interpret the findings. Austenite phase islands act like reversible hydrogen traps, capturing hydrogen during charging, which reduces apparent hydrogen diffusivity, and releasing it to newly formed dislocations during plastic deformation. Short-term annealing (30 and 45 s) at 1050 °C after 90 % thickness reduction produced alternating, continuous stripe-like austenite (γ) and ferrite (α) morphologies, enhancing both yield strength and HE resistance compared to conventional hot-rolled material with elongated γ islands embedded within the α matrix. This improvement is attributed to the continuous γ stripes, which hinder hydrogen diffusion by disrupting the α-phase pathway and facilitate co-deformation with the α phase. The co-deformation induces dislocations in the γ phase, trapping hydrogen and limiting its release to the α phase. In contrast, prolonged annealing (1800 s) resulted in a dispersed and discontinuous γ island morphology, which was less effective in impeding hydrogen diffusion. This led to increased plastic deformation and dislocation formation in the α phase, promoting hydrogen release from the γ islands to the α matrix, thus exacerbating HE. To mitigate HE in duplex materials, optimizing phase morphology and mechanical properties is recommended, ensuring that the HE-resistant phase undergoes plastic deformation simultaneously with or prior to the HE-susceptible phase.