Hydrogen embrittlement of duplex stainless steel: Effect of tensile prestrain

This study investigates the effect of deformation-induced microstructures on the hydrogen embrittlement (HE) sensitivity of duplex stainless steel (DSS). By varying the pre-strain temperature (room temperature and 80 °C) and strain level (5–15 %), the microstructural evolution—particularly the distribution of geometrically necessary dislocations (GNDs) in ferrite phase and deformation twins in austenite phase was tailored. Slow strain rate tensile testing (5 × 10⁻⁶ s⁻¹) under in-situ hydrogen charging revealed that prestraining mitigates HE sensitivity, with the degree of improvement depending on temperature and strain level. For room-temperature pre-straining, the HE sensitivity decreased by 31–34 % at 5–10 % strain, but only by 15 % at 15 % strain. In contrast, pre-straining at 80 °C led to a modest reduction (∼10 %) at 5–10 % strain, but a more pronounced decrease (∼32 %) at 15 % strain. Notably, samples pre-strained at 80 °C with 5–10 % strain showed a strength–ductility product comparable to that of the annealed material under hydrogen charging, but with a markedly higher strength (over 40 % increase). The improved HE resistance is primarily attributed to the formation of dense GND networks, which act as strong hydrogen traps, thereby limiting hydrogen concentration at crack tips. In contrast, a high pre-strain level (15 %) applied at room temperature promotes extensive deformation twinning and slip bands in austenite, which facilitates hydrogen-assisted cracking and thus reduces HE resistance.