A nanotwinned austenite stainless steel with high hydrogen embrittlement resistance.

Abstract A nanotwinned 304 steel with a favorable combination of strength and ductility has been made in this work through the dynamic plastic deformation (DPD) treatment followed by a proper heat treatment. The DPD, DPD-annealed and coarse grain (CG) 304 samples were tensile tested with slow strain rate under electrochemical hydrogen charging condition. Compared with CG sample, DPD-annealed sample with a mixed structure of nanotwins (41% volume fraction), recrystallization grain (RXG, 32% volume fraction) and dislocation structures (27% volume fraction) possesses a high HE resistance. Hydrogen causes a 12.5% reduction in yield strength and 5.4% reduction in tensile strength of DPD-annealed sample because hydrogen enhances dislocations/twin boundaries (TBs) interactions and the subsequent dislocation mobility during the TB-mediated slip transfer. Hydrogen charging also causes a 41% reduction in strain induced martensite of DPD-annealed sample. Strain localization is supposed to be mitigated by the bundle form of TBs and the micro-sized RXGs, accounting for the high HE resistance of DPD-annealed alloy. Our findings suggest a new strategy to design high strength alloys with low HE susceptibility. Highlights • The nanotwinned austenitic steel shows a high hydrogen embrittlement resistance. • H-charging suppresses the martensite transformation of DPD-annealed alloy. • Slip localization at twin boundary (TB) is mitigated by the bundle form of TB. [ABSTRACT FROM AUTHOR]