<p>This study compared the hydrogen embrittlement of austenitic stainless and high-manganese steels under in-situ electrochemical hydrogen charging conditions through slow strain-rate tests (SSRTs) with notched tensile specimens. The in-situ SSRT results revealed that hydrogen significantly altered the fracture modes of both steels, notably inducing a transition from ductile to brittle behavior. High-manganese steel exhibited lower hydrogen embrittlement resistance at higher current densities compared to austenitic stainless steel, primarily due to differences in hydrogen solubility and diffusivity linked to alloying elements. Although the deformed microstructures at the notch root were similar in both steels, their fracture behaviors under in-situ electrochemical hydrogen charging conditions showed significant differences. At the notch root, austenitic stainless steel displayed a quasi-cleavage fracture, while high-manganese steel exhibited intergranular fracture influenced by high-stress states, manganese segregation, and deformation twinning.</p> Graphical abstract <p></p>