Notch tensile behavior of 304L and 316L stainless steels under in-situ and ex-situ electrochemical hydrogen charging

This study examines the notch tensile behavior of 304L and 316L stainless steels under in-situ and ex-situ electrochemical hydrogen charging conditions using slow strain-rate tests (SSRTs). Thermal desorption spectrometry (TDS) analysis results revealed that the total hydrogen content in 304L and 316L stainless steels varied due to differences in grain size and alloying elements. In-situ SSRT results showed that a high localized hydrogen concentration ahead of the notch tip substantially reduced ductility and accelerated failure, transitioning the fracture morphology of both steels from ductile to brittle behavior. Microstructural analysis after in-situ SSRT indicated that hydrogen accumulation ahead of the notch tip prevented sufficient plastic deformation for strain-induced martensite transformation. Additionally, the lower austenite stability of 304L stainless steel in comparison with 316L stainless steel contributed to some strain-induced martensite formation, which facilitated hydrogen diffusion and thereby reduced hydrogen embrittlement resistance. On the other hand, the ex-situ hydrogen charging method exhibited minimal hydrogen embrittlement as hydrogen was uniformly distributed within the notched tensile specimen.