Hydrogen-induced delayed fracture behavior of notched 316L austenitic stainless steel: Role of grain refinement

Generally, grain refinement is considered to strengthen and mitigate the hydrogen embrittlement resistance of material. However, the effect of grain refinement on hydrogen-induced delayed fracture is rarely reported, especially concerning the extensive existence of geometric in- homogeneity such as notches. In this work, the effect of grain size on hydrogen-induced delayed cracking of notched 316L stainless steel under in-situ hydrogen charging is investigated. It is found that the brittle zone of delayed fracture of notched specimens is much larger than that in slow strain rate tensile of smooth specimens. This is due to the alternation of hydrogen diffusion and crack propagation during delayed fracture. After grain refinement, the time of delayed fracture increases significantly for the notched specimens, even the fracture does not happen, owing to the increase of austenitic stability. It is unusual that, regardless of grain size, alpha' martensite is not detected at the crack tip, because the accumulated hydrogen at crack tip reduces plastic strains and suppresses martensite transformation.