Temperature dependency of hydrogen-related impact energy degradation of type 304 austenitic stainless steel

The influence of hydrogen on the impact energy of 304 austenitic stainless steel (ASS) and the corresponding fracture mechanism were investigated at temperatures from 25 °C to −196 °C. Hydrogen was pre-introduced into the test specimens via thermal pre-charging. Degradation of the impact energy was not observed in the hydrogen pre-charged specimens at temperatures ranging from 25 °C to −20 °C. In the temperature range of −20 to −196 °C, the degree of hydrogen embrittlement (HE) susceptibility increased with a decrease in the temperature and reached a saturated state at −100 °C. The characteristics of the ductile brittle transition temperature (DBTT) curve were significantly changed by the internal hydrogen. Specifically, the lower shelf energy was reduced by approximately 22 % and the DBTT value increased by approximately 40 % compared to those of the non-charged specimens. The tendency of HE susceptibility obtained for the impact test was in agreement with the results obtained for the SSRT test in the temperature range of −50 °C to 25 °C, which is attributed to the effect of SIM, α′ transformation on the hydrogen diffusion. The consistency of the HE susceptibility at temperatures below the maximum HE temperature is caused by the insignificant effect of the hydrogen diffusion rate owing to the extremely high strain rate. Strain-induced martensite (SIM) α′ is dominantly initiated along the grain boundary and the deformation twins on the hydrogen pre-charged specimens.