Inclusions, grain boundaries and hydrogen attack

Optical metallography, scanning electron microscopy, and X-ray spectrometry were used to study the roles of grain boundaries and inclusions in the nucleation process and fissure growth during the rapid stage of hydrogen attack on 1020 steel in the annealed condition at temperatures up to 600 C and a hydrogen pressure of 10.3 MN/sq m. It is found that intergranular fracture occurred when specimens were fractured at 77 K after hydrogen exposure and that macroscopically observable fissures formed due to the coalescence of bubbles which nucleated at inclusions in grain boundaries. The inclusions are tentatively identified as MnS.