Ductile cast iron (DCI) is a prospective structural material for hydrogen equipment because of low-cost and good mechanical properties comparable to carbon steel. Toward the safety use of ductile cast iron, it is important to understand the mechanism of hydrogen embrittlement of DCI and its remarkable difference from that of carbon steel.
In a previous study, it was reported that the graphite nodules in DCI have a remarkable capability for hydrogen storage compared with ferritic matrix. In addition, the tensile tests of hydrogen-charged ferritic DCI demonstrated the marked ductility loss caused by quasi-cleavage fracture originated from graphite nodules. Though similar ductility loss occurs also in hydrogen-charged ferritic carbon steel, the fracture mechanism is completely different and it is associated with void growth and coalescence. In essence, a large amount of hydrogen is stored in graphite in DCI and this hydrogen storage within graphite is considered to play a key role in the unique fracture mechanism of hydrogen-charged DCI. In order to elucidate the hydrogen embrittlement mechanism of DCI, in this study, the tensile tests were carried out using hydrogen-charged ferritic DCI and ferritic carbon steel. The difference in the hydrogen embrittlement mechanism between these two materials was discussed in terms of the behavior of hydrogen associated with graphite in DCI.