Carbon neutrality is an essential action toward the resolution of global climate change. Hydrogen energy utilization is one route to achieve the carbon-neutral society. From the standpoint of material engineering, hydrogen embrittlement, i.e. degradation of strength characteristics of metallic materials due to hydrogen intake, is an obstacle for the safety use of hydrogen. In general, materials which are less susceptible to hydrogen are limited to relatively expensive materials like an austenitic stainless steel. To realize hydrogen society, the range of available material for hydrogen energy equipment needs to be extended to include common, low-cost materials such as carbon steel and low alloy steel.

Ferritic-pearlitic ductile cast irons (FP-DCIs) are one of the perspective candidates for a low-cost, common material used for hydrogen applications. The mechanical properties of FP-DCIs are widely tailored to fit requirements by controlling microstructural factors such as matrix structure, graphite size, and graphite volume fraction. Therefore, it is reasonable to expect that hydrogen storage and hydrogen embrittlement properties of a FP-DCI are also strongly influenced by such microstructural factors. In this study, the effect of microstructural factors on the hydrogen storage and hydrogen embrittlement properties of FP-DCIs were investigated. Several types of FP-DCI were prepared by the control of chemical composition, cooling rate in casting process and heat treatment, and hydrogen was charged into a specimen by soaking the specimen in the aqueous solution of NH₄SCN.

The hydrogen storage capability of ferritic DCI was strongly dependent on the graphite size, and it sharply increased at a mean graphite diameter of around 13 micro meters. On the other hand, the hydrogen storage of FP-DCIs was also influenced by their matrix structure. That is, it was revealed that the amount of hydrogen storage of pearlitic DCI was significantly lower than that of ferritic DCI. However, since a ferritizing annealing did not increase the hydrogen absorption capacity of pearlitic DCI despite matrix transformation from pearlite to ferrite, the matrix structure is considered not to have a primary impact on the hydrogen storage capability of FP-DCIs. In this study, how microstructural condition impacts the hydrogen storage capability and the hydrogen embrittlement of FP-DCIs were discussed.