Climate change is a global challenging issue, and carbon neutrality is an essential worldwide action toward the resolution of this issue. Hydrogen energy utilization is one route to achieve the carbon-neutral society. Currently, hydrogen production by renewable energy and efficient transport and use of hydrogen have been developed. 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. In order toward the realization of a 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.

Ductile cast iron is one of the prospective candidates, and it is characterized by extensive strength properties obtained by controlling microstructural factors such as graphite size, volume fraction of graphite, matrix structure and so on. In this study, the effect of matrix structure on the hydrogen embrittlement properties of ferritic-pearlitic ductile cast irons (FP-DCIs) was focused.

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 amount of hydrogen absorption of the specimens was evaluated by a gas chromatographic thermal desorption analyzer, and it was found that the ferritic DCI absorbed much more hydrogen than the pearlitic DCI. Although the matrix structure of the pearlitic DCI changed to almost ferrite by ferritizing annealing, this ferritized DCI showed a hydrogen storage capability similar to the pearlitic DCI. In addition, as the period of annealing for the pearlitic DCI increased, there was not significant change in the degree of matrix transformation but remarkable increase in the hydrogen storage. These results imply that the matrix structure does not have a primary impact on the hydrogen storage capability of FP-DCIs. In this study, the hydrogen storage properties of FP-DCIs with various microstructural circumstances were investigated, and what parameter dominantly affects on the hydrogen storage and the hydrogen embrittlement of FP-DCIs was discussed.