Evaluations of mechanical properties under high pressure hydrogen gas environments are difficult because special testing equipment which can obtain data under high pressure hydrogen gas is necessary and the cost of installing those machines is very high. Therefore, a method for predicting mechanical properties under high pressure hydrogen gas without special equipment was investigated in this study. A JIS SCM435 steel, of which the typical chemical composition is Fe-0.35%C-0.2%Si-0.75%Mn-1.1%Cr-0.2%Mo, was used. Material with the size of 22mm in square and 200mm in length was heat-treated by quenching in oil and tempering, followed by water cooling. The material microstructure was tempered martensite, and the tensile strength of the steel was about 1000MPa. The fatigue property was evaluated in cathodic hydrogen charging service and high pressure hydrogen gas service. The fatigue property obtained by the cathodic charging method was almost the same as the property under the high pressure hydrogen gas condition. The reason is conjectured to be that the hydrogen fugacity on the specimen surface and the surface state of the specimen under those test services was substantially the same.

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