Hydrogen is one of the main candidates in replacing fossil fuels in the forthcoming years. However, hydrogen technologies must deal with safety aspects due to the specific sub�stance properties. This study aims to provide an overview on the loss of mechanical properties of cryogenic materials, which may lead to serious consequences, such as fires and explosions. The hydrogen embrittlement of cryogenic steels was investigated through slow strain rate tensile tests (SSRTs) and thermal desorption analyses of electrochemically H-charged specimens. As a prior study to confirm mechanical properties under liquid hydrogen conditions, the amount of diffusive hydrogen that causes hydrogen embrittlement was confirmed after charging hydrogen using an electrochemical method for 4 types of steel materials applied as cryogenic materials did. When exposed to the same hydrogen charging conditions, the amount of hydrogen diffused into the 9% nickel steel is the highest compared to the austenitic steel type. It is considered that this is because the diffusion and integration of hydrogen into the interior is easy. It is necessary to analyze the relationship between hydrogen loading and mechanical properties, and this will be carried out in a follow-up study.

Due to global warming and environmental pollution, environmental regulations are getting stronger, and the International Maritime Organization announced regulations to reduce CO2 emissions in 2018. In order to respond to this, interest in hydrogen energy is growing, and research on liquid hydrogen is spotlighted for storage and transport of large amounts of hydrogen. Hydrogen reduces in volume to 1/800 when liquefied, but its boiling point is close to absolute zero(-253°C), and hydrogen embrittlement that penetrates other materials and weakens mechanical properties. In this study, the change of mechanical properties under cryogenic conditions (-196 degrees below zero) was confirmed after charging hydrogen into existing cryogenic materials (Stainless steel, High Manganese steel, 9% Nickel steel). In Part I, hydrogen was charged using an electrochemical method and quantitative evaluation was performed. In all four materials, as the changing time increased, the diffusible hydrogen concentration increased. After 24 hours charging, the hydrogen loading of 20 wppm in 9% Ni steel and 15 wppm in high-Mn steel was confirmed. In a follow-up study, we plan to study the effect of hydrogen charging by comparing the results of the mechanical properties test with the above results.