Liquid Hydrogen Properties Affecting Fracture Toughness

In this study, fracture toughness with the base metal of 9% Ni steel, a cryogenic steel, was evaluated under conditions without hydrogen charging (WO-H) and with hydrogen charging (W-H). Hydrogen charging was performed using an electrochemical cathodic charging method in a electrolyte of 3% NaCl + 0.3% NH4SCN at 19℃ with a current density of 50 A/m². Fracture toughness was assessed at -80℃, -100℃, -130℃, and -160℃ using CTOD (Crack Tip Opening Displacement) tests. The results for WO-H indicated a decrease in fracture toughness values with decreasing temperature, while the results for W-H showed an increase in fracture toughness values as the temperature decreased. In addition, the fracture surfaces and fracture toughness of WO-H and W-H became increasingly similar as the temperature decreased, as observed through scanning electron microscopy (SEM). At -80℃, there was a significant difference in fracture toughness between the WO-H and W-H conditions. WO-H was influenced only by the low temperature, whereas W-H was affected by both low temperature and hydrogen, showing combined effects that led to a decrease in fracture toughness due to hydrogen embrittlement. However, at -160℃, the fracture toughness values for both WO-H and W-H conditions were nearly identical. This suggests that the temperature effect on fracture toughness reduction is greater than hydrogen embrittlement at very low temperatures.