Experimental Study of the Hydrogen Fracture Behavior of 30CrMo Steel and Simulation of Hydrogen Diffusion

The tensile properties and fatigue crack propagation mechanism of 30CrMo steel were investigated under electrochemical hydrogenation conditions by tensile and fatigue crack propagation tests. The results indicate that, following electrochemical pre-hydrogenation, the tensile strength of the material is marginally enhanced, while its plasticity is significantly diminished. Furthermore, its elongation is reduced from 30.91% in the absence of pre-hydrogenation to 22.35% in the presence of pre-hydrogenation. Additionally, the fatigue life following pre-hydrogenation was observed to diminish by 15%. The rate of crack propagation is approximately four times that observed in the absence of pre-hydrogenation. Scanning electron microscope (SEM) fracture analysis revealed a shift in the fracture mechanism from ductile fracture without pre-hydrogenation to quasi-dissociative fracture after pre-hydrogenation. The analysis by digital image correlation (DIC) technique showed that the specimens treated with pre-hydrogen were more open at the P/P_max of 35% and the strain at the fast fracture stage increased significantly from 908.92 to 1021.41 compared to the specimens without pre-hydrogenation. In addition, finite element simulation of the hydrogen diffusion mechanism in the steel using Comsol software revealed that, under stress, the hydrogen atoms were significantly enriched at the crack tip, and the hydrogen concentration at the crack tip increased from 32.1 mol/m³ to 48.5 mol/m³ with the increase of the hydrogen charging time up to 180 min; the further away from the crack tip, the smaller the hydrogen concentration, regardless of the stress.