Irreversible hydrogen embrittlement study of B1500HS high strength boron steel

The reversible/irreversible recovery of mechanical properties, and the microstructure characteristics of a typical hot-stamped steel B1500HS have been studied under different conditions of hydrogen permeation. Initially, all tested specimens were permeated by hydrogen atoms through an electrochemical hydrogen charging scheme. Then, the comparisons between different currents and charging time were performed. The influence of different storage time was compared as well. Additionally, the effect of the plastic strain introduced by pre-stretching was also investigated. The experimental results showed that the negative impact of hydrogen embrittlement was altered from reversible to irreversible as the magnitude of the charging current increased. The hydrogen blistering and the hydrogen charging-induced cracks were both observed and inspected in the tested samples regarding the irreversible situation. Moreover, the adverse influence of hydrogen embrittlement was enhanced by plastic pre-straining or extending the charging period. At the micro-level, hydrogen charging-induced cracks generally were generated at defect locations, such as the prior austenite grain boundaries and lath martensite interfaces. Particularly, crack direction occurred perpendicular to the orientation of lath martensite, and transgranular fracture occurred at the prior austenite grains.