Preferential Locations of Hydrogen Accumulation and Damage in 1.2 GPa and 1.8 GPa Grade Hot-Stamped Steels: A Comparative Study

Abstract

In this work, hydrogen segregation and damage sites in 1.2 GPa and 1.8 GPa grade hot-stamped steels were comparatively investigated by hydrogen permeation experiments and the hydrogen microprint technique (HMT). Compared with 1.2 GPa steel, 1.8 GPa steel exhibited a lower hydrogen diffusion coefficient (Deff) and a higher number of hydrogen trapping sites (Nt) due to its finer microstructure and richer nano-sized precipitates. The results of HMT showed that the grain boundaries in both steels played a role in initial hydrogen segregation, and then the martensitic laths became the locations of hydrogen accumulation. For 1.2 GPa and 1.8 GPa steels, however, hydrogen accumulation appeared preferentially on martensitic laths and grain boundaries, respectively, resulting in various damage behaviors. The introduced nano-sized carbides as “good hydrogen traps” played an important role in hydrogen diffusion, accumulation, and damage, which greatly alleviated hydrogen-induced cracking for the 1.8 GPa steel. Moreover, electron backscatter diffraction (EBSD) analysis further revealed that the damage behavior was also controlled by the low-angle grain boundary, stress distribution, and recrystallization fraction of the samples.