Understanding hydrogen desorption mechanisms in aluminized PHS

Press hardenable steels (PHS) coated with Al-Si alloy are widely used in the automotive industry owing to their good mechanical properties (YS > 1200 MPa and TS > 1500 MPa). The presence of Al-Si coating prevents oxidation and decarburization of steel during austenitization. It has been found that aluminized PHS are more sensitive to hydrogen absorption during austenitization in comparison to uncoated PHS. After quenching, Al-Si coating indeed acts as a hydrogen-diffusion barrier at room temperature and the diffusible hydrogen present in aluminized PHS can lead to hydrogen embrittlement (HE). In this context, this thesis aims at investigate the mechanisms that govern the rate of hydrogen absorption and desorption in coated PHS. Thermal Desorption Analysis (TDA) is the main characterization technique used throughout this thesis. Besides, austenitization of coated samples was carried out in controlled atmosphere containing D2O instead of H2O to avoid any atmospheric contamination which could compromise further accurate quantification. In order to assess hydrogen trapping sites in aluminized PHS, mechanical removal of the coating from the steel substrate was performed. This highlighted that hydrogen in aluminized PHS is reversibly trapped in the dislocation strain fields in the steel substrate. Additionally, the origin of multiple peaks in D2 desorption profiles of aluminized steels are attributed to different D diffusion paths. The first peak is related to desorption of D from cut bare edges, while high temperature peaks are related to desorption of D