Effect of coating on hydrogen embrittlement of hot stamping 22MnB5 high strength steel during electrochemical charging

This study investigated the effect of Al–Si coating and its service condition on hydrogen embrittlement (HE) of hot-stamped ultra-high strength martensitic steels (22MnB5) through electrochemical hydrogen charging. The HE behaviour of coated and uncoated specimens under different charging conditions was investigated. The deterioration degree of mechanical properties of charged specimens with charging current is monotonous. At low-current charging, the more severe deterioration of coated specimens due to the excess hydrogen which was provided by corroded coatings. Contrary, with high-current charging, the integral coatings provided effective protection and retarded HE behaviour. Furthermore, the scanning electron microscopy revealed a similar transition of fractography, i.e., from ductile (uncharged) to quasi-cleavage (0.001A-2h) and a mixture of quasi-cleavage and intergranular fracture (0.1A-2h). Additionally, the coated tailor rolled blank steel was selected to investigate the effect of coating condition on HE. It revealed that the deformation-induced defects on coatings would impair the resistance to HE. Thus, we demonstrated that the Al–Si coating which effectively alleviate HE, was dependent on its integrality.