Improvement of Hydrogen Embrittlement by Void Formation at Coating Layers of Sb-Added Al-Si-Coated Hot-Press-Forming Steels

Al-Si coating prevents the oxidation or decarburization of hot-press forming (HPF) steel. However, the high reactivity of Al with moisture promotes H uptake, and the coating hinders the out-diffusion of absorbed H atoms inside the steel, leading to hydrogen embrittlement (HE). This study added Sb to adjust Fe and Al/Si diffusivity, and forming H-trapping voids within the coating. Simultanesouly, these voids provided routes for the emission of H atoms, thereby improving the resistance to crack propagation during bending. The optimal design of the Al-Si coating by adjusting the Sb content and void fraction would enable extensive applications of HPF steel.