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

Abstract

Al-Si coating prevents the oxidation or decarburization of hot-press forming (HPF) steel; however, high reactivity of Al with the moisture promotes H atoms uptaking, and the coating prevents the out-diffusion of H atoms absorbed inside the steel, causing hydrogen embrittlement (HE). In this study, the addition of Sb adjusted the diffusivity of Fe and Al/Si and formed voids, H-trapping sites, inside the coating. Concurrently, the voids provided emission routes of H atoms, thereby improving the resistance to bending crack propagation. The optimal Al-Si coating design by adjusting the Sb content and void fraction would secure wide applications of HPF steel.

Keywords: Hot-press-forming (HPF) steel, Hydrogen embrittlement (HE), Sb addition, Al-Si coating, Sb-enriched zone, Intrusion and emission of H atoms