Optimizing bendability of AlSi-coated 2GPa-grade press-hardened steel by double austenitization

The present work, for the first time, demonstrates that a new heat treatment process involving double austenitization can effectively optimize the coating structure and prior austenite grain size (PAGS) of an AlSi-coated 2GPa-grade press hardened steel (PHS), resulting in an improvement of bendability while keeping similar ultimate tensile strength (UTS). It is found that the interdiffusion ferrite layer in the coating structure is responsible for the improvement of bendability while the controlled PAGS keeps similar UTS. More specifically, it shows that the interdiffusion ferrite layer with high Al content is brittle and detrimental to bendability. Consequently, a double austenitization process is employed to produce an interdiffusion ferrite layer with an Al content lower than 4 wt.%, resulting in an improvement of bending angle over 60° while keeping similar UTS.