Fracture Strain of Al-Si-Coated Press-Hardened Steels under Plane-Strain Bending

Press-hardened steel (PHS) is widely applied to fabricate vehicle body structures for attaining mass reduction and fuel economy without sacrificing occupant safety. The VDA bendability test is often used to characterize the fracture resistance of PHS under plane-strain bending conditions. As lightweighting continues to be a design imperative in the automotive industry, it is desirable to develop and adopt more press-hardened components with higher fracture resistance. In this work, four Al-Si-coated 22MnB5 steels with various initial thicknesses and coating weights were studied. A newly developed methodology was used to calculate the fracture limit strain under plane-strain bending. The results indicate that although the four investigated 22MnB5 steels exhibit similar tensile properties under uniaxial tension, their bending performance per the VDA 238-100 standard differs significantly. The PHS with a low coating weight possesses a higher bending angle and, hence, a larger fracture limit strain. Meanwhile, the peak bending force can be 10% higher than the PHS with a standard coating weight at the same sheet thickness. Therefore, it is expected that PHS with higher fracture strain will have the potential for lightweighting due to its enhanced resistance to fracture and higher energy absorption capability.