Effect of microstructural features on the fatigue behavior of ultra-high strength press hardened steels

Nowadays, high-strength press-hardened steels (PHS) have gained wide applications in automotive body-in-white owing to excellent mechanical properties. Nevertheless, the fatigue properties of high-strength PHS and associated failure mechanisms have not been clearly revealed, which restricts their potential applications in other parts of automobiles involving fluctuating and repetitive stresses, such as wheels or beams. In this work, the fatigue behavior of 1900 and 2000 MPa grade PHS is systematically studied, with the main focus on the associated deformation and fatigue cracking mechanisms. The fatigue behavior of these two steels is similar, and the ratio of fatigue strength to tensile strength is around 0.5. The fatigue damage mechanism of high-strength PHS is dominated by surface cracking, as the fine martensite structures reduce the stress concentration and cracking at small-sized inclusions. This work can provide guidance for the application of high-strength PHS in alternating loads scenarios.