Towards fatigue-resistant steels: Interfacial fatigue crack mechanisms in complex inclusions revealed by TEM and atomic simulations

• Reproducing the complex inclusions interfacial behavior under fatigue loading. • Chemical bonding governs inclusion interface stability, not van der Waals forces. • Compression-induced distortion loss triggers interfacial crack nucleation during tension. • Multiscale models link atomic mechanisms to macroscopic fatigue crack. Despite the significance of inclusions on fatigue properties, a thorough and physics-based understanding of the failure behavior of complex inclusions is still missing due to experimental limitations. An atomic-scale simulation approach is proposed for investigating the interfacial cracking behavior of Ca 2 Al 2 SiO 7 /CaS complex inclusion in steel under tensile-compressive cyclic loading conditions. The results show that regular parallel lattice distortions are induced in CaS to generate stable interfacial structures. Interestingly, these distortion rows will gradually disappear under compression and eventually deteriorate the distortions adjacent to the interfacial region, which become the crack nucleation sites under tension. This study provides an in-depth understanding of the fatigue mechanism of modern steels with complex inclusions and potentially offers a physics-based bottom-up method to determine the fatigue life of materials.