Dependence of microstructures on fatigue performance of polycrystals: A comparative study of conventional and additively manufactured 316L stainless steel

•Fatigue properties and microstructural evolution of AM steel were systematically studied and compared with its wrought counterpart.•Unique microstructures of AM steel contribute greatly to its superior fatigue property, and underlying mechanisms were studied.•Pre-existing high-density dislocations and chemical microsegregation in AM steel partly contribute to its superior fatigue property.•The enhanced planar slip by its unique microstructures in AM steel plays an additional role in the superior fatigue property.•The unique cell structure has more positive effects on LCF performance of AM steel due to the enhanced ductility.