Microstructure and fatigue behavior of 24CrNiMo low alloy steel prepared by selective laser melting

The microstructure and fatigue performance of 24CrNiMo low alloy steel by selective laser melting (SLM) were investigated through SEM, EBSD and fatigue tester. The results indicated that the SLM sample with relatively high fatigue strength (580 MPa) was obtained. The excellent fatigue behavior was mainly contributed to the excellent combination of strength and plasticity as indicated by EBSD analysis showing fine grain sizes, high kernel average misorientation (KAM) and Schmid factor (SF) values. Both manufacturing defects (e.g., lack of fusion, pore) and the matrix can act as crack initiation sites, meanwhile, the former can be divided into surface and interior defects considering the defect location at the origin of fatigue micro-cracks. According to the scatter degree of the fatigue data in the S–N curve, the difference in the location of original cracks showed a greater impact on the fatigue lifetime than that in the type of original cracks. The fracture mechanism of the SLM sample evolved from brittle fracture in the fatigue crack propagation zone to ductile fracture in the instantaneous fracture zone.