The cellular boundary with high density of dislocations governed the strengthening mechanism in selective laser melted 316L stainless steel

The cellular sub-grain was widely reported as the main contributor to the high yield strength of selective laser melted stainless steels, but its underlying strengthening mechanism was still unclear. In this study, the high yield strength of selective laser melted 316L stainless steel was studied by manipulating the cellular sub-grain through various heat treatments. Although the cellular sub-grain still existed in the heat-treated samples, the yield strength decreases significantly after heat treatment. This study firstly demonstrated that the high density of dislocations at the cellular boundary played a key role in the interfacial strengthening effect. Despite the small misorientation between the neighbouring cellular sub-grain, the cellular boundary acted as the high-angle grain boundary during deformation. The dislocation network consisted of the cellular boundaries provided a high density of interfaces that significantly inhibited the dislocation motion, resulting in higher yield strength.