  The observation of sub-grained cellular features in additively manufactured
(AM)/selectively laser melted (SLM) 316L stainless steel components has
remained an interesting, though incompletely understood phenomenon. However,
the recently observed correlation linking the presence of these features with
significantly enhanced mechanical strength in SLM 316L materials has driven a
renewed interest and effort toward elucidating the mechanism(s) by which they
are formed. To date, the dominant hypothesis, cellular solidification followed
by dislocation-solute entanglement, remains incompatible with the ensemble of
reported observations from multiple independent studies. This effort offers
direct evidence of a previously unrecognized interaction of phenomena, that,
when acting in concert, give rise to this commonly observed substructure. These
phenomena include SLM-induced intrinsic strain-aging, Cottrell atmosphere
formation, and twin-boundary enhanced mass diffusion to structural defects.
