Influence of solidification conditions on chemical heterogeneities and dislocations patterning in additively manufactured 316L stainless steel

The dendritic substructure of 316L stainless steel processed by Laser Powder Bed Fusion (L-PBF) is experimentally investigated on three specimens built with significantly different scanning speeds and solidification cooling rates. Microstructural features of interest are misorientations between dendrites, gradients of chemical composition and dislocations structures. Similar amplitudes of chemical heterogeneities are found for all three samples, possibly related to the conjunction of relatively low variations of solidification rates and large partition coefficients for the considered solute elements. No crystalline misorientations between neighboring dendrites are observed, implying that interdendritic dislocations are not geometrically necessary dislocations stemming from solidification but arise from thermomechanical straining during post-solidification cooling. Dislocations patterning appear to be closely correlated to the periodicity of microsegregations, hinting at an effect of the local chemistry. No simple HallPetch-like effect of the dendrite size is observed on compression tests, possibly due to different strengthening mechanisms depending on the dislocations structures.