Strengthening mechanisms in selective laser melted 316L stainless steel

Abstract

The microstructure and chemical composition of a 316L stainless steel prepared by selective laser melting have been characterized using electron backscatter diffraction, transmission electron microscopy and atom probe tomography (APT). A multi-scale microstructure in the 316L stainless steel was observed in the as-built samples, consisting of equiaxed and columnar grains, dislocation cell blocks, dislocation cells, individual dislocations and nano-sized particles. The misorientations across dislocation cells were determined based on local crystallographic orientation measurements using a Kikuchi pattern method. The dislocation cells have very small misorientation angles with an average angle of 0.9°, and are arranged to form dislocation cell-blocks with cell-block boundary misorientation angles generally larger than 2°. APT data reveal that alloying elements are evenly distributed in the matrix as well as a high nitrogen content in the as-built material. Based on quantification of the microstructural parameters, good agreement is achieved between the yield strength as calculated from a linear sum of different strengthening contributions, and the experimentally measured value, with significant contributions from dislocation strengthening and solid solution strengthening effects.