Revealing relationships between heterogeneous microstructure and strengthening mechanism of austenitic stainless steels fabricated by directed energy deposition (DED)

Abstract

The heterogeneous trans-scale structures play important roles in achieving high strength and toughness in austenitic stainless steels fabricated by directed energy deposition (DED). In this study, systematic annealing investigations were demonstrated the evolution of trans-scale heterogeneous structures such as dislocations, chemical cells, nano-oxides, grains and recrystallization behavior. Their effects on yield strength were quantified. The experimentally observed yield strength of as-received and annealed samples agrees well with the estimated yield strength using standard Taylor hardening formulae. The dislocation intensity accounted for 200 MPa and became the main strength contributor, among which GND type of dislocation accounted for more than 60% of the total dislocation. Despite the development of DED steel micro inclusions, the synergistic effect of deformation twinning and pre-existing GND-induced back stress results in high tensile plasticity. This research helps to better understand the interplay between DED processing, the microstructure of 316L stainless steel and the mechanical properties that are crucial to meeting new demands.