An austenite-rich composite of stainless steels with high strength and favorable ductility via selective laser melting of a powder mixture

Abstract

Austenitic stainless steels (SSs) with excellent mechanical properties can be fabricated by selective laser melting (SLM). To enrich the variety of SLM-fabricated austenitic SSs and develop some SSs which possess desired properties and cost, an austenite-rich composite of stainless steels was fabricated by SLM of a powder mixture composed of 310 S and 430 SSs. The effect of laser energy density on the defects, microstructure and mechanical properties of materials was investigated. At an appropriate energy density (89.3 J/mm3), samples exhibited the best ultimate tensile strength (∼701 MPa) and elongation to failure (∼46.6%). However, the occurrence of strong keyholing and spattering phenomena severely weakened the tensile properties of samples at the highest energy density (113.6 J/mm3). For all samples, their microstructure was mainly composed of lots of austenite phase and some delta (δ) ferrite phase. The existence of ultra-fine sub-grains surrounded by dislocation networks played an important role in the tensile properties of samples. Particularly, the formation of fine δ-ferrite at grain boundaries of austenite could hamper the growth of austenite grains, and lots of dislocations are formed at the interface between austenite and δ-ferrite. The existence of δ-ferrite with a circular flow feature could inhibit the epitaxial growth of austenite grains.