Mechanisms controlling fracture toughness of additively manufactured stainless steel 316L

Additive manufacturing (AM) has emerged as an alternative tool to overcome the challenges in conventionally processed metallic components. It is gaining wide acceptability because of the superior properties of the manufactured components compared to their wrought processed counterparts. Among the available AM processed materials, austenitic stainless steel 316L is widely explored wherein an excellent strength-ductility trade-off has been reported. However, the mechanisms underlying fracture toughness of AM stainless steel 316L vis-a-vis wrought processed stainless steel 316L material are not yet explored. The present investigation is aimed at examining the mechanisms accountable for the fracture toughness of AM processed stainless steel 316L. The specimens are produced by two different AM techniques namely, selective laser melting (SLM) and wire arc additive manufacturing (WAAM). A wrought processed stainless steel 316L was used as a control material for comparison. Three-point bending tests were carried out on fatigue pre-cracked single edge notched specimens and crack initiation fracture toughness was evaluated. Digital image correlation was used for strain analysis and to monitor crack propagation. The SLM manufactured sample has shown higher fracture toughness whereas WAAM has exhibited nearly the same fracture toughness when compared to the wrought processed stainless steel 316L sample. Microstructure of fractured samples consists of a significantly higher twin density and a higher propensity of dislocation slip was observed in the SLM sample than the other two. It has been argued that a very fine cellular structure, minimized process-induced defects, enhanced twin density led to promising toughness in the SLM processed stainless steel 316L.