Influence of annealing temperature on the Charpy fracture characteristics of selective laser melted 316L steel at ambient and cryogenic temperatures

The effect of high-temperature annealing on the Charpy fracture properties of 316L stainless steel manufactured via Selective Laser Melting (SLM) was studied at ambient (25 oC) and cryogenic (–196 oC, LNT) temperatures. Charpy V-notched specimens (5×10×55 mm) were built along the Z-axis and annealed (5 h) at 900oC, 1050oC, or 1200oC, followed by water quenching. Impact tests were performed with the force-displacement curves recording. Microstructure was analysed using OM, SEM, EBSD, and EDX. The SLM-316L exhibited impact toughness (KCV) of one-third that of rolled 316L due to SLM’s cellular structure and specific micro-defects. Annealing at 900 oC removed the cellular structure, slightly improving impact toughness, while annealing at 1200 oC reduced it by a factor of 1.5 due to (MnCrSiAl)O3 precipitation. At –196 oC, absorbed energy decreased compared to 25 oC by a factor of 1.7-2.2. At 25oC, crack propagation energy (KVprop) exceeded crack initiation energy (KVini) across all conditions. At –196 oC, the KVprop fraction in annealed samples decreased because of deformation-induced martensitic transformation. The cellular structure of as-printed steel promoted a higher KVprop fraction at –196 oC. Ratio KCVLNT/KCVRT (0.46-0.59) indicates no ductile-brittle transition threshold, supporting the suitability of SLM-316L steel for cryogenic applications.