Influence of processing parameters on mechanical and fatigue properties of 316 L steel manufactured by selective laser melting

The Selective Laser Melting process involves multiple factors that are detrimental to fatigue life. It is crucial to select optimal processing parameters to avoid internal porosity, source of early failure through crack initiation mechanisms. Surface condition, especially high roughness values, may also be a critical factor for crack initiation. Influence of surface condition must be studied in the industrial context, where parts may not be completely machined before implementation. This work first focused on finding optimal parameters for producing low-porosity 316 L parts by the SLM process. Once a suitable set of parameters was found, a set of samples was characterized mechanically. Fatigue samples were then produced and submitted to various surface treatments (machining, polishing, …), while some were left as-built. They were then tested in high-cycle fatigue and S-N curves produced for each sample type. This study indicates that high-cycle fatigue life of SLM 316 L is generally inferior to wrought 316 L, with as-built samples exhibiting lower fatigue limits. This was explained by surface roughness acting as crack initiation sites. Porosity was also found to be a very significant factor in fatigue life of SLM 316 L.