Investigation of effects of process parameters on microstructure and hardness of SLM manufactured SS316L

Highlights: • Energy density (50–80 J/mm³) is proportional to hardness. • Porosity is found an inverse function of hardness. • Normal and transverse surfaces exhibit differences (anisotropy) in hardness. • Study reveals martensite phase in the austenite (γ) matrix. Porosity is one of the major defects threatening mechanical properties in parts manufactured with Selected Laser Melting (SLM) method. Optimizing densification of materials is thus a key target of SLM as well as other similar methods to achieve the desired properties as per applications. In this study, porosity levels in Stainless Steel (SS) 316L parts manufactured with SLM were studied in relation to the effects of process parameters on microstructure and material hardness. Materials studied were manufactured in the energy density range of 50–80 J/mm³ and investigations have been conducted using various characterization techniques. The current study confirmed a strong relationship of energy density with porosity and hardness and it exhibits as the most influential variable that could control porosity and improve density of materials. In the range of energy density between 50 and 80 J/mm³, porosity decreases nearly exponentially and hardness increases linearly, with increasing energy density. The result is well in agreement with reports in the literature and demonstrates fabrication of SS316L with SLM to a highest density (>99.8%) and predicts possibility of optimization to achieve maximum density by further increasing energy density. In addition to austenite (γ), the analysis of microstructure with TEM reveals presence of tiny structures of martensite and/or ferrite in the austenite matrix of the SLM-fabricated SS316L.