Impact of volumetric energy densities on the mechanical properties of stainless steel 310 fabricated through selective laser melting

Additive manufacturing (AM) produces lightweight, durable, and intricate forms, whereas selective laser melting (SLM) uses laser energy to melt metal powder layers, creating almost dense components. The volumetric energy density (VED) is a crucial factor in evaluating consolidation with unfused or unmelted LPBF particles and is affected by the laser power, scan speed, scan spacing, and layer thickness. This study investigated the impact of VED ranging from 74.67 J/mm³ to 178.57 J/mm³ on the morphology and mechanical properties of the SS 310 samples, specifically their hardness and tensile strength. The top residual stresses (TRS) were greater than those on the lateral surfaces (LRS). The results also revealed that VED significantly influences recrystallisation, reducing VED by decreasing the dislocation density. High VED reduces porosity and defects, increasing part of the density. As the VED increased, the as-built samples exhibited an austenite phase and larger columnar grains. The hardness of the samples ranges from 280.4±3.81 (S1) to 300.8±4.34 HV (S24), with an increase due to reduced void formation, whereas pores allow deeper penetration, resulting in lower HV values. The ultimate tensile strength (UTS) ranged from 768.55±5.34 MPa (S25) to 854.57±2.73 MPa (S3), whereas the tensile ductility ranged from 4.72% to 12.08%. The difference was 10% between the highest and lowest UTS values. The decrease in VED resulted in increased defects, which affected elongation. Fractography revealed defects causing premature failure of the SS310 samples, with internal defects influencing crack propagation and decreasing mechanical properties. The most suitable VED range for achieving a maximum hardness of 300.8±4.34 HV (S24) and the highest UTS of 854.57±2.73 MPa (S3) with 7.4% elongation were 125 J/mm³ and 91.26 J/mm³, respectively.