Enhancing microstructural and mechanical properties of 316L stainless steel through Material Extrusion (MEX) optimization

The advent of Material Extrusion (MEX) additive manufacturing for metallic feedstocks presents an opportunity for the cost-effective production of complex austenitic stainless-steel components. However, the widespread adoption of this technology is currently limited by challenges related to porosity, anisotropic shrinkage, and suboptimal interlayer bonding, particularly when utilizing standard parameters derived from polymer processing. This paper presents results of studies focused on the influence of critical printing parameters like specifically nozzle diameter, extrusion temperature, and deposition strategy on the mechanical and microstructural properties of BASF Ultrafuse 316L stainless steel. The study employs a rigorous two-stage experimental design. Stage 1 characterises the limitations of standard processing parameters (0.4 mm nozzle), revealing high porosity and insufficient tensile strength (MPa). Stage 2 implements an optimised strategy utilizing a 0.6 mm nozzle and elevated printing temperatures (250 °C), resulting in an enhancement of mechanical performance, with ultimate tensile strength rising to 483 MPa and elongation at break exceeding 50%. Furthermore, a critical comparative analysis is conducted between specimens printed to net shape and those machined from bulk preforms, elucidating the “shell effect” and its role in mechanical reliability. The findings demonstrate that through precise thermal and shear rate management, MEX 316L can achieve properties competitive with Metal Injection Moulding (MIM), thereby validating the technology for functional structural applications.