Microstructure, mechanical properties and machinability of 316L stainless steel fabricated by direct energy deposition

Additive/subtractive hybrid manufacturing (ASHM) technology is mostly based on direct energy deposition technology and achieves the direct forming of functional components by the timely use of alternating deposition and milling. This technology combines the high efficiency and material utilization of additive manufacturing (AM) with the high dimensional accuracy and surface quality of subtractive manufacturing (SM). In this work, the AM forming was utilized to rapidly generate the basic configuration of a 316L stainless steel components and the SM milling achieved its machined surface, aiming to study the forming mechanism and their effects on machinability. The rapid cooling rate in the direct energy deposition process contributed to grain refinement and precipitation of ferrite, which resulted in the improvement of hardness and tensile strength. There was no obvious linear relationship between work hardening and cutting speed or feed per tooth because the work hardening was affected by a combination of shear strain strengthening effect and thermal softening effect. The fine grains and more molten pool boundaries in the stainless steel by AM process leaded to the larger depth of work hardening during SM process. Finally, a variety of stainless steel components exhibited the good surface quality and dimensional accuracy by ASHM process.