Effect of post process shear straining on structure and mechanical properties of 316 L stainless steel manufactured via powder bed fusion

Abstract

Powder Bed Fusion (PBF) has become popular despite the fact that PBF-prepared components feature characteristic defects. Their performance, however, can be shifted to the next level by the application of post-processing, advantageously via intensive plastic deformation. The study characterizes the effects of rotary swaging performed at hot, cold, and cryogenic conditions on the (sub)structure and mechanical properties of workpieces of AISI 316 L stainless steel, favourably used in constructions as well as medicine, manufactured by PBF. The workpieces built in the horizontal and vertical directions were analysed to assess their structures, residual strain and stress, density, and porosity; porosity was observed primarily in the horizontally built workpiece also featuring lower density and larger average grain size. Subsequently, the workpieces were subjected to rotary swaging, which contributed to (almost) complete elimination of porosity, evident substructure development, and significant grain refinement – the vertically built workpiece exhibited the avg. grain size of 2.3 µm, 1.8 µm, and 0.1 µm after hot, cold, and cryo swaging. The cryo-swaged sample also exhibited specific texture, room temperature ultimate tensile strength (UTS) of more than 2 000 MPa, and two times higher microhardness compared to the as-build workpiece. All the swaged pieces exhibited significantly improved mechanical properties, even at the testing temperature of 900 °C. • rotary swaging reduced/eliminated printing defects of as-printed workpieces. • structure significantly refined, down to ultra-fine-grain level after cryo-swaging. • specific texture contributed to exceptional mechanical behaviour (at elevated temperatures). • combining powder bed fusion plus rotary swaging is a promising prospective production technology.