Immersion corrosion of material extrusion steel 316 L: Influence of  immersion time and surface roughness

This work investigates the influence of surface roughness on the immersion corrosion of Steel 316 L fabricated  via the material extrusion (ME) additive manufacturing (AM) method. For that purpose, a metal-polymer filament was used to produce ME specimens via fused filament fabrication. An experimental investigation was  performed on both ME and wrought Steel 316 L specimens which were immersion-tested in a NaCl corrosive  solution for three different exposure times. The specimens were also separated into to two groups according to  their surface roughness. The corrosion-tested ME Steel 316 L presented an austenitic microstructure with twins  and polygonal grains. Approximately ten percent of the phase volume was found to be in ferrite form, which is a  known factor promoting corrosion in steel alloys. Moreover, substantial porosity was observed, manifested in the  form of inclusions and irregular/spherical defects, which are typically caused by the ME fabrication process. The  ME Steel 316 L has exhibited an unstable corrosion resistance, unlike the wrought material. The varying  corrosion performance of the ME Steel 316 L amy be attributed to a weaker passivation ability, relative to its  wrought counterpart, owe to the combined effect of δ–ferrite in the microstructure and macroscopic porosity. n  statistical evaluation of the results, via ANOVA, suggested that the exposure time can be an influential factor for  the ME Steel 316 L corrosion resistance. Surface roughness may also have an effect, however less significant. This  study has identified, for the first time, the transitional character of the corrosion behaviour of ME Steel 316 L at  lower exposure times. These new findings for the ME Steel 316 L and the results from the present analysis can  inform the community seeking to use this AM alloy within corrosive environments.