Postprocessing of additively manufactured (AM) metal parts to remove support structures or improve the surface condition can be a manually intensive process. One novel solution is a two-step, self-terminating etching process (STEP), which achieves both support removal and surface smoothing. While the STEP has been demonstrated for laser powder bed fusion (L-PBF) 316L stainless steel, this work evaluates the impact of pre-STEP heat treatments and resulting changes in dislocation density and microstructure on the resulting surface roughness and amount of material removed. Two pre-STEP heat treatments were evaluated: stress relief at 470°C for 5 h and recrystallization–solution annealing at 1060°C for 1 h. Additionally, one set of specimens was processed without the pre-STEP heat treatment (as-printed condition). Dislocation density and phase composition were quantified using X-ray diffraction along with standard, metallurgical stain-etching techniques. This work, for the first time, highlights the mechanisms of sensitization of AM L-PBF 316L stainless steel and provides fundamental insights into selective etching of these materials. Results showed that the sensitization depth decreased with increasing dislocation density. For samples etched at a STEP bias of 540 mV_SHE, material removal terminated at grain boundaries; therefore, the fine-grained stress-relieved specimen had the lowest post-STEP surface roughness. For surface roughness optimization, parts should be stress relived pre-STEP. However, to achieve more material removal, pre-STEP solution annealing should be performed.

The poor surface finish of as-printed (AP) laser powder bed fusion (L-PBF) 316L stainless steels has detrimental impacts on the resulting fatigue and corrosion performance. One postprocessing method, a self-terminating etching process (STEP), can improve the surface finish of parts up to 76%, but the resulting effects on fatigue life and corrosion reliability remain unknown. This work evaluates the effect of the STEP on the fatigue and corrosion performance of L-PBF 316L. In addition, to determine the influence of changing the microstructures from the as-built condition, specimens having undergone a pre-STEP stress relief (SR + STEP) heat treatment and a pre-STEP solution anneal (SA + STEP) were evaluated. The results showed that a pre-STEP SR resulted in the best Sa roughness, while a pre-STEP SA had the biggest improvement in Sv roughness. Despite Sv roughness being a major indicator of fatigue performance, the coarse grains and internal porosity in the SA specimens resulted in the poorest fatigue performance. The SR + STEP specimens' fatigue lives were 10 × higher than the AP samples under a load of 275 MPa and 2–3 × higher under a 350 MPa load. The SR + STEP specimen also had the best corrosion performance in a sodium chloride electrolyte due to the smoother surface and least remnant surface carbides.

Post-processing of additively manufactured components, including the removal of support structures and the reduction in surface roughness, presents significant challenges. Conventional milling struggles to access internal cavities, while the Self-Terminating Etching Process (STEP) offers a promising solution. STEP effectively smooths surfaces and dissolves supports without substantial changes in geometry. However, it can lead to compositional changes and precipitation, affecting the material properties and necessitating a design strategy to mitigate them. In this study, STEP is applied to stainless steel 316L (SS316L) produced via laser powder bed fusion, reducing surface roughness from 7 to 2 μm. After STEP, the surface carbon exhibited a threefold increase, leading to the formation of M₂₃C₆ clusters. This significantly impacted the yield strength, resulting in a 37% reduction compared to the as-built condition. The key to overcoming this challenge was using computational simulations, which guided the determination of the decarburization conditions: 1000 °C for 60 min, ensuring maximum M₂₃C₆ dissolution and surface carbon reduction with minimal grain coarsening. Following these conditions, the yield strength of SS316L was restored to the level observed in the as-built condition. These findings underscore the potential of the proposed design strategy to enhance the mechanical performance of additively manufactured components significantly.