This study investigates the stress corrosion cracking (SCC) behavior of type 316L stainless steel (SS316L) produced with sinter-based material extrusion additive manufacturing (AM). Sinter-based material extrusion AM produces SS316L with microstructures and mechanical properties comparable to its wrought counterpart in the annealed condition. However, despite extensive research on SCC of SS316L, little is known about the SCC of sinter-based AM SS316L. This study focuses on the influence of sintered microstructures on SCC initiation and crack-branching susceptibility. Custom-made C-rings were exposed to different stress levels in acidic chloride solutions at various temperatures. Solution-annealed (SA) and cold-drawn (CD) wrought SS316L were also tested to understand the SCC behavior of SS316L better. Results showed that sinter-based AM SS316L was more susceptible to SCC initiation than SA wrought SS316L but more resistant than CD wrought SS316L, as determined by the crack initiation time. Sinter-based AM SS316L showed a noticeably lower tendency for crack-branching than both wrought SS316L counterparts. The investigation was supported by comprehensive pre- and post-test microanalysis using light optical microscopy, scanning electron microscopy, electron backscatter diffraction, and micro-computed tomography.

The pit stability product of 316L stainless steel (SS) under a salt film was examined by experimental techniques, analytical methods, and numerical modeling. Both analytical and numerical results suggested that electromigration had a measurable contribution to the dissolution current during stable pit growth under a salt film, preventing the use of the 1D Fick’s law of diffusion to obtain the pit stability product under such conditions. Moreover, the numerical results indicated that migration contributed to almost ⅔ of the mass transport limiting current. Although the diffusion coefficient of metal cations decreased with an increasing concentration inside the pit, it could be replaced by a constant diffusion coefficient, defined as an equivalent diffusion coefficient. When the complexation reaction was cconsidered, the modeling results agreed with the experimental data, indicating that a 4.2 M FeCl₂ could be used as a simplified pit-like electrolyte to estimate the pit stability product under a salt film for 316L SS.

Probing dynamic and localized electrode processes occurring on steel buried in inhomogeneous soils is a technological challenge. In this work, current mapping obtained with an electrochemically integrated multielectrode array has been used, in conjunction with electrode potential and surface pH monitoring, to address this challenge by enabling the visualization of dynamic localized electrode processes occurring on steel surfaces buried in soil. This has enabled understanding of localized corrosion initiation behavior of steel in soil with different moisture contents under the scenario that cathodic protection (CP) was disrupted. Soil moisture contents was found to influence the initiation of localized corrosion by affecting prior-CP generated surface pH and local hydroxyl depletion rates. The maximum localized corrosion was found to occur at 60% water holding capacity. Electrochemically calculated corrosion damages have been verified by surface profilometry measurements.