Role of non-metallic inclusions in the initiation and propagation of corrosion in wire arc additive manufactured low-alloy steel

This work explores the early stages of corrosion in a low-alloy steel produced by Wire Arc Additive Manufacturing (WAAM). Specimens were exposed to a marine environment, and the influence of non-metallic inclusions on corrosion was examined. Although Mn-silicates are commonly reported in additively manufactured steels due to rapid solidification, they are generally considered inert with respect to corrosion in some AM steel grades, such as stainless steel. For the present work, however, it was observed that in the case of WAAM low-alloy steel, these inclusions can contain small MnS-rich regions that act as preferential sites for pitting corrosion initiation, due to their chemical instability. As the exposure time in a marine environment increases, the metallic matrix surrounding MnS-rich regions undergoes localized dissolution, leading to inclusion detachment and pit formation, followed by the development of a surrounding circular corrosion front. This front progressively spreads, encompassing and detaching adjacent inclusions, ultimately transitioning from localized to general corrosion.