Corrosion mechanism of additively manufactured 316 L stainless steel in 3.5 wt.% NaCl solution

Abstract

Additively manufactured stainless steel has received widespread attention due to its excellent mechanical properties, while its corrosion mechanism in Cl--containing environments is still vague. This work investigates the pitting and passivation behavior of additively manufactured 316 L stainless steel (AM SS316 L) in 3.5 wt.% NaCl solution and its comparison to wrought counterpart, by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The results show that AM SS316 L exhibits a fine sub-grain structure with a diameter of approximately 5 μm, and dislocations and Mo elements enriched at the sub-grain boundary. Compared with the wrought 316 L stainless steel (SS316 L), a large number of sub-grain boundaries and high dislocation density in AM SS316 L promote the formation of a more compact and thicker passive film, consequently enhances its general corrosion resistance. However, the low hydroxide content in the passive film and the micro-galvanic corrosion effect between Mo-rich sub-grain boundaries and sub-grains reduce the self-repairing ability of the passive film, thus the pitting corrosion resistance of AM SS316 L.