Why Does 3D Printed Stainless Steel Corrode in a Marine Environment?

Why is 3D printed 316L stainless steel prone to pitting corrosion in seawater? That is the question researchers from Lawrence Livermore National Laboratory have been diligently trying to answer. Their thorough study of this metal, utilized in naval applications, aims to uncover the underlying causes of its degradation. Their findings suggest that slag, left behind during laser melting, accumulates on the surface of the material, resulting in the formation of cavities or pits.

Used in many industrial applications, metals are often subject to corrosion, i.e., degradation by chemical reactions caused by the environment. Corrosion can be controlled, but it’s important to know what causes it. There are several forms of corrosion, including pitting. In concrete terms, the metal undergoes degradation of its protective oxide layer, and loses electrons in the process. When present in an aquatic environment, an electrochemical reaction occurs, resulting in the creation of small holes, hence the name “pitting corrosion”. The severity of the repercussions for the part in question varies depending on the depth of these cavities. Interestingly, controlling pitting corrosion in seawater poses significant challenges. This is precisely why naval applications opt for 316L stainless steel, known for its exceptional mechanical properties and resistance to such pitting corrosion.

Meta degradation (or corrosion).

However, can 3D printed 316L stainless steel effectively mitigate pitting corrosion? With the marine industry showing a growing interest in additive manufacturing, both in polymer and metal, this question gains significance, particularly concerning metal certification. This is the very reason why researchers at Lawrence Livermore National Laboratory embarked on this study. Lead author Shohini Sen-Britain explains, “Pitting corrosion is extremely difficult to understand due to its stochastic nature, but we determined the material characteristics that cause or initiate this type of corrosion. While our slags looked different than what had been observed in conventionally manufactured materials, we hypothesized that they could be a cause of pitting corrosion in 316L.”