Study on Corrosion Properties of Additive Manufactured 316L Stainless Steel and Alloy 625 in Seawater

Additive manufacturing (AM), also known as 3D printing, is relatively new technology as a manufacturing method for metallic materials compared to conventional manufacturing techniques such as casting and metal working. The products from AM are made stacking metallic materials in a layer by layer fashion according to CAD-drawn 3D models. The technique allows immense freedom in a dimension of the produced parts, enabling fabrication of complex-shaped parts that are very difficult or sometimes impossible to be realized otherwise. This is beneficial in multiple ways. A total weight of AM parts and manufacturing process time can be hugely saved. The part that is originally made by joining of smaller parts can be made in a single piece, improving productivity and also eliminating joint problems. Due to the reasons described, additive manufacturing has been popular in many industrial and military fields of application for past decades [1,2,3]. However, it is not until recently that the technology starts to gain attention from the marine and shipbuilding industry. The effort to utilize the advantages of AM in the maritime sector has been made collaboratively by major shipyards and governmental bodies [4] for the special purpose parts. Classification societies are also making involvements in this current trend. However, it is not completely certain whether the 3D printed metallic parts can meet high expectations of the shipbuilding industries. In most cases, metallic parts for marine purposes are a subject of many demands, e.g., structural load carrying capabilities, anti-corrosion properties and other functional purposes. In this work, 3D printed 316L stainless steel and alloy 625, actively used corrosion resistance alloys (CRA) in shipbuilding, are evaluated to study on their corrosion resistance in seawater, as seawater is a very important liquid actively utilized by the ship for ballasting, firefighting, and many other utility purposes. Due to the presence of chloride ions in seawater, the liquid tends to offer very harsh conditions to many metals.