Pitting corrosion sensitivity of AISI 316L stainless steel produced by selective laser melting and wire arc additive manufacturing

Additive Layer Manufacturing (ALM) processes have been booming in recent years. They open up a whole new field of possibilities for the design of metal parts with complex geometries and multi-scale structural patterns like lattice structures. Compared to the possibilities offered by conventional, so-called subtractive processes, these technologies allow gains in cost, mass, functional performance and realization. However, the lack of knowledge on the properties and durability of the parts obtained limits their use at present. The characterization of parts made by additive manufacturing is a key point for the deployment of these technologies. Thus, more and more studies are conducted to address issues related to this production method, including the sensitivity to corrosion of metals obtained by ALM. In this study, we are interested in the AISI 316L austenitic stainless steel which is used in many fields such as chemical, pharmaceutical, oil, food and maritime industries. Its resistance to the marine and acid environment and its important ductility make it a widely used material. This is why the development of 316L stainless steel by additive manufacturing is a real issue. Two additive manufacturing technologies are studied, the first is the selective laser melting (SLM) and the second is the wire arc additive manufacturing (WAAM). The properties of the materials obtained with these manufacturing technologies are compared with those of an AISI 316L stainless steel from the conventional industry. The investigations focus on the impact of the manufacturing process and of a heat treatment aiming at erasing the thermo-mechanical transition of the part, on the microstructure of the material and the effect of this one on the sensitivity to corrosion. The coupling between the microstructure and the corrosion resistance is studied using an original approach coupling potentiostatic pulses tests and a statistical analysis of the damage to compare the sensitivity to pitting corrosion of the materials and to allow a better understanding of the damage mechanisms. (author)