Hierarchical structures of stainless steel 316L manufactured by Electron Beam Melting

Abstract

One of the serious obstacles preventing wide industrial use of additive manufacturing (AM) in metals and alloys is a lack of materials available for this technology. It is particularly true for the Electron Beam Melting (EBM®) process, where only a few materials are commercially available, which significantly limits the use of the method. One of the dominant trends in AM today is developing processes for technological materials already widely used by other methods and developed for other industrial applications, gaining further advantages through the unique value added by additive manufacturing. Developing new materials specifically for additive manufacturing that can utilize the properties and specifics of the method in full is still a research and development subject, and such materials are yet far from full scale industrial usage. Stainless steels are widely used in industry due to good mechanical properties, corrosion resistance and low cost of material. Hence, there is potentially a market for this material and one possible business driver compared with casting for example is that lead times could be cut drastically by utilizing an additive approach for one-off or small series production. This paper presents results from the additive manufacturing of components from the known alloy 316L using EBM®. Previously the samples of 316L were made by laser-based AM technology. This work was performed as a part of the large project with the long term aim to use additively manufactured components in a nuclear fusion reactor. Components and test samples successfully made from 316L stainless steel using EBM® process show promising mechanical properties, density and hardness compared to its counterpart made by powder metallurgy (hot isostatic pressing, HIP). As with the other materials made by EBM® process, 316L samples show rather low porosity. Present paper also reports on the hierarchical microstructure features of the 316L material processed by EBM® characterized by optical and electron microscopy.