EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Duplex ferritic-austenitic stainless steels (DSS) receive much attention thanks to their high corrosion resistance and excellent mechanical properties. The phase balance is controlled by the chemical composition and thermal cycles, where the best combination of properties is usually achieved for approximately equal amounts of ferrite and austenite. Additive manufacturing (AM) has provided new opportunities to fabricate near-net-shape DSS components with a low waste of material, tailored properties, and complex geometries. Laser Metal Deposition with Wire (LMDw) AM has the advantage of comparatively high productivity and is, therefore, suitable for the production of relatively large parts. This study aims at the production of a full-size 25 kg additive manufactured cylinder using LMDw. A four-stage methodology with deposition of a single-bead layer, a single-bead wall, a block, and finally a full-size cylinder was employed. This approach made it possible to systematically evaluate the effects of deposition parameters, shielding gas, and heat treatment on the microstructure and properties. The combination of high cooling rates, some loss of nitrogen, and complex AM thermal cycles resulted in an inhomogeneous microstructure in the as-deposited condition. This includes highly ferritic regions with more than 80% ferrite resulting in low mechanical properties. For each stage, a subsequent 1h heat treatment at 1100℃ homogenized the microstructure and balanced the ferrite/austenite fraction, which improved the mechanical properties. After heat treatment of the block, for example, the impact toughness increased from 206 to 240J along the deposition direction and from 230 to 260J along the build direction. Finally, the implementation of this stepwise methodology made it possible to achieve a stable and consistent LMDw process and provided very useful input for future fabrication of high-performance DSS AM components.