Study on Duplex Stainless Steel Powder Compositions for the Coating of Thick Plates for Laser Beam Welding

Duplex stainless steels combine the positive properties of its two phases, austenite and ferrite. Due to its good corrosion resistance, high tensile strength, and good ductility, it has multiple applications. But laser beam welding of duplex steels changes the balanced phase distribution in favor of ferrite. This results in a higher vulnerability to corrosion and a lower ductility. Herein, different powder combinations consisting of duplex and nickel for coating layers by laser metal deposition (LMD) are investigated. Afterward, laser tracks are welded, and the temperature cycles are measured. The ferrite content of the tracks is analyzed by feritscope, metallographic analysis, and electron backscatter diffraction. The goal is the development of a powder mixture allowing for a duplex microstructure in a two‐step process, where first the edges of the weld partners are coated with the powder mixture by LMD and second those edges are laser beam welded. The powder mixture identified by the pretests is tested in the two‐step process and analyzed by metallographic analysis, energy‐dispersive X‐ray spectroscopy, and Vickers hardness tests. The resulting weld seams show a balanced duplex microstructure with a homogenous nickel distribution and a hardness of the weld seam similar to the base material. Duplex stainless steels change their phase distribution and their properties when subjected to welding procedures with high cooling rates like laser beam welding. Laser metal disposition coatings on the edges of the weld partners consisting of duplex powder with a higher nickel content and nitrogen as shielding gas lead to a balanced and homogenous microstructure after laser beam welding.