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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. In this study different powder combinations consisting of duplex and nickel for coating layers by laser metal deposition are investigated. Afterwards laser tracks are welded, and the temperature cycles measured. The ferrite content of the tracks are 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 firstly the edges of the weld partners are coated with the powder mixture by LMD and secondly 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.
Because of its excellent corrosion resistance, high tensile strength and high ductility, duplex stainless steel 2205 offers many areas of application. Though laser beam welding accompanied by high cooling rates, duplex steels tend to perform higher ferrite contents in weld metal as the base metal, which leads to a reduction of ductility and corrosion resistance of the weld joint. To overcome this problem, a solution, based on buttering the plate edges by laser metal deposition (LMD) with material containing higher Ni concentrations prior to laser welding was suggested.
In this context different process parameters for LMD and different mixtures of duplex and nickel powder, were investigated. In a second step the possibility of welding those edges defect free while achieving balanced austenite-ferrite ratio was verified with metallographic analysis, Electron Backscatter Diffraction (EBSD) and impact testing according to Charpy. The improved corrosion resistance was observed with ASTM G48 standard test method.
Because of its excellent corrosion resistance, a high tensile strength together with a high ductility, duplex stainless steel 2205 offers many areas of application in the chemical and the offshore industry, to name just two. Though welding, especially laser beam welding accompanied by high cooling rates, duplex steels tend to perform higher ferrite contents in weld metal upon cooling down from melting temperature as the base metal. This trend leads to a reduction of the ductility as well as the corrosion resistance of the weld joint. To overcome this problem a solution, based on buffering the plate edges by laser metal deposition with material containing higher Ni concentrations prior to the laser welding was suggested. This method offers more benefits in comparison to conventional usage of higher Ni-alloyed filler wire due to the better control over Ni-distribution in the weld seam, resulting in balanced austenite- ferrite ratio everywhere in the weld metal.
In this context different mixtures of duplex and nickel powder were investigated as well as different process parameters, that enable a smooth surface structure with slightly reduced ferrite contents. In a second step the possibility of welding those edges defect free with standard parameters while achieving balanced austenite- ferrite ratio was verified with metallographic analysis of the microstructure, Electron Backscatter Diffraction (EBSD) and impact testing according to Charpy. The improved corrosion resistance of the welds in comparison to unbuffered ones was observed with the ASTM G48 standard test method.