Microstructural characterization of dissimilar laser beam welded joints between Incoloy 800HT and P91 steel

This study investigates the microstructural characterization of dissimilar joints between Incoloy 800HT and P91 steel, fabricated using Yb laser beam welding. The research focuses on understanding the effects of various laser welding parameters, including power, speed, and focal length, on the weld quality. Detailed analysis reveals the formation of different grain structures, such as equiaxed and columnar dendritic structures, influenced by the temperature gradient and solidification rates. The study also examines the formation of Type I and Type II grain boundaries, and the presence of δ-ferrite in the weld metal, which contributes to the weld's mechanical properties. The elemental distribution, particularly the roles of Fe, Cr, and Ni, is analyzed using EPMA, highlighting significant changes across the weld zone. The findings demonstrate the critical role of optimizing laser welding parameters to achieve defect-free, high-strength welds suitable for high-temperature applications such as power plants and gas turbines.