MICROSTRUCTURAL STUDIES ON LASER WELDING OF INCONEL 718 TO 2304 DUPLEX STAINLESS STEEL WITH A FOCUS ON OPTIMAZING PROCESS PARAMETERS AND ACHIEVING THE MAXIMUM FRACTURE STRENGTH

In this research, microstructure and mechanical properties of laser welded joints between 2304 duplex stainless steel and Inconel 718 nickel-based super alloy were investigated. Microstructural evolution in the various areas of welded joints and also the effect of welding parameters on the mechanical properties of dissimilar joints were studied. Response surface methodology based on the central composite design was used in order to find the optimum welding parameters. Effective parameters of the welding process including laser power, travel speed and defocusing distance were set in the range of 1000 to 1900 W, 1 to 5 mm/s and -1 to 1 mm, respectively. Uniaxial tensile test was used to evaluate the fracture force of weld joints. The microstructural observations and phase evolutions were studied using optical microscope. It was found that the fracture force of the weld joints firstly increased by travel speed and defocusing distance and then decreased by further increase. The maximum fracture force was obtained when laser power, travel speed and defocusing distance were 1900 W, 3 mm/s and 0 mm, respectively. The center line of weld metal was mainly consisted of equiaxed grains where, columnar grains were formed in the fusion line. The obtained results from the hardness measurement showed that the hardness of Inconel 718 was decreased due to dissolution of TiC and NbC particles.