Influence of heat input on intermetallic formation in dissimilar autogenous laser welding between Inconel 718 and AISI 316L steel

Intermetallic formation during dissimilar welding of Inconel and stainless steel significantly hinders producing sound-quality weld. In the present work, a high-power CO2 laser welding system is employed to join Inconel 718 and AISI 3 16L stainless steel without using any filler materials. The finite element based thermal model provides the temperature distribution in the weld zone and consequently the solidification parameters (G/R and G.R). The micro-segregation and intermetallic formation in laser welding are correlated with these solidification parameters. The segregation of principal alloying elements triggers the formation of intermetallic phases during solidification. The presence of various phases like Laves, NbC, and TiC in the fusion zone reduces with increase in heat input. The amount of these intermetallic phases present in the weld zone is estimated by XRD analysis. With an increase in heat input, the mode of solidification changes from columnar to equiaxed dendrites that is characterized at reduced value of solidification parameter (G/R). The intermetallic Laves particle diminishes significantly (more than 90%) with a reduction of G/R parameter. In equiaxed dendrites, the segregation and formation of these secondary particles reduces to more than 40% compared to the columnar dendritic structure. Overall, the reduction in the intermetallic particles improves the joint efficiency up to 100% with an elongation of 14.2% for the equiaxed structure of the laser welding system.

Automated summary

In this study, a high-power CO2 laser welding system was used to weld Inconel and stainless steel, and a finite element thermal model was employed to analyze the temperature distribution and solidification parameters in the weld zone. It was found that the formation of intermetallic phases during welding was correlated with the solidification parameters and segregation of principal alloying elements. The amount of intermetallic phases in the weld zone was estimated by XRD analysis. With an increase in heat input, the solidification mode changed from columnar to equiaxed dendrites, resulting in a reduction in intermetallic formation. The reduction in intermetallic particles improved the joint efficiency of the laser welding system.