Metallurgical investigations on optimized tensile strength of Yb fiber laser welded Incoloy 800 joints

A nickel based super alloy Incoloy 800 is known for its high tensile strength and good for corrosive environments and hence it used in the heat exchanger and boiler tubes. Ytterbium fiber laser welding can be utilized to join Incoloy 800 alloy to enhance the weld quality and productivity. In this paper, Yb Fiber Laser Welding (FLW) process parameters, namely laser power, duty cycle, welding speed, and frequency, were optimized to obtain highest ultimate tensile strength by Central Composite design of Response Surface Methodology to join Incoloy 800 plates of 2 mm thickness. The developed second − order empirical relationships were used to predict the ultimate tensile strength with an acceptable accuracy. The effect of ranges of process parameters (Viz., Power as 650 W to 850 W, duty cycle as 65 % to 85 %, welding speed as 650 mm/min to 850 mm/min and frequency as 4850 Hz to 5000 Hz) on Ultimate tensile strength and hardness are studied. The optimized value of the ultimate tensile strength of 515.19 MPa, which is higher than that of the base metal (i.e., 510 MPa). Analysis of Variance (ANOVA) identifies welding speed as the most influential process parameter. The weld zone exhibited high hardness across all experiments. The highest hardness value obtained among the experiments is 184 Hv. Optical Microscopic (OM) images reveal the cellular to columnar dendritic structures. The presence of Lave’s phase is noticed in the SEM microstructure in the weld bed fabricated at lower welding speed and compromises the strength of the weld.