ENHANCING CORROSION RESISTANCE OF A-TIG WELDED UNS S32750 JOINT BY OPTIMIZING ITS TECHNOLOGICAL PARAMETERS

In this paper, an attempt was made to improve the corrosion resistance of activated tungsten inert gas welded super duplex stainless steel such as UNS S 32750. Joints were fabricated by fluctuating the important process parameters such as welding speed, shielding gas flow rate and welding current, using NiO as activation flux. A central composited design model was developed for identification of the Activated Tungsten Inert Gas welding process parameter values for fabricating twenty joints. The welded joints were subjected to pitting corrosion test using an electrochemical corrosion testing system and salt spray testing was done for 48 h. Empirical relationships were developed for the process parameters with variations in the pitting potential and the rate of mass loss. The significance of the developed model was ascertained using analysis of variance method and optimization was done using response surface methodology. The joints fabricated at welding speed of 54.26 mm/min, welding current of 157 A and gas flow rate of 14.8 L/min, were found to have maximum pitting potential of - 252.36 eV and minimum mass loss of 0.0108 g. Using validation experiments, the error was identified within three percentage which indicated that the optimization model was developed with very high predictability.