Study on Microstructure and Pitting Corrosion Behavior of Super Duplex Stainless Steel

UNS S32750 is a SDSS (super duplex stainless steel) grade, and it is widely used in gas industry and petrochemical processing plant due to its remarkable combination of mechanical characteristics and corrosion resistance. It contains a substantial quantity of chromium, which results in solid solution strengthening and better corrosion resistance. Even in chloride and sulfur-rich conditions, this alloy shows resistance to severe destructive corrosion forms like pitting. Welding is the typical manufacturing technique employed to fabricate components for industrial utilization. Due to changes in microstructure in distinct zones of a weld, the welding process influences both mechanical characteristics and corrosion resistance. An effort has been made in the current study to evaluate the influence of MMA, GTA welding processes on UNSS32750 alloy by analyzing microstructural changes during welding and developing an understanding of the pitting corrosion. Microstructural analysis for weld zone (WZ), heat affected zone (HAZ), and base metal in a weldment were conducted using scanning electron microscopy and optical microscopy. The weld zone microstructure exhibits Widmanstatten structure in the GTA welds. Superior properties of GTA welds were observed in the present study with optimum combination of fine microstructural characteristics and corrosion resistance. The slower cooling rate associated with GTA welding, which results in increased austenite formation and a more balanced ferrite-to-austenite ratio, may account for the enhanced characteristics compared to MMA welding, as rate of cooling is the crucial factor that influences the corrosion behavior of these welds.