Influence of Tungsten inert gas welding thermal cycles on the microstructural morphological changes and mechanical properties of SS 316 weldments

Abstract Stainless steel (SS) 316 is extensively used in aerospace, marine, and nuclear industries because of its superior mechanical properties and corrosion resistance. Nevertheless, its microstructure and mechanical behavior are greatly affected by welding-induced thermal cycles. In this research, the influence of Tungsten Inert Gas (TIG) welding on the microstructural development and mechanical properties of analogous SS316 weldments is explored. A multi-pass (two-pass) TIG welded process was used, and the weld joints were characterized by microstructural characterization, tensile testing, microhardness testing, and infrared (IR) thermography. IR thermography was used to record temperature gradients during welding at various stages, indicating heat buildup and thermal gradients influencing microstructural development. Microstructural analysis indicated columnar dendrites in the fusion zone and grain coarsening in the heat-affected zone (HAZ). Mo and Cr segregation in inter-dendritic areas was seen, and these can affect corrosion resistance and mechanical performance. Tensile test results revealed that the weld joints had an ultimate tensile strength (UTS) of 636–640 MPa with minor fluctuations because of heat build-up. Among the three tensile-tested specimens, two exhibited failure in the HAZ. However, specimen 3 failed just adjacent to the weld zone, suggesting that localized heat input at the commencement of welding influenced the failure location. Microhardness analysis revealed a hardness value of 94–99 HV in the weld and 97–99 HV in the HAZ, which followed grain refinement and thermal effects. The results of this research offer significant information on the optimization of welding parameters to improve joint performance, ensuring the reliability of SS316 components in critical applications.