Thermal field and residual stress analyses of similar and dissimilar weldments joined by constant and pulsed current TIG welding techniques

Higher heat input rates and uneven thermal cycles involved in fusion welding processes effect HAZ properties and causes to develop residual stress across fusion zones. These thermal stresses reduce the service life of welded structures. To understand the thermal cycles, In-Situ peak temperatures and their distribution over the weld surface of similar and dissimilar combinations of Monel 400 and AISI 316 base plates joined by constant and pulsed current TIG welding processes are measured with Infrared thermography technique at different time intervals. After welding the joints, thermal stresses developed across the joints were measured using X-ray diffraction technique. The stress measurements were made on weld surfaces of fusion zone and HAZ on either side of base metals. Higher temperature values were recorded during constant welding technique than the pulsed welding technique. Also, the heat affected area was more in weldments of constant welding technique. The maximum temperatures of 1657 0C, 1711 0C and 1748 0C were recorded in CCGTAW process during pass-1, pass-2 and pass-3 welding, respectively. Whereas, in PCGTAW process, maximum temperatures of 1434 0C, 1509 0C and 1634 0C were recorded during pass-1, pass-2 and pass-3 welding, respectively. The overall reduction in temperatures in PCGTAW process was 10.6%, which could affect the cooling cycles during solidification. Both the welding techniques have exhibited development of compressive natured residual stresses in dissimilar joints. The heat concentration at fusion area was reduced in pulsed technique that resulted in lower residual stresses.