Effect of post-weld heat treatment on the metallurgical studies of dissimilar weldments of SS 316L welded with DSS 2205

Abstract

The present work discusses the macrostructure, microstructure, and microhardness of dissimilar metal weld joints between AISI 316L SS-DSS 2205 developed by gas tungsten arc welding (GTAW) welding. Post-weld heat treatments (PWHT) were carried out at temperatures of 750°C for 24 h and 850°C for 0.5 h. The macrostructure and microstructure of the welding joints at different welding conditions were observed by scanning electron microscope. The macrostructure study results indicated that all the welded joints were fully penetrated and free from defects. However, the microstructure investigation revealed a solid-state transformation of ferrite into grain boundary austenite, widmanstatten austenite, intergranular austenite, and partially transformed austenite. The post-weld heat treatment processes enhanced the precipitation of the sigma phase in the ferrite matrix. Secondly, the microhardness across and along the weld bead has been evaluated, and the results are compared. It was observed that the microhardness of the heat-affected zone of DSS 2205 is found to be higher as compared to a heat-affected zone of AISI 316L, the weld metal zone, and base metals at all welding currents (i.e. 90 A, 109 A, and 132 A). The microhardness values decrease when transverse from the face of the weld toward the root pass. Microhardness values at the fill (top) pass of the weld zone at 90 A, 109 A, and 132 A were 268.3 HV, 257 HV, and 255 HV respectively. It was found that the microhardness has improved significantly after post-weld heat treatments and was highest for 750°C/24 h. It may be due to higher holding time which led to the involvement of carbides.