The Evaluation of Microstructure and Impact Toughness of Dissimilar Welds of AISI 347 Stainless Steel to ASTM A335 Low Alloy Steel

In the present study، the microstructure of dissimilar welds of AISI 347austenitic stainless steel to ASTM A335 low alloy steel by using gas tungsten direct current arc welding process with a negatively charged electrode (DCEN) was investigated. For this purpose، two filler metals، ER309L and ERNiCr-3، were used. After welding، the microstructure of the different zones of each joint، including weld metals، Heat affected zone (HAZ)، interface and unmixed zones (UMZ) were evaluated by using optical microscope (OM). The (SEM) equipped (EDS) were used to investigate the precipitates and fracture of different samples. The microstructure of base and weld metals were evaluated by using OM. The fracture surfaces was investigated by (SEM) equipped to (EDS). The microstructural evaluations showed that a two-phase structure، consist of dendritic and inter-dendritic regions with primary austenite solidification was observed in ERNiCr-3 (filer metal)، and a primary skeleton-shaped ferrite in austenitic matrix was observed in the 309L (filer metal). The epitaxial growth was observed in interface between 347austenitic stainless steel and two filler metals and a narrow zone was observed in interface between A335low alloy steel and filler metals، and also the coarse grains occurred in HAZ zone of both weld metals. Also، the impact toughness and fractography of samples were investigated. The maximum impact energy obtained in to the ERNiCr-3 (filer metal) specimens. Finally، it can be noted that for the joints between the AISI 347 austenitic stainless steel and A335low alloy steel، the ERNICr-3 filler material provides the optimum qualities.