The comparative evaluation of AISI 316/A387-Gr.91 steels dissimilar weld metal produced by CCGTAW and PCGTAW processes

The mechanical properties (impact toughness and hardness profile) and the microstructure of dissimilar weld metal of AISI 316 and A387-Gr.91 steels produced by constant and pulsed currents GTAW were studied. The microstructural studies showed that the pulsed current application leads to finer and equiaxed dendrites in the weld metal central region, as well as to the expansion of this region. In addition, the pulsed current produces finer secondary phases with more uniform distribution. The chemical analysis of the dendritic and interdendritic zones revealed that the segregation of alloy elements takes place in the entire weld metals and that it is more intensive with the constant current. The segregation is recognized as the main agent in forming the secondary phases, such as MC carbides ((Nb, Ti) C) and intermetallic compounds. Moreover, the microstructure images and map analysis of the weld metal near the fusion line indicated that a filler-deficient zone, including beaches, peninsulas and islands with a chemical composition similar to the base metal is developed. It was disclosed that the zone scope is decreased by the pulsed current. It was observed that the use of the pulsed current increases the weld metal fracture toughness and hardness simultaneously.