Influence of Post-weld Heat Treatment on Microstructure and Corrosion Behavior of Dissimilar Friction Welded Joint of IN713LC Superalloy and AISI 4140 Steel

In the present work, effect of post-weld heat treatment (PWHT) on the microstructure, hardness, and corrosion behavior of friction welded IN713LC superalloy and AISI 4140 steel joint was investigated. Microstructural characterization was performed using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques. The microstructure near weld interface (WI)/thermo-mechanically affected (TMAZ) region of IN713LC was changed from coarse dendritic structure to fine equiaxed grains. Due to dynamic recrystallization (DRX), as compared to base materials, increase in fraction of high-angle grain boundary (HAGB) and decrease in fraction of low-angle grain boundary (LAGB) were observed in WI/TMAZ (both as-welded and PWHT samples). Lath martensite was observed at WI/TMAZ of AISI 4140 steel of as-welded specimen; however, after PWHT, it transformed into the tempered martensite. The electrochemical corrosion behavior was evaluated using potentiodynamic polarization tests in 3.5 wt. % NaCl solution. Result showed that corrosion resistance of welded joint was higher than that of AISI 4140 steel and reduced after PWHT.