Pitting Behavior of Thermally Aged Inconel 625 Weld Claddings Made Using SMAW and GMAW Process

Abstract

Comparative investigations were carried out where multipass multi-layers of Inconel 625 (UNS N06625) weld claddings were overlaid on 12 mm thick austenitic stainless steel plates (AISI 304L) using SMAW (shielded metal arc welding process) and GMAW (gas metal arc welding) process. The specimens extracted from the cladded plates were subjected to four different post weld thermal aging treatments (650 °C/10 h, 650 °C/100 h, 850 °C/10 h and 850 °C/100 h). The pitting corrosion of Inconel 625 clads was evaluated using PAP (Potentiodynamic anodic polarization) technique and the results were generated as pitting curves which depicted their behavior. Pitting potential (Epitt) for these welds varied from 31.77 to 922.7 mV. Under all conditions, the GMA welds showed better pitting performance than the SMA welds. Aging treatment of 650 °C/10 h improved the pitting resistance of both the welds, as pitting potential of 922.7 mV (which was recorded as the highest value of Epitt among all the welds) was observed in case of GMA weld and 384 mV for the SMA weld. Precipitation strengthening occurred under this aging condition which was attributable to the presence of Laves phase, γ′ and γ″-phase, besides carbides in Inconel 625 weld/clad metal. However, a loss of pitting resistance was observed under aging conditions 850 °C/10 h and 100 h, which could be attributed to the segregation behavior of alloying elements as well as the formation of delta phase which promoted the tendencies for pit nucleation and their subsequent growth in the matrix of the weld metal.