Welding input effect on the corrosion behavior and microstructure of heat treated GTAW welds of Inconel 718

The susceptibility to corrosion of Inconel 718 weldments after double aging heat treatment was studied by the use of potentiodynamic tests. Plates of 3 mm thick were homogenized at 1080 °C during 1 hour and air cooled, then subjected to a solution process at 980 °C during 1 hour and air cooled. The double aging heat treatment was; (1) aging at 720 °C during 8h and oven cooled at 55 °C/h, and (2) aging at 620 °C during 8h and air cooled at room temperature. After heat treatment, the plates were welded by using gas tungsten arc welding process with low and high heat input. The base metal (BM) and the weldments were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The potentiodynamic tests were carried out in a 3.5% NaCl for the welded samples. The results show that, as the heat input increases, the corrosion rate increases in the weldments. This behavior can be attributed to the microsegregation of Nb and Mo, resulting in a Fe dilution into the weld pool.