Investigation on Role of Aluminum on the Susceptibility to Localized Micro-Galvanic Corrosion of Fusion Zone in the Hadfield Steel Weld Joints

In this study, the effect of Al on the corrosion resistance of Hadfield steel weld joints’ fusion zone was investigated. For this purpose, 4 austenitized sheets (two sheets without Al and two sheets containing 1.7wt. %Al) with thickness 2mm prepared from Hadfield steel and then SMAW process was used for welding. Then potentiodynamic polarization and electrochemical impedance spectroscopy methods were used to evaluate corrosion behavior of welded joints’ fusion zone in the 3.5wt. %NaCl solution. The evaluation of the microstructures of weld metal in welding joints were conducted by optical microscopy and the corrosion mechanism were determined by scanning electron microscopy examination. The result of corrosion tests indicated that welded joints’ fusion zone of Al containing plates were more corrosion resistant. Because Al addition increased the solubility of carbon in austenite phase and as a result factors enhancing localized micro-galvanic corrosion such as grain boundaries and carbides were reduced. However as clearly was visible in scanning electron microscopy images, using joints design containing Al in comparison with joints design without Al led to changed weld metal corrosion mechanism from uniform corrosion to localized micro-galvanic corrosion in the Hadfield steel weld joints.