Improvement of microstructure and hardness property of MMA welded ADI workpiece using newly developed electrode.

Austempered ductile iron (ADI) offers a good combination of mechanical properties with low cost and successfully replaces cast and forged steel in many applications. Manual metal arc welding (MMAW) of such iron causes the formation of martensite in the heat-affected zone and an undesirable growth of iron carbide in the partial fusion zone. Although avoidance of hard products is accomplished at present by using Ni alloys as electrodes, they fail to satisfy the mechanical requirements apart from the high cost of Ni-based electrodes. Furthermore, such electrodes do not respond to austempering heat treatment. In the present study, an attempt has been made to develop a coated electrode with cost-effectiveness and response to austempering heat treatment by adjusting the alloying elements through flux coating on their ability to eliminate free carbides and response austemperability. The microstructures of different weld deposits and at different layers of each weld deposit have been evaluated in as-welded and after austempering treatment using an optical microscope, SEM with EDX. However, it has been possible to develop coated electrodes with shallow Ni content (0.71%), which responded to austempering resulting in a microstructure consisting of graphite nodules in a matrix of lower bainite. Microhardness of weldment (WM) was also carried out, which showed good agreement with microstructure characteristics. [ABSTRACT FROM AUTHOR]