Some Aspects on the Welding Characteristics and Formation of Microstructures in a Newly Developed Coated Electrode for Austempered Ductile Iron (ADI)

In this study, six different coated electrodes were manufactured to select compatible one for ADI and only two electrodes were further studied (Trial 3 and Trial 4) to check their compatibility. Welding conditions were established to obtain crack free weld deposit on DI plate by varying preheat (200°C, 300°C and 400°C for lhour) as well as PWHT (maintaining same preheat temperature) at constant heat input using two selected electrodes. Only preheating at 300°C was possible to obtain sound weld for Trial 3, whereasboth preheat (300°C) and PWHT (300°C) were required for Trial 4. Although the as-deposited microstructures of FZ and PMZ consisting of ledeburitic carbide and alloyed pearlite in both the electrodes were same, the amount of microstructural constituents varied significantly. More ledeburitic carbide and less alloyed pearlite were observed in Trial 3 compared to Trial 4. However, microstructures of HAZ for both the electrodes showed bainitic and pearlite. Austempering heat treatment comprising of austenitization at 900°C for 2 hr and austempering at two different temperatures (300°C and 350°C) for different holding time was carried out for both the weld deposits. Interestingly, for both the weld deposits austempered microstructures show bainitic ferrite and retained austenite with graphite nodules. Increasing austempering temperature from 300°C and 350°C the lower bainite transformed to upper bainite and vol. % of retained austenite was also increased.