Influence of nickel on microstructure and weld metal toughness of shielded metal arc welded low carbon steel plates
Fusion welding may lead to changes in the microstructure and degrade the impact toughness around the welded joint. This work aims to investigate the microstructure evolution due to the addition of nickel and its effect on the impact toughness of low carbon steel butt weld. The multipass welding in flat position was performed on 16 mm thick low carbon steel plates using shielded metal arc welding (SMAW). Three experimental group samples were fabricated using 3.2 mm diameter electrodes containing 0.3% Ni, 0.95% Ni and combination of 0.3% and 0.95% Ni, respectively. The microstructures of the weld metals were investigated with an optical microscope and scanning electron microscopy (SEM). Furthermore, the mechanical properties of the welded joints were evaluated by tensile, Vickers hardness and Charpy impact tests. The impact energy was measured at test temperatures of 25 °C, 0 °C, and -25 °C. The results showed that the tensile strength of the joints were satisfactory where there was no fracture occur on the welded joints. Impact tests of the weld metals showed that the impact energy decreased when the test temperature decreased. The weld metal produced by using the electrode containing 0.95% Ni generated the finer grains with better impact toughness compared to the weld metal using electrode containing 0.3% Ni. The weld metal using combination of two electrodes, 0.3% and 0.95% Ni get almost the same result with 0.3% Ni.