Effect of Nickel Addition on the Microstructure and Toughness of Shielded Metal Arc Welded SS400 Steel

Nickel alloying element has been known to play a role in controlling the formation of microstructures in the weld metal (WM). This experiment aims to study the relationship between nickel addition to the microstructure evolution and toughness of shielded metal arc welded SS400 low carbon steel plates. Three welded samples, Ni-01, Ni-03 and Ni-09 were fabricated using electrodes containing different nickel: <0.1% Ni, 0.3% Ni, and 0.95% Ni, respectively. Microstructure of WM was examined using an optical microscope and scanning electron microscopy, and mechanical properties were measured in strength and toughness. The results showed the impact toughness increased when the nickel content of electrodes increased. From the three experimental welded samples, WM of Ni-09 which using electrodes containing 0.95% Ni demonstrated the best result for the impact toughness. It may caused Ni-09 has more AF and finer grains size compared to Ni-01 and Ni-03. It seems with nickel addition in the WM, finer grain size and acicular ferrite (AF) formation were developed.