Microstructure and impact toughness relationship for different nickel level of electrode in multi-pass FCA welded SM570-TMC steel joint

A study was carried out to evaluate the relationship of microstructure and impact toughness for different nickel level of electrodes in multipass flux-cored arc welded SM570-TMC steel joint. The base metal used in this study was SM570-TMC plate with 16 mm thickness. The multipass welds were run by using flux-cored arc welding (FCAW) with a flat position (1G). Three SM570-TMC welded plates were fabricated with varying amounts of the nickel content of electrodes, 0.4, 1.0 and 1.5% Ni. The effects of nickel were studied on the weld metals. The investigations consist of observation on the microstructure and mechanical tests. The results indicated that at a temperature of 25 °C and 0 °C there was no obvious different impact energy value of weld metal by using electrodes 0.4 and 1.0% Ni. Besides, at a temperature of -20 °C the impact energy of weld metal containing 1.0% Ni was superior to the other. It seems the acicular ferrite (AF) formation on the weld metal containing 1.0% Ni effectively improves low-temperature impact toughness. On the other hand, the impact energy of weld metal, 1.5% Ni was the lowest. It is found that the higher nickel content caused the microsegregation as observed by the electron probe micro analyzer (EPMA).