Microstructure and impact toughness of flux-cored arc welded sm570-tmc steel at low and high heat input

This work investigated microstructure and impact toughness of multi-pass flux-cored arc welded SM570-TMC steel. A comparison was made between weldments fabricated with an average heat input of 0.9 kJ/mm and 1.4 kJ/mm, respectively. SM570 steel plate with 16 mm nominal thickness and 1.2 mm diameter of E81-Ni1 flux-cored wire were selected in this experiment. Multi-pass flux-cored arc welding (FCAW) was performed using carbon dioxide shielding gas. Then the weldments were observed using optical microscopy, scanning electron microscope (SEM) and electron probe microanalyzer (EPMA). The steel joint strength was measured via a tensile test, and Charpy impact test was performed at three different test temperatures. The microstructure observation exhibited the base metal mainly consists of ferrite and pearlite features, while the weld metal contained the acicular ferrites, polygonal ferrites, and M-A constituent at both different heat inputs. The impact toughness of base metal is superior to weld metals. The weld metals fabricated at an average heat input of 0.9 kJ/mm have a higher low-temperature impact toughness than using heat input of 1.4 kJ/mm. The acicular ferrites amount that significantly reduced at the higher heat input may degrade the toughness at low temperatures.