ABSTRACT An endeavour for creating an understanding of the effect of filler wires (ER-70S6 and ER-80SG) on the mechanical performance of metal inert gas (MIG) weldments of two E410 graded structural steels that differed majorly in carbon contents i.e. 0.04 wt.%C and 0.17 wt.%C was undertaken. Improvements in yield stress (YS) with ER-80SG for MIG weldments of both investigated E410 structural steels were noticed; however, %elongation and room temperature (RT) impact toughness deteriorated as regards to ER-70S6. Almost ⁓5% increase in YS and a drop by ⁓4%, ⁓22%, and ⁓60% in ultimate tensile stress (UTS), %elongation, and toughness, correspondingly, were obtained for 0.04 wt.%C structural E410 steel with ER-80SG over ER-70S6. While moderate ⁓9% and ⁓8% increments in YS and UTS and a decrement of ⁓7% and ⁓40% in %elongation and toughness, respectively, were observed for 0.17 wt.%C steel with ER-80SG over ER-70S6. Enhancement in YS and a fall in %elongation and toughness with ER-80SG compared to ER-70S6 were due to high heat input for performing MIG welding of E410 steel, leading to thorough phase transformations providing fine Widmanstätten ferrite and acicular ferrite structures in weld metal with variable-sized inclusions and dissolved cementite and pearlite sub-structures in heat affected (HAZ) subzones of 0.04 wt.%C and 0.17 wt.%C steels, respectively.