In this work, heterogeneous tungsten inert gas (TIG) welding has been performed on an EN-08 steel plate using Mild Steel BS1453A3 filler material. For obtaining a full penetration, welding testing has been carried out for a wide range of welding currents and gas flow rates. The ultimate strength of steel is enhanced with an increase in welding current up to 63 A, and after that, it decreases. Steel has a peak ultimate strength of 860 MPa for the gas flow rate of 15 L/min. At this value, the depth of penetration, the rate at which the filler rod melts, the volume of base material melted, dilution, fusion depth, amperage, and the deposition rates were all good, and optimum weldability was achieved. As the welding current increases, the hardness of low-carbon steel shows a rapid increase and after 65 A, the current is almost constant. The increase in hardness is due to the formation of martensite or bainite in the weldments. Also, an increase in heat input increases the grain size in the microstructure of the metal, thus giving rise to a coarse grain. As the gas flow rate increases, the ultimate strength first increases and achieves a maximum value; after that, it decreases. At a gas flow of 8 L/min, scaling or oxidation is found more as compared to 15 L/min and 22 L/min. At a gas flow rate of 22 L/min, the weld bead form is more distracted due to the high flow rate; the cooling effect is also greater.