Abstract
This study investigates the effect of double-pass tungsten inert gas welding on the mechanical and microstructural properties of type AISI 1008 mild steel joints. A butt joint configuration was adopted to weld the plates maintaining a root gap of 2.5 mm between plates for all welded samples. The double-pass tungsten inert gas welded AISI 1008 joints showed improved ultimate tensile strengths compared to the unwelded parent material, with the least joint efficiency of 82.67 % (weld W3). However, the parent material yield strength (295.9 MPa) was higher than those obtained from the welded samples (weld W1-270.4, W2-240.2, W3-284.1), respectively. This result is worth noting for design applications, especially for mechanical load-bearing members, as it gives information on the limit below which failure will not occur. The weld metal hardness for all welds increased with increased heat input, whereas the heat-affected zones hardness first increased and then decreased as heat input increased. The internal geometry of the welds reveals an increase in the bead width, height of reinforcement, width of the heat-affected zone, and weld metal area as the heat input increases. Lastly, the microstructural evolutions of the weld metal zones were primarily dominated by widmanstatten ferrite, acicular ferrite, and pearlite structures which accounted for the improved tensile strength and hardness of the joints. In contrast, the heat-affected zones were characterised by coarse columnar dendrite structures resulting in lower hardness.