Effect of heat input on the microstructural and mechanical properties of TIG-MIG hybrid welded AISI 1008 steel

The mechanical performance of welded assembly depends on the resulted microstructural and mechanical properties. These properties are formed as a result of the amount of thermal energy imputed during the welding process. Although simple relations may exist for single welding processes, it becomes a more complex relationship with dual heat sources models. This study investigates the effects of heat input on the mechanical performance and microstructural features of the TIG-MIG hybrid welded AISI 1008 steel joints. The study employs microscopic investigation, hardness testing and axial tensile testing. Results indicated that welds produced by TIG-MIG hybrid welding constituted 'a wine-cup' profiles. Indeed, inhomogeneous microstructures were observed due to dual heat sources. Refined grains were observed in the lower portion of the weld, while dendritic pearlite structures and acicular ferrite characterised the upper portion. Higher heat input resulted in higher hardness values for both fusion zones and heat-affected zones. The welds produced with higher heat input show better penetration at the back bead. Although the initial increase in the heat input leads to an increase in the tensile strength, the continual increase in heat input does not necessarily lead to corresponding weld strength but increases the hardness further which may result in brittle weld joints.