Microstructural Characteristics and Load Carrying Capability of Resistance Spot Welded Dual Phase (DP800) Steel Joints

摘要

Similar joints of DP800 (Dual Phase) steel in lap joint configuration were fabricated using resis- tance spot welding (RSW) process. The welding current was varied at five levels (from minimum to maximum) and other parameters such as electrode force and welding time were kept constant. The tensile shear fracture load (TSFL) of joints was evaluated using universal testing machine. Microhardness variations across the weld cross-section was recorded using Vickers's microhardness tester. Microstructural features were analyzed using optical microscopy (OM), and scanning electron microscopy (SEM). From this investigation, it is understood that increase in welding current increases the nugget zone size and it led to increasing the degrease of softening in the HAZ. The tensile shear strength is found to increase with increase in welding current up to a certain limit and then it decreases. The microhardness profile shows a peak hardness in nugget zone and the hard- ness is lower in the HAZ. The softening of HAZ is mainly attributed to inter-critical heating during welding.