In this paper a series of 4130 steel plates were joined by resistance spot welding using different currents. Hardness maps were determined over the large area of weld zone, including the heat affected zone and base plate. Hardness map was used to investigate the effects of current on hardness and microstructure in different regions of weld. The expulsion effect was observed in hardness maps. It was found that increasing the weld current is led to coarsening the microstructure of weld and HAZ

Welding current; Microstructure; Hardness map; Expulsion; Martensite