An experimental study was conducted on ASTM A588 Grade A and ASTM A572 Grade 50 microalloyed steels submerged arc welded with Linde 40B weld metal to determine the fracture properties of base plates, weld metal and heat-affected zones.The effects of plate orientation, heat treatment, heat input, and postweld heat treatments on heat-affected zone toughness were included in the investigation.Tensile properties were evaluated for the weld metal and base plates.Hardness tests were done on weld heat-affected zones (HAZ).Charpy impact tests were performed over a temperature range for plates, welds and heat-affected zones. The nil-ductility transition temperature was determined for the plates and the weld metal.