ABSTRACT
The ductile fracture behavior of welded joints of Highly ductile steel (HDS) and conventional YP36 steel were experimentally investigated. Butt welded joints were fabricated using two welding methods: flux cored arc welding (FCAW) and electro gas welding (EGW). Cross weld tensile tests were performed using specimens with a gauge length of 200 mm and parallel section width of 40 mm. Consequently, the welded joints of HDS fractured at the base metal and no significant deterioration of ductility was observed. In contrast, the EGW joint of the conventional steel fractured at the heat-affected zone (HAZ) and ductility deteriorated significantly. Further investigations were conducted by wide plate tensile tests of the welded joints and the same result trend was obtained. The hardness of the HAZ in the welded joints of HDS was almost same as that of the base metal regardless of the welding method; contrastingly, HAZ softening was observed in the EG welded joint of conventional steel. The ductility of conventional steel was significantly decreased by the concentration of strain in the HAZ softening zone. Finally, elasto-plastic finite element analyses simulating the tensile tests of the welded joints were conducted. The analysis results show that the location of fracture initiation varies depending on the degree and extent of HAZ softening and plate thickness.
