Effect of Different Heat Inputs on Impact Performance of AH36 Steel Laser-MAG Hybrid Welded T-Joints

The T-joints of 6 mm thick AH36 shipbuilding steel were welded using the laser-MAG hybrid welding method. A testing device for the impact performance of shipbuilding steel T-joints was designed, and drop hammer impact tests were conducted on T-joint welds at different heat inputs to determine the critical height of the 6 mm thick AH36 shipbuilding steel T-joints. The process of fracture during impact was recorded using high-speed cameras and sensors. The microstructure and fracture characteristics of the joints were observed using SEM and OM. The results show that the critical height for the drop hammer impact of the 6 mm thick AH36 steel T-joints is 290 mm. The impact fracture energy of the sample with a heat input of 6.2 kJ/cm is 1873.3 J, and the impact fracture energy of the sample with a heat input of 8.2 kJ/cm is 1720.6 J, representing a decrease of 152.7 J in impact fracture energy. Compared to high heat input, the sample under low heat input conditions exhibited a larger displacement before fracture and took longer to fracture. From the analysis of the fracture surface, the dimples of the low heat input were larger, deeper, and absorbed more energy. Therefore, under the condition of ensuring good joint formation, a smaller heat input contributes to improving the impact performance of the joint.