Temperature Field Simulation and Mechanical Properties of Laser Welded DP980 Steel Joints

High strength steel DP980 was welded using fiber laser, and the temperature field was evaluated via numerical simulation. The results reveal that the peak temperature of weld center reached 3204℃ and then martensite microstructure forms after rapid cooling. The fusion zone mainly contains martensitic microstructure with hardness 30% higher than that of the base metal. The ultimate tensile strength of the fusion zone reaches 1115.7 MPa, while the elongation is decreased by 49.1% compared with that of the base metal. The stress-strain curve of the softened zone exhibits obvious yield platform, and the ultimate tensile strength (850.7 MPa) is significantly lower than that of the base metal (986.9 MPa). The ultimate tensile strength of the welded joint reaches 87.1% of that of the base metal, while the elongation reaches 32.7% of that of the base metal. All the tensile and Erichsen test samples fail at the softened zone. The major strain of the base metal is higher than that of the welded joint.