Study on Mechanical Properties of Laser Welded Joints of DP980 High Strength Dual Phase Steel

In order to reveal the correlation between mechanical properties and welding process parameters of laser welded joints of DP980 high strength dual phase steel, five joints with different welding heat input were obtained by changing laser power and welding speed. The cross-sectional macromorphology, local microstructure, microhardness and tensile properties of the joints were studied. The results show that the width of weld zone and local heat affected zones decreases with the decrease of welding heat input. The weld zone, coarse grain zone and fine grain zone have higher microhardness due to the formation of lath martensite. Local softening occurs in the softening zone due to the tempering decomposition of martensite.The decrease of welding heat input can significantly reduce the width of softening zone and improve the elongation of joint,while it has no obvious effect on the softening degree of joints. When the heat input is lower than 51 J/mm, the fracture area of joint changes from the heat affected zone to the base metal.