Effect of heat input on microstructures and mechanical properties of Q890/Q550 dissimilar steel joint by laser－MAG hybrid welding

The laser-MAG hybrid welding of Q890/Q550 dissimilar steel joints was studied,and the effects of different welding heat input on microstructures and mechanical properties of dissimilar steel joints were tested and analyzed. Results show that at the same heat input,the overheated zones on both sides of the weld mainly consist of martensite and a small amount of bainite. Dense martensite is observed in the fine grained region. The martensite in the Q890 steel side is more than that in the Q550 steel side,the weld fracture has the characteristics of shear dimples and the impact toughness of the weld is higher than that of the heat affected zone. As the heat input increases from 3.5kJ/cm to 9.6kJ/cm,the amount of bainite gradually increases with the grain coarsening,and the impact energy of weld zone and heat affected zone slightly decrease. All The tensile specimens of three kinds of heat input are fractured in the Q550 steel,the fracture mode is ductile fracture,and the joint strength is higher than that of the base metal.