Research On Dissimilar Inertia Friction Welding Of K418 Ni-based Superalloy Turbine Disk And 42CrMo Shaft

Turbochargers can increase the power of engines by 20% ~ 35%,and are increasingly widely used in the automotive industry.Working temperature of the turbocharger is generally higher than 600 ?.K418 nickel-based alloy were adopted.The high temperature alloy has better thermal structure stability,heat resistant corrosion resistance and heat resistance,but the manufacture cost is greater.In order to decrease the cost,turbocharger is expected to be manufactured by "K418 turbine disc-42 CrMo shaft welding".Owing to the higher differences in chemical composition,thermo-physical properties and high temperature mechanical properties,the poor weldability becomes a technical problem to be solved.So in this paper,42 CrMo alloy steel and K418 nickel-based alloy were the base materials.The weldability of the two materials for inertial friction welding was carried out.The inertial friction welding technology of the 42 CrMo shaft and K418 turbine disk also was investigated.And the interfacial bonding mechanism of the two materials was analyzed.The main research results are as follows:(1)By studying the inertial friction weldability of rod-shaped 42 CrMo and K418 samples,a good welding joint could be obtained between 42 CrMo and K418 under appropriate process parameters.And only a small number of defects of not welded and micro-cracks existed in the peripheral area of the welding interface.With increasing initial kinetic energy,the temperature of the welding interface increases and the K418 side deforms in a narrow area.The 42 CrMo deformation area increases and dynamic recrystallization occurs,and machining hardening occurs at the same time.The joint action of the two makes the welding interface achieve good metallurgical bonding and mechanical occlusion.When the initial kinetic energy is 50.60 kJ,the average tensile strength of the joint reached 772 MPa(88% of the base material).And the tensile fracture occurs at K418 side near the interface,which is a brittle fracture.(2)In the process of inertial friction welding of 42 CrMo shaft and K418 turbine disc,the joint structure of the hollow shaft and plane is adopted to improve the heat distribution at the interface.The tensile strength of the joint increases with the increase of initial kinetic energy and upset pressure,and the tensile fracture is characterized with brittle fracture.When the top forging pressure remains unchanged and the initial kinetic energy of the flywheel is 4.21 kJ.The joint tensile fracture occurs at the welding interface.When the initial kinetic energy increases to 29.91 kJ,the tensile fracture of the joint is at the side of K418,and the average tensile strength of the product reaches the maximum value of 1129 MPa.When the initial kinetic energy remains unchanged and the upset pressure is 154 kN,the average tensile strength of the product gets to the peak value of 1090 MPa.And the fracture also occurs on the side of K418.The high-temperature tensile strength of the joint is better than the 42 CrMo of high-temperature tensile strength under certain technological parameters.(3)When the welding heat input is sufficient,the element of C in the welding interface diffuses from 42 CrMo to the side of K418.The mechanism should be as follows: the high concentration of C element in 42 CrMo increases the interface temperature due to the friction in the welding process,providing diffusion activation energy for the diffusion of C atom.In addition,dynamic recrystallization occurred at the interface,resulting in grain refinement and grain boundary increase,which created conditions for short circuit diffusion of C atom along the grain boundary.The element of C aggregates in the heat affected zone on the side of K418,and forms a discontinuous carbide zone with strong carbide elements,which makes this area brittle.(4)Inertial friction welding is a process of physical and chemical interaction.Under thermal-mechanical coupling,plastic flow,mechanical occlusion,element diffusion and dynamic recrystallization occur in the interface metal.Dynamic recrystallization occurs in the microstructure of the plastic deformation zone.The recrystallized grains in the central area of the interface are small,the grains in the peripheral area grow up under the action of heat,and a few coarse grains exist in the heat-affected zone and thermal-mechanical affected zone.The plastic deformation layer has finer grain,denser structure and higher mechanical properties.