Study On Continuous Drive Friction Welding Of K418/42CrMo Dissimilar Metal

According to the continuous drive friction welding of turbo rotors, through laboratory testsand theoretical analysis, microstructure, alloy elements diffusion behavior and mechanicalproperties of different K418/42CrMo dissimilar metal welding joints are discussed, providestheoretical basis for the optimization of welding technological parameters.The results of microstructure analysis show that because of the differences betweenphysical and chemical performances of the welded materials, the friction interface transformsfrom the interface between K418/42CrMo to the interior of K418superalloy, and forms asecondary friction interface. Recrystallization occurs between welding joint and secondaryfriction interface. Some carbon diverts from42CrMo to K418and enriches at the secondaryfriction interface at high temperature. During cooling, the carbide precipitates at the secondaryfriction interface. As a result, the hardness become higher with a carbon-rich region appeared inK418and lower with a carbon-depleted region appeared in42CrMo. There is also a migrationof Ni, Fe, Cr and other elements.The results of welding test show that the high specification with big pressure and shorttime is better, the tensile strength can reach755MPa. The tensile strength of low specificationwith small pressure and long time are generally lower than755MPa with more welding defects.Ⅰ-friction is primarily a preheating process, it has prominent influence on low specification butnearly no influence on high specification. Ⅱ-friction is the main process of welding, Ⅱ-frictionpressure and time have great effect on friction welding. Forging and heat treatment afterwelding also play an important role in improving welding quality.Through the research, the optimal parameter of K418/42CrMo dissimilar metal welding is0.8MPa×1s+4.0MPa×8s+4.0MPa×5s. The welding process parameter has been successfullyapplied to production by the excellent effect.