Linear friction welding of rail materials: Thermal analysis and resulting microstructures of pearlitic and bainitic steels
Övrigt - Research report - Department of Mechanics and Maritime Sciences: 2019:04, 2019
Friction welding, a solid state process, is a method that uses heat produced from friction. The produced heat in combination with an external pressure joins the two pieces of material in a weld. Friction welding has several benefits such as lower heat input compared to conventional welding, resulting in a narrower heat affected zone (HAZ), low environmental impact and no melting-solidification phenomena resulting in a structure free of impurities which gives better fatigue properties. These benefits are of particular interest to an ongoing EU-project ”Innovative Weld Processes for New Rail infrastructures” (WRIST). The present study considers the linear friction welding method (LFW), a method based on relative linear motion of two pieces under compression. A thermal finite element analysis is performed for the LFW process for two different steels, R260 and B360. For the simulations different heat generation models, pressures and welding times are used in different combinations. The microstructure, based on the cooling rates obtained from the simulations, is presented and then validated to experiments. Reaching the microstructures pearlite and bainite and avoiding the microstructure martensite are crucial for the functionality of the resulting weld for both R260 and B360. It is found that avoiding the formation of martensite is difficult when using the provided welding parameters from the experiments. As a contribution to the WRIST project it is recommended to preheat the material, which was not included in previous experiments. If preheating of the material is considered, it is demonstrated that martensite can be avoided for R260, but not entirely avoided for B360.
Thermal Finite Element Analysis