Abstract: Within railway engineering practice continuous rails is created by welding lengths of rail. Conventional rail welding processes include aluminothermic/thermite welding and flash-butt welding. Both welding processes result in a large width of the weld and heat affected zone (HAZ). The weld and HAZ show irregularities along the rail surface including hardness variations, microstructural disturbances and/or inclusions. This makes welds in particular susceptible to damage. Laser welding of rails is proposed to create welds with a smaller weld and HAZ width. This thesis investigates the feasibility of laser welding for rails. The evolution of microstructures in R260Mn rail steel has been studied using x-ray fluorescence, dilatometry, optical microscopy, scanning electron microscopy and hardness measurements. From the data obtained from these experiments and thermal models that have been constructed, an appropriate set of welding conditions was determined and used for laser welding. The welding conditions considered are laser power, welding speed and pre-heating temperature. The main focus was put on welding speed and pre-heating. Preliminary welds consisted of a mainly martensitic and thus unacceptable microstructure. By selecting the welding conditions accordingly, the cooling rate could be decreased to form a pearlitic microstructure instead. Especially pre-heating was found to be a valuable method to reduce cooling rate and achieve an acceptable weld in terms of microstructure. The welded samples did contain welding defects like solidication cracking and porosity. The amount of welding defects is observed to decrease for higher welding speeds. It can be concluded that laser welding can be used to achieve an acceptable weld in terms of microstructure, especially when a pre-heating is applied to the rails. Further optimisation of the welding conditions may resolve welding defects.
Publication Year: 2017
Publication Date: 2017-01-01
Language: en
Type: article
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