Abstract
Magnetic arc deflection was applied to improve gas metal arc root welds on R260 pearlitic rail steel foot samples. During laboratory welding trials parameter optimization was carried out which comprised the welding current, voltage and speed, layer sequence, filler wire diameter, and the external magnetic field. Results were evaluated by visual inspection, and the lateral and diagonal penetration in cross-sections, as well as the microstructure and the hardness in the HAZ. Additionally, the influence of the external magnetic field on the process was studied using a high-speed camera. Overall best results were finally obtained in high welding current spray arc mode (380-400A) with the 1,6mm solid wire and at high welding speed (65cm/min) and two pass per layer sequence, in combination with maximum 30mT magnetic flux density and increased welding voltage (30-31V) for longer arc. A continuously well-formed root with sufficient lateral penetration was achieved and a smooth transition from base metal to weld metal at the lower edges could be achieved. Inside base metal HAZ the microstructure was fully pearlitic and no soft zone occurred. Furthermore, the size of the HAZ was in comparison to aluminothermic weld reduced by more than 75% in comparison to an AT rail weld.
Highlights
Welded rail strings are common today for multiple reasons
In order to fit the weld pool backing a clearance was milled into the support plate. Along both sides of the weld gap at the bottom edges ceramic tubes were pressed into the remaining gap between steel strip, samples and support plate in order to back the penetrating weld metal and shape a smooth transition collar from base metal to weld metal
3.1 Welding parameter optimization First of all, for what concerns the diameter of the filler wire the best results were obtain by using the largest dF of 1.6mm wire
Summary
Welded rail strings are common today for multiple reasons. the welds can still represent weak spots of the track. Aluminothermic (AT) welding is still the preferred process for joining rails in the track, accounting for about 3 Mio welds per year worldwide [5]. Amongst this process’s advantages are the very little demand in equipment and infrastructure and little costs, as well as the very good gap bridging tolerances. There is an unavoidable hardness drop at the outer limits of the heat affected zone (HAZ) [6]–[8] as a result of the process’ high heat input This regions shows reduced resistance to wear and rolling contact fatigue. Being a fully manual process, the quality of the joint depends on the welder’s skills and personal condition
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