PSI - Issue 53

Daniel R. Galán-Rivera et al. / Procedia Structural Integrity 53 (2024) 407–415 Daniel R. Galán-Rivera et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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• Preheating the metal powders at 70ºC • Reduce the gas flow • Modify the milling zone to flat machining • Preheating base material at 100-200ºC followed by a controlled slow cooling • Reduce the metal powder injection • Changes in the orientation of the nozzle related to the laser beam position

First two alternatives do not produce any improvements in the results. The third option removes the isolated silicates. The fourth alternative avoid the presence of cracking during the cooling stages. The last two strategies solve the silicates problem. In all cases, the resulting microstructure in the heat affected zone was martensitic (Fig. 6). About the obtained hardness, this type of metal powder (usually required to obtain hard coatings) produced a high increasing in the hardness values of deposited overlay, exceeding 500HV in some areas. The inner layers have shown a considerably lower hardness values due to the tempering caused by the later layers deposited (Table 2). Based on the subsequent machining of the rail to give it back its original geometry, it is recommended to carry out a superficial thermal treatment to re-tempering the outer layer and thus reducing hardness. Lowering in hardness contributes to the machineability of pieces.

Fig. 5. Macrograph and detail of the tram rail repaired with “Material 3 ”

Fig. 6. Micrograph of the heat affected zone (HAZ) in the coarse-grained zona (a) and in the fine-grained zone (b) of “Material 3”