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Analysis of the Microcrack Inducing Mechanism Resulting from Graphite Inclusion in the Bond Area and the Influence of Process Parameters for the Laser Repairing of Grey Cast Iron
P. Yi, X-H. Zhan, P-F. Xiao, Y-C. Liu and Y-J. Shi

On account of the microcrack problems in repairing area, experimental researches are developed on grey cast iron surface to clarify the microcrack formation mechanism and influence law of graphite phase in bond area. The results show that unreasonable morphology of flake graphite phase in bond area is an important cause of microcrack initiation and propagation. Their cusps almost cross toward the molten layer and through the bond area. Then the microcrack grows along the grain boundary. Additionally, under condition of certain specific energy input, an appropriate increase in laser power and scanning speed can enhance molten mass convection. It can be also helpful for the distribution rationalization of graphite phase and reduce crack sources. Besides, more reasonable parameter combinations are derived such as collocation of laser power as 2900 to 3100 W and first layer scanning speed as 360 to 420 mm/min. With using these, higher crack toughness and less rigid phase organization can be obtained.

Keywords: CO2 laser, grey cast iron HT250, laser repairing, microcrack, graphite morphology, process parameters

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