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The Effect of Thermal Shock on As-cast Grey Ironʹs Microstructure

In this investigation has been presented the effect of high thermal shock on microstructure of as cast Grey Irons and interface of graphite and metallic matrix. In order to reach this goal some notched samples with dimension 5x5x20 mm of the cast iron GG25 were provided (like impact test). They were exposed to cyclic heating between 900°C and 0°C. Investigating the metallographic images and micro hardness results before and after the thermal shock cycles, it can be inferred that thermal shocks can cause the matrix decomposition and the precipitating of the solute carbon on initial free graphite flakes. This expanded graphite flakes, however, are porous and fragile. Growth of the graphite will be lead to fracture during more cycles. Also perlitic matrix was transformed to perlite. Keywords: Thermal fatigue, Graphite, Cast Iron, Thermal Shock, Microstructure