The solidification morphology of compacted graphite (CG) iron has been studied by means of quenching experiments. It allows being able to visualize the solidification sequence in cylindrical castings of dia 38 mm (1.5 in.). The CG structure results from insufficient magnesium treatment. The solidification mode is compared to that of gray and ductile irons. Compacted graphite iron exhibits a solidification morphology that is close to the one of ductile iron. A mushy state is created during the initial part of the solidification. After about 40% of the solidification time, the peripheral layer solidifies faster than in the case of ductile iron. It results in an earlier creation of a tight peripheral layer due to the interruption of the continuous liquid channels. The number of nodules, as well as the number of CG particles, continuously increases during the solidification. Literature reveals that the feeding characteristics of CG irons are more akin to those of gray iron. Two reasons explain this behavior. First, the direct growth of the CG particles allows the transfer of the graphite expansion directly to the melt, as opposed to ductile iron where the solid skeleton in the mushy zone passes the expansion onto the mold wall. The second reason is the earlier formation of a tight peripheral layer, which also shifts the feeding features of CG iron in the direction of those of gray iron. The dendrite fraction of ductile iron remains constant in hypereutectic compositions at about 19%. This is opposed to gray iron, which shows a continuous decrease of the dendrite fraction with increasing carbon equivalent.
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