ISSUE 1/2015

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Lampic, M.; Koch, F.; Walz, M. A novel scientific approach to vermicular (compacted graphite) cast iron as per DIN EN 16079 Part 2: The microstructure of GJV

The solidification of GJV as shown on the cooling curve in Figure 4 of the first part* of this publication series, is in first of all controlled by undercooling the stable eutectic temperature by magnesium. While the solidification starts at a temperature corresponding to the actual percentage of residual magnesium, the latter is entirely engaged in the formation of homogeneous olivine nuclei, typical for vermicular graphite. Due to the large segregation coefficient of magnesium, this is done by alternately forming Mg-rich and Mg-poor areas with differently structured crystallite sectors. The metallic matrix responds to the existing bond conditions (a, g, e depending on the temperature and pressure and the chemical composition. In this respect, among the period IV elements of the PSE, manganese showed an unexpected influence, which then was investigated more closely. There is already much information available about the formation of graphite from liquid iron in the literature, and the electron theory of metals, on which this is based, was proved in another reference. Therefore, it makes sense to only discus those events and mechanisms which are important and typical for vermicular graphite. 

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