The existing literature concerning the thermal conductivity of cast iron is reviewed. The thermal conductivity/diffusivity is clearly affected by the amount and morphology of graphite, alloying elements and matrix as well as by temperature. The literature is consistent to some extent, but uncertainties still exist, for instance, about the effects of some alloying elements. Some attempts to model the thermal conductivity of cast iron are discussed. The existing models are based on composite theories. Hence, the accuracy principally depends on how well the morphology and individual properties of the compounds can be determined. In the case of cast iron, the analysis is complex and often based on old and sometimes conflicting experimental data.IJC/575

The thermal conductivity of ferritic spheroidal graphite iron samples containing various amounts of chunky or spheroidal graphite was investigated by means of the laser flash method. Scanning electron microscopy studies were performed to investigate the graphite morphology. Although chunky graphite is believed to grow in large interconnected eutectic cells, no beneficial effects on the thermal transport properties can be established for spheroidal graphite irons containing considerable amounts of chunky graphite. The results can be explained by the growth mode of chunky graphite with the c-axis of the hexagonal crystal as the dominating growth direction. This produces less favorable paths for the propagation of heat throughout the material as compared to lamellar and compacted graphite, owing to the low thermal conductivity of graphite along the prism planes. The crystallographic orientation of the hexagonal unit cells within lamellar, compacted, spheroidal, and chunky graphite was analyzed by means of electron backscatter diffraction (EBSD) and related to the thermal transport properties.

The thermal transport properties of five predominately pearlitic grades of grey, compacted graphite and spheroidal graphite iron have been investigated by the laser flash technique. Samples have been taken from cylinders cast in controlled thermal environments designed to produce three dissimilar cooling rates. Digital image analysis has been utilised in order to characterise the different graphite morphologies. The results indicated linear relationships between the thermal transport properties and the roundness of the graphite and the nodularity for compacted graphite and spheroidal graphite iron. A pronounced decrease in the thermal conductivity occurred when the lamellar graphite structure was transformed into compacted graphite. The thermal conductivity of compacted and spheroidal graphite iron has been recalculated with good accuracy over a temperature range of 25-500uC by means of regression analysis.

Different levels of magnesium were added to a standard grey iron alloy in order to obtain a range of graphite morphologies from lamellar to compacted graphite. The thermal conductivity/ diffusivity of samples, solidified at different cooling rates, was investigated by means of the laser flash technique. There is a significant decrease in the thermal conductivity as the morphology transits from lamellar to compacted graphite. The thermal conductivity of grey iron decreases considerably at elevated temperatures, whereas the thermal conductivity of compacted graphite iron is less sensitive to changes in temperature. At increased nodularities, compacted graphite irons exhibit a maximum thermal conductivity at y400uC. The influence from the cooling conditions on the thermal conductivity decreases as the morphology alters from lamellar graphite to compacted graphite. The effective thermal conductivity of cast iron is modelled by means of existing models for composites.

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