Effects of transition from lamellar to compacted graphite on thermal conductivity of cast iron

Abstract

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.

Investigation on dynamic strain aging behaviour of ferritic-pearlitic ductile cast irons

“…However, the results show that spheroidal graphite cast irons can rival lamellar graphite alloys, if the main optimization parameter is thermal conductivity. The main trends of the three different cast iron groups is evident in Figure 8, which matches those in established literature [58][59][60]. Lamellar graphite conductivity only decreases with increasing temperature, while compacted and spheroidal graphite variant conductivity increase up to a certain point and starts to decrease in the final test temperatures.…”

“…The largest improvement in mechanical properties coincides with the lowest thermal conductivity. In line with established literature [58][59][60], no studied alloy shows improvement in both mechanical and thermal properties with the used treatment parameters. However, the results show that spheroidal graphite cast irons can rival lamellar graphite alloys, if the main optimization parameter is thermal conductivity.…”

Regression Analysis of Thermal Conductivity Based on Measurements of Compacted Graphite Irons

“…The negative influence of nodules on the thermal conductivity is well known [3,12,14] and could be illustrated by measurements on the samples with varying magnesium content, i.e., Mg 1, Mg 2, and Mg 3 cast in furan sand molds ( Figure 5). From the figure it is evident that an increasing amount of nodular graphite particles decreased the thermal conductivity.…”

“…The time needed for a 50 pct temperature increase was used when calculating the thermal diffusivity, and for adiabatic conditions the thermal diffusivity was calculated according to Eq. [3]:…”

“…Previous cast iron investigations have concluded that graphite morphology generally has the largest influence on the thermal conductivity. [1][2][3] Gray cast iron, with lamellar-shaped graphite, conducts heat more efficiently than compacted graphite iron (CGI) and the worst thermal properties are found in ductile cast iron, with nodular-shaped graphite. Gray cast iron has therefore been the material of choice in most engine components, due to its ability to remove heat rather than its strength.…”