Influence of matrix structure on physical properties of an alloyed ductile cast iron

Abstract

Measurements of thermal diffusivity, specific heat capacity, and density are reported for seven different matrix structures of a ductile iron of composition Fe–3·5C–2·64Si–0·67Mn–0·007P–0·013S–0·25Mo–0·25Cu–0·04Mg (wt-%). These measurements are used to calculate the thermal conductivity over the temperature range 200–580°C. The matrix structures examined were ferritic–pearlitic, martensitic, and austempered. Matrix structure is shown to play a significant role in determining the thermal conductivity of the ductile iron. The ferritic–pearlitic matrix structures display a higher thermal conductivity than the austempered matrix structures. Matrix structure changes during heating were identified from the thermal diffusivity and specific heat measurements and from microstructural observations. Transformations which occur during heating and promote ferrite formation (such as tempering of martensite and the stage II reaction in the austempered matrix structure) increase the thermal conductivity.