Thermal Conductivity of Cast Iron: Influences of Microstructure on the Thermal Conductivity of Cast Iron

Doktorsavhandling, 2006

The thermal transport properties of cast iron are important in high temperature applications, where the temperatures should be kept low and the thermal gradients within the component small. Dimensional and microstructural changes, thermally induced stresses and even failure might be catastrophic consequences of intense and/or unevenly distributed temperatures. Enhanced material properties are required in the future to enable a more efficient and complete combustion in heavy truck and marine engines necessary to encounter global environmental demands. The development is a requirement to meet customer needs together with present and future legislation. The purpose of this work is to correlate the thermal conductivity of cast iron to the microstructure. Initially, an analytical work including numerical calculations and simulations using the finite difference method, FDM, is discussed where the effects of e.g. the thermal conductivity and the wall thickness on the temperature distribution of cast iron components operating at elevated temperatures are evaluated. A literature survey is presented, covering a great deal of the existing works dealing with the influences from chemical composition, microstructure constituents and graphite morphology on the thermal conductivity of cast iron. Additionally, some modelling approaches are discussed. In the work, the effects of solidification rate, carbon content and inoculation of grey iron, graphite morphology of various grades of cast iron and graphite growth direction on the thermal conductivity are examined experimentally. Several relationships are established, e.g. between the carbon content and the fraction of primary austenite in grey iron, the nodularity and the roundness of the graphite for compacted graphite and ductile iron. Expressions describing the thermal conductivity of a pearlitic cast iron matrix are developed and utilized in order to model the thermal conductivity of grey iron both at room temperature and at elevated temperatures. Good agreement is achieved between experimental results and the models. Regression analysis is performed to identify variables influencing the thermal conductivity of compacted graphite and ductile irons, which also is remodelled with good accuracy by means of derived equations. Finally, the thermal conductivity of grey and compacted