The usage of ductile irons at thermo mechanically loaded components is increasing, necessitating more knowledge of material properties in elevated temperatures. A study of elevated temperature mechanical properties was done, investigating the effect of different pearlite fractions along with silicon content tests in fully ferritic microstructure. Effect of pearlite fraction and silicon content to tensile and yield strength were measured in different temperatures from room temperature up to 450°C. Models were developed, based on those measurements. These resulting regression models were tested with data gathered from literature.These can be used in various design tools, such as FEM calculations and in the optimisation of thermally and cyclic loaded ductile iron components.

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The aim of this study was to provide insight on thermal conductivity of three cast iron groups, namely lamellar, compacted and spheroidal graphite irons at elevated temperatures up to 673 K (400°C) in as-cast and austempered states. Austempering treatments increased mechanical properties of all the studied materials while decreasing thermal conductivity across the line. The effects of austempering on conductivity were lower for grey and compacted graphite iron than for spheroidal graphite irons. The results indicate that heat treating can be a viable option in increasing cast iron performance in thermally stressed applications. One ferritic low-silicon spheroidal graphite iron surpassed lamellar graphite iron in conductivity at elevated temperatures, while high-silicon spheroidal graphite irons exhibited low conductivities.

Publication 1: Elevated temperature thermal conductivities of some as-cast and austempered cast irons. In this study, first author contribution consists of thermal conductivity testing, design of experiments and data analysis. Co-authors took part in design of experiments, heat treatments and alloy production. The results were interpreted and commented together by the co-authors. Publication 2: Effect of Silicon and Microstructure on Spheroidal Graphite Cast Iron Thermal Conductivity at Elevated Temperatures. In this study, first author contribution consists of thermal conductivity testing, design of experiments, heat treatments and regression modelling. Co-authors took part in design of experiments, heat treatments and alloy production. The results were interpreted together by the co-authors. Publication 3: Investigations on dynamic strain aging behavior of ferriticpearlitic ductile irons. In this study, first author contribution consists of data analysis and interpretation. Co-authors took part in design of experiments, heat treatments, alloy production and experimental setup. The results were interpreted and commented together by the co-authors.

The mechanical and thermal properties of ferritic–pearlitic ductile irons vary widely according to their silicon and pearlite contents. Thus, different combinations of silicon and pearlite affect components’ lifetime under mechanical and thermal stress. An excellent example of the usage of such irons is combustion engine cylinder heads. They experience transient thermal loading (heating and cooling) during starting and stopping in addition to mechanical loading (combustion) during engine operation. An optimization approach and calculation models for the estimation of the optimal ductile iron composition are presented in this study. The approach allows selection of the most suitable base composition for subsequent analyses, such as casting simulation and final accurate finite element modelling and fatigue calculations.