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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In this work, the meaning of the solidification structure and how it is related to defect formation in grey cast iron will be discussed. The work also confirms observations made earlier. In previous work the formation of shrinkage porosity in grey cast iron cylinder heads was investigated. It was found that the defect is located around solidification units resembling primary austenite grains. The solidification of grey cast iron starts with the formation of primary austenite grains, followed by the eutectic solidification. The primary grains nucleate and grow either as columnar or equiaxed grains, creating a columnar to equiaxed transition between the two zones. Based on the presence of a migrating hot spot, and other characteristics found on the cylinder heads, a geometry was developed that promote the formation of shrinkage porosity. The primary solidification structure, normally transformed during the solid state transformation, was preserved using a technique called Direct Austempering After Solidification (DAAS). After solidification, the samples were cut and prepared for investigation using a Scanning Electron Microscope (SEM) equipped with a detector for Electron Back Scattered Diffraction (EBSD). Individual grains were identified and the primary solidification structure around the defects was revealed. The investigation shows how shrinkage porosity is formed and located between primary austenite grains. This confirms that the primary solidification structure has a large influence on the formation of defects in grey cast iron. The investigation also confirms the correctness of earlier results as well as the validity of the DAAS technique.

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.

Defective castings produce unnecessary costs for foundries. Common flaws in spheroidal graphite cast iron castings are shrinkage defects. The literature on the subject suggests that by controlling the precipitation of graphite, it is possible to suppress the shrinkage propensity of the melt. The most influential way of affecting the precipitation of graphite is inoculation. In this work, the effectiveness of different commercial inoculant products and inoculation methods in reducing the shrinkage defects for cast components were researched. Significant differences in performance were observed between ladle inoculation and stream inoculation methods in preference of stream inoculation. Differences were also observed for different inoculants and, when both ladle and stream inoculants were used, also for their behaviour as a combination. It was observed that not all of the combinations were beneficial. In order to decrease the cost caused by shrinkage defects, a proper selection of inoculation method and inoculant is of importance.