Solidification of lamellar cast iron is a complex mechanism due to the contracting austenite phase and the expanding graphite phase precipitation. The combined effect of contraction-expansion has an influence on the volume change related defects (shrinkage porosity and penetration). Critical moments in measuring volume change are the methods used for measurement together with the interpretation of the solidification based on the macrostructure. Reliable results are obtained using displacement measurement in both axial and radial direction of a cylindrical sample in combination with using two thermocouples and a force measurement unit. Common drawback of the used method together with other methods presented in the literature is the early expansion observed before the coherence of the solidifying grains. The introduced force measurement gives a novel interpretation of the columnar to equiaxed transition, and the displacement measurement in different directions within a cast sample reveal the anisotropic character of the volume change.

Complex-shaped lamellar graphite iron castings are susceptible to casting defects related to the volume change during solidification. The formations of these recurring defects are caused by the flow of the liquid in the intradendritic area, between the austenite dendrite arms, and in the extradendritic area between the austenite grains. The conditions for the liquid flow, in turn, are determined by the solidification behavior. The present study suggests a new measurement method and a novel calculation algorithm to determine the pressure of the extradendritic liquid during solidification. The method involves a spherical sample suspended in a measurement device, where the temperature and the volume changes are measured during solidification. The calculation algorithm is based on the numerical interpretation of the ClausiusClapeyron equation where the temperature variation, the volume change and the released latent heat are processed to determine the local pressure of the extradendritic liquid area during solidification.

The solidification of gray cast iron starts with the precipitation of primary austenite. This phase nucleates either as columnar or equiaxed dendrites depending on whether nucleation occurs on the mould wall or on particles and impurities in the melt. In this work, the nucleation of primary austenite and its influence on the eutectic solidification has been investigated using different amounts of iron powder as inoculants. Besides, the influence of different cooling rates was also examined. Within each austenite grain there is a microstructure, and this microstructure was investigated using a color etching technique to reveal the eutectic cells and the dendritic network. It is shown how the cooling rate affects the dendritic network and the secondary dendrite arm spacing, and how the microstructure can be related to the macrostructure through dendrite arm spacing. The secondary dendrite arm spacing is a quantification of the primary austenite belonging to the primary solidification, and it will be shown how the eutectic cell size is related to the secondary dendrite arm spacing. The total amount of oxygen influences the microstructural dimensions. This effect, on the other hand, is influenced by the cooling rate. The number of eutectic cells versus eutectic cell size show two distinct behaviors depending on whether being inoculated with iron powder or a mixture of iron powder and commercial inoculant. The addition of a commercial inoculant decreases eutectic cell size and increases the number of cells, while iron powder almost only changes cell size.

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Shrinkage porosity and metal expansion penetration are two casting defects that appear frequently during the production of complex-shaped lamellar graphite iron components. These casting defects are formed during the solidification and usually form in the part of the casting which solidifies last. The position of the area that solidifies last is dependent on the thermal conditions. Test castings with thermal conditions like those existing in a complex-shaped casting were successfully applied to provoke a shrinkage porosity defect and a metal expansion penetration defect. The investigation of the primary dendrite morphology in the defected positions indicates a maximum intradendritic space, where the shrinkage porosity and metal expansion penetration defects appear. Moving away from the defect formation area, the intradendritic space decreases. A comparison of the intradendritic space with the simulated local solidification times indicates a strong relationship, which can be explained by the dynamic coarsening process. More specifically, long local solidification times facilitates the formation of a locally coarsened austenite morphology. This, in turn, enables the formation of a shrinkage porosity or a metal expansion penetration.