Solidification and microstructure of thin walled ductile cast iron

Research output: ResearchPh.D. thesis – Annual report year: 2006


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In the recent years there has been an increasing interest in light constructions in order to save weight in e.g. cars. Ductile cast iron has good mechanical properties but it is necessary to re­duce the wall thicknesses of the castings in order to reduce the weight. Reducing the wall thicknesses of the casting will increase the cooling rates and by that change the conditions for nucleation and growth during solidification.

Solidification of thin walled castings has been investigated experimentally using thermal analysis and metallographic examination. Castings with plate thicknesses from 1.5 to 8 mm have been investigated with the main focus on plate thicknesses from 2 to 4.3 mm. Both hypereutectic, near eutectic and hypoeutectic melts have been investigated with the main focus on the hypereutectic and near eutectic melts.

An experimental method for reproduceable temperature measurement in thin walled iron castings has been developed. The temperature measurements can give useful information about the solidification process. The measured temperature will however be about 20°C too low in the thinner castings (thickness ≤ 4 mm) while in an 8 mm plate the measuring error will be in the order of 3°C.

Temperature measurement and metallographic examination has revealed that in thin walled hypereutectic castings (thickness ≤ 4.3 mm) off-eutectic austenite dendrites precipitate before the main eutectic reaction. Due to nucleation of graphite nodules further undercooling is necessary before the onset of the main eutectic reaction. The effect of off-eutectic austenite dendrites was not observed in the 8 mm plates.

The near eutectic castings have higher undercooling and recalescence than the hypereutectic castings. The maximum temperature after the recalescence is however similar for the thin plates for both the hypereutectic and near eutectic castings. The difference in undercooling and recalescence can be explained by differences in nucleation of graphite.

The experimental results have been combined with 1-D numerical simulations using a solidification model that takes the precipitation of off-eutectic austenite dendrites into account. Results from the numerical model have confirmed the effect of precipitation of off-eutectic austenite dendrites in thin walled hypereutectic castings and have shown that nucleation and growth kinetics of austenite play an important role in solidification of thin walled ductile cast iron.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark (DTU)
Number of pages266
StatePublished - Jan 2006

    Research areas

  • Ductile iron, Temperature measurement, Solidification, Microstructure, Thin walled, Casting
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