Influence of the inoculation process, the chemical composition and the cooling rate, on the solidification macro and microstructure of ductile iron

Abstract

The solidification structure of any casting has a marked influence on its final microstructure and properties. Nevertheless, the correlation between solidification structure, microstructure and properties has not been clearly established for ductile irons. The objective of this investigation is to study the influence of the inoculation process, the chemical composition and the cooling rate on the solidification macro and microstructure of ductile irons cast in sand moulds. The results show that primary and eutectic austenite always grow dendritically, even for hypereutectic alloys. The solidification macrostructure is characterised by the grain size and morphology of the austenite, revealed by using a special technique developed earlier by the authors. The solidification microstructure is characterised by a parameter related with the location of the microsegregated last to freeze regions. Changes in the inoculation process do not cause significant modifications in the degree of the refinement of the solidification macro and microstructures. The carbon equivalent affects the grain size. The cooling rate, on the other hand, has a weak effect on the grain size and morphology, but strongly affects the dendrite arm spacing of the austenite.