Date of Award


Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering (PhD)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Paul Sanders

Committee Member 1

María Pérez López

Committee Member 2

Douglas Swenson

Committee Member 3

Stephen Hackney


Ductile Iron is a material that is constantly evolving. Consequently, the ferrous industry is not only focusing on lightweighting but also on improving the impact strength and fracture toughness of typical ferritic-pearlitic ductile iron grades and solid solution strengthened ferritic ductile irons. Recently, the demand for thin-wall ductile iron and solid solution strengthened ferritic ductile iron grades has increased. The challenges behind the fabrication of these two ductile iron materials are the presence of carbides and the embrittlement of ferrite. In response, research has been focused on looking at alternative methods that can mitigate carbide formation in thin sections and counteract the detrimental effects of high silicon contents in the impact toughness of these materials. One way to reduce carbides is by increasing the silicon, but high silicon contents embrittle the ferrite and result in low static and dynamic mechanical properties. Cobalt in ductile iron is known to increase the nodule count resulting in a higher ferrite content in the as-cast condition, and it also hardens the ferrite via solid solution strengthening. Therefore, the ability of cobalt to inhibit carbide formation and its effect on the toughness of two different types of ductile irons was studied. Firstly, it was found that the addition of 4 wt.% Co reduces carbides in thin sections with a silicon level around 2.41 wt.% Si. Secondly, partial substitution of silicon with 2 wt.% and 3 wt% Co provided higher strength in a 600-10 SSFDI grade. Nonetheless, the impact strength and fracture toughness were not improved with cobalt additions. It was established that cobalt increases the ductile to brittle transition temperature.