Development of as-cast dual matrix structure (DMS) ductile iron

Ductile iron is widely used due to its low cost and higher ductility than other cast irons. There has been an increased interest during the last years in improving the strength of these materials by means of heat-treating to obtain dual matrix structures (DMS) that enhance the properties found in Austempered Ductile Irons (ADI). This work studies the fabrication of DMS ductile cast irons with martensitic and bainitic structures in the as-cast condition, reducing costs related to heat treating processing while improving the mechanical behavior of the material. Cast irons alloyed with nickel ranging from 0% up to 7% were produced in order to evaluate the effect of Ni-Mo content on the phase transformations and mechanical properties of the material. The effect of cooling rate in phase transformations and mechanical properties were studied using molds with different wall thicknesses, finding that addition of Nickel and Molybdenum improves substantially the strength of the as-cast ductile iron, making unnecessary any further heat treating according to the level of properties desired.