This study prepared ductile irons with different contents of silicon, sulfur and manganese. Optical microscope was used to analyze the sizes and distribution of inclusion particles in the chilled samples. The effects of the inclusion particles on the microstructure of ADIs were observed and compared by SEM. Experimental results showed that the sulfur, manganese and silicon contents in base irons affected the quantities and sizes of inclusion particles in the chilled samples. Different sizes of particles led to the formation of acicular or blocky ferrite during the austempering treatment and these structures affected the mechanical properties of high strength ADIs. Increasing sulfur and manganese contents increased the coarse particles and thus the variation in the micro-hardness of the matrix of ADIs. Contrarily, increasing the silicon content caused the increase of fine particles and meanwhile reduced the variation in the micro-hardness.
Austempered ductile iron (ADI) Micro-hardness Impact energy Inclusion particle