Microstructure of thin-wall ductile iron castings

Step plate castings with section thicknesses of 1.5 mm to 6 mm and individual (single) castings with section thicknesses of 2 mm to 6 mm were produced using a ductile iron chemistry. Microstructures of these thin wall ductal iron castings were characterized quantitatively using an image analyzer. Matrix structure (amount of pearlite, ferrite, and massive carbides) and graphite structure (volume fraction, nodule size, nodule content, and nodularity) were investigated as a function of section thickness. Pearlite content, nodule count, and nodularity increased with decreasing section thickness, whereas the nodule size decreased. Nodule content exceeded 2000 nodules per mm{sup 2} at the thinnest sections. Statistical analysis was performed to investigate the effect of casting parameters on the microstructure