Influence of Gating System, Sand Grain Size, and Mould Coating on Microstructure and Mechanical Properties of Thin-Wall Ductile Iron

Two gating systems namely stepped and tapered runners were used to cast strip samples with different thicknesses by CO2/silicate process using sand grain sizes of AFS 151 and 171. To assess the effect of mould coating on the properties of thin-wall ductile iron, half of the moulds were coated whilst the rest were not coated. Molten metal with the carbon equivalent of 4.29% was prepared and poured at 1 450 °C. Microstructure of the specimens was analyzed by optical and scanning electron microscopes. Count, area fraction, roundness and diameter of the graphite nodules of the samples were measured by image analyzer. Brinell hardness and tensile tests of all the samples were also conducted. The results show that by using stepped runner gating system with uncoated and coarse sand mould, roundness and count of the graphite nodules decrease whereas diameter and area fraction increase. Although fine sand and coated mould cause longer distance of molten metal travel, hardness and strength of the samples decrease.