Effect of mould runner and coating on graphite nodule characteristics and hardness of thin wall ductile iron

Abstract

Due to its attractive characteristics, thin wall ductile iron (TWDI), has been increasingly considered as a preference for reducing material consumption in order to save energy and contribute less environment pollutions as well as decreasing costs. In this research, the effect of two mould runner gating systems and mould coating on graphite nodule characteristics and hardness values of TWDI casting was studied. Strip samples with various thicknesses of 2.3, 3.3, 4.5, 5.4, 6.5, 7.5 and 8.5 mm were casted into CO2 Silicate moulds designed by two gating systems namely stepped and tapered runners. Half of the moulds were coated by graphite-based zircon material to investigate the effect of mould coating on the graphite nodule qualities and quantities. The molten metal prepared contained carbon equivalent (CE) of 4.29% and was poured at the temperatures of 1450°C. Optical microscope (OM) and Clemex Image Analyzer (CIA) were used to evaluate graphite nodule count, roundness and diameter of the nodules of the TWDI cast samples. Brinell hardness test was performed on all samples. The results show that roundness and graphite nodule counts in the microstructure of the samples produced in stepped runner gating system and uncoated mould decrease whereas graphite nodules diameter shows opposite behaviour. Furthermore, molten metal experienced a superior fluidity in coated moulds. Moreover, the TWDI samples achieved a significant improvement in the value of hardness.