EFFECTS OF SECTION SIZE ON THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF GREY CAST IRON

Abstract

The same chemical compositions all through were used to produce grey cast iron samples of various sizes (15 mm, 20 mm, 25 mm, 30 mm, and 35 mm). The charges (ferrosilicon, graphite and cast iron scraps) were heated in a rotary furnace at 1450 ^oC to produce melt and tapped into a preheated clay ladle at 1270 ^oC. Green moulding sand was used to produce the moulds. It was a plastic mixture of silica sand, clay (bentonite), additive (coal dust) with water. Hard wooden patterns machined with woodworking lathe machine into cylindrical shapes, 200 mm long and of different diameters were used for making the sand moulds. The moulds were prepared in moulding boxes. The prepared moulds were allowed to dry to eliminate moisture content before receiving the molten metal and the castings were subsequently obtained after 24 hours of solidification. A stainless wire brush was used to remove sand adhered to the castings after solidification. Abrasive wheel cutting machine was used to remove gates and risers associated with the castings. Then, the castings were machined into standard test samples using lathe machine, for mechanical tests. Optical metallurgical microscope was used to examine the microstructure of the produced grey cast iron samples. The results of the mechanical properties such as the hardness and the tensile strength were observed to decrease with increasing cast sample sizes. However, the impact toughness was observed to increase with increasing cast sample sizes. The graphite flakes in the microstructure were observed to be finer in thin section than those in thick sections.