Statistical Analysis of the Mechanical Properties of Thin Walled Ductile Iron Castings

Ductile iron castings have long been used in the automotive market. Ductile iron is inexpensive to produce and has desirable fracture resistance and mechanical properties. However, the weight of ductile iron is driving an effort to reduce wall thickness in order to increase fuel economy. Traditionally, cast iron has been cast into thick, bulky shapes. Reducing the section size of cast iron can be done, but pushes foundry practice into new areas. A consortium of foundries, foundry suppliers, and automotive manufacturers has been pursuing the use of thin walled ductile cast iron. This paper investigates the mechanical behavior of three experimental heats of thin-wall castings in order to evaluate property trends and limits. Castings as thin as 1.7 mm (0.07 in) have been successfully cast. The study was designed to investigate the effects of thickness and different casting heats on the dependent variables of ultimate tensile strength, yield strength, elongation-to-failure, reduction in area, and hardness. The ultimate tensile strength of the castings is found to increase as the casting thickness decreases. Conversely, the elongation-to-failure is found to decrease as the casting thickness decreases. Heat-to-heat differences were found, but they were usually within the scatter of the data.