Javaid A, Thomson J, Davis K G, Sahoo M

Abstract: The effect of microstructure achieved under various molten metal processing conditions (i.e., chemistry, pre-conditioning of the base iron, inoculation type and practice, etc.) on the tensile and impact properties of thin-wall ductile iron castings has been investigated. Microstructures in 3 and 12 mm sections within the same casting were compared. While many samples from 3 mm sections showed low elongation values, caused by a high pearlite content and/or the presence of carbides, many others showed high elongations and superior strengths. At moderate to high elongations, the 3 mm section samples were significantly stronger as a result of more refined and homogeneous microstructure, i.e., higher nodule count, better nodularity, reduced segregation, etc. In the 12 mm sections, the microstructures developed as a result of different molten metal processing conditions and the chemical composition had a controlling influence on the tensile and impact properties. In the 3 mm sections, while the tensile properties were also strongly dependent on microstructure, the impact properties were relatively insensitive. Both sections showed a drop in Charpy impact energy with increased nodule count. Of the elements contained in the iron, an increase in the silicon content had the greatest effect in improving the tensile properties for both sections, as a result of an enhanced ferrite content. Despite the promotion of ferrite by silicon, the Charpy toughness decreased with increased silicon in the 12 mm sections, and was essentially independent of silicon content in the 3 mm sections.

Keywords: Ductile iron castings, Effect, Mechanical properties, Microstructure, Thin-wall