Study of the Effect of the Casting Skin on the Tensile Properties of Light Weight Ductile Iron Castings

Download or read book Study of the Effect of the Casting Skin on the Tensile Properties of Light Weight Ductile Iron Castings written by Stephanie Karen Collins and published by . This book was released on 2007 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Thin wall ductile iron and compacted graphite iron castings are becoming more popular due to their high strength to weight ratio, but reduced mechanical properties can be observed if a casting skin forms at the surface. The skin usually consists of a layer of degenerated or flake graphite and a matrix that is inconsistent with the bulk matrix such as a pearlitic rim. The skin is most detrimental to thin wall castings because the skin becomes a significant percentage of the wall thickness. The width and severity of the skin depends on many metal casting processing parameters as well as materials such as sand, coating, and binder types, and is formed by interactions at the mold/metal interface. A test cast design was created using Magmasoft as a modeling platform The final design is a stacked mold design consisting of five molds each containing a 2.5, 4, and 6mm plate separated by semi-cylindrical risers. A methodology to characterize graphite shape was developed using image analysis software. Graphite shape parameters such as sphericity, compactness, roundness, and aspect ratio were measured on ductile iron samples from the University of Alabama and on compacted graphite iron samples from Ashland Casting Solutions using the developed methodology. Sphericity was determined to be the most accurate graphite shape measurement due to its use of the actual perimeter. Using the image analysis characterization along with microhardness, the depth of the casting skin could be determined as well as the presence of a pearlitic rim. The mechanical properties of samples produced from a test casting design created at the Ohio State University were compared to the ASTM minimum standard. Increasing metallostatic height was shown to increase the surface roughness of the samples. This trend was to be expected since a higher metallostatic height allows for deeper penetration of the molten metal into the mold. Little to no correlation was found between the elongation at failure and the metallostatic height and only a weak positive correlation was found between the ultimate tensile strength and the metallostatic height.