Production of thick walled spheroidal graphite iron castings for casks

In order to develop the sound thick-walled castings made of spheroidal graphite cast iron for spent fuel casks in place of forging products and evaluate their material properties, the research was conducted on the cylindrical model casting with bottom which had 500 mm thickness, 2,000 mm outer diameter and 2,000 mm height. Internal quality of the castings is superior in terms of cavity and macrosegregation. Graphite nodularity of more than 75 percent and ferrite content of more than 95 percent can be obtained at any location, while there is a decreasing tendency in those at inner and top positions. A model casting shows an uniformity of mechanical strength indicating tensile strength of about 35 kgf/mm2 and yield strength of about 22 kgf/mm2 and improved impact strength of more than 2 kgf·m/cm2. Minimum elongation of 12 percent is ensured at any location, while it varies through the wall thickness and in the top-bottom direction. Fracture toughness tests indicate excellent KIC and KId greater than 330 kgf·mm-3/2. (author)