Influence of Free Nitrogen on Tendency of Chill Formation in Spheroidal Graphite Iron Castings

Abstract

In this study, the most influential factor for causing chill formation in spheroidal graphite iron castings was surveyed. A 30 ton electric arc furnace with magnesia linings using in commercial operation was used for melting. Chill depth of wedge samples was tested through the process from melting to pouring, and the tendency was compared with the changes of temperature, chemical compositions, and gas elements at the same stages. As the results, it was cleared that chill depth was mostly influenced with the change of free nitrogen (N_F). Chill depth was deeper when N_F was higher value. This indicates that chill structure will be able to be avoided by denitrification. It was considered that N_F might replace carbon (C) atom in ledeburite cementite (Fe₃C) crystal structure and might promote chill formation. The denitrification would be able to promote full graphitization and might prevent chilling. On the other hand, it looked an important to minimize nitrification after denitrification.