Improvement of the Metallurgical Quality of Ductile Iron in Heating Pouring Units through Appropriate inoculation

The metallurgical quality of ductile iron is strongly affected by the nucleation potential of the metal. Silicates, oxides, sulfides and nitrides, play an important role stimulating the graphite nucleation. The number of these non-metallic inclusions is totally influenced by the extreme conditions of temperature and holding time suffered by the treated melt in the heating pouring units (HPU). This situation provokes a lack of response in the effect of late inoculation with a clear trend to form intermediate carbides and microshrinkage. An improvement of the metallurgical quality of the melts with low nucleation potential by adding special commercial inoculants is thus a key objective. Additions of iron sulfide and micro additions of pure selenium seem to enhance the efficiency of these inoculants increasing the nodule count and favoring a better graphite distribution. The goal of present work is to investigate in different industrial situations the role of these elements. Both sulfur and selenium, seem to modify the number and size of graphite particles, with the generation of smaller nodules, reducing in most of cases the volume of microshrinkage. Their influence on the nucleation process with the formation of new nuclei is also demonstrated through advanced scanning electron microscope techniques.