Unraveling Compacted and Nodular Cast Iron Porosity: Case Studies Approach

Abstract

Porosity is the culprit for a large fraction of scrap in cast iron foundries, resulting in significant environmental and productivity losses. The present work focuses on characterizing and explaining porosity defects in industrial compacted and nodular graphite cast iron components, utilizing current literature for reference. The goal is to identify existing knowledge gaps in the field, fostering further research work. Complex-shaped castings were sampled from three foundries, weighing between 100 and 300 kg. These were carefully selected to capture recurring defects during stable production. The mechanisms behind these defects were discussed, and the findings were compared to the literature. Scanning electron microscopy (SEM) was used to investigate the inner surfaces of the pores with secondary electron imaging. The surrounding microstructure was captured with optical microscopy in combination with image analysis, where panoramic images and nodularity maps were built. Ultimately, etching based on Si segregation was employed. The results suggest that the understanding of pore surface film formation remains limited, particularly regarding graphite film formation. Notably, the observations reveal a multitude of previously unreported graphite structures within the pores, some with particles in their centers containing Ce, Ca, La and S. These novel structures can provide additional insights regarding pore formation chronology.