A Study of Oxygen Activities Before the Start of Solidification of Cast Irons

The focus of this work was to study dissolved oxygen content and oxygen activities in different cast irons. Plant trials were performed on three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities ranged from 0.03 to 0.1 ppm for lamellar graphite iron (LGI), around 0.02 ppm for compacted graphite iron and 0.001 ppm for spheroidal graphite iron. In addition, it was found that as oxygen activities increase with time after an Mg treatment, the ability to form compacted graphite or nodular graphite in Mg-treated iron melts was lowered. Also, oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for LGI at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels are believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.