On Line Oxygen Activity Measurements to Determine Optimal Graphite form During Compacted Graphite Iron Production

Lately, the present authors published a study where oxygen activities were measured using a commercial sensor, which became recently available. In ductile cast iron melts with ferritic and pearlitic structure, optimal properties occur for a well-defined oxygen activity. Castings poured in these circumstances present maximal nodularity, elongation and ferrite content combined with lowest hardness. Additionally, the first results for compacted graphite cast iron were published. The present contribution examines in much more detail the effect of sulfur and oxygen activity on several phenomena important during production of compacted graphite cast iron. These phenomena are the limit for which mechanical properties as defined in ISO16112 are met, the transition from compacted graphite to lamellar graphite and the point at which 20 percent nodularity occurs. Taking into account that the oxygen activity measurement is obtained in about 12 seconds, the sensor seems to be very promising for compacted iron process control.