Optimizing Control of Nodularization of Ductile Iron Based on Oxygen Activity Measurement

Abstract

Dissolved oxygen in molten iron is one of the most important metallurgical factors affecting nodularization effect and casting properties. In present paper, the metallurgical behaviors of active oxygen in molten iron are discussed during nodularization through a ZrO₂ (MgO partly stabilized) solid electrolyte battery for ultra-low oxygen condition of nodularized iron liquid. Combining with the results of thermal analysis obtained almost after active oxygen content measurement, the optimization control of nodularization process for ductile iron is studied. Results show that nodularization extremely disturbs the metallurgy equilibrium in molten iron, over-nodularization promotes this non-equilibrium degree. Inoculation can decrease the non-equilibrium trend and improve the solidification model by graphite nucleation. Nodularization effect degeneration began with the inoculation fading, with the active oxygen content slight increase, the volume fraction of nodular graphite decreased with rounded morphology. Followingly, as the active oxygen content continuous increase, the nodularity began to decrease. Therefore, it is promising to achieve more accurate control of nodularization by this combined on-line measurement technique.