Abstract
Oxygen and sulfur have an important influence on nodularization during ductile iron preparation. In this paper, the metallurgical behavior of oxygen and sulfur for nodularization were studied by thermal analysis with Al-contained sample cup. The results show that oxygen has a significant influence on both primary phase and eutectic solidification of base iron because of its greater chemical affinity with carbon and silicon. The morphology and status of oxidized products obtained during nodularization affect eutectic graphite crystallization while sulfur with less electron affinity affects eutectic graphite nucleation and growth by combining sulfides as aided nucleation substrate. After nodularization, the formation and aggregation of sulfide particles are relatively slow in iron liquid. The dispersive deoxidization and desulfurization composites suspending in iron melt may be the beneficial core of spherical graphite. From the view of thermodynamics and kinetics, the direct anti-spherification action of sulfur is always weaker than that of oxygen.

Key words
ductile iron, oxygen and sulfur, metallurgical characteristics, thermal analysis, experimental study

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