Microstructure evolution in grey cast iron during directional solidification

Xian-fei Ding^1,2，Xiao-zheng Li³，Qiang Feng^2,3

1. National Center for Materials Service Safety, University of Science and Technology Beijing2. Beijing Key Laboratory of Special Melting and Preparation of High-end Metal, University of Science and Technology Beijing3. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing

摘 要：The solidification characteristics and microstructure evolution in grey cast iron were investigated through Jmat-Pro simulations and quenching performed during directional solidification. The phase transition sequence of grey cast iron was determined as L → L + γ→ L + γ + G →γ + G → P（α + Fe₃C） + α + G. The graphite can be formed in three ways: directly nucleated from liquid through the eutectic reaction（L →γ + G）, independently precipitated from the oversaturated γ phase（γ→γ + G）, and produced via the eutectoid transformation（γ→ G + α）. The area fraction and length of graphite as well as the primary dendrite spacing decrease with increasing cooling rate. Type-A graphite is formed at a low cooling rate, whereas a high cooling rate results in the precipitation of type-D graphite. After analyzing the graphite precipitation in the as-cast and transition regions separately solidified with and without inoculation, we concluded that, induced by the inoculant addition, the location of graphite precipitation changes from mainly the γ interdendritic region to the entire γ matrix. It suggests that inoculation mainly acts on graphite precipitation in the γ matrix, not in the liquid or at the solid–liquid front.

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