Engineering Nucleation Kinetics of Graphite Nodules in Inoculated Cast Iron for Reducing Porosity

Abstract

Inoculation of cast iron with spherical graphite (SGI) controls nucleation kinetics of graphite nodules and is used for improving casting performance and eliminating solidification micro-porosity. In this study, thermodynamic simulations were used to design inoculants. Thermal and chemical stability of different potential heterogeneous nuclei formed in the melt above the liquidus temperature and in the mushy zone during solidification was predicted. Several inoculation treatments of SGI were performed in laboratory heats. An automated SEM/EDX analysis was applied to examine the graphite nodule size distribution and the family of the non-metallic inclusions in the experimental castings. The data were used to reconstruct a relative graphite nodule nucleation rate in the castings. It was shown that the graphite nodule nucleation kinetics in the castings were significantly different from those predicted by classical nucleation models. In inoculated SGI, the observed bi-modal distribution of graphite nodules was related to a continuous nucleation that occurred towards the end of solidification. The origin of the continuous nucleation and the possibility of engineering graphite nodules nucleation kinetics to control SGI casting soundness by inoculation are discussed.

Department(s)

Materials Science and Engineering

Keywords and Phrases

Chemical stability; Graphite; Kinetics; Nucleation; Porosity; Solidification, Automated SEM/EDX analysis; Bimodal distribution; Classical nucleation; Heterogeneous nucleus; Liquidus temperature; Non-metallic inclusions; Thermal and chemical stabilities; Thermodynamic simulations, Cast iron

International Standard Serial Number (ISSN)

1073-5615; 1543-1916

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2019 The Minerals, Metals & Materials Society and ASM International, All rights reserved.

Publication Date

15 Apr 2019

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