Examination of Spheroidal Graphite Growth and Austenite Solidification in Ductile Iron


Microstructures of a ductile iron alloy at different solidification stages were captured in quenching experiments. Etched microstructures showed that spheroidal graphite particles and austenite dendrites nucleated independently to a significant extent. Growth of the austenite dendrite engulfed the spheroidal graphite particles after first contacting the nodule and then by forming an austenite shell around the spheroidal graphite particle. Statistical analysis of the graphite size distribution was used to determine the nodule diameter when the austenite shell was completed. In addition, multiple graphite nucleation events were discerned from the graphite particle distributions. Majority of graphite growth occurred when the graphite was in contact with the austenite. Circumferential growth of curved graphene layers appeared as faceted growth fronts sweeping around the entire surface of a spheroidal graphite particle which was at the early growth stage. Mismatches between competing graphene growth fronts created gaps, which divided the spheroidal graphite particle into radially oriented conical substructures. Graphene layers continued growing in each conical substructure to further extend the size of the spheroidal graphite particle.


Materials Science and Engineering

Keywords and Phrases

Ductility; Microstructure; Solidification; Austenite dendrites; Early growth; Faceted growth; Graphene growth; Graphene layers; Graphite particles; Graphite sizes; Spheroidal graphite

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Document Type

Article - Journal

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© 2016 Springer Boston, All rights reserved.

Publication Date

01 Dec 2016