Microstructure evolution in grey cast iron during directional solidification

Xian-Fei Ding,Qiang Feng,Warkentin Matthias,Xiao-Zheng Li,Shi-Yao Huang

doi:10.1007/s12613-017-1474-6

Abstract

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.

Highlights

Because of its good thermal properties with balanced strength, grey cast iron is one of the most widely used materials in automobile components such as brake rotors and flywheels
The solidification characteristics and microstructure evolution in grey cast iron were investigated through Jmat-Pro simulations and quenching performed during directional solidification
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)

Summary

Introduction

Because of its good thermal properties with balanced strength, grey cast iron is one of the most widely used materials in automobile components such as brake rotors and flywheels. Because the mechanical properties as well as the thermal properties are closely related to the as-cast microstructures, microstructure control during cast processing is a major challenge for improving the properties of grey cast iron. Solidification behavior can provide useful information for the casting process of grey cast irons. Hejazi et al reported that the morphology of graphite in grey cast iron is related to the cooling rate [1]. Oloyede et al investigated the microstructure and properties of grey cast iron under rapid solidification [3]. The scopes of most of these investigations on solidification microstructure characteristics have not included the solidification procedure or phase transformations during cooling, resulting in an incomplete understanding of the solidification behavior. A deep understanding of the solidification behavior and phase transition is still required to enable control of the as-cast microstructure of grey cast iron

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