Abstract
In this paper, we aim at characterizing three different cast iron alloys and their microstructural features, namely lamellar, compacted and nodular graphite iron. The characterization of microscopic features is essential for the development of methods to optimize the behavior of cast iron alloys; e.g. maximize thermal dissipation and/or maximize ductility while maintaining strength. The variation of these properties is commonly analyzed by metallography on two-dimensional representations of the alloy. However, more precise estimates of the morphologies and material characteristics is obtained by three-dimensional reconstruction of microstructures. The use of X-ray microtomography provides an excellent tool to generate high resolution three-dimensional microstructure images. The characteristics of the graphite constituent in the microstructure, including the size, shape and connectivity, were analyzed for the different cast iron alloys. It was observed that the lamellar and compacted graphite iron alloys have relatively large connected graphite morphologies, as opposed to ductile iron where the graphite is present as nodules. The results of the characterization for the different alloys were ultimately used to generate finite element models.
Highlights
IntroductionCast iron was only known as white or gray. The invention of the microscope in 1860 opened up for an improved understanding of the microstructure of cast iron
In the beginning, cast iron was only known as white or gray
We aim to study the 3D microstructures of Spherical Graphite Iron (SGI), Compacted Graphite Iron (CGI) and Lamellar Graphite Iron (LGI) with the use of μ−CT combined with images analysis, generating Finite Element Models of the microstructures
Summary
Cast iron was only known as white or gray. The invention of the microscope in 1860 opened up for an improved understanding of the microstructure of cast iron. Known as nodular iron, was independently invented by Adey, Millis and Morrogh just before 1940. During the 1970s, compacted graphite iron was developed and the major effect of the alloying elements magnesium and cerium was understood [1]. Later studies clarified the influence of oxygen, where decreasing oxygen content in the melt caused transformation from flake graphite to compacted and eventually to spheroidal shape graphite [2]. In most cases the graphite is part of a eutectic reaction following the primary growth of austenite, and for example for ductile iron, the eutectic reaction is highly divorced. Direct austempering is necessary to reveal the primary austenite, but this will affect solid-state transformation effect on the precipitation of graphite [3][4]
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