From Individual Graphite Assignment to an Improved Digital Image Analysis of Ductile Iron
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right 2020 The Author(s) https://doi.org/10.1007/s40962-020-00416-3
Abstract Since graphite classification by visual analysis exhibits large variations, a more integrative concept of graphite shape classification is required to evaluate the correlations of process, microstructure and properties, and to fulfill customers’ requirements. The automatic digital image analysis is partly based on visual analysis, but it is not thoroughly defined for graphite shape classification. For example, nodules and thereby nodularity are only defined by the shape parameter roundness, although several studies suggest more sophisticated approaches. Within the first of three successive round robin tests, visual assignment for a variety of graphite particles was performed to obtain a universal digital data set of classified graphite particles. For this, the classification approach from standard EN ISO 945-1 was used and extended with degenerated graphite. The assigned particles were evaluated concerning different
shape parameters showing that roundness and the assigned minimum limit value of 0.6 are not sufficient to distinguish nodules from less ideal graphite particle shapes. Furthermore, the current classification approach does not represent the full spectrum of graphite morphologies and needs to be extended. The development of a universal hierarchical classification method for nodules and other graphite shapes has been initiated, and the results will contribute to an improved image analysis standard for ductile iron, particularly ISO 945-4.
Introduction
that the evaluation of geometrically complex structures, such as various types of graphite in cast iron, represents a challenge.
Increasing demands on cast products are usually accompanied by increasing demands on the material properties. The quantitative description of the microstructure achieved in the product is of high importance, for example the extent of defects or the size and morphology of individual phases. In the course of the increasing digitization of the microstructure description, however, it becomes apparent This paper is an invited submission to IJMC selected from presentations at the 6th Keith Millis on Ductile Iron held October 23–26, 2018, at the Sonesta Resort, Hilton Head Island, SC. It is published in the IJMC by permission of the DIS (Ductile Iron Society).
International Journal of Metalcasting
Keywords: graphite morphology, graphite classification, nodularity, image analysis, ductile iron, spheroidal graphite cast iron
The analysis and description of the graphite morphology in ductile cast iron specifically include graphite content, nodule count, particles sizes, form classification and nodularity. The latter describes the fraction of those particles, which are in the appropriate and acceptable nodule form.1 Nodularity values of at least 80% or 80–85% are considered acceptable,1,2 which is why these values play a crucial role in the quality control.
Since the visual analysis of graphite phases in cast iron exhibits major variations3,4 due to its subj
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