Automatic classification of lamellar graphite in 
grey cast ıron 
Katja Schladitz, Wolfgang Gerber*, Konrad Sandau™ 
Institut fiir Techno- und Wirtschaftsmathematik Kaiserslautern 
* Mannesmann-Rexroth AG Lohr, ** Fachhochschule Darmstadt 
Abstract 
The arrangement of lamellar graphite in grey cast iron is assessed according to the common 
standard EN ISO 945:1994. Up to now the assessment is done manually with the help of stan- 
dard series images. A manual classification can use complex information from metallographic 
images sensitively and, given the needed care, lead to a reliable determination of the content 
enschaien Wi of A-, B-, C-, D-, and E-graphite. However, usually the results of the classification are highly 
dds durch dependent on the person. 
I) It is natural to use image analytic methods in order to make the characterization of grey 
a cast iron more objective and to relieve the laboratory staff of routine tasks. However, this faces 
od Hite difficulties due to the topology of the lamellae, the complexity of the classification criteria, and 
Ie the heterogeneity of grey cast iron structures. 
Here, an image analytic method based on morphological transformations is presented which 
¢ danken die solves these problems to a considerable extent. The classificator integrates expert knowledge 
and allows on this base the determination of the content of A-, D-, and E-graphite in hetero- 
geneous grey cast iron. 
1 The problem 
The content of A-, D-, and E-graphite in heterogeneous grey cast iron shall be determined in 
an objective and repeatable way. (B- and C-graphite were not considered in this study.) 
Graphite in grey cast iron is well suited for image analysis methods because of the good 
contrast between the steel matrix and the graphite precipitations of the carbon. The charac- 
terisation of spheroidal and vermicular graphite can be based on object isolation techniques 
and is thus relatively easy to do. By contrast, lamellar grey cast iron does not allow objective 
object isolation. Therefore so far lamellar graphite in grey cast iron is assessed manually with 
the help of standard series images. 
The common standard EN ISO 945:1994 prescribes classification of the graphite precipita- 
tions according to arrangement and size independently. In practice these two properties are 
highly correlated. Due to the growing conditions of the different types during precipitation 
it is very unlikely that D-graphite has large lamellae or that A-graphite has very small ones. 
These correlations are reflected by the practice of manual (subjective) classification. That is, 
the classification according to arrangement is always affected by the size of the lamellae. 
A careful manual classification uses the information from metallographic images thoroughly 
and results in a consistent classification of large samples. However, the results of different 
experts differ strongly, due to their background knowledge and the range of samples they are 
usually confronted with. See Figure 1 for the results of the manual classification of 120 images 
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