Application of quantitave image analysis of graphite structures for the fatigue strength estimation of cast iron materials

AbstractThe characteristic formation of graphite microstructures defines the physical and mechanical properties of cast irons. The graphite morphology of cast iron structures can be classified according to their shape, arrangement and size using as reference the structure micrographs specified in the standards ASTM A 247-67 and DIN EN ISO 945. These specific values do not provide any mathematical correlation between microstructure and mechanical properties. The application of quantitative image analysis in microstructure investigations allows a statistically reproducible evaluation method. Although cast irons were quite often focus of research works in this sector, the graphite morphology classification has been mainly handled devoid of any quantitative correlation to material properties.In this article an interrelationship between the fatigue strength of cast iron materials and a quantitative characteristic of the graphite microstructure was established. Thereby it is necessary to identify the largest graphite precipitates, which can be statistically considered as potential crack initiation sites. In this context three different cast iron materials were investigated: ENGJL-270, EN-GJV-450 and EN-GJS-700