Spatial distribution and spheroidicity characterization of graphite nodules based on morphological tools

In this paper, the concept of compacity curve was introduced to characterize the spatial distribution of nodules which is a stronger concept than the nodular density itself. This notion was defined according to the concept traditionally known as granulometry by openings. The compacity, which is represented by polynomial curve, is obtained by the granulometric function which refers to the mean of the spatial distribution of curves. Furthermore, the nodular spheroidicity was measured in a simple way by using the conditional bisector transformation. Hence, if the conditional bisector of a nodule is composed of only one connected component, then the nodular shape is similar to a circle. Also, it was noted that the proposed methodology can distinguish between overlapping or touching nodules. The spheroidal graphite together with compacity curves allows a better description of the ductile cast iron quality by image analysis. Both criteria have been computed using the basic morphological tools as the opening, erosion and dilation. The metallographic images were obtained from the mechanical parts employed in the automotive industry, and the results were compared with other reported methods. From the compacity curve it is possible to establish that the quality of the ductile iron cast is better when it trend to have a similar shape to the normal curve.