Characterization of graphite form in nodular graphite cast iron

The subjective character inherent to the method of comparison of the graphite morphology against standard charts has been often pointed out, because the accuracy of this technique depends on the inspector's experience. An objective characterization of the graphite morphology can be performed by image analysis. However, it is important to develop suitable image analysis procedures in order to obtain more comparable results. For example, the nodule number and the average form factor measured in a sample depend on the minimum particle size considered in the analyses. The size of the nodules normally shows a bimodal distribution. The number of small nodules is frequently more important that the number of large ones. Also, the small particles have a form closer to the spherical shape. This work deals with the effect of the smallest nodules on the average form factor obtained by image analysis. A new procedure is proposed in order to overcome such an effect.