Journal of Materials Processing Technology 210 (2010) 335–342 Contents lists available at ScienceDirect Journal of Materials Processing Technology journal homepage: www.elsevier.com/locate/jmatprotec Spatial distribution and spheroidicity characterization of graphite nodules based on morphological tools L.A. Morales-Hernández a,∗ , I.R. Terol-Villalobos b , A. Domínguez-González a , F. Manríquez-Guerrero b , G. Herrera-Ruiz a a Facultad de Ingeniería, Universidad Autónoma de Querétaro, San Juan del Río, Querétaro 76807, Mexico b Centro de Investigación y Desarrollo Tecnológico en Electroquímica S.C., Pedro Escobedo, Querétaro 76700, Mexico article info Article history: Received 26 February 2009 Received in revised form 21 July 2009 Accepted 24 September 2009 Keywords: Spheroidicity Compacity Graphite Conditional bisector Granulometry abstract 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. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The knowledge of the microstructure in metals is a critical factor in order to understand better the behavior of cast iron materials under different conditions. Indeed, microstructure char- acterization is a very important task before the use of a specific metal (Maropoulos et al., 2004). Graphite nodules are features in foundry engineering since they establish mechanical properties such as fracture toughness, impact toughness, yield and tensile strength as demonstrated (Gonzaga and Fernández, 2005). There are research works that have demonstrated that the relationship of the mechanical properties can be determinated by the size and shape of nodules. For instance, Karl-Fredrik and Vratko (2009) have studied the behavior of ductility according to the size and shape of casting defects in the microstructure. Xin et al. (2009) have shown the effects of nodules shape relating with the crack initiation and crack propagation rate. Nabil et al. (2009) have investigated how to get a 100% nodular and the relationship between hardness and tensile strength. ∗ Corresponding author. Tel.: +5 01 427 274 1244; fax: +5 01 427 274 1244. E-mail address: luis morah@yahoo.com (L.A. Morales-Hernández). On the other hand, recent researches have shown that the space between nodules and nodular distribution can modify the mechan- ical properties. Jeong-Du and Jueng-Keun (2006) have related the distance between nodules and the fatigue failure. Dommarco et al. (2006) have shown that the behavior of thin wall castings depends on the number of nodules in the microstructure. Stokes et al. (2007) studied the initiation and growth of crack through the space between nodules. Sosa et al. (2009) proposed a relationship between the residual stresses with nodule count. David et al. (2004) showed that the uniform distribution improves thin wall nodu- lar cast. Borrajo et al. (2002) show the distribution of nodules in thin castings depending on the thickness and nodular distribution changes. In the studies of the aforementioned cases, they mention that nodular density is critical. They use standard methods to evaluate nodularity and nodular density. Nowadays, graphite measurement and the percentage of nodularity are qualitative measurements which are determined by comparing against a pattern of the structure. Each method has a chart pattern in order to do a comparison; for example, the AFS 5-J (2000) reference provides a precision of ±10%, whereas the stan- dard ASTM A 247 characterizes graphite particles by numbers and letters in metallographies allowing an estimation of their sizes and distribution. The standard ISO 9451-1 characterizes the particles of graphite into six types (see Fig. 1). For instance, this method cannot 0924-0136/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2009.09.020