Issue 51

D. Fernandino et alii, Frattura ed Integrità Strutturale, 51 (2020) 477-485; DOI: 10.3221/IGF-ESIS.51.36 484 C ONCLUSIONS n analysis of the microstructural damage mechanisms induced by tensile loading on intercritically austempered ductile iron (IADI) has been presented. The main findings are: - At the beginning of the deformation, the crack initiation is preferentially located at matrix-nodule interface. Then, as strain increases, the crack initiation is also observed at ferritic grain boundaries and at the ausferrite-ferrite interface. - During the damage evolution, a competition between the plastic deformation on internodular zones and crack propagation along ferritic grain boundaries and ausferritic phase takes place. - A mix of ductile and quasi-cleavage fracture surfaces is observed under the experimental procedure carried out. These characteristics of the fracture surfaces are consistent with those resulting from quasi-static loading conditions on ferritic SGI and ADI, respectively. - The final fracture is produced by crack propagation across the internodular ligaments and along the ferritic grain boundaries and ausferrite, that later coalesce into a single dominant crack leading to the material failure. - Further investigations considering different proportions of ausferrite-ferrite and the characterization of the crystallographic direction of the ausferrite phase respect to the crack propagation should be undertaken, in order to generalize the validity of these results. A CKNOWLEDGEMENTS his research has been supported by grants awarded by CONICET-CUIA (Bilateral Cooperation Program-2017), ANPYCT (PICT 2016-3838), the National University of Mar del Plata (ING 458/16). R EFERENCES [1] Ductile Iron Society. Ductile Iron Data for Design Engineers. Rio Tinto Iron & Titanium, Inc.1998. [2] Aranzabal, J., Serramoglia, G. and Rousiere, D. (2002). Development of a new mixed (ferritic–ausferritic) ductile iron for automotive suspension parts, Int. J. Cast. Metal. Res. 16 (1), pp. 185-190. DOI: 10.1080/13640461.2003.11819580. [3] Basso, A., Martínez, R.A. and Sikora, J.A. (2006). Development of dual phase ADI. Proceedings of the Eighth International Symposium on Science and Processing of Cast Iron, Beijing, China, 16-19 October. [4] Aristizabal, R., Hayrynen, K., Foley, R., Griffin, J. and Monroe, C. (2014). Austemperability of Intercritically Austempered Ductile Iron (IADI). AFS Transactions, American Foundry Society, Schaumburg, IL USA. pp. 279-286. [5] Fernandino, D.O., Massone, J.M. and Boeri, R.E. (2013). Characterization of the austemperability of partially austenized ductile iron, J. Mater. Process. Tech., 213, pp. 1801-1809. DOI: 10.1016/j.jmatprotec.2013.05.002. [6] Panneerselvam, S., Putatunda, K., Gundlach, R. and Boileau, J. (2017). Influence of intercritical austempering on the microstructure and mechanical properties of austempered ductile cast iron (ADI), Mat. Sci. Eng. A-Struct., 694, pp. 72-80. DOI: 10.1016/j.msea.2017.03.096. [7] Chen, J.K., Chen, B.T. and Tsai, J.S. (2016). Microstructural evolutions and properties of partially austenitizing and austempered ductile irons, Steel Res. Int., 87 (2), pp. 191-198. DOI: 10.1002/srin.201400603. [8] Basso, A., Sikora, J. and Martínez, R. (2013). Analysis of mechanical properties and its associated fracture surfaces in dual-phase austempered ductile iron, Fatigue Fract. Eng. Mater. Struct., 36 (7), pp. 650-659. DOI: https://doi.org/10.1111/ffe.12032 [9] Kilicli, V. and Erdogan, M. (2010). The nature of the tensile fracture in austempered ductile iron with dual matrix microstructure, J. Mater. Eng. Perform., 19, pp. 142-149. DOI: 10.1007/s11665-009-9386-x. [10] Iacoviello, F., Di Cocco V. and Cavallini, M. (2016). Fatigue crack propagation and overload damaging micromechanisms in a ferritic–pearlitic ductile cast iron, Fatigue Fract. Eng. Mater. Struct., 39(8), pp. 999-1011. DOI: 10.1111/ffe.12443. [11] Iacoviello, F., Di Cocco, V., Rossi, A. and Cavallini, M. (2013). Pearlitic ductile cast iron: damaging micromechanisms at crack tip, Fract. Struct. Integr., 7(25), pp. 102-108. DOI: 10.3221/IGF-ESIS.25.15. A T