Issue 61

A.D. Basso et alii, Frattura ed Integrità Strutturale, 61 (2022) 519-529; DOI: 10.3221/IGF-ESIS.61.35

Influence of free ferrite on the mechanical properties of high strength intercritical Austempered Ductile Iron

A. D. Basso, M. Caldera, N. E. Tenaglia, D. O. Fernandino, R. E. Boeri INTEMA, Universidad Nacional de Mar del Plata-CONICET, Av. Colón 10850, Mar del Plata, B7606BVZ, Argentina

abasso@fi.mdp.edu.ar, https://orcid.org/0000-0002-6167-4426 mcaldera@fi.mdp.edu.ar, https://orcid.org/0000-0002-8677-540X dfernandino@fi.mdp.edu.ar, https://orcid.org/0000-0003-4647-2663 ntenaglia@fi.mdp.edu.ar, http://orcid.org/0000-0001-6372-88816372-8881 boeri@fi.mdp.edu.ar, http://orcid.org/0000-0001-7083-579X579X A BSTRACT . The first stage of this study investigates the precipitation of free ferrite from the austenite on fully austenitized ductile iron. Several sets of samples of low alloy ductile iron are fully austenitized and then cooled down to different temperatures and different times within the intercritical austenite ferrite-graphite phase field. Based on these results, heat treatment cycles aimed at obtaining microstructures composed of free ferrite and ausferrite are carried out. Tensile, impact and toughness tests are performed to characterize the mechanical properties. The results show that, related to the high strength austempered ductile iron grades, the best combinations of properties were obtained from the mixed structures composed of 5% free ferrite and 95% ausferrite, resulting from the austempering at 280°C. These amounts of free ferrite allow obtaining an increase of the elongation (about 50%) and impact toughness (about 10%) while the tensile strength and fracture toughness decrease by about 1.5 and 15% respectively. K EYWORDS . Ductile Iron; Free ferrite; Mechanical properties; Heat treatments.

Citation: Basso, A. D., Caldera, M., Tenaglia, N. E., Fernandino, D. O., Boeri, R. E., Influence of Free Ferrite on the Mechanical Properties of High Strength Intercritical Austempered Ductile Iron, Frattura ed Integrità Strutturale, 61 (2022) 519-529.

Received: 28.05.2022 Accepted: 09.06.2022 Online first: 19.06.2022 Published: 01.07.2022

Copyright: © 2022 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

I NTRODUCTION

he continuous need for the development of ductile irons (DI) of improved mechanical properties has led the researchers to investigate the usefulness of the development of complex microstructures. The applicability of metallic matrices formed by free ferrite and ausferrite obtained through the austempering of partially austenitized ductile irons, a material usually called ‘IADI’ (Intercritically Austempered Ductile Iron), has received some attention [1-13]. Specific thermal cycles have been developed in order to obtain IADI microstructures. The first paper concerning this subject matter was written by Aranzabal et al. [1]. The authors obtained different variants of IADI by modifying the silicon level of T

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