Fatigue design of heavy section ductile irons: Influence of chunky graphite E. Foglio a , D. Lusuardi b , A. Pola a , G.M. La Vecchia a , M. Gelfi a, ⁎ a Department of Mechanical and Industrial Engineering, University of Brescia, via Branze 38, 25123 Brescia, Italy b Fonderie Ariotti S.p.A., via Enrico Fermi 5, 25030 Adro, BS, Italy HIGHLIGHTS • An average content of 33% of chunky graphite reduced the fatigue limit of ductile iron of about 12%. • The reduction of fatigue strength was calculated considering the different lev- el of microporosities in the two sets. • No relationship was found between chunky graphite and the fatigue frac- ture initiation. • Chunky graphite was a preferential path for the propagation of the fatigue crack. • The decrease of fatigue limit due to chunky graphite is equivalent to the re- duction in tensile strength. GRAPHICAL ABSTRACT abstract article info Article history: Received 1 May 2016 Received in revised form 31 August 2016 Accepted 1 September 2016 Available online 02 September 2016 The influence of chunky graphite on mechanical properties, especially on fatigue resistance, of an EN-GJS-400 fer- ritic ductile iron, was investigated by tensile and rotating-bending tests. The samples for the experiments were machined from two heavy section castings. The first one was cast with the addition of a Ce-containing inoculant to promote chunky formation and the second one by using a standard Ce-free inoculant. The presence of chunky graphite in the samples decreased tensile strength and elongation at break, while no significant effect on the hardness and yield strength was measured. Also fatigue strength was negatively affected, with a decrease of fa- tigue limit of about 12%. This value was calculated also taking into account the different amount of microporosity in the two sets of samples and its effect on the fatigue strength by using the Murakami approach. Fracture analysis showed that chunky graphite has a limited influence on fatigue crack nucleation if compared to micro-shrinkages, while it behaves as a preferential path for crack propagation. A simple way to consider the presence of chunky graphite in the fatigue design of heavy section ductile irons is proposed on the basis of the present results and taking into consideration the published data too. © 2016 Elsevier Ltd. All rights reserved. Keywords: Ductile cast iron Chunky graphite Fatigue limit Microporosity Analysis of statistics of extremes Fracture analysis 1. Introduction The effect that micro-scale defects have on the mechanical perfor- mance of metallic materials is one of the main topics in the field of en- gineering design [1–5]. In the same way, the mechanical properties of iron castings are largely influenced by microstructural defects, such as Materials and Design 111 (2016) 353–361 ⁎ Corresponding author. E-mail address: marcello.gelfi@unibs.it (M. Gelfi). http://dx.doi.org/10.1016/j.matdes.2016.09.002 0264-1275/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes