Impact Properties of Copper-Alloyed and Nickel-Copper Alloyed ADI Uma Batra, Subrata Ray, and S.R. Prabhakar (Submitted November 24, 2005; in revised form July 21, 2006) The inﬂuence of austenitization and austempering parameters on the impact properties of copper-alloyed and nickel-copper-alloyed austempered ductile irons (ADIs) has been studied. The austenitization tem- perature of 850 and 900 °C have been used in the present study for which austempering time periods of 120 and 60 min were optimized in an earlier work. The austempering process was carried out for 60 min for three austempering temperatures of 270, 330, and 380 °C to study the effect of austempering temperature. The inﬂuence of the austempering time on impact properties has been studied for austempering temper- ature of 330 °C for time periods of 30-150 min. The variation in impact strength with the austenitization and austempering parameters has been correlated to the morphology, size and amount of austenite and bainitic ferrite in the austempered structure. The fracture surface of ADI failed under impact has been studied using SEM. Keywords austenitization, bainitic transformation, fracture, impact energy 1. Introduction Austempered ductile iron (ADI) is a further development of ductile iron achieved by austempering heat treatment of the later. By varying the temperature and time of austempering, the strength of ADI may be varied from about 950 MPa at 10-15% elongation to 1760 MPa at 1-3% elongation. In recent years, ADI has emerged as a strong candidate for applications in automotive and other industrial components because of its relatively low cost and an excellent combination of properties like high strength, excellent fatigue, and wear resistance (Ref 1-4). In ADI, the properties attained are dependent on the austenitization and austempering parameters, initial matrix structure, and chemical composition. Investigations related to the effect of austenitization temperature, austempering temper- ature, and time on austempered microstructure of the irons being studied have been reported earlier (Ref 5-7). Earlier work (Ref 8) has also shown that the austenitization temperature and time have a signiﬁcant inﬂuence on the microstructure and impact properties of the alloy with an initially pearlite matrix structure. Work by Darwish (Ref 9) has investigated the effect of austempering parameter on the toughness of low-Mn ADI. Aranzbal (Ref 4) has reported that the impact energy of ADI increases with the increase in the amount of retained austenite in the austempered structure. The same fact is supported by other studies also which report the coincidence of the contour maps of volume fraction of retained austenite in austempered microstructure of ADI, and retained austenite in the austem- pered structure of ADI and the impact energy as a function of austempering parameters (Ref 10, 11). The present work deals with the study of the inﬂuence of austempering parameters on the impact properties of copper- alloyed and nickel-copper-alloyed ADI, and establishes the relationship of the impact strength with the austenitization and austempering parameters. 2. Experimental Procedure Two ductile irons with chemical compositions given in Table 1 were prepared in a commercial foundry using an induction melting furnace and cast in the shape of 1 in. Y blocks. Unnotched Charpy specimens of size (55 · 10 · 10) mm as per ASTM speciﬁcations A327-80 were machined from the leg part of Y block castings of both the ductile irons (Ref 12). The samples were austenitized for speciﬁed temperature and time (Ref 6) and transferred rapidly to a salt bath held at a pre-selected temperature for austemper- ing for different time periods before quenching in water. The various heat treatment conditions used in the present work are given in Table 2. The average volume fraction of austenite, X c and the size of bainitic ferrite needle in the austempered structure were determined using x-ray diffraction patterns taken with CuK a radiation (k = 1.54A ˚ ) (Ref 13). The fracture surface of copper-alloyed ADI failed during impact testing has been observed using Scanning Electron Microscope. 3. Results and Discussion The cast microstructures of copper-alloyed and nickel- copper-alloyed ductile irons under study are shown in Fig. 1. Uma Batra, Department of Metallurgical Engineering, Punjab Engineering College, Chandigarh, India160012; Subrata Ray, Department of Metallurgical and Materials Engineering, IIT-Roorkee, Roorkee, UP, India; S.R. Prabhakar, Indo Global College of Engineering and Technology, Chandigarh, India. Contact e-mail: umabatra2@yahoo.com. JMEPEG (2007) 16:485–489 ÓASM International DOI: 10.1007/s11665-007-9069-4 1059-9495/$19.00 Journal of Materials Engineering and Performance Volume 16(4) August 2007—485