Effect of Two-cycle Heat Treatment on Mechanical Properties of Ductile Iron B. Abdullah 1, a , M. F. Idham 1,b , A. Jaffar 1 , A. F. Zubair 1,c , M. Mazlan 1 1 Faculty of Mechanical Engineering, Universiti Teknologi MARA (UiTM), Malaysia a bulanabdullah@gmail.com, b mohdfaizulidham@gmail.com, c ahmadfaiz@ppinang.uitm.edu.my, Keywords: Ductile Iron, Heat Treatment and Mechanical Properties Abstract. The aim of this study is to investigate the mechanical properties of ductile iron after treatment with two-cycle heat treatment process which modified from austempering. The modified eat treatment have two stages holding temperature. Ductile iron was austenitized at 900 ˚C for an hour and followed by transferring the sample to others furnace having temperatures of i) 250 ˚C; ii) 300 ˚C; iii) 350 ˚C without quenching for 1.5 hours. Tensile (ASTM E8M), impact (ASTM-E23-1990) and Rockwell hardness tests were carried out to explore the mechanical properties of the ductile iron. It was found that the sample which heat treated using two-cycle heat treatment process at temperature of 250 ˚C contributed to the better absorbing impact energy properties and hardness properties. Meanwhile, sample that heat treated at 350 ˚C has higher tensile strength. Introduction Heat treatment is one of preferable and important process involved in fabricating metal like cast iron and steels for all engineering components such as crankshaft, gears and cylinder heads for automotive industry [1]. Heat treatment generally defines as heating and cooling processes in cycles applied to metal in solid state condition for specific purpose of altering the properties structurally and physically. The process is most preferable tool nowadays since it can improve mechanical and physical without changing the product shape as well as addition of alloying element [2-4]. Consequences of heat treatment process on ductile iron, new properties of ductile iron such austempered ductile iron, ADI were produced [5]. In practice, desired mechanical properties of ductile iron could be achieved by varying the relative proportions of microstructure constituent, since most engineering properties of metals are related to their structure [4, 6-7]. Realizing the heat treatment variables are important in tailoring microstructure constituent in fact having correlation with mechanical properties, a number of past researchers therefore conducted studies about effect of heat treatment variables. Kiani-Rashid [8] studied about the influence of austenitizing condition during austempering process to mechanical properties of ductile iron. In addition, the approach of heat treatment implemented to the ductile iron such as austempering [5], two-step austempering [3, 9], tempering [4] and boro-tempering [9] likewise influenced the structural behavior and mechanical properties. Since heat treatment approach gives significant effect to the mechanical properties of ductile iron, thus, herein study was carried out by introducing modified heat treatment process which was innovated from austempering process. The modified heat treatment process in practice was carried out commonly as conventional austempering process but the interrupted cooling method was changed to change furnace approach instead of soaks in salt solution. Despite both cooling mediums are seemingly different but the concept of heat transfer was still unchanged, where convection concept of heat transfer was employed in both approaches.