ORIGINAL ARTICLE Effect of Copper and Heat Treatment on Microstructure of Austempered Ductile Iron Niks ˇa C ˇ atipovic ´ 1 • Draz ˇen Z ˇ ivkovic ´ 1 • Zvonimir Dadic ´ 1 • Petar Ljumovic ´ 1 Received: 26 July 2020 / Accepted: 23 February 2021 / Published online: 6 April 2021 Ó The Indian Institute of Metals - IIM 2021 Abstract Austempering of ductile iron was described in this paper. All the influential parameters during production of ADI have been clarified. The literature data indicate that each heat treatment parameter has a certain influence on the final microstructure and, therefore, on the mechanical properties of ADI. Effect of alloying elements in ductile iron has been investigated. Based on the current knowledge and austempering heat treatment parameters, a plan of experiments was designed. In this paper, the influence of the most important heat treatment parameters and copper content on the final microstructure of ADI was determined. By varying the copper content, it is possible to influence the volume fraction of retained austenite in ADI. The results of the planned research could serve as a basis for the development of unique mathematical models that would include the influence of each individual parameter of heat treatment and copper content on the microstructure of ADI. The mathematical models thus developed would serve to predict the final mechanical properties depending on the input parameters of the heat treatment and the copper content. Keywords Austempered ductile iron Á Austempering parameters Á Copper content Á Microstructure Á Mathematical modeling 1 Introduction In recent years, there has been a great demand on the market for solid, durable and economically viable metal materials. Ductile iron is one such material and its pro- duction is increasing year by year. Much research has been done on this material, and the focus has been on improving its mechanical properties using proper heat treatment or alloying with appropriate alloying elements. The reason for the rapid growth of ductile iron production is its favorable physical, mechanical and technological properties such as corrosion resistance, high modulus of elasticity, good castability, favorable strength, surface hardening ability and relatively good workability. When a ductile iron is subjected to austempering, a completely new material is produced, known as Austempered Ductile Iron (ADI), which has significantly better properties than ductile iron, [1]. The ADI has a unique microstructure, the ausferrite, which is a mixture of needle ferrite and carbon-enriched retained austenite, [2, 3]. This new microstructure results in properties superior to many iron and aluminum alloys. The mechanical properties of an ADI depend on its auspherric microstructure. The austempered matrix provides a better ratio of tensile strength and ductility than is possible with any other type of tough cast. Due to different combinations of mechanical properties, because of the ausferrite struc- ture, ADI can be produced depending on the heat treatment parameters and the content of the alloying elements, [4]. Austempering heat treatment consists of austenitization of the ductile, quenching at the austempering temperature by immersion in an adequate refrigerant and cooling to room temperature, [5]. & Niks ˇa C ˇ atipovic ´ Niksa.Catipovic@fesb.hr 1 Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Split, Croatia 123 Trans Indian Inst Met (2021) 74(6):1455–1468 https://doi.org/10.1007/s12666-021-02225-6