TECHNICAL PAPER Indian Foundry Journal Indian Foundry Journal Indian Foundry Journal Indian Foundry Journal Indian Foundry Journal 23 Vol 59  No. 10  October 2013 Effect of Austenitising Temperature on Microstructure and Wear Properties of Low Carbon Equivalent Austempered Ductile Iron Priyanshu Bajaj 1* , Vinayak Poddar 1 , Anirudh Kshemendranath 1 , Ajay Likhite 2 , S.U. Pathak 3 and D.R. Peshwe 3 B. Tech Final Year Student 1 , Associate Professor 2 , Professor 3 , Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology (VNIT), Nagpur, India *Corresponding Author: E-mail – priyanshubajaj.8@gmail.com  Cell - 9503309518 Effect of austenitising temperature on microstructure and wear properties of low carbon equivalent austempered ductile iron (ADI) has been studied. Three Samples were austenitised at 850°C, 900°C, and 950°C respectively for one hour; followed by austempering at 250°C for two hours. Hardness of all the samples was taken. Hardness values were compared with that of conventional ADI and as-cast sample. Microstructural study was done using 2% Nital, 2% Picral, Alkaline Sodium Picrate (ASP) and 10% Sodium Metabisulfite (SMB) as etchants. Coarser needles and blockier austenite was observed at higher austenitising temperature. Carbide contents decreased as the austenitising temperature increased and no carbides were observed in sample austenitised at 950°C. A mix of martensite, acicular ferrite and austenite was observed in the microstructure. The martensite was then tempered at two different temperatures. Pin-on-disc wear test (ASTM G 132- 96) was carried out. Wear properties of low carbon equivalent ADI were found to be much better than conventional ADI; sample austenitised at 950°C gave significantly better wear resistance. Keywords Keywords Keywords Keywords Keywords : : : Austempered Ductile Iron (ADI), Carbon Equivalent (CE), Wear, Austenitising, Microstructure. INTRODUCTION Austempered Ductile Iron (ADI) is a very unique material which possesses a combination of strength and toughness; also it offers a very good wear resistance. It is lighter than steel and its strength-to- weight ratio is higher than aluminium. The material is also cheap, easy to form (thorough casting) and has good machinability. A wide range of mechanical properties can be obtained by varying the heat treatment parameters. Although, a lot of work has been done on this material to study the effect of various processing parameters such as austenitising time and temperature [1-5] and austempering time and temperature [1, 4- 11] on the microstructure and properties, very little information is available about the austempering of high modulus cast iron, i.e. the low carbon equivalent ductile iron. The work presented below is an attempt to throw light on that aspect. BACKGROUND Austenitising is done to produce an austenitic matrix with desired carbon content. The austenitising temperature depends on the desired carbon content in the austenite and the alloy composition [1] . Gong Wenbang developed a formula for calculating carbon content of austenite for a given alloy at a specified austenitising temperature [12] . C a = C S + (T a -T S1 )/η Where, C a is carbon content of austenite, T a is austenitising temperature, C S is carbon content of austenite at upper eutectoid, T S1 is upper eutectoid temperature, η is influencing coefficient of the carbon on the temperature for x% Si [12] . C S = 0.68 – 0.015 x (%) T S1 = 738 + 40 x (°C) η= (416-37.5 x ) / (1.4-0.202 x ) (°C/%) The formula clearly indicates that C a increases as Si content decreases or as the austenitising temperature is increased. As the austenitising time is increased, carbon content increases linearly with it until it becomes constant [5] . On increasing the austenitising temperature, the carbon concentration of the austenite phase increases as per the iron- carbon-silicon phase diagram [1] . This increase in carbon content leads to a depression of M s t temperature [4] . Researchers have also found that with decrease in austenitising temperature rate of ausferrite reaction increases [2] , ferrite needles become finer and more uniformly distributed [3, 5] and volume fraction of retained austenite phase