http://doi.org/10.24867/JPE-2017-02-001 1 JPE (2017) Vol.20 (2) Original Scientific Paper Alabi, A.G.F., Aweda, J.O, Aluko, F.I. INFLUENCE OF FERROSILICON MANGANESE ON THE SULPHUR CONTENT AND MICROSTRUCTURE IN THE PRODUCTION OF AUSTEMPERED DUCTILE IRON (ADI) Received: 22 September 2017 / Accepted: 12 November 2017 Abstract: This study considers the effect of ferrosilicon manganese addition to austempered ductile iron, (ADI) in order to reduce its sulphur level for improved engineering applications of the material. The cast samples were austenitised in a mixture of potassium chloride, sodium chloride and barium chloride solutions and austempered in sodium nitrate and potassium nitrate solutions. Ferrosilicon manganese was added to ADI in various amounts ranging from between 47 to 326 g. The study revealed that the sulphur level retained in ADI decreased from 0.088 wt % for as-cast to 0.027 wt % when 93 g of ferrosilicon manganese was added. Below this amount of ferrosilicon manganese addition, there was no significant reduction in the sulphur level recorded in ADI. The microstructure of the metal revealed bigger graphite nodules scattered in ferrite solutions for the situation when the sulphur level was 0.027 wt. %. From the study, it was discovered that addition of small amount of ferrosilicon manganese was required to produce ADI of low level sulphur content to make the metal more acceptable for other engineering applications. Key words: Ductile iron, sulphur, austempering, nodularizer, ferrosilicon Uticaj ferosilikonskog mangana na sadržaj sumpora i mikrostrukturu u proizvodnji izotermalno poboljšanog gvožđa (ADI). Ova studija razmatra uticaj dodatka ferozilicijevog mangana na izotermalno poboljšano gvožđe (ADI) kako bi smanjio nivo sumpora u cilju poboljšanja inženjerske primene materijala. Uzorci odlivaka su austenitizovani u mešavini kalijum hlorida, natrijum hlorida i rastvora barijum hlorida i austemperovani u rastvorima natrijum nitrata i kalijum nitrata. Ferosilicijum mangan je dodat u ADI u različitim količinama u rasponu od 47 do 326 g. Studija je utvrdila da je nivo sumpora zadržan u ADI je smanjen sa 0,088 tež.% za livenje na 0,027 tež.% kada je dodato 93 g ferosilikon mangana. Ispod ove količine ferosilicijevog manganskog dodatka, nije bilo značajnog smanjenja nivoa sumpora zabeleženog u ADI-u. Mikrostruktura metala otkrila je veće grafitne nodule raspršene u feritnim rastvorima za situaciju kada je nivo sumpora bio 0,027 tež. %. Studija je utvrdila da je dodatak male količine ferosilikovanog mangana potreban za proizvodnju ADI sadržaja sumpora na niskom nivou kako bi metal bio prihvatljiviji za druge inženjerske aplikacije. Ključne reči: Nodularno gvožđe, sumpor, izotermalno poboljšanje, nodularizator, ferosilikon 1. INTRODUCTION Discovering new materials with improved mechanical properties meeting the required applications has engaged the attention of researchers worldwide. In recent years, Austempered Ductile Iron (ADI), obtained from ductile iron, has attracted considerable applications because of its good mechanical properties. Such properties include resistance to fatigue [1-4], good wear resistance [5, 6], high strength with good ductility [7-9] and good rolling contact resistance [10]. The density of ADI is lower than steel [8, 12] which makes it more applicable in the areas of production of engine blocks and other engineering components. ADI is used in the production of swivel pins, rail brakes and pressure pipes in the oil industry [13-16]. Thus, ADI has been found to have higher specific strength than steel [6, 17- 21]. Austempered ductile iron products are used in the automobile and textile industries as crank shafts, cam shafts, gearwheels and thin wall castings reinforced parts [10, 16, 18, 26]. The production of ADI is cheaper when compared with forged steel by 20 % [27, 28]. Compared to steel, ADI exhibits improved properties in terms of machinability, tool life and machining speeds, surface finish, improved safeguard against failure (due to the lubricating effect provided by graphite) [17, 22], good ballistic properties [26], good resistance to bending fatigue [1], good damping capacity (better noise attenuation), amenability to heat treatment [6, 21, 24, 25], good corrosion resistance [24]. Therefore, ADI is considered as an economical substitute for wrought or forged steel in several structural applications [2, 3]. The metal loses less of its toughness than steel at sub-zero temperature. Austempered ductile iron usually work-hardens when stressed and has good vibration damping capability and heat transfer than other ferrous and non-ferrous alloys [18, 22, 26]. Liu [26] in his work suggested that an improved structure of ADI could be obtained by controlling the heat treatment process of nodular cast iron. The microstructure and mechanical properties of ADI can be influenced by the isothermal heat treatment and the temperature of austenite transformed [16]. The temperature of isothermal transformation is in the range of 250 and 450 0 C [18]. When higher transformation