TECHNICAL PAPER The Effect of Slag Optical Basicity on Alloying Element Losses of Steel by Electroslag Remelting (ESR) Burak Birol 1 • Muhlis Nezihi Saridede 1 Received: 8 January 2015 / Accepted: 1 May 2015 / Published online: 30 May 2015 Ó The Indian Institute of Metals - IIM 2015 Abstract Slag properties affect the efficiency of Electro Slag Remelting (ESR) process by removing the quality impairing elements (S, P, etc.), while avoiding valuable alloying element losses. Therefore, a relation between element losses and optical basicity of slags, which may be assumed to be an enhanced approach to basicity concept, would play a crucial role on predicting and selecting the optimum slag composition for ESR process. The primary contribution of this paper is to investigate the effect of optical basicity of various slags on the composition change of high sulphur containing AISI 12L14 (DIN11SMnPb37) free-cutting and AISI M2 (DIN HS6-5-2C) high speed steels. For this purpose steel bars were remelted under different slag compositions at constant melting conditions. According to the chemical analysis of the products, it was observed that the element losses increase related to in- creasing optical basicity of slags. On the other hand, these alloying element changes show variety on steel types. High speed steel shows a relatively low alloying element chan- ges due to its high carbide content, while higher losses were discovered in free cutting steels. Keywords ESR  Slag  Element losses  Optical basicity  AISI 12L14  AISI M2 1 Introduction Increasing mandatory requirements (lower S con- tents, ^30 ppm, lower C contents, \ 0.01 % C, etc.) ex- pected from steels have stimulated a lot of research activity on various refining processes. These refining processes generally depend on removal of impairing elements (S, P, etc.) by slag-metal reactions in liquid phase. In Electro- Slag Remelting (ESR) process, high CaF 2 containing slags are used due to their high electrical conductivity and thermochemical properties. These slags should provide the ability of adequate inclusion and removal of impairing element like sulphur and phosphorus which lower the strength of steel drastically. Therefore, minimizing these inclusions becomes crucial to produce a high quality steel. Sulphur removal from steel takes place by slag-metal and gas-slag reactions as given in Eqs. 1 and 2, respectively. Also the reaction coefficients (K 1 and K 2 ) of these reac- tions are given in Eqs. 3 and 4 [1–3]; S ½ Metal þ O 2 À Á Slag ¼ S 2 À Á Slag þ O ½  Metal ð1Þ 3 2 O 2ðgÞ þ S 2 À Á Slag ¼ O 2 À Á Slag þ SO 2ðgÞ ð2Þ K 1 ¼ a S ½ Metal  a O 2 ð Þ Slag a O ½  Metal  a S 2 ð Þ Slag ) a S 2 ð Þ Slag a S ½ Metal ¼ K 1  a O 2 ð Þ Slag a O ½  Metal ð3Þ K 2 ¼ a O 2 ð Þ Slag  P SO 2 a S 2 ð Þ Slag  P 3=2 O 2 ) P SO 2 a S 2 ð Þ Slag ¼ K 2  P 3=2 O 2 a O 2 ð Þ Slag ð4Þ According to Eq. 3, sulphur transfer from metal to slag (Eq. 1), depends on the O 2- ion activities in metal and slag. In other words, if the oxygen (O 2- ) is lower in metal and higher in slag, desulphurization increases. On the other hand, sulphur transfer from slag to gas phase can be improved by increasing oxygen partial pressure in the & Burak Birol burak.birol@gmail.com Muhlis Nezihi Saridede msaridede@gmail.com 1 Department of Metallurgical and Materials Engineering, Faculty of Chemical and Metallurgy, Yıldız Technical University, Davutpasa, Esenler, 34210 Istanbul, Turkey 123 Trans Indian Inst Met (2016) 69(3):751–757 DOI 10.1007/s12666-015-0549-1