This UNITECR 2022 paper is an open access article under the terms of the Creative Commons Attribution License, CC-BY 4.0, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited. DEVELOPMENT OF Al2O3 – MgAl2O4 SPINEL CASTABLE FOR VARIOUS APPLICATIONS Rajashree Swain*, Dr. Arup Kumar Samanta, Rekha Kumari, Gopal Saha, P. B. Panda TRL Krosaki Refractories Limited, Belpahar-768218, Odisha (India) ABSTRACT To fulfill the needs from automobile industry, ultra-low carbon (ULC) and interstitial-free (IF) grades of steel are getting more importance. The stringent specification of steel can be fulfilled not only the special secondary metallurgical process but also the performance reliability of refractory lining in different equipment. The performance of refractory lining depends on operational safety, life, specific refractory cost along with its contribution for achieving the high demanding metallurgical targets where interaction of steel and refractory plays a vital role. Al2O3 – MgAl2O4 castable is a special grade of castable used in different areas as working lining like steel ladle as well as in different prefabricated refractory items like well block, seating block, porous plug, RH snorkel etc. The application areas are very stringent and therefore high temperature thermo-mechanical properties are very important along with slag corrosion resistance. Spinel is one of the base raw materials, but the type of spinels and its grain size distribution are important while designing this castable. In the present work, one special spinel is incorporated in the matrix which not only gives the excellent slag corrosion resistance but also have better thermal spalling resistance, volume stability and high temperature thermo-mechanical properties like HMOR and RUL. In presence of special material there is enough formation of CA6 which enhance the volume stability and other properties. This castable is used to make seating block and well block for steel ladles and the performance is enhanced significantly. INTRODUCTION The growing interest to use spinel containing castables either in different pre- fabricated (PCPF) items or as monolithic lining is related to improve the performance, reduce the application cost and time. Due to the high corrosion resistance to basic slag, either pre- formed or in situ spinel containing refractory castables are nowadays widely used in steel ladle linings. In 1990s, a second group of spinel castables was developed. Instead of pre-reacted spinel, these castables contain free magnesia in the matrix fines, which form spinel by reacting with alumina during use at high temperatures1-4. Spinel forming castables have shown advantages when compared to spinel containing ones in steel ladle side wall lining and have become a common material for this region in the past 20 years. For other applications like well block, seating block, purging plugs, spinel containing castables are advantageous and have become the standard one. Preformed spinel is added to alumina castables for two major purposes. One is to increase the slag corrosion resistance and other one is to improve the thermo-mechanical properties. The spinel containing castables show less penetration and less corrosion when compared to the pure alumina against basic and acidic slag compositions5. The optimal spinel content is in the range of 15 – 30 wt%, preferably between 20 and 25 wt%. If too little spinel is added, it results in a higher corrosion rate whereas if there is too much spinel, it leads to high penetration because the spinel does not react with the infiltration slag6. Another important aspect is the grain size distribution of the spinel. Spinel must be added predominantly to the fine fraction of the castable formulation to attain the best penetration resistance7. Spinel addition enhances the thermal shock resistance of alumina castables which can be explained by the different thermal expansion cooefficient between alumina and spinel. The different expansion leads to microcracks in the matrix act as crack branchers when the material is thermally stressed8. Another way to design spinel castables is in-situ while introducing fine magnesia and alumina in matrix. The use of magnesia, as one of the reactants for the spinel formation in castables, often causes difficulties such as poor flow or quick setting due to the magnesia hydration. Furthermore, the volume expansion owing to the