Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 1 Conventional Mould Powders
The continuous casting of steel (shown in Fig. 1) is a very successful process and the performance of the mould powder is a key factor in this success. In this process, molten steel flows (from the tundish) down a submerged entry nozzle (SEN) into a copper, water cooled mould which is sealed at the base with a dummy bar. The dummy bar is withdrawn and a steel shell solidifies against the walls of the mould. Two measures are taken to prevent sticking of the shell to the mould (i) the mould is oscillated continuously and (ii) mould powders are fed continuously into the mould and these form a slag film which separates the shell from the mould. The mould powder heats up as it works its way down the mould. As it proceeds, the powder undergoes the following changes (i) moisture evaporates at ca. 370 K (ii) carbonates decompose at ca. (670 770 K) (iii) sintering occurs between 950 and 1 150 K (iv) Carbon particles react with Oxygen to form CO and CO2 (g) at ca. 770 970 K and finally, (iv) melting of the powder occurs at T>1 150 K. Reactions (i) (ii) and (v) are endothermic, whereas carbon combustion (iv) is an exothermic process. The liquid forms a molten pool and molten slag then infiltrates into the channel between the shell and the mould and, subsequently, freezes to form a slag film; this consists of solid (1 2 mm thick) and liquid (ca. 0.1 mm thick) layers. The thickness of the liquid layer (dl) of the slag film controls the lubrication supplied to the Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 1 Conventional Mould Powders