Formation of build-ups in tundish nozzles of billet continuous-casting machines and methods of combating them

The processes of continuous steel casting have advantages over casting into molds: more accurate dimensions of the cross-section of a continuously cast billet (CCB) of square, rectangular, round or other cross-section; actual suppression of zonal liquation; the use of controlled water cooling, forming the macro- and microstructure of the CCB; the possibility of minimizing the development of dendritic, columnar crystalline structure of the billet by increasing the crystallization rate and suppressing the directed gradient growth of dendrites, using electromagnetic stirring (EMS) of liquid metal during its crystallization; the use of a programmable oscillation frequency of the mould, improving the complex of properties of the CCB. The disadvantages of continuous casting include microbreakthroughs and scaling tundish nozzles. They are caused by violation of the technology of CCB production: low temperature of casting — slight overheating of cast steel above the liquidus temperature; presence of refractory non-metallic inclusions (NMI) — build-ups that are deposited on the walls of casting tundish nozzles. At the same time, the internal channels of such nozzles decrease in diameter, as a result of which the casting process slows down or stops. Therefore, such a strand “closes” and the casting continues on the remaining strands. This leads to a decrease in productivity, deterioration in the quality of CCB in some cases, sometimes to reconfiguration of the continuous-casting machine (CCM), emergency shutdowns of equipment are possible. The build-up consists of refractory aluminum oxides (Al2O3), magnesia spinel (MgO∙Al2O3) in the presence of CaO, SiO2. Their formation is caused by the materials of the tundish nozzles, products of steel deoxidation (endogenous NMI) and destruction of linings of steel-pouring ladles and tundishes (exogenous NMI). Technical and technological measures to prevent the formation of build-ups include the selection of effective materials for tundish nozzles that exclude the deposition of build-ups on their inner walls (creation of conditions for non-wetting of the tundish nozzle material with oxides), compliance with the developed technologies of steel smelting, its out-of-furnace - ladle treatment and continuous casting.