IMPROVED CASTABILITY AND SURFACE FINISH ON AL-KILLED RESULPHURISED BLOOMS AT

摘要

Nozzle clogging due to deposits of Al_2O_3-MgO spinels can cause poor castability and surface defects on certain CaSi-treated, Al-killed. steel grades with high (0.03-0.04 percent) S-contents. The deposits consist of Al_2O_3-MgO spinels enclosed in a matrix of calcium aluminates. The Al_2O_3-MgO spinels are believed to be formed when liquid steel with low oxygen potential is in contact with high carbon magnesite refractories for longer periods of time and at elevated temperature. The content of Al_2O_3-MgO spinels can be minimized if the average temperature and treatment time in the ladle furnace and vacuum station is optimized. The time for inclusion flotation, after final wire additions, can thus be increased within the available total treatment time. To optimize the LF and VD treatment time, knowledge of kinetics for S- and H removal as well as temperature control is of utmost importance. Below, process routes for resulphurised steel grades are discussed and some production results of S- and H-removal are presented from the Danieli Centro Met ladle furnace and vacuum station at ABS (ACCIAIERIE BERTOLISAFAU), Italy. Heating philosophies in the ladle furnace and temperature drops during vacuum treatment are also discussed.