Mechanism of Sulfur Influence on Nozzle Clogging During Continuously Cast of LCAK Steel
Abstract
It is known that sulfur increases the nozzle clogging during continuous casting of LCAK steel and it is believed that the main cause of that is formation of solid phase CaS. By our thermodynamic computations it was found that increase of sulfur content in steel not only leads to CaS formation but influences on rate of CaO in calcium aluminates and consequently on their aggregative state. The computations were made for two grades of LCAK steel: 08K (0.02 wt. pct. Al) and 08Yu (0.05 wt. pct. Al) (GOST), with calcium content in the range of 0.002 – 0.004 wt. pct., initial sulfur content 0.01 – 0.02 wt. pct., and t = 1580 °C. The calcium aluminates in 08K steel were liquid for all investigated ranges of calcium and sulfur concentrations, but in 08Yu steel they were liquid only for Ca > 0.003 and S < 0.015 wt. pct. It was found that if S = 0.02 wt. pct. calcium conjuncts into CaS and calcium rate in calcium aluminates does not exceed 32 – 33 wt. pct. The thermodynamic simulation of inclusions transformations during melt cooling from 1590 °C to cast temperature (1545 – 1555 °С) shows that CaO rate in calcium aluminate changes differently for various contents of sulfur and aluminum in the melt.
Key words: castability, LCAK steel, sulfur, CaS, calcium aluminates, thermodynamic simulation, generation and transformation of nonmetallic inclusions, nozzle clogging
