In situ observations and thermal analysis of crystallization phenomena in mold slags

Abstract

During continuous casting the crystallization behavior of a mold slag has a decisive effect on the lubrication and heat transfer between mold wall and steel strand. By means of the Double Hot Thermocouple Technique the crystallization kinetics of a mold slag could be studied in detail over a wide temperature range. TTT and CCT diagrams were obtained and the crystal morphology was determined at different undercooling or cooling rates. The crystalline phase was determined using X-ray diffraction. Experiments with the presence of water vapor in the atmosphere were also conducted. The presence of water vapor increased the nucleation rate and crystal growth rate significantly when compared to experiments carried out in a dry atmosphere. Precipitation of solid crystals also occurred at a temperature above the equilibrium liquidus temperature (1260°C) that is measured in a dry atmosphere. These results suggest that there is significant interaction between water vapor and liquid slags at high temperatures and that the phase diagram for these slags is very sensitive to the equilibrium partial pressure of water vapor in the surrounding atmosphere.