2007 Volume 47 Issue 9 Pages 1284-1293
In strip casting the heat extraction rate is limited by the thermal resistance at the interface between solidified shell and the mold (rolls for twin-roll strip casters). The objective of this work was to assess the effect of the use of atmospheres with gaseous species containing sulfur on the heat transfer rate experienced during droplet solidification against a water-cooled copper mold. This issue was addressed by the use of experimentation in which liquid Fe droplets solidified in direct contact with a copper chill substrate under an atmosphere of Argon mixed with a 95/5 mixture of H2 and H2S. The effect of the atmosphere composition was assessed by measuring in-mold heat transfer rates during solidification and by characterizing the solidified samples by sulfur printing and Scanning and Auger electron microscopy. The results were compared to those obtained using pure Fe in 95/5 atmosphere of Ar/H2. It was found that heat transfer rates were higher when the gas atmosphere contained H2S, result that can be explained by the decrease of the melt surface tension or the increase of the liquidus-solidus temperature difference due to the pick-up of sulfur from the gas phase into liquid iron.
These results suggest that sulfur-containing atmospheres could be used to affect heat transfer rates in strip casting. To further explore this possibility, a simple model was developed in order to predict the change of melt surface tension and the change of sulfur content in the final product when also H2S is used in the shrouding atmosphere above the liquid pool of a twin-roll strip caster.