Instantaneous interfacial heat fluxes during the 4 to 8 m/min casting of carbon steels in a twin-roll caster

Instantaneous heat fluxes between the roll and the solidifying metal were evaluated in a pilot twinroll caster, producing strips of low-carbon steels. This evaluation was based on the solution of an inverse heat-transfer problem, using temperature readings of thermocouples inserted at various locations in the roll sleeve. The response times of the thermocouples were determined and used to correct measured temperatures. The variation of the instantaneous heat fluxes with time of contact between the roll and the melt presented two distinct types of behavior, one exhibiting a single peak and other a double peak, depending on the casting conditions. These different patterns were interpreted in terms of the variation of the metallostatic pressure, solidification shrinkage, thermal expansion of the rolls, and characteristics of the solid shell. Predictions of the amounts of heat extracted by the roll and secondary dendrite arm spacings (SDAS) in the strips, based on the calculated heat fluxes, were in reasonable agreement with experimental values. This also demonstrated that the level of correction applied to the thermocouple readings was appropriate.