On cooling rate of metal melt in steel-teeming ladle and tundish during continuous steel casting

The thermal state of liquid metal at the continuous steel casting stage was studied by methods of correlation analysis under the assumption that measurable objects are random variables. The thermal state of metal melt is characterized by the values of metal temperature T_n at a given stage and duration of stages τ_n , and is described by the integrated index – cooling rate W_n. The cooling rate is the differential quotient of the liquid metal temperatures at the beginning and end of the stage to the duration of this stage. The metal cooling rate at various stages of continuous steel casting phase was calculated. The first stage includes the period from the end of metal processing at the integrated steel processing unit to the beginning of vacuum degassing. The second stage includes the period from the beginning of vacuum degassing to its completion. The third stage includes the period from the end of vacuum degassing to the first temperature measurement in the tundish.  Then there are periods of consecutive temperature measurements in the tundish. The study established that metal cooling rates vary significantly depending on process stages. The absolute values of the cooling rate differ by more than an order of magnitude. The minimum rate of metal cooling was recorded in the tundish. Its value was 0.09 °С/min. The maximum metal cooling rate was detected during tapping from the steel-teeming ladle into the tundish. In this case, the cooling rate was 1.43 °С/min. 
The main factors affecting the metal cooling rate were determined. These factors include: the initial temperature of liquid metal after the end of processing at the integrated steel processing unit; the temperature of liquid metal after vacuum degassing; the presence on the liquid metal surface of the oxide solution formed by slag-forming mixtures; availability and effectiveness of heat insulating mixtures; as well as the heat insulating properties of refractory linings. During vacuum degassing, the metal cooling rate was essentially determined by convective energy losses and energy losses for inert gas heating. After the vacuum degassing stage, the cooling rate significantly decreases due to the use of heat insulating mixtures. The highest rate of metal cooling is achieved when it passes through the steel outlet channel and the metal protection tube during tundish filling. The lowest metal cooling rate was found in the tundish due to the presence of a porous shotcrete layer with low thermal conductivity.

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