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

Abstract

Correlation analysis methods were used to study the thermal state of liquid metal at the stage of steel continuous casting under the assumption that measurable objects are random variables. Thermal state of the metal melt is characterized by the values ​​of the metal temperature Tn at this stage and duration of the stages τn and it is described by an integral indicator – cooling rate Wn . Cooling rate is the ratio of temperature difference of the liquid metal at the beginning and end of the stage to the duration of this stage. The metal cooling rates were calculated at various stages of steel continuous casting. The first stage includes the period from the completion of metal processing at a unit of complex steel processing to the start of vacuum treatment. The second stage includes the period from the start of vacuum treatment to its completion. The third stage includes the period from the end of vacuum treatment to the first temperature measurement in the tundish. And further, there are periods of successive temperature measurements in the tundish. It has been established that the metal cooling rates vary considerably depending on the technological stages. Absolute values ​​of the cooling rate differ by more than an order of magnitude. The minimum metal cooling rate is fixed in the tundish. Its value is 0.09 °С/min. The maximum cooling rate of the metal was revealed when the metal was tapped from the steel-pouring ladle into the tundish, while the cooling rate was 1.43 °C/min. The main factors influencing the metal cooling rate were revealed. These factors include the presence of a layer of liquid slag on the metal melt surface in the steel-pouring ladle after out-of-furnace processing. These factors include initial temperature of the liquid metal after completion of treatment at the unit of complex steel processing, the liquid metal temperature after completion of vacuum treatment, presence of oxide solution formed by slag-forming mixtures on the liquid metal surface, presence and effectiveness of heat-insulating mixtures, as well as the heat-insulating characteristics of refractory linings. During vacuum treatment, the metal cooling rate was essentially determined by convective energy losses and energy losses for heating the inert gas. After the stage of vacuum treatment, the cooling rate is significantly reduced due to the use of heat-insulating mixtures. The highest metal cooling rate is set when it passes through the steel outlet channel and the metal protection pipe when filling the tundish. The lowest metal cooling rate is typical when it is in the tundish, due to the presence of a porous plastic refractory layer with low thermal conductivity.