Study of the conditions of mixing and thermal state of the melt during degassing of steel on a chamber (VD) type equipment
Authors: Piptyuk V.P. , Grekov S.V. , Samokhvalov S.E. , Krasnikov K.S. , Logozinskiy I.N. 
Published: June 2021

Increasing requirements for the quality of metal products are regulated by international, state standards and other documents, in particular, on the content of gases and non-metallic inclusions in metal. In some cases, normative documents stipulate the need for degassing of steel with high quality requirements, including flock-sensitive grades. For this purpose, equipment for chamber (VD, VOD-types) degassing is used at metallurgical and machine-building enterprises of Ukraine. Due to insufficient knowledge of the process of degassing, real numerical studies have been carried out. As the object of study, we determined the installation for the degassing of the Mannesmann Demag company of the above type with a 60t bucket with reinforcement of the lining in impact zone of the PJSC «DSS» enterprise. Based on the initial data of the degassing process, a mathematical model was developed by DSTU to consider heat and mass transfer processes in a liquid metal bath during its degassing. Specialized software has been created that allows you to take into account the changing technological parameters during metal processing in vacuum, the configuration and capacity of the bucket bath. Employees of the ISI of NASU using the database on out-of-furnace processing of electric steel at PJSC «DSS» for the previous period determined that the values of the mass of the heats were in the range from 54t to 66t. Given the previously established that the intensity of argon purging through the bottom (s) tuyeres (s) and different masses of metal in a ladle of the same capacity from smelting to smelting create different hydrodynamic and thermal conditions for metal processing processes in the bucket, and the above information required an additional evaluation of the process degassing. At the first stage of numerical studies, the hydrodynamic conditions of degassing in a metal bath were studied taking into account the listed influence factors. Contour diagrams of the vertical component of the velocity of metal flows in different vertical axial sections of the bath were constructed at 20 minutes of degassing (at a pressure of 1 mm Hg). In the given vertical sections, the descending metal flows are concentrated in the upper half of the bath, and the ascending flows in its lower half. It was noted that with an increase in the flow rate of argon for mixing with the same mass of smelting, the absolute values of the vertical component of the metal velocity increase, and with the same consumption of argon, it decreases with an increase in the mass of smelting, which is similar to processing conditions at normal atmospheric pressure. At the second stage of research, thermal conditions were studied during the degassing of steel at a similar reduced pressure. Contour diagrams with isotherms (average metal temperature in the ladle) are constructed depending on the duration of the degassing process and argon consumption. A comparative assessment of the thermal conditions during degassing on chamber-type equipment and on LF (at normal pressure) with operating conditions at a similar initial temperature and the corresponding argon flow rate was made. An increase in heat loss by metal was found with an increase in argon consumption and with a decrease in smelting mass. Thus, it has been established that the mixing features of the metal bath create different hydrodynamic conditions for the degassing process on the chamber-type equipment, affect its thermal state, which probably can affect the efficiency of gas removal.