FORMATION OF METAL DROPLETS IN THE SLAG OF A TUNDISH DURING INERT GAS PURGING

Abstract

The study demonstrates that the tundish of a continuous casting machine is the final vessel where steel quality can be controlled, specifically through the removal of non-metallic inclusions. It is highlighted that the transfer of nonmetallic inclusions to the metal-slag phase boundary in the tundish is governed by adsorption processes occurring within the metal-slag-inclusion system. It is established that one of the primary quality attributes of the steel is a low content of non-metallic inclusions in the final product. The research reveals that one of the most effective methods for controlling the content of nonmetallic inclusions at the final stage of casting is the purging of liquid steel with argon. It is determined that non-metallic inclusions are efficiently removed during the purging of the metal bath with an inert gas, due to their attachment to gas bubbles at the metal-gas phase boundary. However, it is noted that the mechanism and extent of inclusion removal in this process remain insufficiently studied. It is known that purging steel with an inert gas leads to the formation of a metal emulsion in the slag, which enhances mass transfer between the two immiscible liquids, thereby increasing the rate of assimilation of the nonmetallic phase by the slag. A detailed mathematical and hydrodynamic analysis of the behavior of an argon bubble with a metal film in the slag phase was conducted. It was found that the steel purification process from non-metallic inclusions during inert gas purging primarily depends on the residence time of metal droplets in the slag phase. It is emphasized that the refining process by argon bubbles involves the rupture of the metal film on the argon bubble. The study shows that heterogeneous assimilation reactions of non-metallic inclusions at the phase boundary are of the first order. An equation for the assimilation rate of non-metallic inclusions was derived, utilizing data on residence time. The residence time of metal droplets in the slag phase was determined for varying inert gas flow rates and bubble diameters. It was established that increasing the bubble diameter and gas flow rate leads to an extended residence time of metal droplets in the slag phase, which positively impacts the metal refining process from non-metallic inclusions. It was clarified that, in the context of secondary steel treatment, the intensification of metal mixing in the zone adjacent to the slag is technologically significant, as it enhances phase mixing intensity and the contact surface area. It is demonstrated that mixing promotes more complete reaction progression and significantly improves slag utilization efficiency. It was found that the increase in contact surface area results from the formation of a slag-metal emulsion at the interface of contacting phases during the passage of gas bubbles through the phase boundary.