Study of the Influence of Intermix Conditions on Steel Cleanliness

Abstract

Modern steel plants produce today a large portfolio of various steel grades, many for end-uses demanding high quality. In order to utilize the maximum productivity of the continuous-casting machine, it is sometimes necessary to cast steel grades with different chemical compositions in one sequence. It is important, therefore, to know the possibilities of a specific continuous-casting machine to make the Intermix connections as short as possible. Any interference with established procedures may, however, have a negative impact on the cleanliness of the cast steel. Using physical and numerical simulation tools, it was found that reducing the steel level in the tundish during the exchange of ladles makes it possible to shorten the transition zone. However, when the steel level is reduced, the flow of steel is impaired, which can have a negative effect on the cleanliness of the cast steel and, in extreme cases, may even lead to entrapment of slag in the mold. The cleanliness of cast steel was evaluated using one of the most advanced tools for automatic steel cleanliness evaluation, AZtecFeature (Oxford Instruments, Abingdon, UK), which enables determination of the type, size, distribution, and shape, as well as the chemical composition, of individual types of non-metal inclusions.

Refining and Casting of Steel

“…Under the given conditions, the ULT practice enabled a 20% shortening of the transition zone. The area of higher inclusion concentration during the ULT practice was located in the transition part of the slab, and therefore, had no negative effect on the final quality of the cast steel [7].…”

“…Next, the research focuses on the matters related to the secondary refining processes; fluid's turbulences with nearby metal-slag interface in the ladles [3], the evolution of inclusions for Ti-bearing steels treated by calcium [4], and an influence of aluminum on flux flow in the ladle during Ruhrstahl Heraeus (RH) degassing operations [5]. Other papers are devoted to a geometry of impact area in the tundish [6], cleanliness consequences of an intermixing of the different steel grades in the tundish [7], and the reoxidation of steel from tundish cover flux [8]. Three papers are based on the studies, regarding the processes taking place in the mold from the viewpoint of heat transfer and multiphase flow influenced by deep submerged entry nozzle (SEN) immersion [9], nozzle clogging [10], and mold flux interaction with steel [11].…”

“…Next, the study of authors Bul'ko et al [7] reflects the fact that modern steel plants today produce a large portfolio of various steel grades, many for end-users demanding high quality. In order to utilize the maximum productivity of the continuous-casting machine, it is sometimes necessary to cast steel grades with different chemical compositions in one sequence.…”

“…Using physical and numerical simulation tools, it was found that reducing the steel level in the tundish during the exchange of ladles makes it possible to shorten the transition zone. Based on research results [7], it can be concluded that the ultra-low tundish (ULT) practice produces savings in terms of shorter transition zones, thereby increasing steel yields in the continuous-casting process. Under the given conditions, the ULT practice enabled a 20% shortening of the transition zone.…”

Numerical Analysis of RTD Curves and Inclusions Removal in a Multi-Strand Asymmetric Tundish with Different Configuration of Impact Pad

“…Tundish is one of the most important technology nodes of a continuous casting machine. It primarily serves as the melt reservoir in the sequential casting during the exchange of ladles and ensures the melt distribution into individual casting strands [4][5][6][7][8]. The tundish also regulates the steel mass flow into moulds, reduces ferrostatic pressure of the liquid steel, and homogenizes the melt temperature [9][10][11][12][13].…”