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.
Highlights
Resolution of the Intermix problem, shortening the chemical composition transition zone in cast slabs when various steel grades are cast in succession, generally includes several options and operating parameters, which more or less affect its overall range
The main focus of this research was to verify the impact of the ultra-low tundish practice (ULT), whereby the steel level in the tundish is lowered to 15 tons during the initiation of the operating tests
The results of the research in terms of Intermix evaluation are presented graphically in Figure 5, which presents a direct comparison of the standard transient conditions in the tundish at 20 tons, as well as with the new alternative tested, with an initial steel level of 15 tons in the tundish, i.e., ULT
Summary
Resolution of the Intermix problem, shortening the chemical composition transition zone in cast slabs when various steel grades are cast in succession, generally includes several options and operating parameters, which more or less affect its overall range. Apart from the chemical concept itself and the real possibilities of logistical planning of specific ways of joining different steel grades, the overall range of the Intermix is influenced mainly by the flow and mixing conditions of the liquid steel in the tundish during the casting process. In order to verify certain operations intended to optimize the Intermix range during hard transitions in which the steel level in the tundish [8,9] is deliberately reduced, operational testing of a joining process for alternate batches was performed, in which the effect on the total length. For a more detailed study and definition of the Intermix range, a number of methods and procedures were published regarding the flow conditions of the steel in the tundish [1,2,3,4,5,6], as well as, to a certain extent, in the mold and the casting stream [7].
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