Identification of inclusion sources by slag tracers during the ladle change operation

The cleanness of steel is significantly influenced by the casting conditions during continuous slab casting. Unsteady casting conditions, such as those occurring during a ladle change, may deteriorate the cleanness of the cast product but are process-wise unavoidable. This study investigates the impact of ladle change operation on meso- and macroscopic cleanness levels and seeks to uncover the origin of these non-metallic inclusions (NMIs). To facilitate the identification of the particles’ source, slag tracers were employed to mark ladle and tundish slag. Hot-rolled coils produced from slabs cast during the ladle change were sampled along their entire length and characterised for meso- and macro-NMIs. The inclusions’ positions were then projected to the corresponding positions within the initial strand. The ladle change event significantly deteriorated the strand's meso- and macro-cleanness over a total casting length of approximately 19 m. During the period, as the tundish weight decreased, the largest inclusions were detected. The highest concentration of meso- and macro-NMIs was observed shortly before the start of casting of the subsequent heat. The following sources for meso- and macroscopic NMIs were determined during the ladle change: ladle slag, mould slag and eroded refractory material.