Nonmetallic inclusions are well known to influence product quality and process stability in the production of steel. A process step that is very sensitive to the presence of nonmetallic inclusion (NMI) is continuous casting. Here, the so‐called clogging phenomenon can occur, resulting in a distinct disruption of the casting process and decreased steel quality. The presence of nonmetallic inclusions considerably contributes to the build‐up of deposits in the submerged entry nozzle provoking instabilities in the flow control system. Numerous research studies have been subject to different clogging mechanisms and related influencing parameters. Interfacial properties significantly influence the behavior of inclusions in the steel–refractory system. The present review demonstrates state of the art concerning the role of NMIs in the appearance of clogging. Particular focus is put on the wetting behavior between the different phases and their consequence for the deposition process. Industrial observations and laboratory methods are summarized and discussed; potential countermeasures are evaluated. A steel group that is especially prone to clogging are Ti‐ ultra low carbon (ULC) steels. An overview of the current understanding of their high clogging tendency and possible influences is presented, considering thermodynamic and interfacial aspects.

Acicular ferrite is a microstructure nucleating intergranularly on non-metallic inclusions and forming an arrangement of fine, interlocking grains. This structure is known to improve steel properties, especially steel toughness, essentially. The formation of acicular ferrite is mainly affected by steel composition, cooling rate, inclusion landscape and austenite grain size. In recent decades, extensive research has been conducted to investigate these factors. The present paper provides an overview of the impact of published results and the state of knowledge regarding acicular ferrite formation. Special attention is paid to the effect of carbon, manganese and titanium addition to steel, as well as the optimum size, number and composition of non-metallic inclusions. In addition, the reactions during the nucleation and growth of acicular ferrite needles are briefly addressed. Further, characteristics of acicular ferrite and bainite are summarized, which should help to distinguish these similar structures.

The formation of nonmetallic inclusions in the solidification process can essentially influence the properties of steels. Computational simulation provides an effective and valuable method to study the process due to the difficulty of online investigation. This paper reviews the modeling work of inclusion formation during the solidification of steel. Microsegregation and inclusion formation thermodynamics and kinetics are first introduced, which are the fundamentals to simulate the phenomenon in the solidification process. Next, the thermodynamic and kinetic models coupled with microsegregation dedicated to inclusion formation are briefly described and summarized before the development and future expectations are discussed.