Investigation of particle attraction by steel/refractory and steel/gas interfaces and the associated relevance for clogging in casting processes

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Abstract

Clogging in continuous casting of steel is the buildup of particles in the flow control system. Besides other reasons, pre-existing non-metallic inclusions(NMIs)- mostly resulting from ladle treatment- may build up on the refractory wall, interrupting or disturbing the fluid flow conditions. Since the NMIs in the steel cannot be completely avoided, a deeper understanding of their development and evolution during the process is required. In particular, this includes the deposition of micro-inclusions to the steel/refractory interface in the submerged entry nozzle(SEN) between the tundish and the mold. The deposition mechanism for deoxidation products at the SEN wall is investigated in Chapter 1. The inclusions, which are transported from the bulk melt to the boundary layer, may adhere to the steel/refractory interface. If they are not removed due to detachment forces related to the fluid flow and materials conditions, they sinter inducing changes on the process and product conditions. The interfacial properties of the system NMI-steel-refractory are believed to play a key role in the NMIs adhesion or detachment at the steel/refractory interface. The clogging mechanism and the forces involved in the adhesion of NMI at the wall are presented. Furthermore, several clogging countermeasures are commented. In Chapter 2, the clogging evaluation methods are summarized. The methods are classified into direct and indirect. While direct methods investigate SEN-samples from industrial-plan trials or laboratory-scale experiments, the indirect methods analyze isolated related parameters, such as the interfacial properties of the system NMI-steel-refractory. In this work, the high-temperature laser scanning confocal microscopy(HT-LSCM) has been selected as a qualitative method to investigate how the wettability of the system NMI-steel-refractory affects the clogging problem. For that purpose, a two-step set-up has been developed. The finality of this experimental is the investigation of the effect: (1)NMIs wettability in the deposition of NMIs at a steel/ceramic interface (2)Ceramic wettability in the deposition of NMIs at a steel/ceramic interface. The selected methodology shows a high potential to predict how an interfacial property such as wettability influences the NMI separation tendency at certain refractory interfaces. The results are compared with a theoretical model. Furthermore, high-temperature drop shape analyses(HT-DSA) are performed to confirm the correspondence between the HT-LSCM observations and the wettability. A detailed model is derived to predict the critical conditions needed for detachment of NMIs from the nozzle wall in Chapter 3. This model is based on the local hydrodynamic conditions combined with the specific interfacial properties in the system NMI-steel-refractory. Three detachment criterions are developed at the steel/refractory interface. The model is implemented to investigate how the interfacial properties of the system NMI-steel-refractory may influence the adhesion or detachment of NMIs at the steel/ceramic interface. The injection of argon gas at the flow control area of the SEN is performed to reduce clogging problems. The behavior of the argon bubbles at the steel/refractory interface and the deposition mechanism of NMI at the steel/gas interface is investigated in Chapter 4. Two detachment criteria are developed to investigate the following: (1)The size of bubbles that may be stable at the steel/refractory interface, and (2)the detachment of NMIs from the bubbles once they adhere at the steel/gas interface. The role of argon in the system is discussed in comparison with the model for the adhesion of deoxidation products at the steel/refractory interface. Finally, the associated relevance for clogging of the NMIs deposition at steel/refractory and steel/gas interfaces is presented on Chapter 5. The clogging countermeasure selecti

Details

Translated title of the contributionUntersuchung der Partikelanziehung durch Stahl / Feuerfest und Stahl / Gas Grenzflächen und die damit verbundene Relevanz für Clogging in Gießprozessen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
Supervisors/Advisors
Publication statusPublished - 2018