TY - THES

T1 - Ultra-clean steel production

T2 - Behavior of micro-sized alumina inclusions at the Ar gas/liquid steel interface

AU - Ibraheem, Ahmed Mohamed

N1 - no embargo

PY - 2023

Y1 - 2023

N2 - Nowadays, as the industry is shifting towards more sustainability, the demand for Ultra-clean steel (UCS) is rising. UCS is used in several critical engineering applications where superior specifications are required. At this high level of cleanliness, the presence of even a very small number of inclusions exceeding the critical size can have serious effects on the quality of steel. Numerous methods were developed to improve the cleanliness of steel by minimizing the content of impurities and mitigating the effects of the inevitably occurring content by transforming them into less harmful impurities. The most common cleaning method is to inject argon gas bubbles which pick up the inclusions from the liquid steel bath and transfer them to slag. Non-metallic inclusions (NMIs) are inseparable from the steel making process. They originate from several sources, including deoxidation and reoxidation, refractory liner, the flux, the iron ore, and/or the scrap. NMIs are classified according to numerous criteria, including their origins, their sizes, their chemical composition, and their acidic and alkaline behavior. One of the most common inclusion types -especially in producing Al-killed steel- is alumina inclusions. This type of inclusion has harmful effects on the Continuous casting (CC) process as it leads to the arising of the phenomenon of clogging in the submerged entry nozzle (SEN). Additionally, alumina inclusions affect the steel's mechanical properties since it acts as a crack initiation site that decreases the toughness of steel. Alumina inclusions though usually distributed homogeneously over the melt surface, form clusters rapidly. The phenomenon of clustering of NMIs at the surface of liquid steel is attributed to lateral capillary interaction, which depends on the deformation of the meniscus around. The uniform deformation of the 3-phase contact line between the solid inclusion particle, liquid steel, and the atmosphere (argon gas) occurs under the effect of the inclusion weight. In this case, the microsized inclusions are treated as ¿capillary charges¿. In the case of micro inclusions having negligible masses, the meniscus deformation due to particle weight is negligible. However, it was found that the floating particles still strongly attract each other. Another mechanism was proposed that the meniscus is not uniformly deformed but in an undulated manner. In this case, the capillary charge is replaced by the term `capillary multipole¿ where the type of interaction depends on the meniscus undulation amplitude and the orientation of the floating particle. The attraction force between alumina inclusions floating at the interface between liquid steel and argon gas was investigated using the confocal laser scanning microscope (CSLM) which is capable of in-situ observation of the NMIs behavior at the liquid steel/argon gas interface. The interactions of alumina inclusions were interpreted using the capillary multipole model. The results of 13 cases were analyzed and compared, and the type of lateral capillary interaction was discussed. The dipole-quadrupole model was the best model to interpret the interaction force between alumina inclusions.

AB - Nowadays, as the industry is shifting towards more sustainability, the demand for Ultra-clean steel (UCS) is rising. UCS is used in several critical engineering applications where superior specifications are required. At this high level of cleanliness, the presence of even a very small number of inclusions exceeding the critical size can have serious effects on the quality of steel. Numerous methods were developed to improve the cleanliness of steel by minimizing the content of impurities and mitigating the effects of the inevitably occurring content by transforming them into less harmful impurities. The most common cleaning method is to inject argon gas bubbles which pick up the inclusions from the liquid steel bath and transfer them to slag. Non-metallic inclusions (NMIs) are inseparable from the steel making process. They originate from several sources, including deoxidation and reoxidation, refractory liner, the flux, the iron ore, and/or the scrap. NMIs are classified according to numerous criteria, including their origins, their sizes, their chemical composition, and their acidic and alkaline behavior. One of the most common inclusion types -especially in producing Al-killed steel- is alumina inclusions. This type of inclusion has harmful effects on the Continuous casting (CC) process as it leads to the arising of the phenomenon of clogging in the submerged entry nozzle (SEN). Additionally, alumina inclusions affect the steel's mechanical properties since it acts as a crack initiation site that decreases the toughness of steel. Alumina inclusions though usually distributed homogeneously over the melt surface, form clusters rapidly. The phenomenon of clustering of NMIs at the surface of liquid steel is attributed to lateral capillary interaction, which depends on the deformation of the meniscus around. The uniform deformation of the 3-phase contact line between the solid inclusion particle, liquid steel, and the atmosphere (argon gas) occurs under the effect of the inclusion weight. In this case, the microsized inclusions are treated as ¿capillary charges¿. In the case of micro inclusions having negligible masses, the meniscus deformation due to particle weight is negligible. However, it was found that the floating particles still strongly attract each other. Another mechanism was proposed that the meniscus is not uniformly deformed but in an undulated manner. In this case, the capillary charge is replaced by the term `capillary multipole¿ where the type of interaction depends on the meniscus undulation amplitude and the orientation of the floating particle. The attraction force between alumina inclusions floating at the interface between liquid steel and argon gas was investigated using the confocal laser scanning microscope (CSLM) which is capable of in-situ observation of the NMIs behavior at the liquid steel/argon gas interface. The interactions of alumina inclusions were interpreted using the capillary multipole model. The results of 13 cases were analyzed and compared, and the type of lateral capillary interaction was discussed. The dipole-quadrupole model was the best model to interpret the interaction force between alumina inclusions.

KW - Stahl

KW - Aluminiumoxid

KW - Kapillare

KW - Welligkeit

KW - Meniskus

KW - mehrpolig

KW - CSLM

KW - Einschlüsse

KW - steel

KW - alumina

KW - capillary

KW - meniscus

KW - undulation

KW - multipole

KW - CSLM

KW - inclusions

U2 - 10.34901/mul.pub.2023.30

DO - 10.34901/mul.pub.2023.30

M3 - Master's Thesis

ER -