TY - BOOK

T1 - Experimental investigation of the inclusion behavior in Ti-stabilized interstitial-free steels and its relevance for clogging phenomena in continuous casting processes

AU - Dorrer, Philipp

N1 - embargoed until 13-03-2025

PY - 2020

Y1 - 2020

N2 - Clogging of the submerged entry nozzle (SEN) is a well-known problem during the continuous casting process of certain steel grades. The buildup of accretions leads to constrictions within the SEN, which disturb the steel flow and possibly cause the termination of the casting procedure. Ti-stabilized interstitial-free (Ti-IF) and ultra-low carbon (Ti-ULC) steels are especially prone to clogging. The addition of titanium in the form of ferrotitanium (FeTi) significantly increases the clogging tendency compared to Ti-free IF and ULC steel grades. The statistical evaluation of data from industrial continuous casting operations has shown a remarkable correlation between the Ti/Al-ratio of the steel melts and their casting behavior towards clogging. Despite the complexity of the clogging phenomenon, the main mechanism causing nozzle constrictions can be found in the deposition of solid non-metallic inclusions (NMI). Pre-existing alumina particles play also a key role in case of SEN-clogging of Ti-IF steels, but the clogging promoting effect of the titanium addition is still under discussion. Therefore, a detailed study on the state of the art production and proposed effects of the FeTi-addition on the properties of these steels according to literature is performed. Within this thesis, the consequences of the FeTi-addition for the behavior and the evolution of the inclusion population are investigated by means of experimental methods. The detailed evaluation of SEM/EDS-inclusion data from samples, which are taken during the industrial processing of Ti-IF steels in secondary steelmaking, acts as a reference for subsequent experiments. Based on the results from industrial steel production, laboratory-scale experiments including Al-deoxidation and subsequent FeTi-addition are designed to study the influence of the FeTi on a pre-existing population of alumina inclusions. The present work especially focuses on the changes in inclusion number, size, morphology and chemical composition, which indicate possible mechanisms causing the elevated clogging tendency. The development and application of a new sampling method for improved sample quality regarding their aptitude for automated SEM/EDS inclusion evaluation and an adapted scheme of inclusion classification are of major importance for this study. Since the presence of Ti-bearing alumina inclusions is regularly reported in literature and is proofed also within this work, a new approach is developed for the investigation of their wettability by liquid steel. Ceramic layers of Al2O3 and various contents of TiO2 are manufactured and tested in combination with liquid steel alloys by means of the sessile drop method. The results of the laboratory-scale experiments are critically discussed regarding their transferability to industrial processing and their importance for the inclusion behavior in secondary steelmaking and continuous casting operations. The findings provide important knowledge about the influences of the FeTi-addition on the inclusion population and concrete recommendations are given for the reduction of the clogging propensity of Ti-ULC and IF steel grades.

AB - Clogging of the submerged entry nozzle (SEN) is a well-known problem during the continuous casting process of certain steel grades. The buildup of accretions leads to constrictions within the SEN, which disturb the steel flow and possibly cause the termination of the casting procedure. Ti-stabilized interstitial-free (Ti-IF) and ultra-low carbon (Ti-ULC) steels are especially prone to clogging. The addition of titanium in the form of ferrotitanium (FeTi) significantly increases the clogging tendency compared to Ti-free IF and ULC steel grades. The statistical evaluation of data from industrial continuous casting operations has shown a remarkable correlation between the Ti/Al-ratio of the steel melts and their casting behavior towards clogging. Despite the complexity of the clogging phenomenon, the main mechanism causing nozzle constrictions can be found in the deposition of solid non-metallic inclusions (NMI). Pre-existing alumina particles play also a key role in case of SEN-clogging of Ti-IF steels, but the clogging promoting effect of the titanium addition is still under discussion. Therefore, a detailed study on the state of the art production and proposed effects of the FeTi-addition on the properties of these steels according to literature is performed. Within this thesis, the consequences of the FeTi-addition for the behavior and the evolution of the inclusion population are investigated by means of experimental methods. The detailed evaluation of SEM/EDS-inclusion data from samples, which are taken during the industrial processing of Ti-IF steels in secondary steelmaking, acts as a reference for subsequent experiments. Based on the results from industrial steel production, laboratory-scale experiments including Al-deoxidation and subsequent FeTi-addition are designed to study the influence of the FeTi on a pre-existing population of alumina inclusions. The present work especially focuses on the changes in inclusion number, size, morphology and chemical composition, which indicate possible mechanisms causing the elevated clogging tendency. The development and application of a new sampling method for improved sample quality regarding their aptitude for automated SEM/EDS inclusion evaluation and an adapted scheme of inclusion classification are of major importance for this study. Since the presence of Ti-bearing alumina inclusions is regularly reported in literature and is proofed also within this work, a new approach is developed for the investigation of their wettability by liquid steel. Ceramic layers of Al2O3 and various contents of TiO2 are manufactured and tested in combination with liquid steel alloys by means of the sessile drop method. The results of the laboratory-scale experiments are critically discussed regarding their transferability to industrial processing and their importance for the inclusion behavior in secondary steelmaking and continuous casting operations. The findings provide important knowledge about the influences of the FeTi-addition on the inclusion population and concrete recommendations are given for the reduction of the clogging propensity of Ti-ULC and IF steel grades.

KW - Clogging

KW - Submerged entry nozzle

KW - Ti-stabilized

KW - Interstitial-free steel

KW - Ferrotitanium

KW - Non-metallic inclusions

KW - Secondary steelmaking

KW - Clogging

KW - Eintauchausguss

KW - Ti-stabilisiert

KW - IF-Stahl

KW - Ferrotitan

KW - Nicht-metallische Einschlüsse

KW - Sekundärmetallurgie

M3 - Doctoral Thesis

ER -