TY - THES

T1 - Influence of Alkali Metal Oxides in Secondary Metallurgical Slags on the Behavior and Appearance of Non-Metallic Inclusions in Steel

AU - Preißer, Nikolaus

N1 - no embargo

PY - 2023

Y1 - 2023

N2 - With increasing demands on the mechanical properties of modern steels the role of non metallic inclusions becomes more prominent. The control of their amount, size, morphology, and also chemical composition is the key to the production of highly advanced steel grades. An important factor influencing the steel cleanness are the slags used for ladle treatment in secondary metallurgy. In the course of this work commonly used low basicity pseudo-wollastonitic slags with additional contents of alkali metal oxides were studied. In particular, their capability to remove or affect non-metallic inclusions was analyzed. Thermodynamic calculations showed that the addition of R2O (R=Li, Na, K) to commonly used low basicity pseudo-wollastonitic slags, can lower the melting point drastically. As slag and non-metallic inclusions are interacting, the chemical composition of the particles is influenced. This can be used to decrease the liquidus temperature of the particles, which is often linked with lower hardness and better deformability. For a better understanding of the effects of alkali metal oxides on the non metallic inclusions and therefore the steel cleanness, two sets of experiments were conducted. First dissolution of synthetic particles in alkali metal oxide containing slags was observed using HT CSLM. Furthermore, steel samples were treated with the experimental slags at steelmaking temperatures. The inclusion populations before and after steel-slag interaction were compared using automated SEM/EDS-analysis. A clear impact of the alkali metal oxides on the dissolution behavior was shown. Particles modified with the added alkali elements could be observed as well as a shift in the overall composition of the inclusions.

AB - With increasing demands on the mechanical properties of modern steels the role of non metallic inclusions becomes more prominent. The control of their amount, size, morphology, and also chemical composition is the key to the production of highly advanced steel grades. An important factor influencing the steel cleanness are the slags used for ladle treatment in secondary metallurgy. In the course of this work commonly used low basicity pseudo-wollastonitic slags with additional contents of alkali metal oxides were studied. In particular, their capability to remove or affect non-metallic inclusions was analyzed. Thermodynamic calculations showed that the addition of R2O (R=Li, Na, K) to commonly used low basicity pseudo-wollastonitic slags, can lower the melting point drastically. As slag and non-metallic inclusions are interacting, the chemical composition of the particles is influenced. This can be used to decrease the liquidus temperature of the particles, which is often linked with lower hardness and better deformability. For a better understanding of the effects of alkali metal oxides on the non metallic inclusions and therefore the steel cleanness, two sets of experiments were conducted. First dissolution of synthetic particles in alkali metal oxide containing slags was observed using HT CSLM. Furthermore, steel samples were treated with the experimental slags at steelmaking temperatures. The inclusion populations before and after steel-slag interaction were compared using automated SEM/EDS-analysis. A clear impact of the alkali metal oxides on the dissolution behavior was shown. Particles modified with the added alkali elements could be observed as well as a shift in the overall composition of the inclusions.

KW - Nichtmetallischer Einschluss

KW - Alkalioxide

KW - NME

KW - Schlacke

KW - Sekundärmetallurige

KW - Reinheitsgrad

KW - Non-metallic inclusion

KW - Alkali metal oxide

KW - NMI

KW - Slag

KW - Secondary Meatllurgy

KW - Cleanness

U2 - 10.34901/MUL.PUB.2023.07

DO - 10.34901/MUL.PUB.2023.07

M3 - Master's Thesis

ER -