TY - GEN

T1 - Effect of liquefaction controlling components in carbon-free mould powder for the continuous casting of ultra-low carbon steels

AU - Gruber, Nathalie

PY - 2024

Y1 - 2024

N2 - In the continuous casting of ultralow carbon (ULC) steels, free carbon is used to control the meltingbehaviour of mould powders. If the carbon is not completely removed during melting, it is enrichedat the top of the slag pool. Liquid steel may come into contact with this layer because of theturbulence of the molten metal, resulting in its recarburisation, which negatively affects the desiredproduct quality. Thus, a reduction in carbon input is desirable. For this purpose, SiC and/or Si 3N4with and without antioxidants were selected as melt-control additives to replace carbon in the mouldpowders. Thermodynamic calculations were performed to quantify their effect on the meltingbehaviour based on the chemical composition of a flux already applied to ULC steels. Toexperimentally assess the liquefaction behaviour, laboratory mould powders were prepared andannealed in steel crucibles closed with a lid. Crucibles were inserted into a furnace that was alreadypreheated to selected temperatures between 900–1200°C for 10 mins and quenched to roomtemperature. Subsequently, the samples were mineralogically investigated. The results confirmedthose obtained from the thermodynamic calculations. Si 3N4, and SiC in particular, are suitable rawmaterials for delaying the solid-solid reactions of raw material components during melting. Owing totheir stability at high temperatures, the necessary SiO 2 content to form a liquid phase is not available,resulting in lower amounts of the liquid phase. The addition of antioxidants to delay the oxidation ofSiC further reduces this positive effect. Attempts to decrease the SiC content without negativelyaffecting the melting behaviour resulted in a reduction in the CO 2 emission by at least 27 g CO 2/kgof mould powder when compared to the carbon-containing standard mould powder. Theseinvestigations revealed differences in the melting behaviours of granules and loose powders, whichare related to their respective production processes.

AB - In the continuous casting of ultralow carbon (ULC) steels, free carbon is used to control the meltingbehaviour of mould powders. If the carbon is not completely removed during melting, it is enrichedat the top of the slag pool. Liquid steel may come into contact with this layer because of theturbulence of the molten metal, resulting in its recarburisation, which negatively affects the desiredproduct quality. Thus, a reduction in carbon input is desirable. For this purpose, SiC and/or Si 3N4with and without antioxidants were selected as melt-control additives to replace carbon in the mouldpowders. Thermodynamic calculations were performed to quantify their effect on the meltingbehaviour based on the chemical composition of a flux already applied to ULC steels. Toexperimentally assess the liquefaction behaviour, laboratory mould powders were prepared andannealed in steel crucibles closed with a lid. Crucibles were inserted into a furnace that was alreadypreheated to selected temperatures between 900–1200°C for 10 mins and quenched to roomtemperature. Subsequently, the samples were mineralogically investigated. The results confirmedthose obtained from the thermodynamic calculations. Si 3N4, and SiC in particular, are suitable rawmaterials for delaying the solid-solid reactions of raw material components during melting. Owing totheir stability at high temperatures, the necessary SiO 2 content to form a liquid phase is not available,resulting in lower amounts of the liquid phase. The addition of antioxidants to delay the oxidation ofSiC further reduces this positive effect. Attempts to decrease the SiC content without negativelyaffecting the melting behaviour resulted in a reduction in the CO 2 emission by at least 27 g CO 2/kgof mould powder when compared to the carbon-containing standard mould powder. Theseinvestigations revealed differences in the melting behaviours of granules and loose powders, whichare related to their respective production processes.

KW - mold powder

KW - low carbon

KW - melting behavior

KW - carbon substitutes

KW - silicon carbide

KW - Silicon nitride

M3 - Conference contribution

VL - 3/2024

SP - 979

EP - 996

BT - MOLTEN 2024 Conference Proceedings

A2 - Hayes, Peter

A2 - Jak, Evgueni

CY - Carlton Victoria, Australia

T2 - 12th International Conference on Molten Slags, Fluxes and Salts

Y2 - 17 June 2024 through 19 June 2024

ER -