In the continuous casting of ultralow carbon (ULC) steels, free carbon is used to control the melting
behaviour of mould powders. If the carbon is not completely removed during melting, it is enriched
at the top of the slag pool. Liquid steel may come into contact with this layer because of the
turbulence of the molten metal, resulting in its recarburisation, which negatively affects the desired
product quality. Thus, a reduction in carbon input is desirable. For this purpose, SiC and/or Si 3N4
with and without antioxidants were selected as melt-control additives to replace carbon in the mould
powders. Thermodynamic calculations were performed to quantify their effect on the melting
behaviour based on the chemical composition of a flux already applied to ULC steels. To
experimentally assess the liquefaction behaviour, laboratory mould powders were prepared and
annealed in steel crucibles closed with a lid. Crucibles were inserted into a furnace that was already
preheated to selected temperatures between 900–1200°C for 10 mins and quenched to room
temperature. Subsequently, the samples were mineralogically investigated. The results confirmed
those obtained from the thermodynamic calculations. Si 3N4, and SiC in particular, are suitable raw
materials for delaying the solid-solid reactions of raw material components during melting. Owing to
their 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 of
SiC further reduces this positive effect. Attempts to decrease the SiC content without negatively
affecting the melting behaviour resulted in a reduction in the CO 2 emission by at least 27 g CO 2/kg
of mould powder when compared to the carbon-containing standard mould powder. These
investigations revealed differences in the melting behaviours of granules and loose powders, which
are related to their respective production processes.