TY - CONF

T1 - Effect of carbon on the melting behavior of a mold powder under high heating rates

AU - Gruber, Nathalie

PY - 2022/12

Y1 - 2022/12

N2 - Mold powders used for the continuous casting of steels contain different carbon carriers controlling the melting behavior. If carbon is not totally removed during melting, the particles accumulate at the liquid slag pool surface. This carbon layer is responsible for the recarburization of the steel, which significantly changes the product quality. Thus, to reduce or prevent the carbon absorption of the steel, mold powders with considerably reduced carbon contents or even without free carbon are required. To replace it by another melting controlling component, its effect on the melting behavior of mold powders under near process conditions, e.g. high heating rates, has to be investigated. These requirements were not satisfied in previous studies, however. Consequently, to evaluate different carbon contents on the melting behavior, a different procedure was developed: a granulated ULC mold powder was selected and different amounts of graphite were added additionally (0%, 1%, 2%, 5%). Furthermore, a sample obtained by disintegration of the granules and by adding 5% graphite was produced to see the effect of the granules in comparison to a powdery sample. Then 20 g of each powder were filled into a covered steel crucible to reduce oxygen supply. The crucibles were inserted into a preheated furnace (700-1300°C), held at selected temperatures for 10 min and quenched to room temperature. Afterwards the samples were investigated mineralogically. The results revealed that the experimental procedure is applicable for the characterization of the melting behavior of mold powders. At lower temperatures, carbon reduces reactions between raw material components due to the reduction of the particle contacts and prevents the formation of new solid phases, e.g. cuspidine, and liquid phases, respectively. With increasing carbon content reactions are shifted to higher temperatures, which further delays liquid phase formation. This effect is more evident in powdery than in granulated mold powders, because raw materials are in closer contact to the graphite particles. With increasing temperatures and simultaneous carbon oxidation, its amount was reduced in all samples. At temperatures above 1100°C, despite of their different carbon contents a similar appearance of the samples is observed. Whereas the powdery sample comprises a coherent liquid phase, granules melted independently from each other. Droplets are formed by the liquefaction of each granule, which do not agglomerate to form a coherent liquid phase. This work implies that carbon substitutes need to delay reactions between raw material components and be stable until high temperatures. Thus, nitrides or carbides are suggested.

AB - Mold powders used for the continuous casting of steels contain different carbon carriers controlling the melting behavior. If carbon is not totally removed during melting, the particles accumulate at the liquid slag pool surface. This carbon layer is responsible for the recarburization of the steel, which significantly changes the product quality. Thus, to reduce or prevent the carbon absorption of the steel, mold powders with considerably reduced carbon contents or even without free carbon are required. To replace it by another melting controlling component, its effect on the melting behavior of mold powders under near process conditions, e.g. high heating rates, has to be investigated. These requirements were not satisfied in previous studies, however. Consequently, to evaluate different carbon contents on the melting behavior, a different procedure was developed: a granulated ULC mold powder was selected and different amounts of graphite were added additionally (0%, 1%, 2%, 5%). Furthermore, a sample obtained by disintegration of the granules and by adding 5% graphite was produced to see the effect of the granules in comparison to a powdery sample. Then 20 g of each powder were filled into a covered steel crucible to reduce oxygen supply. The crucibles were inserted into a preheated furnace (700-1300°C), held at selected temperatures for 10 min and quenched to room temperature. Afterwards the samples were investigated mineralogically. The results revealed that the experimental procedure is applicable for the characterization of the melting behavior of mold powders. At lower temperatures, carbon reduces reactions between raw material components due to the reduction of the particle contacts and prevents the formation of new solid phases, e.g. cuspidine, and liquid phases, respectively. With increasing carbon content reactions are shifted to higher temperatures, which further delays liquid phase formation. This effect is more evident in powdery than in granulated mold powders, because raw materials are in closer contact to the graphite particles. With increasing temperatures and simultaneous carbon oxidation, its amount was reduced in all samples. At temperatures above 1100°C, despite of their different carbon contents a similar appearance of the samples is observed. Whereas the powdery sample comprises a coherent liquid phase, granules melted independently from each other. Droplets are formed by the liquefaction of each granule, which do not agglomerate to form a coherent liquid phase. This work implies that carbon substitutes need to delay reactions between raw material components and be stable until high temperatures. Thus, nitrides or carbides are suggested.

KW - mold powders

KW - melting behavior

KW - effect of carbon

M3 - Presentation

T2 - 2nd International Workshop of Surface Quality of Continuously Cast Products

Y2 - 1 December 2022 through 2 December 2022

ER -