Identification of secondary raw materials in mold powders and their melting behavior

Irmtraud Marschall,Christina Atzenhofer,Harald Harmuth,Nathalie Kölbl

doi:10.1007/s42243-019-00254-6

Irmtraud Marschall, Christina Atzenhofer + Show 2 more

Open Access

https://doi.org/10.1007/s42243-019-00254-6

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Abstract

Commercial mold powders use a limited number of main mineral constituents, but may differ significantly in chemical composition. The main mineral raw materials of specimens investigated here are quartz, fluorite and free carbon, as well as wollastonite and carbonates. The investigations revealed the use of secondary raw materials like blast furnace slag, fly ash, glass scrap and phosphorous slag as further components. Since the formation of cuspidine was one major point of interest, the influence of the silica source on its formation was identified. A replacement of wollastonite by blast furnace slag reduced the temperature of the first precipitation of cuspidine by about 100 °C; the dissociation of sodium carbonate was lowered by ~ 40 °C. The lowest temperature of the first Na2CO3 dissociation could be achieved by using fluorine in combination with blast furnace slag. Cuspidine formation from the melt is further decreased if sodium and fluorine are both present. The use of glass scrap and phosphorous slag strongly reduced the temperature of first melt formation and enhanced cuspidine formation.

Highlights

Mold powders are used in the continuous steel casting process and are added to the meniscus in the mold to facilitate this procedure
In the case of a granulation process with spray drying, a precipitation process leads to the formation of shortite (Na2Ca2(CO3)3) and/or gaylussite (Na2Ca(CO3)2 Á 5H2O), and this process is similar to known reactions in the glass industry [29]
A combined use of fluorite and blast furnace slag leads to the lowest temperature of first dissociation of carbonates

Summary

Introduction

Mold powders are used in the continuous steel casting process and are added to the meniscus in the mold to facilitate this procedure. Due to the high temperatures within the mold, the powder melts and infiltrates the gap between the mold and the strand to act as a lubricant and to control the heat flow. One of the most important concerns in the continuous casting process is providing stable casting conditions and guaranteeing the appropriate product surface qualities. The melting behavior of the mold powder is of major importance since it controls the liquid slag pool depth on the meniscus [1, 2]. The size and shape of the slag rims formed in the meniscus zone are affected by the melting properties of the powder [3,4,5]. Only the chemical composition of the material is reported on the data sheet, but the melting procedure is

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