Effects of B2O3 on Crystallization, Structure, and Heat Transfer of CaO-Al2O3-Based Mold Fluxes

Abstract

The reaction between traditional CaO-SiO2-based mold fluxes and high-Al steel inevitably changes flux composition, and, consequently, flux properties. This problem can be mitigated by using CaO-Al2O3-based mold fluxes. To maintain appropriate melting properties, CaO-Al2O3-based mold fluxes contain B2O3, which is an effective fluxing agent that decreases the liquidus temperature. In this article, the effects of B2O3 on crystallization behavior, structure, and heat transfer of CaO-Al2O3-based mold fluxes were studied using single/double hot thermocouple technique, Raman spectroscopy, and infrared emitter technique. The increase of B2O3 content from 7.6 to 13.1 mass pct suppressed the crystallization tendency of mold fluxes in continuous cooling experiments and isothermal experiments conducted over 1273 K (1000 °C). The isothermal crystallization below 1273 K (1000 °C) was also inhibited when B2O3 content increased from 7.6 to 9.6 mass pct; but a further increase of B2O3 content to 13.1 mass pct did not show a visible effect on the crystallization tendency. The increase of B2O3 content from 9.6 to 13.1 mass pct improved the heat fluxes under an incident thermal radiation of 1.6 MW/m2; however, the increase of B2O3 content from 7.6 to 9.6 mass pct slightly decreased the heat transfer rate. Crystallization of fluxes and heat transfer were discussed in relation to flux structure.