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

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2019-02, Vol.50 (1), p.291-303
• Main Authors: Yang, Jian, Zhang, Jianqiang, Ostrovski, Oleg, Zhang, Chen, Cai, Dexiang
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Boron oxides; Characterization and Evaluation of Materials; Chemistry and Materials Science; Crystallization; Emitters; Fluxing; Heat flux; Heat transfer; Heat treating; Liquidus; Materials Science; Metallic Materials; Mold fluxes; Nanotechnology; Raman spectroscopy; Silicon dioxide; Structural Materials; Surfaces and Interfaces; Thermal radiation; Thermocouples; Thin Films
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-018-1467-5

The reaction between traditional CaO-SiO 2 -based mold fluxes and high-Al steel inevitably changes flux composition, and, consequently, flux properties. This problem can be mitigated by using CaO-Al 2 O 3 -based mold fluxes. To maintain appropriate melting properties, CaO-Al 2 O 3 -based mold fluxes contain B 2 O 3 , which is an effective fluxing agent that decreases the liquidus temperature. In this article, the effects of B 2 O 3 on crystallization behavior, structure, and heat transfer of CaO-Al 2 O 3 -based mold fluxes were studied using single/double hot thermocouple technique, Raman spectroscopy, and infrared emitter technique. The increase of B 2 O 3 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 B 2 O 3 content increased from 7.6 to 9.6 mass pct; but a further increase of B 2 O 3 content to 13.1 mass pct did not show a visible effect on the crystallization tendency. The increase of B 2 O 3 content from 9.6 to 13.1 mass pct improved the heat fluxes under an incident thermal radiation of 1.6 MW/m 2 ; however, the increase of B 2 O 3 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.