The properties of top slags play a very important role in secondary steelmaking. Fluxes should be
chosen based on the ladle furnace (LF) slag requirements like viscosity, melting temperature, sulfide
capacity, etc. CaF2 and CaO-Al2O3-based synthetic slags are the most used fluxes in secondary
steelmaking to improve slag fluidity and interfacial chemical reactions. CaF2 is obsolete due to
fluorine pollution and CaO-Al2O3 based slags have 40–50 wt per cent Al2O3 and 30–40 per cent CaO
which is not beneficial for desulfurisation. Yet another drawback is that LF slag disintegrates into fine
powder during cooling due to phase transformation C2S (2CaO.SiO2). Hence, there is a need for the
development of low melting fluxes with high CaO content and the capability to prevent slag
disintegration. The current work studied the effect of 0–9 wt per cent B2O3 on physico-chemical
properties and characterisation of LF slags. X-ray diffraction (XRD) analyses were carried out to
identify mineralogical phases present in slag and Fourier-transform infrared spectroscopy (FT-IR)
analysis was done to understand the changes in bonds of B2O3 added LF slag. The characteristic
temperature of slag was determined by a hemispherical method using high-temperature microscopy.
Empirical models were used to calculate viscosity, break temperature, and sulfide capacity.
FactSage™, ver 8.2 (by GTT-Technologies) simulations were carried out to find the equilibrium
phase fractions and percentage of liquid slag at different temperatures. New phases such as
Ca11B2Si4O22 and Ca2B3O5 were formed in LF slag with B2O3 addition. Based on the results, 0.5–1.0
wt per cent B2O3 was found to be sufficient to prevent C2S-driven disintegration of LF slag. Also, the
melting temperature and viscosity of LF slag were reduced by adding 3–8 wt per cent B2O3 due to
the formation of BO3 planar triangular structure and low melting eutectics in slag. Liquid slag started
forming at a temperature as low as 800°C when B2O3 is >6 wt per cent. It was found that the sulfide
capacity, viscosity, and break temperature of the slag decreased with increasing wt per cent B2O3.
Based on the analysis carried out, B2O3 can be a promising fluxing material in secondary
steelmaking, for improving the desulfurisation kinetics and valourisation potential of LF slag.