Thermodynamics of Oxygen Solution in Fe–Ni Melts Containing Boron

Abstract

Fe–Ni alloys are widely used in engineering today. They are sometimes alloyed with boron. Oxygen is a harmful impurity in Fe–Ni alloys. It may be present in dissolved form or as nonmetallic inclusions. The presence of oxygen in Fe–Ni alloys impairs their performance. Research on the thermodynamics of oxygen solutions in Fe–Ni melts containing boron is of considerable interest in order to improve alloy production. The present work offers a thermodynamic analysis of solutions of oxygen in Fe–Ni melts containing boron. The equilibrium constant of the reaction between boron and oxygen dissolved in the melt in such systems is determined. The activity coefficients at infinite dilution and the interaction parameters in melts of different composition are also calculated. When boron reacts with oxygen in Fe–Ni melts, the oxide phase contains not only B2O3 but also FeO and NiO. The mole fractions of B2O3, FeO, and NiO in the oxide phase are calculated for different boron concentrations in Fe–Ni melts at 1873 K. For iron melts with low boron content, the mole fraction of boron oxide is ~0.1. With increase in the nickel and boron content in the melts, the boron-oxide content in the oxide phase increases. Its mole fraction is close to one for pure nickel. The solubility of oxygen in Fe–Ni melts is calculated as a function of the nickel and boron content. The deoxidizing ability of the boron improve significantly with increase in nickel content in the melt. The curves of oxygen solubility in Fe‒Ni melts containing boron pass through a minimum, which is shifted to higher boron content with increase in nickel content in the melt. The boron content at the minima on the curves of oxygen solubility are determined, as well as the corresponding minimum oxygen concentrations.