Structural State and Thermodynamic Stability of Fe-B-C Alloys

The studies were performed for the specimens of Fe-B-C alloys with boron content of 0.005 - 7.0 wt.% and carbon content of 0.4 - 5.5 wt.%, the rest was iron. From the data of microstructure analysis, X-ray structural and differential thermal analyses, we determined the primary phases formed as a result of crystallization of Fe-B-C system alloys, depending on content of boron and carbon in the alloy. As a result of the experiment carried out in this work, the phase composition and phase transformations occurring in the alloys are investigated and the liquidus surface is constructed; it is shown that the point with minimum temperature of 1375 K at the liquidus surface is observed at boron content of 2.9 wt.% and carbon content of 1.3 wt. %. For the first time, considering the contribution of the first degree approximation of high-temperature expansion of thermodynamic potential into the Gibbs energy of Fe-B-C melt, we obtain the surface of thermodynamic stability of Fe-B-C melt, depending on temperature and content of boron and carbon in the alloy. The findings show that in order to obtain the homogeneous Fe-B-C melt, which does not contain microinhomogeneous structures in the form of short-range microregions, it is necessary to perform overheating more than to 150 K.