Investigation of the Liquidus Line on the Fe-B State Diagram
Abstract
In this paper we determine the crystallization temperature of a melt of the Fe-B system depending on the boron content and. The thermodynamic properties of the boron-bearing phases are studied. The investigation was performed for alloys with the boron content of 2.0-4.2.0% (wt.), the rest is iron. The smelting of Fe-B system alloy was carried out in a furnace in alundum saggers in the argon atmosphere. The cooling rate of as-cast alloys was 10 K/s. To ascertain the structural condition of alloys we used the microstructure analysis, the differential thermal and the X-ray structural analyses. In the paper, based on experimental data for the Fe-B alloys, we determined the crystallization temperatures of alloys under consideration, depending on the content of boron in the alloy. In addition, we revealed that the γ-Fe+Fe2B eutectic transformation occurs at the temperature of 1441 K and at the boron content of 3.8% (wt.). To determine the thermodynamic functions of the phases we used the quasi-chemical method. With accounting for the contribution of the first degree approximation of the high-temperature expansion for the thermodynamic potential we derived expressions for the free energy of the melt of the binary Fe-B alloy, the boron-doped austenite and the Fe2B boride. The expressions obtained for the free energy potential and the chemical potential of the melt of the binary Fe-B alloy, the austenite and the Fe2B boride enable to obtain the Fe-В phase diagram liquidus boundaries. The calculations performed in this paper made it possible to obtain the numerical values of the crystallization temperature of the alloy, depending on the boron content, and to determine the temperature of the γ-Fe+Fe2B eutectic transformation and the boron content, at which this transformation takes place in the alloy. Such an approach allows describing most completely from the thermodynamic point of view the crystallization process and the eutectic transformation. The results of the calculations obtained in this paper are in good agreement with the experimental data.
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References
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