Liquidus Surface Projection of the Fe-Nb-C System in the Iron-Rich Corner

Abstract

In the present study, the liquidus surface projection of the Fe-Nb-C system is proposed in the iron-rich corner using different techniques (differential thermal analysis (DTA), optical microscopy, scanning electron microscopy with energy dispersive X-ray analysis (EDX), and quantitative electron probe microanalysis (EPMA)). Thus, the primary crystallization phases, γ(Fe), δ(Fe), NbC1−x , and Fe2Nb, are identified. In addition, three invariant ternary reactions are proposed: two invariant eutectic ternary reactions: L ↔ δ(Fe) + Fe2Nb + NbC1−x and L ↔ γ(Fe) + NbC1−x + Fe3C; and a quasi-peritectic reaction: L + δ(Fe) ↔ γ(Fe) + NbC1−x as well as the univariant reactions in solid phase. However, the univariant line separating the primary crystallization surfaces δ(Fe) and NbC1−x goes through a maximum; the temperature is estimated in this work at 1456 °C < T < 1457 °C.