Carbide eutectic in vanadium steels

Abstract

1. Eutectic equilibrium is observed in vanadium steels with a low carbon and vanadium content: L⇌γ+VC. Due to strong dendritic segregation of vanadium the eutectic crystallization (L→γ+VC) can occur with a vanadium content∼0.1%. 2. During eutectic solidification of rapidly cooled pure vanadium steels a more or less fine vanadium carbide eutectic is formed. The colonies (grains) consist of a continuous skeleton of vanadium carbide with threadlike and lamellar branches and an austenitic matrix. Pseudoprimary cross-shaped crystals of vanadium carbide are often observed in the eutectic, which are the crystallization centers of eutectic colonies. 3. Complete separation of the phases occurs easily during eutectic crystallization, particularly with slow cooling, and the eutectic proper is not formed; more or less large crystals of vanadium carbide are observed in the boundaries of dendritic branches of austenite. 4. The melting point of the vanadium carbide eutectic varies greatly with the carbon and vanadium content of the steel — it decreases from∼1360° for steels with∼0.4% C and 0.5% V to∼1250° for steels with 1.7 and 2.8% V. 5. In analyzing the effect of vanadium on the structure and properties of steels one must take into account the strong dendritic segregation — the substantial increase of the vanadium concentration in the peripheral sections of dendritic branches and the possibility of eutectic carbides being formed in their boundaries even when the vanadium content of the steel is low.