Quantitative measurements of phase equilibria at migrating α/γ interface and dispersion of VC interphase precipitates: Evaluation of driving force for interphase precipitation

For better industrial application of nano-sized interphase precipitates formed at migrating ferrite (α)/austenite (γ) interface during α transformation, microstructural control on its dispersion is of great significance. Although the driving force for its precipitation was known to be one of the important factors, the estimation on its value in literature without experimental supports was still questionable. Therefore, the present study aimed to quantitatively estimate the driving force for interphase precipitation based on experimental investigation in a series of V-added alloys isothermally transformed at various temperatures. Field emission-electron probe microanalysis (FE-EPMA) on α/γ interfacial C content reveals that α/γ phase equilibria can be well explained by negligible-partition local equilibrium (NPLE) model. Both number density and average radius of VC interphase precipitates quantified by using three-dimensional atom probe (3DAP) show good correlations with the calculated driving force for interphase precipitation at migrating α/γ interface under NPLE condition. Larger size of VC than the expected one from the driving force implies the possible growth after its nucleation at migrating α/γ interface.