Weak influence of ferrite growth rate and strong influence of driving force on dispersion of VC interphase precipitation in low carbon steels

Dispersion of nano-sized alloy carbides formed by interphase precipitation at migrating ferrite/austenite interphase boundaries is expected to be affected by local conditions at the boundaries, including ferrite growth rate and driving force for precipitation. The effects of these two factors were systematically investigated by changing alloy composition and transformation temperature. Quantitative analyses by using three-dimensional atom probe reveal that VC interphase precipitation becomes higher in number density and smaller in size at lower transformation temperature or with higher V content. The dispersion of VC is also slightly refined by lower Mn or higher Si content, but remains almost unchanged by increasing the C content. Such variations show good correlations with the driving force for its precipitation that finer VC precipitates can be obtained by enlarging the driving force. In contrast, the influence of the ferrite growth rate on the dispersion in most cases is quite small in the range of this study, which can be explained by considering nucleation kinetics of VC at migrating ferrite/austenite interface.