THERMODYNAMICS OF ACICULAR FERRITE NUCLEATION

The thermodynamic driving force necessary to stimulate the nucleation of acicular ferrite and bainite is investigated for a series of high s trength weld metals, using a combination of dilatometry, scanning elec tron microscopy, and thermodynamic calculations. The results indicate that the nucleation of acicular ferrite and bainite can be represented by the same thermodynamic model. It therefore appears that the nuclea tion mechanism of acicular ferrite on non-metallic inclusions in weld metals is essentially similar to that of bainite at the austenite grai n boundaries. Metallographic observations confirm the notion that acic ular ferrite is essentially intragranularly nucleated bainite.