Thermodynamics of acicular ferrite nucleation

Abstract

The thermodynamic driving force necessary to stimulate the nucleation of acicular ferrite and bainite is investigated for a series of high strength weld metals, using a combination of dilatometry, scanning electron 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 nucleation mechanism of acicular ferrite on non-metallic inclusions in weld metals is essentially similar to that of bainite at the austenite grain boundaries. Metallographic observations confirm the notion that acicular ferrite is essentially intragranularly nucleated bainite. MST/1897