New insights of heterogeneous nucleation and anisotropic growth of acicular ferrite on non-metallic inclusion

Abstract

This work studies the acicular ferrite (AF) nucleation and growth from a classical defect, i.e. non-metallic inclusion surface. The heterogeneous AF-nucleation probability on NMI is predicted by a mathematical model following the classical nucleation theory. The calculation results are in consistent with the experimental data. The current model includes the exact form of the activation energy and Zeldovich factor for heterogeneous nucleation on pre-existing spherical surface. It generates an interaction map that for the first time quantitatively describes the superposition influences of the interfacial energies and NMI-size on the AF-nucleation potency. In the AF-growth aspect, we systematically reveal the single AF-plate evolution behavior through the synergy between the experimental observations and multiphase-field simulations. It is found that the AF-tip morphology is impacted by the misorientation angle between the favorable growth direction and normal vector. It also influences the AF-lengthening and widening kinetics. Additionally, the anisotropic stress field induced by the AF-NMI interface plays a significant role in controlling the complex curvature of the AF-plate. The current study opens new perspectives for understanding the AF-precipitation mechanisms.