Exploring Inhibition Mechanism of Si on Cementite Nucleation in Hypereutectoid Steel: Experiments and First-Principles Calculations

Abstract

To clarify the influence of Si on cementite nucleation during the solidification of hypereutectoid steel, the types and microstructure of cementite in hypereutectoid steel with various Si concentrations were investigated by X-ray diffraction and scanning electron microscopy. Additionally, the interfacial properties of γ-Fe/Fe3C were studied using the first-principles density functional theory, including work on adhesion, interfacial energy, and electronic structure, with the aim of elucidating the impact mechanism of Si on the cementite nucleation. The results showed that increasing Si concentrations (0–0.42 wt.%) had a negligible effect on the types of cementite in as-cast hypereutectoid steel. However, the average number of cementite lamellae per unit area decreased significantly, indicating that an increase in Si concentrations has an inhibitory effect on cementite nucleation. This can be attributed to the effect of Si on the interfacial properties of γ-Fe (010)/Fe3C (010), where the presence of Si disrupts the charge distribution of the γ-Fe (010)/Fe3C (010) interface and decreases the hybridization of atom orbits on each side of the interface, resulting in a decrease in the interatomic interaction force. This is reflected in the decrease in the work of adhesion (from 6.92 J·m−2 to 6.78 J·m−2) and the increase in the interfacial energy (from −1.42 J·m−2 to −1.31 J·m−2). As a result, the stability of the γ-Fe (010)/Fe3C (010) interface is reduced, making it difficult for the composite structure to form. This indicates that Si doping inhibits cementite nucleation on austenite.