Effectiveness evaluation model of oxide metallurgy for non-metallic inclusions in steel

Oxide metallurgy technology demonstrates remarkable effectiveness in refining material microstructures.This strengthening mechanism is closely related to the interface characteristics between non-metallic inclusions and the matrix. Based on the two-dimensional mismatch theory and interface nucleation theory, a theoretical model was established to systematically evaluate the effectiveness of non-metallic inclusions in oxide metallurgy, and performed calculation verification with typical TiN inclusions as an example. First, the lattice matching of TiN with ferrite and austenite was calculated by the two-dimensional mismatch theory. The results show that the mismatch of TiN(100)/BCC-Fe(100) and TiN(110)/BCC-Fe(110) is 4. 61%, indicating that TiN can serve as a potential substrate for ferrite nucleation. In contrast, the mismatch between TiN and austenite is large, making it difficult to form a stable interface structure. Subsequently, based on the surface convergence test, 5-layer BCC-Fe, 7-layer FCC-Fe and 9-layer TiN surface structures were selected to establish the interface structures. First-principles calculations of interface energies reveal that the adhesion work of TiN/FCC-Fe interfaces is negative, confirming that TiN cannot serve as a nucleation core for austenite. Instead, it hinders austenite grain growth and acts as a pinning mechanism. TiN/BCC-Fe interfaces exhibit positive adhesion work, indicating that TiN can effectively induce ferrite nucleation. Notably, the interface energy of TiN/BCC-Fe is significantly lower than that of TiN/FCC-Fe. This thermodynamic advantage provides a theoretical basis for the nucleation of ferrite within austenite. In the TiN/BCCFe system, the TiN(100)/BCC-Fe(100)-N interface has the larger adhesion work and the lowest interface energy, demonstrating the strongest stability. The electronic structure analysis reveals that Fe—N ionic bonds are formed at the interfaces of TiN(100)/BCC-Fe(100)-N, TiN(110)/BCC-Fe(110)-Ti and TiN(110)/BCC-Fe(110)-N. The study results provide a new theoretical perspective for understanding the inclusion-induced phase transformation mechanism in oxide metallurgy.