This study addresses the strength-plasticity trade-off induced by elevated carbon content in high-carbon steel through performance optimization via trace niobium microalloying, focusing on enhancing the stability of undercooled austenite. Combined with thermal simulation experiments and first-principles calculations, the multi-scale regulation mechanism of solid solution niobium on austenite stability was systematically elucidated. The results show that solid solution niobium can significantly reduce the pearlite transformation temperature (the maximum decrease is 44 \(^{\circ }\) C) and inhibit the recrystallization of austenite, indicating that Nb can significantly enhance the stability of undercooled austenite. The study of the microscopic mechanism shows that niobium enhances the bonding strength between Fe atoms by reconstructing the charge density distribution of austenite matrix, improves the lattice binding energy, significantly improves the elastic modulus, causing the phonon spectrum to have no imaginary frequency, and simultaneously enhances the mechanical and thermodynamic stability of austenite. At the same time, solid solution niobium doubles the carbon diffusion barrier, effectively blocks the migration of carbon atoms and delays the phase transformation process, further enhancing the stability of undercooled austenite. These findings provide theoretical underpinnings for mitigating the strength-plasticity trade-off in high-carbon steels, offering significant engineering implications for developing ultra-high-strength hard wire steels.
