Article ID: ISIJINT-2025-314
This study systematically investigates the dual effects of Sb on the oxidation behavior of 65Mn steel, combining laboratory experiments with industrial-scale validation. Key findings demonstrate that Sb additions significantly suppress both continuous and isothermal oxidation, with 0.03 wt% Sb reducing mass gain by 15.9% (continuous oxidation) and achieving maximal suppression of 85.2% at 800°C (isothermal oxidation), while increasing the oxidation activation energy from 184.0 kJ·mol-1 (Sb-free) to 200.7 kJ·mol-1. Notably, Sb nearly eliminates IGO at the "nose temperature" of 777.6°C, where IGO depth peaks at 18.5 μm in Sb-free specimens. However, excessive Sb (0.21 wt%) induces hot shortness due to grain boundary segregation of low-melting-point Sb-rich phases (Fe-ε(FeSb) eutectic phase), causing edge cracking during hot rolling, where industrial trials reveal local Sb enrichment exceeding 26–29 wt% at crack sites (>120× bulk content). Incomplete descaling coverage at edge regions ("descaling shadow zones") combined with localized undercooling (ΔT ≈ 120°C) promotes Sb enrichment beyond its solid solubility limit, which elucidates why Sb-induced cracking occurs exclusively at strip edges. Mechanistically, Sb enrichment at oxide/substrate interfaces blocks Fe2-/O2- diffusion, while its volatility prevents stable oxide formation, creating a kinetic barrier. The study identifies an optimal Sb content of 0.03 wt% that balances oxidation inhibition (IGO suppression >90%) with hot shortness.
