Oxide Scale Decomposition‐Driven Intergranular Oxidation in Hot‐Rolled Hot Stamping Steel: Mechanism and Process Control

Intergranular oxidation (IGO) in 22MnB5 steel degrades automotive component performance, yet oxygen supply mechanisms under low oxygen potentials remain unclear. This study reveals that IGO occurs exclusively below 900 °C, with the depth exhibiting a C‐curve temperature dependence with a 751 °C nose temperature. Depth evolution follows logarithmic kinetics rather than Wagner’s parabolic law due to grain boundary diffusion channel blockage. Crucially, the oxide scale decomposition‐driven oxygen supply mechanism is systematically quantified for the first time: Under vacuum, oxide scale decomposition releases oxygen that propagates IGO to 26.4 μm after 8 h at 750 °C—a 136% increase over conventional oxidizing conditions—causing monotonic depth growth deviating from classical C‐curve behavior. Focused ion beam–energy‐dispersive X‐ray spectroscopy reveals a core–shell oxide structure (SiO 2 core/Cr 2 O 3 inner shell/MnO outer shell) governed by selective oxidation thermodynamics and diffusion kinetics. Industrial validation confirms 15 μm IGO depth in hot coil slow‐cooling zones, matching laboratory FeO decomposition results. Accordingly, optimized processing—lower coiling temperatures, front‐stage laminar cooling, and forced post‐coil cooling—was validated to suppress IGO below 5 μm. This work establishes a thermodynamic–kinetic framework for IGO in hot stamping steels, bridging fundamental mechanisms with industrial practice to resolve surface quality degradation through targeted process control strategies.