Mechanisms of interfacial reactions between 316L stainless steel and MnO–SiO₂ oxide during isothermal heating

Diffusion couple experiments were performed to study the thermodynamic and kinetic mechanisms of interfacial reactions between the 316L stainless steel and the composite MnO–SiO₂ oxide during isothermal heating at 1473 K (1200 °C) for 1, 3, 5, and 10 h and at 1173, 1273, 1373, 1473, and 1573 K (900, 1000, 1100, 1200, and 1300 °C) for 3 h. Compositional variations in the 316L stainless steel and the composite MnO–SiO₂ oxide in the vicinity of the steel–oxide interface in each diffusion couple specimen were determined. Before and after isothermal heating, thermodynamic equilibria between the oxide and steel at the interface were estimated in accordance with the calculation of the Gibbs free energy change in the interfacial steel–oxide reactions. The diffusion coefficients of Mn, Cr, and Si in 316L stainless steel under different experimental conditions were quantitatively acquired. The results showed that solid-state interfacial reactions occurred between the Cr in the 316L stainless steel and composite MnO–SiO₂ oxide during isothermal heating, which resulted in the depletion of Cr and accumulation of Si and Mn in the steel in the vicinity of the steel–oxide interface. The widths of the Cr-depleted zone, Mn-accumulated zone and Si-accumulated zone all showed increasing trends with increasing isothermal heating temperature and time. The average values of the diffusion coefficients of Mn, Cr, and Si in the steel at 1473 K (1200 °C) were 1.21 × 10^–14 ± 2.96 × 10^–15, 1.69 × 10^–14 ± 2.54 × 10^–15, and 1.00 × 10^–14 ± 1.96 × 10^–15 m² s⁻¹, respectively, and they continued to increase with increasing isothermal heating temperature.