Shohei Nakakubo

Calculation of Boundary Conditions between Internal and External Oxidation of Silicon or Chromium Containing Steels

The boundary constants between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were calculated in order to clarify the formation mechanism of fayalite scale (Fe2SiO4) or chromite scale (FeCr2O4), which can form as a “sub-scale” in Si or Cr containing steels. The diffusion coefficient of oxygen in the alloy, Do, and the oxygen concentration at the specimen surface, NO(s), which are constituents of the internal oxidation rate constant, (2DONO(s)/NB(O)n), were calculated for various oxidation conditions, and the rate equation for internal oxidation was derived. By comparing the calculated and measured values of (2DONO(s)/NB(O)n), we confirmed that the rate equation determined for internal oxidation was reasonable. The boundary condition between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were also calculated by substituting the calculated values of DO and NO(s) into the rate equation.