Investigation of the Selective Oxidation Process for High Strength Steels

Abstract

In the present work, a 1D implicit model has been developed to simulate simultaneous diffusion of chemical species and precipitation of simple and mixed oxides in the steel matrices for different alloy compositions and dew points. Thermo Gravimetric Analysis has been done by heating the samples (Fe-1.58 wt.% Mn) at 15 K/min and holding them at the peak temperatures of 650 ℃,750 ℃ and 850 ℃ for 2 h in an atmosphere of Ar + CO + CO₂, having CO₂/CO ratio of 1, 2 and 3 followed by cooling at 15 K/min. From the precipitation simulation at 800 ℃ temperature and −40 ℃ dew point for 1.235, 1.58, 2.52, 3.58 wt. % Mn steel, internal oxidation depth of 0.38 µm was obtained. Increase in dew point results increase of internal oxidation zone’s depth exponentially. The simulation data of Fe-1.225 wt.% Mn-0.075 wt.% Si steel oxidised at 800 ℃ at −40 ℃ dew point shows precipitation of MnO solely at the surface node while SiO₂ precipitate over a large region (up to 0.98 µm depth). Parabolic growth followed by linear growth has been observed from the TGA graphs. With increasing temperature, parabolic region decreased and linear growth dominates. Top surface morphology of the oxidised sample changes with increasing temperature and the oxide particle size found to be increase with increasing CO₂/CO ratio.