Effect of Si Content and Temperature on Oxidation Resistance of Fe-Si Alloys

Hot-rolled Fe-(0.75-2.20)Si (mass%) alloys were oxidized in dry air at 600-1200 degrees C. The oxidation process was carried out by thermal gravimetric analysis (TGA). At 600-1150 degrees C, oxidation gain curves were approximately parabolic. Electron probe microanalysis (EPMA) was applied to investigate cross-section morphology of oxide layer and element distribution across the layer. At lower temperature of 700 degrees C, the oxide layer consisted of internal oxidation zone (IOZ), inner Si-rich layer (conglomerate of fayalite and magnetite) and outer hematite layer, while at higher temperature of 1200 degrees C, fayalite and wustite were observed in external oxide scale. Liquidus temperature of fayalite was detected by differential scanning calorimetry (DSC). Through comparing the oxidation mass gain and parabolic rate constant of the alloys, it was found that oxidation resistance of Fe-Si alloy was enhanced by increasing Si content below 1150 degrees C while increasing Si content of the alloy resulted in higher oxidation rate above 1150 degrees C owing to the liquid fayalite formation.