High temperature oxidation of steels in air and CO2-O2 atmosphere

Three kinds of hot rolled steel slabs, viz. high strength steel, bake hardened steel and low carbon steel, were oxidized isothermally between 1100 and 1250 degrees C for up to 2 hr in 1 atm of air and an 85%N-2-10%CO2-5%O-2 gas mixture. The steels were oxidized in a similar fashion in both the atmospheres. The oxidation process followed an initial linear rate law, which then gradually transformed to a nearly parabolic rate law. Thick, porous and nonadherent scales formed rapidly, due to the high oxidation temperature. The scales formed consisted of Fe2O3,(Fe2O3+Fe3O4), (Fe3O4+Fe2O3 +FeO) and (FeO+Fe3O4) from the outer surface. The presence of supersaturated oxygen beneath the scale resulted in grain boundary oxidation and the formation of internal oxide precipitates.