THE EFFECT OF OXYGEN CONCENTRATION ON THE OXIDATION OF LOW-CARBON STEEL IN THE TEMPERATURE-RANGE 1000 TO 1250-DEGREES-C

This paper describes the oxidation behavior of low-carbon steel sample s in binary gas mixtures of oxygen and nitrogen, at oxygen concentrati ons ranging between 1% and 15% and temperatures ranging between 1000 a nd 1250 degrees C. Sample weight gains versus time were analyzed, alon g with measurements and calculations of sample heating rates due to ex othermic heat of reaction at the sample surface. It was found that ini tial rates of oxidation depended on oxygen content in the gas mixture and that these reaction rates were linear up to oxide thicknesses of 0 .4 to 0.5 mm. Calculations of linear oxidation rate constants based on equations for mass transport of oxygen in the gas mixture to the samp le surface showed good agreement with those measured experimentally, i ndicating that the initial period of oxidation is controlled by the ma ss transport of oxygen to the reaction interface. The linear rate cons tants showed little dependency on temperature, an activation energy of approximately 17 kJ/mole being obtained. Measurements of sample surfa ce temperatures have shown that within this linear-oxidation regime, i nterfacial temperatures of the samples increase with increasing oxygen contents in the gas mixture, owing to exothermic heats of oxidation. Subsequent oxidation kinetics were found to be parabolic. Measured par abolic rates constants were in good agreement with previous investigat ions, with activation energy values of approximately 127 kJ/mole.