On the oxidation of steel in CO/sub 2/ and air

Abstract

Oxidation of a low alloy 0.3% carbon steel (SAE 4130) was investigated using SEM, X-ray diffraction and optical metallography. Closed cylindrical specimens were treated at 860/spl deg/C for up to 2h in air and carbon dioxide, under pressure in the range of 0.1-0.7 MPa. At the initial stage, wustite grew through the coalescence of small clusters of crystallites. The size of wustite grains was dependent on the kind of gas and independent of the gas pressure. The time dependence of wustite grain growth has been studied. It was found that during the initial stage of oxidation wustite grains grow epitaxially and by grain coalescence. Isothermal transformation of wustite into magnetite (Fe/sub 3/O/sub 4/) was studied in the temperature range of 550/spl deg/C-610/spl deg/C. The results suggest that it may be possible to have the desired proportion of wustite and magnetite, which can be controlled by the processing environment.