The mechanical property of the oxide scale on Fe-Cr alloy steels

In this study, we investigated the influence of the Cr content on the microstructure and interfacial adhesion of the oxide scale formed on steel alloys. The four different alloys selected for this study are stainless steels and low- and medium-carbon steels with different Cr and Si contents. The model steels were oxidized at 1100-1200 degrees C for 4-5 h. The types of oxide phases in the scale were analyzed by X-ray diffraction (XRD), and the results were compared with the phases predicted by thermodynamic calculations. The cross-sectional scale microstructures were analyzed by electron probe micro-analysis (EPMA). The interfacial adhesion strength of the scale with the model alloys were analyzed by a uniaxial tension test. According to our results, continuous Cr-oxide layers are formed along the interfaces; the thickness of these layers proportionally increases with Cr, while the total thickness of the scale is inversely proportional to the Cr content. The thick Cr-oxide layers seem to hinder the interdiffusion of Fe and O between the scale and the substrate, which decreases the growth rate of Fe-oxides on the top surface. The predicted phases in the scale and the minimum oxygen partial pressure at which each oxide phase is formed agree well with the microstructural analysis results. Our results also revealed that the Cr-oxide layers survived the tension test for up to 5% of the strain, whereas the scale on top of the Cr-oxides cracked and delaminated. Based on these results, the Cr content determines the adhesion strength of the scale. (C) 2012 Elsevier B.V. All rights reserved.