The oxidation behavior of iron polycrystals and single crystals with (110) surface orientation was studied at 450°C. Energy-dispersive diffraction with synchrotron radiation provided in situ information regarding the evolution of stress gradients and fiber texture in the oxide scales. Within this low-temperature regime, grain boundaries caused the oxidation kinetics of polycrystalline iron to be more rapid than iron single crystals only during the first minutes of oxidation. Epitaxial growth of iron oxides occurred only on single crystal substrates during the initial oxidation. In situ stress analyses suggested that stress relief occurred invariably in the magnetite layer due to the formation of a fine-grained seam near the iron substrates. Above the magnetite and in the hematite layer, the growth stresses depend initially on volumetric strains and later on inner oxide formation and creep of the hematite.

The evolution of microstructure and growth stresses in oxide scales grown on a (110) iron single crystal surface at 650°C was studied by electron backscatter diffraction and in situ energy-dispersive diffraction with synchrotron radiation. Within this high temperature regime, the oxidation kinetics and scale microstructure were not significantly different from those encountered in the oxidation of ferrous polycrystals. Thus, epitaxial strains did not determine the stress state within the oxide scale. Relevant sources of growth stresses were inferred to be volumetric differences between the iron oxides in the early stages, and later, inner oxide formation, scale consumption as well as pore formation. These sources caused time-dependent stress cycles in magnetite and wüstite during oxidation. In the hematite layer stress cycles did not occur and creep appeared to be the predominant stress relieving mechanism. On cooling, the differences in thermal expansion caused residual stress gradients through the oxide scale.

Mass gain during oxidation, texture and residual stresses in oxide layers on polycrystalline Armco iron substrates with different surface conditions are investigated using thermogravimetry microscopy and synchrotron X-rays. The mass gain during oxidation in all samples follows a parabolic law. The parabolic oxidation constant increases with increasing roughness of a mechanically ground respectively polished oxide layer. Electrolytic polishing (grain surface etching) reduces while grain boundary etching increases the parabolic oxidation constant compared to the mechanically polished sample. All oxide layers show columnar growth of the magnetite and a moderate fiber texture. The magnetite contains compressive residual stresses. Under the conditions chosen for the oxidation treatment the magnitude of these compressive residual stresses does not depend on the substrate surface condition.

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