Stress measurement in the iron oxide scale formed on pure Fe during isothermal transformation by in situ high-temperature X-ray diffraction

The stress development in the iron oxide scale formed on pure Fe during isothermal oxidation at 700 degrees C followed by isothermal transformation at 500 or 380 degrees C was measured by in situ high-temperature X-ray diffraction with the sin(2)psi method. The eutectoid transformation resulted in compressive stress generation in the Fe3O4 and Fe in the eutectoid structure. This compressive stress was relaxed during the isothermal heat treatment after the eutectoid reaction. The stress generation was ascribed primarily to volume changes associated with the oxidation and/or reduction of the iron oxide at the interfaces, Fe3O4 precipitation, and the eutectoid reaction.