In situ X-ray diffraction of surface oxide on type 430 stainless steel in breakaway condition using synchrotron radiation

Changes in the crystal structure of type 430 stainless steel and the oxides on its surface were studied in situ at 1373 K using a high-intensity synchrotron X-ray source provided by SPring-8 in Japan. The surface of the steel was initially covered with Cr2O3, which was then converted to FeCr2O4, and finally Fe3O4 and Fe2O3 formed on it. These results indicated that the reason for the breakaway oxidation in type 430 stainless steel is Cr depletion beneath Cr2O3 layer and the subsequent ionisation of Fe, not the simple mechanical failure of Cr2O3.

► Breakaway studied with Synchrotron radiation X-ray.
► Local equilibria between phases established during high-temperature oxidation.
► Chemical failure model well describes the breakaway.