Selective Oxidation of Fe-Cr-Mn Stainless Steel in Supercritical Water

Oxidation of austenitic Fe-Cr-Mn stainless steel (Nitronic® 32) in supercritical water (25 MPa) was assessed to determine the (i) ability to form a ferrite surface layer from selective oxidation of Mn and (ii) protection provided by the oxide scale. X-ray diffraction and electron microscopy techniques revealed a layered oxide scale forms, complete with a ferrite surface layer within a zone depleted of alloying elements after 500 h at 550°C. While intact during immersion, the oxide spalled during cooling, indicating a sensitivity to thermal stresses. The suitability of Fe-Cr-Mn alloy fuel claddings for the supercritical water-cooled reactor concept is discussed.