Incoloy 800H is used for high temperature section of heat transfer tubes of the first high temperature gascooled reactor nuclear power unit in China

of which the highest design temperature is 675℃.The steam oxidation properties of the Incoloy 800H at the design temperature are investigated.The structure of oxide scale of the Incoloy 800H is characterized by scanning electron microscopy (SEM)

transmission electron microscopy (TEM) and X-ray energy dispersive spectroscopy (EDS).The results show that

the oxidation kinetic curve of the 800H alloy in steam at 675℃is close to the cubic law

namely the cubic of the weight gain is nearly proportional to the oxidation time.The oxide scale has a double-layer structure.The outer layer is mainly composed of Fe_3O_4

Fe_2O_3 and a small amount of Ni

and the inner layer is Cr_2O_3 nanocrystalline with a small amount of Ni

Al_2O_3 and TiO_2 particles distributed in it.Some internal oxide particles of Cr_2O_3

Al_2O_3 and TiO_2 are distributed in the matrix metal adjacent to the oxide layer.