INFLUENCE OF HIGH-TEMPERATURE TREATMENT ON THE COMPOSITION AND STRUCTURE OF SCALE ON 25KH3M3NBTSA

The chemical composition of the skin formed on 25Kh3M3NBTsA steel afte r low-(20 degrees C) and high-temperature (900 degrees C, 5.5 hr) oxid ation is determined by X-ray photoelectron spectroscopy, with layer-by -layer analysis. The oxidation mechanism is analogous to catastrophic oxidation and involves the participation of MoO3 and MoO2, which are f ormed after the oxidation of the intermetallide Fe2Mo. Most of the oxi de scale (75-98%) is ferrochrome spinel, with the partial introduction of Ni2+ ions in its crystal lattice. The skin includes molybdenum tri oxide and dioxide and complex oxides based on them: Cr2O3. MoO3, Cr2O3 . 3MoO(3), NiO . MoO2, NiO . MoO3. In the presence of Nb (0.11 mass %) , the complex nonstoichiometric oxide ZrO2-delta (delta approximate to 0.19) with possible oxygen anionic conductivity, stabilized by the ox ides of Cr3+, Nb3+, and Nb2+, may appear in the scale after low-temper ature oxidation of the steel. The compound Zr2Nb2O7 and compounds of t ype MeNbO4 (Me = Fe3+, Cr3+) may be formed in the scale after high-tem perature oxidation when the steel contains niobium, The scale contains considerable quantities of chemosorbed oxygen.