A new insight into high-temperature oxidation mechanism of super-austenitic stainless steel S32654 in air

High temperature oxidation behavior and mechanisms for super-austenitic stainless steel S32654 were investigated at 900, 1000 and 1200 degrees C in air. The oxide layers were characterized by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), electron-probe microanalysis (EPMA), x-ray diffraction (XRD) and transmission electron spectroscopy (TEM). At 900 degrees C, oxidation follows parabolic law within the initial 10 h, and the external solid MnMoO4 molybdate oxide layer and the internal spinel oxide layer prevent oxygen or metal cations diffusion. The parabolic law then changes to a linear law due to the molten MnMoO4-MoO3 molybdate electrochemical reaction and oxide layer cracking. At 1000 and 1200 degrees C, oxidation follows linear law. The nitrogen in air plays a very important role in accelerating oxidation. The synergistic effects of the molten MnMoO4-MoO3 molybdate electrochemical reaction and discontinuous Cr2N precipitation strongly promote catastrophic oxidation. (C) 2016 Elsevier B.V. All rights reserved.