Corrosion behavior of 304 stainless steel in high temperature, hydrogenated water

The corrosion behavior of an austenitic stainless steel (UNS S30400) has been characterized in a 10,000 h test conducted in hydrogenated, ammoniated water at 260 degreesC. The corrosion kinetics were observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 1.16 mg dm(-2) h(=1/2). X-ray photoelectron spectroscopy, in combination with argon ion milling and target factor analysis, was applied to provide an independent estimate of the rate constant that agreed with the gravimetric result. Based on the distribution of the three oxidized alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, it was found that: (a) corrosion occurs in a non-selective manner, and (b) the corrosion film consists of two spinel oxide layers-a ferrite-based outer layer (Ni0.2Fe0.8)(Fe0.95Cr0.05)(2)O-4 on top of a chromite-based inner layer (Ni0.2Fe0.8)(Cr0.7Fe0.3)(2)O-4. These compositions agree closely with the solvi phases created by immiscibility in the Fe3O4-FeCr2O4 binary, implying that immiscibility plays an important role in the phase separation process. (C) 2002 Elsevier Science Ltd. All rights reserved.