Abstract
Cyclic hot corrosion conducted on Haynes 230 at temperatures of 871 and 1093δ C indicated that catastrophic corrosion occurred. The corrosion rate was related to the high content of tungsten and chromium in the alloy. The concept of basic and acid fluxing was applied to explain the dissolution of the protective film of Cr2O3 and volatile WO3 by an Na2SO4-rich liquid due to the formation of Na2CrO4 and Na2WO4. As the basic melts were acidified by continuously consuming oxygen ions, plate-like crystals of Cr2O3 were precipitated on the free surface by conversion from Na2CrO4. Acid fluxing was achieved by the refractory oxide, WO3, consuming oxygen ions. The presence of sulphur suppressed the diffusion of chromium outward to form protective Cr2O3. Internal chromium-rich sulphide particles were observed. It was suggested that at very lowPO2, sulphur reacted with chromium to form CrS initially. As oxygen penetrated through the porous layer, the CrS was oxidized internally to Cr2O3.
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