The effect of SO2(g) on the initial oxidation of the stainless-steel 304L, sprayed with 0.1 mg/cm2 KCl and exposed in 5% O2 and 40% H2O at 600 °C, was investigated. In the absence of SO2(g), KCl accelerates the corrosion attack by the formation of K2CrO4. The reaction with KCl depletes the oxide in chromium and converts it into an iron-rich, poorly protective oxide. When SO2(g) was introduced to the gas flow, KCl rapidly transformed into K2SO4. In contrast to KCl, K2SO4 does not form K2CrO4. Hence, it does not accelerate the corrosion rate. Although the conversion of KCl to K2SO4 is fast, the corrosion rate of KCl samples exposed in the presence of SO2(g) is higher than samples exposed in the presence of K2SO4. It is therefore suggested that small amounts of unreacted KCl react initially with the protective oxide, forming K2CrO4, which depletes the oxide in chromium. However, because of the presence of SO2(g), K2CrO4 immediately reacts with SO2(g) to form K2SO4. This study shows that the initial stages of the corrosion attack are of great importance. The initial complex interactions between the flue gas, deposit, and oxide scale affect the future corrosion resistance of the steel.

Ambient-temperature, low-cycle dwell-time and conventional low-cycle fatigue tests were performed on Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242). Specimens were solution annealed at various temperatures below the beta transus to control the volume fraction of primary alpha phase and were subsequently shot-peened. The influence of the changes in primary alpha phase on the low-cycle dwell-time fatigue life (LCDF) were determined and compared to the conventional low-cycle fatigue (LCF) properties of the alloy. A 120-second dwell significantly decreased the number of cycles to failure, although the factor decrease of LCF from a dwell, in general, diminished with decreasing stress. The Increasing primary alpha phase associated with lower solution temperatures appears to increase susceptibility to low-cycle dwell-time fatigue. It also appears that the susceptibility to dwell fatigue may be associated with ambient-temperature, time-dependent, cyclic (creep) plasticity.

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