Corrosion Fatigue Behavior of Alloy 600 in High-Salinity Brine

The corrosion fatigue behavior of alloy 600 was studied as a function of applied potential and heat treatment in high-salinity brine (4 M NaCl) in the absence and presence of low concentrations (10⁻⁴ M) of sodium tetrathionate and sodium thiosulfate. It was found that the corrosion fatigue resistance of the solution-annealed material in pure chloride solution decreased by increasing the applied potential from −900 mV_SCE (cathodic range) to −400 mV_SCE (passive range) and to −100 mV_SCE (above the pitting potential). The corrosion fatigue resistance was improved by heat treatment of the solution-annealed (SA) material at 800 C for 10 and 50 h. This improvement is attributed to the intergranular precipitation of chromium carbides. The addition of tetrathionate to the chloride solution did not change the fatigue life of the SA material with respect to that in pure chloride solution, while the addition of thiosulfate improved the corrosion fatigue resistance.