The effect of heat treatment and applied potential on the stress corrosion cracking of alloy 600 in thiosulfate solution

The effects of heat treatment and applied potential on the stress corrosion cracking (SCC) behavior of Alloy 600 in thiosulfate solution were investigated. Electrochemical Potentiokinetic Reactivation (EPR) tests and modified Huey tests showed that a thermal stabilization treatment (990°C/5 min + 705°C/15 h) could climinate the sensitization of Alloy 600 and result in a lowering of the degree of sensitization as compared with other heat treatments. Electrochemical polarization curves showed that Alloy 600 could passivate in thiosulfate solution and exhibited two anodic peaks located around −500 and +100 mV (SCE), respectively, independent of the heat treatment. The polarization curves also showed that Cr played an important role in the electrochemical behavior of Alloy 600 in thiosulfate solution. Under applied potential conditions, intergranular stress corrosion cracking (IGSCC) was observed in sensitized and stabilized Alloy 600 in 0.01 M thiosulfate solution at 95°C. The severity of IGSCC was less after the stabilization heat treatment than after the sensitization heat treatment. In these conditions the susceptibility of IGSCC was strongly affected by the applied potential. In general, the crack initiation time decreased with increasing applied potential in the anodic potential region.