Intergranular corrosion temperature effect

Effect of Thermal History of Austenitic Stainless Steels on Susceptibility to Intergranular Corrosion. The time dependence for the local depletion of chromium sufficient to cause susceptibility to intergranular corrosion as functions of temperature and carbon content is of the form represented in Fig. 7.54 (Ref 83). The curves are typical of type 3xx alloys with nominal chromium concentrations of 17 to 25 wt% and, since they represent times for initiation of intergranular corrosion,... 

These steels can also be liable to intergranular corrosion. In addition to Cr carbides, Cr nitrides may be precipitated and thus contribute to the depletion of Cr at the grain boundaries. The mechanism is in principle the same as for austenitic steels, but in the ferritic steels the attacks can occur for a wider spectrum of environments and lower contents of C + N. The critical range of temperatures that makes the metal sensitive is higher, namely above 925°C, and the attack occurs therefore close to the weld or in the weld metal itself. The material becomes resistant again after annealing for 10-60 minutes at 650-815°C. It is noted that the effects of the different temperature ranges are opposite to what is the case for the austenitic steels. 

Intergranular stress-corrosion cracking (IG-SCC) can occur in some sensitized materials when placed under tensile stress. Thus DL-EPR has been used to study the effects of aging time on the susceptibility of Alloy 600 to IGSCC, as shown in Fig. 41 (39). This work also shows the need to modify the experimental parameters of the test to achieve optimal correlation for alloys other than Type 304SS, in this case lowering the KCNS concentration and the temperature while raising the peak potential and the scan rate. 

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