Intergranular corrosion time-temperature-sensitization

Fig. 7.54 Time-temperature-sensitization curves for susceptibility to intergranular corrosion. Parameters are carbon concentrations in type 304-based stainless steels. Redrawn from Ref 83...

Fig. 7.56 Time-temperature-sensitization curves for intergranular corrosion of type 347 stainless steel in boiling 65% nitric acid, mpy, mils per year. Source Ref 85...

Intergranular corrosion depends on the length of time the steel is exposed to the sensitizing temperature (500-750°C), even if made from low-carbon or titanium-or niobium-stabilized steel. 

The susceptibility to intergranular corrosion of a chemically resistant steel depends on the carbon content, the duration of the sensitizing temperature, and the temperature of prior solution annealing, it is represented in a time-temperature diagram. Curves of this type are shown in Fignre 20.26 for an austenitic steel with approximately 18% chromium, 8% nickel, and various carbon contents. The curve encompasses the respective area of susceptibility. 

The susceptibility to intergranular corrosion depends on the carbon content of the alloy and the duration and temperature of sensitizing. A typical time-temperature diagram for austenitic steel containing 18% Cr, 8% Ni and different carbon contents is shown in Fig. 1-7 (Rocha, 1962). The lines encompass the beginning of the susceptibility for intergranular attack. 

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. 

---