Intergranular corrosion/sensitization is a well known phenomenon that occurs in 18-8 austenitic stainless steel. Does it also occur in case of ferritic stainless steel? Why/Why not?
The ferritic stainless steels are even more sensitive to intergranular corrosion than austenitic stainless steels. In ferritic stainless steels with 13% chromium, this leads to pitting even under very mild corrosion conditions (three-phase boundary between air and pure water). The corrosion mechanism is identical in both cases, but ferritic stainless steels are generally much less corrosion-resistant (to get pitting in austenitic stainless steels with 18% Cr and 8% Ni you need more than pure water).
Strangely, the duplex steels (something between ferritic and austenitic stainless steels) show better resistance to intergranular corrosion than purely ferritic and purely austenitic stainless steels. This is explained by the higher chromium content.
On the material side, it is always a question of how homogeneously chromium or other important elements are distributed in the material. Grain boundaries are often affected, as this is often where the chromium-rich precipitates are located, with the adjacent Cr-depleted areas. And therefore, of course, it can also affect ferritic stainless steels. On the media side, it is often those conditions that are critical where element-depleted areas cannot passivate or repassivate well. It is mostly related to the passivation and reactivation current density. This can be investigated very well by means of EPR experiments. Therefore, this publication by me and my colleague may be of interest to you:
Article Quantitative evaluation of global and local chromium content...
Sensitization can occur in both austenitic and ferritic stainless steels. The amount of chromium carbide that precipitates is a function of carbon content, time at the sensitizing temperature, and the temperature. Lower carbon content stainless steels are less susceptible to sensitization.
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