Bulletin No. 26 - Sensitization


What is Sensitization?

Sensitization refers to a zone of chromium depletion at grain boundaries associated with carbide precipitation in certain corrosion resistant alloys, causing the alloy to be susceptible to intergranular corrosion and stress corrosion cracking.

A key thing to remember is that carbide precipitation occurs only at high temperatures where no aqueous phase can be present, but the resulting corrosion/cracking only happens at lower temperatures in the presence of aqueous conditions. The carbide precipitation associated with sensitization has almost no effect on any high temperature mechanical properties or on high temperature corrosion rates. Furthermore, room temperature ductility loss due to carbide precipitation is normally not significant.

All the 300-series austenitic stainless steels, 400-series ferritic stainless steels, many other chromium-containing austenitic alloys and some nickel base alloys are susceptible.

Sensitization is a concern in the refining and chemical industries, and it also comes up in the nuclear industry.