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Intergranular Corrosion
A form of corrosion that attacks the grain boundaries of a metal, commonly occurring in sensitized stainless steels where chromium carbides have precipitated, depleting the adjacent areas of chromium.
Understanding IGC
Intergranular corrosion (IGC) occurs when chromium carbides (Cr23C6) precipitate at grain boundaries during exposure to 450-850C (the sensitization range). This depletes chromium from adjacent areas below the 12% minimum needed for passivation.
Prevention
- Use low-carbon grades (304L, 316L)
- Use stabilized grades (321 with Ti, 347 with Nb)
- Solution anneal after welding