Intergranular Corrosion

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Corrosion & Protection

Definition

Preferential corrosion attack along grain boundaries of a metal, often caused by compositional differences or the precipitation of detrimental phases at the grain boundaries compared to the grain interiors.

Detailed Explanation

Sensitization of austenitic stainless steel is a classic example: when heated to 425–850°C (the sensitization range), chromium carbides precipitate at grain boundaries, depleting the adjacent zones in chromium below the passive threshold and making them anodically active. The resulting loss of corrosion resistance is termed sensitization, and the remedy is either solution annealing (to re-dissolve the carbides) or using low-carbon grades (e.g., 304L or 316L) or titanium/niobium-stabilized grades. Weld heat-affected zones are particularly vulnerable to this attack.