Sensitisation
The precipitation of chromium carbides at grain boundaries between roughly 425 and 815 °C, which strips chromium from the adjacent metal and leaves it open to intergranular corrosion.
Where it happens
The heat affected zone beside a weld passes straight through the sensitisation range on cooling. In a standard-carbon grade like 304 or 316, chromium carbides form at the grain boundaries and the metal next to them loses its corrosion resistance.
How to avoid it
Two routes. Use a low-carbon grade — 304L or 316L, carbon capped at 0.030% — so there is not enough carbon to form the carbides. Or use a stabilised grade — 321 (titanium) or 347 (niobium) — where carbon is tied up as a stable carbide instead. Stabilised grades are preferred where the equipment also runs hot in service.
Related terms
Where this applies
Austenitic Stainless Steel Plate
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