Corrosion concentrated at the grain boundaries while the grains themselves barely corrode, so the metal loses strength with little visible surface loss. The classic case is sensitization of austenitic stainless steel: time between about 425 and 815 C, as in a weld heat-affected zone, precipitates chromium carbides at the boundaries and leaves chromium-depleted zones. Low-carbon L grades and stabilized grades such as 321 and 347 resist it, and the oxalic acid and Strauss tests check for it.
Weld decay right along the HAZ, the shop used straight 304 instead of 304L, so we got intergranular corrosion.
Check carbon on the mill cert: L grades stay at or under 0.03 percent, and dual-certified 304/304L covers both strength and weld decay.
Also heard as
- IGC
- intergranular attack
- IGA
- weld decay
Related terms
SCC
Stress corrosion cracking: brittle cracking caused by tensile stress acting together with a specific corrosive environment.
Pitting
Localized corrosion that drills small, deep cavities into metal while the surface around them stays nearly intact.
PREN
Pitting resistance equivalent number: an index of a stainless alloy's chloride pitting resistance from its chemistry.