Intergranular corrosion occurs when certain metals and alloys reach temperatures between 425 and 870 degrees c (887 and 1598 degrees F).
These temperatures are most common during welding, heat treatment, or high-temperature operations.
When a metal is subjected to such extreme temperatures, it changes on a structural level.
Chromium in the alloy reacts with carbon to form chromium carbide near grain boundaries.
The formation of this carbide essentially transforms the boundary into an anode cell.
The interior of the grain then acts as a cathode cell, and intergranular corrosion begins.
