Where does intergranular corrosion preferentially occur?

Intergranular corrosion preferentially occurs at the grain boundaries of a metal. This type of corrosion is a form of localized attack that affects the boundaries between the different crystalline grains in the metal. The grain boundaries are often sites of weakness because they may contain different compositions, impurities, or phases compared to the grains themselves.

In many alloys, especially stainless steels, elements such as chromium can be depleted at the grain boundaries, leading to a decrease in corrosion resistance in those areas. As a result, when the metal is exposed to corrosive environments, the grain boundaries are more susceptible to attack, leading to a deterioration that can compromise the structural integrity of the material.

In contrast, metal surfaces exposed to water may experience corrosion, but not specifically intergranular corrosion unless the conditions are favorable for that mechanism. Exposed edges of coated surfaces might experience edge corrosion, which is different from intergranular corrosion, and areas with high mechanical stress may lead to stress corrosion cracking but do not specifically define intergranular corrosion.