How can grain boundaries contribute to corrosion in metals?

In materials science, grain boundaries are the interfaces where the randomly oriented crystallites (grains) of a metal meet. These boundaries can become sites of localized degradation through a process known as intergranular corrosion.12

This type of corrosion occurs when the internal boundaries between crystal regions are selectively attacked. A common example is found in austenitic stainless steel or other chromium-depleted alloys. In these materials, the precipitation of carbide particles at the grain boundaries can deplete the surrounding area of protective elements like chromium. This localized chemical imbalance makes the grain boundaries more susceptible to electrochemical reactions than the rest of the metal, leading to weakened boundaries and potential structural failure.2