Occuring along grain boundaries for some alloys, intergranular corrosion can be a real danger in the right environment. On the left, a piece of stainless steel (especially suspectible to intergranular corrosion) has seen severe corrosion just an inch from a weld. The heating of some materials causes chromium carbide to form from the chromium and the carbon in the metals.
This leaves a chromium deficient boundary just shy of the where the metal was heated for welding. To avoid this problem, the material can be subjected to high temperatures to redissolve the chromium carbide particles. Low carbon materials can also be used to minimize the formation of chromium carbide. Finally, the material can be alloyed with another material such as Titanium which forms carbides more readily so that the chromium remains in place.
Description: Intergranular Corrosion
Figure 5: Intergranular Corrosion