Cracking

There are two general forms of cracking corrosion, both associated with the configuration of the crack. These are intergranular cracking, which occurs between grain boundaries and transgranular cracking, which takes place across a grain boundary. Intergranular cracks usually occur at anodic grain boundaries. Stress corrosion cracking of austenitic and martensitic stainless steels provides an example of one such attack. 

During manufacture, a metal is often left in a stressed state; it can crack perpendicular to the direction of the stress. The attack is aided by high temperatures, the presence of high chloride concentrations, or other corrosive conditions. Proper manufacturing procedures can minimize the problem by heat treatment to remove residual stresses. 

The presence of crevices should be eliminated. Transgranular cracking occurs under cyclical stress conditions (corrosion fatigue); pure metals are more resistant to this form of cracking.