Intergranular Cracking: Intergranular cracking is a condition in the steel that that will occur between the grain boundaries of the steel.

Generally (but not in all cases), it is caused by the diffusion of oxygen into the steel surface that leads to a condition known as intergranular oxidation (IGO). IGO will initiate fractures at the granular faces and grain boundaries. It is caused by heating in an oxygen-rich atmosphere or prolonged soak times at elevated carburizing temperatures.