What Does Transgranular Corrosion Mean?
Transgranular corrosion is a type of localized corrosion which occurs along cracks or faults across the crystals in metals and alloys. It follows the pattern of grains in the individual lattices of the material. Stress corrosion of austenitic steels is usually transgranular.
Stress corrosion cracking can proceed in one of two ways:
- Intergranular stress corrosion cracking (IGSCC) - Cracks propagate along the grain boundaries.
- Transgranular stress corrosion cracking (TGSCC) - Cracks run through the individual grains.
Transgranular corrosion is also known as intragranular corrosion and transcrystalline corrosion.
Corrosionpedia Explains Transgranular Corrosion
Transgranular corrosion occurs through or across a crystal or grain. In transgranular corrosion, the fracture travels through the grain of the material. The fracture changes direction from grain to grain due to the different lattice orientation of atoms in each grain. In other words, when the fracture or crack reaches a new grain, it may have to find a new path or plane of atoms to travel on because it is easier to change direction for the crack than it is to rip through. Corrosion chooses the path of least resistance. Since the corrosion proceeds preferentially within the grain, the grain boundary material is retained.
In this type of corrosion, a small volume of metal is removed in preferential paths that proceeds across or through the grains. It sometimes accelerated by tensile stress. In extreme cases, the cracks proceed through the entire metal, causing rupture or perforation. Chloride is the leading cause of transgranular cracking.
Transgranular attack has a very characteristic branching habit which is easily recognizable in scanning electron microscopy (SEM) fractographic and metallographic section examination. Transgranular stress corrosion cracking occurs mainly in chloride cracking of austenitic steels.