Definition - What does Intergranular Cracking mean?
Intergranular cracking is a form of corrosive attack that progresses preferentially along grain boundaries.
Intergranular cracking is also known as intergranular corrosion, intergranular corrosion cracking, intergranular stress corrosion cracking (IGSCC), intercrystalline corrosion, interdendritic corrosion or intergranular attack.
Corrosionpedia explains Intergranular Cracking
Intergranular cracking is not visible on the surface and is very destructive. It spreads through the interior of the metal along the grain boundaries, reducing the strength and destroying the ability of the metal to be formed or shaped. Positive identification of this type of corrosion usually requires microstructure examination under a microscope, although sometimes it is visually recognizable.
Among the metals affected by this type of corrosion are stainless steel, certain magnesium alloys, and the copper-bearing aluminum alloys. Intergranular corrosion occurs in certain grades of stainless steel when the steel is heated, as in welding. Brittleness results, causing the metal to crack near the weld. For this reason, a post-weld heat treatment is needed before reinstalling stainless steel parts that have been welded.
There are several processes that can lead to intergranular fracture:
- Micro-void nucleation and coalescence at inclusions or second-phase particles located along grain boundaries
- Grain boundary crack and cavity formation associated with elevated temperature stress rupture conditions
- De-cohesion between contiguous grains due to the presence of impurity at grain boundaries and in the presence of hydrogen and liquid metals
- Stress corrosion cracking associated with chemical dissolution along grain boundaries
- Cyclic loading when the material has lost its ability to accommodate plastic deformation between contiguous grains leading to grain boundaries
Intergranular corrosion can be prevented through:
- Use of low carbon grade stainless steels
- Use of stabilized grades alloyed with titanium or niobium. Titanium and niobium are strong carbide formers. They react with the carbon to form the corresponding carbides, thereby preventing chromium depletion.
- Use of post-weld heat treatment