Definition - What does Cold Cracking mean?
Cold cracking is cracking that occurs as the result of hydrogen dissolving in the weld metal and then diffusing into the heat affected zone (HAZ). Cold cracks mostly develop long after the weld metal solidifies, but sometimes appear sooner. Cold weld cracking occurs at temperatures well below 600°F. It is considered a serious welding defect because it can significantly affect the integrity of infrastructure.
Cold cracking is also known as hydrogen-induced cracking, delayed cracking or underbead cracking.
Corrosionpedia explains Cold Cracking
Cold cracking is especially common in thick materials, as they tend to create areas of high restraint and can serve as a heat sink that leads to fast cooling rates. Rapid cooling causes the microstructure in the HAZ to form a new crystalline microstructure called martensite, which very hard, very brittle and lacks ductility. Martensite provides a location for diffusible hydrogen to gather, which causes residual stresses to build in the HAZ. Once these residual stresses reach a critical level, cold cracking occurs.
Cold cracking may occur fpr the following reasons:
- There is hydrogen in the weld material or atmosphere
- Susceptible microstructure (martensite)
- Mechanical stresses (thermal or residual stresses)
The following can be done to prevent cold cracking of a metal:
- Pre-heating the base material in order to reduce the speed of cooling, preventing the formation of martensite on the weld and allowing the hydrogen to be removed from the weld
- Reducing tension concentration, avoiding discontinuities on the weld or carefully selecting the disposition of the welds and the assembly sequence of the structure
- Using welding consumables with low hydrogen to minimize the hydrogen diffusion on the weld
- Selecting the appropriate welding process