Cold Crack
Cold crack is a crack that forms only after cooling to ambient temperature. It is promoted by diffusing hydrogen and locked-in residual stresses. Martensitic microstructures are particularly susceptible.
Physical-chemical mechanism
Cold cracks occur when hydrogen diffuses into the metal and degasses during cooling. This leads to local stresses in the microstructure, which can cause cracks at low temperatures.
Metallurgical relevance & risks in welding
Cold cracks are especially dangerous in martensitic microstructures, as these have high hardness and low ductility. They can lead to sudden cracking and significantly shorten the service life of components.
Workshop practice & action instructions
To avoid cold cracks, you should:
• Use hydrogen-free welding methods like CO2 welding or nitrogen welding.
• Control and slow down the cooling process to minimize locked-in stresses.
• For martensitic microstructures, perform post-weld heat treatment (PWHT) to regulate the microstructure.