Constitutional supercooling
Undercooling constitution is the state before the solidification front where the temperature is below the liquidus temperature and promotes dendrite formation.
Physico-chemical mechanism of action
Undercooling constitution occurs when the weld is cooler than the liquid metal before the solidification front. This leads to unequal temperature distribution and the formation of dendrites that spread like tree branches.
Metallurgical relevance & risks during welding
Undercooling constitution can lead to fine cracks and damage in the weld. The dendrites can increase hardness and reduce toughness, leading to a shorter component life.
Workshop practice & instructions
To avoid undercooling constitution, the weld should be cooled as quickly as possible. This can be achieved by a high cooling rate, for example by reducing the welding wire diameter or using cooling water with high flow. Optimum cooling time should be between 5 and 10 seconds.