Constitutional Supercooling
Constitutional undercooling is the local cooling of the melt ahead of the solidification front due to concentration gradients of dissolved elements, promoting dendritic growth.
Physicochemical mechanism of action
Constitutional undercooling occurs when concentrated amounts of dissolved elements (e.g., silicon or carbon) ahead of the solidification front. These elements carry heat away, cooling the local region and leading to faster cooling there.
Metallurgical relevance & welding risks
Constitutional undercooling can cause dendritic growth, forming strong crystals. These crystals can impair the mechanical properties of the weld and lead to cracks or fractures. It can also increase stress states in the weld, raising hot cracking risk.
Shop practice & action items
To minimize constitutional undercooling, the melt temperature should be set below the eutectic point. This prevents rapid dendrite growth. Also, uniform cooling of the weld is important, achievable through proper cooling time and appropriate cooling medium.