Constitutional undercooling
Constitutional supercooling is premature cooling of the melt due to segregation and enrichment of alloying elements. It promotes the growth of dendrites (dendritic growth) and improves mechanical properties of the weld.
Physicochemical mechanism of action
Constitutional supercooling occurs when the melt and alloying elements segregate, causing premature cooling before the solidification front is reached. Dendrites form, promoting crystal growth.
Metallurgical relevance & welding risks
Constitutional supercooling improves weld mechanical properties by creating a finer grain and better toughness. However, excessive dendritic growth can lead to porosity if cooling is uncontrolled, causing strength loss and cracking.
Shop practice & action items
To ensure effective constitutional supercooling, the melt must be cooled in a controlled manner ahead of the solidification front. This requires careful regulation of cooling steps and use of appropriate alloying elements. Too rapid supercooling can cause glass-hard grain, while too slow supercooling results in coarse grain and reduced mechanical properties.