Core Segregation
Segregation is an enrichment of alloying elements and impurities in the center of an ingot due to directional solidification. This can lead to uneven properties within the casting.
Physical-Chemical Mechanism
Segregation occurs when a casting cools from the outside in and the metal near the surface solidifies first. This causes alloying elements and impurities to concentrate in the center of the casting.
Metallurgical Relevance & Welding Risks
Segregation can lead to uneven mechanical properties within a casting, which increases stress distribution and crack risk during welding. Especially if the center of the casting is harder than the surroundings, this can lead to stress concentrations and hot cracks in the weld.
Workshop Practice & Instructions
To avoid or minimize segregation, castings should be cooled as evenly as possible. This can be achieved by using cooling water with an appropriate flow rate and applying cooling strips. For heavily affected castings, diffusion annealing is required to homogenize the uneven properties.