Macrosegmentation in Ingot Casting
Macrosegregation is the buildup of concentration differences in a cast ingot during solidification. It leads to uneven stresses and can cause cracks or distortion.
Physical-Chemical Mechanism of Action
During cooling of a casting, global melt convections and gravity-driven flows occur. These move the liquid and cause uneven concentrations of gases, substances, and stresses across the entire volume of the block.
Metallurgical Relevance & Risks in Welding
Macrosegregation can lead to high mechanical stresses in the casting. These can cause cracks or deformations in the weld and the surrounding area of the casting. Especially with rigid materials such as high-performance nickel-alloyed steel, macrosegregation is an important factor for the quality of the weld.
Workshop Practice & Action Guidelines
To minimize macrosegregation, the casting should be cooled uniformly. This can be achieved through controlled cooling techniques such as spray cooling or the use of cooling walls. A temperature difference between the inner and outer area of the block should be avoided, as this leads to uneven stresses. For special materials, it is important to precisely control the cooling curve to avoid macrosegregation.