Macroscopic ingot segregation
Macroscopic ingot segregation is a large-scale chemical inhomogeneity in cast steels, caused by convection currents and gravity during solidification. It leads to uneven distribution of alloying elements and requires forging or rolling steps to homogenize.
Physical-Chemical Mechanism of Action
During the casting process, convection currents occur, causing the steel to solidify at different rates in different parts. This uneven solidification leads to macrosegregation, where certain alloying elements (like carbon) concentrate in specific regions.
Metallurgical Relevance & Welding Risks
Macrosegregation can result in non-uniform mechanical properties, such as varying hardness and strength within the steel. This can lead to cracking or fracturing during weld formation, especially if the segregation is pronounced. Additionally, it affects thermal conductivity and the weld metal's microstructure.
Shop Practice & Action Guidelines
To minimize macrosegregation, careful attention must be paid to convection currents and solidification rates during the casting process. After casting, forming operations like forging or rolling are necessary to even out chemical inhomogeneity. When welding, it's important to consider the segregation pattern and, if necessary, perform additional forming steps to ensure a homogeneous weld.