2. Solidification at dendrite and grain scale

Whether the texture of the cast metal is columnar or equiaxed, its basic element on the scale of centimeters or millimeters (exceptionally 1/10 mm) is the grain. . The most common observation of a metallographic cross-section of a steel ingot, light alloy or superalloy casting reveals a periodic two-dimensional network within each grain, with an average period generally between 50 and 500 µm (figure 9 ): this is the dendritic network. The dendritic structure, a basic element at the 100 µm scale, corresponds to chemical heterogeneities: minor segregation.

The segregation rate is defined as the ratio :