Local variations of the chemical composition, that is, compositional inhomogeneities, play an important role in the thermodynamic stability and spatial distribution of phases in multiphase steels. As is already known, the inhomogeneity of the distribution of chemical elements in the structure of structural grade carbon steels is formed mainly during their crystallization, during the hardening of the ingot or continuously cast billet. The limited solubility of alloying elements in the solid state in steel leads to liquation during solidification. During crystallization, the solute is partitioned between the solid and the liquid to enrich or deplete the interdendritic regions. This naturally leads to variations in the composition on a micrometer scale, i.e., microsegregation. The formation of the liquation background (dendritic pattern) is due to the alternate enrichment of elements of individual microzones (segregation) during steel crystallization. The areas of segregation of manganese and silicon even in carbon steels have a strong influence on the morphology and arrangement of phases of the final structure formed in carbon steel products. Diffusion of solid elements during the reheat cycle, particularly aluminium and manganese, is too slow to result in chemical homogenization. As a result, the segregation profiles present after casting remain during all subsequent processes and have a significant impact on the final striated in homogeneity of the microstructure. Thus, the control of microsegregation during hardening in modern steels is crucial for obtaining uniform mechanical properties of the final product, since phase transformations occurring during thermal and/or deformation treatments determine the final microstructure and are reflected by the local distribution of hardness.